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LFA A OA OUGP NUN med ae > Sy “ee - Ree :
pS alin Se i pt aay n ; ew deen y Rr es Gi &.

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sy s . a 5 5 es . Aus . 2 : f PE Ot Bea wR es
eee 4 iene Sg FAS EES TERA Bee ATT SEDER v Re rips Pa ba "9 hy Sy ia

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: |
THE Fe

LONDON, EDINBURGH, ann DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

CONDUCTED BY
SIR ROBERT KANE, LL.D. F.R.S. M.R.LA. F.C.S.
AUGUSTUS MATTHIESSEN, Pu.D. F.R.S. F.C:S.

AND

WILLIAM FRANCIS, Pu.D. F.L.S. F.R.A.S. F.C.S.

“Nec aranearum sane textus ideo melior quia ex se fila gignunt, nec noster
vilior quia ex alienis libamus ut apes.” Just. Lips. Polit. lib. i. cap. 1. Not.

VOL. XXXVII.— FOURTH SERIES.
JANUARY—JUNE 1869.

\

legt (o"
LONDON. a

TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET,
Printers and Publishers to the University of London ;

SOLD BY LONGMANS, GREEN, READER, AND DYER; SIMPKIN, MARSHALL AND CO. ;
WHITTAKER AND CO.; AND KENT AND CO., LONDON:—BY ADAM AND
CHARLES BLACK, AND THOMAS CLARK, EDINBURGII:

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““Meditationis est perscrutari occulta; contemplationis est admirari
perspicua..... Admiratio generat queestionem, queestio investigationem,
investigatio inventionem.”—Hugo de S. Victore.

—‘* Cur spirent venti, cur terra dehiscat,

Cur mare turgescat, pelago cur tantus amaror,
Cur caput obscura Phoebus ferrugine condat,
Quid toties diros cogat flagrare cometas ;

Quid pariat nubes, veniant cur fulmina ccelo,
Quo micet igne Iris, superos quis conciat orbes

Tam vario motu.”’
J. B. Pinelli ad Mazonium.

CONTENTS OF VOL. XXXVIL.

(FOURTH SERIES.)

NUMBER CCXLVI.—JANUARY 1869.

Prof. R. Bunsen on the Washing of Precipitates. (With a Plate.)
Mr. F. A. Paget on a New Form of Permanent Magnet......
Messrs. E. ‘I. Chapman and M. H. Smith on the Action of De-
hydrating Agents on Organic Bodies .............0000:
M. O.E. Meyer on the Explanation of Stewart and Tait’s Ex-
periments on the Heating of a Disk rotating in a Vacuum ..
Mr. 8S. Newcomb on Hansen’s Theory of the Physical Consti-
enumengathommigon! 850 22 ee eas eee a
Mr. R. Edmonds on Extraordinary Agitations of the Sea not
proumced by Windsor Tides’ 22. 0. 8) Sab eed ss
Prof. E. Edlund’s Experimental Proof that the Electric Spark is
MMM ECEROMMOGOT. 2s oo ee a es ais bo de wena eas ae
Mr. H. Wilde on a Property of the Magneto-electric Current to
contrel and render Synchronous the Rotations of the Arma-
tures of a number of Electromagnetic Induction Machines. .
Notices respecting New Books :—
Mr. G. Fownes’s Manual of Elementary Chemistry, The-
eteticaltand Practical 22280. V2 18 UO. Lok AS.
Dr. F. Guthrie’s Elements of Heat and of Non-metallic
Chemistry. Especially designed for Candidates for the
Matriculation Pass Examination of the University of
LACUD CIO 20 Gon AR se Mate oR eS Boe AE
Proceedings of the Royal Society :—
Mr. B. Stewart’s Account of certain Experiments on Ane-
roid Barometers, made at Kew Observatory....... ..
Mr. R. J. Wright on an Easy Method of measuring ap-
proximately the Intensity of Total Daylight ........
On the Dispersive Power of Gases and Vapours, by M. Croul-
PRU Spee Re tives Shee em or NG ROME Aor te
On the Generation of Ozone in Oxygen and in Air under the
influence of the condensed Electrical Spark, by MM. L’Hote
GES Giies Meat. Muee ore Nikhil, Hele Te
On a New Method of Estimating minute traces of Metals, spe-
cially designed for Water-analysis, by J. Alfred Wanklyn
and Banest Wheophron Chapman. {..).)s 4020-85 flbel-e,

62

65

79

80

1V CONTENTS OF VOL. XXXVII.—FOURTH SERIES,

NUMBER CCXLVII.—FEBRUARY.

