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[ENTIFIC MEMOIRS,
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SELECTED FROM
THE TRANSACTIONS OF
FOREIGN ACADEMIES OF SCIENCE
AND LEARNED SOCIETIES,
AND FROM
FOREIGN JOURNALS.
EDITED BY
RICHARD TAYLOR, F‘S.A.,
fELLOW OF THE LINNZAN, GEOLOGICAL, ASTRONOMICAL, ASIATIC, STATISTICAL,
AND GEOGRAPHICAL SOCIETIES OF LONDON ;
HONORARY MEMBER OF THE NATURAL HISTORY SOCIETY OF MOSCOW.
UNDER SECRETARY. OF THE LINNZAN SOCIETY.
VOL. I.
LONDON:
PRINTED BY RICHARD AND JOHN E. TAYLOR,
RED LION COURT, FLEET STREET.
SOLD BY LONGMAN, REES, ORME, BROWN, GREEN, AND LONGMAN; BALDWIN AND
CRADOCK; CADELL; RIDGWAY AND SONS; SHERWOOD, GILBERT, AND PIPER;
SIMPKIN AND MARSHALL ; B. FELLOWES; S. HIGHLEY ; WHITTAKER AND CO.; AND
J. B. BAILLIERE, LONDON :—AND BY A. AND C. BLACK, AND THOMAS CLARK, EDIN-
BURGH; SMITH AND SON, GLASGOW :—MILLIKEN AND SON, AND HODGES AND
NW’ ARTHUR, DUBLIN :—DOBSON, PHILADELPHIA ‘AND GOODHUGH, NEW YORK.
1837.
pie tes @.
PREFACE.
——
IN the publication of the four parts which complete the pre-
sent volume of the Scientific Memoirs, I have ventured to make
the experiment how far I might be able to succeed in supplying
an auxiliary which, as was stated in the Advertisement prefixt to
the First Part, appeared to be much needed for the progress and
advancement of science in this country.
My own conviction of the utility of such a work has been
much strengthened since I have been engaged in it, both by
the importance of the materials that present themselves, and by
the expressed opinions of persons most competent to judge.
How great ihdeed the disadvantage must be, under which those
are placed who are engaged in any branch of scientific inquiry,
from being uninformed as to what is doing, or has been done,
by our active and laborious neighbours on the Continent, must
be obvious to every one: and the cases are numerous to which
the remark of Lenz, p. 312, speaking of Ohm’s theory of the gal-
vanic battery, will apply,—that, although given to the world
several years ago, yet, “being only published in the German
language, it is unknown both in France and in England.”
With regard to the execution of the work, I must submit it
to the candid judgement of those who are aware of the difficulty
of the task,—having availed myself of the valuable suggestions
with which I have been favoured in the selection of memoirs,
and of the best assistance within my reach for their translation.
I shall be satisfied if what has been done should render the
present volume useful to science, and if what there is still to
do should induce the public to enable me to continue the work.
Hitherto, as I can hardly yet boast of the sale of 250 copies, I
am very far from having been repaid the cost of publication, to
say nothing of the care and labour which have been required :
nor could I be expected, having now finished a volume, which,
from the nature of its materials, may be considered a complete
work in itself, to proceed further unaided, until I have ascer-
iv PREFACE.
tained whether I may calculate upon adequate support. This,
however, I cannot yet think it improbable that I shall obtain,
when the plan and contents of the present volume shall have
become better known ; and with this view, I shall gladly receive
the names of those who may be disposed to uphold the work by
purchasing what has been published, and forming the list of my
future subscribers.
I should hardly have been disposed to persevere further, had
it not been for repeated expressions of strong interest in the
success of the work, which have reached me from persons of the
highest scientific eminence; among whom [ may perhaps
without impropriety mention the names of Ivory, of Babbage,
Powell, Forbes, Lloyd, Challis, Owen, Wheatstone, Phillips,
Talbot, Hamilton, Faraday, and others in this country, and
of Hare, Henry, and Bache in the United States. To several
of them I have been indebted for very important suggestions ;
and to Professor Wheatstone especially, for his valuable con-
tributions.
From the kind assistance of men of science, and from an
increased acquaintance with the sources whence the best mate-
rials are to be derived*, I think I may fairly hold out to the
public the prospect of some considerable improvements in the
work: and I shall be thankful for any suggestion for this
purpose. I may perhaps give the titles or early notices of such
foreign scientific papers as shall not be adopted for immediate
translation: and as our first volume may be said to have cleared
off some arrears, we may now come nearer to the present time,
and endeavour to supply what is of the latest date and of in-
trinsic value.
However, this, as I have already stated, must depend upon
my prospect of future support, and the success of the present
volume ;—and, glad to have finished my humble but laborious
task in completing it, I shall be able at my leisure to decide as
to the future.
RICHARD TAYLOR.
Red Lion Court,
June 29, 1837.
* Arrangements have been made for obtaining such as may appear in the Swedish,
Dutch, and Italian languages.
CONTENTS OF VOL. I.
\
PART I.
Advertisement to the Reader.
Art. I—Memoir on the Free Transmission of Radiant Heat
through different Solid and Liquid Bodies ; presented to the
Academy of Sciences of Paris, on the 4th of February, 1833.
(AN OLLIE RE a cea Bo eee ts PAC ec i ae
Art. IJ.—New Researches relative to the Immediate Transmis-
sion of Radiant Heat through different Solid and Liquid
Bodies ; presented to the Academy of Sciences on the 21st of
April, 1834, and intended as a Supplement to the Memoir
on the same subject presented to the Academy on the 4th of
Memrmity S05... By IV. MELLONT n .. cecuhe me ooh. « eae op «
Art. III.—Experiments on the Circular Polarization of Light.
By Prof. H. W. Dove of Berlin ......
Arr. 1V.—Description of an Apparatus for ae i Paes
nomena of the Rectilinear, Elliptic, and Circular Palos
of Light. By Prof. H.W. Dove. :
Art. V.—Memoirs on Colours in Sersiy aad erence ona
new Chromatic Scale deduced from Metallochromy for Sci-
entific and Practical Purposes. By M. Leoroitp Nositt of
Reggio. . mee amet
Arr. VI. >On “ates Mathematical aici cite Heat ae S. D.
Potsson, Member of the Institute, &c.. 5
Art. VII.—Researches on the Elasticity oF MBodies seen ne
stallize regularly. By Ferix Savarr..
Art. VIII.—Experiments on the Essential Oil of ig oes
Ulmaria, or Meadow-Sweet. By Dr. Lowrie, Professor of
Chemistry at Zurich .........
Art. IX.—Researches relative to tie’ Wicca, Se ‘to ‘the
Ancients and Moderns, by which the Vine_is infested, and on
the Means of prey hi their ae By M. Le Baron
WALCKENAER. . = Nalanda aie:
Page.
~I
oO
86
94:
122
139
153
167
vi j €ONTENTS.
PART II.
Page.
Art. IX. eb tnshiaenye: 5 1 See. CLE
Art. X.—The Kingdoms of Nate this Life “ahd Aitinitys By
Dr. C. G. Carus, he. - to His Majesty the King of
Saxony ... 223
Art. XI. Researches: on the ‘Bastia of Bodies high ery fale
lize regularly. By Fexrix Savart..... 225
Arr. XII.—Researches concerning the Nsture or the Bleatiing
Compounds of Chlorine. By J. A. Batarp ..... . 269
Art. XIII.—On the Laws of the Conducting Powers of Wires =
different Lengths and Diameters for Electricity. By E. Lenz 311
Art. XIV.—Memoir on the Polarization of Heat. By M. Met-
LONE 5.4 82a serge Spee eee oe ae
PART: IIt:
Advertisement on the Publication of Part III.
Art. XV.—Memoir on the Motive Power of Heat. By E.
CLapeyron, Mining Engineer ..... oe OST,
Arr. XVJ.—Remarks on the cause of the ‘Sound ‘produced by
Insects in flying. By Dr. Hermann Burmeister, of the
University of Berlin ome
Art. XVII.—Note on the ficAuctiont of feighnant Heat. By M.
WEMELON Ess y'o5 eke os ee ae anit 2 Oe 383
Art. XVIII.—Observations and Experiments on the Theory of
the Identity of the Agents which produce Light and Radiant
377
Heat. . By M MELEONI 20m oo aes spe ca oe 388
Art. XIX.—On the Constitution of the Superior Regions of the
Earth’s Atmosphere. By M. Brot ....... .* 393
Art. XX.—Remarks on the real Occurrence of F ‘att furan
and their extensive Diffusion. By Prof. EHRENBERG...... 400
Further Notices of Fossil Infusoria. By the Same ........ 407
Art. XXI. On the Chemical Effects of Electric Currents of low
tension, in producing the Crystallization of Metallic Oxides,
Sulphurets, Sulphates, &c.; in forms frequently closely re-
sembling the native combinations. By M. BecqurreL .... 414
Art. XXII. Ona New Combination of the Anhydrous Sulphuric _
and Sulphurous Acids. By Henry Ross, Professor of Che-
mistry at the Royal University of Berlin ...... 443
Arr. XXIII.—On the Forces which regulate the Internal Consti-
tution of Bodies. By O. F. Mossorrs. oH ommunicated nee
M. Farapay, Esq., D.C.L., F.R.S., &¢.). . x, ... 448
CONTENTS. Vii
Page.
Art. XXITV.—On certain Combinations of a New Acid formed of
Azote, Sulphur, and Oxygen. By J. Petouze ..... . 470
Art. XXV.—An Attempt to explain the Absorption of Take ac-
cording to the Shenae wie By Baron FaBian von
Warvr Ee ak oe. eI a ea ga nin UE,
PART IV.
Art. XXV.—(continued.) . . 483
Art. XXVI.—On the Repidation of Bader Ni orptileriy a ee
Movement of Machines. By M.H. Jacos1, Doctorof Science,
and Professor at the University of Dorpat .............. 503
Note on the Application of Electro-Magnetism as a Mechanical
Power. By I. D. Borro, Professor of Natural Philosophy in
the Royal University of Turin ...... 532
Part of a Lecture on Electro-Magnetism, Welivened, rm the Phi-
losophical Society at Zurich, erie the 18th, 1833. By the
late Dr. R. ScHULTHESS ...... . 534
On the Influence of a Spiral Conductor ir in fee ae sithe init
sity of Electricity from a Galvanic Arrangement of a Single
Pair, &c.- By Professor Henry, of New Jersey, U.S. .... 540
Art. XXVIJ.—A singular case of the Equilibrium of Incompres-
sible Fluids. By M. Ostrocrapskvy. . 548
Art. XXVIII.—On the Origin of Organic Matter frot Be:
Perceptible Matter, and on Organie Molecules and Atoms ;
together with some Remarks on the Power of Vision of the
Human Eye. By Prof. C. G. EHRENBERG ..... 555
Art. XXIX.—On the Application of Circular electra | to Or.
ganic Chemistry. By M.M. Bror and CHEvreuL........ 584
On the Application of Circular Polarization to the Analysis of
the Vegetation of the Graminez. By M. Biot .......... 584:
Examination of an Optical Character, by which, according to
M. Biot, Vegetable Juices capable of producing Sugar ana-
logous to Cane Sugar, and those capable only of producing
Sugar similar to Grape Sugar, may be immediately distin-
guished. By M. Cuevreur ...... . 591
On the Application of the Laws of Ginemiae Beldeeation to Gite
Researches of Chemistry. By M. Bior ..... 600
Arr. XXX.—On the Laws according to which the Mapnet acts
upon a Spiral, when it is suddenly approached to or removed
from it; and on the most advantageous Mode of constructing
Spirals for Magneto-Electrical purposes. By E. Lenz .... 608
Vili
¥;
VII.
LIST OF PLATES.
LIST OF PLATES.
M. Mettonr’s Experiments on the Immediate Transmission of
Radiant Heat, pp. 42 and 55.
Dove’s Apparatus for the Polarization of Light, p. 79.
. Savart’s Researches on the Elasticity of Bodies by means of
Sonorous Vibrations, p. 143.
Savart’s Researches on the Elasticity of Bodies which cry-
stallize regularly, p. 262.
BurMEIsTER’s Remarks on the Sound produced by Insects; and
EnReENBERG’s Memoirs on Fossil Infusoria, pp. 378 and 413.
VI. To illustrate Baron von WreEDE’s Memoir on the Absorption
of Light, p. 480.
Jacosi’s Electro-magnetic Machine, p. 507 ; and ScHULTHESsS’s
Electro-magnetic Machine, p. 539.
a]
Fe TW Gs Yes Get 3) 5) En cas
ERRATA.
156, line 4, for 8°35. read 5°35
158, line 37, insert a comma after Calcium
160, line 41, for 0:350 carbon read 0°350 carbonic acid
—., line 43, for 0°450 carbon read 0°450 carbonic acid
—, line 43, for 0°0759 read 0:075 water
162, line 3, for sesquichromate read sesquichloride
164, line 6, for them read bases
— , line 22, for *754 read 0°754
—., line 34, after stated that insert from
—., line 34, omit contained
—., line 35, after chloride of spiroil insert more obtained
—., line 37, for 11°56 read 111°56
165, line 18, for 0°510 water read 0'119 water
470, line 5, for vol. xvi. read vol. lxvi
—., four lines from bottom, for (Reaum.) read (Centigr.)
471, last line, for precipitated read before-mentioned
472, line 11, for in the same manner, read of the same kind
—, line 33, for discoloured read decoloured
—., line 41, for — 15° read 15°
473, two lines from bottom, for give them read give it
474, three lines from bottom, for of read and
475, line 28, for Ka? read K a,
476, line 6, for sulphur read sulphite
SCIENTIFIC MEMOIRS.
VOL. I.—PART I.
ARTICLE I.
Memoir on the Free Transmission of Radiant Heat through
different Solid and Liquid Bodies ; presented to the Royal
Academy of Sciences of Paris, on the 4th of February, 1833,
by M. Metuont1.
From the Annales de Chimie et de Physique, t. i111. p. 1.
Manrrorte was the first, so far as I am aware, who attempted to
appretiate the action of diaphanous substances in transmitting or inter-
cepting the calorific rays which emanate from terrestrial sources. After
having observed that solar heat concentrated at the focus of a metallic
mirror, suffered no sensible diminution of intensity by being made to
pass through a glass plate, he took and placed his apparatus before the fire
of a stove, and found, that at the distance of five or six feet the tempe-
rature of the reflected image at the focus, when the rays were allowed to
meet there without impediment, was such as the hand could not bear;
but that when the plate of glass was interposed there was no longer
any sensible heat, although the image had lost none of its brillianey.
Whence he concluded that none *, or certainly but a very small portion,
of the heat of terrestrial fire passes through glass.
About a century after Mariotte’s time, the same experiment was re-
peated by Scheele, who, instead of imitating the cautious reserve of his
predecessor, asserted that from the moment when the glass was inter-
posed there was no longer any heat whatever at the focus of the mirror +.
* Mariotte, Z'raité de la Nature des Couleurs; Paris, 1686, part 2, at the
end of the Introduction.
+ Scheele, Vraité del Air et du Feu ; Paris, 1781, § 56.—The original work
of Scheele was published in 1777. Mariotte died in 1684.
Vor. I—Parrt 1. B
g M. MELLONI ON THE FREE TRANSMISSION
Pictet, however, corrected the mistake by means of the apparatus known
by the name of conjugate mirrors. A very transparent square of glass
was placed between a thermometer and the heat of a lighted candle
concentrated by the apparatus; the mercury in some moments rose se-
veral degrees ; there was a perceptible elevation of temperature also when
the candle was removed and a small jar filled with boiling water put in
its place *.
Some years later Herschel undertook a very extensive series of ex-
periments on the same subject. They are described in the volume of the
Philosophical Transactions for 1800. The author employs no artifice
to increase the action of the rays of heat, and contents himself with the
direct measurement of their effect by placing the thermometer at a very
short distance from the diaphanous body.
But doubts were started as to the conclusions drawn from these dif-
ferent results. It was objected that part of the radiant heat was first
stopped at the nearer surface of the glass, that it was gradually accu-
mulated there and afterwards propagated from layer to layer, until it
reached the further surface whence it began again to radiate on the ther-
mometer. It was maintained even that nearly the whole of the effect
was produced by this propagation. In short, some went so far as to deny
altogether that the heat emitted by terrestrial bodies can be freely trans-
mitted through any other diaphanous substance than atmospheric air.
M. Prevost, by means of a very ingenious contrivance, demonstrated
the erroneousness of this opinion. Having attached to the pipe of a
fountain a spout consisting of two parallel plates, he obtained a strip of
water about a quarter of a line in thickness. On one side of this he
placed an air thermometer and on the other a lighted candle or a hot
iron. The thermometer rose, almost always, some fraction of a de-
gree+. Now it is quite evident that, in this case, a successive propa-
gation through the several layers of the screen, which was in a state of
perpetual change, could not take place. It was admitted, therefore,
that other diaphanous media besides atmospheric air sometimes transmit
the rays of heat as instantaneously as they always transmit those of
light.
M. Prevost’s process could not however be applied to solid bodies. It
was therefore impossible to determine, by means of it, whether caloric was
immediately transmitted through screens of glass. Delaroche completely
solved this problem by employing a method invented by Maycock tf.
* Pictet, Essai sur le Feu, § 52 et seq.
+ Journal de Physique, de Chimie, d'Histoire Naturelle et des Arts, par M.
Delametherie, 1811.—P. Prevost, Mémoire sur la Transmission du Calorique a
travers l Eau et d'autres Substances, § 42 et 43.
t Nicholson, A Journal of Natural Philosophy, Chemistry and the Arts,
vol. xxvi. May and June 1810.—J, D. Maycock, Remarks on Professor Leslie’s
Doctrine of Radiant Heat.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 3
The method consists in observing the thermometer as in the preceding
eases; that is, when the caloric rays fall upon it after having passed
through the plate of glass. We thus obtain a complex measure of the ef-
fects produced by immediate transmission and by that conducting power
of the layers to which we have given the name of successive propagation.
If we know the value of either of these, we have that of the other. Now
it is easy to determine the influence of the conducting power by repeating
the experiment after having blackened with Indian ink that surface of the
plate which is turned towards the calorific source. In this case, theimme-
diate radiation being intercepted, it is clear that the elevation of the tem-
perature at the other side must be attributed only to the conducting power
of the layers. Should the elevation be now found less than it was at first,
it will be a decisive proof of immediate transmission. And such was
the fact in almost all the experiments of Delaroche; I say almost all, be-
cause it was found that the quantity of heat freely transmitted varied
with the temperatures of the source. For temperatures lower than that of
boiling water it was nothing, and when an Argand lamp* was employed,
it was found to be more than half of the whole quantity.
No doubt can be raised as to the truth of this beautiful discovery of
Delaroche ; and yet the method which he has employed to measure the
quantities of heat freely transmitted is by no means exact, especially in
respect to high temperatures. In order to understand this seeming para-
dox two things are to be observed; Ist, the difference produced by change
of surface between the two quantities of heat which penetrate the glass
by reason of its conducting power; 2nd, the difference produced be-
tween those two quantities by the total or partial interception of the
calorific rays.
It is fully proved by the experiments of Leslie and others, that glass,
when blackened with Indian ink, absorbs all the rays of heat, though, in
its natural state, it reflects a certain number of them. The quantity of
heat which penetrates the screen will therefore be greater in the former
than in the latter case. However, as polished glass reflects but a very
small portion of caloric rays, the error arising from a difference in the
state of the surface will be reduced to a very inconsiderable quantity and
may be safely disregarded. But the case is different when we examine
the error produced by the total or partial interception of the caloric ra-
diation. In some of the experiments of Delaroche one half, at least, of
the incident rays immediately passed through the screen. Thus it was
evident that it was the other only which was stopped at the first surface
of the glass. The effect of conduction must therefore be limited to this
latter half. Butas the screen, when blackened, stops the whole radiation,
* Journal de Physique, §c., par Delametherie, 1812,—Delaroche, Observa-
tions sur le Calorique rayonnant.
BQ
4 M. MELLONI ON THE FREE TRANSMISSION
itis then exposed to a heat twice as strong, and therefore exhibits a far
greater effect of conduction. Hence it follows that when we deduct from
the observation furnished by the transparent glass the observation fur-
nished by the glass blackened, the result obtained will be lower than the
true temperature of the rays transmitted freely. But the error will not
be the same in all cases. Being of no account when boiling water is em-
ployed, it will increase in proportion as the temperature of the source is
raised. The measures of the free radiations which suffer the greatest
diminution will be those furnished by the highest temperatures. Hence
it is evident that this latter cause of error in the measure of the imme-
diate irradiation, instead of invalidating the law of Delaroche, serves
only to give it greater certainty. We are therefore justified in saying,
as we have said, that the want of exactness in the method has no
influence whatsoever on the truth of the law which it has served to
establish.
To Delaroche we are also indebted for a discovery, no less important
than the foregoing, relative to the amount of loss sustained by the same
rays of heat in passing successively through two squares of glass. But
I abstain, for the present, from entering into any detail on this subject,
as I shall have occasion to speak of it hereafter *.
None of those whose labours we have been thus briefly noticing has
thought of making an exact comparison between the transmissions of
caloric rays through screens of different kinds; and, if we except the
experiments of M. Prevost and those of Herschel, from which no con-
sequence can be deduced, all the others were confined to the single pur-
pose of.ascertaining the law of transmission through glass only. Neither
has sufficient attention been given to the influence of the state of the
* I must not omit to mention that, notwithstanding the results obtained by
Delaroche, some most eminent philosophers (and of these it will be sufficient to
name Laplace and Brewster) continued to deny the immediate transmission of
heat through transparent solid bodies. ‘Their principal objection was founded
on an experiment of that author, from which it was inferred that a thick glass
intercepted a greater quantity of radiant heat than a thin glass, though the for-
mer was much more transparent. It was insisted that this circumstance proved
the presence and action of heat successively propagated from one surface to
the other, and every elevation of temperature observed on the other side of the
sereen was assigned to the conductible caloric. This opinion can no longer be
maintained in defiance of the results furnished by the application of the ther-
momultiplier to this species of phenomena. It will be seen, further, that the
calorific action through a transparent layer is instantaneous, and that the time
necessary for the instrument to mark its total effect is the same, whatever be the
quality or thickness of the screens. Let the direct rays from an unvarying
source of heat be received on the thermoelectric pile; let them be first made to
pass through any diaphanous screen of one hundred millimetres in thickness:
the index of the galvanometer sets itself in motion from the instant when the
communications are established, and stops after having described an are of
greater or less extent in an unvarying interval, which, with my apparatus, I
find to be ninety seconds.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 5
surface, or that of the thickness of the layers and their internal structure
on the quantities of heat which freely pass through them. I have en-
deavoured to supply these different omissions, but the undertaking has
proved too vast for me, and several parts of it are therefore incomplete.
I hope however that I shall be able hereafter to return to these, and
to treat them in a manner more satisfactory.
In the mean time I present to the Academy the results of my first re-
searches disposed in two memoirs. That which I offer at present con-
tains an account of the method pursued in the measurement of calorific
transmission and the application of the method in the case of an unva-
rying source acting on bodies of different kinds. In the second I shall
explain the facts connected with the succession of the screens and the
variation of the sources.
A
General Considerations on the Free Transmission of Caloric through
Bodies, and the Manner of Measuring it by means of the Thermo-
multiplier.
We have already observed that a diaphanous screen placed at a cer-
tain distance from a calorific source stops a portion of the rays which
strike its first surface, while the rest pass freely through. We have re-
marked besides that after a certain time the heat stopped at the anterior
surface, and accumulated there by successive radiations, passes on from
layer to layer till it reaches the other surface, whence it begins to ra-
diate anew ; and that this radiation mingling with the heat which passes
through the screen by immediate transmission, prevents its being mea-
sured exactly.
- When the screens are liquid, the influence of the conducting power of
the layers may always be destroyed if we incessantly renew the matter
of the screen by means analogous to the strip of water employed by
M. Prevost. But it would be always very difficult, and often impossible,
to apply this artifice to solid bodies and even to such liquids as can be
obtained only in small quantities. In order therefore to attain the same
end in a general manner, and to render the experiments in some degree
independent of conduction, other means must be employed.
If we consider with due attention the manner in which the second
surface of the interposed plate is heated, and the radiation which results
from it, we shall see that the latter possesses properties very different
from those that belong to the caloric which is freely transmitted. In
order to be satisfied of this, we have only to observe that its action
changes with the change of distance between the screen and the source ;
a thing which does not happen, even in the slightest degree, to those
rays that are transmitted freely. In fact, it is with the caloric trans-
mitted immediately, as it is with light.
6 M. MELLONI ON THE FREE TRANSMISSION
If between the flame of a candle and the eye we interpose a plate of
glass or any other substance more or less transparent, we find the di-
minution of the intensity of the light always the same, however the di-
stance between the plate and the candle may vary. The effect produced
by distance on the freely transmitted caloric is exactly similar; and if
at a certain distance from the active source there be a thermoscopic
apparatus sensible to this portion of heat, the apparatus will always give
the same indication, whether the screen be laid close to the source or
to the thermoscope.
But it is clear that it must happen quite otherwise to the conductible
caloric ; for this portion of the heat, when it has reached the further sur-
face of the screen, leaves it in the form of diverging rays which become
weaker in proportion to the distance. In other words, the further sur-
face of the screen being heated becomes a new calorific source whose
intensity of radiation must decrease as the distance increases.
We possess, therefore, a very simple contrivance for destroying the
influence of conduction, if we keep the action of the free radiation in-
tact. This contrivance consists in removing the screen so far from the
thermoscope that the radiation of its own heat may, on account of its
extreme feebleness, be totally disregarded.
There are, however, some precautions to be taken; for in proportion
as the distance between the screen and the thermoscope is increased,
the distance between the source and the screen is diminished. The
latter is therefore more heated, and radiates with greater force upon
the instrument. It is easy to show by calculation that we always gain;
that is, that we always weaken the conductible caloric more and more
by removing the screen from the thermoscope, until we have placed it
midway between the thermoscope and the source*. Let us, therefore,
put the screen in this position (which is the most favourable of all), and
we shall see that its heat has then no appretiable influence on the re-
* Let a be the distance from the source to the thermoscope, « the distance
from the thermoscope to the screen, i the calorific intensity of the source, we
i He : } :
shall have (G@—aps the expression for the radiation which strikes the anterior
ci
surface of the screen. This quantity will become C=, at the further sur-
face, c being a constant quantity depending on the conducting power of the
matter of the screen. In fine, the radiation of the further surface on the ther-
moscope will be expressed by 77 its minimum (y) is to be determined.
: oar =a 2ci(2a—a : . .
Now, by differentiating we obtain a = aa ; the equation which gives
. . a
the quantity will then be 2~—a=0, whence a= g.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. "{
sults obtained by means of the thermomultiplier*, and a source whose
radiation is much weakened by distance.
The apparatus is disposed in the following manner. A thermoelectric
pile of thirty pairs is closed at one end and enveloped, at the other, in
a small tube blackened inside to prevent reflection. Ata certain distance
there is placed a large metallic diaphragm, with an aperture at the
centre equal to the section of the pile. On the other side, in the same
line, there is a lighted lamp, which is brought more or less close, until
the needle which serves as the index of the galvanometer, marks an
elevation of 30°. The radiation is afterwards intercepted by a screen
of polished metal placed between the lamp and the diaphragm, and the
needle returns to zero. Then there is placed on the other side of the
diaphragm a stand, with a plate of glass fixed on it, and the whole ap-
paratus is moved gently until it is brought midway between the pile and
the calorific source.
This being done, the opake screen is removed; the rays passing
through the glass fall on the pile, and immediately cause the galvano-
meter to move. In 58 or 6° it is driven through an are of nearly 215,
but it afterwards returns nearly to zero, oscillates in an are of greater
or less extent, and at last settles definitively at 21°. This last deviation
decidedly marks the whole effect; for it is useless to continue the
experiment for 15° or 20°. There is no longer any perceptible move-
ment.
The time which the needle takes to attain its position of steady equi-
librium is a minute and a half+. When the experiment is repeated
* For the description of this instrument see the number of the Annales de
Chimie for October 1831.
+ Although the velocity with which radiant heat is propagated is unknown,
we are nevertheless pretty certain, since the experiments of Saussure and Pictet,
that this agent traverses spaces of from fifty to sixty feet in a time altogether
inappretiable. It might be asked, therefore, why does not our apparatus in-
stantaneously indicate the presence and the intensity of the rays emitted by the
source? To this I answer, Ist, that the index of the galvanometer deviates at
the very instant when the calorific communications are established, and we have
just seen that in five or six seconds it describes almost the whole are of devia-
tion. Ifa few seconds more are required to mark the entire action steadily, it
is because the great conducting power of the bismuth and the antimony, and
the great powers of absorption and emission belonging to their blackened sur-
faces, render the lapse of a certain interval necessary, in order that a balance
may take place between the rays which enter the pile and those which leave it
or are extinguished within its interior. But the time required for the definitive
equilibrium is much greater when common thermometers are used. If, for
instance, one of Rumford’s most delicate thermoscopes, having the ball black-
ened, and a metallic cover perforated on the side towards the source of heat, be
submitted to the action of calorific radiation, it will be found that the time re-
quisite to mark the whole effect is four or five times more than that required
by the thermomultiplier. This delay is the consequence of the obstructions en-
countered by the conductible heat in its passage through the glass, and in its
8 M. MELLONI ON THE FREE TRANSMISSION
with other plates of glass, or of any transparent substance whatsoever,
possessing different degrees of thickness, from the hundredth part of a
line to five or six inches, the galvanometer exhibits deviations greater
or less than 21°; but the time requisite to attain the equilibrium is in
all cases the same. In short, if we mark the time which the needle
takes to arrive at 30°, we shall find it to be one minute and a half.
The invariability of this time, in such a variety of circumstances,
affords the most decisive evidence that the deviations of the galvano-
meter are exclusively due to that portion of heat which reaches the
pile by immediate transmission. Whence it follows, that in the arrange-
ment we have adopted, the heat of the transparent body has no appre-
tiable influence on the instrument.
But a direct proof of this proposition may be obtained by operating
on opake screens.
I take a plate of glass a millimetre in thickness. I blacken it on one
uniform distribution over all the points of the mass of air within,—a distribution
which will necessarily take place, because of the fluidity of the thermoscopic
body.
Another inconvenience produced by the interposition of the glass, and from
which the thermomultiplier is free, is the lapse of a perceptible interval between
the commencement of the action and its manifestation on the instrument; for
there is always some time required, in order that the heat may pass from one
surface to the other. I speak not here of the caloric which might pass to the
air by free transmission through the diaphanous sides of the cover; for when
we have to estimate the intensities of caloric rays by means of thermoscopes, we
cannot dispense with the blackening of the glass. So necessary indeed is this,
that in order to make sure of the opacity of the glass, it must be overlaid with
several coats of colouring matter. Otherwise, a portion of the rays would freely
pass through the mass of air contained in the ball without dilating it.
Now, in the common thermoscopes, we always measure the radiation through
an opake plate of glass. This plate, however thin, must offer a considerable
resistance to the propagation of heat, because of the feebleness of its conducting
power, and will therefore, as we have already observed, render the apparatus
msensible during the first moments of action. Let it be observed, moreover,
that the more we endeavour to increase the sensibility of the thermoscope
by enlarging the dimensions of the balls, the more we diminish the promptitude
of its indications ; for the increase of volume is proportionally greater than that
of the part of the surface turned towards the source, and the mass of air within
is increased in a proportionally greater degree than those points of the glass
which can communicate to it the heat they have acquired. Hence arises a
greater difficulty in attaining the moment of equal temperature in all the points
of the fluid mass, and, of course, the necessity of a longer time to mark the en-
tire effect.
In fine, the thermoscopes are utterly useless when it is required to measure
caloric rays that are very feeble, and distributed according to given lines, or
forming sheaves of small dimension. In fact, it would be necessary in this case
to preserve the whole sensibility of the instrument by considerably reducing
the size of the balls. But this is impossible.
Whoever takes the trouble to weigh these considerations duly, will not, I
think, hesitate for a moment to prefer the thermomultiplier to every other ther-
moscopic apparatus in studying the subject of caloric radiation.
OF RADIANT HEAT THROUGH DIFFERENT BODIES, 9
side, and put it in the place of the transparent plate, taking care to turn
its blackened surface to the lamp. The needle remains stationary, al-
though the calorie rays continually fall on the anterior surface. It will
be found immoveable also, if we employ a plate of copper coated on
both sides with black colouring matter, or a thin flake of wood, or even
a sheet of paper. Thus, though we should suppose the screen to be
diaphanous, exceedingly thin, an excellent conductor of caloric, and
possessing great powers of absorption and emission, the utmost eleva-
tion of temperature that can be acquired during the experiment would
not furnish rays sufficiently strong to move the index of the galvano-
meter.
~ One is surprised at first to see caloric rays capable of giving a de-
viation of 30° fail to produce any effect when they are absorbed by the
screen, which must necessarily send its acquired heat upon the appa-
ratus. But our surprise ceases when we reflect that this heat is sent
equally in all directions by every point of the heated screen, and there-
fore that the portion of total radiation which reaches the apparatus is
but a very small fraction.
We shall see hereafter, that the anterior surface of the pile does not
measure six square centimetres. With these data, if we suppose even
that the thirty degrees of heat are completely absorbed by the screen,
and afterwards dispersed through space, we find that the quantity of
the rays which reach the thermoscopic body dees not amount to the
six-hundredth part of the whole. But the galvanometer that I use is
capable, at the most, of marking only the 150th part of the force which
moves the needle to 30°. Thus, even though the instrument were
capable of discovering the presence of a heat four times as feeble, there
would be no perceptible action.
The experiments which I have been deseribing seem to me to leave
no doubt whatsoever as to the truth of the proposition just now enun-
ciated ; namely, that in my mode of operating the deviation of the gal-
vanometer proceeds entirely from the heat instantaneously transmitted
through the screen. These proofs, though so conclusive to my mind,
seem however not to have been equally convincing to others ; for I have
heard some persons say, “‘ We grant that the deviation of 21° obtained
through the screen does not arise from the caloric propagated by con-
duction from the anterior to the other surface, but it may be main-
tained that it is caused by a heat instantaneously diffused, in the same
manner as light, over all the points of the glass.” Before we admit such
a mode of transmission, it seems to me that we ought to demonstrate its
existence by some decisive experiment. But supposing it true, then we
must also suppose one of these two things,—either that the molecules of
the glass acquire from the action of the source such modifications that
they themselves become so many calorific centres, and return to their
10 M. MELLONI ON THE FREE TRANSMISSION
natural state when the radiation is stopped; or that the heat, which is
supposed to be diffused through the material points of the screen, is but
common caloric obeying the known laws of equilibrium. In the first case
we should be only attempting to explain the very cause of the transmis-
sion, and the hypothesis, true or false, does not at all invalidate the fact
which we are desirous to establish. In the second case, this heat, when it
has reached the interior of the body, must take some time to issue from
it; besides, this time must vary with the thickness of the screen, and its
powers of conduction and emission. But let us intercept the calorific
communication in our apparatus ; let us remove the diaphanous screen
from its stand, and expose it for some moments to the free radiation of
the lamp on the other side of the diaphragm: if the supposition be true,
the internal molecules of the glass will instantaneously acquire some
heat. In order to see whether this heat really exists, let us replace the
screen on its stand before the pile, still leaving the calorific communi-
cation with the lamp intercepted. The further-surface of the plate of
glass will, according to the hypothesis, immediately begin to emit to-
wards the pile that caloric which reaches it successively from within,
and the index of the galvanometer must lose its equilibrium. But what-
ever be the nature or the thickness of the screen with which this expe-
riment is performed, we never obtain the slightest indication of a move-
ment in the magnetic needle. It is therefore completely demonstrated that
the deviations of the galvanometer exhibited in the experiments made
with the diaphanous sereens are not to be attributed, in the least degree,
either to the external or the internal heat of the screen itself, but solely
and exclusively to free transmission. Thus, whenever, in consequence
of the radiant heat of the source being made to fall on a screen, a
deviation of the galvanometer is perceptible, we may rest assured that
the whole of the effect produced is to be ascribed to the rays of heat
immediately transmitted through it, in the same manner as luminous
rays.
Before I conclude these preliminary considerations, it is necessary to
remark, Ist, that galvanometers of very great sensibility, such as must
be used for the thermomultiplier, do not directly indicate quantities
less than half-degrees ; 2ndly, that the ratios of the degrees of the gal-
vanometer and the forces of deviation are unknown. But it is often
useful to have the fractions below the half-degree, and in certain cir-
cumstances it is absolutely indispensable to know the ratios of the seve-
ral degrees of calorific action which move the magnetic needles to dif-
ferent distances from their primitive position.
To find the fractions sought, we have only to take the means of a
certain number of observations. As to the ratio of the deviations and
the forces, it is difficult and, in the present state of the science, perhaps
impossible to determine it generally. But electric piles, such as those
OF RADIANT HEAT THROUGH DIFFERENT BODIES. ll
employed in the construction of the thermomultiplier, furnish suffi-
ciently simple means of solying the question in each particular case.
Indeed there is nothing easier than to keep the index of the galvano-
meter at any degree of deviation. All that is required for this purpose
is to place a lighted lamp at proper distance from either side of the
thermoelectrical pile. To prevent the possibility of mistake on this
point, let us suppose the axis of the pile to be perpendicular to the
magnetic meridian, and the communications so fully established that,
when the left or the right side of the pile is heated, a corresponding de-
viation will be exhibited by the galvanometer. Let there be now pro-
duced a sufficiently marked deviation by placing a lamp near enough
at the same side. Let this deviation be 44°. After having brought the
needle back to 0° by interposing a metallic screen, let us make it move
to the 42nd degree of deviation on the left, by means of a second lamp
placed on the other side. To bring the needle back again to the zero
point of the scale, we have only to stop the radiation by means of a
metallic screen, as before.
It is natural to ask what will be the effect now produced by the heat
of both lamps being brought to bear simultaneously upon the opposite
sides of the pile. The calorific effects will be partially destroyed, and
the instrument will mark but their difference. If the same force were
always required to make the needles describe arcs containing the same
number of degrees, the index would stop at the second degree of devia-
tion to the right; but we know that these effects continually increase to
the right and to the left of zero. The difference of two degrees just
now observed between the partial deviations of 44° and 42° was owing
to the application of a force greater than what is required to make the
index traverse the first two degrees of the scale. The position marked
2° will therefore be exceeded, and the more so in proportion as the first
force is greater than the second, and the are described will, when com-
pared with the difference of the two deviations, immediately give the
measure of the corresponding force. If, for instance, the needle stops
at 8°, it will be inferred that the force required to make the needle pass
from 42° to 44° is four times greater than that required to make it pass
from zero to 2°.. This effect would be five times greater if the needle
stopped at 10°, and so of the rest.
I shall not attempt to conceal the fact, that in this process the propor-
tionality of the forces to the degrees in the are employed as a compara~
tive measure is tacitly assumed. But the assumption is fully justified
by experience ; for we find that in galvanometers whose astatic system
has been brought to a high degree of perfection, the magnetic needles,
through the whole extent of the arc comprised between zero and the
twentieth degree nearly, describe arcs proportional to the action of the
electric current to which they are subjected. To be convinced of this,
12 M. MELLONI ON THE FREE TRANSMISSION
it is by no means necessary to review in succession all the degrees that
contribute to the formation of this are. The application of our method
to the angles of 20° and 10° will be quite sufficient. This being done,
we shall find an equal quantity between their difference and the effect
produced by the simultaneous action of the moving forces. In other
words, let us produce a deviation of 20° to the right and one of 10° to
the left: let us then simultaneously expose the two opposite faces of the
pile to the two radiations which produce these galvanometric indica-
tions: the index will move to the right, and stop precisely at 10°.
Hence we infer that the force necessary to make the needle describe
the are comprised between 10° and 20° is equal to the force required
to make it pass over the first ten degrees of the scale. Thus the pro-
portion of the degrees to the forces is perceptible as far as the 20th de-
gree on each side of zero.
This fact seems opposed to the inference which might have been
made in examining the nature of the galvanometric action ; for, in the
successive rotation of the astatic system, the poles of the magnetic
needles depart from the mean line of the electric currents. The inten-
sity of the repulsive forces, therefore, decreases in proportion as the
angle of deviation increases. Whence we should conclude that the
effort necessary to make the needles exceed a given are should change
as soon as the first degrees of the scale are passed. This would un-
doubtedly take place if all the electric currents lay in a vertical plane
passing through the line marked 0° ; but the cireumvolutions of the me-
tallic wire which is wound on the frame placed under the graduated
circle are distributed to a certain extent on each side of this plain. In
the galvanometer which I have employed in my experiments, they cover
the two opposite arcs of 76°, the chords of which are perpendicular to
the line marked 0°. Thus so long as the oscillations take place within
certain limits there will always be electric currents situated on each side
of the needles. Now when the intensity of these currents is extremely
feeble, their sensible effect on the needles must cease at a very short
distance. Let us suppose this distance to be 18° of the division of the
galvanometer intended to show the degrees of electric action which
cause the deviations to the right and left for the first 20° of the scale.
These degrees of action must be extremely feeble in a very delicate gal-
vanometer. If, during these oscillations, the system of the needles is
confined within the two initial ares of 20°, it is clear that it will always
be subject to the same action, whatever may be the position in which it
is placed; for there will always be near its plane a series of currents
extending to 18° on each side, even when the system will occupy the
extreme limits. The influence of the currents that are further distant
will, according to our hypothesis, be nothing. As the moving force
will therefore have a constant value, we shall have to consider only the
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 13
modifications which the active part of this force is made to undergo by
the different inclination of the needles to the direction of the currents ;
and these modifications are quite analogous to those which take place
in the portion of gravity that acts on the pendulum in different ares of
oscillation.
Now the force necessary to make the pendulum vibrate from one in-
clination to the other, is proportional to the difference of the cosines of
the angles which the two directions form with the vertical. Whence it
is clear that it remains sensibly constant in the ares that are not far re-
moved from the line of rest. The same effect must therefore be pro-
duced in the galvanometer also ; or, in other words, the force required
in this apparatus to increase the deviation of the index by a degree will
be constant near the line of zero, as is shown by experiment.
From what we have just said it will be easy to see that the relation
between the degrees of the galvanometer and the forces which cause
the deviations of the needles, must depend on the sensibility of the
astatic system and the distribution of the wire on the frame*. It will
vary, therefore, according to the construction of the instrument, but
may be always determined by the method we have mentioned.
Experiment having shown that in my galvanometer the proportion of
* In order to understand this clearly, it is sufficient to suppose a galvanome-
ter in which the circumvolutions of the wire are more numerous towards the
extremities than towards the central part. It is evident that under the action
of such a system the forces which produce the deviations, instead of increasing
or being merely proportional in the ares near zero, must decrease as we approach
the extremities of the frame, in order to increase afterwards when the index has
passed these positions. !
As to the influence of the sensibility of the astatic system, we shall be able to
form a tolerably exact idea of it, if we imagine a galvanometer with the two
needles possessing very different degrees of magnetism. Then the terrestrial
globe will very powerfully affect both combined; and, in order to produce the
least deviations, electric currents must be employed possessing much greater
force than those required to produce small deviations in a more perfect astatic
system. In the positions near zero, the electro-magnetic action produced by
the most distant currents, that is, the action of the currents situated at the ex-
tremities of the frame, will possess an energy sufficient at least to overcome the
resistance arising from the twisting of the suspension thread and the inertia of
the astatic system. It will therefore always contribute to move the oscillating
mass. Hence it is evident that if the needles are displaced in the slightest de-
gree, the consequence will be a loss in the moving force; for if the system ap-
proaches a certain arc at a certain extremity, it recedes at the same time double
the distance from the opposite extremity. Now we have already seen that, in
delicate galvanometers, the moving force is constant when the angles are small ;
and we have assigned the cause of this fact upon the incontestible principle that,
in small deviations of the instrument, the action of the currents situated towards
the extremities of the frame must be disregarded, not indeed because they have
no value, but because it becomes, in consequence of its distance, extremely
feeble, and incapable of surmounting the obstacles opposed to it by the torsion
of the silk thread and the inertia of the needles.
14 M. MELLONI ON THE FREE TRANSMISSION
the degrees to the forces was perceptible as far as the twentieth degree
of the scale, I have attentively observed the passage of the index through
every 4°, by commencing with this position and continuing my obser-
vations as far as the forty-fourth degree. There I stopped; for my ex-
periments on calorific transmission were to be confined to radiations
considerably weakened by distance.
The ares passed once in virtue of the forces acting on the system of
the needles at different points of their course are in the following ratios
to one another:
The are comprised between
20° and 24° is equivalent to 5°12, commencing at zero.
24 — 28 6°44:
28 — 32 —— 8 -00
32 — 36 — 9°92
36 — 40 —-——. 12 44
40 — 44 19 *04
Each number in the third column represents the mean of eight obser-
vations, which agreed with one another as exactly as could be expected
from the nature of the instrument. Often equal, sometimes differing
by 0%5, their greatest disagreement never exceeded 1°. A better proof
cannot be given of the exactness of the method.
The linear construction of these results, which gives a very regular
curve convex towards the axis of the wes, has enabled me to obtain the
values of the intermediate forces, degree by degree, from 20° to 45°.
By connecting them with the fundamental observations, I have formed
the following table of the intensities :
Degrees. | Forces. | Degrees. | Forces. | Degrees. | Forces.
29° 33°4: 38°
30 airy, 39
31 374
32 39°6
33 41°8
34 440]
35 46°7
36 49°5
37 52-4
The use of a table requires no explanations. All the forces are re-
ferred to that which makes the index describe the first degree of the
scale. The values corresponding with the first twenty degrees are not
exhibited in it; for through the whole extent of this are the number
representing the force is equal to the number of degrees contained in
the are passed over by the index. Thus, for instance, when we look
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 15
for the forces which produce the deviations 35° and 16°, the first (46°7)
will be found in the table, but the second, being under 20°, will have
the same value as the arc; that is to say, 16. When we want to find
the forces which correspond to fractions of a degree, we have only to
ascertain the proportional part of the degree in question ; for, in the
interval between one degree and another, the curve visibly coincides
with the tangent. If, for example, we wish to know the force that cor-
responds to the deviation 31°7, it will be sufficient to take at first the
difference between 37:4 and 39°6 (the intensities of the forces belong-
ing to 31° and 32°); this difference being 22, we shall find the value
(x) of the force corresponding to seven tenths of the degree contained
between 30° and 32° by this proportion,
Petes aie 2 ou lea
Adding this to the number 37-4, which represents the force correspond-
ing to 31°, we shall have 38-9 as the value sought.
Of the Polish, the Thickness, and the Nature of the Screens.
The suggestions which we have offered as to the manner of measuring
the quantity of caloric instantaneously transmitted by diaphanous bodies,
and as to the precautions to be taken during the experiments, leave us
searcely anything more to say on this subject. Nevertheless it may not
be amiss to mention some particulars relative to the construction of the
apparatus before we proceed to the exposition of the results.
The pile employed in these researches is of the form of a quadrangu-
lar prism; its two ends are plane surfaces, each measuring 4°24 centi-
metres; it consists of 27 pairs and a half, or 5 elements of bismuth and
antimony, 32 millimetres long, 2°5 broad, and 1 in thickness. It was
not without considerable difficulty that we succeeded in combining and
soldering together these minute bars. The facility with which liquid
antimony oxidizes, the difference between its fusibility and that of the
bismuth, and the extreme fragility of the two metals, presented so many
obstacles, that it cost many an effort to overcome them. But a pile of
very small dimensions was indispensable in the investigation of the laws
of immediate transmission through rare liquids and crystallized solids.
This was, therefore, to be obtained, or the experiments to be aban-
doned. By this conviction we have been induced to persevere in spite
of repeated disappointments, and by redoubling our patience have at
last succeeded.
The electric pile is passed into a ring formed of a thin square flake
of copper internally lined with pasteboard and having a screw which
serves to fix it on the stand, so that the axis naturally takes that hori-
zontal position which it is to keep during the greatest part of the ex-
periments. To each side of the ring there is fitted a tube of six cen-
16 M. MELLONI ON THE FREE TRANSMISSION
timetres in length, blackened on the inside; and at a certain distance
from the mouths of these tubes are placed the stands destined to receive
the screens. In strictness, a single tube and a single stand would be
sufficient, and one of the sides of the pile might be closed by means of
asmall metallic cover ; but, when we have to operate on bodies differing
in quality and thickness, it often happens that they differ in tempera-
ture not only from one another but from the pile also. Then if we
place but one screen before the apparatus, the calorific actions at the
two sides are unequal, the index of the galvanometer moves away from
zero, and we must wait for some time until the equilibrium of the tem-
perature is established and the index returns to its original position.
Now this inconvenience cannot occur when the pile is furnished with
two tubes and two stands; for, by placing before each side of it a plate
of the same quality and thickness, it is clear that, if care be previously
taken to place the two in the same circumstances, they will have the
same temperature, and will consequently emit the same quantity of heat
on the two sides of the pile. The index of the galvanometer will re-
main stationary, whatever may be the difference of temperature between
the plates and the thermoscopic body, and we may therefore immediately
proceed with the experiments. Hence, if we would save time, we should
always have a pair of screens of each sort; and, as we have just observed,
put both sides of the pile in the same state.
In order to ascertain the influence exercised on free transmission, by
the different circumstances relating to the surface, the volume, and the
composition of the sereens, we must procure a constant source of heat.
For this purpose, there is nothing better than a good lamp with a double
current of air and a constant level. When this apparatus is well pre-
pared and filled with oil freed from mucilage, by means of sulphuric acid,
we obtain a flame which maintains an invariable temperature for more
than two hours. Of this I have been able to satisfy myself by means of the
thermomultiplier. But in order to have things in this preparatory state,
we must wait some moments until the pipe, the oil, and the glass funnel
of the lamp shall have attained a maximum of temperature. This time,
which varies a little with the construction of the lamp, is about ten or
fifteen minutes.
There may be some objections raised against the employment of an
Argand lamp asa calorific source. It will be said, perhaps, that in this
lamp the heat acts only through the glass funnel; that the funnel itself
becomes heated, and mixes its rays of nonluminous heat with the lumi-
nous caloric of the flame; and lastly, that such a source of heat is
neither uniform nor separated from the agent which usually accom-
panies it in high temperatures.
But I wish it to be particularly observed, that the only thing about
which we are interested at present is, to know whether the state of the.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 17
surface, the colour, and the internal structure of a body, as well as its
chemical composition, have any influence whatever in the quantity of
heat which it transmits immediately; and that, in this point of view, the
origin and the qualities of the caloric rays become objects of perfect
indifference; for it is enough for our purpose that the rays be invari-
able and identical in all the circumstances in which they are employed.
Now this actually is the case with the rays issuing from the well sup-
ported flame of a Quinquet lamp placed at a fixed distance.
When we shall have found the ratios of the quantities of heat trans-
mitted by screens of different kinds under the influence of a constant
source, then, agreeably to what we have stated in the introduction, we
shall examine the changes which those ratios undergo in consequence
of the variation of the sources.
All our experiments of comparison have been made with the same
calorific radiation. Previously to the commencement of each series
the rays were allowed to fall directly on the pile, and the distance of
the lamp was modified until the needle of the galvanometer fixed itself
at 30° of the scale.
’ We have remarked in the preliminary considerations, that all the
external parts of the thermoscope are sheltered from the caloric rays by
means of a large screen of polished metal, having in its central part a hole
to correspond with the opening of the pile turned towards the lamp.
In order to establish or to intercept the communication between this
aperture and the source of heat securely and commodiously, we make
use of a moveable copper screen, consisting of two or three parallel
plates fixed on the same support. The side of the pile opposite to the
lamp may also be closed and opened by means of a screen altogether
similar, and for the following purpose :
When, after having observed the effect of any radiation whatsoever,
we intercept the action of the source, we must wait until that face of
the pile on which the rays of heat are darted has been restored to its
natural state before we make a second observation. Now it appears
that the heat emitted by the flame penetrates the apparatus with greater
ease than it issues from it, because of its natural tendency to an equili-
brium. At least the experiment shows that the time requisite to pro-
duce the deviation is to that in which the needle recovers its original
position nearly as one to five ; for the latter is from 7% to 88, and we
have seen that the whole deviation is produced in a minute and a half:
Whatever be the cause of this difference between the time required for
heating and that required for cooling, we must always allow 8° to elapse
after one experiment before we proceed to another, if we confine our-
selves to the placing of the first moveable screen before the radiating
source. But let the opposite side of the pile be opened and a lighted
candle brought close to the corresponding face: it is evident that if the
Vor. L—Parr I. c
18 M. MELLONI ON THE FREE TRANSMISSION
candle be held for some minutes at a suitable distancé, and the com-
munication then intercepted, the needle will be forced back to zero in
an interval of time less than 8°. These operations would be impossible
if the side of the pile opposite to the lamp were hermetically closed.
The second moveable screen serves then to abridge the duration of the
experiments. It is particularly useful when the calorific action has
been very powerful or considerably prolonged, which sometimes happens
in the first attempts at adjustment. During these, the portions of heat
penetrate the pile toa great depth, and cannot return until a considerable
time has elapsed. Before these simple means of correction had occurred
to me, the difficulty of restoring the equilibrium of the two extremes of
the pile, as well as that which I experienced in respect to ‘he different
temperatures of the screens and the apparatus, often obliged me to stand
still for fifteen or twenty minutes between two consecutive experiments.
When any object of research requires numerous experiments, we
should endeavour from the very outset to avail ourselves of all that
contributes to make them more expeditious; for the least delay arising
from imperfectness of method will, by gradually accumulating, ulti-
mately render the labour of whole days utterly fruitless. Yet, the at-
tention being absorbed by the main object, these little defects are at
first unnoticed. At length, however, we become sensible of them, and
endeavour to apply aremedy when it is almost too late. But the result
of the experiment is not without its use, since it may be more or less
serviceable in analogous circumstances. This consideration must be
my apology for the minuteness of detail into which I have entered.
The first problem that presents: itself, in the series of questions rela-
tive to the passage of radiant heat through solid bodies, is to determine
the influence which the degree of their, polish has, and the quantity of
rays transmitted. In order to solve this, we have but to apply our
thermometrical method to several screens perfectly similar in all re-
spects, except as to the state of the surface.
Out of the glass of a mirror which was very pure, and nine milli-
metres in thickness, I cut eight pieces sufficiently large to cover the
central aperture of the screen when they were placed on the stand; and,
after having removed the quicksilver, I wore them down with sand,
emery, and other such substances, so as to form by their succession a
complete series of plane surfaces more or less finely wrought, from the
first and coarsest to the highest and most perfect polish. These dif-
ferent pieces reduced to one common thickness of 8™™-371* and ex-
* All the measures of small degrees of thickness contained in this Memoir
have been taken with a pair of calipers with pivots, a species of double com-
passes, with a spring and with legs of unequal lengths, much used in the manu-
facture of clockwork. This instrument measures directly, and with great nicety,
even the fortieth part of a line.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 19
posed to a radiation of 30° of the thermomultiplier, have furnished the
following results :
Order of the screens. Deviations of the
galvanometer.
PoP. 4.60.2: .canteceuseders 538
QD. ——— hee eecseceeenees 6°50
Be ———$———. hs ss sncceccncceccscneces 8°66
Re Eien tS OE ENG 12°58
Oo Sar eR Re SCO COE CEC OC ERSCEL 14°79
C. Suehibe dal a5 ..ctge ssi excaeie 17°42
Met MEAN SDATOUG os nannnanchs ch =srned 18°79
8. 19°15
These transmissions present nothing extraordinary: the quantity of
heat which passes through the medium is greater in proportion as the
surface is more finely polished, as it happens in respect to light. The
only thing to be remarked is, that in the high degrees of polish a slight
difference produces a very slight effect. This is evident from the ob-
servations made on Nos. 7 and 8.
Similar processes enable us to determine the influence of thickness,
which is one of the elements most necessary to be known in the theory
of transmission.
Four pieces cut out of a fine mirror were reduced with great nicety
to different degrees of thickness in the ratio of 1, 2, 3, 4: particular
care was taken to give to their principal surfaces a perfect parallelism,
and the highest polish possible. The following are the deviations which
they successively produced in the index of the galvanometer under the
action of the same radiation, namely 30°:
Thickness of the screens Deviations of the Corresponding
in millimetres. galvanometer. forces.
°
. 2:068 21°625 21°850
4°136 20°312 20°343
6°202 19°687 19°687
8272 19°375 19°375
Each number in the second column is deduced from fifteen observa-
tions: the quantities registered under the denomination of forces,
representing in this particular case the respective temperatures or
quantities of rays transmitted, have been calculated according to the
principles with the exposition of which we concluded our general ob-
servations. The force or temperature answering to 30°, as given by
the table of intensities, is 35°3; now, by dividing each number of the
third column by 35°3, we shall obtain the ratios of the transmitted rays
to the incident rays. The difference between each of these quotients and
unity will give the corresponding loss; that is, the proportional part of
ss Bits
-
20 M. MELLONI ON THE FREE TRANSMISSION
;
the rays that are stopped. By performing these operations, and repre-
senting the whole radiation by 1000, we obtain
TABLE A.
Order of the Transmitted
screens. rays. nore stopped.
1. 619 ok aa
2. 576 4.24.
3. 558 442
4. 549 451
Let us imagine the thickest of the screens split into four equal layers ;
the quantities of heat falling upon each will be
1000, 619, 576, 558,
and the quantities lost in successively traversing the four intervals
381, 424—381, 442-424, 451—442;
that is to say,
$81, 43, 18, 9.
_ Weshall then have for the ratios of the respective losses to the incident
quantities,
381 43 18 9
1000’ 619° 576° 553°
or
0°381, 0-071, 0-031, 0-016.
Thus the losses continue to decrease with great rapidity as the thickness
increases by a constant quantity.
We have seen that the action of the radiation on the thermomulti-
plier commences at the instant when the communications are established,
produces the greatest part of its effect in the first five or six seconds,
and ceases entirely after a minute and a half. These facts, which are
equally true of the direct rays and of those which reach the pile after
having passed through screens of any thickness whatsoever, constitute
the best proof that caloric is transmitted by radiation through the inte-
rior of the diaphanous bodies. . If, nevertheless, a new confirmation of
this truth were desired, it would be found in the successive diminution
of the losses which the rays undergo in crossing the different layers of
a transparent medium. Were the heat, which is the subject of our im-
mediate inquiries, the effect of a species of conducting power, the losses
would continually increase from layer to layer, or would remain con-
stant, from the moment when the rays penetrated the medium, and
could never follow the opposite law of decrease.
The progressive diminution of the losses is, moreover, entirely pecu-
liar to the calorific radiation, whose properties in this and in many other
respects are altogether different from those of the luminous rays. In
OF RADIANT HEAT THROUGH DIFFERENT BODIES. oT
fact, everything leads us to believe that the equal layers which succeed
one another in a diaphanous medium act in the same manner on the
rays of light which come in succession to pass through them, and that
they consequently absorb or reflect a quantity of light. proportional
to the intensity of the incident rays; that is to say, that the loss sus-
tained by the luminous radiation at every layer of equal thickness is
constant. In the case under consideration, the invariable decrement of
the light at each of the layers into which we suppose the screen divided
is found to be none at all, or extremely feeble, because of the perfect
transparency of the glass; and yet the caloric rays undergo in their
successive passages an absorption, the sum of which is equal to about
the half of their whole value ; and the losses at each layer, instead of
being constant, as happens to those sustained by the luminous rays, are
found to differ enormously from one another, being in the proportion of
the numbers 381, 71, 31, and 16.
The resistance of diaphanous media to the immediate transmission of
the rays of heat is therefore of a nature altogether different from that
which is presented by the same media to the propagation of light.
Whatever be the cause of this singular difference, it is highly im-
portant to determine with certainty whether it takes place at great di-
stances from the surface at which the rays enter; and this may be done
by repeating the experiments on layers of glass much thicker than those
which we have been using. .
With this view I took several pieces of the glass of Saint-Gobain, and
caused them to be recast. This operation was not completely suecess-
ful. The matter either formed itself into layers that were too thin, or
was slightly striated. From among the thick pieces I selected that which
was the purest. It was six inches in length. I divided it into three parts,
of one, two, and three inches in thickness. The defects being uniformly
distributed over all the points of the mass might probably enough alter
the quantity of the caloric rays that would have passed through a per-
fectly pure mass of the same matter and thickness; but it is clear that
they could have no influence on the nature of the progression of the
losses which these rays might undergo in passing from one layer to an-
other.
The following are the results obtained by exposing these screens to
the ordinary radiation of 30° :
Thickness of the screens
See tae Galvanometric deviations.
in millimetres.
o
27 177105
54 13°458
81 - 10°702
By a calculation exactly similar to that already made we find that,
22 M. MELLONI ON THE FREE TRANSMISSION
of every thousand rays emanating from the source, each screen transmits
or stops the following quantities :
Order. Rays transmitted. Rays stopped.
1. 484 516
2. ae 380 620
3. 303 697
By means of these data we obtain as the values of the calorific losses,
considered with reference to the quantities of rays which present them-
selves successively to pass through the three equal layers into which we
may suppose the last screen divided,
0°516 0°215 0°203.
These losses are still greater than those preceding, because of the
badness of the material and the greater thickness of the layers, but they
are still in a decreasing progression. Thus the diminution continues
beyond 54 millimetres.
To compare this diminution with that which took place in the last
screen in the preceding experiments we must multiply 0012 (the differ-
ence between 0°215 and 0°203) by 2:068, and divide the product by 27.
In this way we obtain the mean diminution for a thickness of 2™-068
in passing from 54 to 81 millimetres, which is nearly 0-001; in the pre-
ceding experiment it was fifteen times as much while the rays passed
through the same layer of 2"™-068 placed at a distance of 6 millimetres.
The difference would be still greater if we had used very transparent
layers of glass, such as flakes of the glass of a mirror attenuated.
Nevertheless I had some doubts as to the homogeneity of the glass:
I was afraid that the striz might not be equally distributed over all the
points of the mass. But not being able to procure large pieces of this
material entirely free from defects, I thought that analogous experi-
ments performed with liquids might answer quite as well. In employ-
ing these instead of glass there was, in case of success, the additional
advantage of extending the law of calorific transmission by making it
independent of the physical constitution of the medium.
I procured therefore several copper troughs, of the same breadth but
of different lengths, bounded at each end by a glass plate. These I placed
successively between the perforated screen and the pile in such a manner
that the anterior glass plate was quite near the screen, the distance of
which remained constantly the same. The common section of the troughs
was much larger than the central aperture of the screen; the reflexions
on the lateral faces could not take place, and the only rays that entered
a little out of the perpendicular direction reached the anterior surface of
the pile. The lamp was moved up so near that the needle of the gal-
vanometer exhibited a deviation of 30° through the two glass plates of
each trough. The radiation was then intercepted, the trough filled with.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 23
oil of colza*, and after having waited until the needle recovered its ori-
ginal position we reestablished the calorific communication.
The deviations obtained through the different thicknesses of the li-
quid are exhibited in the following table.
Degrees of thickness of Deviations of the galva-
the liquid layer. nometer.
mm o
6°767 15°642
13°535 12°831
27:069 10°389
54°139 9°540
81°209 8-988
108°279 8512
The free radiation being always represented by 1000, the respective
quantities of the rays transmitted and those stopped are found to be :
TaBLeE B.
Degree of hckness of Guay transmitted, Rays slope
mm
6°767- 443 557
13°535 363 637
27:069 294 706
54°139 270 730
71-209 255 745
108°279 44 756
If we suppose the last layer (of 108™"-274) subdivided into six paral-
lel slices of the following degrees of thickness : 6™"*767, 6°767, 13°535,
27-069, 27-069, and 27-069, we shall be able to determine, by means
of the numbers contained in the two last columns, the quantity of heat
incident to the first surface of each of these slices and the quantity lost
in the passage. Dividing the second by the first we shall ascertain the
loss. It is unnecessary to exhibit the operations in detail, as they are in
all respects similar to those which have been performed in reference to
the screens of glass. Here are the final results:
Degrees of thickness of the six Losses in the respective transmissions
successive slices into which referred to the quantities of
we suppose the layer of rays which arrive at the
108"™-274 to be divided. surface of each slice.
mm
6°767 0°557
6°767 0°180
13°535 0°190
27-069 0°082
27:069 0°056
27°069 0:040
[* It may be proper to inform the English reader that “oil of colza”’ is an oil
expressed from the seeds of the ChowColza of the French, Brassica arvensis, Linn.
It must not be confounded with the rape oi! of England, obtained from the Rape,
Brassica Napus—Evit.]
24: M. MELLONI ON THE FREE TRANSMISSION
Whence it is concluded that the losses still decrease at a distance of
about 100 millimetres.
To comprehend at a single glance the law of the propagation of ca-
loric radiating through diaphanous media we have only to reduce the
results contained in the first two columns of the Tables A. and B, to a
linear construction.
The mere inspection of the curves thus constructed shows that the rays
lose very considerably when they are entering the first layers of the me-
dium. But in proportion to their distance from the surface we see that
the loss decreases and that at a certain distance it is almost imperceptible,
and the rays seem to continue their progress, retaining all their inten-
sity ; so that in glass and in oil of colza, and probably in all other dia-
phanous media, the portion of heat which has forced its passage through
the first layers must penetrate to very great depths.
Delaroche had found that the heat which has passed through one
plate of glass becomes less subject to absorption when it is passing
through a second. The identity of this fact with the law of resistance
in continuous media shows that the solution of the continuity and the
interposition of the atmosphere between the two screens do not alter
the nature of the modifications which the rays undergo in the first plate
of glass. It is therefore exceedingly probable that the proposition of
Delaroche is true with respect to a very numerous series of thin screens;
for we have just seen that in the same medium the losses still diminish to
the depth of 80 or 100 millimetres. In reference to this point, the follow-
ing is the result of the experiments I have made with four plates of the
same glass that had been employed in the first attempts to investigate the
law of propagation through continuous media ©The common thickness
of these plates was 2™™-068.
Numbers of Deviations of the galva-
the screens. nometer.
°o
8 21°62
2: 18°75
3. 17°10
4. 15°90
It is scarcely necessary to observe that the common radiation to which
the screens had been exposed was always 30 degrees, answering to a
force or temperature of 35:3. If we represent this radiation by 1000, as
we have done in all the foregoing cases, we have:
Numbers of the screens. Rays transmitted. Rays stopped.
l. 619 381
2. 531 469
Se 484 515
4 4.50 540
Whence oe have
0381, 07134, 0'087, 0:058,
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 25
as the losses suffered by the rays in successively passing through the four
plates of glass; it being carefully kept in mind that these values are not
referred to the initial quantity, but to the number of rays which arrive
at the surface of each screen.
Thus the proposition of Delaroche is true as far as the third and the
fourth screens; for in the transition from one loss to another a dimi-
nution of each loss is observable.
It will have been observed that the losses were not so great in re-
spect to the four equal layers of the screen of a fourfold thickness ; and
that this should happen will be easily conceived if we consider that in
the latter case there is a solution of continuity which causes a greater
dispersion of the heat by reflexion. But we see that in both cases the
difference between two successive losses becomes less in proportion as
the distance from the surface, at which the rays entered, is greater.
Let us now proceed to consider the influence exercised on calorific
transmission by the composition of the substance of the screen.
M. Prevost had concluded from the experiments described in a me-
moir already quoted, that water and glass ought to transmit rays of heat
in different quantities ; for by causing the sheet of water to fall between
the lighted candle and a very delicate air-thermometer, he obtained no
indication of heat being transmitted unless when he had blackened the
ball of the thermometer, and even then the increase of temperature was
extremely small ; whilst a plate of glass substituted for the sheet of water
produced effects sufficiently manifest*. But it was objected to him that
the difference between the action of the water and that of the glass was
owing to the conductible caloric which was perceptible in the latter
case only. Delaroche subsequently observed that a square of greenish
glass transmitted more heat than a plate of another species of glass
perfectly pure. However, as the first flake was much thinner than
the second, it was insisted that the difference in the effects was owing
to the difference of thickness. At length, some time after the in-
vention of the thermomultiplier, M. Nobili and myself made some ex-
periments on olive oil, alcohol, water, and nitric acid; whence we in-
ferred that water opposed a greater resistance than any of the three
other liquids did to the passage of rays of heat emanating from a hot
iron+. But these experiments are to be regarded only as mere trials,
tending to show the facility with which the thermomultiplier may be
employed in all sorts of inquiries relative to calorific radiation ; for we
did not take sufficient precautions to prevent the heat from passing by
_ * His own words are: “It appears, therefore, that water does not allow so
much caloric to pass immediately as glass does. At least it affords a passage of
that kind ouly to a quantity of caloric more minute than that which passes
through the glass.” (Mem. already quoted, § 48.)
+ See the note in page 4,
26 M. MELLONI ON THE FREE TRANSMISSION
means of conduction, and to be sure that the temperature was the same
throughout. Thus it was still believed that the portion of heat trans-
mitted through solid or liquid substances was governed by the same
laws as the transmission of light, and that, ceteris paribus, the most
diaphanous bodies transmitted the greatest quantity of caloric rays.
The results which I am about to state seem to me to establish beyond
the possibility of doubt a fundamental proposition in the theory of ra-
diant heat, namely, that the power of transmitting caloric rays is by
no means proportioned to the transparency of the media; it is subject
to a different law, which, in bodies without regular crystallization, ap-
pears to have many affinities to refrangibility. In crystals the pheeno-
mena are still more interesting, since in them we find that bodies pos-
sessing a high degree of transparency intercept nearly the whole of the
caloric rays, while some others act in a manner directly contrary. These
properties are invariably manifested whatever be the temperature of the
source, and become yet more singular at low temperatures ; for in the
latter case we find that the ordinary heat of the hand passes immediately
through a solid body of. several inches in thickness. Let us not, how-
ever, anticipate as to the facts, but first of all examine the methods pur-
sued in this third series of experiments.
In the first place it is unnecessary to dwell on the manner in which
the solid screens have been exposed to the radiation and the indications
of the thermomultiplier, for in this respect everything was the same as
in the previous experiments. As to the liquids, these bodies are less
permeable to radiant heat than solid bodies are. They must therefore
be brought nearer to the thermoscope in order to obtain a well-marked
transmission; but then the proper heat of the molecules themselves
might be able to act on the instrument, and this the more certainly as
the motions always developed in liquids unequally heated easily transfer
the particles of the anterior to the further surface of the layers exposed
to the source of heat. This effect of conductibility cannot be neutralized
in a general manner by continually renewing the interposed layer, as in
the experiments of M. Prevost ; for some of the liquids can be procured
only in small quantities ; others, as soon as they are exposed to atmo-
spherie air, undergo considerable alterations and evaporations which
produce corresponding elevations or depressions of temperature that
prove very annoying in experiments of this kind. The contrivance
which I have employed for the purpose of avoiding these inconve-
niences is very simple. It consists in putting the liquids into very flat
glass recipients, whose two large lateral surfaces are perfectly parallel,
and the height four or five times that of the surface of the thermo-
electrical pile. The lower part of these vessels is applied to the mouth
of the tube that envelops the face of the apparatus turned towards the
source. The heat stopped by the anterior face of the vessel penetrates
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 27
the first infinitely thin layer of the liquid; but this layer, while it is
becoming hot, undergoes a certain dilatation, becomes lighter than the
rest of the fluid mass, and ascends immediately to the upper part of the
vessel, whence it can have no longer any influence on the pile. It is
replaced by a second layer, which undergoes a similar process, and this
again by others; so that by these partial renovations of the liquid
sereen, the hinder part of the glass applied to the aperture of the tube
is not in contact with heated molecules, and retains the same tempera-
ture for a long time.
It was extremely difficult to make flat glass vessels with very regular
surfaces of the same thickness throughout, and with the opposite sides
exactly parallel. Metallic frames and glasses joined with gum could
not be employed because of the corrosive action of the several liquids.
After many a fruitless effort to surmount this difficulty, I thought at last
that the process by which the index of refraction of liquids is measured
in optics might be available in this case also. With this view I had
quadrangular pieces of two centimetres in breadth and nine centi-
metres in length cut out of several pieces of the same mirror unsil-
vered and sufficiently thick. I laid close to the two faces of each of the
pieces from which the excision had been made two flakes made out of
another and a much thinner glass. It is known that the mere adhesion
of two plates of polished glass is sufficient to prevent the passage of
liquids. However, in order to be more secure, I introduced each reci-
pient between two metallic frames, which held the thin glasses in their
places by means of four screws placed at the angles. The liquid was
poured into these vessels at a small aperture made at the top, and fur-
nished with a glass stopper. In such a system there could be no doubt
of the parallelism of the faces and the equal thickness of the layers.
The results furnished by the several bodies, both solid and liquid, I
have disposed in several tables, each of them exhibiting at the top the
common thickness of the screens employed and, beside the substance,
the indications of the thermomultiplier and the quantity of rays trans-
mitted as compared with the whole radiation. This distribution, while
it allows the use of plates of different thicknesses, has the additional ad-
vantage of presenting distinct groups of each class of bodies. The free ra~
diation in each case was 30°. In order to link the results of these tables
together, I have commenced the second and the third with the numbers
given by a flake of glass placed in the same circumstances as the plates
which constitute each group: thus the glass set down in the table of
liquids was contained between the two thin plates of the recipients, and
made of the thick looking-glass employed in their construction. It was
therefore exactly of the same thickness as the liquid layers, and, like
them, came into contact with the thin plates which formed the faces of
the recipients. But as those faces themselves intercepted a portion of
28 M. MELLONI ON THE FREE TRANSMISSION
the heat, the lamp was brought nearer and nearer until we obtained,
through the combination of the three plates, the same indication of 19°
that was furnished by the thick glass when exposed singly to the radia-
tion of 30°.
TaBLeE I.— Glass (uncoloured). Common thickness 188.
Deviations of Rays
the galvanometer. transmitted.
No screen . noetgurceseae 30°00 100
Flint-glass - Guinand) .. Br 22°90 67
Flint-glass skank MOS 22°43 65
Flint-glass (French)... ag ligaivdnt re 22°36 64
Another kind. ..,:s000 cos sean <onsinvervasiy se 22°19 64
Mirror-gass .......cscecsrcesssseceresenenees 21°89 62
Another kind . ...,...ccseccccccesercessoeses 21°10 60
PATIOGHED KING" St, ccnusnaesccsens oes cevesaess 20°78 59
Crown-glass (French) ... by dt a ge 20°58 58
Window-glass (common)... oR R 19°25 54
Another kind ° Was Sac teuisere eeaees 18°56 52
Another kind ..... cvabih sfuaaiete-sfplhe 17°83 50
Crown-glass (English)... IR Ae Meets 17-22 49
Tas_e II.—JZiquids... Common thickness 9™™21,
Deviations of Rays |
the galvanometer. transmitted.
Mirror-glass .. leds 19°10 53:
Carburet of sulphur (colourless)... biaabhstenis 21°96 63
Chloride of sulphur (of a strong brown-
ISTE COLOUL) cos usaspestacesneh same dehe 21°83 63
Protochloride of phosphorus Sener 21°80 Ga. +
Hydrocarburet of chlorine (colourless 13:27 37
Nut-oil (yellow) v.i..... 0c. secesssescneees 11710 31
Essence of turpentine (colourless) ...... 10°83 31
Essence of rosemary piNeeest eoceowee 10°46 30
Oil of colza (yellow) . ania 10°38 30
Oil of olives (greenish yellow) meen ok 10°35 30
Naphtha (natural—a light brown yellow) Sat it 28
Balsam of copaiba (a sufficiently decided
brown yellow) ¢.2.0..00. 022 oo eoseecens 9°39 26
Essence of lavender (colourless)......... 9°28 26
Oil of pink [Auzle deillet)} (very om
yellowish) ... eae 9°26 26
Naphtha (rectified, colourless) oanaiinads 9°10 26
Sulphuric zther (colourless) .......+++++ 759 21
Pure sulphuric acid (colourless) ... Bree 615 17
Sulphuric acid (of Nordhausen, of a suf- ‘
ficiently decided brown) .........6600+- 6°09 17
Hydrate of ammonia (colourless). 547 icp uk
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 29
Taste I[.—continued.
Deviations of Rays
the galvanometer. transmitted.
Nitric acid (pure and colourless) ...... 5°36 15,
Alcohol (absolute and colourless) ...... 5°30 15
Hydrate of potassium (colourless) ...... 4°63 i3
Acetic acid (rectified, colourless) ...... 4°25 12
Pyroligneous acid (of a slightly brown-
ish colour)........ 4°28 12
Sugared water [ean sucrée ] (colourless) 4°20 12
Alum water (colourless) ..............+++ 4°16 12
Salt water (colourless)* '.............+.+0 4°15 12
White of eggs (slightly sina res 4-00 11
Distilled water . Basins 3°80 1]
Tas eE III.— Crystallized bodies. Common thickness 2™62.
Deviations of Rays
the galvanometer. transmitted.
Mirror-glass ......... si Batccet 21°60 62
Rock salt (diaphanous) patra 28°46 92
Iceland spar (diaphanous) .. shaver Meas 21°80 62
Another species (diaphanous)............ 21°30 61
Rock crystal, colourless (diaphanous)... 21°64 62
Rock crystal, smoky (diaphanous and
very decidedly brown)... 20°25 57
Brazil topaz, colourless (diaphanous) ... 19°18 54
Carbonate of lead (diaphanous) ......... 18°35 52
White agate (translucid) ............ 00... 12°48 5,
Sulphate of barytes (veined, dully dia-
BRIE tte sates Ga ttacafa site nics ack etn 2 11°72 33
Emerald (diaphanous, of a light blue)... 10°16 29
Yellow agate (translucid, yellow) ...... 10°10 29
Borate of soda (translucid) .............. 9°87 28
Green tourmaline (diaphanous, Sheer 9°54 27
Adularia (diaphanous, dull, veined) . 8°30 24.
Sulphate of lime (diaphanous)... TMG 20
Fluate of lime (diaphanous, dull, veined) 5°40 15
Citric acid (diaphanous) .................. 5°15 15
Sardoine (translucid) ............s:00000 4-98 14
Carbonate of ammonia (diaphanous, dull,
' striated) ..... 4°50 13
Tartrate of potash and soda (diaphanous) 4°40 12
Alum, crystal (diaphanous)... 4°36 12
Sulphate of “naa (strongly diaphanous
Dlune) vcci.cs..... 0:00 0
} * In this solution we used very diaphanous pieces of rock salt; the same may
be said of the solution immediately preceding—the water was completely satu-
rated with the alum.
30 M. MELLONI ON THE FREE TRANSMISSION
Tasie 1V.—Glass (coloured). Common thickness 1™*85.
Deviations of Rays
the galvanometer. transmitted.
Deep violet ..... cous aleetiainee 18°62 aS
Yellowish red (flaked) ... ceteesenseaeudass ‘ 18°58 53
Parple red (flaked)*:.........002-deceatoues 18:10 51
Wevid ted \, siiicc i Se8 0 os scat eens 16°54 47
PANS: VIG Cb vine jsiccnaises np duade sesicesladtreeheaees 16°08 45
Orage E05 <2 5 digs tiennans venue Matec 15°49 44.
CHOOSING, 05 sesanka tots taeavabionanah texevns te 15°00 42
Deep Veuow -...s.ucnes sop oop cee eheneebive 14°12 40
Brigue yellow” we. Av. Mess .ssveebesdoeent 12:08 34:
Galen y HOW i o0so3 ee ene eee 175 33
Peepiblte 205 201s ies se cenaas menses sees 1160, 33
PAINS ASVOON cc woinckis Gaipscius dave tans eeeunea a S15 26
WithePal BPeeT sisi cbc vel ectetenstebense 8:20 23
Wete GeeR We: 6. 2 ccc cne aynnarines snd eaeea 6°88 19
It is sufficient to cast the eye rapidly over the second and third tables
to be fully sensible of the truth of the proposition, that “ the capacity
which bodies possess of transmitting radiant heat is totally independent
of their degree of transparency.”
In fact, the liquid chloride of sulphur of a tolerably deep red brown
transmits a considerably greater number of caloric rays than the fat
oils of nut, the olive, and colza having a clearer tint; while these
oils, although of a very decided yellow colour, are more permeable
to radiant heat than several other liquids which are perfectly limpid,
such as concentrated sulphuric and nitric acid, ether, alcohol, and water.
The case is the same with solid bodies, among which we see sulphate
of lime, citric acid, and other very diaphanous substances allow a
much smaller quantity of heat to pass than some other bodies coloured
or translucid, such as emerald, agate, tourmaline, borax, adularia, and
sulphate of barytes.
But nothing is better calculated to demonstrate that transparency
has little or no effect in the transmission of heat than a comparison
of the effects obtained by the crystal of alum with those obtained by
means of the smoky rock crystal. The table shows that, in respect to
these substances as well as the others which we have just mentioned,
the capacity to transmit radiant heat is inversely as the capacity of
transmitting the rays of light. I was anxious to try how far this in-
verse ratio of the calorific to the luminous transmissions might extend,
by varying the degrees of thickness so as to give to the light all the ad-
vantage and the whole of the loss to the caloric. We submitted to the
test a plate of well-polished and perfectly transparent alum only one
millimetre and a half in thickness, and a smoky rock erystal the thick-
ness of which in the direction of its polished faces was 86 millimetres.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 31
The brown colour of the crystal was so decided that when it was laid
on a printed page in which the letters were very large, and placed in
the fullest light, even the traces of the letters could not be distinguished.
The paper and the printed characters became confounded together and
presented the same dark hue. This crystal, however, transmitted 19°,
while the thin plate of alum transmitted only 6°.
A body may then be very opake and afford a very easy passage to
the rays of heat ; or very transparent and intercept the greatest part
of them. It is therefore necessary to distinguish those bodies which
possess a capacity for calorific transmission from those which possess a
capacity for luminous transmission, by giving them different denomina-
tions. The terms ¢ranscaloric and diathermanous* (transcaloriques ou
diathermanes) seem to me to be best suited to this purpose, as being
most analogous in form to the epithets ¢ransparent and diaphanous,
applied to bodies endowed with the property of transmitting light.
After the statement made in respect to the smoky rock crystal, one
might be tempted to ask whether there are any transcaloric substances
totally opake. To that question no answer can be given until the effect
of calorific radiation upon all known bodies has been tried, and this I
am far from having done. I can only go so far as to say that pyro-
ligneous acid in the rough state, and Peruvian balsam, though almost
completely opake, afford perceptible transmissions of radiant heat. But
all the diathermanous substances that I have subjected to experi-
ment are comprised within that class of bodies which possess some de-
gree of transparepcy. Those kinds of metal, wood, and marble which
totally obstruct the passage of light obstruct that of heat also. Some
other bodies, such as carburet of sulphur, rock salt, and Iceland spar,
allow both kinds of rays to pass at the same time. It is therefore pro-
bable that calorific transmission cannot take place without a certain de-
gree of transparency}; but it cannot take place abundantly without the
cooperation of another quality, which varies as the bodies happen to be
erystallized or without crystallization. We find, in fact, that in the dif-
ferent sorts of glass and liquids it follows the order of the different de-
grees of refrangibility ; for flint-glass possessing a greater refracting
power than crown-glass affords an easier passage to the caloric radia-
tion. Carburet of sulphur is at the same time more refracting and
__ * The first of these terms requires no explanation. The second is derived
_ from dic, through, and Szeuciva, to heat, as the word diaphanous is derived from
bid, through, and Qulva, to show.
_ + have since found that the perfectly opake glass employed in the con-
_ struction of mirrors designed to show the polarization of light transmits a eon-
siderable quantity of caloric rays. ‘These obscure rays emerging from the dark
pice may be employed in some curious experiments which we shall mention
n the second Memoir.
bi
$2 M. MELLONI ON THE FREE TRANSMISSION
more diathermanous than the essence of turpentine; the same may be
said of turpentine as compared with olive oil, and so on until we come
to pure water ; a liquid which, as it possesses the least power of refrac-
tion, possesses also the least power of transmitting heat. It is very true
that, in the tables, glass appears almost as diathermanous as carburet of
sulphur, although its refracting power is considerably less; but this
equality is but in appearance ; and to be convinced that it is so, we
have only to recollect the manner in which the liquids have been sub-
jected to the experiments. Before they can reach the liquid layer, the
rays must have passed through the anterior face of the vessel contain-
ing it, and the glass gives but a transmission of from 21 to 22 for 35°3.
Thus the radiation that will penetrate to the interior of the vessel will
be of no greater force than this; so that even if the liquid transmitted
all the rays that reached it, the quantity issuing from the recipient can-
not exceed 22. This explanation is confirmed in a very striking manner
by the transmissions of the chloride of sulphur and the protochloride of
phosphorus. The indices of refraction of these two liquids, though not
well known, are certainly higher than that of glass, and have different
values ; a fact from which it may be inferred with great probability
that the quantities of transmitted heat are also different, though in the
tables both these quantities appear equal to the transmission assigned to
the carburet of sulphur.
There are, it is true, some real anomalies in the transmissions through
balsam of copaiba and sulphuric ether. But the differences are very
small, and may probably be referred to some slight error in the measure
of the transmission or the refraction. The proportionality of these two
elements is obvious, and so fully established in such a variety of cases,
that it may hold as a general law for liquids, for the several kinds of
glass,and probably for all those bodies which are without regular erystal-
lization.
But this law totally fails with respect to crystallized bodies. We see,
in fact, that carbonate of lead, a highly refractive and colourless sub-
stance, transmits less heat than Iceland spar and rock erystal, which are
much inferior to it in refracting power; while rock salt, possessing the
same transparency and the same index of refraction as citric acid and
alum, gives six times their amount of calorific transmission.
The transparent and colourless bodies contained in the third table are
nine in number, namely, rock salt, Iceland spar, rock crystal, topaz,
carbonate of lead, sulphate of lime, citric acid, tartrate of potash and
soda, and alum. These crystals transmit the following quantities of heat
respectively :
a
92, 62, 54, 52, 20, 15, 12.*
* Such as have not a thermoscopic apparatus similar to that which we have
employed may easily satisfy themselves that rock salt transmits almost all the
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 33
Differences so striking in bodies of the same aspect seem to arise rather
from the particular structure of each crystal than from the chemical
composition of the molecules; for a block of common sea salt being
divided into flakes instantly arrests calorific radiation ; and we perceive
besides, by means of the second and third tables, that the transmissive
power of pure water is increased nearly in the same degree whether we
dissolve in it alum or rock salt, two substances which, in their solid state,
transmit very different quantities of heat. But we perceive no relation
between the power of transmitting heat and the primitive or the secon-
dary form of crystallization.
M. Mitscherlich has found that the dilatation of crystals, when they
are submitted to the action of heat, is not equal on all sides. Although
such an effect may not proceed from the radiant heat, yet it might be
thought that a difference in the direction in which the plates are cut out
of the crystal would produce a difference of transmission. I have had
plates of equal thickness cut out of rock crystal in all the principal di-
rections relatively to its axes. The transmission varied in no case. I
obtained the same results from Iceland spar.
Radiant heat is capable of passing through crystallized bodies of very
considerable thickness. It may be affirmed, also, that the rays do not
lose so much in the interior of these bodies as they do in the masses of
glasses and of liquids. For we have seen that the deviation changed
only from 21°6 to 19°, though the smoky rock crystal first employed
was replaced by one of fifty-seven or fifty-eight times its thickness.
I have exposed to the action of radiant heat a piece of Iceland spar 92
millimetres* in length. The deviation, which was 21°:8 through a flake
of the same substance 2™™6 in length, fell no lower than 18-5; a cireum-
radiant heat that falls on its surface, by fixing vertically, on the same stand, a
plate of this substance and a plate of glass or alum of the same dimensions, and
by bringing the stand quite close to the fire of astove. Ifit is allowed to remain
in this state for five or six minutes, the glass becomes burning hot, while the
rock salt, if applied to the most tender part of the hand, will produce no sensa-
tion of heat. These differences of temperature exist not merely in appearance,
but are as palpable as those that are felt when we touch wood and marble that
have been exposed to the sun. To prove this, we need only lay some pieces of
wax or suet on the two bodies. Those laid on the glass will melt rapidly, but
those laid on the rock salt will continue in their solid state. We may also de-
monstrate in a direct manner, and without the aid of a thermomultiplier, the
great transmissiveness of rock salt as compared with other diaphanous sub-
stances. Let the two plates be brought close together in the same plane, and
_ behind them let two metallic tubes be placed, with the blackened balls of two
common thermometers of equal sensibility fixed at their further extremities. If
we now place a red-hot bullet at a certain distance from the plates, the thermo-
_ meter that is to indicate the transmissive power of the alum will ascend but 1°,
while the other will ascend 8° or 10°,
4 [A millimétre, it will be remembered, is equal to :03937 of an English inch.
—Epir. }
Vor. IL—Parrt I, D
34 M. MELLONI ON THE FREE TRANSMISSION
stance which shows that the diminution of effect was only about one
seventh for an increase of thickness equal to thirty-five times that of
the first piece. The experiment was still more interesting when I em-
ployed rock salt, in which I was unable to discover that thickness had
any influence whatever on the amount of the transmission: for pieces
of 2™™ gave the same galvanometric deviation as pieces of 30™™
and 40™™.
From these observations it follows that the numbers in the second
column of the table of crystals, though they express the ratios of the
calorific transmissions of those bodies reduced to the common thickness
of 2™™-6, may be employed also to represent approximately the ratios of
the transmissions, even when the common thickness is greater. I say
approximately, because, in order to determine the true specific trans-
missions, it would be necessary to know the exact law of the loss at the
several points of the media. If the losses, as compared with the quan-
tities of heat which arrive at each of the thin laminz into which we may
imagine the medium to be divided, were constant, the intensity of the
rays would decrease in a geometrical, while the layers increased in an
arithmetical ratio; and in order to know how much one substance is
more diathermanous than another, we should vary the relative degrees
of thickness of the plates until we obtained the same transmission in the
two cases. The ratio sought would be inversely as the degrees of thick-
ness which produced an equality of action *. Now we have seen that
this constancy in the loss does not exist. But in the particular case
of crystallized bodies, the differences are so very small when the thick-
ness is increased beyond 3™, that the ratios obtained by operating on
thicker screens would not differ materially from those which we have
found.
But even if we had succeeded in ascertaining the specific transmissive
powers of the different substances, the question would not yet be solved
in a general manner ; for we shall see in the second Memoir, that if,
while we vary the temperature of the calorific source, we do not change
the order of the transmissions also, the relations of these quantities are
no longer the same. To perceive this we have only to recollect what
has been already stated as to the action of rays emitted from a source of
low temperature on certain substances; that is, that the heat of the
human body instantly passes through a certain crystal, and that crystal
is rock salt.
It is known that the caloric rays of the hand are completely stopped
by glass. Hence, although the ratio of transmission between glass and
rock salt, when the source is an Argand lamp, be 62 : 92, it becomes
~ * For the demonstration of this proposition, see-Bouguer, Traité d'Optique
sur la Gradation de la Lumiere, Paris, 1760, liv. 111. sect. 1'¢, art. 1, 2,3, 4.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 35
1 to infinity when we consider the effects produced by sources of a low
temperature.
' Hitherto we have made no account of the colours [of the diather-
manous bodies ], or, rather, have considered them only in relation to the
diminution of transparency, or to the greater or less opacity which they
always cause in diaphanous substances*.
We must now examine them more particularly, and determine their
influence: on transmission. Such is the object of the fourth table. The
tints of those kinds of glass marked with an asterisk are the purest, and
approach nearest to those prismatic ‘colours ‘that bear the same names.
Of this I have satisfied myself by the following experiments. Having
by means ‘of a heliostat: ititroduced a horizontal sheaf of solar rays
into a dark chamber, I divided it into two by causing it'to pass through
two apertures made in an’opake sereen. ‘I contrived to make one of
the sheaves fall on a vertical prism, and the other on a coloured glass
which I wished to try. Thus the solar spectrum was seen cast on one side,
and a coloured spot in the line of the direct rays. To bring this spot into
contiguity with the corresponding colotir of the spectrum, I placed behind
the glass a second vertical prism which turned about until the desired
effect was obtained. The two analogous tints are always easily com-
pared when they are near each other, and at the same time we are able
to judge whether the colour of the glass be more or less pure by the
new tints which are always developed in the passage of the coloured rays
of the glass through the prism. Of fourteen colours selected from several
species of glass, I have found but five making any near approach to the
prismatic colours and producing very feeble secondary tints. These tints
were absolutely imperceptible only in the case of red glass.
There is another mode (and it has not been overlooked) of appretia-
* J was lately told by an eminent philosopher, that to think of comparing the
intensities of different colours would be as absurd as it would be to institute a
comparison between heterogeneous elements. Waiving all inquiry as to the
correctness of such an assertion, J beg leave to remark that in certain cases
itis unanimously agreed that a tint is more or less clear than another tint of a
different kind, without giving rise to any metaphysical ideas opposed to the ge-
neral opinion. _ Let us take, for instance, the solar spectrum. Has it not been
always held that the maximum of brightness is to be found in the yellow, and
hat on each side of it luminous intensity decreases? The principle put forward
by me seems equally plain. When I assert that colours always introduce some
opacity into diaphanous bodies, no one.is at a loss for my meaning. Put.some
pure water between two parallel plates of colourless glass: let an observer be
placed at one side, and at the other a piece of writing, which is to be moved just
so far from its first position as to become illegible. Now, for the water substi-
‘tute wine or oil or any other diaphanous liquid more: or less coloured ; the di-
stance at which the writing may be read will become less in proportion to the
greater depth of the colour independently of its kind. Thus when the writing
will be legible at the same distance through a yellow and a red liquid, these two
media will, in respect to us, be equally transparent.
n@2
36 M. MELLONI ON THE FREE TRANSMISSION
ting the influence of colour in diaphanous media. It consists in causing
corresponding rays of the spectrum to pass through the glasses. The
passage is attended only with a very inconsiderable loss when the tints
are very pure. Now by fixing one side of my five plates of glass at
proper distances on the margin of a sheet of pasteboard exposed to the
coloured sheaf of the prism, I found that each prismatic ray traversed
glass of the same colour without suffering any loss of intensity. At least,
the alteration produced by these glasses on the corresponding solar rays
was nearly the same in all cases. This fact is inferred from a compa-
rison of the prismatic rays which fall on the wall directly and those which
reach it after having passed through the coloured pieces of glass. The
shadows brought by the latter rays are so very light as to be almost im-
perceptible. In every other case they are very strongly marked. If
for instance we substitute the violet for the red, the spot on the wall is
almost dark ; if the violet be not perfectly pure, it will not at least trans-
mit a quantity of red rays less than that which passes through the red
glass.
It is known that in the solar spectrum produced by a prism of com-
mon glass, the greatest heat is found in the red, and that the interme-
diate temperatures continually decrease until we come tothe violet. Does
this calorific distribution in the coloured rays, separated by the refract-
ing power of the prism, exist also when they are separated by the ab-
sorptive power of the colouring matter?
In order to ascertain this we have only to compare, at the different
temperatures of the spectrum, the numbers which represent the calo-
rific transmissions of our five coloured glasses ; they are as follows:
violet ow blue green
53, 34, 33, 26.
The order of the @®fours considered relatively to their degrees of heat
and the numerical relations of those degrees are so altered that the violet
light, which in the spectrum possesses a temperature twenty-five or
thirty times lower than that of the red light, appears here of a higher
temperature. Such a difference is not to be explained by supposing
that, in the transmission of the violet glass, there passes a great quantity
of red rays; for it should, on this hypothesis, be found to transmit them
in a greater proportion than they are transmitted by the red glass;
which, according to the preceding experiments, is impossible.
These facts seem to be opposed to the opinion of those philosophers
who hold that in luminous heat the same rays simultaneously excite the
two sensations of light and heat, but would be easily comprehended if
we supposed caloric and light to be two distinct agents. In the latter
case we should say that in the prism the refractive force acts unequally
on the different caloric rays, as it does, in a greater or less degree, on
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 37
the different luminous rays, and thus throws certain quantities of heat
on the very spaces occupied by the different colours of the spectrum ;
but that in the coloured glasses and, generally, in bodies more or less
diathermanous, the absorbent force does not act in the same manner as
the force of refraction, which sometimes extinguishes more heat than
light and at others more light than heat.
But those who maintain the identity of the two agents will reply, that
the differences observed in the calorific and luminous transmissions of
the diaphanous or coloured media are produced by rays of obscure
heat which mix if great quantities with the rays of light emitted by
the flame.
In order to decide how far it is allowable to maintain the one or the
other hypothesis, we should have data which, at present, are not within
ourreach. We shall resume this subject at the end of the next Memoir,
and conclude the present one with an account of a very remarkable ap-
plication of the numerical results contained in the foregoing tables.
It had been established by the beautiful experiments of Seebeck that
the place of the maximum of temperature in the solar spectrum varies
with the chemical composition of the substance of which the prism is
made. This eminent philosopher observed that the highest degree of
heat which, in the spectrum furnished by a prism of crown glass, was
in the red, passed to the orange when the prism employed was a hollow
glass one filled with sulphuric acid, and was found in the yellow when
the same prism was filled with pure water*.
I discovered some months since that the caloric rays scattered on the
colours given by a common prism do not undergo the same alteration
in passing through a layer of water; the loss varies inversely as the re-
frangibility, so that the most refrangible rays pass undiminished and the
least refrangible are entirely stopped by the liquid +.
This experiment led to a very simple explanation of the results ob-
tained by Seebeck.
The solar heat which presents itself to the anterior face of the prism
of water contains rays of every degree of refrangibility. Now the ray
which has the same index of refraction as the red light, suffers in pass-
ing through the prism a loss porportionally greater than the ray which
possesses the refrangibility of orange light, and less is lost by the latter
in the passage than by the heat of the yellow ray. These increasing
ratios in the losses of heat sustained by the less refrangible rays have
an evident tendency to transfer the maximum to the violet. It may
therefore be stopt at the yellow.
* Schweigger’s Jahrbuch der Chemie und Physik, vol. x. [A translation of
the memoir of Seebeck here referred to will be found in the Philosophical Ma-
gazine, first serics, vol. Ixvi. p. 330, e¢ seg.—Ep1r. ]
+ Annales de Chimie et de Physique, Décembre 1831.
38 M. MELLONI ON THE TRANSMISSION OF RADIANT HEAT.
If we suppose the action of sulphuric acid analogous;to that of water;
but not so energetic, we shall see, the reason why, with the prism of acid,
the maximum takes place in the.orange.. In short, the very glass.of
which the common prisms are mademust, operate in. a) similar manner,
and cause in each ray a loss inversely proportioned. to its refrangibility.
Therefore, if we employed in the. construction of the common prism a
substance less active than common glass, the losses sustained by the
less refrangible rays would be diminished in a greater ratio ; so that they
would gain on the more refrangible rays, and the maximum would pass
in a direction opposite to the preceding, that is, frem the violet to the
red.
This is exactly the result obtained by Herschel, Englefield, and See-
beck by operating on prisms of flint glass; for the maximum was trans-
ferred to the obscure space quite close,to the,last red stripe. of the
spectrum. : ;
Let us compare these, effects with the numbers which represent the
calorific transmissions. We shall find that. the maximum of heat, in
passing from the yellow, where it is found when we use a prism of water,
departs from it always in thesame direction in proportion as the sub-
stances of the prisms substituted for the water are more diathermanous.
It passes a little out of the spectrum when, instead of, crown, we em-
ploy flint glass. Admitting then the,correetness of such a-theory, the
line of greatest heat must pass quite, beyond the colours imto a,space
far distant from the red limit if we employ rock salt, a substance. pos-
sessing a far greater diathermaney as compared with, flint glass than
flint glass does as compared with crown. I tried the experiment; it was
completely successful. I found that the maximum of temperature in the
spectrum derived from the prism of. salt was thrown into the dark space
as far at least from the last band as the blue is (in an opposite direction)
from the red.. At the moment I cannot-assign more exact measures ;
for in the first place I operated with very small prisms,.and when I sub;
sequently obtained larger pieces the; season.did not .allow me to re-
consider and study the.result more. nicely... But the effect-has been so
marked in the experiment which I, made, and. so invariable in several
suecessive repetitions, that I look upon it as decisive, and, have-not the
least doubt as to the removal of the maximum of temperature. tothe
last band of the red rays in the spectrum produced with rock salt *.
The distribution of the degrees of temperature in the-solar spectrum
* I have since obtained the same results with five prisms of rock salt whose
angles of refractivu vary between 30° and 70°. These prisms have been made
out of several pieces taken from the mines of Cordona, Wieliecza, and Vicq:
they have been cut in different directions relatively to the axis of crystallization.
I shall give the numerical data in a work in which it is intended to treat spe-
cially of the analysis of the caloric solar rays.
M. MELLONI ON THE TRANSMISSION OF RADIANT HEAT. 89
is therefore a phenomenon entirely depending on the order which we
have found to exist in respect to the calorific transmissions of diaphanous
bodies. i (
This. phenomenon now constitutes a striking relation between the
properties of the caloric rays of the sun and those of the radiant heat
of terrestrial bodies ; but we shall see relations yet more intimate ap-
pear between these two species of rays when we examine the alterations
produced in calorific transmissions by changing the temperature of the
radiating source.
ARTICLE II.
New Researches relative to the Immediate Transmission of Ra-
diant Heat through different Solid and Liquid Bodies ; pre-
sented to the Academy of Sciences on the 21st of April, 1834,
and intended as a Supplement to the Memoir on the same sub-
ject presented to the Academy on the 4th of February, 1833;
by M. ME.tLont.
From the Annales de Chimie et de Physique, t. uv. p. 337.
Of the modifications which Calorific Transmissions undergo in consequence
of the Radiating Source being changed.
Tue experiments described in the former Memoir have shown that
diaphanous bodies do not act in the same manner on the rays of heat
and the rays of light simultaneously emanating from the most brilliant
flame. We have seen, in fact, that thin flakes of alum and of citric
acid, because of their transparency, perceptibly transmit all the luminous
rays of an Argand lamp, and stop from eight to nine tenths of the ca-
lorie ; while, on the other hand, thick pieces of smoky rock crystal inter-
cept nearly the whole of the light and allow the radiant heat to pass
freely. Do the different properties thus exhibited by each body, rela-
_ tively to the two agents, and the relations of the calorific transmissions
i
é
¥
of the one screen to those of the other, remain constant, whatever be the
source (luminous or obscure) whence the rays emanate? Such are the
first questions that I have undertaken to solve in this second series of
researches.
That the comparison between the quantities transmitted in each par-
ticular case might he fairly made, it was necessary to operate upon rays
40 M. MELLONI ON THE IMMEDIATE TRANSMISSION
emitted by a source having a constant temperature. This condition
could be complied with by means only of certain flames and boiling li-
quids. I was therefore unable to vary the experiments so much as I
should have desired. The sources however which I have employed pre-
sent the most remarkable phases of the heating and combustion of bo-
dies. They are four in number; namely, the flame of oil without the
interposition of glass, incandescent platina, copper heated to 390°, and
boiling water. Thus I had two luminous and two non-luminous sources.
The first is furnished by a Locatelli lamp*; the second is a spiral of
platina wire kept in a state of incandescence by means of a lamp fed with
spirit of wine; the third is obtained by covering a flame of alcohol with
a plate of copper, which soon acquires a fixed temperature whose mean
value, as found by the method of immersion, is 390°Cent. (732° Fahr.) ;
and the last source is merely a vessel of thin copper, blackened on the
outside and filled with boiling water.
The intensities of the radiations have been always ascertained by the
thermomultiplier. The means necessary to be adopted in order to ob-
tain with this instrument the measure of the immediate transmission
having been stated in the Memoir already quoted, I think it needless to
enter here into further detail as to the arrangement of the apparatus and
the nature of the galvanometric indications. I shall only remind the
reader that as this method requires that the operation should be per-
formed under the influence of a radiation equivalent to 30° of my ther-
momultiplier, the diaphanous substances, if placed at a suitable distance
between the thermoelectric pile and the source of heat, cannot acquire
a temperature sufficient to produce in the instrument any perceptible
action. This is proved in three ways: first, by placing the screens on their
stand after having exposed them to a calorific radiation of the same in-
tensity as that to which they are exposed during the experiment; secondly,
by substituting for the diaphanous body plates of blackened glass or
metal, flakes of wood or stone, or sheets of paper; thirdly, by varying the
nature and thickness of the medium (more or less transparent) through
which the rays are to pass, from the thinnest plate of mica to pieces of
rock crystal, glass, or Iceland spar several inches.in thickness. In the
first case the index of the galvanometer remains unmoved, notwithstand-
* The Locatelli lamp is merely a common lamp with one current of air and
fed with oil. It has a wick of the shape of a quadrangular prism, which exactly
fills the beak, but has no funnel. It gives a fine flame of constant tempera-
ture. The Argand lamp produces a flame of much greater intensity.
In the first series of experiments the main object was to determine the differ-
ence between the calorific and the luminous transparency. We therefore pre-
ferred the source which was least favourable to the establishment of the principal
fact which it was then our purpose to verify. In the present experiments we
proposed more particularly to examine the calorific transparency by itself. It
was therefore necessary to operate upon rays that had not been forced to un-
dergo a transmission previously to their being employed in the experiments.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 41
ing the heat acquired by the screens ; in the second case also it remains
unmoved, although in this case the plates (blackened or opake) are sub-
mitted to the actual radiation of the source itself. In the third case the
index of the galvanometer leaves its position of equilibrium and describes
ares of greater or less extent according to the quality and thickness of
the screen. But the time which it takes to reach the extremity of
these arcs is invariable, and equal to that which it takes to describe a
deviation of 30° when there is no screen interposed.
This third proof, though indirect, is nevertheless the most convincing,
and possesses the additional advantage of showing, as it were, palpably,
that the manner in which radiant heat is transmitted in the interior of
diathermanous substances is altogether analogous to that.in which light
is propagated through transparent media whether solid or fluid. For in
respect to the latter we perceive no appretiable difference between the
times which the luminous rays take to pass through layers of any quality
and thickness whatsoever.
The analogy between the transmission of light and that of radiant heat
is rendered still more striking if, by shaking or otherwise, a motion is
produced in the mass of the screen submitted to the experiment. I have
passed the different parts of a large square of glass rapidly before the
narrow aperture of the metallic plate through which the calorific rays
that strike the surface of the pile are transmitted. By means of a bow
I made it vibrate ; it emitted sounds more or less acute: the index of
the galvanometer pointed invariably to the same degree of its scale. I
found the deviation of the magnetic needle equally invariable when I
measured the intensity of the calorific radiation through a layer of
acidulated water, at first still, but afterwards set in motion by agitators
or traversed by a strong electric current.
Here then, though under different forms, the fact observed in the
experiments of Pictet and Saussure when we agitate the mass of air in-
terposed betwen the reflectors is reproduced; namely, the impossibility
of altering by these means the direction or the intensity of the luminous
or the calorific rays passing through Curae air or any other dia-
phanous medium.
These different considerations seem to me well calculated to dispel every
shade of doubt that may yet be entertained as to the immediate trans-
mission of radiant heat by diathermanous bodies, whether solid or liquid.
_ But (to return to the four sources) we have already observed that in
our method of proceeding it is necessary to operate uniformly under
the influence of a radiation equal to 30° of my thermomultiplier. Now
to effect this with sources of various temperatures they must be brought
more or less close to the thermoelectric pile until we have obtained the
galvanometric indication required, and such is the way in which we have
proceeded in all our experiments of transmission. The same screen
42 ~ Ms MELLONI ON THE IMMEDIATE TRANSMISSION,
being, in those different circumstances, submitted to the same quantity
of radiant heat, the different degrees of diminution suffered by this heat
in passing through it must evidently be attributed only to the peculiar
quality of each radiation. This reflection will give still greater force
to the truth of the consequences which we are about to deduce from the
results of our experiments,
Seven plates of glass of different degrees of thickness submitted to
the action of the on sorts of calorific rays in succession have given the
following transmissions :
Transmissions of the glass out of 100 rays
of heat issuing from
Thickness | —__—- A mais ony
of the blackened | blackened
plates. a Locatelli | incandescent copper copp
lamp. platina,
77 57
54 37
46 31
41 25
Si 20
535 18
33°5 17
Although we do not exactly know the degree of heat given by the
flame of oil or by platina kept in a state of incandescence by an alcohol
lamp, we are nevertheless quite certain that the first of these possesses
a higher temperature than the second, and that this again exceeds the
390° of the first plate of copper. Now a glance at the table is sufficient
to show that the number of rays transmitted by the same plate decreases
with the temperature of the calorific source, a fact which confirms the
well-known law of Delaroche. But the decrease is more or less rapid
in proportion to the greater or less thickness of the plate.
Let OM, ON, (Plate I. Fig. 1.) be two rectangular axes of the same
length; let the first represent the thickness of the screen of 8™™ and the
second the total quantity of incident heat. Let us pee OM into six parts,
Be Oo Oc, Od, Oe, Of respectively equal to °” OM, °20M, 40M,
+ OM, z OM, and 7 OM; and. through the points of division let us _
draw on perpendiculars aa! = 4 ON, 60! = 7, ON, ec’ = 4 ON,
dd' =" ON, ee =S,0N, ff =30N,Mg' = “2 ON. Thecurve
(a' b! ti d'e ae e' f'g') passing through the extremities of these perpendicu-
lars will represent the decreasing intensity of the Locatelli lamp at each
point of the sereen of 8™™ in thickness. ,
2
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 43
_~ A-similar construction will give the curves a! b!c!d!efllg!', all! bl!!
el diel f"l'g'"', a bY, representing the decreasing intensities, of the
three.other radiations: Ss
~ Let.us now suppose the screen cut by any plane (P P’) parallel to ON;
the emergent rays of the detached plate will be determined by the points
at which the plane intersects the curves; so that PP’, PP", PP,'"’ will re-
present the quantities of heat that issue from the plateOP when.exposed
to the first three sources; for the rays of the fourth are completely ex-
tinguished at the distance of one millimetre. We now see that the ra-
tios of the distance from those points of intersection to the axis OM
decrease in proportion as the.thickness of the interposed layer is less,
The distances from those points to the axis are pretty nearly equal when
the section. coincides with the ordinate aa’ at: which the observations
commence; they will become yet more so in the interior of the first layer
Oa, so that within a limit: very. close to the surface at which the rays
enter the differences will almost.vanish*. b
The first infinitely thin plate will therefore transmit sensibly equal
quantities of radiant heat from the four sources. The diminutions how-
ever which the rays from each source will suffer.in the interior. of this
elementary plate, though so exceedingly small that they may be disre-
garded in reference to the quantities transmitted, must nevertheless
bear very different ratios to one another ; for it is to such diminutions,
several times repeated by the action of the successive layers, that we
are to attribute the remarkable differences in the .quantities.of heat
transmitted from each source by a screen of a given thickness.
The law of Delaroche did not show whether the variable interception
* I have been unable to procure plates of glass thinner than +2, of a milli-
metre. But we shall see presently that all other diaphanous substances, whether
natural or artificial, are in their effects more or less analogous to glass. Now
there are several crystals which spontaneously separate into plates of great te-
nuity, and are, consequently, well calculated to show that the ratios of the quan-
tities of heat transmitted by a screen exposed to the radiations of the four sources
approximate to equality in proportion as the thickness of the screen is reduced.
Thus a plate of sulphate of lime 2™™-6 in thickness gave for the four transmis-
sions respectively,
on 5 O45. Oi
These transmissions became
Sesasi8." | 7 aai0
when the thickness was reduced to 0™™-4; and
64, 51, 32, 21
when the thickness was reduced 0™™-01],
A plate of mica, 0™™-02 thick, gave for the four transmissions
80, 76, 39, 26.
An extremely thin flake was taken from this plate (which was however not
coloured) : the four transmissions through this flake were,
86, 85, 61, 46.
44 M. MELLONI ON THE IMMEDIATE TRANSMISSION
of the same flake arose from an internal or external action of the screen.
Nay; more; the ordinary properties of the caloric seemed to lead to the
far more probable consequence that the interception was entirely super-
ficial; or in other words, that as the same plate of glass successively
exposed to the radiations from several sources gave different calorific
transmissions, it was natural to suppose that the heat was first stopped
at the external surface in a proportion varying with the temperature of
the source, and subsequently propagated inwards according to the known
laws of conductibility. But the experiments which I have just men-
tioned seem to me to demonstrate clearly that the calorific rays from
different sources are more or less quickly extinguished in the very interior
of the mass.
Thus the molecules of glass act upon radiant heat with a real absorp-
tive force, the activity of which is greater in proportion as the tempe-
rature of the source is lower. It will perhaps be now asked whether this
kind of action be common to all diaphanous substances or peculiar to
glass only.
To determine this, it is not necessary to repeat on all the bodies those
experiments which we have made on different thicknesses of glass;
for, the law of Delaroche being once established, it will follow that the
substance of which the flake is composed operates on the rays of heat
with an absorptive force inversely as the temperature of the source: and
as this force acts from all points of the mass, it is clear that the differ-
ence between one transmission and another must decrease with the thick-
ness of the screen. The question is therefore reduced to this ; whether
all bodies more or less transparent act upon heat radiating from different
sources in a manner analogous to that which we have .observed in one
only of our flakes of glass.
I have registered in the following table the quantities of heat imme-
diately transmitted from each of the four sources through plates of dif-
ferent kinds reduced to the common thickness of 2-6. The transmis-
sions are expressed in hundredth parts of the incident quantity. They
are uniformly measured, like the preceding, under the action of a radia-
tion of the same force derived from each source of heat.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 45
Transmissions
from 100 rays of heat issuing from
Names of the interposed substances
(common thickness, 2""'6.)
Rock salt (diaphanous, colourless) ...
Fluate of lime (diaphanous, colourless)
Rock salt (diaphanous, dull)
Beryl (diaphanous, greenish yellow)...
Fluate of lime (diaphanous, greenish)
Iceland spar (diaphanous, colourless)...
Another species (diaph., colourless) ...
Mirror glass (diaphanous, colourless)...
Another kind (diaph., colourless)
Rock crystal (diaphanous, colourless
Rock crystal, smoky (diaph., brownish
Acid chromate of potash (a vivid orange
White topaz (diaphanous, colourless
Carbonate of lead (diaph., colourless)...
Sulphate of barytes, pure, (diapha-
nous, rather dullish)
White agate (translucid, pearly)
Adularia felspar (diaph., dull, veined)
Amethyst (diaphanous, violet)
Amber, artificial (diaph., yellow)
Emerald (diaph. bluish green)
Agate, yellow (translucid, yellow)
Borate of soda (translucid, white)
Green tourmaline (diaph., deep green)
Cowhorn (translucid, hazel) ............
Common gum (diaph., yellowish
Sulphate of barytes (diaph., dull veined)
Sulphate of lime (diaph., colourless)...
Sardoine (translucid, brown)............
Citric acid (diaphanous, colourless) ...
Carbonate of ammonia (diaphanous,
MUM SITIMLCD) oon scccnes access sesesczis
Tartrate of potash and soda (diapha-
- nous, colourless)
Amber, natural (translucid, yellowish)
Alum (diaphanous, colourless)
Glue, strong (diaph., yellowish brown)
Mother-of-pearl (translucid, white) ...
Sugar-candy (diaphanous, colourless)
Green fluate of lime (translucid, mar-
__ bled green) :
Melted sugar (diaphanous, yellowish)...
Ice very pure (diaphanous, colourless)
SCOP COCO OCO CC SCNHOHTOSTHHHONONHNANH HFPPABRHRAMAAG
cow CSCOOCSCO Co ocooscoocoeocecocoocecoe osooocecec|eo
oon coonwnwa$ oo bo wT Ol 09
46 M. MELLONI ON THE IMMEDIATE TRANSMISSION
Before we proceed to consider these results, it is necessary to recollect
that they have all been obtained under the free action of an invariable
radiation of 30° measured by the thermomultiplier. _ Now the half de-
grees of the galvanometer are very distinctly legible. Thus the trans-
missions are exact to oth of the incident heat ; but the observations
being repeated, the hundredth part becomes easily appretiable.
In the quantity of rays transmitted through the same substance there
is a variation of several hundredth parts according to its greater or less
purity. It was therefore useless in giving the measure of this element
to attempt a degree of exactness exceeding the hundredth part of the
whole; but it was desirable to ascertain the limits of the insensible trans-
missions with more precision. In this case’ therefore I have always car-
ried the approximation to x}s, and sometimes to zis, so that if the zero
does not represent a transmission really equal to nothing, it is at least
certain that, if there are any rays of heat transmitted, their amount does
not exceed z4odth of the whole incident quantity.
In order therefore to reduce the probability of error, it has been found
necessary to operate on stronger radiations. Now the table of intensi-
ties given in my first Memoir does not exhibit the forces which move the
galvanometric index beyond the 45th degree. IT could have extended
it to the higher-degrees of the quadrant by the method followed in its
construction. But I thought it better to employ at each step a very
simple artifice which immediately gives the force of any radiation what-
soever as well as the required limit of error. To make this clear, let us
suppose that it is desired to verify a particular case of the transmissions
in the table; for instance, that it is requisite to prove that the transmis-
sions of alum, sugar, or ice exposed to the rays emitted by copper heated
to 390° are either null or less than zixdth of the whole of the incident
heat.
The table shows that a plate of glass, of rock erystal, or of Iceland
spar transmits from five to six hundredths of those rays; that is. to
say, that for a free radiation of 30° we obtain about 2° through the
plate. We know moreover that in this feeble indication there is a pos-
sible error of z'sth of the whole heat. The limit of error would be “>
if we wished to be rigorously exact, for by the table of intensities we
see that, in the deviations below 20°, one degree is equivalent to a55 of
the force which moves the needle to 30°. But let us admit only the
limit z's, which will have the advantage of rendering the values inde-
pendent of a knowledge of the ratios existing between the degrees of
the galvanometer and the corresponding forces of deviation. Let us
bring the source near, in order that we may obtain through the same
plate of glass a deviation exceeding 2°; a deviation, for instance, of 8°.
The quantity of incident heat is now increased fourfold, and the pro-
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 47
bability of error is diminished in the same degree*. Let us now sub:
stitute for the plate of glass a flake of alum, sugar, or ice; we shall find
that the needle of the galvanometer is perfectly at rest : if there is any
heat transmitted, it is therefore not more than 4.35 = z4a of the whole
radiation. Thus it is true that the transmission of these three substances
reduced to plates of 2™™-6 in thickness and exposed to the radiation of a
body heated to 390° is null or less than z}sdth part of the whole in-
cident heat. It is by operations analogous to this that I have been able
to ascertain the limits of the values of the zeros of transmission.
Now that we know the degree of exactness to which the measures
contained in our table have been carried, we may proceed to state the
consequences to which theyead.
Let us, for the moment, not notice the results obtained with the rock
salt. The order of the transmissions has no relation to the degree of
transparency, as we have already determined in our first series of expe-
riments. It is not strictly the same when we change the calorific source ;
but each substance exposed to the successive action of the four radia-
tions presents a like order of decrease in respect to the quantities which
it transmits from each of the sources; that is to say, that all the sub-
stances transmit quantities of heat which are feeble in proportion as the
temperature of the radiating source is low. There are several cases
in which the transmissions are nothing; but these cases do not make
* This mode of estimating the energy of the calorific radiations enables us to
determine without difficulty the ratios existing between the arcs described by
the magnetic needle of the galvanometer and the corresponding forces. Let us
suppose the calorific source removed sufficiently far from the pile to produce
but a feeble deviation of the galvanometer; one of 10°, for example. In the
passage of the calorific rays let there be interposed a plate which transmits a
certain fraction of the incident heat. We shall suppose this fraction to be 3; the
needle will descend to 2°. __ By bringing the source near, the deviation produced
through the plate will be increased. Let us stop, when the needle shall have
reached 4°, 6°, 8°, &c. successively the calorific source will then emit upon
the pile twice, thrice, or four times as much heat as before; for the transmission
through the same plate exposed to a constant source of heat is always in a con-
stant ratio, and the forces of deviation are proportional to the degrees in those
ares that are very near zero. Let the force which causes the galvanometer to
describe the first degree of the scale be represented as 1, we shall then have 10
for the first force or quantity of incident heat, 20 for the second, 30 for the third,
40 for the fourth, &c. Now we know that the first force answers to 10°. In
order to determine the deviation produced by the force 20 we have only to re-
nove the plate when the galvanometer points to 4°; the calorific rays will then
fall immediately on the pile, the angle of deviation will increase, and if the pro-
- portionality of the degrees to the forces continues through the whole extent of
the are of the first 20 degrees we shall see the index stop at 20°: at all events
we shall have the corresponding indication. By repeating the same operation
when the galvanometer points to 6°, 8°, we shall obtain the quantities sought,
that is to say, the degrees answering to the forces 20, 30, 40, &c. Thus we
may verify the results contained in the tables of intensities already made, or de-
termine the elements necessary for the construction of new tables.
48 M. MELLONI ON THE IMMEDIATE TRANSMISSION
against the principle as the zero is never followed by appretiable trans:
missions.
The same principle holds in respect to all the liquids that I have been
able to submit to experiment. It will be recollected that, in my mode of
operating, the rays of heat, before they reach the liquid layer, must pass
through a plate of glass. Now this substance becomes more and more
interceptive in proportion as the sources employed are of a less elevated
temperature, and consequently acts upon the calorific rays with an effect
the same as that which a screen of variable transparency would produce
in respect to light. The process therefore which I pursued in my first
Memoir could not enable me to determine the exact ratios of the ca-
lorific transmissions through the same liquids when the source is changed;
but it was possible to make it available for the purpose of establishing,
in the greatest number of cases, the general law of decrease which we
have just determined in respect to solid bodies.
Let us suppose that a thick plate of glass being submitted to the suc-
cessive action of an equal quantity of heat, emanating from our four
sources, gives these transmissions :
30," 18; 2; "0:
Let us suppose a parallelopiped, with sides parallel to the faces of the
plate, to be cut out of the glass, and the cavity thus made to be filled
with a given liquid: let us then suppose that the transmissions of the
system become all respectively inferior to the preceding, and are re-
duced, for instance, to
20 a tSy salons
it will be immediately concluded that the liquid acts on the calorific rays
from different sources in the same manner in which its glass case does ;
that is, that it exhibits an order of decrease similar to that exhibited
by the glass and by solid bodies in general. Now this is precisely the
result furnished by the liquids contained in my glass vessels *.
* In many instances I was unable to obtain any transmission, even by em-
ploying a very powerful radiation. It is thus that water, which transmits six
or seven hundredths of the rays from a Locatelli lamp, completely intercepts the
heat of the last three sources. Calculating the limit of error for the case least
favourable to interception I found it ,4, : the source was then brought very close
to the liquid and an equal layer of oil employed, which caused in the index of
the galvanometer a deviation of several degrees. Now if the water allows a
passage to the radiation from bodies heated even to incandescence or brought
to lower temperatures, the part transmitted must be less than ,4, of the incident
quantity. I here speak of a layer of 3"™ or 4™™ in thickness : for it is possible
and even very probable that layers much thinner than these may be in some
slight degree permeable to rays of this kind. Thus we have seen glass of 0-07
in thickness transmit 14%, of the rays emanating from boiling water, while a
plate of 1™™ intercepted them totally. But as, in order to compare different
transparencies, we must operate on a certain thickness of each medium (for the
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 49
In eight-and-twenty cases there have occurred but the three excep-
tions presented by carburet of sulphur, chloride of sulphur, and proto-
chloride of phosphorus, in which the transmissions did not change when
the liquid was substituted for glass. I found it therefore impossible to
decide at first whether these three substances acted in the same manner
as the others; for if they had acted even in a contrary way, provided their
least transmission were equal to 30°, the result obtained would be the
same. But in all probability these three anomalies are merely apparent ;
for the chloride of sulphur, the carburet of sulphur, and the protochlo-
ride of phosphorus being in a high degree permeable to radiant heat, the
same thing will happen in respect to these three liquids inclosed in glass
vessels that happens when very pure fluate of lime is substituted for them;
that is to say, the transmissions of the system retain their proper values,
though the fluate of lime itself be subject to the general law.
Thus the radiant heat from different sources is absorbed in greater or
less proportions while it is passing through diaphanous bodies (solid or
liquid); but while it is passing through the same body the absorption
constantly increases as the temperature of the source decreases.
It happens quite otherwise to the luminous rays. Let us look through
a plate of glass at the most vivid flame or at any other phosphorescent
substance. If the plate is very pure, its interposition will produce no
sensible effect, and the images will retain all the relations of intensity
which they had when viewed directly. The pale phosphoric gleam
therefore suffers in the interior of the glass screen the same absorption
as the strong light of the flame does.
The bodies on which I have made my experiments have been taken
indiscriminately from the three kingdoms of nature: some crystallized,
others amorphous; some solid, others liquid; some natural, and others
artificial : yet they all act in a similar order relatively to the rays of the
different sources of caloric. Does not this constancy in their manner of
acting, notwithstanding such great differences in their physical and
chemical constitutions, indicate that this law of decrement belongs to
the very nature of the heat? We should not however infer from this
that there are not bodies which afford a passage equally free to calorific
rays of every kind. For we see by the table that a flake of rock salt,
most opake bodies become diaphanous when they are sufficiently attenuated),
so, in order to judge of the ealorific transmissions through different bodies, we
must take the greatest possible care not to employ excessively thin plates, or at
least, if we are compelled by particular circumstances to use such, the substances
compared should be perfectly equal in thickness; for in that state of tenuity the
_ least difference of thickness might disturb the order of permeability and cause
us to attribute a greater calorific transparency to substances possessing this pro-
: perty in an inferior degree. This is probably the cause of the mistake into which
_ those have fallen who have fancied that they could prove by their experiments
that water is more diathermanous than glass.
Vor. I.—Parr I. E
50 M. MELLONI ON THE IMMEDIATE TRANSMISSION
whether exposed to the radiations of flame, of incandescent platina, of
copper heated to 390°, or of boiling water, always transmits 92 of every
hundred incident rays.
The same constancy of transmission is observable when we operate on
sources of a temperature yet lower than that of boiling water; such,
for instance, as vessels containing this liquid heated to 40° or 50°. It is
observable also when we employ pieces of rock salt 15™™ or 20™ thick.
I have placed all the flakes of salt that I could dispose of side by side,
so that the thickness of them all amounted to 86"". The quantity of
heat transmitted by this series of flakes was considerably less than +34;,
because of the great number of successive reflexions; but it was always
invariable relatively to the four sources. Between these limits of thick-
ness, therefore, rock salt really acts in respect to radiant heat just as co-
lourless glass and colourless diaphanous bodies in general act in respect to
light.
This being premised, it is clear that if each substance contained in
the table acted like the second specimen of rock salt, that is, if it trans-
mitted the heat in a proportion less than 7% but always the same for
each of the four sources, all these substances would be to radiant heat
that which diaphanous bodies more or less dusky are to light. But they
allow the rays from certain sources to pass through them and intercept
the rays from others: they act therefore in respect to heat as coloured
media act on light*.
What do we find when we expose the same coloured glass successively
* It appears that Sir David Brewster had lately arrived at the same conclusion
by means only of the experiments of Delaroche and Seebeck on the transmis-
sion through glass and on the distribution of heat in the solar spectra produced
with different prisms. (See Report. of the First and Second Meetings of the
British Association for the Advancement of Science. London, 1838, p. 294.) But
these experiments did not prove that the rays in passing through the different
bodies suffer a real internal absorption analogous to that which light suffers:
above all, they were far from proving that this absorptive force, varying in each
substance according to the temperature of the calorific source, could, in some
particular cases, become constant, and in all respects similar to the action of co-
lourless diaphanous media on luminous rays. On this ground it may be said
that the inference of Brewster was yet premature; besides, the illustrious Scotch-
man rested his conjectures on the erroneous supposition that water has the same
absorbent force in respect to all sorts of calorific rays. Experiment indeed leads
to the opposite conclusion, as we have already proved in respect to solar heat
by the different action of a layer of water on the temperatures distributed in each
band of the solar spectrum; an action so widely different relatively to two dif-
ferent rays that all the heat of the violet light passes through the liquid without
suffering any sensible diminution, while the nonluminous heat of the isothermal
band is totally absorbed, (Annales de Chimie et de Physique, December 1831,) and
we have just seen in the preceding note that analogous phenomena are obser-
vable in the radiations from terrestrial sources also; for a mass of water some
millimetres in thickness intercepts all but a very small portion of the radiant
heat issuing from flame and the whole of those rays that issue from any other
source.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 51
to differently coloured lights? Lights of the same tint as the glass pass
abundantly, the rest are almost totally intercepted.
These analogies lead us therefore to consider the radiations from dif-
ferent sources of heat as not being of the same nature. This seems in-
deed sufficiently established by the mere fact that the calorific trans-
mission of glass, Iceland spar, or any other diathermanous body varies
with the temperature of the radiating source.
Thus boiling water, copper heated to 390°, incandescent platina, and
the flame of oil will be to us the sources of a heat that is more or less
coloured, that is to say, sources each of which gives out a greater quan-
tity of calorific rays of a certain quality; but the flame will furnish ca-
lorie rays of every kind as it furnishes light of all colours.
We shall distinguish bodies into diathermanous and athermanous*.
The diathermanous we shall subdivide into universal and partial. The
first of these subdivisions, which is analogous to colourless media, will
contain but one substance, namely, rock salt; the second, which cor-
responds with the coloured media, will contain all the bodies comprised
in our table, in addition to diaphanous liquids and diaphanous substances
in general.
As to the class of athermanous bodies I had supposed at first that
every substance which completely intercepted light intercepted the whole
of the radiant heat also. This is found to be the fact in the greatest
number of cases. But subsequent experiments have shown me that flakes
of black mica and black glass, though they completely intercept the most
intense solar light, yet exhibit very strongly marked calorific transmis-
sions. The following are the results:
Transmissions
out of 100 rays issuing from
@ i)
a incan- | copper | copper
Locatelli] descent at
lamp. | platina. | 390°.
Black glass(1™™ in thickness)| 26 25 12
Ditto (2™™ ditto } 16 15°5 8
Black mica(O™™-6 ditto 29 28 13
Ditto (0™™9 ditto ) 20 20 9
* Athermanous, in contradistinction to diathermanous, evidently signifies the
absence of the power of transmitting heat. I adopt this term merely for con-
venience, without attaching to it a definite meaning; for, as there is no body
which, if reduced to an extremely thin plate, may not become in some degree’
transparent, I think also that some rays of heat may pass through all substances
in a state of great tenuity.
Eg
52 M. MELLONI ON THE IMMEDIATE TRANSMISSION
The black mica and black glass then, though perfectly opake, are dia-
thermanous, but yet only partially diathermanous, because while they al-
low some rays of heat to pass they intercept others.
We may see, besides, that the heat of incandescent platina and that
of the flame of oil are transmitted in nearly equal quantities by these two
substances. As soon as I had made my first experiments on the trans-
mission of opake bodies I found that the rays from incandescent pla-
tina pass through a plate of black glass in a greater proportion than
those from an Argand lamp. Now as it happens quite otherwise in
respect to transparent glass and other diathermanous bodies, I thought
at first that, in the particular case of the black glass, the variation in the
quantity of heat transmitted was inversely as the temperature of the ra-
diating source*. But it was not long before I discovered my mistake ;
for, exposing two flakes of glass, the one colourless and the other opake,
first to the direct rays of a Locatelli lamp and next to the rays that passed
through a screen of common glass, I found that if the transmission
through the first plate increases, as I have already stated in my first Me-
moir, the transmission through the second decreases. These opposite
variations exhibited by the transmissions of the black and the white
glass relatively to the radiations from the Argand lamp. and the incan-
descent platina, do not arise from any peculiar action of the calorific
sources on the two bodies, but from a particular modification which the
cylindrical screen or glass funnel attached to the Argand lamp pro-
duces in the calorific rays passing through it,—a modification which
changes their capability of ulterior transmission and enables them to
pass through the other bodies in a greater or less quantity than if they
were in their natural state.
We shall presently see that almost all the screens produce analogous
effects.
The similarity of the action of glass and transparent bodies in general
upon radiant heat to that of coloured media upon light, is established
even in its most minute details by all the phenomena of transmission that
we have been able to observe. For we have seen that the calorific
rays from the flame of an Argand lamp lose much of their intensity
while passing into the interior of a thick piece of colourless glass, and
that their subsequent losses decrease in proportion as the distance from
the surface at which they enter increases. Now the same thing takes
place if we expose to white light any coloured transparent body, a red
liquid, for instance; for in this case nearly all the rays, blue, green, yel-
low, &c., which enter into the composition of this light are absorbed
more or less rapidly by the first layers of the liquid, and the red rays
alone penetrate to a certain depth.
* Bulletin de la Société Philomatique, July 1838.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 53
It is also known from the experiments of Delaroche and others that
the radiant heat which has traversed a plate of glass and suffered a cer-
tain loss will in passing through a second plate sustain a second loss pro-
portionally less than the first. In the same manner does the ineident
white light in passing through the first layer of a coloured substance be-
come considerably weaker, while the emergent colowred light passes al-
most without suffering any diminution of intensity.
By exposing a given plate of a diaphanous substance successively to
equal quantities of calorific rays from different sources we have seen
their transmissions vary with the temperature of the source, that is to
say, with the nature of the rays emitted. We have seen moreover that
the differences between one transmission and another decrease in pro-
portion as the plates employed are thinner, until within a certain limit
of tenuity they vanish or have a tendency to vanish altogether. All
these effects are observable in the differently coloured lights transmitted
through a coloured medium; for if the medium be red the quantities of
light transmitted will be greater in proportion to the greater number of
red rays contained in each radiation. The other rays will be absorbed
in a greater or less degree. But the quantities of light transmitted ap-
proach more nearly to an equality in proportion as the plate to be passed
through is thinner. In short, the coloured media become more faint as
their mass is reduced, and when sufficiently attenuated retain no sensible
tint whatsoever, in other words, they become permeable to luminous rays
of all colours.
We have several times remarked the striking differences exhibited
in the calorific transmissions of diaphanous substances. But this cu-
rious fact, which constitutes, as it were, the basis of our inquiries, ceases
to surprise us as soon as we feel convinced that bodies which are trans-
parent and colourless act upon heat in a manner similar to that in which
coloured media act upon light. For, as upon the intensity of the co-
lour depends the degree of transparency, that is, the number of lumi-
nous rays that.pass through the coloured substances, in like manner upon
this species of invisible calorific tint which diaphanous bodies possess
will depend whether a greater or a less quantity of heat be transmitted*.
* Seeing that in respect to all the substances given in the table, the rock salt
excepted, the order of decrement is similar though the sources of heat are dif-
ferent, one might be inclined at first to infer that they belong to the same species
of partially diathermanous bodies, that is, that they may be compared with co-
loured media. But that such a conclusion is not legitimate will be shown by
~ one example: let a be the species of rays transmitted by the medium A, b that
species which is transmitted by the medium B, and c the rays intercepted by the
same media. Let us suppose a calorific source that will give 30 a, 30 b, and
40 c; it is clear that the two media A and B will intercept 70 parts of the hundred
and transmit 30. However, the rays emerging from A will be different from
those which emerge from B, If we suppose a second source of heat such: as
will give 20 a, 20 b, and 60 c, we shall have 80 as the quantity intercepted and
54 M. MELLONI ON THE IMMEDIATE TRANSMISSION
We shall presently see yet more striking analogies between the two
classes of phenomena when we consider the modifications which the ca-
lorific rays undergo in their passage from one screen to the other. But
before we dismiss the present subject it may be advisable to bestow a
few moments’ attention on the purposes to which the calorific proper-
ties of rock salt may be applied.
Glass is a substance but very slightly diathermanous, especially when
the temperature of the source is low. The common prisms or convex ©
lenses could not therefore be employed for the purpose of ascertaining
whether radiant heat be subject to changes of direction analogous to
those of light in penetrating to the interior of refracting media. It was
owing to the use of such instruments that some who applied themselves
to the investigation of this point attained but very indecisive results, and
often drew from them very false conclusions. Scheele asserted that
“bright points not possessing the least heat may be formed before the
fire with burning-glasses*.” Carefully conducted experiments have
more recently shown that a thermometer rises some degrees when placed
in the focus of a lens exposed to the radiation of flame or of incan-
descent bodies+. But as the heat is then luminous, and as no very de-
cided effect is observed if the operation is performed with nonluminous
heat, it was inferred that the elevation of temperature was owing to the
light absorbed by the thermometer and that isolated radiant heat is not
susceptible of refraction. . This notion might derive additional support
from the fact that lenses of rock crystal, Iceland spar, alum, and other
diaphanous substances acted analogously to the glass lens: and yet it
would have been wrong to attribute to the agent an effect which was due
only to the particular structure of all those substances. To be satisfied
of this we need only operate with a lens of rock salt; for the focal ther-
mometer then always exhibits a marked elevation of temperature, even
though the radiant heat be totally separated from the light. But it has
been attempted to explain the effect of the lenses by an inequality in the
heating of their different parts. It has been said that the heat is accu-
mulated towards the centre, that the parts towards the margin, because
of their thinness, quickly grow cold again, and that it is not surprising
therefore to see the thermometer rise more rapidly when placed in the
prolongation of the axis of the lens than in any other direction}. It
would however still remain to be explained why the experiment is no
20 as the quantity transmitted by each of the screens. If the source gave 10a,
10 4, and 80 c, the transmission would be 10 and the interception 90. Thus two-
substances exposed fo different radiations may furnish calorific transmissions not
only varying according to thesame order of decrement, but equal inall their periods
of variation, although the rays emerging from each may be of a different kind.
* Scheele, Zraité de I’ Air et du Feu, Paris, 1778, § 56.
+ W. Herschel and Brande, Philosophical Transactions for 1800 and 1820.
t Philosophical Transactions, vol. cvi.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 55
longer equally successful when for the salt we substitute alum or any
other diaphanous substance. But as recourse might be had to sup-
posed differences between the conducting, the absorptive, or the emis-
sive powers of these bodies, it seems advisable first to prove the refrac-
tion of the nonluminous rays without using lenses.
With this view I place, at a certain distance from the thermoelectric
pile and out of the direction of its axis, a plate of copper heated to 390°
by an alcoholic lamp, or, what is still better, a vessel filled with water
in a state of ebullition. The pile being lodged at the bottom of a me-
tallic tube blackened inside, the rays of nonluminous heat emitted from
the vessel in a direction oblique to the axis cannot reach the thermosco-
pie body, and the index of the galvanometer remains perfectly at rest.
Matters being now in this state, I take a prism of rock salt and fix it at
the mouth of the tube with its axis placed vertically and its refractive
angle turned towards the angle formed by a line drawn from the source
to the extremity of the tube. (See Plate I. fig. 2.) A considerable de-
viation is immediately perceived inthe galvanometer. The rays of heat
are therefore conveyed into the tube by the action of the prism.
To show that the effect is really due to the refraction and not to the
heat of the salt it will be sufficient to turn the angle of refraction in a
contrary direction; for as soon as this is done the needle falls again to
zero, notwithstanding the presence of the prism. The experiment is no
less successful with the heat of the lamp, or that of the incandescent
platina. Calorifie rays of every kind are therefore, like luminous rays,
susceptible of refraction.
But on the principle of analogy, as each species of light, so will each
species of heat possess a different refrangibility. Hence it is evident that
if the prism be left in its position and the radiant source changed it
would become necessary at the same time to change the angle formed
by the axis of the pile with the direction of the rays, in order to obtain
the desired effect on the galvanometer. If however we attempt to ve-
rify this conjecture we obtain no decisive result. This is easily con-
ceived when we reflect that the aperture of the tube has a certain dia-
meter and that it is placed quite close to the prism, so that the rays
refracted at angles differing but very little from each other can always
reach the pile though no change should be made in the inclination of
the axis of the tube.
But there is another process by means of which, if we cannot exactly
measure the refrangibility of each, species of calorific rays, we prove at
least that the angle of refraction varies with the measure of the radiating
source. I took a graduated circle ABC (Plate I. fig. 3.) 22 inches
in diameter carrying aruler CD as a moveable radius. At the extremity
of this ruler I placed a thermoelectric pile M composed of fifteen pairs
disposed in one line perpendicular to the plane of the circle.
56 M. MELLONI ON THE IMMEDIATE TRANSMISSION
This apparatus being placed horizontally on a table, the centre C was
brought within a little distance of the bottom of a vertical prism(N) of
rock salt, so that when the ruler CD was properly placed the refracted
parcel of hot rays fell on all the points of the linear pile.
By establishing the electric communications with the galvanometer
and moving the ruler over the graduated arc, the point at which the
deviation of the magnetic index attained its greatest value was easily
determined. The radiating source was then changed while everything
else was allowed to remain in the same state. We had now a calorific
action more or less intense than the preceding; but in order to obtain
the maximum of effect it was necessary to slide the ruler in one direction
or the other. Thus, for instance, when I commenced the experiment
with the incandescent platina, that is, when I had found the correspond-
ing position of the pile that gives the greatest galvanometric deviation, it
was necessary to move the ruler about two lines towards B, on the side
to which the most refrangible rays are directed, if I substituted the
Locatelli lamp for the platina. But if I substituted for the platina a
plate of copper heated to 390° I was obliged to slide the ruler three lines
towards A, in the direction of the less refrangible rays. The action of
the boiling water in this experiment was too feeble to be compared with
that of any of the three other sources.
The refraction and constant transmission of the calorific rays through
the rock salt being placed beyond the possibility of doubt, we imme-
diately see the use that may be made of this substance in investigating
the nature of radiant heat. If, for instance, it is proposed to propagate
to great distances the action of a heated body of small dimensions, we
are now certain that we have only to place the body at the focus of a
lens of rock salt, which will refract the calorific rays and make them form
a real pharos of heat by issuing in a direction parallel to the axis. Is
it desired that extremely feeble rays emanating from any source should
be rendered perceptible? Let them be received on a lens of this sub-
stance having a thermoscopic body placed in its focus. In this manner
we may, with the aid of an ordinary differential thermometer with small
balls, obtain very decided indications of the heat issuing from a vessel
filled with tepid water and placed at a great distance. In short, rock
salt formed into lenses and prisms acts upon calorific rays in a manner
perfectly analogous to that in which optical instruments act upon lumi-
nous rays. It constitutes then the ¢rwe glass of radiant heat, and there-
fore the only glass that should be employed in appreciating the effects
of its intensity. All other transparent bodies are but partial and in-
complete transmitters of heat, totally intercepting calorific rays of a
certain kind. It is easy to conceive, from these considerations, with
what serious disadvantages those persons have had to contend who have
undertaken to investigate the composition of solar heat with common
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 57
prisms of flint or crown glass, water, alcohol, or some other diaphanous
body. It was exactly the same as if they pretended to be able to analyse
solar light with a prism formed of coloured glass.
Of the properties of the calorific rays immediately transmitted by different
bodies.
The radiant heat which has passed through a plate of glass is trans-
mitted in a greater proportion by a second plate of the same substance
and the same thickness ; the rays issuing from the second will be trans-
mitted in a still greater proportion by a third, and so through any number
of successive screens. The losses sustained by the calorific rays in their
passage through a succession of screens, as compared with the quantity
incident on each plate, will therefore form a decreasing series. But the
difference between every two terms of this series becomes less and less
as the number of terms increases, so that there must be somewhere a
limit beyond which the difference has a tendency to vanish. We may
conclude therefore that the rays after they have passed through a cer-
tain number of screens, will in their further transmission be subject to
a loss reducible to a constant quantity as compared with the quantity of
heat incident to each of the screens through which this further transmis-
sion is made.
The same phenomena may be traced in a continuous mass of diather-
manous matter; that is to say, that if we imagine a piece of glass di-
vided into several equal layers and measure the loss sustained by the
radiant heat in its passage through each layer, the greater the distance
of the layer from the surface at which the heat enters, the less will be
the diminution suffered by the rays passing through that layer, and the
losses have a tendency to become constant within a limit depending
on the thickness of the layers. Some of these results we have already
verified in the preceding memoir, and it is easy to establish their truth,
in reference to the sources of heat employed in our present inquiry, by
means of the numbers which represent the transmissions of the plates
contained in the first table*.
* Let us imagine the screen of 8™™ divided into seven layers having for their
degrees of thickness the differences between two consecutive plates. (See the first
table in this Memoir.) The quantities of heat incident on the layers when the
radiation is from a Locatelli lamp are
100, 77, 54, 46, 41, 37, 35, 33-5,
and the Seeentien lost in the successive transmissions are
23, 23, 8, 5, 4, 2, 1d.
Now the mean losses for the fuindxedth part ofa millimetre of each screen will be
23 23 8 5 4 2 1:5
7’ 43’ 50’ 100’ 100’ 100’ 100°
or 3:286, 0-535, 0:160, 0-050, 0-020, 0-010, 0-007."
Hence the losses sustained by the rays of the lamp in the first hundredth part
58 M. MELLONI ON THE IMMEDIATE TRANSMISSION
The only difference observable between the transmission through a
continuous medium and the transmission through a series of detached
screens is in the amount of the losses, which, for a given thickness, are
found to be greater in the latter, because of the reflexions produced by
each separate surface. :
These facts cannot surprise us after the idea we have formed to our-
selves of the influence exercised by diaphanous substances on radiant
heat. For the calorific sources always emit a certain portion of rays
heterogeneous (if we may use the expression) to the calorific tint of the
glass, which, through the absorbent action of the matter constituting
the continuous medium or the detached screens, are successively extin-
guished until no rays remain but those that are homogeneous to this tint.
Now these homogeneous rays must suffer a loss greater or less in its
amount, but constant in respect to layers of equal thickness, as is the case,
in the transmission of light, with red rays passing through a medium of
the same colour, and with white rays passing through a medium diapha-
nous and colourless. What we have said of glass is equally true of
every other partially diathermanous substance.
The calorific transmission through aseries of homogeneous screens is
then absolutely of the same nature as that which is effected through the
of a millimetre of each layer, when referred to the quantities of incident heat,
will have the values
3286 0°535 0:160 0:050 0:020 0:010 0-007
100 77 54 46 41 37 35
that is, 0°0328 0:0070 0:0030 0:0011 0:0005 0°0003 0-0002.
By similar calculations the successive losses sustained by the radiations from
the incandescent platina and the copper heated to 390° will be found to be
0:0614 0-0081 0°0032 0:0019 0:0010 0:0005 0-:0003
0:0943 0:0155 0°0050 0:0022 0-0014 0:0010 0-0008.
Now the differences between every two terms of these series are for the
Ist, 0°0258 0-0040 0-0019 0-0006 0:0002 0-0001;
2nd, 0:0523 0:0049 0:0013 0:0009 0:0005 0:0002;
3rd, 00780 0:0105 0:0028 0:0008 0-0004 0-0002.
As to the fourth source it is useless to speak of it, as its rays are completely
extinguished at the distance of one millimetre.
Thus, notwithstanding the inequalities of the increase of the distance from
the second and the third layer to the surface of entrance, we observe in the
three series the two principles we have laid down, namely, Ist, the decrease of
the losses; 2nd, the tendency of this decrease towards a limit at which the loss
becomes constant: but for each particular case the points of the medium at
which the rays begin to suffer this constant action are evidently placed at a fixed
distance from the origin. Therefore, if the glass be divided into equal layers,
the limit of the decrease of the losses will be attained more slowly in proportion
as theayers are more numerous, that is to say, thinner. It is for this reason
that in each series the limit at which the losses become constant depends, as
we have already said, on the thickness of the elementary layers.
a
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 59
interior of one continuous medium. This transmission we have ex-
amined, and, as we have just seen, it presents nothing contrary to its ana-
logy with the transmission of light through coloured media. There is
however a particular case in which two homogeneous screens act in so
singular a manner in respect to light that it must be interesting to know
whether something analogous does not take place in respect to caloric.
The optical phenomena presented by most of the slices of tour-
maline cut parallel to the axis of crystallization are universally known.
If these slices are placed one over the other and their axes laid in the
same direction, they transmit light in considerable quantities. But if
they be laid at right angles to one another, the light is totally intercepted.
Do these phzenomena, arising, as is well known, from the polarization of
the light in the interior of the slices, take place in respect to calorific
rays also; or, in other words, is radiant heat capable of being polarized
in its passage through tourmaline ?
In order to ascertain this I have taken two square plates of the same
dimensions. I have made an aperture in the centre of each. This
aperture was likewise a square having its sides parallel to those of the
plate and each equal to the least breadth of the two polarizing slices.
I then took some soft wax and attached a tourmaline to each aperture,
holding the axis of the former parallel to one of the sides of the latter.
These two plates being laid one over the other, it evidently depended on
one of the sides of the one plate being placed parallel or perpendicular
to a side of the other whether the light was to be transmitted or inter-
cepted. Yet this pair of plates being placed vertically on the stand of
my thermoelectric apparatus and exposed to the radiation of a lamp or
incandescent platina, uniformly produced the same calorific transmission,
whatever might be the relative direction of the sides of each plate.
That this fact might be put beyond the reach of doubt the galvano-
metric index was carried to the 18th or 20th degree, and the calorific
communication now established was suffered to remain while we placed
one of the plates on each of its sides in succession. The flame or the
incandescent platina was then observed to appear and disappear alter-
nately while the magnetic needle continued invariably at the same point
of deviation. .
This experiment was repeated many times with several tourmalines,
and the angle formed by the intersection of their axes varied. The re-
sult was in all cases the same. The quantity of calorific rays trans-
mitted through the two polarizing slices is then independent of the re-
spective directions given to their axes of crystallization; that is to say,
the heat radiating from terrestrial sources is not polarized in its passage
through tourmalines*,
* This result seems opposed to the experiments of M. Bérard on the polari-
zation of reflected heat; but, ignorant as we are of the nature of the relations
60 M. MELLONI ON THE IMMEDIATE TRANSMISSION
Let us now proceed to consider the transmission of heat through he-
terogeneous screens. The calorific rays emerging from each plate ex-
posed to the action of the same source produce a particular elevation of
temperature when they fall on the thermoscopic body of our apparatus.
Whence we have inferred that the quantity of heat which passes through
a given screen varies according to the quality and thickness of the sub-
stance. But, it may be asked, is this the only difference between the
rays immediately transmitted through bodies of different kinds ?
For the purpose of answering this question we have made the follow-
ing experiments.
If the rays from a Locatelli lamp be brought to act on a thermoelec-
tric pile after having previously passed through a screen of diaphanous
matter (such as citric acid) but in a slight degree permeable to radiant
heat, the effect obtained in the ordinary case, in which the whole ac-
tion is equivalent to 30° of the thermomultiplier, will be very inconsi-
derable ; but it may be increased by bringing the source of heat nearer,
or by concentrating its rays on the plate with the help of metallic mir-
rors or lenses of rock salt. I suppose then that a deviation of 25° or
30° of the galvanometer has been produced through a plate of citric
acid. I now interpose a plate of alum in such a manner that the rays
emerging from the citric acid may be forced to pass through it before
they can reach the thermoscopic body; the magnetic needle descends
only about 3 or 4 degrees.”
I now recommence the operation on any other diaphanous and colour-
less substance different from the citric acid; that is to say, I vary the
distance from the lamp to the pile until I obtain the same galvanome-
tric deviation of 25° or 30° by the action of the radiant heat on this new
substance also. I then interpose the plate of alum, and the magnetic
index, as in the case of the citric acid, descends again not more than
about 3 or 4 degrees, but it approaches nearer to zero, and the retro-
that caloric and light bear to one another, we have no means of proving that, as
no polarization of heat is produced by the transmission through the tourmalines,
none can be produced by reflexion at the surface of the glass. Iam bound also
to remark that some very able experimental philosophers having lately tried to
polarize light by M. Bérard’s process, their efforts proved unavailing. Mr. Powell
informs us that although he had taken the necessary precautions against the
heating of the glass and other causes of error he has never been able to discover
the least appearance of polarization when operating with nonluminous heat.
But he thinks that when he employed luminous sources he was enabled to ob-
‘serve a small perceptible effect by making the rays previously pass through a
screen of glass (Edinb. Journal of Science, N. S., vol. vi.) Mr. Lloyd communi-
cated at the last meeting of the British Association for the Advancement of
Science (Cambridge 1833) some new results tending to support the conclusions
derived by Mr. Powell from his own experiments. [No communication upon
this subject by Professor Lloyd appears in the Report of the British Association
for 1833,—Epir. |
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 61
grade movement is sometimes so marked that the needle nearly resumes
its natural position of equilibrium.
If instead of alum other substances were employed as the invariable
plate on which the rays issuing from each diaphanous body are succes-
sively made to fall, we should still observe differences in the correspond-
ing deviations of the galvanometer; but they would be in general of a
less decided kind. It is on this account that we have preferred the
alum.
The following are the results, in hundredth parts, of the constant
quantity of heat that falls on the plate of alum:
Screens from which there issue 100 rays
of heat which are made to fall succes- Number of rays transmitted
sively on the same plate of alum. J es
ORBISON WLS, chee. i otdin seus een 9
Fockisalt (limpid)ciec usc. de Seeds ove 9
Rock salt SS aN Ceon Th 9
EES OL SOAD. ono utansiennsier'piaes axes, itd
AGULATIA TIDAL | oon... ccncenocaesene 14
MECIATU SPaly coetircscsidecsenncettoscse OE
Bisehs crystal Ai: os. aeee cow cas cotess 25
Mirror elass ts) See 27
Carbonate of ammonia ............... 31
Sulphate of inten: 05... ssvwscetedcnvassihinn C2
Tartrate of potash and Jee Ehcrtde nce 80
WipmeraCldy. ster dee ase ch teeroechs + OD
J: \IRELTEN Sy aia RRS BG Ra eS 90
We see that radiations of the same intensity emanating from the dia-
phanous and colourless bodies contained in the tables pass through the
same plate of alum in very different quantities. In the same manner
sheaves of luminous rays issuing from different coloured media are
transmitted some in greater and others in less proportions by a second
transparent substance equally coloured, as the tint of each medium hap-
pens to be more or less analogous to that of the invariable substance
through which they are to pass.
The calorific rays issuing from the diaphanous screens are therefore
of different qualities and possess (if we may use the term) the diather-
mancy * peculiar to each of the substances through which they have
passed. The citric acid, the tartrate of potash and soda, and the sul-
phate of lime transmit rays which pass abundantly through alum; the
* IT employ the word diathermancy as the equivalent of calorific coloration or
caloric tint, lest the latter should be confounded with tints or colours properly
so called. The word has been suggested to me by M. Ampére, who has conti-
nued to assist me with his valuable advice in the composition of this Memoir,
for which I here take the opportwhity to tender him my grateful acknowledge-
ments.
62 M. MELLONI ON THE IMMEDIATE TRANSMISSION
diathermancy of these bodies therefore approximates nearly to that of
the alum. The glass, the rock crystal, and the Iceland spar have evi-
dently a different diathermancy, for the rays which pass through them
are less transmissible by the invariable screen. ‘The same may be said
of borax, adularia, and carbonate of ammonia. As to the heat emerging
from rock salt (limpid or dull) it acts in a manner similar to that in which
the unobstructed light of the lamp would. The reason is evident, since
the salt, acting equally on the different species of calorific rays, must
transmit them all without reflecting their relative properties in any man-
ner whatsoever.
These facts then completely confirm the conclusions which we had
drawn from the preceding experiments: namely, that, 1st, flame sends
forth rays of several kinds; 2nd, that diaphanous colourless bodies, with
the exception of rock salt, act so as to extinguish certain caloric rays
and allow others to pass, just as coloured media act in respect to light.
Here a very interesting question is naturally suggested. If the dia-
thermancy or quality which constitutes the tint of a medium relatively
to the radiant caloric is invisible, what part then do colours act in the
transmission of heat ?
When the quantity of radiant heat that passes through coloured glass
is measured, it is always found to be less than that which passes through
white glass of the same thickness. The difference indeed is sometimes
considerable, though having no apparent relation to the prismatic order
or intensity of the colour. We have already remarked this in the first
memoir, and the truth of the remark will be readily admitted by any
one who casts an eye over the following little table.
Screens of glass exposed to the
radiation of a Locatelli lamp.
(Common thickness 1"™-85.)
Transmissions
out of 100 rays of heat.
CABS; TBS) Leh PS RBS, eee 40
ny ROH (deep) i. lassen <inadepn 33
mre i) OFRDER os cassis eds aepeaes pasar cane’ 29°
— yellow (brilliant) ................. 22
— green (apple).....cscssscesseesencee 25
— green Gece cantons cua tae ste ect 23
ee RRS ere Nd ates Perret 21
pert 0 REAR 3 bor sdcon cnc caosacccbiguon 12
== violet (deep) te acenthes chi. 0500 34
—~- black.(opake)jssacpacusisag-uppsice» sas 17
It is therefore not to be doubted that an absorption of caloric is caused
by the colouring matter. But is the power of absorption elective like the
action of the invisible calorific tints in colourless diaphanous bodies, or
does it affect all sorts of rays indiscriminately? We are about to inves-
tigate this point by means of experiments similar to the preceding, in
which we have taken equal quantities of heat issuing from different
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 63
screens of differently coloured glass, in order to make them pass through
one common screen of alum. -
Screens from which the 100 rays issue
that are made to fall successively
on the same slice of alum.
Number of rays
transmitted by this slice.
Relay WiRIte . O84, «iin acindeasadeeeesbatiemlees Ul
soe BRR 2 ld nebo npso i octal mana ards Seta Veal
=o OMT SRocdrOasccnccto-Sbsoncens cna. ZT)
ah MOMOW a cacns gan taes cece: <satpetie Whee
aaa Pree) (Apple ee tenis te cose ss geen 4 pil
— green DAE Poa Crete 3
= | Ca sae 27
et ENO ac anna ass. « votes Ralaalhta yes 27
SE NIOIEE cncs enna: 27
meee (DUCE) conics tewnc seas 1
We see here that the rays emerging from the red, orange, yellow,
blue, indigo, and violet are transmitted through the plate of alum in the
same proportion as the rays that issue from the white glass. The co-
louring matter introduced into the composition of these different kinds
of glass has no other effect than to extinguish part of the calorific sheaf
which passed through the white, without perceptibly altering the rela-
tions of quantity between the several species of rays of which that sheaf
is composed: they act in respect to radiant heat just as brown or black-
ish substances dipped in a transparent fluid would act in respect to light.
But the case is different with respect to green and opake black; for
these being introduced into the composition of glass, it will stop nearly
all the rays that the alum is capable of transmitting. This effect arises
from the green or opake colouring matter producing a certain modifi-
cation in the diathermancy of the glass, and we have just seen that this
species of calorific colouration is invisible and totally independent of co-
loration properly so called, since it exists in bodies possessing the great-
est transparency. It is then extremely probable that the black or the
green should not be supposed to enter as mere neutrals into this phe-
nomenon, which will thenceforth depend on such or such a property
of these colouring materials. I have found, in fact, some green glasses,
which produced a much feebler action than others of the same tint but
possessing a less brilliant colouration. The green glasses which act most
powerfully are of a bluish cast ; from which circumstance it would seem
to follow that they contain a considerable quantity of oxide of copper.
Whatever may be said of this singular property of green and black
opake glasses and the cause by which it is produced, it is nevertheless
an indisputable fact which everg man can easily verify and of which we
intend to give some new proofs presently. But it will perhaps be ad-
visable previously to adduce the results furnished by several diather-
64 M. MELLONI ON THE IMMEDIATE TRANSMISSION
manous substances examined by that process to which we have sub-
mitted the coloured glasses and the diaphanous colourless bodies.
Screens emitting 100 rays of heat which
are made to fall successively on
the same slice of alum.
Mica, blackopake (22 .w.ciokte eee eS
Tourmaline, -green.......0.002sses0e see vel OE
Sulphate of barytes .........ssceceeeeeee 12
Acid chromate of potash ............... 14
Mites We). (ccc aecitvrocewesirentleater sere, Me
Beryl <2ic-.cicavst.veieewivecks-shdebsetoctoe lo
Hime ralgiey ys cacrecleteuesccceceecseccsenvett MLO
Number of rays
transmitted by this slice.
Agate, pearly ......cceccoessccessowessers 24:
Agate, yellows c..csccessccecevsececesscsene 24:
Amber, yellow : ...s0.s00scecsescessoensess 30
OPIN, fa'staot icceisics snc ebalan'a sete oes Fannie 45
On these numbers we have two remarks to make: first, that the green
tourmaline and the black mica act in a manner analogous to glass of
the same colour; second, that the beryl and emerald emit rays equally
transmissible by the alum, although the colours of these two kinds of
the same substance are different. The same happens to the two kinds
of agate. These facts may perhaps be turned to some account by the
mineralogist in examining certain coloured substances which belong to
the different varieties of one mineralogical species.
We have been hitherto investigating the action of alum on a constant
quantity of rays emerging from several diathermanous substances. Let
us now reverse the problem and see what will be the effect when these
substances are interposed in the passage of an invariable radiation is-
suing from alum.
In the third column of the following table will be found the results
furnished by this class of experiments. It is almost unnecessary to ob-
serve that they have been obtained by successively placing the several
bodies between the alum and the pile, after having produced in the
galvanometer the ordinary deviation of 30° through the first substance.
I have placed in the columns after the third the values of the trans-
missions of the same bodies exposed to the rays emerging from four
substances different from alum; namely, sulphate of lime, acid chromate
of potash, and green and black glass. The natural values of the calorific
transmissions, that is to say, the results obtained under the immediate
action of the lamp, are indicated in the second column.
OF RADIANT HEAT THROUGH DIFFERENT BODIES.
Names of the substances
interposed.
(Those plates whose thickness is
not specially indicated have the
common thickness of 2-6.)
CT eS eee
Fluate of lime
DRE e acc tay coe ses ves doe tences ccs
1 SE 0 re
Glass (thick. 075) ...2........
EWS Si) eet
BNE GEN SEL ne jne on ansinns-cs
Chromate of potash
Sulphate of barytes
White agate ..0522.0...00.0.0.1.
Adularia felspar...............00
Yellow amber ....
Black opake mica(thick. omm. 9)
Yellow agate
Emerald
Bee wee eeeees
Seem eee eee ee tewees
He ewe eee ewe eee testes eeneee
sere eee eee eeeeee
eee ee
Common gum *. 2.060... ..00..00.
Sulphate of lime ...............
Sulphate of lime (thick. 12™™)
Carbonate of ammonia.........
MUSEUM so ccc stcinepats cab sie «ue
Tartrate of potash and soda ...
Alum
Coloured glasses,
(common thickness 1™™-85.)
Glass, white
SIDLCLMEsc bat cde srcchec tt.
PEON eth cathe ceaseeee
MEAS Ss cin miedo das icnsosssive
green (apple) ............
green (mineral )
eee eee eee ee eee eee
tee wwe eee
black (opake).......
RUE” cxtcccsases:
WoL. l—PART I.
Rays immediately from
the lamp.
alum,
Rays emerging from the
(thickness 2™™6, )
Transmissions out of 100 rays.
65
(thickness 2™™°6,)
Rays emerging from the
sulphate of lime,
owe
mre LO
IEP N1OnDDO
@M~TCo A bd Ga ©
An
- co
12
m 69 Gi D
oe a
omen!
& bo
Hm D Or 09
ION HA
|
|
chromate of potash,
Rays emerging from the
Rays emerging from the
(thickness 2™™-6,)
ie)
bo
88
66
OL ope) |
bo ~1 OD
= bo © 09 fo +I
Aowonr-
SS bo
D
t
i
bo
oo
re DO
Or Or D ~TO DO
green glass
(thickness 1™-85.)
©
bo
90
Dowaa oa
DBWOA~IOS
LO HHO OHH ALD
PWWOANOBESSABDWSWS
Rays emerging from the
black glass,
(thickness 1™™°85,)
66 M. MELLONI ON THE IMMEDIATE TRANSMISSION
Several of the numerical results contained in this table may be verified
by. calculation.
For, when two plates of different kinds are exposed together to the
radiation of the source, their position relative to the entrance and the
issue of the calorific rays does not affect the quantity of heat which passes
through this system. This is easily proved by putting the first plate in
the place of the second ; for the thermomultiplier, notwithstanding this
change of order, continues to mark the same degree of its scale. Let
us now take two plates and place them alternately in each of the two
positions, for instance, the plate of alum and the chromate of potash.
These two substances, exposed separately to 100 rays of heat emanating
directly from the source, transmit 9 and 34 respectively. The quantities
of heat that should fall on each of the two plates in order that 100 may
emerge in each case is easily determined by these simple proportions:
9 : 100 :: 100: 2a,
Sho OO mse LOO saa,
which give 1111 for the alum and 294 for the chromate of potash. Now
we know by experiment that chromate of potash exposed to 100 rays is-
suing from alum transmits 57, and that alum exposed to 100 rays issuing
from chromate of potash transmits 15.
But the order of succession has no influence on the transmission of
the pair: let us therefore reverse the system only in one case or the
other. We shall then have the same plates exposed in the same man-
ner to the two radiations of 1111 and 294. The quantities transmitted
under both circumstances should accordingly be proportional to the
incident quantities, as is actually proved within the limits of approxi-
mation compatible with the nature of the experiments; for we have,
BT es ES PEL 3294:
The table contains ten pairs which are submitted in both ways to the
radiations of the source; there are in it consequently twenty numbers
which should be in proportions analogous to the preceding. It is evi-
dent too that these calculations require that the five plates emitting the
100 rays which fall successively on the whole series of diathermanous
bodies should be those that are indicated by the same names in the first
column. I have accordingly taken care that this condition should be
satisfied.
The bodies submitted to the heat emerging from the screens present
no longer the same order of transmission that they presented under the
immediate action of the radiation of the lamp. The changes which
take place have no apparent regularity whether we compare one series
with another or consider only the different terms of the same series.
Thus glass, Iceland spar, and rock crystal are more diathermanous to
the heat emerging from the five screens than to that which comes di-
OF RADIANT HEAT THROUGH DIFFERENT BODIES. _ 67
rectly from the source. Citric acid and tartrate of potash become
more permeable to the rays issuing from the alum and sulphate of
lime, and less permeable to those which proceed from black or green
glass. With the opake mica and the tourmaline the case is directly
the contrary. Some substances are equally permeable to the heat ra-
diating from several screens. Others experience variations so great as
to exhibit all the phases of the phenomenon, from an extremely abun-
dant to an excessively feeble transmission*.
Through all these vicissitudes the action of the rock salt continues the
same and uniformly transmits 92 rays out of 100. Hence follows the
inverse proportion that if the series of plates be exposed to one hundred
rays emerging from a plate of rock salt, the ratios of the quantities of
heat transmitted would be the same as those obtained through the action
of the immediate radiation; a proposition which I have besides verified
by direct experiments,
After what we have so often repeated respecting the action of uni-
versal and partial diathermanous bodies, it would be superfluous again
to point out the perfect similarity between these facts and the ana-
logous phzenomena presented by the transmission of light through dia-
phanous media, colourless and coloured. We shall therefore confine
ourselves to a single observation on the nature of the rays which tra-
verse certain screens.
The heat emerging from alum is almost totally absorbed by the opake
* This change in the faculty of ulterior transmission is not the only modifi-
cation that radiant heat undergoes in passing through the diathermanous bodies.
It becomes also more or less susceptible of being absorbed in different quantities
by the black and the white surfaces. This fact can be thus proved by expe-
riment:
We take two thermometers of equal sensibility, and after haying coloured
one of the balls black and the other white we expose them simultaneously to the
radiant heat, sometimes direct, sometimes transmitted through a plate of glass.
The two thermometers are then observed to rise unequally, but the inequality is
eater when the transmitted heat is employed. Mr. Powell, to whom we
are indebted for this ingenious experiment, has performed it on calorific radia-
tions from a bright red hot iron and from an Argand lamp. ‘The means of se-
veral series of observations furnished, as the ratio of absorption of the thermo-
meter with the black to that of the thermometer with the white ball, 100 :78
when the red hot iron was employed, and 100: 72 when the lamp was used.
These ratios became 100: 50 and 100: 57 when he operated on the rays trans-
mitted through glass. (Report of the First and Second Meetings of the British
Association for the Advancement of Science, pp. 274, 275.)
I haye obtained numerical data perfectly analogous, by means of the thermo-
multiplier. The pile of the apparatus was well washed, afterwards whitened on
one side and blackened on the other. The two colours were made from lamp
black and Spanish white mingled with gumwater. Turning the pile on its
stand I caused the direct or transmitted rays of a Locatelli lamp to fall succes-
sively on the two coloured surfaces, and observed the corresponding indications
of the galvanometer. This experiment is promptly and easily executed. It has
moreover the advantage of requiring no more than one thermoscopic body, a
FQ
68 M. MELLONI ON THE IMMEDIATE TRANSMISSION
screens, but is abundantly transmitted by all the diaphanous colourless
plates. It suffers no appreciable loss when the thickness of the plates
is varied within certain limits. Its properties of transmission therefore
bear a close resemblance to those of light and solar heat.
Let us now direct our attention to the rays which issue from the last
two screens. The opake bodies transmit nearly the half of them; the
circumstance which makes it easier to compare the results than it is found to be
when we are obliged to have recourse to ¢wo thermoscopes, which seldom or never
possess the same degree of sensibility.
I shall now give the ratios derived from this process applied to direct heat,
and to heat transmitted through several screens. The calorific effect produced
each time on the black surface is represented by 100.
t Absorbent
Radiant heat from a Locatelli lamp, power of the faces
(direct, or transmitted through several screens). | ——____
Se
black. white.
Rays direct from the lamp....... ieee detest shaooskice 100 80:5
Rays transmitted through rock salt .........+++e0++0 — 80°5
2 ee eee LTT Net oHiancd esaRDeneS _ 42°9
ee glass, colourless ...:.:... =: 54:2
ee bright red......... — 60°6
a ee deepireditp 7.052. — 77'8
bright yellow... — 55°5
Se deep yellow ...... — 63°6
———————— bright green ...... — 67°4
eee deep green ...... — 70°5
pee es — bright blue ...... — 61:0
—— deep blue ......... — 66:9
Se ee ee ee ee bright violet ...... — 67:6
ee ee pviOletmisnens — 76°7
ee opake black ...... _ 84-6
Thus the interposition of the rock salt has no influence on the ratio of the quan-
tities of heat absorbed by the two surfaces; but the alum affects it so strongly
that the heat which has traversed a plate of this substance is much less capable
than the direct heat is of being absorbed by the white surface. Colourless glass
acts in a similar manner though with somewhat less energy. As to coloured
glasses, their action is more feeble in proportion as their tint is less vivid. In
short the greatest decrease in the absorption of the white surface is produced by
the interposition of a yellow glass, and the least by the interposition of the red
and the violet, and, as to each pair of plates of the same tint, the less effect is
invariably derived from that in which the tint isdeeper. This decrease of action
which takes place in the vitreous matter in proportion as its transparency is di-
minished by addition of colouring substances more and more sombre, continues
even when the glass loses its transparency altogether; for the plate of opake
black glass is that which produces the least difference of absorption between the
black and the white surfaces. It is however an exceedingly curious fact that the
rays of heat in their passage through the black glass become more absorbable by
the white surface than the rays issuing immediately from the lamp, so that the
interposition of the black glass has on the direct heat an effect contrary to that
produced on it by the interposition of the white glass.
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 69
diaphanous substances intercept them in very different quantities, and
the portions transmitted are considerably diminished by increasing the
thickness of the flakes. Thus, the rays emerging from the black or the
green glasses are in respect to their properties of transmission as it were
antagonist to the preceding, and analogous to those of the direct heat
of the flame though still more decidedly marked, for they are almost
completely absorbed by bodies possessing the greatest transparency.
I have availed myself of these last facts for the purpose of proving by
a very simple process that solar light contains some calorific rays analo-
gous to those which compose the radiant heat of terrestrial sources.
With this view I introduced a solar ray into a dark room through an
aperture having a screen of green glass as a stopper. To the light
transmitted I exposed one of the blackened balls of a very delicate dif-
ferential thermometer. The liquid column descended several degrees.
I now placed quite close to the mouth of the aperture a thin plate
of colourless glass; the liquid came back a little, but the retrograde
movement became more decided when I interposed instead of the thin
glass a plate of greater thickness. I took away the white glass and put
in its place a plate of rock salt: the column was forcibly driven back,
but reascended very nearly to its original position when I substituted
for the salt a plate of very limpid alum. It is clear therefore that
amongst the calorific rays of the sun there are some which have a re-
semblance to terrestrial heat. On the other hand we have seen that the
rays from terrestrial flame which traverse a flake of alum suffer, like
solar heat, only a very slight diminution in passing through glass and
other diaphanous substances. Whence we infer that amongst the ca-
lorific rays from flame some are found similar to the heat of the sun.
The differences observed between solar and terrestrial heat, as to their
properties of transmission, are therefore to be attributed merely to the
mixture, in different proportions, of several species of rays.
But, to return to the heat emerging from the screens exposed to the
radiation of the lamp. We have said that the red, orange, yellow, blue, in-
digo, and violet matters which enter into the composition of the coloured
glasses, act upon radiant heat as the black substances introduced into a
coloured medium act relatively to light ; that is, they diminish the quan-
tity of heat transmitted by the glass without altering its diathermancy
[diathermansie}. ‘This proposition being admitted, it will necessarily
follow, when rays of different species, such as issue from the five screens
contained in the table, fall on a series of coloured glasses, that the ca-
lorifie transparencies of these plates will be increased or diminished in
proportion to the variation produced in the diathermaneity [déather-
manéué | of white glass. It has so happened in our experiments: for
if we take the natural transmissions of the white, red, orange, yellow,
blue, indigo, and violet, and compare these with their transmissions when
70 M. MELLONI ON THE IMMEDIATE TRANSMISSION
submitted to the rays emerging from any one of our five screens, we
shall always find the same ratios between the different terms of each
series.
As to the black and the green glasses, their changes of transmission
occur sometimes similar, sometimes contrary to those of the other plates.
We should not however be surprised at these irregularities, as the green
and black colours alter the natural diathermancy of the glass and give it
an aptitude to transmit quantities of heat which will be more or less con-
siderable in proportion as the rays issuing from the different screens
possess themselves a diathermancy more or less analogous to that intro-
duced into the vitreous substance by these two colouring materials*.
* Inanote to the preceding Memoir (page 8) I have said that, for the study of ca-
lorific radiations the thermomultiplier is preferable to every former thermoscopic
apparatus. The great number of experiments that I have since performed by
means of that instrument have produced in my mind a thorough conviction of
the truth of that opinion. As there are still many experimental researches to be
made not only in that class of phenomena, of the history of which we have
scarcely given an outline, but in every branch of the study of radiant heat, it is to
be wished, for the interests of science, that every investigator would furnish him-
self with a thermomultiplier. ‘This apparatus, in the state of perfection neces-
sary to ensure good observations, is unfortunately one of those which a person
cannot construct for himself until he has made several attempts which are at-
tended with a great loss of time, and which cannot succeed in many places for
want of the requisite means. For these reasons I have thought it advisable to
put some one in Paris in the way of supplying them to the public. There are
excellent ones to be had at M. F. Gourjon’s, rue des Nonandiéres, N° 2. The
description of the ingenious means employed by this able mechanic to give
to the instrument every improvement which I was desirous of having in-
troduced into it would occupy too much time. I shall therefore confine my-
self to the mention of the principal defects found in the first instruments of this
kind presented to the Academy of Sciences by M. Nobili and myself (at the
sitting of the 5th of September 1831), but now laid aside for the improved
thermomultipliers constructed by M. Gourjon.
In the first place the volume of the thermoelectric pile was too bulky, (being
from 36 to 40 centimetres square in section,) a circumstance which rendered it
impossible to operate on small pencils of calorific rays: in the next place the
galvanometer did not mark fractions lower than halfa degree, and the magnetic
needles, instead of standing at the zero of the scale, settled sometimes to the
right and sometimes to the left at a particular distance for each galvanometer,
amounting in some instances to10 degrees. In fine, the mountings being almost
all of wood the pieces became warped by the hygrometrical variations in the
atmosphere, and the instrument was rendered unserviceable.
The thermomultipliers of M. Gourjon have thermoelectric piles the acting
surfaces of which are not larger than the section of acommon thermometer (3
centimetres square). As to the galvanometers they are mounted entirely in
copper with the exception of the small pieces necessary for the purpose of iso-
lation ; the minuteness of their indications extends to a fourth and even a sixth
part of a degree, and the needles, when at rest, stand exactly at the zero of the
seale. It is almost needless to add that with these improvements the instrument
has lost nothing in sensibility.
OF RADIANT HEAT THROUGH DIFFERENT EODIES, 71
Conclusion.
I had intended to introduce here some general reflections on the dif-
ferent hypotheses which have been proposed to explain the phenomena
of heat, and on the question of the identity of radiant heat and light.
But as these two agents are nowhere more intimately united than in
the rays of the sun, such considerations should be preceded by a to-
lerably complete statement of the numerical results obtained by the
application of our several processes to solar heat. The experiments
however which I have hitherto been able to make with this view are too
deficient in number and variety to justify my attempting any statement
of the kind. I will therefore not enter, for the present, into any dis-
sertation on the nature of heat, but will conclude with a recapitulation
of the principal consequences to which I have been Jed by my inquiries
into the properties of the radiant heat emitted by terrestrial sources, in
order that being thus comprehended at a single glance they may be
more easily compared with the analogous properties of light.
Radiant heat passes instantaneously, and in greater or less quantities,
through a certain class of bodies, solid as well as liquid. This class does
not consist exactly of diaphanous substances, since opake plates or plates
possessing but a feeble transparency are more diathermanous or perme-
able to radiant heat than other plates possessing perfect transparency.
There are different species of calorific rays. They are all emitted
simultaneously and in different proportions by flame, but in the heat from
other sources some of them are always wanting.
Rock salt reduced to a plate and successively exposed to radiations
of the same force from different sources always transmits immediately
the same quantity of heat. A plate of any other diathermanous sub-
stance will, under the same circumstances, transmit quantities less con-
siderable in proportion as the temperature of the source is less elevated:
but the differences between one transmission and another decrease as the
plate on which we operate is more attenuated. Whence it follows that
the calorific rays from different sources are intercepted in a greater or
less quantity, not at the surface and in virtue of an absorbent power va-
rying with the temperature of the source, but in the very interior of the
plate and in virtue of an absorbent force similar to that which extinguishes
certain species of light in a coloured medium.
The same conclusion is attained by considering the losses which the
ealorific radiation from a source at a high temperature undergoes in
passing through the successive elements which constitute a thick plate
of any other diathermanous substance than rock salt. For if we ima-
gine the plate divided into several equal layers, and determine by expe-
riment what ratio the quantity lost bears to the quantity incident upon
each of the layers, we find that the loss thus calculated decreases rapidly
U2 M. MELLONI ON THE IMMEDIATE TRANSMISSION
as the distance from the surface of entrance increases; but the diminution
becomes less and less perceptible, so that it must become invariable when
the rays have penetrated to a certain depth. This is precisely what
happens to a pencil of ordinary light when it enters a coloured medium;
for, those rays that are of a colour different from that of the medium
being extinguished in the first layers, the losses of intensity sustained
by the luminous pencil are at first very great, but they afterwards be-
come gradually less and are at last very small, but constant when the
only rays remaining are those of the same colour as the medium.
In fine the successive transmissions through heterogeneous screens
furnish a third proof of the analogy which the action of diathermanous
bodies on radiant heat bears to that of coloured media on light. The
luminous rays issuing from a coloured plate either pass in abundance
through a second coloured plate or undergo in it a powerful absorption
according to the greater or less analogy of the colour of the second to
that of the first plate. Now we observe facts perfectly similar to this in
the successive transmission of radiant heat through screens of different
kinds. And in this case too the rock salt acts in respect to the other
bodies as it does in the case of rays emanating from sources of different
temperatures. A given plate, if it be of rock salt, being successively
exposed to calorific radiations of the same force emerging from different
screens, transmits a constant quantity of heat ; if the plate be of any other
diathermanous substance the quantity transmitted will be variable.
There is therefore but one colourless and diaphanous body that really
acts in the same manner on luminous and calorific rays. All other
diaphanous bodies besides this indiscriminately suffer all kinds of light
to pass through them, but of the rays of heat they allow some to pass
while they absorb others : thus we discover in this one substance a real
calorific coloration, to which, as it is invisible, and therefore totally di-
stinct from coloration properly so called, we have given the name of dia-
thermancy.
The colours introduced into a diaphanous medium always diminish
its diathermancy in a greater or a less degree, without communicating
to it any tendency to arrest certain calorific rays rather than others: they
affect the transmission of radiant heat as dusky bodies affect the transmis-
sion of light. There is, it is true, an exception to be made in respect to
green and opake black, at least in certain kinds of coloured glass. But
these two colouring matters appear, in this case, to do no more than
modify the quality to which we give the name of diathermancy, and
which, as we have already seen, is totally independent of coloration. - -
The quantity of radiant heat which passes through polarizing plates
of tourmaline is not affected by any change made in the angle at which
their axes of crystallization are made to cross one another. Rays of
heat are therefore not polarized in this mode of transmission and are in
OF RADIANT HEAT THROUGH DIFFERENT BODIES. 13.
this respect entirely different from rays of light*. But they resemble
them in the property of refrangibility. This is completely proved by;
means of the rock salt, the only diathermanous body that is capable of
transmitting the calorific rays emanating from every source.
As to lenses and common prisms they refract a certain portion only
of the radiant heat; for the glass intercepts several sorts of calorific rays
issuing from sources at a high temperature, and absorbs nearly the whole
of the heat given out by bodies whose temperature is below incandes-
cence. To this circumstance it is that we must attribute the doubt
hitherto entertained as to the refrangibility of nonluminous heat.
NOTE.
( We annex to the foregoing papers of M. Melloni, various references
to other Memoirs on the Transmission of Radiant Heat, and to former
views of the results obtained by him.
In the “ Report of the Third Meeting of the British Association,”
p-381, isan “Account of some recent Experiments on Radiant Heat,” com-
municated by Professor Forbes, and reciting M. Melloni’s Experiments;
and also, p. 382, an abstract of his subsequent discoveries communicated
by himself to Professor Forbes, in order to be laid before the British
Association.
The “ Notices of Communications to the British Association at Dublin,
August 1835,” contains, p. 9, some remarks by Professor Powell on
Melloni’s repetition of his original experiment described in the Philoso-
phical Transactions for 1825, and in the Philosophical Magazine, First
Series, vol. lxv. p. 437, and a notice of Dr. Hudson’s Experiments with
the Thermomultiplier, rendering it questionable, in his judgement,
whether the results obtained by Melloni on diathermanous bodies were
not attributable to conduction. These notices will also be found in the
London and Edinburgh Philosophical Magazine, vol. vii. pp. 296, 298.
Prof. Forbes’s Memoir “On the Refraction and Polarization of Heat”
is contained in the Transactions of the Royal Society of Edinburgh,
vol. xiii. p. 131, e¢ seg.; and also in Lond. and Edinb. Phil. Mag., vol. vi.
p- 134, et seq.
Re
um following papers and notices have appeared exclusively in the
London and Edinb. Philosophical Magazine:
_ A Note relative to the Polarization of Heat, by Professor Forbes
E
__ * [Professor Forbes, however, in his Memoir, Lond. and Edinb. Phil. Mag.,
ol. vi. p. 205, et seg., referred to in the Note which we have annexed, has
iblished the fact of the polarization of rays of heat by this means, as well as
y those of refraction and reflexion.—Eo171. |
¥
a
7A M. MELLONI ON THE TRANSMISSION OF RADIANT HEAT.
arising from Professor Powell’s remarks in the Notices of the British Asso-
ciation, referred to above, with a Postscript containing Professor Powell's
explanation: vol. vii. p. 349.
M. Melloni on the Immediate Transmission of Calorific Rays through
Diathermal Bodies, in reference to the objections of Dr. Hudson and
Professor Powell, vol. vii. p. 475. Remarks on M. Melloni’s paper by
Professor Powell, vol.viii.p.23. Remarks on both the foregoing papers,
by Dr. Hudson, ibid., p. 109, confirming Melloni’s original inductions.
Professor Powell’s Note on the Transmission of Radiant Heat, in refer-
ence to his remarks on Melloni’s results, ibid., p. 187.
Professor Forbes’s Note respecting the Undulatory Theory of Heat,
and the Circular Polarization of Heat by Total Reflexion, abid., p. 246.
Dr. Hope’s Address on the Delivery of the Keith Prize Medal to Prof.
Forbes, giving a sketch of the history of our knowledge of radiant
heat, zbid., p. 424.—EpIr. ]
In Part II. of Screntiric Memorrs will appear translations of the
subsequent papers of Melloni, and also of other memoirs relating to the
same subject.
~i
oy
ARTICLE III.
Experiments on the Circular Polarization of Light.
By H. W. Dove.
From J. C. Poggendorff’s Annalen der Physik und Chemie; Berlin,
Second Series, vol. v. p. 579.
1. Circular Polarization of Light by Compressed G'lasses.
Wiuen two systems of waves, of equal intensity, propagated in the
same direction, and polarized perpendicularly to each other, differ in
their path by an odd number of quarter-undulations, the particles in
the resulting system of waves will describe small circles of a similar
velocity around their points of equilibrium ; that is to say, the light will
be circularly polarized. Every means of equally satisfying these two
conditions, namely, that of the similar intensity of the system of waves
polarized perpendicularly to each other, and that of the determinate
difference of path, consisting of an uneven number of quarter-undula-
tions, will therefore furnish a method of circularly polarizing light.
Fresnel and Airy have effected this in different ways. The third mode,
which I shall here explain, is in practice at least as convenient as those
hitherto used, and gives moreover a fuller explanation of the phenomena
of compressed and cooled glasses in polarized light.
The condition of the equal intensity of the systems polarized per-
pendicularly to one another is satisfied by Fresnel by polarizing the
incident light in a plane which forms an angle of 45° or 135° with the
plane of the total reflexion in a glass parallelopiped. The quantities
of light polarized in, and also perpendicularly to the plane of reflexion,
are then, according to Fresnel’s formula of intensity, equal to each other.
He obtains the difference of phases of a quarter-undulation by twice-
| repeated total reflexion, since after a single one under the given circum-
ces the periods of vibration of the reflected waves no longer coincide,
but exhibit a difference of phases of an 1-undulation.
wher method which Airy has adopted depends upon another principle.
en a thin plate of an uniaxal crystal cut parallel to the axis, and
whose axis forms with the plane of polarization of the incident light
an angle a, is observed through a rhombohedron of Iceland spar, the
incipal section of which is inclined toward the plane of primitive
f polarization under the angle 64, then, if I,, 1, indicate the intensities
so .
76 DOVE’S EXPERIMENTS ON THE
the two figures polarized perpendicularly to one another, we have ge-
nerally,
I, = cos? 6 — sin 2a sin 2 (a — b) cos? (°=*)
I, =sin?d + sin 2a sin 2 (a— bd) sin? r (° % ‘);
in which A indicates the length of undulation for a definite colour, o—e
the difference of path of both rays, and I the intensity of the polarized
light falling perpendicularly upon the crystal plate. Now if the axis of
the plate is made to form an angle of 45° with the plane of primitive po-
larization, that is to say, if we suppose a = 45°, we shall have,
I, = cos?b — cos 2 b cos? x (°=)
JT. =sin? 6 + cos 2 6 sin’ (C=),
If then by any means we can make the difference between the paths of
both rays equal to an uneven number of quarter-undulations, the second
condition will also be satisfied as well as the first, viz. that of the equal
intensity. Suppose, for instance,
o—e=[ ane t)al,
4
I, =cos?b— cos2b=
I, =sin®?b+4cos2b=H.
The difference of path o—e depends on two quantities; on the thickness
of the plate, to which it is in direct proportion, and on the difference of
velocity of the two rays which pass through the plate, that is to say, on
the constant of double refraction.
Airy’s method consists only in varying the thickness of the plate by
splitting it, whilst the double refraction remains the same, until the dif-
ference between the paths of the rays is equal to an uneven number of —
quarter-undulations. As biaxal mica under a perpendicular incidence
of the light is similar to an uniaxal crystal and best allows splitting
into larger plates, its application will therefore be preferable. I, on the
contrary, alter the double refraction of the substance, whilst the thick-
ness remains the same, until the required difference of path is obtained.
To alter the refraction of rays in a crystallized lamina by pressure
or change of temperature, so that it may exhibit the desired effect in a
given thickness, would afford no convenient practical arrangement. It
is, however, very easy by means of pressure or cooling to change the
uncrystallized into a double-refracting body, which gives precisely the
required effect. In the apparatus proposed by Fresnel, consisting of
then will
Tt po]
CIRCULAR POLARIZATION OF LIGHT. a7
four prisms, by which the double refraction of the glass is directly in-
dicated, one of the two images which arise is polarized parallel to the
axis of compression and the other perpendicular to it; whence it follows
that the axis of the double refraction coincides with the axis of com-
pression. If a square or circular plate of glass therefore is compressed
so that the axis of compression forms an angle of 45° or 135° with the
plane of primitive polarization, the light passing through the centre of
the glass at a certain degree of the pressure will be circularly polarized.
Let us now suppose a division of a circle so placed upon the incident
ray that the plane of polarization passes through the points 90° and 270°;
then, if the axis of compression passes through 45° and 295°, a plate of
_ Iceland spar cut perpendicularly to the axis exhibits in the light passing
. through the centre of the compressed glass, instead of the black cross,
rings in the second and fourth quadrants (on the right side above and
on the left side below) advanced forwards by a quarter-interval from the
centre, and on the contrary in the same proportion approaching nearer —
to the centre when in the first and third quadrant (on the left above
and on the right below). Exactly the reverse takes place when the
axis of compression passes through the points of division 135° and 315°.
Hence we see that the angles which in the parallelopiped of Fresnel
are formed by the plane of the twice-repeated total internal reflexion
with the plane of primitive polarization, must be equal to the angles
under which the plane perpendicular to the axis of compression is
inclined towards the plane of primitive polarization, when the same
phzenomena are to be produced by both those arrangements.
| No further particular explanation is now required to show that during
, acomplete revolution of the plate in its plane round the perpendicular
incident ray as an axis of revolution, the light is polarized four times
rectilinearly and four times circularly; rectilinearly when the com-
pressing screw acts on the points 0°, 90°, 180°, 270°, that is to say,
when the axis of compression is perpendicular to the plane of primitive
polarization or lies within it; and on the contrary, it is polarized cir-
ceularly when that point of action corresponds to the points of division
45°, 135°, 225°, 315°, whilst 45° and 225°, as also 135° and 315°, ex-
hibit a similar effect.
By a combination of two compressed plates and two tourmaline plates,
_ so that the mutually perpendicular axes of compression of the glass
plates, which are between the crossed tourmaline plates, form with their
_ axes an angle of 45°, a lamina of Iceland spar laid between the glass
plates exhibits the rings without a cross with the black spot in the centre,
and complementary ones on the contrary when we make the axes of the
tourmalines or the axes of compression of the glass plates parallel to
each other. If we make an axis of compression parallel to a tourmaline
plate we obtain displacement of the rings in the four quadrants by a
:
73 DOVE'S EXPERIMENTS ON THE
quarter-interval; but the phenomenon is in that case not reciprocal, as a
revolution here takes place similar to that which occurs when we look
from the opposite side at an electric current in which the circuit is com-
plete, and which is made to proceed in a circular form; the first and third
quadrant then become the second and fourth, and vice ver'sd. By placing
the tourmaline axes and the axes of compression parallel severally to each
other, we obtain the phenomena of rectilinearly polarized light.*
If between the crossed mirrors we insert a round or square plate com-
pressed to a certain degree, so that the axis of compression coincides
with one of the planes of reflexion of the mirror, we see upon it a black
cross with white vacant spaces at the corners. If by means of the plate
of Iceland spar these four white vacant spaces be examined, we find that
those which belong to the same diagonal are similar to each other, but
in opposition to the two white vacant spaces of the other diagonal; and it
will be found that the light proceeding from them is circularly polarized,
in the one diagonal to the right and in the other to the left. Hence it
directly follows, that when the plate is turned in its plane 90°, all the
white vacant spaces have exactly exchanged their effect in the diagonals.
The plates I made use of in these experiments were 114 lines in dia-
meter, and 34 lines in thickness.
2. Circular Polarization by Cooled Glasses.
I carefully cooled a glass cube of 17 lines each side, so that when
the diagonals of the surface of the cube turned towards the eye form
with the plane of polarization an angle of 45°, it exhibited between the
crossed mirrors in the centre a dark cross, and inthe four corners only
the white surrounding it. The light of the four white vacant spaces
was exactly similar to the light of the four white vacant spaces of the
compressed plate, when their axis of compression lay perpendicularly
to, or within, the plane of polarization. By turning the cube excentri-
eally round the ray perpendicularly escaping through one of the white
vacant spaces, as round an axis of revolution, similar variations are
produced, whilst at 90° revolution the diagonals interchange their effect.
Instead of turning the cube round, it may, in order to obtain the same
variations, be so moved that two of the parallel sides of the surface
turned towards the eye are carried forwards perpendicularly to their
direction, whilst the other two advance in their own path. We pass
from the white vacant space of the one diagonal into that of the other.
The combinations of the cooled glasses, for the purpose of analysing
circularly a circularly polarized light, explain themselves. In order to
obtain the system of rings without the cross with the black spot in
the centre, they must be combined as in Plate II. fig. 5.
So far as I am aware, we possess as yet no direct experiments upon
the double refraetion of the cooled glass ; and as in the theory of the
CIRCULAR POLARIZATION OF LIGHT. 79
so-called moveable polarization the double refraction was not considered
as a necessary consequence of the appearance of its colour in the recti-
linearly polarized light, it is desirable to confirm by new experiments
the proofs that these colours originate in the difference of path of the rays
passing through the glass. The following therefore, for the explanation
of the colours upon the principle of interference, seems to me not un-
important.
When a ray polarized rectilinearly in the azimuth of 45°, after two
total reflexions in the interior of a Fresnel’s parallelopiped, exhibits a
difference of phase of a quarter-undulation, between the quantities of
light polarized perpendicularly to each other, of uniform intensity, this
difference will in this case, after four reflexions, become a half-undu-
lation; the ray consequently will be again polarized rectilinearly, but
perpendicularly to the plane of primitive polarization. After six re-
flexions it is again circular, but left-handed, if after the two reflexions
it was right-handed, since the azimuth of the rectilinearly polarized in-
eident light is now — 45° instead of + 45°. Finally, after eight re-
flexions the plane of the restored polarization coincides with that of the
primitive one. The explanation of the observed phenomena of circular
polarization in the above-mentioned experiments, depended upon making
the difference of path of the two rays exactly equal to the quarter-
undulation, by means of a determinate change of heat in the interior of
the body made use of, its thickness remaining unaltered. If this expla-
nation is correct, precisely the same phenomena would be obtained by
gradual heating as by successive reflexions in the interior of the Fresnel’s
rhomboid, but with this difference, that instead of the direction of the
polarization varying by successive steps we should expect a continual
transition through all degrees of elliptic polarization. The experiments
eonfirm this perfectly. They must of course be made in homogeneous
light.
3. Phenomena during the Heating and Cooling of the Glasses.
The apparatus (Plate I. fig. 1.) more particularly described in the
succeeding paper was adjusted before a monochromatic lamp giving
yellow light, so that the plate of Iceland spar in the ring Z, cut perpen-
dicularly to the axis, exhibited distinctly the black rings with the dark
cross, when the glass cube reduced by a new heating and cooling to
perfect loss of action upon polarized light, was thus interposed be-
tween k and 0, before the Nicol’s polarizing prism. In order to heat it
| conveniently over a lamp, the three-sided prism or rod bc, carr ying all
the polarizing arrangements, was placed in such a manner in its case as
to bring those arrangements from their vertical situation over the rod to
“a position in which they projected on one side of it; their position as re-
resented in the figure must therefore be imagined as altered 120°. In
80 ~. DOVE’S EXPERIMENTS ON THE
the ring m the screw was withdrawn a turn, in order that the motion of
the rings, either away from the central point or towards it, might be the
more easily observed.
The lamp having been lighted, the black cross began directly to open
in the centre; the circular ares in the second and fourth quadrant re-
ceded from the central point, whilst the first and third approached it.
After some time the dark ares of the odd quadrants exactly corresponded
with the bright vacant spaces of the even ones; the light was circularly
polarized, and the difference of path was a quarter-undulation. Whilst this
was going on, with the exception of the points proceeding from the centre
which remained black, the dark cross had become brighter and brighter.
When it had entirely disappeared, the ares, growing shorter at their
ends, had gradually advanced, so that the two black spots proceeding
from the centre formed with the parts approaching each other from the
two other quadrants, the inner ring, separated by four bright interven-
ing vacant spaces. All the other rings were in the same state. The figure
given by the Iceland spar had thus changed, precisely as if the polarizing
prism had been revolved 90°; the light was therefore polarized linearly
and perpendicularly to the plane of primitive polarization: the difference
of path of both rays was a half-undulation. On a further heating, as the
difference of path became three quarters of an undulation, the light was
again circularly polarized, with the difference, however, that now the rings
in the first and third quadrant were the nearest, those in the second and
fourth the more distant ; in which case the direction of the motion of the
ares in the single quadrants naturally remained the same. Finally, when
the difference of path amounted to an entire undulation, the white cross
became darkened into a perfect black; the arcs previously separated
closed in whole circles; the light was polarized rectilinearly in the same
direction as at the beginning of the experiment. The lamp was now
removed and the opposite phenomena were observed in regular succes-
sion during the cooling of the apparatus *; consequently the action of the
glass, becoming gradually heated from below upwards, upon the incident
light, is as follows. The particles of ether, which at first vibrate recti-
linearly, begin to open into ellipses, the excentricity of which diminishes
continually, until they become circles. The axis which at first was the
* Precisely the same succession of phznomena may naturally be produced
by the gradual increase of pressure or its relaxation. With the plates, however,
which I had employed I was able to carry it only as far as a difference of path
of three quarters of an undulation in the proximity of the points of action of the
screw. On applying a stronger pressure the plates broke. Now it is evident
that when a cooled glass plate, which in white light exhibits a regular series of
colours proceeding from black, is interposed, in homogeneous light the same
phenomena will be observed in the plate of Iceland spar, if it be slowly moved
along before the aperture of the polarizing prism. The thicker the plate the
nearer to each other are the differently-acting vacant spaces.
CIRCULAR POLARIZATLON OF LIGHT. 81
larger now becomes the smaller one, and vice versd. With increasing
excentricity the elliptic vibrations, which are perpendicular to the initial
ones, pass directly over them. During all this process, the direction of
the vibrations did not change; supposing it to have been from left to
right, it remained so. When however the second rectilineal vibration
opens into an elliptic one, and the direction of the motion has become
inverted, the vibration now takes place from left to right, supposing it to
have been before from right toleft. The vibrations then return through ~
circular again into the initial vibrations.
The light proceeding from the cube was now circularly analysed, by
means of the interposition of a lamina of mica f of a proper thickness be-
tween the plate of Iceland spar and the analysing prism. The axis of
this lamina lay so that the segments of the arcs were removed from the
central point to the first and third quadrants. When the cube was yet
unheated, its action was thus in direct opposition to its action in the first
degree of its heating. When, proceeding from this point, the rings with-
out the cross and with the black spot in the centre were formed, this
spot, on the heat being increased, divided itself into two, which removed
themselves from the centre into the second and fourth quadrants, and
after having passed through the figure in the circular light, closed into
a circle with the ares proceeding from the first and third quadrants, so as
to produce the system of rings with a bright centre, which would have
been obtained at the very beginning by turning the polarizing prism 90°.
The ares, approaching nearer to the central point from the first and third
quadrants, formed then the opposite circular figure, and united them-
selves at last in the centre into a black spot, whilst all the ares closed
themselves into circles. Inthisprocess, the phenomena before described
of the linear analyses will again be easily recognised as a conditional ele-
ment, without the necessity of particularly describing the alteration in
form of the rings before they disunite into separate arcs.
To make circular light incident, is simply to add to the difference of
2n—1
4
undulations; that is to say, to alter the starting-point of the ex-
phases produced by the heated cube a constant quantity, viz. or
2n+1
4
periment. Having therefore inserted the lamina of micag between the
polarizing prism and the heated cube, I obtained by linear analysis the
phenomena first described, and by circular analysis those last described,
beginning at another starting-point.
4. Phanomena in the different Colours of the Spectrum.
The foregoing experiments were made in incident homogeneous light,
the length of whose waves was X. In another part of the spectrum,
however, \ has another value. Let \, represent this: and if
o—e=m)d, o—e=m,X,;
Wor. .—PART I. G
82 DOVE’S EXPERIMENTS ON THE
1 1
then will m — m, = (0 —e) ( a x ):
1 ’ |
As + x is a constant quantity for a definite substance, the dif-
/
ference m—m, will be proportional to the quantity o—e. Hence it
follows, That when for one definite colour the light is circularly pola-
rized by an interposed crystallized lumina, it may for the other colours
be linearly and oppositely circularly polarized, and that the difference
between the single colours increases with the thickness of the lamina and
with the intensity of the double refraction.
If the incident light is circular for the centre of the spectrum, when
the difference of path is 4 for this centre, the light is not yet linear for
the extreme limits of the spectrum. If it is here linear in the red, with
a 4+ undulation difference of path, in the blue it is circular. With 4 dif-
ference of path in the red, it will, if it is circular to the right, be linear
in the blue, and circular to the left in the extreme violet. Linear light
in the red, with difference of ‘path 1, gives on the left in the green a
circular light, in the indigo a linear light perpendicular thereto and
approaching the circular on the right in the extreme violet ; finally, on
the left, circular in the red, with difference of path 5, will give linear in
the yellow, circular on the right where the blue passes into the indigo,
and perpendicular to it linear at the commencement of the violet, and
so forth. In order to prove this by experiment an equilateral prism of
Guinand’s flint glass was placed upright, so that after the removal of
the condensing-lens p the red end of the spectrum fell exactly upon the
aperture e of the Nicol’s polarizing prism. The cube had by gradual
heating exhibited the phenomena which corresponded to a difference
of path of 4, +, 3 undulation, and the other coloured rays were brought
into the axis of the polarizing-apparatus, and the alteration of the Iceland
spar figure examined. This might easily be accomplished without re-
volving the prism, as the height of the instrument may be altered at
pleasure by means of the sliding-tube, as may its inclination by means
of the motion of the prismatic rod. Mica plates of various thicknesses
were examined in the same manner as the heated cube. The changes
may be seen most beautifully when, beginning with the violet, the instru-
ment is slowly lowered in the sliding-tube through the single colours
of the spectrum. The gradual transitions are, in respect to the difference
of colours from one end of it to the other, exactly the same as those
which are obtained by the heating and cooling of the cube.
In the same manner the phenomena, when the incident light is cir-
cularly analysed by a mica plate inserted before the Iceland spar, are
throughout similar to those before described. Instead of the homo-
geneous rays of the spectrum, we can of course also employ in these
experiments a monochromatic lamp or absorption by coloured glasses.
It is only when the light has been circularly polarized in one colour
fu
CIRCULAR POLARIZATION OF LIGHT. $5
through a plate of definite thickness that we can determine, whether the
24-1 fal 2n+1
4 4
If, however, the same plate is examined in the different parts of the
spectrum, we obtain by the experiments just mentioned x itself. It is
manifest that if we wish to obtain by refraction phenomena of circular
polarization in white light, it is advisable so to determine the thickness
of the plate or the temperature of the glass that the difference of path
for the central rays will become 4 undulation. For this purpose I use
the flame of alcohol coloured yellow by common salt or nitrate of soda.
undulation.
difference of path of the two rays be
5. Phenomena of Colours of combined Crystals in White Light.
It now becomes easy to account for the complicated phznomena of
colours obtained by the insertion of a crystallized plate parallel to the axis
and of any given thickness behind a crystallized lamina cut perpendicular-
ly to the axis. For as the light is circularly polarized for one colour on
the right, for the other on the left, and rectilinearly for an intermediate
one, the black tufts on their two sides assume different colours: the
phznomena in the even quadrants differ essentially from those in the
odd ones, but the rings of colours in both are essentially different from
the succession of colours in Newton’s rings. The phenomenon may be
previously determined from the known values of the indices of refraction,
the length of waves for the homogeneous rays of the spectrum, and the
thickness of the plate; but it may also be experimentally exhibited by
adjusting the condensing-lens p of the apparatus so that the spectrum
in the aperture of the Nicol’s polarizing prism e be concentrated to white;
a confirmation, the frequent repetition of which, howeyer, is not advis-
able, on account of the intensity of the light of the apparatus.
6. Phenomena of Colours in Twin- Crystals.
Tn passing from the artificial combinations of two crystals to natural
twin-erystals we have to distinguish them into three classes: namely,
the axes of the united individual crystals are either perpendicular or pa-
rallel to each other, or they are inclined at some angle with one another.
The section is always to be made perpendicular to the axis of one of
. the individual crystals. Though the first case may immediately give
the phenomena just mentioned, yet, as far as I am aware, it does not
occur with transparent crystals, whilst the second case may occasion the
phenomena of colours with biaxal crystals only. Thus, if (as for in-
stance in arragonite,) a very thin crystal is so united with another that
its erystallographic-axis lies parallel to the axis of the crystal which is
divided by it into two parts, these two parts (since the optical axes of
this lamella render perceptible, however small, angles with the bounding
planes, ) will operate as double-refracting prisms upon the light passing
through these axes, because their optical axes do not lie in the plane of
G2
S4 DOVE’S EXPERIMENTS ON THE
the axes of the lamella. The particular construction of this natural po-
larizing apparatus described by Erman, which from the thinness of the
lamella exhibits the systems of rings of an unusual size, and considerably
removed toward their optical axes on account of the obliquity of the
surface of emergence, is obtained optically by comparing these systems
of rings seen without previous polarization, in size and position, with
those which evolve light previously polarized rectilinearly and afterwards
analysed also around the optical axes of the including individuals, of
which the one serves for the polarizing, the other for the analysing ar-
rangement. That this last is the case, is moreover apparent from the
following observation, that when a tourmaline is revolved before the
crystal viewed in ordinary light, one of the systems of rings disappears
alternately without changing its form. As however the phenomenon
remains the same when the crystal is revolved, the same holds good for
the polarizing prism, with which also the alterations of intensity of the
rings agree when the crystal is viewed with the naked eye in rectilinearly
polarized light. A decisive proof, however, that the individual behind
polarizes rectilinearly, lies, as it seems to me, in the following fact, that
the rings seen with the naked eye do not take the form which corre-
sponds with the light when this is circularly incident.
The third case, in which the axis of the lamina growing into the other
is inclined at an angle toward the axis of the including crystal, is also of
importance for uniaxal crystals. The modification of the system of rings
round the axis of the including crystal thus produced must coincide
with that in two exactly central plates when a crystallized lamina of de-
finite thickness is inserted between them. As that lamina may here be
replaced by another similarly acting crystal, this case may be treated in
the same way without difficulty. Among seven plates of Iceland spar
exhibiting a deviation from the usual system of rings, I found two which
produced a very regular figure, namely, a black cross with curves alter-
nately oseulating, which appeared to me to be circles and lemniscates ;
the interior curve was completely entwined into a figure of 8. . If the
plate is turned in its own plane, the interior part of the system of rings
consists of four triangular vacant spaces. I obtained precisely the same
phenomena by inserting a lamina of mica of definite thickness between
two plates exactly centred and producing the regular system of rings,
and by turning that lamina in its own plane.
7. Experiments on Circular Polarization by other Modifications.
Fluor spar is the only crystallized substance of the regular system
which I have examined with respect to the effect of an unequal distri-
bution of temperature within the body. The fragment I used in this in-
stance was quite colourless and transparent, 14 inch long, and was lent to
me for these experiments by Professor Weiss. At a heat in which the
difference of path had become § undulation in the glass cube, it exhi-
ree“
CIRCULAR POLARIZATION OF LIGHT. 85
bited throughout noeffect uponthe rectilinearly polarized light, although,
in order to increase the difference of heat, I was continually cooling its
upper end with sulphuric zther, whilst the lower end stood upon the
hot steel plate*. Sonorous plates vibrating transversely acted neither
upon the linear nor the circular incident light. But it is well known
that Biot obtained a flash of light between the cross mirrors by the lon-
gitudinal vibrations of long strips of glass. Although in the experiments
made with reference to this, the cross of the Iceland spar figure ap-
peared to me to open, yet those experiments stand in need of being
repeated with a better acoustic apparatus.
8. Difference between the Action of Glass when it is Heating and
when it is Cooling.
Two square plates 3 lines thick, the side of one 11+ lines, and that of
the other 134 lines, produced on being heated at first a circular light
on the right, and then a rectilinearly polarized one ; on their cooling,
however, after they had returned to the rectilinear through the circular
one on the right, they produced circular light on the left. The reason
of this phenomenon is as follows: The lower end of the glass plate
heated upon the hot steel plate cools when the lamp is taken away
quicker than the upper one, to which heat is also communicated by con-
duction. After some time therefore the centre of the plate becomes its
warmest part. As the lower end, standing upon the rapidly cooled
conductor of heat, becomes still cooler, the warmer spot moves upwards
until finally the upper angle becomes the warmest. That this is truly
the reason of the phenomenon may be seen by examining the cooling
plate between the crossed mirrors. The four white vacant spaces of
the diagonals do not disappear on the spot where they had been formed;
the lower ones rather move upwards, so that the dark cross becomes
changed into two parallels, which are intersected by a perpendicular
line. Finally, the central white vacant spaces dislodge the upper ones,
whilst those newly arrived from below occupy the lower spot. By heating
the plate so that its lower part constantly preserves the strongest heat,
the progress of the phenomena must of course be more simple.
The action of a determined point of a cooled or compressed glassas a
circularly polarizing apparatus, in the homogeneous rays of the spectrum,
gives immediately the elements of determination for the colour which the
glass presents in rectilinearly polarized light.
* Brewster says in reference to the colours which fluor spar acquires by
rapid cooling, “ Fluor spar was very slightly affected.”
Articie IV.
Description of an Apparatus for exhibiting the Phenomena of
the Rectilinear, Elliptic, and Circular Polarization of iy
by H. W. Dove.
From J. C. Poggendorff’s Annalen der Physik und Chemie; Berlin,
Second Series, vol. v. p. 596,
Upon a common tripod brass telescope-stand with a horizontal and
vertical motion, which, from its containing a sliding-tube, may be raised
from 16 to 25 inches by means of a tightening-serew a (Plate II. fig. 1.),
is placed in a case / a three-sidéd: moveable brass prism 0 e, two feet long,
atid dividéd into Paris inches and lines. This prism carries five sliders s,,
Siy 83, Sy S;, Which, by means of tightening-screws, may be fixed at plea-
sure at any part of the scale. Two of them s,, s,, the front view of which
is separately drawn of the actual size in fig. 2, carry stands terminating
above in rings, which by means of a pivot at r (fig. 2.) may be placed
horizontally and vertically, so that the apertures of the Nicol’s prisms ¢¢
revolvable in these rings, with the centre of the convex lens k, serewed
into the ring of the slider sj, (the stand of the convex lens being provided
with exactly stich a pivot, and in a perpendicular position also to the
centre of the condensing-lens p which is carried by the slider s,, the fo-
cal distance of the condensing-léns being 12 inches and its aperture 3;)
lie ina straight line parallel to the rod 4c, this line being at the sanie
time the optical axis of the instrament. The Nicol’s prism of the stand sj,
which is the nearest to this condensing-lens, may be called the pola-
rizing, and that which is more distant from tlie stand s,, the atalysing
one. ;
If parallel light is incident upon the condensing-lehs, the pola-
rizing prism must be in its focus, in order to polarize all the incident
light ; if, on the contrary, the light of a lamp is employed, the pola-
rizing prism must be in the point of convergence of the rays which fall
divergingly upon the condensing-lens. During this process it is of course
not the prism but the condensing-lens that is to be moved until the con-
centrated light of the lamp falls exactly upon the aperture of the prism.
Tn order to alter at will the planes of polarization of the two prisms,
graduated brass plates are placed at the rings of the stands s,, s,, upon
which plates is placed a moving index, which, when intended to be pro-
longed backwards over the fastening-point, coincides with the longer
diagonal of the rhomboidal bases of the Nicol’s prism. The graduation
APPARATUS FOR EXHIBITING THE POLARIZATION OF LIGHT. 87
of the circle is arranged so that, in the vertical position of the stand, the
straight line passing through the points 0° and 180° lies horizontally.
Fig. 2. exhibits of the actual size a view of these plates, which are not
drawn in fig. 1. It is preferable to graduate that side of both plates
which is turned toward the eye. The dotted stand in fig. 2. is there-
fore to be imagined behind the plate, when it belongs to the polarizing
prism, and on the contrary before the plate and the graduation on the
back of the plate, when the plate belongs to the analysing prism d. It
will seldom be requisite to alter the plane of polarization of the incident
light; it is most convenient to place it once for all horizontally, that is
to say, to place the index of the polarizing prism upon 0° or 180°. In
clear weather, when the light reflected by the sky is already more or less
polarized, the instrument is to be directed, where this is possible, toward
a wall on which the sun shines. If, however, the light reflected by the
sky is to be directly employed, and in the greatest possible intensity,
this may be most completely performed as follows. The polarizing
prism with its plate having been placed horizontally, the analysing one
is turned, until the system of rings with the black tufts is obtained in a
plate of Iceland spar cut perpendicularly to the axis; within the ring Z
of the stand s, the polarizing prism e is then placed vertically again, and
turned round until the same phenomenon is perceived in the Iceland
spar. The index of the polarizing prism e then indicates the direction
of the plane of polarization of the incident light, and the rings appear
with greater distinctness.
The light diverging from the polarizing prism is at first intercepted
by a convex lens indicated by v, two inches in diameter, and distant +
inches from the aperture e, and which is screwed into the lower end
of that part which passes through the plate and is the holder of the
prism: it then falls upon the lens three inches distant upon the stand s,,
and haying 13 inch focal distance. From this point it passes through
the crystal of the stand s, in the ring J, and which is to be examined
in the polarized light, and proceeds into the analysing prism d, into
whose lower end is screwed a concave lens indicated by uw, and of four or
five inches focal distance. Any inclination to the axis of the instrument
may be given at pleasure to the ring /, by means of a ball and socket
which is represented in fig. 1., or by means of a motion on points (as in
the illuminating lenses or mirrors of common microscopes). Since now
the crystal in this ring may also revolve in its plane, its optical axes may
be altered at will in reference to their position with respect to the plane
of polarization of the incident light. If however, for the exhibition of the
isochromatic curves, two crystal plates cut parallel to the axis, or two
laminze of mica of uniform thickness are to be combined, the process is
as follows: two turns of the screw must be given to the ring, which is
to be inserted, of which the one that is represented on ‘ine ian ger cy-
88 DOVE’S DESCRIPTION OF AN APPARATUS
linder enters into /, but the other, which is on the narrower cylinder,
passes through, so that on the side toward a second crystal is serewed
in, whose axis may in this manner be made to assume at pleasure any
angle to the axis of the first crystal.
The ring m, nearly in the focal distance of k, is intended for the re-
ception of cooled glasses, thin laminz of gypsum, and amethysts. Fast-
ened to a pin, its central point is exactly in the axis of the instrument,
when the pin is exactly vertical. Similar rings of wood, provided with
straight pins, may be placed in the case of the stand s,. Biaxal crystals
are fastened to the pins, so that when the ring is turned round the pin,
the systems of rings of the two axes pass one after another through the
field of view; if therefore the indexes of the two Nicol’s prisms stand
at 0° and 90°, the black tufts of the systems of rings lie in a horizontal
line. The ring m may also serve for the reception of a micrometric ar-
rangement for the systems of rings of the crystals observed in J.
In order to change the rectilinear into circular polarization, the arms
fand g, which revolve round the pegs z and 0, contain laminz of biaxal
mica* of such a thickness as to produce a difference of path of exactly a
quarter-undulation between the two rays, when the axes of those arms ff
and gq (Plate II. fig. 2.) form with the plane of primitive polarization ee
angles of 45° and 135°. Instead of the laminz of mica cooled or com-
pressed glasses may be employed, and combined (fig. 5.) in the manner
particularly described in the foregoing paper.
If the two thin plates are turned aside, the rectilinearly polarized light
is rectilinearly analysed. In order to analyse circularly, the rectilinearly
polarized light fis brought forwards. In-order to analyse rectilinearly
the circularly polarized light, f is to be turned aside, and g placed for-
ward. The two plates must be brought forward, as in fig. 1., when the
circular polarized light is to be circularly analysed. The axis of the
thin mica plate is indicated upon its frame. If that axis, instead of
corresponding with the points 45° and 135°, passes through other
points of graduation, we obtain the phenomena of elliptic polarization.
If a small pin be fixed in the direction of the axis gg, the position of
the axis of the lamina of mica may easily be drawn upon the graduation
of the stand s,.
In order to perform the simple experiments of intensity, it is advan-
tageous to uncover the field of view. This is accomplished by a hollow
cylinder one inch in height screwed into the somewhat projecting end
of the frame of the lens k up towards m. The aperture of the opake
diaphragm in the bottom of this cylinder is 14 line. This well-defined
bright circle furnishes a very good object for these experiments. If
* Although the same phenomena may be obtained by the determinate incli-
nation of a thin plate of uniaxal mica, yet the employment of the. biaxal mica
appears tome much more conyenient.
FOR EXHIBITING THE POLARIZATION OF LIGHT. 89
the analysing prism is turned in its frame, we obtain the decrease ac-
cording to the law of Malus; if one of the laminz of mica is placed be-
fore, on turning the intensity of the light remains unchanged. If, instead
of the analysing Nicol’s prism an achromatic double-refracting prism in
a similar frame is screwed in, the analogous phenomena are obtained for
both images.
When the polarizing prism e is bent on one side, a double-refracting
prism screwed into the ring / gives two mutually perpendicular polarized
images of the aperture in the diaphragm, the changes of intensity of
which are obtained by turning the analysing prism w. If the thin la-
mina of mica f is placed forwards, the images, when the principal sec-
tion of the double-refracting prism lies perpendicularly or horizontally,
become circular on the right and left, and an arrangement coinciding
with the apparatus proposed by Fresnel is obtained, consisting of three
rock-crystal prisms, of which two belong to a crystal turned to the
right and the single one to that turned to the left. By turning the
analysing prism, the intensity of the images remains unchanged. If the
analysing prism be also a double-refracting one, on turning it, two
images with unchanged intensity (the mica plate lying between) move
round the two stationary images with the same property.
Ifa mica or gypsum plate of a determinate thickness be in the ring m,
on its turning round the pin to which it is fastened we obtain the phe-
nomena of the so-called coloured polarization between the two Nicol’s
prisms. The complementary colours appear of great intensity, and give
white where they overlap each other, when the analysing Nicol’s prism
is exchanged for a double-refracting one. Should we wish to combine
two double-refracting prisms as above, the mica plate f must be ex-
changed for a thicker one. When the aperture of the diaphragm is
diminished the images separate from each other. If a plate of Iceland
spar, cut perpendicularly to the axis, is screwed upon the universal
setting of the Nicol’s analysing prism, the corresponding modifications
of the system of rings in the separated and circularly polarized vacant
spaces are obtained, when the double-refracting prism is in Z; if on
the contrary there is in the ring / a second plate of Iceland spar like-
wise cut perpendicularly to the axis, it is easy by turning this ring to
cause the centres of the second and first plates to coincide. In this
Manner we may imitate the phenomena (as described in the preceding
paper) of certain twin-crystals of Iceland spar by interposing a mica
plate of definite thickness inf. If f lies at the side, by turning the
ring / the isochromatic curves originating from the combination of two
plates of which the centres do not coincide are obtained*. In a similar
_ * In order to obtain the four mutually involved spirals of a rock-crystal plate
ned right and left, I combine a right-handed plate ground plano-concave
with a left-handed crystal ground with parallel faces. ;
90 DOVE’S DESCRIPTION OF AN APPARATUS
manner the plates of different crystallized bodies are combined, in order
to examine the positive or negative character of their axes.
If, instead of white, either homogeneous or dichromatic light is to
be miade incident, small rings of wood one inch in diameter, with —
coloured glasses, must he fastened before the aperture of the polarizing |
prism e. When the concentrated light of a lamp giving white light falls |
upon dichromatie glasses, they exhibit with biaxal crystals different opti- —
cal axes for the various colours, and with uniaxal crystals they yield
beautiful changes of differently coloured rings. Blue glasses, which sepa-
rately trarismitted the extremes of the spectrum, exhibit (in arragonite,
for instance,) the inner curve divided into two particoloured vacant
spaces and corresponding changes within each ring; on the contrary,
the two inner rings in the Iceland spar are exhibited of a deep red sur-
rounded by violet rings gradually passing more and more into each
other, during which, lighted by a flame of spirits of wine coloured
by chloride of strontium, the three inner rings are violet, to which three
red Ones then succeed, and so forth, Through a ruby glass we now obtain
only a very homogeneous red, then dark rings, in the red field of view.
A flame of spirits of wine coloured yellow with common salt, or nitrate
of soda, yields the most beautiful phenomenon. The dark rings and the
junction-curves of the different systems of rings of twin-crystals of ar-
ragonite then appear in the linear and circular light with the utmost
distinctness. For blue and violet it is best to employ the colours of the
spectrum. The condensing-lens is then removed, in order that the light
may fall directly upon the aperture of the polarizing prism.
The apparatus shown in Plate II. fig. 3. serves to analyse the light
by reflexion, and is screwed into the pillar s, instead of the analysing
prism. The screw at w holds a concave lens of an equal focal distance.
The unbordered mirror inclined at the angle of polarization is 4 ineh
long and § inch wide. ~A line is drawn over the three parts of the hinge
q on the left side of fig.1. Ifthe parts of this line form one straight line,
the rod dc is inclined towards a horizontal mirror at the angle of pola-
rization. If # and v are placed aside, the light polarized by reflexion
may be analysed either linearly by the prism, by the mirror in w, or cireu-
larly by means of f. But in order to examine larger cooled glasses
in circularly polarized incident light, I employ a larger lamina of mica
than that in g, which may be called g, and which fixed td the screw of.
the condensing-lens p is screwed directly upon a wooden ring of 2
inches internal diameter. The axis of this mica lies like that of the
thin plate in g, which is turned aside. The concave lens in w is
taken out, and the stand supporting the cooled glasses is brought to
the distance most suitable to the eye. By holding the glasses in the
hand, the various phenomena of the linear and circular light may be
observed without alteration of the apparatus. If the glass be held
FOR EXHIBITING THE POLARIZATION OF LIGHT. 91
between the condensing-lens and the mirror, f and g, being placed for-
wards, there is seen a cooled cube upon the mirror darkened by the ana-
lysing prism, fig. 6.; and consequently when the cube is turned 45°,
fig. 7, the same. pheenomena are observed as if both the mica plates
had been removed. Between the two mica-plates; whose axes cross
each other at right angles, appears fig. 8, and indeed unchanged when
the tube is turned in its ring. Fig. 9. is the complementary figure to it,
which is obtained by turning the analysing prism to 90°, without
changing the position of the mica plates. If f is bent backwards, there
appears the modification of the linear figure, which produces circu-
larly polarized incident light linearly analysed.
Of this as well as of that modification produced by circular analysis of
the linear light which follows when the cube is close to the condensing-
lens, it is easy to form an idea, by imagining the linear figure divided
into four equal quadrants by two perpendicular lines, and the even
quadrants removed from the central point about ; interval, and the
odd ones approaching to within the same distance ; or vice versd; these
removed, whilst those are made to approach. To polarize lamp-light
by reflexion, the better way is to fix upon the condensing-lens (itself
capable of revolving, )a mirror inclined at the fixed angle of polarization.
If, by means of the polarizing prism, the instrument has before been
placed upon the lamp, after the prism is turned aside and the mirror is
fixed, that instrument, without changing its inclination, is turned round
its perpendicular stand, until the system of rings is seen anew in the Ice-
Jand spar within the ring. Instead of employing Nicol’s prisms, the light
may be polarized by absorption in tourmaline plates, or by successive
refractions through aseries of glass plates. These are screwed into the
stands in similar frames.
In order to obtain the deviation of the plane of polarization by |
refraction, the refracting bodies are introduced into the stand s,. The
deviation by reflexion may be conveniently observed by turning the
rod at an angle toward a definite point. As, however, this experiment
is easily made in another manner, I thought it unnecessary to com-
cate the apparatus for it. In the same manner the apparatus may be
anged into a polarizing microscope, with a still larger field of view,
y the addition of somie lensés and stands. But as this will be desifa-
le in very few experiments, besides that the construction of such an
paratus by means of single rings fitting one another is easy, I omit-
d them in this instrument.
’ When a glass warming or cooling is to be examined in the polarized
ht, the prismatic rod is so inserted into thé frame / that one of its
es which have hitherto formed the sides, is brought into a horizon-
al position below. All the stands are then at the side of the horizon-
Wal rod turned to 120°, which presents no obstacle to the heating by
92 DOVE’'S DESCRIPTION OF AN APPARATUS
an interposed lamp. If instead of looking into the prism w we look
into e, on a slight change of the distance of the lens we obtain pre=
cisely the same phenomena. Thus an inverted order may also be given
to all the stands with respect to the condensing-lens.
' The superior advantages of the apparatus just described appear to
me to be as follows:
1. The intensity of its light, which is so great that the flame of spirit
of wine, 12 feet distant and coloured yellow by common salt, exhibits
the system of rings of Iceland spar with great distinctness in an undark~
ened room.
2. The easy change of the linear into circular and elliptic polari-
zation.
3. Its rendering unnecessary a particular arrangement for illumi-
nation.
4. The extent of the field of view*.
5. The purity of the colours, which are produced by colourless — 1
crystals only.
6. The cheapness of the instrument, since it serves equally as a
model of an open telescope and as a microscope (the condensing-lens is
the object-glass of the telescope; the stands 59, 55, s; form the eye-
glass, s, becomes the stand for the microscopic objects).
7. The easy execution of all single changes in the various experi-
ments above described.
The mechanician Hirschmann, of this place [ Berlin], whose Nicol’s —
prisms are in the hands of many natural philosophers, has already exe-
cuted this apparatus according to my instructions in several sets made
to order. Its price, if it is to be used both as an open telescope and —
microscope, is 60 rix-dollars.
Postscript.
Fig. 4. Plate II. represents a small apparatus consisting of a single
piece of glass, which exhibits united the modifications of the light by
reflexion. The mutually parallel surfaces ad and be are perpendicular
to the parallel surfaces ae and bd; but, on the contrary, ad is inclined at
45° towards ad, and ed towards bd. The light therefore, falling per-
pendicularly upon ad, will after being reflected by ab and ed proceed
from bd. The prismatic ares bounding the vacant space of total and
partial reflexion, th refore, intersect each other, as in the annexed
figure. In the rca opgce the light, after two reflexions, is un-
polarized ; in the vacant spac®s o and x it is polarized perpendicularly ;
* In order not to diminish this, the arm f must move to and fro, close by w.
The cylindrical setting of the polarizing prism must not be higher than half an
inch,
FOR EXHIBITING THE POLARIZATION OF LIGHT. 93
and in the vacant space p, on the contrary, the partially polarized
incident light is changed in the direction of the second reflexion. The
light of the vacant space m differs from that in a Fresnel’s parallelopiped
by having the planes of the two reflexions perpendicular to each other,
instead of coinciding as they do when that is used.
The phenomena of cooled glasses in circular light have not yet
been described particularly, and those of compressed glasses not at all;
we shall therefore add a few words respecting them.
In circular analysis solid cooled cylinders have the same properties
as Iceland spar plates. In linear analysis they exhibit the system of
rings without the cross displaced in the quadrants. The same may be
said of the rings of colours of hollow cylinders, which are concentric
with the inner black ring, and abruptly separated. The cross in three-
sided plates consists of four black points (with two plates placed upon
each other it consists of four triangles), which, united by bright gray
shades, forma Y. In six- and eight-sided plates the black central spot
becomes a six- and eight-sided star, while the colours of the angles
are arranging themselves into a very regular inclosure particularly when
by turning the analysing prism the centre becomes white: figs. 8.
and 9. represent the figures of cooled cubes. The isochromatic lines
of rectangularly crossed parallelopipedal plates remain, with regard
to their form, identical with those in the linear light, which appear when
the plane of polarization bisects the right angle between the plates.
All the figures remain unchanged when the glasses are turned in their
plane at the time of circular polarization and analysis. The irregu-
larities of the figures produced by unequal cooling appear in the cir-
cular light, particularly with thin plates, and often even with those
which appear regular in the linear light; nevertheless, I have also ob-
served precisely the reverse, and that indeed with a six-sided plate.
A cylinder* compressed by brass wire wound round it had the
same properties as a cooled one. Square and circular plates diametri-
cally compressed by a screw, exhibit between the rings originating at
the compressing points of the screw a coloured junction without a cross.
If the axis of compression lies in the plane of polarization of the recti-
linearly polarized incident light, the figure is also here displaced in the
quadrants, when the light becomes circularly analysed.
* This application of Weber’s method of compressing glass to the phenomena
of polarization was shown to me by Prof. Mitscherlich. (Compare Poggen-
dorff’s Annalen, vol. xx. p. 1.)
yw
ARTICLE VY.
Memoir on Colours in general, and particularly on a new Chro-
matic Scale deduced from Metallochromy for Scientific and
Practical Purposes. By M. Lxorotp Nosix1 of Reggio.
From the Bibliotheque Universelle des Sciences, §c. vol. xliv. xlv. Geneva.
(1830, vol. 1. p. 337, vol. 11. p. 35, Aug. and Sept.)
I DISCOVERED in 1826 a new class of facts and gave them the name
of electro-chemical appearances. The following is one of the principal
experiments connected with those facts.
A plate of platina is laid horizontally at the bottom of a vessel made
of glass or china. A platina point is vertically suspended over this in
such a manner that the distance between the point and the plate may be
about half a line. A solution of acetate of lead is next poured into the
vessel so as not only to cover the plate, but to rise two or three lines
higher than the point. The plate and the point are now brought into
communication, the former with the positive and the latter with the ne-
gative pole of an electric pile. At the moment when the voltaic circuit
is closed, a series of rings similar to those formed at the centre of the
Newtonian lenses is to be seen on the surface of the plate precisely under
the point. This fact, which could not fail to strike any one observing
it for the first time, led me to the discovery of others, which I have com-
municated to the public in four successive Memoirs*. I foresaw from
the very first the advantages that the arts were likely to derive from
this new method of colouring metals; but it was not until toward the
close of 1827 that I began to attend seriously to its application. My
first attempts I forbear to mention, being more desirous to call attention
to the productions which I obtained in the course of 1828, and in the
November of that year presented to the French Institute. These pro-
ductions consisted of several plates of coloured metal, and excited the
particular attention of that illustrious body by the beauty and vividness
of their tints, the precision of their outlines, and the softness of their
blendings+. '
* Biblioth. Univ. vol. xxxut. Xxxiv, Xxxv. XxXvI. (Old Series.) Annales de
Chimie et de Physique, vol. xxxtv. and xxxv.
+ [A specimen of the productions of this beautiful art was presented by the
inventor to the Royal Society, in whose Library it may be seen.—Enrr. |
M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE, 95
The invention being now so far advanced as to be entitled to a place
among the arts, it was thought that it should have its distinctive ap-
pellation, and by the advice of the same illustrious body, that of Metallo-
chromy was adopted. Since that period I have made such improvements
in my method that the first results, though they appeared satisfactory at
the time, make but a sorry figure when compared with those now obtained.
One of the great difficulties consisted in the necessity of producing a uni-
formity of tint on plates of certain dimensions ; for, my colours being ob-
tained by the effect of very thin plates applied to the surface of metals,
it is easy to conceive how hard it was to preserve such plates of a uni-
form thickness over the whole of an extensive surface. Great however
as the difficulties were, I thought I owed it both to art and to science to
do my utmost to surmount them. I thought it due to art, because this
would be extended by means of the uniformity of the tints, and to science,
because in the tints produced by plates of a particular thickness the
experimental philosopher would find the means of investigating with
peculiar advantage the nature and properties of colours.
At present I abstain from all detail relative to the method of obtain-
ing the homogeneous tints. The principle of the electro-chemical ap-
pearances seems now so fertile in results that its full development re-
quires a particular treatise. It will be a work of considerable labour,
and I have already commenced it by collecting and classifying all the
materials of this new department of physics in which, besides the other
methods of coloration, I intend to explain in detail those connected
with the production of uniform tints. In this place it is sufficient to
state that these tints are produced by substituting plates for the platina
point which forms the coloured rings.
The object of this Memoir is more limited. It is to arrange these
homogeneous tints in their natural order, so that they may form a
scale or gamut which I shall henceforth designate by the epithet chro-
matic.
Science never consults its interests so truly as when it aims at some
useful object connected with the arts. Such, I would fain hope, will
be the direction of these researches. Artists, it is true; being generally
unacquainted with physical theories, will find it difficult to follow me in
my inquiries. My labour, however will not be altogether useless to them,
if, as I intended, I have succeeded in treating certain parts of the sub-
ject in a manner likely to bring them within the reach of every under-
standing.
The formation of the chromatic scales requires considerable time
and a hand well practised in work of this description. Asthey might be
generally useful I regret that the difficulty of their construction renders
a prompt and wide-spread circulation of them impossible. I have tried
and am still trying to have them copied in oil and water colours, but
96 -M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
the attempts hitherto made give little or no hope that the best executed
copies can give more than an imperfect idea of the original colours.
The effect produced by these tints when disposed in the order set
forth in the scale bafiles description; it bears a resemblance however
to that produced on the ear by a scale of semitones executed by a per-
fect voice. I have shown my scale to several, and especially to those eru-
dite and learned persons who have favoured me with a passing visit at
Reggio. In all it excited but one feeling of delight. So gradual indeed
is the transition from one tint to another and such the harmony with
which they are blended, that if the eye be accidentally turned away, it
reverts inamoment as if moved by an irresistible desire to gaze still longer
on the display. Thisstatement is no exaggeration. It is but the mere fact,
in respect to which a language much more glowing would be perfectly
consistent with truth: so overpowering is the charm which, if I may use
the expression, pervades the scale of our coloured plates.
Chromatic Scale.
This scale consists of forty-four tints, each of which is applied to a plate
of steel. A Table subjoined to this Memoir exhibits the forty-four plates
arranged one under the other in a column, and opposite to each number
is the name of its peculiar tint. These tints are disposed in the same
order as the layers or thin plates by which they are produced. The co-
lour of the thinnest plate is placed first, and the others follow in the order
of the progressively increasing thickness of the plates*. In this arrange-
ment I cannot be mistaken, because the layers or thin plates which
produce the several colours are all applied by the same electro-chemical
process. The pile, the solution, the distances remain exactly the same.
There is nothing variable but the duration of the action, which in respect
to the layer No. 1. is very short, a little longer in respect to the second,
and increases progressively from the lowest to the highest number.
Other criterions also contribute to verify the accuracy with which its
place is assigned to each tint.
These colours are produced by very thin layers or plates analogous to
those which produce the colours in soap-bubbles and the rings observed
* The numerals placed within parentheses (in the Table) are designed to
indicate the thickness of the plates which produce the different colours. These
numbers are taken from Newton’s table, the fractional parts only being omitted.
The numbers are those which apply to thin layers of water. The unit of mea-
sure is the millionth part of an English inch. Our scale should then commence
with a layer measuring four of these units in thickness and end with a layer
measuring thirty, if we suppose our electro-chemical layers to possess the same
refractive power as water. It is probably somewhat less. At all events it is
useful to have these numbers immediately before our eyes, in order that we may
know, if not the absolute, at least the relative thickness of the attenuated layers
which effectively cover our plates of steel.
PRODUCED BY ELECTRO-CHEMICAL ACTION. 97
by Newton around the point of contact of two slightly convex glasses or
lenses. The order of the latter colours should therefore correspond ex-
actly with that of my scale. It does so in fact; but that the correspond-
ence may be perceived, it will be necessary first to rectify some errors
which have arisen respecting the rings of Newton, either in consequence
of their small dimensions, or of their having been examined under the
influence of some prejudice.
Our scale embraces the extent of the first four rings, and consists, as
we have already stated, of forty-four tints.
The tints of No. 1 to No. 10 (inclusive) correspond to the Ist ring.
11 28 2nd —
29 —— 38 3rd —
39 —— 44 4th —
Fundamental Principle.
It is well known that the colours of the thin layers around the point
of contact of Newton’s glasses are formed in the following manner. At
the point which allows all the rays of the transmitted light to pass there
appears a dark speck, and this remains the same whatever may be the
quality of the light. If the incident light is white, the central speck is
succeeded by several irises or concentric rings. If the light is homo-
geneous or produced by one species of rays, the irises are changed into
rings of the same colour as the incident rays, and separated from each
other by dark intervals. These rings, whatever be their colour, have
their commencement all at the verge of the central speck, but they oc-
cupy different spaces. The violet rings are the narrowest and nearest ;
the red are the widest and most distant; the rings of the intermediate co-
lours are of intermediate dimensions andat intermediate distances. When
the incident light is white, the series of homogeneous rings are formed
simultaneously and overlap each other ; all the colours are intermixed in
different proportions, and none stands isolated. It is to these combina-
tions that we are to attribute the tints of the thin layers which we are
about to analyse on our scale.
First Ring—From No. 1 to No. 10 (inclusive).
The Scale commences with the blond* colour: of this there are four
gradations, the first of which is silvery, and 2, 3, 4 are gradually deeper.
The blond is succeeded by the tawny+. Of this there are three species,
* [The term blond employed in the original has been retained in the trans-
lation to avoid the difficulty of giving an exact equivalent. Those brownish tints
which in reference to human hair we term light or fair are evidently intended.
—Eoir.
+ [In the original the name of this colour is fauve, from the Latin fulvus; and
the author says that he employs it in order to avoid the circumlocution of ‘Jion-
colour’.—Epir.]
Vor. I.—Parr I. i
98 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
5, 6, 7; the last of which is called a copper-red on account of the analogy
it bears to the colour of that metal. No. 8 is an ochre colour, No.9 a
violaceous ochre, and No. 10 a violaceous fire-red.
According to Newton the first ring should be composed of
Blue, White, Yellow, Orange, Red.
I find neither blue, nor the tints placed after the white and designated
as yellow and orange. It seems to me that the tints of Newton’s ring
may be defined easily enough. They differ essentially from yellow and
orange, and are in reality nothing else than the blond and tawny co-
lours of our scale mixed together. Of this we shall have a direct proof
by compressing these seven tints into a space as narrow as that which
they occupy in Newton's first ring: for as soon as this is done we see
the orange-yellow* which succeeds the white in the ring make its ap-
pearance. The blond and tawny colours of the scale are very com-
pound tints: they possess a certain fieriness on account of the red
which enters into their composition, have a slight resemblance to the
colours of gold and copper, and are very difficult to be imitated, be-
cause their composition is such as to remove them further than the
others from the prismatic colours. In nature they are found particu-
larly in
1. The hair of animals.
2. The feathers of birds.
3. The fibres of certain species of dry wood, such as the walnut-tree,
the pear-tree, &c.
4. The beard of corn, such as wheat, barley, rye, &e.
5. The smoke at the top of a flame.
6. The decoctions of roasted grain, such as barley, coffee, &c.
7. The halo seen around the moon when overcast with fog or
light clouds.
The colours which the clouds assume are in general
Black, or very pure ash-colour;
White, or very light ash-colour;
The colour of smoke or coffee ;
Red, more or less fiery ;
Blue, very deep, and sometimes approaching to violet.
These are exactly the tints that would constitute the first ring were
we to include in it the first two colours of the second ring. The tints
* The absence of the blue does not affect the theory of the colours of thin plates:
indeed I take it as a necessary consequence of the theory. All the homogeneous
‘rings commence at the same place; namely, at the verge of the central speck.
In this position the thin plate reflects rays of every kind, and this circumstance
it is that gives the white without any trace of blue. It is perhaps to the con-
trast between the white and the black that we are to ascribe the illusion at the
place where the two contrary appearances are produced.
PRODUCED BY ELECTRO-CHEMICAL ACTION. 99
of smoke result from the more or less thorough blending of the blond
and the tawny; those of fire from Nos. 8,9, and 10; the deep blue
is produced by the Nos. 10, 11, 12, which are the deepest tints of the
scale.
The first blond is properly that of light hair in childhood, and it is
a fact worthy of remark, that as children grow older it becomes pro-
gressively deeper and deeper, in the order of the Nos. 2, 3, 4 in the
scale. The perfect resemblance of the first tints on the scale to those
which we observe about the moon when she is surrounded by clouds
is equally remarkable: it seems in fact that this luminous appearance
may be thus definitively explained. Tints of this kind do not arise from
refraction and diffraction; they are produced only by means of thin
plates: the luminous halo in question is therefore a pheenomenon pro-
duced by thin plates.
This observation, combined with the fact that the tints exhibited by
the clouds in every variety of aspect are almost all comprised in the first
ring, leads to another consequence relative to the constitution of vesicular
vapours. The measurements and experiments of Newton have shown
what are the dimensions of the layers of air, of water, and of glass, which
produce the colours of the several rings. The red of No. 10 is the last
tint of the first ring: the indigo (No. 12) belongs to the second, and
the thickness of the layer of water which produces it by reflexion is
about the ten-millionth part of an English inch. As we know then, on
the one hand, that the vesicular vapours are formed of water, and on the
other that they do not reflect or transmit any tint beyond No. 12, we
may conclude that their external film is in no case thicker than the
ten-millionth part of an inch.
This result appears to me so decidedly certain as to be entitled to a
place in science.
Second Ring—From No. 11 to No. 28 (inclusive).
This interval commences at the deep violet No. 11, and extends to the
lake-red No. 28. It comprises the most beautiful of all the gradations ;
namely,
Blue, Azure, Yellow, Orange, Red.
- Newton places a green tint between the azure and the yellow. My
seale exhibits no trace of green, and, with whatever attention I have
examined Newton’s second ring, I have never been able to perceive, in
the place where the green should be found, anything but white tinged
with azure and answering to the Nos. 15, 16, 17 of my scale. It is
true that in the solar spectrum we meet with green in passing from
the blue to the yellow: but the colours of the prism are simple, those
of the thin plates are compound, and the order of their succession re-
H 2
100 M.NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
sembles but very imperfectly that of the colours in the prismatic spec-
trum *.
My scale is developed in such a manner that no illusion can take
place. The interval comprised in the second ring is entirely free from
green; neither is it to be found in the first order. Hence it is inferred,
that among the thin layers of the two first orders there is none capable
of reflecting any portion of green. The result is curious, and we have
remarked it in the hope that, under different circumstances, it may be
turned to account.
In speaking of the tints of the first ring we have stated that they are
further removed than the others from the nature of the prismatic co-
lours. The tints which, on the contrary, approach it most nearly are
those of the second ring: yet even these are too distinct from it to be
confounded with the simple colours of the prism. _ We have the sky,
their type in nature, constantly before our eyes; for who is there that
knows not the dawn, “with rosy forehead and golden feet”? Beginning.
with No. 12 of the scale, let us run our eye over it as far as No.'28,
and we shall find the tints of the sky disposed there in the order in
which they present themselves in the magnificent spectacle of the dawn-
ing day. This succession, as we have already observed, is the most
beautiful of all: Newton’s second ring gives no idea of it, because its
colours are not, and cannot be, sufficiently developed to produce the ef-
fect. Painters, if I mistake not, will do well to avail themselves of this
part of the scale: they will find in it a faithful copy of the beautiful tints
of the morning, and endeavour to transfer them to their compositions.
Natural philosophers will not fail to remark, that among the various tints
of the sky there is no trace of green. This would heretofore have been
found a perplexing circumstance, but may now be satisfactorily explained,
merely by reflecting that the tints of the sky belong to the second order,
in which also there is no tinge of green. From the blue to the yellow
the transition is through a very faint gradation of azure-yellow, and this
is observed to be exactly the case in nature.
The tints produced by vapours and clouds belong to the second order.
They contain in general more fire than the natural tints of the sky, but
this quality is nothing in comparison with the purity, vividness and va-
riety displayed in the tints of the second order. The appearance of the
sun is never so magnificent as when the air is perfectly pure. Toward
evening the lower regions of the atmosphere are always more or less
‘ * Professor Amici has been so kind as, at my request, to employ all the means
at his command in acareful examination of Newton’s rings. He has seen them
exactly as I have; for he has found neither blue in the first nor green in the
second ring. I value the testimony of my illustrious friend and colleague too
highly not to avail myself of it in this case.
PRODUCED BY ELECTRO-CHEMICAL ACTION. 101
charged with vapours, the air no longer retains its morning transpa-
rency, and the setting of the sun is attended by a fiery tint which
greatly mars the tranquil beauty of the spectacle. It is to those vapours
that we are to attribute the inflamed appearance of the sky, because
they possess the power of transmitting the tints of the first order, and
these are of that fiery cast. Were it not for this cireumstance the set-
ting of the sun might justly vie with its rising.
Philosophers had long since settled their opinions as to the co-
lours of the sky. These they explained by assigning to the air the
property of reflecting the higher colours of the spectrum (violet, indigo,
&c.), and that of transmitting the lower, (red, orange, &¢c.). The ex-
planation was correct so far as it went, but to make it complete the
exact quality of the tints should be determined by indicating the order
to which they belong. It was necessary also to ascertain how light is
affected by the presence of vapours. The considerations which we have
just stated will perhaps supply both these deficiencies.
Third and Fourth Rings-—From No. 29 to 38, and from 39 to 44.
These two rings comprise (if I may use the expression) the richest
tints. The tints of the first ring are distinguished by their fiery and
metallic appearance ; those of the second by their transparency and
vividness ; those of the third and fourth by their intensity, and by the
presence of green, which is wanting in the first and second orders. The
first appearance of green is in the third order at No. 32: it appears
again in the fourth order at No. 41. These two greens differ but little
from one another, and are both beautiful in a very high degree: they
have a strong resemblance to the green of the emerald. The tints of
the third ring do not differ much from those of the fourth: their most
marked difference consists in the diminution of transparency observable
in passing from the third to the fourth order.
The colours contained in these two series abound in the three king-
doms of nature ; the vegetable kingdom however seems to present them
in the greatest proportion.
The predominant colours in these two parts of the scale are the red,
the green, and the yellow-green. There is here, properly speaking, no
species of blue, but its absence is counterbalanced by the presence of
the green, which is not to be found in the first two rings. It would
seem as if the blue belonged peculiarly to the spacious vault of heaven,
and the green to the surface of the earth. They are two dominant
colours in nature, but their domains are separated, and the separation
seems to me not to be accidental. It was necessary, I suppose, that the
atmosphere should be composed of the most subtile particles, in order
that they might remain suspended in space; the earth did not require
to be of so delicate a texture. Hence we have two very distinct orders
102 M.NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
of particles or thin layers ; the terrestrial, which are grosser and capa»
ble of reflecting the green tints; and the aérial, which are more subtile
and capable of reflecting the azure tints.
Laws of Varying Colours.
Newton had observed that the colours of the rings changed their
position as the angle of incidence, under which they were viewed, was
changed. In certain rings a certain colour viewed at an incidence
nearly perpendicular appears to form a given eircle, but expands and
forms a larger circle if viewed obliquely. These changes are much
more perceptible in the outer than the inner rings. An obliquity of 40°,
for instance, is sufficient to change the tone of a colour of the fourth or-
der, though at the same angle of incidence a colour of the first or the
second order undergoes little or no change. We must not omit to
mention the effect of refraction, which is to render the transitions from
one tint to another more slow in proportion to the greater density of the
substance which forms the thin layer. This law may be included in
the first, because the rings produced by dense layers are interior in
reference to the corresponding rings produced by layers of inferior
density, and the exterior rings are the more liable to change.
The colours of the scale are produced by thin plates, and are subject
to the same laws as those of Newton's rings. It seems to me; however,
that in respect to the law of the changing colours there is an anomaly
that has not yet been mentioned. The higher tints comprised between
the red (No. 44) and the yellow (No. 21) conform to the general law.
If we view these tints at a certain inclination, we see No. 44 change to
No. 43, No.43 to No. 42, and so on in succession; each superior num-
ber exhibiting the appearance of the next inferior number. This law
prevails until we come to No. 21: after this the phenomenon chahges.
The beautiful yellows 19 and 20 become azure-green; the brighter
yellows 18 and 17 are changed to red; the azures 16 and 15 become
yellowish ; the blues 14 and 13 suffer no change, and with them tlie
anomaly ends, for the general law prevails again from No. 12 to No. 1
inclusive.
This difference has not been indicated until now, and, as I mentidn
it for the first time, I deem it necessary to state that it escapes the eye
when we endeavour to observe it in Newton’s rings, in consequence
perhaps of their being so limited in extent*. The anomaly prevails in
the central part of the second ring, where the thin plate reflects a great
quantity of white light, and this part is the brightest of our scale: I
remark this circumstance, in order that it may receive due attention
from those who would thoroughly investigate this point. In such an
investigation it will probably be necessary to take into account the
* See additional Note at the end.
PRODUCED BY ELECTRO-CHEMICAL ACTION. 103
variations of the law of refraction, when the obliquities of inclination
are great,—such, for example, as those to which we must have recourse
in order to account for the changes of tone in the colours of the first
two rings.
Exceptions to the Law of Varying Colours.
Tf bodies where composed of thin layers suchas those which form the
chromatic scale and Newton’s rings, their colours would change with
every change of incidence, conformably to the law which we have just
indicated. In nature the number of those colours that change is but
small in comparison with those that remain fixed. Hence it may be
inferred, either that the colours of bodies depend in general ona princi-
ple different from that of the colours of thin plates, or that this principle
is modified in its application, the bodies not being constituted exactly
as such an explanation would require. A few observations will perhaps
be sufficient to fix our ideas on this very interesting point in the theory
of colours.
Varying Colours in Nature.
In each of the three kingdoms of nature we have specimens of these
colours. The animal kingdom especially affords some that are highly
interesting, both in respect to their number and their beauty. It will
be sufficient to mention the wings of butterflies and insects, and above
all the feathers of different birds. Who is there that does not know,
for instance, the variety of pleasing hues displayed in the plumage of
the peacock? In this case, as well as in others of a similar kind, the
colour that we observe is not given out by one continuous surface, such
as that of a single plate: it is produced by a multitude of threads or
fibres, so nicely overlapping one another that they seem to form a perfect
plane, although they are really but a vast number of distinct minute sur-
faces, the position and thickness of which it would be necessary to know
in order to apply the general law to them with any prospect of success.
The phznomenon possesses all the characteristics of that produced by
thin plates; but instead of a single layer, the number in this case is
infinite, and, though disposed in an order calculated to excite our ad-
miration, still it complicates the action of the light so as to prevent us
from tracing it through all its variations.
The varying hue most frequently exhibited by the plumage of birds,
is a beautiful green of the same intensity as No. 32. This number in
the scale retains almost all its intensity, even at an inclination of 40°:
at dn angle of 50° it presents the appearance of No. 31, whichis a purple
colour with a greenish tinge ; beyond that the original colour completely
vanishes, and in its stead we have the violet-lake of No. 30.
But the varying green of feathers begins to change much sooner :
when the inclination is near the 40th degree, it already presents the
104 M.NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
violaceous tint of No. 12. The intermediate steps of the transition can-
not be discerned,—a decisive proof that the surfaces of the fibres which
produce the green when the incidence is perpendicular, are not those
which produce it when the incidence is oblique. The transition from
No. 32 to No. 12 is so abrupt as to warrant this inference.
At all events the properties of the yarying hues presented in nature
are sufficiently interesting to be made the subject of a specific inquiry.
I am at present engaged in collecting these colours, and hope that
naturalists and experimental philosophers will contribute whatever they
can toward the execution of a design likely to be attended with adyan-
tages, not only to Optics, but to other branches of science.
Unvarying Colours.
Nature presents a multitude of colours corresponding with the colours
of the scale; but these are extremely changeable, while the natural
colours are altogether unchangeable, except in the particular cases spe-
cified in the last paragraph but one. Let us fix our attention for a
moment on the green, which is more prevalent than any other colour.
Every herb, every leaf, is more or less of this colour. The green tints in
the scale, of whatever order they may be, become red when the inci-
dence is oblique: the same colours in herbs and leaves furnish no sign
of such a transformation.
We know already, that the changes of tone to which the tints of the
thin plates are subject diminish as the density of the plates increases.
Were the substance of herbs and leaves much more dense than that of
water, it might be said that it is owing to their excessive density that
they suffer no perceptible change of tint from obliquity of incidence.
But their density is far from being considerable; it is not so great as
that of water. The phenomenon must therefore be explained in a dif-
ferent, and, as I think, in the following manner.
In applying the principle of the thin layers or plates to the explanation
of the colours of bodies, it is supposed that those bodies are composed
of layers analogous to the air and water introduced between Newton's
glasses. Bodies are undoubtedly formed of very subtile particles; but
have those particles or elementary groups the form of plates or laminz ?
It does not appear so; it seems rather, on the principles of crystallo-
graphy, which divides them into cubes, octahedrons, tetrahedrons, &c.,
that their forms are [polyhedral] solids. This circumstance makes a
serious difference, and ought to be attentively examined.
Let us take, for example, the cubical, which is one of the simpileat
forms. Let us suppose the section of one of these cubes made in the
plane of reflexion, and aé the side or face on which the incident rays fall.
In passing from the perpendicular incidence 0 m to the oblique inci-
dences pm, gm, it is evident that, allowance being made for the effect
PRODUCED BY ELECTRO-CHEMICAL ACTION. ? 105
of refraction, the last ray subjected to the influence of interference reule
be the ray p m which passes through the an-
gle a. It falls on the inferior surface ed at
the middle point m, and, being reflected in the
direction mo’, reaches the eye at o!: every
more oblique ray, such as gm, falls beyond
the face ab, meets the vertical face ae, and
contributes nothing to the coloration, which
depends on the distance of the two faces ab
and ed. In order to comprise the ray gm
within this interval, a 6 should be prolonged to a! on the side of the
incident, and to b' on the side of the reflected rays. But as it termi-
nates at a and 8, its field of coloration is confined ne the limits m p,
mo'. Now the angle omp, the sine of which is —= (because abcd
¥
is a square) does not amount to 27°, and this is an opening too small to
admit the manifestation of any change whatever in the tints.
If the refraction (which precedes the reflexion) tends, as is evidently
the case, to enlarge the field of coloration, it has a still greater tendency
to diminish the effect of the change of the tints. It may therefore be
considered certain, that the integrant particles of which bodies are
composed cannot, in general, favour the play of the varying colours,
unless, in defiance of all other observations taken collectively, we assign
them avery considerable magnitude.
After the foregoing reflexions there remains, so far as I can see, but
one point to be cleared. It being once admitted that the field of
coloration of the integrant molecules is confined within narrow limits,
how then, it will be asked, do bodies appear coloured in every direc-
tion? In general the molecules hold, in the bodies which they form,
all sorts of positions, and are divided, relatively to the eye, into two
classes ; those of the one presenting their faces, and those of the others
their angles toward the observer. The first are those which colour
bodies ; the second are those which in one position of the mass con-
tribute, but in another do not contribute, to its coloration. In short,
the eye is always in the field of coloration of a vast number of particles.
When the field of one particle disappears, it is replaced by the field of
another ; so that the entire system always continues of a certain colour.
Symmetrical arrangements present an exception, and we have already
treated of these in the preceding paragraph.
Metallic Colours.
According to painters there are but three primitive colours, red, yellow,
and blue. By combining these tints in various proportions with black
and white they form the others. In richness and variety their produc-+
106 M.NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
tions are far surpassed by those of the thin lamine. If we imagine one
of the colours of the laminze combined with another, we have the im-
pression of a new tint. The combinations that may be obtained in this
way are almost innumerable, and, it will be said, need well be so, in
order to match the variety which nature exhibits. Such is our opinion
too; but we shall not attempt to conceal the difficulty presented by
the fact, that several of the natural colours, especially those of the me-
tallic substances, have but a very slight resemblance to the colours of
thin plates, among which it were vain to seek, for example, either the
yellow of gold or the red of copper. The colours of the plates which
approach them most nearly are found among the first seven or eight
tints of the scale. The gold might be placed among the blond colours,
and the copper among the tawny; but the difference is still so striking
that it would be unwarrantable, before it is accounted for, to put entire
and implicit confidence in the principle of the lamine.
This principle requires, as a primary condition, that the integrant —
molecules of bodies should be transparent. It is true that almost all —
bodies reduced to a certain degree of tenuity are permeable to light ;
but it is equally true that the existence of a single body perfectly opaque
and yet exhibiting a colour, would render it necessary to look for an-
other principle of coloration besides Newton's, which is applicable only
to diaphanous substances.
In my Memoirs on the electro-chemical appearances, I haye shown
that they are not exclusively produced by one of the poles of the pile,
The appearances which constitute the chromatic scale are due to the
electro-negative elements of the solution (oxygen and acid), which being —
transferred by the current to the positive pole, are there spread out
into thin transparent films, from which all the colours of the scale arise,
The electro-positive elements (such as hydrogen and the metallic bases)
are, on the contrary, transferred to the negative pole, and there depo-
sited in layers which never produce the colours of thin plates. Here
it is impossible to mistake in any case, but more particularly in respect
to the solutions of certain salts with a base of gold or of copper, which
produce negative appearances invariably of the same colour as the me-
tallic base. It cannot be said in this case that the substance has not
been brought to the degree of tenuity necessary to render it transparent.
The electro-chemical layers commence with the first degree of attenu- —
ation at the positive as well as the negative pole... If the layers of the
positive pole produce the ordinary colours of the plates, while the oppo-
site pole completely fails to present any other than that of the metallic
base, it necessarily follows, either that these bases are perfectly opaque,
or at least that their transparency is so imperfect as to render it im-—
possible to apply the general laws to them, unless with very important
restrictions. Indeed we have here a decisive proof that the colours
PRODUCED BY ELECTRO-CHEMICAL ACTION. . 107
which depend on the tenuity of plates are not to be traced on all classes
of bodies; that they can be produced by those bodies only which are
endowed with a certain degree of transparency ; and that metallic sub-
stances are too opaque to be numbered among these. This is a positive
fact, and ought therefore, without any regard to particular systems, to
be entered in the register of science.
Gold and Copper.
It cannot be doubted, says Newton, that the colours of gold and
copper belong to the second or the third order*. To us they seem, on
the contrary, to belong to the first order, that being the only one which
includes tints of a metallic appearance. If we only recollect that the
first colours of the scale are far from being distinct in the first of New-
ton’s rings, we shall feel less surprised that it should be necessary to
correct the classification of that great philosopher. The resemblance
in question is, however, as we have observed already, very far from
being perfect. The tints that come nearest to the yellow of gold are
the blond colours Nos. 2 and 3: but these are evidently less yellow,
and at the same time more compounded than the colour of gold; for
they contain a tinge of green, which does not exist in the more decided
colour of gold. Transparent gold-leaf appears green when held before
the light: this fact has been classed by several persons among the
phznomena connected with thin lamine, because these lamine are
known to reflect a given colour, in the same position in which they
transmit its complementary colour. However I will say with a great
philosopher, that “ there isin Newton’s rings no yellow that has green
for its complement: the colour transmitted is invariably the blue; and
_ this fact accords with the construction given by Newton for the com-
position of colours. But extract from this blue (which is necessarily
- compounded) a certain number of violet and blue rays, such as may be
_ absorbed by the substance of gold, and there will remain greent+.”
It is a fact demonstrated by a great number of observations, that
light in its passage through coloured substances is partially absorbed
and extinguished. This fact not only renders Biot’s explanation plausi-
ble, but warrants the supposition that light undergoes in reflexion a
diminution analogous to that which takes place in its transmission.
For if some of the rays destined to be transmitted are absorbed by the
very substance of the gold, how can all the other rays, which are de-
stined to be reflected in the interior of the same substance, escape undi-
minished ? If the phenomenon be incomplete in respect to transmission,
it will be equally so in respect to reflexion, and the tint formed will be
* Optics, Book II. part 3. prop. 5.
+ Biot, Zraité de Physique, vol. iy. p. 127.
108 M.NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
necessarily different from that produced by the ordinary thin plates,
which are so transparent as to arrest no species of rays whatsoever.
The blond, as already observed, contains a tinge of green which is not
found in the beautiful yellow of gold. If we leave out this green, by
supposing it absorbed in the process of reflexion, the result will be a tint
very closely resembling, if not exactly equal to, that of gold.
The red of copper requires a similar reduction. The colour nearest
to it is the tawny of No. 7. But this contains a cast of violet, which
is not in the copper, and the removal of it will make the resemblance,
if not complete, certainly much less imperfect.
It is not my purpose in this place to enter further into the question,
‘or to investigate the causes to which it is owing, that coloured bodies
absorb certain rays more rapidly than others. The fact itself is proved,
and it is unnecessary to go further for the attainment of our object,
which was to discover the cause of the great difference between me-
tallic colours and those of thin plates.
Colours developed on Metals by the Action of Fire.
The prismatic colours produced on steel and copper by the action of
heat are universally known. Analogous colours are also exhibited by
tin, bismuth, lead, &c., when they are in a state of fusion.
As to these colours, the most generally received opinion is, that they
depend on a principle of oxidation. Berzelius calls the metallic layer
which is thus coloured a suboxide*.
I have always entertained some doubts as to the correctness of this
explanation ; because each degree of oxidation has a colour peculiar to
itself, and in no way related to that variety of tints of which we speak.
I was also struck by the well-known practice of giving steel a violet
colour in order to secure it from rust. We know that this colour is
produced by means of fire, in the process of giving steel a particu-
lar temper,—a demper which is called violet, because it is produced
simultaneously with the colour. Were this tint, as it is presumed to be, —
the effect of oxidation, it would, in my opinion, instead of preventing,
serve only to accelerate oxidation. A very high degree of polish, I
allow, will keep off rust for a long time, but cannot stop it when once
the action has commenced.
* Some persons fancy that the phenomenon arises from the mere displacing
of the parts, and thus exclude the intervention of any other substance. Ac-
cording to this notion it is but the metal dividing itself into laminz of different
degrees of thickness, and thus becoming capable of producing the different
colours. Such an opinion, however, is opposed to a positive fact already de-
monstrated; I mean the fact of their opacity being in all cases too great to
admit of their furnishing lamine sufficiently transparent to produce the colours
in question.
PRODUCED BY ELECTRO-CHEMICAL ACTION. 109
But this is not all: the superficial colours of which we speak are
changeable, and belong evidently to the same class as those produced
by thin plates. Now the pure metals, as we have already seen, are,
from their opacity, incapable of this species of coloration. Can they
acquire that capacity in their first degree of oxidation by becoming sud-
denly transparent in consequence of their union with a small quantity
of oxygen? The hypothesis far exceeds the bounds of probability, and
the phenomenon requires to be otherwise explained.
Let us return, for an instant, to the experiment of the coloured rings
developed on a surface of platina by means of the electro-chemical ap-
paratus described in the beginning of this Memoir. The platina
surface belongs to the positive pole of the pile, and the electro-negative
elements of the solution (which in the present case are the oxygen of
water and the acid of acetate of lead) are deposited at this pole. I will
hot undertake to say by what species of affinity or force it is that these
elements are attracted to each other and spread out into thin films on
the platina. It is certain, however, that they attach themselves to the
platina without oxidizing it in the slightest degree. We must not
suppose that this happens because platina is a metal difficult to be
oxidized. Iron and steel belong to the class of metals most easily ox-
idized, and yet it is well known that they will bear to be covered with
electro-negative layers without becoming rusted. My electro-chemical
experiments, multiplied and varied in a thousand ways, leave no room
for reasonable doubt on this point: they show that oxygen and cer-
tain acids may adhere to the surfaces of metals without producing the
slightest chemical change in them. This is a novel state for oxygen
and the acids, and is distinguished from their ordinary combination by
the three following peculiarities: Ist, The metal retains, beneath the
deposited layer, its natural brilliancy ; 2nd, this layer produces the phe-
nomenon of the coloured rings in all its beauty; 3rd, instead of ox-
idizing the metal, these electro-negative elements contribute to secure
it against oxidation in every part to which they are applied*.
A fact so unprecedented is interesting to chemistry and is entitled to
particular attention, as tending to enrich the science by the introduc-
tion of new ideas+. Confining myself in this place to the colours pro-
duced on metals by the action of fire, I do not hesitate to say that I think
* In order to give an idea of the efficacy of this preservative, it will be
sufficient to quote the following experiment performed in Paris two years ago.
I took two steel plates of the same quality and polish. I coloured one of them
ie ordinary process, and exposed both in the open air to all the vicissitudes
arainy autumn. At the end of amonth the uncoloured plate was all rusted ;
the other had lost a little of its colour but was free from rust.
_ + If it were allowed me to offer an hypothesis relative to this novel state, I
should say that the electro-negative elements disposed in thin layers on the
surface of the metals are at too great a distance from the molecules of these
their origin now placed beyond the reach of doubt. It may be safely
laid down as a general proposition that the oxygen of the atmosphere
produces them, not, as is supposed, by oxidizing the surface of the
metal, but by becoming fixed in the form of a thin plate or film similar
to those of the electro-chemical appearances.
Copper, tin, and bismuth are pure metals, and I know not any layer
by which they could be coloured, except that which has been just men- —
tioned. Let a plate of copper be laid on a piece of red-hot iron: the
plate becomes gradually heated, and all at once exhibits the most beau-
tiful colours, but they disappear as suddenly. Before it becomes
coloured the plate has a metallic lustre; it subsequently ceases to
shine, and becomes evidently oxidized. It is therefore at the moment
when the colours manifest themselves that the oxygen of the air
precipitates itself on the copper. In the next moment the chemical
combination is effected, which takes place whenever the action of the,
heat is sufficiently prolonged. If the plate of copper be removed from
the red-hot iron as soon as the first indication of a change of colour is
perceived at any point, the process of coloration will then go on more
slowly, the copper will not be oxidized, and the oxygen, which would
produce this effect under a more prolonged action of the heat, now —
covers the plate with a film, which adheres to it like a varnish, and by —
its transparency produces the usual colours.
The origin of the violet colour given to steel to prevent it from rusting
is the same. The layer however which produces this tint in the steel
does not perhaps consist solely of oxygen, as it does when the metals
are pure. Steel is a carburet of iron, and the oxygen of the air in
being precipitated on this compound, becoming combined with the
carbon in some manner or other might form the layer in question. A
all events the layer does not change its nature; it is always electro-
hegative, and secures the metal from oxidation as effectually as th
layers applied by the electro-chemical process.
The electro-chemical appearances are formed with surprising ra-
pidity, and the colours developed on metals exposed to the action o
heat are produced with equal promptitude. It is therefore essential to
the production of the phenomenon of thin plates that the electro-
negative elements should be precipitated on the metal with a certain
110 M.NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
substances to enter into combination with them. This idea, which accords wit!
the spirit of other theories, being admitted, we see at once how these layers
preserve the transparency required to produce the coloured rings, and do no
attack the metal so long as they are kept at such a distance as to be unable t
combine with its particles. Berzelius was more sensible of the difficulty, pe
haps, than any one else: but would not an open avowal have been better tha
the attempt to evade it by the adoption of the term subowide, which is quite a
vague and undefined as the principle of oxidation, for which it was offered as
substitute ? a?
“PRODUCED BY ELECTRO-CHEMICAL ACTION. 111
velocity. Does not the necessity of this condition show why these
layers, in order to produce the desired effect, should be brought into
contact with the metallic surface by the agency either of fire or elec-
tricity? The humid way is perhaps too tedious in all cases; it gradually
oxidizes the surfaces of the metals, but never covers them with that
thin and extended veil, the application of which requires a rapidity un-
attainable in this circumstance.
Nature presents in the specular iron a beautiful instance of the co-
loration which we have been considering. The ordinary colour of this
ore is an iron gray ; yet the faces of its crystals often display beautiful
tints of every kind. They commence, in general, with the blue (No.
13) of the second, and go onas far as the reds (37 and 38) of the third
order. ‘These colours change as those of the scale do, and are so very
like them that I thought they might be successfully imitated. I was
not mistaken: a crystal of specular iron coloured by nature could not
be distinguished from one coloured by the application of the electro-
chemical process. There is no doubt as to the origin of these crystals;
they are produced by fire, and it is that which has given them their
colour by covering their surfaces with thin layers analogous to the
electro-chemical. The humid way would have produced a yery dif-
ferent effect: it would have destroyed their metallic brilliancy, and
corroded their surfaces by the ordinary process of oxidation.
Singular Property of some Tints of the Scale.
A drop of alcohol is let fall on the violet (No. 11), and spread so as
to cover part of the colour. The part thus made wet is no longer the
same: we see instead of it a feeble tint resembling that of coffee
mixed with milk; but the other part remains unchanged. The com-
parison can be instantaneously made, and the difference between the
two tints is so striking, that we are at a loss to conceive how a trans-
parent and very limpid film of alcohol can produce such a change in the
violet colour on which it is placed. The alcohol gradually evaporates,
and the colour recovers its former brilliancy.
Water, oil, and the different saline solutions produce the same effect;
the thickness of the liquid film does not affect the phenomenon, and
the colour undergoes the same change whether it be a thin film ora
considerable mass. When transparent solids, such as glass, crystals,
&c., are laid over the violet colour, it suffers no change. The liquids
with which the plate is overspread adhere to its surface, so that this
condition seems necessary to the production of the phenomenon. .
Below the violet the indigo No. 12 and the blue No. 13, and (yet
lower down) the red No. 10, the ochres Nos. 8 and 9 are subject to very
marked variations. In the other colours of the scale when submitted
to the experiment of the humid films no changes are visible,—none at
112 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
least but such as are extremely slight in comparison with those which
take place in the group of tints formed about the violet No. 11. There
is no other fact connected with this. Such at least is my opinion, after
having examined it under various aspects without being able to arrive
at a satisfactory explanation. I am therefore unable to say more about
it for the present.
Effect of Artificial Light during the Night.
It is an admitted fact, that we cannot judge of colours without the
presence of daylight. But what changes do they undergo when viewed
in the evening? The following are those that I have observed in the
tints of my scale when examined at that time. The two conflicting opi-
nions of those whom I consulted on this subject I forbear to mention.
. The greens increase in beauty and intensity.
. The yellows and the azure are tarnished and become deeper.
- The blues and the indigo become greenish.
. The violets approximate to a blue.
. The violet-reds become more violet.
- The first eight tints of the scale become more like each other,
and approach more nearly to the metallic colours.
. The other tints remain nearly unchanged.
IT Ane wnwe
Some of those changes are produced even by day if the colours of
the scale are viewed through a green crystal, and others if they are
viewed through yellow or azure crystals. Artificial light is without
doubt differently constituted from that of the sun: it contains pro-
bably a scanty mixture of red rays with an abundance of the yellow;
green, and azure. But what is the coloured diaphragm that should be
interposed in the passage of the light of day, in order to reduce it to
the same proportions as that of night? The problem is an interesting
one, but it remains as yet without solution.
Harmony of Colours.
My scale appears to all persons to be eminently harmonious. I have
already mentioned the delight which it afforded those who saw it. I
have now to add that artists are astonished not to find the green in its
usual place, between the yellow and theazure colours of the second order.
But I take the two finest greens in the scale, Nos. 32 and 41, and call
upon the most accomplished artists to assign them a more suitable place
than that which they occupy. Influenced by habit they unhesitatingly
place them among the yellows and the blues of the second interval, hay-
ing no doubt that this is their proper place. They are however soon un-
deceived by the result ; the green is found unpleasing here; the harmony
is destroyed, and cannot be re-established until the colours are restored
to their original position. But what is this harmony? It is an effect
PRODUCED BY ELECTRO-CHEMICAL ACTION. 113
by a reference to the law of imaginary colours. It is necessary to give
a brief development of the principle of this theory.
Let any colour whatsoever be exposed to some given degree of light
and let the eyes be kept steadily fixed on it for some time : if the eyes be
afterwards closed we have the impression of a different colour, which
though it is never the same for one tint that it is for another, is always
the same for the same tint. These colours, in some measure the off-
spring of the real colours, are called imaginary by philosophers, and
by others they are named fantastic or accidental. The following is a
table of them :—
Real Colour. Corresponding imaginary Colour.
BEEN ae eo eedasnececrcsacges saeco”, JV ZUTC-STeENs
PRRMPCIN Pe rcct ces cictecccesee sso SOA.
Green-yellow* ............... .. Violet.
PADTC-PTCOD Jods eapcvoe des'aseso oy MOO.
Indigo ..... a aN Spee = Golden.
WIGISE oo. cnescenoncnssooccsnensaa, 9 CATCLN-Yelow,
After this table I cannot do better in reference to the present topic
than give the following extract from Venturi.
“ The combination or succession of those colours which have such a
mutual correspondence, that the perception of the one is followed by the
imaginary sensation of the other, is agreeable and harmonious.”
“ Women of good taste know the colour of the trimming which has
a good or a bad effect in combination with the fundamental colour of
their dress. Leonardo da Vinci promised to give a table showing the
colours which harmonize with one dnother and those which do not}:
but he did not fulfill the promise, and no other painter that I know has
pointed out precise rules for the harmony of colours. Several have
observed merely that red combined with green has an agreeable effect ;
Newton apprises us that orange agrees with indigo; and Virgil was per-
haps of the same opinion when he put this verse into the mouth of his
Naiad,
Mollia luteola pingit vaccinia caltha.
“ Mengs extols the union of violet and yellow; the same author says
that the combination of red, yellow and azure is disagreeable {; but that
each of them should rather be joined with the colour intermediate be-
tween the two others; the red with the green, the yellow with the violet,
_ and the azure with the orange.”
“ These different opinions have their origin and foundation in the
_ transitions from the real to the imaginary state, which, as we have seen,
naturally follow the involuntary movement of the retina; so that the
* When the names of two colours are thus joined, the idea intended to be
_ conveyed is that of the intermediate tint.
+ On Painting, chap. 89. t Mengs, Legons de Peinture.
Vor. I—Parr I. I
114 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
general law of the harmony of the eye will be this: That the corre-
sponding colours in the Table hereafter mentioned will be in harmony
with one another.”
“Tn fact, if the organ of vision, after having been fixed on an orange
colour, directs itself spontaneously, and uninfluenced by any external
impulse, towards the indigo, or vice versdé; or if in nature a violet-
coloured hyacinth is placed beside a jonquil, and the optic axis is turned
from the one flower upon the other, the centre of the retina passes over
that succession of colours which is demanded by the nature of the or-
gan and cannot be felt but with pleasure and satisfaction. These two
colours harmonize, because the one leads to the other; and, for the con-
trary reason, if the eye has to pass from one colour to another, not cor-
responding with it in the table, it will necessarily have to make a dis-
agreeable effort, because it will find itself in a position not in harmony
with its former state. If the ocular harpsichord of Caslet were pos-
sible, the modulation of the colours would be executed on it accord-
ing to the principle just laid down*.”
I will not deny that the aptitude of the retina to cause an imaginary
to arise from a real colour is of some account in the effect produced by
colour. I am even inclined to believe that colours attentively observed
are, by this tendency of the organ, associated with a sentiment and
endowed with an eapression which they could not otherwise possess.
This however would be a species of melody and not of harmony.
Harmony is an instantaneous effect produced on the mind by several
colours united altogether independent of the development of imaginary
colours. Before this development can take place, the eye must be fixed
for some time on a real colour; nor is this all, it is also necessary that
the real colour should be seen in a bright light. Now, when I have
one or two colours before my eyes, I can judge of their harmony with-
out being obliged to look at them for a long time or requiring a very
bright light. If I observe them for a single instant, my judgement is
already pronounced, with the same promptitude with which the ear
decides when it is affected by the harmony of sounds. Suppose for a
moment that real sounds had their corresponding imaginary sounds,
and the latter were determined when the ear had been for some time
affected by a single quality of sounds suitably sustained. In the first
place, these imaginary sounds could make no impression except in the
particular case in which the notes are sustained for some time; but if
we suppose that they accompanied the real sound necessarily and in
every circumstance, they would not be in harmony with it; they would
be perceived an instant after it, and would produce melody.
When a particular colour is ill-assorted with another, the eye is of-
fended, as the ear is hurt by adiscord. If we pass from one of these
* Venturi, Recherche Physique sur les Couleurs, for which the prize of the
Italian Society was awarded. Modena, 1802.
oe eee
PRODUCED BY ELECTRO-CHEMICAL ACTION. 115
colours to the other through the intermediate tints, the first feeling
will be changed into an agreeable sensation. Our scale, I repeat it,
produces the same agreeable impression upon all, and it is to the inimi-
table beauty of its colours, and the manner in which they melt into each
other, that this effect is due.
According to the law of imaginary colours red harmonizes well with
green. In our scale the lakes, which are the finest reds in nature, are
between the green tints and the orange, and combine agreeably with
both. According to the same law the violet should agree only with the
yellow; in the scale the violet tints are between the azures and the
ochres, where they produce a very fine effect. The same law is opposed
to the combination of yellow and azure, but the scale proves that these
two tints combine agreeably, provided they have a certain tone and a
certain degree of brightness. It is unnecessary, I believe, to multiply
instances. The beauty of the tints and the graduation of the transitions
constitute together one of the first secrets of art revealed by the effect
of the chromatic scale. But it is not always allowed us to resort to the
graduation of the transitions, and the artist requires another guide to
show him what he is to do in all circumstances. It cannot be doubted
that as there are combinations of sounds more perfect to the ear than
others, such as the octave, the fifth and the third, there are likewise con-
cords of colours more pleasing to the eye than others. But these con-
cords should be determined. The field of inquiry is still new; it is
possible however that the pursuit may be attended with most success
by having recourse to the chromatic scale, which presents the tints in
their greatest purity, and so arranged as to form the gamut of colours.
This circumstance is an additional recommendation of the scale to the
attention of philosophers as well as of artists.
Concluding Reflexions on the Qualities of Colours considered both philo-
sophically and pictorially.
In physics it is usual to speak only of the brightness of colours. But
besides being more or less bright, they are more or less intense or deep,
beautiful, cheerful, &c. These epithets have been long in common use
and are constantly on the lips of painters. In my opinion it is time
that they should be admitted into science, and reduced to a more deter-
minate signification than they have in ordinary language.
Brightness.
All who observe the seven colours of the spectrum will instantly per-
ceive that they differ greatly in brightness. The clearest of them is the
yellow. Fraunhofer, who has analysed the spectrum with so much ping
assigns to that colour the highest degree of brightness.
‘The tints of our scale as well as the natural colours are far from being
12
116 =-M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
pure: they are all composed of several others. Hence arises a law of
brightness different from that of the prismatic colours. The clearest
on our scale are,
Ist, The azures .................. Nos. 16 and 17.
Inds -Thesplondsie 2c see land 2.
3rd, The yellows......00ssaesees 18 and 19.
The most obscure tints are Nos. 10, 11, and 12, in which the violet and
blue predominate.
Depth.
Depth, or intensity, and brightness are very different qualities. No
one indeed confounds the intensity of a fine red with the brightness of a
fine yellow. In the scale of the latter quality the white occupies the
first place. A bright tint may be considered as a mixture, in which
there is a little colour with a great quantity of white light; and, vice
versd, a strong or deep colour, as a mixture of much colour with a little
white light. Painters therefore when they want to give brightness to
their colours add white, but when they want to increase their intensity
they add a different colour.
The most intense colours of the scale are the lakes, especially No. 28
and No. 29. The feeblest are the azures No. 16 and No. 17, the blonds
No. 1 and No. 2, and the yellow No. 18.
Some colours strengthen each other; some have no such effect. Thus,
for example, the red of the spectrum combined with the violet forms
a very beautiful lake, which is a much more vivid red than that of the
prism. The same red combined with the green forms a mixture which
possesses more intensity. The tints of the scale include all the pris-
matie colours, and their strength depends exactly on the proportion of
the elements which enter into their composition. The lakes abound in
red and violet, which are the two colours that give most depth to each
other, as if one were the octave of the other. The sky-colours are too
feeble, because with the exception of the blue, which they contain in a
quantity rather excessive, the colours which enter into their composition
will, when mixed, produce only white.
It is not strictly true that the intensity is in the inverse ratio of the
brightness, because the more obscure tints Nos. 10, 11 and 12 are
less intense than the lakes Nos. 28 and 29. Nevertheless there is a
manifest relation between the two qualities; for it is certain that the
feeblest colours are among those of the brightest class, and the most in-
tense among those of the most obscure.
Thin plates according to their different degrees of tenuity reflect dif-
ferent colours ; either these reflected colours are such as mutually to
strengthen each other, so that there results from them a strong tint ;
or they do not strengthen each other, and the result of this is a white
which predominates in the tint. Thus, the cause which generally renders
a ° e. >
Se are —-
PRODUCED BY ELECTRO-CHEMICAL ACTION. 117
it impossible to obtain brightness of tint unless by sacrificing intensity,
is sufficiently demonstrated.
Beauty and Monotony.
Beauty consists in a certain variety which some tints possess in a
higher degree than others. The yellow, for example, and the red of the
spectrum have a tone peculiar to themselves: the golden contains the
essence of the red and the yellow, and is more agreeable to the eye than
either.
The most beautiful tints in the scale commence at the orange colours
22 and 23, and continue to the end.
The first element of pleasing is variety; in this point of view the
purity and homogeneity of a colour are defects, of which philosophical
painters must have been sensible when they recommended the use of
compound in preference to simple colours *.
The purest tint of the scale is perhaps that of the yellow No.19. At
the first glance it is extremely pleasing, but soon becomes monotonous
and the eye turns away for relief to the higher tints, each of which pro-
duces the sensation of several colours. A painting in which there is
much yellow will therefore always fail to please on account of this mo-
notony; for its effect is most disagreeable.
Nothing can be more beautiful than the varying colours: when we
call them varying it is unnecessary to say why they please. Painters,
we know, in order to give a finish to their productions, overlay them
with certain tints. The colours of the painting appear through the
tint, are mingled but not confounded with it, and thus are produced
a variety and vividness unattainable by any other means.
Warmth and Coldness.
Those tints which contain the element of red are by painters called
warm, and those in which the element of azure abounds are termed cold.
Red is the strongest and the most vivid colour : it is the colour of fire
and of blood, and it warms and inflames all the tints into which it is in-
troduced.
If the idea of warmth is associated with red, azure gives rise to a
very different feeling: it is indeed preeminently the cold colour.
Yellow approaches more nearly to the nature of red than to that of
azure, and is consequently rather warm than cold. Pure green cannot
be said to be cold or warm: it inclines however to the former or to the
latter accordingly as it is combined with blue or with yellow.
Cheerfulness and G'loominess.
Cheerfulness is not to be confounded with beauty, nor gloominess with
monotony: they are more distinct sensations and seem to belong, the
* Lecons Pratiques de Peinture, § v.
118 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
first to the lower colours of the spectrum, such as the red, orange, &c.,
and the second to the superior colours, such as the violet, indigo, &c.
The most gloomy tints on the scale are, according to the generally
received opinion, those of Nos. 10, 11 and 12, in which the higher co-
lours of the spectrum abound. These colours, it cannot be denied, are
also the least bright, and this quality may well be the cause of the
gloominess which is felt in viewing them.
It is possible however that there may be in this case an unknown ge-
neral law, which it would be worth while to investigate with the aid of
the analogies afforded by acoustic phenomena, of which the principles
are better known.
On the Pathetic and the Cheerful in Music and Painting.
An exclamation or shout of joy consists of notes ascending from the
grave to the acute; a cry proceeding from grief or pain consists, on the
contrary, of notes descending from the acute to the grave. It is not more
singular than true, although it has never before been remarked, that
the same notes sung or executed on an instrument will produce in the
ascending scale a very different effect from that which they produce in
the descending scale. In the first case the feeling excited is decidedly
cheerful; in the second it is as decidedly sad. This is a fact which
in both a physical and a physiological point of view remains yet un-
explained, but may serve nevertheless as a law for all analogous
cases.
Violet is a colour which certainly awakes a feeling of sadness. Can
it be owing to a similar law that it produces such a sensation? I inspect
the table of imaginary colours, and find that the green-yellow corresponds
to the violet. We know that according to the theory of vibrations the
violet is produced by shorter and the red by longer vibrations. The
transition then from the violet, which is the real colour, to the green-
yellow, which is the imaginary, is a transition from the acute to the grave,
and analogous to that which takes place in the notes that produce sad-
ness. The only difference between the two cases is, that in the one the
sensation is the direct and immediate effect of the notes conveyed to the
ear from without, whilst in the other the eye receives from without no-
thing more than the impression of the violet colour, the rest of the ef-
fect depending on the internal action of the optical nerves which are en-
dowed with the power of passing of themselves from the real to the ima-
ginary colour. A. difference of this kind however is not incompatible
with the existence of the analogy : it only leads to the inference that the
eye possesses the more exquisite sensibility, since in this organ a mere
disposition or tendency is sufficient to produce an effect which in the ear
is due to an external cause: for, the superior delicacy of the eye is evi-
dently the cause of the existence of these imaginary colours, which have
oe oo
PRODUCED BY ELECTRO-CHEMICAL ACTION. 119
no counterpart in the other sense,—no succession of imaginary sounds
resulting from those which had previously reached the tympanum.
~ In music there is awell-known and long-established distinction between
harmony and melody: the former arises from a certain series of sounds
produced all at the same time, the latter from the succession of certain
sounds produeed according to a certain rule. Can the science of colours
lay claim to a similar distinction ? I look at a fine painting, and amiat once
struck with the harmonious disposition of its beautiful colours. This isthe
first feeling excited, and it is excited ina moment. I afterwards examine
and study the composition by looking attentively now at one point and then
at another. The merit of the piece was at first confined to the beauty
and harmony of the tints; now the same tints being observed with more
attention awaken, or tend to awaken, the idea of the imaginary colours,
and thus acquire an expression which was wanting to them when they
were passed rapidly over. -It has already been observed that the green-
yellow arose from the violet, and that the latter colour had a tendency
to produce a sensation of sadness on account of its involving a necessary
transition from an acute to a grave tone. The lower colours of the
spectrum (the red and the golden) have as their imaginary colours
azure-green and indigo. In both these cases the passage is from the
grave to the acute, and the two colours should, according to the law
under consideration, excite a feeling of cheerfulness. The theoretical
inference is confirmed by every one’s experience.
This analogy between sounds and colours may, after all, be rather ap-
parent than real. I thought myself bound nevertheless to mention it,
with a view to its development, and on account of the new ideas which
it might suggest.
Additional Note on the Law of Varying Colours.
In speaking of this law, I have remarked an analogy which presents
itself in the central tints of the second ring. After having concluded
my labours it occurred to me to examine this interval once more, and I
noticed a fact which had escaped me in my first inquiries. Beginning
with the perpendicular incidence, in order to pursue the examination
through the other incidences, I observed the rings attentively. As my
point of view I took the central part of the second ring, and there, at an
angle between 70° and 80°,I perceived a new ring formed. This ap-
pearance was not accompanied by the disappearance of any of the
other rings: it was really a new ring formed under this great inclina-
tion at the centre of the second, which was at first almost entirely white.
I shall distinguish this ring from the others by the epithet intruded *.
* It may not be useless, perhaps, to mention that my rings are inverse to
those of Newton; his begin at the centre, mine at the circumference, where,
from the nature of the electro-chemical process, the thinnest layers are depo-
sited: the thickest layers are evidently those of the centre. :
120 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE
My rings can easily be so enlarged that the intruded ring may occupy
a space two or three lines in breadth. The tints composing it will then
be seen very distinctly, and will correspond exactly with those which are
seen in detail on the plates 20, 19, 18, 17, 16 and 15; with this difference
only, that, in place of these tints, a ring will be seen pererec of green,
red and yellow.
When the rings are smaller, as they usually are when oiitedned under
the platina point, the intruded ring appears in the same place, and the
observation, though made under circumstances less favourable, is equally
decisive.
Newton’s rings give no idea of this phenomenon: they vanish from
the eye of the observer before the last degrees of obliquity are attained,
and are consequently unavailable in an observation for which these great
inclinations are an indispensable condition. ‘The smallness of the di-
mensions of the rings cannot cause the observation to fail, whenever it
can be made on my rings whether large or small.
I cover a portion of my rings with a layer of alcohol, oil, or water, &c.,
and when the observation is made at the before-mentioned inclination of
from 70° to 80°, the intruded ring appears only where the humid layer
is wanting. Thus the phenomenon connects itself still more with the
law of refraction. In my opinion there are but few facts that can puta
theory so severely to the test as this, and the theory which can completely
explain it will have every claim to credit.
Ishall always add to my chromatic scales a plate exhibiting on its sur-
face the coloured rings as much enlarged as is requisite for the conve-
nient study of the properties of the intruded ring. This I feel the more
inclined to do, as these large rings are likely to be useful in other re-
spects ; they will serve, for instance, as a key to the chromatic scale,
which is in reality no more than the development of the rings them-
selves ; and this development is indispensable when we would judge of a
colour. In the coloured rings, however large they may be, there is al-
ways found between every two tints a third into which they melt: its
tone and the feeling which it produces are always confounded with
those of the contiguous tints. For this inconvenience there is no re-
medy but to isolate the tints, so that the eye may be fixed on each of
them without receiving at the same time any sensation from the others.
The chromatic scale affords this advantage in its detached plates, not to
mention the other advantages which in the course of this Memoir it
has been proved to possess, and which it is therefore unnecessary to enu-
merate here.
Reggio, June 29, 1830.
PRODUCED BY ELECTRO-CHEMICAL ACTION. 121
CHROMATIC SCALE.
44 | Lacca-rosea. Laque-rose. Rose-lake. (30
43 | Verde-giallo-rossic c. Vert-jaune rougeatre. Reddish yellow-green.(28
42 | Verde-giallo. Vert-jaunatre. Yellowish-green. er
41 | Verde. Vert. Green. (26
40 | Violaceo-verdognolo. Violet-verdatre. Greenish-violet. (25
39 | Lacca-violacea. Laque-violette. Violet-lake. (24
38 | Lacca-rosea. Laque-rose. Rose-lake. (22
37 | Rancio-roseo. Orange-rose. Rose-orange.
36 | Rancio-verde. Orange-verdatre. Greenish-orange. (21
35 | Verde-rancio. Vert-orangé. Orange-green.
34 | Verde-giallo. Vert-jaune. Yellow-green. (20
33 | Verde-giallognolo. Vert-jaunatre. Yellowish-green.
32 | Verde. Vert. Green. et
31 | Porpora-verdognola. Pourpre-verdatre. | Greenish-purple. (18
30 | Lacca-turchiniccia. Laque-bleuatre. Blueish-lake. (17
29 | Lacca-purpurea. Laque-pourprée. Purpled-lake. (16
28 | Lacca-accesa. Laque éclatante. Brilliant-lake. 15
27 | Lacca. Laque. Lake.
26 | Lacca-rancia. Laque-orangée. Orange-lake. (14
25 | Rosso-rancio. Rouge-orangé. Orange-red.
24. | Rancio-rosso. Orange-rouge. Red-orange.
23 | Rancio-rossiccio. | Orange-rougeatre. _ Reddish-orange.
22 | Rancio. Orange. Orange. (13
21 | Giallo-rancio. Jaune-orangé. Orange-yellow.
20 | Giallo-aeceso. Jaune éclatant. Brilliant-yellow.
19 | Giallo. Jaune. Yellow.
18 | Giallo-chiarissimo. Jaune trés-clair. Very bright yellow. (12
17 | Celeste-giallognolo. Azur-jaunatre. Yellowish-azure.
16 | Celeste. Azur. Azure.
15 | Bleu-chiaro. Bleu-clair. Clear-blue.
14 | Bleu. Bleu. Blue.
13 | Bleu-carico. Bleu-foncé. Deep-blue.
12 | Indaco. Indigo. Indigo. (10
|11 | Violetto. Violet. Violet. (8
10 | Rosso-violaceo. Rouge-violet. Violet-red. (7
9 | Ocria-violacea. Ocre-violette. Violet-ochre.
| 8 | Ocria. Ocre. Ochre.
| 7 | Rosso di rame. Rouge de cuivre. Copper-red. (6
6 | Fulvo-acceso. Fauve éclatant. Brilliant-tawny.
| 5 | Fulvo. Fauve. Tawny.
| 4 | Biondo-acceso. Blond éelatant. Brilliant-blond. (5
3 | Biondo d’ oro. Blond-doreé. Golden-blond.
2 | Biondo. Blond. Blond.
_1 | Biondo-argentino. Blond-argentin. Silver-blond. (4
122
ArrTicLe VI.
On the Mathematical Theory of Heat ; hy S8.D. Poisson,
Member of the Institute, &c.*
From the Annales de Chimie et de Physique, vol. u1x. p. 71 et seq.
Tue work which I have just published under the title of The Mathe-
matical Theory of Heat ( Théorie Mathématique de la Chaleur), forms
the second part of a treatise on Mathematical Physics (Physique Mathé-
matique), the first’ of which is the New Theory of Capillary Action
(Nouvelle Théorie de U Action Capillaire), which appeared four years
ago. It contains twelve chapters, preceded by some pages in which I
recapitulate in a few words the first applications of the caleulus which
have been made to the theory of heat, and the principal researches of
geometers upon that subject, which have been- made of late years,
namely, since the first Memoir presented by Fourier to the Institute in
1807. Iwill here transcribe the contents of the Preface; on the im-
portant question of the heat of the earth.
“In applying to the earth the general solution of the problem of a
sphere at first heated in any manner whatever, Laplace was led to par-
ticipate in the opinion of Fourier, which attributes to the primitive heat
of the earth the increase in temperature which is observed in descend-
ing from the surface, and the amount of which is not the same in all lo-
calities. This hypothesis of a temperature proceeding from the original
heat of the globe (da chaleur dorigine), and which must rise to millions
of degrees in its central layers, has been generally adopted; but the dif-
ficulties it presents appear to me to render it improbable. I have pro-
posed a different explanation of the increasing temperature which has
long since been observed at all depths to which man has penetrated.
“ Aceording tothis new explanation the phenomenon depends on-the
inequality of temperature of those regions of space which the earth sue-
cessively passes through in its translatory motion, and which are com-
mon to the sun and all the planets. It would be indeed opposed to all pro-
bability that the temperature of space should everywhere be the same;
the variations to which it is subject from one point to another, sepa-
rated by very great distances, may be very considerable, and ought to
produce corresponding variations in the temperature of the earth, ex-
* The work of which this article is an analysis, is described as a quarto volume
of more than 500 pages, with a plate ; published by Bachelier, Quai des Augus-
tins, Paris.
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 125
tending to various depths according to their duration and amplitude.
Suppose, for the sake of example, a block of stone transported from the
equator to our latitudes ; its cooling will have commenced at the surface,
and then become propagated into the interior; and if the cooling has ex-
tended throughout the whole mass, because the time of its transporta-
tion has been very short, that body thus transported to our climate
will present the phenomenon of an increase of temperature with the
distance from the surface. The earth is in the case of this block of stone;
—it is a body coming from a region the temperature of which was
higher than that of the place in which it now is; or we may regard itasa
thermometer moveable in space, but which has not had time, on account
of its magnitude and according to its degree of conducting power, to
take throughout its mass the temperatures of the different regions through
which it has passed. At present the degree of temperature of the globe
is increasing below the surface ; the contrary has in former times been,
and will hereafter be, the case: besides, at epochs separated by many series
of ages this temperature must have been, and will in future be, much
higher or lower than what it is at present; a circumstance, which renders
it impossible that the earth should always be habitable by man, and has
perhaps contributed to the successive revolutions the traces of which
have been discovered in its exterior crust. It is necessary to observe
that the alternations of temperature of space are positive causes which
have an increasing influence upon the heat of the globe at least near its
surface; while the original heat of the earth (chaleur dorigine de la
terre), however slow it may be in dissipating, is but a transitory circum-
stance, the existence of which it would not be possible at the present
epoch to demonstrate, and to which we should not be forced to have
recourse as a hypothesis except in the case of the permanent and neces-
sary causes being insufficient to explain the different phenomena.”
The following are the titles of the different chapters of the work, to-
gether with a short abstract of the contents of each.
Carter I. Preliminary Notions — After having given the definition
of temperature and many other definitions, it is explained how we have
been led to the principle of a continual radiation and absorption of heat
by the molecules of all bodies. The interchange of heat between
material particles of an insensible magnitude, but yet comprising im-
mense numbers of molecules, cannot disturb the equality of their tem-
peratures when it actually exists. From this condition we conclude, that
for each particle the ratio of the emitting to the absorbing power is inde-
pendent of the substance and of density, and that it ean only depend on
_ temperature. In the case of the inequality of temperatures, we give the
- general expression of their variations during every instant, equal and
contrary for two material particles, radiating one toward the other. We
124 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
also give the law of absorption of radiant heat in the interior of homo-
geneous bodies. ;
Cuarpter II. Laws of Radiant Heat.—If a body be placed within a
vacuous sphere on every side (enceinte vide fermée de toutes parts), the
temperature of which is supposed to be invariable and everywhere the
same, we demonstrate that the result of the interchange of heat between
an element of its surface and an element of the surface of the inclosing
sphere, is independent of the matter of which the sphere is formed, and
proportional, ceteris paribus, to the cosines of the angle which the normal
to the second element forms with the right line from one to the other
element. Experiments, not as yet made, only can decide whether this
law of the cosine is equally applicable to the elements of the surface of
the body, of which the temperature is not invariable like that of the
sphere; and until such experiments are made we may be allowed
to doubt its existence while the body is heating or cooling. By consi-
dering the number of successive reflexions which take place at the
surface of the sphere we demonstrate also that in general the pas-
sage (flux) of heat through every element in the surface of the body
which it contains is independent of the form, of the dimensions, and
of the material of the sphere; there is no exception, but when the
heat, in the series of reflexions which it experiences, falls one or many
times upon the surface of the body. It follows from this theorem that
a thermometer placed in any point whatever of the space which the
sphere terminates, will finally indicate the same temperature, which
will be equal to that of the sphere; but in the case of the exception
just mentioned, the time which it will employ in attaining that tem-
perature will vary according to the place it occupies. The general ex-
pression of the passage of heat through every element of the surface of
a body of which the temperature varies, is composed of one factor re-
lative both to the state of that surface and to the material of the body,
multiplied by the difference of two similar functions, one of which
depends on the variable temperature of the body, the other on the
fixed temperature of the sphere, which are the same for all bodies;
a result which agrees with the law of cooling im vacuo discovered by
MM. Dulong and Petit. We next suppose in this second chapter,
that many bodies differing in temperature are contained in the sphere
of which the temperature is constant, and arrive then at a general for-
mula, which will serve to solve the problems of the catoptrics of heat,
the principal applications of which we indicate. When all these bodies
form round one of them a closed sphere the temperature of which,
variable with the time, is not the same throughout, the passage of
heat to the surface of the interior body does not depend on its tempe-
rature and that of the inclosure only, at least when these bodies are
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT, 125
formed of the same material. After having considered the influence
of the air upon radiation which we had at first eliminated, we give at
the end of this chapter a formula which expresses the instantaneous
variations of temperature of two material particles of insensible magni-
tude, by means of which the exchange of heat takes place after one or
many reflexions upon the surfaces of other bodies through air or through
any gas whatever.
Cuarter III. The Laws of Cooling in Bodies having the same Tem-
perature throughout.—While a homogeneous body of small dimensions
is heating or cooling, its variable temperature is the same at every
point; but if the body is composed of many parts formed of different
substances in juxtaposition, they may preserve unequal temperatures
during all the time that these temperatures vary, as we show in an-
other chapter. Inthe present we determine, in functions of the time,
the velocity and the temperature which we suppose to be common to
all the points in a body placed alone in a sphere either vacuous or
full of air, and the temperature of which is variable. If the sphere
contains many bodies subject to their mutual influence upon each other,
the determination of their temperatures would depend on the integra-
tion,of a system of simultaneous equations, which are only linear in the
case of ordinary temperatures, but in which we cannot separate the
variables when we investigate high temperatures, and when the radia-
tion is supposed not to be proportional to their differences.
Experiment has shown that in a cooling body, covered by a thin
layer or stratum of a substance different from that of which it is itself
composed, the velocity of refrigeration only arrives at its maximum when
the thickness of this additive stratum, though always very small, has
notwithstanding attained a certain limit. We develop the consequences
of this important fact in what regards extension of molecular radiation,
and explain how those consequences agree with the expression of the
passage of heat found in the preceding chapter.
Cuapter IV. Motion of Heat in the Interior of Solid or Liquid
Bodies.—We arrive by two different processes at the general equation of
the motion of heat; these two methods are exempt from the difficulties
which the Committee of the Institute, which awarded the prize of 1812*
to Fourier, had raised against the exactitude of the principle upon which
his method was sustained. The equation under consideration is appli-
cable both to homogeneous and heterogeneous bodies, solid or fluid, at
rest or in motion. It was unnecessary, as they appeared to have
thought, to find for fluids an equation different from the one I ob-
* This Committee consisted of MM. Lagrange, Laplace, Legendre, Haiiy and
Malus.
126 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT:
tained long since for heterogeneous bodies. The variations of tem-
perature which take place at every instant, and arise from the mutual
radiation of the neighbouring molecules, depend in fact only on their
actual positions, and not at all on the positions in which they will be
the instant after in consequence of the motions produced by their
calorific action or by other causes : it is thus that in the problem of the
flux and reflux of the tides, for example, we calculate the attraction of
the sea upon each point of its mass, as if it were solid and at rest at the
moment under consideration, and independently of the motions which
this attraction may produce.
Notwithstanding that the interior radiation takes place only between
molecules the temperatures of which are extremely different, the
equation of motion of the heat contains terms derived from the squares
of their differences, and of the same order of magnitude as those which
result from their first power; so that the exact equation differs, in
the case of a homogeneous body, from that which we had already
given; and it is not, like that, independent of the conductibility when
the body has arrived at an invariable state. This equation of par-
tial differences changes its form, when we cannot consider the extent
of the interior radiation as insensible; it is then of a higher order, which
introduces, in its integral, new constants or arbitrary functions. From
this a difficulty of analysis arises, of which we give the solution, and
explain how in every case the redundant quantities will be made to
disappear, as will be seen from a particular example in another chapter.
We form in this the general expression of the passage of heat through
every element of a surface traced in the interior of a body which is
heated or cooled, orhas arrived at an invariable state, and in which the
extent of the interior radiation is considered as insensible. This pas-
sage proceeds from the exchange of heat between the molecules of the
two parts of that body near their surface of separation, and the tempe-
ratures of which are very different; whilst the interior passage results
from the exchanges between the molecules adjacent to the surface of
the body and those of a surrounding medium, or of other bodies which
may have much higher or much lower temperatures ; and notwithstand-
ing that the respective magnitudes of these two passages (ces deux flux),
due to causes also unequal, must be of the same order and com-
parable with one another. We show how that condition is fulfilled, by
means of a quantity resulting from the rapid decrease of temperature
which takes place very near the surface of a body whilst heating or
cooling. In this manner interior and exterior passages are found united
with one another; and the law of interior conductibility expressed in
functions of the temperature is deduced from that of exterior radiation
which MM. Dulong and Petit have discovered.
In a homogeneous prism which has arrived at an inyariable state,
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 127,
and the lateral surface of which is supposed to be inrpermeable to heat
and its two bases retained at constant temperatures, the passage of heat
across every section perpendicular to its length is the same through-
out its length. Its magnitude is proportional to the temperature of
the two bases, and in the inverse ratio of the distance which separates
them. This principle is easy to demonstrate, or rather it may be con-
sidered as evident. Thus expressed, it is independent of the mode of
communication of heat, and it takes place whatever be the length of the
prism: but it was erroneous to have attributed it without restriction to
the infinitely thin slices of one body, the temperature of which varies,
either with the time, or from one point to another; and to have ex-
cluded from it the circumstance, that the equation of the movement
of heat, deduced from that of extension, is independent of any hypothesis
and comparable in its generality to the theorems of statics. When we
make no supposition respecting the mode of communication of heat, or
the law of interior radiation, the passage of heat through each face of
an infinitely thin slice is no longer simply proportional to the infinitely
small difference of the temperatures of the two faces, or in the inverse
ratio of the thickness of the slices; the exact expression of it will be
found in the chapter in which we treat specially of the distribution of
heat in a prismatic bar.
CuaprTer V. On the Movement of Heat at the Surface of a Body of any
Form.—We demonstrate that the passages of heat are equal, or become
so after a very short time, in the two extremities of a prism which has
for its base an element of the surface of a body, and is in height a little
greater than the thickness of the superficial layer, in which the tempe-
rature varies very rapidly. From this equality, and from the expression
of the exterior radiation, given by observation, we determine the equa-
tion of the motion of heat at the surface of a body of any form what-
soever. The expression of the interior passage not being applicable to
the surface itself, it follows that the demonstration of this general equa-
tion, which consists in immediately equalizing that expression to the ex-
pression of the exterior radiation, is altogether illusory.
When a body is composed of two parts of different materials, two
equations of the motion of heat exist at their surface of separation, which
are demonstrated in the same manner as the equation relative to the sur-
face; they contain one quantity depending on the material of those two
parts respectively, and which can only be determined by experiment.
Cuaprer VI. A Digression on the Integrals of Equations of partial
Differences.—By the consideration of series, we demonstrate that the
number of arbitrary constants contained in the complete integral of a
differential equation ought always to be equal to that which indicates
128 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
the order of that equation: we prove by the same means, that in the
integral of an equation of partial differences the number of arbitrary
functions may be less, and change as the integral is developed in
series, according to the powers of one or other variable; and when
the equation of partial differences is linear, we show that by conve-
niently choosing this variable all the arbitrary functions may dis-
appear and be replaced by constants, infinite in number, without the
integral ceasing to be complete. To elucidate these general considera-
tions, we apply them to examples by means of which we show that
the different integrals, in the series of the same equation of partial dif-
ferences, are transformed into one another, and may be expressed under
a finite form by definite integrals, which also contain one or several
arbitrary functions. In the single case, in which the integral in series
contains only arbitrary constants, every term of the series by itself satis-
fies the given equation, so that the general integral is found expressed
by the sum of an infinite number of particular integrals. Integrals
of this form have appeared from the origin of the calculus of partial
differences ; but in order that their use in different problems should
not leave any doubt respecting the generality of the solutions, it would
have been necessary to have demonstrated @ priori, as I did long since,
that these expressions in series, although not containing any arbitrary
function, as well as those containing a greater or smaller number of
them, are not less on that account the most general solutions of equa-
tions of partial differences ; or else it would have been necessary to
verify in every example that, after having satisfied all the equations of
one problem relative to contiguous points infinite in number, the series
of this nature might still represent the initial and entirely arbitrary state
of this system of material points; a verification which, until now, it has
not been possible to give, except in very particular cases. The solu-
tion which Fourier was the first to offer of the problem of the distribution
of heat in a homogeneous sphere, of which all the points equidistant
from the centre have equal temperatures, does not satisfy for example
either of these two conditions; it was no doubt on this account that
the members of the Committee, whose judgement we mentioned above,
thought that his (Fourier’s) analysis was not satisfactory in regard to
generality ; and, in fact, in this solution it is not at all demonstrated
that the series which expresses the initial temperature can represent a
function, entirely arbitrary, of the distance from the centre.
For the use of these series of particular solutions, it will be neces-
sary to proceed in a manner proper to determine their coefficients ac-
cording to the initial state of the system. On the occasion of a pro-
blem relative to the heat of a sphere composed of two different sub-
stances, I have given for this purpose in the Journal del Ecole Polytech-
nique, (cahier 19, p.377 et seg.,) a direct and general method, of
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 129
which I have since made a great number of applications, and which
I shall also constantly follow in this work. The Sixth Chapter con-
tains already the application to the general equations of the mo-
tion of heat in the interior and on the surface of a body of any
form either homogeneous or heterogeneous. It leads in every case
to two remarkable equations, one of which serves to determine, inde-
pendently of one another, the coefficients of the terms of each series,
and the other to demonstrate the reality of the constant quantities
by which the time is multiplied in all these terms. These constants
are roots of transcendental equations, the nature of which it will be
very difficult to discover, by reason of the very complicated form of
these equations. From their reality this general consequence is drawn;
viz. when a body, heated in any manner whatever, is placed in a me-
dium the temperature of which is zero, it always attains, before its
complete cooling, a regular state in which the temperatures of all its
points decrease in the same geometrical progression for equal increments
of time. We shall demonstrate in another chapter, that, if that body is
a homogeneous sphere, these temperatures will be equal for all the points
at an equal distance from the centre, and the same as if the initial heat of
each of its concentric strata had been uniformly distributed throughout
its extent.
The equations of partial differences upon which depend the laws of
cooling in bodies are of the first order in regard to time, whilst the equa-
tions relative to the vibrations of elastic bodies and of fluids are of the
second order; there result essential differences between the expressions
of the temperatures and those of the velocities at a given instant, and for
that reason it appears at least very difficult to conceive that the phzeno-
mena which may result from a molecular radiation should be equally ex-
‘plicable by attributing them to the vibrations of an elastic fluid. When we
have obtained the expressions of the unknown quantities in functions of
the time, in either of these kinds of questions, if we make the time in
them equal to zero, we deduce from that, series of different forms which
represent, for all the points of the system which we consider, arbitrary
functions, continuous or discontinuous, of their coordinates. These ex-
pressions in series, although we might not be able to verify them, except
in particular examples, ought always to be admitted as a necessary con-
sequence of the solution of every problem, the generality of which has
been demonstrated @ priori; it will however be desirable that we should
also obtain them in a more direct manner; and we might perhaps so at-
tain them, by means of the analysis of which I had made use in my first
Memoir on the theory of heat, to determine the law of temperatures in a
bar of a given length, according to the integral under a finite form of the
equation of partial differences.
Vou. I.—Parrt I. K
130 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
CuarrterVII. A Digression onthe Manner of expressing Arbitrary Func-
tions by Series of Periodical Quantities —Lagrange was the first to give a
series of quantities proper to represent the values of an arbitrary function,
continuous or discontinuous, in a determined interval of the values of
the variable. This formula supposes that the function vanishes at the
two extremes of this interval ; it proceeds according to the sines of the
multiples of the variable; many others exist of the same nature which
proceed according to the sines or cosines of these multiples, even or
uneven, and which differ from one another in conditions relative to each
extreme. A complete theory of formule of this kind will be found in
this chapter, which I have abstracted from my old memoirs, and in which
I have considered the periodical series which they contain as limits of
other converging series, the sums of which are integrals, themselves
having for limits the arbitrary functions which it is our object to repre-
sent. Supposing in one or other of these expressions in series, the interval
of the values of the variable for which it takes place to be infinite, there
results from it the formula with a double integral, which belongs to
Fourier; it is extended without difficulty, as well as each of those which
only subsists for a limited interval, to two or a greater number of va-
riables.
CuapTer VIII. Continuation of the Digression on the Manner of re-
presenting Arbitrary Functions by Series of Periodical Quantities—An
arbitrary function of two angles, one of which is comprised between zero
and 180°, and the other between zero and 360°, may always be repre-
sented between those limits by a series of certain periodical quantities,
which have not received particular denominations, although they have
special and very remarkable properties. It is to that expression in series
that we have recourse in a great number of questions of celestial mecha-
nics and of physics, relative to spheroids; it had however been disputed
whether they agreed with any function whatever; but the demonstration
of this important formula, which I had already given and now repro-
duce in this chapter, will leave no doubt of its nature and generality.
This demonstration is founded on a theorem, which is deduced from
considerations similar to those of the preceding chapter. We examine
what the series becomes at the limits of the values of the two angles;
we then demonstrate the properties of the functions of which its terms
are formed ; then it is shown that they always end by decreasing inde-
finitely, which is a necessary consequence and sufficient to prevent the
Series from becoming diverging, for which purpose its use is always al-
lowable. Finally, it is proved, that for the same function there is never
more than one development of that kind; which does not happen in
the developments in series of sines and cosines of the multiples of the va-
riables. This chapter terminates with the demonstration of another theo-
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 13i
rem, by means of which we reduce a numerous class of double integrals
to simple integrals.
Cuarter IX. Distribution of Heat in.a Bar, the transverse Dimensions
of which are very small—We form directly the equation of the motion
of heat in a bar, either straight or curved, homogeneous or heterogeneous,
the transverse sections of which are variable or invariable, and which
radiates across its lateral surface. We then verify the coincidence of
this equation with that which is deduced from the general equation of
Chapter IV., when the lateral radiation is abstracted and the bar is cy-
lindrical or prismatic. This equation is first applied to the invariable
state of a bar the two extremities of which are kept at constant and
given temperatures. It is then supposed, successively, that the extent
of the interior radiation is not insensible, that the exterior radiation
ceases to be proportional to the differences of temperature, that the ex-
terior conductibility varies according to the degree of heat, and the
influence of those different causes on the law of the permanent tempera-
tures of the bar is determined. Formule are also given, which will
serve to deduce from this law, by experiment, the respective conducti-
bility of different substances, and the quantity relative to the passage from
one substance into another, in the case of a bar formed of two heteroge-
neous parts placed contiguous to and following one another. After
having thus considered in detail the case of permanent temperatures, we
resolve the equation of partial differences relative to the case of va-
riable temperatures; which leads toan expression of the unknown quan-
tity of the problem, in a series of exponentials, the coefficients of which
are determined by the general process indicated in Chapter VIL., what-
eyer may be the variations of substance and of the transverse sections
of the bar. We then apply that solution to the principal particular
_ cases. When the bar is indefinitely lengthened, or supposed to be
heated only in one part of its length, the laws of the propagation of heat
on each side of the heated place are determined; this propagation is in-
stantaneous to any distance; a result of the theory presenting a real
difficulty, but the explanation of which is given.
CuarrTer X. On the Distribution of Heat in Spherical Bodies —The
problem of the distribution of heat in a sphere, all the points of which
equally distant from the centre have equal temperatures, is easily brought
to a particular case of the same question with regard to a cylindrical
bar. It is also solved directly; the solution is then applied to the two
extreme cases, one of a very small radius, and another of a very great
one. In the case of an infinite radius, the laws are inferred of the pro-
pagation of caloric in a homogeneous body, round the part of its mass
to which the heat has been communicated, similarly in all directions.
We then determine the distribution of heat in a homogeneous sphere
K 2
132 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
covered with a stratum, also homogeneous, formed of a substance differ-
ent from that of the nucleus. During the whole time of cooling, the tem-
perature of this stratum, however small its thickness may be, is differ-
ent from that of the sphere in the centre, and the ratio of the tempera-
tures of these two parts, at the same instant, depends on the quantity
relative to the passage from one substance into the other, of which we
have already spoken. From this circumstance an objection arises
against the method employed by all natural philosophers to determine,
by the comparison of the velocities of cooling, the ratio of the specific
heat of different bodies, after having brought their surfaces to the same
state by means of a very thin stratum of the same substance for all
these bodies. The quantity relative to the passage of the heat of each
body in the additive stratum, is contained in the ratio of the velocities
of cooling ; it is therefore necessary that it should be known in order
to be able to deduce from this ratio, that of their specific heats. A
recent experiment by M. Melloni proves that a liquid contained in a
thin envelope, the interior surface of which is successively placed in dif-
ferent states by polishing or scratching it, always cools with the same
velocity, whilst the ratios of the velocity change very considerably,
as was known long before, when it is the exterior part of the vessel
that is more or less polished or scratched. The quantity relative to the
passage of caloric across the surface of separation of the vessel and the
liquid, is therefore independent of the state of that surface, a cireum-
‘stance which assimilates the cooling power of liquids to that of the
stratum of air in contact with bodies, which in the same manner does
not depend on the state of their surface, according to the experiments
‘of MM. Dulong and Petit.
When a homogeneous sphere, the cooling of which we are consider-
ing, is changed into a body terminated by an indefinite plane, and is
indefinitely prolonged on one side only of that plane, the analytical ex-
pression for the temperature of any point whatever changes its form, in
such a manner that that temperature, instead of tending to diminish in
geometrical progression, converges continually towards a very different
law, which depends on the initial state of the body; but however great a
body may be, it has always finite and determined dimensions; and it is al-
ways the law of final decrease enunciated in ChapterVI. which it is neces-
sary to apply ; even in the case, for example, of the cooling of the earth.
If the distribution of heat in a sphere, or in a body of another form,
has been determined, by supposing this body to be placed in a medium
the temperature of which is zero, this first solution of the problem may
afterwards be extended to the case in which the exterior temperature va-
ries according to any law whatever. In my first Memoir on the theory of
heat, I have followed, in regard to this part of the question, a direct me-
thod applicable to all cases. According to this method, one part of the
value of the temperature in a function of the time is expressed in the
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 133
general case by a quadruple integral, which can always be reduced to
a double integral like each of the other parts. By the method which
I have used to effect this reduction we obtain the value of different de-
finite integrals, which it would be difficult in general to determine in a
different manner, and the accuracy of which is verified whenever they
enter into known formule.
Cuapter XI. On the Distribution of Heat in certain Bodies, and
especially in a homogeneous Sphere primitively heated in any Manner.—
It is explained how, in every case, the complete expression of exterior
temperature, which may depend on the different sources of heat, and
which must be employed in the equation of the motion of heat relative
to the surface of bodies submitted to their influence, will be formed.
After having enumerated the different forms of bodies for which we
have hitherto arrived at the solution of the problem of the distribution
of heat, the complete solution is given for the case of a homogeneous
rectangular parallelopiped the six faces of which radiate unequally.
In order to apply the general equations of the fourth and fifth chap-
ters to the case of a homogeneous sphere primitively heated in any
manner, the orthogonal coordinates in them are transformed into polar
coordinates; the temperature at any instant and in any point is then
expressed by means of the general series of Chapter VIII., and of the
integrals found in Chapter VI.; the coefficients of that series are next
determined according to the initial state of the sphere, by supposing at
first the exterior temperature to be zero: by the process already em-
ployed in the preceding Chapter, this solution is finally extended to
the case of an exterior temperature, varying with the time and from
one point to another. Among the consequences of this general solu-
tion of the problem the most important is that for which we are in-
debted to Laplace ; it consists in this: That in a sphere of very large di-
mensions, and at distances from the surface very small in proportion to
its radius, the part of the temperature independent of the time does not
vary sensibly with these distances; and, that upon the normal at each
point, whether at the surface or at an inconsiderable depth, it may be
regarded as equal to the invariable part of the exterior temperature
which corresponds to the same point. Hence it results, that the in-
crease of heat in the direction of the depth which is observed near the
surface of the earth cannot be attributed to the inequality of tempera-
tures of different climates, and that it is necessary to look for the cause
in circumstances which vary very slowly with the time. Whatever this
cause may be, the difference of the mean temperatures of the surface
and beyond, corresponding to the same point of the superficies, is pro-
portional (according to a remark made by Fourier) to the increase of
temperature upon the normal referred to the unity of length, so that
134 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
this difference may be determined from the observed increase, and from
a quantity depending on the nature of the ground. This remark and
that of Laplace are not applicable to the localities where the tempera-
ture varies very rapidly round the vertical: it is shown that in these
cases of exception the temperature varies even upon the vertical :
and the law of this variation is determined from the variation which has
taken place at the surface or in the exterior temperature. The mean
temperature at a very small distance contains also a term which is not
proportional to this depth, and which arises from the influence of the
heat on the conductibility of the substance.
CuArter XII. On the Motion of Heat in the Interior and upon the
Surface of the Eurth.—It is shown that the formule of the preceding
chapter, although relating to a homogeneous sphere the surface of which
is everywhere in the same state, may notwithstanding serve to determine
the temperatures of the points of the earth at a distance from the sur-
face which is very small with regard to its radius, but which exceeds
however all accessible depths. These formule contain two constants,
depending on the nature of the soil, the numerical values of which may
be determined in every point of the globe from the temperatures ob-
served at different known depths.
Observation in harmony with theory shows that the diurnal inequali-
ties of the temperature of the earth disappear at very small depths, and
the annual inequalities at greater depths, in such a manner that at a di-
stance from the surface of about 20 metres and. beyond those two kinds
of inequalities are entirely insensible. In this chapter are given tables of
the temperatures, indicated by the thermometer, of the caves of the
Observatory, at the depth of 28 metres. The mean of 352 observations,
made from 1817 to the end of 1834, is 11%834.
The increase of the mean temperature of the earth, in proportion as
we descend below the surface, has long been established as a fact in all
deep places, at different latitudes, and at different elevations of the soil
above the level of the sea. The most adequate means to determine it is
by sounding and boring. The results, still very few, which have hitherto
been obtained are given. At Paris, this increase appears to be one de-
gree for about 38 metres of increase in depth.
As to the cause of this phenomenon, the difficulties are stated which
the explanation of Fourier presents, founded upon the original heat of
the globe, still sensible at the present time near the surface; the new
explanation alluded to at the beginning of this article is then proposed.
The following reflections extracted from the work tend to prove that
the solidification of the earth must have commenced by central strata,
and that before reaching the surface the cooling of the globe must have
been incomparably more rapid.
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 135
“The nearly spherical form of the earth and planets, and their flattening
at the poles of rotation, evidently show that these bodies were originally
in a fluid or perhaps in an aériform state. Beginning from this initial
state, the earth could not, wholly or partly, become solid, except by a loss
of heat arising from its temperature exceeding that of the medium in
which it was placed. But it is not demonstrated that the solidification
of the earth could have commenced at the surface and been propagated
towards the centre, as the state of the globe still fluid in the greatest
part of the interior would lead us to suppose; the contrary appears to me
more probable. For the extreme parts, or those nearer to the surface,
being the first cooled, must have descended to the interior and been
replaced by internal portions which had ascended to cool at the surface
and to descend again in their turn. This double current must have
maintained an equality of temperature in the mass, or at least must have
prevented the inequality from becoming in any way so great as ina
solid body, which cools from the surface; and we may add that this
mixture of the parts of the fluid, and the equalization of their tempera-
tures, must have been favoured by the oscillations of the whole mass,
which must have taken place until the globe attained a permanent figure
and rotation. On the other hand, the excessively great pressure sustain-
ed by the central strata may have determined their solidification long
before that of those nearer the surface; that is to say, the first may
have become solid by the effect of this extreme pressure at a tempera-
ture equal or even superior to that of the strata more distant from the
centre, and consequently subjected to a much less degree of pressure.
Experiment has shown, for example, that water at the ordinary tempe-
rature being submitted to a pressure of 1000 atmospheres, experiences
a condensation of about ~,th of its primitive volume. Now let us con-
ceive a column of water whose height is equal to one radius of the
globe, and let us reduce its weight to half of that which we observe at
the surface of the earth, in order to render it equal to the mean gravity
which would exist along each radius of the earth upon the hypothesis of
its homogeneity; the inferior strata of this liquid column would experience
a pressure of more than three millions of atmospheres, or equal to more
than three thousand times the pressure which would reduce water to
+4ths of its volume; but without knowing the law of the compression
of this liquid, and although we do not know in what manner this law
may depend on the temperature, we may believe, notwithstanding, that
so enormous a pressure would reduce the inferior strata of the mass
of water to the solid state, even when the temperature is very high.
It seems therefore more natural to conceive that the solidification
of the earth began at the centre and was successively propagated to-
wards the surface; at a certain temperature, which might be extremely
high, the strata nearer the centre became at first solid, by reason of the
excessive pressure which they experienced ; the succeeding strata were
136 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
then solidified at a lower temperature and under a less degree of pres-
sure, and thus in progressive succession to the surface.”
If the increase observed in the temperature of the earth near its sur-
face is due to its original heat, it follows that at the present epoch at
Paris this heat raises the temperature of the surface itself only by the
fortieth part of a degree. Not knowing the radiating power of the
substance of the globe, we cannot estimate the quantity of this initial
heat which traverses in a given time from within to without an extent,
also given, of the surface ; but such would be its slowness in dissipating
into space, that more than one thousand million of centuries must elapse
to reduce the small increase of the fortieth of a degree to one half.
With regard to periodical inequalities, the relation which exists be-
tween each inequality at a given depth and the inequality corre-
sponding to the exterior temperature is determined. Relations of this
nature, for the knowledge of which we are indebted to M. Fourier,
take place between the interior inequalities and those of the surface of
the ground; these relations leave unknown the ratios of these latter in-
equalities to those of the outside which are the immediate data of the
question.
' The interior temperature to which the earth is subjected arises from
three different sources, namely, from sidereal heat, from atmospherical
heat, acting either by radiation or by contact, and from solar heat.
These three sources of heat are successively examined. With regard to
the first it is observed, that it is not at all probable that radiant heat
emanating from the stars has the same intensity in all directions when it
arrives at the earth. The experiments are indicated which it would be
necessary to make in order to ascertain whether it really varies in the
different regions of the sky. M. Melloni intends immediately to apply
himself to these experiments, employing in them an extremely sensible
instrument, of which he has made use in his researches on heat ; a cir-
cumstance which cannot fail to lead to the solution of this important
question of celestial physics.
Before considering the influence of atmospherical heat, I have formeda
complete expression for the temperature, marked every instant by ather-
mometer suspended in the air, at any height above the surface of the
earth exposed in the shade or in the direct rays of the sun. Although the
greatest part of the quantities which this formula contains are unknown
to us, many general consequences may however be deduced from it,
which accord with experiment; it hence follows, that to determine the
proper temperature of the air, it is necessary to employ the simultaneous
observation of three thermometers, the surfaces of which are in a differ-
ent state, and not two thermometers only, as is generally said. This for-
mula also furnishes the means of comparing the temperatures indicated by
different thermometers in relation to their radiating powers and to their
property of absorbing the rays of the sun.
M. POISSON ON THE MATHEMATICAL THEORY OF HEAT. 137
The mean of the annual temperatures, marked by a thermometer ex~
posed in the open air and in the shade, forms the elimateric temperature.
It varies with the elevation of places above the level of the sea, and witlr
the longitude and latitude, according to unknown laws. At Paris it is
10°822, as M. Bouvard has concluded after 29 years of observations.
There will be found in this Chapter a table of the mean temperatures for
the twelve months of each of those years, which that gentleman has been
pleased to communicate to us, and which had not before been published.
It appears that in every point of the earth this climateric temperature
differs very little from the mean temperature of the surface of the soil,
as is shown by several examples. Notwithstanding, the variable tem-
perature of this surface, and that which is marked at the same instant
by a thermometer as little elevated above the surface as may be, are
often very different from each other ; it hence follows, that in a year
the excess of the highest above the lowest temperature of the soil
is at Paris nearly 24°, as will be seen in the course of this Chapter; and
only about 17° for the thermometer suspended in the air and in the
shade.
We now determine the part of exterior temperature which results from
the atmospherical heat combined with sidereal heat. The necessary data
for calculating its numerical value, @ priori, being unknown to us, we
show how this value, for every point of the globe, may be deduced from
the mean temperature of its surface. At Paris this exterior temperature
is 13°. Although we cannot determine separately the portion of this
temperature of the earth which arises from the atmospherical heat, there
is reason to think that it is also negative, so that the other portion arising
_ from sidereal heat must be less than 13° below zero. If we suppose that
radiant heat emanating from the stars falls in the same quantity on
all points of the globe, this temperature, higher than 13°, will be that
of space at the place where the earth is at this time. Without being
able to assign the degree of heat of space, we may however admit,
that its temperature differs little from zero, instead of being, as had
been asserted, below the temperature of the coldest regions in the
globe, and even of the freezing-point of mercury. As to the central
temperature of the whole mass of the earth, even supposing its ori-
ginal heat to be entirely dissipated, and that it is no longer equal to
the present temperature of space, we have no means of obtaining a
knowledge of it.
According to a theorem of Lambert, the whole amount of solar heat
which falls upon the earth is the same during different seasons, notwith-
standing the inequality of their lengths, which is found to be com-
pensated by that of the distances from the sun tothe earth. This quan-
tity of heat varies in the inverse ratio of the parameter of the ellipse
_ described by the earth ; it also varies with the obliquity of the ecliptic,
138 M. POISSON ON THE MATHEMATICAL THEORY OF HEAT.
but it does not appear that these variations can ever produce any consi-
derable effect on the heat of the globe. The quantities of solar heat
which fall in equal times upon the two hemispheres are nearly equal ;
but on account of the different states of their surfaces, those quantities
are absorbed in different proportions; and the power of absorbing the
rays of the sun inereasing in a greater ratio than the radiating power,
which is greater for dry land than for the sea, we conclude that the
mean temperature of our hemisphere, where dry land is ina greater pro-
portion, must be greater than that of the southern hemisphere; which
agrees with observation.
The solar heat, which reaches each point of the globe, varies at dif-
ferent hours of the day ; it is null when the sun is beneath the horizon ;
during the year it varies also with its declination; and the expression
changes its form as the latitude of the point under consideration is
greater or less than the complement of the obliquity of the ecliptic. I
have therefore considered the part of the exterior temperature which
arises from this souree of heat as a discontinuous function of the horary
angle, and of the longitude of thesun, to which I have applied the formule
of the preceding Chapters, in order to convert it into series of sines and
cosines of the multiples of these two angles. By this means I have ob-
tained the complete expressions of the diurnal and annual inequalities of
the temperature of the earth which arise from its double motion. These
formule show, that at the equator the annual inequalities are much less
than elsewhere; a circumstance which furnishes the explanation of a
fact observed by M. Boussingault in his journey to the Cordilleras, and
upon which he had relied in order to determine with great facility the
climateric temperatures of the places which he visited. The same for-.
mulz agree also, in a remarkable manner, with the temperatures which
M. Arago has observed at Paris during many years, and at depths vary-
ing from two to eight metres (from 6°56 to 26°24 English feet).
——
139
ArticueE VII.
Researches on the Elasticity of Bodies which crystallize regu-
larly ; by Fevix Savart.
(Read to the Academy of Sciences of Paris, January 26th, 1829.)
From the Annales de Chimie et de Physique, yol. xu. p. 5, et seq.
Hirnerrto precise notions respecting the intimate structure of bo-
dies could be acquired only by two means: first by cleavage, for opake
or transparent substances regularly crystallized ; secondly, for transparent
substances only, by the modifications ete they occasion in the propa-
gation of light.
The first of these means has taught us that crystallized bodies are col-
lections of lamine parallel to certain faces of the crystal; but it has given
us no information respecting the force with which these laminz adhere
together nor their elastic state. The second, far more powerful than
the first, because it renders evident actions depending on the very form
of the particles, has given rise to the discovery of phenomena the exist-
ence of which cleavage alone would never have allowed us to suspect.
But although these two experimental processes have introduced many
new ideas and notions into the science, yet it may be said that the part
of physics which treats of the arrangement of the particles of bodies,
and the properties resulting from it, as elasticity, hardness, fragility,
malleability, &c. is still in its infancy.
The investigations of Chladni respecting the modes of vibration of
laminz of glass or metal, and the researches which I have published on
the same subject, especially those which relate to the modes of division
of dises of a fibrous substance, such as wood, allow us to suspect that we
might acquire by this means new notions respecting the distribution of
elasticity in solid bodies; but it was not clearly seen by what process
this result might be attained, though the road which it was necessary
to follow was one of great simplicity.
But if this mode of experiment, which we are about to describe, is
simple in itself, it is not the less surrounded by a multitude of difficul-
_ ties of detail, which cannot be removed without numerous attempts; and
I hope this will serve to excuse the incompleteness of these researches,
_ which I only give as the first rudiments of a more extensive investi-
gation.
140 FELIX SAVART’S RESEARCHES ON THE
§ 1. Statement of the Means of Examination employed in these
Researches.
Circular plates which produce normal vibrations are susceptible of
several modes of division ; sometimes they are divided into a greater or
fewer number of equal sectors, always even in number, which perform
their vibrations in the same time; at other times they are divided into
a greater or fewer number of concentric zones; and these two series of
modes of division again may be combined together, so that the acoustic
figures which result are circular lines divided into equal parts by dia-
metrical nodal lines.
If the plate which is caused to sound is perfectly homogeneous, cir-
cular, and equal in thickness, it is obvious that in the case when the
figure consists of diametrical lines only, the system which they form
ought to be capable of placing itself in every direction, that is to say,
that any point whatever of the circumference of the plate, being taken
as the place of excitation, this single condition determines the position
of the nodal figure, since the point directly put in motion is always the
middle of a vibrating part. In the case of circular lines, under the con-
ditions we have just supposed, these lines would be exactly concentric
with the circumference of the plate. These results are a natural conse-
quence of the symmetry which is supposed to exist either in the form or
in the structure of the plate; but if this symmetry is deranged, it will
easily be conceived that an acoustical figure composed of diametrical
nodal lines ought no longer to place itself in a direction depending
solely on the position of the point of excitation, and that, with regard to
a figure consisting of circular lines, these lines ought to be modified, and
will become, for example, elliptical or of some other more complicated
form. It is thus that the system of two nodal lines which intersect
each other rectangularly, can upon an elliptical plate only place itself
in a single position, which is on the axes of the ellipse. There is how-
ever a second position in which this mode of division can establish it-
self; but then it is modified in its form, and it resembles the two
branches of a hyperbola, the transverse axis of which corresponds with
the greater axis of the ellipse: in this latter case, the number of vibra-
tions is less than in the first, and more so as the axes of the ellipse differ
more from each other. A similar phenomenon is observed when the
same mode of division is attempted to be produced on a circular plate
of brass, of very equal thickness, and in which several parallel saw-cuts
have been made, penetrating only to a small distance from the surface :
one of the crossed nodal lines always corresponds to a saw-cut which
has been made in the direction of a diameter, and the system of the two
hyperbolic lines arranges itself in such a manner that the same saw-cut
becomes the conjugate axis of the hyperbola. Thus, in both cases,
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 14]
the transverse axis of the hyperbola is always in the direction of the
least resistance to flexure. ;
Let us now suppose that, the plate remaining perfectly circular and
of equal thickness, it possesses in its plane a degree of elasticity which
is not the same in two directions perpendicular to each other; the sym-
metrical disposition round the centre being then found to be destroyed,
although in another manner than in the two examples we have just ad-
duced, an analogous result ought still to be obtained.
Thus, if we take a plate of this description, a plate of wood, for in-
stance, cut parallel to the fibres, and fixing it lightly by its centre, en-
deayour to make it produce the mode of division consisting of two lines
crossed rectangularly, we shall find that when it thus divides itself, the lines
of rest always place themselves according to the directions of the greatest
and least resistance to flexure, and that putting it afterwards in motion
at the extremity of the preceding lines, it may be made to produce a
second mode of division, which presents itself under the aspect of a hy-
perbola the branches of which are much straightened, and which would
have for its conjugate axis that line of the cross which corresponds to the
direction of the greatest resistance to flexure. In short, when the sym-
metrical disposition round the centre is destroyed, no matter in what
way, the mode of division formed by two nodal lines which intersect
each other rectangularly can place itself only in two determinate posi-
tions, for one of which it presents frequently the appearance of two hy-
perbolic branches more or less straightened; and, as we shall soon see,
it may even happen that, for certain distributions of elasticity, this mode
of division presents itself undef the form of two hyperbolic curves in
the two positions in’ which it becomes possible. Lastly, if a similar
plate be caused to produce some of the high modes of division, but yet
consisting of diametrical lines, experiment shows that they can likewise
place themselves in two invariable positions, and pass through certain
modifications analogous to those which the system of two lines crossed
at right angles undergoes. Thus the immoveability of the nodal figures,
and the double position which they can assume, are distinctive cha-
racters of circular plates all the diameters of which do not possess a uni-
form elasticity or cohesion.
It follows therefore from the preceding, that by forming with different
substances circular plates of very equal thickness, we may, by the fixed
or indeterminate position of an acoustic figure consisting of diametrical
nodal lines, ascertain whether the properties of the substance in ques-
tion are the same in all directions. By applying this mode of examina-
tion to a great number of plates formed of different substances regularly
or confusedly crystallized, as the metals, glass, sulphur, rock-crystal, carbo-
nate of lime, sulphate of lime, gypsum, &c., it is constantly found that the
acoustic figure, formed of twolines crossed rectangularly, can only place
142 FELIX SAVART’S RESEARCHES ON THE
itself on them in a single position; and that there is a second position
in which two hyperbolic curved lines are obtained which are accompa-
nied, according to the different cases, by a sound which differs more or
less from that which is produced when the crossed lines occur. Plates
are also met with which are incapable of assuming the mode of di-
vision formed of two straight lines, and in which only two systems of
hyperbolic curves are obtained, sometimes similar, yet giving different
sounds. In short, I have yet found no body for which the same nodal
figure can place itself in every direction; which seems to indicate
that there are very few solid substances which possess the same pro-
perties throughout. But what appears still more extraordinary is, that
if in the same body, a mass of metal for instance, plates are cut accord-
ing to different directions, some are susceptible of the mode of division
consisting of two lines which cross each other rectangularly, whilst
others present only two systems of hyperbolic curves. In both cases,
the sounds of the two systems may differ greatly: there may, for example,
be an interval between them of more than a fifth.
To arrive at the discovery of the experimental laws of this kind of
phenomena, it would be necessary therefore to be able to study them,
at first in the most simple cases, for example, upon bodies the elastic
state of which, previously known, would differ only according to two di-
rections. This would obtain in a body which might be composed by
placing flat plates formed of two heterogeneous substances upon each
other in such a manner thatall the odd plates might be of one substance,
and all the even plates of another, the elasticity in all directions of the
plane of each of them being the same. * But it has appeared to me dif-
ficult to attain this condition, since I have yet found no body the elasti-
city of which was the same in all directions.
- The most simple structure after the preceding would be that ofa body
composed of cylindrical and concentric layers, the nature of which should —
be alternately different for the layers next each other, as is nearly the ©
case in the branch of a tree free from knots. It is evident that the elasti-
city ought to be sensibly the same in every direction of the plane of
a plate cut perpendicularly to the axis of the cylinder, and it ought to
differ greatly from that which is observed in the direction of the axis.
Consequently we shall commence by examining this first case; after
which we shall pass to that in which the elasticity would be different ac-
‘cording to three directions perpendicular to each other, as would take
place in a body composed of flat plates alternately of two different sub-
stances, and the elastic state of which would not be the same, according
to two directions perpendicular to each other. Wood fulfills again
these different conditions; for ina tree of very considerable diameter, the
ligneous layers may be considered as sensibly plane for a small number
of degrees of the circumference; and if we confine ourselves to plates of
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES, 143
a small diameter, cut at a little distance from the surface, we may sup-
pose without any very notable error, at least for the whole of the phe-
nomena, that the experiments have been made on a body the elasticity
of which is not the same, according to three directions rectangular to
each other, since, as is well known, this property does not exist in the
same degree according to the direction of the fibres, according to that
of the radius of the tree, and according to a direction perpendicular to
the fibres and tangential to the ligneous layers.
After these two cases—the most simple that we have been able to
study—we shall pass to the much more complicated phenomena which
regularly crystallized bodies, such as rock crystal and carbonate of lime,
present.
§ II. Analysis of Wood by means of Sonorous Vibrations.
Let us suppose that fig. 1 (Plate III.) represents a cylinder of wood the
annual layers of which are concentric to the circumference ; let B C D E,
fig. 2, be any plane passing through the axis A Y of the cylinder, and let
nm n' be a line normal to this plane: it is obvious that the plates taken
perpendicularly to BC DE, and according to the different directions
1, 2, 3, 4, 5, &c. round nx’, ought to present different phenomena, since
they all will contain the axis of least elasticity 2m! in their plane, and
the resistance to flexure, according to the lines 1, 2, 3, 4, 5, will go on
increasing in proportion as the plates shall more nearly approach being
parallel to the axis of greatest elasticity A Y.
For the plate No. 1, fig. 3, perpendicular to this axis, all being sym-
metrical around the centre, the mode of division consisting of two
lines which intersect each other at right angles, ought to be able to
place itself in all kinds of directions, according as the place of excitation
shall occupy different points of the circumference: this is really the
‘ease; but it is no longer so, for the plate No. 2 inclined 22° 5! to the
preceding. In the latter, the elasticity becoming a little greater in the
direction 7 s contained in the plane B C D E, than in the direction x »/
normal to this plane, this circumstance ought to determine the nodal
lines to place themselves according to these two directions. However,
as this difference is very slight, the system of these two lines may still
be displaced, when the place of excitation is made to vary ; but it will
change its form a little, and it will assume the appearance of two hyper-
bolic branches when it has arrived at 45° from its first position. In the
plate No. 3, inclined 45° to the axis A Y, the difference of the two
extreme elasticities being greater, the system of crossed lines becomes
entirely fixed, or rather it can only move through a few degrees to the
right or left of the position which it assumes in preference; but the
hyperbolic system, the summits a and 6 of which recede more from
each other than in fig. 2, will present the remarkable peculiarity of
144 FELIX SAVART’S RESEARCHES ON THE
being capable of transforming itself into the rectangular system, when
the position of the point put directly in motion is made to vary.
Examining with care the nodal lines in fig. 2, it is found equally that
its two nodal systems can thus change themselves one into the other;
and the same phenomenon is reproduced in the plate No. 4, in which
the values of the extreme elasticities differ still more, and in which the
points a and 6 recede from each other at the same time as the curves
become more straightened. In the plate No. 5, parallel to the axis A Y,
these curves are no longer susceptible of assuming any other position
than that indicated in the figure. Thus, in No. 1, the centres a and }
coalesce into one, and there is only a single figure consisting of two
crossed lines, the system of which can assume any position; these centres
afterwards gradually receding, the modes of division can change them-
selves from one into the other, and at last, when the branches of the
curve are nearly straight lines, the two figures become perfectly fixed.
The existence of these nodal points or centres is, without doubt, a
very remarkable phenomenon, and which it will be important to study
with great care. In order to give an accurate idea of it, I have in fig. 4
indicated by a dotted line the successive modifications which the two
hyperbolic lines assume when the plate is fixed at one of the points a
or b, and the place of excitation moves gradually from e to e! e!’, passing
over a quarter of the circumference of the plate. When the motion is
excited in the vicinity of e", the curves are by the union of their sum-
mits transformed into two straight lines which intersect each other
rectangularly ; and it is obvious that if it had been excited near e'”,
the two branches of the curve would re-appear, but with this peculiarity,
that their transverse axis would take the position assumed by the conju-
gate, when the motion was produced on the other side of e’’.
As to the numbers of the vibrations which correspond to each mode
of division, for the different degrees of inclination of the plates, it will
be seen by examining fig. 3, that, at first equal in No. 1, they go on
continually increasing and receding from each other up to No. 5, which
contains the axis of the cylinder; and it is indeed evident, that the elas-
ticity in the direction perpendicular to the axis remaining the same for
all the plates, whilst that which is perpendicular to this direction goes
on continually increasing, this ought to be, in general, the progress of
the phenomenon.
These experiments were made with plates of oak 8-4 cent. (3°3071
inches) in diameter, and 3™7 (+1456 inch) in thickness: they were
repeated with plates of beech-wood, and analogous results were ob-
tained; only the ratio between the two elasticities not being the same,
the interval between the two sounds of each plate was found to be
greater.
The most general consequence that can be deduced from the pre-
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 145
ceding experiments is, that in wood in which the annual layers are
. hearly cylindrical and concentric, the elasticity is sensibly uniform in alt
the diameters of any section perpendicular to the axis of the branch.
We shall see further on, that plates of carbonate of lime or rock crystal,
cut perpendicularly to the axis, very seldom present this uniformity of
structure for all their diameters, although the modifications which such
plates impress on polarized light appear symmetrical round this same
axis.
In the case which we have just examined, two of the three axes of
elasticity being equal, the phenomena are, as we have just seen, exempt
from any great complication. It is not so when the three axes possess
each a different elasticity: it would then be indispensable to cut, first a
series of plates round each of the axes, then a fourth series round a line
equally inclined with respect to the three axes, and lastly, it would be ne-
cessary again to take aseries round each of the lines which divide equally
into two the angle contained between any two of the axes; and not-
withstanding the great number of results which would be obtained by
this process, the end would. be far from attained, since these different
series would want connexion with each other, and consequently this
process cannot give a clear idea of the whole of the transformations of
the nodal lines. Nevertheless, I shall content myself to follow this
route, which appears to me less complicated than any other, and is
sufficient to render fully evident all the principal peculiarities of this
kind of phenomena.
In order that the relative positions of the lines round which I have
cut the different series of plates of which I have spoken, and the rela-
tions they have to the planes of the ligneous layers, as well as to the
direction of their fibres, may be more easily represented, I shall refer
them all to the edges of a cube A E fig. 5, the face of which AX BZ
I shall suppose is parallel to the ligneous layers, and the edge A X to
the direction of the fibres, which will allow the three edges A X, A Y,
A Z to be considered as being themselves the axes of elasticity. After-
wards I shall indicate the different degrees of inclination of the plates
of each series, on a plane normal to the line round which they are to be
cut; the position and outline of this plane being at the same time re-
ferred to the natural faces of the cube.
But before commencing to describe the phenomena which each of
these series presents, it is indispensable to endeavour to determine the
ratio of the resistance to flexion, in wood, in the direction of each of the
three axes of elasticity: this may be easily done by means of vibrations,
by cutting three small square prismatic rods, of the same dimensions,
- according to the three directions just indicated ; for, the degree of their
- elasticity can be ascertained by comparing the numbers of the vibrations
which they perform, for the same mode of division, knowing besides
Vor, I.—Part I. L
146 : FELIX SAVART’S RESEARCHES ON THE
that, in reference to the transversal motion, the numbers of the vibra-
tions are as the square roots of the resistance to flexion, or, which is
the same thing, that the resistance to flexion is as the square of the
number of oscillations.
Fig. 6 shows the results of an experiment of this kind which was
made upon the same piece of beech-wood from which I cut all the
plates which I shall mention hereafter. In this figure I have, to impress
the mind more strongly, given to these rods directions parallel to the
edges A X, A Y, AZ of the cube fig. 5, and I have supposed that the
faces of the rods are parallel to those of the cube. It is to be remarked
that two sounds may be heard for the same mode of division of each
rod, according as it vibrates in a 6 or ed; but when they are very thin
the difference which exists between them is so slight that it may be
neglected. The inspection of fig. 6 shows, therefore, that the ‘resistance
to flexion is the least in the direction A Z, and is such, that being re-
presented by unity, the resistance in the direction A Y becomes 2°25,
and 16 in the direction of A X. It is evident that the elasticity in any
other direction must be always intermediate to that of the directions we
have just considered.
This being well established, we shall proceed to the pepe in
detail of the different series of plates we have mentioned above.
First Sertes.— Plates taken round the axis AY and perpendicular to
the face A X BZ of the cube.
In the plates of this series, one of the modes of division remains con-
stantly the same. (See figs. 5, 7 and 8.) It consists of two lines crossed
rectangularly, one of which, a y, places itself constantly on the axis A Y
of mean elasticity; but although this system always presents the same
appearance, it is not accompanied, for the different inclinations of the
plates, by the same number of vibrations; this ought to be the case,
since the influence of the axis of greatest elasticity ought to be more
sensible as the plates more nearly approach containing it in their plane:
the sound of this system ought therefore to ascend in proportion as the
plates become more nearly parallel to the plane CY A X. As to the ~
hyperbolic system, it undergoes remarkable transformations, which de-
pend on this circumstance, that the line a y remaining the axis of mean
elasticity in all the plates, the line ed, which is the axis of least elasti-
city in No. 1, transforms itself gradually into that of the greatest elas-
ticity, which is contained in the plane of the plate No.6. It hence
follows that there ought to be a certain degree of inclination for which
the elasticities, according to the two directions ay, e d, ought to be
equal: now, this actually happens with respect to the plate No. 3; and
this equality may be proved by cutting in this plate, in the direction
of ay and its perpendicular, two small rods of the same dimensions: it
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 147
will be seen, on causing them to vibrate in the same mode of trans-
versal motion, that they produce the same sound. It also follows, because
the elasticity in the direction ay is sometimes smaller and sometimes
greater than that which exists in the direction of ed, that the first axis
of the nodal hyperbola ought to change its position to be able to remain
always perpendicular to that of the lines ay, ed, which possess the
greatest elasticity; thus, in Nos. 1 and 2, ed possessing the least elas-
ticity, it becomes the transverse axis of the hyperbola, whilst in Nos. 4,
5 and 6, the elasticity being greater in the direction ed than in that
of a y, the transverse axis of the hyperbola places itself on the latter
line. As the ratio of the two elasticities varies: only gradually, it is
obvious that the modifications impressed on the hyperbolic system ought
in the same manner to be gradual: thus the summits of these curves,
at first separated in No. 1 by a certain distance (which will depend on
the nature of the wood), will approach nearer and nearer, for the fol-
lowing plates, until they coalesce as in No. 3, at a certain degree of
inclination, which was 45° in the experiment to which } now refer, but
which might be a different number of degrees for another kind of wood.
At the point where we have seen that the elasticities are equal in the
direction of the axis, the two Gurves: transform themselves. into ‘two
straight lines which intersect each other rectangularly, after which they
again separate; but their separation is effected in a direction perpen-
dicular to that of their coalescence. The sounds of the hyperbolic
system follow nearly the same’ course as those of the system of crossed
lines; that is to say, they become higher in proportion as the plates
more nearly approach being parallel to the axis of greatest elasticity;
but it deserves to be remarked, that the plate No. 3, for which'the elas+
ticity is the same in the two directions a y, ed, is that between the two
sounds {of which there is the greatest interval: this’ evidently depends
on the elasticity in the two directions: y, cd being very different from
that which exists in the other directions of the plate.
Lastly, it is to be remarked that, in the four first plates, the sound of
the hyperbolic system is sharper than that of the system of crossed
lines, and that it is the contrary for the plate No. 6, which renders it
necessary that there should be between No. 4 and No. 6 a plate, the
sounds of which are equal, which in the present case is exemplified in
No. 5, although its two modes of division differ greatly from each other.
There is another thing remarkable in this plate; its two modes of di-
vision can transform themselves gradually into éach other by changing
the position of the place of excitation, so that the two points e and ec’
| becoming two nodal centres, are in every respect. in the conditions
indicated by fig. 4.
_ The interval included between the grayest and the sharpest sounds
of this series was an augmented sixth.
L2
148 FELIX SAVART’S RESEARCHES ON THE
It is almost useless to observe that the plates taken in the directions
I, II, II, inclined on the other side of the axis A X the same number
of degrees as the plates 1, 2, 3, would present exactly the same phzeno-
mena as these latter. This observation being equally applicable to the
following series, we shall not mention it again.
Seconp Sertes—Plates taken round the axis A Z of least elasticity
and perpendicular to the plane CY AX; figs. 9 and 10.
As in the preceding case, one of the nodal systems of the plates of
this series consists of two lines crossed rectangularly, one of which, a z,
corresponds with the axis A Z; whence it follows that the second may
be considered as the projection of the two other axes on the plane of
the plate, which, whatever its inclination may be, ought consequently
to possess a greater elasticity in the direction fg than in the direction
az: thus the hyperbolic system of this series cannot present the trans-
formations which we saw in the preceding series, where ed, fig. 8, possesses
sometimes a less, at other times a greater elasticity than that of ay.
In the present case, a@ z remaining constantly the axis of least elasticity,
the resistance to flexion in the direction fg goes on gradually increasing
from the plate No. 1 to the plate No. 6 parallel to the plane A X BZ,
and the branches of the hyperbola straighten themselves in proportion as
the plates more nearly approach this last position. As to the sounds which
correspond to each of these nodal systems, it is observed that they ascend
gradually from No. 1 to No. 6, and that the sound of the hyperbolic
system is sharper in a part of the series than that of the system of crossed
lines, whilst they become graver in the other part. There is therefore a
certain inclination for which the sounds of the two systems ought to be
equal; and this evidently would have taken place in the present expe-
riment for a plate intermediate to No. 4.and No. 5.
The interval between the gravest and the sharpest sound of each
series was an augmented fifth.
TuirD SertEes.—Plates taken round the axis A X of greatest elasticity,
and perpendicular to the plane A Y DZ; figs. 11 and 12.
The elastic state of these plates cannot present such remarkable dif-
ferences as those we have observed in the preceding series; for, being
all cut round the axis of greatest elasticity, they can only contain in
their plane that of least or that of mean elasticity, or lastly, those in-
termediate between these limits, which do not vary greatly from each
other. Thus it is seen that their modes of division differ very little from
each other, and that the sounds which correspond to them present
rather slight differences, although they go on ascending in proportion
as the plates more nearly approach containing the axis of mean elas-
ticity in their plane. Here, as in the other series, one of the nodal
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 149
systems consists of two lines crossed rectangularly, one of which, a 2,
places itself always on the axis of greatest elasticity, and this line serves
as the second axis to the hyperbolic curves which compose the noda{
system. Doubtlessly these curves are not entirely similar in the different
plates; but Ihave not beenable to perceive any very remarkable difference
between them, unless that it appears that their summits gradually ap-
proach bya very small quantity, in proportion as the plates more nearly
approach containing the intermediate axis in their plane.
Fourtu Series.—Plates cut round the diagonal AD, and perpendi-
cular to the plane BC Y Z; figs. 13 and 14.
These plates present much more complicated phenomena than those
we have hitherto observed. Except for the first and the last, neither
of the two nodal systems consists of lines crossed rectangularly, which
shows that this kind of acoustic figure can only occur on plates which
contain at least one of the axes of elasticity in their plane, since Nos.
2, 3, 4, 5, which are inclined to the three axes, present only hyperbolic
lines, whilst No. 1, which contains two of the axes of elasticity, and
No. 6, which contains only one, are susceptible of assuming this kind
of division.
- In this series, neither of the modes of division remains constantly the
same for the different degrees of inclination of the plates: setting out
from the plate No. 1, one of the systems gradually passes from two
crossed lines to two hyperbolic branches, which are nearly transformed
into parallel straight lines in No. 6; on the contrary, the other system
appears in No. 1 under the form of two hyperbolic curves, the summits
of which approach nearer and nearer until they coalesce in No. 6, where
they assume the form of two straight lines which cut each other at
right angles and this contrary course in the modifications of the two
systems is such, that there is a certain inclination (No.3) for which the
two modes of division are the same, although the sounds which cor-
respond to them are very different.
As in the preceding series, and for the same reasons, the sound of
each nodal system goes on always ascending in proportion as the plate
more nearly approaches containing the axis of greatest elasticity in its
plane.
Firru Series.—Plates cut round the diagonal A E, and perpendicular
to the planer s t; figs. 5.
2 Bising all the plates which may be cut round the diagonal A E of
Paice cube fig. 5, there are three each of which contains one of the axes
vof elasticity, and which consequently we have already had occasion to
observe; thus the plate No. 3, fig. 8, which passes through the diagonal
“AB, and through the edge A Y, contains the diagonal A E in its
150 FELIX SAVART’S RESEARCHES ON THE |
plane; also, the plate No. 4, fig. 10, which passes through one of the
diagonals X Y or A C, and which is perpendicular to the plane C Y A X,
contains also A E in its plane; and lastly, the plate No. 3 of fig. 12,
parallel to the plane ADE X, is cireumstanced in the same manner.
Thus, if rst, fig. 15, is a plane perpendicular to the diagonal A E, and
if the lines 1, 3, 5 indicate the directions of the three plates we have
just spoken of, in order to become acquainted with the progress of the
transformations which connect the modes of division of these plates
together, it will be sufficient to take round A E, the projection of which
is in c, a few other plates such as 2, 4,6. The Nos. 1, 2, 3 of fig. 16
represent this series thus completed, and the dotted line ae indicates
in all the direction of the diagonal of the cube.
The nodal system represented by the unbroken lines consists, for
No. 1, of two crossed nodal lines, one of which, ay, places itself upon
the axis A Y, and the other in a perpendicular direction; it transforms
itself in No. 2 into hyperbolic curves, which by the approximation: of
their summits again become straight lines in No. 3, which contains the
axis A Y of greatest elasticity: these curves afterwards recede again,
No. 4, and in the same direction as No. 2; they then change a third
time into straight lines in No. 5, which contains the axis A Z of least
elasticity ; and lastly, they reassume the appearance of two mypesidfic
branches in No. 6,
The transformations of the dotted system are much less saeglicalials
since it appears as two straight lines crossed rectangularly in No.1,
and afterwards only changes into two hyperbolic branches, which con-
tinue to become straighter until a certain limit, which appears to be at
No. 3, and the summits of which afterwards approach each other,
Nos. 5 and 6, in order to coalesce again in No, 1.
As to the general course observed by the sounds of the two nodal sy-
stems, it is very simple, and it was easy to determine it previously. Thus,
the plate No. 5, containing in its plane the axis A Z of least elasticity, the
two gravest sounds of the entire series is heard; these sounds afterwards
gradually rise until No. 3, which contains the axis AX of greatest
elasticity ; after which they redescend by degrees in Nos. 2 and 1, (the
latter contains the axis A Y of intermediate elasticity in its plane,) and
they return at last to their point of departure in the plates Nos. 6 and 5,
The transformations of the nodal lines of this series, by establishing
a link between the three series of plates cut round the axes, makes us
conceive the possibility of arriving at the determination of nodal sur-
faces, which we might suppose to exist within bodies having’three rect-
angular axes of elasticity, and the knowledge of which might enable
us to determine, @ priori, the modes of division of a circular plate in-
clined in any manner with respect to these axes. But it is obvious, that
to attempt such an investigation it would be necessary to base it on
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 151
experiments made with a substance the three axes of which shall be
accurately perpendicular to each other, which is not entirely the case
in wood.
It would now remain for us to examine two other series of plates,
one taken round the diagonal A B, and the other round the diagonal
AC; but as it is evident that the arrangements of nodal lines which
they would present would differ very little from those of the fourth
series, we may dispense with their examination.
Such are, in general, the phenomena which are observed in bodies
which, like that we have just examined, possess three axes of elasticity:
collected into a few propositions, the results we have obtained are re-
ducible to the following general data. —
Ist. When one of the axes of elasticity occurs in the plane of the
plate, one of the nodal figures always consists of two straight lines, which
intersect each other at right angles, and one of which invariably places
itself in the exact direction of this axis; the other figure is then formed
by two curves which resemble the branches of a hyperbola.
2nd. When the plate contains neither of the axes in its plane, the
two nodal figures are constantly hyperbolic curves; straight lines never
enter into their composition.
3rd. The numbers of vibrations which accompany each mode of di-
vision are, in general, higher as the inclination of the plane to the axis
of greatest elasticity becomes less.
4th. The plate which gives the sharpest sound, or which is suscep-
tible of producing the greatest number of vibrations, is that which
contains in its plane the axis of greatest elasticity and that of mean
elasticity.
5th. The plate which is perpendicular to the axis of greatest elasti-
city is that from which the gravest sound is obtained, or which is sus-
ceptible of producing the least number of vibrations.
6th. When one of the axes is in the plane of the plate, and the elas-
ticity in the direction perpendicular to this axis is equal to that which
itself possesses, the two nodal systems are similar; they each consist of
two straight lines which intersect each other rectangularly, and they
oceupy positions 45° from each other. In a body which possesses three
unequal axes of elasticity there are only two planes which possess this
property.
7th. The transverse axis of the nodal curves always occurs in the di-
rection of the least resistance to flexion; it hence follows, that when in
a series of plates this axis places itself in the direction at first occupied
by the conjugate axis, it is because the elasticity in this direction has
become relatively less than in the other.
_ 8th. In a body which possesses three unequal axes of elasticity, there
“are four planes in which the elasticity is so distributed that the two
a
152 SAVART ON THE ELASTICITY OF CRYSTALLIZED BODIES.
sounds of the plates parallel to these planes become equal, and the two
modes of division gradually transform themselves into each other, by
turning round two fixed points, which, for this reason, I have called no-
dal centres.
9th. The numbers of vibrations are only indirectly connected with
the modes of division, since two similar nodal figures, as in No. 3, fig. 8,
and in No. 3, fig. 14, are accompanied by very different sounds ; whilst,
on the other side, the same sounds are produced on the occurrence of
very different figures, as is the case for No. 5 of fig. 8.
10th. Lastly, a more general consequence which may be deduced
from the different facts we have just examined is, that when a circular
plate does not possess the same properties in every direction, or, in other
words, when the parts of which it consists are not symmetrically arranged
round its centre, the modes of division of which it is susceptible assume
positions determined by the peculiar structure of the body; and that
each mode of division, considered separately, may always, subject how-
ever to alternations more or less considerable, establish themselves in
two positions equally determined, so that it may be said that, in hetero-
geneous circular plates, all the modes of division are double.
By the aid of these data, which are no doubt still very few and im-
perfect, a notion may be formed, to a certain point, of the elastic state
of crystallized bodies, by submitting them to the same mode of investi-
gation: this is what we have attempted for rock crystal, in a series of
experiments which will be the subject of § 111. of this Memoir.
‘
153
ArTicxeE VIII.
Experiments on the Essential Oil of the Spirea Ulmaria, or
Meadow-Sweet ; by Dr. Lowie, Professor of Chemistry at
Lurich*.
From J. C. Poggendorff’s Annalen der Physik und Chemie; Berlin,
Second Series, vol. v. p. 596.
Wuusr by the examination of plants and vegetable matters we
have acquired the knowledge of a great number of oxyacids with
compound radicals, with the exception of prussic acid no such hydracid
has been shown to exist in organic nature; and of hydracids with ter-
nary radicals, if we except the sulphocyanic acid, we have not the
slightest knowledge.
The constancy of the phenomena which oil of bitter almonds pre-
sents, have not only led to the positive knowledge of the existence of
ternary radicals, but also to the fact that oxyacids exist with ternary
bases containing oxygen.
By means of the experiments made with the essential oil of the blos-
soms of the Spirea Ulmaria, described in the following treatise, the first
hydracid with a ternary radical in organic nature has been discovered
in a most extraordinary manner, and they give every reason to hope
that the radical of the same may also be isolated.
The reader must excuse the circumstances that the experiments are not
carried further, and that some of the most important appearances when
remarked have not been further pursued, as for all the experiments,
there was only a very small quantity of material at the disposal of the
experimenter.
If also, on account of the small quantity of the oil which could be
subjected to research, each experiment was conducted only on a small
seale, especially as regards the analysis, and could only be seldom re-
peated, the coincidence of each separate experiment may perhaps in
part supply the want of repetition. Should however the analytical re-
sults experience any small change by later repeated experiments, we
may nevertheless be sure that the facts themselves of which this Memoir
treats will lose nothing in importance.
By means of this communication the attention of chemists may be
drawn to the oil of the Spirea, so that not only a repetition of these
experiments, but also a further extension of them may be expected with
_ certainty from other chemists.
° [The Editor is indebted for the translation of this Paper to E.Solly, jun., Esq. ]
154 DR. LOWIG ON THE ESSENTIAL OIL
M. Pagenstuher, an apothecary in Berne, had already drawn attention
to the oil and distilled water of the blossoms of Spirea Ulmaria in a
treatise which may be found in Buchner’s Repertorium, vol. xL1x. p. 337.
He there describes exactly almost all the combinations which are the
subject of this Memoir; and had he made analyses of the elements with
only a few substances, the real nature, not only of the oil itself, but also
several decompositions and recompositions which it experiences would
not then have escaped him.
M. Pagenstuher had the kindness to give me the oil for all the in-
vestigations, and also to communicate to me his observations made
up to that time. All his experiments which were of any importance
on the present subject are incorporated into this Memoir, so that in
many respects the present work may be considered as undertaken eon-
jointly with M. Pagenstuher. To facilitate the general view of the fol-
lowing experiments, a few of the leading results may be first stated.
The oil of the blossoms of the SpireaUlmaria is a hydracid; it con-
sists of one eq. of a radical = C12 HS O4, and one eq. of hydrogen,
which uniting with the radical forms an acid. If the hydrogen, which
by uniting with the radical forms the acid, be oxidized by nitric acid, 4
additional eqs. of oxygen are taken up by the radical, thus forming the
oxyacid of the same radical. Instead of 1 eq. of hydrogen, the radical
can unite with 1 eq. of chlorine, bromine, iodine, or even of a metal.
These latter combinations are also formed when the hydracid is made
to act on metallic oxides. With ammonia, on the contrary, the hydracid
unites without undergoing any change. From these combinations the
following compounds result:
C12 H5 04+4 04
(C12 H5 O44 H) + NH3 or ammonia.
The radical is designated by the name Spirzoyl, or for the conve-
nience of shortness Spiroil. Another name would have been chosen for
it had not a similar nomenclature been already applied to another sub-
stance nearly allied to it. It is always doubtful policy to derive the
name of a vegetable principle from the plant in whielf it is first disco-
vered, for generally with great probability the same body may be found
in other plants. Names which designate any principal peculiarity of the
substance are therefore in such cases always preferable. One of the pe-
culiarities of spiroil is its property of forming yellow compounds with
oxygen, and withthe metals, alkalies, and earths; a name therefore which
had reference to this quality would have been very suitable. A name
OF THE MEADOW-SWEET. 155
however, is only a sign for a certain expression, and thus considered it is
perfectly indifferent what name may be chosen for any substance.
Hydrospiroilie Acid.
The fluid oil of the blossoms of the Spirea Ulmaria is hydrospiroilic
acid. This may be obtained by distilling the flowers with water ; about
as much water is to be distilled off as was originally employed.
‘The product of the distillation is however subjected to a redistillation
till about 3th is come over in the receiver. A concentrated aqueous so-
lution of the oil is thus obtained, and the oil itself, though only in very
minute quantities. The oil is heavier than water, is of a light yellow
colour, and possesses the odour of the blossoms in a very great degree.
It mixes in all proportions with alcohol and zther, and is slightly so-
luble in water. It causes a burning sensation on the tongue. The fumes
which come over during the distillation of the oil first render litmus-
paper green, and then bleach it. The aqueous solution of the oil first of
all slightly reddens tincture of litmus, and then deprives it of its colour
excepting a greenish shade. It is inflammable, and burns with a shining
smoky flame. If the oil be passed through a red-hot tube containing
pieces of iron, neither ammonia nor prussic acid is obtained nor can the
formation of any sulphuret of iron be detected. The oil does not ex-
perience any change either in dry or moist oxygen gas ; it volatilizes
unchanged. It solidifies at a temperature of —20°*. Its boiling-point is
about + 85°*, when it evaporates entirely without leaving any residue.
With the bases of salts, namely, with the alkalies and alkaline earths,
it easily combines, forming insoluble or difficultly soluble compounds.
Concentrated sulphuric acid converts the oil into a black carbona-
ceous mass. Chlorine and bromine decompose it instantaneously, hy-
drochloric or hydrobromic acid and chloride or bromide of spiroil being
formed. Nitric acid, if not too concentrated, immediately forms spiroilic
acid; if however the acid be very concentrated and fuming, it imme-
diately changes it into a yellow, very volatile, bitter-tasting compound,
having the appearance of butter.
The experiments on the composition of the anhydrous oil, as well as the
other compounds, were made in the usual manner with oxide of copper.
0°290 grms. of the oil gave 0°694 carb. acid 191-89 carbon
OES water 16°10 hydrogen;
_ according to which 290 parts of the oil contain
SCOR ON ses tey <riers 191°89 orin 100 parts 66°17
Fiydrogen ... 02,0. 16°10 ————___ 5°55
Oxygen os. .s..--0 SLOL — 28:28
290°00 100:00
Lyi
.
Pelee . * Probably Centigrade,—Transuaton.
156 DR. LOWIG ON THE ESSENTIAL OIL
from whence we may deduce the following eq.
in 100 parts
12 eqs. Carbon ~ = “73°56 = 66°92
6 — Hydrogen = 600 = 835
4.— Oxygen = 32:00 = 27°73
1 Hydrospiroilic acid 111°56 100°00
The combination of the oil with copper was also subjected to analysis.
This compound was obtained by agitating together an aqueous solution
of the oil with freshly prepared quite pure hydrated oxide of copper,
taking care that the oil should be in excess; and the green compound
thus obtained was dried at + 160°. At this temperature the combi-
nation is not decomposed, which is evident, as the oil may again be ob-
tained unaltered on the addition of an acid. By other means, by dou-
ble decomposition for instance, the combination with copper may be
obtained, but not quite pure, as it then contains slight traces of the acid
which was united with the copper, even if excess of alkali be employed
as a precipitant.
0'174 grm of the compound with copper yielded 0°324 c. a. 89°58 carbon
0°174 0:054 water 5°99 hydr.
Also by burning the cupreous combination in contact with the air, 0°130
of the compound yielded
0:03719 oxide of copper 29°68 copper.