Page
M. Dumas’s Remarks on Affinity... 81
Messrs. B. Stewart and P. G. 'T ait on the Heating of a Disk
by rapid'rotation 7 vacuo 3.0... 20. eas eee 97
Prof. W. A. Norton on the Fundamental Principles of Molecular
Physies yf occa ek Se a Leeks rr 98
M. H. St.-Claire Deville on the Temperature of Flames, and its
relations with the Pressure: 7. 2..').. S202 - pee I11
Prof. J. A. Wanklyn on Ethylate of Sodium and Ethylate of Po-
tassium.=—Part. To 3... < cccmin oicdnnemis. 2 0 errr Ly
Mr. T. Graham on the Relation of Hydrogen to Palladium .. 122
Prof. J. LeConte on some Phenomena of Binocular Vision.... 131
Notices respecting New Books :—Mr. J. N. Lockyer’s Elemen-
tary;Lessons in’ Astronomy... s. 42+... 0.5: eee 141
Proceedings of the Royal Society :—
Lieut. J. Herschel on the Lightning Spectrum AR ct 142
Mr. J. N. Lockyer on the Spectrum of a Solar Prominence;
and Spectroscopic Observations of the Sun ...... 143, 144
Proceedings of the Geological Society :—
Dr. J. Schmidt on the Eruption of the Kaimeni of Santorin. 145
Mr. J. Prestwich on the Structure of the Crag-beds of Nor-
folk and Suffolk. . set . 146
Mr. J. Thomson on some e Genera of Carboniferous Corals. 148
Mr. 8. V. Wood, Jun., on the Pebble-beds of Middlesex,
Essex, and Herts’ ...0...... 6.0050 ae 148
Mr. W. Topley on the Cretaceous Rocks of the Bas-Bou-
Jonnais; «5 2isesnesle sw heals vee SE ee ee 149
Mr. C. H. Weston on the Mendip Anticlinal .......... 150
Mr. R. B. Foote on the Distribution of Stone Implements
in Southern India... 150
Mr. G. V. Du Noyer on worked Flint Flakes from Carrick-
fergus and Larne 4.2.) 3:2... v.cse 2. Gee 152
Mr. A. Murray on the Diminution in the Volume of the
Sea during past Geological Epochs ................ 152
Messrs. A. L. Adams and G. Busk: Has the Asiatic Ele-
phant been found in a Fossil State 2-2 22-e eee 152
Sir Philip de M. Grey Egerton on the Characters of some
new fossil Fish from the Lias of Lyme Regis .. 152
Capt. I’. Baker on the Geology of Port Santa Cruz ie 153
Dr. F. Stoliczka on the Jurassic Deposits in the N.W.
Himalaya : 5 153
Mr. J. W. Salter on a true Coal- plant from Sinai . Pet Loe
Messrs. J. W. Salter and H. Hicks on some Fossils from
the Menevian Group .. sfieloe
Mr. H. F. Holt on Earthquakes ; in 1 Nocehecn once . 154
Mr. A. B. Mitford on the Coal-mines of Iwanai, Island of
Vesso, Japan. ose -< eosee sop seeders eer 154
Mr. W. B. Dawkins on a new Species of Fossil Deer from
Clacton, and from:the Norwich Crag 0) eee 154

CONTENTS OF VOL. XXXVII.—FOUKTH SERIES.

Mr. T. Codrington on a section of the Strata from the Chalk

to the Bembridge Limestone at Whitecliff Bay. .
Dr. H. A. Nicholson on the Graptolites of the Coniston
LEE? 25): i Ee ee ae eae
Mr. @. W. Ormerod on the ‘‘ Waterstone Beds” of the
STIS! pis, Sl ofEi>,,. 10! Adis ope whe sia so, MShz} -.tg ee
Mr. E. R. Lankester on the remains of Wenetihas Fishes
muwewonshire aud; Cornwall). jj.) yuds sais 3 a see an
Captain James Clark on the Geological peculiarities of the
Bearcats ADAH Man i eh Egos 25 235 Sei aicsgass lap ete hotel Le Bel ve
On the Temperature of Flames and Dissociation, by E. Vicaire.
On a Friction and Induction Electrical Machine, by F. Carré.
On the Shape of the Flame of a Bunsen’s Burner, by A. Poppe.

NUMBER CCXLVIII.—MARCH.