"
Ifnow in the ecupreous combination the copper is considered to have
been in the metallic state we obtain
Carbon = 89°58 or 5148
Hydrogen = 5:99 — 3°44
Oxygen = 38°71. — 22:20
Copper = 39°72 — 22°88
‘ 17400 100°00
which in eq.
PQS: dl NUMerte sed sretussescss sont Om Ol tao k
Gr Enydroeens. cs cceseesa sees 500 — 3°51
Ay mm ORV OOM: 50s sc canis weneee <tc 32:00 — 22°51
1 — ,Copper ....:0ssnansves teen YO — , B2O7
1 eq. Spiroilide of copper......142°26 100°00
These experiments confirm the truth of the above-mentioned view,
that the oil is a hydracid with a ternary base, and they likewise show —
that the action of this hydracid with metals is exactly the same as that
of those which were before known.
This view receives still further confirmation by the fact that when
.
OF THE MEADOW-SWEET. 157
chlorine is passed over one of the metallic combinations, as spiroilide of
copper or spiroilide of silver, chloride of copper or silver, and chloride
of spiroil are formed without the slightest trace of muriatic acid.
The most striking proof, however, that the oil is really a hydracid is,
that when potassium is brought into contact with the oil over mercury and
gently warmed, hydrogen is evolved, spiroilide of potassium being formed,
Srom which latter the oil may again be obtained, possessed of all its ori-
ginal properties, by the action of muriatic acid.
The action of the oil and potassium, which at common temperatures
goes on but slowly, is by a very gentle heat so much increased, that
during the evolution of the hydrogen the combination of the spiroil and
potassium is attended with the evolution of heat and light. At the same
time not the slightest trace of carbon or of any carbonaceous matter is
deposited, and the hydrogen which is evolved is quite pure. If the oil
which is employed for these experiments be not quite free from water,
evolution of hydrogen takes place as soon as it comes into contact with
the potassium ; this however ceases (almost entirely) in a few moments:
if however the apparatus be now gently warmed, which may be done
by gradually bringing near a glowing coal, the evolution of gas begins
again in great quantity and with the same violence as when the anhy-
drous oil was employed.
Hydrospiroilate of Ammonia.
If a concentrated solution of ammonia is poured upon pure hydrospi-
roilic acid, the fluid mixture after a few seconds is converted into a solid
mass of hydrospiroilate of ammonia, giving out heat and undergoing a
considerable increase of bulk during the action: it may be freed from
water and excess of acid by washing with alcohol. It possesses a weak
aromatic smell resembling a rose, is tasteless, and has a yellow colour.
The compound is almost insoluble in water, which nevertheless when
left for some time in contact with it, acquires a yellow colour. In com-
mon cold spirit of wine the hydrospiroilate of ammonia is only slightly
soluble, but on the contrary it is dissolved in great quantities both in
hot and cold pure alcohol. If the boiling solution be allowed to cool,
hydrospiroilate of ammonia is obtained in transparent delicate tufts of
acicular crystals of alight yellow colour. If it be preserved in close
vessels in a moist state it is decomposed ; after a short time it becomes
_ gradually black, then semifluid, ammonia is evolved, and an exceedingly
strong penetrating odour of oil of roses is perceptible.
At the boiling-point of water, hydrospiroilate of ammonia undergoes
no change.
_ At + 115° it is fluid, melting like wax; heated a few eae above
its boiling-point it volatilizes in the form of a yellow vapour without
Teaving“any residue and without undergoing any alteration. If solution
158 DR. LOWIG ON THE ESSENTIAL OIL
of potash or soda be poured over this salt, the ammoniacal odour is not
immediately developed, but. becomes so after continued contact or the
application of heat. This circumstance might lead to the supposition,
that in this compound there is a similar relation between the acid and
the alkali as in the cyanate of ammonia.
At the same time it must be observed, that acids immediately decom-
pose this compound, the oil being deposited, undecomposed, and a cor-
responding salt of ammonia formed. 0°213grm. of hydrospiroilate_of
ammonia obtained in crystals by evaporating the alcoholic solution
was decomposed by dilute muriatic acid; the solution thus obtained was
evaporated to dryness in a water-bath, and the remaining neutral sa-
line mass again dissolved in water. By precipitation with nitrate of sil-
ver, 0°239grm. of chloride of silver were obtained; as these correspond
to 0°0288 of ammonia, the above 0°213grm. consist of
Ammonia ......... 0°0288, or in 100 parts 13°52
Hydrospiroilic acid 0°1850 86°48
0°2138 100-00
1 equivalent ammonia = 1718 or 13°38
1 hydrospiroilic acid = 11156 — 8662
1 eq. hydrospiroilate of ammonia 128°74 100°00
Spiroilide of Potassium.
The spiroilide of potassium may be obtained either by gently heat-
ing together potassium and hydrospiroilic acid, hydrogen being evolved,
or by bringing together either the pure or the watery hydrospiroilic acid
and solution of potash. Spiroilide of potassium is difficulty soluble in
water.
If the aqueous solution be slowly evaporated, small prismatic straw-
coloured crystals are obtained. Left in contact with the air it soon
decomposes, absorbing moisture and carbonic acid, like the hydro-
spiroilate of ammonia. It may nevertheless be kept unaltered for a long
time in close vessels. The smell resembling that of roses is likewise
perceptible during the decomposition of this substance; at the end,
carbonate of potash remains.
1 ex. potassium 39:20 26°87 24°93
1 eq. spiroil 110°56 73°13 75°07
_ 1 eq. spiroilide potassium 149°76 100:00 100:00
Spiroilides of Sodium, Calcium and Barium. These possess similar
properties to the spiroilide of potassium, but the two latter compounds
are still less soluble in water.
Spiroilide of Magnesium may be obtained by agitating together the
OF THE MEADOW-SWEET. © 159
watery hydrospiroilic acid and hydrate of magnesia. It appears as a
light yellow and almost insoluble powder.
Protospiroilide of Iron. The aqueous solution of hydrospiroilic acid
has no action on protochloride of iron; on the addition of ammonia
however a deep violet blue precipitate falls.
Sesquispiroilide of Iron. Sesquichloride of iron immediately changes
the colour of the aqueous solution of hydrospiroilic acid to a fine deep
cherry-red colour, without any precipitate.
If this fluid be exposed to the air it loses its red colour in a short time,
and a pure solution of sesquichloride of iron remains, in which a fresh
addition of hydrospiroilic acid again causes the cherry-red colour to
appear.
Subspiroilide of Copper. ydrospiroilic acid has no action on the
subehloride of copper ; a slight addition of ammonia however causes
a light brown precipitate in this mixture.
Protospiroilide of Copper. This compound is best obtained by agi-
tating together an aqueous solution of hydrospiroilic acid and newly
prepared hydrated oxide of copper. This latter immediately loses its
blue colour and becomes green.
If solutions of sulphate of copper and spiroilide of potassium be
mixed, a voluminous precipitate falls, which however is but slowly depo-
sited and possesses a distinct crystalline texture.
Spiroilide of Zinc. When oxide of zinc is agitated with the aqueous
solution of hydrospiroilic acid, it very soon absorbs the acid from the
water, which latter acquires a yellow colour. By evaporation under
the airpump, a yellow pulverulent substance is obtained. The aque-
ous solution of spiroilide of zinc is coloured cherry-red ,by sesquichlo-
ride of iron.
_ Spiroilide of Lead. When pure oxide of lead is brought into contact
with hydrospiroilic acid no spiroilide of lead is formed. Newly pre-
pared hydrated oxide of lead however, when left for some time in con
tact with the aqueous acid, becomes converted into a light yellow pow-
der, consisting of small shining laminz of spiroilide of lead.
_ Spiroilide of Mercury. The aqueous solution of the acid has no ac-
tion on red oxide of mercury when they are left together in close ves-
sels, even though frequently agitated.
_ Spiroilide of mercury is however obtained when a concentrated solu-
tion of corrosive sublimate is poured over hydrospiroilate of ammonia.
A pale straw-coloured flocky voluminous precipitate is formed.
_ Spiroilide of Silver. Oxide of silver is partially dissolved by the
‘aqueous solution of hydrospiroilie acid.
_ The solution is of a yellow colour, and has a bitter metallic taste. By
evaporation in vacuo a brownish black residue is obtained, which in-
flames with detonation in the candle, leaving behind. metallic silver,
160 DR. LOWIG ON THE ESSENTIAL OIL
The undissolved portion of the oxide, which has also acquired a brown-
ish black colour, possesses the same property.
_ The greater number of the compounds of the metals with spiroil
may be obtained by double affinity, but for this purpose the spiroilic
combinations must be difficultly soluble or insoluble, and very concen-
trated solutions of easily soluble salts must be employed. For this rea-
son, in order to obtain the combination with lime, solution of chloride
of calcium is employed; for the combination with zinc, acetate of zinc;
for the magnesian compound, chloride of magnesium; and for the com-
pounds with iron, the proto- and the sesqui-chloride of iron. The best
combination of spiroil to employ is the hydrospiroilate of ammonia,
over which the concentrated solution of the salt is to be poured. The
spiroilide of barium, which is best obtained by saturating baryta water
with the acid, may be advantageously employed in the state of a solu-
tion for the preparation of several of the compounds of spiroil. The
compounds as obtained by double decomposition are seldom erystalline,
but are obtained almost always as a fine and soft powder.
Spiroilic Acid. .
If hydrospiroilic acid be gently and carefully heated with nitric acid
not too concentrated, and care be taken that the acid be not used in
excess, the oil is converted under evolution of nitrous fumes into a so-
lid crystalline body; the substance thus obtained is spiroilic acid.
If the gas which is evolved during this operation be conducted into
a solution of chloride of barium mixed with ammonia, not the slightest
trace of carbonate of barytes will be formed.
-. The acid is nearly devoid of odour: its taste is at first not strik-
ing ; afterwards however much irritation in the throat, and a strong in-
élination to cough are experienced. Spiroilic acid is fusible, and shows
strong inclination to crystallize, especially on returning to the solid state
after having been heated. In close vessels it may be sublimed; never-
theless by this operation the greater part is decomposed, leaving behind
a carbonaceous mass.
In the anhydrous state, as it is obtained by fusion, spiroilic acid is of a
pale yellow colour, if however it be exposed to the air it deliquesces and
becomes of a deep yellow colour. It is easily soluble in aleohol and ether;
only slightly so however inwater. The solutions stain the skin and nails
permanently yellow. Litmus-paper is stained deep yellow; no redden-
ing effect can however be observed. If the alcoholic solution of the
spiroilic acid be left to spontaneous evaporation, the acid is obtained in
delicate transparent prisms of a golden yellow colour.
Ist,’ 0°190 fused spiroilic acid gave 0°350 carbon = 96°77 car.
0°190 ditto gave 0°060 water=6°66 hydr.
Qndly, 0°243 ditto gave0°450 carb = 124°42 carb. 0'0759=8'33 hyd.
OF THE MEADOW-SWEET. 161
From these proportions we obtain the following for 100 parts: —
. Il.
ATO Disasiegs sendecsdy pst wiwqesens evar GOP AMeaenas 51°18
PEON OOD by snc abies tnnne ssnontesnyt (mao nmatat 3°43
na esc emees nasjonee 4: <5 ge MOET cue 45°39
100°00 100-00
or reckoned in equivalents,—
12 eqs. carbon ......... T3850 51°58
5 — hydrogen ...... SOOM Res 3°50
8 — oxygen......... 64:00 peisse cs 44°92
1 eq. spiroilic acid 142°56 100:00
From these experiments we may deduce, that in the moment that the
one equivalent of hydrogen of the hydrospiroilic acid is oxidized, four
more equivalents of oxygen are taken up by the radical. This likewise
explains the formation of so large a portion of nitrous acid, even when
a very small quantity only of the oil is employed.
It appeared probable that during the oxidation a portion of nitric
or nitrous acid was absorbed by the radical, and this opinion was sup-
ported by the fact, that spiroilic acid stains the skin and nails perma-
nently yellow,—a property which is likewise possessed by the spiroilide
of potassium and several other metallic spiroilides; several experiments
were undertaken to detect the nitrogen or the acid, but unsuccessfully
with regard to either.
If spiroilic acid be slightly heated with potassium over mercury, a
most violent evolution of heat and light suddenly takes place, by which
the vessel isalways broken with great violence. Even should excess of po-
tassium be employed in this experiment, only a portion of the spiroilic
acid is decomposed; a porous carbon is deposited, and a mixture of
spiroilide of potassium and carbonate of potash is formed.
The pure alkalies unite very readily with spiroilic acid, forming yel-
low compounds, by evaporating the aqueous solutions of which small
yellow crystals may be obtained.
If spiroilic acid be dissolved in ether, and the solution agitated with
solutions of potash or soda, the ether is immediately abstracted from the
acid. The alkaline salts of spiroilic acid are also soluble in alcohol.
If ammonia be saturated with spiroilic acid, a deep blood-red solution
is obtained. If this be evaporated to dryness a yellow residue remains,
which if rubbed with caustic alkali immediately develops a strong am-
moniacal odour. If spiroilate of ammonia be subjected to a high tem-
perature in close vessels it is decomposed, some ammonia is evolved, and
_ an oily body comes over, the exact nature of which has not been deter-
mined on account of the minuteness of the quantity.
Vor. I.—Parr I. M
162 DR. LOWIG- ON THE ESSENTIAL OIL
The aqueous solution of spiroilate of soda gives with acetate of Tead
a yellow, and with salts of copper a green, precipitate.
Sesquichromate of iron is not precipitated by spiroilate of soda, but
is coloured deep cherry-red by it, as well as by the spiroilide.
If the salts of spiroilic acid are heated in contact with the air, they
detonate briskly, leaving behind either a pure or carbonated fhane; and
a soft powdery carbon. 3
If spiroilic acid be mixed with an easily jalesminailile substance, as sul-
phur, the mixture detonates when heated.
Fuming nitric acid acts very violently upon spiroilic acid fumes of ni-
trousacid are immediately evolved, whilst a yellow semifluid massis formed,
which solidifies only after several days. Thisyellowsubstance has an in-
tensely bitter taste, and colours the saliva, skin, and nails, &c. deep yellow;
it is fusible and may be distilled, and possesses in a striking degree the
smell of fresh butter; no oxalic acid is formed. Submitted to distil-
lation with water, it distils over undecomposed with the water, partially
dissolved and partly as a yellow powder.
If the residue of the aqueous solution after the yellow body has gone
over be slowly evaporated, transparent colourless prismatic crystals are
obtained, the nature of which requires further investigation.
An analysis of this substance, which appeared to possess acid proper-
ties, was several times commenced; but even by the most careful appli-
cation of heat, the oxide of copper was always projected into the tube
containing the chloride of calcium, whilst part of the substance was often
conducted undecomposed into the potash apparatus. Nevertheless the
determination of the carbonic acid has several times been accomplished:
from the data thus obtained, this yellow substance must be very rich in
oxygen.
Chloride of Spiroil.
Chloride of spiroil may be obtained by decomposing hydrospiroilie
acid by means of chlorine. In a suitable apparatus and without the ap-
plication of heat, dry chlorine gas was passed over the anhydrous acid;
evolution of muriatic acid immediately commenced : if the chlorine be
evolved but slowly, only a slight elevation of temperature takes place.
Chlorine is to be passed through this solution so long as fumes of mu-
riatic acid are evolved: the hydrospiroilic acid isentirely converted into
a white crystalline mass.
If however the oil is become solid, the chlorine apparatus must be
moved, and the chloride of spiroil which has been formed must be sub-
limed by the lowest possible heat.
The most beautiful crystalline plates of a dazzling whiteness are ob-
tained,which melt at a very low heat, and, as has been before remarked
may easily be sublimed.
- OF THE MEADOW-SWEET. ri 163
- If chloride of spiroil be briskly heated, the melted mass gradually be~
comes darker, and a slight carbonaceous residue remains.
No other products besides muriatic acid and chloride of spiroil are
formed.
' Pure chloride of spiroil possesses a peculiar and somewhat aromatic
edour, which nevertheless has much similarity to the smell of diluted
prussic acid. Its boiling point does not appear to exceed that of water.
It is inflammable, and burns with a greenish sooty flame.
' It is quite insoluble in water.
' When it is boiled with water it evaporates entirely; by this operation
not the slightest trace of muriatic acid is formed. Neither dry nor
moist air has any action on it. Chloride of spiroil is easily soluble in
ether and alcohol. '
The alcoholic solution gives with acetate of copper a greenish yel-
low precipitate; salts of lead are precipitated yellow. Baryta water im-
mediately separates chloride of spiroil from the alcoholic solution, and
uniting with it a yellow precipitate falls.
© Chloride of spiroil forms yellow, neutral, difficultly soluble conipounds
with the alkalies. The salts of iron are also coloured blueish black by
the same.
«In the combinations of chloride of spiroil with the metallic oxides and
the alkalies, it appears to combine unaltered, as it may again be obtain-
ed unaltered when these compounds are decomposed by an acid.
Nitrate of silver causes a scarcely perceptible milkiness in the filtered
solutions of the alkaline compounds which have been decomposed by
nitric acid. 0-780 grm. of chloride of spiroil treated in the above-men-
tioned way gave 0:09 grm. chloride of silver, therefore searcely 0-02 grm.
chlorine. This small amount of chlorine was no doubt due to the pre-
sence of muriatic acid, as from 0°628 grm. hydrospiroilic acid 0°795
grm. of chloride of spiroil was obtained; therefore at least 0°157 grm.
chlorine must have been taken up.
If chloride of spiroil be melted with potassium by the iplloation of
avery gentle heat, violent evolution of heat and light suddenly takes
place. A portion of the chloride of spiroil is decomposed thereby; car-
bon is deposited, whilst another portion unites with the potash which
has been formed.’ If the remaining mass be dissolved in water, and the so-
lution decomposed by nitric acid, pure chloride of spiroil is precipitated.
| Tf this same fluid be filtered, nitrate of silver gives a large precipitate of
chloride of silver. If the neutral solution of the chlorospiroilide be
slowly evaporated, yellow tasteless crystals are obtained which are inso-
} ublein alcohol. If these crystals be heated ina platinum crucible, heat
light are evolved long before the crucible is red hot. The mass
‘Dlackens and by the continued application of heat is converted into
‘pure chloride of potassium, in the aqueous solution of which not-the
M 2
164 DR. LOWIG ON THE ESSENTIAL OIL
slightest alkaline reaction is visible. All these experiments séem to con-
firm the above-mentioned view, that chloride of spiroil combines with-,
out decomposition with the bases of salts.
The question may here be asked, whether the acid properties of the:
chloride of spiroil arise from chlorine, and whether such a chloracid (in
the same way as oxyacids) could combine with them?
. Till now no such combinations were known, and therefore perhaps ‘it
might be simpler to state that when chloride of spiroil is brought toge-.
ther with a metallic oxide, 4 eqs.of ametallicchlorideand 1 of a spiroilate
are formed. If an acid be added to the solution of these salts, chloride
of spiroil, is again thrown down and a corresponding metallic salt form-
ed. In the same manner one may imagine double combinations, con-
sisting of a metallic chloride and a salt of a bromacid, from which on.
the addition of another acid chloride of bromine might be sepentelte
-. 0327 grm. of fused chloride of spiroil yielded
0°593grm. carbonic acid = 162°94 carbon.
0-099 water = 10°98 hydrogen.
0°327 grm. chloride of spiroil dissolved in potash entirely free from
chlorine, the solution evaporated, and the dry residue heated ina platinum
crucible yielded, after the mass which had been heated was dissolved in
’ water and saturated with nitric acid, 0°306 fused chioridle of silver =
-°'754 chlorine.
Carbon T6294 | sivsvsecs oe: AN8S
Hydrogen 1098S... ave sanesaes 3°35
Oxygen MELAS, to atch asian tivas 23°77
OLINS JOR ewcepmassese ae
327-00 100°00
1 eq. of chloride of spiroil therefore consists of
12 eqS. CarbON ......ceeceveeee eeeseeeees T9°'IG.0+ 004 00.00S3S
5 — hydrogen .......ecscseeceveseeees 5D. e005 3°42
4: —s'OXY BEM ..cccece cvccsccscveveness O2O0Q0.as 045 ..19°36
Dip CDIGRINC ann davnce eda suesbuvgvene GOAT atemsiiiy 26°84
14603 100-00
It has been stated that 0°628 grm. hydrospiroilic acid contained 0°795
chloride of spiroil. According to the established eq. 111°56 Ey Ors:
spiroil should yield 146-03 chloride of spiroil :
11°56 : 146°03 = 0°628 : 0°790.
Bromide of Spiroil. .
~ Bromide of spiroil is easiest obtained by pouring bromine upon hydro-
spiroilic acid ina deep glass: hydrobromic acid is immediately evolved,
the mixture becomes perceptibly warm, and at last solidifies into a
greyish white crystalline mass. Bromide of spiroil may also be easily
OF THE MEADOW-SWEET. > 465
obtained by agitating the aqueous solution of hydrospiroilic acid with
solution of bromine ; it is immediately precipitated in white flocks : the
supernatant liquid is colourless, has no smell, and contains hydrobromic
acid. In order to free the bromide of spiroil from excess of bromine
and hydrospiroil, it must be kept melted in a water-bath so long as
acid fumes are given off. Bromide of spiroil is exactly similar to the
chloride of spiroil in all its properties; it is quite insoluble in water,
and is easily soluble in ether and alcohol... By the spontaneous evapo-
ration of the alcoholic solution it is obtained crystallized ; bromide of
spiroil melts at a rather higher temperature than the chloride, and like
the latter may also be entirely sublimed: when boiled with water it
evaporates unaltered. Its behaviour, with regard to the saline bases,
is exactly the same as chloride of spiroil, but the alkaline salts are more
difficultly soluble: 0-480 grm. bromide of spiroil dissolved in potash
and decomposed by nitric acid yielded only 0-02 bromide of silver.
I. 0-510 grm, fused bromide of spiroil yielded
0°690 carbonic acid = 190°78 carbon.
0°510 water = 13:11 hydrogen.
Further, by solution as above-mentioned in pure caustic potash, and
combustion of the compound formed, 0-510 grm. bromide of spiroil
became 0°485 bromide of silver = to about 0°2036 bromine.
aEBON <i. s00 ca. LOT soc dnns 37-41
Hydrogen ...... ol pers Pee 257
Oxyeen’.,:.sc2.. TODA cca eas 20°02
me ae 20S GO east 40°00
510,00 ? 100°00
II. 0°325 grm. bromide of spiroil yielded
0°457 grm. carbonic acid = 126-00 earbon.
OSI Sesaks water = 8-99 hydrogen.
III. 0°305 grm. bromide of spiroil yielded
0°409 grm. carbonic acid = 113°00 carbon,
OTE aa: water = 7°88 hydrogen.
If the proportions of bromine in I. be taken, we obtain in 100 parts
I.
Carbone 2at;<:% SST Ties 37°05
Hydrogen...... pt fa 2°55
Oxygen......... i 99 Ra ee 20°40
Bromine ...... 40°00 ...... 40°00
166 DR. LOWIG ON THE’ESSENTIAL OIL OF THE MEADOW-SWEET-
~ Reckoned in equivalents :
- 12 eqs. carbon......... 73°56 ...... 38°80
5 — hydrogen ...... B00» ..0i000 2°62
4— oxygen ......... AMD! ose. 17°10
1 — bromine......... FO various 41°48
1 bromide of spiroil = 188-95 100°00
Lodide of Spiroil.
Hydrospiroilic acid dissolves iodine in great quantities, and forms
with it a brownish black fluid; the formation of hydriodic’acid is how-
ever not perceptible. Iodide of spiroil may be obtained by distilling
chloride or bromide of spiroil with iodide of potassium; even by rubbing
these substances together decomposition commences, and by the appli-
‘eation of heat iodide of spiroil sublimes: it is solid, of a dark brown
colour, easily fusible, and shows in general the same properties with
regard to solubility in water, ether and alcohol, and its relations to
saline bases, as chloride and bromide of spiroil.
P73 : 167
ARTICLE IX.
Researches relative to the Insects, known to the Ancients and
Moderns, hy which the Vine is infested, and on the means of
' preventing their Ravages. By M. te BARon WALCKENAER.
From the Annales de la Société Entomologique de France, vol. iv. p. 687, et seq.
Introduction.
General Considerations.— Division of these Researches into three Sections.
Wuen the human intellect began in Europe to emerge from the
darkness and ignorance in which it had for many centuries been buried,
its progress was everywhere the same, and the same method was adopted
for the advancement of knowledge in all the sciences.
Before the invention of printing the ancients were the only sources
of instruction ; after the discovery of that art their works became more
extensively circulated and better known, and as the necessary conse-
quence of the abundance and the perfection of their labours, the admira-
tion which they had excited wasaugmented, and increased effect was given
to the ascendency they had acquired over the human mind. The only
ambition of the learned was to understand, to arrange, and to comment
upon the notions which they had transmitted to us. A treatise upon
any branch whatever of human knowledge was merely a compilation,
more or less complete and methodical, of what the ancients had written
upon the subject: an addition was sometimes made of what the moderns
had thought or observed on the same topies, but these supplements had
not the same weight and authority as the rest of the work in the estima-
tion of either the author or the reader. A remark or a proposition was
judged of little value to which could not be added wt ait Aristoteles,
ut ait Plinius, ut ait Hippocrates, or other similar phrases.
Happily for the progress of natural history, the great number of
new productions brought into Europe from the countries recently dis-
covered, at the end of the fifteenth and the commencement of the six-
teenth centuries, soon rendered apparent the insufficiency of the works
of the ancients with respect to this science.
' It was perceived that the greater number of objects for the obser-
vation and description of which opportunity was afforded were unknown
to them, and that they had very superficially observed and very imper-
168 BARON WALCKENAER ON THE INSECTS
fectly-described those with which they were acquainted. This conr-
viction was quickly impressed upon the mind with regard to the smaller
species of animals, because upon this point their ignorance was the
greatest, and the application of the notions which they had aequired to
the knowledge of the moderns the most difficult and perplexing.
With regard to insects in particular, it was easy to see that the an-
cients had treated of only a very small number, and that with great in-
accuracy ; their works on this elass of animals consequently ceased to
occupy attention, which was exclusively devoted to the study of na-
ture, and the science soon advanced rapidly.
However, the names that the ancients had imposed upon some classes
of insects easily recognised remained, having passed from the ancient
languages into the vernacular tongues. The more obscure names, the
signification of which was doubtful or unknown, were employed by the
modern naturalists for the numerous genera which the progress of science
rendered it necessary to establish. Naturalists did not resolve to invent
new names until all those employed by the ancients in the elasses which
they were studying were exhausted; and even then all, excepting M-
Adanson, composed the new names from Greek or Latin roots. But
even when naturalists gave names employed by the ancients to the ge-
nera of insects which they had formed, it was generally without any idea
of applying them to the species which they had been employed by the
ancients to designate, and without any attempt to aid in the recognition
of those species. That a name had been used by some ancient author
to designate an insect of some kind, or that there was no certain proof
of the contrary, has been deemed a sufficient reason by modern ento-
mologists for the application of an ancient name to a new genus. Our
entomological systems contain names employed by the ancients, the signi-
fication of which is so entirely lost that it is matter of doubt whether they
belonged to an animal or a plant.
It is necessary for the object that I have in view to illustrate this by
an example, which is far from being the only one which I could pro-
duce.
M. Camus, the translator into Freneh of Aristotle’s Natural History
of Animals*, remarks with reason in his notes, that commentators are
divided with regard to the signification of the word Staphylinus, em-
ployed by that philosopher. Some have considered it as the name of
an insect, others as that of a plant; but, says Camus, on the authority
of the “Dictionnaire d’ Histoire Naturelle de Valmont de Bomare,” in
which he found the word Staphylinus, “The Staphylinus is an insect
well known to naturalists, because it has preserved its name as well in
the Latin as in the French.” From these words we learn that Camus
* Camus, Hist. Nat. des Animaux d’ Aristote, Ato, t. ii. p. 783.
BY WHICH THE VINE IS INFESTED. 169
was ignorant that the application of the word Staphylinus to a genus of
insects of the class Coleoptera, now divided into a great number of ge-
nera bearing other names, is not more ancient than the time of Linnzus,
who was the first to employ this word in its present signification, with-
out attempting to determine that which it bears in Aristotle, whom he
does not quote.
As to the superior orders of animals, such as quadrupeds, birds, fishes,
and reptiles, naturalists have been careful to establish, whenever it was
possible, the identity of the species which they have deseribed with
those mentioned by the ancients; and for this reason, that the latter nave
recorded facts that have not since been so well observed, and some that
have not been observed at all,and because still they all form part of the
science; but this is not the case with insects. Notwithstanding the im-
perfection of the science of entomology, the most difficult branch of
natural history, the moderns have made such progress in it that they
have nothing to learn from the ancients upon this subject; if, therefore,
we except the domestic bee, the caterpillar of Bombix Mori, or the
silk-worm, two species of insects as important as the largest animals in
the history of man, of commerce, and of the arts, we shall find that the
moderns have occupied themselves yery little with what the ancients
have said upon insects: at the same time, the names that they have
borrowed from them prove that they had read their works upon the
subject, and that they would willingly have established, by the identity
of the objects upon which they were employed, a direct relation between
their labours and those of ‘the naturalists who had preceded them in
ancient times ; but they appear to haye considered this to be too difficult,
or as impossible to be undertaken with success. This is the reason that
the number of dissertations upon this subject is so small; and even of
the few that we possess the object is only to discover to what class of
insects the ancient name should be applied, not to determine the genus
or the species.
If the science of natural history has little to hope from such investi-
gations, they may yet be subservient to the acquisition of a better and
more exact interpretation of the ancient texts; and the difficulties with
which the subject is attended ought not to induce us to neglect it. With
regard to this, as well as all the uncultivated parts of the vast field of
erudition, we may say, if this had been easy it is probable that it would
not have remained undone.
The above are the considerations which have induced me to write,
and submit to the Academy the researches*, to which I was led by a
question which one of my learned brethren did me the honour of ad-
* These researches were read before the Academy of Inscriptions, of which
the author is a member, before they were communicated to the Entomological
Society.
170. BARON WALCKENAER ON THE INSECTS
dressing to me, respecting the interpretation of the name of an insect
infesting the vine mentioned by Plautus. The text of this author in
the passage alluded to is so explicit that I ventured immediately to
give the solution required. To assure myself that I was not mistaken
I commenced an examination of what ancient and modern authors had
written on the species of insects infesting the vine, and the means of
destroying them; but in explaining and arranging the ancient texts, and
in afterwards applying them to the observations of the moderns, I found
more difficulties than I expected; I however exerted all my efforts to
surmount them. Such was the origin of this Memoir. The subject will
doubtless appear minute, but as learning, natural history, and agriculture
are equally interested in it, I think it cannot be considered either futile
or unworthy of attention.
- This Memoir will be divided into three sections. The first, which
will be in some degree preparatory, will contain acritical examination of
the ancient texts relative to the signification of the names of insects
designated in them as being particularly injurious to the vine.
: in the second section, by means of results obtained in the first, I shall
determine which are the species of insects known to the ancients and
moderns as being those injurious to the vine: I shall then indicate the
means of preventing their ravages.
In the third section this dissertation will be terminated by a concord-
ance of names, that is to say, a synonymy of all the species of insects
mentioned in these researches, arranged in classes, which will render its
application to use easy to those naturalists and agriculturists who may
think proper to have recourse to it.
First Section.
Critical examination of the ancient texts with respect to the signification
of the names of insects which are therein mentioned as being parti-
cularly injurious to the vine.
I. Preliminaries.—This section is, as I have already said, only pre-
paratory to the principal object of the Memoir.
No application of modern names to interpret the ancient texts will
here be made; but we shall content ourselves with investigating the sig-
nification of the ancient words, by means of the use to which the an-
cients themselves have applied them. In the second section the cireum-
stances or the particulars of this use will enable us to interpret the an-
cient names, that is to say, to ascertain the names corresponding to them
in the language of naturalists, the only names applicable to the defini-
tions and descriptions proper to determine with precision the objects
named. The vulgar names will be only a secondary consideration.
For objects, the differences of which escape superficial observation, the
’ BY WHICH THE VINE IS: INFESTED: 171
ancient as well as the modern Janguages furnish only general denomina-
tions, common to several objects or species, and are consequently ex-
tremely vague, a single word being employed to designate beings of very
different natures. Scholars, grammarians, and lexicographers frequently
add error to the confusion by their false distinctions, and sometimes
the prodigious erudition of modern commentators increases the difficulty
still more.
The true method of acquiring a complete and exact idea of the no-
tions represented by each of the names we seek to explain appears to
be this; to examine all the texts in which these names are employed,
and afterwards to endeavour to remove the obscurity of the various
meanings which have been assigned to them when they have been em-
ployed in different significations. By this method we can establish our
opinions and conjectures upon the ancient texts with security, and with-
out being exposed to the danger, to which we often yield without per-
ceiving it, and sometimes even consciously, of selecting from the an-
eient authors only such passages as support our interpretations and
systems, while we keep out of sight all those whieh are in opposition to
‘them.
Il. List of the Names of Insects injurious to the Vine mentioned
by the Ancients——The following are all the names of insects infesting
the vine, or mentioned in connexion with it, that I have been able to
discover in ancient authors :
1. Thola, Tholea or Tholaat. 9. Joulos or Julus.
2, Gaza. 10. Biurus or Bythurus.
3. Ips. 11. Involvolus, Involvulus, Invol-
4, Iks. vus.
5. Spondyle or Sphondyle. 12. Convolvulus.
6. Cantharis. 13. Volvox.
7. Phteire or Phteira. 14. Volucra.
-_ 8. Kampé. 15. Eruca.
III. List of the Authors in whom the above Names are found, and whose
texts are explained in these Researches.—The following are the authors in
whom the names above mentioned are found, and who will consequently
receive some explanation in this dissertation :
. ‘The Bible. Cicero. Ammonius.
Homer. Strabo. Herodian (the gram-
. Ctesias. Pliny. marian).
Aleman. Columella. Festus.
Aristotle. . Athenzeus. Suidas.
Theophrastus. Origen. . Hesychius.
Plautus. St. John Chrysostom. -Eustathius.
Cato. - St. Epiphamius. — Philo.
172 BARON. WALCKENAER ON THE INSECTS
IV. Thola, or Tholea, or Tholaath—This is a Hebrew word, and is
found in Deuteronomy, in the part which treats of the punishments with
which the Israelites were menaced if they abandoned the law of God*.
This verse is thus rendered in the translation of the Greek and Hebrew
texts by the pastors and professors of the Church of Genevat.
“You shall plant vines, you shall cultivate them, you shall not dna
the wine of them and you shall gather nothing from them, because the
worms shall eat their frit.”
De Sacy, after the Vulgate, translates it in the following manner:
“You shall plant a vine and you shall dress it, but you shall not drink
the wine of it, and you shall gather nothing from it, because it shall be
destroyed by the worms.”
In the first of these translations the word fruit is printed in italies,
because in fact it is not in the Hebrew; but it ought not to be added,
for it is useless to the sense, which is complete without it, and it may
jead to error; for the insects which injure the vine by cutting the root
are not the same as those which knaw the leaves, nor are the latter the
same as those which eat the fruit.
The word Tholath in the interlineary version of the Hebrew Bible by
‘Arias Montanust is also translated by Vermis. But the Hebrews had
also another word for worm, rimma. This word is often employed
figuratively in the Bible in the same sense as ¢hola, to designate a vile
being or an animal engendered from corruption.
The word rimma is employed several times in this sense in the Book
of Job ; in Exodus, chap. xvi. verse 24 ; in Hosea, chap. xiv. verse 11.
The word tholaat is also employed in Job, chap. xxiii. verse 6; in
Exodus, chap. xvi. verse 20; in the passage already cited of Deutero-
nomy; in Psalm xxii. verse 17 ; and lastly in Jonas, chap. iv. verse 7.
But it is necessary for our object to cite the whole of this last passage,
and to justify the translation we shall give, which will differ from that
of the professors of Geneva and from the Vulgate of De Sacy. In this
chapter it is said, that the prophet having quitted the city, and stopped
at a place in the east, made himself a shed.
“Then, said the prophet, God caused a plant (kikajon) to spring up, —
which being elevated above Jonas, became a shadow for his head, which 5
pleased Jonas extremely ; but at the dawn of the next day God prepared
a worm (tholaat), which wounded the plant (kikajon) and caused it to
wither.”
I can easily show that I am right i in translating it thus, i in preference
to adopting any of the three versions that are before me.
* Deuteronomy, chap. xxviii. verse 29.
+ La Sainte Bible, ou le Vieux et le Nouveau Testament, traduits par les Pas-
teurs et les Professeurs de l’Eglise de Genéve. Geneve, 1805, t. i. p. 276.
{ Bible of Arias Montanus.
BY WHICH THE VINE IS INFESTED. 173
The word that I have rendered “plant” is kikajon in the Hebrew,
and the sense of the passage shows that it was a plant large enough
to have foliage sufficient to form a shade. But what is this plant? No
one is acquainted with it. In the Septuagint it is called a gourd, and
St. Jerome makes it an ivy, but St. Augustine informs us in a letter to
that Father, that the people of Africa were greatly shocked by this alter-
ation, and obliged their bishop to remove the word ivy from the version
of St. Jerome. De Sacy, who retains in his version the ivy of St. Jerome
because it is the text of the Vulgate, inclines to the idea that it‘is a vine or
a fig-tree. The pastors of Geneva and M. Gesenius* make the Kikajon
a Ricinus agreeing with Bochart}+, who leans to the same opinion; but
he, far from having proved it, brings dios us texts which support the
contrary opinion.
But if we indulge in conjectures encsing the plant mentioned in
this passage of Jerome, we must for the same reason conjecture the
species of insect which caused its destruction, and shall thus be liable
to give to the word Tholaat a different signification from that really be-
longing to it. The liability to error is much, increased if we translate
with De Sacy, “it pricked the ivy at the root,” a circumstance which is
not mentioned either in the Hebrew text or in the Vulgate, and which
would expose us to the danger of drawing consequences from false pre-
mises, which would be erroneous in proportion to the regularity and
learning with which they were deduced.
I have therefore altered the translation of the text in such a manner
as to leave nothing that may not be read with certitude.
From all that has just been said it appears that the words Rimma,
and Thola or Tholaath, are often indifferently employed in the Bible,
one for the other, in the sense of worm or grub, of an animal born of
corruption, vile, and despicable ; but with this difference, that the word
Thola or Tholaat is twice used in the Bible to designate a worm which
preys upon a plant. In the first of the passages alluded to this plant is
the vine ; we are ignorant of the species of plant intended in the second
passage, but we are certain that it is a plant. We know that such an
animal, though it possesses the form of a worm, is not one strictly
speaking ; we are certain that it is either a grub, or a little insect, or
the larva of an insect subject to metamorphosis. The word Rimma
has never been employed in this last sense, at least not in the Bible.
It appears therefore that in this point of view the Hebrew language is
richer than our own, since in ordinary discourse we have only one
word to designate the worms of the nut, pear, apple, and all other fruits,
and likewise the earthworm, though these animals differ not only in
genus, but belong to very different orderst.
* Gesenius, Handbuch, &c., 1828, 8vo, p. 883.
+ Bocharti Hieroxoicon, vol. ii. p. 623.
} Vide Cuvier, Regné Animal, t.iii, p. 180, on the third grand division of ar-
174 BARON WALCKENAER ON THE INSECTS
~ ¥. Gaza.—Gaza is another Hebrew word which is once used in the
Bible as the name of an insect particularly injurious to the vine, but it is
afterwards frequently employed as the name of an insect which devas-
tates all sorts of plants; with several other names of insects which have
given occasion to a great number of dissertations, some of which extend
to volumes. We have examined the modern names which appear to
correspond to the ancient ones of the insects mentioned in the Bible
in connexion with the word Gaza; and this examination may perhaps
form the subject of another memoir. At present we shall confine our
investigations to the word Gaza, because it is the only one among these
names employed todenote an insect particularly injurious to the vine; and
we shall notice the other names of insects which accompany the word
Gaza, only so far as may be necessary for its interpretation. But such
is the diversity of opinion among translators, that to obtain clear ideas
it will be necessary to produce the passages in which this word occurs,
giving our own translation of them, but retaining the Hebrew names.
The following passage in which Gaza is employed as the name of ari
insect destructive to the vine is in the prophet Amos, chap. iv. v. 9:
“ T have smitten you with ascorching wind, and with mildew. Gaza
has devoured your gardens, all your vines, and all your olive plants and
fig-trees, and you have not returned to me, saith the Lord.”
We find the word Gaza again in Joel, chap. ii. v. 25:
« T will restore you the fruits of the year, and all that you have lost
by Arbeh, Jelek, Chazil and Gaza, that destroying multitude that I
sent to you.”
But there is a passage in Joel, chap. i. ver. 4, of still greater import-
ance with regard to the translation of the word Gaza:
“That which the Gaza leaves, the Arbeh eats ; that which the Arbeh
leaves, the Jelek eats; and that which the Jelek leaves, the Chazil
eats.”
- In all these passages the Seventy have translated Gaza by Kampé,
and the Vulgate by Erwca, that is to say, a caterpillar. The pastors of
‘Geneva and De Sacy have adopted this translation. It has also the ap-
proval of Bochart* and Michaelis. But the Chaldee Version applies
‘Gaza to a sort of creeping locust, and the Talmud enumerates ten spe-
‘cies of locusts mentioned in the Prophets alone, and among these is the
‘Gaza.
The three other names of insects mentioned in the same verse of Joel,
‘Arbeh, Jelek, and Chazil, are included in the ten species of locusts enu-
merated i in the Talmud by the Hebrew doctors. j
a animals, in which this naturalist proves that the worms, otherwise
called Annelida, ought to be placed at the head of this division, and as the
Crustacea, the Arachnida, and Insects.
* Bocharti Hieroxoicon, part ii. p. 483.
= BY WHICH THE VINE IS INFESTED. + 175
- The expositors of the Bible are divided in opinion upon the significa-
tion of the words Jelek and Chazil, but are all agreed upon that of the
word Arbeh. There can be no doubt that a locust is signified by
this word. The Chaldee Version, the Septuagint, and the Vulgate, all
agree in their rendering of those passages of the Bible in which this
word is found. The Arbeh is the first of the four species of insects, or
creeping animals, named by Moses as proper for the food of man; and
Forskael informs us that the Arabs at the present day give the name of
Arbeh to the species of locust which is used among them for food. Now
we know from Joel that what the Gaza leaves the Arbeh destroys ; we
are therefore entitled to conclude with certainty that Gaza was the
name of an insect not only particularly destructive to the vine, but also
to plants of every kind; and that to its ravages succeeded those of se-
yeral species of locusts, which consumed all that was left undevoured
by this formidable insect. Several learned expositors have considered
this insect to be a caterpillar, while others of equal authority have de-
cided it to be a sort of creeping locust. We shall consider this point
upon another occasion; but at present, faithful to the plan we have
traced for our guidance, having exhausted what the Hebrews have writ-
ten upon the insects destructive of the vine, we shall pass to the Greeks.
VI. Ips, Iks.—I shall treat of these two words in one article, because,
as will be seen, they cannot be separately considered.
_ The word Jps is used in ancient authors as the name of an insect par-
ticularly injurious to the vine; but it is also employed by Homer, St.
John Chrysostom, and the lexicographers and grammarians of the lower
ages, to denote an insect or worm which preys upon horn; and in
these two acceptations this word cannot denote a worm properly so called,
which has another name in the Greek language.
’ We will first consider the Ips of Homer. ;
This word is employed in the Odyssey, book xxi. verse 295, in whicl
Ulysses, who is not yet recognised by his friends, is represented as re-
ceiving his terrible bow. The poet says, “The hero takes the bow, exa-
_ mines it with attention, and turns it in every direction, fearing that in
the absence of its master the horn might have been injured by the Jps.”
- To ascertain what species of horn was subject to the attacks of the
Ips of Homer, we must discover the animal the horns of which were em-
ployed in the time of Homer in the construction of bows of the best
quality, such as were suitable for a king like Ulysses. Upon this
point Homer himself gives us information: in the Iliad, book iv. v. 105,
we read that the bow of the divine Pandarus was made of the horns of
the Aigos, or the /Egagrus or wild goat; that its horns were five feet
four inches in length; and that after being polished and united with care
by askilful workman their extremities were gilt.
176 BARON WALCKENAER ON THE INSECTS
The horns of the A2gagrus are often nearly three feet and a half in
length; they are naturally bent, and when united, as Homer describes,
they would form a bow of the dimensions stated by him.
The A:gagrus, or wild goat, is found, though but rarely, in the moun-
tains of Western Europe. One was killed while I was in the Pyrenees,
and the horns, which I saw, were two feet and a half in length. This
animal is very common in the East: in Persia it is named Paseng.
Burckhardt informs us that the Arabs of Syria give it the name of Bi-
din (Beden), and that the wild goats are found in their countries in herds
of forty and fifty. Their flesh is much esteemed, and the horns are col-
lected and sent to Jerusalem to be made into handles for knives and
poniards. Burckhardt* saw a pair of the horns of these animals which
were three feet and a half in length. We may suppose that the Ips of
Homer must be both known and feared by the warriors of that country.
But the word Ipsis not found thus applied in the Greek authors who
follow Homer; and it is employed in Strabo, Theophrastus, and the
writings of the learned agriculturists whom we shall presently quote,
to denote an insect or a worm injurious to the vine, consequently a larva
which preys upon plants and not upon horn.
We, however, again find the word Ips with the same signification as
when employed by Homer in a remarkable passage of St. John Chry-
sostom, which I shall translate thus: “ The same deleterious effects as
are produced by copper upon the body, by rust upon iron, by moths in
wool, worms in wood, and Ipes in horn, vice produces in the soul+.”
But I repeat that in the most learned Greek authors, and those of the
highest authority, Ips is an insect which preys upon the vine.
We read in Strabo:
“ The Erythrzans give to Hercules the name of Ipoctonus, that is,
destroyer of the Ipes, insects thus named which prey upon the vine.”
Theophrastus §, after describing how worms are produced in corn,
adds that the Ipes are engendered by the south wind ; and in another
place he says, “ There are, however, places where the vines are not in-
* Burckhardt, Travels in Syria and the Holy Land, 1822, p. 405; Fischer,
Synopsis Animalium, p. 483; Cuvier, Réegne Animal (2eme edit.) t. i. p. 275.
+ Sanctus Joannes Chrysost. App. vol. iv. p. 669, E. St. John Chrysostom
employs the word Scolex for the worm which preys upon wood. Scolez signifies
the earth-worm, the true worm ; in fact, in the grammarians of the lower ages,
uccording to the same authorities Scolex also means the worm infesting the ox,
an intestinal worm, or the larva of an insect altogether different to the for-
mer. The Scolex of'St. John Chrysostom, or the worm preying upon wood, can
only be the Jarva of an insect, and in fact Aristotle employs the word with this
meaning when he says that every insect proceeds from a Scolex.
bt be at) ay Almenoven) folio, book xiii. p. 613: in the French translation,
§ Theaphtaitas De Causis Plantarum, book. iii. chap. 22; or 23 of Schneider’s
edit. vol. ii. p. 299. Scaliger translates the word [ps by Convolvulus, for which
we shall see the reason elsewhere.
BY WHICH THE VINE IS INFESTED. Vie
fested by the Zps; this occurs in places exposed to the winds, where
there is a free current of air, and no excess of humidity.”
In the Geoponics* it is said, “that to prevent the little worms named
ZIpas from attacking the vines, the reeds used for the vine-props should
be smoked, because the reeds decomposing in the earth engender little
worms, which will otherwise ascend upon the vine.”
Galien, cited by Aldrovandus, says that the black earth kills the Zpes.
In the Dictionary of Suidas+ the word Jpi is defined by Worm; but it
is remarked that Jps is a better expression. That work, however, does
not furnish any other information upon the word Jps.
But the name Jps in a form slightly altered, or another insect under
a name differing but little from that, is mentioned by several authors as
being very hurtful to the vine.
In a fragment of Aleman quoted by Bochartt, it is said that “the va-
riegated Zka is the scourge of the young shoots of the vine.”
The grammarian Ammonius in his Treatise upon Synonyms §, says
also, “the Zkes are animalcula which destroy the buds of the vine.”
Bochart thinks that Jps and Jks are but one word, according to two
different dialects.
Valckenaer in his notes upon Ammonius is of the same opinion:
Ego verisimilam censeo (says this accomplished critic,) Sam. Bochartt
sententiam qui ab Aleman Ika, ex dialecto pro Ipa positum sagaciter ani-
madvertit, et ex idoneis auctoribus loca produxit in quibus, qui in vitibus
nascuntur vermiculi Ipes dicuntur.’ Valckenaer concludes with Bo-
chart that Zps is the most ancient form of the word.
However in Hesychius, and in another grammarian quoted by
M. Boissonade, these two words are distinguished from each other and
applied to two different insects.
In Hesychius’s Dictionary we find Zks as the name of an animaleulum
(Theridion) which infests the vine; and in the same work Jps has this
explanation, that this word is employed by grammarians to denote an
insect which preys upon horn.
The anonymous grammarian cited by M. Boissonade in his notes to
his edition of Herodian ||, enumerating the various name sattributed to
the different species of worms or larva, according to the substances in
which they lodge, or which they destroy, mentions Zks as the worm of
the vine, and Jps as that of meat and horn.
Have these two species of insects been accurately distinguished from
each other, and the habit acquired of expressing them by different
* Geoponic., edit. Niklas, chap. liii. vers. 423.
+ Suidas, Lewicon, edit. of Kuster, 1705, folio, vol. ii. p. 141.
t Bocharti Hierozoicon, vol. ii. p. 213.
§ Ammonius, tit. 2, chap. v. De Differentia adfinium Vocabulorum, nunc pri-
mum editum ope MSS. prime edit. Aldine. Vulgavit Valckenaer, pp. 73, 74.
|| Herodiani Partitiones, Lond. 1819, 80, p. 58.
Vor. L—Parr I. N
178 BARON WALCKENAER ON THE INSECTS
names? Or is it a distinction erroneously established by grammarians
and lexicographers, who of one word slightly varied haye made two
different words? Whatever may be the fact, the consideration of it is
foreign to our present purpose, and will engage our attention at another
opportunity. We confine ourselves at present to collecting the facts of
the language as we derive themfrom the critical examination of the texts,
without anticipating the consequences which may be deduced from them.
From what has been said we draw the following conclusions :
1st, That in the most learned ancient authors, and in those who have
treated ex professo of agriculture, natural history and geography, the
word Jps has never been employed except to denote the larva of an in-
sect very injurious to the vine.
2nd, That in Homer, St. John Chrysostom, and lexicographers and
grammarians of the period of the decline of literature, the word Jps is
exclusively employed to denote the larva of an insect preying upon
horn. .
3rd, That the word Zks, whether it be considered as a different word
from Jps, or the same in another dialect, is employed by Aleman, and
the lexicographers and grammarians of the lower ages, to designate ex-
clusively a variegated insect, which injures the vine, and preys upon its
buds. 7
VII. Spondyle or Sphondyle.—Aristotle in his Natural History of
Animals*, after describing the mode of coition of flies and beetles, adds
that the Spondyle (or Sphondyle), the Phalangium, and other insects
agree with them in this respect.
I say Spondyle or Sphondyle, because the editors and translators of
Aristotle’s work are divided upon this point. In the Greek text of
Schneider the word is Sphondylai, in that of Camus Sphondylai: they
each represent that it is an insect, because in this passage the meaning
is evident; but in another passage of the same work +, speaking of the
diseases of the horse, Aristotle mentions cases in which that animal
draws up the hip and drags the foot, and says, “the same thing occurs
if he devours the Staphylinus. The Staphylinus is of the same size and
appearance as the Sphondyle.”
M. Camus, in his translation, writes Sphondyle, and agrees with
Hesychius, who represents the Staphylinus, and consequently the Spon-
dyle, as an animal. M. Schneider, on the contrary, who this time also
writes Sphondyle, considers this word to be entirely different from Spon-
dyle, the name of an animal in the first passage which I have quoted.
M. Schneider, adopting the opinion of Scaliger, regards the Staphylinus,
* Aristot., Hist. Anim., book v. chap. 7, edit. Schneider, vol. ii. p. 181 of the
translation ; and vol. i. p. 190 of the Greek ; and book v. chap. 8. vol. i. p. 219
of the translation of Le Camus. ; ;
{ Aristot., book viii. chap, 24, Schneider, vol. iii. p. 276.
—<
<a’
BY WHICH THE VINE IS INFESTED. 179
and consequently the Spondyle mentioned in this last passage, as a plant
(the parsnep)*.
M. Schneider in his note does not attempt to prove the accuracy of
his translation, but contents himself with citing the authority of Scaliger.
I confess that I here lean to the opinion of Le Camus. It is not, however,
necessary to discuss the subject ; and the circumstance that Aristotle has
twice mentioned an insect named Spondyle or Sphondyleis of little im-
portance, since he gives us no information respecting it. In the second
passage, indeed, he compares it to the Staphylinus, but we know still
less of the Staphylinus than of the Spondyle, and in neither passage is
any mention made of the vine. Nor should we have noticed the Spon-
dyle of Aristotle were it he alone who had spoken of it; but Pliny +
remarks upon the Aristolochia and the wild vine ( Vitis silvestris),
which vegetates a year in the shade, that no animal infests the roots of
these plants, nor of others of which he has treated, excepting the Spon-
dyle, a sort of serpent, which attacks them all. “ Et Aristolochia ac
vitis silvestris anno in umbra servantur : et animalium quidem exterorum
nullum aliud radices a nobis dictas attingit excepta Spondyle que omnes
persequitur. Genus id serpentis est.”
Schneider after quoting this passage adds, “Znepté ut solet.”
Pliny has conceived with genius and executed with ability an abridged
encyclopedia of human knowledge; he may perhaps be esteemed
the author of the most learned work ever composed; and it certainly
is not allowable to speak of a writer of such merit with the asperity
and disdain manifested on this occasion by the learned German.
However, if the severity of the criticism sometimes occasioned by the
difficulties we experience from the gross errors into which Pliny
has been led, by the necessity of treating of so many things which he
understood imperfectly, can be excused, it is certainly in the editor or
translator of Aristotle’s Natural History of Animals. Pliny has bor-
rowed extensively from that admirable work; sometimes he is con-
tented with translating it ; but even then he generally confuses, by inac-
curate or pompously obscure phrases, what Aristotle had explained with
clearness and precision, and often mixes with it popular and ridiculous
stories, or erroneous and inconsistent notions. But it would have been
better if M. Schneider, who combines the knowledge of a naturalist with
the erudition of a philologist, instead of allowing himself to use the ex-
_ pression we have cited on this passage of Pliny, had inquired what ad-
vantage might be reaped from it ; he would then have seen that the er-
ror of Pliny will enable us to determine what species of insect is meant
by the Spondyle in the first passage of Aristotle, and perhaps also in
* Schneider, Arist. Anim. Hist., vol. iv. p. 665.
a Plin. Hist. Nat. book xxvii. §. 118. (chap. 13.); vol. viii. p. 106 of the edition
of Franz.
180 ON THE INSECTS BY WHICH THE VINE IS INFESTED.
the second. As it is certain that, in Europe at least, no serpent injures
the roots of plants, from the comparison of this passage of Pliny with
that of Aristotle we deduce the following facts :
Ist. That the larva of the insect named Spondyle by the Greeks was
known to the Latins, and that it devoured the roots of plants of every
kind.
2nd. That this larva was very large, since it was compared to a small
serpent. '
We shall see hereafter the consequences deducible from these cireum-
stances.
It may perhaps be said that this long discussion on the word Spon-
dyle might have been omitted, because Pliny speaks only of the wild
vine, Vitis silvestris, which is not really the vine, nor has it any relation
to the plant producing grapes, but which was an annual, like the Aristo-
lochia, as Pliny himself informs us. To this I reply, that the vine is
included in the plants mentioned by Pliny as being exposed to the at-
tacks of the Spondyle, and that consequently anything relating to this
insect belongs strictly to my subject.
[To be continued. }
SCIENTIFIC MEMOIRS.
VOL. I.—PART II.
ARTICLE IX. concluded.
Researches relative to the Insects, known to the Ancients and
_ Moderns, hy which the Vine is infested, and on the Means of
preventing their Ravages; hy M.tt Baron WALCKENAER,
Hon. Memb. of the Entomological Society of France.
From the Annales de la Société Entomologique de France, vol. iv. p. 711, et seq.,
and vol. v. p. 219, et seg.: read Nov. 18, 1835.
VII. Cantharis — IRECTIONS are given in the Geoponics* for
preventing Cantharides from injuring the vine: these insects are to be
macerated in oil, and the plant rubbed with the preparation.
Another recipe for the preservation of the vine is given in Palladius,
for which the Cantharides of the rose are required ; they are to be ma-
cerated in oil until an unctuous liniment is formed, with which the
branches are to be rubbed}.
j The name Cantharis occurs very frequently in several Greek and
Latin authors without any mention of the vine. Pliny, however}, says,
_ “ Verrucas Cantharides cum uva taminia intrite exedunt,’— “Can-
- tharides pounded with the wa taminia destroy warts.”
' The Uva taminia, which we translate by wild grape, is, I apprehend,
_ unknown; it is certainly not the fruit of the vine.
___ It would be superfluous to produce here the numerous passages of
__ the ancient authors in which the word Kantharis occurs, because there
_ can be no doubt as to its signification. They all prove evidently that
the ancients understood by this word, not the larve of insects, but
* Geoponica, edit. Niclas, 1781, 8vo, p. 418. ch. 49.
+ Palladius, book i. chap. 35; vol. i. p 43, Bipontine edition.
t Pliny, book xxx. chap. 9.
Vor. I.—Panrt II. oO
182 BARON WALCKENAER ON THE INSECTS
perfect insects; that these insects were all of the order Coleoptera,
vulgarly Beetles; and that Cantharis was a general term denoting
several species of beetles, but not all the species indifferently. This
word is always employed by the ancient authors to denote those species
of Coleoptera, or beetles, which are brilliantly coloured and remarkable
for their vesicant or venomous properties; but those authors differ
greatly from each other with regard to the species which they have in
view.
Thus the Cantharis of Aristotle appears to be the same species as that
mentioned by Aristophanes*; but it isan insect very different from that
with black and yellow bands, which has been so well described by Di-
oscorides that it is impossible to be mistaken by modern naturalists.
To this latter insect must be referred the winged Cantharis of a fulvous
colour, to which on account of its malignity and mortal poison Epipha-
nius compares heresy +. The Cantharis of Origen}, produced from the
larva of an insect which lives in the flesh of the ass, is evidently a dif-
ferent species from that of Epiphanius and Dioscorides, and also from that
of Aristotle and Aristophanes, though more resembling the latter.
Pliny mentions several species of Cantharis§, which for want of exact
details are difficult to recognise ; but when he says (book xviii. chap.44.),
“ Est et Canthuris dictus Scarabeus parvus frumenta erodens ||,” we in-
stantly fix upon the small and formidable coleopterous insect to which
he here gives the name of Cantharis. Theophrastus, who has also men-
tioned the little insect engendered in corn, gives it the name of Can-
tharis.
From what has been said it appears that to find the insect named
Cantharis considered by the ancients as injurious to the vine, we must
seek for it among the perfect insects of the class Coleoptera; among
those which are brilliantly coloured and distinguished by their vesicant
venomous quality; and among the largest as well as the smallest species
of that class.
IX. Kampe and Phtheir—I class these two words together for an
instant, regardless of their different signification, because I find them
united in a passage of the Geoponics4], the only place in which the first
is mentioned in connexion with the vine. The author gives a recipe used
by the Africans to preserve the vine from the Phtheirs and Kampes
which infest it. Ctesias also mentions the Phtheirs which destroy the
vine in Greece**,
* Aristophanes quoted in Aldrovandus De Jnsect., chap. iii. vol. i. p. 180.
+ St. Epiphanius, Panar. Rom., p. 1067, A. edit. Petav.
+ Origen, Contra Cels., book iv. chap. 57. p. 549, A. edit. Delarue.
§ Pliny, Hist. Nat., book xxix. chap. 30; vol. iii. p. 107. edit. Miller.
| Pliny, Hist. Nat., chap. 44. or 17. vol. vi. p. 138 of the edition of Franzius.
4] Geoponica, edit. Niclas, chap. xxx. vol. iii. p. 485.
#® Ctesias, Indicorum, chap. xx _ p. 253. edit. Baehr. Frankf. 1824, 8vo.
BY WHICH THE VINE IS INFESTED- 183
X. Kampe.—Aristotle* was well acquainted with the metamor-
phoses of the Butterfly, the larva of which he calls Kampe. He par-
ticularly mentions that which feeds upon the cabbage.
Theophrastus}, in his History of Plants, employs. the word Kampe
for an animal which eats the leaves and flowers of ali sorts of trees.
Pliny {, abridging the passage of Theophrastus alluded to, translates
Kampe by Fruca, Caterpillar.
We have already seen that the word Kampe occurs three times in
the translation of the Bible into Greek by the Seventy, twice in Joel,
and once in Amos§ ; and that in the Latin translation of the same pas-
sages in the Vulgate, the word Hruca is always employed, though, as
we have already remarked, we are not certain that either Kampe or
Eruca gives the sense of the Hebrew Gaza, for which they are used.
St. John Chrysostom, in a remarkable passage, speaks of the Kampes
as having been an object of worship in the times of paganism ||; and this
word is with reason rendered Hrucas, Caterpillars, in the Latin transla-
tion. In the Dialogues of Pope Gregory the Great] mention is made
of Boniface, Bishop of Ferentum, who enters a garden in which are a
very large number of Caterpillars: “Jngressus hortum, magna hune
Erucarum multitudine invenit esse coopertum.”
Pope Zachary, translating the same Dialogues into Greek, renders
the word Eruca by Kampe.
But the following passage of Columella leaves no doubt upon the
subject **:
“ Animalia que a nobis appellantur Eruce Grace autem. KAMITAI
nominantur.” “ The animals that we (the Romans) call Eruce (Cater-
pillars) are named in Greek Kampai.”
Palladius and Columella, though writing in Latin, always prefer the
Greek to the Latin word when they have occasion to mention the ca-
terpillar.
Thus Palladius, giving instructions how to destroy the caterpillars
infesting vegetables and the vine, recommends that the stems of the
plant producing garlic should be burnt in the garden, and the pruning-
knife employed to dress the vine anointed with the garlic, and says:
_* Campas fertur evincere qui fusticulos allii sine eapitibus per horti
omne spatium comburens, nidorum locis pluribus excitavit. Si contra
-
* Aristotle, De Anim., book v. chap. 19.
+ Theophrastus, book iy. chap. 16.
} Pliny, book xii. chap. 24.
§ Joel, i.4; ibid. ii. 25; Amos, iv. 9.
|| St. John Chrysostom, /fomil. 2. in Acta Apostol., vol. iv. p. 621, book xiv
Eton edit. 1612.
4] St. Gregory, Dialogorum Libri IV., hook i. chap. 9. vol. ii. p. 396. Paris
edition, 1675, folio.
** Columella, book xi. chap. 3.
02
184 BARON WALCKENAER ON THE INSECTS
easdem vitibus voluerimus consulere, allio trito falces putatorie ferun-
tur unguende*.”
Columella having occasion to speak of the destruction caused by the
Caterpillar, twice employs the word Campe.
“ Nec solum teneras audent erodere frondes
Tmplicitus conchz limax, hirsutaque Campe f.”
And afterwards:
“Non aliter quam decussa pluit arbore nimbus
Vel teretes mali, vel tectz cortice glandis,
Volvitur ad terram distorto corpore Campe}.”
It is therefore evident that it is among the Caterpillars, or the larve
of the Lepidoptera or Butterflies, that we must search for the Kampes,
which, according to the Geoponics, are produced in the vine and de-
stroy it.
XI. Phtheir—This Greek word is known to apply to the parasitic
insect peculiar to man, the Louse. We shall have to examine whether
Ctesias § and the author of the Geoponics have employed this word to
signify all sorts of insects injurious to the vine, which include implicitly
the Kampes or Caterpillars; or whether they had in view a particular
insect, which being small was for that reason considered by cultivators
as the Louse of the vine.
XII. Julos or Julus—Suidas, an author of the ninth or tenth cen-
tury, says in his Dictionary ||, that the Jzos is a worm of the vine ; that
it has a great number of feet, and is also called Multipede ; that it coils
itself up, and breeds in moist vessels.
From these few particulars the most learned lexicographers have not
hesitated to establish the identity of the Jouwlos with the Ips, Iki, Con-
volvulus, and other insects mentioned by the ancients as injurious to the
vine.
We shall soon see how many errors are accumulated from thus esta-
blishing relations for which there is no authority in any text.
No ancient author has mentioned the Julos in connexion with the
vine, or as an animal destructive of it.
The Latins have employed the word Julus or Julius in several of the
same senses as were given to it by the Greeks; but I am not aware that
they have ever employed it to denote a worm or an insect, or any ani-
mal whatever.
* Palladius, in the Seriptores de Re Rustica, Bipontine edit., vol. i. p. 43.
+ Columella, De Cultu Hort., ver. 324. vol.i. p. 410. Bipontine edit.,1787, 8vo.
t Columella, De Culiu Hort., book x. ver. 366. Gesner in his Dictionary
also quotes Sextus Empiricus, t. 14, on the word Camrr.
§ Ctesias, Indicorum, chap. xxi. p. 253. edit. Baehr. Frankfort, 1824, 8vo. .
|| Suidas, Levicon, vol. ii. p. 126. Frankfort edit.
BY WHICH THE VINE IS.INFESTED. ~ 185
Aristotle speaks of the Julios in his History of Animals*; but all the
information which he gives us is, that it is an insect without wings, like
the Scolopendra.
Speaking of animals in general, Aristotle distinguishes those which
have only four feet from those with a larger number+, and among the
latter he names the Scolopendra and the Bee. It is evident that Aristotle
names these two examples as being the extreme limits of the class; one
animal having but six feet, only two more than the animals of his first
division, or quadrupeds, and the other having a much larger number :
one of Aristotle’s commentators however, forming his judgement in a si-
milar manner to the lexicographers, makes a Wasp of the Scolopendra.
An insect without wings a Wasp !
Aristotle mentions the marine Scolopendraf, a different animal, that
lives in the sea; he describes it, and says that it is similar to the terre-
strial Seclopendra, but of a deeper red colour; that it has a larger num-
ber of feet,and those more slender. He remarks upon the terrestrial
Scolopendra§, that if it be divided into several parts, each part has a
progressive movement.
Pliny ||, translating this passage of Aristotle upon the marine Scolo-
pendra, says that it resembles an insect of the earth named Centipede ;
and in another part of his work he thus defines the Centipedeq: “The
Millipede, which is also named Centipede and Multipede, is a kind of
worm of the earth, which crawls upon all its feet, describing an arch,
and coils itself up on the slightest touch. The Greeks call it Oniscos,
and some of them Zylos.” Further on.he says again: “The species of
Scolopendra which moves without sinuosities, and is named by the
Greeks Seps, and by others Scolopendra, is more venomous.”
“ Millipeda, ab aliis centipeda aut multipeda dicta, animal e vermibus
terre pilosum, multis pedibus arcuatim repens, tactuque contrahens se :
Oniscon Greci vocant, alii Tylon...... Milam (centipedem) autem que
non arcuatur Sepa Greci vocant, alii Seolopendram minorem perni-
ciosamque.”
I may here remark, that in this passage Pliny ** confounds the Julios
with another species of Millipede, to which Aristotle gives the name of
the polypodous Ass, [ Asellus,] ovos 6 roduros; and Pliny afterwards
appears to give the names of Seps and Scolopendra to the Oniscos,
* Arist., Hist. Anim., book iv. chap. 1; vol. i. p. 129 of the Greek text, and
vol. ii. p. 126 of the Latin translation, Schneider’s edition; vol. i. p. 171 of the
translation of Le Camus.
+ Arist., book i. chap. 5. vol. ii. p. 16 of Le Camus’s translation.
t Arist., book ii. chap. 4. § Ibid., book iv. chap. 7.
|| Pliny, Hist. Nat., book ix. chap. 43.
| Zbid., book xxix. chap. 6. vol. x. p. 128.
«* Pliny, Hist. Nat., book xxix. chap.39. vol. viii. p. 273. Arist., list. Anim.,
vol. v. chap. 25. (vulgd 31); Scaliger, 126, vol. ii, p. 224. Schneider's edition.
186 BARON WALCKENAER ON THE INSECTS
and says that it is smaller than the Centipede, and moves without making
sinuosities. Errors of this sort are common in this author.
Numenius, cited by Athenzeus, calls the Judios the entrails of the aisle
Eustathius, commenting upon this passage, and Theon, a more ancient
author, give different reasons for this expression.
Hesychius says that the Joulos is like the Polypus, that it lives in
moist places, and that it is different from the Onos or Asellus.
Lycophron applies the epithet of Juliopezos to a vessel propelled by
a great number of oars.
From all these texts we gather the following particulars: that the
Julos or Julus was an apterous insect, or without wings, and furnished
with a great number of legs; that it rolls itself up immediately upon being
touched ; that it deseribes a curve or sinuosities in moving; that it con-
ceals itself in the earth ; that it is found in moist places; and lastly, that
Suidas alone informs us that this insect preys upon the vine.
XII. Biurus.—We now arrive at names applied by the Romans to in-
sects destructive to the vine, and we shall commence with a word which,
from its etymology, appears to have been derived from the Greek.
The name of Biurusemployed by Cicero to denote an insect injurious
to the vine is only known to us from a passage of Pliny the naturalist.
Speaking of different medical prescriptions, and several curious parti-
culars relative to the history of animals, he concludes a chapter with
these words: “ Marcus Cicero says that there are insects, named Biuri,
which prey upon the vines in Campania.” “ J. Cicero tradit animalia
Biuros vocari gui vites in Campania erodant.”
It has been rightly remarked that this word is derived from the
Greek ouwra, and appears to be a synonym of Bicaudes, insects with
a double tail. This etymology deserves attention, as we learn from it
the only peculiarity by which this insect can be recognised. In the
most ancient manuscripts the word is written Biwros, and we should
reject the orthography of Byturos adopted by certain editors of Pliny.
This latter word has been employed by modern naturalists as the
name of a genus of Dermestes*, while they have neglected the true
orthography.
XIV. Involvolus, Involvulus, or Involvis— The words which remain
to be noticed are purely Latin; they have, if I may be allowed the ex-
pression, a family likeness, and appear to be derived from each other.
We shall commence with the word which the most ancient author
has employed, and which is that which has given occasion to this
memoir.
Involvolus or Involvulus oecurs in Plautus.
In the Cistilliarius, act 1, scene 2, verses 455-458, the slave Lampa-
* See Latreille, in Cuvier’s Regne Animal, vol. iv. p. 506. [edit. of 1829.]
BY WHICH THE VINE IS INFESTED. 187
discus, speaking to his mistress of another slave, says that she imitates
a dangerous beast :
« Imitatur nequam bestiam, et damnificam.”
** What is it, I pray?” says his mistress :
“* Quamnam, amaho?”
The slave replies: “ The Involvolus, which rolls and enyelops itself
in the leaf of the vine. In the same manner does she purposely involve
the meaning of her speech*.”
“ Tnvolvolorum, quze in pampini folio intorta implicat se,
Itidem hee exorditur sibi intortam orationem.”
In the Dictionary of Pomponius Festus we find this definition of the
word Jnvolvus : “ Vermiculi genus qui involvit pampino.”
No one can hesitate to recognise the Jnvolvolus of Plautus in the
Involvus of Festus. The word is the same witha very slight alteration.
The curious industry of this insect is confirmed by the testimony of two
authors ; and we learn from Festus that the destiola of Plautus was not
a perfect insect, but the larva of an insect.
XV. Convolvulus—Mareus Poreius Cato, in his treatise De Re
Rustica, gives a recipe to guard the vine from the attacks of the insect
named Convolvulus, which is there engendered. The directions are, to
boiltheresiduum of oil until it acquires the consistency of honey, and then
to anoint the top and the axilla of each plant with the preparationt.
“Convolvulus iz vinea ne siet, amurcam condito,” &c. And at the end,
* Hoc vitem circum caput, et sub brachia unguito, Convolvulus non nas-
citur.”
Pliny thus quotes this recipe § :
« Ne Convolvulus fiat in vinea, amurce congios duos decoqui in cras-
situdinem mellis,” &c., &e. And in the conclusion, “ Hoe vites circa capita
ae sub brachiis ungi ; ita non fore Convolvulum.”
These passages, which are the only ones in which the name Convol-
vulus occurs, contain no information respecting the insect intended by
it, excepting, indeed, that it greatly injures the vine. We shall have to
examine whether it be the same insect as the Znvolvulus of Plautus, or
whether the two words are applied to two different insects.
XVI. Volvox.—It will not be necessary to inquire whether the insect
* It was necessary for my purpose to translate this passage literally ; Limiers,
Quvres de Plaute, 12m0o, vol. iii. p. 295; Levée, Thédtre des Latins, 8vo, vol. iii.
p- 416; Naudet, 7hédtre de Plaute, Svo, vol. iii. p. 187, may be consulted as
to the manuer in which it has been rendered by various translators.
+ Pomp. Festus, book ix. p. 193. edit. of Dair.
+ M. P. Cato, De Re Rustica, chap.95. vol. i, p. 52, Bipontine edition ; vol. i.
'p. 84. of the Scriptores Rei Agraria, 2nd edit. of Gesner,
§ Pliny, book xvii. chap. 28, 47. vol. ii. p. 91 of the edit. of Hardouin, folio ;
vol. v. p. 741. of the edit. of l'yanzius.
188 BARON WALCKENAER ON THE INSECTS
named Volvox by Pliny is the same as that which he names Coavol-
vulus, for he himself distinguishes them.
After indicating the remedy for the Convolvulus, this author ‘informa
us that the Volvox is another animal which destroys the young grapes ;
and to prevent its propagation, he recommends that the knife em-
ployed to dress the vine should be wiped with the skin of the beaver,
and the plant rubbed with bear's blood.
“ Alii Volvocem appellant animal prerodens pubescentes uvas : quod
ne accidat, falces, cum sint exacute fibrina pelle detergent, atque ita pu-
tant; sanguine ursino liniri volunt post putationem easdem.”
XVI. Voluera.—Eruca.—We must consider these two words toge-
ther, because we find them associated in the same passage of Columella ;
and indeed I am not certain that they ought to be separated from Vol-
vox ; for it must be stated, that in the passage of Pliny which I have
just quoted, several editors read Volucra instead of Volvocem. Vol-
vocem is however the reading of all the ancient manuscripts of Pliny ;
and the reading of Voluera has only been introduced, because there is
a passage in Columella which, though rather different, appears to have
been derived from the same source: and as itis impossible to substitute
Volvox for Volucra in Cotumella,—this latter word being a second time
employed in the plural, in a verse which cannot be altered without de-
stroying the measure,—the editors of Pliny have decided upon altering
thetext to bringit intoagreement with that of Columella. Columella’s com-
mentator, Gesner, justly censures this alteration, and recommends that the
reading of the manuscripts should be preserved in these two authors, and
that consequently the word Volvocem should be re-established in Pliny.
In his treatise upon trees, Columella*, after mentioning the rats and
mice which infest the vine, says: “ Genus est animalis, Volucra appel-
latur, id fere prerodet teneras adhue pampinos et uvas: quod ne fiat,
falces quibus vineam putaveris, peracta putatione sanguine ursino k-
RTE. Vel si pellem fibri habucris, in ipsa putatione quoties faleem
acueris, ea pelle aciem detergito atque ita putare incipito.”
«“ There is a kind of animals named Volucra, which destroys almost
entirely the tender shoots of the vine and the grapes. To prevent its
ravages, the vine after it is dressed should be frequently anointed with
bear’s blood, and the pruning-knife rubbed with beaver's skin every time
it is sharpened.”
Columella in his poem upon the cultivation of gardens, after speak-
ing of culinary vegetables, recapitulates the enemies by which the hopes
of the agriculturist are destroyed, viz. tempests, rain, hail, inundations,
and, which are still more formidable, the Volucra and Caterpillar, ene-
mies of Bacchus and green willow plats, which envenom the seed,
* Columella, De Arboribus, chap. 15. vol. i. p. 54,
BY WHICH THE VINE IS INFESTED. 189
devour the leaves, and leave nothing of the plant but a withered and
barren stem.
‘« Brassica, cumque tument pallentia robora betze,
Mercibus atque olitor gaudet securus adultis,
Et jam maturis querit supponere falcem,
Szepe ferus duros jaculatus Jupiter imbres,
Grandine dilapidans hominumque boumque labores :
Szepe etiam gravidis irrorat pestifer undis,
Ex quibus infestz Baccho, glaucisque salictis
Nascuntur Volucres, serpit Eruca per hortos.
Quos super ingrediens exurit semina morsu,
Quez capitis viduata coma, spoliataque nudo
Vertice, trunca jacent tristi conjuncta veneno*.”
Here the Volucres and the Eruce are mentioned by Columella as
different insects ; the first are described as enemies of the vine, the se-
cond as destructive to the willow. -““ At quibus infeste Baccho nascuntur
Volucres, glaucisque salictis (infesta) serpit Eruca per hortos.”
This interpretation, which does not appear doubtful, suggests a curious
remark. It is this, that with the exception of the Latin translation of
the Bible—the Vulgate—in which the word Gaza has been improperly
rendered Hruca, the word Hruca has never been employed by the La-
tins, in its Latin form, to denote an enemy peculiar to the vine. Pliny
and Columella mention the Eruca as the scourge of trees and plants in
general, without excepting the vine, but they do not speak of it as its
especial enemy ; and when Palladius, in the passage which we have
cited, gives a specific for the caterpillars infesting the vine, we have
seen that he employs the word Campas and not Erucas.
This observation is not made with the intention of inferring from it,
that among the names applied by the Latins to insects infesting the
vine there are none denoting Caterpillars, or the larvae of Lepidoptera;
but it suggests the idea that the insects injurious to the vine mentioned
under the names Jnvolvulus, Convolvulus, Volvox, and Volucres by
the Latins, were considered by them as particular species of worms or
insects, and not as the larve of Lepidoptera, or Caterpillars, or of ani-
mals of the same nature as the Kampai and Eruce ; and that conse-
quently the Latins were unacquainted with the metamorphoses of these
species of insects.
In this critical examination I have been careful not to omit any words
which are found employed in the writings which remain to us of the
Hebrews, Greeks, and Romans to denote insects destructive to the vine.
I shall now pass to the second part of this memoir, in which we shall
explain the ancient texts by the aid of modern science, and offer such
practical considerations as may be useful to the agriculturist.
* Columella, book x., De Culiu Hortorum, ver. 26 to 336. .
190 BARON WALCKENAER ON THE INSECTS
Second Section.
Determination of the species of insects known to the ancients and
moderns, by which the vine is infested, and indication of the means
of preventing their ravages.
I. Preliminary Remarks.—In the first part of these researches, I
examined the ancient texts in which the names of insects injurious to
the vine occur, taking the authors in chronological order whenever
this plan did not destroy the relations of etymology or derivation
existing between the words the signification of which was to be deter-
mined, This method appeared to me the only one adapted to the
attainment of the end which I proposed.
All languages vary, and, like the people by whom they are spoken,
experience the effects of time, revolutions, and custom. Various con-
temporary writers employ the same words in different senses, either
because they do not possess the same degree of knowledge of the
things designated by them, or because they differ from each other with
respect to the intention with which the terms in question are employed ;
one writer being required to limit his meaning to one simple, special, or
rigorous sense, and another, on the contrary, having in view a figura-
tive sense only, or a vague or general notion.
The examination of all the texts in which the same word is employed,
has furnished us with the signification, more or less determinate, which
each author attached to the word, and also with the different circum-
stances and particulars contained in each text relative to the insect
named, which consequently may serve as means to distinguish it.
We have been careful to recapitulate the various significations which
result from our critical examination of each word; to compare the
imperfect notions of the ancients with the more precise knowledge of
the moderns ; it will therefore only be requisite to recall to our minds
the result of each of these examinations, without being perplexed, in
this last and difficult investigation, by philological discussions. Should
we be forced to commence new inquiries of this nature, it will only be
with regard to words which offer matter for curious or useful digres-
sions, and not in relation to those which essentially belong to the sub-
ject of which we are treating.
But it will not here be requisite to follow the same order of discus-
sion which we thought it necessary to adopt in our first section. We
are not now endeavouring to determine the significations given by each
author to a certain word, independently of its real sense, but to ascer-
tain that real sense from the various significations that have been
ascribed to the word, and the different applications which have been
made of it. Things, not words, are now the subjects under considera-
BY WHICH THE VINE IS INFESTED. 191
tion ; things must therefore indicate the order to be followed in deter-
mining the value of words. We therefore commence with insects
which are only slightly connected with our subject, or upon which the
ancients havé furnished us with particulars from “hich only vague and
uncertain or too general notions can be derivéd; and we shall pass sue-
cessively to those insects which are the principal objects of our re-
searches, and for which the texts furnish us with circumstantial details
and more precise methods of determination ; according tothe custom
of algebraists, who first eliminate from their equations the parasitic
quantities, or those which furnish only imperfect data for the solution
of the problems to be solved.
Il. Spondyle, or Sphondyle——Scarabeus Melolontha of Linneus—
The Chafer (Hanneton).—Digression on the various species of Chafers
known to the ancients, on several Scarabei which are allied to that
genus, and on the employment of the word Melolontha by the ancients and
the moderns.
According to the order which we have marked out, the word Spon-
dyle, or Sphondyle, claims priority.
The conclusions derived from the examination and comparison of the
texts are, that the larva of this insect is sufficiently large to have been
taken for a small serpent; and that it preys upon the roots of all sorts of
plants, excepting that of the Aristolochia, or Wild Vine, Vitis sylvestris,
which is the Clematis or another plant, but which is not the Vine*.
We are acquainted with only one species of larva which fulfills these
conditions; it is the common Cockchafer, so well known and so much
dreaded by horticulturists under the name of the white worm. The
larva of the Melolontha Fullo, or of the Melolontha vulgaris of modern
naturalists, according to the results we have obtained, is the Spondyle
of Aristotle and Pliny.
I find in Aldrovandus+ that Agricola said that the modern Greeks
give the name of Spondyle to a species of worm of the size of the
little finger, with the head of a reddish colour, and the body white,
which is found in the earth entwined around the roots of esculent
vegetables. This is certainly the larva of the Chafer. Did Agricola
receive this information from modern Greeks, and is the word Spon-
‘dyle still employed by them to denote the white worm ?
If the Spondyle of Pliny is the same as that of Aristotle, it follows that
‘the latter naturalist, who designated a perfect insect by this name, was
acquainted with its metamorphosis ; which will not appear surprising if
we remember that Aristotle, as I have already observed, has exceedingly
well described the metamorphosis of the Cabbage Butterfly, and that
after that description he generalizes the fact, and remarks that the
* Aristotle and Pliny. See p. 179, antea.
+ Aldrovandus, De Insectis: Frankfort, 1618, p. 225
192 BARON WALCKENAER ON THE INSECTS
greater number of insects come from a worm (scolex): “ the whole
worm grows larger,” he says, “ and becomes an articulated animal*.”
Aristotle has well observed that the Spiders, Grasshoppers, and
Crickets are not produced from worms, but from animals similar to
themselves. These ideas upon the metamorphosis of insects are very
exact, and though Aristotle blends with them a few errors, which it is
unnecessary to consider here, they afford proof of the perseverance with
which he pursued his observations, and the surprising skill which
he possessed for generalizing acquired facts, and for discovering and
predicting those not previously observed.
It must not be forgotten that it is in relation to the manner in which
coition is effected in insects that Aristotle names the Spondyle; and the
Chafer is precisely one of those insects which present themselves most
frequently to our notice in coition.
From the text of Pliny and the assertion of Agricola, it appears that
among the Latins, and the Greeks of the Lower Empire the name of
Spondyle has been retained to denote the larva of the large species
of Chafer, with the metamorphosis of which they were unacquainted.
That an insect so common as the Chafer, and which acts a part so
important to agriculture by the mischief which it occasions, even in the
state of a perfect insect, to the leaves of plants and trees, was known to
the Latins as well as to the Greeks, cannot be doubted; but we are
ignorant whether they gave it a particular name, or whether they in-
cluded it under the general names of Scarabeus and Cantharis, so often
employed by them to denote all kinds of Coleoptera.
Fabricius, who has detached the Chafers from the genus Scara-
beus of Linnzus, has given to this genus the name of Melolontha,
which the Swedish naturalist had assigned as the specific name of the
most common species. This name is borrowed from Aristotle, who —
employs it in the same manner as those of Cantharis and Carabus, to —
denote various species of Searabei, which in our natural systems be-
long to very different families or to very dissimilar genera. It was —
from the opinion of the learned of the time of Aldrovandus+, and
adopted by Bochart{, that Linnzeus made the Melolentha of Aristotle
our common Cockchafer; but, as Latreille has well observed§, from a
comparison of the texts of Suidas, Pollux, and the scholiast on Aristo-
phanes, it appears that the name Melolontha was given, among the —
Greeks, to insects of brilliant colours, a description which does not
apply to the common Cockchafer.
* Aristotle, book v. chap. 19. vol. i. pp. 286 and 287; book i. chap. 4. No. I.
and books v., xii., and xvii. of Schneider’s edition, Svo, 1811, vol. ii. chap. 17.
(vulgo 19. Scaliger 18), vol. ii. p. 207.
+ Aldrovandus, De Animalibus Insectis, p. 17.
t Bochart, Hierozoicon, part ii. book iv. chap. 2.
§ See Latreille’s Memoir upon the Insects painted or sculptured upon the
ancient Monuments of Egypt, in the Mémoires sur divers Sujets, 8vo.
* BY WHICH TME VINE IS INFESTED. 193
’ Aristophanes, in the comedy of the Clouds, puts these words into the
mouth of Socrates when speaking to Strepsiades: “ Let go your
thought, like the Melolontha which is launched into the air with a
thread around its foot.” The ancient scholiast remarks that this
Melolontha is an insect of a golden colour, which children hold witha
thread and cause to fly*. We know that in modern Greece the
children at the present day attach a thread to the foot of the beauti-
ful gold-coloured insect which naturalists call the Cetonia fastuosa,
which is not scarce in that country, where the children amuse them-
selves with it in the same manner as those of our climates do with the
common Cockchafer; the name of Melolontha should therefore have
been applied to the genus Cetonia, not to the genus Chafer.
An interesting question in archeology here arises, in connexion with
the exact interpretation of a passage of Pliny, which is well worthy of
attention. The Roman naturalist, speaking of the different species of
amulets used in his time to cure the quartan ague, says that three sorts
of Scarabzi are employed for this purpose. “ The first,” he says, “ is
the Scarabzeus which rolls pills, gui pilas volvit, and in consideration
of which the Scarabei are placed among the gods by a great part of
Egypt.” This circumstance enables us to distinguish, without any
doubt, two or three insects of the family of the Coprophagi, the Ateu-
chus sacer of Fabricius (Scarabeus sacer of Linneus), or the Ateu-
chus laticollis, and the Ateuchus Aigyptiorum, brought from Nubia by
M. Caillaud, and recently described by M. Latreille+, who considers it
exclusively as the Sacred Scarabzeus so often sculptured by the Egyp-
tians upon their monuments, and separately in hard stones of various
kinds. But I think that he is mistaken; for I have recently examined
all the Scarabeei of Ancient Egypt, sculptured separately, which are
in the Bibliothéque du Roi, where an individual of the Ateuchus A2gyp-
tiorum, presented by M. Caillaud, is also preserved, and I am convinced
that, among the Egyptian stones representing Scarabzi with smooth
elytra, a certain number have been sculptured from the Ateuchus sacer
of Fabricius, and the others (a smaller number) from the Ateuchus
laticollis ; but all those stones which have the elytra striated, or with ribs
and longitudinal furrows, have the Ateuchus Aigyptiorum of M. Cail-
laud for their type. Thus the name Scarabeus, of the Egyptians,
is applicable to three different species, closely allied to each other cer-
tainly, and having probably similar manners and habits, but which, not-
withstanding, it is easy to distinguish in the sculptured monuments
by unequivocal characters}. The Alewchus sacer, which is black,
* See Camus, Notes upon Aristotle’s Hist. Anim., 4to, vol. ii. p. 478.
+ Caillaud, Voyage a Méroé et au Fleuve Blanc, p.172, Atlas d’ Hist. Nat.
et d’ Antiq., pl. 58: Latreille in Cuvier’s Régne Anim., vol. iv. p. 533.
t Compare Olivier, Coléopt., vol. i. No. 3. p. 150. No, 183. pl. 8. fig. 59.
var. B. ‘The pretended var, A. isa different insect; it has aclypeus between
194 PARON WALCKENAER ON THE INSECTS
appears to be much more common than the Ateuchus AZgyptiorum,
which is of a golden green colour, and must be that imitated by the
artists of Lower Egypt; while those of Upper Egypt have chosen the
Ateuchus A2gyptiorum for their model. M. Caillaud found this insect
in Sennaar, but not in. Egypt. He. however discovered the elytra
and other remains of them in the mummy-cases in Egypt, which seems
to prove that this insect has existed, and perhaps still exists, in that
country. As Aristotle and Aristophanes employ the word Cantharis
to denote the Sacred Scarabzeus, I infer that these two authors had in
view the Ateuchus Algyptiorum of M. Caillaud.
This first species of Scarabeus of which Pliny speaks is also,
according to the view we have taken, the first of the three species of
these insects which are mentioned by Horapollo as being held in great
veneration by the Egyptians.
The second species of Scarabzeus used as an amulet for the cure of the
quartan ague, spoken of by Pliny, is employed, he says, by the magi-
cians, but that care must be taken to collect these insects with the left
hand. This species has small reflected horns, eui sunt cornicula reflexa.
From this indication, Hardouin, and other commentators following
him, refer this insect to the Zucani. They are mistaken. .
The Lucanus, vulgarly called the Stag-Beetle, is one of those insects
which Pliny has most correctly described* ; and naturalists have therefore
allowed it to retain the name which he assigned to it. He gives a good de-
scription of its long, indented, and bifureated horns, which he says are
suspended around the neck of children to preserve them from the bite of
venomous beasts: “ Cornua prelonga bisulcis dentata foreipibus in
eacumine.” This will not agree with the little recurved horns of the
other species of Scarabzeus with which it has been identified. This second
species of the Scarabzeus of Pliny appears to be the second species de-
scribed by Horapollo; according to this author it has two horns, and the
form of the bull; it is sacred to the moon. We are disposed to think that
this is the large species of Copris (Bousier ), with two horns, which M. Sa-
vigny brought from Egypt, and named Midas. It is sculptured in the
temple of Karnak, and according to the observation of Latreille appears
to belong to the genus Onitis, recently separated from the Coprophagit.
.M. Millin, in his account of the engraved Egyptian stones in the
Bibliothéque du Roi, says that an engraving of a sculptured Scara-
bzeus may be seen in the cabinet of antiques of St. Geneviéve,
which he considers as the Scarabeus Mimas. In this he is mistaken,
for the Scarabeus Mimas is a species peculiar to America; but the
the elytra, which are also of a different form. Schcenherr, ‘Sy ynonymia Insect.,
vol.\i. p18 ;Caillaud, Voyage a Méroé et au Fleuve Blanc, vol. iv. p. 272,
Atlas d’ Hist. Nat. et d’ Antiq. ii. 58. p. 10.
* Pliny, Hist. Nat., book ii. chap. 34.
+ Latreille, Mémoires, pp. 148, 153. Compare Descript. del’ Eg ypte,vol. iii.p.d4
BY WHICH THE VINE IS INFESTED. 195
error of this estimable archeologist is a slight one, since the Scara-
beus Mimas is a Copris as well as the Midas of Egypt, which it re-
sembles even almost to its colours. There is therefore reason to think
that the Egyptian stone mentioned by M. Millin represented the Copris
Midas which M. Savigny discovered in Egypt.
The third species of Scarabeus employed, according to Pliny, as an
amulet against the effects of the quartan ague, was named the Fuller
(Fullo). This insect was spotted with white; and the mode of em-
ploying it was to divide it into two portions, one of which was affixed
to each arm, while the two other species of insects of which we have
treated were attached. only to the left arm. “ Zertiwm, qui vocatur
Fullo, albis guttis, dissectum utrique lacerto adligant, cetera sinistro.”
All Pliny’s commentators are:silent. upon this remarkable passage, and
upon the.insect named F’ullo by the Romans; but, naturalists have not
been equally careless. _Mouffet, whose work appeared after his death
in 1634, describing the largest species of Chafer of our climates,
which is nearly an inch and a half in length, and is distinguished with
facility by the brilliant white spots upon its corselet and elytra, com-
bats the opinion of those who consider the Fullo of Pliny as a Copris
or a Forficula, and supposes that by this name the Roman naturalist
intended to denote the large species. of Chafer with white. spots which
he (Mouffet) had just described*. Ray, whose History of Insects was
published in 1710, is of the same opinion+ ; and lastly, M. Scheenherr,
in his laborious work specially devoted to the synonymy of insects, cites
Pliny for his Melolontha Fullo }.
It is with regret that I contest an abel apparently so sell estas
bilislied by the suffrages of so many eminent naturalists ; but my own
observations are opposed to it. I have examined a great number. of
antique stones upon which insects were sculptured or engraved, some
of which have perhaps been used as amulets, for they were pierced in
a manner adapted for suspension. at the neck, and they all represented
either Coprophagi or Cetonie§. Not one of them can belong to a
species of Chafer, which may be easily distinguished. from the in-
sects previously mentioned by a more lengthened form. . The fact is
the same with regard to the obelisks, and all the monuments of Egypt
of which drawings have been published. I here speak only of. the
Scarabzi or Coleoptera, and not of the species of Bee or Wasp sculp-
. M.Latreille, who has been engaged
in a similar examination, has Sesiveld at the same conclusion.
* Mouffet, Insect., sive minimorum Animalium Theatrum, 1684, folio, p: 160.
+ J. Ray, "Hist. Insect., 1710, 4to, p. 93.
t C. J. Scheenherr, Synonymia Insect., part iii. Upsalia, 1817, 8vo, p. 164.
§ There are Coprides, but. no Cetonie among the Scarabei at the Biblio-
théque du Roi, but I have seen many of the latter in several other collections.
|| [What insect was really intended to be represented by the sculptures here
196 BARON WALCKENAER ON THE INSECTS
It appears therefore that the Melolontha Fullo of Pliny should be
sought for among the Coprides, (Bousiers,) or among the Cetonia,
and not among the Chafers.
Pliny says that the green Scarabsus possesses the property of ren-
dering the vision more penetrating, and that engravers upon gems rest
their eyes by gazing upon these insects. “ Scarabai viridis natura
contuentium visum exacuit, itaque gemmarum sculptores contuitu eorum
acquiescunt*.” Marcellus Empiricus, copying Pliny, relates the same
fact, but he gives us the additional information that this Searabzus is of
the colour of the emerald, “ Scarabeus coloris smaragdini.” This defini-
tion is exactly suitable to the Cetonia fastuosa, and to the Cetonia
aurata, particularly to the former. These two species are of a beautiful
golden or emerald green, but the Cefonia aurata is distinguished from
the other by white spots upon the elytra (“albis guttis”); it is nine lines
in length, and is frequently found in gardens, upon roses and other
flowers. The great Chafer with white spots, the Melolontha Fullo of
modern naturalists, is, on the contrary, rare, and is found only upon
downs and in the vicinity of the sea.
From all these circumstances I conclude that the Cetonia aurata was
the object of the superstition of which Pliny speaks, and is the insect
to which he gives the name of Fullo.
To recapitulate: the word Spondyle, or Sphondyle, in the works of
Aristotle, denotes the Cockchafer, both the perfect insect and its
larva.
As employed by Pliny, who was unacquainted with the metamorphosis
of the Cockchafer, Spondyle denotes only the larva of this insect, or
the white worm, taken for a small serpent, which in the time of Agri-
cola, in the sixteenth century, was still known to the Greeks by this
_name of Spondyle.
The “ Scarabeus qui pilas volvit” of Pliny, which cured the quartan
ague and was adored by the Egyptians, is the Scarabeus sacer of
Linneus, the Ateuchus sacer and Ateuchus laticollis of Fabricius, and
the Ateuchus egyptiacus of Latreille and Caillaud.
The true Searabzeus of Horapollo, the wings of which form rays
when extended, is also the same insect.
The Sacred Scarabeus, named Cantharis in Aristotle and Aristo-
phanes, is the Ateuchus egyptiacus.
The “ Scarabeus cui sunt cornicula reflewa” of Pliny is the Ateuchus
Midas, the Copris Midas, common in Egypt and brought from that
country by M. Savigny.
The Scarabzeus with two horns, sacred to the moon, of Horapollo, is
also the Copris Midas.
alluded to is still we believe a subject of discussion. See London and Edinburgh
Philosophical Magazine, vol. iv. p. 170.—Epir. }
* Pliny, Hist. Nat., book xxix, chap. 38, yol. viii. p. 270.
BY WHICH TIE VINE IS INFESTED. 197
The Melolontha of Aristotle and the Greek authors, which served as
a toy for children, is the Cetonia fastuosa.
The Scarabeus viridis of Pliny, which the engravers upon gems
loved to contemplate, is also the Cetonia fastuosa.
The Scarabeus Fullo albis guttis of Pliny is the Cetonia aurata, the
Scarabeus auratus of Linneus, which has white spots upon the
elytra.
As it is proved that the Spondyle of Aristotle and Pliny is the
Chafer, we have been right in directing our attention to this word,
for the Chafer destroys the leaves of the vine, as well as of all other
plants. This genus includes a species, smaller than the common one,
which entomologists have named the Chafer of the vine, Melolontha
Vitis, because it is frequently found upon that plant with the Chafer
of Frisch, Melolontha Frischii, which is perhaps only one of its
varieties* ; but this insect is found almost as frequently upon the
leaves of the willow and the rose-tree as upon those of the vine; and it
is not one of those of which our vine-dressers and cultivators particu-
larly complain, nor did it attract the attention of agriculturists among
the ancients.
Before concluding my observations upon the word Spondyle, I must
not forget to remark that Fabricius has employed it to designate a genus
of Coleoptera which he has formed in the family of the Prioni, and
named Spondylis buprestoides, the Attelabus buprestoides of Linnzeus;
but this insect, the larva of which lives in the wood of green trees, has
no relation to the Spondyle of the ancients, the larva of which attacked
the roots of young or annual plants. It was not M. Fabricius’s inten-
tion, in selecting this name, to assume that any relation existed between
them: but what I have said in my preliminary reflections may be ap-
plied to this case, and relieves me from the necessity of extending my
observations upon this subject.
Til. Joulos, or Julus—The Juli—There is still less reason for the
appearance of the name of Joulos among those given to insects injurious
to the vine than for that of Spondyle, although Suidas has said that
the Joulos was a worm of the vine; but this lexicographer is the only
one who has so ill defined the insect of which the ancients have spoken
under the name of Joulos. From a comparison of their texts, it appears
that the Joulos is an apterous or wingless insect, possessing a great num-
ber of feet; that it has the lengthened form of a worm; moves in a
serpentine manner ; coils itself up when touched; and is found in moist
places. Modern naturalists cannot have been mistaken with regard to
this insect, for which they have retained the ancient name. The name
* Walckenaer, Faune Parisienne, vol. i. p. 185. Olivier, Entomologie,
genus Hanneton, No. 39. pl. 2. fig. 12. a, 6, c. p. 84. vol. i, Scheenherr, Syne-
nymia Insect., vol. i. part iii. p. 193.
Vou. I t—Pive IL. P
198. BARON. WALCKENAER ON THE INSECTS
of Julus, given to a genus of insects by the moderns, corresponds
exactly to the Julus or Joulos of the ancients; especially if the moderm
signification of the word be restrained to the genus Julus of Leach*, as
defined in his excellent work upon the polypodous insects, excluding the
Polydesmata and other genera, which have with propriety been removed
from it. The Juli which the ancients had in view were probably the
terrestrial Julus and the Julus sabulosus of modern entomologists, and
the common Julus of M. Soavi, erroneously confounded with the former
two. These insects are found on the earth under stones; they feed
upon the leaves and fruits which fall upon the ground and are there
decomposed; but they neither injure the vine nor any other plant.
As they are found under the shadow of the vine, as well as in all other
dark and humid places, the injuries arising from another cause have
been attributed to them.
IV. Biurus.—Grillo-talpa.—Mole-cricket—The word which, after
Spondyle and Julios, has the least relation to our subject of those which
we have passed in review is Biurus. I find it only in an isolated pas-
sage of Cicero, cited by Pliny, in which it is said that this animal de-
stroys the vines of Campania. Thus, it is not mentioned as an enemy
to the vine, correctly speaking, but as injuring the vines of Campania
in particular, by its rapid multiplication. Perhaps also in this passage,
which Pliny only quotes incidentally, Cicero was speaking of a particular
case in which the Biuri were seen to be injurious to the new planta-
tions of vines in Campania, though they would be incapable of injuring
them when the roots had acquired sufficient hardness to resist their
attacks. Whatever be the fact, the etymology of the word Bi-Uros,
which, as we have seen, implies an insect armed at its posterior extre-
mity with a double tail, directs us to the Mole-cricket and the larger
species of locusts (Sauterelles), the only insects so formed that can
answer to the particulars specified, from their size and the destruction
which they cause, and of ravaging vine plantations extending over a
whole country. But the locust having been well known to the Latins
under the name of Locusta, and to the Greeks under that of Acris+,
it follows that the name of Biurus is applicable only to the Mole-
cricket. The probability of this is increased by these circumstances ;
that this insect is the largest which is known in our parts of Europe, it
being not less than an inch and half in length ; that it is one of the
most singular in its formation, and one of the most destructive ; that it
cannot be recognised in any of the descriptions of insects transmitted to
us by the ancients ; and lastly, that, in all the writings which they have
left us, the name Biurus is the only one that can be applied to it.
* Leach, Zoological Miscellany, 1817, 8vo, vol. iii. p. 32 to 48.
+ Vulgate and Septuagint versions of the Bible. hae De Insectis,
p- 160.
BY WHICH THE VINE IS INFESTED. © 199
- Latreille says that the Mole-cricket was unknown before the time of
Mouffet. This is not the ease: it is true that Mouffet is the first who pub-
lished a good representation of it ;—the first who gave itthe name of Mole-
cricket, or rather Cricket-mole, Grillo-talpa, a description which applies
toitalone*. “ Liceat,” says he, “hic queso nobis pre nominum inopia ono-
matopoiein ;” and he properly rejects the names of Sphondyle and Bupres-
tis, which had been given to it; but this rejection proves that the Mole-
ericket had previously attracted and engaged the attention of naturalists.
In fact, Aldrovandus had given a good description of this insect before
Mouffet, and a representation of it which, though bad, may still be
recognised : he named it Zalpa Ferrantis, because this insect had been
previously named Mole, and Ferrante Imperato had figured it: Meapo-
litanus diligentissimus aromatarius in naturali sua historia, book xxviii.,
says Aldrovandus. Mouffet is therefore indebted to Ferrante for half
the name which he gave this insect; for, that he was acquainted with
his work is evident from his having borrowed from it the figure which
he published of the Tarantula Spider. Ferrante’s work was printed in
Italian after his death in 1599, and translated into Latin. The original
edition is scarcet+, and no naturalist of late times, that I am aware of,
even including Linnzus, was acquainted with it; at least not one of
them has quoted it. They all think that they have done much in
ascending to old Aldrovandus ; but we have just shown that the history
of the Mole-cricket commences before him and Mouffet, and even be-.
fore Ferrante ; for if the application which we have made of the word
Biurus be, as it appears, exact, we must refer to ancient times for the
first mention of this insect.
The Mole-cricket causes great devastation, especially in the southern
parts of Europe ; it digs holes and constructs subterranean galleries,
and cuts and detaches the roots of plants by means of its fore feet,
which are shaped like saws ; but this it does solely to provide a habita-
tion for its posterity, for it neither eats plants nor their roots, but feeds
only upon insects, and destroys a great number of the injurious ones{.
The havoc caused by the Mole-cricket ( Courtilliére) has probably been
confounded with the devastation committed by the white worm of the
Cockchafer, for, according to a recent ‘dictionary of agriculture§, the
name of Courterolle has been given to both in several of the cantons of
France||.
* Mouffet, Insect. Theatr., p. 104. chap. 24. ;
+ Ferrante Imperato, Del Historia Naturale, libri 28, Naples, 1599, p. 787.
Talpa insecto. ‘This representation is better than the one given by Aldrovandus.
t Acheta Grillo-Talpa, Fabr., System. Entom., vol. ii. p. 28. No. 1. Walcke-
naer, Maun. Paris., vol. ii. p. 282.
§ Baron de Morogue, Cours complet d’ Agriculture, 1834, 8vo, vol. vii. p- 349,
at the word CourTERo.Le. :
{| [An elaborate memoir “ On the Anatomy of the Mole-cricket,” by Dr. Kidd,
will be found in the Philosophical Magazine, 1st Series, vol. Ixvi. p.401,—Epit.]
P2
200 BARON WALCK ENAER ON THE INSECTS
V. Gaza.— Saddle Locust :— Locusta ephippiger.— Wingless Lo-
cust :—Locusta aptera.—Nymph Locust :—Locusta Puppa—lIt will be
recollected that from our examination of the name Gaza, employed by
the prophets Amos and Joel, (p. 174,) we ascertained that it was used
as the name of an insect eminently destructive, not only of the vine but
of all kinds of plants ; and that its ravages were succeeded by those of
several species of locusts, which completed the destruction of all that
this formidable insect had left undevoured. The word Gaza is ren-
dered by caterpillar in the Septuagint and Vulgate, and by creeping,
that is, apterous or wingless, locust in the Chaldee version. If it be
remembered that in the days of Ptolemy the Jews of Egypt, to whom
we owe the Greek translation of the Sacred Books, were very im-
perfectly acquainted with Hebrew, which was to them a dead lan-
guage; that St. Jerome, whose translation has served as a basis for
the Vulgate, was still more ignorant with regard to the designation of
material objects, it will be found that the Chaldee version is on these
accounts of higher authority than the two other versions: and if the
works of Rosenmiiller and Oedmann*, who have discussed this point of
criticism with equal sagacity and erudition, be consulted, we shall be
convinced, notwithstanding the opinion to the contrary of Bochart and
Michaélis, that the four different names employed by Amos and Joel
as the names of insects, all denote locusts. The observations of the
judicious traveller Shaw remove all doubt upon the subject. He in-
forms us that in Africa, in the months of March and April, it frequently
happens that the locusts driven by the south wind obscure the sun,
and augment in density until the middle of May, and that after com-
pleting their ravages they remove to lay their eggs, and diminish in
number. Then follow, after the interval of a few days, some smaller
species, moving like the former in troops, which are in turn succeeded
by one or two other species, which complete the devastation.
M. Oedmann thought that completely to vindicate the Chaldee text
it was necessary to suppose the Gaza to be a locust without wings or
elytra, not yet come to its full growth, which was mistaken by the
Hebrews for a perfect insect and distinguished by a particular name.
But the orientals were too well acquainted with locusts, which from
all antiquity had supplied them with food, to allow of our imagining
that the Hebrews could have committed such an error. Neither is it
necessary to suppose it. We now know several species of creeping
locusts which perfectly correspond to the creeping locust of the Chal-
dee version ; a fact of which Oedmann appears to have been ignorant.
* Rosenmiiller, Handbuch der Biblische alterthume Kunde, Leipsic, 4th Band,
1831, 8vo, pp. 386 and 388. Oedmann, Vermischte Sammlungen aus der Na-
turkunde, aus dem Schwedischen, uebersetz. von D. Groning, 1787, 12mo,
2nd Heft, pp. 116, 117,
BY WHICH THE VINE IS INFESTED. 201
There is in particular one species which has a deeply excavated corselet
raised at the back like a saddle; this corselet hides the sonorous and
vaulted elytra, which are very short, and do not serve for flying.
These locusts resemble nymphz, but have however arrived at their
perfect state, and propagate their kind. This species has been
named the Locusta ephippiger. There are even other species of which
the females at least are without wings or elytra, and which perfectly
resemble the larva of the Locust ; such are the species named Locusta
aptera and Locusta Puppa by Fabricius. But I am more inclined to
consider the Saddle-loeust, or the Locusta ephippiger, as the Gaza of
the Bible, than either of the two other species that I have mentioned.
Of all the species of creeping locusts the ephippiger is that which I
have most frequently found upon the vine, though never in sufficient
abundance to produce much injury; and it cannot be classed with the
true insects of the vine, neither is it mentioned as such in Scripture.
VI. Cantharis of the Geoponics—Ninth Cantharis of Aldrovandus.
—Rhynchites Bacchus, or Rhynchites Betuleti, or Attelabus of the Vine.
—Becmar-Diableau.—Lisette, and Green Velvet ( Velours vert) of the
Vine-dressers.— The Coleoptera or Scarabei which destroy the Vine,
and do not answer to the Cantharides of the Geoponics.—Lethrus Cepha-
lotes— Gray Curculiones (Charansons).—The ancient authors give the
name of Cantharis to the insects which they employed when pounded
as an ingredient of the liniment or unguent with which they anointed
the vine to protect it from injurious insects ; but it is in the Geoponies
alone, when treating of this employment of Cantharides, that we are
informed that these insects were engendered in the vine, and were de-
structive to it; and the author or authors of this compilation only give
the recipe of Cantharides macerated in oil as a remedy for the disas-
ters which these insects themselves produce*. We have seen that the
word Cantharis was employed by the Greeks, as well as by the Latins,
as the designation of the Coleoptera or Searabei in general ; that this
name was often applied to the brilliantly-coloured Coleoptera, or those
possessing corrosive or vesicating properties ; and that it was also used
as the name of insects, whether of large or small dimensions, which
were rendered remarkable by their destructive effects. Of the first we
have noticed the Mylabris of the endive, the Mylabris Cichorii of
modern naturalists, so well described by Dioscorides ; and the Lytta or
Meloé vesicatoria, the Cantharides of our apothecaries+. Among the
second, or those which are very small, is the Scarabeus parvus Can-
tharis dictus of Pliny which infests corn, which is the Cureulio grana-
* Latreille in Cuvier’s Regne Anim., vol. v. p. 63. Oliv. Coléop. iii. p. 47.
pl. 1. Schoenherr, Synonymia, 1817, 8vo, p. 31. Mylabris, vol. i. part iii.
p- 31. . Oliv., Znt. iii. 47, 7. vol. i. fig. b,c.
+ Latreille in Cuvier, vol. v. p. 67. Scheenherr, Synonymia, vol. i. p. 20.
202 BARON WALCKENAER ON THE INSECTS
rius or Calandra granarius of our modern naturalists; the Curculio fru-
mentarius of Linneus, the Apion frumentarius of Schcenherr and Latreille.
The former is of a dark fulvous colour ; the latter is red and brilliant, and
is, I think, that of which Pliny speaks, for it attacks wheat, while the
other principally infests oats*. These indications leave us in great un-
certainty relative to the Cantharides of the Geoponics. But as it was
undoubtedly their corrosive or vesicating properties which caused the
Cantharis of the ancients to be employed in the liniment which was
destined to destroy other insects, it is probable that their Cantharides
of the vine were insects of the same nature, or other insects which, from
the resemblance of their colour, were confounded with them. Now, as
no Coleopterous insect, or Scarabzeus, has vesicating properties, as no
Mylabris, Lytta, Meloé, or Cantharis lives upon the vine, it is evident
that the insect of which we are in search must be found among those
which from their colour may be confounded or compared with them,
especially with the yellow-banded Mylabris of the endive and the
brilliant green Cantharis of apothecaries, for we know that these species
were employed by the ancients in medicine and agriculture.
We will now pass in review all the Coleoptera or Scarabzi which injure
the vine, and that which corresponds the best to these indications must be
the Cantharis of the vine of theGeoponies. Thelargest of all these Coleo-
ptera or Scarabzei is the Lethrus Cephalotes, which gnaws the young shoots
of shrubs in general, but particularly those of the vine, and carries them
into its hole.t But this species appears peculiar to Hungary, where it
is named Schneider, cutter ; it is also frequently found in the western
parts of Russia; but neither our cultivators nor those of Italy make any
complaint of it. I do not find anything relative to this insect in the
ancient authors, and if they were acquainted with it, it must have been
comprehended by them under the general name of Scarabeus.
It is different with the Curculiones (Charansons), of which we have
seyeral species which infest the vine. The one which I have found
most frequently upon this plant is the Cureulio picipes of Fabricius,
which is perhaps the same species as the Cureulio Corruptor of Host,
and the Curculio Vastator of Marshamt{. The grey Curculiones, with
globular bodies, devour the shoots of the vine as soon as they come out
of the bud. They prevent its development and the production of grapes;
* Scheenherr, Synonymia Curculionidum, vol. i. p. 283. No. 75, genus Apion.
Walckenaer, Faun. Paris., vol. i. p. 237. No. 15. Latreille, Gener. Crust. et
Insect., vol. ii. pp. 249 and 271. Jbid., Cuvier, vol. v. p. 88. Oliv., Entom.
vol. v. 83, 16, 196.
+ Latreille, Gener. Crust. et Insect., vol. ii. p. 95. Ibid., Cuvier, vol. iv. p. 542.
Fischer, Entom. de la Russie, p. 133. xiii. Kirby, Introd. to Entom., vol. i.
p- 204. Ann, des Scien. Nat., vol.i. p. 221.
;~ Walckenaer, Faun. Paris., vol. i. p. 249. Fabricius, Syst. Eleuth., vol. ii.
p- 540. No, 201. Marsham, Entomologia Britannica, vol. i. p. 300. No. 180.
_BY WHICH THE VINE IS INFESTED. 203
but pear and apple trees are more exposed to their attacks than the
vine, and they are more prejudicial in Germany and the South than in
our climates.
The Eumolpus of the vine, vulgarly called the Coupe-bourgeon, is
a third species of the Coleoptera still more destructive than the two
which we have just mentioned ; but this insect, of which we shall pre-
sently treat more at length, like the two preceding ones, possesses but
little brilliancy of colour.
It appears then that among all the Coleoptera or Scarabeei which in-
fest the vine, there are only two species closely allied, and which must
have been considered as one by the ancients, as they have long been
by the moderns, which appear to correspond by their colour to the par-
ticulars which we have obtained in our examination of the ancient texts
relative to the word Cantharis. These two species are the Rhynchites
Betuleti and the Rhynchites Bacchus of modern naturalists ; the Atte-
labus of the vine, or Aéttelabus Bacchus, and the Attelabus of the birch,
of their predecessors. These two species, considered as one by the
vine-dressers, have received from them in the different dialects and pro-
vinces of France, and even in the different districts of the same pro-
vince, the names of Becmare, Urbec, Urbére or Urbée, Diableau, Beche,
Lisette, Velours vert, Destraux, and perhaps others of which we are
ignorant. The Rhynchites Betuleti* is of a brilliant silky green colour,
or of an equally brilliant and silky violet blue. The Rhynchites Bac-
chus+ is of a golden violet purple or of a golden green mixed with
purple. These insects cut the petioles of the leaves to cause them to
wither and soften so as to allow of their being rolled with greater faci-
lity; this they effect with great dexterity, leaving a cavity in which
they place their eggs, and thus injure greatly the plants to which they
attach themselves. The Rhynchites Bacchus} prefers the leaves of the
vine and cherry tree; the Rhynch. Betuleti those of the vine and the —
white birch. In the environs of Paris I have most frequently found the
R. Bacchus wpon the vine; but it was the R. Betuleti which committed
the extensive ravages among the vines of Burgundy about fifteen years
ago. M. Silbermann told me, at Strasburg, that the R. Betuleti is more
destructive than any other insect to the vines of Alsace and the banks
of the Rhine, and that the R. Bacchus is seldom found there. Accord-
ing to the observations of this able entomologist, the R. Betuleti is
* Walckenaer, Faun. Paris., vol. i. p. 235. Attelabus Betule. Schcenherr,
Synonymia Insect., vol. i. p. 222. Panzer, Faun. Insect. Germ. xx. No. 6.
_ + Scheenherr, Gen. et Spec. Curculionidum, Rhynchuivs Bacchus, vol. i. p. 219.
No. 15. Latreille, Hist. Nat. des Ins., vol. ii. p. 85. dttelabus Bacchus. Pan-
zer, Faun. Ins. Germ., fase. 20. No. 5. Charanson Cramoisi of Geoff. Attclabe
cuivré of Olivier.
t Kirby, Zntrod. to Entom., vol. i. p. 199.
204 BARON WALCKENAER ON THE INSECTS
seen in that country as a perfect insect upon the leaves of the vine
towards the end of August. The larva rolls the leaf to hide itself, and
attacks the young grape, but not the buds, being hatched too late.
Schranck, in his Fauna Boica*, has placed these two inseets in a par-
ticular genus, to which he gives the name of Jnvolvulus; but the Lnvol-
vulus of the ancients, as we shall presently show, does not belong to
the class Coleoptera, but to the Lepidoptera ; and I may remark that
the genus Involvulus of Schranck, being badly constituted, has not been
adopted by any naturalist. Though it contains but few species, some
of them are distributed by M. Sechcenherr among his Apoderi, one
among his Adtelabi, and a third among his Rhynchites. Aldrovandus
was well acquainted with the Rhynchites Bacchus; and I am surprised
that no naturalist has quoted this venerable father of natural history
in modern Europe upon the subject of this small but formidable insect.
He places it among the Cantharides, to which he devotes a chapter,
thus separating them from the true Scarabeei which occupy another
chapter. The following is the description which he gives of this Cur-
culio : “ Nonus numerus significat Convolvulum, Ira G'reeis, Tagliadizzo
vulgo apud Italos agriecolas,corpore ceeruleo, pedibus obscure lutescentibus,
in vite repertum, ac folia ejus depopulantem. Nascitur ex ovis bom-
bicum ovis similibus magnitudine, colore rubicundis. Hie cum parere
vult multa eumulat eonvolvitque folia (unde forte a Latinis id nominis
datum), atque in his sua ova reponit.” Thus the name of Tagliadizzo,—
cutter,—given to it by the vine-dressers of Italy; its bluish colours; the
injury done to the leaves of the vine, which the insect rolls up and in
which it deposits its eggs, all mark with certainty the synonymy of our
Rhynchites Betuleti or R. Bacchus with the ninth Cantharis of Aldro-
vandust. But as to the identity of this insect with the Jps of the
Greeks, and the Convolvulus of the Latin authors, which Aldrovandus
attempts to establish, the continuation of our researches will prove that
it must be rejected.
VI. Ips.—dks.— Volucra.— Volvox.—Eumolpus Vitis.—Bumolpus
of the Vine.—Coupe-bourgeons.— Téte-cache —Beéche.—Lisette— Gri-
bouris de la Vigne—After having treated of the Cantharides, Aldrovan-
dus devotes an entire chapter to the Jps of the Greeks, to confirm his
assertion in the preceding chapter that this insect is the Tagliadizzo of
the cultivators of Italy ; but he remarks that he had only found this
insect upon the vine, though the ancient authors say that it preys also
upon horn. If Aldrovandus was wrong in maintaining that the Jps
of the Greeks was the Convolvulus of the Latins, he was right in
thinking that it belonged to the Coleoptera, and was one of those which
the Italian agriculturists class among the Tagliadizzi, or cutters.
* Schranck, Fauna Boica, vol. i. p. 474. No. 498.
+ Aldrovandus, De Anim. Insect., chap. iv. 1638, folio, p. 472.
BY WHICH THE VINE IS INFESTED. 905
' It appears evident, as has been advanced by Valckenaer, Bochart, and
the most learned philologists, that the Zks of certain authors, an insect
which infests the vine, is the same word as the Jps employed by other
authors as the name of an insect which also infests the vine, and that
Ips, Ipes, Iks, Ikes, ave only differences of dialect.. This agreed, it is
evident from our critical examination, that the conclusion to be formed
from the information we receive from the Greek authors, including the
grammarians and lexicographers of the lower ages, is, that Zps is em-
ployed as the name of an insect which preys upon horn and meat, and
also of one which infests the vine, of which it devours the buds, either
in the state of larva or as the perfect insect. We learn from this that
the name of Zps or [ks was applied by the ancients to two or three
different species of insects or larve of insects. But since the ancients
confounded these species, and assigned them but one name, there must
necessarily be an analogy between them. ‘There is only one species of
the larve of the Coleoptera or Scarabzei possessing trophi, or organs for
manducation, sufficiently hard to pierce horn. The Ips of Homer and
of St. John Chrysostom belongs therefore to the Coleoptera, conse-
quently the ps of meat and of the vine must also belong to that class.
As we are treating of an insect which preys upon horn and meat,
naturalists know that it must belong to Linnzus’s tribe of Dermestes,
the larve of which are so formidable to their collections. They are
not ignorant that these insects are found in warehouses of furs, in
offices, pantries, and all places which receive animal matters, and that
they spare neither horn nor feathers; but our knowledge of them is
not sufficient to determine to what genus of modern entomologists
those Dermestes belong which prey upon old goat’s horn, particu-
larly upon that of the AEgagrus, of which the bow of Ulysses was
formed, and which is particularly mentioned by Homer. We are well
acquainted only with the metamorphoses of the Dermestes lardarius,
and the Dermestes Peilio, the Dermestes of bacon and furs. These in-
sects belong to the numerous family of the Nitidularie of Latreille*.
Degeer+ long ago separated from the Dermestes a genus to which he
judiciously gave the name of Zps; but this name has been since given
to genera very different to that which he had created, though they also
were formed from the numerous family of the Dermestes. It might
possibly be the same larva which infested horn and meat, as is asserted
by the grammarian published by Boissonade ; it is also possible that the
ancients confounded the larvze of two affinal but different genera. But
* Latreille, in Cuvier’s Tab. du Régne Animal, vol. iv. p. 503. Schoenherr,
Synonymia Insect., vol. i. part ii. p. 236. No. 25. Walckenaer, Faun. Paris.,
vol. i. p. 124. No. 2. Panzer, Faun. Insect. Germ. Ixxxix. 12. Fabr., Syst.
Eleuth., vol. i. p. 422.
+ Degeer, Mém. pour servir aU Hist. des Ins., vol. v. p. 190.
206 BARON WALCKENAER ON THE INSECTS
certainly the insect designated by the ancients as preying on horn and
meat cannot be the same as that whose worm or larva feeds upon the
young shoots of the vine. However, to render the same name applicable
to them both, they must have belonged to the class Coleoptera, the larvee
of which could not be confounded with caterpillars, or the larve of
Lepidoptera ; the perfect insect which destroys the shoots of the vine
must also resemble the Dermestes in form and dimensions. All these
conditions meet in the Humolpus Vitis, the Eumolpus of the vine of
modern naturalists, which is one of the greatest scourges of that plant.
This insect, which is of a black and blood-red colour, belongs.to a genus
which has been separated from the Cryptocephali*, and is vulgarly known
under the names of the Cryptocephalus ( Gribouris) of the vine, Béche,
Lisette, and Téte-cache, because its head is covered by its corselet. It
feeds upon the buds of the vine, or on the young shoots of that plant
which still remain herbaceous, which it cuts in two and causes entirely to
perish. It feeds also upon grapes. The great injuries inflicted by this
insect upon the vine is an additional reason for considering it as the Zps
_of the ancients. As Strabo observes, we can imagine that the veneration
in which the memory of Hercules was held in a country planted with the
vine was more on account of his supposed destruction of this plague than
of his victory over the Nemzean lion, and why the cultivators were so
anxious to obtain and employ recipes for the destruction of these vermin.
When the ancients spoke of the Jps or Jks as a worm which appeared in
the spring, they had in view the larva of the Eumolpus of the vine. The
larva of this insect is oval ; it has six feet; its head is scaly and armed
with two small maxille+. The insect named Jps or Jks by the Greeks,
was called Volucra or Volvox by the Latins; but with this difference,
that the word Jps and Jks were applied to the larva of this insect, while
Volucra and Volvox were the names of the perfect insect. This is
proved by the use of the word animal, and not vermis, which Pliny and
Columella employ when speaking of the Voluera or Volvox ; while the
Ips is always spoken of as a worm by the Greeks. The name Volucra
has probably been given to these larvae in consequence of the prompti-
tude with which they escape from the hand which endeavours to seize
them, for they drop down upon the earth as soon as the leaf in which
they are enveloped is touched ; and the name Volvox is undoubtedly
derived from this insect’s habit of rolling itself up in leaves. Forcellini,
in his dictionary, gives the Italian word Ritoritelli as the equivalent of
the word Voluera ; this vulgar name of an insect of the vine in Italy has
evidently the same origin as Volvox. Nearly all the insects of the genus
* Buchoz, Hist. Nat. des Ins. nuisibles a 0 Homme, 1782, 12mo, p. 158 to 163.
+ Latreille, Nowy. Dict. d’Hist. Nat., vol. x. p. 358. He quotes Olivier,
No. 96. pl. 1. fig. 1; but this figure does not represent the insect of the vine, but
is a species from Brazil, the Eunolpus ignitus, which is a diiferent insect.
‘BY WHICH THE VINE IS INFESTED. 207
Dermestes- counterfeit death when they are touched, and this conformity
of habit must have contributed to the error of the ancient authors in
confounding together the Zps which preys upon horn and that which
infests the vine. Butthere are still stronger reasons which prove that the
Volucra or Volvox of the Latins is the same insect as the Jps or Tks of
the Greeks. Pliny and Columella inform us that the Volucra or Vol-
vox was a different insect from the Convolvulus. This difference be-
tween two insects which both infested the vine must necessarily have
been complete and radical, since it was remarked by the ancients, who
possessed so little information upon this class of animals. We shall
show presently that the Convolwulus was one of the Lepidoptera or
Butterflies ; the Volucra or Volvox must belong to a totally different
class. Now among insects there are only the larve and the insects
of the Coleoptera, and the caterpillars or larve of the Lepidoptera,
which are very injurious to the vine ; the Volucra or Volvox must there-
fore belong to the class Coleoptera. Besides, we learn from Pliny and
Columella that the Voluera or Volvox infested both the young shoots and
the grapes. Pliny says, “Volvocem animal prerodens pubescentes uvas ;”
and Columella, “ Genus animalis Volucra prerodit teneras adhue pam-
pinas et uvas.” These expressions apply solely and entirely to the
Eumolpus of the vine and the Jps of the Greeks, and not to the Can-
tharides of the Geoponics, the Rhynchites Bacchus or Betuleti, which
injures the vine by rolling up the leaves and causing them to wither,
but which does not attack the fruit. Neither can they be applied, as
we shall shortly see, to the various species of the caterpillars or larvz
of the Lepidoptera which attack the vine.
It is therefore proved that the Zps or Zks of the Greeks is the Volu-
era or Volvox of the Latins, and the Eumolpus of the vine the Zumol-
pus Vitis of modern entomologists.
VII. Lnvolvulus.— Convolvulus.—Pyralis of Bose d’ Antie.— Ver-
coquin.—Procris Vitis, or Procris ampelophaga.— Vine-moth.— Grape-
moth.—Tortrix Heperana.—Cochylis Roserana.—From the recipes given
by Pliny and Cato to prevent the multiplication of the Convolvulus,
we learn that it was an insect eminently destructive of the vine; but
as they neither give any description of it nor furnish us with any par-
ticulars respecting it, excepting that it was a different species from the
Voluera or Volvox, we have no means of ascertaining whether this name
applies to the same insect as is denoted by the name Znvolvulus em-
ployed by Plautus in the passage which has been quoted. In this un-
certainty, the similarity of the roots and the conformity of the onoma-
topeeia, indicative of similar habits and industry, will not allow us to
separate these two words, and induce us to presume that they were em-
ployed to designate the same object, or rather that they are one name,
to which are adjoined two different particles, which do not alter its sig-
208 BARON WALCKENAER ON THE INSECTS
nification. The description of the industry attributed by Plautus to the
Involvulus, to the little beast, “ bestiola que in pampini folio intorta
implicat se,” can be applied only to caterpillars or the larvae of the Lepi-
doptera. The caterpillar not only coils up the leaf of the plant in which
it envelops itself, like the larva of the Eumolpus or Coupe-bourgeon,
but it attaches itself to it, and by means of silken filaments which it
draws from its own body, constructs for its metamorphosis a web of silk,
in which it envelops itself, “ implicat se.” The caterpillars of a whole
family of Lepidoptera envelop themselves in this manner in the leaves
of plants. To discover the Jnvolvulus or Convolvulus of the ancients
it is therefore only necessary to examine those insects of the numerous |
family of the Phalene Tortrices of which the caterpillar attacks the vine.
According to the observations of Bosc, the cultivators of the South of
France give the name of Vine-moth to one of the Lepidoptera which is
seldom found in the environs of Paris. The caterpillar or larva of this
moth attacks the grapes when they have attained half of their full growth,
and it proceeds from one grape to another by means of a gallery which
it constructs*. There is another species named Grape-motht, which
also devours this fruit, and commences its ravages at the same period
as the former, but it seldom attacks more than one grape at a time ;
this species committed great depredations in the vineyards in the vicinity
of Constance a few years ago. A species similar to this, or to the pre-
ceding one, and of which one or two insects are sufficient to destroy a
whole vine, was observed in the Crimea by Pallast. This species appears
to be the caterpillar of a Procris or Zigena (a genus separated from
the genus Sphina:), and is said to be nearly allied to the Zigena Statices ;
it is found upon the sorrel and dock in the environs of Paris§. The
Pyralis fasciana\|, which has anterior wings of a dark cinder colour,
with a brown line and points of the same colour, has also been men-
tioned as infesting the vine, or as corresponding to one of the species
just alluded to. There is also another species which may be ranked
among the insects to which our cultivators have given the names of
Vine-moth and Grape-moth, we mean Hiibner’s Tinea ambiguellaq. But
* Bosc, Notice sur la Pyrale et autres Insectes qui nuisent auxVignobles; Esprit
des Journaux, p. 139, and Bulletin de la Société d’ Encouragement.
+ Kirby, Jntroduct. to Entomology, vol. i. p. 205.
+ Pallas, Travels in Russia, vol. ii. p. 241.
§ Walckenaer, Maun. Paris., vol. ii. p. 284. No. 2. Fabricius, Entom. Syst.,
vol. iii. part i. p. 406. No.8, Godart, Hist. des Lépidoptéres de France, vol. iti.
p- 158. pl. 22. Dict. Classique d’ Hist. Nat., vol. xiv. p. 289, at the word Procris. —
| Fabricius, Hntom. Syst., vol. iii. part ii. p. 261. No. 78, Fabricius considers —
it to be the Vortria Heparana of the Catalogue of Vienna; it is not the Fasci-
ana of Linnzus. Compare Friedrich Treitschke, Die Schmetterlinge von Eu-
ropa, vol. viii. p. 28.
q Hiibner, tab. 22. fig. 153. sect. 64. No. 61 of the text. Treitschke, Die
BY WHICH THE VINE JS INFESTED. 209°
to determine the synonymy of the various species of the Lepidoptera
more particularly injurious to the vine, which I have found mentioned in
the works of naturalists, travellers, and agriculturists, I have had recourse
to the skilful and practised eye, and the judicious criticism of M. Dupon-
chel, one of the most accomplished lepidopterists of Europe.
From an attentive examination of this subject we conclude that, with
the exception of those which are occasionally found upon the vine, as
well as upon other plants, without producing much injury, and of which
we shall treat in the following sections, all the species of Lepidoptera
which may be considered as particularly detrimental to the vine are
reduced to the four following, all producing caterpillars which envelop
themselves in leaves, and to which may equally be applied the ancient
names of Jnvolvulus and Convolvulus. In fact we cannot possibly sup-
pose that the ancients made observations sufficiently exact to distinguish
differences which the moderns themselves, notwithstanding the extended
inquiries lately made upon the subject, have great difficulty in proving.
The first of these species is that which was observed by Bosc, and
which he names Pyralis Vitis ; Fabricius has described this insect under
the name of Pyralis Vitana, from the specimen in Bosc’s collection.
For reasons, unfortunately too decisive, which we shall presently al-
lege, we shall not preserve either of these names: we name it Pyralis
Danticana, from Bosc’s second name Dantic, the name Bosc having
been employed by Fabricius in his description of another Pyralis which
he calls Pyralis Boscana. The second species is the Procris ampelo-
phaga of Duponchel, Bayle, and Passerini, the Procris Vitis of Bois-
duval. The third species is the Tortrix Roserana of Frolich, the Co-
chylis Roserana of Duponchel and Treitschke, and the Tinea ambiguella
of Hiibner. The fourth is the Tortrix Heperana of Treitschke and Du-
ponchel, the Pyralis fasciana of Fabricius.
The caterpillar of the Cochylis Roserana, mentioned by Frélich as
causing great devastations in the vineyards near Stuttgard, has not been
described by him or any other entomologist that I am acquainted with.
There remains then the Pyralis Danticana*, the ampelophagat of
Bayle and Passerini, and the Fasciana, the destructive effects of which
upon the vine cannot be called in question. The caterpillars of the
Schmetterlinge von Europa, vol. viii. p. 280 and 281, No. 8. Cochylis Roserana
alis anticis argenteis ochroleucis nitidis, fascia media intus angustiore fusca.
* Pyralis Vitana, alis fusco virescentibus ; fasciis tribus obliquis fuscis margi-
nalibus. Bosc Dantic, Mém, de la Société d’ Agriculture, 1786, for the summer
quarter, p. 22. pl. 4. fig. 6. Pyralis Vitis, Fabricius, Entom. Syst., vol. iii. p. 2.
pl. 249; A. J, Coquebert, [llustratio Iconographica Specierum Insect. que in
Museis Parisinis observavit, J.C. Fabricius, duas 1. tab. 7. fig. 9.
+ Procris ampelophaga, C. Passerini, Memoria sopra duo Specie d’ Insetti no-
civi. Zigena ampelophaga, Bayle-Barelle, Degli Insetti nocivi al Uomo, alle
Bestie, al Agricoltore; Milano, 1824, pl. 1. fig. 7 to 12.
Q10 BARON WALCKENAER ON THE INSECTS
first two species are the only ones upon which we have continued ob-
servations; these we proceed to mention. The larva or caterpillar of
the first of these two species, the P. Danticana*, according to Bose, is
eomprehended with other species in the environs of Paris under the
collective name of larve or worms which injure the vine ; in Burgundy
and the vine provinces it is called Ver-coquin, a denomination which is
also sometimes given to the white worm of the Cockchafer, the Spon-
dyle of Pliny. This caterpillar of the Pyralis of the vine is, shortly
after its birth, a centimetre in length; its head is black and its body
green, and it has a yellow spot on each side of the neck. Its first ap-
pearance is about the end of May, but its greatest devastations are made
in the middle of June. It cuts the petioles of the leaves in halves, which
causes them to wither, and enables the insect to roll them with greater
facility. When the leaf first attacked withers, in consequence of the
wound which it has made in the petiole, it proceeds to attack another ;
and thus one of these caterpillars will destroy several leaves, weaken
the vine, and prevent the grapes from becoming large and sweet. This
insect does not attack the fruit, but destroys the peduncle of the bunch,
which, if it do not wither, remains small and without flavour. When
the greater part of the leaves are infested, all the bunches are soon in
the same condition, because they grow at the bottom of the stem, and
it is there that this caterpillar commences its ravages. The butterfly or
Pyralis of this caterpillar is of the size of the nail of the little finger ;
its wings are of a green fulvous colour, with three oblique bands of
brown. These Pyralides are most abundant in the month of July.
During the day they remain clinging upon the stems, under the leaves,
whence they fly upon the slightest approach of danger. Towards the
decline of the day, inthe dusk, the male seeks the female; but those which
leave their retreats at an earlier hour become the prey of the swallows
and other insectivorous birds.
I have remarked that Bose identified the butterfly which he described
under the name of Pyralis Vitis with a new species that Fabricius
names Pyralis Vitana. This species, as I have said, was described by
Fabricius at Paris from a specimen in Bosc’s collection; and he adds
five or six lines of technical description. M.Coquebert, of Reims,
published at the same time four fasciculi of insects, drawn, engraved
and coloured from the specimens observed and described by the Danish
naturalist in the collections of Paris, and among the number is the
Pyralis Vitana or Pyralis Vitis of Bosc. It would appear that no in-
sect ought to be better known than the one we are treating of; this
however is not the fact. After a most attentive examination, Dupon-
chel finds the descriptions of Fabricius and Bosc too short, and insuffi-
* Bosc, Nouv. Dict, d’ Hist. Nat., vol. xxxv. p. 392.
BY WHICH THE VINE IS INFESTED. Q11
cient for the recognition of the insect and the determination of its spe-
cies ; he considers Coquebert’s figure of it as too coarsely drawn to
throw any light upon the descriptions. This is also the case with the
descriptions of Bosc, and the figures by which his memoirs are accom-
panied. The German authors, Frolich, Treitschke, and others, who in
latter times have particularly devoted themselves to the study of the
smaller species of Phaleenz, or Moths, are of the same opinion as Dupon-
chel, for not one of them mentions the Pyralis Vitana of Fabricius.
This species is not mentioned in their voluminous works specially de-
voted to these insects ; or if it be mentioned, it is without their being
themselves aware of it. If in the numerous species which they have
described they had discovered the Pyralis Vitana they would not have
failed to cite Fabricius, whose works are in the hands of every entomo-
logist. In this difficulty Duponchel has had recourse to Bosc’s collec-
tion, which now forms part of the collection at the Museum; and he
has found there, under the name of Vitana, a Pyralis which is figured
and described by the German authors under the name of Pillerana.
Now, according to them, the caterpillar of this Pyralis lives upon the
Stachys Germania, a plant too entirely distinct from the vine to allow
of it being easily admitted that it lives indifferently upon the two vege-
tables. But besides, Fabricius has also described the Pyralis Pillerana,
and the description which he gives of it differs essentially from the
Pyralis Vitana ; the latter is marked with three bands, the Pillerana
has only two; the colour of the ground in the Vitana is of a brownish
green, that of the Pillerana is of a golden green. From these circum-
stances M. Duponchel thinks that Bose has committed the error of
labelling one species for another; or, which is more probable, that the
_ label of the Pyralis Vitana has been displaced in his collection, which
is in great disorder. Duponchel has compared the description given
by Bose of the caterpillar of the Pyralis Vitana with those of all the
caterpillars of the Pyralides or Tortrices mentioned in the authors who
have treated of this family, and has not found one which appeared to
apply to it. I however maintain, and remarked to him, that even if we
could suppose that Bosc had been deceived with regard to the butterfly
proceeding from the caterpillar, he was not so with regard to the existence
of the caterpillar itself, and the curious observations which he had made
upon it; and that being myself, two years ago, at Braubach on the
Rhine, in the state of Nassau, I remarked a cultivator (the innkeeper
of the place) engaged in pulling off such of the leaves of his vines as
were coiled up, and he told me it was to destroy an insect which made
great havoc in them. I opened several of these leaves, and found in
them a very small caterpillar, which I examined with a lens; I perceived
that it was the caterpillar described by Bosc, and which I had also pre-
viously observed in the environs of Paris. I expressed my surprise to
AIPA BARON WALCKENAER ON THE INSECTS
M. Duponchel that after the progress which had been made by the
united efforts of French and German naturalists in this branch of ento-
mology, we could not recognise a butterfly which had been twice drawn
and described by skilful naturalists, and which must be common, since
its caterpillar was so. To this M. Duponchel replied that he thought
I was mistaken in supposing myself certain of having distinguished the
caterpillar described by Bosc, because the description given of it by
this naturalist in his memoir is so far from precise that it may be ap-
plied to all the caterpillars of this genus which have green bodies and
black heads, but which differ in other characters of which he does not
speak, such, for example, as the colour of the verrucose points with which
all the caterpillars of this group are decorated. As to the butterfly, the
description and figure by Bosc, the description by Fabricius, and Coque-
bert’s figure, drawn from the individual described by Fabricius in Bose’s
collection, may equally be applied to the four following species of
Phalene : the Cerasana and Riberana of Treitschke, and the Corylana
and Fasciana of Fabricius. ‘The last approaches more nearly than
the others to Bose’s description ; but this species is also described by
Fabricius, and Bosc has not recognised it as his own. Still more, after
saying that Réaumur had not anywhere mentioned the caterpillar which
was the subject of his memoir, he adds: “ It appears to be equally rare
in other climates, for neither Linnzeus, Fabricius, nor Scopoli has de-
scribed the Phaleenz which it produces.”
From these researches and explanations it appears that if the Pyralis
Danticana, Pyralis Vitana of Fabricius, has not been confounded by him
and Bose with the Fasciana; that if it be not the same species as the
latter, it must be considered as a species still unknown, and which can-
not be well known until we have bred all the caterpillars found upon
the vine which resemble the one described by Bose. To deduce this
deficiency in science is almost to acquire the certainty of its being
speedily supplied. Although the silence of the Italian naturalists rela-
tive to this caterpillar be not a decisive reason for thinking that it is not
found in Italy, and did not receive from the ancients the name of Jn-
volvulus, yet this is more especially true with regard to another cater-
pillar to which the names Convolvulus and Involvulus appear more —
peculiarly applicable. More attentive observations have been made
upon this caterpillar than upon that described by Bosc, and its butter-
fly is well known as the Procris ampelophaga, or Procris of the vine so
much dreaded by all the cultivators of Tuscany. ‘This caterpillar some-
times injures considerably the buds and young shoots of the vine. In
Piedmont it sometimes devours half the vine-plots. It is five or six
lines in length, and two lines or two and half in width; its colour is a
brown gray, and the hair is disposed in stars in four longitudmal rows
in semi-globular relief towards the anterior part. The inferior surface
' BY WHICH THE VINE IS INFESTED. - 213
of the abdomen is smooth and of a yellow white; it attains its full
growth towards the end of May, and it is then that it destroys the leaves
of the vine. It attaches itself to the upper part of the leaf, and if the
branch upon which it is found be shaken, it bends itself in the form of
a bow by resting upon the two extremities of its body, and drops down
upon the earth. The greatest number of these caterpillars that are to
be found upon one vine amounts to about ten; they are generally much
fewer. Between the 20th and 30th of May this caterpillar spins a cod
of long white flocks, in which it remains motionless, and is transformed
into a chrysalis from the 5th to the 10th of June, The chrysalis is at.
first yellow, with black points upon each segment, but at the moment.
of transformation the colour increases in intensity and is changed into.
a deep azure blue. The transformation of the chrysalis into the butter-
fly generally commences on the 19th of June, and is not concluded till
the 25th. This butterfly is the Procris Vitis, or Procris ampelophaga
of modern entomologists. ts wings are of a dark colour, approaching
to black, and changing into a sombre green; the body is of a blueish
green. The Musca brevis often introduces its eggs into the body of
the chrysalis of this butterfly ; the larve of the fly feed on the substance
of the chrysalis without altering its exterior, and the chrysalis thus ap-
pears to be metamorphosed into a fly instead of producing a butterfly,
Each female of this Procris lays about three hundred straw-coloured
eggs, of so small a size that they are scarcely visible to the naked eye.
Towards the 3rd of July these eggs produce small whitish caterpillars,
which are transparent, and covered with almost imperceptible hairs.
The caterpillars of this second race are metamorphosed about the 26th
of August.
I have myself verified in part the observations made upon the cater.
illar of the Pyralis Danticana by Bose. The habits of the Procris
ampelophaga are only known to me from the memoir of M. Passerini.
But if the first species be as abundant in Italy as the second, I shall
-be induced to think that it is to it that the ancients more parti-
cularly applied the names of Involvolus, Involvulus, Involvus, and
Convolvulus.
1X. Kampe.— Eruca.— Caterpillars of the Sphinx Elpenor, or
Sphinz of the Vine,—of the Bombyx purpurea, or Ecaille mouchetée
(Spotted Tiger-moth),—and of the Sphinx Porcellus, or Sphinx with red
bands.—The other caterpillars that are found upon the vine, and which
may occasionally injure it, as well as plants of every other kind, do not
belong to the tribe of Tortrices, or Pyralides, nor to the genus Procris.
The species which I have most frequently had occasion to remark, are
the Bombyx purpurea of Fabricius, the Arctia purpurea of modern na-
turalists, and the Ecaille mouchetée of Geoffroy, which lives also upon
Vou, I—Pant II. Q
214 BARON WALCKENAER ON THE INSECTS
the common broom, the elm, and twenty other plants*. The Sphinx
Elpenor, or the Sphinx of the vine of Geoffroy, (this is not the Sphinx
Vitis of modern entomologists, an American butterfly which does not
live upon the vine,) is frequently found upon the vine, but it is also
met with not less frequently upon:the Epilobium, the Salicaria, the
balsam, and the convolvulus +. Lastly, the Sphinx Porcellus, or the
Sphinx with red indented bands, the caterpillar of which is sometimes
found upon the vine, but still more often upon the honey-suckle, la-
vender, and more especially upon the yellow bed-straw, Galiwm ve-
rum{. The last two species have caterpillars as large as the little
finger, and as they keep upon the summit of the shoots they may be
easily removed.
These are the caterpillars or larve of Lepidoptera which the Greeks
and Latins, when speaking of insects infesting the vine, designated by
the general names of Kampe or Eruca; but they did not confound
these larvee with worms, and they knew that they underwent metamor-
phoses.
X. Phtheir—Tholea or Tholaath—Coccus Vitis —Kermes of the
Vine—Coceus Adonidum.—Greenhouse Coccus.—The Phtheir or
louse of the vine, which Ctesias mentions as an insect which causes the
vine to perish, and which in the Geoponics is classed with the cater-
pillars among that plant’s greatest enemies, can correspond only to the
Coccus Vitis, to the Cocci, or the Kermes of the vine §. We know
that the Cocci or gall-insects, or the Cochineals, with the Aphides,
are the insects which, from their small size and their rapid multiplica-
tion, are the most similar to the louse ; their females also, like lice, are
apterous, or without wings. The Cocci cover so completely the bark
of the trees that it has a scurfy appearance. When the female has de-
posited her eggs, her body dries up and becomes a solid crust, which
covers the eggs, and its squamous surface is not unlike fat nits. These
insects do harm by piercing the wood with their sharp proboscis, which is
formed of a sheath having numerous joints, and three bristles or darts of
great tenuity. With this tube they suck the sap and cause it to flow.
* Aretia purpurea, Fabr. Entom. Syst., vol. iii. part 1. p. 466. No. 185.
Walckenaer, Faun. Paris., vol. ii. p. 291. Godart, Papillons nocturnes, vol. i.
p. 339. No. 105.
+ Sphinx Elpenor, Fabr. Ent. Syst., vol. iii. p. 372. No. 51. Walckenaer,
Faun. Paris, vol. ii. p. 276. No. 6. Godart, Crépusculaires, p. 46.
t Sphinx Porcellus, Fabr. Ent. Syst., vol. iii. p. 873. Walckenaer, Faun.
Paris., vol.ii. p. 279. Godart, Crépusculaires, p. 51. Duponchel, Iconographie
des Chenilles, tribe of Sphingide, pl. 5. fig. 1, a, b.
§ Ctesias, Indicorum, cap. 21. p. 253. edit. Baehr, Frankf., 1824, 8vo.
Ctesias speaks of a red insect which in India destroys the trees producing am-
ber, as in Greece the Phtheir destroys the vine: Larcher, p. 341. vol. vi. of his
translation of Herodotus, has badly rendered this passage. :
BY WHICH THE VINE IS INFESTED. 215
Our cultivators do not complain of these insects, and know but little of
them, because the annual pruning which the vines undergo prevents
their multiplication, as the Cocci can only live upon young wood,
while its epidermis is still tender. They are however sometimes very
abundant upon neglected vines ; and in countries where the vine is only
cultivated in greenhouses, they multiply extremely, whilst the other
enemies of the vine are there unknown*. But the vines in green-
houses are not attacked by the same species of Cocci as they are ex-
posed to in the open air. In the former situation they are attacked by the
Coccus Adonidum+, not by the Coceus Vitis. If, as has been asserted,
this insect originally came from Senegal, it is not among the species
treated of by the ancients, who also could never have distinguished
from each other the various species of the Coccus, which is as much as
can be effected by the practised eye of the modern entomologist, aided
by a powerful lens, even since the beautiful and recent work of
M. Boyer de Fonscolombe upon these insects. This skilful naturalist
remarks with truth that there are no well-established limits between
the Kermes and the Cocci, between the Gall-insect and the Progall-
insects of Réaumur. He therefore makes but one genus of the Coccus
and the Kermes; but this he subdivides into several sections, and the
Coccus of the vinet belongs to the section which is composed of spe-
cies which at the time of laying have naked bodies, without any trace
of rings or members, and rest upon a very cottony nest. The Coccus
Adonidum, or Kermes of the greenhouse, is also remarkable for the
white and downy substance which transudes through its skin, and
which gives it a mealy aspect.
The interpretation of the word Thola, Tholea, or Tholaath employed
in the Bible, which we considered at the commencement of these re-
searches, applies to the name Phtheir given to the Gall-insect by the
author of the Geoponics. It will be recollected that the result of our
long discussion upon this subject was, that Thola is employed in the
Bible to signify not only a worm, vermin, an insect or larva of an insect,
or an animal vile and despicable, but also an insect or larva of an in-
sect which infested the vine, and another plant, the name of which we
are unacquainted with, but which we know to have been a large tree,
because it gave an extensive shade. Indications so vague would not
* J. Major, (Landseape Gardener,) A Treatise on the Insects most prevalent
on Fruit Trees and Garden Produce, 1829, 8vo, p. 112.
+ Coccus Adonidum, Fabr. Syst. Rhyngotor., 1803, 8vo, p. 307. No.4. Major,
as just referred to, p. 144, the Mealy-Bug.
t Coccus Vitis, Boyer de Fonscolombe, Ann. de la Soc. Entom., vol. iii. p. 214.
No. 14. Réaumur, Mem. Insect., vol. iv. p. 62. pl. 6, figs. 1 to 7, Fabr. Syst.
Rhyngotor., p. 310. No. 4. Coceus vitis vinifere.
Q2
216 PRARON WALCKENAER ON THE INSE€TS
lead us to any probable conjecture upon the subject of the Thola or
Tholea, if this word, which in the Bible is employed separately, were not
elsewhere frequently found in conjunction with the word Dibaphi* to
denote the insect that the Arabs term Kermes, and which, when heated
with vinegar, produces a fine red colour, in a word, the Cochineal in-
-sect. The species of cochineal which produces this colour in Europe
are the Coccus Ilicis, which attaches itself to the green oak+, and which
consequently may be the insect mentioned in the Bible as the destroyer
of a tree giving shade; and the Coccus Polonicus, which adheres to
the roots of the annual Scleranthus and other plantst. The Coccus of
the yine does not produce this colour, but the resemblance of these in-
sects, and their generic affinities, must have caused them to be con-
founded with the other Coccus, or the Tholaath Dibaphi, or at least
comprehended under the same denomination. Thus we say, and with
much less propriety, the worm of the apple and the nut, though these
are the larvze of insects of very dissimilar genera. The word Thola or
Tholaath in the Bible was employed for vermin, louse, a small, insig-
nificant, vile, and contemptible insect, as the Phtheir ; but the epithet
Dibaphi, designating the Kermes or insect useful in dyeing, which was
sometimes added to the word Thola or Tholaath, indicated sufficiently,
by the similarity of the species, the nature of the insect or vermin in-
tended by the word, and which was productive of so great injury to
the vine and certain trees, .
XI. Means which are to be employed to destroy the Insects which infest
the. Vine-—The recipes of Pliny and Columella for the protection of
the vine from the insects which attack it appear to prove that the Coeci
committed greater ravages upon the vines in ancient than in modern
times. Their directions were to rub the stems and branches of this plant
with greasy substances, such as oil or bear’s fat, to which was also added
the use of vesicating substances. Modern cultivators, as I have said,
protect the vine See the Coccus by pruning it. But other methods
must be employed for the destruction of the Weevils (Becmares) and
Coupe-bourgeons, the Rhynchites Bacchus and Rhynch. Betuleti, and
the Eumolpus Vitis. The best of all is to choose the moment when
these insects have undergone metamorphosis and begin to copulate, and
to place under each vine a kind of basin made for the purpose in the
form of a deeply recurved crescent, so as to surround the stem or branch
* Bochart, Hierozoicon, p. 22.
+ Coccus Ilicis, Fabr. Syst. Rhyngotor., p. 308. Réaumur, Jnsect., iv. tab. 5:
Garide], Plantes des Environs @ Aix, p. 250. pl. 35. Boyer de Fonscolombe,
a de la Société Entom., vol. iii. p. 210.
t Coccus Polonicus, Fabr. Syst. Rhy yngoter:. p- 310, No. 26. © Frisch., Insect.
56. -Walckenaer, Faun. Paris., vol. ii. p. 363.
BY WHICH THE VINE IS INFESTED. - 217
under which it is placed, and then to shake the branches and make the
insects fall into it. . The substitution for the basin of a very wide tin
funnel with a bag at the extremity, into which the insects fall, has
been proposed; also that of linen twisted into the same form. The same
means may be applied for the caterpillars of the butterfly or moth as
for the Coleoptera, especially when they have arrived at a certain size.
The devastation is then indeed almost completed, for the leaves are de-
-eayed and partly devoured ; but the repetition of the evil in the follow-
‘ing years may be precluded by thus preventing the reproduction’ of the
insects. To this method may be added another, which is. particularly
adapted to the destruction of the Pyralis of the vine, the Procris ampe-
_lophaga of Passerini, and in general to that of all the small species of Pha-
lene which attack the vine: it is that of lighting fires at the commence-
ment of the night in a direction opposite to the wind. The insects come
in crowds to the fire and are burned. These fires must be renewed for
ten or twelve days in succession, but not when there is much rain or
wind; for not only the flame will not burn, but the butterflies in such
weather remain obstinately fixed to the leaves to which they have at-
tached themselves. The most effectual method of destroying all the
larvee of the Lepidoptera and Coleoptera which attack the vine is to
“remove, one by one, the coiled leaves in which these insects have de-
posited their eggs, and to throw them into a furnace and burn them.
This method is the most tedious and expensive, but it is also the most
certain ; and I have seen it pursued with great patience and care in the
state of Nassau by the cultivators on the banks of the Rhine.
Third Section.
Synonymy of all the species of insects which have been mentioned in
these researches.
We shall present in this section one of the principal summaries of
these investigations by giving the synonymy of all the insects of which ‘
we have had occasion to treat ; but to adapt it to the end in view we
* must proceed in an order the inverse of that which we followed in the
preceding section ; that is, we must first give the synonymy of the in-
sects which are most detrimental to the vine plants, and then proceed
to those which only injure them occasionally, and conclude with those
which the ancients have erroneously designated as the enemies of the
vine ; carefully conforming, with regard to each of these three sorts of
insects, to the classification most generally adopted by modern. natural-
ists. Finally, we shall conclude by giving a list of insects which do not
injure the vine, but the synonymy of which has been incidentally deter-
mined in these researches.
218
BARON WALCKENAER ON THE INSECTS
I. Synonymy of the Insects most injurious to the Vine.
COLEOPTERA.
Names of Modern Naturalists,
Latin and French.
Eumolpus Vitis (the larva).
Ancient Names.
1. Greek. Ips (Vitis).
Iks.
2. Latin. Volucra. Eumolpus Vitis (the perfect
insect).
Eumolpe de la Vigne.
1, Rhynchites Bacchus (the
larva).
2. Attelabus
larva).
Attelabe de la Vigne.
Charanson de la Vigne.
1. Rhynchites Bacchus (the
perfect insect).
2. Rhynchites Betuleti (the
perfect insect).
Attelabe de la Vigne.
Charanson de Ja Vigne.
Lethrus Cephalotes.
3. Latin. Volvox.
Betuleti (the
4. Greek. Kantharis.
5. Greek. Kantharis.
Melolontha.
Latin. Scarabeus.
ORTHOPTERA.
1. Locusta Ephippiger(Saute~
relle aselle oud cymbale).
2. Locusta aptera (Sauterelle
1. Hebrew. Gaza.
aptére).
3. Locusta Puppa (Sauterelle-
Nymphe).
HEMIPTERA.
1. Hebrew. Thola, Tholea, or ;1. Coccus Vitis ; Cochenille de
Tholaath. la Vigne.
Tholaath Dibaphi.
Greek. Phtheir. Adonidum.
—Ilicis.
Polonicus.
LEPIDOPTERA.
1. Latin. Involvulus or Invol- | Pyralis Danticana (the cater-
volus. pillar)?
Involvus. Pyralis Vitis. Bose Dantic,
Convolyulus. Mém. de la Société d’ Agric.
Campe. 1786, p. 22, pl. 4. fig. 6.
Pyralis Vitana.
Pyralis Fasciana. Fabric., En-
tom, System.
Greek. Kampe.
Common Names.
French. Gribouri dela Vigne
(the larva).—Coupe-bour-
geon.— Ebourgeonneur.—
Couturiére.— Ver de la
Vigne.
Gribouri de la Vigne (the per-
fect insect).
Coupe-bourgeon, &c.
Urbie. —Béche. — Lisette.—
Diableaux.—Destreaux.
Italian. Tagliadizzo.
Becmare.—Eng. Weevil.
Velours vert.
German. Schneider (Cutter).
English. Saddle Locust.
Wingless Locust.
Nymph Locust.
English. Mealy-bug (Punaise
farineuse). Kermes of the
vine.
Cochenille des Serres (Green-
house Coccus).
Cochenille du Chéne vert.
Cochenille de la Scleranthe.
Fr. Ver-Coquin.
Teigne de la Vigne.
Eng. Vine-moth.
Ancient Names.
2. Latin. Convolvulus.
Involvulus.
3. Involvulus.
Convolvulus.
4. Involvulus.
Convolvulus.
Names of Modern Naturalists,
Latin and French.
Procris ampelophaga (the ca-
terpillar). Duponchel, Suppl.
aUHist. des Lépid. t. 2, p.
92, pl. 8, fig. 2.
Procris ampelophaga. Bayle-
Barelle, Det Insetti nocivi ;
Milano, 1824,
Procris ampelophaga. Passe-
rini, Mem. sopra due Specie
d’Insetti nocivi, nelle Mem.
dell’ Accad. dei Georgifili,
1830, p. 4, t. 1, fig. le 14.
Sphinx ampelophaga. Hiibn.
Suppl. t. 24, fig. 153 et 154.
Atychia ampelophaga. T’reit-
schke, t. 10, Suppl. p. 100.
Sphinx Vitis. Freyer, Beytr.
ii., Bd. xii., Ht. 5, 69, tab. 68.
Procris Vitis. Boisduval, Icones
Historiques des Lépidopteres
nouveaux, t. 2, p. 79, pl. 56,
fig. 2 et 3.
Cochylis Roserana. Dupon-
chel, Hist. des Lépidopt. t.
9, p. 418, pl. 257, fig. 8.
Tortrix Roserana. J reelich,
Enumer. Tortricum Wiir-
temb, indig. p. 52. No. 511.
Tinea ambiguella. Hiibner,
tab. 22, fig. 153 (foem.).
Cochylis Roserana. Treit-
schke, t. 8, p. 280.
Tortrix Heperana (the cater-
pillar).
Tortrix Heperana (the cater-
pillar). Duponchel, Hist.
des Lépidoptéres de France,
t. 9, p. 67, pl. 238, fig. 7.
Tortrix Heperana. Wien,
verz.? Illiger, Schranck,
Gotze et Treitschke, t. viii.
p- 58, No. 8.
Tortrix Padana. Schranck,
Faun. Boica, ii., 32, Abth.
5, 78, No. 1755.
Tortrix Carpiniana. Hiibner,
tab. 18, fig. 16 (foem.).
Tortrix Pasquayana. Fre-
lich, Wien, Verz. p.36,No0.55
Pyralis Fasciana. Fabricius,
Ent. Syst. iii. 2, 348, 24.
Lozotenia Carpiniana. Ste-
phens, Syst. Cat. of British
Insects, p. 169, No. 6852.
La Chape-Brune. Geoffroy,
t. 2, p. 169, No. 118. ~
Phaléne Chape-Brune du Li-
las. Degeer, t. 1. Mem. 13,}
p- 403.
BY WHICH THE VINE IS INFESTED,
Common Names.
Fr. Teigne du Raisin.
Ver-Coquin.
Ital. Ritoritello.
Eng. Grape-moth.
Teigne de la Vigne.
Rouleuse.
Tordeuse.
Eng. Leaf-roller.
Small Brown-bar.
Chape-Brune.
Teigne du Lilas.
Teigne du Raisin.
Teigne de la Vigne.
Eng. Dark Oblique-bar.
19
220 BARON WALCKENAER ON THE INSECTS
Il. Insects which only occasionally injure the Vine.
COLEOPTERA. .
Ancient Names. Names of Modern Naturalists, Common Names.
Latin and French. ;
1. Greek. Spondyle. Melolontha vulgaris. — Le| Le Hanneton.—Eng. Cock-
Hanneton vulgaire. chafer; May-bug; Oak-web.
2. Latin. Spondyle genus ser- | Melolontha vulgaris (the lar- | Ver blanc.
pentis (Plin.). va). Ture.
Melolontha Vitis (the larva). | Man.
Courterolle.
Petit Hanneton d’été, ou Han-
neton vert (the grub).
ORTHOPTERA.
1, Biurus. Acheta Grillo-Talpa (Fabr.).| La Courtilligre—Eng. Mole-
Talpa Ferrantis (Aldr.). cricket.
LEPIDOPTERA.
1. Greek. Kampe. 1. Arctia purpurea (the cater-|Chenilles de la Vigne.
Latin. Eruca. pillar). Vine Caterpillars.
L’Ecaille mouchetée.
2. Sphinx Elpenor (the ca-| ng. Elephant Moth.
terpillar).
Sphinx ou Papillon rouge
de la Vigne.
3. Sphinx Porcellus (the ca-| Eng. Small Elephant Moth.
terpillar).
Sphinx ou Papillon a bande
rouge dentelée.
Ill. Insects erroneously described by the ancients as injuring the Vine.
POLYPODA.
1. Greek. Tulios. 1. Julius sabulosus, Jules des| Mille-Pieds.
Latin. Centipedes. sables. Eng. Galley-worm.
Millipedes. 2. Julius terrestris, Jules ter-
restre.
3. Julius communis, Jules
commun.
COLEOPTERA,
1. Greek. Kantharis. 1. Mylabris Cichorii, Mylabre | Mouches-cantharides.
Latin. Cantharis, de la Chicorée.
%. Lytta vesicatoria, la Can-| Eng. Spanish Fly.
tharide.
2. Greek. Ips (Homer). Dermestes (the larva). Ver.—Eng. Leather-eater.
IV. Names of Insects mentioned by the Ancients, which do not injure the
Vine, but the modern names of which have been determined in these investi- _
gations.
1. Greek. Melolontha. Coleoptera of Linnzus. Scarabées.
Kantharis. Eleutherata of Fabricius. Escarbots. j
Latin. Scarabeus. Eng. Beetles, Chaffers, Dors,
Cantharis. Clocks, and Bobs.
2. Greek. Kantharis. Latin. 1. Ateuchus sacer. Le Pillulaire,
Scarabeeus sacer.
BY WHICH THE VINE IS INFESTED. 991.
Ancient Names. Names of Modern Naturalists, Common Names.
‘ Latin and French.
Latin. 1. Scarabeus qui pilas 2. Ateuchus Aigypti-] Eng. Tumble-dung Beetle.
volvit (Plin.). orum.
’ F Scarabée sacré.
Bousier sacré.
3. 2. Scarabzus cui sunt | Latin. Onitis Midas. Le Pillulaire.
cornicula reflexa | French. Bousier a deux cornes.
(Plin.). Bousier of
Horapollo, which
has two horns
and resembles a
bull.
4, 8. Lucanus cui sunt} Zatin. Lucanus cervus.
cornua prezlonga| French. Lucane Cerf-volant. | Le Cerf-volant—Eng. Stag-
bisulcis dentata beetle. Pinch-bob.
forcipibus in ca-
cumine (Plin.).
Ge 4. Scarabzus Fullo al- | Latin. Cetonia aurata.
bis guttis (Plin.). | French. Cétoine dorée. Eng. Green or Rose Beetle.
6. 5. Ipsof Homer, of St.| Larva of the Dermestes Pel-
JohnChrysostom,| lio, of the Dermestes Lar-
and of the gram-| . darius; the larva not yet
marians of the| known ofa species of Der-
middle ages. mestes which is related to
these two species, and
which gnaws the horn of
the AEgagrus, or wild goat.
7. Greek. Kantharis. Latin. 1. Curculio granarius, | Corn-weevil.
Calandra granaria.
Latin. Scarabeus parvus| French. La Calandre, ou le
Cantharis dictus (Plin.).| | Charanson des Grains.
4 Latin.2. Curculio frumenta-
rius, Apion frumentarius.
French. Charanson du Fro-
ment.
V. Summary of the Synonymy of the Insects mentioned in these researches,
_ arranged according to their natural order.—To accommodate agrono-
mers and the learned, we thought it necessary in the preceding para-
_ graph to divide the synonymy of the insects which have been mentioned
in these researches into three sections. For the use of naturalists it
must be repeated according |to the natural order, and without any di-
stinction of those which injure the vine much, or little, or not at all. For
the sake of brevity we shall be satisfied with designating the insect by
the name which it bears in our best systems; it will be immediately
followed by the French or common name most generally in use, and lastly
by the ancient names, printed in small capitals.
‘ MYRIAPODA. CoLEoPTERA.
1. Julus sabulosus, Jule des sables. 1. Dermestes Lardarius,
JuLios, CENTIPEDES, MILLEPEDES. Dermestes Pellio, aut species proxima ;
2. Julus terrestris, Jule terrestre. (the larva).
JuLios, CENTIPEDES, MILLEPEDES. Le Dermeste des fourrures ou de la corne
3. Julus communis, Jule commun. (the larva).
Juxios, CenTIrEDES, MILLEPEDES. Irs of Homer.
222
2. Ateuchus sacer, le Bousier sacré, le Pil-
lulaire.
CANTHARIS, SCARABEUS QUI
votvitT (Plin.).
3. Ateuchus Egyptiorum, BousierEgyptien.
CANTHARIS, SCARABZUS QUI PILAS
voLuvirT (Plin.).
4. Onitis Midas, le Bousier 4 deux cornes.
SCARABZUS CUI SUNT CORNICULA RE-
FLEXA,
5. Lethrus Cephalotes, Schneider (Cutter).
KANTHARIS, MELOLONTHA,SCARABZUS.
6. Melolontha vulgaris, le Hanneton ordi-
naire.
Spondyle (the perfect insect).
Sphondyle genus serpentis (Plin.) (the
larva).
7. Cetonia aurata, la Cetoine dorée.
ScARABZUS FULLO ALBIS GUTTIS (Plin.).
8. Lucanus Cervus, le Cerf-volant.
Lucanus.
9. Mylabris cichorii, Mylabre de la chicorée.
KANTHARIS, CANTHARIS.
10. Lytta vesicatoria, la Cantharide.
KANTHARIS, CANTHARIS.
11. Eumolpus Vitis, Gribouri de la Vigne
(the perfect insect). Ver-Coquin (the
larva).
Ips (the larva). VoLucra (the perfecti n-
sect).
12. Rhynchites Bacchus, Attelabe de la
Vigne, Becmare, Tagliadizzo.
Votvox, CANTHARIS.
13. Rhynchites Betuleti, Velours-Vert.
CaANTHARIS.
14, Calandra granaria, la Calandre, Cha-
ranson des grains.
ScARABZUS PARVUSCANTHARIS DICTUS
(Plin.).
15. Curculio frumentarius, Charanson du
Froment.
SCARABEUS PARVUSCANTHARIS DICTUS
(Plin.).
PILAS
Thus there are thirty-six species of insects known by the moderns, of
which we think we have determined the corresponding names in He-
brew, in Greek, and in Latin.
VI. Conelusion—In France at the present day, 800,000 hectares
[1,976,914 acres] of land are planted with the vine, the fruit of which,
converted into wine, yields an annual produce of 760,000,000 franes,
[30,158,7302. sterling.] The consideration therefore of the insects
destructive of a plant which is the source of so much wealth does not
appear superfluous; and to lessen my regret at having so long occupied
the time devoted by the Academy to researches of more importance, I
would at least persuade myself that these minute inquiries are not —
devoid either of interest or of utility.
ON THE INSECTS BY WHICH THE VINE IS INFESTED.
ORTHOPTERA.
1. Acheta Gryllo-Talpa, le Grillon-Taupe,
la Courtiliére.
Brurus (Cicero, Plin.).
2. LocustaEphippiger, Loc. aptera, Loc. Pupa.
Sauterelle 4 Cymbales, Sauterelle aptére,
Sauterelle Nymphe.
Gaza (Hebrew).
HEMIPTERA.
1, Coccus Vitis, Coc. Adonidum, Coc. Poloni-
cus, Cochenille de laVigne,Cochenille des
Serres, Cochenille de la Scléranthe.
THOLA or THOLAATH( Hebrew). PHTHEIR
(Greek).
LEPIDOPTERA.
1. Arctia purpurea, |’Ecaille mouchetée.
KampE, Ervca (the caterpillar).
2. Sphinx Elpenor, Pap. rouge de la Vigne.
Kampe, Ervuca.
3. Sphinx Porcellus, Papillon a bande rouge
dentelée.
Kampe, Eruca (the caterpillar).
4, Pyralis Danticana, P. Vitana, Chenille ou
Teigne de la Vigne, Ver-coquin, la
Chenette.
CamPer, INVOLVULUS, INvoLVUs, CoN-
VOLVULUS.
5. Procris ampelophaga, Atychia ampelo-
phaga, Procris Vitis, Teigne du Raisin,
Ritoritello.
Camper, InvoLvuLus, INvotvus, Con-
VOLVULUs (the caterpillar).
6. Cochylis Roserana, Tortrix Roserana, Ti-
nea ambiguella, Teigne de la Vigne.
Camper, InvoLtvuLus, INnvoLvus, Con-
VOLVULUs (the caterpillar).
7. Tortrix Heperana, Pyralis Fasciana,Lozo-
teenia Carpiniana, Tort. Padana, T. Pas-
quayana, Chenille de la Chape-brune,
Teigne du Lilas,Teigne de laVigne. -
Camper, INvoLvuLUsS, INVOLVUs, CoN-
VOLVULUS, (the caterpillar).
to
bo
iS)
ARTICLE X.
The Kingdoms of Nature, their Life and Affinity ;
by Dr. C. G. Carus.
From the Zeitschrift fiir Natur und Heilkunde, Band 1.Hefte 1. Dresden, 1819,
Wauen man awakes from that state in which he is but the passive
recipient of impressions from the external world, and when therefore, in-
stead of reposing in the consciousness of his increasing in strength and
stature and exhibiting a reciprocity of bodily action of various kinds
with surrounding objects, he feels the spirit, the infusion of the breath of
God, in motion within him, he is powerfully impelled to endeavour, by
bringing the relations between the spirit within and the phenomena
without into a clear point of view, to obtain a clearer knowledge of him-
self. This desire has its origin in a most distinct conviction that without
such knowledge no real harmony, no true internal equilibrium can be
conceived to exist in man, and that nature and he must therefore stand
as two eternally separated beings. But a feeling that things are sepa-
rated which at the same moment exist in and through each other, is
totally incompatible with that internal repose which, as we ourselves
are one, is to be found not in the sense of separation but in the con-
sciousness of unity. In this fact we clearly see what it was that gave
birth to those speculations, by means of which it was sought for so
many ages, sometimes with more and sometimes with less sincerity and
freedom, to ascertain the relations between the phenomena of nature
and the laws of mind. In those speculations, however, we have oceasion
to observe, how frequently that which stands forth in us most plainly and
undisguisedly, and which for that reason should be supposed discernible
and known at the very first, was exactly the least heeded and last dis-
covered. It was, no doubt, owing to this circumstance, that many a
truth which presented itself almost unveiled to the pure and unsophis-
ticated feeling of the genuine children of nature remained a hidden
mystery to the sages of mankind.
In order to avoid such errors it is particularly important that we
should give a general and exact definition of the terms proof and expla-
nation. Now to explain is but to consider a phenomenon in the clear-
ness of a superior light, and to prove is but to trace a subordinate
proposition up to a higher, or rather to aprimary truth. The supreme and
one, which is alike the foundation of nature and mind, can therefore
no more be proved or explained than the splendour of the sun ean
be increased by means of some terrestrial light. On the contrary, the
294 DR. CARUS ON THE KINGDOMS OF NATURE,
immediate consciousness of a supreme and eternal unity is the primary
standard by which we distinguish the just, the true, and the beautiful.
Without this principle we should indeed be incapable of pursuing any
general inquiry and of forming any judgement, so that demonstration and
science can exist for those only who recognise a positive and supreme
principle. We hold, therefore, that the true end of scientific inquiry
(so far as it is to furnish explanation) is not to define and demonstrate
the highest principle, but to trace other truths up to this, to show the
harmony which,exists between nature and mind, or to discover a unity
of law in the multiplicity of phenomena.
It is hoped that these general remarks may be sufficient to indicate
the guiding principle of the following inquiries, which, being designed
to lead to a clear conception of Life in general, and its single forms in
particular, are here recommended by their author to the friendly atten-
tion and examination of medical men and naturalists, previously to
their being, perhaps, at some future time, presented by himself or by
some one else, in that strictly scientific form which is found so indispen-
sably necessary to all who would penetrate the essence of nature, and
obtain, instead of the vague and negative notions which commonly
prevail, a distinct and positive knowledge.
If, with this view, we direct our attention to one only of the end- —
less variety of forms which life assumes ; if we observe, for instance,
how a plant through internal instinct and under external relations un-
folds itself from an obscure and insignificant seed, how its parts mul-
tiply, and how their organization becomes progressively more and more
refined, until it reaches its acme in the flower, where the plastic power
again concentrates itself into a seed, and thus closes the circle of its
being in that form out of which it had first issued, we find throughout
this chain of phenomena an internal pervading principle, a certain de-
terminate succession, a regularity which compels us to expound all these
movements, changes, and developments as parts of a whole, as the ope-
yations of one internal universal cause in which all others are compre-
hended. It is evident that this internal, this essential and efficient
principle can be no single thing, such ‘as the body of the plant, the
chemical change of its substance, or the circulation of its sap, and
still less the effect of external influences, but rather all these together—
a something in which all these inhere as their common cause, and which
we characterize as a unity by the generic appellation /ife. Hence it is
easy to perceive how erroneous it would be, for instance, to suppose the
plant first-organized, and life then added to it as an attribute and con-
sequently as something extrinsic, nearly in the same manner as we should
‘conceive of a machine as a thing consisting of several parts put together
and possessing, at first, no inherent power of acting, but having this
power imparted to it when it is completed. On the contrary, life is
necessarily the original principle, and the body one of its particular
THEIR LIFE AND AFFINITY. ; 295
phenomena, conceived therefore not as permanent but as perpetually
changing ; and this idea of it is conveyed in the term formation, inas-
much as it signifies a thing not only formed but forming itself. We
know, for example, that the human body after a series of years is a
very different thing from what it was at an earlier period; nay, that the
body of the adult does not contain even a single atom of that which
constituted the foetus; and nevertheless, that the internal, the living
principle, the man, as every one’s consciousness undeniably assures him,
is still the same, nothing being changed but the phenomena of life,
among which, as we have already shown, the body is to be included.
As it follows from the foregoing observations that life is not a single
isolated reality, we shall be obliged to define it generally as the constant
manifestation of an ideal unity through a real multiplicity, that is, the
manifestation of an internal principle or law through outward forms.
This view of the subject willindeed derive additional light from the analo-
gous character of that inward principle which we call sow/, inasmuch
as this also consists not in this or that particular thought, or in the mere
succession of our thoughts, or anything else of the sort, but in the
whole spiritual life in general, that is, in the constant revelation and
manifestation of an internal unity—of the deepest consciousness of the
individual identity through an infinite variety of sensations and ideas.
If we now cast a look on that universal nature which surrounds us,
the endless multiplicity of its phenomena is indisputably manifest ; and
as it would be an absurdity to imagine a highest number to which
another number cannot be added, we can fix the limits of nature no-
where, either in the great or in the small, because the infinite divisibility.
of each would lead again to infinity. These infinities are nevertheless
included in the comprehensiveness of the whole ; there is but one whole,
(the word has no plural form in our language,) and the idea of this
necessarily contains at the same time the internal multiplicity, or rather
infinity ; for it would be a manifest inconsistency to conceive of a real
whole as a unity, while in its strict reality it implies rather the idea of an
infinity of individuals. Thus we find in fact the idea of life, that is, the
constant manifestation of unity through multiplicity, exhibited by univer-
salnature ; and are therefore bound to consider nature collectively as one
yast and infinite life, in which, though the extinction of any one of its va~
rious modifications, or the merging of a single external form of life in the
universal life, is possible, an absolute and proper death is inconceivable.
_ Proceeding from this general view to the consideration of single
beings, we perceive that all those individuals, so far as they are inte-
grant parts of universal nature, must partake more or less of its essential
properties,—that whatever is essential to the one must be partially re-
peated in the other. Every natural being must therefore appear, like
nature in general, partly as a unity (in which light only it is an indivi-
dual), and partly as a multiplicity, in which light it is infinitely divisi-
226 DR. CARUS ON THE KINGDOMS OF NATURE,
ble*, and its action and reaction upon the different other individuals may
also be infinite. At the same time it still further appears that such an
individual approaches more nearly to general nature in proportion as
the multiplicity manifesting itself in its unity is more comprehensive
and striking. A substance therefore (a geometrical body, for instance, )
which is merely multiform and infinitely divisible in space but immu-
table in time, has far less claim to this affinity than a body, such as that
of a plant or an animal, which changes in time also because of its con-
tinued growth and progress toward an independent life. Although, as
has been shown already, the idea of life is in full and perfect accord-
ance with universal nature, and consequently no natural body can, in
this general view, be accounted anything more than a living member of
the whole, yet there is a vast difference perceptible between individuals,
inasmuch as the collective idea of life, a life proper to themselves, ma-
nifests itself in some, while others are less independent and can be re-
cognised only as necessary parts of other individuals.
Now it is clear that the idea of life and that of an organism are es-
sentially the same; for any unity that continually develops itself in-
wardly and outwardly into a real multiplicity is named—so far as it pro-
duces means, that is to say, instruments or organs suited to its own de-
velopment—an organism or organized body, and everything belonging
to it is termed organic. Its action is therefore named organic life, and
that which is generated in space by this living action the organic body.
Universal nature is consequently to be considered as the highest, the
most complete, the original organism ; and 7” nature those individuals
only are to be called organisms which, as unities under certain external
conditions, that is in their relation to other natural unities, continually de- |
velop themselves inwardly and outwardly into a real multiplicity. Among
such organisms the most prominent are those bodies which, including ©
our planet, constitute the system of the universe, and display them-—
selves in continual motion and formation; those on our planet consist
of plants and animals. |
Now, as in an animal a piece of bone, muscle, or skin, and in a
plant a fragment of the wood, leaf, or fruit, may be considered as or- ;
ganic, but cannot be called an organism, all substances, except plants and —
animals, observable in and upon the body of the earth, so far indeed as ;
they are parts of the terrestrial organism, are to be regarded as organic
and as parts of a living thing, but not as organisms possessing an inde-_
pendent life. :
According to this view we must include among those things which
do not as unities develop themselves into multiplicity, —that is, among
* [An investigation of this part of the subject will be found in a paper “ On —
the Origin and Production of Matter, and on its alleged Infinite Divisibility,”
in the Philosophical Magazine, First Series, vol. Ixii. p. 360, et seg. See also B
vol, lxiii. p. 8372,—Eprr. }
THEIR LIFE AND AFFINITY. 227
Inorganisms,—\st, all substances which, though infinitely divisible, being
but mechanically so, are incapable of being developed into various parts
and of maintaining at the same time their individual existence ; and
therefore all elementary bodies, such for instance as oxygen, hydrogen,
carbon, the metals, sulphur, &e. 2nd, All substances whose resolution or
development into their elements annihilates their individual existence ;
as, for instance, water, which, as soon as it is decomposed by the influ-
ence of galvanism into oxygen and hydrogen gas, ceases to be water,—
widely differing in this respect from the plant, which, when it develops
itself into leaves, branches, flowers, and fruit, remains still the same
plant, or rather becomes then for the first time completely a plant. To
these we must add the acids, salts, &c., nay, the constituent parts of or-
ganic bodies themselves, which being resolved into their elements are,
as organic bodies, utterly destroyed. 3rd, All bodies which owe not their
existence and multiplicity to spontaneous development, but are composed
by nature or by art out of materials already prepared; for instance, float-
ing islands, buildings formed by animals, all automata, machines, &c.
But as we find in real organisms single subordinate parts or organs,
which in a certain degree reproduce the idea of the whole; nay, as we
see that in less perfect organisms that bond of unity which holds the
developed parts together is yet so feeble that if it is separated the part
appears to be really a whole, (for instance, the shoot of a plant separated
from its parent often becomes a new plant, and the parts of a polypus
become new polypi,) so do we not unfrequently observe the idea of
the living thing to which they belong reproduced to a certain extent
by natural bodies which, so far as-they are parts of a greater organism,
have not the appearance of being organisms themselves. Of this fact
we have an instance in the formation of a water-drop, which, as mani-
festing a certain force of gravity or tendency to internal unity, is es-
‘sentially analogous to the spherical formation of the heavenly bodies ;
and in crystallization, the growth of metals, &c. we see a repetition of
the process by which the earth was formed out of fluids. If we turn
our attention to these intimations of individual life in unorganized
‘bodies, the idea of the living principle pervading all nature presents
itself anew and more distinctly to our minds, and we are forced to ad-
mit the relations of the unorganized to organized bodies, which could
exist only in this connexion and under their other relations to universal
nature. From all this we are finally led to infer the universal connex-
jon, the combination, the never-ceasing action and reaction of all the
powers of nature, sometimes in sympathy, sometimes in antipathy, as
‘necessary to the production of an immeasurably vast and magnificent
whole,—an action and reaction which would be impossible, were not all
‘originally pervaded by one living principle, were not all in this respect
similar and allied to each other.
228 DR. CARUS ON THE KINGDOMS OF NATURE,
From these general conclusions we proceed to a survey of the dif-
ferent kingdoms of nature, in order to submit to a closer examination
the peculiarity of their life and their mutual relations. For this pur-
pose we must define more exactly the boundaries of each separate
kingdom. Here we must first make a distinction between the celestial
and the terrestrial bodies. To the former belong the solar systems, in-
cluding the earth considered as aplanet. ‘The idea of terrestrial bodies
comprehends all the different single objects perceptible by the senses in
and on the earth. Now, terrestrial bodies, according to their appearing
or not appearing as independent organisms, form two principal classes,
and this leads to a second division of bodies into the organized and unor-
ganized. We divide the inorganic bodies likewise, as far as we con-
sider them members of the planet, into the constituent parts of the
body of the earth, and the constituent parts of the atmosphere, viz.
1. Fossils and liquids ; 2. Gases and vapours. The organic bodies are
divided into vegetable and animal bodies. We have therefore four
kingdoms of nature, and four different departments of natural philo-
sophy belonging to them, The kingdom of the earth (Geology) ; the
kingdom of the air (Atmospherology); the vegetable kingdom (Phyto-
logy, Botany) ; the animal kingdom (Zoology).
Of the Inorganie Kingdom.
The great elementary masses of the earth are formed and governed
by many powers, among which we may distinguish those which relate
to the individual preservation of the planet, from those which originate
in other heavenly bodies. Of the former the most remarkable is Gra-
vitation, which manifests itself as the immediate principle of internal
unity, the sensible tendency of all parts of the earth to a common centre,
_and therefore to an ideal unity, since according to Euclid no point can
be represented materially. But another effect presenting itself in the
visible relation of the earth to other heavenly bodies, is that which we
perceive under the form of Light. These two powers, when united,
produce other phenomena ; for instance, heat, which results from the
opposition between the rays of light and the direction of gravity:
wherefore we observe the heat of the earth to be more intense, the more
the heated body is found to be in a straight line between the illumi-
nating and the illuminated object, that is, between the centre of the sun
and that of the earth. To these also belongs the phenomenon called
magnetism, as the effect of the gravitation of the earth, and its po-
sition with respect to the other planets, i.e. the direction of its axis. In
heat the predominant principle is light ; whereas the predominant prin-
ciple in magnetism is gravitation. To these we find new powers still —
added, among which the mechanical and the chemical appear to be
allied to gravitation and magnetism, (for the laws of mechanics are es-
THEIR LIFE AND AFFINITY. : 229
sentially connected with those of gravitation, as the chemical laws in-
clude the compositions and decompositions, the attractions and repul-
sions of ponderable bodies, ) while electricity and galvanism, on the con-
trary, being more connected with light and heat, are found less inherent
in terrestrial substances. A body which is an electric or galvanic con-
ductor can be conceived to exist without electric or galvanic power;
whereas no earthly substance can be imagined without the chemical
effects proper to its composition, and the mechanical operations proper
to its form. It is moreover worthy of remark how all this series of
powers, which constitute in their totality the life of the planet, is found
also in its single parts constantly and in the most various forms; for we
find in every object a proportionate gravitation of the mass toward its
centre. This fact explains the mutual attraction of two bodies floating
in a fluid, the formation of a drop of water, and the nature of the glo-
bular form in general as one in which all the radii, or the relations of
the periphery to its centre, are equal. It explains also the mutual illu-
mination of single terrestrial bodies ; the production of heat as the re-
sult of the collision of different bodies ; the manifestation of electricity,
not only in the stormy atmosphere, but also in resin and glass; and
the manifestation of terrestrial magnetism in the smallest bar of iron.
These objects, for the complete examination of their endless variety and
eternal regularity, require a full development of the laws of chemistry
and natural philosophy,—a development which would exceed the limits
of this treatise as much as it does the powers of the author, and which,
in its full and scientific comprehensiveness, is still a desideratum.
But our purpose demands a particular examination of the relation of
water to the other atmospherical and terrestrial substances, more parti-
cularly because it forms, as we shall show, the most essential link
between organized and unorganized bodies, or rather the constant
source from which the former arise. Water considered in its threefold
form, as solid, fluid, and gaseous, presents a true middle and connect-
ing member between the planet and its atmosphere. It may be consi-
dered as the indifference of both,—on which fact depends its decom-
position into a combustible element (hydrogen), and an element
promoting combustion (oxygen), nay, it is in its purity really indif-
ferent in respect to the other terrestrial as well as to atmospherical
substances. But the manifold in nature, however far back in point of
time we trace its origin, will be found constantly issuing out of the
simple and indifferent; and on this very account water, as far as it
appears an indifference, becomes the germ and source of an infinity of
other forms ; indeed it is a question whether we are not already justified
in supposing, and whether further inquiries will not establish the fact,
that both the planet and its atmosphere are but different develop-
ments of one and the same original fluid. Several,of the older chemists
(Leidenfrost, Wallerius, Markgraff) have attempted to show, that even
Vor. I—Parrt II. R
230 DR. CARUS ON THE KINGDOMS OF NATURE,
now, during: certain chemical processes, particles of water are changed
into earth; and though Lavoisier has sufficiently refuted that opinion,
he: has not demonstrated the impossibility of the decomposition of an
original fluid into water, air, and earth*. That water is of the utmost
importance in the general formation of the earth, has been proved
beyond doubt by the excellent experiments of the immortal Werner ;
and we are justified in continuing still to believe in its importance to
the preservation and life of the planet, when we take into consideration
both its quantity and its continual motion. In regard to its quantity,
we find that of the sum total of the surface of the globe (9,000,000
square miles,) the water occupies nearly 6,500,000 and the land only
2,500,000+. The water is so deep also that several points of the sea
are unfathomable, although latterly it has been fathomed to a depth
amounting to 4600 feet. The motion of the water, on the other hand,
depends partly on gravitation, as in the running of rivers and streams ;
partly on the attraction of other planets, (viz. the sun and moon,) as
in its ebbing and flowing in the tides{, and in its ascending and
descending between the earth and sky in the form of vapour, dew,
rain, snow, &c. Comparing animal with planetary life, we are there-
fore led to conclude, that as a homogeneous fluid, in continual circu-
lation, the blood, is the source in which all forms and reproductions
of the organism originate, so is water one of the members most
important to the life of the earth. This internal life of the fluid
becomes indeed more evident when we consider the individual forma-
tions of the solid to which it gives birth. The most striking illustration
of this is the process of crystallization, which exhibits a near approach
of the inorganic to the organic life; for we cannot deny, even to the
crystal, a certain inward peculiar life at the moment of its formation.
The only difference between an organic body and a crystal is, that the
life of the latter, the principle of action and reaction, terminates as soon
as its formation is accomplished. One might be tempted to say that
the crystal lives only to form itself; for as soon as it is formed it
dies; while true organisms, on the contrary, form themselves only in
order to live, and it is only when they are perfectly formed that their
life is truly and properly evident. But the formation of the crystals,
as a process nearly allied to organic life, is not the only phenomenon
remarkable inthem. The very forms of the crystal are, in their approxi-
mation to the form of the organized being, well worthy of a closer at-
tention. We find in all earthy, as well as in many metallic or combus-
tible fossils, the purely geometrical form of the crystal, which, in pro-
portion as it is more compact, and presents a more limited coincidence
* See the experiments of J. F. W. Otto’s System in an Universal Hydro-
graphy of the Earth. Berlin, 1800.
¢ See Kant’s Physic. Geograph., edited by Rink, Pt. I. p. 61.
. $ See Otto’s Universal Hydrography, p. 520—550.
eee nL —
THEIR LIFE AND AFFINITY. : 931
a
of surface with other forms, approaches more nearly the spherical form,
as that which is perfectly compact, thoroughly symmetrical, and there-
fore fundamentally organic. The icosahedron, for instance, approaches
the spherical form more nearly than the octahedron does; it is also
important to observe that the most precious crystals, and especially the
diamond, (which being pure carbon, is therefore, from its composition,
most closely allied to the organized bodies,) are those wherein we ob-
serve the most compact crystallization, at least that which approaches
most nearly to the sphere and is therefore in nowise columnar ; where-
fore the diamond, particularly on account of its power of refraction,
has a closer resemblance to a solid drop of water*. This view, by
showing how crystallization may be examined, from the three-sided
pyramid and the cube upwards to the most many-sided forms, or those
which approach nearest to the sphere, may place the theory of ecrystal-
lization on a more natural and therefore a more philosophical basis.
On the other hand we must also take into consideration the copies, or
rather the prototypes, of the form of really organized bodies which
occur in the solidification of the fluid. It is by no means without a
cause, nor to be regarded as a mere dusus nature, (a very unmeaning
expression,) that pure water in its crystallization assumes forms whicht
correspond most closely with those of inferior organizations: thus the
flakes of snow represent the forms of Polypi, Asteriz, and Medusze ;
we find in the ice on windows the forms of many vegetable sub-
stances, leaves, stems, flowers; the earth too and some metallic sub-
stances present, when melted or united with water, similar types, in
which we see the condition under which Dendrites and the manifold
forms of native ores originate. In all this the moving creating life of
the original fluid cannot pass unnoticed, and becomes still more
evident if we examine the history of the origin of organized bodies,
in which the fluid appears as the basis both of animal and ve-
getable life; and thus the very germ of individual organisms is inti-
mately connected with the life of the planet. Indeed this is partly true
of the solid parts of the earth; for it is easy to show, even in the fossil
kingdom, a transition partly to animal and partly to vegetable life ; so
much so, that a philosophical inquirer, Henry Steffens+, has been led,
from a comparison of several facts, to establish two very probable pro-
positions relating to this subject :
“1. In the whole silicious series (of fossils),—-which constitutes the
chief mass in the oldest and principal mountains of our earth, which goes
through all periods, and in its bituminous substances exhibits the re-
mains of an extinct vegetation, yet connected as a living member with
the whole existing vegetation by the marsh-turf,—carbon and hydrogen
(the essential elements of the vegetable kingdom) are the principal
* On the formation of the water-drop, seep. 229.
t See Beitrage zur Naturgeschichte der Erde: pp. 58 and 69. Freyberg, 1801.
R2
239 DR. CARUS ON THE KINGDOMS OF NATURE,
characteristics. 2. In the whole calcareous series,—which begins in
the oldest mountains of our earth, proceeds through all periods, is of
the greatest magnitude in those of the latest formation, presents in the
petrifactions the relics of an extinct animalization, and is connected as
a living member (in the coral-banks), with the existing animal world,—
nitrogen and hydrogen (the essential elements of the animal world) are
the principal characteristics.
The connexion between inorganic and organic life, however, is shown
more immediately and more clearly in the production of organisms
from pure water; to which we must refer both the origin of the Infusoria
obtained by the pouring of water over mineral substances, as observed
by Gruithuisen, and still more, the origin of the so-called green matter,
the history of which has been so admirably traced by Priestley and In-
genhousz. These show more than all other experiments, that in the
purest water, under the free influence of air, light, and heat, beings are
formed which, oscillating as it were between the animal and the plant,
exhibit the primitive germs of both kingdoms. The succession of the
changes which take place in the formation of the Infusoria is of such
importance that we cannot avoid considering them more in detail, and
therefore select from the acute G. R. Treviranus * the following passage
in reference to those cases.
“If we expose spring water} to the sun in open, or even in alana
but transparent vessels, after a few days bubbles rise from the bottom,
or from the sides of the vessel, and a green crust is formed at the same
time. Upon observing this crust through a microscope, we discover a
mass of green particles, generally of a round or oval form, very minute,
and overlaid with a transparent mucous covering, some of them
moving freely, whilst others perfectly similar to these remain motionless
and attached to the sides of the vessel. This motion is sometimes
greater than at others. The animalcules frequently lie as if torpid, but
‘soon recover their former activity.
“ As the corpuscles constantly become more numerous, the erust in-
creases likewise. After a few weeks the latter acquires a certain thick-
ness and consistency. If we examine it in this state, it appears exactly
as described by Priestley. It looks in fact like a slimy sediment of the
water, which has become green under the influence of the sun without
presenting any trace of organization. The green particles, which were
visible at the time of their formation, are now so crowded together, and
perhaps so changed in their organization, that the most attentive ob-
server, unless he had closely followed their metamorphosis step by step,
would hardly be able to discover the traces of their primitive form.
“‘ A few weeks later, when the crust has assumed a still greater con-
* Biologie, vol. ii. p. 302. ;
+ Similar results are obtained from distilled best gee far more rapidly
when mixed with organic substances. .
— a ee
~
27 2 RE = LCI.
THEIR LIFE AND AFFINITY, 233
sistency, it appears to have become a confused mass,’ or an indurated
green mucus. When the mass is broken and observed through a good
microscope, the original green corpuscles appear again, but changed in
form, enveloped in a slimy matter, and interwoven with small transpa-
rent threads resembling slender colourless glass tubes, and show irregular
yet visible movements. ‘They approach each other, return again to
their former position, become entangled with each other, and again dis-
entangle themselves. If observed at the instant when such movements
occur with the greatest energy, these little filaments have all the appear-
ance of diminutive eels; in fact they are in some degree similar to the
small vermiculations observed in vinegar. We may often discover in
them even peristaltic motions. The white colour and the motion of these
filaments last but a certain time. After a few weeks more, the crust
becomes more solid, uneven, and raised here and there into irregular
protuberances. The threads (or filaments) become more distinct ; they
are green, and scattered about without order, chiefly on the most pro-
minent part of the crust, without however rising over its surface, which
remains smooth and rather hard to the touch. The crust itself presents
scarcely any traces of the original animalcules.
“Tf the crust be left undisturbed, and the water be now and then,
but seldom, renewed, the unevennesses of the crust increase and rise in
a pyramidal form. As soon as the pyramids are formed, the green
threads, winding irregularly through the unevennesses of the green
crust, rise also, become developed, and dispose themselves along the
pyramidal bodies, toward the upper parts of which they become par-
ticularly visible; the rest is of a gelatinous substance, of a sufficient
consistence to maintain its form as long as it remains under water. If
these productions belong to the class of zoophytes, they must be ranked
among the Tremelle.” j
Some have indeed denied the actual production of organized from
unorganized matter, since distilled water over quicksilver does not pro-
duce any green matter. But in the first place it is not easy to see why
ametamorphosis should not be regarded as such because it occurs only
‘under certain given circumstances ; in the second place, it is also very
possible that in a process so little favoured even by pure water, the
quicksilver, on account of its property of counteracting production (a
‘property which renders it so useful as medicine), may destroy or pre-
-yent the infusorial fermentation, as it has been called.
We think therefore that we are not in error when (combining the
consideration of these important changes with our general inquiries
into unorganized matter,) we recur to the proposition we have before
laid down, viz. that the multiplicity of the phenomena of nature
‘rests upon one unity; that nature therefore nowhere presents either an
absolute difference (for such changes would then be inexplicable), or
an absolute identity; and consequently, if we give the name of sud-
234 DR. CARUS ON THE KINGDOMS OF NATURE,
stance to the real, or that which is the condition of the phenomena of
nature, this eternal substance causes by a continual metamorphosis
the appearance and disappearance, the perpetual change of natural
objects; a real creation and annihilation being as inconceivable as a
limit to universal nature.
Of the Organic Kingdom.
The animal stands in the same relation to the vegetable kingdom as
organized bodies in general do to the unorganized, that is, as unities un-
folding themselves into multiplicity ; for as in the activity of individual
terrestrial organisms we observe not merely a power peculiar to them as
organisms, viz. organic life, but likewise that activity which appertains
to them as parts of universal nature, viz. physical life, gravitation, che-
mical properties, &c.: so also we find in the animal kingdom, besides
the life peculiar to animals, the properties peculiar to vegetation. But
further, according to our previous inquiries, so little difference can we
trace between the unorganized and the organized in their essence and
their various relations, that the organized merely presents the unorga-
nized body in higher power, and in closer unity, and in more perfect
independence. In like manner the absolute and essential difference
between an animal and a plant is so little, that the animal is to be con-
sidered only as a plant which has attained a more complete unity, inde~
pendence, freedom, and power; which will be more satisfactorily proved
in the following pages, where we intend to submit the life of plants, as
well as that of animals, to a closer examination.
The Vegetable Kingdom.
Speaking of the crystal, we stated that it forms itself by an inward
living principle, but that when formed it appears deprived of indivi-
dual life; whilst organisms, on the contrary, (though to be considered
as in a state of continual transformation and growth,) first manifest
‘their real life when they are completely developed: In the same manner
we may say of the plant when compared with the animal, that though
the plant be in one view formed in order to live, yet even when deve-
loped it strives only after a progressive organic formation and real
development as the highest aim of its life ; whilst, on the other hand, the
whole end of the activity of animal life is not mere organic formation,
‘but also free self-determination and ideal development. A proposition
which may be also thus briefly expressed : If in universal nature, and in
every individual that forms a part of the universe, we must distinguish
between the internal unity or law, and external multiplicity or sen-
sible phenomena, we find that in the plant the multiplicity overbalances
the unity; in the animal, on the contrary, the unity overbalances the
multiplicity. But since a body which possesses less unity is thereby more
precisely marked as an integrant part of a superior whole, and, on the
contrary, a body possessing greater internal unity appears to be on that
THEIR LIFE AND AFFINITY. 235
account more a whole in itself, hence we know why the plant is from
necessity more closely connected with the organism of the earth than
the animal; considered in which point of view, the principal pecu-
liarities of vegetable organization are capable of a general explanation.
As the first consequence of the above fundamental peculiarity, we
have to consider the division of the plant according to the direction
of the two principal properties of the terrestrial organism, that is, in
its tendency to inward unity (gravitation), and in its relation to the
higher natural bodies (light). In this point of view, the plant must
be regarded as consisting of two parts, the terrestrial and the aérial,
the former consisting of the roots and stem, the latter of the leaves
and flowers. From the division, or dualism, thus characterizing the
plant, there follows also as a second consequence the want of internal
unity in the formation of the plant in its relation to space. Moreover,
while we see the animal endowed with different systems of organiza-
tion, the one for absorption, assimilation, and secretion [ Stoffwechsel],
the other for sensation and motion, and the first system inclosed
within the second in the form of intestines; the plant, on the contrary,
wants the intestines properly so called, and possesses nothing to cor-
respond with the absorbing and assimilating intestines of the animal,
but that which we call the root; so that while the animal, as a unity
in relation to space, exists one half within the other, the plant, on the
contrary, as a duality in relation to space, appears one half wpon the
other. Hence we may moreover infer the original homogeneity of
both halves; and this circumstance renders the reversion of their func-
tions possible, so that the branch is converted into a root, and the root
into branch, leaves, flowers, &c., as is proved by experiment. A third
consequence is, that as the union of two points appears as a line, the
line is the archetype of the plant; while, on the contrary, (as we shall
show hereafter,) the globular form is the archetype of the animal
body. The root, being subject to the law of gravitation, strikes down-
ward toward the centre of the earth; the stem, the leaves, and the flowers,
on the contrary, follow the light, and rise in the opposite direction, so
that the whole represents a perpendicular line. The experiments
instituted by Count Buquoi, in order to ascertain the constancy of
these directions under unusual external circumstances, are in this
respect well worthy of attention*. Seeds were put into a layer of
mould lying loose at the top and bottom ; but, though placed closer to
the lower surface, instead of growing out of this, they pierced through
the far stiffer part of the layer, so as to grow out of its surface.
Plants which were set upside down in a flowerpot always bent their
flower-stem around the edge of the pot, and grew upwards. A
fourth consequence of that fundamental property of the plant is its
* Shixxen zu einem Gesetxbuche der Natur. Leipzig, 1817, p. 315.
236. DR. CARUS ON THE KINGDOMS OF NATURE,
fixing itself upon a given spot; while, on the other hand, locomo-.
tion is the characteristic of the animal kingdom. For there is no
comparison between plants taking root, and the adhesion of some
animals, corals, and oysters, to the ground by means of their shells.
In the latter case there is not, as there is in that of the plant, an active
dynamical intrusion into the maternal bosom of the earth for the sake:
of nourishment and life, but a mere mechanical hold of the surface.
A fifth consequence is the more marked dependence of vegetable life
on the life of the earth. Whether the vegetative organization awakes
and develops itself, or sleeps and dies, depends accordingly on the
position of the planet with respect to the sun and other heavenly
bodies, as well as on the peculiar development of the soil. Though
these circumstances affect animal life also, it is not to be denied that
they do so ina far inferior degree, and that the progress of animal
organization imparts an independence of which the plant is utterly in-
capable. As the sixth and last consequence arising from the less perfect
unity of the plant, we are to consider not only the dualism already men-
tioned, but the peculiar nature of every bud; and every internodium
may be considered as a whole in itself, or in some measure an indi-
vidual plant; wherefore a bush or a tree is more properly compared
to an aggregate of animals (a coral bank) than to a single animal.
In this way we shall easily comprehend the various modes of propa-
gating plants, in which a bud (an eye) and the shoots that issue from
it renew the parent organism, and that which we see in the bud is exhi-
bited likewise as tubercles in the root or also (as in the genus Allium)
near the flower, or as the bulb, and always possessing the power of repro-
ducing the whole plant out of itself; nay the very seed is but an im-
proved and more perfectly compact picture of the bud.
If we closely examine the structure and composition of plants, we find
that, like the organism of the earth itself, they contain solid, fluid, and
gaseous elementary particles. We see that in the plant, as well as in the
earth, the fluid contributes to the formation of the solid parts, and that
the finer and therefore more destructible organization of the plant is
composed of chemical elements, namely, the carbonic, hydrogen, and
oxygen gases. The transition of the fluids into solids, and consequently
the history of the formation of the proper body of the plant itself, is evi-
dent in its primary structure, that is, in its cellular tissue. If we call
to our recollection the history of the primitive formation of the rudi-
ments »f organic bodies in the green matter of Priestley, and see in
this the conditions of this formation,—whilst, under the influence of light
and gravitation, some particles of the original fluid attain the nature of in-
dividual beings, as well as a tendency to internal unity, and consequently
a globular form,—it becomes clear that this development cannot occur
without a separation of those particles from the rest, without an indi-
vidual limitation in form of a spherical surface; so that the rudiment of
THEIR LIFE AND AFFINITY. é 37°
animal life appears to be a hollow globular body. Consequently when
the effort to attain a higher unity or a more perfect organization
presses several of these globuli, possessing solid though weak sur-
faces, one toward the other, the surfaces, by mutual pressure, are ne-
cessarily modified into different geometrical angular bodies*. In the
most imperfect plants we observe, as a consequence of an imperfectly de-
veloped internal structure, that in their single cells, which press each other
but slightly, the globular form prevails, although on account of the linear
direction peculiar to plants (see p.235) it is elongated into the’ellipsoid ;
while in the more perfect plants, on the contrary, the single cells of
their tissue appear, in consequence of the mutual pressure, in the form
of regular dodecahedrons. Looking upon the cellular formation as the
basis of the whole plant, and considering that the plant itself ‘in its
primitive destination is dependent on its relation to the planet and its
unity (gravitation), we are fully entitled to identify the anatomical
system of the cellular tissue}, as the proper reproductive system of the
plant, with terrestrial gravitation and the planetary body itself, inas-
much as that principle may be considered the basis of the whole organ-
ism of the earth. But since, in the organism of the earth, light and
air, as constituting a second integrant part, stand opposed to gravita-
tion [der Nachtseite], and since the plant bears a relation not only
to grayitation but to light also (see p. 235) when its formation is com-
plete, it will necessarily present a second anatomical system, namely
that of the spiral vessels, which have been very justly considered of
late as the organs that perform in plants the functions of nerves,
The lower plants, which want no light for their development, are not
provided with spiral vessels; in the more perfect plants, on the con-
trary, the spiral vessels are as essential a part of the organization as
the cellular tissue. In fine, between both these systems of the cellular
tissue and the spiral vessels (the earth and water system, and the light
and air system, as they are called by Kieser},) the epidermis stands
as a binding and connecting member, whose vessels appear to be
the more perfect intercellular ducts, and its pores the orifices of these
vesselst.
As the anatomical systems of plants are therefore but very few, the
multiplicity of their external organs, which unfolds itself in the most
beautiful progression and regularity, is so much the more important.
Whilst the root, penetrating more deeply in the direction of the earth,
spreads itself with uniformity, the plant elevates itself more and more
into the light, and attains a more delicate and perfect organization; in
which process it is a fact deserving most particular attention, that this
perfectibility does not manifest itself in the production of new organs
_ * Kieser’s Grundziige der Anatomie der Planxen. Jena, 1815, p. 9.
+ Ibid., pp. 16—19.
¢ Ibid., p.19. © : @
238 DR. CARUS ON THE KINGDOMS OF NATURE,
entirely different from the former, but in a continually progressive trans-
formation of the original types, a succession of metamorphoses, on the
nature of which we have received the most interesting information in
the excellent observations of Goethe*. It appears that while the first
rough type, as it were, of the whole plant is contained in the coatings or
leaves of the seed (cotyledons), which abound with a gross and yet
unelaborated sap; the same type is manifested more plainly in the
successive divisions of the stem (internodia), and in the leaves, in which,
when we compare the upper with the lower leaves which surround the
stem, its progressive improvement becomes very distinctly evident.
As soon as the plant has formed its leaves, which perform the functions
of the organs of respiration and secretion, and has thus purified its
fluids, it goes on to produce the flower, which is its most complete
organ, entirely under the influence of the light. Even this transition is
not performed suddenly, but is prepared by the formation of the calyx,
wherein the leaves of the stem begin to contract themselves, while they
unite in greater numbers around a common axis in the same plane: this
formation shows itself most evidently in the collective calyx of flowers
belonging to the class Syngenesia, in which the pappus performs the
function of the calyx of single flowers. Moreover, the calyx itself
constitutes the most evident transition to the corolla, the functions
_of which it often performs ; and the corolla is only a finer calyx for the
organs of generation, which, as the most compact and perfect organs,
issue forth from their last organ of development and preparation, as
from a covering which they have last thrown aside. It is a remarkable
fact, and one which places the correctness of these views beyond doubt,
that too rich a nourishment, and the accumulation of too many fluids
not yet properly purified, may cause a retrograde organization of these
parts; the organs of generation may be transformed into flower-leaves
(as in double flowers), the leaves of the calyx may be changed back
again into leaves of the stem (as is often the case in the calyx of the
rose ),and instead of the organs of generation, a new shoot or internodium,
-bearing a new flower, may appear (as in the proliferous roses or Rose-
kingst ). When, after such successive progression, the plant has reached
the highest point of polarity between root and flower (gravitation and
light), between which the stem and leaves may be considered as mere
connecting links, similar in their function to that of the epidermis be-
tween the cellular system and the system of the spiral vessels, the same
opposition appears once more under the form of male and female sta~
mina; the latter of which, as containing the germ of a new plant (the
seed), belong more to the reproductive system, and stand more under
the influence of the earth. Wherefore the inferior plants, such as
* Versuch die Metamorphose der Planzen xu erkliren. Gotha, 1790, Re-
printed in the Hefte zur Naturwissenschaft und Morphologie, 1817, i.
(+ Rosenkonigen, Germ. ]
THEIR LIFE AND AFFINITY. ; 239
mushrooms, ferns, &c., produce their seeds immediately without the
aid of the male stamina, and this circumstance accords with their tex-
ture, which is merely composed of cellular tissue. On the other hand,
the male stamina, containing a generating life-imparting principle, that
is, the operation of light, come nearer to animal nature. This view is
in perfect accordance with the power of motion which is often to be
observed in these parts, as well as with the very probable hypothesis,
that the cause of the scent and of the colour of flowers may be
traced to the elements of the male pollen*, which is contained in
their leaves. We have already stated that the seed itself being an
indifference emanating from this highest polarity, contains the most
concentrated image of the bud. As it has thus within itself in idea
the whole organism of the plant, it is capable of reproducing in reality
the whole plant out of itself.
Proceeding from this short survey of the principal phenomena of the
development of plants to a further examination of their active manifes-
tation of life, we shall find that even in this respect the vegetable king-
dom, as a part of universal life, is connected with inorganic nature. It
has been already observed that the life of the plant consists chiefly in
the formation of its organs; whence it follows, that its most essential
and fundamental activity manifests itself in the process of assimilation
and secretion, as well as in the circulation of the sap, which is no-
thing but a repetition of the chemical attraction and repulsion ob-
served in unorganized matter. But since the circulation of the sap
is not effected by any independent peculiar organ of circulation, (such,
for instance, as a kind of heart,) we must suppose this movement to be,
like the ebbing and flowing of the tides, the effect of a certain attrac-
tion, partly originating in the structure of the plant, and partly in its
external relations; unless we should prefer ascribing it entirely to the
motion of fluids in capillary vessels, that is, in other words, to the laws
of capillary attraction. But the laws of capillarity have surely but a
limited influence in this case: capillarity may indeed enable us to ex-
plain the phenomenon of the rising of fluids, but not their progres-
sive motion, and still less the flowing off of the sap when the plant
is cut or injured ; because a capillary tube never can overflow, and that
for the very cause which makes fluids ascend, namely, their adhesion to
the inner surface of the vessel. Hence, although capillary attraction
has some share in the circulation of the plant, it is evident that this
depends upon some higher cause. It has been already shown that the
polarity of the plant between root and flower, which depends on the
‘elementary polarity between gravitation and light, is also visible in the
relation of the functions of both those parts, the root being particularly
adapted to attraction and absorption, but less fit for secretion, and the
* Gocthe’s Morphologie, p. 23.
240 DR. CARUS ON THE KINGDOMS OF NATURE,
leaves and flowers being particularly capable of secretion and ex-
piration, but less fit for absorption. Polarity is therefore the cause
which brings the sap into motion by reciprocal attraction and repul-
sion from the root to the leaves and flowers, and from the leaves and
flowers again to the root: a motion on which, moreover, the physical
powers—which, as the condition of both these parts, we have named
vegetative poles, namely the powers of light and gravitation—must have
amost decided influence; since, for instance, it is a well-known fact,
that the perspiration of plants is very different according to the degrees
in which they are exposed or withdrawn from the light of the sun.
But besides those active properties which contribute to the organic
formation of plants, some of them possess a peculiar mobility, which
seems to arise from real sensibility, and at the first glance presents a
perfect line of demarcation between the vegetable and inorganic bodies.
In order to have a clear insight into this fact, it is necessary to fix our
idea of the word sensibility, as that which we would be understood to
convey most correctly, if we say that it consists ix the change operated
by outward or inward circumstances in the feelings of a being conscious
that it exists as a unity; consequently if we deny sensibility to the
stone or the mineral, it is not because such a body isnot subject to the
most various agitations and changes, but because it is merely a member
of a higher unity, and in itself is to be considered as an individual, not
as a true unity. Inregard to the plant we may say that it has become an
organic unity; but onaccount of the dualism (see p. 235.) prevailing in its
totality, and its being therefore bound as it were to the external world, we
may with safety deny that it is conscious of its own unity ; for in order
to have self-consciousness, or an internal perception of unity, there
must be, not merely that ideal unity which belongs to organized beings
in general, but that veal manifestation of unity which arises from the
continual action and reaction of all the organs and an organic centre.
But such action and reaction are not to be found in the plant, in which
each bud may be considered as a whole; so that this real unity, as
we shall hereafter see, is possible only in the animal, in which the
organs are connected with a unity by means of the vascular and
nervous systems. But if we cannot suppose plants to be possessed
of sensibility, how can we account for their movements towards the
light, the shrinking of the sensitive plant from the touch, the closing
_of the Dionzea by mechanical irritation, or the inclining of the stamina
towards the stigma, and the regular embracing of extraneous bodies,
and in definite directions, by the creeping plants, &c.? In our opinion all
these phenomena are to be accounted for in the same way as the rota-
tion of the earth, the motion of falling bodies, the oscillation of the
.sea in its ebbing and flowing, the attraction and repulsion of the cork
balls in the electrometer ; that is to say, we think that they are entirely
the effects of external disposing causes, and therefore the consequence
‘“THEIR LIFE AND AFFINITY. > ~~ 947
of a susceptibility or capacity to be effected by those external causes.
This property, so far as it is conducive to the excitement of organic ac-
tivity, has been named irritability, but always without annexing to the
word a sufficiently precise idea. We think it therefore not superfluous
to illustrate it by some examples; when, for instance, a body is to be
put in motion by an impulse, it is necessary that it possess mobility, or
the capacity to be put in motion. It is the same with chemical opera-
tions: in order that a body be acted upon and decomposed by another
body, it is requisite that the former be susceptible of this chemical
action. The case is the same if an organism as a whole, comprehended
in an enduring form, is to be affected by external influences ; except that
we must here distinguish whether the activity called forth by this influ-
ence appears as a change in its physical properties, for instance in its ex-
tension; or as a change in its own organic activity, its formation; or in
the mutual relation of its single parts. In the former case we name
this property a physical receptivity, in the second irritability, and the
exciting power a stimulant; from which it is clear that the same in-
fluence can act both asa mere physical power and as a stimulant: heat,
for instance, can expand a body, and at the same time quicken its or-
ganic formation or growth; in the latter case it acts as a stimulant.
Hence it follows that the irritability of the plant stands in the same re-
lation to animal sensibility, as its own physical receptivity stands to its
irritability. While the plant therefore, from being indebted for its own
movements to the influence of external causes, approaches more nearly
to universal nature, and is therefore further separated from animal life,
to which it approximates again in the inclining of the stamina towards
the stigma, this movement, though independent of its own will, origi-
nates in an attraction inherent in the plant itself.
Having hitherto been occupied in considering the influence of the
organization of the earth upon plants, it necessarily follows that we
should consider the influence which the vegetable kingdom exercises
_ upon the life of the earth; for even though we should not be inelined
_ ‘to consider that the origin of the vegetable kingdom in general neces-
sarily marks an important epoch in the formation of the earth,—as
for instance, in the development of the plant, the production of a single
organ (as the flower) from a particular influence is to the whole
plant,—yet the transformation of vast masses of vegetable substances
into strata of pit and Bovey coals, into strata of turf and of vegetable
‘mould, and particularly the influence of living vegetation upon the
surface of the earth and atmosphere, are objects too striking to pass
unnoticed. In the latter point of view it is particularly worthy of
‘remark, that the origin of brooks and streams is owing to the exis-
tence of woody mountains, and their greater attraction of atmospheric
*vapours; wherefore we often see streams dried up, on account of
‘the destruction of the forests in which their sources lay; a. cir-
242 DR. CARUS ON THE KINGDOMS OF NATURE,
cumstance to which modern travellers ascribe the present dry desert
state of Greece, in which several streams celebrated by the an-
cients have totally disappeared, leaving behind a dry and barren soil,
because the woods which contained their springs were wasted and
destroyed through barbarism and neglect. If, lastly, we consider how
essential an influence the course and deposition of rivers have upon the
surface of the earth; how far all countries have been produced by their
rivers (as, for instance, Lower Egypt by the Nile, or the regions of
America, towards the lower part of the Mississippi, by the alluviations of
this river); we find here again the bond of mutual relation and affinity
which connects organized and unorganized terrestrial bodies by means
of vegetable life manifested with sufficient distinctness.
The Animal Kingdom.
As the plant may be considered a crystal continually developing it-
self in a constant change of its matter, in like manner the living ani-
mal body so nearly represents a plant which has reached a higher unity
and faculty of self-determination, that although the animal still remains
a part of a higher unity, and is closely hound to the earth by the ne-
cessities of life, yet this hold taken of the animal as compared with
that taken of the plant, is even less in degree than that which we ob-
serve in the plant as compared with the unorganized body. For this
very reason, the animal presents, among natural bodies, the most per-
fect idea of an organism (see p. 226); and as we can prove mathe-
matically that there are only three fundamental numbers (which are
continually repeated in all forms of perception, namely, unity, its di-
vision into duality, and the reunion of the unity and duality in trinity),
which are exemplified in our conception of space through the three-
fold dimension of length, breadth, and thickness,—in like manner the
threefold succession of inorganic vegetable and animal life exhibits the
members which together afford the idea of an organism, viz. multipli-
city, development, and unity.
Since the addition of the idea of unity constitutes the perfect idea of
an organism, just as thickness, added to length and breadth, con-
stitutes the idea of a body, it is evident that the unity of the animal
body presents and affords in reality a perfect idea of an individual or-
ganism. We have already observed that the peculiarities of vegetable
life may very well be collectively ascribed to its want of inward self-
independence ; in a similar way we may deduce all the peculiarities of
the animal] organism already alluded to, from the idea of oe unity
which is characteristic of animal life.
Consequence the first.—If the plant, exposed alike to gravitation and ~
light, is divided into root and stem, into a terrestrial and an atmospheric
part, the animal, being more independent, is less bound to the organism
-of the planet to which it originally belongs, and is consequently more
‘THEIR LIFE AND AFFINITY. 2 243
under the influence of light; wherefore, though sometimes fettered to
the earth, it is by no means fixed or rooted in it, to which circum-
stance it owes its faculty of locomotion.
A further consequence which flows from the above consideration is,
that the animal cannot, like the plant, draw its nourishing juices from
the soil, because its whole organism has a tendency to inward unity; its
very root-organs are turned inwards and formed into intestines; from
which we are able to show most evidently the origin of the excretory
canal and of the absorbent and circulating vessels. Let us suppose
for instance a plant A, living with the atmospheric part + above-
ground, and with its terrestrial part — underground; let us now detach
it from the ground so that all the fibres of its root, abe c, having
struck back into the internal parts of the stem and of the leaves, may
be reversed inwards; we shall then have the figure B, in which the part
subjected to the light perfectly encompasses that subjected to the earth;
and a 6 appears as the alimentary duct; 6, as the cavity of the stomach,
and ¢ ¢ as the vessels for distributing the sap.
Here we observe how very much in this metamorphosis the plant has
assumed the type of the animal body, such as we observe it among the
lower classes of animals. In this way we may now see why in the Medusa,
the Sea-star, the Echinus, and other inferior kinds of animals, the aperture
of the mouth is turned downwards, and the alimentary duct upwards*;
or in this way we may see that the lower classes want the opposite or pos-
terior opening of the excretory ducts (anus), or that (as is likewise par-
ticularly evident in the Medusa+ ) the vascular organs branch out imme-
diately from the cavity of the stomach, and that the leaf-formed parts
-B, a a, furnish an explanation of the appearance of a kind of exter-
* Carus, Lehrbuch der Zootomie, p.327. _ + Ibid., p. 578.
244: DR. CARUS ON THE KINGDOMS OF NATURE,
nal respiratory organs or gills (nearly as in the Clio* and the Cleodora);
or lastly, we may see that the germ y grows opposite to the mouth, at
the hinder extremity of the body, as the generator of a new interno-
dium, that is (in the plant) as the producer of a new whole, or the or-
gan of the plant’s propagation; and we are thereby enabled to account
for the usual place assigned by nature to the organs of generation. In
this way we shall always recognise that which has hitherto escaped the
attention of the observer, namely, the analogy that exists between the
body of the animal and that of the plant as above metamorphosed, as
well as the manifest derivation -of the former from the latter.
A third consequence of the above is, that the animal being the reali-
zation of the abstract idea of unity, in which all parts must relate to a
common centre, the sphere must be of necessity the original type of
animal organization, the globe being that which tends to its centre
with perfectly equal relations (radii). But, so far as the animal
is not merely the upper part of the plant become detached, but like-
wise contains in itself the organs of the root, the globe must be hol-
low, and contain within itself the intestines, which can be most clearly
pointed out in the lower animals. Because, without taking into account
that the Infusoria appear merely as so many living hollow globules or
cells (see the history of the green matter of Priestley, page 232, &c.), this
kind of structure is evident in the bladder-worm (Cysticercus), in which
(see fig. C.) the absorbing proboscis 6 (therefore called the head) is in
reality curved inwards into the cavity of the body a, exactly in the
manner described in the hypothetical metamorphosis of the plant into
an animal. Similar forms are also exhibited by the Echinus tribe, to
which we must add, that microscopical observations show most clearly
that the whole of the organic mass of higher animals is composed of
minute globuli.
The fourth consequence is, that as unity is the characteristic peculi-
arity of an organism, there must exist, because of the greater multi-
plicity of its form, a bond which, while it again unites that multitude,
exhibits that relationship to a common centre which accords with its
organization. However, since the-animal presents two sides, a higher
one, turned toward the outer world, and peculiarly animal, and a lower
one, turned into itself, destined for reproduction, and so far purely
vegetative, the above bond must likewise of necessity be twofold, —
-bear a particular relation to each side.
Fifth consequence. —No reciprocal action can take place jictieen
two bodies, except in two directions, (just as the organism itself appears
-essentially as body and life under two forms only), namely, in its ten-
dency to produce a change and combination of particles,-or to a reci-
procal transmission of power. Inasmuch as in the animal the change
* Carus, Lehrbuch der Zootomie, p. 482.
THEIR LIFE AND AFFINITY. 245
of particles belongs properly to its internal vegetative side, its external
side (for the very reason that it is turned immediately to the outer
world) will appear as a perceptive and reciprocating activity*. But
since we may constantly recognise in every mutual relation of body as
well as of action a threefold momentum, viz. action, reaction, and con-
nexion or the indifference of both, these three elements must therefore
be found also in each of the two sides of the animal organism. In fact
we find them in the external (animal) side, as perception, motion, and
the connexion of both through the nerves; in the internal vegetative
side, as assimilation, secretion, and the connexion of both by circulation.
But whatever is true of the bond which in these two spheres gives every
form its centricity, the same must naturally be found in the so-called
connecting nervous and vascular systems. Yet these two systems must
not perhaps be considered as occasioning a real dualism in the organi-
zation, but as equally subordinate and reduced to a unity, namely the
nervous system, as being the higher, because it belongs to the animal
which includes the vegetative sphere.
Sixth consequence. As the plant is not merely occupied with its own
change of particles and continual transformation, but when it has at-
tained its perfect development produces the seed, as the representative
of all its properties, the true reproduction of the species, we find in the
animal likewise a similar reproduction of the species, in so far as even
the animal is but a more perfect vegetable nature. The system thus
established in respect to the animal, viz. the sexual system, possesses in
its nature a polarity similar to that of the plant ; for we find in the more
perfectly organized animals, a female reproductive and a male impreg-
nating organ. But, on the contrary, we find the lower animals, like
the inferior plants (see p. 239), endowed with female organs only. The
activity of this system, manifesting itself especially in assimilation, se-
cretion, and (as the basis of these two momenta) in vascular action, be-
longs to the sphere of vegetation; and there is nothing to be compared
with it in the animal sphere, except that activity by virtue of which, in
the most perfect animal organism, that is the human, the idea of nature
is reproduced by means of spiritual power, and truly developed through
science and art.
We have now further to consider the composition and internal forma-
tion of the animal body, as well as the nature and direction of its active
faculties of life. In the first point of view, we observe that it contains,
like the organism of the earth and of the plant, a combination of solids,
fluids, yapours, and gases, among which the fluids are again the sources
of the rest. Its ultimate elements are principally hydrogen, oxygen, and
_ # It is only in this way that the origin of the sensible side is capable of a
scientific construction.
Vox. l—Part I. s
246: DR. CARUS ON THE KINGDOMS OF NATURE,
carbonic acid gas, with the additional one of nitrogen, which peculiarly
belongs to this kingdom, and the volatile nature of which perfectly
agrees with the rapid merging of animal bodies in the universal life of
nature, as soon as their individual life is extinct; to which passage,
however, the earthy parts, such as bones and shells, offer somewhat
longer resistance. In regard to the internal formation of the solid parts
of the animal body, it has been already remarked (see p. 244) that the
spherical type, in so far as it is peculiar to animal forms in general, is also
visible in the basis of all animal matter, so that the molecular substance
is the basis of the collective animal body. If we now reflect likewise
how in the Infusoria and Priestley’s matter, the rudiments of the animal
kingdom appear as so many animated globuli, we shall thence perceive
that the largest animal bodies themselves must be viewed as an innu-
merable aggregate of Infusoria, but at the same time united into a living
whole. It is moreover worthy of remark, that very essential differences
present themselves in respect to the primary formation of the animal
body in its different systems. It is also a remarkable fact, that in the
organs exclusively proper to the animal,—for instance, in those of sense,
motion, and the nerves,—this molecular mass is clearly discernible, partly
as the marrow of the nerves (a peculiar grey substance), partly as de-
veloped nervous and muscular fibres ; while in the organs which are
more immediately borrowed from the plant (the vascular system, the
skin, and the intestines), we remark again a very decided tendency to
cellular formation.
We have now before us two modes of perceiving in its true nature the
further formation of the primary animal mass into the single organs of the
animal body; either that of attentively watching the development of one
complete animal organism in its different stages, or that of observing
the succession of the species according to the order of animals in the
development of their animalism. Of these two we shall give only the
principal outlines of the first series of formation*, in which we shall find
a great analogy to the development of the plant, but more especially
a manifold confirmation of that which we have advanced in regard to
the metamorphosis, or rather elevation, of vegetable into animal life.
But in tracing the development of the individual animal body through
its several stages, we shall take as the main object of our observations the
human organization as the most perfect ; and thus we shall have occa-
sion to recur to that of other animals in those cases only in which the
observations made on the human being itself are deficient in regard to
its first rudiments.
* The observation of the development of organization in the series of ani-
mals, is the idea upon which Carus’s Manual of Zootomy is founded, to which
he here refers his readers.
THEIR LIFE AND AFFINITY. 247
One thing, however, we know with certainty, namely, that the human
body, like that of other animals, has its origin in the egg. But the egg
itself must be considered as the original animal, as the infusorial crea-
ture, appearing in the globular or primary form of animal life, and, like
the seed of the plant, containing ideally within itself the whole ani-
mal, which, under given external circumstances, it develops really out
of itself. Recent observations have shown that the first rudiment of
the embryo is formed on the inner surface of the hollow globe of the
egg, by folding or turning inwardly a part of the integuments of the
egg; which reminds us distinctly of the purely vegetative bladder-worm
(Cysticercus, see p. 244), in which the so-called head, or the absorbing
orifice, is turned inwards. It is plain therefore that we must consider
the egg in this first period of development also as a plant with a root
turned inwards (see p. 243) ; and we find this moreover confirmed by
the functionary attributes of its parts, since the first introversion of the
integument forms the cavity of the stomach and the intestines, as the first
rudiment of the embryo. On the other hand, the external covering of
the egg being somewhat similar to the green (breathing) surface of the
plant, performs the breathing function of the embryo, and contains also
(as the latest observations of Pander have shown), in the external envelop
of the cuticle, the origin of the organs of sensation. Ina further stage of
development we see the activity of formation concentrating itself more
in the point turned inwards, and thus producing new opposites. The
rudiment of the embryo repeats the above-described form, and the higher
animal organs, which commence with the spinal marrow and the vertebral
column, originate above the germ of the intestines of the cavity of the
stomach. It is now in particular plainly seen how the animal is as it
were transformed from a plant into an animal in the manner above de-
scribed (p.234). For at the very first the intestines are only attached to
the foetus, that is, the gut lies as yet in the umbilical cord, just as at first
the root is attached to and not 27 the plant; but the intestines are soon
afterwards drawn more and more inwards, and by degrees are completely
enveloped by the animal organs, which grow simultaneously forwards
on both sides out of the vertebral column; and here for the first time
the foetus presents the appearance of an independent animal organism.
The vascular system, however, is much more slow in connecting itself
perfectly with the foetus; since it is rather a general connecting me-
dium in the vegetative sphere, and therefore performs the function of
a bond of union between the integument of the egg and the foetus so
long as it remains inclosed in the egg. Even at this period of deve-
lopment the relation of the parts of the egg reminds us of the plant;
as the foetus, by means of the umbilical cord, is united to the placenta
and integuments of the egg, held in organic connexion with the ma-
ternal organism, just as the flower (which it resembles in respect to the
s2
248 DR. CARUS ON THE KINGDOMS OF NATURE,
development of the organs of generation,) is united by means of the
stem to the root, which is held in connexion with the organism of the
earth. It is also remarkable, that in the foetus the direction of the de-
velopment from the insertion of the umbilical cord is upwards, as we
see in the plant that the flower is directed upwards from the insertion
of the stalk. For instance, the anthers are never turned back toward
the stem and the fruit-germ, or directed downwards, but on the con-
trary are invariably and wholly directed upwards, unless the flower-
stalk and fruit-germ are turned downwards, in which case they also are
directed downwards with them. This explains the development of the
vertebral column into the head, in which the flower of the collected ani-
mal organization appears as completely as the flower of the egg does in
the entire foetus. This fact is still more clearly observable in the cen-
tral structure of the vertebral column, viz. the spinal marrow, the fibres
of which we see more perfectly developing themselves as they ascend
upwards, till they terminate in the perfect and noble formation of the
brain.
This direction of development in the foetus, the truth of which is
most clearly established by many physiological as well as pathological ob-
servations, is also indicated by the position of the entire foetus, in which
we find the head usually turned downwards, but the lower extremity
turned toward the insertion of the umbilical cord; in the same man-
ner as the flower of the plant, and the head of the more perfect animal,
rise upwards from the ground. Moreover, that the greater weight of
the head which occasions it to sink downwards in the uterus is not the
only use of that position of the foetus, is evident from the parturition
of the quadruped mammalia, since although their standing on four
feet must prevent the operation of such a cause, they nevertheless bring
forth their young with the head (nay even with the face) forwards.
We can here give but general outlines of the further development
of the different systems and organs formed in the feetus; and with
respect to the systems belonging to the animal side of the animal
body, and which corresponds to the light side of the plant, we ob-
serve that from their constituting the parts originally turned toward
the outer world, they are endowed with a tendency to develop their
structure in a direction radiating outwards from an internal cen-
tre; for which reason we see the nervous system form itself as the
radii of a central mass (the brain and the spinal marrow), which de-
velops itself with a perfection continually increasing in proportion as
the radiation outwards increases; we see also the ends of the nerves
forming themselves either into the organs of sensation, or, as being de-
stined to re-act upon external objects, inserting themselves into the
molecular mass of the animal; so that these molecules, disposed into
muscular fibres, are drawn, sometimes more and sometimes less
THEIR LIFE AND AFFINITY. 249
strongly, towards that insertion of the nerves, according as the action
of the nerves is increased or diminished by its centricity ; and it is
thus that they determine the muscular contraction, and all animal
motion. The following figure will explain the contraction and relaxa-
tion of the muscle: a } represents the relaxed muscle, and c the nerve
in its usual state; de the contracted muscle, and ec? the nerve in in-
creased action. In the second figure, the contraction of the muscle by
means of a diminution of volume is explained by the closer approxi-
mation of the points to the centre.
But besides this twofold termination, the nervous system finally branches
out also into the vegetative sphere of the body, thus partly determining
both sensation and motion, and partly constituting the bond of unity
between the different organs of the vegetative system. In the latter
point of view the very form of the nervous fibres is remarkable, since
they all have an evident tendency to inclose the intestines and vessels
in a kind of network. In the same point of view it becomes clear also
that, as the inclosing of the lower system in the higher one is charac-
teristic of animal organization, and the rudiments of the nerves always
show this peripherous type, the higher animals, and man in particular,—
in whom the spinal nerves encompass the common cavity of the trunk,
somewhat similarly to the bending of the ribs,—possess a system of
nerves appropriated to the vegetative structure, and perfectly analogous
to the nervous system of the inferior animals, namely, the ganglionic
system, or that of the great sympathetic nerve.
The osseous system is developed uniformly with that of the nerves,
and issues out of the vertebral column, as the nervous system does out
of the spinal marrow; whilst the vertebral column forms at first but an
isolating sheath around the latter, as an earthly substance most power-
fully attracted by the nervous system, acting like the sun, and for
the most part antagonistically upon the other parts of the body. In
a somewhat similar manner, among falling bodies of different specific
gravities, the heaviest will always lie undermost and nearest to the at-
tracting centre of the earth. Where the osseous system has acquired
its most perfect structure (in the skull) it presents also the original
type, the spherical form; on the contrary, like the radii of the nervous
system, it branches out more and more in the extremities, a fact which
is clearly seen in the increasing number of the bones in each member,
from their root in the trunk to the ramification in the fingers and
toes,
250 DR. CARUS ON THE KINGDOMS OF NATURE,
In examining the origin of the individual members of the vegetative
sphere, of which we have already observed that the formation from with-
out toward the internal parts, namely from the umbilical cord into
the cavity of the stomach, presents the organs of digestion (as the in-
ternal nourishing root of the animal) and the bowels,—we find that in
the progress of organization new organs are formed for the functions
of respiration and secretion, to correspond to those of nutrition and ab-
sorption. The function of respiration indicates the connexion of the
individual organism with the atmosphere, as on the other hand the ab-
sorption of grosser matter indicates its connexion with the earth by the
root.
As long as the foetus is inclosed in the placenta it can have no im-
mediate connexion with the terrestrial organism, but maintains rather a
reciprocal action with the maternal organism, as is seen in its manner
of breathing, which is originally performed through the integuments of
the egg (see p.247). But since it is necessary that an independent
organ of respiration be prepared for the time when the fcetus leaves the
maternal body and the integuments die away, we find the external sur-
face of the foetus itself (the skin) developed with its continuation
(the internal organs of respiration). The vascular system (hitherto
the connecting medium between the foetus and the integuments of the
egg, see p. 247), then becomes the connecting medium between the
organs of digestion, respiration, and secretion. The organs of secre-
tion, however, may in a certain respect be considered as a repetition of
the organs of respiration, since the evaporation and secretion of gases
form a prominent part in the process of respiration. The plant de-
velops, besides the organs of general assimilation and secretion, those
of generation: a similar development takes place in the animal also,
and precisely at the point where the germ of the fruit is developed in
the plant, at a point which is therefore analogous to the insertion of
the stamen in the flower; in other words, at the insertion of the umbi-
lical cord into the abdominal cavity, which in the first stage of forma-
tion, where we observe the embryo with its pointed lower extremity
attached to the inner surface of the egg, is the basin that incloses the
genitalia as the calyx does the fruit-germ.
After having considered the transition of the form of the plant into
that of the animal, it remains for us now to examine the peculiarity of
the active living principle of the animal, in order to ascertain how far
this is derived from the active living principle of the plant. But we
must first carefully observe, that if we were right in considering (page
239) the chief end of the active living principle of the plant to be its
formation, the first active living principle in the animal likewise must
be a tendency to acquire individual existence. The whole animal body,
as far as regards nutrition, growth, secretion, and its being engaged
THEIR LIFE AND AFFINITY. 251
in a continual change of matter in the parts already formed (the vege-
tative as well as the higher and properly animal parts), lives absolutely
the life of the plant. We likewise observe, that here also the fluid
parts are the sources from which the several solid parts are formed by
different attractive affinities, for this reason, that the external nourish-
ing substances first enter into the fluids, but at the same time the se-
cretions which are given off from the fluid parts of the body are carried
away in the form of liquids, vapours, or gases. However, to perform
this attraction and repulsion, one condition is requisite which is equally
necessary in the life of plants, and that is the circulation of the fluids.
This circulation we have seen performed in the plant through the
polarity between the root and the flower, and therefore in a linear di-
rection from one end to the other. But since the animal is a plant the
root of which is turned inwards, a similar motion of the fluids, from
the absorbing to the exhaling pole, instead of being directed linearly
from one extremity of the body to the other, must take a centrifugal
and centripetal direction, inasmuch as it is but an action and reaction
between external and internal organs. We have observed that the cir-
culation of the fluids in the embryo is between the embryo as a centre
and the integuments of the egg as the periphery; and that the circula-
tion is not confined to the embryo itself until it has attained its full
maturity *, at which period it is observed alternating between the heart
(as the centre of vegetation) and the periphery; and in the higher ani-
mals and man, partly toward the whole bodily structure and its common
integument the epidermis, partly toward the epidermis turned inwards
in the organ of respiration, and vice versd. Hence it follows that this
movement of the sap or blood is not properly a circular motion, and
has therefore no true resemblance to the rotatory motion of the hea-
venly bodies; because these have an intermediate movement which is
the result of attraction and repulsion ; whereas the movement of the
blood appears as an alternation of attraction and repulsion, which is
most analogous to the ascending and descending movement of the sap
inthe plant. This also leads to the conclusion that both this movement
and its direction are originally the mere effect of the polar attraction
and repulsion of the fluid itself. Wherefore this circulation may take
place without needing any other mechanical aid, as for instance the
pressure of the vascular surfaces, of which aid many animals are for the
most part destitute. Indeed, the original unimportance of such aids is
rendered fully evident by the fact that the vessels, like all other solid
parts, are formed only by the circulating fluids,—consequently, that
_ * The essential difference between the earliest and the later form of the cir-
culation in the egg during the process of incubation has been recently demon-
strated in the beautiful experiments of Pander,
252 DR. CARUS ON THE KINGDOMS OF NATURE,
the fluids exist before the vessels, and that the direction of the vessels
is the necessary consequence of the direction of the fluids.
Whilst through these general considerations we see how the move-
ments of the original fluids maintain reproduction in all parts of the
body, a due attention to the different polar directions of vascular
activity, according to the different natures of the several parts of the
body, will enable us also to perceive their differences of assimilation as
well as secretion, and the laws to which they are subject; but these in-
quiries we cannot here pursue further. We now turn our attention to
animal sensation, in order to observe the difference between it and the
receptivity of the plant. The animal, containing within itself the organ-
ism of the plant, its organic functions must, like those of the plant,
be liable to be modified by external influences. This property in the
plant we have termed irritability, because irritation immediately causes
and calls forth re-action. In the animal, however, the nervous life (as
the expression and type of unity, which embraces all the parts of the
organism and forms them into a whole,) stands between irritation
and re-action; and as each local irritation is communicated through
the nervous life to the whole organic unity, to the consciousness of the
animal, the perception of the irritation rises to a sensation, and thus it
depends more on the free will of the animal whether or not irritation
be followed by re-action. The more intense this consciousness is, (it
being the unity out of which the multiplicity of organic phenomena is
developed, ) the purer and more varied must the sensation be, (because
a more marked individuality necessarily causes a more varied relation-
ship with external objects,) and the more free the action toward the
external world; i. e. the less it will depend on external influence, and the
more it will be determined from within. We find therefore that the
lower animals, and indeed even the parts of the human body which are
less closely connected with the system of nerves proceeding from the
brain and spine, exhibit in a greater degree the irritability of the plant;
while, on the contrary, the higher nervous life of the human organism
presents the flower (or perfection) of individual activity in psychical
life, in self-consciousness, the manifestation of which has often been
separated from the other branches of organic activity, no less erroneously
than its essence (according to the notion of the materialists) has been
considered as the sum or result of a certain corporeal mechanism *.
We have already observed in our introductory remarks on the idea
of life, that the inward unity, or the highest idea of an individual or-
ganism, is by no means the effect or the result, but the ground and
cause, of external multiplicity, and this is also the case with the psy-
* [Rather,—as the sum or result of the powers and properties, physical, vital
and sentient, with which the Creator has endowed the human frame.—En1r. |
THEIR LIFE AND AFFINITY. 253
chical life*—(wherefore the doctrine of Stahl, that the soul forms its
own body, if properly understood, is very admissible,—and we hope
soon to have the opportunity more fully to develop these views, for
which we have not space here, and to confirm the above propositions
by more convincing proofs. For the present we have only to observe
in general, having already spoken of the manner in which animal re-
action depends on muscular motion (see p. 237), how far the more pre-
cise independence and the more certain self-consciousness of the animal
give rise to the individual forms of sensation.
In the plant, in which irritation causes re-action at the point where it
acts, and the single parts of which are independent, but not the whole,
irritability (belonging to all the parts) must be general; and this gene-
ral irritability (raised into a sensation only through the relation of each
irritating action to the whole,) is possessed by the animal in common
with the plant, and it is therefore included in the comprehensive term
feeling. But since in the animal the sensation of each individual part
is related to the whole, this sensation can be concentrated and particu-
larly developed, on certain individual points, without injury, or rather
with advantage to the whole; wherefore we see that the different sides
of perception turned toward the outer world, correspond in number
with the different organic systems turned toward the outer world, and
with the qualitative influences of various kinds acting upon the organ-
ism; so that if mere Feeling gives us only a knowledge of the state of
our own organism, the zzdividual senses of hearing, seeing, smelling,
tasting, touching, &c. afford us a clearer consciousness of the external
world, through a local alteration of our own condition.
If in closing these observations, intended to show the progressive
development of animal life out of the life of the lower kingdoms of
nature, we look to the changes which animal life operates upon them,
facts present themselves worthy of the most serious consideration. We
have seen how the vegetative life is nourished by inorganic life, and
how vegetation in its turn operates changes in many ways upon the
surface of the earth, and even on the atmosphere. So again we find
that the animal kingdom maintains the most active relation with the
vegetable life and with the elements of the earth and of the air. We see
coral rocks and islands raised from the bottom of the sea by animated
beings apparently insignificant, which, existing before the creation of
Adam, now elevate their lofty tops as mountains of the continent ; we
see the animal kingdom penetrating into parts of the earth seemingly
impenetrable to all living creaturest ; moreover, we observe that here
also, where, according to the eternal laws of nature, the highest is
« ee ccen Leben, Germ.] :
+ See on this subject the observations which G. R. Treviranus (Biologie,
vol, ii. p. 7) has collected from the instructive reports of other naturalists.
254 DR. CARUS ON THE KINGDOMS OF NATURE, ETC.
connected with the lowest, and the human organization itself falls at last
into inorganic dust, the form and culture of the land, the course of the
rivers, vegetation, and population, along with different animal species,
are in various ways changed by the activity of man. If therefore we
compare the condition of countries which have once flourished and
exhibited the activity of human industry, with the desert state which
they now present, when, after the fall of these nations, they are deprived
of the care and culture of man, we shall be convinced that, as a mo-
dern writer* expresses himself on this subject, “ Not only does man
need the earth in order to live and be active, but the earth also stands
in need of man.”
We may hope now to have attained the object of the present essay,
if, by throwing some new light upon certain aspects of infinite nature
which have hitherto remained less observed, we have awakened a new
attention to the indissoluble union as well as the beauty and regularity
of the phenomena surrounding man and existing within him; and as
the contemplation of these must necessarily stimulate us, not only to
penetrate more deeply into the mysteries of science, but also to conform
our own inward life to that harmony and purity which are presented
by universal nature; for what would be the value of all scientific
knowledge, did it not manifest itself in ennobling and elevating the
human mind ?
* T. F. Koreff, De Regionibus Italie aere pernicioso contaminatis Observa-
tiones. Berol. 1817. 4.
NOTE.
[In some of his reasonings the Author will, perhaps, be thought to
deal with abstract terms as if they were real essences, or to employ them
in a sense somewhat peculiar. Whatever difference of opinion may,
however, exist with regard to the speculative parts of this memoir, it
will, it is presumed, be acceptable and interesting to many readers, as
showing the manner in which physiological subjects are viewed by
some distinguished writers on the Continent—EDbITr. ]
255
ARTICLE XI.
Researches on the Elasticity of Bodies which Crystallize
regularly ; by Fevix SAvarr.
(Read to the Academy of Sciences of Paris, January 26th, 1829.)
From the Annales de Chimie et de Physique, vol. xu. p..5, et seq.
[Continued from p. 152.]
— § III. Analysis of Rock Crystal by means of Sonorous Vibrations,
Rocx Crystal most ordinarily occurs under the form of a hexahedral
prism, terminated by pyramids with six faces (fig. 1. pl. IV.). Although
this substance does not admit of cleavage by the ordinary means, it is
assumed, from analogy, that its primitive form is a rhombohedron, like
that which would be obtained if the crystal were susceptible of cleavage
parallel to the three non-adjacent faces of the pyramid, such, for ex-
ample, as aX b, eX f, eXd, and their parallels a’ Y b', e' Y f', c' Yd’. The
accuracy of this induction is besides confirmed by a very simple expe-
riment, which consists in making a prism of rock crystal red hot, and
suddenly cooling it; an operation which determines its fracture, and
which most frequently, gives as the result pieces of crystal which have
the form of rhombohedrons.
Setting out with these notions with which mineralogy furnishes us,
it is obvious that circular plates taken parallel or perpendicular to the
axis, parallel to a face of cleavage or of non-cleavage of the pyramid, &c.
ought to present different phenomena with respect to sonorous vibra-
tions, since the cohesion and elasticity are not the same in these dif-
ferent directions. Consequently, to simplify as much as possible the
examination of these phenomena, we have had cut, from different
pieces of rock crystal, a considerable number of circular plates, at first
taken in different azimuths of a plane perpendicular to the axis, fig. 2.
and fig. 2, bs; then, according to the azimuths of a plane perpendicular
to two parallel faces of the hexahedron, and passing through its axis,
fig. 3. and fig. 3, bis; lastly, according to the different azimuths ofa plane
passing through the axis and two opposite edges of the crystal fig. 4.
and 4 bis.
As it was necessary to support this general disposition of the expe-
riments by facts, it was indispensable to ascertain first, that the elastic
state of the crystal is the same for all the planes parallel to the natural
faces of the hexahedron, and next, that it is also the same for all the
256 FELIX SAVART’S RESEARCHES ON THE
planes perpendicular to the preceding and passing through the axis,
although it be different in the latter from what it is in the former; lastly,
it was necessary to verify whether the plates cut parallel to the faces a X46,
eX f, eXd of the pyramid were really susceptible of assuming the same
modes of division, and whether these modes were different from those
of the three plates cut parallel to the faces b Xe, d Xe, aX f, these latter
being besides similar to each other. Experiment having shown the
affirmative of these positions, it is evident that all the series of plates
perpendicular to a plane normal to any two parallel faces of the prism,
and passing through its axis, ought to present identical phenomena for
the same degrees of inclination, and that the same ought to be the case
for the series of plates perpendicular to any plane passing through two
opposite edges of the hexahedron. All the plates we have employed
are 23 or 27 lines in diameter and 1 line in thickness; they have
been cut with great care and are polished, in order that the phenomena
they exhibit with respect to light might be compared with those they
present relative to sonorous vibrations. Lastly, although they have
been taken from five or six different crystals and from different coun-
tries, it may be supposed that they belong to the same piece of quartz,
because, whenever it was necessary to pass from one crystal to another,
the precaution was taken of causing to be cut in the new specimen a
certain number of plates, for the sole purpose of repeating the experi-
ments already made; and by this process we may assure ourselves
that crystals of very different appearance, such as those of Madagascar
and of Dauphiny, do not however present remarkable differences in
their structure.
Before proceeding to the description of the phenomena which are
related to each series of plates, we shall observe, that in all the figures
the line 2 y represents the axis itself of the crystal when it is contained
in the plane of the plate, or its projection in the contrary case, and that
the position of this axis has been determined with great care, for each
plate individually, by means of polarized light; so that with this datum
and the details into which we shall enter, the position occupied by any
plate within the mass of the crystal may easily be represented to the mind.
First Series. Plates parallel to the Axis of the Hexahedron.
If we consider first the plates 1., v., 1x., fig. 2. and 2, bis, which are
parallel to the faces of the hexahedron, we see that they assume ex-
actly the same modes of division: one of these modes, that which is
represented by dotted lines, consists of two nodal lines, which cross
each other rectangularly, whilst the other resembles the two branches
of a hyperbola, to which the two preceding lines serve as axes. The
sound of the first system being F, that of the second is the Df of the
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 2577
same octave. Thus, in any plate taken parallel to the faces of the
hexahedron, one of the nodal lines of the rectangular system always
corresponds with the axis of the crystal. In this case everything
occurs the same as in plates composed of parallel fibres and which con-
tain in their plane at least one of the axes of elasticity ; but this is no
longer the case for the plates 111., viI., x1., perpendicular to two paral-
lel faces of the hexahedron, although they are also parallel to the axis
like the preceding: instead of a system of lines crossed rectangularly
and a hyperbolic system, they exhibit only two hyperbolic systems,
which appear exactly similar, and which however are accompanied by
very different sounds, since one of them gives D and the other Fg
of the same octave. The principal axes 7m, l'm! of each of the two
hyperbolic curves appear to intersect each other at the centre of the
plate; their mutual inclination is from 51° to 52°, so that the branches
of these curves intersect each other ; and if a line o p be drawn through
the centre of the plate equally inclined to each of the axes J m, I! m’,
and this line be supposed to be the section of a plane perpendicular to
the plate, this plane will, for the plate 111., be parallel to the face eX f
of the pyramid fig. 1.; for the plate vir., to the face aX6; and lastly,
for the plate x1., to the face eXd; so that it must hence be concluded
that the six faces of the pyramid do not possess the same properties,
and that the three we have just indicated perform an important part in
the phenomena in question. It must be remarked that the modes of
division of these plates are exactly the same as those of the plate No. 3
of fig. 14, Pl. III.*, which contains neither of the axes of elasticity in its
plane. Now, if we consider the plates 11., Iv., VI., VIII., X., XII. inter-
mediate to the preceding and to those which are parallel to the faces
of the hexahedron, we find also in them properties which seem to de-
pend on both jointly, as well with respect to the nodal lines of the two
systems as to the sounds they produce. Thus with reference to the pro-
cess of investigation which we have employed, all the plates parallel to
the axis do not possess the same properties, whilst with regard to light
it is well known that they exhibit exactly the same appearances.
Although this result has been verified many times, it was still impor-
tant to verify it again, which I did in the following manner: I took,
first, two plates like Nos. 1. and v., and then two plates like m1. and
vil., and after having crossed their optic axes, I placed successively
each of these pairs in the path of a large pencil of light polarized by
a black glass, the plane of the plates being placed perpendicularly to
the luminous rays, and their axes making an angle of 45° with the plane
of polarization. It is known that if we look through a similar pair by
means of a tourmaline, the axis of which is in the plane of polarization,
we perceive two systems of coloured hyperbolas, the tints of which
* For Pl. III. see Scientific Memoirs, Part I.
258 FELIX SAVART’S RESEARCHES ON THE
appear to follow sensibly in their succession the order of those of New-
ton’s rings: it was required therefore only to compare the phenomena
observed in the two cases, and to see whether they presented any hi-
therto unobserved differences; but it was impossible to recognise any.
Thinking that perhaps a considerable augmentation of thickness in the
plates might bring to view some appreciable differences, I repeated the
experiment with pieces of rock crystal which were eight centimetres
(3°149 inches) in thickness, and I saw nothing that could indicate that
all the plates parallel to the axis did not comport themselves in the
same manner with regard to light: whence it must be concluded that
what we can learn respecting the structure of crystals by means of
light, is not of the same order as that which sonorous vibrations may
enable us to discover. It would appear from what precedes, that this
latter process indicates more specially the elastic state and the force of
cohesion of the integrant particles in the different directions of every
plane, whilst the phenomena of light, depending more specially on the
form of the particles and on the position they assume round their
centre of gravity, are, to a certain point, independent of the mode of
junction of the different plates of which the crystal is formed.
Seconp Series. Plates cut round the Edge a b, fig. 1, and according
to the different Azimuths of the Plane mn X op Y, fig. 3, normal to
the Faces No. 1. and No. 4. of the Hexahedron and passing through
its axis.
One of the modes of division of all the plates of this series remains
constantly the same, fig. 3, bis; it is formed of two straight lines cross-
ing each other rectangularly, and xy, one of these lines, is always the
projection of the axis of the crystal on the plane of the plate. The
other mode of division consists of two hyperbolic curves, which undergo
various modifications depending on the inclination of the plates to the
axis of the hexahedron, and which are in general analogous to those
we have observed in the two first series of plates belonging to bodies
possessing three rectangular axes of elasticity.
No. 1. represents the two modes of division of the plate perpendi-
cular to the axis X Y; they are both composed of straight lines; or, if
either is formed of two curves, their summits are so near each other
that they appear to coalesce. Rock crystal being a crystal with one
axis, in respect to light, it was natural to presume that the elasticity
would be equal in every direction of the plane of the plate in question,
and that, in consequence, this plate might assume only a single mode
of division, having the property of placing itself in any direction ; but
this is not the case, even in plates cut with extreme care, and which by
their optical properties appear sensibly perpendicular to the axis. Ne-
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 259.
vertheless, the interval which is observed between the sounds of the two
systems being always very small, and not being constant in different cry-
stals, it appears more natural to attribute this difference of elasticity to
an irregularity of structure than to suppose that it depends on a deter-
minate and regular arrangement, the more so as in very large crystals,
like those I have employed, it is very rare not to meet with irregularities
of structure sufficiently obvious even to be recognised by the naked
eye.
The plate No. 2, inclined 78° to the axis, begins to present a differ-
ence in the disposition of these two systems of nodal lines; one of the
two transforms itself into two hyperbolic branches, which become more
straightened in the plate No. 3, inclined 75° to the axis, and which
afterwards approach each other again, and become two straight lines,
which intersect each other at right angles in the plate No. 4, inclined
about 51° to the axis, and which consequently is nearly perpendicular
to the face a X b of the pyramid fig. 1; the inclination of the faces of
the pyramid to those of the hexahedron being 140° 40!.
The numbers of vibrations which were nearly the same for No. 1,
from which only the sounds D and D+ were obtained, differ more as
the plate approaches No. 4, when the gravest sound being C, the second
is the G of the same octave, although the two modes of division are
‘the same as those of No.1. It is this sound C, given by one of the
modes of division of the plate perpendicular to the face of the pyramid,
which I have taken as the term of comparison, and to which the sounds
of all the other plates are referred. Recommencing with the plate
No. 4, the variable system separates once more, but in the contrary
way; the curves which form it continue to straighten, whilst their
summits recede from each other, and at the same time the two sounds
approximate until they are sensibly the same in No.8, inclined about
12° to the axis. The hyperbolic system ceases to assume a determined
position, and it can, without the sound undergoing any change, trans-
form itself gradually into the rectangular system which form the axes,
so that this plate appears to be exactly in the same conditions as No. 5
of fig. 8, PI.III. In a crystal of quartz there are three planes analogous
to the preceding, since the phznomena which are presented by the
plates cut round the edge a6 of the base of the prism, are, as I have
satisfied myself, precisely the same as those which are presented, for
the same degrees of inclination, by plates cut round the two other edges
ed, ef.
Beyond No. 8. the sounds begin to differ from each other, and the
branches of the hyperbola continue to straighten until No. 11, parallel
to the second face of the pyramid. There the distance between their
summits is greater than for any other degree of inclination of the
plates, and the sound of the rectangular system is the same as that of
260 , FELIX SAVART’S RESEARCHES ON THE
the same mode of division in No. 4, perpendicular to the face a Xb of
the pyramid. Lastly, from No.1] until the plate perpendicular to the
axis, the sounds approximate again, as well as the summits of the hy-
perbolic curves, and at the same time the two systems of nodal lines
again become rectangular ; the sounds thus become almost the same.
- Among the plates which we have just examined there are two which
merit particular attention; these are Nos. 5 and 11, parallel to the
the faces eXd and aXb of the pyramid, and the elastic state of which
undoubtedly differs very much, since in one it is the hyperbolic system
which gives the gravest sound, whilst in the other it is the rectangular
system, and that, besides, there is a great difference between the sounds
which correspond to each of their nodal systems. The faces aXb and
and eXd of the pyramid being opposite, one of the two ought to be
susceptible of cleavage, whilst the other ought not to be capable of
this mechanical division ; consequently if we knew which of the two
plates Nos. 5 and 11 possesses this property, we might, by examining
its acoustic figures, determine which are the faces of the pyramid pa-
rallel to the faces of the primitive rhombohedron. Rock erystal not
yielding in the least to any attempt at dividing it into regular layers in
any direction, it was impossible for me to ascertain directly which of
the two faces aXb or eXd were those of cleavage; but this question
ean be resolved with ferriferous carbonate of lime, a substance which
is cleaved with almost the same facility as pure carbonate of lime, and
which appears to possess, in reference to sonorous vibrations, properties
in general analogous to those of rock crystal. Now, if we cut in such
a crystal two plates,—one taken parallel to a natural face of the rhom-
bohedron, the other corresponding with a plane inclined to the axis
by the same number of degrees as these faces, and which are besides
equally inclined to the two faces which form one of the obtuse solid
angles,—we find that the first possesses the same properties as No. 11,
whilst the second has a structure analogous to that of No.5; whence
it ought to be concluded, from analogy, that the face aX 6 of the
pyramid fig. 1. is that which is susceptible of cleavage. This once
established, it is not even requisite, in order to ascertain which of the
faces is susceptible of cleavage, to cut a plate parallel to one of these
faces; it is obvious that a plate parallel to the axis and normal to two
parallel faces of the hexahedron should be sufficient to attain this end.
Thus, let fig. 5, a be de f, be the horizontal projection of the prism
represented fig. 1 ; according to what has been said, 7 s ¢ v will be the’
projection of the primitive rhombohedron ; again, let 7Z' be the projec-
tion of a plate parallel to the axis and equally inclined to the two faces
of a and f of the hexahedron; according to what we have above said,
this plate will assume the mode of division of No. 3, fig. 2, és, and the line
op will be parallel to the plane 7 s¢w normal to the plate, that is tosay,.
ee ee —
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 961
to one of the cleavage planes; thus the direction of this line, in a plate
parallel to the axis and normal to two faces of the hexahedron, is suffi-
cient to enable us to ascertain which of the faces of the pyramid are
susceptible of cleavage.
In order to complete all that relates to the transformations of the
nodal lines of this series of plates, it would have been important to de-
termine with accuracy the degree of inclination to the axis, of the
plane situated between No.3 and No. 4, for which the summits of the
nodal hyperbola are at the greatest distance from each other: but, hav-
ing been stopped in these investigations by the difficulty of procuring
a sufficient quantity of rock crystal very pure and regularly crystal-
lized, I have been reduced to determine this maximum of recession
on another substance, and I have chosen for this purpose the ferriferous
carbonate of lime, a substance whose primitive form is a rhombohe-
dron, which differs from that of rock crystal only in the angles formed
by its terminating planes. As we have already observed, there is a
sufficiently great analogy between the phenomena presented by these
two substances, with respect to sonorous vibrations, to enable us to
admit that what occurs in one occurs also in the other: thus, let A E,
fig.6, be a rhombohedron of carbonate of lime, of which A is one of
the obtuse solid angles; A BC D corresponding to the face of cleavage
of the pyramid of rock crystal, the diagonal B D will be the line round
which all the plates must be supposed to be cut; and they are conse-
quently normal to A C EG, represented separately in fig. 7, in which
the lines 1, 2, 3, &e., are their projections, and indicate at the same time
the angles which they make with the axis AE. We will first remark
that the modes of division of the plate No. 1, fig. 7, dts, perpendicular
to the axis, are the same as those of the corresponding plate of rock
crystal, and that the plate No. 5, perpendicular to A C, assumes also
the same modes of division as the plate perpendicular to the cleavable
face of the pyramid of rock crystal, which establishes a sufficient ana-
logy between the two orders of phenomena. The inspection of fig. 7, bis,
shows then that the branches of the nodal hyperbola of No.3, parallel
to AG, consequently to the plane BDF H, are straighter than those
of the plates which precede or follow it; and admitting that this maxi-
mum of recession occurs equally in quartz for the corresponding dia-
gonal plane of its rhombohedron, as this plane forms with the cleavable
face of the pyramid an angle of 96° 0' 13", the plate in question will
be inclined 57° 40! 13" to the axis of the crystal, the face of the pyra-
mid forming with this axis an angle of 38° 20'; thus the projection of
this plate on the plane mn X op Y of fig. 3. will be the line A B.
Now since the maximum of recession of the summits of the nodal
hyperbola is in this manner determined, it is easy to recognise a great
analogy between the phenomena of fig. 8, PI]. III., and those of fig. 3, bis,
Vor. L—Part I. r
262 FELIX SAVART’S RESEARCHES ON THE
PI. IV.; for, supposing several intermediate plates between Nos. 3 and 4,
that which would be inclined 57° to the axis would correspond to No.1
of fig.8, Pl]. III.; No. 4 in the crystal would correspond to No.3 in the
wood; and lastly, No. 11 of the erystal plates, in which a second maxi-
mum of recession of the summits of the hyperbola occurs, would corre-
spond to No.6 of the plates of wood; so that the same phenomena,
which are included, in a body having three rectangular axes of elas-
ticity, in an are only of 90°, to be afterwards reproduced in a contrary
direction in the following quadrant, are included in rock erystal in an
are of 96° 0’ 13", and cannot be entirely reproduced, because similar
pheenomena to those we have just observed for a series of plates cut
round @ 6, fig. 1, Pl. IV., occurring, for the same degrees of inclination, in
the two series of plates which might be cut round ed and ef, both are
confounded together in the vicinity of the plate perpendicular to X Y.
Tuirp Series. Plates cut round the diagonal ac, fig.1, and accord-
ing to the different Azimuths of the Plane be! Yb'e X, fig. 4.
These plates present phenomena much more complicated than those
of the two preceding series. It may be easily conceived that this
ought to be the case, since the plates parallel to the two adjacent faces
of the pyramid assume very different modes of division, which supposes
that their elastic state also greatly differs: consequently the plates perpen-
dicular to the plane which passes through the two opposite edges of the
hexahedron ought to participate in the properties of both. Itis thus that
the plates perpendicular to two parallel faces of the prism, and passing
through its axis, assume a disposition of nodal lines in which the direc-
tion of the planes of cleavage, parallel to one of the faces of the pyra-
mid, exercises a considerable influence.
In the plates of this series (fig. 4, bis,) neither mode of division is
constant ; nevertheless, in order that they may be easily distinguished
from each other, I have continued to indicate them, one by uninter-
rupted lines, the other by dotted lines. And for the purpose of pre-
serving, in all the plates, the projection 2 y of the axis parallel to the
axis X Y of fig.1, I have here supposed that the crystal had been
turned round until its edge de’ was in front. This is besides suffi-
ciently indicated by figure A, which represents the modes of division
of the plate perpendicular to the axis, as it also does the section of the
hexahedron by a plane parallel to this plate.
The inspection of figures A, B, C, D, E.... shows that the nodal system
indicated by the perfect lines is formed of two hyperbolic branches
which at first straighten themselves, and the summits of which recede
more from each other, so far as the plate E inclined 51° to the axis,
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 263
beyond which they approach each other until they coalesce in K, after
which they again diverge until the plate N, which is parallel to the axis.
The nodal system indicated by the dotted lines follows another
course; the summits of the two curves which compose it at first recede
from each other, but they soon reapproach each other, and these curves
transform themselves into two straight lines in the plate E, where the
curves of the other mode of division attain their maximum of recession:
beyond this limit they separate, but in a perpendicular direction to
that in which they approached, and they attain their maximum of
recession towards the plate H, for which the two systems of curves are
nearly similar: they afterwards approach each other, and like those of
the other system, they transform themselves, in K, into two straight
lines, which intersect each other at right angles. Lastly, starting from
this point, they diverge again, until the plate N, for which the two
systems again become equal, assuming, with respect to the axis of the
erystal, a direction different from that which they had taken at I and at
H. I must observe that my supply of rock crystal having failed at the
end of my experiments, I have not been able to cut the plate K; but
the transformations of the nodal lines so clearly indicate that there
ought to be a plate which presents these modes of division, that I have
not hesitated to admit its existence.
The course which the two sounds follow, in this series of plates, is
much more simple than that of the nodal figures: at first those of the
dotted system become lower, commencing with the plate A, and pro-
ceeding as far as the plate E, inclined 51° to the axis, and which gives
the sound C like the plate No. 4, inclined the same number of degrees
to the axis; afterwards the sound of this system gradually ascends until
the plate N parallel to the axis, where it attains its maximum of eleva-
tion. As to the sounds of the other series of modes of division, it is
observed that they gradually ascend from the plate perpendicular to the
axis unto K, in which the nodal systems both consist of lines crossed
rectangularly, and that they afterwards descend again until the plate
N parallel to the axis. It is obvious that it is not necessary to examine
such plates as A’, B’, C’, D’, fig. 4, since they ought to present the
same phenomena as the corresponding plates A, B, C, D: only, that
which was inclined to the right of the axis in the plates B, C, D is
found inclined to the left in the plates B', C’, D’.
There is none of the modes of division of this series which is not
analogous to some one of those which have been presented to us by
bodies in which there are evidently three rectangular axes of elasticity;
nevertheless, considered all together, the transformations we have just
described present peculiarities which do not exist in the fourth series of
plates of wood, fig. 14, Pl. III. ‘The most striking consists in this, that
in the transformations of this last series, none of the systems, except
tT 2
264 FELIX SAVART’S RESEARCHES ON THE
the first and the last, was rectangular, whilst in rock crystal this mode
of division may establish itself.
Summary.
Ist. The elasticity of all the diameters of any plane perpendicular to
the axis of a prism of rock crystal, may be considered as being sensibly
the same.
2nd. All the planes parallel to the axis are far from possessing the
same elastic state; but if any three of these planes be taken, restricting
ourselves only to this condition, that the angles which they form with
each other are equal, then their elastic state is the same.
3rd. The transformations of the nodal lines of a series of plates cut
round one of the edges of the base of the prism are perfectly analo-
gous to those which are observed in a series of plates cut round the
intermediate axis in bodies which possess three unequal and rectangu-
lar axes of elasticity.
4th. The transformations of a series of plates perpendicular to any
one of the three planes which pass through two opposite edges of the
hexahedron are, in general, analogous to those of a series of plates cut
round a line which divides into two equal parts the plane angle in-
cluded between two of the three axes of elasticity in bodies where
these axes are unequal and rectangular.
5th. By means of the acoustic figures of a plate cut in a prism of
rock crystal, nearly parallel to the axis, and not parallel to the two
faces of the hexahedron, we can always distinguish which are the faces
of the pyramid susceptible of cleavage. The same result may be
obtained by the disposition of the modes of. division of a plate taken
nearly parallel to one of the faces of the pyramids.
6th. Whatever be the direction of the plates, the optical axis, or its
projection on their plane, always occupies a position on them which is in-
timately connected with the arrangement of the acoustic lines: thus,
for example, in all the plates cut round one of the edges of the base of
the prism, the optical axis, or its projection, invariably corresponds with
one of the two straight lines which compose the nodal system formed
of two lines which intersect each other rectangularly.
Although there is doubtless a great analogy between the phenomena
which rock crystal has just presented to us, and those we have observed
in bodies in which the elasticity is different according to three direc-
tions perpendicular to each other, nevertheless we are forced to acknow-
ledge that, with respect to the mode of experiment we have employed —
in these researches, rock crystal cannot be placed in the number of
substances with three rectangular and unequal axes of elasticity, and
still less in the number of those all the parts of which are symmetri-
cally arranged round a single straight line. For the same phenomena
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 265
are constantly reproduced in it in three different positions; and it seems
that everything in it has reference to the different directions of cleavage,
to the faces, and to the edges of the primitive rhombohedron. Thus
all the plates cut parallel to the natural faces of the hexahedron possess
exactly the same properties, and these properties are very different from
those of the plates equally parallel to the axis, but which are normal
to two faces of the hexahedron. Likewise, the plates parallel to the
cleavable faces of the pyramid produce the same sounds, and exhibit
the same acoustic figures; whilst the plates parallel to the three other
faces present figures different from those of the preceding plates. It
appears therefore to result from this identity of phenomena for three
distinct positions, that there are in rock crystal three systems of axes
or principal lines of elasticity.
But in this point of view, what would be the precise directions of
these axes for each system? This can, to a certain point, be deter-
mined by comparing the phenomena we have observed in rock crystal
with those presented to us by wood. For, all the plates cut round one of
the edges which result from the junction of a face of the pyramid with
the adjacent face of the hexahedron, producing a nodal system com-
posed of two lines cutting each other rectangularly, one of which
always corresponds with the edge in question ; and the transformations
of the acoustic lines in it being entirely analogous to those of a series
of plates cut round the intermediate axis in wood, it follows that
this edge, which is nothing else than the great diagonal of the primi-
tive rhombohedron, ought to be regarded as the intermediate axis of
elasticity. In the next place, as the maximum of straightening and of
deviation of the branches of the nodal hyperbola takes place in the
plate No. 11, fig. 3, bis, parallel to the cleavable face of the pyramid,
and as at the same time this plate is a limit for the sounds which it
produces, it is equally natural to suppose that it ought also to con-
tain in its plane another axis of elasticity, which can correspond only
to the second of the crossed nodal lines, that is to say, to that which
serves as the second axis of the nodal hyperbola, and which is, at the
same time, the smaller diagonal of the lozenge face of the primitive
rhombohedron. This line may therefore be considered as the axis of
greatest elasticity of each system. Lastly, following the same analogy,
as the plate which is cut parallel to the diagonal plane, the intersection
of which with the lozenge face of the rhombohedron forms its great
diagonal, is besides a maximum of deviation for the summits of the no-
dal hyperbola, it must thence be concluded that this plane contains the
axis of least elasticity, and, at the same time, that this axis is perpendi-
cular to the intermediate axis, and forms with that of greatest elasti-
city an angle of 57° 40’ 13”, since such is the inclination of the face of
the rhombohedron to the diagonal plane. Thus, first, the axis of
266 a FELIX SAVART’S RESEARCHES ON THE
greatest elasticity and the intermediate axis are contained in the plane
which forms the face of the rhombohedron, and they are perpendicular
to each other; secondly, the intermediate axis and the axis of least
elasticity are contained in the diagonal plane, and they are in like
manner perpendicular to each other.
Such are the consequences to which the analogy observed between
the successive transformations of the nodal lines in plates of wood and
of rock erystal seems to lead. The co-existence of three systems of
axes of elasticity in the latter body, introduces however so great a
complication in the particulars of the phenomenon, especially in the
progression of the sounds, that the elastic state of this substance
can only be definitively determined by a method analogous to that
which I have above employed for wood, that is to say, by comparing
together the numbers of vibrations of a series of small rods of the same
dimensions, and cut according to the different directions in which
the preceding experiments appear to indicate that the elasticity differs
the most. Without in the least prejudging the results to which these
new researches might lead us, we may even now foresee that there
ought to bea great difference between the greatest and the least degree
of elasticity in rock crystal, since, among the various plates of beech-
wood, a substance in which these two extremes are as one to sixteen,
there is none the sounds of which have a greater interval than that of
a major third between them, whilst, among the plates of erystal, there
are some, the two sounds of which are a fifth from each other.
As we have already remarked above, the transparent carbonate of
lime and the ferriferous carbonate of lime appear to possess elastic
properties which are, for the most part, analogous to those of rock
erystal; three systems of principal lines of elasticity, which appear
exactly similar to each other, are likewise recognised in them; but the
extreme facility with which carbonate of lime may be cleaved, enables
us to discover in it a peculiarity which cannot be perceived in rock
crystal, and which may explain why it is that the plates cut round one
of the edges of the base of the hexahedron, all present a nodal system
composed of two lines crossed rectangularly.
It is well known that the rhombohedron of carbonate of lime is fre-
quently susceptible of a mechanical division according to the directions
parallel to its diagonal planes; now, these planes cutting each other per-
pendicularly two and two, the intersection of each of these pairs with
the lozenge faces of the crystal, forms the great and small diagonal of
each of them, so that, ifa plane be imagined which turns round the great
diagonal, it ought always to remain normal to the supernumerary joint
which passes through the small diagonal. It hence results that, if a
series of plates be cut round the same line, their structure, considered
in the different directions of their plane, will differ according to two
ELASTICITY OF REGULARLY CRYSTALLIZED BODIES. 267
directions perpendicular to each other ; this explains the production of
the nodal lines crossed at right angles, as in the series of plates cut
round one of the axes of elasticity, in bodies in which these axes are rect-
angular. It appears therefore that we may conclude from this obser-
vation that rock crystal possesses, like carbonate of lime, supernumerary
planes of cleavage parallel to the diagonal planes of its primitive rhom-
bohedron, and that it is to the existence of these supernumerary joints
that the principal peculiarities of the elastic state of this substance
must be attributed.
The only striking difference there appears to be between the strue-
ture of carbonate of lime and that of quartz consists in this, that, in
the first of these substances, the small diagonal of the rhombohedron is
the axis of least elasticity, whilst it is that of greatest elasticity in the
second. To be convinced of the accuracy of this assertion, it is suffi-
cient to cut, in a rhombohedron of carbonate of lime, a plate taken
parallel to one of its natural faces, and to examine the arrangement of
its two nodal systems, one of which consists of two lines crossed rect-
angularly, which are always placed on the diagonals of the lozenge,
the primitive outline of the plate, and the other is formed of two hyper-
bolic branches, to which the preceding lines serve as axes (see fig. 7,
bis, No. 6); but with this peculiarity, that it is the small diagonal
which becomes the first axis of the hyperbola, whilst it is its second
axis in the corresponding plate of rock crystal (see fig. 3, bis, No. 11).
It may be here asked how far this difference of structure may influence
the phznomena of light which are peculiar to each of these two sub-
stances, one of which is a crystal with attractive (positive) double re-
fraction, and the other with repulsive (negative) double refraction.
It appears, therefore, to result from this approximation between the
phznomena presented by carbonate of lime and rock crystal, with
respect to sonorous vibrations, that the arrangement of the acoustic
figures, and the numbers of vibrations by which they are accompanied,
are always found intimately connected with the directions of cleavage
in each plate; and it may be said in general, that if these directions
intersect each other at right angles, in the plane of the plate, one of
the two modes of division will always consist of two lines crossed rect-
angularly ; whilst if they are inclined to each other the two nodal
systems will be hyperbolic curves.
The disposition of the nodal lines upon circular plates of sulphate
of lime gives additional support to this conclusion. For thin plates of
this substance break according to two directions inclined to each other
at 113° 8’; and experiment shows that the two modes of division of
which they are susceptible are two nearly similar hyperbolic curves, one
of which appears to have for its asymptotes the directions of cleavage,
and the other for its principal axis that one of these two directions in
968 SAVART ON THE ELASTICITY OF CRYSTALLIZED BODIES.
which the plates do not break clean off; for there is, it is well known, an_
obvious difference in the manner in which sulphate of lime breaks ac-
cording to one direction or the other. We will, on concluding, re-
mark, that these modes of division are precisely the same as those of a
dise of rock crystal parallel to the axis and perpendicular to two faces
of the hexahedron, and that the mean of the optic axes in sulphate of
lime occupies in it the same position relatively to the nodal curves, as
the projection of the single axis of rock crystal assumes in that of the
plates of this substance of which we have just spoken. (See fig. 2, bis,
No. 3.)
The preceding researches are, doubtless, far from deserving to be
considered as a complete examination of the elastic state of rock crystal
and of carbonate of lime ; nevertheless we hope they will be sufficient
to show that the mode of experiment we have employed may hereafter
become a powerful means of studying the structure of solid bodies,
regularly or even confusedly crystallized. Thus, for instance, the
relations which exist between the modes of division and the primi-
tive form of crystals allow us to presume that the primitive form of
certain substances which do not at all yield to a mere mechanical
division may be determined by sonorous vibrations. It is equally
natural to think that less imperfect notions respecting the elastic state
and cohesion of crystals than those we now possess, may throw light
upon many peculiarities of crystallization: for example, it is not im-
possible that the degrees of elasticity of a determinate substance may
not be exactly the same, for the same direction referred to the primitive
form, when the secondary form is different ; and, if it be so, as some
facts induce me to suspect, the determination of the elastic state of
crystals will lead to the explanation of the most complicated phno-
mena of the structure of bodies. Lastly, it appears that the comparison
of the results furnished concerning the constitution of bodies, on the
one hand by means of light, and on the other hand by means of sono-
rous vibrations, ought necessarily to contribute to the progress of light
itself, as well as to that of acoustics.
ArricLte XII.
Researches concerning the Nature of the Bleaching Compounds
of Chlorine; by J. A. BAvarRD.
From the Annales de Chimie et de Physique, vol. lvii. p. 225.
AMonG the remarkable properties which chlorine possesses, there
is one which became advantageous to manufactures very shortly after
its discovery, viz. its energetic action on colouring matter. _ The illus-
trious Swede to whom we owe the knowledge of this body, mentioned
the facility with which it destroys vegetable colours ; but that which to
Scheele was merely an interesting experiment, became to Berthollet
the basis of a new art. Berthollet conceived the happy idea of apply-
ing the decolorizing property of chlorine to the purpose of bleaching,
and the success which he obtained even in his first attempts exceeded
his hopes. Up to this period, cotton and linen manufactures were
spread in meadows, and by exposing them alternately moist and dry to
heat and cold, light and shade, they were indeed, after a very long
time, perfectly bleached.
The eagerness with which a new process was welcomed will be con-
ceived, when manufacturers could produce by it in a few hours what
previously occupied several months. The new process of bleaching, to
which public gratitude gave the name of the Berthollean method, was
generally adopted, and chlorine thus proceeded from the laboratory
of the chemist to the workshop of the arts. Manufactures were first
bleached with chlorine gas, and afterwards with the aqueous solution ;
but it was soon found that its penetrating smell, and its powerful action
on the lungs, were very prejudicial to the workmen employed. In his
endeavours to free them from these dangerous exhalations, Berthollet
perceived that by the addition of a little quicklime, and even carbon-
ate of lime or of magnesia, the penetrating smell of the chlorine was
removed from the aqueous solution, without diminishing its bleaching
power. This important observation conducted him to another still
more important. He stated that if, instead of dissolving the alkali in
aqueous solution of chlorine, a current of the gas was made to pass:
into the alkaline solution, it would dissolve a much larger quantity than
mere water, and the liquid possessed decolorizing power in a much
higher degree.
These new compounds, in which the chlorine seemed in some degree
270 BALARD'S RESEARCHES CONCERNING THE NATURE OF
deprived of its hurtful properties, while it retained only those which
are useful, were soon generally employed in the art of bleaching. They
were at first prepared with the solution, and as the first trials were made
in the manufactory of Javelle, the new liquid with which industry was
enriched was called eau de Javelle. But in 1798, Tennant and Knox
of Glasgow attempted to substitute hydrate of lime, which forms a solid
bleaching compound, while chlorine retains its power only when diluted
with a large quantity of water. This substitution was generally adopted,
and the new compound, which is more easily preserved and prepared,
and at a less price, and more easy of transport, soon became an article
of manufacture and considerable commerce, under the name of bleach-
ing powder.
The employment of these compounds of chlorine was further ex-
tended in 1822. M. Labarraque, an apothecary of Paris, proved at this
period, by numerous trials, that these compounds, which had rendered
so many services to the art of bleaching, might be as successfully used
for disinfecting. His own trials, and the fresh proofs that his example
incited, placed the decolorizing compound of chlorine decidedly among
the most valuable resources of the art of preserving health.
We should be at first inclined to believe that the nature of these
eompounds, which had rendered us such various services, was perfectly
understood by chemists; but it is not at all so; and notwithstanding
the researches which they have occasioned, the place which they ought
to occupy in a classification is not clearly determined. It is, indeed,
true that their elementary composition and immediate analysis are well
known. In fact, obtained by the action of chlorine upon a metallic
oxide, they evidently must be formed merely of chlorine, oxygen, and
a metal; on the other hand, the experiments of several chemists have
proved that in these compounds, for every two atoms of chlorine*, there
is one atom each of oxygen and metal. But how are these three ele-
ments arranged? This is not at present known with certainty; and
yet this knowledge is indispensable for determining by what reactions
they serve in decolorizing and disinfecting.
§ 1. Of the Opinions which have been entertained as to the Nature of the
decolorizing Compounds of Chlorine.
The opinions of chemists on this subject are divisible into two hy-
potheses. According to some, these compounds are merely chlorides
of oxides ; according to others, they are to be considered as mixtures of
metallic chlorides with a salt which contains an acid of chlorine, less
oxygenated than the chloric, and which it has been proposed to eall
chlorous acid.
* Not so in England, but foreign chemists reckon the weight of chlorine only
half that of English chemists, hence the author states two atoms.—LEp.
THE BLEACHING COMPOUNDS OF CHLORINE: 271
On the first supposition it is admitted, that chlorine, in acting on
some metallic oxides, combines with, without decomposing them, so as
to form compounds which are not very permanent. The gas being thus
but slightly retained, acts upon vegetable colours as if it were free; that
is to say, it destroys them, either by dehydrogenating them in a direct
manner, or occasioning their oxidation by means of the oxygen of the
water. The chlorine, by taking away the hydrogen, either of the water
or the colouring matter itself, is converted into hydrochloric acid, and
subsequently into a hydrochlorate.
On the second supposition, on the contrary, it is supposed that the
chlorine acts upon the metallic oxide employed, so as to decompose
part of it; that one portion of this chlorine unites to the metal to form
a chloride, and the other to its oxygen to become chlorous acid; and
that this, saturating the portion of the base undecomposed, thus forms
a true chlorite. In this manner of regarding the subject, the product
obtained. is complex, and contains a mixture of chloride and chlorite.
It is thus supposed that chlorine and water act upon the metallic oxides
like sulphur, which, under the same circumstances, produces a mixture
of sulphuret and hyposulphite. It is also supposed that these chlorites,
coming into contact with putrid organic or colouring matter, yield to
them all the oxygen both of their acid and base, and are converted into
chlorides; and that it is thus entirely by an oxidizing action that they
serve as decolorants and disinfectants.
In attempting to resolve the question @ priori, upon theoretical con-
siderations, we are tempted to consider this last supposition as the most
probable. In fact, the combinations of simple with compound bodies
are not common; and although the hydrates of chlorine, bromine, and
phosphorus are incontestible examples of the union of a simple body
with an oxygenated compound, combinations of this nature are not
numerous. It is therefore good logic to admit of the existence of simi-
lar compounds, only when the phenomena which are concerned in their
production cannot be explained by other views more consistent with
general facts. It appears, also, difficult to suppose, that a body which
so readily combines with the metals as chlorine does, could unite with
their oxides without decomposing them, as is the case with the other
metalloids, and remain in contact with the metals, with which it forms
very neutral and permanent compounds, without so doing.
The facts hitherto observed agree with theory, and seem to support
in preference the hypothesis of the chlorites.
_ Chemists, indeed, considering that the compounds which we are now
considering had the property of disinfecting and decolorizing, like chlo-
rine itself, were at first induced to think that this body existed in them
in some sort of ephemeral combination, which allowed of its exerting
the same kind of action as if it were free. But it has been since ad-
272 BALARD’S RESEARCHES CONCERNING THE NATURE OF
mitted, that it is not only chlorine and the analogous bodies which pos-
sess decolorizing power; the same property was found in oxygenated
water, and the hypermanganates; and at present everything tends to
the opinion that oxygenating agents are as effective as chlorine in pro-
ducing decoloration. Perhaps indeed, as many chemists suppose, chlo-
rine, when acting with water on coloured bodies, produces this effect by
indirect oxidation, induced by its tendency to combine with hydrogen.
Welter had, however, made an experiment on this subject which
seemed to prove the existence of chlorides of oxides; he found that the
decolorizing power of chlorine was constant, whether it was free, dis-
solved in water, or combined with an oxide.
This remarkable fact could scarcely be explained but by supposing
that the chlorine existed in the two cases in analogous conditions. Sup-
posing, therefore, that it was in a state of solution in water saturated
with chlorine, it must be admitted that it existed in the state of a chlo-
ride of oxide in the decolorizing compound; or, if the latter was a
chlorite, it followed that the solution of chlorine in water was a mix-
ture of chlorous and hydrochloric acid; for how can it be supposed
that two different bodies, producing decoloration by different causes,
can effect it with precisely the same efficacy? The greater number of
chemists adopted the first supposition; Berzelius alone preferred the
second, although it appeared to be less probable.
The experiments of Soubeiran have since explained these facts. They
have shown that Welter’s statement was correct only when a solution of
sulphate of indigo was used, which, on account of the sulphuric acid it
contained, decomposed the decolorizing chloride, and evolved all the
chlorine which had served to form it. But if an ink which is not acid
or a vegetable infusion be employed as a chlorometric liquor, it is found
that the decolorizing power is no longer the same, and that it may al-
ways be increased by more than half, by means of an acid which sets
free the chlorine contained in the solution of the chlorides.
The property which is possessed by the decolorizing chlorides, of
yielding the whole of the chlorine which they contain by the action of
the weakest acids, such, for example, as the carbonic acid, has been re-
garded as a strong proof in favour of their being chlorides of oxides ;
and it must be admitted that these phenomena of decomposition are
much more easily explained by this hypothesis than the other. Nothing
is in fact more easily conceivable than the action of an acid combining
with a base, and thus disengaging the simple body with which it had
formed an ephemeral compound. But this disengagement of chlorine
is also easily explained by the hypothesis of chlorites ; for it may be
conceived that the chlorous acid, set free by the acids themselves, de-
termines a double decomposition, by reacting upon the metallic chlo-
rides with which the chlorites are necessarily mixed by the very mode
THE BLEACHING COMPOUNDS OF CHLORINE. 273
of their preparation. The results of this double decomposition would
be, the oxidation of the metal of the chloride, which in this new state
would saturate, as the base of the chlorite, the acid employed; and a
disengagement of gaseous chlorine would take place from a double
source: from the chlorous acid and the metallic chloride.
Although this explanation may appear less natural than the other, it
is nevertheless supported by analogous chemical facts. If, for example,
a mixture of phosphuret of calcium and phosphate of lime be made red
hot, phosphorus is evolved, and the residue is lime nearly pure ; this for
a long time favoured the supposition that this mixture was a phosphuret
of oxide, whilst the contrary is now demonstrated.
The phznomena of oxidizement produced by the action of decolori-
zing compounds do not clear up the doubts which exist as to their true
nature, for these phenomena may be explained by both hypotheses. Un-
doubtedly some are more readily so by one and some by the other, but
there is no one to which they may not both be strictly applied.
We are, however, indebted to M. Liebig for some experiments
which seem to render ‘the hypothesis of the chlorites preferable. This
able chemist observed that chlorine could not only expel carbonic acid
from the bicarbonates, but also acetic acid, which is stronger, so as to
form decolorizing compounds. Now it is difficult to conceive that a
simple body can expel an acid from combination with a base; it is more
natural to suppose that it is another acid, which overcomes the affinity
even of the acetic acid; and this cireumstance seems to justify the suppo-
sition of the existence of chlorous acid. It may seem astonishing, at first
sight, that an acid so weak as chlorous acid, and which may be expelled
from its combinations by carbonic acid, should, in its turn, expel acetic
acid from its combinations. But the science presents us with facts
equally singular, and which are well ascertained. Acetic acid itself,
for example, decomposes the carbonates, and yet carbonic acid acting
upon acetate of lead precipitates carbonate from it, and sets acetic acid
free, which may be distilled.
Berzelius first undertook this subject, and among other interesting
experiments, we are indebted to him for one, which, if it has not
entirely settled the question, has at least thrown great light upon it.
On passing a current of chlorine into a solution of carbonate of potash,
saturated with chloride of potassium, this learned chemist observed,
that from the first moment of the disengagement, the liquor became
strongly decolorizing, and much pure chloride of potassium was depo-
sited. The first action of the chlorine on the metallic oxide seemed to
produce chloride of potassium. Then, as no chlorate was as yet depo-
sited, and as in this experiment no deutoxide of hydrogen is formed,
nor is any oxygen disengaged, it must be admitted that what is expelled
from the metal by the chlorine has acted upon a portion of this elemen-
yary body, and formed with it some oxygenated compound, which is not
QT 4 BALARD’S RESEARCHES CONCERNING THE NATURE OF
ehloric acid. Although this fact may be consistently explained by sup-
posing that the presence of a chloride of an oxide in the saturated so-
lution of chloride of potassium has diminished, in this case, the solvent
power of the liquid with respect to this compound, and that the salt
which is obtained is only a portion of that which previously existed in
the liquor, and thus is not produced by the action of the chlorine, as
supposed by Berzelius, the first explanation is yet the most probable,
and induces the belief that metallic chlorides exist ready formed in the
decolorizing compounds.
M. Soubeiran has confirmed this fact by an experiment which
appears to me to be at present the only one not liable to objections.
After having determined, by a preliminary trial, the intensity of the
decolorizing power of a given volume of chloride of soda, he evaporated
it in vacuo to dryness. He has stated that during the evaporation
eubic crystals of chloride of sodium are formed, which may be sepa-
rated in a state of perfect purity ; and that the remaining solid residue
dissolved in water and tested with a coloured but not acid liquor,
possessed absolutely the same decolorizing power as the liquid from
which it was procured. This decolorizing power not having suffered any
diminution, it cannot be admitted that the chloride of sodium obtained
was the product of the decomposition of the decolorizing compound.
This chloride of sodium, therefore, existed in the solution of the alka-
line chloride before its evaporation. If, then, in acting upon an alkali,
the chlorine had formed chloride of sodium, without the production of
a corresponding quantity of chlorate, of oxygenated water, or of gas-
eous oxygen, it necessarily follows that an oxygenated compound was
formed, different from chloric acid. :
The crystallization of chlorite of soda ix vacuo, led M. Soubeiran to
hope that he should succeed in isolating chlorous acid. But the con-
tinuation of his researches, although announced three years since, has
not yet been published.
It will be observed, from what has preceded, that there may still
exist among chemists some indecision as to the choice which may be
made between the two hypotheses proposed as to the nature of the
decolorizing compounds of chlorine. Although the hypothesis of
chlorites is by much the most probable, it is nevertheless true, that not
only chlorous acid has not been obtained in a free state, but even
chlorites also; they not having been yet procured, but in a state of
mixture with the metallic chlorides.
Thus, although very probable, the existence of these salts is far
from being demonstrated, and the composition of chlorous acid, which
was supposed to be formed of two volumes of chlorine and three
volumes of oxygen, remains undecided.
It appeared, therefore, to me desirable to attempt some fresh expe-
riments, with the endeavour of elucidating a theoretical chemical
_
i
+
THE BLEACHING COMPOUNDS OF CHLORINE. Qs
question, which is not only of itself of considerable importance, but the
solution of which might also throw some light on the true mode of
action possessed by these decolorizing compounds, the uses of which
are daily multiplied in medicine and the arts.
I think that I have succeeded in proving that these compounds are
really saline combinations of a peculiar acid formed of chlorine and oxy-
gen. It is this acid, which I have isolated, that forms the subject of this
essay, in which I shall treat successively of the manner of obtaining it,
of the properties by which it is distinguished, the proofs of its composi-
tion, and the generic characters of the combinations which it forms.
Until a knowledge of the proportion of its elements, of which I shall
treat in a following paragraph, allows of my stating the true name
which the rules of chemical nomenclature assign to this acid, I shall
continue to call it chlorous acid, and designate its compounds by the
name of chlorites.
§ 2. On the Processes by which Chlorous Acid may be prepared.
When reflecting on the best mode of proceeding in these researches,
it will be soon perceived in reasoning on the hypothesis of the exis-
tence of chlorites, that the question would be on the point of being
determined, if the supposed chlorite could be separated from the chlo-
ride with which it is considered as mixed in the decolorizing compound.
Nothing would be easier to perform, if there existed a metal which
would form with chlorine a compound soluble in water, and the ox-
ide of which could at the same time form with the chlorous acid a
compound insoluble in this liquid. But, unfortunately, all the known
decolorizing compounds are soluble in’ water, and therefore nothing is
to behoped for in this respect.
This separation would also be very easy if, on the contrary, a metal
was known which would form an insoluble compound with chlorine, and
the oxide of which, by uniting with chlorous acid, would form a soluble
and stable compound, up to a certain point. But the metallic chlo-
rides are all soluble in water, except chloride of silver, lead, and proto-
chloride of mercury; these three metals are therefore evidently those
only which afford a choice.
Economical motives made me at first think of the salts of protoxide
of mercury and of lead; but I soon found that no good result could be
obtained by-employing them.
When a solution of chloride of lime or of soda is treated with proto-
nitrate of mercury, there is immediately precipitated a great. quantity
of protochloride of mercury, and the supernatant liquid is strongly de-
colorizing ; but this property soon disappears, and the liquor then con-
tains a notable quantity of deutochloride of mercury: the precipitate soon
becomes red, and changes to an oxichloride.
276 BALARD’S RESEARCHES CONCERNING THE NATURE OF
The salts of lead possess no advantage over those of mercury. If a
solution of acetate or nitrate of lead be poured into a decolorizing
chloride, a precipitate of chloride of lead is immediately formed ; but
this chloride is itself susceptible of being altered by the chlorite. If it
is not soon separated from the liquor, it becomes quickly brown, is
converted into peroxide, and gives out a strong smell of chlorine. This
double phenomenon is undoubtedly effected by the decomposition of
the chlorous acid.
Since the salts of lead did not, any more than those of mercury, lead
to the end intended, I was compelled to have recourse to the action of
those of silver ; they are more costly, it is true, but they apparently
would be followed with more success. My attempt was not altogether
unsuccessful. Nevertheless the employment of the salts of silver is
attended with some inconveniences which it is requisite to state.
If a neutral solution of nitrate of silver be precipitated by a solution of
chloride of lime, containing a slight excess of lime, a great quantity of
chloride of silver is precipitated, and there is formed at the same time
oxide of silver, which imparts a grey colour to the deposit obtained.
The supernatant liquid is strongly decolorizing; but if an attempt be
made to separate it by filtration, a brisk effervescence is produced as
soon as a little has filtered, and when the filtration is over the liquor has
completely lost its decolorizing property. The gas which is evolved in
this case is oxygen. Berzelius had previously observed the phenome-
non which I have now mentioned, and discovered the cause of it. I
have ascertained in operating directly with the chlorites and the oxide
of silver, that these salts occasioned the formation of chloride of silver
and a disengagement of oxygen. This oxygen is produced, both from
the chlorous acid and the decomposed oxide. A portion of this oxygen
gas evolved is absorbed by the portion of oxide in excess in the liquor,
and converts it into peroxide, whilst the remainder is given out in the
state of gas. In trying to obtain free chlorites, the precipitation of oxide
of silver must be avoided, and the decolorizing chlorides must have no
excess of alkali, which is avoided by neutralizing them with nitric
acid; but it is requisite not to add excess of it, which would be as
active, though a different cause of the decomposition of the chlorite.
If, indeed, a solution of chloride of lime supersaturated with nitric
acid be precipitated by nitrate of silver, the mass of chloride of
silver formed is soon raised by abundant bubbles of chlorine gas, and
the decolorizing property is in a great degree lost. If an attempt be
made quickly to remove the chloride of silver, which is the cause of
this decomposition, from the supernatant liquid, by throwing it in a
cloth and pressing it strongly, the reaction is accompanied with a
disengagement of a very considerable degree of heat. Some direct expe-
riments, which I shall state hereafter, have proved that the chlorous
NATURE°OF THE BLEACHING COMPOUNDS OF CHLORINE. 277
acid, which is in this case set at liberty, exerts the same re-action on
the chloride of silver which it produces on the other chlorides, and
that the presence of a small excess of nitric acid much accelerates this
decomposition.
It will be observed, then, that in order to have a chance of success
in this operation, it is requisite to make use of a decolorizing chloride
which is perfectly neutral. It is impossible to prove that it is in this
state by means of coloured tests, for their tint is not merely modified
but completely destroyed by the chlorides. It is preferable to prepare
it by adding nitric acid drop by drop, and until the precipitate formed
by the chloride in the solution of silver ceases to have the brown tint
which the oxide of silver communicates to it when they are mixed.
When this perfect neutralization is attained, and not exceeded, the
metallic chloride and the alkaline chlorite are decomposed, chloride of
silver is deposited, and the liquid possesses decolorizing power in a very
high degree, which is undoubtedly due to the chlorite of silver remain-
ing in the liquor.
But the substance which it contains is extremely easy of decomposi-
tion ; it was impossible to obtain the liquid clear even by filtration ; it
becomes turbid, precipitates, and deposits much chloride of silver. The
liquor gradually ceases to be decolorizing, and it then contains chlorate
of silver. Thus the attempts which I made to separate chlorous acid
haye almost always been fruitless, and therefore it was necessary to make
fresh ones.
According to what I have stated as to the action of the salts of silver
on the decolorizing compounds of chlorine, it appears to me that it
must be admitted that the oxide of this metal can form with chlorine
compounds similar to those which it yields with the alkalis, though they
are less permanent. It seemed to me therefore proper, as I had so
little success in treating the alkaline chlorides with the salts of silver,
to try the action of oxide of silver upon chlorine itself.
Chemists are generally of opinion that, when chlorine acts upon the
salts of silver, it converts them into chlorate and chloride. Vauquelin
_ mentions having observed the same phenomena in treating chlorine
with free oxide of silver simply diffused in water. But I had every
reason to think, according to the facts above stated, that these two
compounds were formed only by the decomposition of a chlorite.
Some pure oxide of silver was therefore suspended in distilled water,
and agitated with chlorine. This was absorbed. The portion of oxide
which was in contact with the chlorine formed a white compound, and
the other portion became of a very deep black colour. I ascertained
that the first was chloride of silver; as to the second, it possessed all
‘the characters of peroxide of silver. During this re-action heat was
evolved, but I did not perceive any disengagement of oxygen. ‘This
liquid immediately after filtration was limpid and strongly decolorizing,
Vor. I.—Parrt II. U
ch
.
278 BALARD’S RESEARCHES CONCERNING THE
but it did not long retain either of these properties; in a few seconds,
and without any action of the,air towards the production of the pheno-
mena, it became turbid, deposited chloride of silver, and the liquor
contained chlorate.
Analogous phenomena occur when the solutions of any salt of silver,
the nitrate, acetate, chlorate, &c. are treated with chlorine. Chlorate
of silver is formed, and the acids of these salts are set free. But the
filtered liquor, which in its limpid state decolorizes strongly, very soon
loses its limpidity and its decolorizing power; a chloride is deposited,
and chlorate of silver remains in solution.
The facts which I have now adduced show that, whether the deco-
lorizing combinations of chlorine with the alkalis are treated with
nitrate of silver, or chlorine is made to act upon oxide of silver, or
finally a salt of silver itself is acted upon by this agent, a soluble
combination of silver is obtained which is strongly decolorizing, and
which every circumstance leads to the supposition of being a chlorite;
but that this combination is almost ephemeral, and changes rapidly at
common temperatures into chlorate and chloride of silver.
It would be in vain to attempt the conversion of this compound into
another of the same nature, and more stable, by treating it with an
alkaline substance; for this conversion could not be effected without
precipitating the oxide of silver, and this could not fail to re-act on the
chlorite in the manner which I have already indicated ; that is to say,
it would be changed into chloride and oxide of silver, and would disen-
gage oxygen gas.
That which appeared to me to be the most efficacious manner of
retarding a decomposition, which in the heat of summer proceeds with
great rapidity, and quickly destroys the chlorous acid, consists in pre-
cipitating the base of the chlorite of silver by chlorine itself. I have
already mentioned that chlorine, in acting upon any salt of silver what-
ever, decomposes its base; and these two bodies are converted into
chloride of silver and chlorous acid.
It is therefore evident that if this chlorine be made to act upon a
liquid which contains chlorite of silver, there can only be obtained, as
a last result, insoluble chloride of silver and chlorous acid in solution,
derived from a double origin. This is, in fact, what constantly hap-
pens, when in the execution of one of three operations which I have
mentioned a slight excess of chlorine is employed.
The liquid which is obtained after the separation of chloride of silver
by filtration is not however pure chlorous acid. When a decolorizing
compound of chlorine is precipitated by nitrate of silver, it contains a
nitrate of the base employed, besides chlorous acid. If a salt of silver
has been decomposed by chlorine, it contains the acid which forms part
of these salts, mixed with chlorous acid. Lastly, in the case. even in
which the operation is conducted with chlorine and oxide of silver dif-
NATURE OF THE BLEACHING COMPOUNDS OF CHLORINE. 279
fused in water, the chlorous acid, which would seem to be ‘pure, is
nevertheless mixed with a large quantity of chloric acid.
Indeed, when chlorine is agitated with oxide of silver, it is an ope-
ration which, whatever be the rapidity with which it is conducted,
requires a minute or two that the absorption of the chlorine may be
complete ; even in this case a portion of the chlorite is decomposed,
and converted, as usually happens, into chloride and chlorate, and the
latter decomposed in its turn by the chlorine produces chloric acid.
Thus, in whatever manner the operation is conducted, a notable por-
tion of the chlorous acid is changed into this new compound.
But this chlorous acid is fortunately possessed of a volatility which
allows of its separation from the bodies with which it is mixed, and it
may be obtained diluted with water by distilling the liquid prepared
by employing one of these three methods. However, as a high tem-
perature may decompose it in part, and as at the heat of boiling water
some of the substances with which it is mixed, as hydrochloric and
‘nitric acid, may come over in distillation, it is better to operate in
vacuo, or at least under low pressure, at a temperature below 212°
Fahrenheit. A solution of chlorous acid is thus obtained, but diluted
with much water. The first product is the richest in chlorous acid; if
this be kept apart and be again distilled, chlorous acid may be obtained
in a concentrated state.
These methods supply, it is true, but very small quantities, and I
should have renounced the study of the properties of this new oxigen-
ated compound of chlorine, if I had not discovered a more economical
and productive process. This method consists in treating chlorine with
red oxide of mercury suspended in water.
The action of chlorine upon this compound has been already studied
by M.Grouvelle. This chemist has stated that oxichloride of mer-
-eury, very slightly soluble in cold water, was formed. M. Thénard,
on the other hand, has observed that the liquid contained chloride and
chlorate of mercury also in solution; but I am at liberty to suppose
that these bodies are only formed consecutively, and that their exist-
ence had been preceded by that of a mercurial chlorite, as takes place
with the salts of silver.
Certain theoretical considerations made me conceive some hope in
employing oxide of mercury. In fact, if we reflect on the conditions
which appear the most favourable for producing and isolating chlorous
acid, it will be seen that they are reducible to the four following; Ist,
-the action of chlorine on a strongly alkaline oxide; 2ndly, that this
_ oxide should form a chlorite possessing a certain degree of stability ;
Srdly, that the metallic chloride formed may, on account of its insolu-
_ bility, easily separate from the chlorite; 4thly, and lastly, that it
_ should re-act but feebly on the chlorous acid when it is separated by
u2
“sca
280 BALARD’S RESEARCIFES CONCERNING THE
distillation. The red oxide of mercury seemed to me to present all
these advantages. Its alkaline power is strongly marked. I had no
fear that chlorite of mercury could be compared, with respect to its
instability, to chlorite of silver, which does not decompose so readily,”
merely on account of the insolubility of the chloride. Although solu-
ble in water, the chloride of mercury [bichloride] loses much of its
solubility by combining with oxide, and thus forming an oxichloride;
and this state of combination would retard to a certain point the de-
composition which the chlorous acid would readily produce in other
circumstances. My attempt was followed by success: by employing
this substance, I obtained in fact chlorous acid in larger proportion
and more concentrated.
This operation may be conveniently performed as follows: the spe-
cifie gravity of red oxide of mercury does not allow of its being sub-
jected to the action of chlorine in a Woulfe’s apparatus; it is much
more convenient to pour the red oxide of mercury reduced to a fine
powder by trituration, and mixed with about twelve times its weight of
distilled water, into bottles filled with chlorine gas.
By strong agitation the absorption of chlorine takes place rapidly, and
operates as quickly as if the gas were treated with an alkaline solution.
It has happened to me during this operation, that bottles which were
perfectly stopped have broken in my hands, on account of the almost
perfect vacuum which is produced in this case. If the proportion of
red oxide of mercury employed is insufficient, the powder deposited at
the bottom of the bottle is white, and the colour of the gas indicates
the presence of chlorine. If the red oxide of mercury, on the con-
trary, is in slight excess, it colours the deposit spoken of red, and the
chlorine then disappears completely. It appeared to me to be preferable
to operate with a slight excess of oxide of mercury, to prevent the
chlorous acid from being mixed with free chlorine. When the ab-
sorption of the chlorine is complete, the matter contained in the bottle
should be thrown upon a filter, upon which there remains the greater
part of the oxichloride formed: the liquor which filters, subjected to
distillation in vacuo, furnishes weak chlorous acid, but it may be
brought to greater state of concentration by subjecting the first products
to a second distillation.
§ 3.—Properties of the Aqueous Solution of Chlorous Acid.
The chlorous acid diluted with water, obtained as above stated, has
the following properties: it is a transparent liquid and slightly yellow-
coloured when it is concentrated. Its smell is penetrating, and quite
distinct from that of chlorine and the deutoxide of chlorine of Davy.
It more nearly, however, resembles the first than the apie _ Its taste
is extremely strong, but not sour.
NATURE-OF THE BLEACHING COMPOUNDS OF CHLORINE. 981
’ It attacks the epidermis with great activity. A drop left in contact
with the skin for half a minute destroys it, and more deeply than nitric
acid does in the same space of time. The tint which it acquires is red-
dish brown, and not yellow.
Chlorous acid when slightly concentrated is extremely unstable, and
decomposes partially even at common temperatures. During the great
heat of summer it can only be preserved for a few days, except by
keeping it inice. When more diluted and kept from the light it may,
on the contrary, be preserved for a much longer time. During this
decomposition it disengages an infinite number of small bubbles, which
are merely chlorine gas, and at the same time a certain quantity of
chloric acid is formed. Agitation, especially with angular bodies,
hastens this decomposition; and when fragments of powdered glass
are thrown into this acid, their contact with the liquor is followed by
a well-marked effervescence.
At a moderately high temperature, the decomposition is much more
rapid. Yet it is only partial at 212°, for chlorous acid may be distilled
at the usual pressure, and thus brought to a higher degree of concen-
tration.
A strong light produces similar decomposition. A few moments
exposure to the solar rays are sufficient to conyert it into chlorine and
ehloric acid. Sometimes also deutoxide of chlorine is formed.
When an aqueous solution of chlorous acid is exposed to the influ-
ence of the voltaic pile, an abundant disengagement of oxygen takes
place at the positive pole. The portion of the liquid in the midst of
which this disengagement is effected, does not appear to change its
nature by absorbing a certain quantity of the gas. It does not deepen
in colour, nor does its decolorizing property appear to diminish. Thus
the action even of nascent oxygen does not seem to have the power of
changing chlcrous acid into chloric acid or deutoxide of chlorine.
In this experiment no chlorine is disengaged at the positive pole,
There is no doubt that chlorous acid and water are simultaneously de-
composed, and that the hydrogen and chlorine, meeting in the nascent
state, form hydrochloric acid. What tends to induce this opinion is,
that at the end of a certain time the oxygen obtained is mixed with
chlorine; a phenomenon which could not occur, except there be formed
in the liquid a compound in which this body is electro-negative.
Chlorine cannot exert any action on the aqueous solution of chlorous
acid ; but it is different with bromine and iodine. Each of these bodies
is susceptible of decomposing it, and of acidification at the expense of
its oxygen.
_ Ifa few drops of bromine be put in contact with a small quantity of
ehlorous acid, a disengagement of chlorine is perceived on the surface
of the drops of bromine. On exposing this liquid to the contact of the
air for a few seconds, this latter compound is liberated, and free bromie
282 BALARD’S RESEARCHES CONCERNING THE
acid remains. This is a process which might be successfully adopted
for preparing bromic acid, if others easier of execution did not exist.
‘ Jodine acts in the same manner, but, as might be anticipated, its
action is more energetic ; when the chlorous acid is concentrated it is
accompanied with a slight disengagement of heat. Chlorine is abun-
dantly evolved, and a portion of iodine is acidified, whilst another
small portion is changed into chloride of iodine.
The acid formed under these circumstances, treated by nitrate of
silver, gives a white and not a yellow precipitate soluble in ammonia,
and which is merely iodate of silver. The product of this action is
merely iodic and not hyperiodic acid, as might be suspected according
to the mode of preparing this acid proposed by MM. Magnus and Am-
mermuller, to whom the discovery of it is owing.
Among the simple non-metallic combustibles, azote and hydrogen
in the gaseous state appear to have no action upon chlorous acid; but
sulphur, selenium, phosphorus and arsenic act upon it with great
energy. By their contact with this compound they undergo analogous
alterations ; they are acidified, and give rise to an abundant disengage-
ment of chlorine gas. The sulphur is converted into sulphuric acid,
the phosphorus into phosphoric acid, and the arsenic into arsenic acid,
as happens when they are treated with nitric acid. As to selenium,
it produces also selenic and not selenious acid; that is to say, the
chlorous acid performs then what nitric acid itself cannot effect. The
whole of the chlorine is not disengaged in the state of gas; a small
portion combines with the elementary body, so that there are produced
at the same time chloride of phosphorus, of sulphur, of arsenic, &c. ;
these by the contact of water undergo double decomposition, the pro-
ducts of which are water and additional portions of phosphoric, sul-
phuric, and arsenic acids.
Charcoal in powder did not appear to me to exert any action on
chlorous acid. As to that of boron and silicium, the want of materials
has not allowed of my ascertaining it.
Chlorous acid acts variously with metallic substances; potassium
thrown in pieces into chlorous acid burns immediately without any
disengagement of chlorine being perceived. The product of this com-
bination is formed of chloride of potassium and chlorite of potash. The
presence of water, which may complicate the action, does not allow of
accurately determining what passes during its operation. It is, however,
probable that it is at the expense of the chlorous acid, that these two
compounds of chlorine are formed, and that the water merely dissolves
the results of this decomposition.
Tron filings, when made to act upon chlorous acid, decompose it in-
stantaneously ; the action is accompanied with an abundant emission of
heat, and a brisk effervescence produced by the chlorine. ‘The iron is
oxidized, the chlorine is partly disengaged, and also in part combines
NATURE OF THE BLEACHING COMPOUNDS OF CHLORINE. 2985
with the metal, which it converts into a liquid of deep yellow colour,
which is acid but does not decolorize ; it appears to be perchloride of
iron ; it does not seem to be mixed with chlorate. We might be tempted
to suppose that the action of chlorous acid on other metals is compara-
ble to that which it exerts upon iron; but this is not the case. The
greater number of the other metallic substances, put into contact with
chlorous acid, cannot decompose it, and I am yet entirely ignorant of
the cause of the peculiarity of iron in this respect.
Tin filings may remain in contact with weak chlorous acid for
several days, without causing it to undergo any sensible decomposition, -
and without losing their metallic lustre. The same is the case with
zine, with fragments of antimony, bismuth, and lead. But the presence
of another acid renders these metals capable of effecting this decompo-
sition.
The nature of the acid employed for this purpose is not a matter of
indifference. This acid must form a compound, soluble in water, with
the oxide of the metal employed. Thus with zine and tin, sulphuric
acid causes the decomposition of the chlorous acid most rapidly ; with
antimony, sulphuric acid and even nitric acid does not answer, but
tartaric acid succeeds extremely well in causing its oxidation; lastly,
chlorous acid, which alone or mixed with sulphuric acid scarcely acts
upon lead, exerts an intense action upon it when mixed with a little
nitric or even acetic acid.
In this re-action, induced by the presence of these acids mixed with
the chlorous acid, the metal, in order that it may saturate them, must
decompose the acid, and not the water; for in combining with the
oxygen, it is chlorine, and not hydrogen, which it sets at liberty. How-
ever when in operating with chlorous and sulphuric acid on zine or
tin, the gas obtained contains a little hydrogen, which indicates that
in some cases it is at the expense of the water itself that the oxidation
occurs.
If concentrated chlorous acid be used, the action is not at first
more energetic, but it becomes so at the end of a certain time. During
its spontaneous decomposition chlorous acid forms chloric acid, the
mode of action of which is the same as that of sulphuric, nitric, and
other acids, as I determined by direct means.
Gold and platina do not appear to suffer any action by chlorous
acid, either alone, or mixed with nitric and sulphuric acid ; but copper,
mercury, and silver decompose it, and each with a peculiar mode of ac-
tion. Copper filings put into contact with chlorous acid are partly
dissolved: the solution after some time is found to contain chloride
of copper. There is also formed at the same time a green powder,
which appears to be merely oxichloride of copper, and it disengages
chlorine mixed with a very small proportion of oxygen.
284 BALARD’S RESEARCHES CONCERNING THE
It is probable that the disposition of oxide of copper to combine
with the chloride of this metal to form an oxichloride, contributed to
render copper, though less oxidizable than zine or tin, proper to produce
the decpmposition of chlorous acid,—an operation which these two last
metals cannot effect.
This is probably also the cause which renders the action of mercury
so prompt. When a few globules of this metal are shaken with chlo-
rous acid, it is almost instantaneously decomposed, without any appa-
rent disengagement of gas of any kind, and oxichloride of mercury is
found to be the product of this re-action. The disposition which the two
products of this decomposition have to combine is undoubtedly the
reason which renders it so easy of execution.
The kind of alteration which silver causes chlorous acid to undergo,
is precisely the reverse of that of the bodies whose action upon this
acid has been hitherto described. When very finely divided silver is
put into contact with chlorous acid, a brisk effervescence takes place,
which is produced by a disengagement of oxygen gas, without any
trace of chlorine, and the whole of this combines with the silver and
converts it into chloride.
To recapitulate:—The bodies which I have tried, chlorine and the
metals of the last section of Thénard excepted, decompose chlorous
acid; they are oxigenated at its expense, and set some chlorine at
liberty, which can be only partially absorbed by the combustible,
except in some peculiar circumstances. Silver alone is an exception to
this law of disengaging oxygen : and this phenomenon, as well as the
decomposition of fluoride of silver by chlorine, indicates the very
peculiar affinity which exists between these two bodies.
Chlorous acid is therefore one of the most energetic oxidizing
agents. The property which it has of converting bromine into bromie
acid, and selenium into selenic, and not selenious acid, gives it in this
respect an incalculable advantage over nitric acid, and up to a certain
point over oxigenated water.
To judge of its effects as an oxidizing agent only by its action on the
metals, it might perhaps be ranged below nitric acid; but it must be
remembered, that the action of nitric acid on metallie substances does
not depend on their oxidability alone, and the easy decomposition of
the acid, but also on their disposition to form a nitrate, and a nitrate
soluble in acid, of the degree of concentration employed. This is
proved by the singular action which it exerts upon iron and tin in
certain cases.
Chlorous acid not having much power to form salts, except with the
oxides of those metals which yield energetic bases, it ought not to |
cause surprise that they excite so little definite action upon the others.
This power of oxidizement possessed by chlorous acid is a perfectly
NATURE OF THE BLEACHING COMPOUNDS OF CHLORINE. 285
natural circumstance, and one which exhibits the instability of the oxi-
genated combinations of chlorine. But what is much less so, is the dis-
engagement of chlorine gas, which almost always accompanies its decom-
position. The energetic affinity of chlorine for the greater part of the
metalloids and metals is well known; from this it might be supposed
that, in the re-action of these bodies upon chlorous acid, the chlorine
would combine with them as well as the oxygen, and that this decom-
position would take place in a somewhat latent manner, since, each of
the elements uniting with the combustible, nothing would be eliminated.
It does not however so happen, and the facts which I have related
prove that it is almost uniformly by its oxygen that chlorous acid acts
upon various simple combustibles.
The phenomena which accompany the decomposition of chlorous acid
by the compound combustibles prove the same fact, and show this body
to be one of the most energetic agents of oxidation, but at the same time
as very little calculated for chloridation.
I haye not attempted to put those bodies in contact with this acid
which are altered by water itself: for the presence of this fluid in the
chlorous acid of which I made use would have complicated the re-actions,
and would have prevented me from assigning the products which I
should have obtained to their true origin. On this account I have not
_ experimented with the chlorides, bromides, &c. of sulphur, of phospho-
rus, and of selenium: I preferred employing the action of chlorous acid
upon the compound combustibles which suffered no decomposition by
water.
The compounds of halogéne bodies with carbon are not only unal-
terable by water, but even resist the action of several of the most ener-
getic chemical agents; I was therefore curious to see how chlorous acid
acted upon them.
The several chlorides and bromides of carbon, as well as the hydro-
carburets of chlorine and bromine, although attacked by chlorous acid,
appear to me to exert a very slow action upon it, and one which I have
not hitherto perfectly appreciated. As to the periodide of carbon of Sé-
rullas, that on the contrary is attacked with great energy by chlorous
acid. At common temperatures it produces a rapid disengagement of
gas, which is a mixture of chlorine, carbonic acid, and oxide of carbon,
and iodine is deposited ; the liquid contains a mixture of iodic acid and
hydrochloric acid. If the chlorous acid is in excess, no deposit of iodine
is observed, it being converted into iodic acid.
Chlorous acid also decomposes cyanogen. If a few drops of chlorous
acid be added to a bottle containing this gas, effervescence is soon ob-
served, and the bottle is filled with chlorine, recognisable by its yellow
tint. At the bottom of the liquid, which has ceased to decolorize, and
286 BALARD’S RESEARCHES CONCERNING THE
which has changed its nature, there appear a few drops of an oily liquid,
which seems to be a mixture of the chloride of cyanogen and of azote,
described by Sérullas. The liquid contains hydrochloric acid and cyanic
acid of Sérullas, and the compressed gas which fills the bottle is a mix-
ture of chlorine, azote, carbonic acid, and chloride of cyanogen.
Sulphuret of phosphorus is also decomposed by chlorous acid. The
action at first is slow in the cold; but the mixture gradually becomes
warm, and it is then more rapid. The elements of these compounds
both combine with oxygen, and chlorine is disengaged in abundance.
The liquor contains however, besides sulphuric and phosphoric acid,
some hydrochloric acid.
Sulphuret of carbon acts in the same manner with chlorous acid; but
the effervescence is more brisk, for the gas which is disengaged is a mix-
ture of chlorine and carbonic acid. The liquid contains both sulphuric
and hydrochloric acid ; which leads to the supposition that, in this case,
as in the former, part of the sulphur is converted by the nascent chlo-
rine into chloride of sulphur, which is afterwards decomposed by the
contact of the water.
Marsh carburetted hydrogen is not acted on by chlorous acid, either
in the dark or in the solar light ; but it is not the same with bicarbu-
retted hydrogen. This gas is decomposed at common temperatures,
chlorine is disengaged, and there are found at the bottom of the vessel
some drops of an oily fluid, which are heavier than water and have an
ethereal smell; these are undoubtedly a chloride of carbon, the na-
ture of which I have not directly determined.
Chlorous acid and ammonia give rise by their mutual action to very
different phenomena, according to the circumstances under which the
action occurs.
If very dilute ammonia be added to chlorous acid, also very dilute,
a disengagement of bubbles of azote is perceived ; it is however not co-
pious, and much less than it would be if the whole of the substances
mixed were decomposed. The liquid which is thus obtained, rendered
alkaline by a sufficient addition of ammonia, still possesses the property
of decolorizing the solution of sulphate of indigo. But the disengage-—
ment of bubbles of gas continues to take place; the alkalinity gradually
disappears, and on the contrary the liquor becomes acid, and in this
state it no longer decolorizes indigo. These facts render the existence
of a chlorite of ammonia very probable, which is an ephemeral chlorite,
already described by M. Soubeiran.
If a mixture of a more concentrated ammoniacal solution and
chlorous acid be made with the greatest precaution, and so as to keep
down the slight heat which is developed during their re-action, a
white cloud is produced, which renders the liquor opake for some time.
NATURE OF THE BLEACHING COMPOUNDS OF CHLORINE. 287
This cloud is sometimes deposited in oily drops, which have all the pro-
perties of chloride of azote; it is however more frequently carried off
in the state of vapour by the gas which continues to be disengaged.
This chloride of azote is very easily produced, especially when there
is suspended in dilute chlorous acid a fragment of an ammoniacal salt,
as for example of sulphate, phosphate, &c. The decomposition then
goes on very slowly, but a small quantity of gas is absorbed, which is
in this case a mixture of chlorine and azote, and not of pure azote, and
there is formed at the same time a notable quantity of chloride of azote.
This process appears to me the most convenient that can be employed
for the preparation of this substance. A very small quantity of it how-
ever is obtained, if, instead of placing the fragment of salt in chlorous
acid, it is mixed with the acid after being dissolved in water. The ac-
tion then occurring instantaneously and rapidly on the whole mass, and
no chloride of azote is obtained; or at any rate, if this compound is
formed, it is carried off by the brisk effervescence which occurs in this
case.
It is almost useless to say, that no chloride of azote is obtained when
concentrated chlorous acid is poured into concentrated ammonia. The
action is then very rapid; it is accompanied with so great a disengage-
ment of chlorine and so abundant an emission of gas, that it takes place
with a sort of detonation.
This action is still more vivid when bubbles of ammoniacal gas are
added to a few drops of chlorous acid in a receiver over mercury. There
is not only a great disengagement of heat, but an emission of yellow
light, and the upper part of the receiver contains a mixture of azote
and chlorine gas.
It will be readily perceived that in all these circumstances it is prin-
cipally by the oxygen of chlorous acid that the decomposition of the
ammonia is effected, and that the chlorine and azote, simultaneously set
free, sometimes coalesce to form chloride of azote, and are at others
disengaged in a state of aériform existence, according to circumstances.
The two elements of the compound combustible are, on the contrary,
completely burnt, in great measure by the oxygen when chlorous acid
_is made to act upon gaseous hydrogenated combinations of phosphorus,
arsenic, and of sulphur. Phosphuretted hydrogen, introduced into a
small receiver containing a few drops of chlorous acid, burns on coming
into contact with this liquid. There are produced phosphoric acid and
chloride of phosphorus, which are ultimately decomposed into hydro-
chlorie and phosphoric acid. No uncombined phosphorus is observed,
but pure chlorine is collected in the upper part of the bottle.
- The same phenomena occur with arseniuretted hydrogen. The
combustion takes place with a flame of a blue tint. In the place of
chlorous acid are found arsenic and hydrochloric acids, and the upper
288 BALARD’S RESEARCHES CONCERNING THE
part of the receivers is filled with gaseous chlorine. In this case, as
when phosphuretted hydrogen is operated with, the disengagement of
chlorine can only be procured on adding the gas bubble by bubble, and
so as never to be in excess; for then it would burn at the expense of
the chlorine itself.
Hydrosulphuric acid acts in the same manner, but with this difference,
that its action on the chlorous acid is not accompanied with emission
of light, although the heat developed is very strong. There are formed
water and sulphuric acid, and chlorine is disengaged, which afterwards
exerts its usual action on the fresh bubbles as they arise.
The phenomena are nearly the same when a current of these gases
is passed into chlorous acid, nor does the nature of the products at all
vary ; water, and phosphoric, arsenic, and sulphuric acids are always
formed. The greater part of the chlorine is disengaged in the gaseous
state, producing a brisk effervescence, whilst a portion remains liquid
in the state of hydrochloric acid.
Chlorous acid acts upon the liquid or gaseous hydracids nearly in a
similar manner. In operating with hydriodie acid gas I obtained water,
iodic acid, and a disengagement of chlorine gas. In this case a violet
tint is, though scarcely, perceptible, which evidently arises from the
action of chlorine set free upon some bubbles of hydriodie acid which
have escaped the chlorous acid. Much heat, but no light, is given out
in this experiment.
A disengagement of heat only, occurs when chlorous acid is made to
act upon these hydracids dissolved in water; the decomposition is in-
stantaneous. With hydrochloric acid, water and a disengagement of
chlorine is produced ; with hydrobromic acid, there are obtained bromic
acid, bromine, chloride of bromine and an abundant disengagement of
chlorine. Hydriodic acid gives rise to similar phenomena.
Anhydrous hydrocyanic acid and chlorous acid also exert a remark~-
able action on each other. Chlorine is produced in abundance, and
the liquid, besides hydrochloric acid and the cyanic acid of Sérullas,
contains a certain quantity of chloride of cyanogen.
The metallic sulphurets, treated with liquid chlorous acid are imme-
diately converted into sulphates. Heat is produced, and chlorine is
disengaged : sometimes also I have perceived the odour of chloride of
sulphur. I obtained analogous results, in causing chlorous acid to act
upon phosphuret of lime [calcium? ].
The action of compound combustibles on chlorous acid fully con-
firms then what itsmanner of acting upon simple combustibles had
before indicated, and shows it to be one of the most marked agents of
oxidation, and at the same time but little calculated to act by the chlo-
rine which it contains. Nevertheless, when the action proceeds slowly,
its two elements combine with the two elements of the compound com-
NATURE OF THE BLEACHING COMPOUNDS OF CHLORINE. 289
bustible; and the oxygen, seizing the most electro-positive of the two;
leaves to the chlorine the most electro-negative. It is in this way, for
example, that it takes place in the action of chlorous acid upon bicar-
buretted hydrogen and ammonia. In other cases, the chlorine com-
bines well with one portion of the electro-negative element, but it dis-
engages a portion which is larger according as the temperature is
higher. When it reaches incandescence, the two elements of the com-
pound combustible are almost totally burnt by the oxygen, as if the
affinity of oxygen for bodies increased with the temperature in a higher
ratio than than of chlorine for them.
It may nevertheless be supposed that the composition of chlorous
acid is such, that the electro-negative element of the compound com-
bustible being saturated with chlorine, an excess of this gas may re-
main; but this is not the case. On comparing its composition, which
I shall hereafter state, with that of phosphuretted hydrogen, for ex-
ample, even admitting that all the hydrogen is burnt by the oxygen,
the chlorine is insufficient to combine with the phosphorus. Yet in
this decomposition a large proportion of this gas is set free, which ap-
pears to me to render it very probable that in this case, as in the greater
part of others, it is with the oxygen of chlorous acid that the elements
of the compound combustible are both combined.
It is easy to foresee, according to this, how chlorous acid must: act
with the combinations of oxygen which are not saturated with this
principle. These combinations are almost always carried to the high-
est degree of oxigenation, and the chlorine set free is disengaged in
the gaseous form.
There are some, however, which do not appear to be altered by chlo-
rous acid, as the oxide of carbon: but, on the contrary, it exerts most
energetic action on oxalic acid; a fragment of this acid, when thrown
into moderately concentrated chlorous acid, occasions an intense emis-
sion of light, and a very strong effervescence produced by the disen-
gagement of a mixture of carbonic acid and chlorine, as might be ex-
pected.
Nor does the first degree of oxidation of azote appear susceptible of
being acted upon by chlorous acid; but all the other oxigenated com-
binations of this gas, the deutoxide of azote, nitrous vapours, hypo-
nitrous acid, fuming nitric acid impregnated either with hyponitrous
acid or deutoxide of azote, act very energetically upon chlorous acid.
Colourless nitric acid and chlorine gas are produced.
In the series of oxigenated compounds of sulphur, the hyposulphuric
acid exhibits the same anomaly as that which characterizes the manner
‘in which oxide of carbon and protoxide of azote act with chlorous acid.
It is not altered by this oxigenating agent; whereas sulphurous acid,
whether gaseous or liquid, is immediately converted by it into sulphuric
290 BALARD’S RESEARCHES CONCERNING THE NATURE OF
acid, with the disengagement of chlorine. This peculiarity may, per-
haps, furnish those chemists with an additional reason, who think that
hyposulphuric acid is not a primary compound of sulphur and oxygen,
but a secondary combination of sulphuric acid and sulphurous acid.
The compounds of oxygen and phosphorus do not present anything
similar. In fact, oxide of phosphorus, hypophosphorous acid, phospho-
rous acid, and even phosphatic acid, are all immediately converted into
phosphoric acid, with the disengagement of heat and of chlorine gas.
The same is also the case with arsenious acid, which is converted
into arsenic acid, and with selenious acid, which is changed into selenic
acid, giving rise to the production of the same phenomena, to an eyo-
lution of chlorine, and a considerable disengagement of heat.
The metallic oxides act variously with liquid chlorous acid. It will
be imagined that so energetic an agent of oxidation would convert the
greater part of these compounds susceptible of it into peroxides, but
that it would not exert any action on those which are already saturated
with oxygen. This is what actually happens. The deutoxide of tin,
the peroxide of iron, &c. suffer no change by chlorous acid; whereas
the protoxide of iron, tin, manganese, nickel, cobalt and lead are con-
verted into peroxides with the evolution of chlorine. The protoxide of
chromium is immediately converted into chromic acid. There are, how-
ever, some oxides susceptible of a higher degree of oxidation, such as
the oxide of bismuth, and the peroxide of manganese, upon which chlo-
rous acid does not appear to act.
Although the alkaline oxides can, under some circumstances, com-
bine with a larger proportion of oxygen,-chlorous acid, instead of super-
oxidizing them, merely combines with them. Still further, it decom-
poses the peroxides of these metals, and disengaging oxygen it reduces
them to the state of protoxides, with which it forms decolorizing chlo-
rites. It is at any rate in this way that I have observed it to act with
the peroxide of barium.
With the peroxide of lead and the two oxides of silver, which are
metals with which chlorine forms insoluble compounds, it acts in an
entirely different manner. These oxides are decomposed with the pro-
duction of chlorides, and not chlorites, and with a disengagement of
oxygen mixed with a little chlorine. This happens from the re-action
of chlorous acid upon the chloride formed.
The metallic chlorides are decomposed by chlorous acid. This de-
composition is always accompanied with an abundant disengagement of
chlorine, and the metal is oxidated. As to the nature of the definitive
product, it evidently depends upon the manner in which this oxide acts
either with chlorine or with chlorous acid. Thus the chlorides of the
alkaline metals form mixtures of chlorides and chlorites. Those of
manganese, iron, nickel, cobalt, lead, and tin, occasion a disengagement
!
THE BLEACHING COMPOUNDS OF CHLORINE. 291
of chlorine and form peroxides. The chloride of copper forms both chlo-
ride and oxichloride of copper. The protochloride of mercury changes,
without evolving gas, into a red powder, which is unquestionably an
oxichloride. The perchloride of mercury and the chloride of silver are
also attacked, but very slowly, by concentrated chlorous acid: the gas
disengaged is chlorine, mixed with a small quantity of oxygen. I do
not at present know how to explain the production of the last-men-
tioned gas.
The bromides undergo a slightly different action. I have observed
that with those of potassium, mercury, and silver, there is a disengage-
ment of chlorine, bromine, and chloride of bromine, and the formation
of a bromate and a metallic chloride.
The iodides of potassium, mercury, and silver appeared to produce
analogous phenomena.
Saline compounds suffer two kinds of action by chlorous acid: it may
decompose them by evolving their acid: it may, on the contrary, be
itself decomposed, and by superoxidizing their acid or base, thus con-
vert them into new salts.
There are but few acids which can be expelled from their saline com-
binations by chlorous acid, but it expels with effervescence the acid
from the carbonate of soda and of lime, and forms a chlorite with the
base. When an acetate is treated with chlorous acid, especially if
heated, the odour of acetic acid is perceived, chlorine mixed with a
little oxygen is disengaged, and after a certain time chlorate of potash
is formed, which agrees perfectly with the observation of M. Liebig.
Bromic acid even is expelled from its combinations by chlorous acid.
The same phenomena occur as with the acetates,—disengagement of
chlorine mixed with a little oxygen, formation of a chlorate, and evo-
lution of a part of the bromic acid.
As to the action which chlorous acid exerts on the salts as an oxi-
dizing agent, it may be stated in a few words. With respect to their
acids, it acts as if they were free; that is to say, not at all upon those
salts the acids of which are saturated with oxygen, and it converts
those to this condition which were not so previously. Thus the oxa-
lates are converted into carbonates, the sulphites into sulphates, &c.
All these re-actions occur with the disengagement of chlorine, and
frequently with heat, without altering the neutrality of the salt; the
iodates and chlorates are not however converted into hyperiodates and
_ hyperchlorates ; the same anomaly occurs here which I have noticed
_when speaking of the action of chlorous acid upon these free acids. The
_hyposulphate of barytes, which nitric acid converts into sulphate, is not
acted upon by chlorous acid, notwithstanding the insolubility of the
product which would be formed by the oxidation of its acid.
Chlorous acid acts in the same manner on salts with respect to their
292 BALARD’S RESEARCHES CONCERNING THE NATURE OF
bases; that is to say, the protoxides are immediately converted into per
oxides, provided always that they can neutralize the acid. Thus the
salts of protoxide of iron, of copper, and of tin, are immediately con-
verted into salts of the peroxides: but as to those of nickel, cobalt,
and lead, they suffer no alteration. If the base were superoxidized, it
would cease, in this case, to be proper to saturate the acid, and the
chlorous acid would then act so as to destroy a combination already
existing, instead of contributing to form more neutral and stable com-
pounds, as when it changes the salts in z¢e to salts inate. Nevertheless
the salts of protoxide of manganese, treated with chlorous acid, deposit
peroxide, and the solution becomes acid; but the action is so slow, that
I think it may be attributed to the disengagement of chlorine, which
always accompanies the spontaneous decomposition of chlorous acid,
and not to this acid itself.
It was natural to suppose that organic substances would be essentially
altered in their constitution by chlorous acid, which we have seen act
energetically on several inorganie compounds; this opinion was con-
firmed by experience. I put a great number of vegetable and animal
substances into contact with this acid, and in almost every case I per-
ceived indications of a re-action, which was frequently very vivid. It
forms no part of the plan which I have proposed, to describe in detail
the modifications which each organic substance underwent in this ease.
It will be sufficient to say in a general manner, that in the greater num-
ber of them the re-actions were accompanied with a disengagement of
chlorine mixed with variable proportions of carbonic acid gas. When
the substance contains azote, it is disengaged, but the odour of the gas
indicates that chloride of azote is also formed. ‘This is especially ob-
served with urea, lithic acid, and the vegetable alkalis which did not
appear to me susceptible of forming chlorites.
In some eases the quantity of carbonic acid obtained represented the
oxygen which enters into the composition of chlorous acid. I thought
that I perceived this in operating on indigo, a colouring matter which
chlorous acid instantly changes into a yellow substance, which is soluble
in aleohol and rather bitter.
In the greater number of cases but very little carbonic acid is ob-
tained; a notable portion of oxygen disappears at the same time, and
contributes to form new and more oxigenated compounds. Thus the
products of its action on sugar, gum, starch, &c. are strongly acid.
Sometimes, however, the decomposition is slow, and the two elements
of the chlorous acid are both absorbed by the organic matter. This is
observed with alcohol; this liquid, by mixture with chlorous acid, is
converted into acetic acid, and there is obtained at the same time a cer-
tain quantity of an oily liquid, produced by the action of the chlorine
upon the alcohol.
THE BLEACHING COMPOUNDS OF CHLORINE. 293
* Tt appears to me that these observations are sufficient to prove that
chlorous acid acts upon organic bodies principally on account of the
oxygen which it contains.
Could not an oxidizing agent, very superior to nitric acid, give rise
‘to some new compounds in acting upon several organic compounds ?
It is natural to think so, and to suppose that a knowledge of chlorous
acid may thus, in an indirect manner, contribute to the progress of or-
ganic chemistry, by exciting fresh researches, which I propose hereafter
to undertake, as soon as I have hopes of doing so with success.
§ 4. Chlorous Acid Gas.
I had repeatedly observed that the aqueous solution of chlorous acid,
when exposed to the air, soon lost its tint, and a great part of its odour.
This change of properties, which I satisfied myself was not derived either
‘from the absorption of the oxygen or the moisture of the air, made me
-think that chlorous acid was volatile, and that I should be able to ob-
tain it in the gaseous state, and it was towards this end that I directed
‘my researches.
I first tried the action of heat on concentrated liquid chlorous acid. |
~At a temperature much below ebullition, I observed in fact that it dis-
engaged a very small quantity of a yellow-coloured gas, which, passing
‘through the mercury in small bubbles, was absorbed by it, leaving occa-
"sionally a residue of oxygen. As to the liquid, even after being some
time exposed to a temperature near ebullition, it retained the property
-of acting on combustible bodies with the same activity as at first. I
“presumed from this that chlorous acid had great affinity for water, and
‘that by the action upon liquid chlorous acid of a substance having great
-affinity for this water, I should obtain the acid in the state of gas.
I first attempted this with sulphuric acid, and I succeeded in obtain-
“ing a gaseous body. But this gas was of a very deep yellow colour,
“and its smell, instead of resembling that of liquid chlorous acid, was
“more like deutoxide of chlorine. The water with which I attempted to
“act upon it dissolved a certain quantity, and left as a residue a mixture
of much chlorine and very little oxygen: the solution did not resemble
‘liquid chlorous acid; it was of a very deep yellow, and possessed the
“properties of a solution of deutoxide. The sulphuric acid, therefore,
while taking the water from the chlorous acid, had converted it into
- oxygen, chlorine, and deutoxide.
I suspected from this, that chlorous acid, like the nitric, chloric, bro-
“mic, and other acids, could not exist without water; but before I pro-
ceeded on this idea, I thought I would try other bodies, which, although
- greedy of water, like sulphuric acid, would not excite any such marked
action. It being impossible to employ chloride of calcium, I had re-
Vor. J.—Parr II. x
294: BALARD’S RESEARCHES CONCERNING THE NATURE OF
course to nitrate of lime, a very deliquescent calcareous salt, the action
of which changed my idea on the subject. ,
When a mixture is made of nearly equal. volumes of concentrated
liquid chlorous acid, and very dry solid nitrate of lime, a brisk effer-
vescence ensues, and a gas is produced, which re-dissolyed in water
gives a product possessed of all the properties of liquid chlorous acid,
and which ought consequently to be considered as pure chlorous acid
gas. The same results are obtained by using vitreous phosphoric acid*
instead of nitrate of lime. '
If an attempt be made to collect chlorous acid gas in the mercurial
trough in the usual way, the metal is attacked, and oxygen alone re-
mains; sometimes indeed the absorption is complete. It is then neces-
sary, in order to obtain it, to operate in a peculiar manner. The fol-
lowing method has always succeeded.
After having introduced into a receiver filled with mercury about
x'sth of its volume of concentrated chlorous acid, I gradually passed up
fragments of dry nitrate of lime. The gas is disengaged with effer-
vescence, and, as it does not touch the mercury, being separated from
it by the solution of nitrate of lime, it may be kept in the trough for a
long time. Afterwards it may be transferred from one receiver to an-
other, provided this operation be effected rapidly ; for it is but slightly
decomposed by the metal, when it passes through it in large bubbles.
Chlorous acid gas is of a yellow colour, and but little deeper than
that of chlorine, with which in the course of my researches I had long
confounded it, on account of this similarity of tint. Its smell is ex-
tremely pungent, and like that of the liquid acid; it is completely ab-
sorbable by mercury, which it converts into red oxichloride.
Water dissolves many times its volume. I have not determined this
solubility very exactly, but I believe it to be more than 100. The so-
lution is very slightly coloured, and has the properties of liquid chlo-
rous acid. The solution of chlorous acid in water takes place very
rapidly, but there always remains, after the operation is over, a very
small residue of chlorine and oxygen, which indicates a very slight de-
composition of this gas during its preparation. A small increase of
temperature separates its elements with explosion, and a very conside-
rable disengagement of, heat and light. Although it appears to me
more difficultly decomposable by increase of temperature than the ox-
ides of chlorine, it has happened to me that it has exploded during
transfer. On this account, care should be taken to add the nitrate of
* Care must be taken to use phosphoric acid which is not prepared by the de-
composition of phosphate of ammonia by heat. As this often retains a little
ammonia, it produces chloride of azote, which, by the slightest increase of tem-
perature, gives rise to detonations, which are the more dangerous as not being
foreseen,
- THE BLEACHING COMPOUNDS OF CHLORINE. 295
lime gradually during its preparation, in order that the heat which is
generated during the solution of this salt should not be too strong. I
have frequently seen chlorous acid gas detonate by the influence of this
cause; and although this detonation is not in itself very dangerous,—
for the receiver, which is projected vertically, is never broken into small
fragments,—yet the chlorous acid being then dispersed in small drops,
which are extremely corrosive, it is prudent to prevent it.
An exposure of some hours to a weak diffused light did not appear
to me susceptible of altering chlorous acid; but solar light decomposes
it in a few minutes without detonation.
The manner in which different bodies act upon the gaseous acid is
similar to that upon liquid chlorous acid.
Oxygen and chlorine cannot act upon chlorous acid: hydrogen, at
common temperatures, exerts no action upon it; but if a lighted taper
be put to a mixture of these two gases, a loud detonation is produced,
and white thick vapours of hydrochloric acid gas are observable.
I have not tried what effect boron and silicium produce upon this
gas, but I have stated what bromine and iodine can do. Ifa small
quantity of these substances be added to a proper volume of chlorous
acid gas, it is quickly absorbed, and chloric and_ bromic acids are pro-
duced, and chlorides of bromine and iodine. }
This action of bromine and iodine takes place slowly and without
detonation. This is not the case when sulphur, selenium, phosphorus,
and arsenic are operated with. Scarcely do these bodies come into con-
tact with the chlorous acid gas when they decompose it with a strong
detonation and a vivid light. The arsenic and phosphorus are con-
verted into arsenic and phosphoric acids ; the sulphur forms sulphurous
acid. I have not determined whether selenious or selenic acid is pro-
duced by selenium. One part of the chlorine combines with the com-
bustible bodies, but a notable portion is disengaged in the gaseous state.
This gaseous chlorine is moreover always mixed with a quantity of oxy-
gen. When charcoal is used, there is also immediate detonation; but
the gas obtained is a mixture of oxygen and chlorine, and contains but
very little carbonic acid. I believe that, in this case, the decomposition
is effected less by the affinity of the carbon for oxygen, than by the heat
which is developed by the absorption of the gas in the pores of the char-
coal. , .
The metals act differently with chlorous acid gas according to the
circumstances under which they are brought into contact with it. If
fragments of several of the metals, wrapped in sized paper to prevent
amalgamation, be passed into a rather narrow jar containing a small
quantity of chlorous acid, it is absorbed completely in a few moments,
and without detonation. There are formed both an oxide and a chlo-
ride. But if the quantity of chlorous acid employed measures several
x2
296 BALARD’S RESEARCHES CONCERNING THE NATURE OF
cubic inches, the absorption, which begins to take place very slowly,
terminates with a detonation accompanied with disengagement of light,
and there is then found in the upper part of the receiver a mixture of
chlorine and oxygen. It is probable that the heat developed in this case
by chemical action occasions the decomposition of the portion of gas
which had not been absorbed.
Silver leaf also acts upon chlorous acid after a certain time. The
metal is partly converted into chloride, and oxygen is disengaged ; but
the heat developed by this re-action also occasions the decomposition of
a part of the gas, and chlorine is found mixed with oxygen.
Chlorous acid gas is also decomposed by the greater part of the com-
pound combustibles. Cyanogen and chlorous acid gas act but slowly
upon each other; however, at the end of a certain time, chlorine is
found in the receiver, carbonic acid and azote, and the gaseous mixture
gives out the odour of chloride of cyanogen.
Common carburetted hydrogen does not act upon chlorous acid ; but
this acid and bicarburetted hydrogen decompose each other, without
evolving heat and light, water and a chloride of carbon being produced.
Phosphuretted and arseniuretted hydrogen gases, on the contrary,
occasion detonation, and the gaseous residue found is chlorine mixed
with a little oxygen. The combination of sulphuretted hydrogen is
accompanied with a blue flame, similar to that afforded by sulphur
when it is burnt in contact with the air. The detonation produced by
ammonia is also very vivid, and, in this case like the former ones, much
chlorine is set free.
Sulphuret of carbon also produced a vivid explosion, after which
there was found in the receiver in which it occurred, chlorine, sulphurous
and carbonic acid. The odour of these gases indicates that there is
formed at the same time a small quantity of chloride of sulphur.
The decomposition of chlorous acid by hydrochloric acid is accom-
panied with the disengagement of heat only, without producing light. It
is the same when hydriodie acid is operated with.
Phosphuret of lime [calcium? ] instantly occasions the decomposition
of chlorous acid with a loud detonation, and the gaseous residue con-
tains much chlorine. ;
The greater number of sulphurets—those of barium, tin, mercury,
antimony, &c.—produce in a few seconds the same effect. When there
is but little gas it may be absorbed without the occurrence of detona-
tion. In the latter case, the odour indicates the formation of chloride
of sulphur.
Oxalic acid also decomposes chlorous acid without producing ex-
plosion. Oxide of carbon, upon which the liquid acid did not appear
to exert any action, decomposes chlorous acid gas but slowly. After
the lapse of some hours the colour of the mixture disappears, and the
THE BLEACHING COMPOUNDS OF CHLORINE. 297
gas has the penetrating odour of chlorocarbonic acid. Nitrous oxide
gas does not appear to undergo any alteration by chlorous acid; but
with nitric oxide gas this acid occasions a violent detonation. This is
accompanied with the production of nitrous gas, which fresh bubbles of
chlorous acid are susceptible of converting into nitric acid.
Sulphurous acid gas, when dry, is but slowly attacked by chlorous
acid; yet, after some hours, the gaseous mixture placed over mer-
cury disappears, and the sulphurous acid is converted into sulphuric
acid.
Filtering paper and indigo are the only organic matters which I have
put in contact with chlorous acid gas. The first occasioned detonation,
but very little carbonic acid was produced. The receiver, after the
explosion, was found full of oxygen and chlorine, nearly in the propor-
tions which constitute chlorous acid; this indicates that it was chiefly
by the heat disengaged in its action on the paper that the gas detonated.
Indigo also decomposes chlorous acid without detonation, and con-
verts it into a compound of a yellow colour. The volume of carbonic
acid produced is much smaller than that of the oxygen contained in
the acid employed; and the chlorine evolved is in part absorbed by the
mercury, and partly retained in the pores of the vegetable matter,
which yields, undoubtedly from this cause, acid vapours when heated.
The facts which I have now detailed prove, as it appears to me,
that chlorous acid in the state of gas acts nearly in the same way as
when it is liquid. If its two elements are absorbed together when
the temperature is but little raised, it is on the other hand principally
owing to the oxygen gas which it contains that it acts whenever much
heat is emitted. The disengagement of chlorine gas which accompanies
the greater number of its re-actions appears to me to be a sufficient
proof of the truth of this assertion.
It may be thought at first that the chlorine comes from the denien:
position of a portion of the gas, occasioned by the high temperature
which the action of a combustible body most commonly develops;
but only one portion of the chlorine can be attributed to such an
origin. In fact, the quantity of oxygen with which it is mixed, is al-
most always smaller than that which in chlorous acid is united with
the volume of chlorine obtained; which induces the opinion, that in
these cases the two combustible elements of the compound are princi-
pally combined with oxygen.
§ 5. Composition of Chlorous Acid,
_ The experiments which I have now related are sufficient to determine
that the new compound, which I have described under the name of
chlorous acid, is uniformly composed of chlorine and oxygen; but they
do not determine the proportions in which these two elements are united.
298 BALARD’S RESEARCHES CONCERNING THE NATURE OF
It was necessary therefore to attempt some more exact experiments, iu
order to proceed to its exact analysis.
I first made them upon chlorous acid in the state of aqueous solution,
When I had afterwards sueceeded in extracting pure chlorous acid gas,
I verified by direct analysis the results which I had obtained with the
aqueous acid,
Several methods suggest themselves for analysing chlorousaeid diluted
with water. It may, in fact, be decomposed by a combustible, which sets
the chlorine free, and then appreciating together the proportions of this
gas and those of the oxigenated compound which is produced at the same
time with it. On the contrary, it may be treated with metallic silver, and
the quantities of oxygen and of chloride of silver formed may be ascer-
tained; but in both these methods only one of the elements of the
chlorous acid is obtained in the state of gas: it is requisite to determine
the volume of the other by weighings and calculation, which render
these analytic processes rather long in executing. I therefore endea-
voured to find another, which would allow of my attaching the compo-
sition of chlorous acid to the nature of some well-known combination,
and to reduce its analysis to that of a gaseous mixture, a kind of ope-
ration which unites the double advantage of accuracy and brevity.
The action ‘which chlorous acid exerts on oxalic acid, and -in which
these two bodies are converted into chlorine and carbonic acid, ap-
peared to offer an easy method. It is well known that oxalic acid
yields, by decomposition, equal volumes of carbonic acid and oxide of
carbon, and that the latter requires half its yolume of oxygen to con-
vert itintoa volume of carbonic acid equal to its own. It results from
this, that when oxalic acid is changed into carbonic acid, the quarter
of the volume of this gas obtained represents that of the additional
oxygen necessary for this alteration.
The analysis of chlorous acid is brought by this method to that of
a mixture of chlorine and carbonic acid, which is easy of execution by
means of mercury.
I made in this way various attempts, which, although they indicated
that the volume of chlorine was almost double that of the oxygen,
differed however too much from this result, and did not besides agree
sufficiently together to inspire me with confidence. I persevered ne-
vertheless, for the method is easy and it appeared to me to be certain.
Convinced, however, at last that the results obtained were not attribu-
table to any fault in the execution, I examined by nitrate of silver the
residue of a re-action of this kind in which the oxalic acid was in
excess, and the quantity of chloride of silver insoluble in nitric acid
which I obtained proved that a notable portion of chlorine remained
in the liquid. I have since convinced myself that the quantity which
is not disengaged in.a gaseous form is greater as the chlorous acid. is
THE BLEACHING COMPOUNDS OF-CHLORINE. 299.
more dilute. I am ignorant of'the state in which this chlorine exists :
perhaps it forms alittle of the chloroxalic acid, which M. Dumas obtained
by exposing acetic acid and chlorine to the influence of the solar rays ;
perhaps also it existed in the state of hydrochloric acid, a state to which
it might be reduced by the decomposition of water, the oxygen of which
would contribute to the formation of the carbonic acid.
- Inexact as this method of analysis is; it renders it very probable that
chlorous acid is formed of two volumes of chlorine and one volume of
oxygen. But the manner of its’ action with hydrochloric acid leaves
no doubt on this subject.
Chlorous acid and‘hydrochloric acid produce, by their double decom-
position, water and chlorine, as already mentioned. Then if an excess
of chlorous acid be made to act upon a given quantity of hydrochloric
acid, the relation between the volumes of the acid gas decomposed and
of the chlorine obtained, will allow the composition of the chlorous acid
to be inferred from that of the hydrochloric acid.
- Tattempted to effect this decomposition, both by passing hydrochloric
acid gas over mercury into a graduated tube containing in its upper
part a little’ very concentrated chlorous acid, and by introducing
chlorous acid into a tube already containing hydrochloric acid gas.
But the decomposition was in both cases produced in a very imperfect
manner. The chlorine gas which is disengaged at first renders the so-
lution of the hydrochloric acid gas difficult. In order that it may be
complete, recourse must be had to agitation, which cannot be effected
without a portion of the chlorine being absorbed by the mercury.
The following mode’ of operating, howevér, succeeded perfectly :
after having filled a stopped bottle with hydrochloric acid gas in the
mercurial apparatus, I introduced a small phial of glass filled with
chlorous acid and hermetically sealed’; I stopped the bottle, and I
shook it so as to break the small phial. As soon as the chlorous and
hydrochloric acid’ came into contact, decomposition took place with
disengagement of heat, and the interior of the bottle assumed a yellow
tint. When this had returned to the temperature of the atmosphere I
was able to open the phial over the mercury without a drop of this liquid
metal entering or a bubble of gas escaping. The gas which thus filled
it was entirely absorbed by mercury.
In its decomposition by chlorous acid, the hydrochloric acid had
been converted into an equal volume of chlorine. Then in this vo-
lume of hydrochloric acid there was half a volume of hydrogen : the
chlorous acid which had converted this hydrogen into water had
yielded a quarter of a volume of oxygen. On the other hand, the hy-
drochloric acid decomposed could give only half a volume of chlorine ;
and, as a whole volume had been produced, the other half volume must
300. BALARD’S RESEARCHES CONCERNING THE NATURE OF
have been furnished by the chlorous acid. The latter was therefore
manifestly composed of two volumes of chlorine and one volume of
oxygen.
I was however apprehensive that one circumstance might contr shite.
to render this mode of analysis imperfect, which however appeared
to me as simple as it is elegant. It was, in fact, possible that the heat
generated might disengage a portion of the chlorous acid in the gas-
eous state, which, as I have already stated, is completely absorbable by
mercury. The gas then obtained would have contained something be-
sides chlorine, and the volume of this gas elicited would not then have
been rigorously equal to that of the hydrochloric acid employed.
When also I had afterwards observed that concentrated sulphuric
acid, in acting upon liquid chlorous acid, disengaged from it, if not pure
chlorous acid, at least the gaseous products of its decomposition, I de-
termined to ascertain in what proportion they contained chlorine and
oxygen.
For this purpose, I submitted 50 volumes of this gas to the action of
heat, in order to effect its detonation. I thus obtained 72 volumes,
which treated with an alkaline solution were reduced to 25 volumes
of oxygen gas. If it be considered that in this mode of experimenting a
small portion of chlorine is necessarily absorbed by the mercury, the
slight loss sustained will be readily explained ; and, as it appears to me,
it will be concluded that this experiment proves, as well as the former
ones, that chlorous acid is composed of two volumes of chlorine and one
volume of oxygen.
When the methods which I have described allowed of my procuring
pure chlorous acid, I confirmed the previously obtained results by direct
analysis. By the detonation of 45 volumes of this gas I procured 69
volumes of a gaseous mixture, which was reduced to 23 volumes when
I agitated it with an alkaline solution. This last experiment, not only
justifies the results with which other methods had already furnished me,
but allows of appreciating the contraction which the chlorine and oxygen
undergo in combining to form chlorous acid. It will be observed, in
fact, that this contraction is one third of the whole volume, and equal
to that of the oxygen which enters into its composition. The number
67:5, the product of 45 by 1°5, differs too little, it appears to me, from
the number 69 which I obtained, to allow of any doubt remaining in
this respect.
The analysis of chlorous acid thus shows that ‘t is formed of the same
elements and in the same proportions as the gas obtained from chlorate
of potash and hydrochloric acid, a gas which chemists have long consi-
dered as protoxide of chlorine. If it were satisfactorily demonstrated
that this product is really a distinct compound, as it differs much from
THE BLEACHING COMPOUNDS OF CHLORINE. 301.
the chlorous acid which I have been describing, these two bodies would:
afford a fresh example of isomerism. But the recent labours of M. Sou-
beiran have rendered it extremely probable that this supposed protoxide
is merely a mixture of chlorine and deutoxide of chlorine, which had
long been suspected by chemists on account of the peculiar condensation. .
of its elements.
This composition of chlorous acid differs, it will be observed, very much
from that which had previously been assigned to it by chemists. On.
account of the impossibility of directly analysing chlorous acid, chemists
have endeavoured to determine its composition either according to the
re-actions which are produced during its formation or when the decolo-
rizing chlorides are in contact with certain compounds, or from theore-
tical considerations ; but it is easy to prove that these observations, the
accuracy of which on account of the ability of the chemists who made
them is unquestionable, agree perfectly with the results which I have
obtained, and that my views are most consistent with theory.
M. Liebig, by causing the decolorizing compound of chlorine to act
upon the sulphurets of barium, lead, &c., observed that they were im-
mediately converted into sulphates, without evolving chlorine or pre-
cipitating sulphur. Now in order to convert 1 atom of these sulphur-
ets into sulphate, 4 atoms of oxygen are requisite, 3 to form the acid
and | to form the base. M. Liebig has supposed that this effect was
produced by | atom of chlorite ; and, as the base of this chlorite could
only yield 1 atom, he has admitted that the other 3 atoms were fur-
nished by the chlorous acid. On the other hand, the atom of metal of
the base is found in the liquor in the state of chloride; there were re-
quired therefore 2 atoms of chlorine to form this compound.
Chlorous acid, according to this, seems to be composed of 2 of chlorine
and 3 of oxygen. But if it be supposed that 2 atoms of this acid are
necessary to convert 1 atom of sulphuret into sulphate, the observa-
tions of M. Liebig will then entirely agree with mine. Of the 4 atoms
of oxygen requisite, 2 will be furnished by the 2 atoms of acid, and the
2 others by the 2 atoms of base; and the 4 atoms of chlorine combining
with 2 atoms of metal will form 2 atoms of chloride.
M. Soubeiran arrived at the same conclusions as M. Liebig from the
following considerations: if chlorous acid, he says, is formed as chemists
suppose, it is necessary for its production that 3 atoms of metallic
_ oxide should be decomposed to furnish the 3 atoms of oxygen which
enter into its composition, and there should be produced 3 atoms of
metallic chloride ; so that the decolorizing compounds of chlorine must
contain 3 atoms of chlorine in every atom of chlorite.
In order to verify this supposition, M. Soubeiran converts a solution
containing 4 atoms of soda into decolorizing chloride. He evaporated
this in vacuo, and treated the residue of the evaporation with a satu-
302° BALARD’S RESEARCHES CONCERNING THE NATURE OF
rated solution of common salt, intended to dissolve the chlorite, leaving
the chloride unacted upon. He found this quantity of chloride of sodiuni
equivalent to 2°] atoms of soda ; and, with a little too much allowance,
as it seems to me, he concluded that these 2°1 atoms were equal to 3,
and thence that chlorous acid:is.very probably formed of 2 of chlorine
and 3 of oxygen. If it be considered that in such a mode of experi-
menting, the quantity of metallic ‘chloride ought rather to be’ greater
than smaller than that at»first formed by the re-action'of the chlorine
upon the soda, no doubt can be: entertained that these 2-1 should be
reckoned only:as 2, and this-establishes a perfect agreement between
my results and those of M. Soubeiran, and gives for the composition
of chlorous acid the numbers: which I have already adopted.
M. Morin, in his workon the decolorizing chlorides, has decidedly
proved that during their decomposition, whether spontaneous or effected
by heat, these combinations ‘are converted into 17 atoms-of chloride
for 1 atom. of chlorate, and that 12 atoms of oxygen are at the same
time disengaged, two thirds of what they previously contained. In
supposing that chlorous acid is formed of 2 of chlorine and 3 of oxy-
gen, the following table is the expression of the atomic re-action.
Atoms employed.
9 atoms oxide ... = 9 atoms metal.
9 atoms oxygen.
9 atoms avidiy.wiet { 18 atoms chlorine.
9 atoms chlorite = 1
27 atoms oxygen.
Atoms produced.
24 atoms oxygen.
’ 2,atoms metal.
{ 2 atoms oxygen.
2 atoms acid Ls 4, atoms CHIOr ie.
sree “| 10 atoms oxygen.
7 atoms metal.’
14 atoms chlorine.
If to these 7 atoms of chloride there be added the 27 which were
mixed with the 9 atoms of chlorite in the decolorizing compound, there
would be 34 atoms of chloride for 2 of chlorate, 17 for 1.
But the supposition that chlorous acid is formed of 2 atoms of chlo-
rine and 2 of oxygen, agrees also with these results; the atomic re-
action may then be much more simply expressed, as shown by the fol-
lowing table.
2 atoms oxide... =
2 atoms chlorate =
7 atoms chloride =
Atoms employed.
Oiatanis aan pr 18 atoms chlorine.
git 9 atoms oxygen.
={ 9 atoms metal.
9 atoms chlorite = 1
9 atoms oxygen. ©
9 atoms base ....
THE BLEACHING COMPOUNDS OF CHLORINE. 303
Atoms produced.
12 atoms oxygen.
1 atom acid...... = 2 atoms chlorine.
5 atoms oxygen.
act 1 atom metal.
1. atom base...... = { 1 atom oxygen.
8 atoms metal.
16 atoms chlorine.
The 8 atoms of chloride formed, and the nine with which they were
mixed,—admitting that chlorous acid is composed as I state,—make
the 17 atoms for 1 of chlorate obtained by M. Morin.
There is only one fact which does not agree with the new compo-
‘sition which I assign to chlorous acid; it is an experiment of Berzelius,
in which this chemist observed, when precipitating chloride of lime by
nitrate of silver, that the metallic chlorite while decomposing produced
an atom of chloride, while 2 atoms of silver remained in solution, un-
questionably in the state of chlorate. But according to my view of
the constitution of chlorous acid there ought on the contrary to be
formed 2 atoms of chloride for 1 of chlorate. But it must be stated that
Berzelius does not attach any such importance to this result, so as to
deduce the composition of chlorous acid from it; for this mode of experi-
menting cannot be exact. I have already shown, that during the preci-
pitation of the chloride by the salt of silver and the filtration of the liquid,
the chlorite of silver decomposes; and of the two products of this de-
composition, the chlorate only is obtained, which remains in solution,
while the corresponding chloride is retained by the filter: the result of
this in the experiment of Berzelius ought to have been to increase the
quantity of chlorate, and to diminish that of the chloride formed by the
decomposition of the chlorite of silver.
It is not only on account of the facts which I have mentioned that
chemists had assigned the supposed composition to chlorous acid, but
they were also guided by certain theoretical considerations.
The experiments made up to the present time prove with certainty,
that in the decolorizing liquors which chlorine forms with the alkaline
oxides, the proportions of their elements are 1 atom radical, 1 atom
oxygen, 2 atoms chlorine*; and in the hypothesis of chlorides of
oxides, this composition was represented by this formula R C2. It is
evident that, whatever other supposition may be adopted with respect
to the nature of these combinations, it ought to fulfill the double con-
dition, and that the same relations should always subsist, and the num-
ber of the atoms be expressed by a whole number. In multiplying
the first formula by the natural series of whole numbers, and arranging
1 atom chlorate = {
8 atoms chloride =
* In England 1 atom chlorine also, for a reason already stated, viz. that the
weight of the atom is double that of foreign chemists.
304 BALARD’S RESEARCHES CONCERNING THE NATURE OF
the atoms so as to form of them metallic chlorides and salts with an
oxacid of chlorine, we shall have the following results:
R+0+2ClixX2= RCe+CER.
R+0+2C1X3=2RC+ CPR.
R+04+2Clx4=3RCP + CPR.
R+O042C1X5=4R C+ CPR.
Of these different formule, the third has been preferred by chemists,
and chlorous acid has been assimilated as to its composition to nitrous
and phosphorous acid. But why not adopt the second, which is cer-
tainly more simple, and in which chlorous acid is equivalent to hypo-
sulphurous acid ?
Omitting all experimental proof, this supposition is much more na-
tural than the other; for the cireumstances under which chlorous acid
is formed do not at all resemble those under which nitrous and phos-
phorous acid &c. are obtained, whereas they are identically the same
as those which produce hyposulphurous acid. It is well known, in
fact, that it is by treating the alkaline oxides with sulphur and water,
that mixtures of 1 atom of hyposulphite and 1 atom of polysulphuret
are obtained. If on this re-action we substitute chlorine for sulphur,
we shall have 1 atom of chlorite and 1 atom of chloride. The only dif-
ference existing between the two cases is, that the number which ex-
presses the chemical equivalent of chlorine being double that which re-
presents its atom, while with sulphur these two numbers are equal, we
shall have Cl? for the formula of chlorous acid, whilst that of sulphurous
acid will be S*.
The supposition which contributed to the adoption of the fourth for-
mula by chemists, is that of Davy’s protoxide of chlorine being a distinct
compound. But as it was very evident that it was not the acid of the chlo-
rites, the second.[fourth? ] formula, which led to this conclusion, was ne-
cessarily rejected. It is only since the experiments of M. Soubeiran have
rendered it almost certain that the supposed protoxide of chlorine is
merely a mixture of chlorine and of deutoxide, that the true composition
of chlorous acid could be ascertained @ priori. What denomination ought
now to be assigned to this compound; It is evident that the name of chlo-
rous acid can no longer be given to it, and that it is much more proper
to call it hypochlorous, a name which recalls its analogy of constitution
with the hyposulphurous, hypophosphorous acids, &c., formed like it of
one equivalent of their radical and one equivalent of oxygen. Its combi-
nations will be called hypochlorites. If this denomination were adopted,
* This inconsistency does not happen when the number for chlorine is doubled.
| THE BLEACHING COMPOUNDS OF CHLORINE. ~ - 305
the name of chlorous acid would be reserved for the yet unknown com-
bination of two volumes of chlorine and three of oxygen, and that of
hypochloric would signify, as M. Thénard has proposed, the compound
now called deutoxide of chlorine.
§ 6.— Of the Hypochlorites.
The hypochlorous acid, which is obtained, with difficulty it is true,
from the decolorizing compounds of chlorine, by employing the pro-
cesses which I have described, presents the same characters as that fur-
nished by the action of this gas on the red oxide of mercury. It is
therefore extremely probable that these compounds contain hypochlo-
rites mixed with chlorides. But as it is not impossible that the hypo-
chlorous acid obtained from them, instead of being really formed in
these bodies, is merely a product of their decomposition, it appeared to
me proper, in order to render the demonstration more complete, to study
the general properties of the compounds of this acid with bases, and, by
showing that they are the same as those which have been ascertained in
the decolorizing compounds, to confirm by synthesis the results obtained
by analysis.
Pure hypochlorites may be obtained in two different modes, one di-
rect and the other by double decomposition.
The direct combination of concentrated hypochlorous acid with pow-
erful bases, whether solid or in concentrated solutions, is accompanied
with the disengagement of intense heat. This heat, when it is a little
too great, changes the hypochlorite into chlorate and chloride.
The presence of a certain excess of base prevents this conversion,
whereas it is very rapidly effected when the chlorous acid is in excess.
It is therefore necessary to add the alkaline substance to the acid, in
quantity insufficient for saturation, and constantly to agitate the bottle,
immersed in cold water; and not to reverse the operation, by gradually
saturating the acid with the base. By taking these precautions, con-
centrated solutions of hypochlorous acid and potash may be used with-
out precipitating chlorate of potash, notwithstanding the sparing solu-
bility of this salt ; this proves, that if any is formed the quantity is very
small. If either of these precautions be neglected, chlorate is abun-
dantly precipitated ; when both are observed, the hypochlorous acid
combines simply with the base, and no gas is disengaged ; but when a
high temperature or an excess of chlorous acid occasion the decompo-
sition of the hypochlorite, a gaseous disengagement occurs. This gas
is pure oxygen if the base is in excess ; when on the contrary the hy-
pochlorous acid predominates, it is oxygen mixed with chlorine.
It is easy to explain this double phenomenon. The experiments of
M. Morin have proved, on the one hand, that the decolorizing compounds
of chlorine lose part of their oxygen when they are converted into chlo-
306: BALARD'S RESEARCHES CONCERNING THE NATURE OF
rates ; and, on the:other hand, I havé already stated,‘ that the metallic
chlorides are decomposed by chlorous acid, and yield, among other pro-
ducts, chlorine gas. The forniation of a chlorate is therefore always
accompanied with a corresponding production of chloride.
The hypochlorites of barytes and lime serve for the preparation of
other hypochlorites, by double decomposition.
Potash, soda, lithia, strontia, barytes, lime and magnesia are bases
which, by combining with hypochlorous acid, form salts with it, the ex-
istence of which is incontestible. I could not however forget that
M. Grouvelle, while examining the decolorizing combinations of chlo-
rine, observed that peroxide of iron, oxide of copper and of zine, ab-
sorbed this gas very rapidly, and formed with them decolorizing com-
pounds, which heat and exsiccation converted into chlorine and oxides.
I therefore endeavoured to produce the hypochlorites of these metals,
either by directly combining hypochlorous acid with their oxides, or by
double decomposition between the sulphates of these bases and the hy-
pochlorite of lime and barytes.
In experimenting with iron, I did not obtain indications of combination
by either of these methods. On the one hand hypochlorous acid, made to
act upon peroxide of iron, did not dissolve the slightest portion of it ; and
on the other, by the decomposition of hypochlorite of lime by persul-
phate of iron, I obtained sulphate of lime and peroxide together ; and
the liquor, which contained free hypochlorous acid, contained no iron.
This proves two things ; first, that hypochlorous acid is extremely weak,
since the base with which it was combined acts with persulphate of iron
as if it were uncombined; and secondly, that hypochlorite of peroxide
of iron cannot exist.
The results which I have obtained thus differ from those observed
by M. Grouvelle ; and I endeavoured to discover the cause of this dis-
agreement. When operating as he did, that is to say by subjecting
hydrate of iron to the action of chlorine, I found that the gas was
slowly absorbed, and that the liquor was, as he stated, strongly decoloriz-
ing, even after boiling for a quarter of an hour ; but I also convinced
mipsel that during the ebullition not only chlorine, but chlorous acid,
was liberated.
The liquid, before ébullition, contained a persalt of iron; but during
distillation almost the whole of the peroxide was deposited in a pure state.’
It appears, then, that in the action of peroxide of iron upon chlorine,
both perchloride of iron and chlorous acid were formed, compounds
which might co-exist, on account of the diluted condition of both of them.
The intervention of heat had the effect of destroying that which had
been produéed in the cold, and of producing an inverse re-action, from
which there resulted peroxide of iron and chlorine, while a portion of
engagement of oxygen. Nevertheless, with the addition of certain cir-
THE BLEACHING COMPOUNDS OF CHLORINE. 307
the chlorous acid escaped decomposition and. .»was disengaged in the
form of vapour.
The phenomena are rather different when oxide of copper or of zinc
is employed ; the solutions of the sulphates of these metals are decom-
posed by hypochlorite of lime, and sulphate of lime and the metallic
oxide are precipitated together. If the: chlorite of lime is in excess, the
liquor does not retain the slightest portion of either metal, and by dis-
tillation hypochlorous acid only is obtained.
When however the hydrates of zine and copper are treated with
chlorous acid, a certain quantity of them is dissolved, and the liquid
possesses decolorizing properties. Since, then, perfectly free chlorous
acid dissolves these oxides, and these compounds are precipitated by
solutions of alkaline chlorites, which contain an excess of chlorous acid,
it is natural to suppose that in these cases this chlorous acid is not in a
perfectly free state. It is therefore probable that some alkaline oxides,
lime for example, are susceptible of forming bihypochlorites, which
are decomposed by evaporation in vacuo into neutral hypochlorites and
hypochlorous acid. :
The hypochlorites of zinc and copper, the existence of which is ren-
dered probable by what I have stated, suffer decomposition very readily.
When they are distilled they evolve hypochlorous acid, and probably a
little oxygen, and they are converted into oxichlorides. The oxichloride
of copper is of a fine green colour ; that of zinc is white, with an agree-
able pearly lustre ;it:decomposes spontaneously into chloride and chlo-
rate, with the disengagement of oxygem and a little chlorine. As to
that.of copper, it is decomposed: by:an excess of oxide, which it con-
verts: into. insoluble ee also: so bane a mixture sg oxygen
-and:chlorine. ok ORM t
_ These chlorites, sited with ‘Gidatidoss maybe chieinel as ‘annsicaiia
vn M. Grouvelle, by agitating either of these oxides, diffused through
water, with chlorine. The absorption of the gas is rapid, especially by
-the oxide of zinc ; the distilled liquor precipitates an oxichloride, as ob-
served by M. Grouvelleé, and it contains a metallic chloride in solution.
A portion of dilute hypochlorous acid is condensed. : In the absence of
“peroxide of mercury; the oxide of zine and that of copper may serve for
the preparation of this acid. The hypochlorites of powerful-bases pos-
sess the following properties: their odour and colour are identically the
same as the corresponding decolorizing compounds of chlorine, from
which it is impossible to distinguish them: by their physical properties;
they are salts of a very changeable constitution. A slight increase of
temperature, the influence of solar light, even of diffused light;:converts
them into chlorides and chlorates. I have not estimated the relation
between the atomic quantities of these two salts.
-. This change is effected in the greatest numberof cases with the dis-
308 BALARD’S RESEARCHES CONCERNING THE NATURE OF
cumstances, which I have yet imperfectly ascertained, I have not per-
ceived any disengagement of this gas. I shall, however, soon endeavour
to supply this hiatus ; for the exact determination of the circumstances
may greatly influence the fabrication of chlorate of potash. It is evi-
dent that if the conversion into chlorite occurred without the disengage-
ment of oxygen, then would be obtained, for a given weight of potash,
three times more of this salt than is usually procured. The presence
of an excess of base may prevent the decomposition of the chlorites, but
this base must be powerful; oxide of zinc and magnesia are insuffi-
ciently so for it. Therefore their chlorites, soon after formation, yield
oxygen gas mixed with chlorine if they have an excess of acid, and are
converted into chlorates and chlorides. The attempt to obtain these in
a dry state would be fruitless, even when mixed with an excess of oxide,
and the evaporation performed by the air-pump.
The case is different with those with a base of potash, soda, lime,
barytes, and strontia. These may be obtained in a solid state by eva-
poration in a dry vacuum, or even by distillation at a low temperature;
but for this there must always be a great excess of alkali. But notwith-
standing this precaution, it often happens that during this evaporation,
even in vacuo, a notable portion of hypochlorite is converted into chlo-
rate and chloride.
The hypochlorites are very readily decomposed by the acids. Al-
though hypochlorous acid expels carbonic acid from its combinations,
it is in its turn expelled from its own by a current of carbonic acid gas,
which shows how weak are its affinities for bases. When the dry hypo-
chlorites are pure, they may be used for preparing hypochlorous acid gas,
provided they are treated with an acid which contains but little water,
—concentrated phosphoric acid for example. But as it is difficult toob-
tain them both diy and free from chlorides and chlorates, and, as in this
case, the hypochlorous acid gas is mixed with chlorine, it is better to. em-
ploy the process which I have already described for preparing it. .
It has already been stated that the decolorizing compounds of chlo-
rine have a great disposition to convert sulphur, iodine, phosphorus
and arsenic, into sulphuric, iodic, phosphoric, and arsenic acid, which,
combining with the oxide of these compounds, give rise to saline com-
-binations. I have also observed the same property in the hypochlorites.
Fragments of arsenic blackened on their surface by a little protoxide,
put into a solution of these salts, have their metallic lustre immediately
restored, as stated by M. Soubeiran to occur with the chlorides of lime,
‘soda, &e.
The metals act with the hypochlorites as with the decolorizing com-
binations themselves. Gold and-platina are not altered. Silver is trans- |
formed, though slowly, into chloride, with the disengagement of oxygen.
Iron is very readily oxidized. As to tin and copper, they readily be-
THE BLEACHING COMPOUNDS OF CHLORINE. 309
come oxichlorides, giving rise to a slight disengagement of chlorine
mixed with oxygen. Mercury is changed into red oxichloride by con-
tact with hypochlorite of lime.
The recently precipitated sulphurets are immediately converted into
sulphates by the hypochlorites ; and these salts, as well as the hypochlo-
rous acid, might undoubtedly, as well as oxigenated water, serve for the
restoration of pictures, in which the white colour employed in painting
has become black by the change of carbonate of lead into sulphuret.
The greater part of the combinations of oxygen which are not satu-
rated with this principle, undergo the same action by the hypochlorites
as by hypochlorous acid itself. Thus nitric oxide is absorbed by them
as by the decolorizing chlorides, and converted into nitric acid. The
metallic protoxides are converted into peroxides, and the salts in ife are
converted into salts in ate. It is not necessary to enumerate in detail
all these re-actions, which are absolutely the same, as chemists have
already observed, with the decolorizing chlorides.
The comparative action of the hypochlorites and decolorizing chlo-
rides upon some organic matters proves, as well as the preceding facts,
that a perfect identity exists between these bodies. Both possess the
same power of destroying vegetable colours ; but for this purpose they
must not have excess of base; for alkaline hypochlorite of lime and
tincture of litmus may remain during some hours in contact without
the colour being destroyed.
It is well known with what activity concentrated decolorizing chlo-
rides attack fabrics. The pure hypochlorites, unmixed with chlorides,
possess also this property in a high degree: their action upon lignin,
and especially upon filtering-paper, is attended with a considerable dis-
engagement of heat; and as the hypochlorites are susceptible, as I have
already stated, of being converted by heat into chlorides and chlorates
with the disengagement of oxygen, the heat developed effects this con-
version and produces this disengagement. The paper is essentially
altered ; it usually becomes friable, but it is not carbonized ; and when
the operation is conducted in a close vessel, so as to collect the gases,
it is found that little but oxygen is disengaged, mixed with a small
quantity of carbonic acid. But if rather a large quantity be acted
upon, the heat developed is more intense ; the paper then inflames, and
there is a production in this case, not of oxygen, but of carbonic acid.
The experiments of M. Soubeiran and of M. Liebig have proved that
_ the decolorizing chlorides can convert alcohol into a peculiar chloride
of carbon. I readily convinced myself that the hypochlorites possess
‘the same property. I have not analysed the compound of chlorine and
carbon which is produced in this case ; but its physical properties, and
especially its odour, so much resemble those of the chloride of carbon
examined by M. Liebig, that I have no doubt of their being identical,
Vor. L—Panrr II. ¥
310 BALARD ON THE BLEACHING COMPOUNDS OF CHLORINE.
which induces the opinion that they are derived from a similar coms
pound.
Time has not allowed of my further extending the comparison be-
tween the hypochlorites and the decolorizing chlorides: I am also of
opinion that such an undertaking would be quite useless. The facts
which I have announced in this chapter appear to me to be sufficient
to justify the three following conclusions: 1st, the hypochlorites possess
a great number of properties which characterize free hypochlorous acid:
2ndly, these properties are identically the same as those previously ob-
served in the decolorizing chlorides; and these latter ought hereafter
to be considered as mixtures of one atom of chloride and one atom of
hypochlorite ; 3rdly and lastly, the presence of a metallic chloride in
these decolorizing compounds does not alter the properties of the hy-
pochlorite itself. But how do these compounds serve for decolorizing
and disinfecting? The answer is easy, and it arises from all the facts
which I have detailed in this memoir. In the case in which an acid
is added to them, they disengage chlorine, and it is then this chlo-
rine itself which decolorizes and disinfects, by a mode of action which
is not well known, but every circumstance induces the belief that it is
an oxidation, produced in an indirect manner at the expense of the
elements of water. If, on the contrary, they act without the assistance
of acids, it is entirely by the oxygen of the acid and of the base of the
hypochlorite that they decolorize and disinfect, and they are converted
into chlorides.
The analogies which associate chlorine and bromine afford a pre-
sentiment that there must also exist an oxacid of this body, corre-
sponding with the new compound of chlorine which I have now de-
scribed; and this is in fact confirmed by experiment. By operating in
modes similar to those by which I succeeded in obtaining hypochlorous
acid, I obtained a new acid of bromine, which bears so strong a resem-
blance to it, that I have no hesitation in naming it hypobromous ‘acid
although the investigation which I have undertaken is not yet com-
pleted, and I have not determined its composition by direct experi-
ments. I content myself at present with announcing its existence,
waiting till additional researches permit me to trace its history in a less
imperfect manner.
311
ARTICLE XIII.
On the Laws of the Conducting Powers of Wires of different
Lengths and Diameters for Electricity ; by E. LEnz.
(Read to the Academy of St. Petersburgh, the 28th of November, 1834.)
From the Mémoires de l’ Académie Impériale des Sciences de St. Petersbourg:
VI™. series, tom. i. 1835.
Tuovceu Van Marum, Priestley, Children, Harris, and Davy* had
previous to Galvani’s brilliant discovery endeavoured to determine the
eonductibility of different metal wires by discharges of the Leyden bat-
tery, yet the first more accurate experiments on this subject were made
at a later period by means of the electromotor and the voltaic pile ; but,
strange to say, these later and more accurate experiments have led to
results at variance with each other. Whilst the experiments of Davy,
Pouillet, Beequerel, Christie, Ohm, and Fechner prove the law that
wires of the same metal conduct electricity inversely as their lengths,
and directly as their sections—that is to say, as the squares of their
diameters—Barlow and Cumming consider, according to their experi-
ments, that the conductibility is inversely proportionate to the square
of the lengths, and directly as the diameters of the wires (or as the
square roots of their sections). Ritchie, whose observations on this sub-
_ ject are the most recent (Phil. Trans. for 1833, p. 313), but who, un-
fortunately, like most English authors, is totally unacquainted with the
works of the German natural philosophers Ohm and Fechner, endea-
vours to explain this contradiction by assuming that the conductibility
of the wires varies according to the force of the current; for having
connected two wires with two different batteries, he found by means of
his galvanometer that the strength of the currents were not in the
same proportion to each other. He explains this according to his own
view of the conductibility of electricity in the following manner :
“Let us suppose that there is no actual transfer of electricity along
the wire, but that all the phenomena of deflection, &c. result from 2
definite arrangement of the electric fluid essentially belonging to the
wire itself. Let us further suppose that a section of wire contains one
hundred particles of electricity, and that the battery is capable of ar-
* [M. Lenz is here in error; the experiments of Children, Davy, and Harris
were all made subsequently to the discoyery of Galyani.—Eprr.]
y2
312 LENZ ON THE VARIOUS CONDUCTING POWERS
ranging one fourth of these, or twenty-five particles, then there will only
remain seventy-five to be arranged by any increase of power. Let us
now suppose we have another wire of the same length, whose section
contains only twenty-five atoms; it is obvious that this battery will be
able to arrange more than one fourth of this number, so that the ratio
of the conducting powers cannot be as one to four, but will be found
by actual experiment a very different ratio. If we increase the size of
the battery, suppose the size of the plates to be doubled, then it is ob-
vious we shall not double the deflecting power. For out of one hun-
dred particles there are only seventy-five remaining, a part of which
only can be arranged by the increased part of the battery. Hence the
deflecting force increases very slowly with the increased size or energy
of the battery.”
That this view of Ritchie’s is wrong may easily be proved by ex-
periments, of which the numerical determinations of Fechner afford
numerous examples. There are, in fact, some arrangements, particu-
larly in closed galvanic series, which show such a relation between the
pile and the connecting wires, that the increase of the plates does not
perceptibly increase the strength of the current in the wire. This
would, according to Ritchie’s opinion, prove the whole of the fluid to
be already entirely disposed of, and that it would be impossible to pass
any more fluid through the same wire. But this is by no means the
case; for if, instead of doubling the number of plates, their size be
doubled, the force will be almost exactly double. This proves, there-
fore, that the whole of the fluid has not yet been disposed of, and that
another arrangement of the voltaic pile only was required to produce
the arrangement of a double number of particles of the fluid. Besides,
Ritchie's theory does not explain the difference of effect produced by
a voltaic pile of many plates, and by one of fewer plates but of larger
size.
Ohm however several years ago furnished us with a theory of the gal-
vanic battery which supplies this deficiency ; but being only published
in German, it is unknown both in France and in England. This theory
explains perfectly the difference between Barlow’s results and those of
other natural philosophers who have occupied themselves with this
subject, as well as the doubts of Ritchie. The latter says, in his paper
above quoted, that “ The conducting power of a wire must be a func-
tion of all the quantities concerned in the experiment. These quantities
are obviously the diameter of the wire, its length, the size of the battery,
and the strength of the acid.” Had he, instead of the term “ conducting
power” used that of strength of the current, he would have been nearer
the mark, and given a proper explanation of those apparent anomalies.
Before quoting the simple formula of Ohm we must observe, that
this philosopher always uses the term conducting resistance instead of
OF WIRES FOR ELECTRICITY. 313
the term conductibility. _The latter is inversely proportional to the con-
ductibility, so that when L signifies conducting resistance,
te 1
~~ conductibility”
If therefore the conducting resistance of a galvanic arrangement be ex-
pressed by L, and its electromotive power by A (which we may here
suppose to be produced either by contact or chemical affinity), then
Ohm’s formula for the power of the current will be
; A
LC
But L expresses not only the conducting resistance of the connecting
wire, but that of the entire voltaic arrangement; that is to say, the sum
of all the conducting resistances of the fluid and of the fixed parts of the
circuit. If we take for unity of conducting resistance the length and
thickness of a wire of a given substance, we may in this unity express
by / the resistance of the battery itself (both plates and acid taken to-
gether); and by J the resistance of the connecting wire, the conducti-
bility of which is to be ascertained; and the formula will then stand
thus:
weexe:'
ao %
which will give for the conducting resistance of the connecting wire
A
ES FO Z.
We may take the electromotive power itself for unity, should it re-
main unaltered, which is almost always the case in experiments on the
conductibility of wires; the formula will then stand thus:
r
1
= —l.
i F
By closing now the battery with wires of different conducting re-
)sistances, d/ 1), cay» Agyy Kes and denoting the corresponding currents
“by Fay Foy Fig) we shall have the following proportion :
1 1 1
Xa)? Xa? cy pirates =(9-")? Gi"): Gai-?):
The conducting resistances therefore are not in an inverse ratio to
the intensities of the observed currents, or in a direct ratio to the con-
_ ~ duetibilities ; but we must deduct from the latter the constant quantity
_ *lbefore such proportion can obtain.
After having established this simple principle, let us now return to the
_ above-mentioned experiments of various philosophers on the conducti-
$14 LENZ ON THE VARIOUS CONDUCTING POWERS
bility of wires, and we shall find that Ohm and Fechner calculated the
results of their experiments according to this principle ; whilst Davy and
Becquerel conducted their experiments in such a manner as to avoid the
errors which otherwise would have been the consequence of disregard-
ing it. This explains why the results of their experiments agree with
those of the German philosophers. Davy, for instance, connected the
poles of a voltaic pile in two ways at the same time; the one was by a sim-
ple wire, the other by an apparatus for decomposing water: the current
therefore was divided between these two paths, and the conducting power
of the current passing through the metal conductor was so far increased,
by shortening the length and increasing the thickness of the conductor,
that the current passing through the water became so weak that no de-
composition took place. Davy endeavoured to obtain the same limit
by means of wires of different thicknesses, and in this manner found that
two wires of different thicknesses attained the same limit when their
lengths were proportional to their sections. Both connecting wires at-
taining thus the same strength of current, it would be necessary to bring
the conductibility of one wire to be exactly equal to that of the other,
independent of every theory of the dependence of the intensity of the
current on the parts of the voltaic arrangement, in order to ascertain the
proportion of the length to the thickness. Such experiments would
certainly produce results containing no decisive errors; they will, how-
ever, admit but little accuracy of determination.
Becquerel coiled two wires of the same substance, but of different
length and thickness, round the frame of a multiplier, so that the coils
of the one laid between those of the other; when therefore a current of
the same strength was passed through them in opposite directions the
needle of the multiplier remained at rest. He joined the ends of each
wire with the same voltaic pile, but in opposite directions with respect
to its poles. The wires having different sections, the current was, for
equal lengths, stronger in the thicker than in the thinner wire, and he
therefore found a deviation of the needle of the multiplier. He then
diminished the length of the thinner wire till the current became equal
in both,—that is to say, till the index returned to its place of rest. He
thus obtained two wires of different length and thickness, which both
conducted the electricity equally well; and concluded, from comparing
their dimensions, that in equally good conducting wires of the same
substance the lengths are proportional to the masses, that is to say, to
the sections. It is this proposition alone which the experiments of Davy
also demonstrate, and Ritchie is perfectly right in objecting to experi-
ments of this kind; but he unjustly charges Becquerel with not having
well observed it himself. It was only after having ascertained by other
experiments that the conductors are in an inverse ratio to the lengths,
OF WIRES FOR ELECTRICITY. 315
that Becquerel arrived, from the above-mentioned experiments, at the
conclusion that they are in a direct ratio to the sections.
Pouillet placed successively various wires between the poles of one
and the same pile, and determined the strength of the current by the
tangent of the angle of deviation. He asserts that he found the con-
ductibility proportional to the section ; and with respect to the length,
he came to this interesting result, that the strength of the current is in
an inverse ratio to the length of the wires, if constant quantities are added
tothem. If we denote the strength of two currents by F and F’, the
corresponding lengths of the conducting wires by \ and X’, and a con-
stant quality by 7, Pouillet’s formula will be
ee Ss ks Se
FOU I+N ’
but this is only the immediate consequence of our formula for the
strength of the current according to Ohm’s theory, for according to it
we have for the conducting resistances \ and \! (which are propor-
tional to the lengths),
A
pe i ;
F= any, > and F Tawi
therefore
Fi _ed+n2
ee oe,
which exactly resembles Pouillet’s formula, with the difference merely
that 7 has here a determinate signification ; itis, namely, the conducting
resistance of all the other parts of the circuit, except that of the wire
experimented upon. A very careful series of experiments referring to
the point in question is furnished us in a paper by Christie on the pro-
duction of currents by electro-magnetic induction by means of Knight's
great magnet. Totally unacquainted with the theory of Ohm, he was,
like Pouillet, induced, by an accurate discussion of his own observations,
to add to the conducting power of the wires employed in the experi-
ments a constant expressing the conducting resistance of the wire of the
multiplier. He must have obtained in this manner correct results,
D2
and was in fact led to the formula for conductibility sa at in which D
signifies the diameter of the wire and Lits length. Calculating by means
of this formula the angles of deviation, he found that the calculations
perfectly agreed with the observations made*.
* We perceive in Christie’s otherwise very valuable paper the want of a cor-
rect distinction between the electromotive power and the generated current;
the latter being equal to the former divided by the resistance to conduction.
The electromotive power induced by the magnet in spirals, of any substance and
dimension whatever, isalways the same (see Mémoires del’ Académie de St. Péters-
bourg,—Sciences Mathém., vol, ii. p. 427,) whilst the current is in an inyerse
316 LENZ ON THE VARIOUS CONDUCTING POWERS
Barlow made his experiments in the same manner as Pouillet, and
would have obtained the same results had he added, as Poullet did, a
constant to the conducting power of his wires, without which his results
necessarily proved erroneous. He supposed that the conducting power
was inversely as the square root of the length, and directly as the sec-
tion. Such a proportion may indeed easily be found between the resist-
ance of the pile and the two wires employed for the experiment, that,
according to Barlow’s calculation, nearly such a law may be obtained.
Had he employed, for instance, two wires of the same diameter, the
lengths of which were m and », his view must have been confirmed,
when the conducting resistance of the pile itself was reduced to that of
one wire of the same diameter and the length
m f(n)— 2 Jf (m)
af (m) — of (n)
It is indeed not very probable that such would have always been the
condition of the pile, but the experiments agree so little with the calcu-
lations performed according to his principle, that differences of 6° and
7° may be found in them.
Cumming used the thermo-electric pile to excite the current, but he
also did not in the least consider the conductibility of the thermo-
electric metals; and he himself owns that the experiments agree but
approximately with his theory *.
We perceive, then, by the above, that all the contradictory results of
Barlow's, Cumming’s, and Ritchie’s experiments, in opposition to the
law established by other philosophers, are reduced to a mere nothing by
an accurate appreciation of the mode in which they performed their
experiments. The axiom that the conductibility of wires of the same
substance is inversely as their lengths and directly as their sections
is established by Ohm and Fechner in so conclusive a manner, and with
such a full appreciation of all the connected circumstances, that a
further and more minute illustration seems to be almost superfluous;
still the method of determining the power of conductibility by the in-
duced electro-dynamic current+ offers so much facility and accuracy
ratio to the resistance; andas in the experiment on this subject by Faraday the
entire resistance of the voltaic arrangement remained the same, when the wires
were compared two by two, the currents produced by induction must also have
been the same.
* [The results obtained by Harris, by means of his thermo-electrometer,
(Trans. Royal Soc. of Edin. 1832,) are also easily reconciled with the theory
here advocated. This able experimentalist found that the differences in the
conducting powers of wires of different diameters became more apparent within
certain limits, as the force of the battery increased. These experiments were
made with wires of very short lengths and small diameters.—Epir. }
+ Christie has also employed, in his above-mentioned experiments, currents
produced by electro-dynamic induction, but more recently than I have. His
paper was presented to the Royal Society on February the 8th, 1833, whilst
OF WIRES FOR ELECTRICITY. 317.
in observation*, that it appears to me worth while to apply this method,
and thus exhaust all the proofs of this important point in the theory of
the pile. I shall therefore propound them in the following series of
experiments, which, though they do not establish a new law, will yet
I hope secure for ever the old one against all further objections.
The manner in which these experiments have been performed does
not at all differ from that described in the above-mentioned memoirs,
and I refer therefore to them for the description of the apparatus and
the manner of experimenting. I shall but expatiate upon one point,
which should have there been more fully investigated. Having fastened
the horse-shoe magnet in a vertical position, I suddenly detached from
it the cylindrical keeper with the surrounding electromotive spiral in
order to produce the current, and observed through a glass the sud-
denly produced deviation of the needle of the multiplier. From this
mode of proceeding a doubt may arise, whether the current thus pro-
duced was always of the same strength, or whether the suddenness of
the disruption, which cannot be always strictly equal, did not exercise
a real influence ; and Christie has indeed, for fear this might be the
case, performed the disruption by the fall of a determined weight from
a determined elevation. I convinced myself however at the very be-
ginning by experiments that the suddenness of the disruption, haying
surpassed a certain term, exercises no influence whatever on the strength
of the current. The results of the experiments were the following :
Experiment.
ee
Average.
By purposely breaking contact
very slowly 100°7 | 100°7| 100°8| 100-73
By purposely breaking contact
very suddenly .................. | 100°7} 101°0| 100°6| 100°77
By breaking contact with ordinary
quickness 101°0} 100°2| 100°7| 100°63
The averages show that the influence of the suddenness of disruption
may be considered as = 0, the differences of the deviations of the needle
not surpassing +7, of a degree. Besides the above experiments, per-
formed solely for this purpose, there are also numerous confirmations of
my first paper on this subject was read before the Imperial Academy of Sciences
on November the 7th, 1832. (See Mémoires,—Sciences Mathém. et Phys., vol. ii.
p- 427.)
: iy Mémoires de V Acad. Imp. de St, Petersb. (Sciences Mathém. et Phys.,
vol. ii.
318 LENZ ON THE VARIOUS CONDUCTING POWERS
these results in my former memoirs; where, in many places, the same
observations of deviation were successively repeated in order to obtain
a greater accuracy, and where the results leave nothing to wish as to
their accordance. Convincing proofs may moreover be found in the
following series of experiments.
The reason why the strength of the current cannot depend on the sud-
denness of the disruption might also be easily demonstrated by theo-
retical considerations. The current in the electromotive spiral arises
from this cause, that the magnetic intensity of the keeper of soft iron
about which the spiral is coiled diminishes from a maximum to a mini-
mum,—the latter approaching nearer to 0 in proportion as the iron pos-
sesses a less coercitive power. We may imagine this diminution of
the magnetic intensity of the keeper to be divided into indefinitely
small parts, each of them producing in the spiral an indefinitely small
current, and this again exercising an indefinitely small effect on the
needle of the multiplier: all these effects taken together produce the
entire deviation of the needle. If, therefore, the whole series of inde-
finitely small effects act on the needle successively, but in so short a
time that they exercise their whole force when the needle is in a posi-
tion very little different from the normal one, the sum of the effects will
be as great as that which would be produced by the whole force acting
at once, or by the iron passing suddenly from the maximum to the mi-
nimum ; and within these limits suddenness of disruption will have no
influence over the deviation. Experience teaches therefore that the sud-
denness I commonly employed was within these limits; which will be
more easily conceivable from the circumstance that the intensity of the
keeper diminishes in the beginning much more quickly than at the end:
so that we may take it for granted that more than +, of the indefinitely
small diminution of intensity takes place during the contact of the magnet
with the keeper and within the distance of one inch from it.
My first experiments refer to the law of conductibility of wires of
different lengths. I cut for this purpose a copper wire (0°023 Engl.
inch thick), covered with silk, into five pieces, so that each was 7 Engl.
feet long, and observed the deviations of the needle produced by the dis-
ruption.of the keeper, together with the electromotoric spiral from the
magnet, by inserting ‘between the wire of the multiplier and the elec-
tromotive spiral either no wire at all, or one, two, four, &c. wires suc-
cessively. Their extremities were connected by immersion in mercury.
The following table shows the results of these experiments; the signi-
fication of the numbers 1, 2, 3, 4 will be found in my former Memoir.
OF WIRES FOR ELECTRICITY.. 319
Angles of deviation.
Calculated
Differences.
o
any wire< the experiment...| 85°3 i x
interposed | at its end 85°7| 89°3| 89°8| 88°55 88°31 | 88°52} +4+-0°21
With interposed wire 7 feet long 52°3) 52°4| 54°5| 53°4| 53°15] 53°21)/+0-06
———_—- lh 38°2 38°1) 39°6| 39°1} 38°75
21 29°7| 29°8| 31°5| 30°6| 30°40
— 28 24°3) 24 : *8| 24°87 | 2493/4 0:06
35 20°9} 20°6| 22:0| 20°9] 21°10} 21-21/+-0°11
Without : at the beginning of
The calculation of the values of the 7th column was performed in the
following manner. I took for the unit of the conducting resistance the
length of 1 English foot of the wire, from which the five pieces had been
cut, and represented the unknown strength of the current correspond-
ing to this resistance by py: and I assumed z for the equally unknown
conducting resistances of the wire of the multiplier and the electromotive
spiral taken together. Assuming the hypothesis that the resistances
of the wires are proportional to their lengths, and designating the devia-
tions observed in the above table for the resistances x,x+7,x% 4+ 14,
&e. by a, a, 47 4,414 &c. we shall find, by means of the formule
given in the former Memoir, the following equations :
=p* sin (@ a, )
A ,
+7? (34.47)
A =—=n°sj I
| SE iam ee Oc 1's NR
Dividing the rest of the equations by the first, and designating the values
sin (}a,,), sin (3a, +7) sin ($a, + 14), &c. for brevity sake by a,a',
a'', &c. we shall obtain
w=; and therefore ax — y =0
a+ 7=% adex—y+7a'=0 (A)
e+lt=% — ale—yt+l4a'=0.
&e,
$20 LENZ ON. THE VARIOUS CONDUCTING) POWERS
Now by solving these equations with regard to a and y according to
the method of the least squares, we shall obtain
x = 12'5386 y = 8°7508
If we substitute these values in the equations( A) and ascertain from them
the values a, a’, a'', or sin(4.a,), sin (4 Oy 4 7)» sin (4.4, rs 14)» we shall
obtain the angles .a,, 4.4, +7 $4, 41 and multiplying them by 2
we shall find out the angles of the seventh column.
The very slight differences of the values indicated in the 8th column
from those observed, convince us that the hypothesis which is the base
of the calculation is correct, and that therefore the resistances of the
wires are in a direct ratio, and their conductibilities in an inverse ratio
to their lengths. :
I performed a short time previously another series of experiments,
and diminished the electromotive spiral by two coils without shorten-
ing its length or altering its resistance. The results are contained in
the following table:
Angles of Deviation.
1
lf 2. 4, |Average.
3
at the beginning of the} a lee a
Without any experiment..........0 77°9| 81°1| 81°7|81°7 | 80°6
wire interposed . 77°3| 80°2| 81:3 oe ‘
at the end of it. ... { 77.3! 80-2 81-2798 79°69
With interposed wire 7 feet long ...... 47°6| 48°7| 49°9/49°5 | 48°92
14. ——_. ....., 34°8| 35°0) 36°6|3.5°8 | 35°55
== 21 ——— ...... 27°4| 27°7| 28°4/28°6 | 28°02
——_———_——— _ 28 ——__ ...... 22:5) 23°3| 23°4'22'8 | 23°00
——_—_——. 35 ———_. ...... 19*4) 18°8) 19°8|19°3 | 19°32
We perceive by the deviations which occurred at the beginning and
end of the series of experiments, performed without inserting the wires
between the spiral and the wire of the multiplier, that the power of the
magnet was a little diminished during the experiment. This induced
me, therefore, before the calculation of the results of the experiment,
to make a slight correction of the angles of deviation, founded on the
principle that the diminution of power was proportional to the time,
and that the observations with various lengths of wire followed
each other at equal intervals, which was nearly the case. I repre-
sented the angle of deviation when no wires were interposed at the
beginning of the experiment by a,, and at the end of it by a) and
found
sin 5 @y = (1 + m)sin (Fa(2)) 3
OF WIRES FOR ELECTRICITY. 321
consequently
_ 2° cos 3 (ax + x) sind (ax — a(z)),
sin $ Q(x)
Having in this manner found out m for the end of the series of experi-
ments, the correction of other angles became easy by multiplying the
sines of their halves respectively by
(+8) (at) (+See
In this manner the angles of deviation of the 2nd column of the follow-
ing table are calculated.
mm
Angles of Deviation
Difference.
observed. | calculated.
Without any interposed wires 80°60 80°53
With interposed wires 7 feet long} 48-96 49°05
——_———_— —— 35°60 35°62
28:09 | 28°03
23°07 23°12
19°73 19°69
The 3rd column is calculated entirely according to the above for-
mulz (A). The smallness of the differences of the 4th column proves
likewise the correctness of the proportionality of the conducting resist-
ances to the lengths of the wires. The following values were obtained
for x and y:
x = 12°583 y = 8133.
x was according to the previous calculation = 12°539, the difference
therefore of the resistances was only = 0:044 of an English foot: y con-
siderably differed from the preceding value, the electromotive spiral
having here two coils less.
Passing now to experiments which are to indicate the proportion of the
conductibility with reference to the diameters of the wires, I must pre-
viously observe, that the difficulty of obtaining accurately agreeing re-
sults is here far greater than in making experiments with wires of the
same diameter though of different lengths. The reason of this is the
difficulty of obtaining wires of different diameters quite equal in every
other quality. Should we, for instance, take copper wires of different
thickness as they are sold in shops, we should then obtain entirely dif-
ferent results. I once obtained two copper wires, of which that having
the greater diameter was a worse conductor than that which was thinner,
contrary to all previous approved experiments, all observers agreeing
322 LENZ ON THE VARIOUS CONDUCTING POWERS
that thick conductors conduct electricity better than thin ones. How
far the conductibility of metals is altered by even a very slight mixture
of foreign substances, is proved by the experiments of Pouillet with
wires made of different alloys of silver with copper, and gold with silver.
These prove that their conductibility is far below that of pure unalloyed
metals. Thus, for instance, the conductibility of fine gold = 84°41,
that of the 18-carat gold = 14°77, whilst the silver with which the gold
is alloyed is a much better conductor than fine gold itself.
In order to avoid the inequality of the purity of the copper, I pro-
cured the wires myself by cutting a thick piece of copper into smaller
pieces, and drawing it afterwards to different thicknesses: but the thinner
wires become thus by drawing somewhat more dense than the thicker
ones, which produces always a difference in the substance. I endea-
voured to remedy this evil by making the wires red hot before covering
them with silk ; but the greater or less degree of heat may perhaps have
some influence.
From these observation it follows, that so close an agreement cannot
be expected from the following experiments as from those made for
the purpose of ascertaining the influence of the length of wires on their
conductibility ; this agreement will, however, be sufficiently close to
remove every doubt with respect to the correctness of the law to be
established.
The wires employed were, as has already been said, wrought all
out of the same piece of thick wire, and drawn through the holes
1, 6, 11, 18, 24, 30, with which numbers they are also marked in the
table ; they were all heated to redness and overspun with silk, and were
successively inserted between the electromotive spiral and the wire of
the multiplier, and the deviation determined in the same manner as in
the previous experiments. In order to obtain the proportion of the
sections of the wires, I took 2 feet of each and weighed them before
they were covered with silk. The weight is proportional to the section,
and is as follows:
Weight of 2 feet of wire No. 1 ...... 7°7370 grammes.
MG GIL. 2. 50250
5. Cs Oe 32408
ING. 18"...... 1°4783
Nov24 ,..... 0°7750
NorSO™... 2. 0°3616.
It is not of much importance to know the absolute thickness of the
wires, but it may be easily deduced from this, that the diameter of the
wire No. 1 was nearly 0°046 Engl. line.
The experiments were thus performed : I observed first the deviation
without any wire being interposed, then with the interposition of No.1, 2,
OF WIRES FOR ELECTRICITY. 323
to 6, and back from 6, 5, to 1, and finally without any interposition. Ta-
king afterwards the average of observations ofthe same kind, the influence
which the loss of the power of the magnet might have exercised has been
thus entirely removed. The length of all the wires collectively was
= 16 feet Engl. The experiments are stated in the following table :
Angles of Deviation.
———— ee erare:
Without any wire interposed ... | 90°7| 93-6) 94°9| 95°3
16 feet of wire No. 1 interposed | 64:2) 66°3| 67°0| 67-4:
No. 6 ————— | 55°0} 57°1) 57°9] 58°5
No. 1 1 ——-——— | 44-9] 4'7°4| 47°6] 48°6
No. 18 ————— | 29°6} 31°5} 312) 32°0
No. 24 ——_—— | 19:0} 19°8} 19°6] 19-7
No. 30 ————— | 9°3} 11°4) 10°8] 11°5
No. 30 —————|_ 96 11°6] 11-0} 11-7
No. 24 ——-—— | 18:1] 20:3] 19:0) 20°2
No. 18 ——-—— | 29°4| 31°5| 31:3} 31°8
No. 11 ————— | 4.5°2| 4:7°5| 48:0] 48°6
No. 6 ———— | 55:4) 55:3) 58°0| 57°3
No. 1 — | 64°9} 65°4| 67-0} 67°7
Without any interposition 91°3| 91-9) 93°6| 94°7| 92°87
Taking the average of observations made in similar circumstances,
the values will be
Angles of Deviation
Difference;
observed. | calculated.
Without any wire interposed 93°24. 91°53
With the wire No. 1 66°24 65°84
ee No. 6 56°94 57-52
No. 11 47°16 48°09
No. 18 31°04 31°22
— No. 24 19°46 19°78
No. 30 10°86 10°56
The calculation was performed in the following manner :
_ Let the strength of the current when it passes through a wire of
the’ length used in these experiments (that is to say 16 feet), and of
such a thickness that 2 feet of it weigh 1 gramme, be = py (where y is
an unknown quantity to be determined by the experiment) ; and let the
length of the wire of the multiplier, together with the length of the
electromotive spiral reduced to the same thickness as the wire be, = x.
324 LENZ ON THE CONDUCTIBILITY OF WIRES FOR ELECTRICITY.
Supposing therefore that the conductibility is in a direct, and the con-
ducting resistance in an inverse ratio to the thickness of the wires, and
that a, a', a!' represent the angles of deviation, we have the following
equations :
A —
rite 1
A :
= =p sin (4a)
- A = p' sin (Za')
pia
7;
A
w+
7 =P sin($ a!’
5,025
&e.
Dividing the first equation by all the following seven, and putting
for brevity sake
. a! q!!
sin (La') = a’, &c. and ame 8, oer 3", &e.,
we obtain the following equations :
ax—y =10)
: x—y+e =0
a'x—y+o' =0
a"e—y+ uu
&e.
From these equations were determined, accanlgy to the method of
the least squares, the values
a = 0°40679 y = 029146.
and finally the values a, a’, a’, by substituting He foreegng Mik id in
the equations, and developing a, a’, a”....or sin 4a, sin $a’, sin} a”,
&e. These values are placed in the Shave table under the head « tals
culated Deviations.” The differences between these and the observe
angles of deviation, contained in the last column, are greater th
those of the preceding observations, and even greater than can be as
cribed to mere errors of observation ; but the reasons of this have been
.already explained. Their agreement, however, is in every case grea‘
enough to remove every doubt with respect to the correctness of th
hypothesis (which is the basis of the calculation), that the conductibili.
of wires is in a direct ratio to their sections.
ARTICLE XIV.
Memoir on the Polarization of Heat ; by Macepo1ne
MELLoNnI.
From the Annales de Chimie et de Physique, vol.1xi., April, 1836.
Asovut twenty-five years since, M. Berard, of Montpellier, an-
nounced that heat was capable of undergoing double refraction and
polarization*. His experiments, which were repeated in presence of
Berthollet and Dulong, were universally admitted by philosophers until
towards the close of 1829, when doubts as to the certainty of the con-
clusions which had been deduced from them were raised by Mr. Powell,
in his account of some unsuccessful experiments of the same kind,
made with an apparatus similar to that employed by Berard for the
purpose of polarizing heat by reflection+. In 1834, I found that calo-
rific rays, in their passage through plates of tourmaline which com-
pletely polarized light, gave no apparent sign of polarization{. Nobili,
whose recent death science has so much cause to deplore, arrived some
time subsequently at the same result. He attempted also to polarize
heat by reflexion, but obtained no satisfactory indication§. At last
Mr. Forbes observed, about the close of 1834, signs of polarization
_ in the heat transmitted through tourmalines and small piles of mica
_ placed at a proper inclination to the incident rays. In these experi-
ments, the greatest proportion of polarized heat was given by a system
of piles composed of plates of mica, and amounted to 34°, when
3 _ Mr. Forbes operated on the calorific rays of a spiral of platina kept in
_astate of versaned by the flame of alcohol; but this proportion
. was reduced to +;% or +45 when the same piles were brought to act on
- the caloric issuing oben a vessel heated by mercury or by water in a
_ state of ebullition ||.
_ ‘The different temperatures of the calorific rays are to radiant heat
what the different colours of the luminous rays are to light. Now, it
is known that the latter are all equally polarized by the action of the
same polarizing system. The experiments of Mr. Forbes would seem
* Mémoires de Physique et de Chimie de la Société d’ Arcueil, tom. iii. page 5.
P + Edinburgh Journal of Science, S.S. vol. vi. and x.
t Annales de Chimie et de Physique, tom. lv. page 375.
_ § Bibliotheque Universelle de Geneve, tom. vii. p. 1.
|| Transactions of the Royal Society of Edinburgh, vol. xiii. part. 1. p. 152:
’
7 Vor. I.—Parrt II. Z
326 M. MELLONI ON THE POLARIZATION OF HEAT.
then to indicate a very marked difference in this respect between the
laws of polarization of heat and those of light.
Are calorific rays really susceptible of polarization? Are they all
equally and completely so? Such are the questions which I propose
to consider in this memoir, endeavouring at the same time to account
for the contradictions (more or less obvious) exhibited by the results
at which the different observers just quoted have arrived.
The instrument invariably employed by me in these researches is an
excellent thermomultiplier constructed by M. Gourgon. In order to
give the reader an idea of its great sensibility, it will be sufficient to
state that the natural heat of the hand placed near one of the extre-
mities of the tubes with which the pile is furnished, will impel the
index to its maximum of deviation when the temperature of the atmo-
sphere is below 15°. The pile, which has its two terminating faces
perfectly symmetrical, consists of thirty pairs (bismuth and antimony,)
‘formed into a bundle measuring eight lines in the diameter of its trans-
verse section and ten lines in length*: the tubes or cylindrical appen-
dages which envelop its two faces are nearly of the same breadth as
the pile, but three times as long. ‘The astatic system of the galvano-
meter, which consists of two needles very powerfully magnetized, mea-
suring O™"-47 in diameter and 53™ in length, makes but two
oscillations a minute. If, however, after the communication with the
pile has been interrupted, the system is turned aside 35 or 40 degrees
* The symmetry, or rather the equality of the two opposite sides of the pile is
a condition indispensably necessary, in order to render the observations inde-
pendent of the slight changes of temperature that may take place in the sur-
rounding air during the experiments. In fact, if the bars of bismuth and anti-
mony were stronger, or their solderings less extended, on either of the two
sides than on the other, the heating or cooling of the air would no longer be
communicated (by contact) with equal promptitude to them both, and the ex-
tremities which presented the least mass in proportion to the extent of the sol-
dering would be heated or cooled more rapidly than the opposite ends. This
circumstance would produce a current which, by its intervention, would disturb
the calorific effect of the rays that are received by the anterior face of the pile
Hence it is obvious that with piles having their opposite faces unequal, exac.
measures of the calorific radiations are attainable only in that case in which the
temperature of the atmosphere undergoes no sensible variation. If it varies,
the results will be less accurate in proportion to the greater rapidity of the va-
riation and the greater length of time required to make the experiments. The
piles [a rayons et a biseau,] described by Nobili in the 57th volume of the
Bibliotheque Universelle have not their opposite faces symmetrical; they are
therefore not free from the defect just mentioned. The author himself admits
it in the 8th page of the same volume, where, after having given the different
rates of calorific transmission obtained in a series of bodies by means of his pile,
he adds, that the conditions of temperature which could affect the results, and
consequently change them by their variations, are the following: Ist, the tem -
perature of the source ; 2nd, that of the bodies themselves, and particularly th .
of the surrounding air.
M. MELLONI ON THE POLARIZATION OF HEAT. 327
by means of a magnet or a piece of soft iron held at a proper distance,
and is then left to itself, it resumes its natural position of equilibrium,
and stands perfectly steady at the zero of the scale after the lapse of
three or four minutes. This quick return to a state of rest is the effect
of the neutralizing action of the copper disc placed for that purpose
beneath the divided circle; for, since the beautiful discovery of
M. Arago, it is well known that the action of this disc diminishes the
amplitude without changing the time of the oscillations ; so that the
oscillatory motion of the needles about the point of equilibrium is con-
siderably reduced in duration, though the forces by which it is pro-
duced have undergone no change of intensity. The time required for
the return is still less when the galvanometer is left in communication
with the pile, and the deviation of 35° or 40° is produced by the calo-
rific radiation ; for then about two minutes are sufficient to cause the
index to resume its stationary position at zero after the interception of
the radiation. In this case, the heat still remaining for some time on
that face of the pile which has been exposed to the radiation may be
said to sustain the needles in their fall, and prevent them from oscil-
lating to the opposite side of zero, at which they arrive almost exactly
within the time required for the re-establishment of the equilibrium of
temperature between the two faces of the pile.
But in order to observe the latter periods with the utmost possible
exactness, it was necessary to secure the pile from the differently heated
eurrents of air which come successively into contact with each of the
two appendages. These differences of temperature, though exceedingly
_ small and imperceptible with the best common thermoscopes, are suffi-
cient to produce, in the instrument used by me, such deviations to the
right and left as occasionally amount to some degrees, and interfere
_ most inconveniently with the action of the calorific rays. To prevent
_ this inconvenience, I placed the pile and its stand in a large metallic
_ receptacle or case resembling a trough with the bottom turned up-
wards, and measuring eighteen inches in length by eight in breadth.
_ The sides of this trough (which are double) are of such a height that the
bottom may not touch the most elevated parts of the mounting of the
_ pile; and the interval between the interior and exterior side is filled
with cotton at the lower edge, in order as much as possible to prevent
_ the entrance of the external air. The wires which establish the coimn-
_ munication between the pile and the galvanometer are passed under
| the edges, which for this purpose are grooved at one of the extremities
_ of the case.
In one of the shorter sides there is, at the same elevation as the pile,
bad circular aperture about an inch in diameter; but this may be reduced
_ to any degree of minuteness by sliding into an exterior frame a plate
i A
% Z
hs
:
328 M. MELLONI ON THE POLARIZATION OF HEAT.
with a smaller aperture. A longitudinal opening made from end to
end in the superior surface of the case enables us to see whether the
axis of the pile is placed in the direction of the radiation. By gently.
moving the case in one direction or another, the circular aperture is
brought into the proper position relatively to the pile, which continues
to occupy the same part of the table on which it has been placed.
By means of this double ease, the air surrounding the thermoscopic
body is kept perfectly calm. At least the motions produced in it by.
its slow variations of temperature react upon the two sides of the pile
with such uniformity that the index of the thermomultiplier stands
exactly at the zero of the scale, and when a specific deviation has been
produced by the influence of an exterior calorific radiation, returns to
that point in some minutes after the communication of the rays has
been intercepted by means of a metallic screen.
Those who are in the habit of frequently using astatiec galvanometers
must have remarked, no doubt, that these instruments, whatever may
be the solidity of the table on which they stand, suffer, in consequence
of the observer's changing his place or of the passing of vehicles in the
neighbourhood, a slight tremulous motion, which, being transmitted to
the suspension thread and to the needles, causes them to oscillate like
a pendulum for a period of greater or less duration. For the purpose
of preventing these eccentric oscillations, which prove so embarrassing
in very delicate observations, we have but to fix the instrument on the
marble slab of a chimney or any other horizontal plane firmly fastened
to one of the solid walls of the building in which we are carrying on
our operations. The wire will then always preserve its vertical direc-
tion; the needles will be no longer susceptible of any other than hori-
zontal movements ; and the index will deviate with so much regularity
under the action of the electric currents, that, upon seeing it, one might
fancy that, instead of being suspended by a thread, it moves on a
pivot.
In the particular instance under consideration, the deviation com-
mences as soon as the rays of the calorific source, at a constant tempe-
rature, have reached the anterior face of the pile through the aperture
in the receptacle. The motion of the needles is at first very slow, but
becomes gradually accelerated, and, having attained its maximum of ve-
locity, is again retarded by imperceptible gradations, until at last it
ceases altogether: the needles then return gently towards zero, de-
scribe an arc of some degrees, resume the direction of the first motion,
and, after having made three or four oscillations successively decreasing
in extent, stand still and take a fixed position. Now this steady devi-
ation is always a little inferior to the deviation indicated by the needles
at their first departure from the point of repose. The difference varies
M. MELLONI ON THE POLARIZATION OF HEAT. 829
with the amplitude of the primitive deviation, which we shall call the
are of impulsion ; and we perceive that, the slowness of the motion at
the extremity of this are enabling us to observe it with considerable
exactness, it may be afterwards compared with the corresponding
steady indication; which comparison may be easily extended to all
points of the circuit if we vary the intensity of the calorific radiation by
making the requisite change in the distance between the source and the
pile. Moreover, the fixed deviations being given, the corresponding
forces may always be determined by experiment*. We are therefore
in possession of all the elements necessary for the construction of such
a table as may immediately show the ratios of the forces according to
the arcs of impulsion. The forces, as we know, represent the tempe-
ratures+ : thus, by means of our table, the relative intensities of two ca-
* For the description of the methods, see Bibliotheque Universelle, tom. lv.
page9; and Mémoires de l’ Académie des Sciences, tom. xiv. p. 445 and 446.
+ M. Becquerel had shown in 1826 (Ann. de Chimie et de Physique, tom.
XXxi. page 371) that the intensities of the thermoelectric currents of copper,
platina, and other metals, are proportional to the temperatures through the
whole extent of the thermometric scale. Now, the currents which produce the
greatest possible deviation in the common thermomultipliers are derived from a
heat, which scarcely rises to a few degrees, acting on one of their faces: the
proportionality between the forces of magnetic deviation and the temperatures
was therefore already established by experiment when I was commencing my
inquiries into the nature of radiant heat. Hence it is that I have admitted
_ that proportionality, as a known fact, in the preceding Memoirs on this subject.
Nevertheless, as M. Becquerel had not operated directly on the metals which
enter into the composition of the pile, the committee appointed by the Aca-
demy of Sciences to examine my experiments on heat, manifested a desire that
_ the proportionality of the forces to the temperatures in the thermomultiplier
itself should be placed beyond the reach of doubt by some special experiments.
- With this view I procured a thermoelectric pile of four very minute elements (bis-
_muth and antimony) bent like a siphon, in order that each of the two termina-
_ ting faces might be introduced into a separate recipient and different tempe-
ratures imparted to them by the contact of heated liquids. The extremities of
the two last elements stood out of the vessels into which the ends of the curved
electric bundle had been plunged, and communicated with the galvanometer by
_ two copper wires. But as a difference of some degrees was sufficient to drive
the magnetic needles to the extremity of the scale, I placed in the electric
circuit a very fine iron wire of several feet in length, The current then be-
came so weak that a variation of a centigrade degree of temperature between
_ the two faces produced in the galvanometer no more than a deviation of about
one degree. Matters being now in this state, water more or less heated was
_ successively introduced into one of the vessels and thawing ice into the other.
The second face was thus kept constantly at zero, while the first tovk, in suc-
cession, the different temperatures of the water, which were determined by a
ry delicate mercurial thermometer. The numbers of the degrees indicated
1 by the thermometer plunged in the hot water were found exactly proportional
to the corresponding electric forces or intensities indicated by the deviations of
Hie galvanometer. The experiment was now varied in order to obtain a nearer
| approach to the circumstances in which the thermamultiplier is commonly em-
330 M. MELLONI ON THE POLARIZATION OF HEAT,
lorific radiations will be obtained by the mere inspection of the two ares
of impulsion which they successively describe on the galvanometer,
The time required by the needles to arrive at the extremity of these
arcs is from ten to twelve seconds : they do not remain steady until after
an interval of from eighty to a hundred seconds. Now the sources of
ployed. That branch of the pile which was surrounded with ice was carefully
dried and then left exposed to the free action of the air, the other remaining
still plunged in the water successively raised to different temperatures. In this
instance the intensities of the electric currents became proportional to the ex-
cess of the temperature of the water in the vessel over that of the surrounding
air; for the conducting powers of the bismuth and the antimony in minute
bars are so very feeble that the heat communicated by the water to one of the
faces can scarcely reach the other in any such quantity as to excite in it an ap-
preciable elevation of temperature.
Although these experiments were repeated with equal success in different at-
mospheric temperatures, I did not yet consider them perfectly satisfactory. In
fact, the pile received by contact the differences of temperature which produce
the electric currents, and in the ordinary mode of using the thermomultiplier
the differences of temperature arise from the action of radiation. It became
necessary therefore to demonstrate, by means of radiant heat, that which had
been proved by means of heat communicated by contact. After the preceding
experiments, the only question now remaining was this: “* Whether calorific
rays produce in thermoscopic substances equal dilatations, when they excite in the
thermomultinlier equal currents of electricity, whatever may be the intensities
and origin of those rays or the modifications they may have undergone in conse-
quence of transmission, reflection, or refraction.’’ In order to ascertain how far
this question might be correctly answered in the affirmative, I engaged Mr.
Bunten to construct an air thermoscope having its reservoirs made of thin cop-
per, and its dimensions and mounting, as nearly as possible, the same as those
of the pile of the thermomultiplier. The communications between the reser-
voirs were established by means of a glass tube, which at first deseended very
obliquely on each side to the horizon, and then took a horizontal direction in
the intermediate part containing the liquid index: the extreme faces inclosed
in the metallic appendages were, as well as the interior of these appendages,
covered with lamp-black: the instrument was lastly furnished with a stem of
the same thickness as that of the pile, so that the same stand might serve for
either. 1 now opened the two tubes of the pile of the thermomultiplier, and
brought the radiation of a different source to bear on each of its faces; for in-
stance, that of the Locatelli on the one, and that of copper heated to 400° on
the other; I then placed the weaker of the two sources more or less near until
the index of the galvanometer stood fixed at zero. After having thus obtained
two opposite calorific actions producing electric currents of the same force, I
removed the pile and put the air thermoscope in its place. The same immobi-
lity was exhibited by the Jiquid index. This delicate experiment was repeated
with the greatest care on different species of radiations; at first on those that
were direct and rendered more or less intense by a suitable approximation of
the sources; then on those that were transmitted through plates of different
kinds or concentrated by means of lenses; and lastly upon the heat given back
by reflectors. The result was always the same ; namely, that all calorific radia-
tions whatsoever, if they excite in the pile equal currents of electricity or equal
electromagnetic actions, will also produce equal dilatations or temperatures in
the air thermoscope. (For further details see the report of M. Biot in the x1yth
volume of Mémoires de ’ Académie des Sciences.)
Nea: i mS
sociale 20th
’M. MELLONI ON THE POLARIZATION OF HEAT. 331
_.eat, however constant, are subject to slight changes in their physical
vate, which cause variations of the same order in the temperature ; so
iat it is always desirable to abridge the time that elapses between two
- omparative experiments. The table which I have just mentioned will
herefore render the observations more prompt and more exact than
hey would be if we directly observed the fixed deviations. I have ac-
‘ordingly always employed this method in the course of this Memoir,
und the force corresponding to each result will be found beside the
»bserved arc of impulsion. It is almost unnecessary to add, that the
force to which all the others are referred is that which causes the
needles to describe the first degree of the scale.
Having by various contrivances provided myself with a thermoscopic
instrument of very great sensibility, promptitude, and certainty in its
indications, I proceeded to the experiments on polarization by com-
mencing with tourmalines.
The great difficulty that first presents itself in studying the polariza-
tion of heat by tourmalines, is the feeble calorific transmission of these
substances ; a circumstance which, together with the usual smallness of
iheir dimensions, renders the intensity of the emergent rays extremely
feeble, and scarcely appreciable with the most delicate thermomultipliers.
Hence it becomes necessary to bring the source very close to the sy-
stem of the tourmalines, in order that they may receive the greatest pos-
-ible quantity of the calorific rays. But this extreme proximity of the
source heats the tourmalines in a sensible degree, causes them to ra-
liate on the pile, and, by the effect of this secondary heat, disturbs the
sction of the rays immediately transmitted by the system.
The quantity of incident heat might indeed be augmented, without a
change in the ordinary distance of the source, by concentrating it on
__ the tourmalines by means of a rock-salt lens. But then the plates be-
come still more heated, and the pile must necessarily be placed at a
great distance behind the tourmalines, in order to withdraw it from the
disturbing force of this second calorific source. Now the distance of
_ the pile from the tourmalines cannot be thus increased without sub-
jecting us again to that very inconvenience of an over-feeble radiation,
which it is our purpose to avoid ; for the rays, after having crossed each
_ other in the focus, undergo a considerable divergence and a rapid de-
erease of intensity as they proceed to a distance from the plates. In
order to avoid both these inconveniences, and to obtain a calorific
stream consisting solely of the rays directly transmitted by the tourma-
lines and yet powerfully acting on the thermoscope, I first receive the
pencil of calorific rays on a large rock-salt lens, after having made them
parallel by means of a reflector. The concentrated heat reaches the
tourmalines ; a great portion of it is absorbed, and converted into ordi-
332 M. MELLONI ON THE POLARIZATION OF HEAT.
nary heat; the rest pursues its way without losing its radiating state, is
afterwards dispersed, and falls upon a second lens with a shorter focus,
placed beyond the first at a distance precisely equal to its own principal
focal distance. The rays received by this second lens in a state of di-
vergence are parallel to each other when they leave it; and form a pencil
of condensed heat, which enters the thermoscopic case, and finally
reaches the pile, which stands at a suitable distance from the aperture.
The section of the pencil being a little less than that of the pile, all its
parts concur in the production of the thermoscopic effect, and thus we
lose the calorific effect of none of the rays that issue from the polar-
izing system.
It is very important to observe, that the common centre of the two
superposed plates of tourmaline is not placed exactly in the common
focus of the two conjugate lenses, but a little nearer to the second, in
order that the portion of heat absorbed by those plates, and radiated on
the second lens, may be necessarily refracted in diverging rays whose
action becomes weaker, and is completely destroyed at a short distance,
without influencing the thermoscopic body, which is thus affected only
by the heat arising from direct transmission. That this condition is
actually fulfilled may be ascertained by blackening the tourmalines, or
by substituting for them any other plates well covered with lampblack ;
for the index of the galvanometer reassumes its natural position in equi-
librio, and retains it whether the communication with the calorific
source be established or intercepted.
By this simple contrivance we cause very minute plates of tourmaline
to transmit a bundle of rays almost as broad as the surface of the first
lens, and then bring a// the emergent rays, and these alone, pure, and
unmixed with even the smallest particle of the caloric derived from the
heating of the plates, to produce their effect on the thermosecope.
Combining a lens of two inches and a half in diameter and three
inches in the focus, with a lens of fourteen lines, I obtain a quantity of
rays emerging from the tourmalines, such as, in several instances, pro-
duces a deviation of the needles, amounting to between 60° and 80°, at
the distance of a metre from the small flame of a Locatelli lamp fur-
nished with a reflector. This energetic action, though necessary for
the experiments which I had in view, is then too great; but there
is an easy way of reducing it as much as we wish: we have only to
render the rays more or less divergent by a proper approximation of the
lenses.
The plates of tourmaline are adjusted to the central part of two pa-
rallel covers of cork filling the interior of a round box, which is suffi-
ciently shallow, has a small circular aperture at the centre, and is sup-
ported at the proper height by a metallic screen with a similar aperture.
Sige
se!
ARG TINS GELS
M- MELLONI ON THE POLARIZATION OF HEAT. 333
One of the plates is fixed, the other is moveable together with that half
of the box in which it is contained. Marks traced on their edges enable
us to distinguish with ease the two principal positions of the axes of
erystallization.
I exhibit here in a single table the results which I obtained by ope-
rating on nine pairs of tourmalines borrowed from different individuals.
All these pairs polarized luminous rays almost completely ; that is to say,
that to a person looking at the flame of a wax taper through each of
these systems, it appeared sufficiently vivid and brilliant, so long as the
axes were parallel; but the image became nearly extinct when the axes
were perpendicular.
Tas_e I.
Source of Heat, the flame of a Locatelli lamp.
Calorific transmissions
in the position of the axes.
Colour
of — =a Soe icwey
each pair Parallel. Perpendicular.
of
: SS
tourmalines. ieee Nea
ofimpul-| Forces. |ofimpul-
sion. sion.
———- ——____
Numbers indicating the order.
the axes are parallel.
Indices of polarization in
tity of heat transmitted when
hundredth p:
Deep ereenry iy. fk 90° 27°50 | 29°78
Bluish green : 26°51 | 28°22
Blue green , 29°40 | 30°11
Yellowish green : 28°51 | 29:32
Yellowish green : 30°18 | 30°01
Yellow green : 29°07 | 29°11
Reddish brown ‘ 26°62 | 25°32
Muddy violet i 27°67 | 25°45
Pale yellow...............] 31°27 | 28°37 | 25°60
&
~I
—
OBINADAH Lowe
After what we have already stated, the numbers in the four columns
which precede the last require no explanation. I have therefore only
to observe, that each number under the head “ares of impulsion” re-
presents the mean of several observations, made alternately in the paral-
lel and in the perpendicular positions of the axes; that is to say, that
the are described in consequence of the transmission through the plates
with their axes parallel was first observed, and then the are described
in consequence of the transmission through the same tourmalines with
334, M. MELLONI ON THE POLARIZATION OF HEAT.
their axes perpendicular. The observations on this pair, as well as
‘those on each of the remaining pairs in each of the two positions, were
several times repeated. This method affords a compensation for any
possible errors of observation, as well as for those that may arise from
the slight variations of intensity to which the radiation of the calorific
source is liable, and which, owing to the perfection of the apparatus,
do not, even in their extreme limits, exceed a fiftieth part of the mean
value. As to the last column, we mean by the index of polarization
that portion of heat which disappears when the axes are perpendicular,
as compared with the quantity transmitted by the system when the axes
are parallel. Thus, the first pair of tourmalines transmits 27°50 when
the axes are parallel, and 26°48 when they are perpendicular: the dif-
ference between these two numbers, which is 1°02, represents the quan-
tity of heat that has disappeared in consequence of the axes being
crossed. In order to obtain the index of calorific polarization in this
pair of tourmalines, expressed in hundredth parts of the quantity trans-
mitted when the axes are parallel, we must evidently resort to the fol-
lowing proportion, 26°48 : 1:02 :: 100: a, which gives x = 3°71.
The column of the indices shows that the proportion of heat polarized
varies with the qualities of the tourmalines which compose each pair of
plates employed. These variations, already numerous enough, if we
consider the number of pairs submitted to experiment, led me to
think that they might be found yet more numerous with other plates,
and that they depended very probably on the diathermancy of each
species of tourmaline, that is, that they arose from these different spe-
cies of the same mineral substance being each permeable to a. differ-
ently constituted calorific stream. In order to verify this conjecture,
I placed on the apparatus that pair which polarized the greatest pro-
portion of heat ; and, after having made such arrangements as to render
the quantity of heat transmitted as great as possible, I successively in-
terposed, in the passage of the rays concentrated by the first lens, plates
of different substances. The heat which fell on the tourmalines was
thus more or less diminished by the partial absorption of the interposed
screen; but I took care to make a suitable change in the reciprocal di-
stance of the two rock-salt lenses, in order to obtain an almost constant
calorific transmission through these different systems when the axes of
the two tourmalines were parallel.
The results of this second series of experiments, performed on rays
emanating from the same source, and with the same pair of tourmalines,
are registered in the following table:
‘M. MELLONI ON THE POLARIZATION OF HEAT. 335
Tasre II. Source of Heat, flame of a Locatelli lamp.
Calorific transmissions
through each interposed layer, and
the same pair of tourmalines
(No. 9 of the preceding table)
in the position of the axes.
err ITE ERE FR cae cs dalek de,
Parallel. Perpendicular.
NAMES
of the
substances interposed
before the introduction
of the
calorific radiation
into the
tourmalines.
SE oS A,
Arcs Ares
ofimpul-| Forces, jofimpul-| Forces.
i sion,
Thickness of the layers
formed by these substances,
reckoned in millimetres.
plates when the axes of the tourma-
mitted by the system of the three
lines are parallel.
Indices of polarization in hundredth
parts of the quantity of heat trans-
1737 13°47 | 11°76
17°93 rDo,| Vo O4e) Ta LS
coloured (red) ...| 1° 16°75 | 14 13°04} 11°40
rang) ‘ 17°21 ‘ 13°31} 11°66
yellow 17°83 : 13°84 | 12:07
-(blue)...| 1°83 | 17:59 | 15°24 | 13-66| 11-92
(indigo) : 17°29 | 14° 13°44| 11°74
—_________(violet) | 1°81] 1681] 14°59 | 1302] 11-39
Glass coloured a, Pl
PETS) ecncevecsss ancl’ O" 16°99 | 14° 15°95 | 13°86
Ditto : 17°32 i 16°85 | 14°62
Glass (opake black) ...} 0° 17°85)| 15° 16°76 | 14°55
Ditto a 17:80 ¢ 17°52 | 15°19
Sulphate of barytes ...| 2° 17710 ; 13°18 | 11°52
———— of lime ........| 2° 16°95 : 10°54} 9°18
Oil of colza y 16°97 10°40} 9:05
Tartrate of Het and
soda . : : 17°39 ? 9°49
Water saturated with
) : 17-49 | 15: 5°78
bo
—
<e)
—_
17°56 : 5°81
tartaric acid : 17°3S : 5°76
MLOte teste cesses el) 07 16°96 : 10°76
Water (distilled). F 16°77 : 5°54
Ditto E 17°20 : 10°91
: Amber ainagé ; 17-23 : 8°35
a Alum . Bes oie 16°98 G 0°58
: * The physical characters of this species of glass, which acts so differently from
the other species of coloured glass in all the phenomena of calorific absorption,
are, 1st, its intercepting almost totally the rays which pass through alum ; 2nd
its entirely absorbing the red rays of the solar spectrum. I have already stated
that their coloration is produced almost entirely by the oxide of Bam
+ The temperature of these different saturated solutions was about 15
336 M. MELLONI ON THE POLARIZATION OF HEAT.
We were already aware that the rays immediately transmitted through
bodies differing in their nature pass in very different proportions through
a given plate of a diathermanous substance*: we were also aware that
those rays are differently absorbed by the surfaces of certain opake
bodies+. To these distinctive characteristics we are now enabled to add,
that they undergo in the same system of tourmalines an apparent vari-
able polarization.
We see, in fact, that of every hundred rays of heat transmitted by
the tourmalines when they are placed with their axes parallel, about 22
are made to disappear by merely crossing the axes. This proportion suf-
fers no very decided change in the rays transmitted by the common, the
red, the orange, the yellow, the blue, the indigo, and the violet glass ;
but is reduced to +45 or +s When we employ green or opake-black
glass ; and when we employ sulphate of lime, yellow amber, water either
pure or saturated with salts, and alum, the quantity of heat polarized
amounts successively to 7s%x» 1080 10's» 10> and 53,57.
It is a fact worthy of remark, that the character derived from the in-
dex of polarization leads to the same consequences that we have deduced
from the experiments of transmission. Indeed, the latter analytical
process had authorized us to admit that the colouring matter introduced
into the composition of coloured glass merely extinguishes a part of the
calorific stream transmitted by the colourless glass, without sensibly af-
fecting the proportions which the groups of rays composing that stream
bear to each other in respect to quantity; so that the effect produced
by that matter relatively to radiant heat is analogous to that which
would be produced relatively to light by brown or blackish substances
diluted in a liquid having no chemical influence on those substances f.
Now, since the proportion of heat polarized by the tourmalines varies
with the quality of the calorific rays transmitted by the different screens,
the constancy of this proportion between the rays which issue from the
coloured and those which issue from the uncoloured glass clearly shows,
as in the experiments of transmission, that the colouring matters do not
affect the composition of the calorific stream transmitted by the glass.
True, the green and the opake-black glasses furnish a very marked ex-
ception; but the experiments of transmission furnish an exception
completely analogous §.
* Ann. de Chim. et de Phys., tom. ly. p. 384.
+ Id., p. 388.
t Id., p. 381.
§ The same consequences are derived from the experimentsof refraction.
With this view, one of the faces of the refracting angle of a rock-salt prism is
covered with a plate of coloured glass, and the distribution of temperature in the
bands of the spectrum produced by exposing this system to the light of the sun
is then observed. If we change the colour of the glass, we not only find the
4
>
a
M. MELLONI ON THE POLARIZATION OF HEAT. 337.
We have found by transmission that the rays emerging from the green
and opake-black glasses may be said to possess properties diametrically
opposite to those of the rays issuing from alum*. The same antagonism
of properties is manifested with respect to the apparent polarization
which these two species of heat undergo in their passage through the
tourmalines ; for in the one the index of polarization increases three- or
four-fold, while in the other it suffers a diminution of eight or nine
tenths.
In fine, experiment has shown that the calorific rays immediately trans-
mitted by alum approximate closely to the luminous rays, both in their
abundant transmission through all uncoloured diaphanous substances
form of the calorific spectrum preserved with great regularity, as we have seen
elsewhere (Ann. de Chim. et de Phys., tom. 1x. p. 426. ; Scientific Memoirs, vol. i.
part i.), that is to say, possessing one maximum, and lower temperatures regu-
larly decreasing on each side of it, but we see that the distances from this maxi-
mum and the surrounding bands toa given zone of the luminous normal spectrum
remain sensibly invariable. As to the absolute quantity of heat, it varies con-
siderably with the tint and nature of the glass; but this variation is always
proportional to the value of the ordinates which represent the temperatures of
the different zones for any one of the coloured plates; so that the intensities of
the maximum and the adjacent bands are more or less affected in a constant
ratio through the whole extent of each new spectrum produced by changing
the glass. From these two facts it clearly follows that the quality of the calo-
rific stream transmitted by the different plates of coloured glass does not vary
in its passage from one plate to another. In this however, asin the other ana-
lyses that we have made of this phenomenon, the green glass possessing the
qualities already mentioned presents a very striking exception: for this species
of glass displaces the calorific spectrum and throws it, in the direction of the in-
ferior refraction, almost totally beyond those limits that are common to the
spectra produced by all the other species of coloured glass.
Wi.en several different methods (and the processes of absorption, polarization,
and refraction described here and elsewhere are really such,) lead to one and the
same conclusion, it seems to me that the conclusion is sufficiently secure to be
ranked among truths firmly established by experiment. é;
_ Thus the colouring matters of the coloured glasses, while they so power-~
fully affect the relations of quantity which the different rays of ordinary light
bear to each other, exercise no elective action on the concomitant calorific
_ rays. This curious phenomenon is the more remarkable, as the same colouring
matters absorb, almost always, a very considerable portion of the heat naturally
transmitted by the glass. The following are, in fact, the calorific transmissions
of the seven coloured glasses referred to the transmission of the colourless glass
which is represented by 100: Red glass 82:5, Orange 72:5, Yellow 55, Bluish
green 57°5, Blue 52-5, Indigo 30, Violet 85. The quantity of heat absorbed
through the action of the colouring substances is therefore 17-5 in the red glass,
27-5 in the orange, 45 in the yellow, 42-5 in the green, 47°5 in the blue, 70 in
the indigo, and 15 in the violet. Now, as these absorptions extinguish a pro-
portional part of each of the rays which constitute the calorific stream trans-
mitted by common glass, they may be compared, as we said before, with the
absorbent action exercised on light by matters more or less deeply brown or
dark when they are immersed in water or some other colourless liquid which
dissolves but does not affect them chemically.
* Ann. de Chim. et de Phys., tom. lv. p. 382.
338 M. MELLONI ON THE POLARIZATION OF HEAT.
and the feeble absorption which they suffer from white surfaces* ; and
this analogy is completed here by the almost total polarization of the
same rays under the influence of the tourmalines.
It will now be easy to account for the differences between the indices
of polarization produced by the different tourmalines. All the calorific
rays emitted by the flame of the lamp do not indiscriminately pass
through the tourmalines, each of which, according to its nature, is per-
meable to particular quantities and qualities of heat. This fact, which
is observable in diathermanous substances in general, is so true in the
particular instance under consideration, that each of the plates composing
the polarizing system indicated in the first table by the numbers 1, 2, 3, 4,
when combined with a plate of alum, fails to afford an appreciable trans-
mission ; an evident proof that the heat which alum is capable of trans-
mitting is not to be found in the calorific stream emerging from these
four systems. Now we have just seen that the different species of heat
contained in the radiation of flame give very different indices of polari-
zation. The calorific stream admitted by each polarizing pair will
therefore necessarily have a mean index of polarization varying with the
quality of the tourmalines.
If we place outside the polarizing system a screen indued with the
same diathermancy as the plates composing this system, namely, a screen
permeable to the same species and the same portions of calorific rays,
then the effect of absolute transmission will, no doubt, be more or less
diminished in proportion as this screen is more or less diathermanous,
but the tourmalines will present no change in their index of polarization:
such is the case with respect to the white, the red, the orange, the yel-
low, the blue, the indigo, and the violet glass. Water, oil, amber, alum,
green, or opake-black glass affect this index in a greater or less degree,
because their diathermancy differs from that of the tourmalines em-
ployed.
But let the polarizing system be changed. It is clear that, if the new
system has not the same diathermancy, the order and the direction of
the variations produced by the different screens in the value of the in-
dex of polarization will be no longer the same. The following is in fact
a series of observations made on the pair of green tourmalines marked
No. 5 in the first table:
* Ann. de Chim. et de Phys., p, 390.
M. MELLONI ON THE POLARIZATION OF HEAT. 339
Tasce III.
Source of heat, the flame of a Locatelli lamp.
sa Ginn
5 Calorific transmissions 3 q ae
NAMES Sy ° through each interposed layer and |5 5 —
o* the same pair of tourmalines EeS5
of the Eg . (No. 5 in the first table) Segs
substances interposed 5 s 2 in the position of the axes. ome
before the introduction |= 2 2 gzES
of the Sag) Coie io ee
calorific radiation g 2 5 Parallel. Perpendicular. 5 & 2 g :
into the SSA C2 Sy
tourmalines. ne Se ie RE. OT OPIN AL as
3 res Arcs Bf roe tics
2 ofimpul-| Forces. |ofimpul-| Forces. | 3 2 = 2 a
cS) sion. sion. Shee a
mm ° °
MEISE 665 05.s0c0sens 0-00 | 17°11 | 14°84} 15°15) 13°15) 11°35
Glass blueish green ...] 1:93 | 17°65| 15°30) 15°54] 13°49] 11°83
opake black ...... 1:98 | 17°10| 14°83} 15°06} 13°05} 11°94
Sulphate of Barytes ...| 2-60 | 17°33 | 15°03] 15°23} 13°21! 12-07
2 oa 8°49 | 17°52} 15°19] 12°95] 12°80) 15°65
Sulphate of Lime ...... 2°71 | 17°76 | 15°39 | 12°74) 12°63} 17-91
Glass uncoloured ...... 1°85 | 17:27} 15°08) 16°24] 14°11 6°46
TEIONGS «is 20d acisoce 8:27 | 17°81} 15°43} 17:05) 14°79 417
Glass coloured (red) ...| 1:80 | 17-49] 15°16] 16:32] 14917} 6-53
—————(orange)} 1:87 | 16-91] 14°67] 15°77! 13°69] 670
——_—_______(yellow)| 1-79 | 17-22} 14°93] 16:12] 14-00] 6-15
|—_—_____(blue)....] 1-83 | 16°87] 14°64| 15°81] 13°73] 690
| indigo)| 1°78 | 16°98 | 14°73| 15°86| 13°78} 6-44
violet)... 1-81 | 17:30] 15:00] 16-20] 1406] 6-29
It is to be observed that the extreme limits of the variations produced
in the index by the interposition of the screens differ considerably less
than they did relatively to the pale yellow tourmalines ; a circumstance
which indicates a greater homogeneity in the calorific stream trans-
mitted by the tourmalines actually employed. Moreover, the index of
polarization undergoes but a very slight alteration under the influence
of the green and the opake-black glasses, which produced a reduction
_of between twelve and nineteen twentieths in the direct index of the
table that precedes the above. The diathermancy of these green tour-
-malines is therefore analogous to that of the green and the opake-black
glasses.
As to the white, red, orange, yellow, blue, indigo, and violet glasses,
they diminish the index of polarization instead of leaving it in its natu-
ral state, as in the instance of the pale yellow tourmalines. In this
there is nothing that should surprise us, since the difference of diather-
mancy proper to the two polarizing systems causes these uncoloured and
340 M. MELLONI ON THE POLARIZATION OF HEAT.
coloured glasses to act in this case like the green and opake-black glasses
of the preceding table, and vice versd.
Moreover, the white, red, orange, yellow, blue, indigo, and violet
glasses all produce very nearly the same alteration in the value of the
index of polarization of the green tourmalines: and we have just ob-
served that these glasses have a very marked effect on the pale yellow
tourmalines. This effect, varying in different systems, but constant in
each particular system through the whole series of plates, is perfectly
analogous to the uniformity of the ratios which, notwithstanding the
changes of intensity, are observed to exist between the quantities of
heat transmitted by the same glasses (coloured and uncoloured) when
successively exposed to the rays emerging from the several kinds of
screens*. We are thus brought back once more to one of the fore-
going conclusions, namely, that the colouring substances have no power
of elective absorption with respect to the rays of the calorific stream
which passes through the glass.
Before we conclude our observations on the effect produced by the
screens in the index of polarization of the tourmalines we shall make
some remarks on the effects produced by the variation of thickness in
the interposed substance and by the solution of salts in water.
On inspecting the second table it is easy to see that the influence of
each substance in augmenting or diminishing the index of polarization
is more powerful in proportion to the greater thickness of the substance.
Thus, water reduced to a layer of 0™™74 in thickness causes the index
of the pale yellow tourmalines to rise from 22 to 36, while a layer of
8™™ yaises it to 67. On the other hand, a plate of dark glass 0™™81
in thickness, which causes the same index to descend from 22 to 4,
would reduce it even to 1°5 if its thickness were about 2™™. All this -
accords with the experiments of successive transmission, which show
that the calorific stream emerging from a given substance becomes more
simple, or, if the expression be preferred, more purified in proportion
to the greater thickness of the substance through which it has passed.
We find this to be the case with white light also in penetrating coloured
media. :
Tartaric acid, rock salt, and alum dissolved to saturation in water
make no sensible change in its action on the index of polarization of
the tourmalines. We have already shown, in a preceding memoir, that
alum and rock salt (which, of all perfectly diaphanous and colourless sub-
stances, are those that possess the maximum and the minimum of diather-
mancy ) donot by being dissolved in water affect the diathermanous power
of this liquid*. The sensible equality of the action of these solutions
and that of pure water on the natural index of polarization of the tour-
* Ann. de Chim. et de Phys., tom: ly. p. 55.
M. MELLONI ON THE POLARIZATION OF HEAT. 341
malines enables us to advance a step further; for this equality shows
that not only the quantity but the quality of the heat transmitted by
pure water is the same as the quality of that transmitted by water
saturated with salt or alum. In short, if we receive on the pile the
calorific streams which issue from distilled water, and the solutions of
rock salt and alum, we shall find the deviations in the galvanometer
very nearly equal in the three cases. It is to be recollected, however,
that this will happen only when the three layers from which the rays
issue are of the same thickness. Now this invariability of action through
layers of equal thickness takes place also if we interpose the same plate
of alum or any other substance behind each of the liquid layers in suc-
cession ; for the common deviation is always diminished by a constant
quantity, even when, by concentrating the calorific radiation with lenses,
we have raised to 35° or 40° the are of impulsion described solely under
the action of the stream transmitted by each of the liquid layers.
In order to conclude the experimental study of the calorific polariza-
tion of the tourmalines, we have only to compare with one another the
polarizing action of these crystallized substances on the radiations of
different sources of heat. For this purpose I select the four systems
marked Nos. 1, 5, 8, and 9 in the first table, and these being exposed,
in the two principal directions of the axes, to the calorific radiations of
an Argand lamp, a Locatelli lamp, a spiral of incandescent platina, and
a plate of copper heated to 400°, give the indices of polarization con-
tained in the following table.
Tas_e IV.
~
o
E ig Indices of polarization for the direct
o - radiations
Sioa Colour ae
Pee of oa a aes
ie 3 each pair of the q
BES! of of platina kept} of a plate
£Se : the Argand/ ofthe | ina state | of copper
2 * tourmalines. lamp with'|1, ocatelli | of incan= heated
25 a glass lamp. descence to about
Es funnel. by the flame} 400°C.
Zz of alcohol.
Deep green ......... 0°37 ord 5°27 0°59
Yellowish green...... Doo 11°30 13°89 3°22
Muddy violet ........ 24°50 20°48 17-20 2°30
Pale yellow ....... ae wd! 21°89 18°16 2°98
N.B. In this table the ares of impulsion are omitted in order to avoid exces-
sive complexity. We think it necessary, however, to observe that these were
often more extensive than those of the preceding tables; and this was indeed
absolutely necessary in order to perceive those indices which in many instances
are extremely feeble. No.1, for example, being exposed to the radiation of the
Vou. l—Parrt II. Qa
342 M. MELLONI ON THE POLARIZATION OF HEAT.
Let us first direct our attention to the two last systems of tourma-
lines. Their indices undergo a gradual increase in passing from the
copper to the Argand lamp. This shows that the radiation of each of
the four sources contains a greater quantity of heat capable of being
polarized by the tourmalines in proportion as the temperature of the
source is more elevated.
Yet the indices of polarization of the systems 1 and 5 undergo, from
the action of the first three sources, changes completely opposed to
those which we have been considering. In order to account for such an
anomaly, we must keep in view the very imperfect diathermancy of this
sort of tourmalines. It is true that the calorific streams of the Argand
and the Locatelli lamps contain rays more capable of being polarized
by the tourmalines than any of those contained in the calorific streams
from the inferior sources; but in the present case such rays scarcely
contribute to increase the index of polarization; for we have seen that
they cannot penetrate the plates which form the polarizing systems. The
green tourmalines, however, are permeable to several species of heat ;
and, as in the radiation of each source there are several of these species,
it is easy to see that if a certain group of rays, possessing an index of
polarization inferior to those of the excluded but superior to those of
the transmitted rays, is more abundant in the calorific stream of the in-
eandescent platina than in that of the Locatelli, the index of polariza-
tion in the two systems of green tourmalines will, in this case, suffer
a decrease in passing from the first to the second source. The same
reasoning will apply to the Locatelli as compared with the Argand
lamp; so that, notwithstanding the fact that the rays are more suscep-
tible of polarization as we proceed from the incandescent platina to the
higher sources, the two systems of green tourmalines will give lower
indices of polarization.
Without a knowledge of the laws of calorific transmission and the
analytical resources they afford, we should perhaps find it impossible
to extricate ourselves from the perplexing difficulty presented by these
singularly anomalous phenomena of polarization. We are now able to
offer the following brief recapitulation of our observations on them.
“The different calorific rays coexisting in the radiation of the same
Argand lamp, gives but a difference of 0°-1 in the two positions of the axes,
the arcs of impulsion being from 26° to 27°; a difference which could not be
rendered perceptible otherwise than by taking the mean of 10 observations; and
I am not yet quite sure that it would not vanish altogether if the experiments
were more numerous, for I frequently obtained a stronger transmission with
the axes perpendicular. The faci is that in operating upon ares of from 15° to
20° the transmission of this system of tourmalines seemed to undergo no vatia-
tion whatsoever in consequence of the axes being crossed ; and indeed, after the
preceding experiments, there is nothing more surprising in the existence of tour-
malines that give no sign of calorific polarization than there would be in the
discovery of tourmalines capable of completely polarizing heat.
M. MELLONI ON THE POLARIZATION OF IIEAT. 343
source of heat, or emitted by different sources, are very unequally
affected by the cause through which the phenomena of polarization in
the tourmalines are rendered sensible. Some of them appear to un-
dergo no action of this kind, others produce indices of polarization
more or less marked, and others are, like rays of light, completely po-
larized. Tourmalines in general, and the green tourmalines in particu-
lar, absorb the most polarizable rays, and transmit those species which
seem totally or partially to escape polarizing action. The consequence
is, that their apparent index of polarization is generally very feeble and
sometimes even inappreciable. But it rises even to 7%,2,, and perhaps
higher, in those systems of plates which are permeable to a greater pro-
portion of heat susceptible of a high degree of polarization, as we see
in the plates of yellow, brown, or violet tourmalines. The index of
apparent polarization in a given system varies considerably in passing
from one source to the other, because a change takes place in the qua-
lity and the grouping of the rays constituting the calorific stream issuing
from the focus of heat. In fine, this index varies, and in certain cases
attains its two extreme limits, 0 and 100, when we introduce between
the same source and the same system of tourmalines diathermanovs
plates of a different kind; because the particular absorption of these
screens affects the relations of quantity existing between the several
groups of rays composing the calorific stream naturally transmitted by
the polarizing system.”
In all these statements we have taken care to apply the qualifying
term apparent to the signs of feeble polarization exhibited by the tour-
malines ; and, in fact, all the rays of heat, whether direct or transmitted
through a screen, might be completely polarized, as light is, in the in-
terior of these crystallized bodies, and yet the polarization not be ren-
dered perceptible by any diminution in the quantity of heat transmitted
by the plates when the parallel is exchanged for the perpendicular a
sition of the axes.
In order to understand this proposition it is necessary to recollect the
phenomena which take place in the polarization of light by tourmalines.
When a ray of natural light falls perpendicularly on a plate of tour-
maline cut parallel to the axis of the needles, the double refraction first
divides the ray into pencils possessing sensibly equal intensities and
polarized at right angles; but, in proportion as these pencils penetrate
into the substance of the tourmaline, they suffer very different degrees
of absorption, that of the pencil which has undergone the ordinary
refraction being much the greater ; so that, beyond a depth often very
inconsiderable, one of the pencils is entirely absorbed, while the other
pursues its path, emerges from the plate, and shows itself in its proper
direction of polarization. This inequality of absorption is proved by
the following experiment, for which we are indebted to M. Biot. We
.
344 M. MELLONI ON THE POLARIZATION OF HEAT.
take a sufficiently thick plate of tourmaline cut parallel to the axis, and
attenuate it obliquely at one side, so that the planes of its two faces
may intersect each other exactly on one of the edges, and thus form a
certain angle. A very narrow slip of white paper, or any other object
equally minute, if viewed across this angle and in the direction of the
edge, will give two images neither lying one upon the other nor con-
founded together, as they are when the faces are parallel, but separated
by the double refraction of the tourmaline. If we achromatize the re-
fringent angle by means of a glass prism in order to have a clearer view,
we find that these two images, viewed through the thinnest part of the
tourmaline, are nearly of the same intensity ; but by passing the thicker
parts successively before the eye, we perceive the image formed by the
ordinary refraction becoming gradually weaker and weaker until it is
finally extinguished.
Thus we see that it is in consequence of the wnegual absorption of
the two pencils formed by double refraction that the polarization in a
plate of tourmaline becomes perceptible. If the absorbency of the mat-
ter of which the plate is composed acted with the same intensity on each
of them, the two pencils would emerge intermixed, and exhibit all the
properties of ordinary light ; so that a second plate of tourmaline would
no longer, by having its axis placed transversely to that of the first, pro-
duce any diminution of intensity in the light transmitted.
Let us now apply these notions to calorific polarization. Let us sup-
pose that all the rays of heat, like those of light, undergo a complete
polarization as soon as they enter a plate of tourmaline, and that each
of them is consequently divided into two pencils or bundles possessing
equal intensities and polarized at right angles. Let us admit, besides,
that the inequality of absorption effected by the matter of the tourma-
line in the two pencils varies with the different calorific rays; that it is
very great with respect to some rays, and little or none with respect to
others: it is evident that the former will issue from the tourmaline en-
tirely polarized in one plane, while the latter will be more or less po-
larized in the two planes standing at right angles to one another, and
will therefore present little or no appearance of polarization.
All the facts which we have stated may then be explained on the hy-
pothesis of a complete polarization of the calorific rays; and we shall
see, indeed, that this hypothesis is rendered more and more probable, nay,
certain, by the following experiments. But before we conclude our
observations on this part of the subject, it will not, perhaps, be useless
to set in contrast, by means of an example easily to be comprehended,
the two different effects which the tourmalines have on the rays of light
and the rays of heat.
Let us imagine a series of alcohol flames coloured by different salts,
and several common flames masked by glasses of different colours. If
M. MELLONI ON THE POLARIZATION OF HEAT. 345
we look at those lights through our systems of tourmalines with their
axes first in the parallel and then in the perpendicular position, all the
coloured images which present themselves with sufficient vividness and
brilliancy in the first case, completely disappear in the second ; or if any
of them remains, it is but an excessively feeble gleam*. The rays of
platina in a state of incandescence, and of copper heated to 400°, repre-
sent, relatively to radiant heat, the coloured alcohol flames; and the rays
of a Locatelli lamp, transmitted through water, glass, or alum, are, in
respect to this heat, no more than the lights of different colours which
we perceive through the coloured glasses. Now we have seen that the
effect of the tourmalines on the several species of rays, so far from being
equal as in the case of light, presents differences so strongly marked,
that sometimes the heat passes in a sensibly equal quantity in all posi-
tions of the axes of crystallization, and at others it is almost completely
intercepted when the axes of the two plates are perpendicular to each
other.
The phenomena of calorific polarization, in a variable proportion,
produced by a system of tourmalines which polarizes the luminous rays
of all colours equally, are analogous to the extremely marked differences
of absorption which the various species of calorific rays undergo in their
passage through a sufficiently thin plate of glass, rock crystal, water, al-
cohol, and almost all perfectly diaphanous substances, the absorbent
force of which, within these limits of thickness, if there be any, is the
same for all sorts of luminous rays+. Among those actions which vary
* M. Biot possesses a prism cut out of a tourmaline of a light violet-red co-
lour, which not only does not completely extinguish the common sheaf, as is
done by the tourmalines that are too thin or too lightly coloured, but colours the
sheaf while it weakens it ; so that the two images of a minute object seen through
this prism are sensibly white and of equal intensity near the apex of the refrin-
gent angle; but, in proportion as the eye moves towards the thickest part, the
ordinary image is observed to decrease in its intensity and to take at the same
time a red tint which becomes gradually deeper, while the extraordinary image
never presents itself in any other colour than a slight tinge of the shade which
belongs to the tourmaline. It appears then that two flakes of this particular kind
_ of tourmaline would not act alike on all the coloured rays, and that in the per-
ercnisr position of the axes they would still be permeable to red light. Per-
aps the red rays themselves would be finally extinguished if the two flakes
were of a certain thickness. However, this case is but an exception; for all
the other tourmalines constantly produce the effect we have just announced ;
that is to say, that they extinguish indiscriminately and equally all the luminous
rays whatever be their colour, provided they are made to pass through the flakes
when their axes are at right angles to each other.
+ The experiments on the different degrees in which coloured and uncoloured
media absorb the light and heat of the solar spectrum (Ann. de Chim. et de Phys.,
Dec. 1835, p. 402; Scientific Memoirs, vol. i. part i.) afford a still more striking
example of the same kind; for the differences then present themselves in pairs
of calorific and luminous rays, which being isolated and, so to speak, purified by
__ by the force of refraction, seem to constitute that species of light and heat which
are most identical. And here I shall take the opportunity to correct a strange
346 M. MELLONI ON THE POLARIZATION OF HEAT.
considerably with respect to different calorific rays, while they remain
sensibly constant with respect to light, we may class the variable ab-
sorbent power exercised on the different species of heat by the white
surfaces of opake bodies which reflect the same proportion of coloured
rays. Such, then, are the conditions to be satisfied henceforth by every
theory that will refer the phenomena of light and radiant heat to a
single principle.
mistake into which the young and able successor of Leslie has fallen with re-
gard to these experiments. I find in a letter of his addressed to the Editors of
the London and Edinburgh Philosophical Magazine (March 1836, p. 245), that
the special aim of my labour was to raise objections against the undulatory
theory of heat: “ M. Melloni lately read a paper to the Academy of Sciences
staling certain objections to the undulatory theory of heat.) Now such was
most assuredly not my intention; and I have, I think, expressed myself to that
effect with sufficient clearness in a note at the end of the memoir. In publishing
those facts my only object was to show that which I announced at the head of
the memoir presented to the Academy, namely, the nonidentity of light and
radiant heat, a proposition which is evidently independent of every theory.
Thus, whether the system adopted be that of emanation or that of undulations,
I do not think it possible to maintain at this day that the same molecule or the
same wave that gives, for instance, yellow light, at a determinate part of the
solar spectrum, produces the concomitant heat also, Such is the only conclu-
sion that I have drawn from the experiments contained in my memoir. The
author of the letter has been probably misled by the enunciation of the propo-
sition, (which I made in terms applicable only to one of the two systems,) as well
as by the arguments, which should in my opinion be brought, on the supposition
of their identity, to answer the objections derived from the previously known
differences between the action of diaphanous and diathermanous media on the
light and heat of terrestrial sources ; arguments which must necessarily be given
in the language of one or the other of the hypotheses on which calorific phzeno-
mena are explained. I chose the language of the undulatory system; but I
might as well have employed that of the system of emanation. It is besides
so true that the arguments contained in the memoir do not apply particularly
to the theory of undulations, that by suppressing certain expressions proper to
this theory, and changing the words wave and length into molecule and species, the
arguments are still good, and we thus arrive at the same general conclusion ex-
pressed in the language of the system of emission; that is, that in the interior
of the solar spectrum the same molecules cannot produce the two effects of light
and heat simultaneously. In short, my only aim in pursuing my researches
with respect to radiant heat is to study the laws and properties of this agent. I
have not the vanity to think that by any new discovery I shall make the parti-
sans of either of the systems tremble. I shall rather tremble myself lest, in
consequence of preadopted notions, I may mistake the truth of the phenomena;
and I suppose there is no one who will censure a timidity so salutary... but I
will frankly avow that I consider any other fear scarcely philosophical.
SCIENTIFIC MEMOIRS.
VOL. I.—PART III.
ARTICLE XV.
Memoir on the Motive Power of Heat ; by KE. CLapryron,
Mining Engineer.
From the Journal de I’ Ecole Royale Polytechnique; Paris; vol. xiv. p. 153 et seq.
§ 1.
Few questions are more worthy of fixing the attention of geometers
and natural philosophers than those which relate to the constitution of
gases and vapours: the functions they exercise in nature, and the ad+
‘vantages which industry derives from them, account sufficiently for the
numerous and important labours of which they have been the object :
this vast question, however, is far from being exhausted. The law of
Mariotte and that of Gay-Lussac, which establish the relations exist-
ing between the volume, the pressure, and the temperature of a given
_ quantity of any gas, have both long since obtained the assent of scientific
The experiments recently made by MM. Arago and Dulong leave
no doubt of the accuracy of the first of those laws within very ex-
tended limits of pressure ; but these important results give no information
Tespecting the quantity of heat which the gases contain, and which is dis-
engaged by pressure or diminution of temperature,—they do not give the
Jaw of the specific caloricswhen the pressure and the volume are constant,
This part of the theory of heat, however, has been the object of profound
researches, among which we may cite those of MM. La Roche and Bé-
rard on the specific caloric of gases. Lastly, M. Dulong, in a memoir
which he published under the title of Recherches sur la Chaleur Spéci-
fique des Fluides Elastiques, has established by experiments free from
. objection, that equal volumes of all elastic Jluids at the same tempe-
re and under the same pressure, being suddenly compressed or di-
by the same Sraction of their volume, aieengage or absorb 7 at same
Bois quantity of heat. .
Vor. I.—Panrr III. 28
348 M.CLAPEYRON ON THE MOTIVE POWER OF HEAT.
Laplace, and subsequently M. Poisson, have made public some very
remarkable theoretical researches on this subject ; but they rest upon
hypothetical data which appear liable to objection. It is admitted in
them that the ratio of the specific caloric when the volume remains con-
stant to the specific caloric under a constant pressure, is invariable, and
that the quantities of heat absorbed by gases are proportional to their
temperatures.
I will finally quote among the works which have appeared on the theory
of heat, one by M.S. Carnot, published in 1824, under the title of Re-
flexions sur la Puissance Motrice du Feu. The idea taken for the basis
of his researches appears to me fertile and incontestible: his demon-
strations are founded on the absurdity which arises from admitting the
possibility of producing absolutely either the motive force or the heat.
The various theorems to which this new method of reasoning con-
ducts us may be enunciated as follows :
1. When a gas without change of temperature passes from a deter-
mined volume and pressure to another volume and pressure equally —
determined, the quantity of caloric absorbed or lost is always the same,
whatever be the nature of the gas subjected to experiment.
&. The difference between the specific heat under a constant pressure
and the specific heat at a constant volume is the same for all gases.
3. When a gas varies in volume without change of temperature, the
quantities of heat absorbed or disengaged by that gas are in arithmetical —
progression, if the increments or diminutions of volume are in geometrical
progression. ,
This new mode of demonstration appears to me worthy of fixing the -
attention of geometers; it is, in my opinion, free from every objection, —
and it has acquired additional importance since its verification by the
labours of M. Dulong, in which the truth of the first theorem which I}
have recited is demonstrated by experiment.
I think it will be of some interest to revive this theory: M. S. Carnot, §
dispensing with mathematical analysis, arrives, by a series of delicate
reasonings difficult to apprehend, at results easily deducible from a more:
general law, which I shall endeavour to establish. But before entering)
upon the subject, it will be useful to return to the fundamental axiom)
upon which the researches of M. Carnot are founded, and which will be.
my starting point also. i
§ Il.
It has long been remarked that heat may be employed to develop
motive force, and reciprocally that by motive force we may develop
heat. In the first case we should observe that there is always a passa
_of a determinate quantity of caloric from a body at a given temperatur
to another body at a lower temperature ; thus in the steam-engine, thi
M.CLAPEYRON ON THE MOTIVE POWER OF HEAT. 349
production of the mechanical force is attended by the passage of a part
of the heat which is developed by combustion in the furnace, the tem-
perature of which is very high, into the water in the condenser, the tem-
_ perature of which is much lower.
Reciprocally, it is always possible to render the passage of caloric from
a hot to a cold body useful for the production of a mechanical force :
to obtain this it is sufficient to construct a machine resembling an ordi-
nary steam-engine, in which the heated body serves to produce steam
and the cold one to condense it. It results from this that there is a loss
of vis viva, of mechanical force, or of quantity of action, whenever im-
mediate contact takes place between two bodies of different tempera-
tures, and heat passes from the one into the other without traversing
an intermediate body ; therefore in every machine intended to make ef-
ficient the motive force developed by heat, there is a loss of power when-
ever a direct communication of heat takes place between bodies of dif-
ferent temperatures, and consequently the maximum of the effect pro-
duced cannot be obtained but by means of a machine in which only
bodies of equal temperature are brought into contact. Now the know-
ledge we possess of the theory of gases and vapours shows the possibi-
lity of attaining this object.
Let us, then, suppose two bodies retained, one at a temperature T,
and another at an inferior temperature ¢; such, for example, as the sides
of a steam-boiler, in which the heat developed by combustion constantly
supplies the place of that which the steam produced carries away ; and
the condenser of the common atmospheric engine, in which a current of
cold water removes, every moment, both the heat which the steam loses in
condensing, and that which belongs to its proper temperature. For the
_ sake of simplicity we will call the first body A and the second B.
Let us now take any gas whatever, at the temperature T, and bring it
into contact with the’source of heat A, representing its volume vp by the
absciss A B, and its pressure by the ordinate C B (fig 1).
_ If the gas is inclosed in an extensible vessel, and which is allowed to
__ extend in a void space in which it cannot lose heat either by radiation or
_ by contact, the source of heat A will supply it, from moment to moment,
_ with the quantity of caloric which its increase of volume renders latent,
and it will preserve the same temperature T. Its pressure, on the con-
_ trary, will diminish according to the law of Mariotte. The law of this
_ variation may be represented by a curve C E, of which the volumes will
_ be the abscisses, and the corresponding pressures the ordinates.
_ Supposing the dilatation of the gas to continue until the volume A B
_ has become A D, and that the pressure corresponding to this new vo-
lume is D E, the gas during its dilatation will have developed a quan-
_ tity of mechanical action, which will have for its value the integral of the
_ product of the pressure by the differential of the volume, and which
252
$50 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
will be represented geometrically by the area comprised between the
axis of the abscisses, the two coordinates C B, D E, and the portion of:
a hyperbola C E. ;
-
}
| Fig. 1.
|
val
:
| \ Ms
i aS be
} ¥K ,
] Pee
| 4 nese ect}
! a
) x Pee
' 4 ~ 1
! nae “st 4
{ [edo NGA ie ae acy
Sad | :
x | | i i iow EF
lee H | t i : i
eee Td eh ee be Spaaen ey cy ahi eae Re
A Be SE eT TDD) GU x
Supposing, again, that the body A is removed and that the dilatation
of the gas continues in an inclosure impermeable to heat; then a part of
its sensible caloric becoming latent, its temperature will diminish and
its pressure will continue to decrease in a more rapid manner and accord-
ing to an unknown law, which law might be represented geometrically
by a curve E F, the abscissee of which would be the volumes of the gas,
and the ordinates the corresponding pressures: we will suppose that the
dilatation of the gas has continued until the successive reductions which
its sensible caloric experiences have reduced the temperature T of the
body A to the temperature ¢ of the body B; its volume will then be A G,
and the corresponding pressure F G. It will also be evident from the
same reasoning, that the gas during this second part of its dilatation
will develop a quantity of mechanical action represented by the area of
the mixtilinear trapezium D E F G.
Now that the gas is brought to the temperature ¢ of the body B, let
us bring them together: if we compress the gas in an inclosure imper-
meable to heat, but in contact with the body B, the temperature of the
gas will tend to rise by the evolution of latent heat rendered sensible by
compression, but will be absorbed in proportion by the body B, so that
the temperature of the gas will remain equal to ¢t. The pressure will
increase according to the law of Mariotte : it will be represented geo-
metrically by the ordinates of a hyperbola K F, and the corresponding
abscisses will represent the corresponding volumes. Suppose the com-
pression to be increased until the heat disengaged and absorbed by the
body B is precisely equal to the heat communicated to the gas by the
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 351
source A during its dilatation in contact with it in the first part of the
process. Let then the volume of gas be A H, and the corresponding
pressure H K: the gas in this state contains the same absolute quan-
tity of heat that it did at the moment of commencing the process, when
it occupied the volume A B under the pressure C B. If therefore
we remove the body B and continue to compress the gas in an inclosure
impermeable to heat, until the volume A H is reduced to the volume
A B, its temperature will successively increase by the evolution of the
latent caloric, which the compression converts into sensible caloric.
The pressure will increase in a corresponding ratio; and when the
volume shall be reduced to A B, the temperature will become T, and
the pressure B C. In fact, the successive states which the same weight
of gas experiences are characterized by the volume, the pressure, the
temperature, and the absolute quantity of caloric which it contains: two
of these four quantities being known, the other two become known as
consequences of the former ; thus in the case in question the absolute
quantity of heat and the volume having become what they were at the
beginning of the process, we may be certain that the temperature and
pressure will also be the same as before. Consequently, the unknown
law according to which the pressure will vary when the volume of
gas is reduced in its inclosure impermeable to heat, will be represented
by a curve K C, which will pass through the point C, and in which
the abscisses always represent the volumes, and the ordinates the
pressures.
However, the reduction of the gaseous volume from A G to A B wilk
have consumed a quantity of mechanical action which, for the reasons
we have stated above, will be represented by the two mixtilinear trape-
ziums F G H K and K H BC. If we subtract from these two trape-
ziums the two first, C B D E and E D G F, which represent the quan-
tity of action during the dilatation of the gas, the difference, which will
be equal to the sort of curvilinear parallelogram C E F K, will represent
the quantity of action developed in the circle of operations which we have
just described, and after the completion of which the gas will be pre-
cisely in the same state in which it was originally. Still, however, the
entire quantity of heat furnished by the body A to the gas during its di-
latation by contact with it, passes into the body B during the condensa-
tion of the gas, which takes place by contact with it.
- Here, then, we have mechanical force developed by the passage of
caloric from a hot to a cold body, and this transfer is effected without
the contact of bodies of different temperatures.
- The inverse operation is equaily possible: thus,we take the same volume
of gas A B at the temperature T and under the pressure B C, inclose
_ it in an envelope impermeable to heat, and dilate it until its tempera-
ture, gradually diminishing, becomes equal to ¢; we continue the dilata-
$52 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
tion in the same envelope,—but after having introduced the body B, which
is at the same temperature,—and carry on the operation until the
body B has restored to the gas the heat which it had received in the.
preceding operation. We next remove the body B, and condense the
gas in an inclosure impermeable to heat until its temperature again be-
comes equal to T. We then introduce the body A, which possesses the
same temperature, and continue the reduction of volume until all the
heat taken from the body B is transferred to the body A. The gas will
then be found to have the same temperature and to contain the same ab-
solute quantity of heat as at the beginning of the operation, whence we
may conclude that it occupies the same volume and is subjected to the
same pressure.
Here the gas passes successively, but in an inverse order, through all
the states of temperature and pressure through which it had passed in
the first series of operations; consequently the dilatations become com-
pressions, and reciprocally, but they follow the same law. Further, the
quantities of action developed in the first case are absorbed in the se-
cond, and reciprocally ; but they retain the same numerical values, for
the elements of the integrals which compose them are the same.
We thus see that by causing heat to pass, in the manner first indi-
cated, from a body retained at a determinate temperature, into a body
retained at an inferior temperature, we develop a certain quantity of
mechanical action, which is equal to the quantity which must be con-
sumed in order to cause the same quantity of heat to pass from a eold
to a hot body, by the inverse process we have subsequently described.
We may arrive at a similar result by converting any liquid into va-
pour. We take the liquid and bring it into contact with the body A in
an extensible envelope impermeable to heat, and suppose the tempera-
ture of the liquid to be equal to the temperature T of the body A.
Upon the axis of the abscisses A X (fig. 2.) we describe a quantity A B
equal to the volume of the liquid, and upon a line parallel to the axis
of the ordinates A Y, a quantity B C equal to the pressure of the vapour
of the liquid, which corresponds to the temperature T.
If we increase the volume of the liquid, a portion of it will pass into
the state of vapour; and as the source of heat A furnishes the latent
caloric necessary to its formation, the temperature will remain constant
and equalto T. Then if quantities representing the successive volumes
occupied by the mixture of liquid and vapour are described upon the
axis of the abscisses, and the corresponding values of the pressures are
taken for ordinates, as the pressure remains constant, the curve of the
pressures will here be reduced to aright line C E parallel to the axis of
the abscisses.
When a certain quantity of vapour has been formed, and the mixture
of liquid and vapour occupies a yolume A D, the body A may be with-
M.CLAPEYRON ON THE MOTIVE POWER OF HEAT. 353
drawn and the dilatation continued. A fresh quantity of liquid will
then pass into the gaseous state, and a part of the sensible caloric be-
coming latent, the temperature of the mixture will diminish as well as
Fig. 2.
4
i
|
|
|
c i
: .
i i\
oe
{ \
! Sn 6
| | "|
| |
eee Sad Se ee <5 ES, eis eee [ee ee ee
A BR i D a
the pressure. Suppose the dilatation to be continued until the tem-
perature diminishing gradually becomes equal to the temperature ¢ of
the body B; let A F be the volume and F G the pressure corresponding
to it. The law of the variation of the pressure will be given by a curve
E G, which will pass through the points E and G.
During this first part of the operation which we are describing, a quan-
tity of action will be developed represented by the surface of the rect-
angle B C E D, and that of the mixtilinear trapezium E G F D.
We will now bring forward the body B, put it in contact with the
mixture of liquid and vapour, and successively reduce its volume; a
part of the vapour will pass into the liquid state, and as the latent heat
disengaged in its condensation will be absorbed by the body B, the
temperature will remain constant and equal to ¢ We shall thus con-
tinue to reduce the volume until all the heat furnished by the body A
in the first part of the operation has been conveyed to the body B.
Let A H then be the volume occupied by the mixture of vapour and
liquid ; the corresponding pressure will be K H equal to G F: the tem-
perature remaining equal to ¢. during the reduction of the volume from
AF to AH, the law of the pressure between these two limits will be re-
presented by the line K G parallel to the axis of the abscisses.
Arrived at this point, the mixture of vapour and liquid upon which
we are operating, which occupies the volume A H under a pressure K H,
354 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
at a temperature ¢, possesses the same absolute quantity of heat
that the liquid possessed at the commencement of the operation ; if,
therefore, we remove the body B, and continue the condensation, in a
vessel impermeable to heat, until the volume again becomes equal to
A B, we shall have the same quantity of matter occupying the same
volume, and possessing the same quantity of heat as at the commence-
ment of the operation : its temperature and its pressure ought, there-
fore, also to be the same as at that epoch; the temperature will thus
again become equal to T, and the pressure equal to C B. The law of
the pressures during this last part of the operation, will therefore be
given by a curve passing through the points K and C; and the quan-
tity of action absorbed during the reduction of the volume from A F
to A B, will be represented by the rectangle FH KG and the mixti-
linear trapezium BCKH. If, then, we deduct from the quantity of
action developed during the dilatation, that which is absorbed during
the compression, we shall have for the difference the surface of the
mixtilinear parallelogram C EG K, which will represent the quantity of
action developed during the entire series of the operations that we
have described, and at the conclusion of which the liquid employed
will be found in its primitive state.
But it is necessary to remark that all the caloric communicated by
the body A has passed to the body B, and that this transmission has
taken place without there having been any other contact than that be-
tween bodies of the same temperature.
It might be proved in the same manner as for the gases, that by re-
peating the same operation in an inverse order, the heat of the body B
may be made to pass to the body A, but that this result will only be
‘obtained by the absorption of a quantity of mechanical action, equal
to that which has been developed in the passage of the same ween
of caloric from the body A to the body B.
From what precedes, it results that a quantity of mechanical action
and a quantity of heat passing from a hot to a cold body, are quan-
tities of the same nature, and that it is possible to substitute the one
for the other reciprocally ; in the same manner as in mechanics a body
falling from a certain height, and a mass endowed with a certain ve-
locity, are quantities of the same order, and can be transformed one
into the other by physical agents.
Hence also it follows that the quantity of action F developed by the
passage of a certain quantity of heat C, from a body A maintained at
a temperature T, to a body B maintained at a temperature ¢, by one
of the processes that we have just indicated, is the same, whatever be
the gas or the liquid employed, and is the greatest that it is possible to
realize.
Suppose that by causing the quantity of heat C of the body A to
M.CLAPEYRON ON THE MOTIVE POWER OF HEAT. 355
pass to the body B, by some other process, it was possible to realize a
larger quantity of mechanical action F’; we should employ one part of
it F, to restore to the body A from the body B the quantity of heat C,
by one of the two means that we have just described. The vis viva F
employed for this purpose would be equal, as we have seen, to that
which would be developed in the passage of the same quantity of heat
C, from the body A to the body B; it is therefore, according to the
hypothesis, smaller than F’; a quantity of action F’ — F, would there-
fore be produced, which would be created absolutely and without con-
sumption of heat; an absurd result, which would imply the possibility
of creating either force or heat ina gratuitous and indefinite manner. It
appears to me that the impossibility of such a result might be accepted
as a fundamental axiom of mechanics: the demonstration by pulleys,
that Lagrange has given, of the principle of virtual velocities, against
which no one has attempted to raise an objection, rests upon an analo-
gous principle. In the same manner it may be proved that no gas or
vapour exists which, employed in the processes described to transmit
the heat of a hot body to a cold one, is capable of developing a larger
quantity of action than any other gas or vapour.
We shall therefore admit the following principles as the basis of
our researches.
Caloric passing from one body to another maintained at a lower tem-
perature may cause the production of a certain quantity of mechanical
action; there is a loss of vis viva whenever bodies of different tem-
perature come into contact. The maximum effect will be produced
when the passage of the caloric from the hot to the cold body takes
place by one of the methods which we have just described. We may
add, that the effect will be found to be independent of the chemical
nature, of the quantity, and of the pressure of the gas or liquid em-
ployed; so that the maximum quantity of action, which the passage of
a determinate quantity of heat from a hot to a cold body can develop,
is independent of the nature of the agents which serve to realize it.
§ Il.
We shall now translate analytically the various operations that have
been described in the preceding paragraph ; we shall deduce from them
the expression of the maximum quantity of action produced by the
passage of a given quantity of heat from a body maintained at a deter-
minate temperature, to another body maintained at a lower tempera-
ture, and we shall arrive at new relations between the volume, the
pressure, the temperature, and the absolute quantity of heat or latent
caloric of solid, liquid, or gaseous bodies.
_ Let us return to the two bodies A and B, and suppose that the tem-
356. M. CLAPEYRON ON THE MOTIVE POWER-OF HEAT.
perature ¢ of the body B is lower by the infinitely small quantity d¢,
than the temperature ¢ of the body A. We shall suppose in the first
instance that a gas serves for the transmission to the body B, of the ca-
loric of the body A. Let v, be the volume of the gas under the pres-
sure py at a temperature of ¢,; let p and v be the volume and the
pressure of the same weight of gas at the temperature ¢ of the body A.
The law enunciated by Mariotte, combined with that of Gay-Lussac,
establishes between these different quantities the relation
= Po Vo 2 e);
tered (Clie)
or, for simplicity, ae - ; =
pv=R (267 + 2).
The body A is brought into contact with the gas. Let me = »,
ae = p (fig.3.). If the gas be allowed to expand by the infinitely
small a ciany dv = eg, the temperature will remain constant, in con-
sequence of the presence of the source of heat A; the pressure will
diminish, and become equal to the ordinate bg. We now remove the
Fig. 3.
sea
body A, and allow the gas to expand, in an inclosure impermeable to
heat, by the infinitely small quantity g/, until the heat becomes latent,
reduces the temperature of the gas by the infinitely small quantity dé,
and thus brings it to the temperature ¢— dé of the body B. In eon-
sequence of this reduction of temperature, the pressure will diminish
more rapidly than in the first part of the operation, and will become
ch. We now take the body B, and reduce the volume mh by the
infinitely small quantity fh, calculated in such a manner that during
this compression the gas may transmit to the body B all the heat
it has derived from the body A during the first part of the opera-
tion. Let fd be the corresponding pressure; that done, we remove
M; CLAPEYRON ON THE MOTIVE POWER OF HEAT. 857
the body B, and continue to compress the gas until it is again reduced
to the volume me. The pressure will then again be equal to ae, as we
have shown in the preceding paragraph; and in the same manner also
it will be proved, that the quadrilateral figure a b ed will be the mea-
sure of the quantity of action produced by the transmission to the body
B, of the heat derived from the body A, during the expansion of the
gas.
Now it is easy to show that this quadrilateral figure is a parallelo-
gram ; this results from the infinitely small values assigned to the va-
riations of the volume and pressure : let us conceive that perpendicu-
lars are erected upon each point of the plane upon which the quadri-
lateral figure abcd is traced, and that on each of them, commencing
at their foot, are described two quantities T and Q, the first equal to
the temperature, the second to the absolute quantity of heat possessed
by the gas, when the volume and the pressure have the value assigned
to them by the absciss v and the ordinate p which correspond to
each point.
The lines a6 and ed belong to the projections of two curves of
equality of temperature, passing through two points infinitely near,
taken upon the surface of temperatures; ab and ed are therefore
parallel: ad and de will be also projections from two curves, for which
Q = const., and which would also pass through two points infinitely
near, taken upon the surface Q = f (pv); these two elements are there-
fore also parallel. The quadrilateral figure abcd is therefore a paral-
lelogram, and it is easy to see that its area may be obtained by multi-
plying the variation of the volume during the contact of the gas with
the body A or the body B, that is to say, eg, or its equal fh, by bx, the
difference of the pressures supported during these two operations, and
corresponding to the same value of the volume v. Now, eg, or fh,
being the differentials of the volume, are equal to dv; bn will be ob-
tained by differentiating the equation pv = R (267 + v), supposing v
constant ; we shall then have bx =dp = R = The expression of
dtdv
v
the quantity of action developed will therefore be R
It remains to determine the quantity of heat necessary to produce
this effect : it is equal to that which the gas has derived from the body
A, whilst its volume has increased by dv, at the same time preserving
the same temperature ¢ Now Q being the absolute quantity of heat
possessed by the gas, ought to be a certain function of p and of v, con-
sidered as independent variables; the quantity of heat absorbed by the
gas will therefore be
RON FQ
358 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
but the temperature remaining constant during the variation of the vo-
lume, we have
vdp+pdv=O0,whencedp = — B dv,
and consequently
_ (4Q_ pdQ
ee (Ge v dp
If we divide the effect produced by this value of dQ, we shall
have
Rat
dQ dQ
ma es Pap
for the expression of the maximum effect which can be developed by
the passage of a quantity of heat equal to unity, from a body main-
tained at the temperature ¢ to a body maintained at the temperature
t — dt.
We have shown that this quantity of action developed is indepen-
dent of the agent which has served to transmit the heat; it is there-
fore the same for all the gases, and is equally independent of the pon-
derable quantity of the body employed: but there is nothing that
proves it to be independent of the temperature; v - a 7; ought
therefore to be equal to an unknown function of ¢, which is the same
for all the gases.
Now by the equation pv = R (267 + 4), ¢ is itself the function of
the product p v; the partial differential equation is therefore
pt dQ
= F(p.v),
Die a fader at Oe oak
having for its integral
Q=f(p-v) —F (p.v) log [ (hyp)p).
No change is effected in the generality of this formula by substitut-
ing for these two arbitrary functions of the product pv, the functions
B and C of the temperature, multiplied by the coefficient R ; we shall
thus have
Q =R(B—C log p).
That this value of Q satisfies all the conditions to which it is sub-
ject may be easily verified ; in fact we have
dQ_p dB p n dC p
dv an ee
dQ dB v dC v 1
eam FL — loo 2: gine ale pisss\ \i
dp Fram ae oe rin c=):
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 359°
whence -
Q dQ _
v To ate ate
and consequently
Rdt mt
»@Q EQ. - pik
er re dp
The function C by which the logarithm of the pressure in the
value of Q is multiplied is, as we see, of great importance; it is inde-
pendent of the nature of the gases, and is a function of the temperature
alone; it is essentially positive, and serves as a measure of the maximum
quantity of action developed by the heat.
We have seen that of the four quantities Q, ¢, p, and v, two being
known, the other two follow from them; they ought therefore to be
united together by two equations; one of them,
pe = R (267 + 4),
results from the combined laws of Mariotte and Gay-Lussac. The
equation
Q=R (B—C lg p),
deduced from our theory, is the second. However, the numerical de-
termination of the alterations produced in the gases, when the volume
and the pressure are varied in an arbitrary manner, requires a know-
ledge of the functions B and C.
We shall see upon another occasion that a value approaching to the
function C may be obtained through a considerable extent of the ther-
mometrical scale; besides, being determined for one gas it will be de-
termined for all. As to the function B, it may vary in different gases;
however, it is probable that it is the same for all the simple gases: that
they ail have the same capacity for heat, is at least the apparent result
of the indications of experiment.
Let us return to the equation
Q=R (B—C logp).
We will compress a gas occupying the volume v, under the pressure
p, until the volume becomes v', and allow it to cool till the tempera-
ture sinks to the same point. Let p! be the new value of the pressure;
let Q' be the new value of Q; we shall have
2)
Q-qQ'= RC log & = RC log —.
The function C being the same for all the gases, it is evident that
equal volumes of all the elastic fluids, taken at the same temperature
and under the same pressure, being compressed or expanded by the same
Sraction of their volume, disengage or absorb the same absolute quantity
of heat. This law M. Dulong has deduced from direct experiment.
860 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
This equation shows also that when a gas varies in volume without
change of temperature, the quantities of heat absorbed or disengaged by
this gas are in arithmetical progression, if the increments or reductions
of volume are in geometrical progression. M. Carnot enunciates this
result in the work already cited.
The equation
Q—Q=RC log (=)
expresses a more general law; it includes all the circumstances by
which the phenomenon can be affected, such as the pressure, the
volume, and the temperature.
In fact, since
i Ti Siar
27 +t 267+¢’
we have
Q- qi 760 TG jor at
per v
This equation exhibits the influence of the pressure; it shows that
equal volumes of all the gases, taken at the same temperature, being com-
pressed or expanded by the same fraction of their volume, disengage or
absorb quantities of heat proportionate to the pressure.
This result explains why the sudden entrance of the air into the va-
cuum of the air-pump does not disengage a sensible quantity of heat.
The vacuum of the air-pump is nothing but a volume of gas v, of
which the pressure p is very small; if atmospheric air be admitted, its
pressure p will suddenly become equal to the pressure of p' of the at-
mosphere, its volume v will be reduced to v', and the expression of the
heat disengaged will be
pv ere v
Cragg Ey > Cpepary log Fe
The heat disengaged by the reentrance of atmospheric air into the
vacuum will therefore be what this expression becomes when p is there
U
made very small; it is then found that log 2 becomes very great,
=
but the product of p by log z is not the less small on that account ;
in fact we have
| p log > =p log p' — plog.p = p (log p! — log p)
a quantity which converges towards zero when p diminishes.
The quantity of heat disengaged will therefore be small in propor-
tion to the feebleness of pressure in the recipient, and it will be re-
duced to zero when the vacuum is perfect.
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 361
We shall add that the equation
Q=R(B— Clogp)
gives the law of the specific calories at a constant pressure and volume.
The expression of the first is
ROOTS
eer Sey ae Poy 3
5 dt. dt og)
of the second,
dBi de 1 dp
eh Ocak 1 OY pee ga
ate dy os ’)
equal to
aB aC C
Berar eR gy 53)
The first may be obtained by differentiating Q with relation to¢, sup-
posing p constant; the second, by supposing v constant. If we take
equal volumes of different gases at the same temperature and under the
same pressure, the quantity R will be the same for all; and accordingly we
see that the excess of specific caloric at a constant pressure, over the spe-
cific caloric of aconstant volume, is thesame forall, and equalto ‘OF
R
267 + t
Sc EV.
The same method of reasoning applied to vapours enables us to esta-
blish a new relation between their latent caloric, their volume, and their
pressure.
We have shown in the second paragraph how a liquid passing into
the state of vapour may serve to transmit the caloric from a body main-
tained at a temperature T, to a body maintained at a lower temperature ¢,
and how this transmission develops the motive force.
Let us suppose that the temperature of the body B is lower by the
infinitely small quantity dt than the temperature of the body A. We
have seen that if cb (fig. 4.) represents the pressure of the vapour
Fig. 4.
|
!
l
| &
|
| H ;
| par ae
| Ladin hind
: ers
| f ponl
A a a See eee A a ees _
a ae ae
$62 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. *
of the liquid corresponding to the temperature ¢ of the body A, and fg
that which corresponds to the temperature ¢ — dt of the body B; 64
the increase of volume due to the vapour formed in contact with the
body A, Ak that which is due to the vapour formed after the body A
has been removed, the formation of which has reduced the temperature
by the quantity dt; we have seen, I say, that the quantity of action de-
veloped by the transmission of the latent caloric furnished by the body
A, [and transmitted] from that body to the body B, is measured by the
quadrilateral figure ede f. Now this surface is equal, if we neglect the
infinitely small quantities of the second order, to the product of the vo-
lume cd by the differential of the pressure dh —ek. Naming p the
pressure of the vapour of the liquid corresponding to the temperature ¢,
p will be a function of ¢, and we shall have dh — ek = ae dt.
ed will be equal to the increase of volume produced in water when it.
passes from the liquid into the gaseous state, under the pressure p, at a
corresponding temperature. If we call p the density of the liquid, 6 that
of the vapour, and v the volume of the vapour formed, ¢ v will be its
weight, and Bs will be the volume of the liquid evaporated. The in-
crease of volume owing to the formation of a volume v of vapour will
therefore be
(aml)
v({1l— —).
Pp
The effect produced will therefore be
6 dp
1-— — — dt.
( iy br
The heat, by means of which this quantity of action has been pro-
duced, is the latent caloric of the volume v of vapour formed; let & be
a function of ¢ representing the latent caloric contained in the unity
of volume of the vapour furnished by the liquid subjected to experiment,
at a temperature ¢, and under a corresponding pressure, the latent ca-
lorie of the volume v will be Av, and the ratio of the effect produced
to the heat expended will be expressed by
2 enep
( 1 =) ee
k
We have demonstrated that it is the greatest which can possibly be
obtained ; that it is independent of the nature of the liquid employed,
and the same as that obtained by the employment of the permanent gases:
now we have seen that this is expressed by 2 C being a function of ¢
independent of the nature of the gases; we shall therefore also have
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 363
ee &\ dp
pjdt 1 af _ b\dp
agg ee whence k = @ yee
With regard to the generality of vapours, the ratio a ae the density
p
of the vapour to that of the liquid from which it is formed may be neg-
lected before it arrives at unity, so long as the temperature is not very
high ; we shall-have therefore, sensibly,
d
kh=C2L.
dt
This equation expresses that the latent caloric contained in equal
volumes of the vapour of different liquids at the same temperature, and
under the corresponding pressure, is proportional to the coefficient oe
of the pressure with regard to the temperature.
Whence it results, that the latent caloric contained in the vapours of
liquids which commence boiling only at high temperatures, as mercury
for example, is very feeble, since for these vapours the quantity ae is
very small.
We shall not insist upon the consequences which result from the equa-
tion
6 \dp
k= ( = \e (On
We shail simply remark that if, as everything leads us to believe, C
and 2 do not become infinite for any value of the temperature, & will
become null when we have 6= p, that is, that when the pressure is strong
enough, and the temperature sufficiently elevated to render the density
of the vapour equal to that of the liquid, the latent caloric is reduced to
zero.
§ V.
Variation is produced in the volume of all the substances of nature
by changes in the temperature and pressure to which they are subjected;
liquids and solids are amenable to this law, and serve equally to deve-
lop the motive power of heat; it has been proposed to substitute them
for the vapour of water, in order to render this motive force available ;
they have even occasionally been advantageously employed, particularly
when it was necessary to develop a very considerable momentaneous
effort, exerted within narrow limits.
In bodies of these kinds, as in the gases, it may be remarked, that of
the four quantities, the volume v, the pressure p, the temperature T, and
the absolute quantity of heat Q, two being determined, the others are
Vor. I.—Parr III. 2c
364 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
deducible from them ; if then we take two of them, p and v for example,
as independent variables, the two others T and Q may be considered as
functions of the former two.
In what manner the quantities T, p, and v, vary with respect to each
other may be ascertained by direct experiments upon the elasticity and
dilatability of bodies ; it is thus that Mariotte’s law relative to the elasti-
city of the gases, and Gay Lussac’s relative to their dilatability, lead to
the equation
pv=R (27+ 24);
all that remains is to determine Q in functions of p and v.
A relation exists between the functions T and Q, which may be de-
duced from principles analogous to those which we have just established.
Let us increase the temperature of the body by the infinitely small quan-
tity d T, and at the same time prevent the increase of the volume; the
pressure will then be augmented; if we represent the volume v by the
absciss a (fig.5), and the primitive pressure by the ordinate 0 d, this
Fig. 5.
augmentation of pressure may be represented by the quantity df, which
will be of the same order as the increase of temperature d T to which it
is owing, that is infinitely small.
Now we will take a source of heat A, maintained at the temperature
T+ dT, and allow the volume v to increase by the quantity 6c; the
presence of the source A, maintained at the temperature T + dT, pre-
yents the reduction of the temperature. During this contact, the quan-
tity Q of heat that the body possesses will increase by the quantity
dQ, which will be derived from the source A. We will afterwards re-
move the source A, and the given body will become cool by the quan-
tity d T, at the same time retaining the volume ae. The pressure will
then diminish by the infinitely small quantity ¢ e.
The temperature of the body being thus reduced to T, which is that
of the source of leat B, we will take B, and reduce the volume of the
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 365
body by a quantity 6c, in such a manner that all the heat developed
by the diminution of volume may be absorbed by the body B, and the
temperature remain equal to its primitive value T. The volume V also
again becoming the same as it was at the commencement of the opera-
tion, it is certain that the pressure will return to its primitive value 6 d,
as will also the absolute quantity of heat Q.
If we now connect the four points f, g, e, d by right lines we shall fornt
a quadrilateral figure, the area of which will measure the quantity of
action developed during the operation described. Now it is easy to see
that fg and de are two elements infinitely near, des¢ribed upon two
curves infinitely near, the equations of which will be T + dT = const.,
and T=const. They ought therefore to be considered as parallel ; the
two ordinates which terminate the quadrilateral figure in the other di-
rection being also parallel, the figure is parallelogrammical, and mea-
sures be X df.
Now fd is nothing but the increase experienced by the pressure p,
the volume v remaining constant, and T becoming T + dT. We have
therefore
— ¢p
df= aT
whence
fd= TT dT.
ie
And be being the increase of volume do
fadxXbe _ dvidT
aT
dp
It only remains to determine the heat consumed in the production of
this quantity of mechanical action.
We have first raised the temperature of the body subjected to expe-
riment by the quantity dT without changing its primitive volume v;
afterwards, when it had become v + dv, we have lowered its tempera-
ture by the same quantity d T without varying its primitive volume
v+dv. Now it may easily be seen that this double operation can
be effected without loss of heat; let us suppose that » being a number
indefinitely great, the interval of temperature dT be divided into a
number z of new intervals Be and that we have z + 1 sources of
heat maintained at the Sig T, T +..— ae , T+ zat. neeicrcrig
n
B+ @—U4F and T + AT.
To raise ite temperature of the body upon which we are operating
2c2
366 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
from T to T + dT, we bring it successively into contact with the se-
cond, the third, and the (7 +1)th of these sources, until it has ac-
quired the temperature of each of them. When, on the contrary, the
volume v of the body being increased by d v, we wish to give it the tem-
perature T, we bring it successively into contact with the wth, the
(x — 1)th, and the first of these sources, until it has acquired the tem-
perature of each of them. We then return to these sources the heat
that has been borrowed from them in the first part of the operation; for
it is not necessary to attend to the differences of an order of inferior mag-
nitude, arising from changes that may have been produced in the speci-
fic caloric of the body, in consequence of the variations of v and Q.
Nothing therefore will have been lost or gained by any of these
sources, excepting always the source of which the temperature is T+ d T,
which will have lost the heat necessary to elevate the temperature of the
body upon which we are operating from T + Aha T+dT,
n
and the source maintained at the temperature T, which will have ac-
quired the heat necessary to reduce the temperature of the same body
“s
from T +—— to T. If we suppose x to be infinitely great, these quan-
tities of Wit may be neglected.
We see, therefore, that when the body in question, (its temperature
being thus reduced to T,) is brought into contact with the source of
heat B, the heat communicated to it from the source A will be all it
has gained from the commencement of the operation. In consequence
of the reduction of its volume in contact with the body B, it will be found
at its original volume and temperature; the quantities Q and P will
therefore have re-assumed their primitive value; it is therefore certain
that all the heat borrowed from the source A, and nothing but that heat,
will have been given to the body B.
Whence it results that the effect produced,
dvd T
dT
dah
is owing to the transmission of the heat absorbed by the body subjected
to the experiment during its contact with the source A, and which has
afterwards flowed into the source B.
The temperature having remained constant during the contact with
the source A, it follows that the variations dp and dv of the pressure
and the volume are connected by the relation
dT dT
ap ——dp+ aut v=0
These variations dp and dv occasion a variation in the absolute A vnc
tity of heat Q, the expression of which is
:
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 367
(5 “y
dota ye?» er igo\a
BOS See deo ree fear ey
L dp}
such is the quantity of heat consumed in the production of the effect
that we have just calculated. The effect produced by a quantity of heat
equal to unity will therefore be
dQ dt dQ aT
dv dp dp dv
It will be shown, as in the case of the gases, that this effect produced,
is the largest which it is possible to realize; and as all the substances of
nature may be employed, in the manner that has just been indicated,
to produce this maximum effect, it is necessarily the same for all.
When this theory has been applied specially to the gases, we have
called z= the coefficient of d T in the expression of this maximum quan-
tity of action; the equation therefore of all thesubstances of nature, solid,
liquid, or gaseous, will be
dQ dT_ dQ aT_
dv dp dp dv
in which C is a function of the temperature which is the same for all.
For the gases we have
T = — 267 + +p,
whence we deduce
ale, 3c A SAR
dp = R and a = R°
The preceding equation applied to the gases takes therefore the
form
dQ dQ _ sks :
Vite TR ap a RC=F(p,v):
it is the equation at which we have already arrived, and of which the
integral is
Q=R(B—Clogp);
that of the general equation
1s of the form
Q=F(T)— Co»);
F(T) is an arbitrary function of the temperature, and ¢ (p, v) a parti-
cular function satisfying the equation
368 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
(See the note appended to this Memoir.)
We shall now deduce various consequences from the general equation
at which we have arrived.
We have previously seen that when we compress a body by the quan-
tity dv, the temperature remaining constant, the heat disengaged by
the condensation is equal to
laa ~ zo (ee) |:
dQ=dv dp ( 7T
sane dp }
dQdT dQdT_
and as
the preceding expression takes the form
ice '&
IQ EM Fs ey
‘Ss ae
This last equation may be put under the form
dv
dQ=-—d mons
Q pc aT
i is the differential coefficient of the volume with regard to the tem-
perature, the pressure remaining constant.
We thus arrive at this general law, which is applicable to all the sub-
stances of nature, solid, liquid, or gaseous : Jf the pressure supported by
different bodies, taken at the same temperature, be augmented by a small
quantity, quantities of heat will be disengaged from it, which will be pro-
portional to their dilatability by heat.
This result is the most general consequence deducible from this axiom:
that it is absurd to suppose that motive force or heat can be created
gratuitously and absolutely.
§ VI.
The function of the temperature C is, as we see, of great importance,
in consequence of the part it. sustains in the theory of heat: it enters
into the expression of the latent calorie which is contained in all sub-
stances, and which is disengaged from them by pressure. Unfortu-
nately no experiments have been made from which we can determine
the values of this function, corresponding to all the values of the tem-
perature. To obtain ¢ = 0 we must proceed in the following manner.
4
a pat
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 369
M. Dulong has shown that the air, and all the other gases taken at
the temperature of 0°, and under the pressure 0™76 of mercury, when
compressed by a of their volume, disengage a quantity of heat, ca-
pable of elevating the same volume of atmospheric air by 0°421.
Suppose that we operate upon a kilogramme of air occupying a
volume v = 0°770 of a cubic metre, under the pressure of the atmo-
sphere p, equivalent to 10230 kilogrammes upon a square metre ; we
have
pv=R (267 + 2),
and
Q=R(B—Clogp).
If a variation be suddenly effected in v by an infinitely small quan-
tity dv, without there being any variation in the absolute quantity of
heat Q, we shall have
pdv+vdp=Rdt,
dB dC d
OS Rf ee — cab? & LA 9
(F log pF; ) ae Rca,
and
or preferably
og (Ge ber $e )=R dp_R (Ato —Rdt—pdv
267 + ¢
d : ie ; ;
Now R ae Se log P) being the partial differential of Q in re-
spect of ¢, p remaining constant, is nothing else than the specific caloric
of the air at a constant pressure; it is the number of unities of heat ne-
cessary to elevate a kilogramme of air under atmospheric pressure by
one degree; we have therefore
dB _¢ =
Roi =
BE tog p) = 0-267.
Then substituting — Py for dv, and 0°421 for dt, we arrive lastly at
1
— = 141.
C
This is the maximum effect producible by a quantity of heat, equal to
that which would elevate by 1° a kilogramme of water taken at zero,
passing from a body maintained at 1° to a body maintained at 0° It
is expressed in kilogrammes raised one metre high.
_ Having the value of C, which corresponds to ¢ = 0, it is interesting
% know, setting out from this point, whether C increases or decreases,
and in what proportion. An experiment of MM. De Laroche and Bé-
_vard upon the variations experienced by the specific caloric of the air,
370 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
when the pressure is varied, enables us to calculate the value of the dif-
dC
dt
In fact, according to our formulas, the specific calorie of the air un-
ferential coeffici
“; rendering this
der two pressures p and p! differs by R Mie log ? ;
be
quantity equal to the difference of the specific calorics, as it has been
deduced from the results of MM. De Laroche and Bérard ; taking the
mean of two experiments, we find
dC 9
dt = = 0°002565.
In these experiments the air entered into the calorimeter at the tem-
perature of 96°90, and quitted it at that of 22°83 ; 0°002565 is therefore
the mean value of the differential coefficient a between these two
temperatures.
From this result we learn, that between these two limits the function
C increases, though very slowly; consequently the quantity é dimi-
nishes ; whence it follows that the effect produced by the heat diminishes
at high temperatures, though very slowly.
The theory of vapours will furnish us with new values of the func-
tion C at other temperatures. Let us return to the formula
which we have demonstrated in paragraph IV. If we neglect the den-
sity of the vapour before that of the fluid, this formula will be reduced
to
dp
1 _dt
hig Sa
We may remark in passing, that at the temperature of ebullition oe
is nearly the same for all vapours; C itself varies little with the tempe-
rature, so that & is nearly constant. This explains the observations of
certain philosophers, who have remarked that at the boiling point, equal
volumes of all vapours contain the same quantity of latent caloric ; but
we see at the same time that we are only approximating to this law, since
it supposes that C and be are the same for all vapours at the boiling
point.
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 371
From the experiments made by several philosophers we are enabled to
calculate the values corresponding to the boiling point of & and £ » for
different liquids; we can therefore deduce from them the corresponding
1
al Pa.
values o CG
T Corre-
empera~ | sponding
ture values
of 1
ebullition. of
NAMES
of
Liquids.
we
Cc
pour at the temp.
of ebullition, the
density of the air
a kilogramme of
being 1.
heat contained in
=
3
ie
z=
aes
=
=
=
2
o
H
3
oO
~
5
5
Ss
=
Density of the va-
Quantity of latent
Sulphuric Ether...
PAICOHON.. 6.0.2 00c0e8
1
sites "4.51 2. . °
eee 391 0°45 543°0 | 100 1115
Ree treo | 8207.) 768. | 1668 | 1-076
pentine ...... 30
These results confirm, in a striking manner, the theory that we are
explaining ; they show that C is slowly augmented with the tempera-
ture, as has been already stated : we have seen that for ¢ = 0, = = 1°41,
whence C = 0°7092; this result is deduced from experiments upon the
velocity of sound.
We here find, starting from experiments upon the vapour of water,
for ¢ = 100°, a = 1115, whence C = 0°8969; C is therefore in-
creased from 0 at 100° to 0°187, which gives as the mean of the dif-
ferential coefficient between these two limits
dC — o00187.
dt
The mean of the two experiments performed by MM. De Laroche
and Bérard gives us, between the limits 22°83 and 96-90, for the mean
value of “ the quantity 0°002565.
These two resulis differ little from each other, and their divergence
will be sufficiently explained, by reflecting on the number and the va-
riety of the experiments whence the data on which they are founded
are derived.
372 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
There is another means of calculating the values of a between
extended limits of the temperature in an approximative manner; for
this it is necessary to admit, that the quantity of caloric contained in a
given weight of the vapour of water is the same whatever be the tem-
perature and the corresponding pressure; and still further, that the
laws relative to the compression and the dilatation of the permanent
gases are equally applicable to vapours: adopting these laws, towards
which we have only approximated, the formula
dp
1 _dt
1) § eK
will express K in function of ¢; = may be deduced from 0 to 100°
from experiments long since made by several philosophers, and from
100° to 224° from recent experiments of MM. Arago and Dulong.
Thus we find for Values of oe
l 1
= 1°586 1°410
t= 35°5 300.
We have already found for
ing to the same values of ¢.
= 1102 1°106
co
]
co
] 1
t= 78:8 = 1142 the values of G correspond- 4 1:208
1
é€= 100° €
1
Tah
t= 1568 = 1072 1-078
These last, deduced from experiments upon sound, the vapours of
sulphuric ether, alcohol, water, and essence of turpentine, accord with
the first ina satisfactory manner.
These remarkable coincidences, obtained by numerical operations
performed upon a great variety of data, furnished by phenomena of
many different kinds, appear to us to add greatly to the evidence of our
theory.
§ VI.
The function C is, as we have seen, of great importance: it is the
connecting link of all the phenomena produced by heat upon solid,
liquid, or gaseous bodies. It is greatly to be desired that experiments
of the most precise exactitude, such as the researches upon the propa-
gation of sound in gases taken at different temperatures, were instituted,
in order to establish this function with all the requisite certainty. It
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 373
would conduce to the determination of several other important elements
of the theory of heat, with regard to which we know nothing, or have
arrived by our experiments at very insufficient approximations only.
In this number may be included the heat disengaged by the compression
of solid or liquid bodies; the theory that we have enunciated enables
us to determine it numerically for all the values of the temperature for
which the function C is known in a manner sufficiently exact, that is to
say, from ¢ = 0 to ¢ = 224°.
We have seen that the heat disengaged by the augmentation of
pressure dp is equal to the dilatation by the heat of the body subjected
to experiment, multiplied by C. With regard to the air taken at zero,
the quantity of heat disengaged may be directly deduced from the ex-
periments upon sound in the following manner.
M. Dulong has shown that a compression of oa raises the tempera-
ture of a volume of air taken at zero by 0°421. Now the 0:267 unity
of heat necessary to elevate a kilogramme of air taken at zero under a
constant pressure by 1°, are equal to the heat necessary to maintain the
temperature of the gas dilated by a of its volume at zero, above the
heat necessary to elevate the dilated volume, maintained) constant, by
1°; the last is equal to mi aI of the first; their sum is therefore equal
to the first multiplied by 1 + OL ; the former therefore, that is the
0°421
heat necessary to maintain the temperature of 1 kil. of air, dilated by
on of its volume, at zero, is equal to (0-267) : ( “ees opi or to
0:07911.
_ We arrive at, the same results by the application of the formula
Q=R (B—C log p);
whence
: ee! ; eer 1
putting C = 75>; and observing that a diminution of volume of 67
1
corresponds to an increase of pressure equal to 267 of an atmosphere.
Knowing the quantity of heat disengaged from gases by compression,
to ascertain that which a similar pressure would disengage from any
substance whatever, from iron for example, we write the proportion:
0:07911 of heat disengaged by a volume of air equal to 0°77 of a cubic
metre, subjected to an. increase of pressure equal to of an ate
374 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
mosphere, is to that disengaged from the same volume of iron under
the same circumstances as 0°00375, the cubic dilatability of the air, is
to 0:00003663, the cubic dilatability of iron. For the second term of
the proportion we find the number 0:0007718. Nowa volume of 0™77
of iron weighs 5996 kilogrammes ; the heat disengaged by one kilo-
gramme will therefore be alti ; for the pressure of an atmosphere
it will be 267 times more considerable, or equal to 0°00003436 ; the
division of this number by the specific caloric of the iron referred to
that of water gives the quantity of the elevation of the temperature of
the iron by the pressure of an atmosphere ; it is, we see, too feeble to be
appreciated by our thermometrical instruments.
§ VIII.
We shall not further insist upon the consequences to the theory of
heat of the results enunciated in this Memoir; but it may, perhaps, be
useful to add a few words upon the employment of heat as a motive
force. M.S. Carnot, in the work already cited, appears to have esta-
blished the true basis of this important part of practical mechanics.
High or low pressure engines without detent (dé¢ente) bring into use
the vis viva developed by the caloric contained in the vapour, in its pas-
sage from the temperature of the boiler to that of the condenser; the
high pressure engines without condenser act as if provided with a con-
denser at a temperature of 100°. In the latter, therefore, all that is
brought into use is the passage of the latent caloric contained in the
vapour, from the temperature of the boiler to the temperature 100°. As
to the sensible caloric of the vapour, it is entirely lost in all the engines
without detent.
The sensible caloric is in part utilized in the engines with detent,
in which the temperature of the vapour is allowed to sink: the cy-
lindrical envelope, the use of which in Woulf’s engines with two cy-
linders is to maintain the vapour at a constant temperature, though very
useful to diminish the limits of the variation of the motive force acting
upon the pistons, has an injurious influence as to the quantity of effect
produced compared to the consumption of fuel.
To render useful all the motive force at our disposal, the detent
should be continued until the temperature of the vapour be reduced to
that of the condenser; but practical considerations, suggested by the
manner in which the motive force of fire is employed in the arts, pre-
vent the attainment of this limit.
We have elsewhere shown that the employment of gases, or of any
other liquid than water, between the same limits of temperature, could
add nothing to the results already obtained; but from the preceding
considerations it follows, that the temperature of the fire being from
=
M. CLAPEYRON ON THE MOTIVE POWER OF HEAT. 375
1000° to 2000° higher than that of the boilers, there is an enormous
loss of vis viva in the passage of the heat from the furnace into the
boiler. It is therefore only from the employment of caloric at high
temperatures, and from the discovery of agents proper to realize its
motive force, that important improvements may be expected in the art
of utilizing the mechanical power of heat.
NOTE.
The integral of the general equation
aQ. dT _dQaT _¢
dv dp dp dv
is, as we have seen,
ECP) — a (gpa es Poa os ee)
F (T) is an arbitrary function of the temperature T, varying from one
body to another; C is a function of the temperature which is the same
for all the substances of nature, and ¢ (p, v) is a particular function of
Pp, and of v satisfying the equation
ET aie Wg pete em
be substituted in the equation (2), it will be
dT de?’ dTd¢’ aT [a
this equation is satisfied by putting
= “ dp
_ P PMY “a.
anes v
v
@" satisfying the equation
aT =
4 ieag a tage ‘al a ne p ad aT
ia ee Ty, = 7 Se ?
dv dp dpdv dp roe d a fi
v
376 M. CLAPEYRON ON THE MOTIVE POWER OF HEAT.
We thus see that ¢ (pv) is given by a series of terms, each of which
is obtained by means of the preceding one, by differentiating it in re-
spect to v, multiplying by the ratio 4 and integrating the result in
dv
a2
respect of p. Thefirst term of this series being / dT, it is evident that
dv
the value of ¢ may be easily obtained; substituting this value in the
equation (1), we have for the expression of the general integral of the
partial differential equation
dQadT: dQdTi2
peice a ai alia oop | 6
dvudp dp dv
the formula
Q=F(T)-—C dp
Sx
dv
d
pasties dp
dp 4 nye
fr arde fo
dv
dT d
dp d dp a =
ao = = ed
tf? afro fs
v dv
+ . . e . . . . . . . . . .
This equation gives the law of the specific calorics, and of the heat
disengaged by the variations of the volume and of the pressure of all
the substances of nature, when the relation which exists between the
temperature, the volume, and the pressure is known.
ARTICLE XVI.
Remarks on the cause of the Sound produced by Insects in
Slying ; by Dr. Hermann Burmeister, of the University
of Berlin.
From Poggendorff’s Annalen derPhysik und Chemie, vol. xxxviii. No. 6. p. 283.*
Ir is an opinion generally entertained by natural philosophers, that
the sound which insects produce during their flight arises from a vibration
of the wings. ‘This notion can have had its origin only in the circum-
stance that no one had taken the trouble to examine sufficiently into the
mechanism which produces thesound. I feel myself the more justified
in making this assertion, as I find merely incidental remarks on the
buzzing of insects recorded by naturalists, who notice the phenomenon
only for the purpose of illustration. Baumgzrtner in his “Naturléhre,”
(3rd edit. 1829, p. 229,) expresses himself thus: “Therefore an insect
can produce a sound through the rapid vibration of the wings :”—and
Wilh. Weber says in his essay on tubes with tongues (Zungenpfeifen),
(Leges Oscillationis oriunde, si duo corpora diversa celeritate oscillantia
ita conjunguntur ut oscillare non possunt nisi simul et synchronice, ex-
emplo illustrate tubulorum linguatorum.—Hale 1827, 4to,) Page 1:
“Insecta v.c. quedam volantia motu alarum sonum certe ultitudinis pro-
ferunt: ale vero neutiquam in ipsis insita earumque partes ad equili-
brium repellente agitantur, sed vi extra alas posita, musculorum nimirum
etnervorum. In both cases, therefore, the cause of the sound is referred
to the motion of the wing as a vibrating body.
In the course of an investigation of the different methods by which
insects produce sound, with the view of communicating them in my
Manual of Entomology (vol.i. p.509, Berlin, 1832), my attention was first
directed to this subject, and [ soon found that the wings have no part
whatever in the formation of the sound, for the hum of the insect
continues even when its wings are entirely cut away. I perceived,
however, a different pitch of the sound; and remarked that the more
of the wing was taken away the higher this became. The insect on
which I made my experiments was Eristalis tenax. I have at this time
no living specimen of this species at hand, but have now another dipte-
rous insect still larger, the Tabanus bovinus, on which I have repeated
all my experiments, and obtained precisely the same result. It appeared to
* The Editor is indebted for the translation to Mr. W. Francis of Berlin.
378 BURMEISTER ON THE SOUND PRODUCED
me, therefore, not improper to call the attention of natural philosophers
to this subject by a special memoir, and in particular to give a sketch
of the mechanism which forms the sound. I must next remark, that
the sound which the insect emits is capable of considerable variations.
It may be that it maintains an equality of pitch and strength during a
uniform motion of the wings, for so in fact it appears; but every
change in the velocity of the flight, every disturbance of the ordinary
motion, generally causes also an alteration in the tone. An idea of the
origin of the tone is however only to be obtained when the insect is held
by the legs, and excited by pressure or other means to go through all its
motions of the wing, and thus to produce a sound. I found in this
manner that the tone of the common gad-fly ( Zabanus bovinus) varied
self from the hands of the troublesome observer was shown with greater
or less energy. Such a difference might be explained, it is true, upon
the supposition that the agitation of the wing produces the tone by the
varying rapidity with which the vibrations are made; but this expla-
nation is untenable, as the same phzenomenon continues when the wings
are entirely cut away; an operation which produces only a variation of
the tone, but does not render its formation impossible.
Before I proceed to assign the true cause of the sound, I think it ne-
cessary to give a short description of that part of the insect by which
alone the sound is produced. This part is the breast or ‘horax. This
consists, in two-winged insects (Diptera, Linn.) of a simple cavity, co-
vered by a thin elastic parchment-like envelope, which exhibits on its
surface various symmetrically arranged elevations and depressions (fig. 7.
Plate V.), but is notwithstanding perfectly continuous. These elevations,
the relative magnitude and form of which differ very much in different
diptera, originate either in the muscles attaching themselves to the in-
ternal surface of the cavity, or in air-bladders forming continuations of
the trachez, which stretch in these parts the coriaceous skin and make it
vesicular. The largest of these elevations is the vaulted partition which
forms the limit between the thorax and the abdomen (Kirby’s mefa-
phragma. Fig. 7. B), and to which the great dorsal muscle, of which a
horizontal section is represented in fig.S. A Plate V., is attached in the di-
rection AB. On the middle of the back the further point of connection of
this muscle forms a broad longitudinal stripe. Near to this, on each side,
appear two elevations, a front one lesser (fig. 7. C), and a hinder one
greater (fig. 7. E, where it appears partly covered by the wing): both
originate in the lateral muscles, which are extended in the direction C D
and EF through the cavity of the thorax. In fig. 8. a section of them
as the effort to extricate it-
BY INSECTS IN FLYING. 379
is also exhibited, the front pair between CD and BB, the hinder pair
between EF and CC. Besides these lateral muscles, there is a pair si-
tuated behind EF, and another pair in the intermediate space between
CD and EP, which has a slanting position, and the whole course of
which may easily be perceived in fig. 8.at DD. These muscles, namely
the single great dorsal muscle and the four pair of lateral muscles, are
capable of contracting the cavity of the thorax in different directions ;
the first only from the fore to the hind part, so as to increase the con-
vexity of the back, the other four pair from the upper to the inferior
part, so that the sides become more arched, and the back flatter. The
other elevations are less interesting to us, and contain the muscles for
the movement of individual organs. Thus, for example, in the elevations
G at fig. 7. lie the muscles which serve to expand and elevate the wings:
they are represented in fig. 8. by E E and FF: in the elevation behind A
lies the muscle which serves to close the air-hole fig. 7*; in the elevations
a, b, ce, which are the hips of the three pair of thighs, are the muscles
for the motion of the legs, &c. The depressions between the elevations
are immaterial: there are however three of them, of which we must take
a more particular notice; namely, the one wherein the further air- or re-
spiration-hole (stigma) is situated (fig. 7*.), the second in which the
hinder air-hole is perceived (fig. 7**), and the third in which the wing
is placed, and which we perceive (fig. 8) in the section at the point of
insertion of each wing (dd). Having thus far considered the structure
of the thorax, we have now only to observe that the spaces between the
muscles are filled up by the tubes which carry air to the trachez, and
that the chain of nerves and the aorta, which are supported by the forked
prolongation of the covering represented at fig. 8, traverse the larger
space beneath the dorsal muscle of the intestinal canal.
We find as the external organs of the thorax, the wings, the poisers
(halteres), the scales, and the legs. The wings, d, are placed in a depres-
sion on the side of the thorax, which is formed by a very thin prolon-
gation of the exterior envelope in a slanting direction, as may be seen
in fig. 7. They consist of a pocket-like folding of the epidermis, sup-
ported and extended by the horny veins. The muscles by which the
wings are expanded and elevated commence at the base of those veins.
Behind the wing is the scale, a circular pellicle (fig.7.g), which is placed
perpendicularly, connected with the basis of the wings, and moved by
muscles of its own. Behind this, quite at the end of the thorax, are si-
tuated the poisers (fig. 8. f.), which are the rudiments of the undeveloped
hinder wings, and are likewise capable of independent movement by
their proper muscles. We have already mentioned that the legs are at-
tached to the hips (fig. 8. a, b, c,); their structure is unimportant to our
investigations.
The movement of the wing, on which the sound in the next place de-
Vor. L—Panrr III. 2D
380 BURMEISTER ON THE SOUND PRODUCED
pends, is produced by the contraction of the lateral muscles ; for, the co-
vering of the back being drawn down presses on the base of the wing, and
thereby the short base end of the wing, projecting freely into the cavity of
the thorax, is forced downwards beneath the wing about the more out-
ward point of support; in consequence of which the opposite end rises.
This raising of the wing is then accelerated by its proper muscles of ele-
vation E E and F F, but ceases as soon as these and the simultaneously
contracted lateral muscles are relaxed. The wing now falls again, which
falling is accelerated by the contraction of the dorsal muscle and the
concomitant curvature of the back. Such then is the mechanism which
produces the action of the wing. But at the same time this mechanism
also causes rhythmical contractions and expansions of the whole thorax
and of thenumerous air- canals of its interior. Now the contraction drives
out a part of the air; the expansion, on the contrary, causes an equal
quantity of fresh air to stream through the air-pipes above described ;
and there is, therefore, connected with the motion of the wings, a con-
stant, proportionally rapid, and intensive breathing ; and this breathing
is the cause of the sound. It produces the sound by the alternate efflux
and influx of the air, just as the current of air sounds the eolian harp
when forced at short intervals through the small holes of the sound-
board, or (to take a more familiar example) by a mechanism similar to
that of the mouth in whistling. The sound of the zolian harp bears
a wonderful resemblance to that of many insects; and the observation
that the sound is no longer heard when the air-holes of the thorax are
closed, without however injuring the insect in any other manner, is de-
cisive. It is true that the insect dies of suffocation soon after this ex-
periment, but not directly, because the respiration through the air-holes
of the abdomen continues for some time; but these emit no sound during
the flight of the insect, for they are then inactive, as other observations
have proved; the insect breathes through the air-holes of the abdominal
part when it sits and crawls, but through the air-holes of the thorax
when on the wing. According to this the hum of insects is in reality a
whistle. The variation which the mutilation of the wings causes in the
tone is easily to be accounted for, if we consider that by this action the
moveable part becomes lighter, and also that the motion of the same, by
the continued equal exertion, is quicker; but this causes a quicker cur-
rent of air, which must produce a higher tone. On the contrary, a mu-
tilation of the moveable apparatus produces a slower motion, a slower
current of air, a deeper tone. I believe that the foregoing facts and
observations offer sufficient evidence, but the reader can satisfy him-
self as to the truth of the phenomenon by performing the same simple
experiments.
Ihave now only to add, that I have, in my Manual of Entomology,
mace mention of small moveable plates which are found behind the aper-
BY INSECTS IN FLYING. 381
ture of the stigma. Their presence however is not general: in the Za-
banus bovinus they do not appear, but are found in Hristalis tenax. I
have given an engraving of the hinder air-hole, magnified forty times, in
which it is shown on the inner side. We find an oval band-like claudent
muscle or sphincter, to both ends of which other muscular bands are
attached: perpendicular to the inner surface of this claudent muscle stand
sixteen to eighteen small horny lamelle, which are of the same breadth
as the muscle, and connected in the middle by another longitudinal
horny band. On the other side, which is directed outwards, the claudent
muscle is clothed with skin, upon which are feathery hairs, which cover
the entrance of the air-pipe like a sieve and exclude foreign bodies. _ I
am at present inclined to consider these small horny lamelle rather as
a mere scaffolding serving to support the claudent muscle, but leave it
to naturalists to decide whether, and how far, they contribute to the for-
mation of the sound. In either case however this can be but of little
consequence, as Many insects possess no such plates.
I have further to combat some objections which have already been
publicly urged against the correctness of my theory of the production
of the sound. M. Silbermann has given publicity to this in France by
a translation of the chapter of my work which treats on this subject in
his Revue Entomologique, by which also M. Goureau was led to perform
similar experiments. The latter finds* all that I have said perfectly exact,
except that the sound is suspended when the stigma is closed, and this
is precisely the main point of the question. On the contrary, however,
I must maintain that, although a sound may be heard as long as the
gum employed to close the stigma is moist, and the air can make its way
through it, none is audible when the gum is perfectly dry. The animal
indeed dies of suffocation soon after. M.Goureau has not taken this cir-
cumstance into consideration, but has even hazarded the opinion that the
sound originates through the friction of the edges of those plates which
compose the thorax. This can however be the case in those insects only
in which we find on the thorax really distinct plates connected by fibres;
and as the diptera are not in possession of such, his theory cannot be
applied to them. But even in respect to the other orders with skeleton
hips his theory is untenable ; first, because the mobility of these hips,
on account of their intimate connection, must be very trifling; and se-
condly, because the sound is far too strong to be produced by the friction
of such minute surfaces. That the feeble sound of the chirping Capri-
corn beetle ( Cerambycina), when the body is in a quiet position, is really
produced by such friction is well known; but it is also obvious, from the
feebleness of this sound, that the loud buzzing of the flying insects,
which besides sounds quite differently, cannot arise from such friction.
* Revue Entomologique, by G. Silbermann, Strasb. 1835, vol. iii. p. 107.
2v2
382 BURMEISTER ON THE SOUND PRODUCED BY INSECTS.
To conclude, I have to mention in addition to the above, that MM. J. F.
Schelver*, Dumeril+, and Chabrier {, are quite of my opinion, even
though Schelver differs from me in some unimportant points; however,
neither their observation, nor the theory of the phenomenon, has been
communicated by them with sufficient detail.
Explanation of the Figures.
Puate V. Fig.’7. A side view of the thorax of Tabanus bovinus, magni-
fied eight times in linear dimension.
Fig. 8. Horizontal section of the same, in the direction between
ED (Fig. 7.), at the same power.
Fig.9. Air-hole of Hristalis tenax, magnified forty times.
* Wiedemann’s Archiv, vol. ii. part 2. p. 210.
+ Essai sur le Vol des Insects. Paris, 1822, p.40 seq.
+ Dictionnaire des Sciences Naturelles, vol. i. p. 15.
{The reader may be amused by referring to The Clouds of Aristophanes, where _
Socrates is described as engaged in an investigation of this subject.—Ep1r. ]
383
ArticLe XVII.
Note on the Reflection of Radiant Heat ; by M. MEttont.
(Read before the Academy of Sciences of Paris, November 2nd, 1835.)
From the Annales de Chimie et de Physique, vol. ux. p. 402.
A.ruoucu the researches of Leslie and Rumford established the
fact that the quantities of calorific rays reflected by different bodies
depend on the nature of those bodies and the polish of their surfaces,
the proportion of the reflected to the incident heat in each particular
case remained yet undetermined. The results presented by my experi-
ments on the immediate transmission of radiant heat enable us to solve
this question with considerable exactness.
When the calorific rays fall perpendicularly on the anterior surface
of a diathermanous plate with parallel faces, they undergo a certain re-
flection, then penetrate into the interior of the plate, reach its further
surface, and, after there undergoing a second reflection, issue forth into
the air, pursuing their original direction. In certain cases there is no
internal absorption, and consequently the difference between the incident
heat and that transmitted, will in such cases be the value of the reflec-
tions produced at both surfaces. The substance in which this fact is
most distinctly perceived is rock salt. We know that plates of this sub-
stance, when very pure and well polished, transmit 0°923 of the incident
heat, whatever may be the thickness of the plates, the nature of the
rays, or the modifications which these may have previously suffered in
their passage through other plates.
Let us suppose, for example, two plates of rock salt, the one measur-
ing one millimetre*, and the other ten millimetres} in thickness. Ac-
cording to what we have just stated, the transmissions of these two plates
will be equal; and if we imagine the thick plate divided into ten layers,
each one millimetre thick, the absorbent power of the nine layers that
succeed the first will be of no appreciable value. Hence we may infer
that, if the rays suffer any absorption, it must be in the first layer. Let
us suppose for a moment that this takes place. On this hypothesis, the
molecules which constitute the first layer of one millimetre in thickness
will retain all the heat that is not completely transmissible by rock salt,
and the quantity of heat lost in the passage through either of the two
plates, that is, 1 — 0-923, or 0:077, will be but the sum of the rays ab-
sorbed or retained, and of those reflected at the two surfaces. Let the
* 0°03987 in. T 0:394 in,
384 M. MELLONI ON THE REFLECTION OF RADIANT HEAT.
heat, as it issues from the source, be received on one of the two plates,
the thinner, for instance, and as it emerges from this let it be trans-
mitted through the other. The supposed absorption or purification will
have taken place in the first plate; and allowance being made for the
rays reflected at the two surfaces, none will reach the second plate but
such as are completely transmissible by its substance, so that the less
suffered by these rays in their passage through the second plate will be
necessarily less than 0°077. But experiment shows that even in passing
through the second plate the quantity of heat transmitted is exactly
0°923, and the quantity lost 0°077. It is clear therefore that no absorp-
tion can have taken place in the passage through the first plate, and that
0°077 is precisely the amount of loss produced by reflection at the first
and the second surface of each plate.
As the nature of the source of heat has no influence on the transmission
of rock salt, the calorific rays must evidently suffer the same loss (0°077)
in the sum of the reflections which they undergo when entering and leay-
ing the plate of rock salt. The same may be said of the different rays
emitted by the same source, for the loss 0°077 is constant with respect
to heat emerging from all sorts of screens exposed to the action of any
calorific radiation whatsoever.
We may now, with the greatest facility, ascertain the proper value of
each of the reflections. Let 1 represent the incident heat, and R the
amount of reflection at the first surface, then 1 — R will be the quan-
tity that penetrates the plate, and R (1 — R) the amount of reflection at
the further surface ; for as the rock salt absorbs none, the whole quan-
tity 1 —R arrives at the further surface, and is there reflected in the
ratio of R:1. Now as the sum of the two reflections added to 0-923
(the quantity transmitted) must reproduce the quantity of incident heat,
which we represent by unity, we have the equation
R+R(—R) +0923 =1*;
* The heat reflected at the second is evidently returned to the first surface,
where it undergoes in the interior of the plate a third reflection, by which it is
again returned to the second surface, and a partial reciprocation of the heat be-
tween the two surfaces is thus continued for some time. It is obvious that
when the plate is perpendicular to the direction of the rays, there is always a
portion of heat issuing from the surface, in combination with the transmitted
rays, after having undergone three, five, seven, or more reflections. Although
the portions thus added to the transmission are of very little value, yet, as their
number is infinite, their sum may be supposed to constitute a sensible part of
the calorific effect indicated by the thermomultiplier placed in the direction of
the rays. Hence it might be reasonably objected that the equation R + R
(1 — R) + 0-923 = 1 is not perfectly true, as it rests on the assumption that
0°923 is the exact value of the direct transmission. Fortunately, however, a
very simple experiment, already described, furnishes a sufficient answer to the
objection. Let the rock-salt lens be inclined at an angle of about 25° or 30° to
the incident rays: the portions of heat which undergo the reflections repre-
sented by the odd numbers 3, 5, 7, &c., will not, in issuing from the plate,
M. MELLONI ON THE REFLECTION OF RADIANT HEAT. 385
whence we derive
R =1 + 0°923 = 1 + 0°9607.
As the first sign of the radical would lead to an absurd result in the
case under consideration, it must be rejected. The reflection at the
surface of the plate will then be 1 —-°09607= 0°0393 to the unit of inci-
dence, and such also will be the ratio of the second reflection to the quan-
tity of heat which reaches the further surface of the rock salt. But if
it be desired to have the absolute value of the second reflection, it will
be found by substituting 0-0393 for R in the expression R (1—R), or
yet more simply by taking the difference between the numbers 0:077
and 0°0393, which gives in each case 0°0377.
It now remains to be seen whether the quantities of heat reflected by
other transparent substances be equal or not equal to those produced by
the surfaces of rock salt. For the solution of this question it is suf-
ficient to observe, that a thick plate of glass, of rock crystal, or any other
diaphanous substance gives a calorific transmission sensibly equal to that
of another plate, the same in substance though different in thickness. If
we take, for instance, one plate of glass 8 millimetres * thick, and an-
other 83, and expose them separately to the radiation of a Locatelli
lamp, we shall find no sensible difference between the two quantities of
heat transmitted. From this experiment it is obvious that the layer of
half a millimetre, which constitutes the difference of thickness between
the two plates, causes no appreciable absorption of the calorific rays,
which have already traversed 8 millimetres of the same substance. Let
us now detach this thin layer from the thicker plate and expose it (thus
separated) to the rays emerging from the plate of 8 millimetres; it will
reflect part of them and transmit a// the rest. The quantity lost will
therefore represent the effect, and only the effect, of the two reflections. If
this experiment be made with care, the number found as the quantity
transmitted will be very nearly 0°923+, and therefore the number repre-
senting the part reflected will still be 0°077. This is true not only with
mingle with the bundle of calorific rays directly transmitted, but will be thrown
laterally. If their action on the thermomultiplier be appreciable, it must be
perceived in the diminution of the effect. But the galvanometer always ex-
hibits the same deviation, both when the plate stands perpendicularly and when
it stands obliquely. These multiplied reflections have, therefore, no sensible
influence whatsoever on the measure of the transmission which is represented
exactly by the number 0-923.
* 0315 in.
+ Are these small variations, which do not amount even to hundredth parts,
to be attributed to a difference of polish in the surfaces, or to a difference of
energy in their reflecting powers? This question seems not to admit of an
easy solution by experiment. However, if we were to judge by the complete
analogy which these phenomena bear to those that occur in the reflection of
light, we should think it highly probable that the trifling differences observed
partly depend on the indices of refraction in the different substances of which
the plates are composed.
$86 M. MELLONI ON THE REFLECTION OF RADIANT HEAT.
respect to glass, but also with respect to rock crystal, alum, fluate of
lime, topaz, sulphate of barytes, &c., so that a thin plate of any of these
substances, if very pure and well polished, will, when placed behind a
thick plate of the same substance, always transmit 0°923 and lose 0:077.
The same numbers will be found also when the thin plate is placed
behind a thick plate of a different substance, provided the latter be less
permeable to the direct rays of the source. Thus a thin plate of rock
crystal transmits 0°923 of the radiation from thick glass ; and a thin plate
of glass transmits the same proportion of the heat emerging from water
oralum. The heat thus transmitted is so purified, that although it issues
from a very thin layer, it is still capable of traversing considerable depths
of glass or rock crystal without suffering any absorption. Hence it is
that plates of glass or rock crystal measuring 7 or 8 millimetres in thick-
ness will, when exposed to the rays emerging from a layer of water or
alum measuring 1 or 2 millimetres in thickness, transmit 0-923, as is done
by plates only half a millimetre thick.
Concluding from all this that radiant heat undergoes a reflection of
about four hundredths of the incident heat which falls perpendicularly on
the surface of a diathermanous substance, we perceive at once the method
that is to be pursued in order to determine the quantity of calorific rays
reflected by athermanous bodies. We first observe the effect of the
calorific transmission through a plate of rock salt when the radiation,
emitted by a constant source, is perpendicular to its faces: the plate is
afterwards inclined towards the incident rays. In the quantity of heat
transmitted, there appears no sensible diminution so long as the inclina-
tion does not exceed 25° or 30° around the normal. The reflection of the
perpendicular rays is then sensibly equal to that of the rays forming an
angle of between 60° and 65° with the reflecting plane. Now, this be-
ing supposed, let us bring a bundle of radiant heat to fall on the well-
polished surface of glass or rock erystal at an incidence of between 60°
and 65°, and receive the reflected portion in the interior of the tube
which envelopes the thermomultiplier. After having marked the calo-
rific force indicated by the galvanometer, let us repeat the same expe-
riment on the polished surface of the athermanous body without making
any change in the respective positions of the several parts of the appa-
ratus.’ We shall thus obtain a second calorific force, differing from the
first. The reflection of the athermanous body will evidently be 0:0393,
which represents the value of the reflection at the surface of the rock
crystal multiplied by the ratio of the observed forces.
The following are the mean results of several comparisons made be-
tween the quantities of heat reflected by rock crystal and yellow copper.
Reflection of — Reflection of Ratios of the Product of the two numbers
Rock Crystal. Yellow Copper. two reflections, (0°0393 and J1°3).
3°15 35°63 11°3 04441.
M. MELLONI ON THE REFLECTION OF RADIANT HEAT. 387
By diminishing the angle of incidence which the calorific rays form
with the surface of the rock crystal, an increase of reflection is obtained,
especially in the small incidences. But this effect is nearly imperceptible
on the metallic surface, for, in passing from 80° to 20°, I have been able
to verify with the plate of brass (/aiton) no more than a difference of 4 or
5 hundredth parts. The concentration of radiant heat by the action of
metallic mirrors of any form will therefore be always inferior to that
produced by rock-salt lenses of the same breadth. Thus, for example,
the conical mirrors of polished brass which are applied to one face of
the pile of the thermomultiplier will never give more than $34 or about
half the effect given by a rock-salt lens having its diameter equal to
that of the opening of these cones.
388
Arricue XVIII.
Observations and Experiments on the Theory of the Identity
of the Agents which produce Light and Radiant Heat ; hy
M. MEL ont.
(Communicated to the Academy of Sciences of Paris, Dec. 21, 1835.)
From the Annales de Chimie et de Physique, vol. i. p. 418.
Aone the hypotheses on which it has been proposed to explain the
radiation of heat, there is a remarkably simple one which M. Ampére
has lately modified and developed with great ingenuity. It consists in
regarding radiant heat as a series of undulations produced in the ether
by the vibrations of bodies possessing heat. Those undulations should be
longer than the undulations which constitute light, if the calorific source
were dark; but when the source is at the same time calorific and lu-
minous, there must always be a group of waves simultaneously possess-
ing the property of heating and that of illuminating. Viewed in this
way, there would be no essential difference between radiant heat and
light. A very extensive series of zthereal undulations coming into con-
tact with the different parts of our body would produce the sensation
of heat: a more limited number of these would also possess the power
of exciting in the retina of the eye a vibratory movement calculated to
produce the sensation of light.
No cause had been yet assigned for the quick transition of the purely
calorific to the shorter waves, which are at the same time calorific and
luminous. M. Ampére has found a very plausible explanation in the
phznomena presented by the immediate transmission of terrestrial heat
through water.
If an iron ball be heated at different times to different temperatures,
and brought each time to act on a thermoscope placed behind a layer of
water (either pure or charged with salt) measuring from three to four
millimetres in thickness, the thermoscope exhibits no indication of heat
so long as the metallic mass remains obscure, but as soon as the ball
becomes decidedly red, it indicates a slight calorific transmission. Now,
as the eye contains a certain quantity of watery humour, an absorption
and transmission similar to that exhibited by the layer of water will
take place in the interior of this organ also, which will therefore suffer
none but the undulations producing luminous heat to arrive at the retina.
On the supposition that both agents are identical, it is needless to
show that the calorific rays are propagated in a straight line, and that
their angle of reflection is equal to their angle of incidence.
-
M. MELLONI ON LIGHT AND RADIANT. HEAT. 389
It is true that there appears a striking disparity in their manner of
propagating themselves when the calorific and the luminous radiations
fall upon the surface of diaphanous bodies, whether solid or liquid. In
this case the medium is immediately traversed by one portion only of
the radiant heat, while the other pertion is slowly transmitted from
layer to layer. But to a certain extent this phenomenon may be ac-
counted for by supposing the ordinary conductible heat to be produced
by a vibratory motion communicated by the ethereal undulations of
every length to the anterior molecules of the medium, and then gra-
dually propagated to its further surface*.
Considerations derived from the different lengths of the ethereal un-
dulations will enable us to account for the two very distinct species of
transparence observable in diaphanous bodies relatively to the rays of
heat and those of light. Thus it will be easy to conceive why certain
substances possess but very little diathermaneity, though they are per-
fectly clear, if it be admitted that they intercept all the obscure waves,
the sum of whose intensities is greater than that of the luminous waves
even in the radiation of the most brilliant flame. On the other hand,
we shall perceive the cause of the diathermaneity of certain perfeetly
opake media, in the supposition that they allow themselves to be pene-
trated by particular groups of obscure undulations.
The hypothesis of identity is sufficient, no doubt, to explain a great
numper of general facts. It would not, however, embrace all particular
ceases, and, if we should proceed to a numerical examination of experi-
ments, would even give rise to some serious objections. But I deem it
useless to enter into detail on this subject, as the phenomena which I
* The propagation of ordinary conductible heat considered as the effect of
molecular vibration is essentially different from the vibratory motion produced
by sound in ponderable matter, or that produced by light in the ether ; for, in
the slow propagation of ordinary heat, the points first heated lose their tem-
perature only by little and little, and this temperature is always higher than
that which is gradually transmitted to the rest of the body, unless it be lowered
by other causes. But in the propagation of sound and light, the points first
agitated immediately communicate their motion to the adjacent points, and then
return to a state of repose, in which they remain until they are again set in
motion by a subsequent impulse. A wave is thus formed which propagates
itself with great velocity, and at any given instant there isno motion except in
the point which the sonorous or luminous wave has attained. The cause of
this difference, which seems inexplicable by the undulatory theory, has been
the object of M. Ampére’s inquiry in a memoir published for the first time in
the Bibliothéque Universelle of Geneva (May, 1832), and subsequently re-
printed in the Annales de Chimie and in the London and Edinburgh Philoso-
phical Magazine. M.Ampére finds that the cause of the difference between the
slow propagation of heat and other undulatory motions is to be assigned to the
distinction which he establishes between the vibrations of the molecules of bo-
dies with respect to one another, and the vibrations of the atoms which consti-
tute each molecule ; inasmuch as these two species of vibration may take place
not only separately but simultaneously in the same points of a body.
390 M. MELLONI ON THE IDENTITY OF THE AGENTS
am about to submit to the consideration of the Academy, seem to me to
leave no doubt whatever that light and radiant heat are the direct ef-
fects of two different causes.
If we decompose a bundle of solar rays by means of a rock-salt
prism, and measure the degree of heat proper to each band of the
spectrum (proceeding from that band in which the refraction is greatest
to that in which it is least), we find that the temperature increases from
the violet to the red, and that even in the dark space on the other side
this increase continues until it has reached a point midway between the
red and the yellow. - At this point a pretty rapid decrease of tempe-
rature takes place, and a total cessation of calorific action is perceptible
in the obscure band, the distance between which and the red is about
one third of the length of the luminous spectrum.
It is known that the refraction of solar undulations is greater in pro-
portion as they are shorter. In the obscure part of the spectrum, we
have none but calorific waves, which become shorter and shorter as
we approach more nearly to the red limit. When we enter the lumi-
nous part, the shortening of the undulations still continues from the
red to the violet. But it is to be recollected that according to the
theory of identity each simple colour is the effect of an undulation
which produces, at the same time and by the same species of vibration,
both heat and light.
Now if all the parts of the spectrum are made to pass through a
layer of water (from two to three millimetres in thickness) contained
between two plates of glass, and the temperatures of the emergent rays
are ascertained, we shall find that the maximum of temperature and
the last obscure limit are both close to the red limit. These effects
will be more decidedly marked if the layer of water be thicker. With
a layer of about four millimetres, the maximum will be found in the
red band. If we continue to increase the thickness of the interposed
layer, we shall find the maximum continually take the same direction
and pass successively over the different parts of the red, the orange,
and the yellow. When the rays have passed through a layer of 300
millimetres, the maximum becomes stationary at the commencement of
the green.
The obscure limit is found in that case much more close to the red
than it is in the normal spectrum; but there is still an appreciable in-
terval between the two, and this interval is necessarily greater when
the thickness of the layer of water is from eight to ten millimetres ;
whence we conclude that a portion of the obscure heat emitted by the
sun penetrates through a considerable depth of this liquid, and passes,
no doubt, through the watery humour of the eye into the retina, with-
out exciting the sensation of light.
But (to continue the explanation of the changes produced in the
WHICH PRODUCE LIGHT AND RADIANT HEAT. 391
calorific and luminous constitution of the solar spectrum by the inter-
position of diaphanous substances, ) if, instead of water, a plate of glass
be employed, the same variations will take place, though on a more
extended scale; in other words, the last obscure limit of the normal
spectrum and the maximum of temperature approaches the most re-
fracted part more nearly than it does when the medium is a layer of
water of equal thickness*. In all cases, the ratios of luminous intensity
between the several parts of the spectrum remain invariable, because of
the perfect transparence of the media traversed by the solar rays.
But if the plate of uncoloured glass be removed and coloured glass
substituted for it, the luminous spectrum will be entirely altered. If,
for example, a blue cobalt glass be employed, not only does the orange
disappear, but a great part of the green, a little of the blue, and the
middle of the red band, so that the spectrum then looks like a series of
zones, more or less broad and luminous, mixed with obscure bands. A
finely violet-coloured glass usually effaces the orange and the yellow,
and leaves but the red on one side and the blue and indigo on the
other. In fine, a red glass, as it intercepts the other rays almost en-
tirely, may be said to afford a passage to none but rays of its own
colour.
Now, in examining the distribution of the heat of the obscure and
the luminous bands, so capriciously coupled together in these several mo-
difications of the spectrum, we find the calorific energy more or less di-
minished according to the nature of the glass interposed; but the maai-
mum always remains nearly in the same position, and the temperatures
* I have shown in my first Memoir on the transmission of heat through solid
and liquid bodies how we may account for the different positions taken by the
maximum of temperature in the solar spectra produced by prisms of different
substances.
The above-mentioned experiments decisively prove that the position of this
maximum must depend not only on the matter, but also on the mean thick-
ness of the prism. To convince ourselves of this, we have only to take a large
hollow prism, filled with water, and partly cover one of its lateral faces with an
opake plate laid in the direction of its length, so as to leave the side situated
towards the refringent angle perfectly free. Upon measuring the temperatures
of the different zones of the spectrum, we shall see that the maximum of heat,
which, when the prism is entirely free, is found in the yellow, now that one
face is partially covered by the plate, approaches the last red limit and that
more closely in proportion as the portion which remains uncovered in the di-
rection of the edge is smaller. These variations are reproduced with more
or less energy by employing for the construction of the prisms solid diaphanous
_ bodies or liquids different from water; but there are no variations when we
employ rock salt. Hence it is clear that this substance, which transmits all the
calorific radiations of terrestrial sources with the same intensity, transmits solar
heat also without producing any change in the relative intensities of the dif-
ferent rays. It is for this reason that I have thought it advisable to make use
of a rock-salt prism in the dispersion of solar heat, and afterwards to consider
the alterations produced in the relative intensities of the refracted rays by the
interposition of transparent bodies.
392 M. MELLONI ON LIGHT AND RADIANT HEAT.
of the successive zones constantly decrease on each side with the great-
est regularity. Thus, notwithstanding the interposition of the coloured
glasses, the intensity of the heat uniformly increases from the violet to
the red, while the intensity of the light undergoes very irregular va-
riations, which render a given zone sometimes stronger and sometimes
more feeble than the succeeding zone.
Let us disregard that which takes place in the obscure part, and fix
our attention on the alterations produced in the visible part of the
normal spectrum, in which each luminous band is accompanied by a
calorific band possessing the same refrangibility. On the one hand we
see uncoloured media which have no influence on the luminous rays
and totally alter the ratios of intensity in the accompanying calorific
rays; on the other, coloured media which totally change the relative
energies of the luminous, without affecting the regularity of the propor-
tions existing between the corresponding calorific rays.
But if heat and light were both produced by the same movement of
the zthereal molecules, it is evident that each reduction of force in a
given ray of pure light should be accompanied by an exactly propor-
tionate reduction in the ray of heat possessing the same refrangibility.
Now the variations of intensity produced in each of the two agents by
the interposition of uncoloured or coloured media, so far from corre-
sponding through the whole of the luminous part of the spectrum, ex-
hibit the most striking diversity. Light and radiant heat, therefore,
proceed from two distinct causes*.
This being admitted, the complete separation of light from heat be-
comes intelligible; and such is the conclusion at which I have arrived,
with respect both to terrestrial fire and the solar rays. The process of
separation is exceedingly simple: it consists in causing the radiation
from the luminous sources to pass through a system of diaphanous bo-
dies which absorb the whole of the calorific, while they extinguish but
a part of the luminous rays. The only substances hitherto employed
by me are water, and a peculiar species of green glass coloured by
means of the oxide of copper. The pure light emerging from this
system contains much yellow, and possesses at the same time a tinge of
bluish green: 7% exhibits no calorific action capable of being rendered
perceptible by the most delicate thermoscopes, even when it is so concen-
trated by lenses as to rival the direct rays of the sun in brilliancy.
* These two causes themselves are, perhaps, but different effects of a single |
cause. The conclusion which appears to me to follow so clearly from my ex-
periments is therefore by no means opposed to the general theory of undula~
tions, according to which light and radiant heat arise from the motions commu-
nicated to the ether by the ‘molecular vibrations of luminous bodies and bodies
possessing heat. It will only be necessary to admit that the luminous and the
calorific rays are two essentially distinet modifications which the z=theneal fluid
suffers in its mode of existence. ?
393
ArtTicLe XIX.
On the Constitution of the Superior Regions of the Earth’s
Atmosphere ; hy M. Brot.
(Read Nov. 21, 1836.)
From the Compie Rendu des Séances de l’ Académie des Sciences.
In the application of mathematics to the phenomena of nature, there
is nothing more satisfactory than to see how analysis discovers the hid-
den links of the chain which unites facts so widely distant from each
other, that ordinary reasoning, far from being able to demonstrate,
could not even suspect their connection. It is thus that the sun’s pa-
rallax and the ellipticity of the flattening of the earth,—two elements
which it cost arduous labours and long voyages to determine,—were
found by the genius of Laplace to be results so intimately connected
with the lunar motions, that their measure is to be most exactly de-
duced from the diligent observation of those motions. When the same
geometer had improved the theory of astronomical refractions, by con-
necting therewith the real constitution of the terrestrial atmosphere
more exactly than they had previously been, it was naturally to be ex-
pected that these two classes of phenomena would thenceforth serve
to throw such light on each other, that the constitution of those layers
of the atmosphere which are rendered inaccessible to us by their ele-
vation, might be discovered by means of the measure of the refractions.
Such an expectation must have been yet more confidently entertained,
after Mr.Ivory had theoretically established atmospheric forms, which,
by representing the refractions still better than they had been by La-
place, likewise reproduced with greater fidelity the decrease of the
densities, and the temperatures near the earth’s surface, where we have
it in our power to observe their law. But in order that the agreement
thus obtained between the refractions and the supposed constitution of
the atmosphere might afford a rigorous proof that this was its real con-
stitution, it was necessary to determine the degree of influence that any
different state whatsoever assigned to the superior layers would exer-
cise on the absolute quantity of the refraction observed here on earth.
‘That could not, however, be accomplished by means of the differential
_ equations, until then applied to the motion of light in the atmosphere,
because they assign to the gas of the atmosphere a composition uniform
throughout, and a refractive power constantly proportional to its
394: M. BIOT ON THE CONSTITUTION OF THE
density,—two conditions which already hypothetically limit the pro-
blem. Besides, as the analytical integrals deduced from those equa-
tions embraced the whole extent of the supposed atmosphere, they
rendered it impossible to distinguish the share which the superior layers
had in the total refraction obtained, and more particularly those shares
which should necessarily be ascribed to them.
The first of these difficulties has been solved in the memoir on Astro-
nomical Refractions presented by me some months ago to the Aca-
demy. Tue differential equations of the motion of light in a spherical
atmosphere, however constituted, are there established. But the ter-
restrial atmosphere presents certain general phenomena which should
be introduced into the equations, and which serve to limit them. Thus,
the absolute smallness of the refractions at every distance from the
zenith, excludes the possibility of the luminous trajectories which re-
enter into themselves, and shows that those trajectories are all but very
slightly curved.
Again, at the elevations which are accessible to us, we find by expe-
riment that the refringent power decreases in proportion as we ascend,
and that the depression of the visible horizon increases. Hence, it is
concluded that as we ascend from the surface of the earth, the angles
formed by the elements of each trajectory, with their central radius
vector, gradually diminish. This species of inflection is virtually proved,
at the height even of Chimborazo, where Bourguer observed refrac-
tions near the horizon; for, by a general theorem, given in my former
memoir, the direction in which these refractions vary is found geome-
trically connected with the mode of inflection in question. Analysis
now shows that this geometrical phenomenon results from the feeble-
ness of the refringent power as compared with the density ; and since,
in the whole of that part of the atmosphere which is placed within our
reach, the relation of these two elements is far from having attained
the limit at which the phenomenon should cease, it is a necessary con-
sequence of the law of the diffusion of the gases that it should exist at
much greater elevations. In fine, even when we can no longer prove
that it exists, we are able at least to assign limits beyond which it can-
not extend: these limits are the result of the small altitude of the ter-
restrial atmosphere. The observation of the twilights proves that the
height of the last particles of air which afford us a perceptible reflection
of light does not exceed, even if it equals, ~}5 of the earth’s semi-
diameter *, and the phenomena of the tails of comets show with what
* Note by M. Arago.—All the determinations of the height of the atmo-
sphere hitherto effected by observing the duration of twilight, rest on the sup-
position that all the solar rays which mark the limit of the phenomenon have
been but once reflected, and that, after being twice reflected on laminz of air,
solar light is too feeble to produce more than an inappreciable glimmering. At
SE ————
SUPERIOR REGIONS OF THE EARTH'S ATMOSPHERE. 395
an excessive tenuity of matter the reflection is perceptible. Thus at
that distance from the earth, the refringent power of the atmosphere
ceases; and, this being granted, we may calculate the angle that each
luminous trajectory forms at this point of emergence, with its radius
vector. We then see that this angle continues to decrease from the
greatest elevations at which it had ceased to be perceptible by the senses.
However the extreme value of it is but slightly different from the last
that can be observed; a fact which, when coupled with the free commu-
nication of the layers of the air with one another, does not allow us to
suppose that the intermediate values depart abruptly, or in any consi-
derable degree, from the order of magnitude assigned by these two
limits. If we then consider any luminous trajectory whatever reaching
an observer placed at the level of the sea, under a certain zenith di-
stance, which will also be the angle formed by the trajectory with its
radius vector at the point, we shall be obliged to admit that while the
former ascends to a very great height in the atmosphere, its element
becomes more and more inclined to the latter. The subsequent vari-
ations of this inclination, of whatever kind they may be, are always very
inconsiderable, and lead to an ultimate value which, though lower, does
not differ much from the values found at an inferior elevation.
This condition, which is proper to the terrestrial atmosphere, being
introduced into the general differential equations, conjointly with the
values of the refringent power, the temperature, the pressure and the
hygrometrical state of the inferior layer, I rigorously deduce from them
for each zenith distance two values of the total refraction; the one ne-
cessarily too high, and the other too low: so that the mean error is al-
ways less than half their difference. Now when the latter becomes
inappreciable by observation, the total refraction is found indepen-
dently of every hypothesis respecting the uniformity of constitution
and constancy of the refringent power of the superior layers, which are
| virtually placed beyond the reach of our examination; for then all
| possible diversities of condition, compatible with the pheenomena which
we have been just now considering, can produce no change in the mean
resent these bases of calculation would be inadmissible. Experiments on po-
arization have shown in fact that multiple reflections contribute materially to
the dissemination of solar light in the atmosphere ; and that, in each direction,
rays reflected several times form a considerable part of the whole bundle that
reaches the eye. As to the rest, it is evident, that by introducing this new
datum into the calculation, we should find the different heights of the atmo-
sphere less than they had been found by the old method.
‘M. Biot’s Remarks on this Note.—The less the thickness of the atmosphere,
the more rapidly convergent are the developments of the refractions, and the
| more confined the definite limits which I have found for the refraction. Ac-
cording to the result announced by M. Arago, those limits will become more
,| arrow than they are given by the numbers which I adopted from the evalua-
| tion of Delambre, and consequently the zenith distances to which those limits
|| may be applied can be extended still further.
Vor. I_—Panrrt III. Qk
$96 M. BIOT ON THE CONSTITUTION OF THE
value, but one so minute that its amount can neither be measured, nor
the fact of its existence established by our instruments.
By applying this reasoning to the meteorological circumstances which
present themselves at the level of the sea, when the pressure is 0", 76
and the temperature 10° of the centesimal thermometer, I find that all
the varieties of constitution that can be assigned to the atmosphere of
the earth do not cause in our mean value of the total refraction a va-
riation amounting to the following quantities, namely, at 45° zenith di-
stance, 0", 001; at 74°,0' 277; at 80°, 2!" 243. These limits increase
in proportion as we descend toward the horizon; but so long as the
trajectory is not excessively low, the shortness of its passage through
the atmosphere, together with the smallness of its curvature, causes
them to deviate nearly in the same degree from the true refraction,
which is then found to differ but little from their mean. The zenith
distance being, for instance, 86°30', the mean error is only 1! 32, if
we take as our term of comparison the very perfect table of Mr. Ivory.
We may calculate in a similar manner the refractions observable in
every other layer of the atmosphere, their meteorological elements
being given, and shall find analogous limits of their values. It is ne-
cessary to observe, however, that in proportion as the station of the
observer is more elevated, these limits approach each other more
nearly, for equal zenith distances ; and their deviation may in that case
be disregarded, though under the same zenith distance, they are by no
means to be neglected, when the observer is at the level of the sea. It
is by these means that I intend to effect the solution of the problem
which I have proposed to myself. For if we consider, for example,
the trajectory which arrives horizontally at the level of the sea, and
cause it to re-ascend into the layers of the air, according to a law of
decrease sufficiently exact to bring it back, without any supposable
error, to the height at which the density is reduced to the hundredth
part of its primitive value (about ;;%5 of the earth’s semidiameter),
the angle which it then forms with its radius vector has become so
small that the part of the refraction produced on the remainder of its
course may be so exactly appreciated by means of our limits, that it may
safely be included among the observations made at the earth’s surface,
for the error cannot amount to 0°15" for the whole refraction. The
superior layers, from which this portion is derived, might therefore be
constituted in any imaginable manner as to their densities and tem-
peratures, and in a certain degree even as to their physical nature,
without our ever perceiving any appreciable effect of these differences
in the total refractions observed; and thus, reciprocally, the observed
refractions afford no idea of those elevated regions of the atmosphere.
All that remains then is, that we endeavour to discover a law of
decrease in the densities and the temperatures, such as may represent
SUPERIOR REGIONS OF THE EARTH’S ATMOSPHERE. 397
with sufficient exactness the lower part of the atmosphere, which
is within reach of observation and experiment, and whose physical
bases are such that this law may be mathematically extended, as an
approximation, to about two-fifths of its whole height. Now this is
easily accomplished, and we are led to it by the refractions them-
selves. For, if they are calculated on the supposition that the pressures
are proportional to the first power of the densities, the value obtained
is too great; but if the second power of the densities be employed,
the value obtained will be too small. The true law lies, therefore, be-
tween these two limits, and an approximation to it may be obtained by
taking an indeterminate expression consisting of two terms affected to
each of those two powers. If this expression be subjected, as it should
be, to the general conditions of equilibrium in the layers, as well as to
the particular circumstances of pressure and temperature which take
place in the inferior layer, and lastly to the decrease of temperature
observed near the earth’s surface, we obtain precisely Mr. Ivory’s at-
mospheric constitution, with all its numerical constants determined, and
identical with those which he obtained by means of other considera-
tions*. Now Mr. Ivory has proved that this law being applied to the
inferior layers perceptibly agrees with the barometrical formula which,
with respect to these layers, is the faithful expression of facts imme-
diately resulting from the decrease of the densities. We are therefore
justified by this combination of identical results, in extending its appli-
cation to the limits of elevation already indicated as being equal to
about +;%5 of the earth’s semidiameter. The rest of the refraction is
then obtained independently of every hypothesis respecting the consti-
tution of the superior layers, with a limit of error less than 0! 15 even
for the horizontal refraction, as has been already asserted.
And it is net only advantageous, but theoretically necessary, that we
should have to form no hypothesis in respect to the state of these last
layers, which are unknown to us. For the law of decrease founded on
the two first powers of the densities, though it adapts itself to all the
* The expressions thus obtained differ from those of Mr. Ivory only in their
including the decrease of the weight which Mr. Ivory has neglected in con-
sideration of the small height of the earth's atmosphere. But theoretically
speaking, this consideration is no longer applicable to the atmospherical system
which he employs in the integration of the differential element of the refraction,
because it still gives an infinite extent to the atmosphere. Mr. Ivory, no
doubt, found it necessary to proceed in that manner, in order to render the
analytical integrations, on which the refraction depends, practicable: but this
restriction is no longer necessary when we employ the numerical quadratures,
and then any expression whatsoever that represents the real state of the atmo-
ee may be employed without limitation. As to the equations of equi-
hbrium which determine the ratios which the pressures and the densities bear to
the height, they are always integrable, and with the same facility when the pres-
sure is expressed by any number of terms, containing any powers whatever of
the densities.
Z2E2
398 M. BIOT ON THE CONSTITUTION OF THE
phenomena observed in the lower layers, becomes unquestionably
defective toward its limits, inasmuch as it would give the atmosphere
an infinite altitude, while its real altitude is certainly limited and very
inconsiderable. There is here also that condition which is always in-
troduced into differential equations, and by means of which they are
limited, before the law of decrease of the densities is introduced as a
function of the height. So that there is an evident contradiction in
afterwards integrating them analytically, by extending this decrement
even to infinity, as the law derived from the first two powers of the
densities requires. Fortunately, however, the effect of this contradic-
tion is little or none as to the total refractions, because the rapidity of
the decrease, depending on the conditions of the lower layers, soon
renders the refringent power insensible at a height which is yet very
inconsiderable, so that the observable result is the same as it would be
in an atmosphere sensibly limited. But this approximation, which is
produced spontaneously, without affording any means of ascertaining
its exactness, is attended also with the inconvenience of leading us to
suppose that the physical state of the most elevated layers of the atmo-
sphere is really the same as that which has been hypothetically as-
signed to them; while the observable results, being determined almost
entirely by the total pressure of that remainder of the atmosphere, and
by the conditions of its contact with the lower layers which support
its weight, depend in no sensible degree on that state, and are conse-
quently incapable of even indicating it.
Though the foregoing considerations establish the utter impossibility
of some inductions which might have proved highly valuable in re-
ference to terrestrial physics, they show us how the tables of refractiou
may be made more perfect, and above all more general, than they are
at present. In fact, those tables have been hitherto constructed with
reference to a certain given constitution of the atmosphere, and by
merely changing the pressure and the temperature conformably to the
indications of the barometer and thermometer in the inferior layer,
they are supposed to be made applicable to all climates and seasons.
But such an identity is in direct opposition to the observed physical
phznomena: for instance, the decrease of temperature near the earth’s
surface appears to vary considerably at the same place in the different
seasons of the year, and it is very unlikely that its absolute amount is
the same in all situations. Now this element affects one of the most
important constants of the tables; and according to a theorem which I
have demonstrated, it is on this that the differences of the refractions
near the horizon principally depend. It is therefore necessary to de-
termine its variations experimentally, at different times and places, for
the heights that are accessible to us; and instead of supposing, as has
been done hitherto, that it is constant and everywhere the same, to
SUPERIOR REGIONS OF THE EARTH'S ATMOSPHERE. 399
take those variations into account in the calculation of the tables. The
next thing to be done would be to observe the hygrometrical state of
the inferior layers, and in particular to measure the amount of its di-
minution in proportion to the height to which we ascend; for these
elements also, though in a very inferior degree, affect the same con-
stants. The real constitution of the atmosphere up to very consider-
able degrees of elevation being known, the methods which I have
given in my Memoir will therefore enable us to deduce the refraction
numerically for the layers to which they are applied. When we have
arrived at elevations at which the valuation by limits becomes sufficient,
the remainder of the refraction will then be obtained by this process
without any hypothesis. We shall then have tables of refraction
adapted to circumstances which are really variable, though supposed
in the present tables to be uniform. And, should we be thus led to
‘discover, (a thing not at all improbable,) that these variations, or at
least the most considerable of them, take place chiefly in those atmo-
spheric layers which are not at a great elevation, it might be possible
in the great observatories of Europe to observe regularly the constants
of those troubled regions of the air by means of small capéive balloons,
carrying with them instruments with indicators, and the results obtained
in this way might be applied as correctives to permanent tables con-
structed for the untroubled region. The only errors then to be appre-
hended would be those which might arise from an accidental alteration
in the supposed sphericity of the refringent layers; such an alteration,
for instance, as might be produced by a violent agitation continued for
along time in one direction. But the effects of these disturbances
being thus isolated, and their extent being known, it would perhaps
be not impossible to give them due attention, if they should be found
to possess any constancy, and analysis would have then done for the
theory of astronomical refractions all that it is allowed us to expect.
400
ARTICLE XX.
Remarks on the real Occurrence of Fossil Infusoria, and their
extensive Diffusion; by Prof. LHRENBERG.
From J.C. Poggendorff’s Annalen der Physik und Chemie, vol. xxxviii. No. 5,
p-213*; with a Plate.
In the month of April of this year I communicated to the Academy +
a remarkable fact relative to the infusoria of the mineral springs of
Carlsbad, namely that they appeared to be the same species as those
met with on the French coasts of the Atlantic and in the Baltic. For
the knowledge of this fact I was indebted to the kindness of the pro-
prietor of the porcelain manufactory in Pirkenhammer, near Carls-
bad, M. Fischer, who, at my request, brought for me to Berlin some
of the water containing living animalcules. In order to follow up the
examination more closely and more extensively, I requested another
supply, which I received a fortnight ago in good condition. At the
same time M. Fischer informed me, in a letter dated 20th June, that
he himself had made a curious observation. He had remarked that the
Kieselguhr{ (announced by M. Radig in the Jahrbicher fiir Deutsch-
lands Heilquellen, &c., edited by MM. von Grefe and Dr. Kalisch,
1836, p.193.), which occurs in the peat-bog of Franzensbad, near Eger
in Bohemia, consists almost entirely of the shields of Navicule, and ap-
pears to owe its origin to the action of volcanic heat on the bottom of
the sea. M. Fischer sent me, together with this information, a piece of
this fossil siliceous body, originally rather more than 2 inches long,
1 inch broad, and $ inch high, which I have presented to the Royal
Mineralogical Cabinet; he requested me at the same to determine
the forms of the animaleulz, and to publish his observations together
with my results. Microscopical examination directly confirmed the
observation of M. Fischer, that the Kieselguhr of Franzensbad con-
sisted almost entirely of Navicule ; and the great transparency and clear-
* This paper was read in the Royal Academy of Sciences of Berlin on the
7th July, 1836. [The translation is by Mr. W. Francis. ]
+ Compare the Report of the Proceedings of the Royal Academy of Berlin,
1836, pp. 36, 50, and 55; and Wiegmann’s Archiv. for Nat. Hist. 1836, p. 240.
t [A kind ofsiliceous paste ; from Kiesel, st/ex, and Guhr, a term used in mins
ing for water carrying dissolved minerals when in a thick liquid state——W. F.]
PROF. EHRENBERG ON FOSSIL INFUSORIA. ° 401
ness of the little siliceous shields made it indeed probable that an intense
heat had caused their accumulation from a more voluminous combus-
tible substance. But the opinion that they have belonged to the bottom
of asea is improbable, since the chief part of the forms, both from their
figure and size, as well as from the number of their inner stripes, agree
very exactly with the Navicula viridis now living in all the fresh water
around Berlin, and widely diffused in other parts. In the sample of the
peat-bog there were also to be perceived Navicule, which, though
mostly different from those of the Kieselguhr, were still living species,
and in quite a different proportion to one another, and generally in a
smaller proportionate quantity in the same space.
After this the original specimens of the Kieselguhr from the Isle of
France, and the Bergmehl from San Fiore in Tuscany, in the Museum
of Berlin, which had been chemically analysed by Klaproth, and to
which were still attached the descriptions in his handwriting, were
microscopically examined. It was found that these substances also
consisted almost wholly of several different forms of fossil infusoria,
so that the whole siliceous contents given by Klaproth are to be assigned
to the infusoria shells.
As early as the year 1834 I announced to the Academy, in the ap-
pendix to my third paper on Organization, that, after having examined
with M. Henry Rose the discovery made by M. Kitzing, that the
shields of the Bacillaria consist of silex, this fact was fully established,
not only for these, but also for other living forms; a fact which the
observations of M. Fischer, and my examination of the Kieselguhr ana-
lysed by Klaproth, confirm anew.
As the interest of this phenomenon appeared to be great, I com-
pared several other siliceous and earthy substances from the Royal
Mineralogical Cabinet, which Professor Weiss had the kindness to place
at my disposal, without however being able to forward the object of
the research. At a fortunate moment it occurred to me that such
siliceous shields might be in use in the arts as polish, like the siliceous
shavegrass, Hguisetum. 1 purchased therefore in Berlin several kinds
of tripoli and polishing earths for examination. I examined first the
common or leaf tripoli, and found at once that this also consisted en-
tirely of the shells of infusoria. All the others were of a different
inorganic nature. A comparison of this tripoli of the shops (which,
as I was informed, comes from the Harz and Dresden) with the sci-
entifically arranged species of tripoli in the Royal Mineralogical Mu-
seum, showed that this so-called leaf-tripoli is evidently the same stone
which was received by Werner as a new species in mineralogy under
the name of Polirschiefer (polishing slate), which it has ever since re-
tained. The specimens at hand from the Kritschelberg, near Bilin, ex-
hibited so perfect a similarity, as well outwardly as in the forms of
402 PROF. EHRENBERG ON FOSSIL INFUSORIA.
the infusoria of which it consisted, that it is evident that the leaf-tri-
poli sold at Berlin comes from Bilin in Bohemia, through Dresden. A
similar stone to this is the Polirschiefer found at Planitz near Zwickau,
if indeed the locality of the specimen examined by me be correct. But
the Klebschiefer from Montmartre, which Klaproth has analysed, exhi-
bited only doubtful traces of infusoria shields. The appearance of the
fossil infusoria in the form of the Polirschiefer of Bilin is plainly of
great importance to our further researches into geognostical rela-
tions. In the same slate are found the impressions of an extinct fish, the
Leucisceus papyraceus of Bronn, (according to Agassiz, ) and several im-
pressions of plants, probably belonging to the tertiary formation.
Thad been inclined, even before these researches, to assign a great
influence in the origin of the Raseneisen (bog-iron-ore) to an infusorium
discovered by me in 1834, and of which I have, in April 1835, given an
engraving in Plate X. of my Codex of Infusoria, under the name of
Gaillonella ferruginea, which is perhaps the same as the Hygroerocis
ochracea of botanists. The minuteness of these corpuscles deterred me
however from publishing this important circumstance ; but since the
discovery of so many and various shield-infusoria as stone masses, and
since I have found that even the animalcule which almost entirely form
the Polirschiefer of Bilin are also a species of the genus Gaillonella, I
no longer hesitate to add this observation to the rest. That the for-
mation of the Raseneisen, or of the Wiesenerz (meadow-earth), as
a continual phenomenon excites great attention, and has given rise
to many but not sufficiently explanatory theories, is well known. I
have every spring observed in the marshes, particularly in the turf di-
stricts about Berlin, large quantities of a substance of a very deep ochre
yellow, sometimes passing into flesh red, often covering to a great ex-
tent the bottom of the ditches from one to several feet deep, and much
developed in small holes and in the footsteps of animals grazing. This
mass is extremely delicate, and without any consistency, dividing itself
at the least touch into an indefinite number of parts. Where it has
become dry, after the evaporation of the water, it appears exactly like
oxide of iron, for which it has been formerly often mistaken. We per-
ceive however under the microscope, with a moderately high magnifying
power, extremely slender articulated threads, the members of which
measure only ;,/,5 of a line, and in which the yellow colour is inherent.
At the beginning of last summer I satisfied myself that these slender _
articulated threads do not lose their form in a strong red heat, but the
colour changes to a red-brown, which is exactly that of iron-ochre.
It was found that by the application of muriatic acid the colour was
dissolved, without the articulated threads being changed: in the solu-
tion precipitated iron was clearly visible. There is also one of the
genus Gaillonella, very similar to the Bacillaria, but a very minute or-
PROF. EHRENBERG ON FOSSIL INFUSORIA. 403
ganic being, containing a yellow ochre colour, in which there is pro-
bably a great proportion of iron, in the same manner as phosphate of
lime is contained in the bones. By extraction of the lime, the gelatine
of the bones retains, as is well known, its form: in the same manner
the Gaillonella ferruginea possesses a siliceous shield, which retains
its form unchanged after the extraction of the iron.
I have already examined with the microscope various specimens of
the Raseneisen from Berlin, from the Ural, from New York, and
other places, and find the extremely voluminous yellow iron oxide
which is attached to them, and which perhaps has originally served to
form them, to consist also of similar connected threads in rows, which
resemble the Gaillonella in size, form, and colour, and which are not
destroyed by the action of heat or muriatic acid, but no longer form
such evident articulated threads as in the living animal. If I compare
it, when its fibres are disjointed, with the Gaillonella distans in the Po-
lirschiefer, I find no reason to consider the phenomenon in the Wiesen-
erz-ochre as a different one. I received, through the kindness of
M. Karsten, the vegetable products of the mineral water of the salt-
works of Colberg, in which there is a yellow earthy substance, in great
quantity, formed on the surface. At first it collects at the surface of
the stagnant water, as I was informed, in a greenish mass, similar
therefore to the protoxide of iron. Dried and exposed to the air it re-
mains of a beautiful ochre yellow, and on being heated it becomes of a
red-brown blood-stone colour. On dissolving it in muriatie acid I
found a great quantity of iron, with remains of silex. This substance
consists, like the marsh-ochre, of articulated threads, which separate
into single members: it resembles also very much the Gaillonella fer-
ruginea. These Gaillonelle are used in Colberg for iron-colour in house-
painting. The circumstance that this production of the salt-spring col-
lects on the surface of a yellowish green colour, and afterwards sinks
to the bottom and changes into yellow, determines perhaps a special and
not otherwise characterized species of the same genus*. Thus the sili-
ceous contents of the Raseneisen, and the incombustible organic form
of the minute bodies constituting the ochre which surrounds it, make it
highly probable that here also an organic relation exists through in-
fusorial formation, though only so far as to form after death, by the
large proportion of iron they contain, a central point or nucleus, towhich
all other iron in solution immediately around it is attracted.
* Another quantity of this mass sent from the Diirrenberg salt-works has
determined this question, since it appears in this that these living animals (?)
also are always yellow; that in dying they rise to the surface of a grayish
green colour (protoxide of iron), and in sinking to the bottom they again take
the yellow colour.
404 PROF. EHRENBERG ON FOSSIL INFUSORIA.
The animals which I found in the above-mentioned fossils are the
following species.
I, Nine species in the stone from Franzensbad.
1. Navicula viridis, as chief mass; 2. N. gibba; 3. N. fulva;
4, N. Librile, all freshwater animalcules, very common in the
neighbourhood of Berlin ;—5. NV. viridula; 6. N. striatula;
both sea animalcules now living: the first I know of only from
the Baltic, nearWismar; the second from near Havre in France,
and in the mineral water of Carlsbad ;—7. Gomphonema pa-
radoxum ; 8. G.clavatum: both species now common near
Berlin ;—9. A species of Gaillonella, G. varians? of which I
have hitherto seen only fragments.
II. In the peat-bog of Franzensbad I found, around the Kieselguhr,
five species:
1. Navicula granulata, as the most usual form, not occurring in
the Kieselguhr; 2. NV. viridis, rare; 3. Bacillaria vulgaris? ;
4. Cocconeis undulata; both sea animals ;—5. Gomphonema
paradoxum (clavatum ?), still found near Berlin.
Only two forms are common to the turf and the Kieselguhr, which
is found in it, and which thence probably owes its origin to a different
period.
III. I found in the Kieselguhr of the Isle of France several species :
1. Bacillaria vulgaris? as chief mass ; 2. B. major, an unknown
species, but perhaps allied to the former, which is a well-
known sea animalcule; 3. A small Navicula, perhaps the in-
fant state of NV. fulva; 4. N. gibba; 5. N. bifrons, a still living
species, occurring rarely near Berlin.
IV. The Bergmehl of Santa Fiora, or San Fiore, of Klaproth’s col-
lection contains nineteen different species:
1. Synedra capitata, new species, as chief mass, between which
2. S. Ulna, an animalcule living both in fresh and sea water ;
—3. Navicula inequalis; 4. N. capitata ; 5. N. viridis ; 6. N.
gibba ; 7. N. phenicenteron; 8. N. Librile; 9. N. Zebra; all
freshwater animalcules ;—10. WV. viridula, a sea animalcule
from the Baltic;—11. N.granulata; 12. N. Follis; two yet un-
known or extinct species;—13. Cocconeis undulata, a sea ani-
malcule ;—14. Gomphonema paradoxum; 15. G.clavatum ;
16. G. acuminatum ; freshwater animals from Berlin;—17.
Cocconema cymbiforme, a freshwater animalcule; 18. Gail-
lonella italica, new species; 19. Siliceous needles of a sea
Spongia, or freshwater Spongilla.
V. In the Polirschiefer of Bilin, specimens of which M. Weiss had
_ himself collected there, I found four species:
s
PROF. EHRENBERG ON FOSSIL INFUSORIA. 405
1. Podosphenia nana, new species, as chief mass; 2. Gaillonella
distans, new species; 3. Navicula Scalprum?; 4. Bacillaria
vulgaris? probably all sea animals.
VI. In the leaf-tripoli of the shops at Berlin, probably received through
Dresden or from the Harz, were found three precisely corresponding
species :
1. Gaillonella distans, as chief mass; 2. Podosphenia nana, new
species; 2. Bacillaria vulgaris?.
VII. In the Klebschiefer from Menilmontant I in two instances
found fragments of Gaillonella distans, but am doubtful whether they
may not have been derived from the Schiefer of Bilin.
It deserves particular notice, that by far the greater number of these
twenty-eight fossil species of infusoria, which all belong to the family
of the Bacillariz, and indeed to eight different genera now existing,—
namely the genera Navicula, Cocconeis, Synedra, Gomphonema, Cocco-
nema, Podosphenia, Bacillaria, Gaillonella,—that of these twenty-eight
species, fourteen were undistinguishable from existing freshwater infu-
soria, and five species from existing marine animals. The other nine
species, therefore not quite one third, are either as yet undiscovered
but existing forms, or extinct ones. It however appears to me more
probable, from a comparison of my extended observations of these na-
tural bodies, and bearing in mind the circumstance that no extinct
species appear exclusively in the above-mentioned fossil relations, that
the new fossil species, among which is no new genus, are not extinct,
but still existing ones which have not yet been discovered.
The great mass of the specimens of these animal forms is in very
good preservation: many of them are so beautifully preserved, that
I have even been able to determine from them the characters of the
living species more precisely ; for a direct comparison of the latter showed
that certain apparent characteristical distinctions are very difficult to
be observed in the living ones, and have hitherto been overlooked
by me. I first discovered the apertures of the Gaillonellz in the Po-
lirschiefer, and I now perceive them in all the species of the genus: I
have never before seen the six apertures of .NVavicula viridis so beau-
tifully *.
The great sharpness and clearness of all the outlines of all these
siliceous shields plainly appears to have been produced by an extra-
_* As botanists have often regarded these forms as plants, the following
reasons why they are considered as animals, which I have already often pointed
out, are deserving of remark: 1. Many Navicule and other Bacillariz have
quite a distinct, powerful, active, crawling motion, by which they move and
push aside other bodies much greater than themselves. 2. The projection of
an organ similar to the foot of a snail, and whose action assists in crawling,
4.06 PROF. EMRENBERG ON FOSSIL INFUSORIA.
ordinary red heat, which has evaporated all organic (particularly ve-
getable) carbon,; for the animals then lived, as at the present day, on
plants: at a later period the soluble earths may have become separated,
while the silex has better resisted all action. Werner, indeed, was of
opinion that subterranean fire had formed the Polirschiefer, an opinion
which has much in its favour.
There is a certain remarkable preponderance in quantity of individual
species in most of the fossil infusoria whose localities have been men-
tioned. Thus the Kieselguhr from Franzensbad consists almost entirely
of Navicula viridis; the mass from the Isle of France of Bacillaria
vulgaris ; that of San Fiore of Synedra capitata ; and that of Bilin is so
entirely formed of Gazllonella distans that the other species of animal-
cules are only scattered through it. .
Finally, the proportion of these animals merits a passing attention.
The millions of the tribe of infusoria have often been mentioned, and
spoken of almost without consideration of their number, perhaps be-
cause little belief is entertained of their corporeality. They have often
been regarded as drops of oil and appearances of various kinds; but since
the Polirschiefer of Bilin must be acknowledged to consist almost en-
tirely of an aggregation of infusoria in layers, without any connecting
medium, these infusoria begin to acquire a greater importance, not
only for science, but for mankind at large. The Kieselguhrs occur,
it is said, only in nests about the size of a fist or a head, and probably
may be of comparatively recent origin. With the Polirschiefer it is dif-
ferent; this forms widely extended layers, containing fossil plants and
fishes. A single druggist’s shop in Berlin consumes yearly more than
20 ewt.: the consumption therefore of infusoria as tripoli and for
casting-moulds in Berlin and the environs may be perhaps estimated at
50 to 60 ewt. yearly, and thence we may in some measure infer the sale
in Bilin. I hope to receive in a short time more extensive details on this
subject : it is sufficient at present to say, that the infusoria supply all the
requisite demands for purposes of practical utility. Passing over the
share they have in the Raseneisen, the soldier cleans his arms with tri-
poli; the worker in metal, the locksmith and the engraver polish with
may be directly recognised in many forms. 3. By a close examination all the
apertures may be seen, which may be considered as apertures of nutrition, of
generation, and of motion. 4. Internal organs may be distinguished, which
may be compared with the polygastric bladders of the infusoria, and others
with the crowned ovary. 5. The infusoria are propagated, besides the highly
probable egg-formation, not by buds as in plants, but also distinctly by separa-
tion, a method of propagation which is wanting in all decided plant-formations,
but which is observed in many decided animals. 6. Some forms, whose motion
is very slow, or which attach themselves like oysters, afford no reason why they
are therefore to be considered as plants. Compare the Report of the Academy
of Berlin, 1836, p. 34. ,
-—
PROF. EHRENBERG ON FOSSIL INFUSORIA. 407
infusoria, which serve also for moulds in founderies. These animals
which are so useful after death, and form entire rocks, have at present
a more special interest in their individuality. The size of a single one of
these infusoria, which form the Polirschiefer, amounts upon an average
and in the greater part to g4, of a line, which equals 3 of the thickness
of a human hair, reckoning its average size at =/, of a line. The glo-
bule of the human blood, considered at 53,, is not much smaller. The
blood globules of a frog are twice as large as one of these animalcules.
As the Polirschiefer of Bilin is slaty, but without cavities, these animal-
cules lie closely compressed. In round numbers, about twenty-three mil-
lions of animals would make up a cubic line, and would in fact be con-
tained in it. There are 1728 cubic lines in a cubic inch, and therefore a
cubic inch would contain on an average about 41,000 millions of these
animals. On weighing a cubic inch of this mass, I found it to be about
220 grains. Of the 41,000 millions of animals, 187 millions go to a
grain, or the siliceous shield of each animalcule weighs about the =4,
millionth part of a grain.
The animalcules of the Raseneisen are only ;)5 line in diameter,
or the z; part of the thickness of a human hair, 4 of the diameter of a
globule of the human blood, 4 of the blood globule of a frog. A cubic line
of such animal iron-ochre would thus, in the same relation, contain one
thousand millions, one cubic inch one billion, and one cube of nine feet
diameter one drillion, of living beings. If we suppose only one fourth
of this multitude to be really present, and take no notice of the other
three fourths, there yet remain such enormous numbers as to merit the
greatest attention.
Further Notices of Fossil Infusoria ; by Prof. LHRENBERG.
From Poggendorff’s Annalen der Physik und Chemie, vol. xxxviii. No. 6,
p. 455, 1836.
Ir has been announced as a well-ascertained fact, that the Polir-
schiefer of Bilin in Bohemia, which is a member of the tertiary forma-
tion, consists almost entirely of the siliceous shields of Gaillonella
distans and other infusoria, without any foreign cement. The recent
Kieselguhr and the Bergmehl from San Fiore, which are of less geolo-
gical interest indeed, consisting of larger infusoria shells, are better
adapted than the Polirschiefer (whose minute animalcules require a high
and clear magnifying power) to make these organic relations more ap-
parent and convincing. The kind exertions and reports of M. Alexander
408 PROF. EHRENBERG ON FOSSIL INFUSORIA.
von Humboldt, who lately visited the district of Bilin in his journey to
Teplitz, and sent me two very rich collections of the mineral pro-
ducts of that district, in various states, have furnished new materials
for the furtherance of my observations.
Before I speak of this valuable addition to our subjects for investiga-
tion, I may mention, that an examination of the Polirschiefer of Planitz
(of which, by the friendly intervention of M. Weiss and the liberality of
M. Freiesleben in Freiberg, I have been enabled to examine a specimen
whose locality was quite certain,) has shown with certainty that this
layer also is a conglomeration of infusoria shells. The specimen exa-
mined resembled the Saugschiefer of Bilin, and the infusoria shells of
the Gaillonella distans are here filled with and connected by a siliceous
cement, which somewhat mars the distinctness of their form; JI have,
however, seen some so plainly that I am convinced of the identity of
these two formations. There is probably also in Planitz a more earthy
form of this stone, similar to the loose. Polirschiefer, which is chiefly
formed of the unchanged Gaillonella distans.
A specimen of the Polirschiefer from Cassel, which M. Carus of Dres-
den had the kindness to send me, and in which he had also recognized
organic forms, was particularly interesting.
I found in the Royal Mineralogical Cabinet some specimens with pe-
trifactions of fish, the Leuciscus papyraceus, from the same locality.
I have also lately been able, through the kindness of M. Keferstein of
Halle, to examine specimens of the stone from the Habichtswald near
Cassel. This Polirschiefer of Cassel contains seven different species of
shield-infusoria, between which is a loose and, for the most part, siliceous
cement, which cannot be plainly reduced to organic fragments. It is
worthy of notice that most of the forms in the Polirschiefer from Bilin
and Planitz are either extinct or as yet undiscovered ; while at the same
time those forms which resemble existing species, belong to such as are
not very striking, and therefore less sure for the detection of their iden-
tity ; but in the Polirschiefer of Cassel two of the most remarkable exist-
ing forms occur, namely Gatllonella varians and Navicula viridis: Na-
vicula striatula appears also to occur in this Polirschiefer. Gazllonella
varians and Navicula viridis appear both in the tertiary formation of
Cassel and in the Bergmehl of San Fiore, and these have a form related
to that of Mavieula Follis. Besides 1. Gaillonella varians, 2. Navicula
viridis, 3. Navicula striatula? 4. Navicula Crux (comp. Navicula
Foilis adulta), I have also found in the stone from Cassel, 5. Navieula,
Sulva juv.? 6. Navicula gracilis? and 7. Navicula Cari, n. species,—
three less clearly defined species: the last however is very numerous
and isunknown to me. Besides these ascertained relations of the distri-
bution of the Infusoria-schiefer as Polirschiefer, the rich parcel sent by
M. von Humboldt from Bilin and the valley of Luschitz has given rise
PROF. EHRENBERG ON FOSSIL INFUSORIA: 409
to very important observations. It consists of a small collection of
minerals from Bilin, made by Dr. Stolz of Bilin, of a larger one by
Dr. Reuss, and also of a great number of specimens collected by M.
von Humboldt. A careful geognostical drawing by Dr. Reuss explains
the position of the rock-masses of that district.
The infusoria rock of Bilin forms the upper layer (fourteen feet deep)
of the Tripelberg, which (differing from the Kritschelberg, with which
it was formerly confounded) is elevated about 300 feet above the level
of the brook Biela. It lies on a bed of clay, which is superincumbent
to the chalkmarl. Beneath these gneiss is found, as the base of all the
minerals of that district. The upper masses of stone lie west of the
Tripelberg on a projected mass of. basalt, which forms the Spitalberg,
and on the other side of which (west) Grobkalk, with many discernible
petrifactions of small chalk sea animals (many Crinoidez) lie on the
gneiss. The firmer masses (Saugschiefer and Semi-opal) lie in the
Polirschiefer towards the exterior upper part, the earthy below, dis-
posed often without order in layers, the inferior ones being almost ho-
rizontal.
The particular attention paid to the Saugschiefer and semi-opal, whose
numerous transitions were exposed to view, has now given the scarcely
unexpected result that these also are in the closest connection with the
infusoria——The Saugschiefer is, upon microscopical observation, plainly
only a Polirschiefer, whose infusoria shells are cemented by and filled
with a formless siliceous matter, just as there are fossil shells both filled
and empty : this produces its greater specific weight, and all its other
characters. In the gradual transitions to the semi-opal we see how
the cement has increased at the expense of the infusoria shells, while
the small shells have decreased in quantity and in sharpness of out-
line.
The formation of the semi-opal in the Polirschiefer appears to be this,
that it lies imbedded in it in nodules, in the most minute transitions from
the Saugschiefer. A close microscopical analysis of the most varying
semi-opals from Bilin, and the neighbouring valley of Luschitz, has
shown that all these stone nodules, which sometimes equal flint in hard-
ness and give sparks, consist partly of infusorial forms held together
by a small quantity of transparent siliceous cement, and partly contain
inclosed within them single infusoria, but of a larger size, just as amber
contains insects. It is often very plainly to be seen, that the disposition
of the Polirschiefer has not otherwise been altered, either by its change
into Saugschiefer (cemented and permeated by amorphous siliceous
matter), or by its change into semi-opal, than that by some means a part
of the infusoria shells, particularly the more delicate ones, have been
eaten away or dissolved, with which another part, especially of the
larger forms, has been covered in an unaltered sfate. In this process
410 PROF. EHRENBERG ON FOSSIL INFUSORIA.
the stratified structure remains as fully visible in the Polirschiefer
‘as it had before been, and forms the stripes of the semi-opal. The
white and less transparent stripes are mostly well-preserved layers of
infusoria. It is not improbable that a dissolving medium may have
acted upon the siliceous shells as drops of water or steam act on
meal. The parts in contact with it were gradually penetrated, and
partly dissolved and changed into opal; or the penetrating matter, pro-
ducing the opal, and which occupies but a small space, has assimilated
to itself a greater or less part of the empty siliceous shells. The true
wood-opal, in which the woody substance is changed into opal, renders
the opinion probable that a peculiar opaline mass has supplanted the
decayed and dissolved parts of the woody substance, retaining however its
form. We cannot easily imagine the expulsion of the siliceous shield-mass
by the opal-mass, and of the latter filling its space: therefore it appears
conceivable that the opal may be probably formed from the infusoria
shells, simply by water or any other dissolving medium except fluoric
acid, just as dough is formed of meal. Unkneaded dough contains stripes
of meal,—semi-opal has often stripes of infusoria: both are hydrates.
In the semi-opal of Bilin and of the valley of Luschitz were visible,
inclosed like insects in amber, 1. Gazllonella distans; 2. Gaillonella
varians, particularly the larger individuals; 3. Gaillonella ferruginea ;
4. siliceous needles of sponges. The first is mostly dissolved, at times
preserved as principal mass, with the outline rather rounded off, although
the connecting medium has quite a glassy appearance. The second
is mostly well preserved, but rather rounded off; the third is sometimes
well preserved in the buff-coloured specimens, but on account of its
minuteness does not admit of a determining character. The latter
however is not unimportant with regard to the question of the action
of voleanic agency: it may perhaps have been deposited in the moist
parts of the previously formed Polirschiefer. Upon heating this yellow
semi-opal, it became red and actedasiron. The red was the articulated
fibres of the Gaillonella: they could not therefore possibly have been
heated in the air. The tranquil horizontal stratification of the Polir-
schiefer (exhibiting perhaps the yearly or periodical deposition of the
layers) speaks also for a neptunian action. Hot vapours of the volcanic
neighbourhood might have much contributed to the purifying of the
mass, without actual fire. The semi-opal of Bilin removes all doubt as
to these organic relations.
Very similar formations, with inclosed forms of organic origin,
were also apparent in the semi-opal from Champigny, that out of the
Dolerit from Steinheim near Hanau, and that from the serpentine for-
mation of Kosemitz in Silesia. The microscopical bodies inclosed in
this stone, very apparently of a spherical form, and never occurring
larger, which are also attached externally to the semi-opal or hornstone
PROF. EHRENBERG ON FOSSIL INFUSORIA. 411
from Kosemitz as a white meal, and filling out its internal cavities,
might partly belong to the still existing genus Pyaidicula. They are
quite different from the stalactitic columns which produce the round
eyes in agate.
It was natural for me now to test again the flint of the chalk, which I
had before often examined : and this time I employed a higher power,
and therefore with more success. The black flint, which broken into
small pieces is transparent, showed no evident traces of an inclosure of
microscopic organic bodies, but such are easily perceptible in the whit-
ish and yellowish opake pieces. The more rare horizontally striped spe-
cimens are very similar to the striped semi-opals. They all contain sphe-
rical and often needle-shaped bodies, at times with apertures, which can
searcely be an optical phenomenon, and which are covered by a trans-
parent siliceous matter. There are sometimes seen in the latter, as in
the Gaillonella varians of Cassel, radial stripes proceeding from a pierced
centre to the periphery, and also somewhat plainly a separate defined
shell. The chalk-like envelope and white covering of the flint does not
effervesce with acids, and is therefore not chalk, but silica, as I have
convinced myself; it does not appear to originate in decomposition, but
is like the meally covering of a lump of dough ; that is to say, it is that
layer of siliceous meal (of evident organisms) which at the formation of
the flint has only been touched by the dissolving or metamorphosing
matter, but not completely penetrated by it. According to this the flint
_ would be formed nearly in the same manner as the semi-opal of the Po-
lirschiefer. The siliceous parts of the chalk would, from their specific
gravity, accumulate in certain places, and form layers of siliceous Berg-
mehl in the chalk ; in the same manner as we see in high perpendicularly
cut heaps of rubbish, things of the same specific gravity, mortar, pieces
of porcelain, bones, &c., arranged separately in stratified horizontal
layers. If now a dissolving elastic or other fluid forced its way into the
__ heap, those nodules must also be formed in horizontal layers and nests,
which have already attracted the special attention of geologists, and of
which some at times take the form of Holothuriz and corals ; the great-
est number however, partly on account of their enormous volume and
partly from their wholly undetermined forms, present great difficulties
to this hypothesis. In the Menilite the nodule formation of a penetrating
_ substance, itself occupying scarcely any space, and not changing the
layers of the primitive mass, is particularly well seen.
I have finally to mention the examination of the precious opal of
Kaschau. In some fragments both of the common serpentine opal of
Kosemitz and of the precious porphyry opal of Kaschau, I saw also in-
closed round bodies like those in the flint; the greatest mass was how-
ever in the interior homogeneous. I examined the matrix of the pre-
cious opal, and found that a mass similar to Steinmark (lithomarge )
Vou. I.—Parr III. 2¥
412 PROF. EHRENBERG ON FOSSIL INFUSORIA.
always immediately surrounds the nodules. This Steinmark of Kaschau
exhibits however, under the microscope, a great resemblance to the
Gaillonella distans, as it appears in the Saugschiefer of Bilin. I have,
from the remarkable character of the primary formation, repeatedly
examined and compared these and similar phenomena, and prefer to
declare them openly than to keep them secret. I shall howeyer continue
my observations with close examination, and publish the results if they
lead to any discovery, when they are sufficiently matured.
The more probable appears the proverb, partly old and partly new,
Omnis calx e vermibus, Omnis silex e vermibus, Omne Serrum e vermi-
bus, the more necessary it is, by continual and close examination, which
cannot be the work of a day, to separate facts from opinions, and not
to envelope them in mystery, but by careful observation to confine them
within the probable and attainable limits which nature has assigned,
We may regard as hitherto ascertained facts that
1. Bergmehl
2. Kieselguhr
Be Polinsithietar 77 asfs. csve-nsackeaanes « v0
4., Saugschiefer .......6:.s00..scseeecen sos Tertiary formations
5. The semi-opal of the Polirschiefer..
consist entirely or partly of the shells of shield-infusoria.
The following species of stone are very probably of the same nature :
6. The semi-opal of the Dolerit .........
7. The (precious) opal of the se iiad
8. The flint of the chalk ,.
9. The Gelberde (yellow earth) teat ae Maatone
10. The Raseneisenstein .........
11. Certain kinds of Steinmark*.
\ Newest formation
Secondary and primary
formations.
* The examination of a boulder from the Mark (Brandenburg) which has
been regarded as Schwimmstein (compare Kléden, Geognost. Mem. 1834,
p- 30.) has lately proved to me that its chief mass consists of just the same
detached siliceous spindles of sponges and of the minute globules (infusoria
Pywidicula?) which the flint boulders of the Mark inclose ‘in great numbers.
These bodies also lie in the meally covering of the flint. This Schwimmstein
therefore bears the same relation to the flint as the Polirschiefer to the semi-
opal, and it belongs to the chalk.
Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. 6.
PROF. EHRENBERG ON FOSSIL INFUSORIA. 413
Explanation of the Figures ( Plate V).
Navicula (Surirella) viridis, } lin. magnitude, in the Kiesel-
guhr of Franzensbad: a, seen from the side surface, where
the mouths of the three apertures are apparent ; 6, the same
individual from the dorsal or ventral side, in which are seen
all the six apertures. The stripes are internal raised bands,
between which were situated the ovaries of the living ani-
mal.
Navicula (Surirella) granulata, from the peat-bog of Franz-
ensbad ; a, side view; 6, the under surface.
1. Synedra capitata, the chief form of the Kieselguhr of San
Fiore; a, side surface; 6, ventral surface. 2. Navicula ine-
qualis, side view.
Bacillaria vulgaris? chief form of the Kieselguhr of the Isle
of France.
Gaillonella distans, 53 to za lin. thick: chief form of the
Polirschiefer of Bilin (the leaf-tripoli); a, 5, c, seen from the
side; d,e, cross surfaces ; f, apertures.
Gaillonella ferruginea, {ooo lin. thick; the animalcule of the
iron-ochre ; a, with the same magnifying power ; 6, two thou-
sand times magnified. Lyngbye has regarded this animal-
cule as the base of his Oscillatoria ochracea. Oscillatorize
are sometimes found parasitically within it; they belong
however to many different genera, and Agardh has there-
fore rightly regarded them as not distinct species.
All the other figures are magnified 290 or nearly 300 times.
414
ARTICLE X XI,
On the Chemical Effects of Electric Currents of low tension,
in producing the Crystallization of Metallic Oxides, Sul-
phurets, Sulphates, &c.; in forms frequently closely resem-
bling the native combinations ; by M. BecauEREL.*
From Becquerel’s 7raité de l'Electricité et du Magnetisme, vol. iii. p. 287.
1. By means of long-continued electrical action proceeding from a
single pair of plates, chemical effects more or less considerable are pro-
duced, whether the affinity of the solution for one of the electrodes adds
its action to these forces or opposes them. We every day observe that
nature, having unlimited time at her disposal, produces with slender
means immense effects. But these means frequently escape our senses,
because they have not been studied with sufficient care, and are not in-
cluded in the ordinary circle of our inquiries. It is only by working on
a small scale, and closely observing every step of our processes, that we
have a chance afforded us of discovering any of the means employed
by nature to produce the phenomena of molecular attraction. With
this view let us observe some of the decompositions obtained by means
of apparently feeble electrical forces.
At present it is not doubted that voltaic action may produce chemi-
cal effects; but we do not know how far this action, when it is very
feeble, influences affinities, and whether, at the very moment when
these become sensible, particular phenomena may not be produced,
which disappear in the general effect, when we employ a pile possessing
a certain energy. We know, for instance, that if two wires of any
metal are plunged into a metallic solution, each of them communi-
cating with one of the poles of a voltaic pile of sufficient energy, we
always obtain at the negative wire either hydrogen, reduced metal, or
oxide. But when the tension is extremely slight, does the phenomenon
take place in the same manner ? Do all metals possess this property
in the same degree? In order to answer these questions, successive
reductions must be made in the intensity of the electricity, and at the
same time what passes in the decompositions must be observed.
Let us put a metallic solution (for instance a solution of copper) into
a cylindrical glass, and then with the greatest care pour over it distilled
or acidulated water, so that the two liquids may remain separate, the
one above the other ; and then immerse a plate of copper into it, we find
after a few hours this plate covered with a precipitate of copper in a
metallic state. Different metallic solutions gave similar results. Hence
* For the selection of this Paper the Editor is indebted to H. J. Brooke,
Esq., F.R.S. A notice of a Memoir on this subject, read by M. Becquerel to
the Academy, is given in the Philos. Magazine and Annals for March 1830.
M. BECQUEREL ON CHEMICAL EFFECTS OF ELECTRICAL ACTION. 415
it is obvious that metals can form, with their own solutions and pure
or acidulated water, currents whose electrical action precipitates the
metal. In this case there are two electrical effects: the one caused by
the re-action of the two liquids one on the other; the second by the
action of the acidulated water on the metallic plate; it is therefore a
compound phenomenon, for the actions are added or subtracted ac-
cording as they have the same or contrary directions. In the case under
consideration the two actions are combined. Certain thermo-electrical
phenomena and simple chemical actions ordinarily disengage electricity
enough to produce decompositions resembling those just mentioned.
Let us first direct our attention to the decompositions produced by
thermo-electrical currents.
2. Several experimentalists have tried to decompose water with thermo-
electrical currents, but in vain; for in order to succeed, they should have
experimented with salts decomposable by a weak current, such as ni-
trate of silver and iodide of potassium, and disposed the apparatus so
as to be able to determine the production of a new compound.
Let us take two wires, the one of platina the other of copper, of a
certain length and about Z of a millimetre* in diameter; forming at
one end of each wire a ring, and hook one ring on the other; the ring
of the platina wire being very small, and that of the copper wire about
three millimetres in diameter. If we solder the two rings, the cur-
rent goes always in the same direction, from the platina to the copper,
whether we heat the wire to the right or to the left of the points of junc-
tion. Let us now solder a copper wire to the free end of the platina
wire, after which burn a small quantity of sulphur upon the copper ring,
and then place under the platina ring an alcohol lamp, so as to raise its
temperature to red heat, keeping the copper ring as cool as possible,
which may be done by placing the platina wire at the extremity of the
white flame, so that this may be at very little distance from the copper
ring. Now if we communicate the free ends of the copper wires with the
ends of the wire which forms the circuit of a galvanometer, we obtain a
current of electricity of considerable energy passing from the platina to
the copper.
The copper ring is made larger than the other, so that it may be less
heated when the temperature of the platina ring is raised to red heat. On
the contrary, if we place the focal heat on the side of the copper wire,
the electrical effects are reversed; and if we substitute in place of the
platina wire another copper wire, the electrical effects will still be the
same. But exposing the two rings to the same temperature, there will be
no effect produced. The layer of sulphur with which the copper ring
is covered sensibly augments the intensity of the current.
Here then are two distinct electrical effects in a closed circuit, con-
sisting of wires of two different metals, according as those wires are
* 4 of a millimetre is about ;'; of an inch ; 3 millimetres is about 4 of an inch.
416 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND ©
soldered or only touch one another at given points. In the first ease
the current has always the same direction, whether we heat the wire to
the right or the left of the points of junction; in the second it is not
so. The only difference arises from there being in the one only simple
contact, while in the other there is contact accompanied by a chemical
action which determines the formation of an oxide or a sulphuret.
3. The following experiment shows the influence of chemical action
in phenomena of this kind. Ifa piece of sulphur be burnt at one of
the extremities of a copper wire which forms the circuit of a galvano-
meter, and the other end be placed over it at the moment that the com-
bustion is in full power, the current of electricity which then takes place
is one of the most energetic, and more intense than the one which pro-
ceeds from a simple difference of temperature.
Suppose now a tube curved in the form of a U, containing a solution
of nitrate or of sulphate of copper; plunge into each branch a cop-
per wire, communicating with the end of a wire forming the apparatus
we have just described ; after one hour's experiment that end which cor-
responds to the negative side is covered with copper precipitated in a
metallic state, while the other is sensibly oxidized. Two tin wires, pre-
pared in the same manner as the copper wires, and plunged into a so-
lution of hydro-chlorate of tin, give the same results; that is, that wire
which communicates with the negative side will be covered with ery-
stals of tin; wires of zinc, silver and lead, plunged in their respective
solutions exhibit the same phenomena.
Platina wires are without action in a solution of platina. We here
perceive the influence of the chemical action which takes place between
the wires and the solutions upon electro-chemical decomposition.
Platina, gold, and silver wires, plunged in solutions of lead, tin, or cop-
per, and prepared as those above, are equally without action on them,
although the current has always the same intensity.
When two silver wires are plunged into solutions of sulphate or ni-
trate of copper, the positive wire is always attacked by the acid, and
the precipitate is not sensibly formed on the negative wire. The oxy-
gen and the acid appear therefore in this case to be more easily trans-
ported to the positive pole than the copper to the negative pole.
Platina wires produce a precipitate in nitrate of silver as well as silver
wires, with this difference that it is more abundant on those of silver than
on those of platina. This difference appears plainly by immersing at
the same time a silver wire rolled round a platina wire in a solution.
Thus, we see that with weak currents of equal intensity, the easily re-
ducible metals are disposed to be precipitated more readily from their
solutions upon plates of the same than upon plates of any other metal
than that which enters into the solution, and which does not of itself pro-
duce a precipitate, as iron when plunged into a solution of copper does.
LLL
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 417
This remarkable fact can only be observed with an electrical apparatus of
very feeble tension, inasmuch as, when this tension possesses a certain
energy, the dissolved metal goes always to the negative pole, be the wire
or plate of metal which is plunged into the solution what it may.
To what cause are we, in this instance, to ascribe the predilection
of a metal, combined with an acid, for a plate of the same metal ? The
force of cohesion, whatever it may be, is the only influence to which
it can be attributed ; for that principle must be supposed to act with
greater force on similar than on dissimilar molecules. In this case, the
force of cohesion added to that of the electric current should determine
the precipitation. It must not be forgotten however that the chemical
action of the solution on the positive wire is also powerfully conducive
to the production of the general effect.
If it be desired to obtain continuous effects with the thermo-electric
apparatus, the copper ring into which the platina ring is passed must
be renewed from time to time, because, at a certain stage of the experi-
ments, the copper being entirely oxidized, the continuity is broken and
the electro-chemical effects consequently cease.
An apparatus with a platina and an iron wire has not sufficient action
to produce decompositions. This negative effect is undoubtedly to be
attributed to the singular electric properties of iron.
The apparatus we are about to describe is intended to produce slow
and continuous electro-chemical actions.
Take two small glass jars (fig. 1); having poured into the one some
Fig. 1.
nitrie acid, and into the other some potash dissolved in water, we esta-
blish a communication between them by means of a bent glass tube
filled with potters’ clay moistened with a solution of nitrate of potash or
chloride of sodium, and then plunge into each liquid a plate of plaftna
fixed to the extremity of a wire of the same metal. At the free end of
418 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
each of the platina wires, the end of a wire of that metal is attached, on
which the experiment is to be made. The plate in contact with the al-
kali receives the negative electricity which disengages itself in its re-
action on the water, or the solution of the nitrate or the chloride, while
the plate in the acid receives the positive electricity which escapes dur-
ing the same reaction. We thus obtain a permanent pile if we only
take care to close the vessels so as to prevent evaporation and the action
of the air on the alkali. By plunging several plates of platina into the
jars we may act on several sets of apparatus at the same time.
Water may also be substituted for potash, and a copper wire plunged
into each vessel. We then obtain a chemical action, and an electric cur-
rent (from the copper to the acid) sufficiently strong to produce decom-
positions similar to those already mentioned.
It cannot be doubted that, in the electro-chemical decompositions
produced by means of currents proceeding from an electricity of low
tension, the oxygen and the acid take the direction of the positive pole,
as they do in the decompositions effected by means of a pile formed of
several elements. The wire communicating with the negative pole is
visibly covered with metal, but it cannot always be seen that the oxygen
and the acid are transferred to the positive pole. In such cases they
have formed an insoluble compound.
We have likewise already shown that when two silver wires, both in
communication with the decomposing apparatus, were plunged into a
solution of nitrate of copper, the positive end became perceptibly dim-
med, while the negative end retained its metallic brilliancy, though no
trace of metallic copper could be perceived on its surface. This is to
be explained either by supposing that the copper, as will sometimes hap-
pen when an insoluble compound can be formed, has remained in the so-
lution, (and in this case there has been no transfer of the elements of the
nitrate although it has been decomposed, ) or that the deposit on the ne-
gative end is so slight as to be imperceptible.
Let us now take two small glass vessels of a cylindrical form, the one
containing a solution of nitrate of barytes, and the other a solution of
sulphate of copper. We establish the communication between these
solutions by means of a bent tube,small in diameter, and containing pot-
ters’ clay moistened with a weak solution of sea salt, in order that the
transfer of the electricity may be effected with ease. Into the sulphate
we plunge the copper wire which corresponds with the negative side of
the apparatus, and the other wire, into the nitrate of barytes. It is evi-
dent that ifthe sulphuric acid goes to the positive pole, it will, in pass-
mg through the solution of nitrate, combine with the barytes and form
a precipitate.
Now the following is what actually takes place: after the experiment
has been continued for four or five hours, the negative end is covered
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION: 419
with copper, the solution of the nitrate of barytes is not perceptibly dis-
turbed, and the positive end is oxidized. Are we to conclude there-
fore that there has been nothing transferred but the oxygen, and that
the sulphuric acid has remained in the sulphate? The answer to this
question is to be obtained only by analysing the secondary productions
formed in the tubes ; but there is every reason to believe that sulphate
of barytes would be found. In general, when there is one of the pro-
ducts of the decomposition not to be found at one of the poles, we may
be certain that it has been arrested, on its way, by superior affinities.
The acetates and subacetates of lead are also decomposed by means
of leaden wires; but the acetate of copper and the saturated solution
of the same salt in ammonia resist the action of an electricity of low
tension when copper wires are plunged into their solutions. These re-
marks are of some importance, inasmuch as these salts are easily de-
composable by the ordinary chemical processes.
Of Electro-chemical Compounds or Secondary Productions.
In stating the phenomena connected with the decompositions pro-
duced by voltaic electricity, we have directed attention to the fact
that the results of these decompositions were simple or compound, ac-
cording to the nature of the bodies submitted to experiment, and that
of the bodies employed as conductors. We have observed, for instance,
that in decomposing a solution of sulphuric acid with a piece of char-
coal, serving as a positive conductor, we obtained, instead of oxygen,
gaseous oxide of carbon and carbonic acid gas, in consequence of the
action of the oxygen (which is in its nascent state) upon the charcoal.
Other instances of the same kind have been cited in treating of the cha-
racters of the bodies developed on the metallic plates, and the definite
nature and extent of electro-chemical decomposition.
We are now about to resume the consideration of this question and
_ earry its solution as far as the present state of science will allow us, in
order to show in what manner the chemical action of electricity may be
applied in explaining a great number of natural phenomena which have
been hitherto considered independent of this universal agent.
For a long time no one could conceive how, by means of electric
forces, feeble in appearance, powerful affinities were to be overcome, for
the purpose of decomposing bodies and producing new combinations. It
was thought that it would be always necessary to employ currents pos-
sessing some degree of energy : but as soon as the electrical effects which
take place in chemical actions were analysed, all doubt was removed as
to the possibility of attaining the same end by making a proper applica-
tion of those effects. It was conceived, in short, that when any voltaic
pair is plunged intoa solution which acts on one of the elements of that
420 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND.
pair, the particles of the solution, at the instant when they are set in
motion by the chemical action, being then in their nascent state, are
most disposed to obey the action of the current produced by the pair.
We have already cited examples in confirmation of this fact, but we
shall have occasion hereafter to notice a still greater number of them.
Of the Formation of Metallic Oxides by Voltaic Action.
Gold.—It was long supposed that gold was converted into a purple
oxide by means of electric discharges ; but it appears that this state is
only the effect of the extreme division of its parts, as it cannot be admitted
that it is oxidized at the temperature at which its oxide is commonly
reduced. It tends to confirm this conjecture, that when gold is preci-
pitated from a very weak solution, we likewise obtain a purple powder
by means of bodies which reduce its oxide.
Iridium.—By exposing iridium to the discharge of a very powerful
electric battery, Children succeeded in reducing this metal to a white
globule, which was very brilliant and yet porous; but he never could
oxidize it.
Silver —This metal when in contact with the air cannot be oxidized
at any temperature; but it is found eapable of oxidation when exposed
in very thin leaves to the action of a very powerful battery.
It may be obtained also in the state of hyper-oxide, a compound for
the discovery of which we are indebted to Ritter. It deposits itself on
the positive conductor of a pile, when that is discharged through a
weak solution of silver, in long erystalline needles crossed by three or
four lines possessing a metallic brilliancy. With a slow action it is ob-
tained in very regular and well-defined tetrahedrons. When subjected
to the action of hydrochloric acid, this compound gives out oxygen, and
is transformed into chloride of silver; under the action of ammonia it is
decomposed and gives out azote, and when mixed with phosphorus it
detonates under the hammer. It decrepitates by heat, is decomposed,
and produces pure silver.
Mercury.—When a very powerful electric pile is discharged through
a very small globule of mercury, the globule is driven in all directions,
becomes oxidized, and produces red sparks.
Palladium is not oxided at the positive pole of the pile.
Antimony.—When a piece of antimony is employed as a positive con-
ductor in order to decompose water, gray flakes are detached from its
surface; these, under the action of hydrochloric acid, are transformed
into antimony which remains, and into oxide of antimony which is dis-
solved. The flakes appear to be a suboxide.
» Zine and the oxidable metals are easily oxidized under voltaic influ-
tremity of a plate of copper is then plunged into each
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 424
ence when they are employed as positive electrodes: but as this effect
presents nothing particularly worthy of remark, we shall forbear to
dwell on it, that we may now proceed to explain some other processes
by means of which we obtain the oxides crystallized.
Of Metallic Oxides Crystallized by Voltaic Action.
Copper.—tin order to obtain crystals of protoxide of copper, we take
a glass tube closed at one end and having at the bottom some deutoxide
of copper (See fig.2.). This tube is filled with a solu-
tion of saturated nitrate of copper, into which there is Fig. 2.
plunged a plate of copper, that touches the deutoxide
also, and the tube is then hermetically sealed. After
an interval of ten days we begin to perceive on the
plate of copper small bright crystals of the form of
an octahedron and of a deep red colour. In order to
discover the electric phenomena by which they are
produced, we must take two capsules of porcelain fill-
ed with asolution of nitrate of copper and connected
with each other by means of a cotton wick. One ex-
of them, while the other is attached to one of the
extremities of the wire of a delicate multiplier. All
things being now alike on one side and the other,
there appears no current. But if we pour some deut-
oxide of copper on that part of one of the plates which is plunged in
the solution, a current is soon produced, the direction of which shows
that the plate in contact with the deutoxide has received the negative
electricity. Hence it follows that the plate in the other capsule is the
negative pole of the small pile which produces the decomposition of the
nitrate of copper. Now, an effect perfectly similar to this takes place
_ in the tube: the part of the plate in contact with the deutoxide is the
positive and the other part the negative pole. We shall presently re-
vert to the cause which produces this pile. The existence of the latter
being established, the portion of the plate of copper which is not in con-
tact with the deutoxide, should attract the copper in a metallic state or
its oxides, according to the force of the current. It is therefore but na-
tural that the protoxide of copper should take that direction if the cur-
rent possesses sufficient energy. It crystallizes, because the electric
and (consequently ) the chemical action being very slow, the molecules
have time to arrange themselves according to the laws of crystallization,
although the body is insoluble,—an advantage which is never obtained
when the chemical forces are of greater intensity.
According to the greater or less quantity of deutoxide of copper in-
closed in the tube the phenomena which take place will vary. Let us
422 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
suppose that the tube contains it in excess: at first protoxide is pro-
duced and crystallized ; the solution gradually loses its colour; then be-
comes colourless, and crystals of nitrate of ammonia are seen on the in-
terior surface of the tube. The liquor now contains nothing but the
saturated solution of this salt and some traces of copper. Sometimes it
takes a year or more to obtain this last result, which depends on the
quantity of deutoxide employed. All this is effected without any con-
tact with the air, since the tube is hermetically sealed, and the forma-
tion of the ammonia must have been owing to the hydrogen of the
water and the azote of the nitric acid.
When the quantity of the deutoxide is very small, the effect is as fol-
lows : the protoxide crystals are formed equally on the plate of copper ;
but by little and little, they lose some of their brilliancy, and experience
at last a discoloration which stops at a certain point. The solution re-
mains always coloured. The experiment is then terminated, and time
produces no change in the solution.
In order to explain the facts just mentioned, and to reascend to the
cause of the electric phenomena by which they have been produced,
we have found it necessary to analyse the octahedral crystals and the
substance that replaces the deutoxide of the same metal. The change
which the deutoxide undergoes is the only thing that can throw a light
on the origin of the electric effects.
Those crystals possess the following properties : their powder is red :
it is soluble in ammonia or in hydrochloric acid without colouring either.
The latter solution is made turbid by the water, and receives a blue tinge
from ammonia. These characters indicate that the crystals really are
protoxide of copper.
Analysis of the Substance which replaces the Deutoxide of Copper
in the Crystallization of the Protoxide.
We took two grammes of this substance. After having well washed
and dried it, we proceeded to operate on it immediately by means of car-
bonate of potash. The filtrated liquor was gradually saturated with
sulphuric acid, until there was no longer any alkaline reaction. Hav-
ing now condensed the solution by evaporation and produced crystal-
lization, we obtained 180 of nitrate of potash besides the mother-water
which we neglected.
The insoluble salt which remained on the strainer was carbonate of
copper, which being dried and weighed amounted to 1&6. Now one
gramme of nitrate of potash, if we admit that an atom of this salt includes
two atoms of acid and one atom of base, will contain 085 of acid and
0°45 of potash.
In like manner the carbonate of copper, being formed of an atom of
deutoxide of copper and an atom of carbonic acid, gives 12 of oxide
and 04 of carbonic acid.
|
:
-
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 493
Hence it follows that the substance subjected to analysis is a subni-
trate consisting of
Calcul. result. Result of exper.
2 atoms'of nitric acid ............... O05 |... O62
3 atoms of deutoxide of copper ... dy palit gos a io Fg
It appears, by this analysis, that the deutoxide of copper is transformed
into subnitrate of copper. This result enables us to explain the elec-
trie effects which give birth to the protoxide of copper and its accom-
panying products.
The hermetically sealed glass tube contains some deutoxide of cop-
per, a saturated solution of nitrate of copper, and a plate of copper in
contact with both. As the deutoxide takes possession of part of the acid
of the nitrate, it follows that the part of the plate which touches the deut-
oxide comes into contact with solution of nitrate of copper, which is less
saturated than that into which the upper extremity is plunged. A cur-
rent should result from that circumstance, since the plate of copper is
plunged into two solutions saturated in different degrees.
The upper extremity is the negative, and the lower extremity the
positive pole: the former should consequently attract the copper or its
oxides, and the latter the acid ; and this is precisely what does take place.
It appears then that there is nothing perplexing in the fact that the prot-
_ oxide of copper is deposited on the upper part of the plate. The action
of this pile must be extremely feeble at first, inasmuch as the deut-
oxide, especially when it is anhydrous, not acting easily on the acid of
the nitrate, the difference between those two liquids is very small. But
as the nitrate gradually loses its acid, which is not suddenly replaced
by that of the upper part, it follows that the difference between the
degree of concentration of the two solutions increases. The chemi-
eal action of the pile should be in the same ratio. Thus at the close of
the operation we perceive crystals of copper especially on the upper
part. As this process is gradual, all the bases from the deutoxide to the
metal, should be obtained in a crystallized state, those however being
excepted which are capable of reacting on the nitrate of copper.
It is proved by experiment that during these different actions no gas
escapes. For this purpose all that is required is, that instead of closing
the tube we should cover it with another tube inverted, and likewise
filled with a solution of nitrate of copper. We find that, whatever may
be the duration of the experiment, no gas is disengaged in the upper
part. It appears that the oxygen which results from reducing the deut-
oxide of the nitrate into protoxide, is carried to the lower part of the
plate (which is the positive pole), in order to oxidize it, so that it may
_ combine with the acid which is also drawn thither by the action of the
current. But as there is a formation of ammonia, it is likewise neces-
424 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
sary that a portion of the water and the acid should be decomposed, in
order to obtain hydrogen and azote. As to the oxygen, it oxidizes the
lower part of the plate. ‘The decompositions take place in such propor-
tions that all the elements arising from them are employed to form new
compounds. Thus the copper decomposes water and acid only in such
quantities that the hydrogen and the azote may be in that proportion
which is requisite to form ammonia. ‘This instance of electro-chemical
decomposition in definite proportions we made known several years since.
The deutoxide, by its action on the solution of the nitrate, is so far
the cause of the electric current established in the system, that the same
effect may be produced by putting things in the state in which they are
subsequently to this action. We take two porcelain capsules, one of which
is filled with a saturated solution of nitrate of copper, and the other with
the same solution and an addition of water. The communication be-
tween them is established by means ‘of a cotton wick, and the end of a
plate of copper is plunged into each of the vessels. This apparatus
is the same as that of the tube when the deutoxide of copper has
begun to combine with part of the acid of the nitrate ; since, in the
one case as well as in the other, the two ends of the plate are plunged
into solutions of nitrate of copper possessing different degrees of con-
centration. Now, as in both cases the electrical effects are the same,
the explanation we have given is necessarily exact. The foregoing facts
enable us to modify, at pleasure, the intensity of the small piles em-
ployed to bring into action the mutual affinities in bodies. In fact, a
plate of copper immersed in two solutions of nitrate of copper, of which
one is and the other is not saturated, will constitute a pile. It follows
from this, that, if the solution which is not saturated be more or less
diluted by the addition of water, we shall have electro-chemical actions of
greater or less energy ; and, as the solution may be progressively diluted,
those actions will be increased or diminished in the same proportion.
It is thus that we may obtain the different oxides of a metal in a cry-
stallized state and distinguish the proximate principles in organic com-
pounds.
Lead.—In order to obtain the crystallized protoxide of lead, we take
a glass tube measuring some millimetres in diameter, and closing it at
one end, place at the bottom some pulverized litharge about a centi-
metre* high. We then pour over it a slightly diluted solution of sub-
acetate of lead, and plunge into it a plate of lead which is equally in
contact with the litharge. The tube is then hermetically sealed. The
surface of the plate becomes gradually covered with small prismatic-nee-
dles of hydrate of lead; occasionally there is to be seen reduced lead ;
and lastly, but rather rarely, a deposit of very clear dodecahedral ery-
stals of protoxide with pentagonal faces, which lose their transparence
* A centimetre is about 3, of an inch.
GRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 425
in contact with the air. These products are undoubtedly the result of
the decomposition of the subacetate of lead arising from actions ana-
logous to those which take place during the production of the protoxide
of copper.
Zine.—The surface of this metal when in contact with the air is usually
covered with a very thin layer of suboxide which is opposed to electro-
chemical action. This compound is slowly dissolved by the acids, and
it is to its presence that we are to ascribe the feeble intensity of the cur-
rents produced by a pile which is charged with a non-acid solution.
The following is a very simple mode of obtaining crystallized oxide of
zinc : we take two small bottles, one containing a solution of zinc in pot-
ash, and the other a solution of nitrate of copper. The communication
between them is established by means of a bent tube filled with potter's
clay moistened with a solution of nitrate of potash. A plate of lead com-
municating with the positive pole of a pile composed of two or three
elements, is immersed in the solution of zinc, and a plate of copper, in
communication with the negative pole, is immersed in the solution of
nitrate of copper.
A pile may even be dispensed with, if the plate of lead and the plate
of copper be put in metallic communication with each other.
The nitrate of copper is decomposed in consequence of the action of
the current proceeding from the action of the alkali on the lead: the
oxygen and the nitric acid are transferred to the plate of lead, and there
produce nitrate of potash and oxide of lead which is dissolved in the al-
kali. After the experiment has been continued for some days there are
found deposited on the plate of lead small clear crystals having the shape
of flat prisms and so disposed as to form rosettes. These crystals are
formed during the slow precipitation of the oxide of zinc by the oxide of
lead, which gradually saturates the solution of potash. In contact with
the air, they become gradually translucid. Exposed to the action of heat
they take a yellow tinge without being melted, and become white when
cooled again ; a property which is characteristic of the oxide of zinc.
Subjected to the action of acetic acid they gave an acetate of zine which
the sulphuret of potash throws down a white precipitate,—a proof that
these crystals contain no lead.
If we substitute a plate of zinc for a plate of lead, the only deposit is
a white substance, which is a combination of zine and potash.
If we continue to let the pile operate with the plate of lead, a yellow
powder is precipitated, which is probably a combination of anhydrous
protoxide of lead with potash.
By substituting for the plate of zinc a plate of copper or platina,-or
any metal not easily oxidable, there will be found deposited on the up-
per side a tritoxide of lead in very simple layers which are easily detached
426 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
and have all the properties of the brown oxide. We shall have occasion
elsewhere to return to this compound.
Lime.—Iit is known that the solution of hydrate of lime in water
becomes, when in contact with the air, covered with a pellicle of carbo-
nate of lime, and that, if this solution be reduced one half by evapo-
ration in a basin and left to cool slowly, the earth becomes crystallized
in the form of small needles. M.Gay-Lussac has found that when the
evaporation takes place in vacuo, the hydrate of lime is crystallized in
regular hexahedrons. It is perfectly easy to obtain the same erystals by
means of the pile, without operating in vacuo. Nothing more is required
for this purpose than to pour some Seine water, which contains a cer-
tain quantity of sulphate of lime, into the two branches of a bent tube
(U) having its lower part filled with moist clay, and then to plunge
into each branch a plate of platina in communication with a pile of
fifteen pair of plates. Not only is the water decomposed, but the sulphate
of lime also. The water in the negative branch becomes alkaline,
thus showing that it contains lime in solution. As the operation is
not interrupted, there arrives a certain moment when the erystalliz-
tion of the hydrate of lime is effected. If the salt with a calcareous base
was more abundant, the quantity of lime that would find its way into
the negative branch of the tube could not fail to disturb the regular
grouping of the molecules. There can be no doubt that, by this pro-
cess, several hydrated oxides, both alkaline and earthy, may be ob-
tained in a crystallized state.
Action of Hydrogen on different bodies, serving as Negative Conductors ;
Formation of Metallic Chlorides.
When the hydrogen arrives at the negative pole, it usually contributes
to the reduction of the oxide by instantly forming with its oxygen a por-
tion of water, which is afterwards decomposed by the action of the cur-
rent. If there are any elements present with which it may combine, the
combination will undoubtedly take place, since the gas is in its nascent
state. We shall now proceed to notice some circumstauces of this kind.
A combination of gold and hydrogen is a thing unknown to chemistry.
It has nevertheless been advanced by Ritter that in decomposing water
with gold wires there was formed at the negative pole a hydruret of this
metal. We mention this result without vouching for its accuracy.
It has been asserted also that by the same means silver might be
combined with hydrogen, but the fact has not been yet proved.
Bismuth has likewise been said to combine with hydrogen when that
metal served as a negative conductor in the decomposition of water. In
this case the metal becomes black and is covered with a black dendritic:
substance.
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 497
Ritter has likewise asserted, that if, for the purpose of decomposing
water, we employ a fragment of tellurium as a negative conductor, the
hydrogen which comes into contact with it combines with the metal, and
produces a brown powder or hydruret of tellurium. But M. Magnus,
who examined this product, ascertained that it was composed of tellu-
rium in its state of greatest division.
Hydrogen and carbon, which combine in different proportions when
they are in their nascent state, (since all animal and vegetable substances
in decomposition give out carbonated hydrogen,) must also be capable
of combining at the negative pole of the pile. This property is of
great importance in electre-chemistry, especially when it is required to
deprive a body of its carbon. The following experiments will serve to
show the use that can be made of anthracite, that is to say, of carbon
almost pure, and of ordinary carbon, in the researches in which we are
engaged.
When we plunge into an acid, in contact with a metal, a piece of
anthracite or charcoal, a current is produced, the direction and intensity
of which depend on the chemical action of the liquid on the charcoal
and the metal. Let us, for instance, take a piece of charcoal freed from
all foreign matter, and attach it to one end of a platina wire in commu-
nication with the multiplier, and then plunge it into nitric acid, which
also communicates with the galvanometer by means of another platina
wire. We then havea current from the carbon to the acid: this result
shows that the carbon has been attacked by the acid.
A pair of carbon and copper plates plunged into hydrochloric acid,
determines a current, which proceeds from the copper to the carbon, in
consequence of the slow action of the acid on the metal. A pair of
carbon and silver plates acts in a similar manner: whence we derive
a very simple process for forming chloride of silver and copper. Into
a glass tube closed at one end, we pour concentrated hydrochloric acid,
and plunge into it a plate of silver, attached by a wire of the same
metal toa piece of anthracite or charcoal. The tube is then almost totally
closed, only a very small aperture being left, in order to afford a vent to
the gas which escapes in the reaction of the bodies upon each other. The
following is the result : the silver being the positive pole of the small pile,
attracts the chlorine and combines with it, while the hydrogen goes to
the carbon, with which it forms a gaseous combination, which escapes.
When the tube is hermetically sealed, the tension acquired by the gas
soon causes it to burst. The chloride of silver that had been formed is
dissolved, and, when the acid is saturated, this compound crystallizes in
beautiful translucid octahedrons of one or two millimetres in length. If,
for the plate of silver, a plate of copper be substituted, the chemical
_eaction produces electric effects which increase the energy of the afii-
nities; the hydrochloric acid is decomposed, and there is a disengage-
ment of carburetted hydrogen. In six months or a year after this, the
Vor. I.—Parr III. 2G
428 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
plate is covered with fine tetrahedral crystals of protochloride of copper,
exceedingly brilliant and possessing great refrangibility. Ifthe experi-
ment be continued so as to exclude all contact with the air, the liquor
‘changes its colour to a deep brown and the crystals are no longer vi-
sible. The carbon is then powerfully attacked, and the result is, a
‘combination which has not yet been examined.
Of the Action of the Pile on the Alkaline Sulphurets.
When a solution of protosulphuret of potassium or sodium is exposed
to the air, the metal and the sulphur are simultaneously oxidized ; there
is produced a hyposulphite, in which the acid and the base contain an
equal quantity of oxygen: the solutions of the other sulphurets undergo
other changes ; so long as the solution retains a yellow tint, the hypo-
sulphite is all that is formed, but as soon as the sulphur is precipitated,
this salt is changed, first into a sulphite, and then into a sulphate.
The alcoholic solution of sulphuret of potash produces likewise, in
contact with the air, hyposulphite of potash, which crystallizes at the
surface of the liquid, at the same time that the sulphur, dissolved by
the alcohol, is abandoned. The other alkaline sulphurets act in the
same manner. ;
As to the sulphurets of barium and strontium, their solutions, in
contact with the air, undergo changes somewhat different: though there
is a formation of hyposulphate, there is none of hyposulphite.
When, in one of the branches of a tube bent like the letter U, (the other
branch containing water, ) asolution of one of the preceding sulphurets
is submitted to the action of the positive pole of a pile composed of a
small number of elements, by means of plates of platina, while the
water is in communication with the negative pole; the solution under-
goes changes similar to those which take place in the air. In fact, the
solution of protosulphuret of potassium or sodium in water is affected,
at first, in the usual manner by the positive pole; that is to say, a por-
tion of it is decomposed, and there is a transfer of potash or soda into
the negative side of the tube, while the sulphur left alone on the other
side combines with one portion of the disengaged oxygen, which trans-
forms it successively into hyposulphurous acid, sulphurous acid, and
sulphuric acid, which combines with the base; for, after some days,
we find only a sulphate. Ifthe operation be continued, this last salt
will itself also experience the decomposing action of the pile. The
same phenomenon is exhibited by the solution of the persulphurets,
except that there is a precipitation of sulphur.
The alcoholic solutions of the protosulphurets do not produce any
particular phenomenon. As to the solution of a persulphuret, in ad-
dition to the formation of the sulphate, it presents on the plate of platina
a fine deposit of crystals of sulphur, possessing great regularity of
form, and admitting an increase of their dimensions by changing the
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 429
solution when it is no longer saturated. The perfect crystallization of
the sulphur is partly owing to the power which the alcohol possesses of
dissolving a certain quantity.
The solutions of the sulphurets of barium and strontium being exposed,
like the preceding solutions, to the action of the positive pole, produce,
after some few moments, a deposit of sulphur and quadrilateral prisms
(which are nearly regular and unalterable in the air), of hyposulphate
of barytes or strontia. By continuing the operation these crystals are
decomposed.
So great is the tendency of the protosulphurets of barium and stron-
tium to undergo a change into hyposulphates, that when a plate of lead
or copper is substituted for one of platina, we still have a hyposulphate,
and only a small quantity of sulphuret of lead or copper deposited.
If we operate with a solution of persulphuret of barium, we shall
have a precipitation of sulphur in the form of small tubercles, and a
formation of hyposulphate. Hence it would seem that the sulphur and
barium are contained in the protosulphuret in the proportions required
for the oxygen arising from the decomposition of the water, and trans-
ferred to the positive pole, to be so divided between the two elements as
to forta the hyposulphate. All the superfluous sulphur contained in
the persulphuret, being unable to enter into the combination, is neces-
sarily abandoned, and, as it acts the part of an electro-negative element,
is naturally carried to the positive pole.
It is perfectly obvious that all the chemical actions which give birth
to these compounds can take place only under certain electric influ-
ences of small energy ; for if we operate with an apparatus the action
of which is too powerful, we isolate all the elements, and no combina-
tion is possible. The whole art consists then in disposing the appa-
ratus in such a manner as to prevent the transfer of certain elements,
and thus force them into combination with other elements which are
conveyed to them by means of the electric currents. This new mode
of producing combinations is fruitful in the variety of its applications,
and promises results of great importance to chemistry.
In the foregoing experiments the sulphuret was submitted to the
action of the positive pole: let us now see what will be the result when
it is in communication with the negative pole. We will take the sul-
phuret of barium: in this case the hydrogen reacts upon this com-
pound ; whence there arises a sulphohydrate of barytes, as will be sa-
tisfactorily proved if we test the solution.
Tf it be desired to obtain this substance in a crystallized state, we must
add to the solution one half its bulk of alcohol: as it does not dissolve in
this liquid, it becomes crystallized in considerable quantity on the plate
of platina as fast as it is formed. If we dissolve these crystals, we find
again all the characteristics of the sulphohydrate of barytes.
262
430 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
Of Double Chlorides, Double Iodides, Double Bromides, Double
Sulphurets, Double Cyanurets, &e.
It was conceived that by theapplication of the principles just explained,
it would be possible to obtain in a crystallized state some double inso-
luble combinations, which by the ordinary processes of chemistry it
would be difficult to produce, for want of sufficient slowness in their
operation, and because they do not enable us to abstract, at pleasure,
any given element of a body, or to add others. Let us first direct our
attention to the chlorides.
We take a tube bent into the form of the letter U, having its trans-
verse part filled with clay moistened with water: in one of the branches
we put nitrate of copper, in the other a solution of the chloride which it
is proposed to subject to experiment, for instance chloride of sodium.
The end of a slip of metal (copper, for example, ) is plunged into each
of them, and kept there by corks. Immediately afterwards, in conse-
quence of the reaction of the two solutions on each other, and that
of the solution of the chloride on the copper, the end immersed in the
solution of the nitrate becomes the negative pole of a small voltaic
apparatus, and is covered with copper in a metallic state: the nitric
acid and the oxygen are transferred into the positive branch, where
both concur in the production of those chemical reactions which we are
now about to describe. The plate of copper immersed in this branch
tends immediately to decompose the chloride; but, in consequence of
the voltaic action, it is oxidated at the expense of the oxygen transfer-
red. The oxide of copper thus formed combines immediately with the
chloride of copper and chloride of sodium; whence we obtain an oxy-
chloride of copper and sodium. By little and little this combination is
formed, on the positive plate, into distinct tetrahedral crystals. If it is
desired to have crystals of two or three millimetres in size, the appa-
ratus must be left in operation for at least a year. The success of the
experiment depends on our preventing the mixture of the liquids con-
tained in the branches of the tube, without impeding the transfer of
the oxygen towards the positive pole. The nitric acid contributes not
only to oxidize the copper but to decompose the sea salt; for there is
found in the solution some nitrate of soda. We have said that this
combination is effected only in proportion as the end immersed in the
solution of sea salt is slowly oxidized; for it does not take place when
we employ an intense electric current. The most effectual mode of
oxidizing a metal, in electro-chemical researches, is to dispose the ap-
paratus in such a manner that it will seize the oxygen which proceeds
from the reduction of an oxide.
This double oxychloride, withdrawn from the contact of the air, re-—
mains unchanged ; but as soon as it is in contact with water it is de-
composed, the chloride of sodium being dissolved, and the oxychloride
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 431
precipitated. Being anxious to analyse the latter product, in order to
know its nature, we proceeded in the following manner. We took
two grammes of the precipitate, after having well washed it, and di-
gested it in a warm solution of carbonate of soda. The precipitate,
when washed and dried, gave 2 grammes of carbonate of copper, con-
sisting of 1°70 of oxide of copper, and 0°94 of carbonic acid. The
oxychloride contained therefore 1°70 of oxide of copper, and 0°30 of
hydrochloric acid,—a proportion which represents 2 atoms of oxide of
copper and 1 atom of hydrochloric acid. We afterwards saturated
the solution with sulphuric acid, and then caused it to crystallize.
The crystals of chloride of sodium furnished the quantity of chlorine
contained in the substance subjected to experiment.
The chlorides of ammonium, calcium, potassium, barium, strontium,
and magnesium will give, with copper, analogous products, which also
crystallize in regular tetrahedrons. They are all isomorphous.
Silver, as well as lead, will also give, with the same chlorides, isomor-
phous combinations similar to the preceding. The double chloride of
potassium and tin crystallizes in prismatic needles, and this we should
__ expect, since the atomic composition of the chloride of tin is net the
same as that of the earthy or alkaline hydrochlorates.
_ We must here notice an observation made respecting the changes
_ sometimes produced in the crystallization of double chlorides. The
erystal is complete at first, but when the apparatus has been a long
time in operation, the angles of the crystal become gradually trun-
cated. It would seem from that circumstance that when the particles
of the substance which crystallizes are not sufficiently abundant, the
_ force which determines the regular grouping of these particles has no
longer the energy requisite to complete the crystal. We have had
_ frequent occasion to make the same remark in several crystallizations
Bot products formed by the aid of electric forces emanating from a
_ single pair.
By making use of the same apparatus we may form double sulphurets,
double iodides, double bromides, &c. The observations which we are
about to make in respect to the metallic iodides and sulphurets alone will
throw some light on the rest of those substances.
On the Crystallization of Metallic Sulphurets.
_ Chemistry has been hitherto unable to obtain, in the moist way,
the metallic sulphurets in a regular form; but this may be accom-
plished by uniting the action of the affinities to that of the electric
forces, and so disposing the apparatus that it may be able to operate
slowly and for a long time. We shall now notice in succession the se-
veral sulphurets which we have prepared.
Sulphuret of Silver—A saturated solution of nitrate of silver is
poured into one branch of the bent tube, and into the other a so-
482 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
lution of hyposulphite of potash, obtained by decomposing in the air
some protosulphuret of potassium. One end of a wire or plate of pure
silver is then plunged into each of them. The reaction of the two so-
lutions on each other, and that of the hyposulphite on the plate of silver,
produce electrical effects, in consequence of which, the plate immersed
in the nitrate becomes the negative pole of a voltaic apparatus. The
nitrate of silver is slowly decomposed, the plate immersed in it is co-
vered with silver in a metallic state, while the oxygen and the nitric
acid pass into the other branch, where they concur in the formation of
a double hyposulphite of silver and potash, which crystallizes in beau-
tiful prisms; but as the oxygen and the acid continue to arrive, they
react on this combination and the hyposulphite of potash: there are
then formed sulphate and nitrate of potash, and sulphuret of silver,
which remains unchanged so long as there is not a quantity of nitric acid
sufficient to act on it. The formation of the sulphate and the nitrate
of potash is easily explained ; but the case is far otherwise with the
formation of the sulphuret. Let us consider the circumstances by
which it is accompanied. In proportion as the liquid evaporates in the
positive branch, we see at the bottom of the tube and above the
clay some pretty octahedral crystals of sulphuret of silver formed
on the plate of silver. These crystals resemble, in appearance, those of
the same substance that are found in silver mines. Like them, they
extend themselves lightly under the hammer ; their colour is a leaden
gray, and their exterior surface is dim. The resemblance, indeed, is so
close that the artificial cannot be distinguished in any respect from the
natural crystals.
Why is it that, in consequence of the reaction of the oxygen and the
nitric acid on the hyposulphite, we cbtain a sulphuret of silver instead
of a hyposulphite, a sulphite, or even a sulphate? This question can-
not be answered but by supposing that the positive pole acts on the
oxide of silver and the hyposulphurous acid so as to disoxidize them ;
when the silver and the sulphur, being in their nascent states, obey
their mutual affinities. As these effects are produced slowly, there
is nothing to oppose the regular grouping of the particles of sulphu-
ret of silver. Nothing of a similar kind is obtained with a solution of
sulphuret of potassium. In this case the results of the experiment are,
sulphate of potash and sulphate of silver. This is very probably to be
ascribed to the influence of the proportions and the energy of the
action.
Sulphuret of Copper.—In order to apply the foregoing principles to
the formation of other sulphurets, and first to that of sulphuret of
copper, let us substitute for the solution of nitrate of silver a solution
of nitrate of copper, and for the plate of silver a plate of copper: there
is quickly formed in that side of the tube which contains the hyposul-
phite of potash, a double hyposulphite of copper and potassium, which
es ten el
=e
CRYSTALLIZATION FRODUCED BY VOLTAIC ACTION. 433°
crystallizes in very fine silky needles. This double hyposulphite is
gradually decomposed, and we obtain at last, on the plate of copper,
flat opake crystals with triangular faces two millimetres* in length.
These crystals are of a metallic gray colour, and some of them exhibit
tints of a bluish cast: their powder is blackish. They are soluble in
ammonia, to which they give a blue colour, and it is easy to perceive
that they are composed only of sulphur and copper. Hitherto there
has not been a sufficient quantity of this sulphuret collected to deter-
mine the relative proportions of the metal and the sulphur.
Oxysulphuret of Antimony.—In order to prepare the kermes, the
same liquids are employed as in the preceding experiment, and the
communication is established between the two tubes by means of an
are, composed of two plates, the one copper and the other antimony ;
the plate of copper being immersed in the nitrate, and the plate of an-
timony in the hyposulphite. The first becomes covered with copper, pro-
ceeding from the decomposition of the nitrate, while the other, as well as
the sides of the tube, becomes covered with a reddish brown precipitate.
Some time afterwards there are formed, on the antimony, small red
octahedral crystals, and crystallized plates of the same nature as the
precipitate. These crystals may be dissolved in neutral hydrosulphate
_ of potash, and give out sulphuretted hydrogen by the action of the
hydrochloric acid in which they are dissolved. They are made yellow
by the alkalis. All these are characteristic of the oxysulphuret of
antimony: the theory of its formation being the same as that of the
_ sulphuret of silver, it is unnecessary to dwell longer on it.
Sulphuret of Tin—Sulphuret of tin may be obtained in very small
crystals, possessing 2 metallic brightness; but the success of the ex-
periment depends on the electro-chemical action being yery feeble.
_ The operation is therefore difficult to be conducted.
Sulphuret of Lead or Galena—This compound also is obtained
in regular tetrahedral crystals, but the method to be pursued is different
from that adopted in a former case. A tube, about one decimetre+ in
length and five or six millimetres{ in diameter, is closed at one end.
The lower part is filled, to the height of two or three centimetres §, with
black sulphuret of mercury. On this we pour a solution of chloride of
magnesium : a plate of lead is then plunged into the liquid to the very
bottom of the tube. The apparatus being hermetically sealed, is
then left to the electro-chemical action. In a month or six weeks
we begin to perceive on the interior surface of the tube, above the sul-
phuret, a very thin layer of a brilliant precipitate (of a metallic gray
colour), which is easily detached, and becomes gradually covered with
small crystals, which appear, when seen through a microscope, to be
regular octahedrons, presenting the same aspect as those of the ga-
lena. When the tube is opened, a gas escapes, which diffuses the
*,ofaninch. + About 3: inches. ¢ About, of an inch. § About 1 inch.
434 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
odour peculiar to the combinations of sulphur with chlorine and hydro-
gen. If the liquor is tested with an acid, there is an escape of sul-
phurous acid. The lower part of the plate of lead has become brittle,
in consequence of the combination of the lead with mercury. In order to
explain these several results, it must be recollected that when the lead
is in contact with an alkaline or earthy chloride, such as that of magne-
sium, a double chloride is formed and magnesia is precipitated. In con-
sequence of this reaction, the lead becomes negative and the solution
positive ; the circulation of the electric fluid is then carried on through
the medium of the infinitely thin layer of liquid which adheres to the sur-
face of the glass. Under the same circumstance, the sulphuret of mer-
cury being dissolved in the chloride, is subjected to the action of the small
pile: the lead, which is the negative pole, attracts the mercury, and the
sulphur is attracted by the double chloride of lead and magnesium. One
portion of the sulphur combines with the lead, whence there arises a sul-
phuret of lead, which crystallizes without any trace of mercury, while
the other portion combines with the chloride of magnesium, and the
chlorine which was combined with the lead ; and thus there is produced
a sulpho-chloride of magnesium and a chloride of sulphur.
The operation being continued for several months, the liquor in the
part adjacent to the sulphuret of mercury assumes a reddish tint, which
is probably owing to the presence of chloride of sulphur. It is neces-
sary to observe, that no trace of lead is found in the liquor; a fact
which proves that it is precipitated as soon as dissolved. “
The action which determines the formation of the sulphuret of lead
being very complex, it would be difficult to say, without having
‘analysed the liquor, how the several decompositions and combinations
first mentioned are effected in definite proportions.
Sulphuret of Iron and Zine.—It is very difficult to form these com-
pounds by the processes which we have been describing, because of
their great liability to be affected by contact with air and with water.
We have succeeded nevertheless in obtaining the first, by means of the
alkaline hyposulphite, in small yellow crystals of great brillianey, which
became rapidly decomposed in contact with the air. As to the sul-
phuret of zine, we have not been yet able to obtain it crystallized.
Sulphuret of Cadmium.—tThe sulphuret is obtained, of an orange
yellow, in a crystalline form, by employing the second process ; namely,
that which gives the sulphuret of lead.
From the facts set forth in this chapter, we may conclude that, in
order to obtain the crystallization of an insoluble substance by means
of electro-chemical reactions, it will be sufficient that we bring it into
combination with another substance which is soluble, and then produce
a very slow decomposition. The same object may be attained, but
with far greater difficulty, by the ordinary resources of chemistry, as
the following observation will show :
.
CRYSTALLIZATIGN PRODUCED BY VOLTAIC ACTION. 435
Some clay, very much divided and moistened with a solution of
arseniate of potash, having been put into a glass tube, there was poured
over it a solution of nitrate of copper: the reaction of the two solutions
took place rapidly in the first few instants at the surface of contact of
the clay and the solution of the nitrate. But the solution having gra-
dually penetrated the mass of the clay, the consequence was, that the
reaction between the arseniate and the nitrate was very slow, and there-
fore favourable to the crystallization of the arseniate of copper. After
the lapse of some time, there were seen in the vacant interstices of the
clay some crystals resembling those of native arseniate of copper.
The formation of double sulphurets and simple sulphurets being
subject to certain laws, we must not use tubes of any dimensions we
please, and must not employ liquids possessing too great an electric
conductibility. If, for example, the quantity of double hyposulphate
formed were too great to be completely decomposed by the acid which
comes from the tube containing the nitrate of copper and the nitrate
of silver, the operation would be incomplete, inasmuch as we should
not have, in that case, the reactions necessary for the formation of the
compounds we wish to obtain. Thus, in proportion as the circum-
stances have been more or less favourable, the result will be a per-
fect or a confused crystallization, or a total absence not only of crystal-
lization but of the production of double sulphuret.
The tubes employed must always be of small dimension, that is to
say, of two or three millimetres* ; for if the acid came in too great
quantities into the tube containing the double combination, it would
react on each of the components, and the desired result would not be
attained. It must not be forgotten that the hyposulphite which we
employed proceeded from a protosulphuret of potassium decomposed in
the air.
Of Metallic Iodides.
It is known that the metallic iodides are subject to the same law
of composition as the sulphurets. We expected therefore to be able to
obtain the insoluble iodides by the same process which has served to
obtain the sulphurets. In thinking thus we are but generalizing the
principle.
Lodide of Lead.—In the electro-chemical apparatus already described
we substitute the iodide of potassium or soda for the alkaline hyposul-
phate; we then plunge a plate of copper into that branch of the bent tube
which contains the nitrate of copper, and a plate of lead into the other
branch, which contains the solution of iodide of potassium. In the latter
‘branch of the tube we obtain at first a double iodide of lead and potas-
sium, which crystallizes in very fine white silky needles; this combina-
tion is gradually decomposed, the decomposition commencing at the
* About »!, of an inch,
*
4.36 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
lower part, which is contiguous to the clay. We then perceive a great
number of crystals, derived from the regular octahedron, and exhibiting
that golden hue and brilliancy of aspect which belong to the iodide of
lead.
Copper, subjected to the same: sort of action, gives at first a double
iodide in white crystallized needles; and then, after the decomposition,
we obtain some octahedral crystals. The iodide of silver also is ob-
tained without difficulty.
It is probable that the other metals whose iodides are insoluble would,
with due precaution, afford similar results. The insoluble bromides
and selenurets can unquestionably be obtained by the same process. We
shall, in this place, confine ourselves to the bare mention of the fact, be-
cause their formation flows from a general principle which has been suffi-
ciently developed in this chapter to render new details unnecessary.
ACCOUNT OF A GENERAL METHOD OF OBTAINING IN A CRYSTAL-
LIZED STATE, SULPHUR, THE SULPHATE, AND THE CARBONATE
OF BARYTES.
The Principle employed in the Formation of those Compounds. —
We have already shown that when a body transferred by a current
meets another body with which it forms an insoluble compound, the
combination takes place, and the precipitate is produced instantaneously.
But we have not yet adverted to that which happens when an acid en-
counters a salt, the base of which has a greater affinity towards that acid
than towards the acid with which it is actually combined. The follow-
ing experiment will show what it is that happens in such a case.
A glass tube several millimetres in diameter, open at each end, and
containing in its lower part some very fine potter’s clay moistened with
a solution of nitrate of potash, and in its upper part some common
alcohol, is placed in another tube filled with a solution of sulphate of
copper. The communication between the two liquids is then esta-
blished externally by means of an arc, consisting of two plates of cop-
per and lead soldered end to end, the copper side being immersed in
the sulphate and the leaden side in the alcohol. The sulphate of
copper is quickly decomposed, in consequence of the electric effects re-
sulting from the reaction of the two liquids on each other, and that of
the alcohol on the lead. The copper of the sulphate is reduced on the
plate of copper, which is the negative pole ; the oxygen and the sulphu-
ric acid are transferred to the side where the plate of lead is; but, in-
stead of obtaining sulphate of lead, we see, after an interval of a few
days, that a great number of octahedral crystals of nitrate of lead have
been formed. This fact proves, beyond all doubt, that the sulphuric
acid, in traversing the clay impregnated with nitrate of potash, decom-
posed this salt and combined itself with the potash, because of its hay-
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 437
ing a greater affinity towards this base than the nitric acid has. The
latter acid being liberated proceeded to the positive pole, where it com-
bined itself with the oxide of lead, formed, in'a great measure, at the
expense of the oxygen of copper. The result was a nitrate of lead,
which crystallized in proportion as it had saturated the aleohol. With
a more powerful voltaic action, the sulphate of potash would have been
decomposed. This example shows how valuable the feeble electric
currents are in the production of combinations. In the case under
consideration, the nitrate of potash was decomposed by the concur-
rence of the electric forces and the chemical affinities.
Let us now apply the foregoing principle to the decomposition of the
sulpho-carbonate of potash, and the formation of some compounds.
lst ExpertmMENT.—The sulpho-carbonate of potash, whose solution
when not very much concentrated is gradually decomposed in the air,
_is peculiarly disposed to admit of changes being produced in the state
of combination of its molecules by the action of feeble forces. The
following is the mode in which we operate on this substance: we take
two glass jars, and pour into the one a solution of sulphate of copper,
and into the other an alcoholic solution of sulpho-carbonate of potash.
_ The communication between the two liquids is then established, on
_ the one hand by means of a bent glass tube, filled with potter’s clay
moistened with a solution of nitrate of potash; and on the other by
means of a metallic arc formed of two plates, one copper and the
other lead, the plate of copper being immersed in the sulphate, and
the plate of lead in the sulpho-carbonate. According to the nature of
the electric effects produced in the various chemical reactions, the lead
is found to be the positive pole of a pile whose intensity is sufficient to
_ decompose the sulphate; the copper is reduced ; the oxygen and the
sulphuric acid are carried towards the lead; the acid, in its passage,
_ decomposes the nitrate of potash, as in the preceding experiment, so
that the oxygen and the nitric acid enter alone into the sulpho-carbo-
nate. As soon as they have penetrated it, they begin to react on its
constituent parts, and this reaction continues so long as the force of the
current is superior to the affinities of the several bodies present: the
transfer of the molecules is continued as far as the positive plate,
where the last reaction takes place. The following products are suc-
cessively formed : neutral carbonate of potash which erystallizes on the
sides of the vessel, sulphate of potash, a sulpho-carbonate of lead and
of potash in acicular crystals, carbonate and sulphate of lead in
needles ; and, in fine, a portion of sulphur proceeding from the decompo-
sition of the sulphuret of carbon and the sulphuret of potash, is depo-
sited on the plate of lead, which is the positive pole, and there crystal-
lized in octahedrons with a rhomboidal base. These octahedrons some-
times attain a millimetre in length when the experiment has been con-
tinued for a month.
438 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
Crystallized sulphur is also obtained by abandoning to the influence
of the air a solution of that substance in carburet of sulphur, or by
melting some sulphur and letting the liquid stand to cool until there is
formed at the surface a solid crust, which is broken in order to draw
off the liquid. But the process which we have described is different
from the two preceding processes, and bears some analogy to that
which nature employs in some circumstances ; for instance, in the slow
decomposition of sulphuretted hydrogen gas and feculent matters
which, in the course of time, deposit well-defined crystals of sulphur.
In both cases the crystallization is the result of an excessively feeble
action, on which we shall have occasion to remark when we come to
treat of spontaneous actions.
The products resulting from the decomposition of the sulpho-carbo-
nate of potash vary according to the intensity of the electric current
and the degree of concentration of the solution. With an alcoholic
solution of sulpho-carbonate, diluted with water, we obtain but little
sulphur, and a great quantity of sulpho-carbonate of lead and potash,
These differences in the results are owing to the ratios which the affi-
nities of the several bodies bear to the intensities of the current, which
vary according to the conductibility of the liquids and the energy of
the chemical action which produces the current. In the present state
of the science, it is impossible to see @ priort what should happen in
any proposed case ; that is to be learnt from experiment only.
The sulpho-carbonates of the other bases submitted to the same
species of experiment gave analogous results. It is owing to the slow-
ness of their decomposition, and to the appropriate choice of metals
with respect to the positive pole, that we obtained the sulphate of ba-
rytes in erystals derived from the primitive form.
Another Application —We fill with a solution of bicarbonate of soda
a tube containing, in its lower part, clay moistened with the same so-
lution, and place it in another which contains a solution of sulphate of
copper. We then plunge into each liquid one of the extremities of a
plate of copper, and observe the following effects: the end which is in
the solution of sulphate being the negative pole decomposes this salt,
and attracts the copper, while the oxygen and the sulphuric acid pass
to the other side. But as the sulphuric acid on its passage meets with
carbonic acid, it expels this from the combination and takes its place.
The carbonic acid then forms with the oxide of copper a carbonate
which, by combining with that of the soda, produces a double carbonate
of copper and potash, which crystallizes in beautiful satin-like needles of
a bluish green colour. This substance, which does not dissolve in water,
is decomposed with the aid of heat; the carbonate of soda is dissolved,
that of copper is precipitated and become brown, like the common car-
bonate when subjected to the action of boiling water.
In the preceding experiments, the power of sulphuric acid in expelling
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 439
acids having a less affinity than itself towards the bases is owing solely
to the small energy of action in the pile; for if the action were more
powerful, all the acids would be indiscriminately transferred to the
positive pole. ,
The electric current employed by us in order to produce decomposi-
tions, may arise from two causes; the chemical reaction which the two
liquids in contact exercise on each other, and the chemical action of
the liquid of the small tube on the metal immersed in it. In the first
case, if the reaction be sufficiently energetic, the second cause may be
dispensed with: in like manner, if the second cause be of sufficient in-
tensity, the first becomes superfluous. But when both are feeble and
the currents resulting from them have the same direction, their sum is
then indispensable to the production of the electro-chemical effects.
In general, whenever the two currents take the same course, their sum
cannot but be favourable to the decompositions and the formation of
the products. It often- happens that these two currents are so weak
that the reduction of the oxide in the great tube cannot take place. In
that case there is no effect produced. If, therefore, after an interval of
some days, we perceive no precipitation of copper on the plate of cop-
per immersed in the solution of the nitrate or the sulphate, it is useless
to continue the experiment longer, and the apparatus must be changed.
In the experiment in which the great tube contains sulphate of copper,
and the small one contains, in its lower part, potter's clay moistened
with a solution of nitrate of potash, and alcohol, the chemical re-
action of the nitrate on the sulphate has had considerable influence in
producing the current which has decomposed the sulphate of copper ;
for the action of the alcohol on the lead must have been sufficiently
feeble to give rise to a sensible electric current. It would be desirable
to operate always on such solutions as would exercise on each other
_chemical actions sufficiently energetic to give out the requisite currents,
when the plate immersed in the liquid is gold or platina, in order that
we may be able to study the phenomena of decomposition and recom-
position with facility, and independently of the reaction of the oxides.
This would be the only course to be taken in order to discover what it
is that takes place in the liquid organic compounds, when, by means of
electricity, we introduce into them such bodies as are capable of carry-
ing off some of their constituent parts. This want of sufficient reac-
tion in the liquids may be supplied by operating with the following
apparatus, which enables us, when we wish, to avoid the action of the
metallic oxides formed at the positive pole. As this apparatus enables us
to operate in a great variety of cases, we shall more minutely describe
its construction and use.
We take three jars A, A’, A", (fig. 3.) placed in a line at a short
distance from each other. The first is filled with a solution of sulphate
or nitrate of copper; the second, with a solution of that substance
440 M. BECQUEREL ON CHEMICAL DECOMPOSITION AND
in the constituent parts of which we wish to produce changes; and the
third, with water rendered a slight conductor of electricity by the ad-
dition of an acid or common salt capable of acting chemically on the
metal which is to be immersed in it. A communicates with A! by
means of a bent tube, abe, filled with potter’s clay moistened with a
saline solution, the nature of which depends on the effect intended
to be produced in A; A!’ and A” communicate with each other
through the medium of a plate (a'b'c') of platina or gold; and A
and A" communicate by means of a voltaic pair (CM Z), composed
of two plates (MC and MZ) of copper and zine; in fine, a safety-tube
(tt) is placed in the vessel A’, in order to indicate the internal pres-
sures resulting from the disengagements of gas. According to this
arrangement, the extremity a! of the plate of platina is the positive pole
of a voltaic apparatus whose action is slow and continuous. When the
liquid contained in A! is a good conductor, the intensity of the electric
forces is sufficient to decompose the sulphate of copper in A. From
that instant the oxygen proceeds towards a’, as well as the sulphuric
acid, which, in passing into the tube (abc) expels those acids which
have a less affinity than it has itself towards the bases. These acids
and the oxygen pass into the liquid A’, where their slow reactions de-
termine the relative changes in the bodies which they find there. This
apparatus allows us to operate on a greater scale, and to ayoid the re-
action of the oxide in the same manner as it was avoided in the appa-
ratus previously described.
We are often compelled to place a fourth jar between A and A/, into
which there is put so much of a saline solution, to be decomposed by
the sulphuric acid, that the effects produced in the liquid A’! may not
be interrupted when all the liquid of the clay has heen decomposed.
Thus, when we wish to bring a gas or an acid in its nascent state into
the liquid of the vessel A‘, we have only to introduce into the clay
a solution which, by its reaction on the sulphuric acid proceeding
from the decomposition of the sulphate of copper, may let the gas or the
acid escape. If, on the contrary, it should be found necessary to con-
duct into the same liquid either hydrogen or an electro-positive gas,
CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 441
the media of communication must be reversed, a'b'c! being put in the
place of ac, and vice versd. In fine, if for the plate of platina there
is substituted a plate of oxidable metal, we introduce into the interme-
diate solution the reaction of an oxide, which being in its nascent state
-conduces to the formation of the products. The bare inspection of the
figure is sufficient to give an idea of the results that may be obtained
by making the requisite variations in the solutions.
Mode of using the Apparatus when the Positive Plate is not oxidable.
Ist ExpeERIMENT. We pour into the vessel A! an alcoholic solution
of sulpho-carbonate of potash; into the vessel A a solution of sulphate
_ of copper; and into the clay of the tube a a solution of nitrate of pot-
ash: after 24 hours’ trial the reaction of the oxygen and the nitric acid
on the solution of the sulpho-carbonate is now perceptible ; for we ob-
serve on the extremity (a’) of the platina plate the products already in-
_ dicated (when the operation was supposed to be performed with a plate
of lead ), that is to say, crystals of sulphur, of neutral carbonate of potash,
&e., but nocarbonate of lead, because there is no oxide of this metal.
_ 2nd Experiment. Crystals of Sulphur ; Sulphate and Carbonate
_ of Barytes.—In the preceding apparatus we substitute for the sulpho-
-earbonate of potash a solution of sulpho-carbonate of barytes : we shall
_ not have long to wait for the appearance of analogous reactions ; a pre-
_ cipitation of sulphur in small erystals, and a formation of sulphate and
carbonate of barytes in prismatic needles. | We should perhaps by this
process obtain crystals of some size, if the plate of platina was so bent as
to form a spoon, and thus prevent the crystals formed on the surface of
_ the plate from falling to the bottom of the vessel.
ray
3rd Experiment. Mode of ascertaining the presence of Nitric Acid
and that of Hydrochloric Acid in any Solution, even when those two acids
exist there in very small quantities—For the plate of platina a’ b'c! a
- plate of gold is substituted : there is then poured into the vessel A a so-
- Tution of sulphate of copper ; and into the vessel A’, and the clay of the
‘tube abe, a solution of the compound which is supposed to contain the
two acids in combination with bases. As soon as the apparatus begins
to operate, the sulphuric acid expels the two acids from their combina-
tions, which, together with the oxygen arising from the reduction of the
oxide of copper, are carried to the extremity (a’) of the plate of gold:
the yellow colour which immediately makes its appearance indicates the
presence of nitric and hydrochloric acids. This reaction is also obtained
when tubes of small dimensions are substituted for the jars. In this pro-
‘ess no part of the acids is lost ; for they are all transferred to the posi-
tive pole, and contribute to the production of hydrochlorate of gold.
Ath Experiment. Sulphite of Copper—tThe vessel A’ is filled with a
solution of sulphite of potash, and for the plate of gold a'b'e! a plate of
442 M.BECQUEREL ON CHEMICAL EFFECTS OF VOLTAIC ACTION.
copper is substituted. The extremity a', which is still the positive pole,
attracts the oxygen and the nitric acid: the latter decomposes the sul-
phite and takes possession of the base; the sulphurous acid is carried
to the oxide of copper, which is formed at the same time, and combines
with it: the sulphite of copper itself combines with the sulphite of pot-
ash, whence there results a compound that crystallizes in beautiful octa-
hedrons; but as the nitric acid still continues to arrive, it decomposes
this double sulphite at last: sulphurous acid gas then escapes, and the
sulphite of potash is transformed into bisulphite and nitrate of potash.
As to the sulphite of copper, it is precipitated in transparent octahedral
crystals, of a vivid red, with the brilliancy of garnets. M. Chevreul,
a long time since, obtained this sulphite of copper by the ordinary
processes of chemistry. We might extend the number of the results yet
further, but the object we have had in view, which was to communicate
the description of an apparatus of very general applicability, seems to us
to be sufficiently attained.
Notes communicated by Golding Bird, Esq.
Potter’s-clay, p. 417, last line but two,
M. Becquerel invariably uses clay as a medium for forming a connection between two fluids when
their mutual reaction is necessary, but he gives a very requisite caution that the clay must be care-
fully tempered with water or a saline solution ; for if too dry, it will not allow the transfer of elec-
tric currents with sufficient facility ; and if too moist, it admits of the admixture of the two fluids,
which (as when the tube curved like the letter U is used) it is intended to separate. Thence it has
not unfrequently happened, that many of the experiments described by M. Becquerel have failed in
the hands of some who have repeated them, merely from inattention to the clay being in a suffi-
ciently moist or dry state. All these difficulties, which although apparently trifling are nevertheless
occasionally fatal to the success of experiments, may be obviated by substituting plaster of Paris
for the potter’s-clay ; for by merely mixing it with water or a saline solution, it may be readily
poured into a tube of any required form, where it rapidly solidifies, and while in this state is suffi-
ciently porous to admit of a very slow admixture of the two fluids employed, as well as to allow of
the ready transfer of the feeblest voltaic current.
P. 422. Crystallization of Protoxide of Copper.
The crystals obtained by the process here described by M. Becquerel are exceedingly distinct, and
very closely resemble some of the native forms of the oxide or ruby copper ore. This protoxide is
generally found native, mixed with crystals of metallic copper ; and by availing ourselves of a very
weak electric current, kept up for some weeks, an exceedingly close imitation of this native com-
bination may be obtained. For this purpose take a glass tube open at both ends, about half an inch
in diameter and tnree inches in length: close one end of this tube by means of a plug of plaster of
Paris, about one-third of an inch in thickness; fill this tube with a solution of the nitrate or chlo-
ride of copper moderately diluted, and place it inside a cylindrical glass vessel nearly filled with a
weak solution of potassa or soda. These two fluids, very slowly mixing through the plug of plaster
of Paris, would, if left to themselves, cause a gradual} formation and deposition of hydrated deutoxide
of copper. Make a compound arc of two pieces of metal, one of copper, the other of lead, taking care
that their surfaces are quite clean, or even polished; plunge the leaden leg of the arc into the outer
cylinder of the little apparatus, and the copper leg into the smaller one, containing the solution of
nitrate or chloride of copper, and leave the apparatus to itself. Slow electric action ensues ; the copper
limb of the arc becoming the negative, and the lead (which slowly dissolves in the alkaline solution)
the positive electrode; the electric currents thus set in motion readily traverse the plaster of Paris
partition, and cause the reduction of the deutoxide of copper (precipitated by the slow admixture of
the alkaline solution with the copper salt) partly to the metallic state and partly to the state of prot-
oxide. ‘That portion of the peroxide which is thus reduced to the metallic state yields very fine and
tolerably large crystals, which are of course deposited on the surface of the copper negative electrode.
Mixed with these crystals, the protoxide is deposited in very delicate, transparent, ruby-red crystals,
not isolated and separate, but deposited in rosette-like patches, which present under a lens an exceed-
ingly beautiful appearance. So closely do some of the specimens of protoxide and metallic copper
thus obtained resemble the native forms, that it would be difficult, if not impossible, even for an ex-
perienced eye to distinguish the native from the factitious specimens, if the nature of the substance
they are precipitated on did not betray their origin.
P.425. Crystallization of Oxide of Zine.
This oxide may be obtained much more conveniently by the use of the apparatus contrived for the
crystallization of the ruby oxide of copper (vide last note) with the substitution of a solution of oxide
of zine in caustic potassa for the uncombined alkali, in the larger vessel. By this arrangement, the
copper leg of the arc becomes, as before, the negative, and the leaden the positive plate of a miniature
battery, sufficient however to cause a very elegant deposition of oxide of zinc on the plate of lead
or positive electrode in the course of a week or ten days; whilst upon the copper plate or negative
electrode a mixed deposit of metallic copper and ruby-coloured protoxide takes place, rivaling in
beauty that obtained by the last-described process. By this modification of the apparatus, the two
oxides (zinc and copper) may be obtained crystallized by one and the same operation, La
443
ARTICLE XXII.
On a New Combination of the Anhydrous Sulphuric and Sul-
phurous Acids; by Henry Rose, Professor of Chemistry at
the Royal University of Berlin*.
From Poggendorff’s Annalen der Physik und Chemie, voi. xxxix. No. 9. 1836.
p- 173.
By passing dry sulphurous acid gas into anhydrous sulphuric acid, I
obtained a limpid fluid, which smelt very strong of sulphurous acid, and
which by exposure to the air evaporated entirely in thick fumes.
This fluid is a combination of the anhydrous, sulphurous, and sulphu-
rie acids, in definite proportions. In order to obtain it several precau-
tions are requisite: the slightest trace of moisture must in particular be
avoided; for should any be present, the compound even when formed
is very easily decomposed; and should either of its components
contain any trace of moisture, its composition would be entirely pre-
vented.
___ In order to avoid this, I passed the sulphurous acid gas first through
_a cooled receiver, and then through a tube at least four feet long, filled
with freshly heated chloride of calcium. From hence it passed very
slowly into a glass vessel, which contained the anhydrous sulphuric acid,
and which was closed by a cork, through which the tube conveying the
_ sulphurous acid was passed. This glass vessel was cooled to about the
_ freezing point of water, but not lower, lest the new compound might con-
- tain free condensed sulphurous acid. As soon asa certain quantity of
_ the fluid was formed, it was poured off from the remaining solid sulphuric
acid into a small glass, and immediately submitted to examination.
The tube containing the chloride of calcium could only be used for
One preparation ; it was obliged to be heated once more previously to
being again employed. When a certain quantity of the compound (a
few grammes for instance) is formed, the formation of a further por-
tion ceases entirely, because the chloride of calcium no longer dries
the sulphurous acid so perfectly as at the beginning of the operation.
On exposure to the air the fluid thus obtained fumes very much, and
_ smells strongly of sulphurous acid. I have always obtained this fluid of
.| 4 brownish colour ; but this is not essential to the compound, which is
colourless, but arises from the cork which closes the vessel containing
' the sulphuric acid. The fluid is so volatile, that when brought into con-
| * [The Editor is indebted for the translation of this Paper to E. Solly, jun. Esq.
Vor. I—Panrt III. Qu
4.44 PROF. ROSE ON A NEW COMBINATION OF THE
tact with the air it very soon evaporates, and then occasionally leaves
behind an exceedingly small portion of hydrous sulphuric acid. This
great volatility, as also the easy decomposability, of the compound, en-
tirely prevented my bringing it into a small glass bulb with a long neck
drawn to a point, as is done with other less volatile and decomposable
fluids, by warming the ball and then dipping the point in the fluid.
When the bulb is quite cooled, the compound does not rise in the
stem, less on account of its own vapour preventing it, than because it is
decomposed in the rarified space in the bulb, and sulphurous acid gas is
evolved. This is also the reason why it is not possible to ascertain the
specific gravity of the vapour of this compound. If ever so small a por-
tion of water be brought in contact with this fluid, a strong effervescence
and evolution of sulphurous acid gas immediately ensues. The com-
pound is entirely decomposed by a small quantity of water. If it be
brought into a glass vessel, so nearly dry that not the slightest moisture
is perceptible on its sides, even then a slight effervescence and decom-
position occur; this is the reason of the necessity for the great care to
avoid the slightest trace of moisture in the formation of this com-
pound, which would otherwise be entirely prevented. Ifa large quantity
of water be added to it, it boils fiercely, through the sudden evolution
of sulphurous acid.
If dry ammoniacal gas be passed into the fluid, anhydrous sulphate
and sulphite of ammonia are formed. The product thus obtained is of
a yellowish colour, and soluble in water; if the solution be saturated
with muriatic acid, sulphurous acid is evolved, but no precipitate of
sulphur falls until the fluid is boiled. A solution of nitrate of silver
causes a precipitate in it, which is at first white, then yellow, brown, and
at last (very quickly if boiled) black. These are the properties of a
combination of dry sulphurous acid and ammonia, which I have before
described*. A solution of chloride of strontium causes a precipitate of
sulphate of strontia, occasioned by the sulphuric acid, which is formed
by the action of the chloride of strontium upon the solution of the an-
hydrous sulphite of ammonia ; if this precipitate be removed, and the
supernatant liquid boiled, a fresh precipitate of sulphate of strontia —
falls, which is one of the properties of the solution of the anhydrous sul- _
phite of ammoniat.
In analysing this substance, I have only succeeded in estimating ex-
actly the quantity of sulphuric acid, not of sulphurous, though I at-
tempted it in several ways. A weighed portion of the compound, in a
very small bottle, which had been weighed previously with the glass
stopper, was oxidized by fuming nitric acid, in such a way that no loss
could be sustained by the violent action. The nitric acid was in a large
* Poggendorff’s Annalen, vol. xxxiii. p. 235. } Ibid. vol. xxxii. p. 81.
nd
ANHYDROUS SULPHURIC AND SULPHUROUS ACIDS. 445
bottle, which by a ground stopper could be rendered air-tight. The
small bottle containing the weighed portion, and without the stopper,
was fastened by a platina wire, and thus quickly introduced into the
large bottle, which was then immediately closed, but in such a manner
that the fluids themselves could not act upon each other, but only their
vapours. After some time I agitated this carefully, but in such a man-
ner that only a little of the compound in the small bottle was thrown out
and could mix with the nitric acid, which always caused a very strong
action, though never the evolution of light. If, on the contrary, by
shaking the bottles, a little nitric acid fell into the small bottle, a ery-
stalline deposit was formed, which I have not examined more closely,
but which perhaps may be the same as that which is often formed
during the preparation of the English oil of vitriol, and which consists
of sulphuric and nitrous acids and water. After the mixture of the
nitric acid and the substance was completed, the whole was diluted
_ with water, and then saturated with a solution of chloride of barium.
From the quantity of sulphuric acid which was contained in the
sulphate of baryta thus obtained, I could easily appreciate the relative
proportions of the sulphuric and sulphurous acids in the compound ;
for what the first contained more than the latter in weight, could only
consist in oxygen which the compound had absorbed.
But in two experiments, both conducted with equal care, I obtained
from the sulphate of baryta less sulphuric acid than I had taken in
weight of the compound; a proof that evidently only a part of the sul-
phurous acid had been oxidized by the nitric acid.
In the first experiment 2:237 grammes of the compound gave 5°633
grammes of sulphate of baryta, which contained 1:936 of sulphuric
acid, equal to 82-08 per cent. of the compound. In the second expe-
riment I obtained, from 1-250 grammes of the compound procured by
another preparation, 3-443 grammes of sulphate of baryta, which con-
tained 1-1834 grammes of sulphuric acid, indicating 94°67 per cent.
of the compound.
This very slight difference shows plainly that it only arises from the
mode of preparation, and that in the combination fuming nitrie acid did
not convert the free sulphurous into sulphuric acid. Perhaps it might
have been effected had more dilute nitric acid been employed, because in
the preparation of the English oil of vitriol the sulphurous can convert
itself into sulphuric acid ; but for a quantitative analysis it did not seem
to me so fitting. Moreover the compound, oxidized by nitric acid
and then diluted with water, did not smell of sulphurous acid. That
the nitric acid did not fully oxidize the sulphurous acid in the com-
pound is evident from the result of a third experiment, in which I took
some of the compound which had been oxidized by fuming nitric
acid, and having mixed it with a weighed quantity of freshly heated
2H 2
446 PROF. ROSE ON A NEW COMBINATION OF THE
oxide of lead, I evaporated the whole to dryness, and heated the mass
to redness. I obtained from 1°613 grammes of the compound, treated
with fuming nitric acid and mixed with 10°739 grammes oxide of lead,
a mass which after being heated weighed 12°238 grammes, and which
contained therefore 1°499 grammes of sulphuric acid, or 92°93 per cent.
This experiment proves that the loss cannot be due to any formation
of hyposulphurie acid.
The result of experiments in which I endeavoured to oxidize the
sulphurous acid by solutions of gold were much more uncertain.
For this purpose I employed a carefully prepared solution of the triple
salt, the chloride of gold, and sodium. The compound was brought
into contact with this in the same manner as in the former experi-
ments with nitric acid. The mixture was submitted, out of contact
with the air, to a moderate heat for about twenty-four hours. Two
experiments, conducted with equal care, gave however such widely
differing results, that it was impossible for me to explain the cause of
the great dissimilarity : for from 1-259 grammes of the compound I ob-
tained in one experiment only 0°058 of a gramme of metallic gold;
whilst in a second experiment I obtained, from a much smaller quan-
tity of the compound, out of 0°667 of a gramme, more gold, namely
0°196 of a gramme.
The estimating of the sulphuric acid in the compound gave much
more satisfactory results; I was obliged to be contented with these, and
to estimate the quantity of sulphurous acid by the loss sustained. The
determination was effected in the following manner: a quantity of the
compound, weighed in a small glass bottle with a stopper, was put into
a larger bottle, which could also be closed by a glass stopper: this
contained a solution of chloride of barium, to which free muriatic acid
was added. As soon as the little bottle was introduced, the larger one
was closed; and by shaking the vessel, the stopper of the little bottle,
which was merely loosely fixed, was thrown off, so that the compound
might mix with the solution of chloride of barium ;—an exceedingly
violent but not dangerous action ensued.
After the sulphate of baryta was deposited, the liquid was quickly
filtered out of contact with the air, and its weight determined. An
addition of muriatic acid to the solution of chloride of barium is quite
necessary, because otherwise the sulphate of baryta cannot easily be
filtered, but passes milky through the filter.
I have analysed four different portions, prepared at different times, in
this manner, and have obtained results which, though they agree much
less than those of less easily decomposable substances, yet on account
of the great decomposability and volatility of the compound, and there-
fore the difficulty of freeing it from uncombined sulphuric or sulphur-
ous acid, agree more nearly than I expected.
ANHYDROUS SULPHURIC AND SULPHUROUS ACIDS, 44:7
The substance contains more sulphuric acid when it is not analysed
immediately after preparation, and after it has given forth some sul-
phurous acid ; less sulphuric acid, on the contrary, when this was the
case, and it therefore contained some free sulphurous acid.
The result of these four experiments carefully conducted, according
as the substance was of newer or older preparation, was as follows:
Weight of Weight of sulphate Percentage of
Compound. of baryta obtained. sulphuric acid.
I. OF529 ers irae Ns 72°90
Il. OF On eT Mate ss'ees Doe Doe pias arate 70:00
Ill. jr Ta a ZO SaOay 68°91
IV. iD ieee ces FOZ mae SAG 67°68.
The compound does not contain, therefore, as I suspected before the
experiment, sulphuric and sulphurous acids in the same proportions as
in the anhydrous hyposulphuric acid (S + S), but 2 eq. of sulphuric
acid to 1 eq. of sulphurous acid (2S + S) which in 100 parts may be
stated as follows:
PSD HNITIC ACI, shy. 66s cnn wustiicodsapessssten’ 71°42
PAP RUTOUS, ACE: 6. saad cst Be'ses eleva sotes 28°58
100:00
As the sulphurous is the least strong acid in the combination, and
may therefore be considered of the two as the base, according to this
view the compound may be considered as a neutral sulphate salt, in
which the sulphuric acid contains three times as much oxygen as the
base.
44S
ARTICLE XXIII.
On the Forces which regulate the Internal Constitution of
Bodies. By O. F. Mossorvt.
From a Memoir addressed to M. Plana, published separately, and communicated
by M. Farapay, Esq., D.C.L., F.R.S., &c.
PRELIMINARY REMARKS.
1, Tue study of the phenomena of nature has led philosophers to
consider bodies as being composed of molecules held in a state of fixed
equilibrium ata certain distance from each other. Such a state re-
quires that they should be endued with a certain action. Some pe-
culiarities of this action we are already able to assign, but its.complete
characteristics are not yet well defined.
As the resistance opposed by bodies to compression increases indefi-
nitely with the reduction of their volume, though their molecules have
not come into contact with each other, it shows that the force which they
exercise is repulsive at the least distances. At a distance greater than
these, but still imperceptible, it must vary with great rapidity, and be-
come attractive, in order that a steady equilibrium of the molecules
may be possible; and finally, when it has become perceptible, it must
decrease in the inverse ratio of the square of the distance, in order to
represent the universal attraction. The limits of the distance at which
the negative action becomes positive vary according to the temperature
and nature of the molecules, and determine whether the body which
they form be solid, liquid, or aériform.
There is a class of phenomena, rather singular at first sight, in
which however it appears that nature designed, by separating the
forces which she employs, to present herself in all her simplicity.
Such are the phenomena which constitute what we denominate
statical electricity. It is well known with what admirable facility
Franklin explained these phenomena, by supposing that the mole-
cules of bodies are surrounded by a quantity of fluid or ether, the
atoms of which, while they repel each other, are attracted by the
molecules. It is known also how Coulomb subsequently proved that
the force with which the repulsion of atoms and the attraction of
the molecules are produced, is, like universal attraction, regulated by
the law of the inverse ratio of the square of the distance. Indeed, the
latter philosopher has substituted for the hypothesis of Franklin, which
is that generally followed in England, Germany, and Italy, another
hypothesis, in which a second fluid is supposed to perform the part as-
signed to matter in that of Franklin; and this mode of explaining the
MOSSOTTI ON THE CONSTITUTION OF BODIES. 449
phenomena has been more generally adopted in France. It is even
asserted that the latter hypothesis is the only one that should be re-
ceived, inasmuch as it has been completely confirmed by the results
of the beautiful analysis with which M. Poisson has begun to enrich
the Memoirs of the Academy of Sciences. But they who put forward
this assertion have not paid due attention to the fact that, although this
illustrious geometer has, for the purpose of establishing his calculations,
adopted the language of his school, the inferences drawn from them are
not more applicable to the one hypothesis than to the other. He sets
out in fact with the principle, that, “ If several bodies, being electric
conductors, are placed in presence of each other, and attain a perma-
nent state, the result of the actions of the electric layers which cover
them, on a point taken anywhere in the interior of a body must, in that
state, be null; otherwise the combined electricity which exists in the
point under consideration would be decomposed ; but this is contrary
to the supposed state of permanence.” Now if for this principle the
following be substituted : “ If several bodies, being electric conductors,
are placed in presence of each other, and thus attain a permanent state,
the result of the actions of the layers of electric fluid which cover them,
and of the exterior layers of matter which are not yet neutralized, on
the electric fluid at a point taken anywhere in the interior of a body,
must, in that state, be null; otherwise the electric fluid which exists in
that point would be displaced, which is contrary to the supposed state
of permanence;’—and if we interpret accordingly the literal denomina-
tions employed by M. Poisson in his equations,—all his results will be
equally true on Franklin’s hypothesis. In general, the action of the
condensed electric fluid will stand for that of the vitreous fluid; and the
action exhibited by the matter, in proportion as it is deprived of a
quantity of its electric fluid, will:stand for that of the resinous fluid.
There is one circumstance, however, which makes a difference between
the hypothesis of Dufay or Coulomb and that of Franklin: it is this,
that, according to the one, the two fluids are moveable in the bodies,
while according to the other the electric fluid is, but the matter is not,
moveable. As the equilibrium, however, requires that we should only
regard the relative position, the mobility of the electric fluid alone is
sufficient for its establishment.
_ ZEpinus, who has reduced Franklin’s hypothesis to the form of a ma-
thematical theory, was the first to remark, that if it be the requisite
condition for the equilibrium of the electric fluids of two bodies, in
their natural state, that “the attraction of the matter and the repulsive
action of the fluid of the first body on the fluid of the second should be
equal, and vice versa,” there are but three forces in operation ; two of
which are attractive, and but one repulsive. In other words, each of
the two bodies attracts the fluid of the other, while the mutual repule
450 MOSSOTTI ON THE FORCES WHICH REGULATE
sion of the two fluids constitutes only a single force, equal to each of the
two attractive forces. If then, with the equilibrium of the fluids, it is
desired to find the equilibrium of the masses also, an equal repulsion
must be allowed between the molecules ; since the bodies would other-
wise forcibly attract each other. But such an attraction is contrary to
what we learn from experience. He felt at first a strong objection to
the admission of such a repulsive force between the material molecules,
as being opposed to the idea entertained of their mutual attraction,
which was so clearly demonstrated on Newton’s principles. But a
little reflection satisfied him that this admission contained nothing that
was opposed to facts, or, as he might rather have said, that was not con-
firmed by facts. Universal attraction itself may follow as a conse-
quence from the principles which regulate the electric forces: for if
we suppose that, the masses being equal, the repulsion of the molecules
of matter is a little less than their attraction of the atoms of the zther,
or than the mutual repulsion of the atoms themselves, this will be suffi-
cient to leave an excess of attraction which, being directly as the pro-
duct of the masses and inversely as the square of the distance, would
exactly represent the universal attraction.
2. While reflecting on these principles, in a course of lectures on
natural philosophy which I gave at the University of Buenos Ayres, I
conceived the idea, that if the molecules of matter, surrounded by their
atmospheres, attract each other when at a greater, and repel each other
when at a less distance, there must be between those two distances an
intermediate point at which a molecule would be neither attracted nor
repelled, but would remain in steady equilibrium ; and that it was very
possible this might be the distance at which it would be placed in the
the composition of bodies. I thought the idea of sufficient importance
to fix it in my memory, but did not at the time pursue its development
further.
On my return to Europe I learned, through the reading of some
memoirs, aud in the course of conversation with men of science, that
the attention of geometers was particularly directed to the molecular
forces, as being those which may lead us more directly to the know-
ledge of the intrinsic properties of bodies. I was thus led to recall my
ideas on the subject, and set about subjecting them to analysis. The
results of my first investigations I here submit to the judgement of
philosophers.
I have supposed that a number of material molecules are plunged
into a boundless zether, and that these molecules and the atoms of the
ather are subject to the actions of the forces required by the theory of
/Epinus, and then endeavoured to ascertain the conditions of equili-
librium of the ether and the molecules. Considering the ether as a
continuous mass, and the molecules as isolated bodies, I found that, if
THE INTERNAL CONSTITUTION OF BODIES. 4.51
the latter be spherical, they are surrounded by an atmosphere the den-
sity of which decreases according to a function of the distance which
contains an exponential factor. The differential equation which deter-
mines the density being linear, is satisfied by any sum of these functions
answering to any number of molecules. Whence it follows that their
atmospheres may overlay or penetrate each other without disturbing
the equilibrium of the ether. Proceeding in the next place to the con-
ditions of equilibrium of the molecules, I observed that, for a first ap-
proximation (which may be sufficient in almost all cases), the recipro-
eal action of two molecules and of their surrounding atmospheres is
independent of the presence of the others, and possesses all the charac-
teristics of molecular action. At first it is repulsive, and contains an
exponential factor which is capable of making it decrease very rapidly :
it vanishes soon after, and at this distance two molecules would be as
much indisposed to approach more nearly as they would be to recede
further from each other ; so that they would remain in a state of steady
equilibrium. Ata greater distance the molecules would attract each
other, and their attraction would increase with their distance up to a
certain point, at which it would attain a maximum: beyond this point
it would diminish, and at a sensible distance would decrease directly as
the product of their mass, and inversely as the square of their distance.
This action, possessing all the properties wita which we can pre-
sume that molecular action is endued, is the more remarkable as it has
been deduced from those forces only whose existence was already ad-
mitted by philosophers, and whose law is characterized by such extra-
ordinary simplicity. When tested in the explanation of the varied
phznomena which are proper to it, it must lead, in case of failure, to
the exclusion of those forces from amongst physical principles ; or, in
case of success, establish their reality; and thus mark in a striking man-
ner the admirable ceconomy of nature.
To apply the formule which we have found, for the purpose of re-
presenting molecular action, to the phenomena of the interior consti-
tution of bodies, requires methods of calculation which are not yet
developed, and which must become still more complicated when the
arrangement of the molecules, their form and their density, are taken into
consideration. I have thought it advisable, however, in consideration
of the use to which it might be applied by able geometers, not to post-
pone the publication of this mode of viewing molecular action. It is a
subject which appears to me entitled to the greatest attention, because
the discovery of the laws of molecular action must lead mathematicians
to establish molecular mechanism on a single principle, just as the dis-
covery of the law of universal attraction led them to erect on a single
basis the most splendid monument of human intellect, the mechanism of
the heavens.
452 MOSSOTTI ON THE FORCES WHICH REGULATE
ANALYSIS.
3. If several material molecules. which mutually repel each other,
are plunged into an elastic fluid, the atoms of which also mutually repel
each other, but are at the same time attracted by the material mole-
cules, and if these attractive and repulsive forces are all directly as the
masses, and inversely as the square of the distance, it is proposed to
determine whether the actions resulting from these forces are sufficient
to bring the molecules into equilibrium, and keep them fixed in that
state. The object of this inquiry, as may be perceived, is to complete
the deductions from the hypothesis of Franklin and pinus. It is al-
ready known that the conditions of equilibrium which it furnishes, in
reference to questions of statical electricity, are in accordance with the
phenomena: it remains to be ascertained, whether the molecular ac-
tions which result from it are also in accordance with those which de-
termine the interior constitution of bodies. An agreement of this
kind would add greatly to the probability that the hypothesis in ques-
tion is well founded, and aftord us a glimpse of the means by which we
should be enabled to consider all physical pheenomena in one and the
same point of view.
Let f be the accelerative force of repulsion existing among the atoms
of the ether at a distance taken as unity; g the density at a point a y z,
and ¢ the measure of the elastic force or pressure at the same point,
referred to the superficial unit. Let g be the accelerative force of at-
traction between the atoms of the ether and the matter of the molecules
at a distance equal to unity, and @ the density at the point £4 of a
molecule which we suppose to be possessed of a certain though very
small extension.
By putting
fq da! dy! dz!
rf; ey a ee
gaudedydt
bh (E20)? + (q—y) 2+ (t— 2) 2}
the triple integral F being extended to the whole space from 2", y’, 2’,
equal to — o, as far as a’, y’, 2’, equal to = «© (the small parts occu-
pied by the molecules being excepted), and the triple integral G being
extended to all the values of §, y, &, that answer to the points occupied
by the molecule, we shall have for the equilibrium of the ether the
equations
de OP dE aap owe dG
da=—Vig tYde +V de + Ge +P ae Fete.
THE INTERNAL CONSTITUTION OF BODIES. 4.53
de dF dG dG, dG, dG,
(1) dy —Vdy +9 dy +4 dy +4 dy cavises ati 5 + etc.
dé “gl dG, aut dG, ,
fe Vag tae ge TY ay OT Gt es
in which G,, G,,... G,, &c. denote the quantities analogous to G
which correspond with the different molecules 1,2... ¥, &c.
Let us likewise put
‘da! dy! dz!
De Peon. aoe ae
pp ey
PA] GP + 0-6-0 F
where y denotes the force of repulsion existing among the molecules of
matter at the distance assumed as unity.
The equations for the equilibrium of a molecule, if we take into
‘consideration the motion of its centre of gravity only, will be
Sfssca ff foigecevs-af {fin
(11) Staff fos dedydt—3f_f fo aganat
[ fiitcf {feteavesff fetes
The sum = is to be extended to all the numbers », that is to say,
to all the molecules except that one the equilibrium of which we are
considering ; the double integral is to be extended to the whole sur-
face of this molecule, and the triple integrals to its whole volume.
4, Let us begin by considering the equilibrium of the ether. The
elasticity possessed by the ether at any point of space can be only the
result of the reciprocal action of the contiguous parts: hence we are
led, by considerations analogous to those employed by Laplace in re-
ference to the repulsion of caloric, inthe 12th book of the Mécanique
Céleste, to conclude that, in a fluid considered as a continuous mass,
the elasticity is proportional to the square of the density. If then &
represents a constant coefficient, we shall have e = 4 g*, and by sub-
stituting this value in the equations (I) we shall derive the following :
dG , dG, , dG,
dF d
PF eae Hea Ts FPO pee +7, tete.
454: MOSSOTTI ON THE FORCES WHICH REGULATE
dq ak , &G €GPraG dG,
[k= 4+ — 4+ Pee. Dots = :
@ afr dy dy + dy cx dy + dy “Fete
dy df dG, d GayaG;: dG,
Ra Phe ae Ti 7 ae eee eens ae Wes + ete.,
which lead directly to the complete integral
(II) kgq=C-—-F+G4+G6,4+G,...... G, + ete.;
C being an arbitrary constant.
In order to determine, by means of this equation, the density g, we
must substitute for F,.G, G,, Gy ..... G,, &c. the integrals which
they represent. Ifthe rectangular co-ordinates are changed into polar
co-ordinates by means of the known formule
x =rsin 6 cos y=rsin §siny go F COS 8
x'=7' sin §' cos p' y' =r" sin 6 sin p' z'=r' cos !
the expression for F' takes the form (see the additions to the Con-
naissance des Temps for the year 1829, p. 356)
(IV) ree isn ay fe al “fade! Py sin ad ay"]
+ 2 ey J bake pee us _)P, sind! ds! ay'|
The coefficient P,, being given by the formula
Pp ai:3.5. + 2n—1)
CS EOS BIO
ert n(n-1) 5 1 n(n—1)(n—2)(n—3 ee
{. SGnaye NGG ete, t
in which
p = cos 6 cos 6! + sin 6 sin 6 cos(y — yp’),
and the limits of the integrals relative to 4’ and ' should be such that
the value of /’ may take in the whole space, except the small portions
occupied by the material molecules.
In order to have the expression for G, let us in like manner put
& = psin w cos ¢, 7=psinwsing, ¢ = pcos
and represent by II, the function P;, when 7’, 6’, p', are therein changed
into p, w, ¢@. Then, if we suppose the origin of the co-ordinates to be
taken in the interior of the molecule, we shall have (see Connaissance
des Temps for the year 1829, p. 357)
(V) Gaz (SS (S92 2" 2ap )ttgsinadands ]
THE INTERNAL CONSTITUTION OF BODIES. 455
EAC gapn+ 2dp )Mrsinwdwde ]
+e | on tag (f= a ; ) Masinw dwde |.
The double integral He ne is to be extended only to the points in
respect to which the radius w from the surface of the molecule is 7 r,
and the integral ‘an wig is to be extended to the points in respect to
ea
which u7 r.
By means of a beautiful theorem which M. Poisson has demonstrated
in the Memoir already quoted, and in the additions to the Connais-
sance des Temps for the year 1831, the functions given by the integrals
r a“ (77
wD
J goor+2ap ate gpa 28 p, ff: rsp.
may be represented by series of integer and rational functions of the
spherical co-ordinates. Let 2 Hn, 2 H'n, © H"n, be these series ; if
the functions H'n, H"', shall be found, so that they may be discon-
tinued, and such that they are reduced to zero, the first for all the
values of x 7 1, and the second for the values of « Z 7, we shall be able
by means of the known theorems to reduce the expression for G to the
form
QD Ag 1 1 : :
ta pear cy tT )-
Such are the expressions for # and G which should be introduced
into the equation (III). We might directly employ those which give
the values of G, because they are always determinable when the po-
sition, figure, and density of the molecules are known; but the same
thing cannot be done with the expression for F. This integral includes
the quantity g, which is still unknown; and we should not be able to
determine it by the condition that it would render the equation (III)
identical without previously performing the integrations, an operation
which would require the same function to be known. In order to
avoid this difficulty, we are about to employ for the purpose of deter-
mining ¢ a differential equation corresponding with that marked (III),
but in which the density g is no longer included under the signs of
integration.
' The sum of these equations (1)', when they are differentiated in re-
ference to x, y, z, respectively, gives
! “9 flops
(VI.) n( 140044 ahinfh.
456 MOSSOTTI ON THE FORCES WHICH REGULATE
and it being observed that
CE @F , @F 2G &G4 , &G
dat Taye + age — — #8 So dt dys ta =
with respect to which see the third volume of the Bulletin de la Société
Philomatique, p. 388.
If in this equation we change the differentials taken relatively to the
rectangular co-ordinates into differentials taken relatively to the polar
co-ordinates, we have
valerie 6 “I
(1)k< @r¢g 1 drq
“dr2 gl r2sin?@ dW? ge i
Let us suppose that 7 q is developed in aseries of integer and rational
functions of the spherical co-ordinates, so that we may have
(2) 7I=QV FAA ++ eee + Q; +ete. ;
in which any one of the quantities Qi renders identical the equation
q(sin6 nie ilbue
(3) (ot) Dh Oy serene
On this supposition the equation (1) will be satisfied by taking in
general
(4) {EG _1GFD9,| ang
In order to integrate this differential equation of the second order *
let us take
O. ; 6,
peawet vee ree i
a= r i adr,
and consequently
1 (1) (1)
dQ: Qi, :1dQ;_ 1 :€2Q;
dr 7? y dr a dr?
1) (1) (1) (1)
€Q;- 5 Qi 2 dQ 1 dQ; 1 dQ;
dr? r? dr r dr? a dr*
* The integration of this equation with the second member negative has also
exercised the ingenuity of the two illustrious geometers Plana and Paoli. See
the Memoirs of the Academy of Turin, vol. xxvi., and those of the Italian
Society, vol. xx.
THE INTERNAL CONSTITUTION OF BODIES. 4.57
By making the substitutions in the equation (4) we shall be able to
exhibit the result in the following form:
k 1 faaMG-lig @) eg aQ; G@—-1)i agi?
dr® re es ile ee r? dr
saan nf gi? _4xf 4ai™
7° 2 dr
The foregoing equation is satisfied by taking
2( 2 @i ie (1) (1)
Ss )=40f Q:
This equation is of the same form with that proposed (4), except
only that 7 is replaced byi —1. If therefore again, in the latter, we put
Q) 4 (2) ni Si (2)
Pe
aE g i= eh
we shall deduce from it another in terms of Q., in which z — 1 will be
replaced by 7 — 2; and by continuing these substitutions we shall finally
obtain the equation
which is integrable by the known methods, and gives
4
; \/ Het Peery
(é)
Q; = f, e +V;e
where 7, and V; may be considered as two arbitrary functions of § and
'W of the order i which satisfy the equation (3).
; (3)
By adopting this value Q;, and by afterwards taking
NOR OSG: d Q”
| Q; Ter Q; any dr
| ey We ed iain
Ga Dowty i: WON
| ey age wit; a de
| (i-2)
) (i—3) (i—2) 1 2Q;
|
458 MOSSOTTI ON THE FORCES WHICH REGULATE
(1) 1Q,,
1 1 i
Oe iy ae oe nay eee
the last of these quantities will satisfy the equation (4), and will be its
complete integral.
If the successive substitutions are performed, and, for brevity’ s sake,
we make
: ey (i—1)
() (1) ae =[- Fe Gt Fea) te ve aL | eee A,
sc sae A A hg :
(0)
which gives, in the particular case of s = 7, a; = [1 +: —— ], we
shall have
(0) 1) 2) 3) (2) (7) os ei
i be: (i) a, dQ; a, dQ, () gi;
i= fag j ate 7 ee + a; 75 ‘
Now if we make
(0) (1) (2) (3)
; a; a; a a; i ar’
2; (7') = Get Si % + Fis Me ato haee + a Cis
(0) (1) (2) ()
j ; Ac a; a; a; ‘ a; i matte’,
Q!; (7) = hig =k re i ob ah Mohsen + 0 & (im eat
where @ is put instead of _ 2 we shall have
Q',= T';0,(r') + V',O! (r'),
and the expression for # may take the form
Oo r
(5) y Lee} Wi aot 3” O, (7") peer Pad
° r o oOo
» 0 9,(7) Tide!
+f pt Np sind b'day’
e r oO
nr
7!
* The brackets are here employed in the same way as in Vandermonde’s no-
tation.
‘THE INTERNAL CONSTITUTION OF BODIES. 459
co
} Desh Ne raw On re Os aM)
oO 38), ~) QO Vt dr
OD .Ae Ec a
+ Ne + 4 P sin #'dé'dw’.
pv
r-so Ui
The functions 7", V', of this expression remain arbitrary; and, as
the sum of an infinite number of these funciions may be employed to
represent any iuvction whaisoever, they wi'l serve as two arbitrary
functions which are to com»leie the iotegral of the equation (1).
When in some particular cases the integrations of the preceding for-
mula sual! have been performed by substivvting its expression in the
equation (‘I}), the funciions 7’, and V, will be determined by com-
paring them w:ih those of the same order introdaced by means of the
different expressions for G; so that this equation may become identi-
cal. All being thus determined, the densi.y g given by the formula (2)
will be known.
We have hitherto left our formule in all their generality, so that one
may be ihe better able to judge of the restrictions to which we shall
subject them while making the first applications of them. Jn the pre-
sent state of our physical knowledge, the figure of the material mole-
cules is totally unknown. We will therefore begin by considering the
most sim ole case,—that i in which their form is spherical, and their den-
sity uniform. We will, besides, assign to these molecules a very small
volume, and suppose them in their state of equilibrium at a mutual di-
‘stance, which is very considerab!e as compared with their dimensions.
‘This manner of consideriog the constitution of bodies has been adopted
_ by several philosophers as that which is most conformable to truth, and
4 ‘presents ai the same time a considerable advantage in an analytical
point of view. Tn adopting i: we shall be able. by approximation, to
eonsider the ether as if it were continuoasly diMfused in all directions ;
and to disregard, in the integration of the formula (5), the small spaces
occupied by the material molecules. But as, by proceeding in this man-
ner, we should include in the repulsion of the ether a sveplus which is
‘due to the actions answering to the points of space which are really
| oeenpied by the molecules, we shall compensate for this surplus by add-
‘ing to the action of each molecule an action equal and contrary to that
of a quantity of ether of the same volume as the molecule, and of the
same density as that which answers to the point of space which the
molecule occupies. This is done by substituting ga + fq for ga in
the expression for G (q representing the density which the ether would
| have at the point occupied by the molecule, and within so small a space
we will suppose that density constant), and by extending the integrals
Vor. I.—Panrt III. 21
460 MOSSOTTI ON THE FORCES WHICH REGULATE
of the formula (5) from 6"'= o to ' = , from f' = 0 top! = 2m, and
from r=otor=o.
Let us begin with performing the integrations of the ‘iene (V).
In consequence of the quantity ga + fq being considered as constant,
and as the spherical form of the molecules renders p independent of w
and ¢, all the terms of the second and third line of this formula will
vanish, and it being observed that we always have
2
fe uf oil sinwdwd@= 0,
n
ify. oO
unless in the case of [1° = 1, which gives
r 2¢
fiat Tl, snwdwdg=4n;
o o
an (gu +fq)®
3
the expression for G will become G = -
, 0 repre-
senting the semidiameter of the molecule.
This integral has been obtained under the supposition that the origin
of the coordinates is in the centre of the molecule; but the origin may
be transferred to any point whatever, by restoring, instead of 7, its
general expression, and writing
Aam(ga + fq)®
3{(w — x) + (yy) + (2a) }*
where x, y, z represent the coordinates of the centre of the molecule.
Before we proceed to the expression for F’, we had better clearly define
the signification of the term ¢ which it contains. We must consider this
quantity (q) such as it is given by the equation (III), not as the entire
value of the density of the ether, but as the value only of its excess or
deficiency above or below the sensibly uniform density which the zther
diffused in equilibrium is supposed to have in that part of space. If we
represent the latter density by go, the equations (III) and (VI), while
we suppress the terms due to the quantities G, G,, G., &c., must be
satisfied by the substitution of g = go: and that, in order that the
ether may remain in equilibrium spontaneously, or in consequence of
the action of the forces not expressed, whose centres must be supposed
to be at a very great distance. If, therefore, we take the difference be-
tween the equations resulting from this substitution and the original
equations themselves, we shall have
(VW) e=
(UY &(q—q)=—F+G+G,+G,...... + G,+ &e.
d*(q—q) , 42(¢—) , 4°(¥— %)
ae eg eee a a
provided that, in F’, we substitute for g the value of g — g resulting |
THE INTERNAL CONSTITUTION OF BODIES. 461
from this last equation, that is to say, that which is given by the for-
mula
(2)! 7 (Y — Go) = Qo + Q, + Q,..~--- + Q;+ &e.
This being premised let us return to the formula (5). As the inte-
grations indicated in the second member of this equation may, accord-
ing to what we have stated at the commencement of this paragraph, be
extended from 7/= 0 to r! = », #’ =oto #!=7, and'= oto = 27,
and as all these limits are independent of each other, observing that
we have in general
r 29
ae P,T',sin ' d0' dy! =o
o
x Qe
ef: Po Pisin t ddioxie
oO
and in particular when 2 = 7;
J “fy! tt ! ! U 4
gf f° P,, T',, sin 9 dé dy Sa in
° 0
rT Q°¢ s A
ihe a P, Vi, sini dtdy =z~ V,.
0 °
we shall find
-
i eet ia A dsl 2 Q,, (7') yl 21 gy!
oO
Dor !
JE Vf a, wire
Are 7” f
Without actually making the substitutions of the expressions pre-
viously given for G, and latterly for F’, in the equation (III)! for the
purpose of comparing the functions of the spherical coordinates of the
same degree which are to render it identical, we see that, as G, G,, G,,
&c., contain none of these functions, all the Ye and ie must be null,
with the exception of 7, and V,, which answer to the value x = 0, and
represent two arbitrary constants.
912
“a “
A462 MOSSOTTI ON THE FORCES WHICH REGULATE
The expression for F’ will then be reduced to
r ar’ —ar’
(5)! Fasnfh fi (Toe. + Voe )aidr'
roa) ar’ —ay’
= anf fe (The +Vee dr!
Tr
All the quantities 7, and V,, being null, except 7’, and V,,, the values
of Q, will also be null, ‘ieee that of Q,: the formula (2)' will then
Toe + Vee.
r
When r = © we must have g = q,; we must then also have 7’, = 0,
give as Jo
oO — OF
and there will remain only g = 7, + >—e
By performing the integrations of the formula (5)! within the limits
indicated, and observing that T, = 0, we shall obtain
F=—hle (e—* =1)3
As, in the differential expression for /, we may change 2’ into a! — x,
and a into a — x, without any change taking place in its value, and as
a similar change may be made in respect to tbe other coordinates, it
follows that, by taking the point x, y, z, as the origin of the coordinates,
we shall be able, in the two preceding formule, to put
Va = + yy) +e
or, Sohne r= Ne —x,)?+(y—y,) + (-z,)
Now if, by placing the origin of the coordinates in the centre of each
molecule respectively, we substitute these expressions of # and g, and
that previously found for G in the equation (IID), and take successively
for V, as many constants as there are molecules, we shall find that the
equation
—ar ail i
Me —_ Me 223 9 _ te Gat FQ
A aa ie | Se on aan
will be satisfied oe taking for each molecule
(»)
Vo =i (92, + f-4,) 3,
(v)
By substituting for V, the value just found, we shall finally have
—er
"oar
vy
avy °° F=-** 39,44) 3°"
THE INTERNAL CONSTITUTION OF BODIES. 463
— ar
4 e
(1)" G= +5539 2, +f4,) 92
where the sums & are to be extended to all the molecules, including the
first.
_ This last equation determines what the density of the ether must be
at each point x y z, in order that it may be in equilibrium when it is
submitied to the action of the spherical molecules of matter. The value
of this density consists of different terms, each of which is due to a par-
ticular molecule, and represents its proper atmosphere. As the quan-
tity of ether diffused through the immensity of space may be considered
as infinite, the atmosphere formed by each molecule for itself is always
the same, and its density is only superadded to that which the ether in
the same places owes to other causes. According to the nature of the
molecular actions, the value of the coefficient a = \/ - ws should
be considered as very great: hence it follows that the density of each
atmosphere will be incomparably greater when quite near or in con-
tact with the molecule, and will decrease very rapidly as its distance
from the molecule increases. This circumstance enables us to deter-
mine with ease, by approximation, the value of q,> or the density of the
ether at the surface of any molecule whatsoever, on the supposition
that the molecules are not too near each other. If, for instance, we
make 7 = @ in the term answering to the first molecule, and 7, = r,,
7, =T,---7, =r, in the other terms, all these will be very small
in comparison with the first, and by neglecting them we shall have
very nearly
4 3
G=H+ 3, 9a+fq)®
whence we derive
. Jo + “tye é°
im ete +i fe
6. We are now in a condition to consider the equilibrium of\any
molecule whatever, such as it is given by the equations (II).
The quantity e under the double integral in these equations must be
replaced by kg. Let us represent the coordinates x, y, z, so far as
they belong to the points in contact with the surface of the molecule,
byx+éy+n.2+2; x,y,z being the coordinates of its centre:
by developing the expression for g, and stopping, because of the small-
ness of the molecule, at the first terms, we shall be able to take
s |
I +2qo4: +2qghn +2q <1.
464 MOSSOTTI ON THE FORCES WHICH REGULATE
If this expression for g? be put in the integral 4 ify dyn dé, and
the limits extended to the whole surface of the molecule, it is easy to
see that it is reduced to kq ef fianas But [fan de ex-
presses the volume v of the molecule, which is equal to z 63; the
term on the right in the first of the equations (II) will therefore be
simply represented by kv q pa It is proper to remark, that in the
x
d . b Laan :
value of q at, we are not to include the term which, in the expression
for g marked (III)" is due to the molecule whose equilibrium we are
considering, because this term undergoes a change of sign at the two
opposite sides of the surface of the molecule, and vanishes within the
limits between which the integral is extended.
The inspection of the triple integral which gives the value @ is suffi-
cient to show that this integral must be given by the same function
that represents F’, in which f, a, y, z may be replaced by g, &n, 2. If,
because of the smallness of the dimensions of the molecule, we consi-
der in the differential OP the coordinates £, n, ¢, which answer to any
point of the surface as being constant, and substitute for them x, y, z
which answer to the centre, then, it being observed that (°/ ae didn
d& represents the volume v of the molecule, the first integral of the
second member of the first of the equations (II) may be represented
by av Litton
dx
The value of & being deduced from the expression for #, such as it
is given by the equation (IV)', will contain, as we have already ob-
served,a surplus of action, due to the zther which is supposed to oceupy
the place of the molecules also. It will therefore be necessary to make
a compensation here also, by adding to the contrary action of the
molecules an equal quantity ; that is to say, by changing in the triple
integral represented by I,, the mass y @y into the mass y @+g9 qu»
If we conceive this change made, the expression for Ty will be of the
same form as that for G marked (V)!, except that 2, y,z and ga + fq
will be replaced by & 7, ¢, and ya, + gq», and x, y,z by X», y», zy Let
us then, by approximation, introduce into the differential n° instead
of the coordinates (& , 2) of the surface, the coordinates (x, y, z) of
the centre considered as constant; if we perform the integration, which
=
aa,
Te
a.
THE INTERNAL CONSTITUTION OF BODIES. 465
is done by substituting the volume v for [/f, didndzZ, the term
which stands under the sign & in the first of the equations (II) will
be represented by a v o :
If we now write in their places all the expressions just found for
the integrals which constitute the first of the equations (II), we shall
have
By similar substitutions the second and the third equation will give
respectively
oh: Metis im i ea
ade ae dT,
qb Fe ge aie O
These three equations must hold good for the particular values x, y,
Ts Yq 21 5-+- 10> ose x,y, 2, &c., which answer to the centre of the
¥ y
molecules in their state of equilibrium; and as each molecule furnishes
three similar equations, the whole collectively will be sufficient to enable
us to determine the unknown quantities.
If from the formule marked (III)", (IV)’, (V)’ we derive, by means
of the changes already indicated, the expressions for 4, gaan,
x dx’ dx’
we find
= ar
dq Tig ON) Lea: Sloe
$4 — Layton; + fay Gene =
( Soman
dt _g ee ee Cen
dx ere | St) ry? a oa
dTyv j _ fee ae
ia (ya +90) = Ty
d q, d@ dT d dq
dy dy’dy"* dv
x into y and into z.
If we introduce these expressions into the foregoing equations, re-
collecting that, according to the hypothesis of Franklin and AZpinus,
we must make f = g, and take y a little less than g, the result will be
and shall obtain —2 &e., by changing in these formule
466 . MOSSOTTI. ON THE FORCES WHICH REGULATE
— ar
Rig |
re
gv (4 +2) 3v(m + g(t anye
—(9— 7) BV Savy —* = 0
(A) gv(qta)iv (m+ qm)(1+an)e eae
—(g—y)aviav,"—I =o
>!
— ar
IV(4 + a) Zw(a +q) (1 tan)e
— g=y) av Sav, 2?
= 0,
where the sums = are to be extended to all the members », that is to
say, to all the molecules except that whose equilibrium we are con-
sidering.
7. The equations which we have just found are those which must
take place in case of equilibrium, or in the natural state of a body com-
posed of spherical molecules, if Franklin’s hypothesis respecting statical
electricity may be applied to the constitution of bodies also. The form
in which the equations present themselves shows that this equiliorium
takes place exactly as if there existed between each pair of molecules
a reciprocal action, in the direction of the straight liae wuich would:
join their centres of gravity, and would be represented by
rien yr
(l+ar)e” 1
1) rer vices aa ani v= Y)VEV, By
1 1
(2) gv(a@+q)v.(7, +4
Let us examine the nature of this action. We are able to distinguish
in its expression the products g v (@ + q). v,(@, + qi); (g—y) @y-
@, V,, the constant 2 and the variable r,.
As the difference (g — y) between these two accelerative forces is
to be supposed very small relatively to g, the product of this foree by
the masses v (a7 + q) v, (7, + q,) will, for a twofold reason, be
greater than the product of the difference g — y by the masses aw v. a,
Vy
The value a depends on that of fand , that is to say on the repul-
sive force of the atoms of the ether, their mutual distances, their
masses, and their volumes, which are all vaknown to us. The agree-
ment of the results of calculation with those of experiment requires
that a should be a very high number.
On the condition that @ is very great, the first term of the expression
a) will decrease rapidly with r,, because of the multiplier e fama aC One
pial i p
_ _— ———
THE INTERNAL CONSTITUTION OF BODIES. 467.
then r, has a greater value than that which renders this expression
null, the foree revresented by the last term will preponderate over that
represented by the first; and if r, be so great that this term may be
neglected as of no value, then the only remaining force will be that
given by the last term. This term being negative, the force which
corresponds with it tends to bring the molecules nearer to each other ;
and as it is in the direct ratio of the product of the masses, and the in-
verse ratio of the square of the distance, it will exactly 1epresent the
universal gravitation which takes place at finite distances.
By diminishing r, we shall obtain a value that will satisfy the equa-
tion
—a@r)
1 je 1
ones ben —(g—y)va.v\a, as
1
(b)9v(a+q)vi(7, +41) r,
At this distance two molecules would remain in equilibrium, and as
the differentiation of this equation gives the result
—ar;
acre
—gv(a+q)y (2, able
]
which is always negative, the equilibrium will be permanently fixed.
Should it be attempted, by the application of an external force, to
bring the molecules nearer to each other, the repulsive force repre-
sented by the first term of the expression (@), which would now in-
crease in a greater ratio than the attractive force represented by the
last term, would produce a resistance to such an approximation: on
the other hand, if it should be sought to remove the molecules to a
greater distance from each other, the repulsive force would decrease in
a greater ratio, and the attractive would preponderate and prevent the
_ separation. These two molecules would therefore be so placed rela-
~
tively to each other as by mutual adhesioa to form a whole, and we
should not be able to remove the one without at the same time remov-
ing the other. Thus these molecules present a picture in which the
hooked atoms of Enicurus are as it were generated by the love and
hatred of the two different matters of Empedocles.
As the attractive force is null at the distance which we have been
just now considering, and at a greater distance decreases as the square
of the distance of the molecules, there must be an intermediate point
at which it reaches its maximum. By the ordinary rules of the dif-
ferential calculus we find that the function (a) is a maximum when
(gv (@+a)vi(m ta) 1 tar + Sarre + (gy)
V@U.V,3,=0;
that is to say, that it is at the distance r, we should find, by the resolu-
468 MOSSOTTI ON THE FORCES WHICH REGULATE
tion of this equation, that the molecules attract each other most
forcibly.
Recapitulating these results, we shall say then, that the action of two
spherical molecules on each other is repulsive, from their point of con-
tact to a distance given by the equation (0). At this distance the two
molecules are in a state of fixed equilibrium, and as it were linked
together; at a greater distance their action is attractive, and the
attraction continues to increase until they are at the distance r, fur-
nished by the equation (¢), which distance is still very inconsiderable
because of the magnitude of a in the exponential term e_ “From
this point the force remains always attractive, and, when the distance
has acquired a sensible value, follows the inverse ratio of the square of
the distance. All these properties of molecular action flow as neces-
sary consequences from Franklin’s hypothesis respecting statical elec-
tricity, and appear perfectly conformable to those indicated by the
phzenomena.
Let us suppose four homogeneous and equal molecules placed at the
points of a regular tetrahedron. If we assume as the origin of the co-
ordinates the ‘place occupied by the molecule whose equilibrium it is
proposed to consider, and as the plane of the x y, a plane parallel to
that in which the three others are found, the coordinates of these
molecules will be given by the formula
= "0 2 Z=0
r My Lagke i 2
x, = —— cos B y, =—— sin Bp nary [2
V3 V3 3
e fle eg alt ay pet penal oa
Xo — V3 cos 3 Yo — V3 ( 3: Zo—Tr, 3
r 4 ay stage 41
X= cos (+ 4") Ww Ty sin (a+ a, :
where r denotes the mutual distance of the molecules, which is the same
for all; ( the angle which is formed in the plane of 2 y with the axis
of the 2, by the projection of the straight line drawn from the molecule
placed at the origin of the coordinates to the first of the three others;
and # the semicircumference.
If these values be substituted in the three equations (A), and it is
observed that we always have, whatever may be the value of 6,
cos 8 + cos (8 + *) + cos (0 + 2 =o, sinB + sin(6+2
+ sin (6+— = 0,
it will be seen that the two first are verified by themselves, and that —
THE INTERNAL CONSTITUTION OF BODIES. 469
the third gives, for the determination of r,
—ar
gv? (@ + q)? id a) 2
If the density of the «ther into which the molecules are plunged, or
the quantity g., becomes greater, the density q given by the equation
(6) will increase also; that value of r which will satisfy the foregoing
equation will consequently become greater, and the molecules will fix
themselves in. equilibrium at a greater distance. We see in this result
that the zther performs the functions of caloric, and that it is to its
greater or less density we are to ascribe the temperature and volume
of the body. For what else, in fact, is an increase or diminution of
temperature in respect to a body, than a new state in which its mole-
cules, placed in equilibrium, form, in consequence of their being more
or less widely separated, a greater or less volume. It has been known
to philosophers since the time of Galileo, who was the first that clearly
pointed out this difference, that we are not to confound the sensation
which we experience while this new arrangement of the molecules of
our body is taking place, with the motion by which it is produced.
Pie |
a ga y) ee pO
NOTE.
__ [The readers of this Memoir will doubtless be interested in referring
to Dr. Roget’s “Treatise on Electricity” in the Library of Useful Know-
~ ledge, published March 15th, 1828; the following passage from which
\
5
was noticed with reference to M. Mossotti’s views, by Prof. Faraday in
his lecture at the Royal Institution, Jan. 20th of the present year.—
Epit. ]
“(239.) It is a great though a common error to imagine, that the
condition assumed by /Epinus, namely that the particles of matter when
devoid of electricity repel one another, is in opposition to the law of
universal gravitation established by the researches of Newton; for this
law applies, in every instance to which inquiry has extended, to matter
in its ordinary state; that is, combined with a certain proportion of
electric fluid. By supposing, indeed, that the mutual repulsive action
between the particles of matter is, by a very small quantity, less than
that between the particles of the electric fluid, a small balance would
be left in favour of the attraction of neutral bodies for one another,
which might constitute the very force which operates under the name
of gravitation; and thus both classes of phenomena may be included
in the same law,”
: 470 —
ARTICLE XXIV.
On certain Combinations of a New Acid, formed of Azote,
Sulphur, and Oxygen ; by J. Pevouze.
From the Annales de Chimie et de Physique, vol. xvi. p. 151.*
Davy made the important observation that nitrous gas (deut-:
oxide of azote) was susceptible oi absorption by a mixture of potash
or soda and an alkaline sulphite, and that from this action a peculiar
matter resulied, whose principal characteristic was to disengage abun-
dantly protoxice of azote when brought into contact with acids. His
experiments are recorded in vol. xx. of the Revue Britannique (‘or
1802): an extract is also given in the Traité de Chimie of Berzelius,
vol. ii. p. 50.
Davy. believing the presence of the potash and soda, in a free state,
necessary to the absorption of the deutoxide of azote by the sulphites,
and remarking moreover that the acids no longer disengaged nitrous
gas, but protoxide of azote, from these new combinations, considered
them as formed of this latter gas and an alkali, and proposed to give
them the name of nitroxides of potash and soda. He attempted unsuc-
cessfully to obtain analogous compounds with ammonia, baryta, strontia,
and lime.
To explain the disappearance of the deutoxide of azote, Davy sup-
posed that the potash and soda, although incapable of absorbing this
gas when wholly formed, might yet take it up during its formation, and
combine with it by the action of the affinities which decompose the ni-
trous gas and convert it into protoxide of azote.
The celebrated English chemist extended his observations no further.
The salts which he had obtained not having been disengaged from the
extrinsic matter with which they were combined, he was unable either
to submit them to analysis, or to examine their principal characteristics ;
and thus he left their description very incomplete.
Upon passing an aqueous solution of sulphite of ammonia, cooled to
the point at which it begins to congeal, into a small tube filled with
deutoxide of azote, which has been exposed for several minvies to a tem-
perature of —15° to —20°(Reaum.), the volume of the gas gradually di-
minishes; and upon withdrawing the tube by degrees from the cooling
mixture, and agitating it until the congealed matter is liquified, repeating
* The Editor is indebted for the translation to Mr. J. E. Taylor.
-PELOUZE ON CERTAIN COMBINATIONS OF A NEW ACID. 47]
this operation several times, the deutoxide of azote is completely ab-
sorbed by the sulphite ; and these two bodies, upon disappearing, give
birth to 2 very remarkable new salt. to which I shall revert presently.
If, instead of causing the deutoxide of azote to act upon the sulphite
at — 15°, we bring them in contact at zero, or rather at the ordinary
temperature, the result is very different : the devtoxide of azote is com-
pletely destroyed, it is true, but it is replaced by hal’ its volume of prot-
_oxide of azote, and instead of a new salt we obtain the neutral sulphate
of ammonia.
Iam not aware that chemistry presents a single similar instance,
namely, an example of actions so diferent at temperatures so nearly
-equal, above all within the lower limits of the thermometrical scale,
It is probable that facts of this nature will eventually muliinly, and
that by the aid oi freezing mixtures we shall succeed in obtaining com-
binations which, though little stable, may nevertheless offer a com po-
_ sition and definite properties.
Yo return to the experiment above described: If, when all the
deuioxide of azote has been absorbed by the sulphite we leave the so-
lution to itself, at the ordinary temperature, the new salt is gradually
desiroved. pure protoxide of azote is disengaged, and the liquid retains
only sulphate of ammonia. The volume of the new gas collected is
found to be precisely equal to half the volume of deutoxide of azote
employed.
The instability of the new substance scarcely allowed me to examine
it completely: at zero, it is converted into protoxide of azote and into
sulphate of ammonia: at the ordinary temperature, its decomposition is
rapid; at 40° and above, its action is violent, and appears like a brisk
effervescence ; farther than this, it is not easy, especially in summer, to
operate on the gases in refrigerating mixtures. It was necessary then
to conirive another mode of preparation, and the following was the rea-
_ soning which led me to discover it. ‘ The salt cannot be what Davy
has said, namely a combination of protoxide of azote and an alkali; for,
since it is possible to obtain it with a neutral sulphite, the su!phurous
acid eliminated from its base by the deuioxide of azote, and converted
into sulphuric acid by the absorption of half the oxygen of the latter
gas, would infallibly decompose it, and a disengagement of protoxide of
azote would be the result; but, on the other hand, Davy obtained these
combinations, although impure, at the ordinary temperature ; he ob-
tained them with sulphites mixed with free alkalies; the alkalies must
therefore increase the stability of the salts in question, and it is proba-
ble that by modifying more or less the process of Davy I shall obtain
‘them pure.”
This is in fact what takes place. The presence of a free alkali re-
tards in a remarkable manner the decomposition of the precipitated
472 PELOUZE ON CERTAIN COMBINATIONS OF A NEW ACID,
combinations, and furnishes at the same time a means of preparing them
with facility. After several attempts, which it is useless to recount
here, I arrived at the following process, in which I have best suc-
ceeded.
A concentrated solution is made of sulphite of ammonia, which is
mixed with five or six times its volume of liquid ammonia; and into
this is passed, during several hours, deutoxide of azote: the experiment
may be conveniently made in Woolff’s apparatus. The gas which is not
absorbed by the liquid contained in the first flask, is taken up by that in
the second or third. A number of beautiful crystals are seen gradually
to deposit themselves, in the same manner as those obtained at a low
temperature with the neutral sulphite of ammonia; these are to be
washed with ammonia previously cooled, which, beside the advan-
tage of retarding their decomposition, offers that of dissolving less of
them than pure water. When the crystals are desiccated, they should
be introduced into a well-closed bottle ; in this state they undergo no
alteration. The same process is applicable to the corresponding salts
of potash and soda.
Before passing to the examination of this new class of bodies, I shall
detail an experiment which throws the clearest light upon their com-
position. Ifa strong solution of caustic potash be passed into a gra-
duated tube, containing a mixture of two volumes of deutoxide of
azote and one volume of sulphurous acid, all the gas after some hours
disappears. If the deutoxide of azote be in a proportion greater than
2:1 to the sulphurous acid, the excess remains free and unabsorbed
above the liquor; and if, again, we employ less nitrous gas than the
quantity indicated, the new salt will be found always mixed with sul-
phite of potash : in a word, the two gases, deutoxide of azote and sul-
phurous acid, never react except in the proportion in volumes of 2 : 1.
It is easy to convince ourselves that the sulphite disappears, and that
the salt which replaces it is formed by a new acid. In fact, the red
sulphate of manganese, introduced into the tube in which the action
takes place, is not discoloured ; whilst the sulphuric solution of indigo
shows plainly, by the permanence of colour, the absence of nitrates and
nitrites; and if, after pouring a salt of baryta into the liquor, we
gather the precipitate which is there formed, wash it several times with
a diluted solution of potash, and treat it afterwards with nitric acid, it
dissolves entirely, and we may thus be assured that there has been no
production of sulphate.
These experiments, added to the complete absorption of the deut-
oxide of azote by a neutral sulphite, at a temperature of —15°, left no
doubt in my mind as to the composition of these new salts. Two
volumes of sulphurous acid, in acting upon four volumes of deutoxide of
azote and one atom of alkali (potash, soda, or ammonia), should pro-
FORMED OF AZOTE, SULPHUR, AND OXYGEN. ATS
duce one atom of a peculiar acid, composed of two atoms of azote, one
atom of sulphur, and four atoms of oxygen. This assumption has been
verified by the direct analysis of the salts. I call this acid nitrosul-
phuric, and the salts which it forms nitrosulphates.
Nitrosulphate of Ammonia.
The nitrosulphate of ammonia is a white salt, of a sharp and
slightly bitter taste, with nothing of that of the sulphites; it does not
act upon either litmus or turmeric paper; it crystallizes in prisms,
with bases of oblique-angular parallelograms, more or less flattened,
and terminated in different manners. It is insoluble in alcohol, either
warm or cold ; it is easily dissolved in water, in which it finally de-
composes, with a rapidity proportioned to the elevation of the tem-
_ perature: the water retains sulphate of ammonia, whilst it disengages
a gas which has the properties of the protoxide of azote. Alcohol pre-
cipitates this salt from its aqueous solution. Exposed to a tempera-
ture of 110°, it resists, but at a few degrees above that point it decom-
_ poses with an explosion, caused by the rapid disengagement of prot-
4 oxide of azote. If thrown upon red-hot coals, it burns with scintilla-
tion.
_.. All the acids disengage from it protoxide of azote, and cause it to
_ pass into the state of sulphate of ammonia; this decomposition is slow
_ with carbonic acid gas, but it proceeds with rapidity when it is dis-
_ solyed in water. In the open air the nitrosulphate of ammonia decom-
| poses gradually, disengages protoxide of azote, effloresces, and yields
_aresidue of pure sulphate of ammonia.
I have above stated that the alkalies increase the stability of the ni-
_ trosulphates ; this however takes place with the nitrosulphate of am-
_ monia only to a certain degree. The salt, mixed with concentrated
“st ammonia, still decomposes very visibly, though much more
_ slowly than in pure water, and yields moreover the same products.
. This decomposition agrees well with what we observe in passing a mix-
_ ture of two volumes of deutoxide of azote and one volume of sul-
phurous acid into a bell-glass containing liquid ammonia: the absorp-
tion is never in this case complete, as it is with the potash; there is
invariably a gaseous residue of protoxide of azote; and if the nitrosul-
phate of ammonia is obtained at the ordinary temperature, by the pro-
cess which I have indicated, this depends upon the much greater
rapidity of its production than of its decomposition. We see by this,
that it is possible for a body to be formed and to exist for a certain
time at the same temperature at which it is decomposed.
__ The excessive mobility of the elements of the nitrosulphate of am-
_ monia, and the stability which the alkalies give them, made me think
it not impossible that this salt might present phenomena of decompo-
4°74 PELOUZE ON CERTAIN COMBINATIONS OF A NEW ACID,
sition of the same class as the singular ones which M. Thénard
observed with oxigenated water. In fact this is the case : many bodies
which decompose the deutoxide of hydrogen, without either losing
or gaining anything, equally decompose the nitrosul hates. Amongst
these are the fine spongy platina, oxide of silver, metallic silver, pow-
dered charcoal, oxide of manganese : the two first bodies act moreover
with extreme rapidity voor the niirosulohate of ammonia.
I convinced myself that this remarkable nbenomenoa was dve, as in
the case of the oxygenated water, to an action of presence, and that
nothing is ever produced but a simyle transformation o: the nitrosul-
phate of ammonia into protoxide.of azote and sulphate or ammonia.
Oxide of silver is not reduced; for if we wash it, aiter having caused
it to decompose a great quantity of salt, it aissoives finally in nitric
acid, without ‘he disengagement of red fumes.
Ii was interesting to attempi to obtain tne metallic nitrosulphates by
-pouring a solution of nitrosu'phate o1 ammonia into salis whose bases
were oxides insoluble in water. The experiment was made with liquids
previously cooled to several degrees below zero; it geve the following
results. Chloride of mercury, the sulphates of zine and copper, the
persulphate of iron, the protonitvate of mercury, the chloruret of
chrome, the nitrate of silver, produced a brisk effervescence, which is
attributable to a disengagement of the protoxide of azote: there was
formed a‘ the same time sulphate of ammonia, which mixed with these
saline solutions withovi lessening theie transparence. With acetate
of iead there was also an efiervescence and procuction of sulphate of
lead.
It would be very difficult to discover the probable cause of these
singular phenomena; bué from this very cause, of their vresent inexplica-
bility, they appeared to me the more to merit the attention of chemists ;
and what indeed is more calculated to excite curiosiiy than to see a salt,
by simple contact wich a body which absolutely gives nothing to it
and takes nothing from it, decompose with an extreme rapidity, and
form new substances, in the midst of which the agent. which pro-
duces these violent actions remains chemically passive ?
We arealready acquainted with two bodies, oxygenated water and
hydruret of sulphur, possessing the property of decomposing under the
influence of a simple action of presence. M. Thénard, to whom we
owe the first observation, had foreseen that facts of this kind would
multiply, and that they would open to the chemist a new field for in-
:quiry which would enlarge every day.
I should not omit to mention another fact, which bringsinto still closer
connection the nitrosulphates of oxigenated water; namely, that these
salts, mixed with alkaline solutions, cease to decompose under the in-
fluence of the same bodies which destroy them so rapidly when they
-—_—_e——__
FORMED OF AZOTE, SULPHUR, AND OXYGEN, AT5
are dissolved in pure water. The nitrosulphate of ammonia contains
one atom of water; its formula is: H® Az? S Az*, O1,+ HO.
Nitrosulphate of Potash.
This salt is white, very soluble in water, insoluble in alcohol, with-
out smell, of a slightly bitter taste, without action upon the test papers ;
it crystallizes in irregular hexagonal prisms, similar to those of nitrate
of potash. Exposed to a heat of from 110° to 115°, it is not de-
composed, nor does it lose any weight; at alittle higher temperature,
nearly 130°, it is destroyed ; but instead of being converted into sul-
phate and protoxide of azote, like the nitrosulphate of ammonia, it
gives rise to a disengagement of deutoxide of azote, and to a residue of
sulphite of potash. The weakest acids disengage from it a gas, which
has been found to possess the properties and the composition of prot-
“oxide of azote.
Platina sponge, oxide of silver, the sulphates uf copper and manga-
nese, chloruret of barium, and acetate of lead, decompose it and
produce the neutral sulphate of potash and protoxide of azote: these
actions are always manifested with greater slowness than with the
nitrosulphate of ammonia. I have already said in general terms that
the stability of the nitrosulphate of potash was greater than that of the
corresponding ammoniacal compound ; it is even sufficient to enable us
to employ boiling water as a means of purifying this salt: in this treat-
ment only a small quantity is decomposed ; and by washing with very
cold water the crystals which are deposited in the solution, we easily
separate them from the sulphate of potasii with which hey. are im-
pregnated.
This salt is anhydrous, and is formed of one atom of potash and one
atom of nitrosulphuric acid. Its formula is: Ka? Az* SO*. By ana-
lysis it has been found to contain 20 parts of protoxide of azote, and 80
of sulphate of potash.
The nitrosulphate of soda is much more soluble ; in other respects
it appears to me to possess the general properties assigned to the last
salt ; and as its preparation is difficult, I have not made it the object of
particular study.
It only remains for me, in concluding this Memoir, to eonsidér two
principal points of view in which it seems to me possible to regard the
constitution of the nitrosulphates: whether they are formed by a pecu-
liar acid, composed of two atoms of azote, one atom of sulphur, and
four atoms of oxygen ; or sulphates combined with protoxide of azote,
acting in an analogous manner to the water of crystallization. The
first hypothesis seems to me preferable, and the following are the rea-
sons on which it is based :
1. The nitrosulphates are not precipitated by baryta-water ; and,
if the protoxide of azote entered into these salts in the way the water
Vor. L—Panrr III. 2K
4:76 PELOUZE ON CERTAIN COMBINATIONS OF A NEW ACID.
of crystallization does into the ordinary’ salts, it is not likely that its
presence could modify the sulphates so far as to cause them to lose
their most characteristic property, that of forming an insoluble sub-
stance with baryta.
2. The nitrosulphate of potash yields, by heat alone, a disengagement
of deutoxide of azote and a residue of sulphur. It is little probable that
the protoxide of azote could become deutoxide at a temperature of
140°, especially when it must take the oxygen which it wants from so
stable a salt as the sulphate of potash. And, moreover, experience has
proved to me that the protoxide has no action upon it at that tem-
perature and above. I would add that, if the action of heat upon the
nitrosulphate of ammonia induces the belief of the pre-existence of the
protoxide of azote in that salt, the entirely different products of the de-
composition of the nitrosulphate of potash by the same agent would
lead us, adopting the same reasoning, to consider the latter salt as
formed of sulphite of potash united with deutoxide of azote.
I am more inclined to see in the action of heat a disorganizing
power, whose effects vary with the nature of the substances upon which
it is exerted. The question seems to me to be precisely the’ same as
that of the nitrates and hyposulphites, from which it has not been pos-
sible to abstract the hyposulphurous and nitrous acids; only that, in-
stead of two elements, the nitrosulphuric acid contains three, of which
there are examples enough in chemistry.
I have endeavoured to isolate this acid, and to prepare it directly,
without the influences of the bases: in this I have not succeeded; but
in the course of my attempts I have had occasion to remark a curious
fact, which is at variance with all that has been said and written upon
the theory of the formation of sulphuric acid; namely, that the deut-
oxide of azote and sulphurous acid are able to produce sulphuric acid
without the necessary presence of the air or of oxygen. The experi-
ment is easily performed, and I have repeated it many times. Two
hundred volumes of deutoxide of azote and one hundred of sulphurous
acid, left alone for some hours at the ordinary temperature, in a gra-
duated tube containing a small quantity of boiled water, are converted
into pure sulphuric acid and a residue of protoxide of azote equal to
one hundred volumes: such is the result; as to the theory, I am in-
duced to believe that nitrosulphuric acid is at first formed, and is after-
wards decomposed in the same manner and with still greater facility
than the nitrosulphates.
Hence the theory, or rather theories, on the formation of sulphuric
acid, in the forms in which they have been propounded, must undergo
a notable modification; for a certain quantity of protoxide of azote
must necessarily be produced in the leaden chambers. I have for a
long time past been occupied with experiments relative to this subject,
and I hope shortly to publish the results.
ARTICLE XXV.
Attempt to explain the Absorption of Light according to the
Undulatory Theory ; by BARON FaBIAN VON WREDE.
From Poggendorff’s Annalen der Physik and Chemie, vol. xxxiii. No. 23. p. 353.
Nos. 24 and 25.*
Tue mathematical accuracy with which most optical phenomena are
explained according to the theory of undulations, and the simplicity of the
first principles of this theory, as well as the analogy which it presupposes
between both the means with which Nature has endowed the living being
for the purpose of enabling it to perceive and distinguish those external
objects by which it is surrounded, render this theory in itself highly pro-
bable, although we have not yet been fortunate enough to bring under
its general laws all the simple phenomena. Though we do not consider
ourselves authorized to judge of the relative value of this theory, yet
everything appears to pronounce in its favour, if we compare it with the
theory of emission; as this, with all its complex and not very probable
auxiliary means, accounts for a limited number only of optical phano-
mena, whilst it leaves without explanation many others which the theory
of undulations not only entirely explains but had even anticipated before
they were observed.
The chief objection made to the theory of undulations is that it leaves
unexplained dispersion and absorption. With respect to dispersion,
Fresnel has it is true not explained it, but he has shown at least that it
does not stand in opposition to the undulatory theory. For he has proved
that the velocity with which light is transmitted through an elastic me-
dium, can only be independent of the length of the waves when the op-
posite spheres of action of the molecules of the elastic medium are so
small that we may consider them as null in comparison with the length of
the waves. If this is not the case, the velocity of transmission for the
Shorter waves of light must be smaller than for the longer waves,
and this therefore the theory of undulations must take for granted, ac-
cording to the observations made on the dispersion of light.
Ishall now proceed to the special object of this paper, The Absorption
of Light. Brewster, who more than any other person has followed up
with attention the phenomena connected with the absorption of light,
* Translated by Mr. W. Francis.
2K2
478 BARON VON WREDE ON THE ABSORPTION OF LIGHT
and has enlarged our knowledge in this as well as in the other branches
of optics, gives (in the paper in which he describes the curious dis-
covery that certain coloured gases possess the property of absorbing a
countless multitude of species of light, while they freely transmit others
lying between these) a collection of those phenomena of absorption which
he regards as contrary to the theory of undulations. Among other re~-
marks he makes the following: “That the undulatory theory is defective
as a physical representation of the pheenomena of light, has been admitted
by the more candid of its supporters; and this defect, insofar as it relates
to the dispersive power of bodies, has been stated by Sir John Herschel
as a ‘most formidable objection.’ That there are other objections to it, as
a physical theory, I shall now proceed to show; and I shall leave it to
the candour of the reader to determine, whether they are more or less
formidable than that which has been stated*.”’ All these new objections
of Brewster against the theory of undulations are derived from the
phenomena of absorption.
Airy +, in his remarks upon this paper of Brewsttr, has certainly fully
acknowledged that the undulatory theory had hitherto given no expla-
nation of the phenomena of absorption; but he has on the other hand
compared the two rival theories in other respects, with so much know-
ledge and clearness that I think it impossible after perusal of this col-
lection of facts to hesitate for a moment which to prefer. I am however
obliged to controvert what Airy has intimated in relation to the absorp-
tion of light, if indeed my own view of this subject be correct. He says
that he did not think that absorption could be considered as an essential
part of the theory of light. “It is,” says he, “a sort of extraneous in-
terruption, which either leaves the ordinary laws in full vigour, or whol-
ly destroys, not the laws, but that which is the subject of the laws.”
Granting this, I do not see how the conclusion may be drawn from it,
that the theory of light need not include the absorption. If we pre-
suppose in bodies certain properties by means of which they act in a
disturbing manner on the phenomena of light, we must also on the
other hand presuppose in light a property through which its phenomena
would allow themselves to be disturbed by the bodies, and we must then
necessarily explain this last property by the theory of light. I have
pursued with attention the interesting phenomenon described by Brew-
ster; but far from drawing the same consequence as he has done, I think
I find in it only a complete confirmation of the theory of light.
When I saw for the first time the spectrum of a light which had tra-
yersed iodic or bromic gas, whose regularity leaves no doubt that all
the absorptions (nearly one hundred) do not praceed from one and the
same cause, I was convinced that the whole was a phenomenon of inter-
* Phil. Mag. and Annals, vol. ii. p.360. + Ibid. p. 419.
|
|
:
|
i
|
f
ACCORDING TO THE UNDULATORY THEORY. 4°79.
ference, although I could not at that time explain satisfactorily to myself
the manner in which it originated.
I will now attempt to show that as soon as we assign to matter a
very simple property which is no way in opposition to the idea we other-
wise conceive of matter, all the phenomena which we include in the
elass of phenomena of absorption become mere corollaries of the ge-
neral principle of interference.
Sir John Herschel has lately shown, in a memoir in many respects in-
teresting and instructive, On the absorption of light by coloured media
viewed in connection with the undulatory theory *, the possibility of con-
sidering the phenomena of absorption as originating in interference.
But he has thus traced each individual absorption back to a different
eause, by which he is obliged to suppose in the absorbing bodies as many
different causes as there are absorptions in the spectrum. If we could
conceive of about two thousand separately acting causes in one and the
same body, as would be the case for example in nitric acid gas, it would
still be difficult to form to ourselves a correct idea of the reason of the
great regularity which we must presuppose for the hundred causes in the
iodie or bromic gas. Moreover he is of opinion that we must relinquish
every notion of a regular functional gradation of this phenomenon,
upon observation of its quantity and apparent irregularity. He states
further, that “if the phenomena were at all reducible to analytical ex-
pression, this must be of a singular and complex nature, and must at all
events involve a great number of arbitrary constants dependent on the
relation of the medium to light, as well as trascendents of a high and
intricate order.”
J will endeavour to prove, on the contrary, that they may be all re-
duced to one, or at least to a very limited number of causes, and that
_they may be all comprehended in one very simple analytical expression,
which contains very few constants, and those dependent on the nature
_of the absorbing medium. The little knowledge we possess of the in-
ternal constitution of matter does not permit us to predict what effect it
exercises upon a traversing wave of light. If however we may imagine
it to be composed of particles which are kept by certain forces at a deter-
minate distance from one another, we may also imagine that these par-
ticles are capable of offering a resistance to the traversing wave of light,
and consequently of partially reflecting it.
The light thus reflected, which proceeds in a direction contrary to the
one it originally had, must be now in like manner reflected in the ori-
ginal direction, in order to experience again a partial reflection in the
contrary one, and so on ad infinitum. Thus arises an endless series
of systems of waves of light, each of which possesses a feebler in-
tensity than the one which had immediately preceded it, and which has
* Phil. Mag. and Annals, vol. iii. p. 401.
480 BARON VON WREDE ON THE ABSORPTION OF LIGHT
been, in comparison with this, diminished by one portion equal to the
double distance between the reflecting surfaces.
If now we confine ourselves to the consideration of the two first sy-
stems, it is clear that their results must depend on the relation between
the length of the wave of light and the amount of retardation which
has taken place in the one system in relation to the other; so that when
this amount equals 3, 3, 3, 3... of the length of the waves of light,
the intensity of the results must be equal to the difference between the
intensity of both the systems; and when it is equal to an entire mul-
tiple of the length of the wave of light, the intensity of the results
must be equal to the sum of the intensities of the systems. If we now
admit that waves of light, of all lengths, from the limit « (the long-
est) to that of 6 (the shortest), traverse a medium which causes a
delay ¢ in one part of this light, it is evident that the intensity of all
kinds of light the half length of whose wave » amounts to > ee,
a, TR
ob ih
6 etc. must be a minimum; that, on the con-
Qm—1l? 2Qm+1
trary, those kinds of light the half length of whose wave is a 2. i,
Be hays golfers etc., must attain their maximum of intensity.
7 at tg d
When these species of light are separated by means of a prism, each one
whose intensity is a minimum must appear as absorbed in relation to
the others situated between them, and the whole spectrum must be
analogous to that which a light which has traversed iodic or bromic
gas presents.
Before I enter further into the comparison between the spectra which,
according to the theory, must originate in consequence of such a simple
retardation, and those which, as experience shows, are produced by ab-
sorbing media, I will try to determine what the consequences are of the
hypothesis just laid down, namely that of an indefinite continued re-
flection. Ifa represents the original intensity of the light, and 7 the part
which is lost at every reflection, the intensities of each of the originating
systems of waves of light attain the value shown in Plate VI. fig. 9.* As
for the rest, the figure requires no other explication than that] determine
the reflecting surfaces with the lines 4d B and CD, and call 6 the di-
stance between these surfaces.
Fresnel has shown, in his excellent paper on the diffraction of light +,
that the velocity of undulation.w which a particle of zther receives
* Plate VI. will be given, with the rest of this Memoir, in Part IV.
+ Poggendorff’s Annalen der Physik und Chemie, vol. xxx. p. 100.
ACCORDING TO THE UNDULATORY THEORY. 481
through a system of waves of light after a lapse of the time ¢, whose
intensity is a and whose length of undulation is A, is expressed by the
equation
u=asin2r (*-=)
in which 2 stands for the distance of the particles from the centre of vi-
bration.
Let us use this formula to determine the velocities of undulation u,
Uy) Us) Us)...» Which the particle of zther acquires through the system
of waves of light, whose intensities are: (1 —7)*@, 7° gaQ— r)? a,
ri(1—r)?a,7° (l—r)?@ ees thus we have:
w= (1 —ra.sin 2x (¢— 5) i
=(1—r)?a.sin27 gees)
u=P (l—na.sinde (--24**)
=r(1—7)a [sin 22 (*— x) cos aid
r X
— cos2r (: — ) sin 2727]
r r
uy =r (1—r)ta.sin ax (¢— 244")
=rt(l—r)*a [ sina = («=4) 00s 2.2528
—cos 2x (¢— 5) sin 2. aa
r Xr
u, =7°(1—7)?a.sin2 x ¢ =e +6")
=ri(1—r)*a [sn on (¢ - =) cos. 2728
— cos 2x (¢ —) sin 3 eee
r oN
a F™ (1 — ry. sin 2 (¢— seen)
482 BARON VON WREDE ON THE ABSORPTION OF LIGHT.
=r" —r)2a{ sin Qa (4 x) cos n, 220
— 08 2x( ¢—<) sinn 2220].
r r
The velocity of undulation UY, which the particle of «ther acquires |
through the action of the collective systems of waves of light, must
now be:
=ut+u, + Uy + us, + Uy, + ....4
and therefore
U=a(1—r)? {sin 2x (¢- =) [2: + 7 cos 20 58
+ ros 2.9m 2° a site” cosn. an]
_ costs (¢—5) [rsinae =
A r
+ rt sind. an ey eu) sit We an 22).
If we now assume
a(1—r)? [2 + 72 cos 27 20 +r 008 9. ance
ie Trey
+ 07 cosn. an 2 |= = A. cosi
a(1—rjr[ 7 sin 2429 + rt sin 2. he a
eH ON
+... Psinn 2] = A.sini
we shall have
U=A.sin[ 2x (¢~=) =i] er
The system of waves of light thence resulting will be quite of the same
nature as the original, only that it has a different intensity and a different
position.
(To be continued.)
SCIENTIFIC MEMOIRS.
VOL. I.—PART IV.
ARTICLE XXV. continued.
Attempt to explain the Absorption of Light according to the
Undulatory Theory; by BARON FABIAN VON WREDE.
From Poggendorff’s Annalen, vol. xxxiii. Nos. 23, 24 and 25.
4
pi In order to find its intensity A, I multiply the equation (2) by
_ s/f —1 and add it to the equation (1); I then obtain
f
A (cosi + “—1.sin i)
2b ae.
=(1—r) afi +r? (cos 2 ~ + 4/—1.sin2az ~)
f +r (cos2.22 50 + y=1.sin 2.2% ~")
b
2 2b — b
| +0" (cos. 2m A> + VHA sin 29) $
| or, since
/ cosmz + v¥—1.sinmz = (cosz + V—1.sinz)”
| A (cosit + 4/— 1.sin?)
| ape 2 2
| =(1-ryaf ite (cos 22 5+ VTi sin 225”)
) 2b Aad
+ r'(cos 2250 + VT. singe 3)? 4
. r
)
2b resi lls
5 OE + rn ( cos2 x + + / Tsing 5)",
| This is a geometrical series, by the summation of which we obtain
| Vor. 1—Panr IV. 21
|
|
484 BARON VON WREDE ON THE ABSORPTION OF LIGHT
A (cosi+ 4/ — 1.sin ¢)
2 1 2b pias 2b
(hes hee (cos an ra SV Ae .sindn 5 )
3 26 uch 2b
1-1? (cos 2x i + f—].sin2a =i
If in this expression, in which 7 is naturally less than 1, we suppose 7
to be infinitely great, we shall have
A (cost + 7 —1.sini)
=(1—7r)*a AS eT oe Geers re 8 A ee
4 oe 2b
1—r8(con2e 24 4 y=. sin 2 5 )
By separating in this expression the real from the imaginary magni-
tudes we obtain
ries ieee Se
cosz (11008 2 = ~) + r2sin 2 sin2 7 ea
=(1—r)°a (4)
and
sin 7 ( —r?.cos27 ~) + r2 cos i. sin x 2° ===i( )
From the last expression we obtain
ee
i) 7? sin 27>
sin ? = eS ee
iJ 1-278 cos 27 2 + 9
and
—}
1—r? at =f
r2cos2 x x
cost =
A/ 1 = 212 0089 29 4 xt
If we substitute this value of sin i and cos? in the formula (5) we have
after reduction
(l—r)?a
0 af ee aera ed ETH (G).2> 4*
4 / 1278 cos 2x 2% + rt
* Considering the partial reflection of a surface as a total reflection of all the
light in contact with the particles of the body, it is evident that, the form of the
particles being neglected, and the reflected part being called as before r a, i. e.
(1 —r) a, that part continuing in the original direction, the whole quantity r @
cannot return in a contrary direction, but that a part of the same must be re-
flected in different directions. ‘To be convinced that such a change in the pre-
supposed hypothesis does not materially alter the results deduced from it, we
have only to suppose that the part of r @ which is reflected in a contrary direction
is called 7’ a, as it is then evident that the intensities of the system of waves of
.
,,
ws )
i
ACCORDING TO THE UNDULATORY THEORY. 485
When this expression, which represents the intensity of the resulting
Bei do stk BO 5
wave of light, is differentiated in relation to _, it is clear that A becomes
: ae Ye 26 : 5
a maximum or minimum, if sin 2 7 a =0; that is, A becomes a maxi-
26 .
mum when ee firs 0, 1, 2, 3, 4, ete., and it becomes a minimum when
ae
a arse? 29 3, 4; 3, &e.
The result of an indefinite quantity of wave-systems of light be-
comes also a maximum or minimum, under precisely the same circum-
stances as the result of only two such systems. To make apparent the
__ hypothesis which I have advanced, I have constructed in fig.1, Plate VI.,
the equation (6) in such manner that the values-of the intensity A,
which represent the different values of nm are taken as_ ordinates,
a
and the logarithms ~ as abscisse. As the difference of the loga-
rithms of two numbers depends on the relation of those numbers, and
not on their absolute magnitude, the difference between two points of
the axis of the abscissee, which represent two lengths of undulation,
standing in a given relation to one another, must be independent of the
representative substituted value of x
sequal magnitude along the whole curve.
In order to examine the phenomena of absorption which are exhi-
bited in a spectrum whose extreme lengths of undulation (red and
, and consequently must be of
_ violet) are to one another as 1°58: 1, I described a spectrum (fig. 2)
whose length, log. 1°58, and whose divisions, red, yellow, green, &c.,
take in the lengths
outermost red limit between red and yellow &e
Lo log. limit between red and yellow log. limit between yellow and green’
ee
If I now at first suppose the distance 6 between the reflecting sur-
faces to be very small, for example equal to 75 of the length of the wave
of the red light, the value po which represents that of the red light
light originating in this case become @ (1—7)*, a (1—r)? r?, a (1—r)?r'4; @
(1—r)?r'®, &c., and the final results are
Ares a(l—r)?
BOGE: PP Bate et
es
26
0 a aa y'4
which according to this differs from the one before obtained only in this parti-
cular, that the magnitude r of the denominator is changed into’. It thence fol-
lows that all the conclusions which may be drawn from one of the formule, may
also be drawn from the other.
>
5 Ap Oy
486 BARON VON WREDE ON THE ABSORPTION OF LIGHT
will equal 20. I now place fig. 2 on fig. 1, in such a manner that the
red end may lie on 20, and see that the whole part of the curve which re-
presents the spectrum lies near the maximum ; and from this I conclude
that the body which makes 2 6 = 1, of the length of the waves of red
light absorbs little light, or is ¢ranslucid, and absorbs all the colours
with an almost equal power, that is, appears colourless.
Let us now suppose 2 6 somewhat greater, for example = 4 of the
length of the wave of red light; fig.2 must then be so placed that
the red end may lie on 4; we then see that the entire spectrum lies
nearer to the minimum of the intensity, but that the violet end lies
nearest to this minimum; from this we conclude that the body is but
slightly translucid, and that its colour must fall into the red.
Let us now move fig.2 a little further; suppose, for example, that
2b is equal to half the length of the wave of green light; we find that
the whole spectrum lies in the minimum of the intensity ; the body must
according to that be nontransparent, when r is so great that the inten-
sity of the minimum lies within the limit of our range of vision; in the
contrary case it must appear black.
If we continue to move fig.2 still further, that is, to suppose con-
stantly increasing retardations, we obtain spectra in which the maximum
of the intensity falls successively on the violet, blue, green, yellow and
red, and in which the complementary colours are more or less absorbed.
Let us now suppose the magnitude of 7, on which the real magnitude
of the intensity, but not the condition of the maxima and minima, de-
pends, to be also unequal on the different bodies ; we then easily per-
ceive that we can zmagine all degrees of the natural colours of the bodies,
as well as their greater or less transparency, as originated in this
manner *.
* If we reckon the resultants of the reflected rays, the intensities of which
(fig. 9) are ra, ra.(1—7)*, ra (1—r)?.7?... ete., in the same manner
as we reckoned before the resultants of the transmitted rays, we obtain for their
intensity
J 1420 —2n cos 202 4 (l—2,r)?
Ai) o> a) ern tel. rie (7)
J 127% cosa 2! +n }
If this expression be differentiated in relation to ai it is evident that A’ be-
: Db ot 2b
comes a maximum when — is 0,1, 2,3,4...., and a minimum when a
is 3, 3, $, 3 +--+, 2. e. under the same circumstances as A. Hence it follows, that
what has been said in respect to the transmitted light holds good also for the
reflected light; so that the natural colour of bodies is explained in the same
manner for reflected light as for transmitted light.
ACCORDING TO THE UNDULATORY THEORY. 487
So long as we take 26 less than from three to four times the length
of the wave of red light, we obtain only one place of the spectrum, or
both its ends absorbed ; but if we increase 6 still more, that is if we
advance fig. 2 still more forwards, we perceive that more maxima and
minima appear in the spectrum, the more indeed the greater 26 is
taken. If we suppose 2 6 = 0-004 of an English inch, we obtain about
the same number of absorptions as by iodic gas.
I have endeavoured to produce artificially those kinds of retardations
which the phenomena of absorption presuppose, and have been so for-
tunate as to produce in a very simple manner any kind of the phezno-
mena of absorption I chose. The simplest, and, as I have found, the
easiest, manner of performing this experiment successfully is the
7 _ following: Bend a piece of a thin plate of mica so that it forms the
_ surface of a perpendicular cylinder; then place at some distance a
_ lighted candle at the same elevation. The flame which is reflected
towards the eye from the cylindrical surface must now appear as a slen-
der vertical line. This light is reflected partly from the front surface
_ of the mica, partly, once or more than once, from its hind surface ;
4 the retardation of the last part is to that of the first in proportion to a
distance whose magnitude depends on the thickness of the mica. If
the thickness of the mica is at all considerable in proportion to the
length of the wave of light, that is about 0°001 inch and more, the re-
‘ flected light appears quite uncoloured. But if we divide this light into
'
‘
=
colours by means of a prism, and observe the spectrum through a tele-
scope, it appears, from the most external red to the most external violet,
1 : filled with stripes, which are quite black, and more numerous the
_ thicker the plate of mica is. After having shown how we can explain
a great number of phanomena of absorption by the supposition of a
single retarding cause, I will endeavour to show how we may explain
o the rest by a further supposition of many other similar retarding
causes. If we suppose light of the intensity a, which has been sub-
_ jected to the action of a retarding medium, and through that brought
| down to the intensity
a.(1—,r)?
Se ee ee
a/ — 2790082 «20 + rt
and subjected anew to a fresh retardation, which ot itself would have
caused the intensity
eC — rie
Ps
ob! 7
1 — 21? cos 2 x — + r't
_ it is evident that the result A! of both retardations must be
488 BARON VON WREDE ON THE ABSORPTION OF LIGHT
i arith
See
a/ — 27" cos 20 7 + 7/4
or
bait a—-ryd— a
L.M.
where
caer = 22 cos 2 2° + v4
and
eAMiib AL. wich ses
M=/1 —2r'? cos2r aa ee
In the same manner the results of the three retarding causes will be
Per OR sade Clos sian (frat);
“a L.M.N. ,
Lay /(1— 29 cosa 2? +0)
¢ > ZI
M=4/(1 — 27" cos 2m 20 7h)
N= 4/127" cos 20 2H" + WH),
From these equations it will be evident that in general A’ or A”
must attain a partial maximum or a partial minimum as often as one
/
of the angles 2 7 2°, 20 ee &c. has completed an entire periphery ;
where
that is to say, there must originate in the resulting spectrum as many
absorptions as would have originated in the sum of each single spec-
trum. It is therefore easy to account for that which must arise
from two or more retardations, in the manner which I will now show
by an example. If we convey light into a vessel into which iodine has
been brought, and which is then gradually heated so that the iodic
gas may increase slowly in intensity, the phenomena of absorption
take place in the manner and order following: as soon as so much
iodie gas is disengaged that the vessel receives a slightly reddish tint,
we perceive in the blue light, or rather at the limit between the blue
and the violet, some slender pale black stripes. The dark stripes be- —
come blacker the more the intensity of the colour increases, and at the
same time we perceive more dark stripes. With increasing intensity of
the colour of the iodie gas the light stripes in the blue commence gra-
dually to decrease in strength, till at last a complete absorption of the
blue end of the spectrum takes place. In proportion as the entire ab-_
ACCORDING TO THE UNDULATORY THEORY. 489
sorption proceeds toward the red end of the spectrum, new black stripes
arise before them, till at last, at a certain intensity of the colour of the
iodie gas, the whole spectrum is absorbed, with the exception of asmall
piece of the red, which is now entirely filled with black stripes. This
beautiful phenomenon of absorption is explained with the greatest ease
and exactness by supposing two different causes of retardation. We
need only presuppose that the one retardation is about equal to the
length of the wave of red light, and the other about 150 times greater.
The part of the curve of the intensity which represents the first re-
tardation has the form A B (fig.3); but that part of it which repre-
sents the second has the form C D (in the same figure). The results
of both may therefore be expressed by a curve of the form of E F.
With increasing intensity of the colour of the iodic gas, we must sup-
pose that r and 7’ are increased, and that this increase can of course
have an influence, not on the station of the maxima and minima, but
merely on the absolute magnitude of the intensity. The greater r and
r' become, the less must also the intensity become. And as we must
imagine that the light, in order to be visible, must have a certain inten-
sity, and as we can also express these limits of perception of the light
by a line, it is evident that the increase of 7 and r' must force down
the curves of the intensity toward this line.
If we now place fig. 2 on fig. 3, and conceive the line A B in
fig. 2 to represent the limit of perceptibility for the eye, we shall
render the effect of the increase in the value of 7 and r’ evident by
sliding fig. 2 gradually higher on fig. 3. If fig. 2 lies on the line
ab, we see some stripes appear in the blue; if we move it higher
towards a’ b', we see that the blue end is absorbed, and the stripes now
make their appearance in the green ; if we move it still higher to a! b”,
we find the whole spectrum absorbed, with the exception of a piece of
red, which is now filled with black stripes. This is precisely the pro-
cess in the spectrum of the iodie gas. The phenomena of absorption in
_bromic gas are explained just in the same manner. In order to ex-
plain the spectra arising from the light which has traversed nitric.acid
gas, or euchlorine, we must suppose several causes of retardation. We
must not be astonished at this difference, as the two last gases belong
to the compound, while the two first belong to those which we consider
as simple. It appears to me quite natural to assume that the ele-
mentary constituent parts of a compound body may each of itself cause
different retardations; and if we consider nitric acid gas as a compound
of nitric acid and nitrogen, instead of considering it as a binary com-
‘pound of azote and oxygen, we then easily conceive how very possible
_ it is that a great number of retarding causes may be contained therein,
_ each of which arises in the same manner as in the single gases.
_ Without endeavouring to explain the presupposed causes of retarda-
490 BARON VON WREDE ON THE ABSORPTION OF LIGHT
tion, or rather the form which we must suppose matter to possess in:
order to produce them, I cannot but remark en passant a circumstance
which has excited my attention, and which perhaps deserves considera-
tion.
Most of the gases retain, when they are in any manner brought
into another aggregate condition, very nearly the same colour. The
retarding cause to which we ascribe the colour of the body must there-
fore be almost independent of the aggregate condition. The other re-
tarding cause, on the contrary, suffers a certain change when that. con-
dition is changed, because the spectrum of the light which has traversed
a solid or liquid body does not possess the black stripes which it would
have if the body had been gaseous. In this fact we have a certain rea-
son for referring the first to the particles of the body, and the latter to
their distance from one another, because we properly think these to be
changeable. A reflection in the znéertor of a particle, or a kind of pro-
pagation of light through it, we are not able to imagine, inasmuch
as we consider it as an elementary particle. Here then we have an in-
creased probability of the truth of the supposition that bodies consist
of such groups of elementary particles as Ampére* has supposed in
order to explain the propagation of caloric; an hypothesis which Herschel
also in other respects thinks probable+. Be this as it may, we must
not be thought too bold when we suggest that by observations on the
absorption of light we may find a new way opened to us of viewing
the constitution of matter which may perhaps lead to results that
could be attained in no other way.
The other facts stated by Brewster, which, as he thinks, remain in-
capable of explanation according to the undulatory theory, are, on the
above supposition, all exceedingly easy to be explained.
In a spectrum of light which has traversed oxalate of chromium and
potash, all the colours are absorbed with the exception of the red, which
contains black stripes. Brewster mentions as a consequence of this,
that this body permits ether to undulate freely to a red ray whose index
of refraction, in flint-glass, is 1°6272, and also to another red ray whose
index is 1°6274; while it is absolutely opake, or its ether will not undu-
lute at all, to a red ray of intermediate refrangibility whose index is
16273.
Set forth under this form, the fact must surely appear as a paradox.
It is, however, easily explained if we suppose two interruptions, one of
nearly the same magnitude as the length of the wave of the red light,
and the other greater, for instance ten times as great. In consequence
of the first retardation, the curve of the intensity obtains the form of
AB (fig.4), and, through the second,the form C D (in the same figure):
the resultant of both must possess the form of E F. If now we consi-
* Poggendorff's dnnalen, vol. xxvi. p. 161. + Ibid., vol. xxxi. p. 255.
ACCORDING TO THE UNDULATORY THEORY. 491
der G H as the limit of perceptibility for the eye, we obtain a spectrum
exactly like that above described.
The phenomena which appear in the spectrum of coloured flames
stand undoubtedly in connection with the present object, and may be
_ explained in the same manner as the phenomena of absorption. But
_ besides the presupposition of retardations, we must here still make an-
other, namely, that certain flames can only produce light of a certain
length of wave, or at least that the produced light is inclosed in certain
limits, which lie closer to one another than the red and violet. Various
_ phenomena in the spectra of coloured flames arise only from this
cause. This, for example, is the case with the bright orange-coloured
_ stripe which is formed in the spectrum of a common candle light. If
we consider the light of a candle, we find it to consist of several divi-
_ sions, differing from one another. The inner and lighting flame con-
tains, as is well known, heated particles, which undergo a real combus-
__ tion then only when they arrive at the outermost border, or where they
come into contact with the air. The outer flame is therefore of quite
a different consistence from the inner; it has also quite a different
_ appearance ; it lights feebly, and possesses a faint orange colour. The
broadest part of the flame has, on the contrary, a blue colour, and re-
sembles in every respect that produced by a slow combustion of coals.
As this flame originates at the point where even the wick comes into
contact with the air, I consider it quite probable that it arises froma
slower combustion of it.
If we place a convex lens between the flame and the opening through
_ which we allow the light to fall on the prism, so as to produce a mag-
_ unified image of flame on the prism, we are then able to bring to the
opening any part of the image of the flame by sliding the lens, and
in that manner to examine any particular part of it. Suppose we then
move the image so that only its outermost border lies on the aperture,
and consequently only the light of the most external flame can pass
_ through it, we find that the spectrum contains nothing else than a part
_ of the orange-coloured stripe. If we change the form or breadth of
_ the aperture, we find that the orange-coloured stripe undergoes just
the same change, so that it always remains a complete copy of the aper-
ture. If we slide the image of the flame so that the inner lighting part
arrives at the aperture, we obtain a complete spectrum ; and the nearer
the middle part of the flame comes to the aperture the greater is the
brightness the spectrum acquires, while the orange-coloured stripe de-
creases more and more. Hence I conclude that the inner flame pro-
duces light of all possible lengths of wave; the outer flame, on the con-
_ trary, only light of a single length of wave, that is, of a completely ho-
_ mogeneous light. If we view a flame of light through a prism, without
letting the light pass through a minute aperture, we naturally obtain an
RIS
~
492 BARON VON WREDE ON THE ABSORPTION OF LIGHT
irregular spectrum, which contains all colours. But in this spectrum
we find a perfectly distinct orange-coloured image of the whole flame
of light produced from the homogeneous light in the outer flame. If
we move the image of the light so that only the inferior blue part
may fall on the aperture, we find that the spectrum contains only violet,
blue, and green light; but at the same time we find three quite appa-
rent and regularly placed maxima, to explain which we must presuppose
a retardation of about 10 or 12 lengths of the waves of light.
One of the most peculiar of this kind of spectra is, without doubt,
that from the light of burning spirits of wine, in which chloride of cop-
per has been dissolved. This spectrum is filled with bright stripes,
which are so arranged that they always appear in pairs with a black
stripe between them, while those belonging to the different pairs are
separated by a broader stripe, as it is represented by K L, fig. 5.
In order to explain this phenomenon we only need suppose two re-
tardations, one twice as great as the other, and having such a position
that the maxima of the smaller one fall on the minima of the greater
one. In the first the curve of intensity obtains the form A B, in the
latter the form C D; the resultants of both must consequently have
the form E F. If GH expresses the limit for the power of per-
ception of the eye, it is evident that the spectrum must receive the ap-
pearance of KL. On the contrary, let us imagine that the maxima of
both components fall together, so that the one has the position A B
(fig. 6), and the other that of C D, the resultant then takes the form
EF. Ifnow GH represents again the limit of the power of percep-
tion of the eye, it is clear that the spectrum produced must contain
black stripes, appearing in pairs, separated by bright ones, or must ap-
pear as K L (fig. 6)*.
In the same manner as we can produce with one piece of mica the phe-
nomena of absorption originating from one retardation, just so we can
* If we put b!= +5 in the formula (8), it is evident that the maxima or
minima corresponding to b’ must come to lie where the maxima of b are. The
lirst-mentioned case, or the appearance in pairs of bright stripes, cannot there-
fore take place when one retardation is exactly twice as great as the other ;
in such a case it is more likely that the stripes occurring in pairs would appear
black. Itis, however, evident that we only need increase the greater retarda-
tion by one single wave-length in order to make one maximum which corre-
sponds to the retardation fall on a minimum,
The other maxima and minima do not indeed then completely coincide one
with another, but they come evidently nearer to one another the greater the
retardations are; and when these are somewhat considerable, the irregularities
arising are so small that the eye is no longer able to discover them. We must
suppose in the flame of chloride of copper that the smaller retardation amounts
to about 40 wave-lengths of the red light, i.e. about 60 of the violet; the
greater need only be increased by s'5 to »35 above the double value of this
magnitude. :
ACCORDING TO THE UNDULATORY THEORY. 4.93
imitate with ¢wo pieces of mica the phenomena arising from two retarda-
tions, &e. To perform this it is only necessary that the light which
is reflected from one plate of mica on the prism must first have been re-
flected from the one plate of mica on the other plate. According to what
has already been proved, a spectrum is then obtained which contains
all the absorptions which have been caused by each single retardation.
The following is, as I have found, the easiest method of performing
this experiment, which indeed, properly speaking, explains nothing, but
which deserves to be mentioned as a beautiful experiment : I generally
take a plate of mica, whose surfaces, besides being even and without
faults, incline one towards the other, so that the plate is thicker at one
border than at the other. Among the plates of mica which I have ex-
amined in this respect, I have found one which possesses these properties
in a high degree. As I bent this plate into the form of the surface of
a vertical cylinder, and placed it so that the light was reflected on the
prism from its thick end, I obtained a perfectly regular prism, with
_ about 120 black stripes ; but the surface of the cylinder being turned
round its axis, so that the reflecting element gradually advanced
_ toward the other end, the distance between the stripes gradually in-
_ ereased, while at the same time their number diminished, till at last
_ from the thin end I received but a few more than 20. In order to
bring the surface of the cylinder to any desired position, I fastened it
on to a small cylindrical pillar, A B (fig. 7), which was fixed by wax,
or any other glutinous substance, to an even support.
In order to produce spectra which contain two series of absorptions,
_ I placed two such cylinder surfaces in the manner shown in A and B
(fig. 8). The light from the lamp C, concentrated by means of a
great convex lens D, is carried to the first cylinder surface A;
from this it is thrown on to the second, B, and from this further on to
the prism E. The light of the flame is hindered from falling on the
surface B, by means of a sliding screen F; and by another similar
_ sereen G that light is received, which otherwise might easily be re-
flected from the surface A to the prism. By turning both cylinder
surfaces round their axes, I can give to the two retardations any de-
sired relation to one another; and in this manner, as just described, I
can change ad infinitum the phenomena of absorption.
Very small retardations, such for instance as are smaller than a wave-
length, cannot, according to this method, be accomplished, because it
is almost impossible to give to the mica the necessary degree of thin-
ness. But in order to produce also the phenomena in which small re-
_ tardations are presupposed, I use coloured fluids which are inclosed in
_ acylindrical tube, between two plates of glass whose distance from one
another can be altered at pleasure. I have completely imitated, with a
red absorbing fluid and a plate of mica, not only the spectrum of iodie
494: BARON VON WREDPE ON THE ABSORPTION OF LIGIIT
gas, but also that which arises through absorption in oxalate of chrome
and potash. In these experiments the magnitudes 7 and 7! can be
varied up to a certain degree, and consequently the breadth of the
black stripes can be changed in proportion to the breadth of the bright
ones. For this purpose it is only necessary to let the light fall on the
surface of the cylinder, under different angles of incidence. For it is
evident that the proportion between the light reflected on the first and
that reflected on the second must be greater the smaller the angle of
incidence is; and consequently that the black stripes must at smaller
angles of incidence be less broad than at greater. If we wish to produce
absorptions with a small difference between the intensities of the maxima
and minima, it is only necessary to let the light pass through a plate
of mica instead of being reflected on it. In this experiment the propor-
tion can be considerably varied by changing the angle of incidence.
The most complex of all the phenomena of absorption is undoubt-
edly the solar spectrum, with its numerous irregularly placed stronger
or fainter black stripes. If we suppose with Herschel that these
stripes arise from absorption in the atmospheres of the sun and earth,
it becomes easy to explain them according to the principles already
laid down. Although I have not yet made any experiments with a
view to ascertain whether and in what measure the different pres-
sures of the gases act on the position of the arising absorptions, yet
I think it highly probable that they have a very considerable influ-
ence on it. In such a case it is evident that the light in its passage
through both the atmospheres, the density of which varies with the di-
stance from their respective bodies, must suffer an indefinite number
of unequal retardations, each of which will produce a certain series of
maxima and minima. The cause of the number and also of the irre-
gular position of the black stripes is consequently easily to be conceived.
But the (at least apparently) vast difference which takes place between
the intensities of the maxima and minima requires a particular explana-
tion, which I will now endeavour to make. We have hitherto considered
only two reflecting surfaces ; it is however evident that, according to
the hypothesis with which I have set out, we must suppose a series
of such surfaces which will be greater in proportion to the greater thick-
ness of the absorbing medium. If we call, as before, a the original in-
tensity of the light, 7 the loss in each reflection, and m the number of
reflecting surfaces, we easily perceive that the intensities of the system
of waves of light must be as we find them given in the following table
(fig. 10), in which A, B,, A, B,, A; B,, &c. represent the reflecting
surfaces.
When the thickness of the absorbing medium is rather considerabie,
m must be a great number; and consequently » must be very small,
because otherwise no considerable portion of light could traverse all
ACCORDING TO THE UNDULATORY THEORY. 4.95
the m surfaces. All members which are multiplied with 7‘, or a still
higher power of r, must therefore become so small, in comparison with
those multiplied with 7%, that they may be neglected. Thus the inten-
sities of the transmitted rays become
2 ae ee for the retardation 0
a(1—r)".7? (m—1) . . kph coineh> 2b
a(1—r)” .r? (m—2)(1—7)* en Seer ae 4b
ED ee CSS 0 | ee 66
a(1—r)”.r? (m—4)(1—7)° Rh oe 8b
a —r)". A (m—n) =n OY) Le) ane,
consequently we have
u=a(1—r)"sin2x(¢—<)
r
fi u,=a(1—7)" 72 (m—1) [sina (¢- 5) cos 2 3°
i)
— cos 2" (¢— 5) sin 2x o
r DN
ug=a(1 —7r)" r2(m — 2) [ sina= (¢- x) cos 2.2 29
— cos2m (¢— +) sin2.29 2°] (1 —r)?
_— = m 2 E=2. S = xv 2b
u =a(l r) r?(m—n) [ sinex (« <) Shah tare
be, cos 2x (¢— =) sin”. on5*| re hres oh
If we reckon from this the resultants of all the retarded systems of
waves of light, z.e. all those just mentioned, with the exception of the
first, U', or the velocity which it represents, becomes
=a (l =r)" mt sin 2 («- x) [(m—1) cos 2.4 2%
+ (m— 2) (1 — nr) 00s 2.9% 28
+..(m—n) (1 ry Yeon. 27 22]
— 08 2 (¢ — x) [ 1) sin 242°
496 BARON VON WREDE ON THE ABSORPTION OF LIGHT
+ (m—2) (1 — rt sing 222!
+. (man) (ary 8) sinn 29 2] be .
If we now put the coefficients of sin 2 7 (: = x) equal to A! cos @,
and the coefficients of cos 2 7 (¢ _ x) equal to A! sin z, we obtain
ur =a’ sin an(¢— =) cos 2 — cos 2m (¢— ~) sini |
a A
= A! sin [2x(#-<) —i]-
nN
Whence it follows that A’ becomes the intensity of the resulting system
of waves of light.
If we multiply A! sin 7 with ./—1, and add it to A’ cos, and put
for shortness
(i—r) (coson 20 4 V/—1. sin2r =")
A A
equal to p, remembering that
cosmz + “—1.sinmz=(cosz + /—1.sinz)”,
we obtain
A! (cost + “—1 « sin?)
=a.(1—r)" 78 (cos 2 2° + As Ip sin 24 =”) x
x (@—- 1) + (m—2)p+ (m—8)p* + -.-.(m—n)p"")..(9)
If we call ((m—1) +(m— 2) p + (m—8)p* +...)
for the sake of shortness S, we have
S=(m—1)Q+ptptp tpt. . ter
—-(tptr tet . raha oie
— (P+ p +p + nl eras L + p"~")
Ba ee ee AD 4 sebyaein + aD
ee
ACCORDING TO THE UNDULATORY THEORY. 497
or
m— I
1— p”
[ eae z
7
1 Sut kn
l—p (» ~ )
| oe (-»")
Poe eee
1 ( a)
] BERT on
= i (» P
or
we 1 £ a +) : 2 3 Ty ms gl
ap Ll 1) eh Dig? or ptt esp)
+(n— 1) p" |
yall n p—p
= 25[ —D-@m—mp ba aie
It is now evident that 2, or the number of the rays which have tra-
versed after the second reflection, must be equal to m — 1, or amount
_ to one less than the number of the reflecting surfaces. Bearing this in
mind we have
i g = (m—1) —(m—2)p tp”
% ip}?
t Although we dare not here suppose m to be, properly, indefinitely
great, it must however be so great that we may consider p” in com-
_ parison with (m — 2) p as evanescent, and m — 1, as well as m — 2,
equal tom. By this we have
6 Om
1—p
If we now put this value of S in the formula (9), and instead of p
its value, and moreover represent 2 7 2 for shortness’ sake by g, we
have
A! (cosi + / —1 . sin)
_e(1— r)" mr? (cosg + VW —1 . sing)
Liss (l=)? (cos 91-4 /aane sing)
498 BARON VON WREDE ON THE ABSORPTION OF LIGHT
By separating the real magnitudes from the imaginary, we obtain
ne eee
‘~ V71—2(01 —rycosg + 1 —r)t
and P
‘is cosg — (1 —r)?
rah es Solis 2(1—rycosg+(1—r)
as well as
Rien a.mr2(1—r)"
~ 4/1 —2(1 —rycosg + (1— 7)
If we designate the velocity U, which represents the resultants of all
the transmitted rays, we have U = w + U’, or
; x
U= [ea —r)m + A! cosi | sin 2m (« _ =)
— A'sinicos2 7 (« = =).
A
If we reduce this expression to the form
U=Asin [2x(+- =) ep,
and A, which must then express the intensity of the whole resultant,
be determined in the common manner, we have
Aa VA8 49a — rent eae
or, by substituting the value already found of A’ and cos 2,
1 +2(m r—(1 —r)? eos qt [ r—(1— ry] (10)
If we differentiate this expression in relation to g, it is clear that A
becomes a maximum or minimum as often as sin g =0, 2.e. A becomes
A=a(1—r)
a maximum when = equals 0, 1, 2,3, 4...., &c., and a minimum
26 . :
when <? equals 4, 3, $, 3, $--- &c, te. under quite the same
circumstances as if only two of the presupposed reflecting surfaces
were present. Hence it follows, that
a ¢ +mrr—(1 —r)?)
A; maximum = a (1 —7) ——j7- = = 75
; * ACCORDING TO THE UNDULATORY THEORY. 499.
and
A; minimum = a (1 — r)” ¢ =r? tC )
1+(1—r)?
ae mr?
=a(l1—r) peice gary
If we now compare the intensities in the maximum and minimum
with one another, we have
4
ak yi il Qr+mr 1+a0- ne
A; min. 1+ (1—r)?—mr ~ or
Bearing now in mind that r must be an extremely small magnitude
the above formula is reduced to
A;max. _ mr
AV urninis a #, 2
_ From this then we see that the proportion between the intensities in
the maximum and in the minimum must become greater the greater
m is, i.e. the denser the absorbing medium is. Hence we obtain a
reason for the considerable difference between the maxima and minima
of the solar spectrum, when the atmospheres of the sun and
h are the absorbing media. There are, however, many circum-
‘stances by which our estimate of the relative intensities in the maxima
and minima are rendered very uncertain. The flames of light, which
suffice to light our chamber in the evening, beeome by day, when
placed in the light of the sun, almost imperceptible. In the same
manner, when we step out of a lighted chamber on a dark evening,
the darkness seems to us so deep that we can scarcely recognise
ceive them quite well. The heavenly bodies, which by night shine
80 brightly but by day are quite imperceptible, present a second
example of the same kind. Moreover we know that the eye itself
nges according to the greater or lesser intensity of the light: the
traction and expansion of the pupils are very likely not the only
mge which the eye undergoes in this respect ; for, indeed, I consider
9 probable that even the pellicle of the eye possesses the property
greater or less irritability. For this reason it is easy to conceive that
he difference between the intensities in the maximum and minimum
may possibly appear to us very great without being so in reality, and
that the intensities in the black stripes may be very considerable, al-
gh the proximity of the brighter stripe makes it imperceptible to
our eye.
Vor. I.—Panr IV. 2m
500. BARON VON WREDE ON THE ABSORPTION OF LIGHT
I have already made the preparations necessary in order to prove by
experiment the identity of the phanomena of absorption and those
which must result from the hypotheses assumed by me for their expla-.
nation. The formule which are required for such an experiment I will
now analyse. I have already proved that when light of all wave-
lengths traverses a medium which causes a retardation ¢, all species of
light whose half wave-length is
Cho Wile a & c c
Sy ae ae ee ee
Se a eG 2m—1'.%2m+1
become minima. Now in order to derive from this a formula for the.
minima which must arise, in consequence of the retardation c, in a
spectrum whose external limits are a (the greatest) and / (the small-
est), I designate this number by s, and suppose that 2 aZ ; 1?
l furth Atl" yt he
but 3 oe. urther 4 F(a Layne” 2a peak i
-
4
'
‘
/
:
Hence we have 2 m — 1 Zac and 2m+1 7 a cm caeeen +1 and
a eames:
7 — — 4, and consequently m = the entire number in = +1
In the same manner we have m+ s 7 a + 4 and 75 — 4, conse-
quently s = entire numb. in (4 +4) — entire numb. in (4 —1 ) (11):
If on the contrary we assume the pheenomenon of absorption as known,
and search for the magnitude of the retardation which causes it, we
must first determine in one manner or the other the wave-lengths of
the species of light which represent any two minima. If I call these a!
and (', and the number of the intermediate absorptions s — 1 (i. e. s de- :
signates the ordinal number of the minimum whose length of undulation — B
is 6', reckoned from that whose length of undulation is «’), and suppose
Aas a a = 4 [7
we have
c= a) ( _ s) =p G +s)— 4)
thence p's
nel eae ‘oe
and consequently
a B's
og Ose. i
_ ACCORDING TO THE UNDULATORY THEORY. 501
When ¢ is given it is easy to determine the difference 3 between the
lengths of undulation for two minima lying close to one another,
namely y and y — 0.
If we then suppose sa i= 4 y and ae i= 4 (vy — 9),
2
tas =k aod oe) ee da
we have - 1 SEE (13)
For another length of undulation 7’ we obtain in the same manner
feb dam
e+y/'
and consequently
Os sO ba i Rein a leanaye
Ce i Ala la ci
12
1 1
if ¢ is rather considerable, ery becomes very nearly equal to ey?
and we then have also very nearly 0: Uv =y?: yy! . . . . (14)
By means of which formula the comparison of the observed with the
calculated phenomena may be effected.
The locality in which I have hitherto performed my experiments has
not allowed me to make an exact calculation of the fixed lines present
in the solar spectrum, although this is the surest way to determine the
relation between the refrangibility and the wave-length, because we can
then make use of the exact calculations of Frauenhofer. I have there-
fore only been able to decide as to the colour corresponding with the
length of the undulation by the eye. The calculations then which I
have hitherto made can only be considered as approximations ; Ishall not
therefore produce them here. Notwithstanding, they have completely
convinced me that the phenomena of absorption and those which must
follow from the hypothesis laid down by me are identical. An example
of this may, however, be worthy of mention, although the calculation
must only be considered as an approximation. In the spectrum of iodic
gas, fifteen stripes occupied 9! 30" from the orange-coloured to the red ;
ten stripes between the yellow and green occupied 5! 30"; I therefore
suppose that the distance between two neighbouring stripes, at the limit
between the red and orange, amounts to 38", and at the limit between
the yellow and green {to 31". If we now insert in the formula (14),
instead of y and +’, the two corresponding wave-lengths (0-0000246
and 00000219 English inch, according to Herschel’s table), we have
é: d= 38:30°6.
As to the rest, it is self-evident that by the undulation-length of a colour
I mean the length of undulation in the absorbing medium. Since in the
examples mentioned the lengths of undulation were taken as they were
calculated in the air, and moreover the squares of the lengths of undu-
2mM2
502: BARON VON WREDE ON THE ABSORPTION OF LICHT.
lation were compared with the distance ‘between two consecutive mi-
nima instead of with the differences between the representing lengths
of undulation, which would presuppose that the refrangibility of a colour
would be proportional to its length of undulation, this can be consi-
dered as proving nothing more than that the reasoning and the expe-
riment coincide in showing that the absorptions in the green colour lie
closer to one another than in the red.»
I must finally remark ‘that, although 1 have considered the retarda-
tions only as arising from reflection between the particles, I also easily
conceive the possibility that this idea may be incorrect, and that all the
retardations may arise from causes as yet quite unknown to us. But |
think I have shown by what I have stated that the phanomena of ab-
sorption may be reduced to a simple mathematical principle ; and that
these pheenomena, as belonging properly to the absorbing bodies, point
to certain determined magnitudes, which can be given in an absolute.
measure, and the closer examination of which, whatsoever their cause.
may be, must always be highly interesting.
Article XXVI.
On the Application of Electro-Magnetism to the Movement of
Machines ; hy M.H.Jacosi, Doctor of Science, and Profes-
sor at the University of Dorpat.
[Published at Potsdam, 1835.]
PREFACE.
THE great discovery of M. Oersted, which has so much extended the
limits of physical science, promises to open a new career to practical me-
chanics. The motive powers which have hitherto served for the move-
ment of machines are not, properly speaking, forces; they are only
masses animated by forces. These masses are made to act upon the point
of application of a machine, and they consequently can only give it a
velocity conformable to their own moving principle. But magnetism
enables us to employ immediately a force; the point of application
is the force itself. We thus perceive a considerable active force
_ produced without any external influence. The interest of such’a phie-
nomenon is increased extremely by the simplicity of the apparatus
and by the facility of conceiving its mode of action. But on examining
it more closely, we find that the forces which are active in producing the
_ movement present a great complication of circumstances. The study
of the phenomena of electricity and magnetism is still in its infancy ;
and we are not surprised that every day makes us acquainted with new
_ phzenomena at once striking and unsuspected. The views which I had
conceived of these forces have in part been confirmed during the course
of my researches, and they have in part been shaken and even com-
pletely changed; as soon, however, as I was cbliged to abandon one
view, another presented itself which led to the disclosure of fruitful re-
sults. For example, the remarkable reaction which prevents the move-
ment from becoming accelerated to infinity has become a new source
of power; the exact knowledge of the galvanic action leads to a minimum
of the expense attending its maintenance. I have restricted myself in
my researches to such experiments as touch immediately upon the object
itself; and from the number of these, I shall only publish those which
have given results, or at least lead us to hope for them: I have sup-
pressed as much as possible all purely theoretical considerations. As to
‘the practical application, it appears to me decided by my experiments;
‘to go further will be only to augment an effect, with which, laying
‘aside sanguine expectations, we may already be content. It is no un-
usual thing to have electro-magnets which lift 2000lbs.; mine carried
504 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
only from 30 to 40 at most: nevertheless, these feeble magnets furnished
me with a mechanical action equal to half the force of aman. To main-
tain this action, during eight hours, scarcely half a pound of zine is
required, everything being properly arranged.
I have not yet been able to construct a larger apparatus, and I there-
fore wished to make as much use as I could of the one I possessed, since
it was capable of showing completely the nature of the active forces.
My experiments may be easily repeated; all depending upon carefully
attending to the construction of the commutator, and likewise that of
the galvanic apparatus. ‘Those who are acquainted with electro-mag-
netic phenomena will easily be able to make the necessary arrangements,
and to give the accurate proportion to the several parts. The object of
this memoir will be attained if it inspire an interest for a subject which
merits it.
Konigsberg, August 21, 1835.
MEMOIR.
1.
In November 1834 I had the honour to lay before the Academy of
Sciences of Paris a note upon a new electro-magnetic apparatus. That
note was read at the meeting of December 1st; and an abstract of
it was printed in the Institute, No. 82, of December 3rd, to which I
refer. Since that time MM. Botto and dal Negro have claimed the
priority of the invention, the former in the Institute (No. 110) of June
17th. The competition in which I find myself engaged with such di-
stinguished men serves only to confirm my conviction of the importance
of this new motive power. A discussion as to priority is only of histo-
rical interest. It is not astonishing that persons, who had scarcely any
communication with each other, should have devoted themselves almost —
at the same time to the study of the same object. But we ought not to —
conceal from ourselves that, after the grand discovery of M. Oersted
and the experiments of Mr. Sturgeon, who, it seems to me, first gave a —
great magnetic intensity to soft iron by means of an electric current, and
viewing the instantaneous manner in which this magnetism may be de-
stroyed or reversed, by merely changing the direction of the current,—it
was not difficult. to conceive the possibility that some motion or some me-
chanical operation might be produced by the electro-magnetic excita-
tion of soft iron. In short we must award the palm to M. Oersted;
whilst we who follow him shall have the merit of having known how to
apply this new power to practical purposes and the wants of life:
and this will be reserved for him who shall best have understood the
mechanical and physical principles of this motive power.
TO THE MOVEMENT OF MACHINES. 505
2.
In May 1834 I constructed the first magnetic apparatus with a pri-
mitive continuous circular motion. It is true that, like M. dal Negro,
(with whose labours I regret that I am not better .acquainted,) I had
several years ago conceived the idea of applying this power to mecha-
nies: but I could not at first divest myself of the idea of making this
application by means of an advancing and receding motion, produced
by the attractive and repulsive power of magnetic bars,—a motion which,
by known means, might have been changed into a continuous circular
one. It seemed to me that an apparatus of this kind would have
only the merit of an amusing toy, which might find a place in the eabi-
nets of men of science, but would be entirely inapplicable on a large
scale with any advantage.
For considering the general equation of active forces applied to the
movement of machines
a a’ 2 2
=f Mds — sf" Pds' = Ximv, — =mv,
the magnetic action, during the amplitude a, and represented by
wd “Mad s, could not be perfectly exhausted by the action = vi "Pd a
alec: the active foree gained during the movement ages ZCYO,
or im v — = mo =0. Now the magnetic attraction is a function of
the space, the form of which we do not sufficiently know, this function
being affected by the nature of the distribution of the magnetism in the
body, of whatever form. The law of this distribution is scarcely esta-
blished with regard to bars of steel of a regular form, magnetized to
saturation and deprived of consecutive points. With regard to bars of
soft iron of considerable dimensions, magnetized by an electro-con-
_ ductive helix, we have analogies only, but no experiments. But however
this may be, we know well that this function must be expressed by a very
_ convergent series, so that the magnetic attraction will be in an inverse
proportion to the square or to the cube of the distance, or, stopping at
the three first members, will perhaps be composed of them. The mag-
netic points then approach each other with an accelerated motion; the
tive forces increase, and reach their maximum at the instant when the
’ eutact i is completed: but this force ought then to be destroyed. It
will destroy itself by the fixed points of the machine, and by the vibra-
tion of the system: but this will be in an unprofitable manner. There
a ‘o *. . 2 2
will be a complete loss of the active force obtained 2mv, — Zmv. We
°o
know the ill effects of shocks in the movement of machines, but there is
_ here another inconvenience which is not simply mechanical. The soft
iron, by these repeated shocks and vibrations, gradually acquires at the
p g y acq
506 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
surface of contact the nature of steel; there will be a considerable
permanent magnetism, and the transient magnetic force, whieh alone
produces the movement, will be weakened in proportion, A num-
ber of experiments which I have made upon the magnetic force of a bar
of soft iron bent into a horseshoe (of which I shall speak hereafter)
has shown me the great disadvantages of oft-repeated shocks, proceed-
ing from the sudden contact of the armature. But, if we stop at the
mechanical principles of magnetism, it may be objected that the active
force gained will not be absolutely lost for the purposes of utility;
that in part the elasticity of the iron will itself reproduce it; that an-
other portion may be regained by springs properly applied, or by other
mechanical methods which may be invented. We leave the appre-
ciation of all these factitious means and of these superadditions to those
who are in the habit of constructing machines; they well know their
insufficiency, the great loss of working power, and how rapidly all the
systems are destroyed, unless the greatest care be paid to the preservation
of the active forces. But we must seek the means of this preservation
in the nature of the forces themselves. The history of the steam-engine
teaches us that its improvement commences with Watt's ingenious idea
of stopping the escape of the steam before the piston had accom-
plished its stroke, and of causing the steam afterwards to act by its own
expansion. Watt understood the subject: all he did was to give to the
function P = ¢(s), which expresses the action of the steam, such a
'
form as sie Pds= ak oe * P'ds', and thus the active force gained be-
comes zero, all the prejudicial and destructive vibrations in the machines
previously constructed cease, and the power of the motive force is con-
verted for the most part into useful action. I must here cite the valuable
researches of M. Poncélet on the construction of hydraulic wheels,—a
work founded upon a profound comprehension of the same principles.
These considerations, at once clear and simple, have induced me to
reject entirely every apparatus in which magnetism is applied to pro-
duce immediately an oscillating motion; these constructions being, as
we have seen, as inadmissible as they are impracticable of execution on
a large scale.
oe
In the note which I had the honour of laying before the Academy
of Sciences of Paris I stated that, in accordance with all experiments,
magnetism is a power acting like universal gravitation, solely in some
function of space. The integral if : Mds comparable with the known
a
number g, represents the mean action furnished by the attraction of two
TO THE MOVEMENT OF MACHINES. 507
points, and is not at all affected by their relative velocity. The inversion
of the poles being effected instantaneously, we should thus have a velocity
infinitely accelerated. Nowasystem moving round an axis, and capable
ofa continuous circular motion, is that whichisalone susceptible of such
avelocity. It cannot become uniform, unless some resisting element, or
some other action depending on the velocity, is introduced into the
system. Putting aside the application to practical use which has to be
made of such an apparatus, the obstacles to be overcome, inseparable from
the system, consist only in the friction of the pivots in the sockets, and
in the resistance of the air. As to the former, repeated experiments
have proved that the friction is independent of the rapidity of rotation,
at least within the limits of experiment; this resistance, therefore, can
in no way contribute to render the’ accelerated motion uniform. It
is in fact the resistance of the air which will act to produce this effect.
Although it might be reduced at pleasure, principally by giving a suitable
form to the rotatory system, it would not be entirely ea But it
_will be allowed, that weshould have reason to be well satisfied with the me-
chanical effect of magnetism, if this were the only cause which tended to
reduce the accelerated movement to a uniform movement. The limits of
such a uniform velocity must be very distant. I do not speak of the great
simplicity of a magnetic machine with a continuous circular motion, of
theadvantages of construction which are gained by being able to trans-
_ form with ease this motion to any other which the working machine
mayrequire. These considerations had strongly impressed my mind, even
whilst the means of execution were still unknown to me, but I always
kept in sight the practical application, and the object appeared too
important for me to exhaust my powers in the construction of see-saw
_ toys, which might claim the honour of being placed in the rank with the
electric chime relatively to their effect, and still more relatively to the
_tinkling with which they are accompanied.
4.
Fig. 1. of the annexed plate represents the magnetic apparatus of eight
_ bars,arranged symmetrically upon a disc moveable round the axis A, and
_ of eight fixed bars similarly arranged uponafixed platform. The arrange-
_tnent of the bars admits of the greatest variety, provided it be exactly
symmetrical, and that it allow the poles to approach each other as nearly
as possible. To prevent the action being too oblique,—since the centre
of magnetic gravity is probably at some distance from the extremity, as
in the ordinary magnetic bars,—it is preferable to make this arrangement
so that the axes of the cylindrical bars shall be situated rectangularly,
and not parallel, as in the figure. It must be further observed, that there
will be some difficulty in forging bars of considerable dimensions into
the horseshoe form, so that the axes of the branches be situated exactly
508 PROF. JACOBL ON THE APPLICATION OF ELECTRO-MAGNETISM
at the same distance, and that the branches themselves be exactly cylindri-
cal. Filing them into shape will perhaps have the disadvantage of hard-
ening too much the surface of the iron, and of rendering it less apt to
receive and to part with the magnetism. The form proposed offers a
further inconvenience, in the application of the copper wire helices,
which have to be previously bent on another cylinder of the same di-
mension. These helices ought very nearly to touch the bars, which
should be covered with silk on account of the insulation which is neces-
sary. In future an arrangement similar to the one in fig. 2 will be pre-
ferred, in which f are the fixed bars, and m the bars moveable around the
axisa. We shall have the advantage of being able to employ cylindrical
bars of soft iron, such as may be had of all dimensions in the shops. It
will only be necessary to cut them into equal pieces, and the helices may
be strongly wound round the bars by means of the lathe.
5.
As the magnetic attraction decreases rapidly as the distance increases,
the integral ve * Mds will always be such a function of the amplitude
oO
a, that its value will not greatly differ from a constant, @ being rather
considerable. Admitting, for an instant, that the magnetic attraction
is in an inverse ratio to the ee of the distances, we shall have
‘han Mds a “ se are tg © 7 d being the distance of the mag-
netic centres when the bars are placed the nearest possible; thus d being ~
very small with respect to a, MU — al ny — = m represent-
ing the number of bars. We shall then have for the action of the mo-
2 -
tor, during one entire revolution, the expression ee The radius of
the circle upon which the bars are arranged does not enter into this
expression 3 and for a stronger reason it will not enter into any of —
the other expressions, if the attraction still decreases more rapidly than
the inverse ratio to the square of the distance. Thus the size of the
circle for the same number of bars scarcely adds anything to the action —
of the motor.
I conceived that the system of bars, which in my apparatus are fixed,
might also be rendered moveable. The'rotation of the two systems will
then be in a contrary direction and have the same velocity, the masses
being equal. These two motions might be combined by means of conical
wheels, in order to produce the motion of a second axis of rotation in-
tended for the work. The action of the motor, during the amplitude a,
that is to say from one meeting of the poles to the other, would be as
above. = z but the poles meeting each other 27 times in one revolu-
TO THE MOVEMENT OF MACHINES. 509
" Qn? fx r f :
tion, we should have ri es double the previous action. We might
even construct wheel-work in such a manner that the velocities of the sy-
stems should be in the ratio of m:1, and that the poles should meet
. (m +1) times, during one revolution. The action would then be
m+1)n? fr , and this increase would be gained by purel e0-
4d g y purely §
metrical means. This is a simple deduction from the fact that velocity
does not enter into magnetic attraction. I have not as yet availed
myself of this advantage in the construction of magnetic apparatus,
since there are some remarkable circumstances, as we shall see here-
after, not sufficiently cleared up, and which may give rise to consider-
able modifications.
6.
The inversion of the poles is an object of the greatest importance.
This inversion should take place instantaneously, and precisely at the
place where the poles are situated opposite to one another. The me-
chanism intended to produce this operation should be put in motion by
the apparatus itself, but no element should be introduced which is
dependent in a geometrical manner upon the rotatory movement of the
system. The velocity of the motion, however great it may be, should
not at all affect this operation. The well-known dbascule, an ingenious
invention of M. Ampére, which is so advantageously employed inelectro-
magnetic experiments, cannot be employed in the magnetic apparatus
with a continuous circular motion; for the number of inversions, in a
given time, cannot be considerable without requiring extraordinary means;
andeven these means willnot guarantee the certain result of anadvancing
and receding movement, repeated as frequently as may be necessary.
I shall not recount here all the attempts I have made, both numerous
and expensive, to arrive at the important result of an inversion of the
poles, exact and precise, divested at once of every element depending
on the velocity. Butit is necessary to say that the greatest difficul-
ties arose by employing mercury, as is usual in electro-magnetic
experiments to form and to break metallic contact. In the liquid
state the adhesion of the mercury to the metallic body plunged into
‘it and afterwards withdrawn, varies with the rapidity of the motion and
with the purity of the mercury. Frequently—I may say always—
the inversion takes place too soon or too late, and thus gives rise to an
attraction or repulsion, in a contrary direction to the rotation. More-
over it is very difficult to preserve the mercury pure when in contact
with other metals; and even the purest mercury is disposed to oxidize
- easily under the influence of the electric sparks. These sparks are pro-
duced, under favourable circumstances, on establishing metallic con-
tact, and always on breaking it. The result is, that the surface of the
510 PROF. JACOBL ON THE APPLICATION OF ELECTRO-MAGNETISM
mercury is soon covered with a coating of oxide, which either entirely
prevents the inetallic contact, or at least weakens it. In employing
amalgamated surfaces this effect is produced still more rapidly. Be~
sides I have by incontestible proofs arrived at the conviction, that
the simple contact of metals with a clean surface is quite sufficient to
conduct the electric current, even of the weakest tension. The con-
tact by means of mercury adds nothing to the energy of this cur-
rent. It is erroneous to judge of this energy by the brilliancy of the
spark, proceeding only from the combustion of the mereury.. I have
thought right to mention these circumstances, though apparently trifling.
In a motor, from which we look to obtain an infinitely accelerated mo-
tion, the smallest details should not be disregarded; the most trivial are
ultimately of importance.
"
Fig. 3. represents the commutator, adapted to the magnetic apparatus,
so as to produce the inversion of the poles: a, b, ¢, d are four discs of
copper fixed upon the axis of rotation ee. The dises a, 6 and e, d are
united by copper tubes f, f, entirely insulated from the axis by the in-
terposition of a tube g, of varnished wood or any other insulating sub-
stance.
The periphery of each disc is divided into eight exactly equal parts,
of which four # are cut into sectors and filled afterwards by pieces of
ebony, forming with the metal an accurate and smooth surface. The dises
are arranged upon the axis of rotation, so that the sectors of wood and
of metal alternately correspond, as represented by the shaded parts of the
figure. ZZ, CC are bars of copper, formed as levers, very move-
able in their supports: they are intended to conduct the current.
The arm of the longest lever forms at its extremity an edge, which rests
on the periphery of the corresponding disc. The other arm is bent and
plunged into a litile jar filled with mercury, k. The jars kk and &! k'
are united by plates of copper, as represented in figure 1. The action of
this commutator will easily be understood. The levers are always in
contact with the discs, and are alternately so with the metallic and
insulating parts. By their mobility in their supports they yield to the
slightest inequality of the surface, and the friction they occasion is very
trifling. The helices which surround the moveable bars are united so
as to form a continuous wire, the ends of which J, m are soldered
respectively to the systems of the discs a, 6 and ce, d. The other
helices, wound round the fixed bars, are also united, and the ends 2 and
o immersed, the one in a jar of mercury p, attached to the voltaic appa-
ratus, and the other in the jar & of the commutator. Thus all the six-
teen helices form only one connecting wire, through the medium of the
commutator. The voltaic apparatus consists of four troughs of copper,
in which plates of zine are immersed, all being united as in a pile. The
TO THE MOVEMENT OF MACHINES. - 5ll
direction of thé current is shown in fig. 3 by little arrows; it is re-
versed each time the poles meet, provided the commutator be so
placed that the edges of the levers shall quit one of the divisions in
order to pass to the other. This inversion acts, as is seen, instanta-
neously, and quite independently of the velocity of rotation. The object
is too simple, and sufficiently explained by the figures, to render it’
necessary to enter more into its details. I may add, further, that this
same system of the inversion of the poles is applicable to any number
of bars, provided that the sections of the discs are equal to them in’
number. I have constructed, for magneto-electric experiments, a
double commutator of eight discs, with seventy-two divisions. - In
this apparatus there are also four levers similar to the former, which
rest upon the cylinders (f) that unite the discs in pairs. The other-
extremities of these levers are likewise immersed in jars of mercury,
intended to receive the ends of a connecting wire, which is to be
traversed by the voltaic or magneto-electric currents, sometimes in one
direction sometimes in the other. The instrument is put in motion by a
handle, which can be easily turned twice in a second, and effect in the
same time 144 double inversions. It will be easy to change or com-
pletely interrupt the electric current 1000 or more times in a second.
The nature of this current or of the magnetism will of course be better
understood by decomposing it into a rapid succession of pulsations: I
am persuaded, for instance, that we should succeed by this means in
charging a Leyden jar, or in effecting any chemical decompositions by
the thermo-electric current of a single pair of elements.
8.
The magnetic power is produced and maintained, as is well known, by
_ the action of the voltaic apparatus. By using zinc as a positive metal,
_ copper as a negative metal, and water acidulated with sulphuric acid
_ as the conducting liquid, it is the transformation of the metallic zine into
sulphate of zine which here constitutes the cost of keeping the appa-
-ratus in action. -It is a matter of the greatest importance to reduce as
much as possible this cost. Let us examine what is the relation be-
tween the magnetism of the connecting wire and the action of the voltaic
apparatus. Since the discovery of electro-magnetism this object has
engaged the attention of distinguished scientific men, but it presents so
many difficulties and such a complication of circumstances, that we
cannot be surprised that the theories and formule which they have
endeavoured to deduce from experiments differ considerably.
_ This is not the place to enter into the criticism of these theories ; but
it appears to me that the theory established by M. Ohn, in a little work
“entitled “ Die galvanische Kette, mathematisch bearbeitet von Dr. G. S:
Ohm (1827),” and developed more fully in various memoirs printed
in the German Journals, presents so much simplicity, and agrees so well
with all the phenomena of the voltaic pile, that [have not hesitated to
512 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
adopt it, in order to obtain from it a general basis for the arrangement of
the different elements of the magnetic apparatus. I may be permitted
here to state the fundamental principles of this theory.
1. In a closed voltaic circuit the same quantity of electricity passes
across each section which is perpendicular to the direction of the
current, whatever be the form or the matter of the different parts of
the circuit.
2. Whatever change is made in one part of the circuit, this change
affects the entire action of the pile, and is not confined merely to the
place where the change takes place.
3. The voltaic action, in whatever manner measured, is in the direct
ratio of the electro-motive power, and inyersely as the resistances
which oppose themselves to the passage of the current, or A==
4. The resistances are composed of —
a) the resistance of the solid conductor or of the connecting wire.
For the same substance this resistance is directly as the length of the
wire, and inversely as the transversal section or as its thickness.
b) the resistance of the liquid conductor: this is in the direct“ratio
of the thickness of the liquid stratum which separates the positive and
negative plates, and inversely as its transversal section, which coin-
cides generally with the surface of the plates. During the action of
the pile this last resistance increases, and at the same time the elec-
tro-motive power, or £, is affected by it. This is caused by chemi-
cal effects which take place and change by degrees the nature of the
liquids, the surface of the metals, and the electric tension. But
fixing any state of the pile, the law cited always exists. The
difficulty of making electro-magnetic experiments comparable with
each other, and the still greater difficulty in obtaining absolute mea-
sures, consist principally in the continual change of these elements.
Thus in expressing by 7 the resistance of the connecting wire, we
l
shall have ma for the resistance of a wire, of a length /, and of a thick-
ry!
ness d; ae will likewise be the resistance of the liquid conductor, the
surface and thickness of which are respectively expressed by d' 7’. There-
fore the action of the current, or the quantity of electricity passing
through the pile, will be A ss
ata
5. The electromotive force is in the direct ratio of the number of
voltaic pairs united in a pile, and at the same time the resistance 7’ in-
creases in the same proportion. Having one pile of ! pairs, the force
n' E
nikentin!
d a’
of the current will be expressed by A =
/
TO THE MOVEMENT OF MACHINES, 513
6. If the electric current is divided into several branches, the lengths
of which, reduced in an inverse ratio to their diameter, may be expressed
by /, 7, l'', &c., the total action will be the same as if there were only a
single connecting wire whose length is expressed by the equation
1 1
7 4 2 + i ,&c. Therefore having 2 wires of the same length,
the total force of the current will be expressed by
yg n EB hankdd E
rl etn rldtrtdnn’
nd* a
As we can avail ourselves of the magnetizing power of each unity of
_ length of the connecting wire by coiling it round bars of the same di-
_ mension, the total power gained by a connecting wire Z will be
att inn'dd'E
rld+rl'dnn"
From this formula the limits of the action of the current may be de-
duced, which cannot be increased by the number or the surface of the
_ voltaic pairs, by the length, thediameter, and the number of the connect-
_ ing branches. Increasing only the surface of the pairs d’, the limit of
: !
_ the total power of the current will be A ae increasing the
, 1
number z’, this limit is A = cal
rei
Again this limit will be, by increasing the length of the wire J,
' ]
A="" — the thickness of the wire d, A = 4 ; the number of
r
U
__ the connecting branches 2, A = a
In general, in order to increase the force of the current to any
_ degree, it is necessary to enlarge the surface of the plates, and at the
same time the thickness of the connecting wire or the number of the
branches. The increase of the number of the pairs requires that of the
length of the connecting wire, in order to attain the same end.
The experiments, as accurate as they are numerous, which M. Fechner
has made on this subject, and which he has published in his work “Maass-
bestimmungen tiber die galvanische Kette (1831),” leave no doubt as to
the justness of these laws, which express in a very simple manner all the
relations of the different elements which constitute the voltaic pile.
These experiments have been made for the most part by employing the
‘method of oscillations, which M. Biot was the first to apply ingeniously
to this kind of experiments.
* 9.
Tn admitting at first that the chemical effects which take place in the
yoltaic pile, and which represent the expense attending the magnetic
514 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
apparatus, are ina direct ratio to the active surfaces, it seemed to me of
great importance to establish the relation between the surface of a voltaic
pair and the weight capable of being supported by a bar of soft iron sub-
mitted to the magnetizing power of the current. A bar of soft iron
1Linch in diameter by 29 inches in length, weighing 144lbs., was
bent into a horseshoe, so that the centres of the branches were seven
inches apart. The bar, covered with silk, was covered by a helix of
copper wire of 11 line thick and 35 feet long. The magnetic power
was measured by means of asteelyard, and a weight supported by rollers,
in order to slip easily over the arm of the lever. The surface of the soft
iron armature was of a somewhat convex form, in order that the ex-
tremities of the branches, forming a flat and smooth face, should only be
touched in the direction of an edge, the position of which formed a right
angle with the direction of the lever. The armature was in contact with
the extremities of the branches when the lever was placed horizontally.
Upon the latter had been marked a scale, the divisions of which indicated
the thirtieth part of the sliding weight, to which was affixedan index: it.
was easy to estimate the tenths of these divisions. I had taken the neces-
sary precautions to avoid as much as possible the errors of observation
arising from the disposition of the apparatus. I shall not enter here into
the details of the construction of this rather complicated apparatus, which
I intend to give elsewhere, as it may be useful for experiments of this
kind. The electromotors which I employed consisted of copper troughs
three quarters of an inch wide, and sufficiently large to enable me to
immerse in them respectively the plates of zine of 4, 16, 36, 64, 100,
144 square inches. The contact of these last with the copper was pre-
vented by the interposition of pieces of wood. The conducting liquid,
of which I had previously prepared a sufficient quantity to serve for a
series of experiments, was acidulated with ten per cent. of concentrated
sulphuric acid of the specific gravity of 1:840. The experiments, with
the same voltaic pair, were made without interruption ; but after each
one precautions were taken to cleanse carefully the zinc plates, to wash
the trough with water and to renew the liquid, in order to restore the
same state of action. But subsequent observations convinced me that
the original state is restored more certainly by exposing the plates, and
especially the negative one, to a current of air, until it is perfectly
dried. It will then be no longer necessary to renew the liquid so fre-
quently, especially when the observation is confined to the primitive
state. It must be acknowledged that I subsequently found the copper
troughs to be ill adapted for electro-magnetic experiments ; concentric
cylinders, which may be plunged in the liquid, are much better. These
cylinders must be fixed firmly enough to remain at the proper distance,
without recurring to the interposition of wood or of any other insu-
lating matter. Much more constant galvanic effects may be obtained
if the space oceupied by the liquid between the two metals be not
by:
=
TO THE MOVEMENT OF MACHINES. 515
too narrow ; at all events it ought to exceed half an inch. I have also
made experiments with voltaic pairs arranged like the calorimotor
of Hare, but there were reasons for rejecting these also. It is a very
different thing to make an isolated observation, and to put in requisition
the galvanic action for whole hours and days. It is in the latter case
that for practical purposes measures are required, the necessity of which
had not been before anticipated. It will be also necessary to reject the
use of copper as a negative metal; the expense of employing silver,
platina, or at least copper well plated with silver, gold, or platina, must
be no obstacle. The solution of the copper in the sulphuric acid, how-
ever weak it may be, and its reduction into a metallic state, by the se-
-condary effects of the nascent hydrogen, give rise to partial galvanic
effects, by which the principal action is much affected, and to avoid
which the greatest pains must be taken. In fact the motion of the
magnetic apparatus was sometimes suddenly slackened or entirely in-
terrupted, and on examining more closely I found that metallic parti-
cles of cementing copper or of iron had been deposited all along the
pieces of wood interposed, or upon the bottom of the troughs, and thus
_ formed a partial circuit. I shall speak of zine hereafter. The following
is the table of observations which I have made on the magnetic power
_0f the horseshoe bar of iron above dsecribed.
|
No. 1.|No. 2.| No. 3.|No. 4.) No. 5.) No. 6.|No. 7.| No. 8.|No. 9.|No.10.
mean.
Ibs. | Ibs. | Ibs. | Ibs. | Ibs. | lbs. | lbs. | lbs. | Ibs.
126°32 |123°43 |125°21 |125°67 |128°47 |130°16 |124°39 |120°55 |130°16 |136°16 |126°45 126
|
156°98 |216°54 |180°04 |189°73 |184°34 }185°30 }205°91 |211 — | 157-38 |162°77 |185 — |182°3
44 |811°8 |221-46 /210°17 |198°88 |210°17 }198°88 |192"23
' 144a* |258°56 |257°66 |254°46 |252°12 |256°22 |253-02
The values given in the last column have been calculated according
Biel (ono 3
~ 9+2
the method of the least squares. It is true that there are considerable
differences between the observations of the same series, but there was
no reason to choose those which agreed the best with each other, and
to attribute the differences to an error of observation.
10.
I have read in an extract from the memoir of the Abbé dal Negro
inserted in the “Annali delle Sc., 1813 [1833?], Marzo e Aprile,
to the formula A , the constants of which were found by
__ * The first series of experiments, which were made with the pair of plates of
144 square inches, presented such different values that no use could be made
them. I have sought in vain for the cause of these anomalies. After a fort-
ight the experiments were repeated, and gave values but little different. ‘This
is proved by the Table.
Vor. l1—Parr IV. Qn
.516 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
105—120,” that this author established a remarkable law, viz. that the
magnetizing power is in the direct ratio of the perimeter of the electro-
motor, and that the surface has scarcely any effect in increasing this
power. I did not delay making some experiments in order to confirm
this law, which appeared to me of great importance for the ceconomical
effects of the magnetic machine. Two plates of zine and copper, 36
inches long and 7 inches wide, were coiled into a helix, and separated
from each other to a distance of one fourth of an inch by small pieces
of wood in the manner of the calorimotor; the whole was plunged
into water acidulated with ten per cent. of sulphuric acid. The mean
weight which the bar was capable of supporting, whilst this pair of
252 square inches was employed, was taken from five experiments and
amounted to 29712 lbs.
From the same piece of copper and zine I also cut two plates,
96 inches long and half an inch wide. These plates were coiled in the
same manner and separated to an equal distance. The mean value of
the magnetic force, when this electromotor of 48 square inches was
employed, was also drawn from five observations and amounted to
133°79 lbs. By employing a liquid much more acidulated the weight
might be increased to 180°49 lbs.
These two experiments cannot be classed with the others, as the cir-
cumstances attending them differed. But the perimeter of the first
electromotive helix being 86 inches long, and that of the second 193
inches, it does not appear that the law of M. dal Negro is confirmed
by these two experiments. There are many empirical formulz in
physics incapable of being carried out to the extremes, but they ought at
least to be sufficiently general not to fail on the slightest attempt to ex-
tend their limits. Besides, I have taken the pains to calculate the ex-
periments of M. dal Negro from the formula of M. Ohm. The fourth
column of the following table indicates the results according to the
41°55 x
leer a’ in which x represents the surface
A+ a
ascertained formula A =
of the pair of plates.
Force
Surface. Perimeter.
observed. calculated.
6 square inches 14 inches 13°85 kilogr. 12:22 kilogr.
iS - 16 18-2 - 18°89 -
18 18 22°8 23°08
24 20 24°6 25°97
22 25°8 28°07
24 29°6 29°68
26 30°3 30°94
28 32°8 32
50 33 32°8
32 35°6 33°51
3,
5
5
TO THE MOVEMENT OF MACHINES. 517
The second column of the preceding table, which contains the perime-
ter of the plates, represents at the same time the forces according to the
law of M. dal Negro. That distinguished experimentalist did not make
these experiments to verify the theory of M. Ohm; but the beautiful
agreement of his observations with that theory sufficiently proves that
they were made with great accuracy.
hg
Since 1831 Mr. Faraday has published from time to time experi-
ments made with a view to investigate the nature of electricity and of
its various effects. These experiments, both from their extent, the cer-
tainty and ingenious sagacity which they manifest, and the abundant
results to which they have led, deserve to be ranked with the most emi-
nent labours which have ever been made in physics. By a happy
chance, which I cannot over-appreciate, these labours coincide with
the efforts which I have made to render available the mechanical action
of magnetism.
In observing a voltaic pair of plates of copper, silver or platina,
and of common zine plunged into acidulated water, we notice a
great development of hydrogen gas. If the circuit be not closed this
gas will be developed only on the surface of the zinc; but if the circuit
be completed, there will be also a development of gas on the surface of
the copper, or in general on the negative plate. This last quantity of
gas is incomparably less than the first, and yet it is from this alone that
the magnetic power of the connecting wire proceeds. The gas, abun-
dantly disengaged on the surface of the zinc, does not contribute any-
thing to this effect. On taking a plate of amalgamated zine, instead of
common zine, or some amalgam of zinc, there will be no develop-
ment of gas except when the circuit is closed; in breaking it this de-
velopment ceases, the zine in this combination not being attacked by
the acid, or not being able of itself to decompose the water. It is not
easy to explain this extraordinary fact. In such a pair of plates all the
_ hydrogen gas, or its equivalent of zinc, serves to produce an electric
_ current, whose magnetic force, calorifying power, and chemical action,
are in a direct ratio to the quantity of disengaged gas or of oxidized
zinc; and these different effects may equally serve to measure the quan-
tity of electricity passing through the connecting wire, or even through
the apparatus. The definite action of electricity, with regard to the
chemical action, to decompose bodies, is incontestably proved by the
numerous and ingenious experiments of Mr. Faraday. It will not be
long before he will prove the law with regard to other effects; but the
conviction of genius gives the right to anticipate experiment, and to
announce great laws.
Amalgamated zinc is much more positive than common zine, and its
effects are much more decided. Moreover a voltaic pair of plates of
2n 2
518 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
this kind possesses a remarkable constancy, provided there are no
secondary effects arising from the precipitation of the negative metal
upon the positive plate. It may happen that some particle of the zine
may not be well amalgamated; in that case a direct action of the acid
upon the zine takes place, there is a development of hydrogen in that
place, the negative metal accidentally dissolved in this liquid will be
reduced in it by the gas, and there will be a partial pile, which will
affect the principal action. These partial effects will be propagated by
degrees over the whole surface, the positive state of which will then
rapidly decrease. This will only take place when the negative metal
is soluble in the acid.
12.
Ihave made many experiments on this subject. A thin plate of zine of
seven inches square, and weighing 848 gr., was amalgamated, in order
to form a voltaic pair with a plate of copper of the same size. The
liquid was sulphuric acid, of a specific gravity of 1105. There was
no development of gas on the surface of the zinc: the bubbles of air
which formed there by degrees rose so slowly, that they might with
propriety have been disregarded, even if there had not been reason to
believe that they were for the most part the atmospheric air contained
in the water. After five hours of action the plate was again weighed,
and had lost only 112 gr.; during this time the pair of plates had been
twice withdrawn from the acid, and dried for five or six minutes near
a stove.
The following is the table of the deviations of the needle which de-
note the decrease of the energy of the current.
err cm
Time. Deviation. Time. Deviation.
sh 12! 61° 10 60°
8b 29! Beh, 105 30! 58°
8 30! 58° 1 oie
8) 49! 574° the pile}was dried
8) 56! 564° bb 5! 61°
gh 10! 5540 115 30’ | 60°
the pile|was dried 1g 593°
9» 16! 62° 12 30! 58°
95 30’ Ge ye 57°
The following day the experiments were repeated with the same
pair of plates. The decrease of the deviation was not so rapid as be-
fore, and the original energy always restorable by drying the plates ;
once it even increased to 65°. At 10" 50! in the evening the devia-
tion was still at 55°. The action must have continued through the
night, but the next morning the plate was found broken in pieces. Amal-
TO THE MOVEMENT OF MACHINES. 519
zamated zinc is too fragile to be employed in too thin plates. In order
to compare the effects, a plate of common zine of the same size was
combined with a plate of copper and plunged into the same acid. The
deviation was at first 554°, after 43! it lowered to 12°, and on drying
the pair of plates 13° was the highest to which it could be restored. On
being subjected to the action of the acid for 134, the plate had disap-
peared, and its insoluble parts only remained.
I have also made experiments upon a liquid amalgam of zinc poured
into a porcelain basin covering a surface of 48 square inches; instead
of a plate I employed a copper wire of 1} lin. diameter, coiled into a
flat spiral, in order to let the gas escape more easily. The effects of
this combination were very extraordinary ; for, without anything being
touched, the needle had during fifteen hours’ action only receded 113°
from 60°, and remained fixed at 494°. After breaking the circuit,
and exposing the spiral to the air for some time, the deviation was re-
stored to 59°. This experiment was the more striking as the multiplier
of the galvanometer consisted only of a single coil of copper wire 14
lin. in thickness; for it is known that the decrease of the needle is
much more feeble on employing avery long and slender wire.
A plate of gilt copper and an amalgam of zinc, composed of one atom
of zine and one of mercury (Zz. Hg.), a composition which is solid
enough to be used in plates, gave also very good effects, both as to the
constancy of the deviation and to its restoration.
In order to try some other compositions, which, according to Ritter,
are still more positive than the amalgam of zinc, I had some plates cast,
of an equal size, of lead, tin and zinc, of different alloys of these metals,
and of different amalgams. The alloys were composed of atom to atom*,
and moreover a plate of each composition was also amalgamated at its
surface. The direction of the deviation of the needle of the galvanome-
ter determined the place which each alloy ought to occupy. The liquid
in which the plates were plunged was sulphuric acid diluted with four
parts of water. I must remark, that the slightest change of the surface
frequently affects the place of the metals the electrical relation of which
_ does not differ much. It is chiefly in lead and its alloys that this phe-
nomenon is most strikingly exhibited. Lead freshly polished is very
positive in relation to lead exposed to the air for some minutes or steeped
in any acid. The following is the result of two series of experiments,
which I have made with the greatest care.
* In the alloys it is usual to combine the metals according to some relative
aie of weight. I united them by atoms, bearing in mind the general
_law of true chemical compositions.
520 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
Tin.
Alloy of lead with tin. (Pl. Sn.)
Lead.
Tin amalgamated.
Lead amalgamated.
Amalgam of tin. (Sn. Hg.)
Alloy of zine with tin. (Zn. Sn.)
Amalgam of lead. (Pl. Hg.)
Alloy of zine with tin and lead.
(Zn. Sn. Pl.)
Alloy of zine with lead. (Zn. Pl.)
Alloy of tin with lead amalgamated.
Zine.
Alloy of zine with tin amalgamated.
Alloy of zine with lead amalga-
mated.
Alloy of zine, tin, and lead amalga-
mated.
Zine amalgamated.
Amalgam of zine. (Zn. Hg.)
Amalgam of an alloy of tin and
lead. (Zn. Pl. Hg.)
Amalgam of an alloy of tin and
zinc. (Sn. Zn. Hy.)
Amalgam of an alloy of tin, zinc,
and lead. (Sn. Zn. Pl. Hg.)
Amalgam of an alloy of zine and
lead. (Zn. Pl. Hg.)
a.
Series I.
Tin.
Lead.
Tin amalgamated. u
Amalgam of an alloy of tin with
lead.
Alloy of lead with tin.
Lead amalgamated.
Amalgam of tin.
Alloy of zine with tin.
Amalgam of lead.
Tin with lead amalgamated.
Alloy of zine, tin, and lead.
Alloy of zine and lead.
Zine.
Zine amalgamated.
Alloy of ‘zinc, tin, and lead amal-
gamated.
Alloy of zine and lead amalga-
mated.
Amalgam of zine.
Amalgam of an alloy of tin and zine.
Amalgam of an alloy of tin, zine,
and lead.
Amalgam of an alloy of zine with
lead.
Alloy of zine with tin amalga-
mated.
a.
Series I.
We see by the above that the alloys, and principally the amalgams,
are always positive with relation to the simple metals.
Most of the
amalgams, excepting those of tin and lead, may be used in plates. As
to the chemical action upon these various compositions, it did not take
place in the amalgamated zinc and the amalgam of zinc, any more than
in any of the alloys and amalgams of tin and lead; but in all the other
compositicns of zine the disengagement of gas was very brisk. In the first
series, the amalgam of an alloy of tin and lead occupies a very positive
place, but the hope of profiting by this is negatived by the second series.
In employing the amalgamated plates or the amalgams of zinc, there
occur various circumstances the cause of which I have not yet been able
to discover. During the voltaic action particles of amalgam are often
detached in the form of flakes, which float on the liquid, and are depo-—
sited on the copper or on the negative plates, so that these become by
TO THE MOVEMENT OF MACHINES. 521
degrees amalgamated. By this the action is considerably weakened,
or ceases altogether; for it is very remarkable that copper, silver, or
platina, amalgamated on their surface, have scarcely any, or at most an
extremely weak power of keeping up an electric current with any other
metal. I have often remarked that the first deviation of the needle was
very strong, and that at length it returned quickly to its first position
of equilibrium, without exhibiting any deviation, whilst the voltaic cir-
euit, composed of zinc and amalgamated copper, remained always
closed. It appears to me also remarkable that a wire of copper, pla-
tina, or iron can be much more easily amalgamated under the influence
of sulphuric acid by mercury containing other metals than by mercury
entirely pure. It is desirable that this point should attract the atten-
tion of scientific men to make similar experiments with more attention.
Pure zinc has nearly the same qualities as amalgamated zinc or the
amalgam of zine, viz. of being very little acted upon by sulphuric acid.
It is only subjected to chemical action when it enters into a voltaic
combination. I refer, on this subject, to the important memoir of
M. Aug. de la Rive, inserted in the Bibliotheque Universelle, vol. xliii.
1830. I have not yet been able to procure any pure zinc to repeat these
experiments and to employ it in the magnetic apparatus. In zinc foun-
dries pure zinc may easily be obtained in great quantity by re-distilling
it until it is purified of the cadmium and other extraneous metals.
Its cost would not be much increased, but hitherto there has not been
sufficient inducement to employ pure zine to risk the expense of the
repeated distillation. M.Fengler, manufacturing chemist at Myslowitz
in Upper Silesia, has constructed the necessary apparatus for preparing
pure zinc in large quantities; he could supply it for nine ecus the
quintal, provided a quantity of three quintals were ordered, but unfor-
tunately his foundry has since been burnt down. His process consists
in interrupting the distillation when all the cadmium is driven off, in
then changing the recipient and again interrupting the process as soon
as he suspects that the other foreign metals are volatilized or mecha-
nically drawn away. He repeats these operations as frequently as he
_ thinks necessary. The zinc thus prepared should not be re-cast in iron
crucibles.
. 13.
The rapid decrease of the voltaic effects in the ordinary voltaic piles
opposes a great obstacle to the application of electro-magnetism. It
may be overcome, partly at least, by an assiduous study of these effects.
The motion of my magnetic apparatus was always very rapid at the
commencement, but its velocity soon diminished, and ceased entirely
after a lapse of time which never exceeded an hour. By employing
amalgamated plates of zine I have succeeded at three different times
in making the apparatus work successively during 20, 22, and 24 hours
_ without making any change whatever in the pile. The experiments
522 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
were always interrupted by some accident, and I think that the action
would otherwise have lasted still longer. The disengagement of gas
was very inconsiderable, and took place only at the surface of the nega-
tive plate. The velocity was always at first from 120 to 122 revolutions
in a minute, and decreased about half an hour after to 62 revolutions;
a circumstance which is attributable to the commutator, which had not
then the present construction. During the rest of the time the motion
of the apparatus was remarkably uniform, making from 58 to 62 revo-
lutions in a minute. I must however confess that I have obtained so
extraordinary an effect only three times. There were always external
circumstances, dependent upon the form of the voltaic apparatus, which
counteracted the effect. I might be able to master most of these cir-
cumstances by constructing a new apparatus, the manipulation of which
will be more convenient and the effect more certain.
14.
We have expressed by A = = the magnetic force of each section of
“a wire traversed by an electric current. This force is measured by
the deviation of the needle or by the magnetizing power of the con-
necting wire. By adopting ‘the law of Faraday we may equally mea-
sure this current by the disengagement of the gas, which represents at
the same time the cost of maintaining in action a voltaic apparatus. If
D be the quantity disengaged, we shall have D so From this it
follows that recurring to the formule of article 8, the ceconomical
effect may be expressed by the magnetic power of the whole extent of
the connecting wire, divided by the development of the gas. This effect
is inno respect changed either by the enlargement of the surface, or by
the employment of various branches wound spirally around different bars
of the same dimension. But by multiplying the helices, and uniting
them to form a continuous wire, the ceconomical effect may be increased
as much as we please. For the disengagement of the gas, in employ-
ing 2 helices or 2 units of length, will be expressed by D = ———_-;
mr+r
but we may put in action the magnetizing power of the whole ex-
tent of the conducting wire, and we shall have for the total force
F= cease ; or sigs n. When the magnetic bars are intended to
mr+r D
produce a mechanical motion, the increase of the ceconomical effect
will reach its limit ; since by multiplying the number of the bars, the
weight of the apparatus and the friction of the pivots in the sockets
will be at the same time increased, so that that effect can only be ex-
aie
pressed by. Z act eas ia The maximum of the ceeconomical
D="
TO THE MOVEMENT OF MACHINES. 523
effect obtainable will depend on the value of f or of the friction. By
differentiating the second member with respect to ”, we shall have for
E—fr'
Dfrirt.
_ The bar which was used in the experiments of article 9 weighed
144 lbs. Being adapted to any moveable apparatus, the friction it oc-
casions would amount at most to $lb. It has been found by experi-
ments: H = 283°6, r! = 20, r=1, and f= 4, thus x = 273°6; that
__ is to say, there would be the greatest possible advantage in employing
_ about 273 bars wound round with helices of the same size. This
number varies with the size of the plates: for a surface m, we have
mE — fr'
this maximum 7 =
In short the magnetic power available for practical
SET si) ste 2 (deafrl)e
eee a = (Bar)
15.
In employing a voltaic battery, the ceconomical effect will be dimi-
nished, unless at the same time the helices united in the same wire be
multiplied ; for Mr. Faraday has proved by the experiments reported in
the articles 990, &c. of the Eighth Series of his Researches, that the same
quantity of electricity passes through a voltaic battery of any number
_ of pairs of plates which traverses a single pair of the same size. The
quantity of gas disengaged at the surface of each plate of the battery
is the same as at the surface of a single pair; this at first sight appears
astonishing, and seems to contradict numerous experiments which have
been made upon the pile; for every one knows that the quantity of
gas disengaged by the decomposing apparatus, and at the same time the
deviation of the needle, increase up to a certain point, by multiplying
the number of plates.
In considering the formula F = rep where n' represents thenum-
ber of pairs of plates, 7’ the resistance of each pair, and r that of the
connecting wire, or of the body which we wish to decompose, we must
suppose that in the experiments of Mr. Faraday (990.) the connecting
wire of the battery and of the single pair of plates were so short that
its resistance r might be entirely neglected in relation to x'r’. We
should not have obtained this striking result if we had employed a con-
necting wire’of any consid@rable length, and still less if we had closed
the circuits of the pair of plates and of the battery by any decomposing
apparatus. Mr. Faraday has established a very exact distinction be-
tween the quantity and intensity of electricity set in motion. The first
may be measured in different ways; but it will be difficult to find
an exact measure for its intensity, nevertheless this would be very
necessary for completing the theory. In admitting the important law
524 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
of equivalents in galvanic decompositions, it appears that we ought to
multiply these equivalents by the number of pairs of plates necessary to
effect the decomposition. This would perhaps be the true measure, for
after all it is necessary to consume a great number of atoms of zine, in
order to decompose a single atom of any other substance less decompo-
sable. In what relates to the difference between quantity and intensity,
ealoric offers analogies; and in judging of a quantity of gas, we
ought always to know its volume and its density. I must here quote
another observation of Mr. Faraday, which is found in the Seventh
Series, art. 853. He is speaking of a current which is, he says, “ pow-
erful enough to retain a platina wire ,3; of an inch in thickness red
hot in the air during the whole time” (33 minutes); and he adds in a
note: “TI have not stated the length of wire used, because I find by ex-
periment, as would be expected in theory, that it is indifferent. The
same quantity of electricity which, passed in a given time, can heat an
inch of platina wire of a certain diameter red hot, can also heat a hun-
dred, a thousand, or any length of the same wire to the same degree,
provided the cooling circumstances are the same for every part in both
eases,” &e. This is quite correct, but we may add that it would be ne-
cessary to multiply the number of pairs of plates in the same proportion
with the length of the wire to obtain a current of the same quantity.
In short in order to heat a wire of 1000 inches to the same degree
to which a wire of a single inch would be heated by a single pair of
plates, it is necessary to disengage 1000 quantities of gas, proceeding from
the same number of pairs. I have thought it right not to suppress this
remark, considering that in the practical employment of the voltaic
pile ceconomy is requisite.
16.
The following is the table of experiments which I have made upon the
deviation of the needle with relation to the quantity of gas developed
at the surface of the negative plate of a voltaic pair of plates of silver and
amalgamated zine. The specific gravity of the sulphuric acid was 1-25.
a
perigee, et the| gage of cab a Pewston oF the gngenent of table inched
4.29 4.5! 50" 296° 30! 189"
41° 30! 57!-5 24° 59! Q17"'
39° 30! 64!"5 23° 52! 931"
34° 45! 89! 93° 7! 24.6!'
32° 29! 108'"*5 21° 30! 290!"
29° 144! 20° 15! 319!
27° 30! 167" 20° 7! 330"
97° 15! 166!"
The bubbles of air rising regularly enough to serve as a measure, I
TO THE MOVEMENT OF MACHINES. 525
i have reckoned, in another series of experiments, the time which elapsed
in developing 10 bubbles of air. The following is the table:
Time elapsed in the disen- Time elapsed in the disen-
pviation of the gagement 10 bubbles o£ Deviation of the gagement ie pobbles of
99!l-5 18° 29! 80"
32° 30! 25!" 15° 15! 101"
gi° 272"5 14° 30! 124!"
922° 56" 14° 20! 126"
B1e. 37" ae 14° 10! 129"
59" 13° 20! 147!
or ie i 160"
_ It is necessary to remark, that there was also a very feeble develop-
ment of gas even at the surface of the zinc, which was taken into
account. But the quantity of gas measured was, I believe, less than
the quantity of gas developed ; for there was a secondary action, which
was manifested by the blackness of the plate of silver, and which we
must attribute to a metallic reduction of the oxides dissolved in the
acid. As it is very difficult to translate into forces the deviation of
the needle*, these tables will not tend to confirm the law of Mr. Fa-
raday: they only show that the deviation of the needle follows the
same course as the development of the gas. I shall repeat the expe-
riments, but reversing the process; that is to say, the development of
gas will be taken for the most exact measure of the force of the
eurrent, and the value of the degrees of the galvanometer will be
deduced from it, either immediately, or by some formula of interpo-
lation of convenient application. The experiments cited are not suf-
ficiently rigorous to form the elements of calculation.
17.
To return to the magnetic machine. We had succeeded in obtaining
an inversion of the direction of the current, both instantaneous and ex-
act, by the commutator described above in article7, the effect of which is
not at all affected by the quickness of rotation. We had even succeeded
in obtaining, at least for some time, a tolerably constant voltaic apparatus.
Tn short, the means have been discovered of reducing the expense of
‘maintenance to a minimum, by preventing the direct action of the acid
“upon the zinc, an action which cannot be turned to any use, and which,
as is known, greatly surpasses that which serves to produce the
yoltaic current. Thus the most important difficulties in the practical
application of electro-magnetism being overcome, it appeared to me
_ time to examine more closely the nature of the forces which I desired
to put in use, and principally to seek for the cause which limits a
* Becquerel’s Treatise on Electricity and Magnetism, vol. ii. p. 20.
526 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
speed which we had reason to suppose must be infinitely accelerated.
This speed had never surpassed 120—130 revolutions in a minute, on
employing a pile of four pairs of plates two feet square. We must not
lightly abandon conclusions founded on the nature of things, and those
to which I refer are drawn solely from the integral f * Mds, expressing
the magnetic attraction and supposed to be independent of the speed.
Besides, it rests upon the legitimate supposition that the electro-mag-
netic excitation of the soft iron operates instantaneously. If this were
not the case, my apparatus would have shown that magnetism and
electricity ought to be attributed to the motion of material parti-
cles, or to oscillations much more perceptible than are those of the pro-
pagation of sound. In short no one can deny that it is the nature of.
a force not to require time to act, and that, if its different effects were
not instantly perceptible, it would then be some molecular motion,
under the influence of mechanical laws, which takes place.
18.
At the end of my first note I said, that in using thermo-electric piles
for the movement of machines, there was reason to fear the magneto-
electric currents developed by magnetism in motion. The reaction
which thence arises would be almost entirely destroyed in the hydro-
electric pile, the liquid conductors offering too much resistance to the
passage of these currents. These considerations were founded upon
detached experiments. On employing a thermo-electric pile, the de-
viation of the needle was affected by a magnet which had been placed
in a helix forming part of the circuit; this was not the case with a
voltaic pair of plates of small dimension. The deviation of the gal-
vanometer, extremely sensitive as it is, was not altered by it. This
did not surprise me, since the conducting power of liquids is much
below that of metals; but in making experiments on the magnetic
force of a bar of soft iron, I have sometimes found considerable dif-
ferences for which I could not account. I was curious to know if
these differences proceeded from the weakening of the electric current
produced by a pair of plates with a surface of half a square foot, or
from the nature of the iron. I therefore inserted in the circuit a gal-
vanometer at some little distance, that it might not be affected imme-
diately by the magnetism of the bar. I was much astonished to see
the needle recede upon my applying the armature, and advance as soon
as it was taken off; for it was the first time that I had recognised the
double office of the connecting wire, viz. that of conducting the voltaic
current, and of representing at the same time a common wire sub-
jected to the influence of a magnet in motion. The helix producing a
magnet by the voltaic current is at the same time a magneto-electric
TO THE MOVEMENT OF MACHINES. 527
helix in which a magnet is inserted. This is the explanation of the
problem of the uniform rapidity of the magnetic machine ; for, being put
‘in motion by the magnetizing power of a voltaic current, it represents
_ simultaneously an apparatus composed of magnets in motion, and ca-
-pable of producing a magneto-electric current, in a direction contrary
_ tothe voltaic current. The first is closed by the pile itself, which, being
composed of a single pair only, does not offer too great a resistance to
_ its passage.
In the connecting wire, formed by the union of the sixteen helices of
the apparatus, I interposed a galvanometer; and then, by closing the
- circuit and preventing the motion of the machine, I observed the devia-
tion of the needle: it amounted to nearly 60°. As soon as the motion
of the apparatus commenced the needle began to recede, and continued
to do so more and more as the speed became more accelerated. The
motion having become uniform, at the rate of 60 revolutions in a mi-
nute, the needle became stationary at a deviation of about 47°. The
needle always advanced when the motion was stopped or retarded ; it
receded, on the contrary, when it was mechanically accelerated. It ap-
pears that the deviation of the needle of 47° corresponds with the state
of equilibrium; for the motion having of itself ceased, the needle did
not quit this position. Thus in the different experiments, whether the
first deviation of the needle exceeded 60°, or was less, it always became
- fixed at about 47°. The voltaic current having been weakened by the
interposition of different branches, until the first deviation amounted
only to 47°, the magnetism was not sufficiently strong to produce the
“movement of the apparatus. Repeated experiments will be necessary
to investigate these interesting phenomena.
19.
I imagined that it would be useful to open two passages or two
separate branches to the magneto-electric current ; one of which should
be the pile, and the other a second connecting metallic wire, so long and
so thin as not too much to affect the quantity of electricity passing
through the principal connecting wire. (Art. 8., No.6.) There was
‘reason to suppose that the counter-current would rather follow the
‘metallic wire than the liquid of the pile: but it was not so. Du-
ng the motion of the apparatus, the needle of the galvanometer
being fixed at 47°, and the second circuit having been suddenly esta-
plished, the needle was not much affected by it. It advanced, it is
e, but only 1°5. Neither did the speed of the apparatus sensibly
ange. On reducing the length of the second wire it was nearly the
The passage of the counter-current across the metallic wire
was proved, at least in part, by the interposition of a second galvanome-
ter. During the accelerated movement the needle of this latter ad-
528 PROF. JACOBI ON THE APPLICATION OF ELECTRQ-MAGNETISM }
vanced in proportion as the needle of the former receded. This might
have been expected, provided the counter-current in the secondary
branch has the same direction as the voltaic current: it is quite con-
formable to the remark which M. Nobili has added to the end of his
first memoir, upon the theory of the electro-dynamic induction. (Anto-
logia di Firenze, 1832, No. 42.) The ends of the connecting wire sur-
rounding the bars must be considered as the poles of an electro-motive
apparatus: moreover the magnetizing power of this counter-current
has been proved by making it pass through a helix bent round a ba
of soft iron.
20.
In short all tended to prove that the greatest part of the counter-
current might be rendered available by employing two apparatus of
the same kind, the connecting wires of which, wound spirally round
bars of each system, should terminate at the same pile. The counter-
current produced by the movement of one apparatus would serve to
strengthen the magnetism of the other, and vice versd: the counter-
currents would counterbalance each other to destroy their effects. The
experiment could be made on a small scale with the bar above described,
the branches of which were encircled with separate helices. Fig. 4.
shows the form of the experiment. The two helices were connected by
the dotted wire ¢ 6 plunged into the little cups filled with mercury e, b.
They thus formed a single connecting wire, the other ends of whick
a, d were united with a pile C Z.. With my hands dipped in acidulated
water I took hold of the connecting wire at the place e, f, and I broke »
the circuit at the place g orf. I felt a violent shock. In other respects
the experiment was the same as the beautiful one of Mr. Jenkins
related by Mr. Faraday. By interposing the multiplying wire of a
galvanometer ‘m in the circuit, the needle deviated to 48° by the vol-
taic current. Then applying the armature, it receded from 48° to 40°.
The deviation on removing the armature was unobservable, the latter
being too firmly attached. Now the helices were connected with the pile
in two branches separated by means of the wiresa 6 and ed. |The wire
eb was withdrawn. I expected, on breaking the circuit, to find that the
magneto-electric current excited in the helix @ ¢ would be conducted |
quite entire by the helix bd, and vice versé; but I was mistaken: the ©
shock was not much less: the needle nevertheless receded. I was
struck by this experiment, but after all I believe I may regard this
magneto-electric arrangement as an unclosed voltaic pile, consisting of
two elements united in such a manner as to form only a single pair of
plates, as is represented in fig. 5.. The currents whose direction is op+
posed with relation to the wires a6, ed, unite in traversing a connect=
ing wire placed in contact with the pointse f. If the galvanic excita>
TO THE MOVEMENT OF MACHINES. 529
tion is not in perfect equilibrium, being stronger on one side than on
the other, there will be a deviation of the needle proportional to the
_ difference of the currents which traverse the wires a6, ed. This
agrees with the experiments which Mr. Faraday has related at the be-
_ ginning of his Eighth Series, on the subject of decompositions produced
by asingle pair of voltaic plates. In short what is termed tension is
gi the effect of forces equal and contrary in direction. In mechanics
such forces destroy themselves, their sum being zero; but in physics it
is different.
With regard to the direction of the magneto-electric current which
occasions the shock, it is the same as that of the voltaic current. This
_ was proved by a galvanometer, the multiplying wire of which ter-
_ minated at the points e, f. There was a deviation on a part of the
voltaic current traversing the secondary branch e, f. On applying the
armature, the needle of this galvanometer advanced, at the same time
_ that the needle m receded. The contrary effect might be observed on
_ removing the armature by the blows of a hammer.
ee ae
21.
The following are some further experiments relative to this subject.
_ The extremities of the bar were surrounded with a thin plate of copper,
_ fig. 6, in the circuit of which was placed a galvanometer. On applying
_ the armature, the needle was unaffected by it ; but after having wound
the ends of the multiplying wire around the points e, f, and the cir-
A cuit being thus closed, a considerable deviation took place.
_ An analogous result is shown in the following experiment. On
plunging two thin plates of copper, held firmly in the hands, in the cups
a, b, or e, d, of the bar, fig. 4, there was no shock when the circuit was
broken by the separation of the wires ab or ed; for the human body
_ formed part of a circuit, in which equal excitations took place on two
opposite sides. The thin plates being plunged into the cups ¢ and 4, a
yiolent action took place at the instant of disjunction.
I formed a thermo-electric circuit of bismuth and antimony, in
_ which was interposed a galvanometer: after having heated the two
‘solderings to the same degree, there was no deviation of the needle; but
the multiplying wire having been placed so as to form an interme-
branch, and the solderings being on opposite sides, there was a
_ considerable deviation. This would not have taken place if the circuit
4 of bismuth and antimony had been in its normal state, for then it
ould have had to conduct the greatest part of the thermo-electric
urrent, provided that the multiplying wire was sufficiently long and
to intercept only an extremely feeble part of it.
_ Itseems to me that there are circumstances which cause metals to
lose their conducting power, and that these same circumstances on the
530 PROF. JACOBI ON THE APPLICATION OF ELECTRO-MAGNETISM
contrary increase that of liquids. Is this the state of bodies which
Mr. Faraday calls electro-tonic ?
22.
In the supplement of No. 105. of the Institute for May 183, 1835,
there is a notice of a memoir by Mr. Faraday the publication of which
we are looking for. The experiment cited at the end of this notice ap-
peared to me so striking and important in connection with the subject
of the present memoir that I did not delay repeating it. Two copper
wires, 400 feet long and ? lin. in diameter, carefully covered with silk
ribbon, were coiled together in a helix round a hollow cylinder of
wood, 14 inch in diameter. The ends of these two wires were united
in asingle one. The effect of this combination was beyond all my
expectations ; for by employing a voltaic pair of silver and zinc plates,
which had only a surface of half a square inch, I obtained at the mo-
ment of disjunction a brilliant spark, and a violent shock which could
scarcely be borne. The same effects took place when the pair of
plates were reduced to a wire of platina and zinc. After having
placed a cylinder of soft iron in the hollow of the wooden cylinder, the
action was still more considerable. These effects were not much in-
creased by the enlargement of the surface of the pair. A conducting
wire of 400 feet having been employed alone, the spark and the shock
were much more feeble ; but on uniting in a circuit the two ends of the
second wire of 400 feet, there was neither spark nor shock. This is
perfectly conformable with Mr. Faraday’s experiment.
Upon this I made the following experiment: In the hollow of the
wooden cylinder I placed a cylinder of soft iron, 13 inch in diameter,
forming the armature of the bar of soft iron. We will call the corre-
sponding extremities of the bar and the armature A,a; B,b. The two
wires of 400 feet of the helix coiled round the armature were united in
one of 800 feet, the ends of which were conducted by a multiplier to
the poles of a voltaic pair of plates about + foot square. The helix
surrounding the bar terminated at a pile of a foot square, by means of
a commutator a@ bascule. The deviation was 16°. The current which
magnetized the horse-shoe bar being directed so as to produce in A the
same magnetism as in a (A, a,, B, b,,), the needle advanced to 30°,
and on reversing the current so as to produce contrary magnetisms
(A, a,, B,, 6,) the needle receded from 16° to 10°, returning after a few
oscillations to its first position at 16°. By employing a single wire of
400 feet, the other wire not forming a circuit, the deviation of the needle
was 21°. By the arrangement A, a,,-B, 6, the needle advanced to
334°; it receded on the contrary to 13° when the magnetism of the
bar and of the armature attracted one another, (A, ay B. 6). After
having united in a circuit the second wire of 400 feet, the deviation
of the needle having been the same as before, that is 21°, the needle
TO THE MOTION OF MACHINES. 531
advanced and receded by the arrangements above mentioned respec-
tively to 30° and 40°. We see that in this case the needle is rather
less affected than in the case of the disjunction of the second wire; but
I expected, as a necessary consequence, that the needle would not be
at all affected, for I had received no shock nor spark in the analo-
_ gous experiment. I confess that at present I am unable to enter into
an explanation of the striking difference which subsists between the
current of reaction and the magneto-electric current.
f 23.
With regard to the magnetic machine, it will be of great importance
to weaken the effect of the counter-current, without at the same time
weakening the magnetism of the bars. It is the alternate combination
of the pairs of plates or the voltaic pile which permits us to increase
the speed of rotation at will. We know that the magnetic power of
the current is not sensibly augmented by increasing the number of the
pairs of plates, but the counter-current is considerably weakened by
it, being forced to pass through a great many layers of liquid. In
fact, on using twelve voltaic pairs, each half a square foot, instead
of four copper troughs, each with a surface of two square feet,
which I had hitherto used, the speed of rotation rose to at least 250
—300 revolutions in a minute, a number which IJ was able only to
estimate, having been unable to count them. The acid which I em-
ployed was extremely weak, and had served for many previous experi-
ments. The development of gas was imperceptible either by sight or
smell. Having immersed two thick copper wires in the cups p and 0,
and having taken hold of them with my hands dipped in salt water, I
received during the motion of the apparatus violent shocks, and felt
an extreme pricking sensation in the upper part of my body. The
mechanical effect of the apparatus corresponding to the speed of 250
to 300 revolutions in a minute has been valued at half the force of a
man. I shall at a future time apply to it an exact dynamometric
apparatus.
I have not been able to make further experiments on this subject,
and I am obliged to interrupt my investigations for a time; but from
what precedes, I may perhaps be justified in maintaining, that the su-
periority of this new motor, with regard to the absence of danger, the
_ simplicity of the application, and the expense of the materials necessary
__ to keep it in action, is placed beyond doubt.
*
Vor. I.—Parrt IV. 20
532 PROF. BOTTO ON THE APPLICATION OF
Note onthe Application of Electro-Magnetism asa Mechanical
Power; by 1. D. Borro, Professor of Natural Philosophy
in the Royal University of Twrin.
From the Bibliothéque Universelle, &c., vol. lvi. Geneva, (1834, vol. 1. p. 312.
July.)
Tue remarkable energy with which the magnetic action is developed
in soft iron by induction from electricity in motion is well known.
The possibility of the application of this new power to machines pos-
sessing some interest, I have decided on publishing the results which I
have obtained relating to this subject*.
The mechanism which I have employed consists first of a lever put
in motion (in the manner of a metronome) by the alternating action of
two fixed electro-magnetic cylinders exerted on a third moveable cy-
linder connected with the lower arm of the lever, the upper arm of
which maintains a metallic wheel, serving in the ordinary way as a re-
gulator, in a continuous gyratory motion.
The apparatus was so disposed, that, the axes of the three cylinders
being perfectly equal and situated in the same vertical plane perpen-
dicular to the axis of motion, the oscillating cylinder placed itself
by one of its extremities alternately in contact with and in the di-
rection of, each of the two other cylinders, stationed at the limits of its
excursions; and each time, at that very instant, the direction of the mag-
netizing current in its spiral was changed, the remainder of the circuit
preserving the same direction, so as to produce poles of the same name
in the fixed cylinders, at the two extremities facing the moveable cy-
linder. The change of direction which has just been mentioned is
obtained by means of the known mechanism of the bascule, the com-
munications of which are interchanged by the motion of the machine
itself.
It is evident that from this arrangement the middle cylinder must
undergo corresponding alternations of attraction and repulsion, by
the effect of which the apparatus is set in motion, as it were by itself,
and maintains itself in action by the ceconomy of the magnetic
forces which animate it, and which are produced by the electric
currents.
I endeavoured to operate without the spiral of the middle cylinder,
and by causing the two fixed cylinders magnetized alternately to act
* I ought to state, that the hope of giving a greater extension to my obser-
vations, and also the necessity of absenting myself from Turin, have caused me
to defer the publication of the facts which I announce, although I should have
done so at the end of June. But I have been obliged to decide respecting it,
having seen in the last number of the Piedmontese Gazette, that M. Jacobi of
Kénigsberg has succeeded in obtaining a phenomenon of continuous motion
by the intervention only of the electro-magnetic power.
Pega +:
=.
ELECTRO-MAGNETISM AS A MECHANICAL POWER. 533
upon the latter. But an adhesion which continued after the ces-
sation of the magnetizing currents then contributed to diminish the
mechanical effect; whilst in the preceding arrangement the adhesion
not only ceased, but to a certain point changed to repulsion, with the
same rapidity with which the current, scarcely interrupted an instant by
the action of the bascule, precipitated itself (the communication being
inverted) into the middle spiral, in a direction contrary to its original one,
resuming its ordinary course in the two other spirals.
The motion of the lever and of the regulator, resulting from this
arrangement, is perfectly free; at first rather slow, it soon and by de-
grees acquires the maximum of velocity which the energy of the cur-
rents producing it allows of,—a velocity which is afterwards maintained
equal to the intensity of the current itself, and as long as the latter
remains in action*.
I shall say nothing at present respecting some observations which I
have on this occasion collected, upon the employment of different acid
and saline solutions, and of sea water.
It is not without especial interest that we contemplate these new
effects of a force developed in so singular a manner from the masses
of bodies; and it is difficult not to be carried away by flattering
anticipations respecting the ulterior applications which the acquisition
of this mysterious motive force suggestst.
The dimensions of the apparatus which has just been described are
small, and such as the, current produced by fifteen elements of nine
square inches can put in motion. The electro-dynamic cylinders, which
principally determine the limits of the mechanical effect, are one deci-
metre in length and a centimetre and a half in diameter; these are sur-
rounded by a wire coiled ina spiral, the length of which is 40 metres, and
half a millimetre in diameter. The lever is of wood; the upper and lower
arms are respectively 35 and 7 centimetres long; the amplitude of its
oscillations is 15°. Lastly, the regulator weighs 24 kilogrammes; and
the total weight of the mechanism is about 5 kilogrammes.
Considerations which readily presented themselves regarding the
relations between the maximum of the magneto-mechanic effect of the
_ apparatus and the dimensions of its different parts, have made me think
* There is a great analogy, both with regard to the general arrangement of
the apparatus and the nature of the motive power, between the electro-mag-
netic apparatus of M. Botto, and the electrical clock of M. Zamboni, described
in the Bibl. Univ., t. xlvii. p. 183. (1831). It will be recollected that Zamboni's
_ clock is put in motion by a pendulum, alternately attracted and repelled by the
_ poles of two of the dry piles which bear his name.—A. pe 1a Rive.
+ The Chey. Avogrado and the Chev. Bidone, who have successively seen
the apparatus in motion, did not dissemble the agreeable surprise which they
experienced, not merely from the novelty of the fact, but also from the reflec-
_ tions suggested by the general relations which may connect this simple result
with the progress of physics and mechanics,
202
534: DR. SCIHULTHESS ON THE APPLICATION OF
of substituting for the cylindrical form the ordinary U form of eleetro-
magnetic bars, and of augmenting within certain limits the number and
magnitude of these pieces, as well as the length of the spirals.
But not having arrived at the termination of my experiments on this
subject, I confine myself for the present to pointing out the above-men-
tioned facts, which I have thought proper to make known, not only as
interesting to science, but also because the study of the new class of
effects with which it is connected may be considered as fertile in useful
consequences in a physico-mechanical point of view*.
Part of a Lecture on Electro-Magnetism, delivered to the
Philosophical Society at Zurich, February the 18th, 1833 ;
by the late Dr. R. ScuutHEsst.
From a work intitled “ Ueber Electromagnetismus, nebst Angabe einer neuen
durch electromagnetische Kriifte bewegten Maschine: Drey Vorlesungen
von Dr. R. Schulthess. Zurich, 1835.”
Tuovcu electro-magnetism from its intrinsic importance certainly
is one of the most remarkable and interesting discoveries of modern
times, yet it would create a much higher interest, and gain in popula-
rity, if it could be rendered practically useful. For some time past I
had been occupied with the idea, whether the power of electro-magnets,
which without doubt might be infinitely increased, could be applied as
a motive power for machinery. It was known from Van Moll’s experi-
ments, that when the electric current which runs through the spiral of
an electro-magnet is rapidly reversed, the magnetic poles are likewise
instantly reversed ; and that a light iron keeper, which is supported from
its poles, falls off at that moment, but is immediately re-attracted. The
experiments of Henry and Ten Eyck showed that the power of such
electro-magnets might be very greatly augmented. The thought struck
me, that a considerably heavier keeper or armature might be suspended
from such an electro-magnet, and that by the attraction and repulsion
of the same a machine might be put in motion; at the same time the
action of the gyrotrope, and thereby the reversion of the poles, might
also be effected: and although the distance which the keeper would
recede from the magnet could be but very inconsiderable, still I thought
that the rapidity with which these motions would follow each other
might in great measure compensate for this defect. I was, however,
* The apparatus mentioned in this Note was constructed by M. Jast, me-
chanician of the Royal University of Turin, who executes with the same success
and the same accuracy ail other kinds of philosophical instruments.
+ The translation has been communicated by E. Solly, jun., Esq.
—
ELECTRO-MAGNETISM AS A MECHANICAL POWER. 535
filled with mistrust on observing that this thought, which appeared to
me so simple and natural, was not mentioned by any of the numerous
natural philosophers who occupy themselves so assiduously with electro-
magnetic experiments. I could not believe but that these notions must
have struck them; but I was forced to suppose that they had either seen
immediately the impracticability of them, or that, even if they had made
some experiments upon the subject, they had met with insurmountable
difficulties in its application. This long deterred me from making any
_ experiments; but in the lecture which I gave before this Society on the
‘ 10th of December 1832, I could not refrain, when speaking of the
powerful electro-magnets of Henry and Ten Eyck, from asking the
question, “whether such a considerable power as that which is ob-
tained by interrupting the electric current and then restoring it, could
not be applied with advantage to mechanical science.” After that lec-
ture I considered the subject again, and thought I had convinced myself
of its practicability ; but that even if it were so, the result could not be
very important, because the motion of the keeper must necessarily be
very small. Notwithstanding, I had a more powerful electro-magnet
made than any I had hitherto possessed, with which I intended to try
the experiment; and I regarded the expense the less, as this apparatus
appeared to me at the same time to be very appropriate for the evolu-
tion of the currents observed by Faraday ; for this purpose the arma-
ture also must be covered with copper wire, and then each time the
poles of the electro-magnet are reversed, a magneto-electric current
circulates through this wire. In the mean time I found another method
whereby the object I had in view might be effected, and which would
allow a greater degree of motion to the armature: I thought I could
effect this in the following manner. I placed on the table two cylin-
drical soft-iron horseshoes bound round with similar wires; so that when
the electrical current was transmitted through both wires, the similar
poles should lie opposite to each other: between these, and at a
small distance from either, I placed a cylinder of soft iron, serving fora
keeper; and then I expected to see the armature play to and fro between
_ the two electro-magnets when I sent the electric current first round the
one and then round the other electro-magnet. After several fruitless
rough experiments it succeeded at last, and I therefore then instructed
-aturner to make an apparatus, that I might be able to repeat, by means
of it, in a more easy and perfect manner, these yet very imperfect ex-
periments. I had proceeded so far, when, on the 4th of January, I
received the latest part of Baumgirtner’s Zeitschrift, published at
Vienna on the 17th of November 1832. I there observed a treatise,
intitled, “ Electro-magnetic Experiments of Salvatore Dal Negro, Pro-
fessor of Natural Philosophy in the Imperial University at Padua,”
_ (translated from the Italian). The author says in the Introduction :
“ Philosophers have already known for some time the power of elec-
536 . DR. SCHULTHESS ON THE APPLICATION OF
tricity to make soft iron magnetic. In the year 1825, Sturgeon mag-
netized cylindrical horseshoes of soft iron by means of copper wires
wound round them, connecting the ends of the wires with the plates of
an electromotor. Professor Van Moll of Utrecht saw this experiment
performed in the physical laboratory of the London University by Mr.
Watkins, and he obtained on repetition those remarkable results de-
scribed in Bibl. Univ., eah. 45. p.19. This new method of communi-
cating such great attractive power to iron created in me the desire of
repeating the experiments, and principally of taking into consideration
the application of this attractive power, which it appears may be
infinitely increased, to some useful purpose. I give these experiments
to the public in the conviction that a force so easily evolved and so very
powerful justifies repeated and varied experiments. In my experiments
the electromotors employed were without doubt smaller than any hi-
therto used, and these notwithstanding produced the same results: new
circumstances and new laws were observed and discovered respecting
the manner of increasing the magnetic power evolved by electromotors,
of producing .in them currents now similar, and now different, some-
times in the same, sometimes in opposite directions, and by the success
of these experiments of setting a lever in motion in different ways, and
thus finally enriching natural philosophy with a new motive power.”
It is easy to imagine with what avidity I read this notice, partly from
joy at seeing my idea, of the practical application of which I still had
many doubts, mentioned by another person, and partly somewhat vexed
that the priority of my invention, if it really was as useful as my fancy
made me think it, was snatched away from me. I therefore read with
intense eagerness this paper; but my expectations were in a great mea-
sure disappointed ; for it was only at the end that Dal Negro gave some
short, and to me not altogether comprehensible hints concerning his ex-
periments on the application of the power of electro-magnets to moving
machinery, after having described a considerable number of other expe-
riments, the principal object of which was to give with the least possible
means to a soft-iron horseshoe the greatest possible magnetic power. He
took seven different horseshoes, varying from 0°29 to 5 killogrammes*
in weight: the copper wire with which he enveloped them, in from 37
to 64 coils, had a diameter of 8°2 to 8°4 mill. ; the zine plates of the four
different electromotors had surfaces = 3, 2, 24, and 42 square feet
each; the dilute acid employed consisted of 74, of sulphuric acid and 35
of nitric acid in 1 of water. With these electro-magnets Dal Negro
obtained remarkably powerful results. The largest, (weighing 5 kil-
log., surrounded with 64 coils of copper wire of 8-4 millim. diameter, )
with the armature weighing 2 killog., when connected with the largest
electromotor, supported from 108 up to 117 killog. Dal Negro attri-
* {1 millimetre = °03937 English inch.
1 killogramme = 2 Ibs. 5 oz, 5 dram.—Trans. |
ELECTRO-MAGNETISM AS A MECHANICAL POWER. 537
butes the greatness of this effect principally to the weight of the arma-
ture, and also to the rounded form of this and also of the poles of the
magnet ; but he seems to think the great thickness of the wire, namely,
8-4 mill., of no moment. With this important particular the reader is
not acquainted till the end of the paper, where a table of the diameter
of the wires is added. He infers from his experiments, “ that a tempo-
rary magnet (as he calls the electro-magnets) can only acquire a mag-
netic power proportional to its mass;” and says, “ experience will show
what is the smallest electro-motive surface required to give the maxi-
mum of power;” and adds, “these experiments will become the more
necessary when electro-magnetic power has been applied to some useful
purpose.”
The following remarks of Dal Negro on the property of some pieces
of iron either not to take any magnetism at all, or only to take it under
certain circumstances from the inverted electric current, were to me
very mysterious and enigmatical. He says:
I. (1.) “Thad several cylindrical soft-iron horseshoes made, of different
weight, and experimented with them according to Sturgeon’s method ;
_ for the most part none of them were at all magnetic. Indeed, in a small
bar of iron which was cut into four pieces, and the single pieces made
into magnets of the above-mentioned size, only one of them became a
powerful magnet; the others were little or not at all magnetic.”
(2.) “In the same way curved square barsgave no appreciable re-
sults: it appears from this that the cylindrical form is essentially ne-
_ eessary to the development of this temporary magnetism. I also endea-
voured, without success, to magnetize hollow cylinders.”
(7.) “ During the first experiments it often happened that when the
weight which the magnet could support had reached its maximum, all
on a sudden the horseshoe would become incapable of re-acquiring
magnetism, not even so much as to be able to support the keeper again.
Van Moll also appears to have observed this phenomenon.”
“ Fortunately it appeared that by continually weakening [abstum-
pfen](?) the same magnet, one is enabled to repeat the experiments,
and each time make it support a considerable weight.”
Til. (5.) “ It is remarkable that I did not observe with these two mag-
nets (namely, the two strongest, ) the pheenomena mentioned in the first
part of this treatise, No. (7). I am much inclined to believe that this
depends upon the magnet being made to support the greatest possible
weight for a longer or shorter time. But here I must not omit to
mention, that often, when I removed from the magnets the helices
which I had been using, either for the purpose of altering the number
of coils or the thickness of the wire composing them, the magnets for
_ several days would not take up the least magnetism. On continuing
these experiments I obtained the same pheenomenon with the magnet C
538 DR. SCHULTHESS ON THE APPLICATION OF
(weighing 0°29 killog.): the original coil had been removed, but imme-
diately replaced by a smaller number of coils. To this magnet (even
after 14 days had elapsed) I could in no way communicate any appre-
ciable magnetic power.”
To me these statements are very enigmatical; at least I have never
observed anything similar in my own experiments; and not only dif-
ferent horseshoes of soft iron, but several varieties of hardened steel have
always appeared to me very susceptible of electro-magnetism ; steel of
course in a less degree than iron, but notwithstanding much more so
than I had expected from the observations of others. Every time when
in my experiments no action was observed, or at most only a very feeble
action, I found that either the circuit was somewhere interrupted, or
the battery was too weak.
I was most interested by the last portion of Dal Negro’s paper; it is
as follows :
“ As I had been successful in producing temporary magnets of very
great power with very small electromotors, I endeavoured to apply this
new power to moving machinery. I will now briefly state by what
means I endeavoured to set a lever in motion. I first used a magnetic
steel bar, placed vertically beneath one end of a temporary magnet:
the bar vibrated from the attractions and repulsions which took place
between its south pole and the north and south poles of the electro-
magnet. In the same way a motion may be effected in a horizontal
plane. I also set in motion a similar bar, by allowing a piece of iron,
set free from the magnet at the moment when its power became = 0,
to fall on one of its ends; after this it was immediately re-attracted.
This can be effected in two ways; the one may be employed when a
quick motion is to be produced, and the second when a greater force is
wanted: in the first case the weight falls only just out of the power of
the magnet’s attraction; and the instant the weight has fallen upon the
bar or lever, it is re-attracted by the magnet that the action may be
repeated : this weight is always very small in comparison with that
which the magnet can support whilst in contact. In the second case
the whole weight which the magnet can carry is employed, and use is
made of the foree which draws it to the magnet. This can be done in
several ways. One of them forms a very powerful electro-magnetic
ram. I shall not fail to make known the action of this new machine,
and hope thereby to satisfy those in particular who are endeavouring to
set a machine in motion at the least possible expense.”
I must confess that I cannot from this too short and uncertain de-
scription form any clear idea of Dal Negro’s process, and I am therefore
very curious to see his forthcoming paper. I could only clearly under-
stand his first method of setting a lever in motion, and I determined to
make these experiments as soon as I had finished those which I had
ELECTRO-MAGNETISM AS A MECHANICAL POWER. 539
previously commenced. I hastened the completion of the apparatus so
that I was enabled to exhibit it before the Mechanics’ Society on the
18th of January. The construction of it is as follows (Plate VII.):
On asmall board A‘ A’, resting on four feet, are placed the two si-
milar electro-magnets GG'; each of them weighs about the 3th part of
a pound, and is wound round with 80 convolutions of copper wire of
0°5 line in diameter, covered with silk: they can be made to recede
from or approach each other, and are fixed in their places by wooden
screws J J'. The board has in the middle a hole BB, cut in it where
the poles lie; in this a frame EE is hung, made out of four laths joined
together, forming an oblong, of which the long sides are vertical. Under
the upper side, and parallel with it, is the iron cylinder or armature K K’.
Fixed in the side laths, and about 14 inch below it, is placed a stout
iron wire F parallel with the cylinder and passing through the sides
of the frame, and two pieces of wood C C fixed in the under side of
the board A!A!; this wire serves as an axis, which allows to the frame
a pendulum-like motion. That part of the frame which is below the
axis is twice as long as the upper part, and weights O O may be placed
on its base EE". The electric current was conveyed to the elec-
tro-magnets through a gyrotrope PP, standing on the board A A,
which serves as a basis to the whole machine. The wires from the elec-
tromotors are connected with the two middle cups of mercury dd’, in
each of which dips the central portion of a wire bent into the form of
an anchor QQ. These two wires are fixed to a wooden bow, by the
motion of which the alternate ends of the two bent wires dip either into
the cups on the one side or into those on the other; into the one cup
d, dip the wires from f, coming from the one plate of the electromotor;
and into the other cup d', those from the other plate. The motion of
this bow is effected in a very simple way by means of the motion of
the frame E E’ E’', so that when the iron cylinder is attracted by the
electro-magnet on the right hand, the bow of the gyrotrope is driven
by the lower part of the frame to the left hand, by which motion the
left-hand electro-magnet is brought into action. The working of this
little self-acting apparatus is so quick and efficient, that another small
machine, for instance, a wheel, might very easily be set in motion by
it. Before the result was quite successful, there was still another dif-
ficulty to be overcome. It is a well-known fact that electro-magnets,
when the connexion of the wires with the electromotors is interrupted,
do not instantly lose all their magnetism, but are capable of carrying a
considerable weight for some time. The bad effects which this remain-
ing magnetism would have on the motion of the armature between the
two electro-magnets would undoubtedly be greatly counteracted by the
magnets being placed with the dissimilar poles opposite to each other.
In this form of arrangement it is evident that the magnet in action
540 PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR
would be much stronger, and assist in destroying the remaining weaker
magnetism in the other magnet. There would therefore be a moment
when the magnetism became = 0, and at that moment I expected that
the armature would be disengaged, and then be attracted to the active
electro-magnet. However, this interval was of such momentary du-
ration that the armature remained attached to the passive magnet. I
then took, instead of the armature of soft iron, a steel magnet of exactly
the same form and shape, and placed it so that its poles were always
opposite to the similar poles of the electro-magnets; but even with
this alteration the same result took place; it also happened when the
electric current was sent at the same time, but in an opposite direction,
to the other electro-magnet. As the power of the electro-magnet was
considerably greater than that of the steel magnet, I could not expect
to obtain more powerful effects than I had obtained with the soft iron.
At last I determined to prevent any possible contact between the arma-
ture and the electro-magnets: this I effected by wrapping the armature
up in paper, so as always to keep it at a small distance from the poles
of the magnet. The result was now quite satisfactory. I also enveloped
the steel magnet in the same way, and it appeared to me that with the
first-mentioned armature the motion was quicker and more energetic
than with the latter. If we consider that electro-magnets have already
been made which were capable of carrying 20 ewt., and that there is
no reason to doubt that they may be made infinitely more powerful, I
think I may assert boldly that electro-magnetism may certainly be em-
ployed for the purpose of moving machines.
On the Influence of a Spiral Conductor in increasing the In-
tensity of Electricity from a Galvanic Arrangement of a
Single Pair, &c. By Professor Henry, of New Jersey,
ipl
In the American Journal of Science for July 1832, I announced a
fact in Galvanism which I believe had never before been published.
The same fact, however, appears to have been since observed by Mr.
Faraday, and has lately been noticed by him in the November number
of the London and Edinburgh Journal of Science for 1834.
The phenomenon as described by me is as follows: “ When asmall
* Read before the American Philosophical Society, Feb. 6th, 1835.—This
has been annexed to the preceding papers as being referred to in them, and as
a slight notice of it only has appeared in this country: see Phil. Mag. and
Annals, vol. x. p. 314.
IN INCREASING THE INTENSITY OF ELECTRICITY. 544
battery is moderately excited by diluted acid, and its poles, terminated
by cups of mercury, are connected by a copper wire not more than a
_ foot in length, no spark is perceived when the connexion is either formed
or broken; but if a wire thirty or forty feet long be used instead of the
short wire, though no spark will be perceptible when the connexion is
made, yet when it is broken by drawing one end of the wire from its
cup of mercury, a vivid spark is produced. If the action of the battery
be very intense, a spark will be given by a short wire; in this case it is
only necessary to wait a few minutes until the action partially subsides,
or no more sparks are given; if the long wire be now substituted, a
spark will again be obtained. The effect appears somewhat increased
by coiling the wire into a helix; it seems also to depend in some mea-
sure on the length and thickness of the wire. I can account for these
phenomena only by supposing the long wire to become charged with
electricity, which, by its reaction on itself, projects a spark when the
connexion is broken*.”
The above was published immediately before my removal from Al-
bany to Princeton ; and new duties interrupted for a time the further
prosecution of the subject. I have, however, been able during the past
year to resume in part my investigations, and among others, have made
a number of observations and experiments which develop some new
circumstances in reference to this curious phenomenon.
These, though not as complete as I could wish, are now presented
to the Society, with the belief that they will be interesting at this time
on account of the recent publication of Mr. Faraday on the same sub-
ject.
The experiments are not given in the precise order in which they
were first made, but in that which I deem best suited to render them
easily understood; they have, however, been repeated for publication
in almost the same order in which they are here given.
1. A galvanic battery, consisting of a single plate of zinc and copper,
and exposing one and a half square feet of zine surface, including both
sides of the plate, was excited with diluted sulphuric acid, and then
permitted to stand until the intensity of the action became nearly con-
stant. The poles connected by a piece of copper bell-wire, of the ordi-
nary size and five inches long, gave no spark when the contact was
broken.
2. A long portion of wire, from the same piece with that used in the
last experiment, was divided into equal lengths of fifteen feet, by making
a loop at each division, which could be inserted into the cups of mer-
eury on the poles of the battery. These loops being amalgamated, and
dipped in succession into one of the cups while the first end of the wire
* Silliman’s Journal, vol. xxii. page 408.
542 PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR
constantly remained in the other, the effect was noted. The first length,
or fifteen feet, gave a very feeble spark, which was scarcely perceptible.
The second, or thirty feet, produced a spark a little more intense, and
the effect constantly increased with each additional length, until one
hundred and twenty feet were used; beyond this there was no percep-
tible increase ; and a wire of two hundred and forty feet gave a spark
of rather less intensity. From other observations I infer, that the length
necessary to produce a maximum result, varies with the intensity of the
action of the battery, and also with its size.
3. With equal lengths of copper wire of unequal diameters, the effect
was greater with the larger: this also appears to depend in some de-
gree on the size of the battery.
4. A length of about forty feet of the wire used in experiments first
and second, was covered with silk, and coiled into a cylindrical helix of
about two inches in height and the same in diameter. This gave a more
intense spark than the same wire when uncoiled.
5. A ribbon of sheet copper, nearly an inch wide and twenty-eight
and a half feet long, was covered with silk, and rolled into a flat spiral
similar to the form in which woollen binding is found in commerce.
With this a vivid spark was produced, accompanied by a loud snap.
The same ribbon uncoiled gave a feeble spark, similar in intensity to
that produced by the wire in experiment third. When coiled again, the
snap was produced as at first. This was repeated many times in suc-
cession, and always with the same result.
6. To test still further the influence of coiling, a second ribbon was
procured precisely similar in length and in all other respects to the one
used in the last experiment. The effect was noted with one of these
coiled into a flat spiral and the other uncoiled, and again with the first
uncoiled and the second coiled. When uncoiled, each gave a feeble
spark of apparently equal intensity ; when coiled, a loud snap. One of
these ribbons was next doubled into two equal strands, and then rolled
into a double spiral with the point of doubling at the centre. By this
arrangement, the electricity, in passing through the spiral, would move
in opposite directions in each contiguous spire, and it was supposed that
in this case the opposite actions which might be produced would neu-
tralize each other. The result was in accordance with the anticipation :
the double spiral gave no spark whatever, while the other ribbon coiled
into a single spiral produced as before aloud snap. Lest the effect might
be due to some accidental touching of the different spires, the double
spiral was covered with an additional coating of silk, and also the other
ribbon was coiled in the same manner; the effect with both was the
same.
7. In order to increase if possible the intensity of the spark while the
battery remained the same, larger spirals were applied in succession.
IN INCREASING THE INTENSITY OF ELECTRICITY. 543
_ The effect was increased, until one of ninety-six feet long, an inch and
a half wide, and weighing fifteen pounds, was used. The snap from
this was so loud that it could be distinctly heard in an adjoining room
with the intervening door closed. Want of materials has prevented me
from trying a larger spiral conductor than this ; but it is probable that
there is a length which, with a given quantity and intensity of galvanism,
would produce a maximum effect. When the size of the battery is
increased, a much greater effect is produced with the same spiral.
Thus when the galvanic apparatus described in the first article is ar-
ranged as a calorimotor of eight pairs, the snap produced on breaking
contact with the spiral last described resembled the discharge of a
small Leyden jar highly charged.
8. A handle of thick copper was soldered on each end of the large
spiral at right angles to the ribbon, similar to those attached to the
wires in Pixii’s magneto-electric machine for giving shocks. When one
of these was grasped by each hand and the contact broken, a shock was
received which was felt at the elbows; and this was repeated as often
as the contact was broken. This shock is rather a singular pheenome-
non, since it appears to be produced by a lateral discharge, and it is
therefore important to determine its direction in reference to the pri-
mary current.
9. A shock is also received when the copper of the battery is grasped
by one hand, and the handle attached to the copper pole of the ribbon
with the other. This may be called the direct shock, since it is pro-
duced by a part of the direct current. It is, however, far less intense
than that produced by the lateral discharge.
10. When the poles were joined by two coils connected by a cup of
mercury between them, a spark was produced by breaking the circuit
at the middle point; and when a pair of platina wires was introduced
into the circuit with the large coil and immersed in a solution of acid,
decomposition took place in the liquid at each rupture of contact, as
was shown by a bubble of gas given off at each wire. It must be re-
collected that the shocks and the decomposition here described were
_ produced by the electricity from a single pair of plates.
_ 11. The contact with the poles of the battery and the large spiral
being broken in a vessel containing a mixture of hydrogen and atmo-
spheric air, an explosion was produced.
I should also mention that the spark is generally attended with a de-
flagration of the mercury, and that when the end of the spiral is brought
in contact with the edge of the copper cup or the plate of the battery,
a vivid deflagration of the metal takes place. The sides of the cup
sometimes give a spark when none can be drawn from the surface of
the mercury. This circumstance requires to be guarded against when
_ experimenting on the comparative intensities of sparks from different
544 PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR
arrangements. If the battery formerly described* be arranged as a ca=
lorimotor, and one end of a large spiral conductor be attached to one
pole, and the other end drawn along the edge of the connector, a series
of loud and rapid explosions is produced, accompanied by a brilliant de-
flagration of the metal; and this takes place when the excitement of the
battery is too feeble to heat to redness a small platina wire.
12. A number of experiments were made to determine the effect of
introducing a cylinder of soft iron into the axis of the flat spiral, in
reference to the shock, the spark, &c.; but no difference could be ob-
served with the large spiral conductor; the effect of the iron was
merged in that of the spiral. When, however, one of the smaller rib-
bons was formed into a hollow cylindrical helix of about nine inches
long, and a cylinder of soft iron an inch and a half in diameter was
inserted, the spark appeared a little more intense than without the iron.
The obliquity of the spires in this case was unfavourable to their mutual
action, while the magnetism was greater than with the flat spiral, since
the conductor closely surrounded the whole length of the cylinder.
I would infer, from these experiments, that some effects heretofore
attributed to magneto-electric action are chiefly due to the reaction on
each other of the several spires of the coil which surround the magnet.
13. One of the most singular results in this investigation was first
obtained in operating with a large galvanic battery. The whole in-
strument was arranged as a calorimotor of eight pairs, and a large
spiral conductor introduced into the circuit, while a piece of thick
copper wire about five inches long united the poles. In this state
an explosion or loud snap was produced, not only when the contact
was broken at the spiral, but also when one end of the short wire
at the other extremity of the apparatus was drawn from its cup.
All the other short moveable connectors of the battery gave a similar
result. When the spiral was removed from the circuit and a short wire
substituted, no effect of the kind was produced. From this experiment
it appears that the influence of the spiral is exerted through at least
eight alternations of zine, acid, and copper, and thus gives to a short
wire at the other extremity of the circuit the power of producing a
spark.
14. The influence of the coil was likewise manifest when the zine
and copper plates of a single pair were separated from each other to
the distance of fourteen inches in a trough without partitions, filled
with diluted acid. Although the electrical intensity in this case must
have been very low, yet there was but little reduction in the apparent
intensity of the spark.
* This battery consisted of eighty-eight elements or pairs, composed of plates
of rolled zine nearly one-eighth of an inch thick, nine inches wide, and twelve
inches long, inserted into copper cases open at top and bottom.
IN INCREASING THE INTENSITY OF ELECTRICITY. . 545
15. The spiral conductor produces, however, little or no increase of
effect when introduced into a galvanic circuit of considerable intensity,
Thus when the large spiral used in experiment seventh, eighth, &c. was
made to connect the poles of two Cruikshank’s troughs, each containing
fifty-six four-inch plates, no greater effect was perceived than with a
short thick wire: in both cases in making the contact a feeble spark
was given, attended with a slight deflagration of the mereury. The
batteries at the same time were in sufficiently intense action to give a
disagreeable shock. It is probable, however, that if the length of the
coil were increased in some proportion to the increase of intensity, an
increased effect would still be produced.
In operating with the apparatus described in the last experiment, a
phznomenon was observed in reference to the action of the battery
itself, which I do not recollect to have seen mentioned, although it is
intimately connected with the facts of magneto-electricity, as well as
with the subject of these investigations, viz. When the body is made to
form a part of a galvanic circuit composed of a number of elements, a
shock is, of course, felt at the moment of completing the circuit. If
the battery be not very large, little or no effect will be perceived during
the uninterrupted circulation of the galvanic current; but if the circuit
_ be interrupted by breaking the contact at any point, a shock will be felt
at the moment, nearly as intense as that given when the contact was
first formed. The secondary shock is rendered more evident, when
the battery is in feeble action, by placing in the mouth the end of one
of the wires connected with the poles; a shock and flash of light will
be perceived when the circuit is completed, and also the same when
the contact is broken at any point; but nothing of the kind will be per-
ceived in the intermediate time, although the circuit may continue un-
interrupted for some minutes. This I consider an important fact in
reference to the action of the voltaic current.
The phznomena described in this paper appear to be intimately con-
nected with those of magneto-electricity, and this opinion I advanced
with the announcement of the first fact of these researches in the Ame-
rican Journal of Science. They may, I conceive, be all referred to that
“species of dynamical Induction discovered by Mr. Faraday, which pro-
duces the following phenomenon, namely: when two wires, A and B,
are placed side by side, but not in contact, and a voltaic current is
passed through A, there is a current produced in B, but in'an opposite
direction. The current in B exists only for an instant, although the
current in A may be indefinitely continued ; but if the current in A be
stopped, there is produced in B a second current, in an opposite direc-
tion however to the first current.
The above fundamental fact in magneto-electricity appears to me to be
a direct consequence of the statical principles of “Electrical Induction”
546 PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR
as mathematically investigated by Cavendish, Poisson, and others. When
the two wires A and B are in their natural state, an equilibrium is
sustained by the attractions and repulsions of the two fluids in each
wire; or, according to the theory of Franklin and Cavendish, by the
attractions and repulsions of the one fluid, and the matter of the two
wires. Ifa current of free electricity be passed through A, the natural
equilibrium of B will be disturbed for an instant, in a similar manner
to the disturbance of the equilibrium in an insulated conductor by the
sudden addition of fluid to a contiguous conductor. On account of the
repulsive action of the fluid, the current in B will have an opposite
direction to that in A; and if the intensity of action remains constant,
a new state of equilibrium will be assumed. ‘The second state, how-
ever, of B may perhaps be regarded as one of tension; and as soon as
the extra action ceases in it, the fluid in B will resume its natural state
of distribution, and thus a returning current for an instant be pro-
duced. ;
The action of the spiral conductor in producing sparks is but another
case of the same action; for since action and reaction are equal and in —
contrary directions, if a current established in A produces a current in
an opposite direction in B, then a current transmitted through B should
accelerate or increase the intensity of a current already existing in the
same direction in A. In this way the current in the several successive
spires of the coil may be conceived to accelerate, or to tend to accelerate
each other; and when the contact is broken, the fluid of the first spire
is projected from it with intensity by the repulsive action of the fluid in
all the succeeding spires.
In the case of the double spiral conductor, in experiment sixth, the
fluid is passing in an opposite direction ; and according to the same
views, a retardation or decrease of intensity should take place.
The phenomenon of the secondary shock with the battery appears
to me to be a consequence of the law of Mr. Faraday. The parts of
the human body contiguous to those through which the principal cur-
rent is passing, may be considered as in the state of the second wire B;
when the principal current ceases, a shock is produced by the returning
current of the natural electricity of the body.
If this explanation be correct, the same principle will readily account
for a curious phenomenon discovered several years since by Savary, but
which I believe still remains an isolated fact. When a current is trans-
mitted through a wire, and a number of small needles are placed trans-
verse to it, but at different distances, the direction of the magnetic
polarity of the needles varies with their distance from the conducting
wire. The action is also periodical; diminishing as the distance in-
creases, until it becomes zero; the polarity of the needles is then in-
verted, acquires a maximum, decreases to zero again, and then resumes
IN INCREASING THE INTENSITY OF ELECTRICITY. 547
a the first polarity ; several alternations of this kind being observed *.
Now this is precisely what would take place if we suppose that the
principal current induces a secondary one in an opposite direction in
__ the air surrounding the conductor, and this again another in an oppo-
_ site direction at a great distance, and so on. The needles at different
distances would be acted on by the different currents, and thus the
_ phzenomena described be produced.
The action of the spiral is also probably connected with the fact in
commion electricity called the lateral discharge: and likewise with an
appearance discovered some years since by Nobili, of a vivid light, pro-
_ duced when a Leyden jar is discharged through a flat spiral.
The foregoing views are not presumed to be given as exhibiting the
actual operation of nature in producing the phenomena described, but
rather as the hypotheses which have served as the basis of my investi-
gations, and which may further serve as formule from which to deduce
new consequences to be established or disproved by experiment.
Many points of this subject are involved in an obscurity which requires
more precise and extended investigation ; we may, however, confidently
anticipate much additional light from the promised publication of Mr.
Faraday’s late researches in this branch o science.
* Cumming’s Demonferrande, p. 247; also Edinburgh Journal, October
1826.
NOTE.
[For an account of some recent investigations relative to the subject of the
preceding Articles, the reader is referred to ‘“‘ An Inquiry into the Possibility and
dyantage of the Application of Magnetism as a Moving Power: By the Rev.
James William M‘Gauley, in the Report of the Dublin Meeting of the British
Association, 1835.” See Phil. Mag. and Annals, vol. vii. p.306. A further
communication was made by the same gentleman at the Bristol Meeting, 1836,
—Epir.]
Vor. I—Panr IV. ap
548
ARTICLE X XVII.
A singular case of the Equilibrium of Incompressible Fluids ;
by M. Osrroagrapsky.
(Read to the Academy of St. Petersburgh, February 19, 1836.)
From “ Mémoires de l' Académie Impériale des Sciences de St. Petersbourg,”
vol. iii. part 3.
ly mechanics there is no other distinction made between different
bodies or different systems of bodies, besides that which relates to their
masses, their positions, and their possible displacements. These displace-
ments, together with the mass or quantity of the inertia of each element
being given, we have all that is requisite as well as indispensable to en-
able us to treat of the equilibrium and movement of any system.
That a system subjected to the action of any forces may remain in
equilibrio, it is necessary that the forces should be incapable of pro-
ducing any of those displacements of which the system is susceptible.
Now, as the forces, though capable of producing all the displacements
of which the whole momentum is positive, are yet unable to produce
any of those which correspond to the zero or the negative momentum,
the equilibrium of the system consequently requires that the whole mo-
mentum should be zero or negative for all the possible displacements.
From this leading principle we may in the easiest and simplest manner
derive the condition of equilibrium of a system without knowing any-
thing more than the masses and the possible displacements. More par-
ticularly with respect to the equilibrium of liquids, we have, for instance,
no need of the experimental principle known by the name of the prin-
ciple of egual pressure, which, before the publication of the Mécanique
Analytique, mathematicians were accustomed to consider as the basis of
the theory of the equilibrium of fluids. It is sufficient to know how a
liquid mass can be displaced, and this is the only datum by means of
which, in the Mécanique Analytique, the equations relative to the equi-
librium of liquids are deduced. But Lagrange having neglected the
consideration of the displacements, accompanied by an augmentation
of volume, though such displacements are evidently possible, was un-
able to deduce from his analysis the essential condition, that the quan-
tity which represents the pressure must necessarily be positive. This
condition being added, the theory of Lagrange will be the most satis-
factory of all those in which the liquids are considered as continu-
ous masses ; and if there is anything further to be remarked, it is that
the incompressibility of the differential parallelopipeds is there taken as
the condition of the incompressibility of the fluid, though it should be
EQUILIBRIUM OF INCOMPRESSIBLE FLUIDS. 549
directly expressed that any portion (whether finite or infinitely small)
of the liquid mass cannot be diminished. It is undoubtedly true that,
as any volume may be supposed to consist of differential elements, the
incompressibility of these elements involves that of the volume as a
necessary consequence. But it would still be desirable to see how the
calculus would directly express the incompressibility of any portion of
the liquid volume.
In order to show this, let x, y, z represent the coordinates of a point
of the liquid, which, because of their variability, will belong to alk
points. Any portion of the liquid volume may then be denoted by the
expression Bf dx dy dz, the integral being taken between the proper
limits. It will then be necessary to find an expression which will re-
present Jf dx dy dz as suffering no diminution during any displace-
ment that the liquid undergoes. For this purpose, let da, dy, dz re-
present the projection of the space which the point (a, y, z) should
have traversed in consequence of a displacement either actually made
or only supposed in the liquid, on the coordinate axes 2, y, z respect-
ively. The point would after the displacement (whether positive
or not) correspond to the coordinates x + da, y +4 y, z + 02, which,
for the sake of brevity, we shall represent by X, Y, Z respectively.
Every other point of the volume fi dx dy dz being similarly dis-
placed, the whole volume would assume another position in space, and
its different points would be determined by the coordinates X, Y, Z,
which may be regarded as functions (of 2, y, 2) altogether arbitrary.
The volume dx dy dz would, in its new position, become
a
i S dX dY dZ, and consequently undergo the variation {1 aXdYdZ
9
4
- f dx dy dz, which we are now about to develop.
a
In order to effect a better comparison of the integrals dXdYdZ
and ff dx dy dz with one another, we must reduce them to the same
variables and the same limits. This will be done by transforming
X, Y, Z into x, y,z by means of the known formule. For this pur-
pose we have
adXdYdZ= 15 OX aZ dX dVaZ waxed tae
dady dz dxdzdy' dydzdzx
_dXdVadZ , dXavaZ
dy dx dz dzdxdy
_dXdYdZ
dex z
dz dy dx Bae?
Q2e2
550 M. OSTROGRADSKY ON A SINGULAR CASE OF
and the variation of the volume will consequently become
@AXdYdZ dXdYdZ adXdYdZ dXdYdZ
dXdVdZ. @X4V42 sy, ay aes
dzdxdy dzdydx i ets
by substituting for X, Y, Z their values 7 + da, y+ dy,2 +42, and
rejecting (on the same principle as they are rejected in the differential
calculus) all the infinitely small quantities, except those of the lowest
order, we have as the variation of the volume
déx ddy , ddz
du dy | dz
or, if we consider the possible displacement alone, the volume can only
increase or continue unchanged. The foregoing variation must then be
either zero or positive for all the possible displacements, and must be so
whatever be the volume under consideration, that is to say, whatever
be the limits of the integral
dia dty ,déz
—— + —+ dzxdy dz:
8 (G2 +9 +F) Se od
which cannot be the case unless we have
dda ddydbz
Wa ty ae
for all possible displacements. We might have employed the polar or
any other coordinates whatever. We might likewise, if it were neces-
sary, express the invariability of a portion of a mass, &c.
The geometers who have treated of the equilibrium of fluids in Euler’s
manner have considered the equilibrium of the differential parallelopi-
peds also, but the equilibrium might be determined for any portion of
the volume, whether finite or infinitely small. Let us imagine, in the
interior of the liquid, any volume at pleasure. The condition of equi-
librium of this volume must be established in virtue of the moving forces
applied to it and of the pressures on its surface. If we employ dm to
represent an element of its mass answering to the coordinates 2, y, 2,
and X, Y, Z to represent the accelerative forces parallel to the coordi-
nate axes, the moving forces will be Xdm, Ydm, Zdm, and even
other elements will be acted upon by similar forces.
This being supposed, let p be the pressure at the surface of the vo-
lume in question. If ds represents an element of this surface, and
A, wv the angles formed with the coordinate axes by the normal to
ds produced beyond the volume, p ds will be the pressure sustained
by the element ds, and —pceos.Ads, —pcospds, — pcosyds
the components of that pressure. Now, each element of the volume
S )ax dy dz:
7 =0
THE EQUILIBRIUM OF {NCOMPRESSIBLE FLUIDS. 551
being subject to the action of the forces X d m, Y dm, Z dm, and each
element of the surface to that of the forees —p cos.Ads, — pcospds
— peosy ds, the equilibrium of the volume must be determined by the
mass of the invariable system. For this purpose we shall suppose that
the volume has become inflexible, and is invariably connected with the
origin of the coordinates: we shall transfer to that point all the forces
Xdm, Ydm, Zdm, —pds cosa, — pds cosp, — pds cosy, and
consider the couples to which this transfer will give rise. All the forces
transferred to the origin of the coordinates will be reduced to three.
Sf Xam —fpas cos A
Sf van— pds cos
Stam — pds cosy
which must vanish in case of equilibrium. This being supposed, we
have
J xan =f pas cos A
J vam=fpas COS PEI gots ie ot hts)
Stdna=f pas COS ¥
The integrals which contain the element (dm) of the mass are re-
ferred to the entire volume of the liquid, and those which contain ds
have reference only to the surface of that volume. The forces X d m,
Ydm, Zdm, in consequence of being transferred to the origin of the
coordinates, will give the couples (2 Y — y X) dm, (yZ —zY) dm,
(«X —xZ) dm, which will be found respectively in the planes of
zy,yz,zx. The forces —pds cosa, —pdscosp, — pds cosy
will likewise give, in the coordinate planes, the couples
— (cos.A — ycosp) pds, — (ycos.v —z cosp) pds,
— (zcosA — x cosy) pds.
The momenta of all the couples situated in the plane of wy being
added together, and those of the couples situated in the planes of y z
and za being likewise added together, all the couples will thus be
reduced to three.
S@x-y® dm =f (x e0s — y cos.) pds
S (y%-2Y)dm — f(y cos .v— 2008p) pds
S (eX =02) am — f (2008 — wos.) pds
552 M. OSTROGRADSKY ON A SINGULAR CASE OF
As these must vanish in case of equilibrium, we have
S @¥-y%) dm = [ (xeos.u —y.cos.a) pds
SJ yt=2%) am =f (ycos-1 = 2 005-4)pas sive)
J ex—2t) am = [ (20os.2— x 008 4) pds.
Now if we have an integral such as
S(t9 aot dR Pink
t-ae
P, Q, R being functions of x, y, z,. aay dw a differential volume, and
if this integral is to be taken in the extent of a volume V, we shall have,
as is known,
dP od dR
S(t t at Tz) de=f Peos. A+Qecos.u~+Reos.v)ds.
The latter integral is taken only for the surface of the volume. We
shall have as a consequence of the foregoing formula
d Dae ae
pdscos.A= da ¢”
d
Sfeeeos ue y cosa) pds _f («#2 sia, -~y 5) de
Sve. yv—zcos.u)pds =f"(¥3 aay) dw
dP
fieeos.r—aeos.rypasaf (24 a dw
The equations of equilibrium (1) and (2) will become
dP
f[xanaf Gee
x
dP
fia=fZ dw
e y
dP
[tinal Gre
J YE Sih) bs dP
SJ@yv-yanz= f 0-9 a,) de
ere
=
Lew.” tn
eli 3
THE EQUILIBRIUM OF INCOMPRESSIBLE FLUIDS. 553
BPAY bP
futz-zan=f (ve -7 ) &
Pps p
Sfex-etyamafe 2g ~ 8 Ge) de,
and as the preceding equations must arise, whatever may be the limits
of the integrals, we must necessarily have
cp eat
dx
‘ple REET LN
dy
Zdm = 5 di,
dm d dP 3
or (by making 7— =¢) 7e=e& Ge =O = eZ:
¢, which expresses the ratio of the mass dm to the volume of dw, is
but the expression of the density.
Let us now particularly consider a homogeneous liquid, the surface
of which is entirely free and suffers no external pressure, we shall have
at first for all the elements of the liquid, whatever dx, dy, dz may be,
dp=e(Xdx+Ydy+Zdz),
and then, for the surface
O=Xdzx+Ydy+Zdz.
The last equation shows that the resultant of X, Y, Z is normal to
the surface of the liquid. It is obvious that in the expression X dx
+Ydy-+ Zdz, the differentials dx, dy, dz belong to the passage from
a molecule of the surface to another molecule situated also at the sur-
face ; but if we passed from a molecule at the surface to a molecule si-
tuated in the interior, we should have Xda+Ydy+Zdz70;
which requires that the resultant of X, Y, Z should be directed towards
the interior of the liquid mass. Thus it appears necessary for the equi-
librium of a homogeneous liquid mass, that the differential Xd 2 +Ydy
+ Zdz should be exact for all the points of the mass, that the result-
ant of the forces X, Y, Z should be normal to the surface in all the
elements of the surface, and that it should always act in the direction
of the interior of the liquid. If these conditions are not fulfilled, it
might be supposed that the liquid mass could never remain in equilibrio.
I have, however, observed a case in which, although the last of these
conditions is not satisfied, yet there is certainly an equilibrium.
Let us suppose that the liquid forms a spherical shell of any given
thickness, and that each of its molecules is attracted towards the centre
by a force proportioned to a function of the distance between the
554 EQUILIBRIUM OF INCOMPRESSIBLE FLUIDS.
molecule and the centre, the equilibrium will necessarily take place.
For the molecules situated at the same distance from the centre of at-
traction must all be moved in the same manner: if one of them ap-
proaches the centre all the others must approach it also, and within the
same distance; and they cannot approach it in such a manner, that all of
those situated on the same spherical surface described from the centre
of attraction would retain the same motion ; for the consequence of this -
would be a diminution of volume. The liquid will thus remain in equi-
librio; but it is evident that the force which attracts each molecule
situated in the interior surface of the shell has its direction outside of
the liquid mass. Let f(r) represent the attractions, a the radius of
the inferior surface, and 6 the radius of the superior surface, we shall
have
dp=—f(r)dr,
p=f'f(ar= “£0 dr.
b
The pressure on the inferior surface will then be if f(r) dr, and
e/ a
whence
this pressure certainly differs from zero, a fact which is contrary to the
generally received opinion.
Here then we have a singular case of equilibrium, which the esta-
blished theory of liquids is not sufficient to explain, and which shows
therefore that this theory is not yet sufficiently comprehensive.
555
ArtricLE XXVIII.
On the Origin of Organic Matter from simple Perceptible
Matter, and on Organic Molecules and Atoms; together
with some Remarks on the Power of Vision of the Human
Eye; by Prof. C. G. Exrensere.
(From Poggendorff’s dnnalen der Physik und Chemie, vol. xxiv. p. 1.*)
Tuere have been philosophers who have considered the magnitude
of the elementary particles of bodies not to be so extremely minute as
to be beyond the reach of the human senses; and there have been che-
mists who have conceived it to be possible to follow the successive
combinations of the primitive substances or simple matter up to the for-
mation of living organisms, indeed, have even given them a place in the
_ class of observed facts. Others have thought that they perceived a
£
1
peculiar process of fermentation, the product of which was the forma-
tion of minute animal and vegetable bodies, and to which process the
name of infusorial fermentation has been given. The probability of
obtaining organic bodies by chemico-synthetical means has of late
gained ground chiefly because we had advanced so far as the prepara-
tion, almost synthetical in appearance, of some organic products by
chemical means, and haye observed galvanic processes or capillary ac-
tions, which are very similar to, perhaps quite the same as, certain or-
ganic phenomena. As this is one of the most interesting and import-
ant subjects of human inquiry, and has excited hopes of great and
speedy results, it may be useful, in order that our inquiries may not de-
viate from the right road, to direct the attention of philosophers and
chemists to some physiological experiments which Iread in the Academy
of Sciences of Berlin, and which I made known last year in a zoological
memoir, extracts of which have been given in other journals devoted to
physics, but which, so to speak, I myself will endeavour to clothe in
a physical dress.
I. Critical examination of the GENERATIO AEQUIVOCA.
I have for a long series of years been occupied in investigating the
conditions of the generatio equivoca of organic bodies. For this pur-
pose it was necessary to subject to careful observation, as to their vital
relations and primitive conditions, those organic bodies of whose origin
a generatio primitiva or spontanea is asserted.
1. Fungi.—By careful examinations of the fungi and of mould, the
* The Editor is indebted for the translation and communication of this paper
to Mr. W. Francis.
556 EHRENBERG ON THE ORIGIN OF ORGANIC MATTER
systematic result of which I made known in the year 1818 in an inau-
gural dissertation, under the title Sylve Mycologice Berolinenses, 1
first discovered, in 1819, the real germination of the seeds of fungi and
of mould, which has indeed been of late hypothetically received and
described here and there, but of which the experiments and correct
observations of the meritorious Florentine botanist, Micheli (1788),
adduced in support of it, furnish no satisfactory proof. He saw,
for instance, fungi grow where he had purposely sowed supposed
seeds; but it is known that often fungi are found where no seeds have
been purposely sown ; and it remained doubtful to every accurate natu-
ralist, whether, notwithstanding the precautions related by Micheli,
those fungi had really origmated from the so-called seeds which had
been sown, or whether both the intended sowing and the origination of
similar fungi coincided in time and place, solely because the conditions
necessary to the generatio spontanea were promoted by it. The more
important and influential the consequences were which might be sup-
ported by these observations, the more necessary it was to submit them
to rigid criticism. The complete investigation of the germination of
single seeds and their growth could alone remove the doubt, which ne-
cessarily increased with the general diffusion of the idea of a generatio
spontanea, of the correctness of that observation ; and this nobody had
made. I at that time followed up these ideas with more careful ob-
servations than those of Micheli, and was so fortunate as not only to
establish the fact, but also to discover the conditions under which the
observation of the real germination of mould seeds may easily be re-
peated at pleasure in every forty-eight hours.
I made known these experiments in 1820, in a German notice in the
Regensburger Flora, or Botanical Journal, part II. page 535, and more
completely in a Latin paper (De Mycetogenesi Epistola. Neesio ab
Esenbeck seripsit Ehrenberg. Nova Acta Nat. Cur., vol. x.) addressed
to the President of the Leopold’s Academy of Bonn. I have there given
figures of the seeds of fungi, their germination and their gradual de-
velopment, to the completion and formation of fresh seeds ; and the same
experiments have been repeated by several others (see Fr. Nees Von
Esenbeck in the Flora or Bot. Journal, 1820, page 531, and Schilling,
in Kastner's Archiv, vol. x. p.429. 1827. The latter gives the obser-
vation in 1827 as his own discovery). With this observation the ten-
dence of the fungi and mould to a cyclical development was established,
and the necessity of a generatio primitiva was removed as far from
those as from other plants. These small bodies, which withdraw
themselves from common view, entered into the series of the other
greater natural bodies, so that the strangeness of their frequently enig-
matical appearance may be referred to the requisite fineness of obser-
vation, and the insurmountable difficulty of such observation in open
nature, whilst a piece of rotten wood and a single rotten pear, &¢., as a
FROM SIMPLE PERCEPTIBLE MATTER. 557
soil for their growth, permit us to have before our eyes, in our room, the
cycle of the development of these forms.
Continued investigations of the most minute organized beings have
of late more and more confirmed me in the opinion that, not only in all
these forms, besides the supposed generatio spontanea, a cyclical deve-
lopment may be ascertained by examination, but they even compel me
to declare that all observations and experiments in support of the gene-
ratio spontanea are by no means sufficiently careful and faultless to
produce conviction; and that the idea of a generatio primitiva of or-
ganic bodies, to have the value of an ascertained fact, must be proved
afresh by more accurate observations.
2. Intestinal Worms.—The idea of the generatio primitiva being
founded not on the fungi and moulds alone, but more particularly on
the inexplicable origin of the intestinal worms and the infusoria, I at a
subsequent period especially directed the whole of my attention to these
forms. In the years 1820 to 1826, and in 1829, I collected, in my
voyages in Africa, Western Asia, and Siberia, as many geographical ob-
servations as possible of all the smallest existing organisms; and by
means of the great quantity of my unbiassed observations pursued for
so many years under very different circumstances, I became more and
more disinclined to the notion of the generatio spontanea, as I acquired
a far clearer insight into the highly perfect organization of these so-
called organic ultimate forms, molecules, or minutest organic beings,
which has disproved the necessity of their primitive origin, and opposes
to it possibilities and realities entirely different.
On examining the intestinal worms, I everywhere found the entire
structure of almost all these animals so decidedly adapted to an oviparous
propagation, that I should rather be led to ascribe the apparent anomaly
and mysteriousness in their origin to their essential relation to the inner
parts of living animal bodies to which they are limited, and the great
difficulty of the direct observation of their cyclical development arising
from that cause, than to an entirely peculiar power of nature, which is
in action there alone where human investigations are excluded and the
senses do not reach. Organs of copulation and production, clearly de-
veloped and never deficient, and the development of which surpasses
for the most part those of other organic systems, plainly point in the in-
testinal worms to a predominant cyclical development, in the same man-
ner as it is exhibited in the larger organisms, and make their generatio
primitiva very improbable, for which indeed there is no other argument
than the difficulty of observation. The occurrence of intestinal worms
in the interior of organic bodies does not appear to me more remarkable
or incomprehensible, considering the numerous frequently crude animal
aliments beginning with the chyle and the milk, than the relative rarity
of those parasitical organisms, considering their enormous predisposition
to increase by eggs. We seldom find, indeed, animal bodies or human
‘
558 EHRENBERG ON THE ORIGIN OF ORGANIC MATTER
corpses without any worms, especially when we diligently look for them.
We find them also as seldom in such abundance as we might expect
from the apparent fecundity of these animals, which are not capable
of any voluntary limit. There must therefore be great and insurmount-
able difficulties for the development of the hundreds and thousands of
eggs which are often found in each individual of these parasites. I
would therefore not object to the older opinion, that the eggs of intestinal
worms are propelled by the circulation of the fluids into all parts of the
body, but develop themselves there only where the particular conditions
requisite for this purpose are favourable. The smaller diameter of the
finest vessels through which they have to pass does not appear to me
to present any important difficulty, because these, as we see in every
inflammation, become easily and quickly expanded as soon as they are
irritated ; and these eggs may, as excretive bodies, like every body which
is foreign to our organism, act in an irritative manner, and may be
taken up by the embouchures of the absorbents and be propelled along
with increased activity through them : that this is the case with mercury,
pus, and other matters, has been already received as an observed fact *,
It is even probable that the eggs of the Entozoa and their propulsion
through the vascular system may be an important morbid matter hi-
therto overlooked, and which causes a part of the phenomena compre-
hended under the name scrofula. In bodies which are particularly
favourable to the development of worms there must necessarily be an
innumerable quantity of secreted eggs of those parasites, which, if they
are not expelled by the intestinal canal or by the prime via, must, as
foreign bodies, produce disorders. If the absorption takes place entirely
or for the most part in the lymphatics, it would occasion their general
or sole influence upon that system. Obstructions in the lymphatics,
but especially in their reticular tissue, the glands, which lead to local
congestions of lymph, inflammations, and morbid appearances of various
kinds, become in this manner very easy of comprehension ; and these as-
suredly deserve the attention of medical science, not as speculations but
as realities. Thousands of eggs of intestinal worms, whose existence in
many bodies cannot be denied, must perish, as they are rarely deve-
loped in such great quantities, from the difficulty of their attaining the
place and conditions favourable for their development; while only some,
very often none, ever actually attain those conditions. This relative
proportion of the number of intestinal worms and of their eggs to the
* Miiller (Physiologie, vol. i. p.17) alleges that Ehrenberg endeavours to
weaken the generatio equivoca of intestinal worms, but proves nothing; and, I
think, with reason; for, according to his view, the eggs are taken up by the
lymphatic vessels and carried to all parts of the body. But how is that possible?
They are evidently too large to enter into the lymphatics ; and how can they cir-
culate in those blood-vessels which are only 000025 of an inchin diameter, and
so reach the products of secretion, such as milk, yolk, &c.? For this must be
supposed, since intestinal worms have been found in the foetus of mammalia and
in hens’ eggs, &c.—W. F.
FROM SIMPLE PERCEPTIBLE MATTER. 559
organs of the larger animals is also found to exist. There are very often
observed in animal dissections a small number of full-grown worms,
filled with an innumerable quantity of eggs without any young in their
proximity ; and I was often astonished to find in the considerable num-
ber of my dissections of animal bodies (I have brought from Africa
alone intestinal worms of 196 species of animals, all of which I have
myself dissected, and of some from 40 to 50 individuals, ) only a few
alive, although these were completely filled with eggs. Thus from la-
borious observations this opinion has become more and more firmly
fixed in my mind, that it is much more astonishing how the great fe-
cundity of the Entozoa should be so limited by the living organs, than
that it should be possible that living worms should inhabit them, and,
considering their diffusion, escape observations which are generally su-
perficial. The Epizoa present to the observer quite a different propor-
tion, although these can for the most part be limited voluntarily by the
animals. The circumstances favourable to their cyclical development in
most cases overcome those which limit it; and a careful observer might
follow with ease the formation and development of their innumerable eggs.
It is not the small size of the Entozoa which forms the difficulty, but
solely their inaccessible station in the interior of living animal bodies.
8. Infusoria.—Of an entirely different nature is the difficulty of ob-
servation in the Infusoria, the third strong hold of the generatio equi-
voca: it lies in their minute size. Observations of Infusoria, which
I pursued with great zeal and repeated on every occasion, showed me
the necessity of a more definite determination of their forms, which I
endeavoured to acquire by drawings and measurements of them. These
severe and often-repeated investigations of individuals enabled me fre-
quently to recognise the most decided traces of a higher internal organi-
zation than had previously been ascribed to them. In the year 1819
Thad already observed that the motion of the zoological monads (Monas
pulvisculus) was by no means a mere rolling effected by a change of
the centre of gravity, as it was thought to be; but I perceived, from
the throwing off of very minute particles of the dirty water, and from
an apparent whirling at the anterior part of the animalcule, the presence
of oarlike cilia, which at times even became visible. Some of these ob-
servations I made known in 1820, in an Appendix to a Memoir by my
friend Friederich Nees von Esenbeck in the Regensburg Botanical Jour-
nal, part ii. p. 535. My friend and subsequently fellow-traveller Dr.
Hemprich often witnessed my observations and experiments, and has also
given, in his Grundrisse der Naturgeschichte, 1820, p. 289 to 291, a sum-
mary account of what I had ascertained at that time (see preface, p.viii.).
I was not then myself desirous of making publicly known any of those
observations, because I saw on the one hand that they were capable of
being carried to much greater perfection, and on the other hand, I pos-
sessed at that time only a very incomplete thirty-shilling wooden com-
560 EHRENBERG ON THE ORIGIN OF ORGANIC MATTER
pound microscope from Nurenberg, which I had, according to my own
views and wants, rendered more powerful, the same indeed with which
I had already discovered the germination of the seeds of moulds, which
however was far inferior to the ingenious microscopes of that time.
Those observations appeared, however, to my friend to be so unques-
tionable, that he would not forego the opportunity of making known the
principal points in his book.
From 1820 I made my observations in Africa with a microscope
made by Hofmann of Leipzig, of the cost of about £6, which, with a
greater magnifying power, gave a much better image; and from the
year 1824 I used together with that an English microscope by Bleuler,
which cost about £15, and the power of which was still higher. With
these instruments I followed up the critical investigation of the generatio
primitiva with increasing care; and the more exact my observations
were, the colder I became towards the idea of an instantaneous coagu-
lation of primitive substances into an organized being. In the whole
series of years, during which I have sometimes for days together conti-
nued those observations, I never, not even in a single instance, saw the
subitaneous origination from slime, cellular tissue of plants, &c., of those
minute organic bodies to me so well known ; still much less had I ob-
served the gradual development of elementary outlines that had suddenly
originated, of Entomostrati and other larger animalcules ; which was an
extraordinary delusion of M. Fray, who took the eauvie and fragments
of minute dead animals for sketches and rudiments of new generations *.
My observations pursued in Africa convinced me more and more
that the origin of the most minute organized beings must also be cycli-
cal; for although circumstances did not enable me there to bring to a
completion my investigations into the structure of the Infusoria, yet I
found always amanifest repetition of forms similar to those which I had
determined by drawings and measurements, and not at all that unlimited
variation of them which we should expect from the idea of a metamor-
phosis of destroyed organic substances into undetermined elementary
forms of life. Thus the basis on which my observations proceeded
continually became firmer. Corti’s discovery, that the eggs of some
Infusoria (Brachionus) burst when the young ones creep out, and leave
* Essai sur l’Origine des Corps organisés et inorganisés, par Fray. Paris,
1817; p.71. “J'ai vu des monocles, des polypes, des vers et d'autres animaua,
qui n’étaient encore qu’ébauchés ; la forme extérieure était jelée, mais Vintée-
rieur n’avait pas recu tous les globules actifs qui devaient le constituer. Ces
esquisses étaient encore immobiles.” ‘This puts one in mind of the celebrated
ancient Egyptian frogs, which were said to come into existence after the inun-
dation, and to hop about with only their fore part developed, while their hinder
part was still mud. Times are altered; for he that sees such frogs at the present
time, does not, even in Egypt, stand with trembling awe at a distance from them,
but lays hold of them, and finds that under the mud of the hinder part some-
thing more than outlines are hidden. So it was with me at the Nile; for I came
there indeed as a sceptic.
FROM SIMPLE PERCEPTIBLE MATTER. 561
behind an empty egg-shell, a true chorion, I had previously made with-
out a knowledge of the original observer; and I had even remarked
that the eggs were suspended by delicate threads, by means of which
they were carried about by the animalcule, as in the crabs. I noticed
also the entire intestinal canal, by means of the whirling of the mouth
aperture and the secretions of the anal aperture ; and, in the wheel ani-
malcules (Fotatoria), when it was completely filled, its whole course.
Some time after I also occasionally perceived traces of beautiful red-
coloured eyes in the wheel animalcules and Brachione; and recognised
more and more clearly a masticating apparatus in all the forms which
I examined, and free muscles insome. In 1827 my views respecting the
wheel animalcules had made a progress to the extent which is represented
in the third and sixth plates of the Phytozoa of my Symbole Physica. The
same decade of engravings I laid before the Association of Naturalists
in Berlin in 1828, but without text. I had used Bory de St. Vincent’s
nomenclature in these plates, although I did not approve it, solely
because I considered the innovations required by my observations
as a useless increase of synonyms until they had been brought to
maturity.
The reputation of Chevalier’s microscope, from Selligue’s intimation
that at a cheaper rate it would produce greater effects than those in
general use, induced me‘to purchase one in 1828 ; and with it I endea-
youred to arrive one step nearer to that physiological goal which I had
so unremittingly pursued during ten years. A review of the Infusoria
showed me not only that my earlier observations were no delusions,
but confirmed them, and inereased my conviction of their evidently
high organization; I convinced myself especially that the supposed
traces of eyes in some wheel-infusoria, Rotifer and Brachionus, were
distinct and constant. Being now accustomed to this new instrument, I
made great use of it on the journey to Siberia which I made in 1829
with Alexander von Humboldt: the extensive series of accurate ob-
servations, drawings, and measurements made during this journey, al-
lowed me, as soon as I returned to Berlin, to institute, with the greatest
advantage, comparisons with the observations, formerly made in Leip-
zig, Berlin, Africa, and Arabia: and as I had now no longer any fear
that the advocates and invstigators of the generatio equivoca might
be in possession of better instruments; having, moreover, already pos-
sessed myself of a most astonishing series of details of structure, I
became gradually convinced of the probability of an. universal high
organization, even in the infusoria, and so-called elementary molecules;
of their cyclical development, and of the numerous errors of earlier
_ observers. I found especially the great incongruity between the state-
ments respecting generation and structure, made by those who pretended
to have actually seen the generatio primitiva, and who stated that they
had observed the spontaneous origin of organic bodies from primitive
562 EHRENBERG ON THE ORIGIN OF ORGANIC MATTER
substances, or its gradual formation, without however having noticed’
their complex internal structure ; whilst at the same time, I myself, who
for a series of years had acquired a progressively deeper insight into
the organization of these minute forms, which were said to be developed,
destitute of organs, or imperfect, could never get a sight of their spon-
taneous or gradual origin from molecules, slime, vegetable tissue, &c.
A comparison of my observations on the bell-animalcule ( Vorticella
Convallaria and other species of this genus), which had been made
under geographical circumstances the most various, greatly confirmed
my impressions; and the repetition, with redoubled care, of my inves-
tigations of their gradual individual change, removed all doubts in
regard to a whole series of beings of various kinds, in which I disco-
vered a determinate cyclus of forms, deriving their origin from one
another. These data, of which I became convinced, in beings so
minute and so simple in appearance, incited me to direct my observa-
tions, with increasing care, to this point, and gave me a certain
anticipation of much more interesting results near at hand. High
organization, and cyclical development of the molecules, were to me
clear truths, floating in my imagination, and capable of more substan-
tial proofs: my only search was for the means to produce them.
Fortunate was the thought which brought to my recollection the
coloured nutritive substances, already often tried by me without suc-
cess. Confident of the result, I put various colouring substances into
the water containing the infusoria, and awaited their reception into
their organs of nutrition. The first experiments with common water-
colours failed, although I had selected many different colouring matters;
my conviction however of a better result was so strong, that I no longer
attributed its want of success to the organization of the animalcules,
but to unsuitable colouring matters. Other experiments also proved
unsuccessful. One day however I remarked, in experimenting, a
whitish sediment at the bottom of the small glass plate on which I had
mixed water colours with the water containing the infusoria; and as
in general the colours of the shops are mixed with white lead, I made
choice of some pure colours, and such as I supposed to be least
disagreeing with animal organization; such I considered indigo, car-
mine, and sap-green, as they are all of purely organic origin. With
these I began my experiments anew, and here also the clew was found;
all infusoria, even the smallest, soon filled themselves with the colouring
matter. The opacity of the water caused by the colour, enabled me
to distinguish much more clearly than the opacity caused by mud,
which I had made use of in my former experiments on the cilia, not
only the presence of the cilia, but also any separate part of the body
to which the vortex caused by the cilia carried the nutritive particles,
and where they were received into the interior of the body.
From the transparency of all these animalcules, I could see very
FROM SIMPLE PERCEPTIBLE MATTER. 563
plainly in their interior, either a developed simple intestinal canal, or
clearly defined, vesicular, coloured pouches similar to stomachs. In
those animalcules which had fully charged themselves, I could also as
plainly perceive in other parts of the body, particularly the hinder
parts, secretions of the superfluous matters through a separate anal
aperture. These traces of organization in the most minute beings were
now no longer useless indications of organs, but evidently real organs
performing their functions—cilia, mouth, intestine, anal aperture. This
result, long sought for indeed, and as it were extorted, to a degree of
clearness beyond expectation, urged me immediately and eagerly to
employ the same means for the investigation of all the species of infu-
soria found in my neighbourhood, which I had before observed in
various ways, and of which I possessed drawings, in order to elucidate
their organs of nutrition, and to delineate and determine their form;
whilst at the same time it was evident that the knowledge of their
organization was by no means completed by the discovery of the organs
already mentioned. The eggs, muscles, and eyes of the wheel-animal-
cules rendered probable the existence of similar systems in the others
also; and hence I not only most carefully reviewed in every manner
all the species occurring near Berlin, as to organs of nutrition, but I
also endeavoured to throw more light on the whole organization of
these minute beings ; thus I ascertained with much greater certainty
the true relation of the free muscles of movement, the whole course of
the intestine, the course and form of the female and male generative
organs, the great frequency of the beautiful red eye-points, regular
branching traces of vessels, and besides, little glandular bodies and
fibres in the interior, which are not at all opposed to the character of
nerves. In the throat I distinguished teeth so evident, that these alone,
had they been sooner discovered, would have sufficed to render cre-
- dible the perfection of the rest of the organization, according to the
type of larger animals. In the smallest infusoria, which up to that time
_ had always been considered as homogeneous globules, I recognised not
only an apparent internal belly, and at times an apparent intestinal
canal, with mouth and anal aperture, but also, at least in one genus
(Euglena), red points similar to eyes.
Of great importance however was, amongst other acquisitions, the
light thrown on their organs of reproduction. I perceived a very fine
granular reticulate matter, filling the intervening spaces of the intes-
tinal canal, to be secreted through the anal aperture, which charac-
terized itself plainly as a laying of eggs: the animalcules became at the
same time smaller, plicated, and edged, sometimes changed their form
very remarkably, but still actively continued to swim. Of a similar
_ character appeared to be the old observation, often repeated by me, of
a spontaneous partial solution of the smaller infusoria into fine granules,
Vou. I.—Parr IV. 2a
564 EHRENBERG ON THE ORIGIN OF ORGANIC MATTER
their living motions all the while continuing; and I searched for
analogies inthe Coceus, in which the death of the mother takes place
before the young ones break the egg, and in the tape-worms ( Tenia),
the hinder parts of whose body separate after, or even at the produc-
tion, while the anterior part continues to live. Finally, I established
and found in these minute infusoria a fourfold mode of reproduction :
by eggs, gemmation, transverse separation, longitudinal separation ;
while in the wheel-animalcules, only eggs, or living young from eggs,
are produced. The smallest Monads observed by me, which yet exhi-
bited internal organs of nutrition evidently filled, were gogq lin. in
diameter. These measurements are made with a glass-micrometer, by
Dollond, which indicates to the ;g4,5 of an inch. The granules of the
ovarium of those minute infusoria which were observed to produce
young, were in their relative magnitude to the mother animal in the
proportion of 40 to 1, or as 80 to 1. The eggs of the wheel-animalcules
were in general as 3 or 4 to 1.
In this way, and by the means which I have stated, I was enabled to esta-
blish at once the doctrine of the infusorial animalcules more completely
and accurately than it had been up to that time; and the easily visible
colouring of the nutritive organs, from the transparency of these bodies,
might well induce others to participate in the results obtained. This
elucidation of the infusorial world I gave in an academical memoir
read in Berlin, and have circulated since 1830 about one hundred
copies by the booksellers. The separate copies have the distinet title
Organisation, Systematik und geographisches Verhdltniss der Infu-
sionsthierchen, von C. G. Ehrenberg ; Berlin, 1830. In this folio work,
which is accompanied by eight copper plates, I separated the so-called
infusorial animalcules, according to their organization, into two quite
distinct classes, one of which is distinguished by the great number of
ventral cells, and to which on that account I have given the name of
ventral animalcules or many-bellied infusoria (Polygastrica); the other,
which is distinguished by wheel organs and a simple intestine, I have
called wheel-animaleules (Rotatoria). The whole of the results of my
observations which I have there given are included in the following
fifteen positions :
1. All infusoria are organized and in part, probably all, highly or-
ganized animals.
2. The infusoria form two quite natural classes according to their
structure ; can be separated scientifically according to their structure ;
and permit no identification of their forms with greater animals, how-
ever similar they often may appear.
3. The existence of infusoria in the four quarters of the globe and
in the sea has been proved ; and they form the chief number, perhaps
the chief mass, of animal organisms endued with life on the earth.
FROM SIMPLE PERCEPTIBLE MATTER. 565
4. Some species are the same in the most remote parts of the world.
5. The geographical diffusion of infusoria on the earth follows the
already known laws of other natural bodies. Southwards there are
more varying forms, supplying the place of those of other parts of the
globe, than westward and eastward, but they are nowhere wanting;
the influence of difference of climate is not confined to the larger kinds.
6. The salt water of the lakes of the Siberian steppes does not ex-
hibit any peculiar infusorial forms varying in any remarkable manner.
7. The water of the sea supports other and larger forms than the
river waters; many however are identical; in none of those known
does the magnitude exceed a line.
8. In the atmospheric vapour which is precipitated as rain and dew,
I have never been able to observe, and I believe no one else with cer-
tainty, living infusoria. (I have related some recent experiments of
mine on this subject.)
9. In the deep subterranean places where atmospheric air, but
scarcely a minimum of reflected light, finds entrance, are found families
of the same infusoria as at the surface.
10. Direct observations in support of the generatio primitiva have
all, as it now appears, been deficient in the requisite exactness. Those
same observers who supposed that they had seen the spontaneous ori-
gin of minute organized beings from primitive matters, have quite
overlooked the very complicated structure of these organisms. Here
a great error cannot be doubted, and the delusion is evident. This is
perhaps less to be ascribed to the fault of the observer's precipitancy
than to the weak powers of the instruments employed, or the want of
practice in their use. Observations on the origin of crustaceous animals
_ and insects from primitive substances are the echos of the olden time,
when caterpillars grew from the leaves.
11. The idea that man was dependent, even if only in part, upon
the will of those infusoria of which he was composed, is proved to be
absurd, from the fact that the infusoria must seek their food, lay eggs,
and never combine into a fixed and growing state*. (Some it is true
unite at times into heaps, but these separate again into individuals.)
12. The development of all those infusorial forms which I have been
able to observe is cyclical, quite certain, but at times abounding in
varying forms, and from that cause delusive and demanding careful
_ observation.
Dr. Carus’s paper on the Kingdoms of Nature, etc. in page 246 of the present
volume, where he says,
_ “If we now reflect likewise how in the infusoria and Priestley’s matter,
the rudiments of the animal kingdom appear as so many animated globuli, we
_ shall thence perceive that the largest animal bodies themselves must be viewed
_ 48 an innumerable aggregate of infusoria, but at the same time united into a
living whole.” W. F.
2Q2
t __ *This may appear an exaggeration, but we need only refer the reader to
566 EHRENBERG ON THE ORIGIN OF ORGANIC MATTER
13. The results of my observations call to mind the old physiolo-
gical proverb, Omne vivum ex ovo. In my observations pursued
with so much zeal for twelve years, I never witnessed the spontaneous
origin of one infusorium from slime or vegetable tissue; but have often
enough seen the laying of eggs, and the young come out of the
larger eggs. Supported by such experience, I am of opinion that these
animals are never formed by generatio primitiva, but originate from
eggs. Whether then the eggs dispersed about are only in part the
product of laying, or in part the product of a generatio primitiva, is a
question which is not quite ripe for determination*.
14. The active motions and contractions in plants and their parts,
especially in Alg@, ought not to give rise to the supposition of an
animal nature, even when they are called infusorial or animal motions.
Internal nutritive organs, and a definite oral aperture for the reception
of solid substances, which may be demonstrated, distinguish the appa-
rently most simple animal from plants. I have never seen in my
numerous experiments the motive alge seeds take up the smallest
quantity of solid nutriment; and thus the fruit-strewing alga may be
distinguished from the monads which swarm round it in the same
manner as the tree from the bird.
15. Finally, I call attention to this fact, that experience displays an
unfathomableness of organic creations referred to the smallest portion
of space, in like manner as the heavenly bodies are to the largest portion,
the preternatural limits of both requiring optical assistance. Hypo-
theses may be started even so far as to the existence of primitive
substances ; it cannot yet be brought before our experience. The
milky way of the smallest organization passes through the genera
Monas, Vibrio, Bacterium, and Bodo.
In a more recent memoir read in 1831, which will appear in a few
days and the finished engravings for which I have already by me, I
have given the following most important additions which I have lately
made on the same subject. Hitherto I had only been able to observe
in the ventral animalcules (Polygastrica) the motive and nutritive
organs, and the ovarium. I had found traces of eyes only in one genus,
namely in the genus Euglena. I have lately found them more often in
the same class, so that I can now name seven genera possessing them
which contain sixteen species. Among these forms are some monads
which are only ;4, lin. in diameter. From this discovery then the traces
of an isolated nervous system are demonstrated down as far as the monads.
* This latter sentence, the restricting of the generatio primitiva to the for-
mation of eggs, appears to me to be modified by my subsequent observations
of the development and astonishing productiveness of the infusoria ; for it now
appears to be a subject of much greater wonder why we do not find more infu-
sorial eggs in water and everywhere, since there is cause for the formation of
an innumerable quantity in the common way.
FROM SIMPLE PERCEPTIBLE MATTER. 567
I have also made a first attempt to divide the two classes of infu-
soria in a greater degree by their internal organs. The nutritive system
gives in each of the two classes only four distinctions. According to this,
the Polygastrica fall into Anentera (possessing no intestine), Cyclocela
(with intestines forming a circle), Orthocela(the intestines straight ),and
Campylocela (the intestines crooked). The Rotatoria fall into Trache-
logastrica (long-throated without a belly), Calogastrica (long intestine,
without belly and with short throat), Gasterodela (with bellies), Tra-
chelocystica (with bladders). The intestine of the latter is very peculiar.
The Rotatoria alone, according to subsequent observations, may be
divided according to their masticatory organs, and fall then into three
groups: Agomphia (without any teeth), of which there are but few;
Gymnogomphia (teeth not fastened to anything),—this contains the
greatest mass; Desmogomphia (teeth connected). Those with uncon-
nected teeth (Gymnogomphia) fall into two great natural and equal
divisions, viz. Monogomphia (one-toothed) with a tooth in each jaw,
and Polygomphia(many-toothed). Those with connected teeth (Des-
mogomphia), whose teeth are not free but fixed on a cartilaginous base,
fall also into two natural divisions, viz. Zygogomphia, with teeth
placed in pairs, and Lochogomphia, with teeth in rows; so that the
following schema may be made :
Agomphia. Gymnogomphia. Desmogomphia.
Monogomphia. Polygomphia. Zygogomphia, Lochogomphia.
I. Il. Ill. Ve Mis
I have there stated my opinion as to the employment of these organic
differences for the purpose of systematic arrangement.
I have also in the same paper recorded my observations on the
development and production of individuals in the infusoria, particu-
larly in regard to time. The result of those observations I consider to
be one of the most important of the whole series in this memoir. A
_ single individual of Hydotina senta, one of the Rotatoria which I had
described at length, and given an engraving of in my first memoir, I
kept separate for the space of eighteen days, during which time I ob-
served it with the greatest care, and as it was already developed when
] isolated it, and did not die of age but accidentally, we may fix the
duration of life at above twenty days. An individual of this kind is,
however, capable in every twenty-four to thirty hours of a quadruple
inerease when the circumstances are favourable; in that space of time
it is able to develop four eggs, from the first activity of the ovarium
to the creeping out of the young. This quadruple increase, if there
}
is no hindrance, and if the individual animalcule lays forty eggs in ten
days, gives in the space of one day in the tenth power (that is on the
tenth day) a million individuals from one mother, on the eleventh day
four millions, on the twelfth sixteen millions, and so forth. - Although
the fecundity of the Rotatoria is the greatest which has ever yet been
&
568 EHRENBERG ON ORGANIC MOLECULES AND ATOMS.
observed in nature, and surpasses by far that of insects, yet it does not
by a vast deal reach that of the polygastrical infusoria. In Parame-
cium Aurelia, which is about 5}; of a lin. in size, and which I observed
with certainty during several days of a long duration of life, I have
seen within twenty-four hours, by simple horizontal division, the oc-
tuple increase of one individual, which would allow the possibility of the
double of that increase. As however these animals increase not only
by separation but also by eggs, and secrete these eggs not singly but
in masses, and besides in addition to these form buds, we have such a
possible immense increase of a single individual in forty-eight hours,
that we may leave off counting and speak of innumerability*.
Who now under such circumstances can wonder if within the space of
two or three days fluids swarm with suck animals ? Is it not more natural
towonder howitis that often itdoes not happen?. Wenolongernow require
a generatio equivoca to explain these phenomena; they belong to those
within the reach of experience and observation ; and where anything
astonishing of this kind may occur, the observer must take great care
that the fault of superficialness be not laid to him. If therefore I
supposed in my first paper that the generatio equivoea of infusoria
might still be ascribed to their eggs, it now appears to me from obser-
vations on the development and increase of individuals, that the neces-
sity of such an hypothesis, and even its probability, must vanish. I
now indeed believe that the generatio primitiva may as an ever-
existing subject of experience have undergone its mortal combat. Upon
this subject however I cannot undertake to solve all the problematic
points relative to it, of which there are many and important ones, par-
ticularly in relation to geology, as they are generally szbjective, and
but rarely objective; but I wish here to urge the consideration of the
indefinitely small, as a main position for all branches of natural history,
from which perhaps at a subsequent period I may also develop my
more special views.
"
%
;
%
Il. On Atoms and Molecules as subjects of experience.
Atomic philosophers have of late years, partly by their ingenious
theories for the explanation of the phenomena of light, and partly by
their ingenious as well as fertile atomic calculations of the doctrine of
porportions in chemistry, obtained an undeniable practical superiority
over dynamists, how much greater soever the satisfaction and recom-
pense of the latter may seem to themselves to be; and hence it has —
happened that in the doctrine of the smallest particles of bodies we —
* This rapidity and great capability of increase of the infusoria might also be
worthy the attention of analysing chemists, as they might quickly preduce a great _
infiuence on erganic substances, namely on some colouring substances. Boiling —
heat, or a few drops of alcohol, precipitate the infusoria, and they may then be —
remoyed as slime with certainty by filtration. It is necessary to operate quickly. —
Pa
.
ogee bh
RTECS
sortie
EHRENBERG ON ORGANIC MOLECULES AND ATOMS. 569
have become rather too bold. Not content with regarding atoms as
ideal unities, or as indefinitely small magnitudes, we have endeavoured
to find for individual atoms or for certain minute groups of them an
expression of a proximate finity, and even to fix its magnitude and to
determine it by numbers. Indeed it appears that but little is wanting
in our days to induce bold theorists to attack in good earnest the ma-
terial primitive particles of bodies, to clutch them fast, and to build
up with them even to organic structures, and thus to sport with them.
Newton indeed thought he might assume the elementary particles of
colours in bodies of a certain magnitude and perceptible to sense. He
says, p. 64, Prop. vii., “ For if those instruments (microscopes) are or
ean be so far improved as with sufficient distinctness to represent ob-
jects five or six hundred times bigger that at a foot distance they appear
to our naked eye, I should hope that we might be able to discover some
of the greatest of those corpuscles. And by one that would magnify
three or four thousand times, perhaps they might all be discovered,
but those which produce blackness.” If we now suppose that Newton
had rightly estimated the natural acuteness of the vision of the human
eye, his elementary particles for the red colour must not amount to less
than 3,455 of a line in diameter, as will be seen lower down; and
between this magnitude and that of ,z,2o, all the elements of colours
except black would be found, It is however probable that Newton sup-
posed the power of vision of the human eye to be less, and therefore
the size of the elementary particles to be much greater. However
we must here not forget, as Herschel has already remarked in his Optics,
that Newton distinguished the elementary particles of colours from
atoms, as later philosophers have also done, although he does not ex-
press himself to that effect. In that passage Newton does not speak of
atoms but of colouring particles. (Vewton’s Opticks (1704), book ii.
part iii. Prop. vii. p. 64.
The small magnitudes which have been employed for the explanation
of the phenomena of light in the undulatory theory give a great defi-
niteness to the calculation ; they can however only be regarded as
hypothetical and not as real demonstrated magnitudes, as the whole
theory, even though it possesses great probability, is in want of full
confirmation. The smallest lengths of a wave of light which can be
shown by an exact calculation, do not amount to more than the z5p555
of an inch, or about g755 of a line. Now as the particles of ether
must be considerably smaller than their undulations, there is in that
number a limit, arbitrary indeed, but yet determinate, for its maximum,
which gives an expression for its smallness. If from the impondera-
bility of very great condensed masses of light or of zther we were to
- form a conclusion as to the smallness of the elementary corpuscles as
ponderable objects, we should be obliged to place the limits of that
maximum ata still much greater distance. All these however, even
570 EHRENBERG ON ORGANIC MOLECULES AND ATOMS.
when they admit of a definite numerical expression, are still hypothe-
tical magnitudes.
The phenomena of colours between glasses almost in contact with
each other admit also of an inference as to the magnitudes of the so-
called elementary particles of colours. The smallest space which gives
the white colour was already fixed by Newton at >7_555 of an inch,
which is rather more than >z4,, of a line; and Hauy has reckoned,
from the different refractions of light of mica, that a plate of mica
which would produce the same effect as that of a stratum of air must
be a5qboo Of a millimetre thick, or s5pgg5 of a line.
Mr. Robert Brown made several admeasurements of inorganic solid
bodies, and also of organic ones, in the years 1827 and 1829, and fixed
the size of the smallest particles which could be observed, and which
he himself saw in spontaneous motion and of round form, at g5595 t®
sodn0 Of an inch, or gq,5t0 gzy5 of aline in diameter. (Brief Account
of Microscopical Observations, by R. Brown, 1828, and Additional
Remarks on active Molecules, by R. Brown, 1829, p. 3.*)
Sir J. F. W. Herschel says, in his Optics, 1829,p.680, that he had seen
bodies which were magnified by an Amici’s microscope to 3000 times
their diameter, from which however we were not at all to suppose that
the object even approached to its solution into atoms.
M. Dumas the chemist has however given to elementary organic
particles very considerable magnitudes. In the year 1825 he taught,
from his own observations, that with a good microscope the elementary
globules of dead organic masses might be seen and counted ; that they
formed, by means of simple combination and an augmentation of the
mass by increasing numbers, living bodies, becoming gradually larger
and more organized, the first forms of which were infusoria, and which
might again be divided into the elementary parts by means of an elec-
trie shock, by which they took a strawberry-like form (un aspect fram-
boisé). (Diction. Class d’ Hist. Natur., art. GENERATION, p. 195.)
One of the editors of the Annales des Sciences Naturelles, who does
not give his name, in tom. v. p. 80, 1825, fixes the magnitude of
the elementary particles of all organic substances at 34, of a millimetre,
or gt; Of a line in diameter. In the same work, p. 81, the author thinks
that, in accordance with the present state of chemistry, it ispossible by
synthetical means to prepare an artificial organic matter; and says,
“ Could we by these means obtain infusorial animalcules, Bonnet’s
theory of reproduction would be overthrown” !
There appeared in Kastner’s Archiv f. Naturlehre, xii. p. 348,
1827, an express chemico-microscopical exposition by M. Keelle. He
says, “ Zymom consists of microscopical globules, and with glyadin
forms gluten” (p. 350). “ Zymom is that matter from which, by a con-
currence of favourable circumstances, originate the lowest forms of
* Phil. Mag. and Annals, vol. iy. p. 161, and vi. p. 161.
EHRENBERG ON ORGANIC MOLECULES AND ATOMS. 571
organic nature” (p. 352). “ Globules of milk and blood are Zymom ;
gelatine, caseum, starch, sugar, &c., contain Zymom” (p. 350).
“ Silica first takes a vegetable formation, and from the Zymom formed
by this process originates further animal life” (p. 358). “ Vegetable ©
substance can be immediately changed into an infusorium” (p. 360).
“ From Zymom may be produced, when favourable conditions concur,
infusoria of this or that form” (p. 358). “ The first infusorium, the
lowest animal creature, is a living Zymom globule” (p. 358). “Zymom
is in a certain relation an egg” (p. 360). “ The yolk of an egg con-
sists merely of Zymom combined with slime” (p. 357). “This is no
hypothesis but a fact” (p. 361)!
That the commencement of many organisms is an action of putre-
faction or of fermentation, and therefore a chemical process, is a very
ancient opinion, and could not fail to be revived in a refined form..
M. Gruithuisen has in the eighth volume of Gehlen’s Journal der
Physik, 1809, p. 519, characterized the formation of the smallest orga-
nisms as a peculiar act of fermentation ; and enumerates, together with
the vinous and acetous fermentation, the infusorial fermentation which
forms organisms. In days of yore Autochthones might have been
thought to originate in this manner ; afterwards fermentation was left
for insects and weeds; but since their manner of living and of re-
production has been better investigated, such an origin is no longer
found to he either necessary or admissible with regard to insects or the
larger plants. It was then thrown upon the fungi and infusoria, on
account of the great difficulty of observing them ; from which how-
ever, in accordance with what has been stated, it must now also be
rejected.
M. Berzelius, who had to treat on the same subject in his Classical
Manual of Chemistry, but who does not offer any observations of his
own, adheres to the data given by other observers, that dead organic
_ matter when moistened with water creates infusoria ; and he finds no
_ improbability in Professor Hornschuch’s idea that the prima germina
_ rerum, which he conceivesto be the infusoria, might develop by various
external influences into other very different bodies. He has however
followed in the doctrine of organic atoms the representations of Dumas
and Milne Edwards ; and those organic atoms which by his doctrine
of chemical proportions have become so eminently useful and of such
extensive influence, are, in proportion to the imaginative capacity for
abstraction of various minds, unities more or less ideal, whose use in
theory seems destined for a long time to come to be of the most im-
portant value in the practical development of chemistry. (Animal
Chemistry (German translation by Wohler, p. 6), and Chemistry, vol.
_ jii. pp. 31 and 179.)
Very recently the well known physicist M. Munke of Heidelberg
has himself made several observations with one of Pldsl’s microscopes,
572 EHRENBERG ON ORGANIC MOLECULES AND ATOMS;
after the manner of the earlier philosophers, and in truth not very
profound, on the nature of the organic bodies in infusions; and he ima-
gines he has arrived at this result, that a transition takes place from
vegetable to animal life, and vice versa. (Isis, 1831, p. 1083.)
The examples mentioned in manuals of physics of the great divisi-
bility and ductility of different bodies are for the most part small
magnitudes merely in appearance, A gold leaf, thin as it may
appear, is about z555 tO apbo of a line in thickness.
It has not here been my intention to give a collection of the opinions
of natural philosophers and chemists respecting atoms, but to call to
memory only a few of those statements as to which I am best informed
and most certain, of the magnitudes of the smallest particles of bodies
which have been observed and calculated, in order to add to them the
results of more recent observations which I am now making known,
and to lay down a seale for them. The most recent theoretical state-
ments do not give any very great degree of minuteness to the ultimate
particles of bodies ; the observations of Mr. R. Brown very nearly ap-
proximate to those statements.
The common opinion that infusoria or mould could be made by
pouring water on dead organic matter I must pronounce to be com-
pletely contradicted by the whole series of my observations. It is true
the phenomenon is very deceptive ; but if we observe carefully, there
appear, even with the very same treatment, at one time some kinds of
infusorial forms, and at another time others; and I have never had it
in my power to produce certain forms with certain infusions, although
this is found stated in all manuals as true, and succeeded (by their own
account) with all earlier observers. There are however, according to
the results which I have obtained, certain common forms, which are
most generally diffused, the eggs or individuals of which may be present
in all liquids, even in some, perhaps only the noxious, parts of plants,
and of which at times the one form, at times another, may rapidly
increase according to the eggs or single individuals which were present
in the water, or had been introduced into it. M. Blainville in the
Dict. des Sci. Naturelles, art. ZoopHyYTES, also from experience pro-
nounces against the generatio @quivoca in infusions: “I haye often
taken great pains without any success to produce any kind of organic
body in small glasses by spontaneous development, although other
glasses by its side containing the same water were soon filled with them.
Besides the discovery of this error respecting infusorial fermentation,
which not only proves false in fact, as is also manifest from the de-
velopment of the forms, my investigations respecting the minutest
organic particles have led me to recognise the following minute mag-
nitudes as really existing and perceptible to the senses.”
I could plainly distinguish with a microscope magnifying nearly 800
times zoological monads or animal organisms, which were filled by
oan Roars
EHRENBERG ON ORGANIC MOLECULES AND ATOMS. 573
the above-mentioned process with colouring nutritive substances, and
which possessed voluntary motions, but the entire and greatest dia-
meter of whose body only amounted to the <4,5 or ggg Of a Parisian
line*. The smallest animal form, to which I have given the name of
Monas Termo, is the same being as that which Otto Fr. Miller has
delineated among the infusoria. I could perceive in the greatest indi-
viduals of this animal form as many as six, and in the smallest as
many as four, internal sacs coloured by blue indigo, which at times did
not occupy quite half of the dimension of the animal. Such a sac
therefore of the Monas Termo, if the animalcule measures 345
of a line, and if we suppose only four sacs occupying the half of it
(therefore not one of the smallest), is 3455 of a lin. in size, which is
five times smaller than the minutest particles observed by Brown. At
the upper part of this animal is perceived, as in all the monads, a
powerful pushing aside of particles still smaller than themselves, when
these come near to ‘them ; and it is therefore probable that they have
a fringe of ten to twenty cilia near the anterior part of the mouth aper-
ture, as in Monas Pulvisculus, and especially in the other still larger
monads. Further, if even we suppose the single colouring particles
with which the bellies are gradually filled not to be numerous, it would
be against all probability not to think that they were filled by several
particles. Let us however only suppose each sac to be filled by three
colouring atoms,—which from the roundness made perceptible by the
motion communicated to them we may well admit,—this alone affords
a proof of the existence of material colouring particles of red and dark
blue moving freely in water, which measure 34,5 of a line, or z39555
of an inch, in diameter ; and calculating these objects from the smallest
of the animalcules, which by actual observation were found to be gg55
of a line in size, and which sometimes contained four coloured points
in the hinder part of the body, these particles, which cannot be dis-
tinguished individually by the eye with a magnifying power of 800,
but yet are to be recognised as corporeal, would amount to zg45, of a
line, or =7¢555 Of an inch, which exceeds the molecules of Brown
_ nearly twenty times in smallness.
The above-mentioned transparent cilia about the mouth of these mo-
‘nads (perceivable only by their action) may also approach in fineness
those just cited; for if they were not less than =34,5, of a line, or the
multiple of forty-eight, withmy magnifying power of 800, there would be
no optical reason, except their transparency, why I should not see them
with that power, as will be evident from the sequel of the memoir. I
‘shall moreover direct attention to the fineness of other parts of these
organic living beings. The smaller monad-bellies are seen isolated in
* I have already mentioned that I make use of a glass micrometer which
Measures +p}-oy Of an inch.
574 EHRENBERG ON ORGANIC MOLECULES AND ATOMS.
the body and with sharp outlines. In larger infusoria which are 34 of
a line or more in diameter, these internal receptacles are recognised as
evident membranaceéous sacs, which often make their appearance isolated
when the animalcule is pressed or when it divides itself, and which have
been supposed to be separate infusoria, internal monads. From this
fact of the reception of nutritive substances by the smallest monads, we
have no reason to admit any other office for the organs of nutrition.
The sharply-outlined coloured points in the interior of the body of mo-
nads are to be regarded as small filled membranaceous vesicles or bellies.
Now in the larger infusoria of similar structure we can discern, when
two such bellies touch one another, that the thickness of the ventral
partition is in comparison with the diameter of the belly extremely
thin ; that the former is seldom perceptible ; and that the membrane
forms around the contents a mere mathematical spherical superficies.
Scarcely any one therefore would suppose a greater proportion than
20 to 1 in the. smallest. Granting however the thickness of the
partition to be only + of the diameter of the belly, this would amount
z of an inch, in individuals of Monas
to zaan00 Of a line, or 7yz0000
1_, of a line in size, in which the bellies measure but 4 of the
Termo 500
whole length of the body, and are therefore =;355 of a line in diameter;
—and since there is reason to look for vessels in these partitions, this
therefore places the organic atoms at a distance which I must, since
they are purely hypothetical, pass over, and leave as a subject of direct
subsequent inquiry.
There are still more powerful reasons for the probability of many
much smaller magnitudes. According to my observations mentioned
in one of the foregoing pages, there is in the body of the polygastrical
infusoriaa substance finely granular and reticular,—either in appearance
from the impressions of the numerous small bellies, or really so,—which
surrounds the whole of the intestinal canal and the masticating appa-
ratus, and is secreted partly upon the solution of the individual forms,
partly by the anal aperture, without any prejudice to the continuation
of their being*. This perceptible substance I have taken to be the ova-
rium: the granules of this ovarium in Kolpoda Cucullus are to the
mother animalcule as 40 to 1, others as 80 to 1; and they appear to
grow finer with the decreasing size of the body, being no longer of
themselves visible. Now it is probable that only their transparency and
the weak power of the microscope hinder us from finding such an
ovarium in the monads in every other respect so similar. We must not
however overlook that there may be young monads still inclosed in the
egg, or just come out from it, the diameter of the whole length of whose
body would be but the sgt50 tO go000 of a line; these may have
bellies which then, in like proportion, would be in diameter ggqgq9 to
* See supra, p. 563.
EHRENBERG ON ORGANIC MOLECULES AND ATOMS. 575
gitoso0 Of a line; the partitions of these monad-bellies will be but
£B0N000 tO saob000 Of a French line in diameter, &c. 1 have besides
seen rudiments of eyes in the monads to which I have given the name
of Microglena monadina, and which are ;}z of a line in diameter.
These often fire-red eye-points appear in larger infusoria to be a fine
granular red pigment, but whose granules, perhaps first covered by
many finer pigment granules, are small lenses, &c.; and although I will
not lay particular stress on the fineness of these parts, yet the existence
of eyes, however rudimentary they may be considered, allows of the
possibility that even in the smallest species they may be present, and
tends to lead us to a not so proximate finity of organic molecules; it
may even give a useful hint for considerations on the elements of
colours* and the theory of light.
Finally I must not pass over in silence a direct observation which
has confirmed me in the opinion that the small organic, apparently hy-
pothetical magnitudes really deserve great consideration. By the
kindness of Professor Enslen, who in the park near Berlin has a pecu-
liar contrivance for the public use of a solar microscope, I have made
with him several experiments. By observing Monas atomus well filled
with indigo, I discerned among them wandering shadows of smaller
_ monads, which could not by a vast deal reach to 3,45, of a line, and
which I could not atall discern inthe same water with the most powerful
magnifier of Chevallier’s microscope : perhaps their transparency might
_ be one reason. Whether these animalcules then be the brood of
_ Monas atomus, or various species of still unknown infusoria, it follows
from the observation, that 3,55 of a line is not at all the limit of or-
ganized beings for observation. It was on this account that I called
_ the smallest monad, which increases so plentifully in animal solutions,
* and which resembles the Monas Termo, page 94 of my memoir of 1830,
_ the Twilight-Monad ; because from this point a new sytem of organized
asa may easily be opened by means of increased power of vision.
____ Let not these calculations be disregarded as appearing to be playful;
_ they are so far in earnest that they are founded on the contemplation
_ of nature, and are not to be considered as a groundless speculation.
* In regard to the phenomena of colours in high achromatic magnifying
_ powers, I will just mention by the way that in some very small beautiful green-
_ coloured globular infusoria from +45 to 74, of a line in size, and especially in
_ Microglena volvocina, at a power of 400 or 800 I always see a fiery red ring
round the animalcule. ‘This ring is evidently an optical spectrum; but
how to be explained? Perhaps the animalcule is thickly covered with fine hairs ;
and this-hairiness causes perhaps, by refraction of light or play of colours, this
phznomenon, which is only apparent inthe periphery. Other similar beautiful
3 green animalcules never exhibit a red ring ; moreover this red is quite similar
tw the yellowish beautiful red which the pigment of the eyes in the Rotatoria
7 Polygastrica exhibit.
2
¥
ot
576 EHRENBERG ON THE POWER OF VISION OF THE EYE
They plainly demonstrate an unfathomableness of organic life in the
direction of the smallest conceivable space; and if the word infinity be
too much for what we know at present, let the word unfathomableness,
which I have purposely employed, avert from me the reproach of exag-
geration, and establish the point of view which the physical, chemical,
and physiological inquiries of our days, should they be rendered fruitful
by new powers, have to take, and what deviations they have to avoid.
III. An attempt to form a judgement respecting the Power of Vision of
the Eye and the Ultimate Power of the Microscope.
I will now connect with the above paper, for its illustration and con-
firmation, a few considerations on the power of the human eye, and on
the confidence and the hopes which we may found upon microscopical
observations and optical instruments. Up to the present moment, so
far as I know, we have never been able to fix a constant measure for
the ultimate possible power of the microscope. M. Amici, in a letter to
the Baron von Zach in the year 1824, (Ferrusac, Budlet. des Se. Ma-
them., p» 221,) has calculated the limit of vision according to the
power of the eye, and stated that a space of y'g of an inch becomes im-
perceptible to the naked eye at the distance of 28 feet. Lately the
angles of vision for the different colours have been calculated by M.
Plateau, but I have no:knowledge of any result from similar observa-
tions having reference to the microscope. I will endeavour to lay down,
without any pretensions, my investigations respecting the limit of vision
by the microscope made in a different way ; and I shall rejoice if they
make an addition to this branch of our knowledge and are not wholly
without utility.
In the numerous opportunities which I have had of watching persons
eager for knowledge who were desirous of acquainting themselves by
personal observation at my house with the wonderful structure of the
infusoria, I found to my astonishment the difference of the power of
vision of individuals by far more nearly coincident than I had expected,
and than itisgenerally stated tobe. When once I had placed the delicate
object in the right point of vision of the instrument, or directed the
attention of the naked eye to a very minute object, fifteen or twenty
persons, to whom I often showed these things at the same time, saw
completely alike and with the same clearness what I myself saw: they
very seldom took another, and then but little different, distance of the
object from the eye, according to what they required. In order to be
quite certain that I was not deceived by the politeness or shame of those
who might not willingly say they had seen nothing, I have often desired
the observers to delineate the objects seen, or minutely to describe
them; by which I learnt with certainty that they saw the object exactly
the same and quite as distinctly as I myself had seen it, and almost
AND THE ULTIMATE POWER OF THE MICROSCOPE. 577
always without its being in the first place necessary to change the po-
sition of the microscope. These observations, continued carefully on
a great number of persons, with the most various distances of vision,
made it seem probable to me that there is a nearly fixed common limit
for the power of vision of the unclouded and healthy human eye, which
will admit of our forming a conclusion as to the ultimate power of the
microscope. Upon this I made various observations, in order to find
out how far the variations of myopical and presbyopical eyes pos-
sessed an influence on the general expression of that power; and I have
convinced myself various times that the not unfrequent opinion that
myopical people could see more and more distinctly than other persons
is quite unfounded. The result of my experience is twofold :
1. There seems to be anormal power for the human eye in reference
to the seeing of the minutest particles; and the deviations from it
_ appear to be much more rare than is generally believed.
We can only speak of those who at some distance or other can see
_ distinct!y. Among more than 100 persons that I have observed, there
_ were those who in the general relations of vision could see most di-
stinetly, not capable of distinguishing more than I myself saw; and those
__ who represented themselves weak-sighted or long-sighted were in ge-
_ neral capable of seeing in the same degree as I did, only they wanted
_ the object more minutely pointed out ; and besides, in seeing with the
naked eye it was necessary to have the object approached to or removed
_ from their eye.
2. The smallest square magnitude attainable in general by the hu-
_ man eye in its natural state amounts for white on black ground, as well
__as for black on white or light-coloured ground, to +, of a Parisian line
in diameter. It is possible by the greatest condensation of light and
_ excitement of the attention to recognise magnitudes between 31, and
4g Of a line, but without sharpness and certainty*.
__ This is the limit of the power of the natural human eye for coloured
bodies, of which everybody can satisfy himself, as I have done, by
_ Strewing on white paper very fine black particles of dust, for instance,
of dried ink, water colours, &c., and then taking the smallest of them
_ with a fine point and placing it on a glass micrometer, which at least
5 gives the =, of a line. Sun- and lamp-light also allow easily of our ob-
_ serving black particles and the like, with or without a mirror, on the
glass micrometer on a light ground. Bodies which are smaller than
i those mentioned, notwithstanding all attempts, cannot be discerned with
__ the naked eye singly, but may be when placed in a simple straight row.
a“
1,
q * To insist on 3, would not be worth while. The next proportions worth
_ notice were ;', or =, of a line, and I have never been able to make any trial
_ whether it could be seen by any one.
578 ENRENBERG ON THE POWER OF VISION OF THE EYE
If there are several near to each other or several rows, they make a
joint impression on our eye and deceive us, as if we saw a greater
simple body or surface*. The general distance which good eyes main-
tain when striving to recognise these minute bodies, I found by mea-
surement to be from four to five inches, often six inches; the latter is
however the general distance for very sharp-sighted persons. Myopical
persons seldom bring the same objects to within four inches, and still
more rarely to three, &c., and become then for the most part like others.
Any one whose distance of clearest vision is four inches cannot by a
greater approaching of the eye to the object increase his power of vision,
but feels pain, and does not see distinctly. If we have once hit on the
object, we may remove it considerably without losing sight of it. I
myself cannot see 3; of a line at twelve inches’ distance black on white;
but having found it at from four to five inches’ distance, I can remove
it to twelve inches and still see the object plainly. This phenomenon
is founded on the known power of the eye to accommodate itself some-
what to distance; we can often discern small objects at a greater di-
stance when our attention is directed to the place, or when they move.
Similar phenomena are found in the air-balloon in a clear sky, and a
ship in the horizon; we easily see them after they have been pointed
out to us, but the faculty of rapidly descrying depends on custom and
on the acuteness of sight, without permitting of any conclusion as to
the power of vision in general. When any person is more strongly ex-
cited by visual impressions than another he discerns them quicker, but
he does not on that account see more than the other, who because he
does not receive these impressions so vividly discovers them slower. I
often employ a glass to seek for objects which I wish to examine
with the naked eye, in order to give them another position with a
pointed instrument; this fact has relation only to finding the place of a
body, and merely furthers quickness of discernment. Myopicaleyesalways
find out things more easily, because they are less separated, and their field
of vision is smaller. Probably there is still a higher degree of the ab-
solute power of vision of the human eye to add, which is that of the
discerning of luminous bodies. In the dark, small luminous bodies
appear, as isknown, much larger than they are; and these, whether they
be themselves luminous or only reflectors of light, are capable ac-
cording to the strength of the light of easily affecting the human eye
at a much less magnitude than the #1; of a line. I have never had the
opportunity of observing self-lighting magnitudes which were really of
so small a diameter that I could direct attention to a limit in regard
* T am accustomed in this manner to discern very fine cilia of the infusoria.
As soon as they are moved they form a small apparent surface, which is percep-
tible ; as soon however as they leave off, their fineness is often such that the
power of vision does not reach them with the microscope.
AND THE ULTIMATE POWER OF THE MICROSCOPE. 579
to this. How far astronomy may afford us data which may be caleu-
lated with exactness, and applied to this subject, I will not discuss; for
even if the measurement of the strength of light did not give a retar-
dation, subject always to the prevailing theory of light and hypothetical,
‘no certain conclusion can be deduced for the want of direct knowledge
aswell of the magnitude as of the distance of the heavenly bodies.
Bodies which reflect light can indeed be examined, but the result of my
_ experience has no particular bearing as to optical instruments. Metal-
jie lustre, which is a very powerful reflector, may, according to my
experiments on gold dust, be discerned with the naked eye in common
‘daylight up to the ;3, of a line, therefore double in proportion to
colours. But this same bright surface when magnified 380 times,
3 appears then dull and uneven, and the corpuscle acts only as a black
_ one, or becomes transparent with a leek-green hue. The coloured
: transparency of gold seems to commence at the thickness of 3555 of a
line in diameter, and is evidently not the consequence of porosity.
_ Fluid metals might probably form the smallest magnitudes attainable ;
i but even could we see with the microscope the reflected light of the
_ multiples of the magnifying power with 100, &c., the outlines of bodies
_ so minute would still remain the more undiscernible the stronger their
reflection of light is in proportion to their magnitude. The dust of
_ diamonds upona black ground in concentrated solar light, may probably
afford the ultimate square power of reflected light; I have however
hitherto not been able to make any observations on this point*.
With lines it is very different. Non-transparent threads 71, of a
line in thickness, by holding them towards the light, may be discerned
with the naked eye. Spider-threads measure 33, to gj/55 of a line;
threads of the silk-worm z3,. The latter in the cocoon are double.
The result of these inquiries is as follows:
_ Optical instruments enable us to see with distinctness of coloured
re parts of a line only multiples of their magnifying power with the
number thirty-six, or at most, but then not distinctly, up to the number
orty-cight. The limit for lines and light impressions lies much further,
is determined by the intensity of the light.
The most accurate microscope, with a distinct magnifying power of
a
* I obtained the finest particles of gold by scraping gilt brass. By filing pure
gold I always obtained much coarser particles.
The thickness of leaf gold used for gilding is quite imperceptible to the naked
_ eye, like the edge of a very sharp knife. If they are distinguished, it is by
_ means of the inequalities of the bent border, and this is an optical deception.
In the gray mercurial ointment the quicksilver forms, if well prepared, almost
equal globules of about 54,5 to rz'no Of a line in diameter, which are hindered
from uniting by the covering of grease. These finest quicksilver globules are
not to be distinguished by the naked eye even in sunshine, but form with the
white lard a gray colour. Larger globules may often be perceived in it. The
t covering may probably dim the metallic lustre.
Vor. 1.—Part IV. 2R
580 EHRENBERG ON THE POWER OF VISION OF THE EYE,
100, never according to this enables us to see, with every effort, square
objects smaller than corpuscles of 5,155 to zg'55 of a line in diameter.
If however all circumstances are not happily combined, as is often the
case, it is impossible to discern even much larger magnitudes. A di-
stinct magnifying power of 400 allows of the possibility of distinguishing
square magnitudes which are of ;z1,5 to zg455 of aline in diameter,
or which amount to nearly the half of the length of a wave of light in
the undulatory theory. With a magnifying power of 1000 we should
be able to discern square bodies which are of 57455 to zg4q5 Of a line,
and we should then distinguish Newton’s elements of the red colour, or
be convinced that they do not exist. With a magnifying power of
3000, like that which Amici’s microscope is said to possess, we should
be able to distinguish the +315, to the 4745, of a line, and with this
must discern almost all Newton’s elements of colours ; nevertheless we
should not yet be able to ascertain the thickness of the partition of the
belly of a monad, but must presume its presence only from the act of
the holding together of the nutritive particles.
To pass over Amici’s improvements of the microscope, which have
become so important, but which unfortunately are still too expensive,
a field has been opened to mechanism by what Selligue has made
public respecting compound microscopes ; andby the method of advan-
tageously combining several simple achromatic object glasses, already
applied by him to simple microscopes, and to other combinations, and
which has been executed by Chevalier in Paris, and by Plosl in Vienna,
with so much ability and success ; from which it appears that by em-
ploying the other auxiliary means, the power of vision of the eye may
be still very greatly raised by increasing the degree of magnifying
power which is compatible with distinctness: and the more we look for
a speedy improvement of optical auxiliary means from the praiseworthy
emulation of the distinguished, and often so completely scientific me-
chanists and opticians of our time, the more it behoves the observer to
tell his views and wants, openly and freely owning his ignorance of
the practical details.
There are, as is obvious, in regard to mechanical discoveries and
improvements, two things especially for mechanists to keep in view.
On the one hand judicious treatment of the object con amore, without
looking to a high price; and secondly, the simplifying of improvements
already discovered, and the greatest possible diminution of the neces-
sary cost by these means, in order to diffuse their application. It is
not indeed to be expected or desired that men who are capable of pro-
ducing permanent works of art should employ their time in rendering
their mechanism more simple; but the incitement of others to the sim-
plification of their discoveries, and the multiplication of the simplest
constructions, which not only include the newest principles, but also
AND THE ULTIMATE POWER OF THE MICROSCOPE. 581
the highest power, should raise in them a stronger interest for diffusing
as much as possible the use of their instruments than it actually does;
and then it is little to be feared that their own satisfaction, honour,
profit, and advantage would be taken from them. I have observed the
greatest power, although with some inconvenience, in one of Plosl’s
best microscopes which our Academy of Sciences possesses. A better
still, one of Amici’s best microscopes, Berlin is wholly destitute of, or it
is not known to me, although it is very desirable that the examination
of such an one were not inaccessible to the scientific persons of this
town.
It is exceedingly gratifying, that in addition to the recent very careful
and successful exertions of M. Ober-Bergrath Schaffrinsky, which un-
fortunately have not extended further, MM. Pistor and Schiek also,
_ whose great scientific accuracy is universally acknowledged, have resolved
to apply their care tothe microscope; and those already produced are, as
I have convinced myself, so excellent, that they are little inferior in
power to my Chevalier’s, and in convenience are evidently superior.* I
will here remark that in the microscope, clearness in small magnifying
_ powers, however great it may be, is no superiority, but a property indis-
_ pensably requisite to the character of a good one; and that the term
superiority can only be applied to the greatest distinctness and conve-
_ nience along with the highest powers.
_ * M.Ehrenberg, it appears, was then not acquainted with Schiek’s new mi-
croscope, and a letter alluding to this subject is found in the same volume of
Poggendorft's Annalen, p. 188, where he says, “ The sharpness and magnifying
ower which M. Schiek has succeeded in giving to this convenient and elegant
_ instrument, filled me with true inspiration ; and since its properties are founded
on a rule determined by him for the combination of the object lenses, and several
_ instruments finished at the same time gave the same clearness of image, I think
it my duty, and advantageous to science, to make known the results of a com-
_ parison of it with the best instruments in this town.” He then enumerates the
_ good and bad qualities of Chevalier’s and Plisl's microscopes, and says, “‘ The
microscope of Schiek unites the chief merits of those microscopes; large field,
extremely sharp and clear light, which leaves nothing to wish for, even in the
__ highest powers; magnifying power equal to the highest of Plésl—twice as high
as that of Chevalier, and moreover a much greater focal distance. Besides this,
‘it possesses a most convenient and elegant form, without being weak in its
_ framework.” In another place: “The great clearness of the image, and the
_ due strength of light, is an advance ; but the union of all these good properties
in such a degree is a still greater one.” Since Ehrenberg wrote this he has had
_ the opportunity of comparing Schiek’s instrument with those of Dollond and
_ Amici. His opinion was that it surpassed them in conveniency and elegance, and
quite 2 pute them in power, largeness of the field, and focal distance.
___ M. Ehrenberg adds that his measurements were made in the same plane with
_ the object, and not at a distance of five, eight, or twelve inches of the eye from it;
__and informs whoever wishes to make a comparison, that his eye-distance from
_ the object was, with a power of 380, 10” 6’; with a power of 800, 1'5!. He
also suggests that in comparing the power of microscopes, the mean length of view
of ordinary sight should be taken as a point of measurement at 8"; and states that
is magnitudes refer to absolute measure, and require no reduction.—W. F.
Z2R2
fc
eee
582 EHRENBERG ON THE POWER OF VISION OF THE EYE,
Mechanists and less experienced observers are very often in error
about this, and imagine that by clearness of the small magnifying pow-
ers they compensate for the strongest. Since, according to the state-
ment of Herschel, Amici’s microscope magnifies with clearness 3000
times, it should be the endeavour of opticians not only to imitate the
form and method of this instrument, but more especially to multiply
and simplify in every possible way that property of the highest distinct
achromatic magnifying power. For the general study of the finer or-
ganization of all organized beings it is needful to possess in our days a
clear achromatic magnifying power of at least 300 to 400 times in dia-
meter. Microscopes which are of less magnifying power are, notwith-
standing all art, beauty and clearness, not to be recommended to stu-
dents and public establishments. Costly screw micrometers, more than
three or four achromatic object glasses, which may be used single or
together, reverberatory apparatus, and glass prisms, are mostly unneces-
sary, and of advantage but rarely and in limited cases; and their use
not proportionate to their cost. On the contrary, there are various
things, especially a fine glass micrometer, and separate powerful mag-
nifying eye-glasses, and double mirror, which really help and supply the
wants of the active and careful observer.
I cannot promise myself much from the solar microscopes until they
are further mechanically developed. Those which I have had the op-
portunity of seeing may certainly be considerably improved, and their
‘power increased. I conclude by again repeating the observation, that
there are, putting aside all inorganic bodies, even in the kingdom of or-
ganic bodies whose constituent parts or molecules are generally con-
sidered to be the coarsest, magnitudes capable of direct proof which
are in diameter z335, Of a line; and others that can be proved indirectly
which may be less than a six millionth part of a Parisian line in diame-
ter; that the ideas often expressed respecting atoms, as subjects of
experience, are somewhat tvo confident ; finally, that the power of
the microscopes which we at present possess does not in its maximum
amount to more than to make distinctly visible long opake threads of
1 1
1,200000 144000
in diameter ; and that for these latter they must be increased forty
times in order to satisfy what is required for reaching directly those mi-
nutest parts of organic bodies whose existence has been inferred from
simple deductions ; and that we are not to entertain a thought of per-
ceptible or ever attainable simple matter, or material primitive con-
stituent particles.
of a line
'’ diameter, and square superficies or globules of
ADDENDA.
1. As regards the Spermatazoa, which might be regarded by many
persons as very important in the decision of the question of the
AND THE ULTIMATE POWER OF THE MICROSCOPE. 583
primitive origination of the Entozoa, and which have not been men-
tioned in the memoir, I will only remark that these bodies are metho-
dically inoculated into every animal being in which they have hitherto
been discovered, which implies nothing wonderful, but only much that
is obscure, and which hereafter may be gradually cleared up by an in-
creased power of the microscope.
2. On the perception of the smallest bright bodies I have had an op-
portunity of obtaining a few more results. On pressing small globules
of quicksilver on a glass micrometer, I easily obtained smaller globules
of th tO aq'oo Of a line in diameter. In the sunshine I could only dis-
cern the reflection of light and the existence of suchglobules as were 335
of a line in diameter with the naked eye; smaller ones did not affect my
eye either in sunshine or with a Chevalier’s reverberatory lamp. I
however remarked, at the same time, that the actual bright part of the
globule did not amount to more than 53, of a line in diameter. Spider-
threads of 5,5," in diameter were still discernible from their lustre.
3. I have lately made some experiments on the dust of diamonds, and
found that a diamond superficies of ;3, of a line in diameter presents a
much more vivid light tothe naked eyethan one of quicksilver of thesame
diameter. I have not yet been able to find smaller particles of diamond
dust possessing a good lustre. The smallest particles were from >755
to 3555 of a line in diameter ; but even under the microscope no lustre
was to be perceived. This, perhaps, was owing to the treatment. The
result of these supplementary observations is, that fluid metals, since a
small part only of their globular superficies shines strongly, make per-
ceptible only very small particles of light; that in proportion much
smaller lamina, especially diamond lamina, may be at least as easily
discerned as considerably larger metallic globules. Whether the pro-
portion is as 1 to 3, further investigations must teach us. Particles of
light having a linear form constitute the utmost limit ofthe power of
vision; and the luminous or light-reflecting corpuscles are the fixed
stars of the microscopic world.
ARTICLE XXIX.
On the Application of Circular Polarization to Organic
Chemistry ; by M. M. Bror and CHEVREUL.
On the Application of Circular Polarization to the Analysis
of the Vegetation of the Gramineae; by M. Brov.
(Read before the Royal Academy of Sciences of Paris, July 1st, 1833.)
From the Nouvelles Annales du Muséum d’ Histoire Naturelle, vol. iii., p. 47, sq.
Ir being my intention to show by experiment in what manner indica-
tions derived from circular polarization may be usefully employed in
chemical researches, principally in those of organic chemistry, the
innumerable transformations effected in carbonated products by vege-
table life appeared to me to be one of the objects of study best adapted
for the attainment of this end. For these products, so various in their
appearances and physical properties, being, under an infinity of cireum-
stances, composed solely of carbon and water united in different pro-
portions, their mixtures, combinations, and transmutations, offer ex-
cellent tests of a method which distinguishes them individually by
inspection alone, and thus ascertains their presence without altering
them. Now organic chemistry was deficient in precisely these cha-
racters recognisable by inspection, the consequence of which was its
difficult, I may even say its often uncertain progress; because, being
unable to recognise bodies otherwise than by isolating them, and this
isolation being effected only by the intervention of special agents
applied to the combinations or mixtures of which they form a part, the
choice and appropriation of the tests to be employed for each case
could only be determined by the conjecture, more or less probable, of
their presence ; and there is often danger of modifying these products
by thus acting upon them, or even of creating new ones by uniting the
principles of which they are formed ; so mobile are the combinations
upon which they depend, and with such facility do they become con-
verted into each other. :
The indications (caractéres indicatifs) furnished by circular polari-
zation certainly will not remove these last-mentioned difficulties, which
are inherent in the subject ; but in very many cases they will abridge
and reduce them to those which are inevitable, by in the first instance
furnishing the chemist with the properties capable of being immediately
observed, predicable of the molecular condition of the combinations on
which he has to treat; then by rendering equally visibleand observable
all the changes by which that primitive state may be altered, so that
M. BIOTS ANALYSIS OF THE VEGETATION OF THE GRAMINER. 585
he may be aware of their occurrence as soon as they take place ; and
lastly, by affording characters of the same order for distinguishing the
greater number of the organic products which he isolates. We do not
here pretend to supply chemical tests, but simply to illustrate in many
cases the convenience of their application, and to characterize imme-
diately the consequences resulting from them by sensible effects; for
it is definitively chemistry and chemistry alone by which the products
ean be isolated and resolved into their component parts.
The employment of this method, as the Academy has seen, has al-
ready enabled me to discover the singular modifications that the foli-
aceous organs of exogenous trees produce in the ascending sap which
supplies them with nourishment in their first development; and it
afterwards assisted me in distinguishing the elaborated products which
these same organs convey under the cortical layers to nourish, or even
perhaps to form the new cellular tissue. Persons conversant with the
study of vegetable physiology can alone give to these researches the
generality necessary for the deduction of its laws. All my ambition
has been to offer them an experimental method of tracing these myste-
rious operations. The results that I now offer to the Academy are
directed to the same end, and are intended to confirm those previously
obtained, while they at the same time render them complete.
The long duration of exogenous trees is accompanied by a propor-
tionate retardation of the total development of the phenomena of their
vitality. The trunks of the Graminee, the existence of which is com-
pleted in a year, presents in this narrow circle the whole series of the
analogous phenomena. From this class I have selected rye and wheat,
with the intention of examining the various phases of their vegetation.
From the researches on germination of physiologists and chemists,
we have learned what takes place immediately after the birth of these
plants. The amylaceous globules (globules féculasés) deposited in the
perisperm of the grain around the embryo are emptied, and the dex-
trine which they contain is converted into sugar, which serves as nou-
rishment to the young stem until its foliaceous organs and roots are
developed. But when this first supply of aliment is exhausted, the
young plant is left to procure such as will continue its development.
Now the nature of these new alimentary products, the modifications
which they undergo in the various parts of the plant, and the manner
in which these various parts contribute successively or simultaneously
to nourish the seed, and to supply it with the substances of which it is
to be composed, by transmitting the new alimentary products to the
feeundated ovary, have not I believe been hitherto experimentally de-
termined.
It is necessary here to distinguish the solid materials, the fixation of
which constitutes the skeleton of the plant, from the juices and soluble
586 M. BIOT ON APPLYING CIRCULAR POLARIZATION TO THE-
products, which being unceasingly formed, destroyed, and renewed, are
conveyed by the life to every part of the vegetable, and conduce to its
nutrition. The fixed materials may be known by the analysis of the
dead cr withered vegetable ; but even among these we have to distin-
guish those which are essential to the existence of the plant, and those
which have been accidentally raised from the earth by the roots, with
the water in which they were dissolved, or held in a state of sufficient
tenuity to be transmitted through the vessels and the vacuous spaces
of the cellular tissue, I shall be careful not to commit myself in these
complex questions, for which all the assistance of chemistry and of the
microscope is scarcely sufficient, I shall confine my remarks to a few
of the alimentary products of plants which are known to be composed
by them, and conveyed into their various parts whilst undergoing the
metamorphosis produced by vitality.
My first trials upon rye were made on the 3rd of May, upon young
shoots, in which the ear was already developed but not yet flowering,
and indeed far from it. The roots, the stems, and the ears were sepa-
rately treated with water, and the extracts submitted to the tests of
circular polarization; then these extracts concentrated but not desic-
cated were treated with alcohol, and the substances whether precipita-
ble or non-precipitable were in the same manner submitted to the tests
of polarization. Finally, these substances thus isolated were brought
into contact with yeast in order to ascertain those which were or which
were not fermentable; after which their rotation was observed, to dis-
cover whether it were diminished, increased, or altered in direction.
The extract of the roots presented indications of an exceedingly fee-
ble rotation directed towards the left. As the extract of the stems acted
in the same direction, I thought that these feeble indications might be
attributed to the roots not having been rigorously separated from them.
I had not then observed that similar almost neutral mixtures may be
produced by sugars having contrary rotation, which are detected and
rendered discernible by fermentation when one of their elements is cane
sugar. The experiment must be renewed and completed by the aid of
this process the following year.
The extract from the stems contained a mixture of grape sugar.
turning to the left, cane sugar turning to the right; and a substance pre-
cipitable by alcohol, which possesses the characters of gum of being
completely soluble in water, and of directing the rotation to the left.
These three substances originally mingled in the extract produced a
resultant of rotation towards the left; this resultant was considerably
weakened when the precipitable substance was separated, to the point of
making the alcoholic extract appear almost neutral. But when the alco-
hol was expelled by heat, and the residuum of the extract brought into
contact with yeast, a lively fermentation took place, and developed a
ANALYSIS OF THE VEGETATION OF THE GRAMINEA. 587 »
strong rotation towards the left, thus detecting the mixture of grape
sugar, not solidified, with cane sugar, which mutually concealed each
other before the latter was interverted. The substance exhibiting a ro-
tation to the left, and precipitable by alcohol, experienced also the alco-
holic fermentation by contact with yeast, this property being either
proper to it or arising from asmall quantity of sugar which might have
been entangled with it in the precipitation. But the effect of the fer-
mentation was ouly to weaken the rotation, without altering its direction.
Twelve days after, on the 15th of May, the ears being more deve-
loped, but still far from flowering, the stems again presented the
mixture of these three substances. But the proportion of cane sugar
was increased, for it determined the resultant of the rotation in its pro-
per direction, towards the right, before fermentation. When this sugar
was destroyed in the extract by boiling it with sulphuric acid, the in-
fluence of this acid changed the direction of the rotation of the sub-
stance precipitable by alcohol, which passed from the left to the right.
This, as M. Persoz and myself have shown, is also a property of gum.
The extract from the ears before flowering presented characters
very different from the extract from the stems. Neither cane nor grape
sugar was detected in it, but only sugar of starch (suere de fécule),
which the fermentation enfeebled without changing. Alcohol also
produced a precipitate in it, but of a different quality to that of the
stems, for it was not soluble in water, or only so in a very small degree ;
and this precipitate viewed with the microscope appeared formed only
of shreds of cellular tissue and the remains of integuments similar to
those which cover the globules of starch, without any sensible mixture
of pulverulent matter. These results agreed with M. Raspail’s observa-
tions, that the pericarp of the Cerealia before fecundation is filled with
starch (fécule) in very small grains, the soluble matter of which is pro-
gressively absorbed by the ovary, and serves as nourishment to it when
the fecundation is effected. But as the extract of the ears made pre-
viously to fecundation here presents us with sugar of starch, not with
dextrine, it is evident that the globules of the pericarp must either con-
tain this sugar ready formed and prepared to be absorbed by the young
ovary, or that the globules are accompanied by a principle analogous
to diastase, which breaks them and converts their dextrine into sugar,
as in germination.
After fecundation is effected the composition of the ears is greatly
altered. On the 15th of June the young grains of rye, taken from
the ears, contained grains of starch ready formed, which were visible
with the microscope. They burst under the influence of sulphuric
_ acid and disengaged a substance soluble in water and precipitable by
aleohol, which is ascertained to be dextrine by the great energy of
_ its rotatory power compared with its density. Sugar of starch ready
588 M. BIOT ON APPLYING CIRCULAR POLARIZATION TO THE
formed is also found in it, the fermentation of which enfeebles the ro~
tation without changing it. There is nothing [in its polarizing action ]
which indicates the existence of cane or grape sugar.
The nature therefore of these two sugars which are contained in the
foliaceous parts of the plant become changed like that of gum, by tra-
versing the collars of the ears; and they serve as materials to the young
grain, by which they are formed into dextrine, and the other products
which compose the perisperm.
I have made analogous experiments upon the young shoots of wheat,
but guided by the preceding, I have taken them more in division, ap-
plying them separately to the various foliaceous organs which in the
rye I had studied as a whole. In these organs I found diversities of
composition, of which I had no suspicion.
I commenced my experiments on the 19th of May, upon young shoots
of wheat in which the ears were not yet developed. Suspecting that
the composition of the leaves was different from that of the stem, and
that they were destined to nourish it after fecundation, in the same
manner as the leaves of trees nourish or form the new annual layer of
bark and alburnum, I carefully detached the cylindrical stalk from the
vaginating leaves which surround it, and treated these two parts sepa-
rately by the processes which I have just described, viz. by water, alco-
hol and fermentation.
The stems, like those of the rye, presented three carbonated sub-
stances, viz. grape sugar turning to the left, cane sugar turning to the
right, and a substance turning to the left which may be precipitated
by alcohol. The relative proportions of these three principles varied
considerably with the progress of vegetation. On the 20th of May their
mixture produced a resultant of rotation directed towards the right,
showing that cane sugar was predominant in it; but on the 4th of
June, the ears having left the stems and flowered, the resultant of the
stems had passed to the left, and was afterwards constantly maintained
in that direction, evincing that the cane sugar had become relatively
less abundant. It will presently be shown that in the ears it had passed
in excess.
The leaves furnished results very different from those of the stems ;
they contained indeed a mixture of grape and cane sugar and a sub-
stance precipitable by alcohol and soluble in water after that precipita-
tion, but, contrary to the stems, the proportion of cane sugar consider-
ably exceeded that of grape sugar; besides, the precipitable matter
having exerted a rotation to the right seemed to be dextrine, while in
the stems the precipitable substance had a rotation to the left, and ap-
peared by this character analogous to gum.
The leaves preserve this state of composition as long as their vitality
continues, but when fecundation is effected they may be seen gradually
"|
:
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ANALYSIS OF THE VEGETATION OF THE GRAMINEA. 589
to become yellow and to wither completely. This effect first takes place
in the lowest leaves, and in each commences at the apex of the leaf and
gradually extends to the point of insertion. When the leaves are com-
pletely withered, if they are gathered and submitted separately to the
tests that have been described, nothing can be found but some insensible
or nearly insensible traces of the saccharine principles and of the precipi-
table substance with which they previously abounded. Whence it appears
that at the period of which we are treating these carbonated principles
pass into the stem and serve it as an aliment, in the same manner as the
analogous principles, elaborated by the leaves of exogenous trees, de-
scend beneath the living cortical layer into the first external layers of
the alburnum, in order to nourish the young cylinder of wood and
bark, which like a hollow stem is annually formed and moulded upon
the ancient skeleton of wood.
In rye and wheat the basis of the stems therefore derive nourishment
partly from the leaves which are attached to them and partly from the
soil. The summit of the stem may also be supplied with aliment by its
own leaves, and may raise the inferior sap ; but the ear, when it has left
the stem, and especially when it has been fecundated, appears to exercise
a powerful faculty of absorption upon the juices contained in the sum-
mit, which must remove them rapidly, in proportion as they are fur-
nished by the base of the stem. To satisfy myself that this was the
fact I divided the stems of wheat, from which the leaves had been re-
moved on the 4th of June, into two parts, the ear being in full flower,
Of the two extracts thus formed, that of the bases contained nearly
twice the quantity of sugar contained in the extract of the summits,
the densities being equal. At this period also of full efflorescence the
saccharine principles are abundant in the ears of wheat. They ex-
ist in them in the state of sugar of starch and cane sugar, adjoined to a
substance precipitable by alcohol, which is perfectly soluble in water,
and has a rotation to the right like dextrine, but having less rotating
energy and susceptible of modification by fermentation. The presence
of cane sugar in the ears is ascertained by the rotation of the extract,
which though strongly directed towards the right before fermentation,
is suddenly thrown towards the left, and becomes very feeble as soon
as that phenomenon is completed. There was nothing to indicate
the existence of this sugar in the ears of rye before flowering, nor
in the young grains of rye, though the stems also contained cane sugar.
Could it arise from a difference of quality proper to the two plants ?
Whatever it might be they each present this remarkable result, that
the grape sugar of the stems does not pass in that state to the ears.
‘ As has been remarked above, in proportion as the fecundated ear is
enlarged the lower leaves become yellow and withered by transmitting
_ their carbonated products to the stem. The base of the stem also
590. M. BIOT ON APPLYING CIRCULAR POLARIZATION TO THE
withers and becomes yellow in its turn, while the superior part which
is still green continues to nourish the ear, as is well known to agricul-
turists. This fact, taken in conjunction with the preceding results, ex-
plains several practices in agriculture, and shows in what their good
effects consist.
Thus when the base of the stem is withered, if the Cerealia be cut
before the grain is ripened, it continues to receive nutriment and to be
ripened at the expense of the stem, as if it still remained adhering to
the soil. When the stems are dry the grain may therefore be brought to
maturity without its being exposed to the losses of spontaneous shedding ;
at least when there is reason to hope that the rains will not fall and
destroy it upon the earth, upon which it has been prematurely ex-
tended. The advantages of thus anticipating a retarded harvest have
been enlarged upon by skilful agriculturists, and the application of the
principle has been commenced.
Secondly, since the leaves and stems of green plants form sugar
and other soluble carbonated products, which are to be absorbed by
the seed, which, as I have just stated, occurs in wheat, rye, and, as
I have ascertained, in several other herbaceous plants, as well as in the
leaves of exogenous trees, if they are buried in the earth in that state
of verdure, it is evident that they will enrich the soil with all these
products, so eminently conducive to the nourishment of the young plants
to be produced from it. Now since it is proved by experiment that the
green parts of vegetables decompose the carbonic acid of the air and
appropriate the carbon, it becomes infinitely probable that this absorp-
tion contributes to form the mass of their saccharine and gummy pro-
ducts, in addition to the juices which they may draw from the earth by
their roots ; and this probability is increased when we see how consi-
derably the carbonated products of the leaves differ from the products
of the stems, which derive their aliment more particularly from the
earth. It is then the natural and legitimate conclusion that one part
of the solid mass of plants is furnished during their life from the car-
bon of atmospheric air, so that by burying them green in the earth more
is rendered to the soil than it has yielded.
Those only who are versed in chemistry and vegetable physiology
can enter deeply into the grand phenomena of the absorption and fixa-
tion of atmospheric principles in plants, whether immediately by their
own organs or by the intermediation of inorganic substances capable of
absorbing those principles, and of afterwards conveying them to plants
in the nascent state. The application of lime in this mode of interme-
diate action has already been suggested, and my own observations fur-
nish evidence in confirmation of the propriety of the suggestion. Pro-
bably analogous effects of absorption and successive transmission may
be produced by other substances, cither upon the carbonic acid or the
ANALYSIS OF THE VEGETATION OF THE GRAMINEX. 591
azote of the air, and their discovery would immensely extend our means
of fertilizing the earth. The processes of investigation that I have here
applied to products formed by living vegetables would be serviceable
in these useful researches by manifesting in numerous instances, by sen-
sible physical characters, the existence of the principles which have
been introduced into them.
When the annual circle of vegetation has been completed I shall col-
lect into a single memoir the results that have thus been obtained, ac-
companied by a detail of the experiments which have been employed to
determine them. This collection of examples, added to my previous
researches and to those which I have pursued in conjunction with M.
Persoz, will be sufficient to show in what manner indications of circu-
lar polarization may be rendered subservient to organic chemistry and
also the manner of applying them to that purpose. The only task that
I proposed for my own performance will then be accomplished, and I
shall expect from the active dexterity of our chemists the almost unli-
mited developments which it appears to promise.
Examination of an Optical Character, by which, according to
M. Biot, Vegetahle Juices capable of producing Sugar
analogous to Cane Sugar, and those capable only of pro-
ducing Sugar similar to Grape Sugar, may he immediately
distinguished; hy M. CHEVREUL.
From the Nouvelles Annales du Muséum d’ Histoire Naturelle,vol. iii. p. 307, sq.
1. I HAVE judged it expedient to devote a special memoir to the
development of the reasons upon which the opinion expressed in the
‘preceding report [on several papers relative to the chemical and physio-
logical history of starch, ] respecting the importance of the optical cha-
racter proposed by M. Biot to be applied to organic chemistry reposes;
in order to show that this opinion has not been formed without due
‘consideration, and that it is in fact only an application of the views
which I have elsewhere explained long ago, upon the relative impor-
tance of the various properties suitable to be employed as characters
in the definition of chemical species, considered individually and col-
lectively.
2. To attain this object I proceed to examine the optical character
proposed by M. Biot:
First, in relation to the objections which may be urged against its
importance in organic analysis, and in the definition of species.
592 M. CHEVREUL’S EXAMINATION OF AN OPTICAL CHARACTER
Secondly, in relation to its probable utility in distinguishing the
various arrangements of the atoms or particles of a particular species,
and in estimating the alterations which may occur in bodies of deter-
minate species mixed together ; and to (in my apprehension) its real use
as a reagent or indication in the determination of chemical species of or-
ganic origin.
§ 1.
On the objections which may be urged against the importance of the op-
tical character.
ArTIcLE I.—On the objections which may be urged against the import-
ance of the optical character in immediate chemical analysis.
3. We examine in succession the cases; first, in which a juice causes
a deviation in the plane of polarization to the left ; secondly, in which
the deviation is to the right; and lastly, in which there is no deviation.
We shall afterwards treat of the difficulty of estimating the quantity of
active matter from the density of the liquid in which it is dissolved, a_
difficulty which arises in the two cases of deviation.
a. Deviation to the left.
4. When a deviation to the left in the plane of polarization is ob-
served, how is it to be immediately ascertained whether this property
belongs to gum Arabic, or to grape sugar not solidified, since it is
common to them both? How are we to be certain that the property
of the juice proceeds from only one of these substances, and is not the
result of the activity of them both? Lastly, what certainty is there
that it is not caused by other bodies than the gum and the grape sugar
not solidified ?
b. Deviation to the right.
5. There is the same uncertainty if the subject of observation be a
deviation to the right; for the dextrine of Biot, cane sugar, sugar of
starch of the first formation, sugar of starch of the second formation,
and solidified grape sugar have all the property of producing a devia-
tion to the right in the plane of polarization.
6. This is not all: sugar of starch of the first formation and cane
sugar have nearly the same energy, so that, as M. Biot acknowledges,
recourse must be had either to alcoholic fermentation which interverts
the plane of polarization of cane sugar to the left, and which leaves
unaltered that of sugar of fecula, or to sulphuric acid which produces
the same results. M. Biot gives the preference to the last method,
because he says that fermentation is an operation not sufficiently un-
derstood. But as sulphuric acid develops sugar of starch and grape
sugar with principles which are not saccharine, may not the employ-
FOR DISTINGUISHING SACCHARINE JUICES. 593
ment of it, at least in some instances, be productive of error? In
short, since it is necessary to have recourse to fermentation or sulphuric
acid, it is evident that the character of circular polarization does not
furnish the means of immediately distinguishing the vegetable juices
which yield sugar analogous to cane sugar, and those which only yield
grape sugar ; and that therefore it has not the advantage of giving a
more precise indication in organic analysis than that furnished by the
chemical processes, which are liable to the objection of disturbing the
equilibrium of the elements of substances, which by their means have
been separated from each other.
c. Case in which there is no deviation.
7. M. Biot quotes a case in which he found a fluid of an extremely
saccharine quality without rotation*, because it contained at the same
time grape sugar solidified and not solidified. He remarked that time
produces an alteration in the solidified sugar, gradually diminishing its
property of rotation to the left and directing it towards the right; thus
the same body spontaneously experiences a molecular alteration which
has a tendency to cause it to pass successively through a series of
states marked by the signs + 0 and —. After such a result, how
is it possible to imagine that the extreme states distinguished by the
signs + and — could be precise characters for other bodies proper to
cause their immediate recognition in the juices of plants ?
d. Difficulty of estimating the quantity of an active principle from the
density of the fluid by which it is held in solution.
8. The action of deviating from the plane of polarization whether to
the left or to the right, being the product of all the active molecules
contained in the liquid upon which the experiment is performed, it
follows that in the most simple case, that in which the activity emanates
from only one principle, when we would determine the specific nature
of this principle, it will be necessary to attend to its proportion relative
to the solvent; for as quantity may compensate for the feebleness of
the action, two solutions may have the same rotatory power, though one
‘may contain a principle much less energetic than the other.
9. How is this proportion to be ascertained? According to M. Biot,
by taking the density of the liquids; but if positive results can be
‘drawn from the determination of the density, it can only be when tables
of the respective solutions of each active principle have previously been
formed, in each of which the densities correspond to determined pro-
portions of the principle dissolved, and to the rotatory powers of solu-
_ tions made according to the same proportions.
* Nouvelles Annales du Muséum d'Histoire Naturelle, 3rd series, vol. ii. p. 341.
594 M. CHEVREUL’S EXAMINATION OF AN OPTICAL CITARACTER
10. Without such researches, without accurate knowledge of the
nature of the bodies which accompany one or several active principles,
of their proportions relative to their solvents, and of their influence
upon the density of the juice in which they are contained, how can a
general rule be formed for the appreciation of the density proper to the
active principle or principles of a vegetable juice, endowed with a pro-
perty of causing a deviation in the plane of polarization, in order to
deduce from it the nature and the proportions of the principle or prin-
ciples? Now science is actually deficient in all the investigations neces-
sary to surmount this difficulty.
ArtIcLe II.— On the oljections which may be urged against the import-
ance of the optical character in the definition of chemical species.
11. Though there is not for the classification and definition of che-
mical species, asubordination of characters comparable to that observed
in natural classifications, among which those endowed with life, such as
the zoological and botanical species, are ordinated into genera, families,
orders, and superior divisions ; yet there are properties in chemistry,
the importance of which rest upon distinctions essential to that science,
which furnish characters more or less rational, for grouping the species
together and distinguishing them from each other. The differences to
be remarked between the classification of chemical species and that of
zoological and botanical species arise principally, as I have elsewhere
shown, from the small number of general properties which are adapted
to serve as general characters of chemical species, from the corre-
lative relation of these properties, and from the circumstance that the
special object of chemistry is the circumscription of the species. We
will now enter upon a few details relative to. the properties capable of
serving as characters of chemical species, whether for grouping them
or for distinguishing each of them in particular, and supplying means
by which they may be known.
12. The combustible and comburent properties of simple bodies, and
‘the acid and alkaline properties of compound bodies, are general pro-
perties of such a nature, that if in consequence of their correlation,
they will not serve for the formation of groups perfectly circumscribed,
yet they serve to give a precise idea of a body which possesses one of
these properties in a certain degree of energy. We will take for ex-
ample the acidity of an oxygenated body when it is sufficiently ener-
getic to remove the alkali from the red substance of litmus.
Since it possesses this property which gives it the function of an acid,
it may be concluded :
Ist. Tha! it will enter into combination with all, or at least with the
greater part of the compounds of an alkaline quality.
=
FOR DISTINGUISHING SACCHARINE JUICES. 595
- 2nd. That the proportion of potash or of any other oxybase neces-
sary to neutralize this acid being once known, it will not be necessary
to have recourse to experiments to ascertain the quantity of the other
oxybases which are capable of neutralizing the same acid.
3rd. That the action of the acid upon organic colouring principles
may be predicted with a great degree of probability.
13. There are properties which, without having the importance of
those which have been noticed, are interesting, inasmuch as they furnish
useful indications. For instance, if a substance precipitates without
alteration the animal matter of the water in which they are held in solu-
tion, it may be inferred with great probability that it will preserve animal
matter, as is the case with the tannins; and I shall show that nearly
all the substances of which this is predicable, though they may differ
widely in their elements, have notwithstanding many analogous pro-
perties ; among others a flavour more or less astringent.
14. The properties which have been considered may be remarked
(12 and 13), though under different relations, when a community of
characters is endeavoured to be established between a greater or less
number of chemical species, differing greatly with regard to their ele-
mentary composition. Let us now examine the properties which are
the best adapted for the definition of particular species.
15. The properties the most suitable for this purpose are certainly
those which are manifested for our observation with equal intensity in
the different conditions in which the specimens of the species possessing
them may be placed. For example, acidity, which we have considered
as one of the most general properties of compound bodies, may become
a specific character of precision when considered in an acid body in
particular, with regard to the proportion in weight of the potash or any
other alkali, that a given quantity of this acid requires in order to its
neutralization. In fact this proportion will be constant as long as the
specific nature of the acid lasts.
16. Properties which are manifested by obvious phanomena of easy
production are also adapted to become specific characters; but I shall
show that these characters are specific in proportion to the small amount
of the alteration sustained by the elementary composition of the species.
With this circumstance in view, I have formed three groups of che-
mical properties from these three species: first, those which do not
undergo any sensible alteration in their composition; secondly, those
which undergo an alteration which does not prevent them from resuming
their first composition ; and lastly, those in which the alteration is suffi-
_ ciently profound to preventthe resumption of the original composition*.
* Considérations générales sur l’ Analyse organique. Levrault, Paris, 1824,
p- 34 to 42.
Voi. I.—Panrr IV. 26
596 M. CHEVREUL’S EXAMINATION OF AN OPTICAL CHARACTER
This distinction is very important when in our researches into the im-
mediate principles of organized beings we are desirous of ascertaining
the value of indications furnished by what in chemistry are called re-
agents*.
17. There are physical properties which furnish characters for di~
stinguishing bodies in analytical researches, which are valuable in pro-
portion to the limitation of the number of species possessing them, and
the facility with which these species may be distinguished among them-
selves by other characters. Such is the property of producing a violet
vapour, which belongs only to iodine and indigo, bodies very distinct,
since the vapour of the first does not undergo any alteration, even at
the most elevated temperatures, while the vapour of the second is com-
pletely altered even below 560d.°
18. Definitively, the properties which furnish the chemist with cha-
racters the best adapted for the classification, definition, and recogni-
tion of chemical species in analyses, are
a. Those which are the most constantly found in a certain species,
whatever be the diversity of circumstances in which it may be placed;
6. Those the existence of which necessarily involves that of others ;
e. Those which are in general concomitants ;
d. Those, easily verified, which belonging only to a very small num-
ber of species, differing widely in other respects, are valuable for ana-
lytical researches, or to concur with other properties in characterizing
these species, but whose existence does not lead to any conjecture rela-
tive to an analogy of properties between the bodies to which they
belong.
We shall now examine, according to the views that I have just ex-
plained, the optical character proposed by M. Biot.
19. Grape sugar which has not been solidified directs the plane of
polarization to the left ; and as, according to M. Biot, its chemical na-
ture is unaltered when it becomes crystallized in grape juice, and as it
then directs the plane of polarization to the right, it follows that this
property is not fundamental, since it is found in the same species with
two different signs ; it does not therefore fulfill the condition 18 a.
20. Cane sugar has certainly less analogy with sugar of starch of the
first formation than the latter has with sugar of starch of the second
formation ; the action however of the two first is equal or nearly equal,
while the action of sugar of starch of the second formation is much
feebler than that of sugar of starch of the first formation. From this tt
is evident that the optical character proposed by M. Biot does not apply
to one of those properties the existence of which necessarily involves that
* Rapport de M. Chevreul sur un Mémoire de M. Donnée. Annales de
Chimie et de Physique, vol. xxxviii. p. 89.
FOR DISTINGUISHING SACCHARINE JUICES. 597
__ of others or leads to their prediction, since it has a tendency to confound
two very different bodies, and since on the other hand it establishes a
difference between two bodies which in other respects have the greatest
analogy of properties and composition.
It does not therefore fulfill the conditions 18 6 e d.
21. From the manner in which M. Biot has related his observations,
it appears to me that, in the actual state of things, the property of caus-
ing a deviation in the plane of polarized light is in its variations con-
nected rather with the various arrangements that the particles of a species
may take without their nature being altered, than it is with the various ar-
rangements which constitute different species ; so that there is not now
_ more reason to establish a mutual relation between species which act in
_ the same direction and with the same energy, than there is to presume
that a decided opposition exists between the properties of two species
which act differently upon the plane of polarization.
§ 2.
On the probable Utility of the Optical Character.
22. I have stated the objections which may be urged against the use
of the optical character as it has been presented by its author ; I shall
now consider in what it is likely to be useful. By this mode of examining
the physical character, the application of which to organic chemistry
has been proposed, I hope to render apparent the object which I
have really in view, which is to restrain within its true limits that which
has been made to exceed them by ascribing to it a generality which
it does not possess, and a degree of precision which it can only attain
by ulterior experiments, and which even then will be confined to the
limits which J attribute to it.
Articie I.— Utility of the Optical Character for the various Ar-
rangements of the Atoms or Particles of a Species.
23. If it be true, as M. Biot thinks, that a body, as grape sugar,
though dissolved in water, affects the molecular state in such a man-
ner as to cause deviation to the right or left of the plane of polarization,
accordingly as the solution has been made with crystallized sugar, or is
such as nature presents us with in the juice which has just been ex-
tracted from the grape, it is undoubtedly interesting to inquire whether
other species of immediate principles present an analogous phenome-
non, in order to judge whether any consequence may be deduced, re-
lative either to the various arrangements of which the atoms or parti-
cles of these species taken separatele may be susceptible, or to the
which produces the variation of the phenomenon,
24. When the object of study is a species of body brought to its
282
5Y8 M. CHEVREUL’S EXAMINATION OF AN OPTICAL CHARACTER
‘greatest degree of purity, it is incontestably important to investigate
the action which it is capable of exercising upon the plane of polariza-
tion, when it is dissolved in any liquid whatever, compared with the
action which it is capable of exercising after having been exposed to
the influence of some agent, such as light, heat, or electricity.
25. I shall show that the importance of these researches to the che-
mist does not arise from their affording proof that an observable altera-
tion has taken place in the rotatory power of a substance submitted
to the action of a certain agent, when the nature of this substance has
been evidently changed ; that is to say, when it has been converted into
a substance absolutely distinct from what it was before the experiment ;
but from their enabling him to ascertain whether an alteration in the
arrangements of the particles has really occurred, in cases in which the
substances submitted to experiment appear at first sight not to have
undergone any such alteration, and in which, without the test of cir-
cular polarization, we should be led to conclude that they had absolutely
not experienced any.
26. The following example will illustrate my proposition :
A solution of starch in boiling water is converted into sugar by sul-
phuric acid. The starch dissolved in water being insoluble in alcohol,
whilst the sugar into which it becomes converted is soluble in that sub-
stance, we have a means of distinguishing in the action of sulphuric
acid upon starch the moment when the conversion of this principle into
saccharine matter commences, and the moment when it is completed.
If it be now discovered that the solution of starch is possessed of a pro-
perty of causing the plane of polarized light to deviate to the right in a
much greater degree than is effected by its sugar, is it not true that the
observation of the diminution of the rotatory power of the solution of
starch submitted to the action of sulphuric acid teaches nothing more
than the preceding facts relative to the alteration effected in the pro-
perties of the starch? And the conversion of a substance essentially in-
sipid and incapable of producing alcohol into a fermentable saccharine
substance, gives a much more exact idea of the change effected in its
composition than that derived from the variation of its rotatory power.
In cases in which a substance submitted to an agent has sustained an
alteration in its rotatory power, which, far from being, as in the exam-
ple of the starch, the result of the conversion of one substance into an-
other perfectly distinct from the first, has on the contrary sustained so
slight an alteration in the distribution of its particles that without
having verified it we should conclude that the substance had not under-
gone any alteration whatever in its properties ; it is then, I repeat, that
the observation of the optical character becomes interesting, as leading
to researches which may render other alterations discernible which
without them might escape the notice of the observer.
FOR DISTINGUISHING SACCHARINE JUICES. 599
Articie II.—Utility of the Optical Character for estimating the
Changes which may occur in determinate Species mingled together.
27. It would be important to ascertain the influence that chemical
species, the relations of which to the property of which I am treating
have been previously perfectly determined, would exercise by their
mutual contact, whether in the destruction or the neutralization of this
property, in its development, augmentation, or diminution. I conceive
that there are mutual actions of certain bodies in solution of which we
are at present ignorant, in consequence of not possessing means of
observing some phenomenon which is only manifested when they are
mutually present. It is, I apprehend, particularly in relation to the or-
ganoleptic properties of bodies that it would be useful to attempt re-
searches of this nature. 1 cannot here enter upon the subject more in
detail; but I reserve the particulars for a work upon the neutrality of
bodies, considered in the most general manner.
Articre II].— Utility of the Optical Character as a Reagent in the
Determination of Chemical Species of Organic Origin.
28. A certain vegetable fluid, or liquid of animal origin, or in a word
any solution the nature of which is investigated by analysis, when sub-
mitted to the action of polarized light, gives a determinate result. Well!
I apprehend that the observation of the optical property may furnish
useful indications in the following cases :
First case:
29. In which the properties of the substance analysed are found in
the separate principles. The optical property of these principles ex-
plains perfectly that of the substance of which they are the consti-
tuents ; consequently this result concurs with other observations to
prove that it has not sustained alteration in the analysis.
Second case :
30. In which all the properties of the substance analysed are not
found in the separate principles. The observation of the optical cha-
racter may here assist in the solution of the question, Has there been
any alteration of the separated principles ? or do not the changes ob-
served arise from the destruction either of a combination or a mutual
influence of principles, while no alteration has occurred in the ele-
mentary composition of these principles? We then enter upon the ques-
tion which I have considered in my “ Considérations générales sur
V Analyse organique.” p. 116.
31. I think that sufficient attention has not been given to ascertain
whether there be not in grape juice and sugar of starch of the first
formation some body foreign to grape sugar and sugar of starch,
600 M. BIOT ON THE APPLICATION OF CIRCULAR POLARIZATION
which exercises some influence upon the results as they have been de-
scribed by M. Biot.
CONCLUSION.
If we admit with M. Biot:
Ist. That a substance such as grape sugar can cause a deviation in
the plane of polarization in one case to the right, and in another to the
left ;-—
2nd. That two substances perfectly distinct, such as cane sugar and
the sugar of starch of the first formation, have sensibly the same rota-
tory power ;—
3rd. That two substances soapproximated as are the sugars of starch of
the first and second formations, have perfectly distinct rotatory powers ;
we must conclude that there is no consequence deducible from the op-
tical character relative to the connection of one species with another ;
and that its indications relate only to differences of molecular arrange-
ments, which have but an inconsiderable influence upon the character-
istic properties of the species.
On the Application of the Laws of Circular Polarization to
the Researches of Chemistry ; by M. Bior.
From the Nouvelles Annales du Muséum d'Histoire Naturelle, vol. iii. p. 502,
et seq.
WHEN a new process of observation is introduced into the sciences,
it is well that it should be contested and criticized by persons of repu-
tation, for if the discussion be conducted by each party with freedom
and sincerity, nothing can be more advantageous to the new invention,
provided it be sufficiently well established to sustain it. With a con-
viction of this truth, I have read the dissertation inserted by M. Che-
vreul in the last number of the Annales d’ Histoire Naturelle, upon
the phenomena of circular polarization which I discovered in a great
number of solid, liquid, and even gaseous substances; and upon the
employment which I proposed to make of it in the most delicate re-
searches of organic chemistry, in which these substances almost exclu-
sively occur.
M. Chevreul divides his dissertation into two parts.
In the first (I quote his own words) he examines the objections
which may be urged against the optical character which I have disco-
vered,
}
Cn ey See a ee ee eae Pr
TO CHEMICAL RESEARCHES, IN REPLY TO M. CHEVREUL. 601
In the second he specifies the use to which he thinks it may be
applied. i
I also shall follow this division of ideas. But in employing this ar-
rangement, it is necessary here to recall with precision the nature of
the character under consideration, as it was conceived and explained by
me when either experimentally determining or applying its physical
laws : for (a circumstance resulting probably from its novelty, and
from the scarcity of the apparatus hitherto constructed for its appli-
eation,) I differ almost as much from M. Chevreul with regard to the
appreciation of the advantages which he attributes to it, as I do with
regard to the limitations to which he supposes it liable. Nor will a
clear and precise explanation of this new method of studying bodies be
misplaced in the annals of natural history, in which I have several times
described the results which I have deduced from it relative to various
particulars of vegetation.
When a ray of homogeneous light is polarized by reflection in a
certain plane, which I shall suppose to be vertical, both sides of this
plane manifest symmetrical properties, when it is analysed immediately
with a doubly refractive achromatic prism. This symmetry is still
preserved when the ray thus prepared traverses certain transparent
liquids, water, alechol, and the fat oils, for example, before it arrives at
the prism ; at least such is the case within the limits of the thickness
in which I have had opportunity of testing them. Other liquids on the
contrary, such as solutions of sugar, camphor, and gum, and many of
the essential oils, destroy this primitive symmetry even when the sur-
faces of entrance and of emergence are perpendicular to the direction
of the transmitted ray. If this ray be analysed after its emergence, it
is again found polarized in one direction, but that different to its pri-
mitive direction, with an angular deviation towards the right or the left
of the observer, according to the quality of the substance interposed.
The angle of deviation for each substance when in a similar state is
exactly in proportion to the thickness that the simple ray has traversed,
which assimilates the observable effect to a continuous and uniform ro-
tation of the plane of polarization. But the arc of rotation described
in each substance of equal thickness differs for the different simple
rays, according to the fixed laws which I have experimentally deter-
mined, and which up to the present time are sensibly identical for all
substances, with the exception of tartaric acid, which alone offers an
anomaly in this respect, whence it may, not without probability, be in-
ferred that it is a combination of two atomic groups of contrary rota-
tions having unequal dispersive powers. Whatever may be the fact,
the general law of the deviation of different rays in all other cases,
enables us to predict numerically the composition and the succession
of the coloured images that the crystallized prism presents when the
602 M. BIOT ON THE APPLICATION OF CIRCULAR POLARIZATION
light transmitted is white; whence results the facility of making obser-
vations with a light of this nature as rigorously as with simple light,
and in a manner infinitely more convenient in practice, and more deli-
cate with respect to the appreciations which can be made by its means.
The single fact that the rotations are proportional to the degree of
thickness in liquid mediums under normal incidences, proves to every
natural philosopher familiar with the general laws of mechanics that
the action thus exerted is molecular; that is, that the total deviation
observed through a limited thickness is the sum of the infinitely small
angular deviations successively produced by the groups of atoms which
compose each infinitely thinlayer of the simple or compound substance
exercising a power of this nature. This molecular power is of such
great importance, and is so evidently the principle of all the chemical
applications of the phenomenon which are possible, that I have em-
ployed the most minute attention and the most diversified tests in
order indubitably to establish its truth.
I endeavoured in the first instance to remove all idea that the effect
could arise from a certain actual relation of position existing among
the molecular groups of the active medium. For this purpose I agi-
tated the particles by moving the medium during the transmission of
the ray, and modified their intervals by the application of heat, without
however carrying it so far as chemically to alter the atomic groups;
the total deviation remained the same, as the mechanical laws had pre-
viously indicated. I again removed these groups much further, and, so
to speak, indefinitely, by mixing active with inactive liquids, or with
those having an action upon each other either in a similar or in a con-
trary direction: the total deviation produced by the mixed system was
always rigorously the sum of the partial deviations that the luminous
ray would have undergone in traversing the same sum of active and
inactive groups placed in succession in separate tubes. These expe-
riments, which M. Chevreul says require now to be made*, I performed,
and published in the memoirs of the Academy sixteen years ago; and I
almost lost my life at that time in performing an experiment by which
I proved that the essence of turpentine preserves its rotatory property
in the state of vapour in motion.
I established all these laws in 1818+, and no addition had been made
to them until a more profound examination of these laws, and an ap-
paratus of much greater sensibility, furnished me with indications of the
rotatory property infinitely more delicate than those which I had pre-
viously employed ; and I succeeded by these means, two years ago, in
discovering this property in a great number of substances of organic
* Rapport sur l Amidon, chap. v.,§ 72. Annales, p. 266.
t+ Vide the Mémoires de /’ Académie des Sctences for the year 1817.
TO CHEMICAL RESEARCHES, IN REPLY TO M. CHEVREUL. 603
origin in which I had not previously suspected its existence. I then
resumed with renewed attention all the experiments which could serve
as bases for establishing the details; and these results were accompanied
by the formule necessary to deduce the comparable consequences; esta-
blishing for each substance, whether simple or compound, what I call
its power of actual molecular rotation, which is the angular deviation
- which it exercises upon the plane of polarization of a certain simple
ray, with a thickness of one millemetre, and a hypothetical density
equal to unity. Though the volume of the Academy in which these
researches are inserted has not yet appeared before the public, I have
sent within about the last year printed copies of them to several che-
mists both Frenchmen and foreigners, and they have served as the
foundation of all my subsequent researches. For I have since found
it sufficient to apply the same methods and the same formule in the
various experiments which I have undertaken, simply extending or cor-
roborating them by the additional processes which the development of
my researches required or suggested; so that to dissipate the different
objections that M. Chevreul has raised, at least those which I have well
understood, I shall merely have to quote the corresponding results
which are already published in these Annals.
But first I shall greatly simplify this discussion by declaring that I
have not any intention of following M. Chevreul in the most extended
article of his dissertation, in which he examines “ the objections which
may be urged against the importance of the optical character in the de-
finition of chemical species.” Having never proposed its application to
such a use, I have not to defend it upon this point ; more especially as
in my own opinion no character taken separately is sufficient to define,
I will not say achemical species in general merely, but even a substance
individually unique. Such definitions are and can be merely the ex-.
pression of our ignorance ; or in other terms, of our actual knowledge.
An attempt was made to class natural solid bodies according to their
erystallization ; but among them were found some rigorously isomor-
phous ; for instance, those which crystallize in cubes or in regular oc-
tahedrons proved to be such by the complete symmetry of their derived
forms. A second attempt was made to class them according to che-
mical composition: this was defeated by the discovery of bodies exactly
isomeric. These two examples may suffice to convince us that the de-
finition of bodies should be established upon the union of the obser-
vable characters that each of them possesses ; and that this definition
must always be merely provisional, as another system of material par-
ticles may be discovered tomorrow, possessing in common the whole
of this first collection of properties. The character derived from cir-
cular polarization is therefore, and can be, nothing more than an addi-
tional element, a new condition of the actual molecular state of the
604 M. BIOT ON THE APPLICATION OF CIRCULAR POLARIZATION
material systems, whether simple or compound, in which it exists; and
I have positively and repeatedly said in the Annales d Histoire Natu-~
relle, that it was in this light that I regarded it*. In agreement with
this view, in my applications of this character I have naturally had
recourse to all auxiliary means suitable to be employed in conjunction
with it. M.Chevreul had no occasion to say, as he has done p. 592,
that, “as M. Biot acknowledges,” when cane sugar and sugar of starch °
are mixed together in one solution, it is necessary in order to distin-
guish them to have recourse to alcoholic fermentation, or to the action
of acids suitably regulated, in order to change the sum of the two ro-
tations into a difference. He ought to have said that the employment
of these auxiliary processes was my constant practice, and one of my
principles formally expressed.
The metaphysical question relative to the species being disposed of,
I proceed to M. Chevreul’s other objections. The first three, which he
ealls a, b, c, consist of inquiries how, when a deviation to the left is
observed, it is to be immediately ascertained whether it belongs to gum
or to grape sugar not solidified, or to a mixture of the two substances,
it being common to them both ; and when a deviation to the right is
observed, how it is to be immediately distinguished whether it be pro-
duced by dextrine or sugar of amidon. Considering these questions in
the positive sense of their experimental application, it is not now ne-
cessary in the actual state of optical chemistry to reply to them; for
not only the particular conditions here suggested, but a great number
of others analogous and more difficult, were long ago determined in
my researches upon vegetation, in which the specialty of function of
various organs, incessantly modified by the progress of life, effectuated
mixtures very differently complicated than those suggested by M.
Chevreul. As I cannot suppose that he is ignorant of these results,
which were published in the Annals, and still less that he wilfully
suppressed them, I must of necessity discover some abstract sense in
the difficulties he has raised, independent of the real applications which
I have made; and a word that I have just written, the word imme-
diately, excites a suspicion in my mind upon the subject. In the title
of my first memoir upon liquid grape sugar, which has since been fol-
lowed by many other more extended applications of my methods, I have
said that by means of the optical character derived from circular po-
larization, the juices of fruits capable of producing sugar analogous to
cane sugar, and those from which only grape sugar might be expected,
may be emmediately distinguished. In fact all the juices of our cli-
* Vide the memoir upon the slow or sudden variations which occur in seve-
ral organic combinations, Nouvelles Annales du Muséum d'Histoire Naturelle,
vol. ii. p. 835. Ibid., vol. iii. p. 48, upon the application of circular polari-
zation to the analysis of the vegetation of the Graminex. [See p. 584.]
TO CHEMICAL RESEARCHES, IN REPLY TO M. CHEVREUL. 605
mates from which cane sugar has hitherto been extracted, those of
beet-root, parsneps, carrots, and marsh-mallows, presented a rotation to
the right, whilst all those which yield only grape sugar invariably
presented a rotation to the left; thus by the word immediately 1
meant instantly, at the very moment; and indeed in my first ob-
servations, I did not seek for other means of distinguishing the
two kinds of sugar in question, not having at that period met with
them naturally mixed sufficiently to conceal or intervert their
proper rotation. Now if it be the word immediately which has
shocked M. Chevreul, as expressing the pretence on my part of
employing solely the optical character, to the exclusion of all other,
and particularly of chemical means, 1 would beg him to observe that
I have never acted in a manner to justify this interpretation. For even
in my first fundamental memoir read before the Academy on the 5th
of October, 1832, I determined the opposite rotations of the two prin-
ciples of honey, the erystallizable and the uncrystallizable, after having
separated them by means of alcohol; and I have never since neglected
to seek all the assistance that chemistry is capable of affording. It is
however; I repeat, with much hesitation that I attribute to M. Chevreul
the suggestion of a difficulty which appears to me to be purely gram-
matical ; for if such were his thought, he could not, without a degree
of injustice of which I believe him incapable, cite my original expres-
sions as he has done, without adding that all my researches subsequently
_ published contradict the idea of exclusion which this interpretation at-
tributes to me; and that I even formally expressed the contrary prin-
ciple at the commencement of my memoir on the analysis of vegetation
in the Graminez, as may easily be seen. As to the rest, it will at least
be eyident from this discussion, that neither am I who have invented
and applied the optical character, nor is M. Chevreul who examines it,
of opinion that it should be separated from the chemical characters
which may aid in its applications ; and this I apprehend is the only sci-
entific point of interest at present.
I now arrive at the last of M. Chevreul’s objections, objection d,
which is expressed in these terms: “ Difficulty of estimating the quan-
tity of an active principle from the density of the liquid by which it is
held in solution.” I cannot possibly understand how, or in what re-
spect this objection can be applied to my formule, or to the results
which I have deduced from them. And certainly it is the intention of
the writer so to apply it; for in his development of it, mentioning the
necessity for distinguishing the proportion of the active substance in the
solyent, in order to decide upon its specific nature, M. Chevreul in
quires (p. 593.) how this proportion is to be ascertained ; and he adds
“it is, according to M. Biot, by taking the densities of the liquids,” a
method which appeared to him, and with truth, to be of difficult em-
606 M. BIOT ON THE APPLICATION OF CIRCULAR POLARIZATION
ployment, and he might have added, very inexact. But there is here
on the part of M. Chevreul some error, though undoubtedly an invo-
luntary one; for I have never proposed or employed such a method,
which may be proved by consulting my formule. It is true that they
contain the density of the solutions observed, as they also enter into
the determination of numerous other physical results ; as, for example,
into the calculation of refractive power, and of capillary forces ; though
certainly it has never been said that these phenomena are estimated
or measured by the density. So in the phenomena of circular polari-
zation there exists for each active substance a necessary mathematical
relation between its power of molecular rotation; the thickness through
which it is observed, whether insulated or in solution ; the angular de-
viation which it produces of the plane of polarization of a simple
ray of a given nature ; and lastly, the actual density of the solution in
which the substance exists, as well as its ponderable proportion in that
solution*. Of these five elements, four being given, the fifth is de-
duced by necessity from the mathematical relation; and if this unknown
fifth be, for example, the ponderable proportion of the active substance,
it may indeed be obtained by calculation, in which the density will
enter as one of the elements. But it will not be from this density, at
least not from it alone, that the proportion will be estimated. It is even
evident from the formule that in aqueous solutions greatly diluted, the
density of which consequently scarcely differs from unity, this element
preserves scarcely any influence upon theponderable proportion, because
it only affects the decimals of a very distant order. For example, when
I say, as I can say, that by means of the apparatus which I now employ
the presence of two thousandths in weight of cane sugar, or one of dex-
trine, in an aqueous solution may immediately be rendered sensible and
appreciable, it is not certainly from the density that such results are
obtained ; for at such degrees of dilution the densities of the solutions
differ so little from unity, that the observation of the density might be
entirely dispensed with, and unity be substituted in its place, without
the ponderable proportions of the substances being affected by it in an
observable degree. The estimation of the ponderable proportion by
the density must not therefore be attributed to me, for it does not in
any degree belong to me, and the supposition that it does would lead
to a very false idea of my processes.
After having thus considered the objections which M. Chevreul
* Not only is the mathematical relation of which I am treating established
in my memoir of the 5th of October, 1832, printed among those of the Aca-
demy ; it is also mentioned in the memoir upon grape sugar which has served
specially as a text to M. Chevreul’s dissertation. Vide the Nouvelles Annales
du Muséum d’ Histoire Naturelle, vol. ii. p. 97, in a note. The numerical table
in the following page is mathematically deduced from that relation.
TO CHEMICAL RESEARCHES, IN REPLY TO M. CHEVREUL. 607
thinks may be urged against the optical character derived from circular
polarization, I intended to follow him in his consideration of its utility ;
but this relating to our own views without affecting those of others,
the consideration of it would not be profitable to science. Those who
labour at the present day to connect by rational relations the innume-
rable transformations to which organic chemistry gives birth, will easily
feel that the specially molecular character of the power of optical ro-
tation assigns new conditions which must necessarily be satisfied, in
selecting the groups of atomic combinations which represent the com-
pound products. I thought that I should be rendering a service to
science by here giving a precise explanation of this character, of which
M. Chevreul’s dissertation appeared to me to present involuntarily a very
inexact idea, which might retard its application. This duty accom-
plished, I leave it to the judgement of experimentalists.
Paris, Dec. 14th, 1834.
608
ARTICLE XXX.
On the Laws according to which the Magnet acts upon a Spiral
when it is suddenly approached to or removed from it ; and
on the most advantageous mode of constructing Spirals for
Magneto-electrical purposes ; by KE. Lenz.
From the Mémoires del’ Académie Impériale des Sciences de St. Petersbourg,
vol. ii., 1833, p. 427. Read on the 7th of November, 1832*.
From the great interest which the late discoveries of Faraday in
the field of electro-magnetism must awaken in all the natural philoso-
phers of Europe, it is to be expected that we shall soon receive many
and various explanations of the momentary action of an electric cur-
rent on an electrical conductor; and as it is allowed according to
Ampeére to reduce the action of a magnet entirely to that of circular
electric currents, the same may be expected with respect to the action
of the magnet upon such a conductor. Up to the present moment we
here in the north are only acquainted with the papers of Becquerel,
Ampére, Nobili, and Antinori and Pohl; and as none of these authors
have occupied themselves with that branch of the subject to which I
have directed my particular attention, I hasten to make known as
quickly as possible the following contribution to the science of mag-
neto-electrism.
After having repeated Faraday’s chief experimentst, I first proposed
to myself to find out in what manner the phenomena of the magnetic
action on a spiral suddenly approached or removed might be produced
in the easiest and most powerful manner. For this purpose I had to
determine what influence
1. The number of coils,
9. The breadth of the coils,
3. The thickness of the wire,
4. The substance of the coils,
of the electromotive spirals (i. e. of those which are acted upon by
the magnet) had upon the phenomenon ; and this determination, toge-
ther with the necessary consequences following from it, are contained
in this present memoir.
* Translated from the German by Mr. W. Francis.
+ In this repetition [ obtained the spark beautifully by means of a spiral
of a wire 70 feet in length and 0-044 inch thick. The apparatus was formed
after the one described by Nobili, so that the horse-shoe magnet (of 22 lbs.
lifting power) caused of itself the closing of the current.
LENZ ON ELECTRO-MAGNETISM. 609
- ‘The following was the apparatus I employed«for my experiments.
A multiplier (with a very sensible double needle of Nobili) of seventy-
four coils of copper wire of 0025 of an English inch in thickness* was
placed in connection by means of conducting wires with the electro-
motive spirals, so that the horseshoe magnet which acted on the spirals
was at a distance of nineteen feet from the multiplier, and had no im-
mediate influence on its needles. I had assured myself of this by
previous experiments. ‘The horseshoe magnet consisted of five single
bent steel bars, firmly connected with one another by screws; the middle
one protruded at the ends about 0-7 of an inch ; it might together with
the armature weigh somewhat more than twenty-two pounds. The
length of the bars was twenty-three inches, the breadth 0:8,-and the
thickness 0°22 ; the middle one projecting beyond the others was
0:4 in thickness; the distance of the arms was 1°64 inch. In order to
be able to approach and remove the spirals, and at the same time to
read off the deviation of the needle without any aid, I constructed my
apparatus in the following way:—I did not cover the multiplier with
its bell glass, but with a glass cylinder open at both ends, and closed
these by means of a plate of mirror glass; I then placed over
it a good mirror under an inclination of 45°, and from a point near
the magnet I observed by means of a good Munich telescope the
reflected image of the scale of the multiplier. The reading off was
thus performed very precisely, and was more certain than with the
naked eye close to the scaie, because at this distance and with a fixed
position of the eye the parallel axis of the index which stands at some
distance from the graduated circle may be considered as evanescent.
The method of exciting the electric current was the same as that
given by Nobih: I wound the electromotive wire about a soft iron
cylinder, which served as an armature and was filed smooth at those
places where it was laid on the magnet, and laid it then on the magnet, or
removed it suddenly from it, by which the magnetism arising at the
moment, or vanishing again in the armature, thus produced the momen-
taneous electric current. But as the removal of the armature can be
performed ina more certain, prompt, and uniform manner than the
placing of it on, I have in all my following experiments only given the
results which were caused by the taking off of the armature, or the
sudden removal of the magnetism in the iron. I must here at the same
time remark that in my experiments it made no difference whether the
magnetism of the iron disappeared really and entirely all at once, or
there still remained a part, provided only the remaining quantity of
magnetism was the same after each removal. I frequently convinced
' * In this memoir the measures are always expressed in English inches, ex-
cept when otherwise remarked.
610 LENZ ON ELECTRO-MAGNETISM.
myself of this by the identity of the results in several repetitions of the
experiment. This also showed me that the electromotive power of the
magnet, at least after having already undergone several removals, did
not become weaker ; proofs of this will also be furnished in some expe-
riments hereafter to be mentioned. In the above-described arrange-
ment of the apparatus, I could now with the right hand perform the
removal of the armature from the magnet, which was fixed to a table,
while at the same time my eye observed in the telescope the consequent
deviation of the index of the multiplier. This index was a thin lath,
which was fixed by means of some wax to the wire which served as a
common axis for the two needles of the multiplier, and formed a dia-
meter of the graduated circle. Being thus able to observe the deviation
for every result which was to be deduced therefrom, first on the one
and then on the other end of the index, I freed this result from the in-
fluence of the eccentricity of the axis of the needles, and turning first
the end A and then the end B of the spirals towards the north arm of
the magnet, and allowing the needles of the multiplier to deviate
first on the one side then on the other, I made the result independent
of a second error which arises if the cocoon threads to which the needles
of the multiplier are suspended possess a rotatory motion. Further, I
carefully avoided every disturbance of the multiplier during a series of
combined experiments, because it is impossible that every coil of the
multiplier could act in the same manner as another (this would pre-
suppose that they were all in the same plane, and parallel to one an-
other), and because even if this might be presupposed, the action would
still vary according as the needle when stationary might be exactly
parallel to the coils, or form a greater or less angle. The positions of
the needles when at rest seldom differ more than 0*-3 from one another.
According to the above statement, a complete experiment always de-
manded four observations, namely, two (at both ends of the hand) for
the position where the end A of the spiral was turned to the north pole,
and two where B was directed to the north pole. Besides this I have
repeated almost every experiment twice over in order to convince
myself that no accidental fault had crept into the reading off; if the
two observations differed much from one another, I again repeated
each of them. The first preparatory experiments were made on
the influence of the combinations of the conducting wires with the
electromotive spirals and with the wires of the multiplier, in order
to see whether I should content myself with winding the ends of the
wires, which had been freed from their silk and were clean, very closely
round one another, or should be obliged to produce a closer connection,
for instance by immersing them in quicksilver. I proceeded on the
supposition that if the connection effected by winding them many times
closely round one another was not sufficient, an increase of conyolutions
ll) ie ee a
LENZ ON ELECTRO-MAGNETISM. 611
would necessarily increase the force of the electrical current, I there-
fore made the following experiment. I wound round the armature ten
conyolutions of copper wire bespun with silk, and the conducting wires
were connected with the ends of this spiral only by asingle twist of the
wires; the result of the four readings off amounted to 36°8; upon this
the same connection was made by twisting the ends of the wires ten
times round one another as tightly as possible; the deviation amounted
again to 36°8 ; I finally pressed the last connection as tightly as pos-
sible together with a pair of pinchers, so that they were very much
flattened ; the deviation was 36°75. We may therefore consider the
connection made by tightly twisting the wires ten times round one
another as quite sufficient, and this was therefore made use of in all the
subsequent experiments. The places where the connection was made
were then wound round with silk stuff in order to secure them from
reciprocal contact.
The second preparatory experiment I made in order to see whether,
when I advanced the electromotive spiral on the armature more to the
north limb or to the south limb of the magnet, it had any influence on
the electric current. For this purpose I obtained with two convolu-
tions the following results :
The convolutions advanced till in contact with the north limb
of the magnet, gave a deviation . . - ooo = EMSS
The convolutions advanced until in contact ae ne south limb
of the magnet, gave a deviation . . . « at) =) SMS
The convolutions advanced to the middle of both sinus gave a
deviation AS (ehetnciiadg a. OO
therefore this influence also of the different ecitiokin of the spirals on
the armature is imperceptible: from this time I always placed them so
that the spirals occupied the middle of the armature.
I thirdly determined, before I proceeded to the proposed experiments,
the thickness of the copper wires employed; I weighed two feet of
each having wound off the silk, by which I obtained the proportions of
_ their diameter on which it principally depended ; but in order to ob-
tain also their absolute thickness, I measured the thickest by means of
_ amicrometrical contrivance : I obtained the following results, in which
I have designated the wires, beginning with the thinnest, Nos. 1, 2, 3,
and 4.
grains inch,
_ 2 feet of wire No. 1 weighed = 23°3; absolute thickness = 0:023
2 —___—— No.2 —— = 27-4; ——____——_. = 0025
(wire of the multiplier)
No. 3 weighed = 83:9; absolute thickness = 0°044
es No 4 — 166-1; ——____—_. = 0-061
All the four kinds of wires were well covered with silk, so that no
; Vou. I.—Parr IV. 27
612 LENZ ON ELECTRO-MAGNETISM.
metal could be perceived except at the ends which served for con-
necting them.
I now proceed to the experiments themselves.
I. On the Influence of the number of Convolutions upon the Electro-
motive Power produced in them. ;
In these experiments I connected the wire No. 3 with the multiplier
so that the conducting wire and the electromotive spirals were formed
of one and the same piece ; the length of this wire was about fifty feet:
here however this is of no consequence, as it remained the same in all
the experiments. The experiments themselves are contained in the
following table.
INDIVIDUAL DEVIATIONS.
Side A of the Spiral|Side B of the Spiral
to the north pole. tothe north pole, | Meandevi-| a in mi- i
ation, or &, nutes,
Number of the
Convolutions
End a of | End 5 of | End a of | End d of
Index. Index. Index. Index.
| |
57 5:8 5-3 58 5:65 | 5°39'| 9°49’
121 | 129 | 111 | 120 | 1200 | 1200 | 600
25-7 | 258 | 229 | 25:2 | 24.90 | 24 54 | 12 27
29-5 | 30:1 | 262 | 285 | 9832 | 2819 | 14 15
325 | 333 | 294 | 320 | 31-80 | 31 48 | 15 54
409 | 353 | 386 | 3877 | 38 46 | 19 23
474 | 488 | 408 | 45-9 | 45-43 | 45 43 | 22 51
493 | 509 | 45-0 | 49:0 | 4955 | 48 33 | 24 16
557 | 568 | 47-6 | 523 | 5310 | 53 6 | 26 33
63:1 | 644 | 541 | 57:8 | 59:80 | 59 48 | 29 54
290 | 71:0 | 71:8 | 628 | 666 | 6805 | 68 3 | 34 1
te
DAorW SOO PFW
oo
iv)
oo
From this series of experiments we must now deduce the electromo-
tive power of the spirals for each number of convolutions, for which
purpose the following considerations will be of service.
The action of the electric current in the wire of the multiplier upon
the magnet needle, is a momentary one, since the current itself exists
only for a moment; we may therefore consider this action as an im-
pulse given to the needle, and shall be able to measure its force by the
velocity which it imparts. But the velocity of the needle at its exit is
evidently as great as that which it acquires when it springs back to the
point of exit; it may therefore be expressed ( f being constant) by
A =f ¥ (sin. vers. a)
where A represents the sought for velocity of the exit; or according
to what has been above stated, the magnitude of the current in the
wire of the multiplier, and a the angle of deviation of the needle pro-
duced by this force. This expression changes however by the sub-
stitution of 2 sin.? } @ instead of sin. vers. a into the following
A = p:sin. ta
if we putp =f v 2.
Sa OCR Ee
,
.
. x
L+i+n.
LENZ ON ELECTRO-MAGNETISM. 613
In order now to find the resistance which the electric current suffers
in its passage through the different wires, I first. reduce their lengths
all to one diagonal, and indeed to that of the wire of the multiplier,
on the principle that two wires of the same metal offer then the same
resistance to conduction when their lengths are in the same proportion
as their diagonals (See Ohm’s Galvanic Chain). In this case therefore
the reduced lengths of the wires express their resistance to conduction:
to have therefore a general idea of the problem, I suppose the mul-
tiplier, the conducting wires, and the electromotive spirals (with their
free ends) to have the three reduced lengths, L, Z, and \, and the elec-
_ tromotive power produced in the spirals to be represented by z, then
will be in effect the current which takes place, and we
therefore have
x c
L+Ip A TP Sin 4a
e=(Lt h+ A)iprsinga@ . «es (A)
If we now consider the electromotive power in a convolution of the
wire as unity, representing the unknown deviation produced by a con-
volution by §, and its reduced length by (A); then granting the pro-
bable hypothesis, that at one and the same distance of the convolutions
the electromotive force is directly as the number of convolutions, the
following relation will take place for the number 7, and for the reduced
lengths X,, belonging to it (this is not necessarily 7 A, because the free
ends of the spirals need not increase in the same ratio for every num-
ber of convolutions)
Ti Gt+l+))p'sin ge
n (L+l+4+ ,)p‘sin.da
therefore
a hdl SS ae eg
I — .
sin. $a = aos wee
In the experiments just mentioned 7 + A continued of the same
magnitude for every number of convolutions, as the conducting and
spiral wire consisted of one piece, besides L remains the same, we
therefore have L + 7 + (A) = L +/+ ., and the equation B be-
comes changed into the following:
Bin. 4, gS 90 Bie Eee Sok Peat ee Se RS)
If we now put instead of § « the values contained in the last column of
our table of experiments, we obtain eleven equations, from which after
the method of the least square, we shall be able to determine &, and if
we bring this value of £ into the equation (C.), we shall find the devi-
ations « belonging to the number ~ of convolutions, and the differences
between this and the observed values will show whether the assumed
Aa ih
‘614 LENZ ON ELECTRO-MAGNETISM.
hypothesis of the proportionality of the number of convolutions and of
the electromotive power is confirmed in reality by the observation.—
The known formula for sin. 4 £ is after the method of the least squares:
= (nm: sin.} a)
EC)
and after having performed the calculation, we have from the foregoing
table
sin.§ § =
£ = 3° 9! or log. sin. 4 § = 8:43989.
This value of ¢ gives for « the following values:
a DIFFERENCES. a DIFFERENCES.
—————— SSS SS eee
Calculated.| Observed, |!" eer and In Degs,] Calculated. | Observed. In shea In Degs.
6° 18’ On 39) |e = 039.1 ee 0-6 45° 99/°| 45° 96’ | —@? 4
12 38 | 12 00 +0 38 |+ 06] 48 48 | 48 32 | +0 16
25 36 | 24 54 +10 32 [4+ 0:5] 52 16 | 53 6 | —O 50
28 42 | 28 19 +0 23 |+ 0:4] 59 26 | 59 48 —0 22
31 58 | 31 48 +0 10 |+ 0-2] 66 50 | 68 1 —1 1l
' 38 36 | 38 46 | —0 10 |4+ 0-2
the coincidence of the calculated with the observed deviations, con-
firming our presupposition that the electromotive power increases as
the number of convolutions.
A second series of experiments on the same subject were made with
the same wire, No. 3, except that the length of the wire through which
the current had to pass, was no longer the same in each number of
convolutions ; we must therefore return to our general formula (B.).
It was
L+l+Q) von Lips
ae me
The wire of the multiplier and of the conductors always remained the ©
same, and was reduced to the diameter of the wire of the multiplier
L + 1 = 673°25 inches.
The lengths X, A, A,,, &e., were however changeable ; I have therefore
added these values, reduced also to the wire of the multiplier in the
following table of the experiments.
L +1 + (d) is = 681-45
sin. 5 a = n°
LENZ ON ELECTRO-MAGNETISM. 615
2a DEVIATIONS.
Se ee ee
Doms)
3 ide A of Spiral to th Side B of Spiral to th ividual Cc let
82 eceerpce tS uodipce. =| Cm Mentors | x (LOE? A
> —_—_—_—_—$—S— |
5 5 End aof | Enddof | End a of | End 3 of
Ze Index. Index. Index. Index.
18°5 18°5 19-8 20°5 19:33 a
5{| ise | iss | 202 | 203 | tose }} 19-40 | 17 | 690-25
=
Se a a eo 33.7 ¢| 3841 | 28 | 701-25
i ier ied rea t| 5818 | 39 | 71225
20 4 on eae tye Eye? 80°91 | 50 | 723-25
25{| i100 | 1128 | 1037 | 22 | lupe }| 20667 | 61 | 73425
did to the first, we obtain
£ = 3°97 and log. sin. 2 £ = 8°53944
and with this value we obtain from formula (B.) the following devia-
tions:
i
_ IPfwe now apply the method of the least squares to this table, as we
|
Rien ae DEVIATIONS.
: Difference.
Convolutions.
Calculated. | Observed.
———
In this place also the calculation coincides well with the observation ;
as I expected however to attain this coincidence still more completely,
if I allowed the length of the conductors to remain the same for all the
experiments, I made a second series of experiments similar to the
above with another multiplier, where \, \', &¢., remained always equal
to one another ; this series has also been performed with more care
than the others above-mentioned, since each of the numbers contained
in the following table is the mean deduced from three observations, in
which mean however I retained only one decimal place. The columns
designated by 1, 2, 3, 4 are intended for the same purpose as the four
columns in the former tables.
616 LENZ ON ELECTRO-MAGNETISM.
Number of
Deviations. Mean Devia-
Convolutions. i tna’
Legucindt. git! ohana “ole oli Le tions or a.
86 8°7 8°5 86 8°63
175A ALPS hen LOE 17°40
96°4 | 27-2 | 26°6 | 25°6 26°45
35°5' | 35°34), 35°6.| 34:6 35°25
45-2 | 46°0 | 45°0 | 442 45°10
56°5.|. 55:0
Hence may be calculated by means of the least squares
€ = 1°73 and log. sin. } § = 818478
therefore we have for the calculated values of «
a
Number, of! fp) ji | 48 6 aes
Convolutions. | Calculated.|Observed.
——
5 8°77 8°60 + Ul?
10 17°60 17°40 + 0°20
15 26°53 16°45 + 0°08
20 35°58 35:25 + 033
25 45°00 45°10 — 010
30 54°67 55°05 — 0°38
Here then the coincidence for this kind of experiments is very great,
so that we may regard the position as entirely confirmed, namely that
“ the electromotive power which the magnet produces in a spiral,
with convolutions of equal magnitude and with a wire of equal thick-
ness and like substance, is directly in the same proportion as the num-
ber of the convolutions.”
Moreover, we must not let it escape our attention, that in all the three
' geries of observations the differences of the calculated and of the ob-
served deviations are in the beginning positive, and then negative ;
which seems to show that the electromotive power increases in a some-
what quicker proportion than the number of the convolutions; but the
differences are so small, and become, when the observations are made
with great care (as the third series proves) smaller and smaller,
I therefore aseribe this little irregularity to the influence of some pecu-
liar circumstance which up to the present moment I have not succeeded
in discovering.
II. On the Influence of the Distance of the Convolutions of Spirals
on the production of the Electromotive Power in them.
In these experiments I employed at first the horseshoe magnet, but
i i i ieee
LENZ ON ELECTRO-MAGNETISM. 617
I soon perceived that from this none but false results could be ob-
tained. By considerably widening the circuit of the spiral, it advanced
nearer and nearer to the upper bow of the magnet ; so that by removing
the armature, not only the sudden disappearance of the magnetism
in it, but also the sudden removal which took place at the same
time from that upper part of the magnet (the bay of the horseshoe)
acts on the spirals, and indeed unequally with unequal diameters of
the spiral; the electromotive power becomes thus greater in larger
spirals than it would otherwise be. On this account I took two strong
rectilinear magnetic systems, each of which consisted of ten single
magnet bars ; I laid them with their opposite poles against one another
so that they lay in a straight direction, and brought the iron cylinder
which had served me in the above-mentioned experiments as an arma-
ture to the horseshoe magnet, between their poles. while the spirals
covered the cylinder ; upon this I let the magnet be suddenly drawn
by two assistants from each other in opposite directions.
I wound at first ten convolutions of wire No. 2 round the iron cy-
linder,
the diameter of the convolutions = 0°73 inch;
upon this I wound ten convolutions of wire No. 2 round a wooden
dise,
the diameter of the convolutions = 6°57 inches ;
the wooden disc was perforated in the centre, into which the iron cy-
linder was inserted. The observation gave
Angle of Deviation.
pape te as eee el Miaan”
1 ye 3 4:
Narrow Conv. 94-6 | 27-1 | 264) 96°5 | 96°15
Wider Con- 22°8 DOF 22:0 29-5 29°50
volutions. { 23°4 | 23°5 | 21°6 | 23:2 | 22:92
Narrow Conv. | 248 | 27°7 | 26:3} 266 | 26°35
I observed the deviation of the wider spirals between the narrower,
in order that the fault which might have originated by diminishing the
magnetic power of the magnet systems might be estimated : we there-
fore have
for the narrower spirals the angle of deviation a = 26°25
for the wider spirals the angle of deviation a! = 22-71
The length of the wire of the multiplier and of the conducting wires
(reduced to the diameter of the first) was as in the former experiments,
i.e. they amounted together to 673°25, or L + 1 = 673°25, A however
is for the narrower conyolutions = 28, and for the wider A' = 203.
618 LENZ ON ELECTRO-MAGNETISM.
By means of formula (A.) we shall therefore obtain for the narrow spi-
rals
v=(L4+/+4+A)p:sin. 4a = 701-25*p* sin. (13° 7’),
for the wide spirals
a! =(L+1+4A')p-sin. 4} a! = 876-25 * p «sin. (11° 21'),
therefore the relation of the electromotive powers, or
ae eae ae (2) T-0uas,
x (O25 “sin (1S*, 7)
therefore not deviating much from 1, that is, the electromotive power
is in both spirals the same.
I endeavoured in a more striking manner to confirm this position by
the following experiment : I wound the wire No.2 in six convolutions
round a great wooden wheel of 28 inches in diameter, and placed the
wheel on the iron cylinder. After having completed, as in the former
cases, the experiment, I wound also six convolutions of the same wire
immediately round the same iron cylinder, where also, as above, the
convolutions again were 0°73 inch in diameter. The experiment gave
| Angle of deviation. Mean
ligt lcs aie SS CMe ROLT ce
ee 2 3 4
Narrower € ' ; : .
edu 113°] |15°8 |12°8 |12°4.| 13°52 | 19°2 | 692°45
Wider y 7-1| 8°7| 7-1] 8°7| 7:90 |549°2 | 1229°75
convolutions.
1222°75 * sin. (3° 52’)
692°45 * sin. (6° 45/5)
Here the proportion of both electromotive powers approaches still
more nearly to unity than in the former case, although the proportion
of the diameter of the spirals is = 1 : 38°3. We may therefore regard
as a thing proved by experiment, the position, that
“the electromotive power which the magnetism produces in the sur-
rounding spirals is the same for every magnitude of the convolutions.”
Since however a spiral wire inclosing the armature presents to the
action of the magnetism in the armature a length greater in proportion as
its diameter or its distance from the armature is greater, it follows from
the law just discovered that the electromotive action of the magnet upon
one and the same particle of the wire decreases in the simple ratio of
the distance. This is as it were the reversal of the law demonstrated
by Biot in the field of electro-magnetism, which, as is known, states
that the action of an electric closing wire upon a magnetic needle de-
creases in the simple ratio of the distance ; and it follows from our ex-
a!
therefore sl OlOn.
LENZ ON ELECTRO-MAGNETISM. 619
periments as from those of Biot, that the action of a particle of the
electric currents which encircle the magnet upon every particle of
the spiral, is in the inverse ratio of the squares of the distance.
It also immediately follows from the law just demonstrated that the
electric current produced in the various wire rings which inclose
the armature, by its removal from the magnet, is in the inverse ratio of
the diameter of the rings; for the electromotive power is the same in
every ring, but the resistance it suffers in being conducted increases as
the diameter of the rings; therefore the electric current, the quotient
of the electromotive power, by the resistance it suffers, decreases as the
diameter of the rings increases.
III. Influence of the Thickness of the Wire of the Electromotive Spirals
on the Electromotive Power produced in them.
I have also again made these experiments with the horseshoe mag-
net, since in this case the convolutions of the wires had always the same
magnitude. I here employed ten convolutions, which I formed from
the wires No. 1, No.3, and No. 4, and in which the diagonals were in
the same proportion as the numbers 233 : 839: 1661. The entire
length of the convolutions in each sort was 33 inches. The deviations
are contained in the following table.
Angle of deviation.
Mean.
1 2 3 4
Spirals 39:3 | 40°4| 35:1 | 37°8 | 38°15 38°19
from No. 1. 39°3 | 40:4] 35:2 | 38°8 | 38°22
Spirals 36°8 | 39°6| 40°2 | 42°0 | 39°65 39-60
from No. 3. 36°4.| 39°4| 40°4] 42°0 | 39°55
Spirals 40°5 | 42°4:| 37°5 | 39°3 | 39°92 39°74
from No. 4. {| 40°3 | 40°4| 37°5 | 40°1 | 39°57
Spirals 38°6 | 40°6 | 35°7 | 37°8 | 38°17 38-00
from No. 1. 38°7 | 40:0] 35:2 | 37°4 | 37°82
If we now combine the observations No. 1, at the beginning and end
of the series of experiments, and take their mean, we have the following
deviations :
For No. 1 the deviation or @ = 381,
— No.3 OLj8, na, 50'G;
ee Nos Anh ON Bolin
‘From the proportion of the diagonals in which that of the wire of the
multiplier is expressed by 274, we find the following reduced lengths
(referred to the wire of the multiplier or No. 2) of our three spirals,
620 LENZ ON ELECTRO-MAGNETISM,
——
A = 38°81 therefore L +/+ aA = 712-06,
a! = 10°78 L+l+A' = 68403,
Al= 544 L +/+ Aa"= 678°69,
the equation (A.) gives therefore
7 = (1s go sero 3),
a! = 68403 * p- sin. (19 48 ),
x= 67869 * p* sin. (19 51),
or, if the two last electromotive powers be compared with the first, the
proportions
@ T1206 sins (19° 3! )ianuerey
a > GSS an. (IS? 481)
x _ 712°06° sin. (19° 3')
— SS — 10085.
x!" . 678°69 > sin..(19°.51")
Both propositions differ so little from unity that we are fully warranted
in concluding that the electromotive power which the magnet produces
in the wire No.1 is quite as strong as those in the wires Nos. 3 and 4,
although the latter possesses a diagonal almost four and seven times
greater, and therefore that the electromotive power is independent of
the thickness of the wires. A second confirmation of this position is
found in the following experiment previously made :
Angle of Deviation.
Mean.
1 2 3 | 4
10 Conv. of wire No.3| 36-3 | 37°8| 33°5| 35°7| 35°82
36:0 | 37-0] 32+1| 349] 340 lay.
No.2) 35-4 | 36-8] $2°6| 35°0| 35°9 \ 34 a2
No.3} 33°6 | 35°5| 35°7| 37-3] 35:52
Consequently we have for
No.2, « = 34°95, further A = 34°00, also L +/+ A=707°25
No. 3, a! = 35°67, a’ = 11°52, and L +7 + a!= 68477,
consequently
#o of OT-25 *\sins. (17° 29!)
a! 684°77 * sin. (17° 50’)
Here also the proportion is so near to unity that we may from this,
combined with the above results, regard it as an established truth, that
“ the electromotive power produced in the spirals by the magnet re-
mains the same for every thickness of the wires,or is independent of it.”
From this law again it immediately follows that in rings of wires of
various thickness surrounding the armature of the magnet, the electric
= 1°013.
LENZ ON ELECTRO-MAGNETISM. 621
current produced by its removal is directly as the diagonals of the
wires ; for the electromotive power remains the same, but the resist-
ance it experiences in being conducted decreases inversely as the dia-
gonals ; consequently the electric currents, or the quotients of the elec-
tromotive powers by the diagonals, increase as the diagonals.
IV. On the Influence of the Substance of the Wires on the Electro-
motive Power produced in the Spirals.
Nobili and Antinori have in their first paper on the electrical phe-
nomena produced by the magnet (Poggendorff’s Annalen, 1832, No.3)
already determined the order in which four different metals are adapted
to produce the electric current. They arrange them in the following
order,—copper, iron, antimony, and bismuth.
It is particularly striking that this order is the same as that which
the above metals occupy also in reference to their capacity of conduct-
ing electricity ; and the idea suddenly struck me whether the electro-
motive power of the spirals did not remain the same in all metals, and
whether the stronger current in the one metal did not arise from its
being a better conductor of electricity than the other. With this view,
therefore, I examined four metals, namely, copper, iron, platina, and
brass, and pursued the following course: In order to avoid entirely the
influence of different conduction, I brought at the same time into the
metallic conducting circle through which the electric current had to
pass, two spirals, equal in all respects excepting that they were of dif-
ferent metals, binding the one end of the first with the one conducting
wire, the one end of the second with the other conducting wire, and
connected the two ends of the spirals which had remained free with a
distinct copper connecting wire. I now brought first the one spiral upon
the iron armature of the horseshoe magnet, and proceeded in the same
way with it as in the former experiments, and then the other. In this
manner the resistance which the electric current suifered in each pro-
cess was naturally quite the same.—I must also remark that I carefully
avoided all thermo-electric disturbing forces, as I surrounded the places
of connection of the various wires with several layers of blotting-paper,
and after having arranged the apparatus I always waited several hours in
order to give the places of connection time to take the temperature of
the room.
The experiments themselves are as follows :
622 LENZ ON ELECTRO-MAGNETISM.
Angle of deviation.
1
°
Copper spir. on the ar- 17°3
mature {
/17'3
Copper and
Iron spirals 17°3
iron spirals
Copper spirals 17°4
Copper and jamacianiel
platina spirals
15°7
Platina spirals 15-7
Copper spir. on the ar- } 15-2
Copper spirals 15°4
Brass spir. on the ar- 184
Copper and
brass spirals. |) Copper spirals
Brass spirals
If we now combine the single means together and convert the deci-
mals of the degrees into minutes, we obtain from this table the follow-
ing results :
Copper spirals, deviation ....@ = 17° 360
Iron spirals, ati CeO == Oe
Copper spirals, deviation....@ = 15° 34"5
Platina spirals, a) = 15 .35°2
Copper spirals, deviation....a = 18° 19'2
Brass spirals, .-..a@'=18 202
Since in this case the resistances remain the same for every pair of
observations, our chief equation (A.) gives, when treated as before, the
following proportions of the electromotive powers, if we designate them
for copper, iron, platina, and brass with a, a', a!’, 2!’:
msn. (8" 2400)
az’ sin. (8° 42"6)
= 1-00033,
a __sin. (7° 47'-2)_
——=2 == 099917,
x! ~ sin. (7° 47"6)
ets (9 OG)
— = = 0°99894.
a sin. (9° 10"2) -
These three proportions are all of them so near to unity that there will
exist no doubt as to the fact, that wires of copper, iron, platina, and
brass suffer one and the same electromotive action; and that I may be
allowed to extend the same position by analogy, even to all other me-
tals and substances in general, until direct experiments shall have left
the matter beyond all doubt. We shall have therefore the law,
“that the electromotive power which the magnet produces in spirals
LENZ ON ELECTRO-MAGNETISM. 623
of wires of different substances, but in every other respect placed in ex-
actly the same circumstances, is completely the same for all these sub-
stances”*.
Hence again it immediately follows that in two perfectly equal wire
rings of different substance, surrounding the magnetic armature, the
electric currents which are produced by taking the armature off or
placing it on the magnet, are in direct proportion as the capacities of
the substances for conducting electricity. Silver and copper wires
therefore are the most advantageous.
From the latter observations we shall easily be able to deduce the
capacity of the four metals for conducting, if we make a second similar
observation, in which instead of bringing into the circle of the electric
current two spirals of different metals, we make use of two of the al-
ready used copper spirals, and then place either of them on the armature,
and determine the angle of deviation. Let this angle be called a; and,
for the other spirals, in the order in which they followed in the obser-
vation (therefore the copper spiral, with that of iron, platina, and brass),
let these angles be designated by a’, a", and a!’. Further, let the com-
bined lengths of the wire of the multiplier of the conducting wires and
that of the connecting wire of both spirals (all reduced to the diameter
of the wire of the multiplier) be called L; but the lengths, which are
equal in all the spirals, reduced also to the same diameter, be };
we will further designate by 1, m’, m!, m!"', the conductive power of
the metals in the above order, where that of the copper is also expressed
by 1.
If we take the general formula (A.), namely
a= (L+/+A)p°sin. da,
we must here, since the wires are no longer of the same kind, substitute
for the resistance (L + / + A), the resistances +
GE +: a); (1 Es *), (1 4 ai) and (1 4 an)
mm m m
since they stand in inverse proportion to the capacities of conduction ;
we have therefore four equations (in which, according to the law just
fonnd, 2) = 2! 2!" are = 2),
x=(L+A)p‘sinia
i Ca! ok
z= (1 +2) p-sin.§ 2
* After I had made the above experiment I saw from No. 5 of Poggendorff’s
Annalen, which I had then just received, that this last law had already been
demonstrated, although in a different way, by Faraday. My experiment may
therefore serve to confirm it.
+ In the following expressions I consider the resistance / jointly with that
of L, since in the multiplier last employed the conducting wires consisted of
one piece with the wire of the multiplier, therefore L + ” must always remain
constant.
624 LENZ ON ELECTRO-MAGNETISM.
all Xenia
r= (L +37) p-sinda
alt } we
= (x +77) posin be s
consequently, by division,
L+a_ sin.ta
sin. L &
i= ee or b+ = (Lt wen
apna sin. 5 & sin. + a!
m'
L+a sin. da sin. $a
sin N Serene or L+—,=(L+ A) siaa
L+ —; 3
m
_ L+a sin. $a sin. } @
uF A: * sind a!” or Lt eh t+ Naty ™?
ml!
from which equations m’, m', and m''’ may be found.
For our case, Lis = 849 inches, A = 841, a@ = 21° 52', a! = 17° 36’,
a'' = 15° 34', a!!! = 18° 20', hence we have
Capacity of conduction of copper ......... = 1-00000,
DIO ON =O 7ocls
———_—_—__—_—_—_—_— pplatina or m’ =0°18370,
brass or m!"... = 0°32106.
We might still find these values more exactly if the lengths of the
wires were greater ; but this investigation did not properly come within
the scope of this paper, I therefore defer it till another occasion.
Consequences of the Laws already established in respect to the Con-
struction of Electromotive Spirals.
In the following experiments I suppose the magnet for the produc-
tion of the electric current to be given here, therefore the question is
to determine those spirals of a certain metal which act most advan-
tageously with this magnet and its cylindrical armature, which is like-
wise given. Further, I suppose the spirals, together with their free,
not wound ends, to consist of one and the same wire; moreover, it is
self-evident that every other property of the ends of the wires not be-
longing to the electromotive spirals may be reduced to those above men-
tioned, if we know the length, the diagonal, and the conducting power
of the pieces of wire brought into the circle.
It is easy to see that by increasing the convolutions ad infinitum we
do not also increase the strengths of the current ad infinitum. In the
first place,—the number of convolutions of a given wire is limited by
Qe se eee
LENZ ON ELECTRO-MAGNETISM. 625
the length of the cylindrical armature; therefore the further increase of
the number of convolutions can only be made by several series of con-
volutions placed one above another. Let the electromotive power of a
series of convolutions which the length of the armature occupies = 9;
the length of the wire of all these convolutions, or, in this case, on ac-
count of the diameter of the wire being equal throughout, the resist-
ance it offers = a; let the length of the necessarily free ends of the
wires together = 6, the power therefore of the current of this first se-
ries of convolutions is
ee
1 TaeR’
let y be the piece of the second series of convolutions by which its
length, on account of its necessarily greater diameter, is greater than
the length « of the first series, the power of the current from these
two series is
26
= Fat y+’
and in the same manner
36
= Bsaty+otPR
where @ designates the quantity by which the first series is surpassed in
length by thethird. If now the second series of convolutions does not
add to the strength of the current, we put ~, = 4, therefore
ee 2 F
a+B 2a+Pry
ane
i.e. as soon as the length of the free ends is only equal to the differ-
ence between the lengths of the second series of convolutions and those
of the first, the second series would then add nothing to the strength
of the current. In order to see what three series would do in this case,
whence we have
let us put 6 = y in the expression for ~, and we obtain
add to Shithiieows
$a+28+4 9°
d however is now greater than y or 6, we therefore put 6 = 6B + p,
where % expresses a positive magnitude ; we obtain by this
= 39 = p
3a+3B+p Zz
(a+p) +4
3
Bs
This last expression for js is evidently smaller than Ser conse.
quently three series of conyolutions would only weaken the action of
one or two series (which actions have been here assumed as equal).
626 LENZ ON ELECTRO-MAGNETISM.
In the same manner we find, if three series have not a more power-
ful action than two
c=3(y = 8B)
i.e. this happens when the length of the free ends is half as great as
half the sum of the differences between the length of the first series and
the lengths of the second and third series.
Having thus proved that by increasing the series of convolutions we
never obtain a maximum of the electric current, and therefore that a
greater increase would only do harm, we proceed to the general consi-
deration of the subject.
We therefore suppose the convolutions of a series of the bespun me-
tallic wire to lie thick on one another. Let the length of the space on
which the convolutions may be wound up be = a, the thickness of the
wire = 6; let the thickness of the wire covered with silk surpass the
thickness of the uncovered wire by the excess f, so that it be = 6 + £,
the length of a convolution be = c, the lengths of the free ends of the
wire = m; the number of convolutions then which can be wound in
a
6+ 6
ec, and the whole length which the elec-
and the length of the wire
one series upon the armature is =
of these convolutions = —“%
6+ 6
tricity has to run through tor one series of convolutions
a
= (+B) e+m
If we assume the resistance offered by a wire of the same substance,
whose length = 1, and whose thickness = 1, as unity, the resistance
for one series of convolutions becomes
a
ee a eoee e et
a CLE :)
Further, let the electromotive power produced in one convolution,
which, according to the second and third of our laws above proved,
remains the same for every magnitude of the convolutions and for
every thickness of the wire, be called f; the electromotive power pro-
duced in a series of convolutions is therefore, according to the first of
the above laws,
aan
and consequently the power of the electric current for a series of con-
yolutions, or
ms abef
Pi ac+(b+ 6) m
We must now for our purpose express the length of a convolution or ¢
LENZ ON ELECTRO-MAGNETISM. 627
in terms of the diameter of the cylindrical armature, and the thickness
of the wire and its silky envelope. We have however the semi-dia-
meter of a convolution, if half the thickness of the iron cylinders is = q,
for the first series = g + a oe B
second = ee = (6 + B)
— third —-=9 +3 @+8)
eS aah —=9+ = (648)
whence we have the length of a convolution or
e for the first series = (24 +(b+ B)) 7
e — second =(29+3(6+6))=
e — third = (29 +5(6+ 6)) 7
c nth — = (29+ (@n—1)(6+6))
__ If we substitute the first value of ¢ in the equation for m, we obtain
abef
Pian (24+ @+ B)) + (b+ B)m
The electromotive power is for two seriesof convolutions with regard
to the above law, No. 2,
SR pp Mahia ha ;
ore
but the resistance is equal to that of the two series of convolutions,
together with the piece m, therefore
pa p2gtb+B)nt+ py 2" + r3(6+8))x +m
= B
=n 2 eR EE) ee BY.
Bb + 6)
consequently the power of the current for two series, or
ee
i) av lst bo ocho ok Soeliey 1 ai
Po= Ga (4g+40+8))+mOtB)
6° (b + B)
2ab*f
~ ae(hg + a Abe se Pd.) +m (b + B)
Vor. I.— Parr IV.
628 LENZ ON ELECTRO-MAGNETISM.
In the same manner we find
pr eeenads wads AS OEE ay pitta b
* ar(6qg+9(b+ B))+m(b+ B)
ED een Oe kay eee
Ps aa(8q + 16(6+B))+m(b +B)
Pa= n abrf (D.)
If I differentiate this general expression of the power of the current
for m series of convolutions in regard to », I obtain
UPn gyn CH ongtn* (68) +m(b+B)—awn(29-+2n(b+B))
dn lam(Qng+n?(b+f6))+m(b + B)}?
If I put this expression = 0, we have after some reductions
m—anrn? =0,
consequently n= a/ (2)
an
I take here the positive sign of the root, because according to its
nature cannot be negative, and m, a, m, are all three positive.
If we further develope pee and put in the expression found this
: m : é :
value of 7 = Abs ( ~) we obtain a negative magnitude; conse-
aw
quently this value of x represents a maximum of the current.
From the discovered value of 2 for the maximum of the current, we
can infer
1. That the maximum of the action of the magnet on our spirals, for
every thickness of the wire, is attained by the same number of series
of convolutions ; for 7 is independent of 6 + 6.
2. That the longer the free ends of the spirals are, or the greater m
is, the greater is the number of the series of convolutions required in
order to attain the maximum of the action.
3. That the longer the space a is on which the convolutions may be
wound round in one series, the less number of series of convolutions
are necessary to produce the greatest current.
4. That the maximum is independent of g, i.e. that it is quite in-
different for the number of series of convolutions necessary to the at-
tainment of the maximum, whether they are immediately wound round
the cylinder of iron, or round another cylinder which is placed on the
other one.
If we put the above found value x = a/ ( ~) in the general ex-
ang
pression of the power which is contained in the equation (D.), we
obtain after some reductions, as the expression for the maximum which
LENZ ON ELECTRO-MAGNETISM. 629
is attained by the current,
= oa
P (maximum) a(3q rahe: /()) - - (E.)
This expression again shows :
1. That the maximum of the current stands in direct proportion to
_ f,i.e., to the power of the magnet, or rather to the strength of the
magnetism which is produced in the armature by the placing on of the
magnet, and which again vanishes.
2. The maximum is more powerful for a thick wire than for a slender
one, for we can bring its expression to the form
is na od
RTD
which shows that the whole expression increases with the increase of 6.
3. The maximum decreases with g, i. e. it becomes so much the
smaller according to the greatness of the cylinder on which the first
series of conyolutions is wound, it being assumed that the armature
does not on that account become greater.
4. It becomes smaller with the increase of m, i. e. the greater the
free connecting ends of the spirals are, the smaller is the ultimate at-
tainable maximum of the current.
5. Finally, the maximum increases when a increases, i. e. when the
space of the armature upon which a series of convolutions can be
wound becomes greater.
We shall consider the power of the current of a single convolution
wound round the armature to be the same as m, then as soon as we
_ put in the general expression (D.) for the current zm = 1,anda = 6 + 6,
we find x ee af
P (a convolution) — 7aqto+B) + Me
If we divide the expression for the maximum of the current (E.) by
this, we may designate the quotients as the maximum of increase, and
find that
|
m
2g +(6+8)+—
Fascia py AAS es
f I propose to find, for instance, with how many series of convolutions
T attain the maximum of the current for my magnet and armature,
hen I take a length of 850 English inches for the wire of the multi-
lier and the connecting wires together, I have
a=1°6,b + B = 0:065 (wire No.4) g = 0:335, m = 850.
The formula 2 = / oe gives for x = 13:07, and the formula (F.)
the maximum of the increase is
ves the maximum of increase = 114°8. We shall obtain therefore the
630 LENZ ON ELECTRO-MAGNETISM.
maximum of the current at somewhat about thirteen series of convo-
lutions, and the current then becomes about 115 times stronger than
when produced by one convolution.
We will here separately consider the case in which m =o, i. e.
where the spirals have no free ends, but close in themselves. If we
put m = o in the expression of the current for one convolution, for one
series of convolutions, and for 2 series of convolutions, we shall then
obtat for a single convolution = Lo COC ae
Ign +7 +P)
of
2qr+7(b + B)
bef
2Qqar+n7(b + B)
whence it follows that here the current in one convolution is just as
strong as in a series consisting of any number of convolutions ; and
that in both these cases it is stronger than when several series of con-
volutions cross one another (for 2 is quite a positive number). The
expression of the current for a convolution may moreover be exhibited
thus it
for a series of convolutions =
for n series of convolutions =
i. e. it is equal to the electromotive power, divided by the resistance
offered by a convolution ; and in effect it is evident that in this case of
m =o a series of convolutions must act just in the same manner as a
single convolution; for with the increase of the number of convolutions
the electromotive power and the resistance become increased in the
same proportion, consequently the quotient of the one by the other, or
the electric current remains unchanged. It is also now evident that in
effect a second series of convolutions can only weaken the current,
since in the second series the electromotive power increases as in the
first, with the increase of the number of convolutions ; while, on the
contrary, the resistance is greater in the two series than double the
same in one series, on account of the enlarged diameter.
But there is one phenomenon of electro-magnetism to which all the
above positions however cannot yet be applied, namely, to the pro-
duction of the spark. This occurs then only, when the metallic con-
ductor of the current is disturbed at some place; there enters therefore
into the circular passage of the current an intermediate conductor,
whose length is almost indefinitely small, but whose resistance is almost
indefinitely great. We must therefore, in order to apply the above-
developed formule, first be in a condition to reduce this intermediate
conductor to a certain length of wire, with the diameter of the wire
given, and thus to determine m ;—but for this reduction we are yet in
want of the data.
INDEX.
Assorrtion, phenomena of, 479.
Absorptive force of glass molecules, 44.
bstract terms, treated by Carus as real
entities, 254.
cid, new, combinations of, 470.
—-, nitric, mode of ascertaining the
_ presence of, 441.
——.,, tartaric, unequal dispersive powers
_ of, 601.
——, chlorous, 270; preparation of, 275;
volatility of, 279; properties of an aque-
ous solution of, 280.
Acids, hydrochloric, 271; carbonic, 272;
acetic, 273; chloric, 274; hydrospiroilic,
155; spiroilic, 160; hyperoidic, 282; cy-
anic, 286; hydrophosphorous, 290; hy-
_ perchlorous, 305; hyperbromous, 310.
—, action of on organic colouring prin-
ciples, 594, 595.
JEpinus, theory of, 449.
Ether, Mossotti on, 450.
Air, reflecting property of, 101.
Alcohol, spectrum of the flame of, 492.
Algz, infusorial motions of, 566.
Alloys, and amalgams, table of, 520.
Amici’s microscope, magnifying power of,
570; improvements of, 580.
Ammonia, hydrospiroilate of, 157; its
composition, 158.
- —, nitrosulphate of, 473.
Ampere on the propagation of heat, 389.
, elementary particles of, 490.
, invention of the bascule of, 509.
, on the action of the magnet, 608.
Analysis, organic, 595, 599.
- of wood, 148.
— of the subnitrate of copper, 422.
Anhydrous, sulphuric, and sulphurous
acids, new combination of, 443.
Animal body, composition and internal
formation of, 245; formation of the
solids of, 246.
inimal bodies, considered as aggregates
of innumerable infusoria united into a
_ living whole, 246, 565; as plants with
_ the roots turned inwards, 243, 247, 251.
imal life, progressive development of,
253; transition into vegetable, 572.
Animal structure, a hollow globe contain-
_ ing its roots withinside, 243, 244, 247.
Animalcules, gradual origin of, 562; cy-
| clical development of, 560; structure of,
| 559; transparency of, 562; solution of,
~563.
——,, infusorial, doctrine of, 564;
Wor, l.—Parr IV.
( 631
)
INDEX TO VOL. I.
division of, into two classes, 564; wheel
organs of, 564; similarity of, with larger
animals, 564; geographical diffusion of,
565; man dependent on the will of, 565.
Animals, crustaceous, origin of, 565.
Antimony, oxysulphuret ef, 433.
Antinori on the electrical phenomena
produced by the magnet, 621; experi-
ments of, 608.
Artificial light, effect of, 112.
Ateuchus sacer ; At. Aegyptiorum, 193.
Atmosphere, constitution of, 397; con-
stitution of the superior regions of, 393;
motion of light in, 393; refringent
power of, 395. ¥
—_——__—,, terrestrial, altitude of, 394.
Atoms, doctrine of, 568; law of the re-
pulsion of, 448; various arrangements
of, 597; angular deviations produced
by, 602.
—— ., hooked, of Epicurus, 476.
——-—, organic, doctrine of, 571; utility
ofinchemistry,571; Ehrenbergon, 555.
Attelabus buprestoides, 197.
Attraction, magnetic, rapid decrease of,
508.
Azote, chloride of, preparation of, 287.
Bacillaria, siliceous shields of, 401.
Balard on the bleaching properties of
chlorine, 269.
Barytes, combinations of, method of ob-
taining in a crystallized state, 436.
Bascule of Ampere, 509.
—, mechanism of, 532.
Battery, galvanic, Olim’s theory on, 312.
Becquerel on the chemical effects of elec-
tric currents, 414, 608.
Beet root, sugar produced from, 605.
Bergmehl, 406; fossil infusoria in, 401.
Berthollean method of bleaching, 269.
Berzelius’s experiments on the chloride
of potassium, 273.
, his views respecting the prima
germina rerum, 571.
Bilin, infusorial rock of, 409.
Biot on the construction of the superior
regions of the atmosphere, 393.
on the application of circular pola-
rization to chemistry, 600; to the ve-
getation of the Graminex, 584.
——, his method of oscillations, 513.
——-, his experiments on electro-magnet-
ism, 618, 619; on the electrical phe-
nomena produced by the magnet, 621.
Biurus of Cicero and Pliny, 198.
2x
632
Bladder-worm, its structure, 244, 247.
Blainville, views respecting the generatio
@quivoca, 572. ‘
Bleaching, Berthollean method of, 269.
Bleuler, microscope of, 560.
Blood, human, globules of, 407.
Bodies, animal and vegetable, forma-
tion of, 555; on obtaining them by
_ chemico-synthetical means, 555.
, coloured, limit of the power of
the human eye for, 577.
, combustible and comburent pro-
- perties of, 594; ductility of, 572; ela-
sticity of, 189, 255; electro-tonic state
of, 530; internal constitution of, 448 ;
classification of, according to their
mode of crystallization, 603; charac-
ters for distinguishing the mutual action
of, 599 ; organoleptic properties of, 599 ;
neutrality of, 599.
, living, formed by combination of
molecules, 570; infusoria, the first forms
of, 570.
, luminous, power of the human eye
for discerning of, 578.
» organic, vital relations and pri-
mitive ccnditions of, 555; nature of in
infusions, 572.
, organic and inorganic, spontane-
ous motion of the particles of, 570.
Bog-iron ore, infuseria of, 402.
Botto on the application of electro-mag-
netism as a mechanical power, 532.
Bonnet, his theory of reproduction, 570.
Brachione, red coloured eyes of, 561.
Brewster, Sir D., his objections to the
undulatory theory, 478.
Bromic gas, spectrum of light of, 478.
Bromide of spiroil, its composition, 164.
Brown, microscopical observations of, 570.
Buquoi, Count, his experiments on vege-
tables, 235.
Burmeister on the sounds produced by
insects, 377.
Cadmium, sulphuret of, crystalline form
of, 434.
Caloric, Jaw of the propagation of, 24;
quantity and intensity of, 524.
Calorific rays, properties of, 57; refrac-
tability of, 55.
Calorific transmissions, modifications of,
39.
Calorimotor of Hare, 515.
Cantharis, 171; method of destroying,
181; mentioned by Aristotle, Aristo-
phanes, Dioscorides, and Pliny, 182.
Carbon, chloride of, 309.
Carlsbad, infusoria in the waters of, 400.
Carrots, sugar produced from, 605.
-Candle-light, spectrum of, 491.
INDEX.
Carus, Dr., on thekingdoms of Nature, 223.
———, terms used by him in peculiar
senses, 254,
Cellular formation of vegetables, 287; of
animals, 246. 4
Centre of organization, 240, 244.
Cerealia, Raspail’s observations on, 587. —
Cetonia aurata, description of, 196.
——— fastuosa, 196.
Chain, galvanic, Ohm’s, 511.
Chemical characteristics of the animal )
and vegetable kingdoms, 232, 246.
Chemical effects of electric currents, 414.
Chevalier, microscope of, 561; reverbe-
ratory lamp of, 583.
Chevreul, examination of an optical cha-
racter by which vegetable juices may
be distinguished, 591.
Chime, electric, 507.
Chladni on the vibrations of laminze of
glass and metal, 139.
Chloride of azote, properties of, 287;
of carbon, 309; of potassium, Berze--
lius’s experiments on, 273; of sodium,
274; of spiroil, 182; properties of, 163;
composition of, 164.
Chlorine, action of, 270; bleaching pro-
perties of, 269; Dr. Liebig’s experiments
on, 273.
Chlorites, preparation of, 273.
Chlorous acid, 270; composition of, 297 ;
analysis of, 298; preparation of, 275;
volatility of, 279.
——, aqueous solution
properties, 280.
Chlorous acid gas, properties of, 293.
Chromatic scale, formation of, 95.
—_——- —, Nobili’s, 120.
Clapeyron on themotive powerofheat, 348
Clock, electrical, of Zamboni, 533.
Coccus Adonidum, mealy aspect of, 215;
method of destroying, 217. :
Coccus, analogies of infuseria with, 564.
Cochylis Roserana, devastations of, 209;
description of, 210.
Coloured food for infusoria, 562.
Colours, comparison of their intensities,
35; combination of, in dress, 113; ele-
mentary particles of, distinct from
atoms, 569; division of light into, 487 ;
gamut of, 115; harmeny of, 112; ima-
ginary or accidental, 113; natural mode
of origination, 486; Newton’s experi-
ments on, 99; size of the particles of,
469; phenomena of, 570; in com-
bined crystals, 83; varying laws of, 102.
and sounds, analogies between,119.
, metallic, 94, 105.
of the spectrum, phenomena in,
of, its
81.
i‘,
"
»
Commutator, construction of, 504.
Convolvulus of Cato and Pliny, 187.
‘Copper, crystals of the protoxide of, 421;
_ subnitrate of, 425.
Corti’s discovery of the eggs of infusoria,
_ 560.
Srystals, combined phenomena of co-
- jours in, 83; dilation of, 33; elastic
state of, 268; life of, 230, 234, 242.
, twin, phenomena of ccloursin,83.
Curculio frumentarius, description of, 202;
_ devastation caused by, 203.
Currents, electric, chemical effects of, 414.
al Negro, experiments of, 505, 535.
‘Davy, experiments of, 470.
Death, an absolute, asserted by Dr. Carus
_ to be inconceivable, 225.
elaroche, his method of measuring quan-
__ tities of heat, s.
Dermestes Pellio, description of, 205.
Dextrine, conversion of, into sugar, 565.
Diamonds, vivid light of dust of, 583.
Diaphanous media, their resistance to the
passage of heat, 21.
Differences between solar and terrestrial
heat, 69.
‘Distribution of heat in a bar, 131; in
[ spherical bodies, 131.
Dollond, glass micrometer of, 564.
Dove's apparatus, description of, 86.
- experiments on circular polariza-
tion of light, 75.
Duality of vegetables, 235, 242, 245.
Dulong’s law of elastic fluids, 359.
Dumas, doctrine of organic atoms of, 571.
- , on the formation of living bodies
_ from elementary organic particles, 570.
Earth’s centre, accumulation of heat to-
_ wards, 54.
Earth, motion of heat in the interior of,
_ 184; primitive state of, 135.
Eau de Javelle, nature of, 270.
ges, circulation of fluids in, 251.
, infusorial, the product of a generatio
primitiva, 566-
Eggs of intestinal worms propelled by the
circulation of fiuids, 558; circulation
of, in the blood vessels, 558.
Ehrenberg, experiments on fungi and
' mould; on fossil infusoria, 400, 407 ;
| on the generatio equivoca of infusoria,
| 559; oa the origin of organic matter,
555; on organic molecules and atoms,
555; on the power of vision, 576; on
the ultimate power of the microscope,
_ 576.
Hlectric chime, 507.
éctricity, influence of, 598 ; calorifying
' power of, 517; distinction between
quantity and intensity, 523; Henry’s
.
INDEX.
x
633
experiments on, 534; Van Moll on, 534;
Ten Eyck on, 534; nature of, 517.
Electricity, chemical, 517.
, statical, Franklin’s hypothe-
sis, Hpinus’s, Mcssotti’s, on, 466.
Electric currents, chemical effects of, 414.
Electro-chemical compounds, 419.
Electro-magnets, lifting power of, 503.
Electro-magnetism, application of to ma-
chines, 532; Schulthess on, 534.
Euglena, red eyes of, 563.
Entomostrati, curious origination of, 560.
Entozoa, eggs of, 558; diseases produced
by, 558; fecundity of, how limited, 559;
inaccessible station of, 559.
Epicurus, hooked atoms of, 476.
Epizoa, vast increase of, 559.
Equivalents, law of, in galvanic decom-
positions, 524.
Eruca of Pliny and the Vulgate, 189.
Esenbeck, on the germination of the seeds
of fungi and mould, 556.
Euler on the equilibrium of fluids, 550.
Eumolpus vitis, ravages of, 204.
Exogenous trees, long duration of, 585.
Eye, human, power of vision of, 555; ir-
ritability of, 499; myopical and pres-
byopical, difference between, 577.
Eyesof infusoria,extreme fineness of, 574.
Faraday on the nature of electricity, 617.
, his law of equivalents in galvanic
decompositions, 524.
Fechner’s experiments on the galvanic
chain, 513.
Fengier’s apparatus for preparing pure
zinc, 521.
Fermentation, alcoholic, action of, 604.
Fermentation, infusorial, 293, 555, 571.»
, peculiar process of, 555.
Ferrault. on organic analysis, 595.
Ferriferous carbonate of lime, 260; struc-
ture of, 260; primitive form of, 261.
Fire, its action on metals, 108.
Fixed stars of the microscopic world, 583.
Flame, coloured, 491.
Flint, formation of, 410.
Fluids, elastic, Dulong’s law of, 359.
, incompressible, equilibrium of,
548.
Fetus, development of the, 247, 248.
Fossil infusoria, their occurrence, 400.
Fourier on the distribution of heat in a
homogeneous atmosphere, 128.
Franklin, hypothesis of, 466.
Frauenhofer, calculations of, 501.
Fray, delusion of, as to the origin of En-
tomostrati, 560.
Fresnel on the diffraction of light, 480.
Frogs’ blood, globules of, 407.
Frogs, celebrated Egyptian, 560.
Z
634
kungi, cyclical development of, 557; ex-
periments of Ehrenberg on, 555 ; ger-
mination of the seeds of, 556.
Gaillonella distans, occurrence of, 403.
ferruginea, description of, 402.
Galvanic battery, Ohm’s theory on, 312.
Galvanic chain, Ohm’s, 51!.
Gas, chlorous acid, properties of, 293.
, iodic, spectrum of light of, 478.
» propagation of sound in, 372.
Gases, action of 494 ; agzregate condition
of, 490; evaporation and secretion of,
250; law of the diffusion of, 394.
Gaza, the locust of Amos and Joel, 200.
Generatio equivoca, critical examination
of, 555.
Geology, relation of infusoria to, 568.
Glass, green, physical properties of, 335.
, its optical action when heating and
cooling, 85.
, cooled, double refraction of, 78.
, laminz of, vibrations of, 139.
Glass molecules, absorptive force of, 44.
Glasses, achromatic object, Selligue’s
method of combining, 580.
Geethe on metamorphoses of plants, 238.
Gold, conductibility of, 322.
—— dust, powerful reflection of, 579;
transparency of, 579.
leaf, thickness of, 572.
Gourjon’s thermomultipliers, description
of, 70.
Goureau’s experiments on sound, 381.
Graminez, analysis of vegetation of, 584.
Grape-sugar, optical phenomenon of, 596.
Green glass, physical characters of, 335.
Greenhouse Coccus, description of, 215.
Gruithuisen, his views on infusoria, 232,
on the formation of orga-
nisms, 571.
Gryllo-Talpa, devastation of, 199.
Gum, property of, 587.
Gyrotrope, action of, 534.
Hare, calorimotor of, 515.
Harpsichord, ocular, Caslet’s, 114.
Hauy on the refractions of light, 372.
Heat and light, identity of, 37; identity
of the agents producing them, 388.
Heat at the surface of a body, movement
of, 127.
Heat, differences between solar and ter-
restrial, 69; influence of, 598; mathe-
matical theory of, 122; maximum of
in the solar spectrum, 37; method of
measuring, 5; velocity of its propaga-
tion, 7; molecular vibration of, 389;
motive power of, 348; polarization of,
$25; propagation of, 24, 389; refran-
gibility of, 392.
——, radiant, concentration of, 387;
INDEX.
—-——, fossil, occurrence of, 400. « »
Ingenhousz, on the green matter, 232.
Insects, Walckenaer on, 167; names of,
laws of, 124 ; motion of, 125; distribu
tion of, 128, 131; reflection of, 2833
transmission of, 1.
Heat, solar, theory on, 137.
Heavens, mechanism of, 451.
Henry, experiments on electricity, 534.
, on the influence of a spiral con
ductor, 540,
Honey, the two principies of, 605.
Hoffinann, microscope of, 560. f
Hornschuch’s views respecting the prima
germina rerum, 57). ?
Human egg, development of, 247.
Hydotina senta, duration of life of, 567.
Hydrate of lime, properties of, 270.
Hydraulic wheels, construction of, 506.
Hydrochloric acid, mode of ascertaining |
the presence of, 441. q
Hydrogen, action of, 426.
Hydrospiroilic acid, composition of, 155.
Hygrocrocis ochracea, 402. ‘
Hypochlorites, properties of, 305; pre=_
paration of, 305.
Identity of the agents producing light and -
heat, theory of, 388. ;
Indigo, its property of producing violet |
vapour, 596. ;
Induction, electro-dynamic, theory on,528.
, dynamical, 545. y
Infusoria, according to Koelle living glo-
bules of Zymom, 570. b,
Infusoria, coloured pouches of, 563; or-
gans of nutrition, 563; generative or-_
gans of, 563; teeth of, 569; consum-—
ption of, 406; occurrence of, 402; Eh-
renberg’s observations on, 559; gene-
ratio equivoca of, 559; formation of, }
232; structure of, 560; fourfold mode |
of reproduction of, 564, 567; ventral |
cells of, 564; geographical diffusion of,
565; man dependent on the will of, |
565; origin from eggs of, 566; high }
organization of, 561; cyclical develop-
ment of, 561; nervous system of, 566 i
internal organs of, 567; division into —
classes, &c., 567; fertility of, 567; oc-
tuple increase of, 568; influence of on
organic substances, 568; how precipi-
tated, 568; relation of to geology, 568;
development of into other- different
bodies, 571; formed of Zymom, 5715
certain forms of, produced by certain
infusions, 572; presence of infusorial
eggs in plants, 572.
, the larger animals considered as
formed of a mass of them, 246.
4
and in ancient writers, 171.
q
Insects, sounds produced by, 377.
Intestines of animals, root-organs turned
_ inwards, 243, 244, 247.
Intensities of colours, comparison of, 35.
Tntroversion of root-organs in animals,
243, 244, 246.
Inyolvolus of Plautus and Festus, 186,
Todide of spiroil, 166.
Jodides, metallic, law of composition, 435.
odine, property of, 596.
Ips of Homer and Chrysostom, 205.
Todic gas, spectrum of light of, 478.
Irritability of plants, 241.
- , vegetable and animal com-
_ pared, 252.
Jacobi, on the application of electro-mag-
netism to machines, 503.
Jenkins, curious experiment of, 528.
Julus of Aristotle and Hesychius, 184.
Kampe, the vine-moth of Aristotle, of
Theophrastus, Pliny, the Septuagint,
Chrysostom, Pope Zachary, Columella,
and Palladius, 183, 220.
Kermes, preparation of, 433.
Kieselguhr, description of, 400.
Kingdoms of nature, life and affinity of
_ the, 223.
Kelle, his chemico-microscopical exposi-
tion, 570.
Klpoda Cucullus, ovarium of, size of the
granules in, 574.
Lagrange, theory of, 548.
Lambert's theory of the solar heat which
_ falls upon the earth, 137.
Lamp, Locatelli’s, description of, 40.
——,, reverberatory, 583.
Laws of cooling in bodies, 125.
Law of the diffusion of gases, 394.
——, of the propagation of caloric, 24.
Lead, erystals of the protoxide of, 424.
Lenz, on the conducting power of wires,
» 311.
on the laws according to which the
_ magnet acts on a spiral, 608.
|Lethrus Cephalotes, 202.
|Leuciscus papyraceus of Agassiz, 402.
Liebig’s experiments on chlorine, 273.
Life, Dr. Carus’s general conception of,
224; its endless variety of forms, 224 ;
an original principle, of which the body
is one of the phenomena, 225; the
a wee
through outward forms, and of unity
_ through multiplicity; nature one in-
finite life, in which single forms are
constantly merging, 225; life of the
different kingdoms of nature; of the
inorganic kingdom, 228; physical life,
_ 235; planetary life, 230; life of the
- earth, water essential to. it, as wellasto
INDEX.
‘manifestation of an internal principle °
635
animal and vegetable life, 230; life of
crystals, as distinguished from organic
life, 230, 234, 242; organic life, 234;
vegetable life, 234; distinguished from
animal life, 234; the line the arche-
type of the plant, the globe the arche-
type of the animal, 234, 244; animal ex-
ists one half within the other; plant, one
half upon the other, 235; relations of
vegetable life to universal life and to
inorganic nature, 239; to the life of the
earth, 241, 242; animal life, 242; per-
fect unity its characteristic, 242; di-
stinguished from vegetable life, 234,
244; its relation to the universal life of
nature, 246; metamorphosis of vege-
table into animal life, 246, 250; of
animal into vegetable, 572; develcp-
ment of the animal organism, 246; ani-
mal an introverted plant, 246; absorb-
ing and exhaling poles, 25!; circulation
of the fluids, centrifugal and centipetal,
251; animal sensation, 252; the ner-
vous life, 252; psychical life and self-
consciousness, 252 ; animal life develop-
ed out of the life of the lower kingdoms
of nature, 253 ; metamorphosis of de-
stroyed organic substances into ele-
mentary forms of life, 560.
Life, infusorial, duration of, 567.
——, organic, unfathomableness of, 576.
, vegetable, carbonated products of,
584.
Light, absorption of, 477; circular polar-
ization of, Dove on, 75; diffraction
of, 480; division of, 491; influence of,
on vegetables, 598; its division into
colours, 487 ; limit of lines determined
by the intensity cf, 579; motion of, in
the atmosphere, 393 ; phenomena of,
theories for the explanation of, 568;
propagation of, 490; refrangibility of,
$92; relative intensities of, 499; theory
of retardation of, 579; undulatory
theory of, 477, 569.
——.,, artificial, effects of, 112.
Light and heat, identity of, 37.
—— , identity of the agents pro-
ducing them, 388.
Lime, effect of, on plants, 589.
, ferriferous carbonate of, 260; struc-
ture of, 260; primitive form of, 261.
, hydrate of, properties of, 270.
Liquids, density of, 593.
Locatelli lamp, description of, 40.
Locusta aptera, devastation of, 200.
Liéwig on the essential oil of Spirea ulma-
ria, 153.
MacGauley, on the application of mag-
netism as a moving power, 547.
636
Machines, application of electro-mag-
netism to the movement of, 503.
Magnet, Jaws according to which it acts
on a spiral, 608 ; electromotive power
of, 610.
, (Antinori and Biot), on the elec-
trical phenomena produced by, 608,
621.
Magnetic power produced by voltaic ap-
paratus, 511.
Magnetism, active force produced by,
508 ; application of, as a moving power,
547; mechanical effect of, 507.
Magnets, electro-, lifting power of, 503.
Mammalia, intestinal worms in the foetus
of, 558.
Materialists, Carus’s representation of
their views respecting life, 252.
Mathematical theory of heat, 122.
Matter, constitution of, 490; elementary
particles of, 490.
, organic, origin of, 555,
Meadow-sweet, essential oil of, 153.
Melloni on the transmission of radiant
heat, 1.
, on the polarization of heat, 325.
——,, on the reflection of radiant heat,
383.
———, on the identity of the agents pro-
ducing light and heat, 388.
Melolountha of Aristophanes, Aristotle,
and Pliny, 193, 195.
Mercury, oxydization of, 509.
Metal, vibrations of the laminz of, 139.
Metallic colours, 105.
oxides, crystallization of, 4145
formation of, 420.
Metallochromy, 95.
Metals, action of fire on, 108; new me-
thod of colo suring, 94.
—, classification of,according to their
electrical properties, 621 ; experiments
of Lenz on, 621,622; Faraday on, 623.
Metamor phosis of “destroyed organic sub-
stances into elementary forms of life,
560.
Micheli’s experiments on the germination
of the seeds of fungi and mould, 556.
Microglena monadina, eyes of, 57
volvocina, fiery ring round, ‘575.
Microscope, Amici’s, 570, 580, 581 ; Che-
valier’s, 561, 580; Pistor and Schiek’s,
581; Hoffmann’ 8, "560; Bleuler’s, 560;
Plasi’s, 57).
Microscopes, ultimate power of, 576.
Milne Edwards, organic atoms, 571.
Mind, analogy between the laws of, and
the phenomena of nature, 223.
Mitscherlich on the dilation of crystals, 33.
Mole cricket, devastation caused by, 199.
INDEX.
Molecules, active, Brown on, 570;
——,,gradual origin of organic beings§)
from, 562.
————,, material, figure of, 459; den-|
sity of, 463.
» organic, Ehrenberg on, 555 si
proximate finity of, 575; organic, per=
fect organization of, 557.
Moll, van, experiments on electricity, 534. |
Mionas pee size of, 573; coloured in-
ternal sacs of, 573. 7
pulvisculus, motion of, not effected
by a change of gravity, 559; cilia of
559; fringe of cilia of, 573 ; ’membra -
naceous sacs, 574.
Monas atonius, experiments on, 575.
Mossotti on the forces which regulate the
internal constitution of bodies, 448,
Motion, molecular, influence of, 526.
Motion of heat, 125; in the interior off
the earth, 134. :
Mould, cyclical development of, 557;
experiments of Ehrenberg on, 555;
germination of the seeds of, 556.
Munke’s microscopical observations, 571.9
Nature, division of, 228; kingdoms of,
Dr. Carus on, 565.
, represented by Carus as one in-|
finite life, in which no proper death is
conceivable, but merely the merging of
a single form in the universal life, 225.
Naviculz, description of, 401.
Newton’s elementary par ‘ticles of colours, }}
569, 580; experiments on colours, 99. 9
Nitric’ acid, mode of ascertaining the pre- ff
sence of, 441. |
Nobili’s chtaratte scale, 120.
theory of electro-dynamic induc. |
tion, 528; double needle, 608, 609;
method of exciting the electric cur-
rent, 609,
Oersted’s discovery, 503, 504.
Ohm on ‘the galvanic battery, $12; his
galvanic chain, 511. am |
Organic life, its connection with inorganic,
232. |
Organisms, or organic bodies, 226; how
distinguished from i inorganic, 227, 243,
Organized matter, its production ‘from |
unorganized, 246, 233. : §
Oscillations, Biot’s experiments on, 513.
Oscillatory beings, between animal and jf
plant, 232, 246.
Osseous system, development of, 249.
Ostrogradsky on the equilibrium of ing
compressible fluids, 548.
Oxychloride, double, analysis of, 431.
Oxides, metallic, crystallization of, 414,
Pander’s experiments on circulation in
the egg, 251.
-
Paramecium Aurelia, long duration of
_ life of, 568; octuple increase of, 568.
arsneps, sugar produced from, 605.
articles, elementary, 490; magnitude of,
555; of Ampére, 490.
Yelouze on certain combinations of a
new acid, 470.
ersoz, on circular polarization, 591.
Ahtheir of Ctesias and the Geoponics, 214.
ile, action of, on alkaline sulphurets, 428.
—, voltaic, chemical effects in, 513.
—,,thermo-electric, hydro-electric, 526.
Pixii’s magneto-electric machine, 543.
Plants, cellular tissue of, 560; gradual
origin of animalcules from, 562.
, irritability of, 241; metamorpho-
| -sis of, 586; presence of infusorial eggs
in, 572; circulation in sap of, 239; sen-
_ sibility of, 240; structure and compo-
_ sition of, 286; sugar contained in the
foliaceous parts of, 588.
Plateau on the angles of vision, 576.
Pohl, experiments of, 608.
Plosl’s microscope, 571.
oisson, on the theory of heat, 122.
olarization, circular, application to ve-
getation, 584; laws of, 600.
‘oles, vegetative, light and gravitation,
240, 245, 251; animal, absorbing and
exhaling, 251.
‘olirschiefer, infusoria of, 401; formation
of, 406.
Poncélet, on hydraulic wheels, 506.
olygastrica, ovarium of, 566.
Potash, nitrosulphate of, 475; nitroxides
of, 470.
|- , sulpho-carbonate of, experiments
on the, 437.
otassium, chloride of, 273 ; experiments
of Berzelius on, 273; spiroilide of,
158; its composition, 158.
ower of transmitting caloric not pro-
*Priestley, green matter of, 232, 236.
Pyralis Vitana, caterpillar of, method of
_ destroying, 211.
Radiant heat, laws of, 124; reflection of,
| 383; transmission of, 1.
Raspail on the Cerealia, 587.
WRetractibility of calorific rays, 55.
Refraction, double, of cooled glass, 78.
Ritter on alloys, and amalgams, 519.
Rive, De la, on the chemico-electric ac-
| tion of zinc, 521.
fRock crystal, optical properties of, 258;
} sonorous vibrations of, 255; primitive
form of, 255.
Rose, H. on a new combination of the an-
a’
;
INDEX.
637
hydrous sulphuric and sulphurous acids,
4438.
Rotatoria, intestinal canal of, 561.
Sap of plants, circulation of, 239.
Savart on elasticity of bodies, 139, 255.
Savary, experiments on the variation of
magnetic needles, 546.
Scale, chromatic, 120.
Schaftrinsky, improvements of, on the mi-
croscope, 581.
Schiek, microscope of, 581.
Schilling’s experiments on thegermination
of the seeds of fungi and mould, 556.
Schulthess, on electro-magnetism, 534.
Screens, polish of, 18; thickness of, 19;
nature of, 15.
Seebeck’s experiments on the maximum
of heat in the solar spectrum, 37.
Seeds, algze, distinct from monads, 566.
Semi-opal, infusoria of, 410.
Sensibility of plants, 240.
Shields, siliceous, of Bacillaria, 401.
Sky, morning tints of, 100.
Slime, coagulation of, into organized be-
ings, 560, 562.
Soda, nitroxides of, 470.
Sodium, chloride of, £74.
Solar spectrum, maximum of heat in, 37.
Solar and terrestrial heat, differences be-
tween, 69.
Solids, formation of, in animals, 246.
Solution, aqueous, of chlorous acid, pro-
perties of, 280.
Soul and psychical life, 225, 252.
Sound, experiments of Goureau on, 381;
propagation of, 372.
Sounds and colours, analogies between,
114, 119.
Sounds produced by insects, 277.
Soubeiran, experiments of, 272.
Spark, electric, occurrence of, 630; no
criterion of electric power, 510.
Spectrum, solar, colours of, phenomena
in, 81; maximum of heat in, 87.
of candle-light, 491; of spirit
flame, 492.
Spermatazoa, primitive origin of, 582;
inoculation of, 583.
Spirea ulmaria, essential oil of, 153.
Spiral conductor, influence of, 540.
Spirals, best construction of, 608, 624.
, electromotive, combinations of,
610.
Spiroil, its properties, 154.
Spiroilic acid, 160; its composition, 161.
Spondyle of Aristotle, of Pliny, 191, 197.
Stahl’s doctrine, that the soul forms its
own body, 253.
Starch, chemical and physiological history
of, 591, 598.
638
Steam, mechanical force of, 349.
Steel, violet colour of, its property, 110.
Steffens, H., on carbon and hydrogen as
characteristics of the silicecus series,
and of vegetables ; nitrogen and hydro-
gen, of the calcareous series, and of
the animal world, 232.
Sturgeon’s experiments, 504, 536.
Streams, their origin from woody meoun-
tains, 241.
Sugar, conversion of dextrine into, 585 ;
curious property of, 592.
———, starch, 592; cane, 592; carrot,
605; parsnep, 605; beet-root, 605.
——, grape, 592 ; optical phenomenon
of, 596.
— , cane, analogy of with starch su-
gar, 596; physical character of, 597.
Sulphuric acid, theory on the formation
of, 476.
Sulphurets, alkaline, action of the pile on,
428.
, metallic, crystallization of, 431.
Sulphurous acid, volatility of, 444.
Tannin, action on animal matter, 595.
Tenia, curious mode of propagation, 564.
Tabanus bovinus, notes produced by, 378.
Ten Eyck’s electric experiments, 534.
Terrestrial atmosphere, altitude of, 394.
Terrestrial and scolar heat, differences be-
tween, 69.
Thermoscopes, description of, 8.
Thermomultiplier, 9; Gourjon’s, 70.
Thorax of insects, description of, 378.
Transmission of radiant heat, capacity of
bodies for, 30.
Transmission,calorific, modifications of,39.
Treviranus’s method of forming infusoria,
232.
Tripoli, 401; infusoria of, 408.
Tourmaline, optical phenomena of, 59.
Twilight-Monad, vast increase of, 575.
Twin crystals, phenomena of colours in,
83.
END OF THE FIRST VOLUME.
PRINTED BY RICHARD AND JOHN E. TAYLOR, RED LION COURT, FLEET STREET.
INDEX.
Undulatory theory, objections to, 477.
Unity, organic, 240, 252; Carus’s notio
of its division into duality, 242. :
Vapour, violet, produced by iodine an
indigo, distinction between, 596.
Vapours, theory of, 370.
Varying colours, laws of, 102.
Vegetable kingdom, influence of, upon the
earth, 241,
Vegetables, dualism of, terrestrial and
aérial, 235; cellular formation of, 237;
metamorphosis of, 288; sensibility o
240; irritability of, 241, 252, 253.
Vessels, formed by circulating fluids, 251.
Vibrations of laminz of glass, &c. 139.
Vine, insects injurious to, 167, 171.
Voltaic action, formation of metallic ox-
ides by, 420, A
pile, chemical effects in, 513.
apparatus, magnetic power pro-
duced by, 511.
Walckenaer on insects of the vine, 167.
Watkins’s experiments on electricity, 536.
Watt, discovery of, 506.
Water-drop, formation of, 229.
Wheel-animalcules, intestinal canal of,
561; red-coloured eyes of, 561.
Wheels, hydraulic, construction of, 506.
Wiesenerz, formation of, 402.
Wires, conducting power of, 311.
Wood, analysis of, 143.
World, infusorial, Milky Way of, 566.
, microscopic, fixed stars of, 583.
Worms, intestinal, Ehrenberg on, 557;
generatio primitiva of, 557; structure
of, 557; cyclical development of, 558;
occurrence of, 558; fecundity of, 558.
Wrede on the absorption of light, 477.
Zamboni’s electrical clock, 533.
Zinc, apparatus for preparing it pure, 521 ;
crystals of the oxide of, 425.
Zoophytes, generatio equivoca of, 572.
Zymom, origination of the lowest forms
from, 570; formed by silica, 571.
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