Mr. C. Tomlinson’s Historical Notes on some Phenomena con-
nected with the Boiling of Liquids ..
Prof. J. A. Wanklyn on “the Compounds of Ethylene- ‘sodium
ete 2 RIOMIOIOP MOS 6 aca 5 0) ase dyes os vwtersrals; Ss o/s: «4 bie
Prof. J. Bayma on the Fundamental Principles of Molecular
SE ii 2a a tac Senta ob hovacag dels ay Ae aeepnietd a
Mile) voon-oen the: Theary of Sound... 2... 6. 2<2 32 3 oe
Mr. J. Croll on the Physical Cause of the Motion of Glaciers.
Mr. R. A. Peacock on Mr. J. Croll’s paper ‘“‘ On Geological
Time, and the probable Date of the Glacial and the Upper
tae ME TUS CN eis ww an ww a sub wwe a mm eww rere ad
Prof. A. Lielegg’s Contributions to the Knowledge of the Spec-
tra of the Flames of Gases containing Carbon ............
Mr. D. Vaughan on the Secular Effects of Tidal Action ......
Mr. J. J. Sylvester on the Story of an eee in Differences
of the Second Order .....
Proceedings of the Royal Society :- —
Mr. W. Crookes on the Measurement of the Luminous In-
LETETN? U6)! OTT ee a soa ea SR ge
Canon Moseley on the Mechanical Possibility of the
Descent of Glaciers by their Weight only............
Formation of an Artificial Spectrum with one Fraunhofer’s
Hbiraeremanie oy NV URUIVET| S oe cS onal Said sean ould a oat
On the Quantity of Electricity produced by the Electrophorus
Machine expressed in Absolute Measure, by F. Kohlrausch. .
On the Interference of Liquid Waves, by M. Lissajous

se ee

NUMBER CCXLIX.—APRIL.
Prof. J. Tyndall on Cometary Theory ..
Chevalier W. von Haidinger’s Remarks on “the iiiaone. “‘Ther-
mal, and Acoustic Phenomena attending the Fall of Meteorites.

Page

155

v1 CONTENTS OF VOL. XXXVII.—FOURTH SERIES.

Prof. How’s Contributions to the Mineralogy of Nova Scotia.. 264
Dr. Paalzow on the Galvanic Resistance of Liquids.......... ig
Prof. J. Bayma on the Fundamental Principles of Molecular _
PY SICS. es ees. RT eb elie eiek dees ee on ole ee 275
M. O. E. Meyer’s Further Remarks on the Explanation of -
Stewart and Tait’s A een on the Heating of a Disk

rotating in vacuo ... 287
Dr. W. Marcet on the F alsetto or - Head- Sounds of the Human

VOIEe re RS A ee rr 289
M. H. Wild on the Absorption of Light by the Air ........ 293
Notices respecting New Books:—Mr. F. S. Barff’s Introduc-

tion to Scientific Chemistry. 0... .... 0... nee 304

Proceedings of the Royal Society :—

The Rev. 8S. Haughton’s Notes of a Comparison of the
Granites of Cornwall and Devonshire with those of
Leinster and Mourne...... 2 nnd i Rei een ern 6

Proceedings of the Geological Society —

Sir R. I. Murchison on the Sich Structure of North-
western Siberia...... ah eee09

Prof. Sandberger on a Section of a Well at Kissingen. . Sy)

Mr. A. Tylor on the Formation of Deltas; and on the ivi:
dence and Cause of great Changes in the Sea-Level
during the Glacial Period «+: .. 1.0). 03.2 310

On the Coloration of Peroxide of Nitrogen, by M. Salet .... 312
On the Magnetism of Chemical Compounds, by Professor Wiede-
IAM eS ee ears Ales Se ries 6 tet tie > Or 314
On the Latent Heat of Volatilization of Sal-ammoniac, - M.
©. Marignac -.1 300.02 secs e's 68s Sb leete tere fe ce ne a eS

NUMBER CCL.—MAY.

Mr. D. Forbes’s Researches in British Mineralogy. 321
Prof. R. Ball’s seule Experiments to “lnstes ae Laws ‘of
Wiotrontgs a :/. sone Ble She Re Sole aan Meme
Mr. J. C. Demis @ on Siow Optometers Cate aig ne Se 340
Mr. W. Baker on the Cause of a Pink Colour in White-Lead
Gorrosions ss P22 eS Oe 344
M. L. Soret on the Colour of the Lake of Geneva .... Si OE
Prof. J. Bayma on the Fundamental Principles of Molecular
Physics) 348
Prof. J. A. Wanklyn c on some Reactions of Hydrated Oxide of
Ethylene-sodiumy | 7)ec:76)e\--eh ho oe 358
Canon Moseley on the Mechanical Impossibility of the De-
scent of Glaciers by their Weight only.................. 363

Canon Moseley on the Uniform "Motion of an Imperfect Fluid. 370

CONTENTS OF VOL. XXXVII.—-FOURTH SERIES.

Mr. J. J. Sylvester’s Note on a new Continued Fraction meg
cable to the Quadrature of the Circle ee
Mr. J. J. Sylvester on two remarkable Resultants : arising out
of the Theory of Rectifiable Compound Logarithmic Waves.
Notices respecting New Books :—

Mr. R. A. Peacock’s Physical and Historical Evidences of
vast Sinkings of Land on the North and West Coasts of
France, and South-western Coasts of eg within
the Historical Period .

Mr. R. A. Peacock on Steam as the Motiv e Power in Earth-
quakes and Volcanoes, and on Cavities in the Earth’s
Crust . beans

Proceedings of the Royal Society :- —

Prof. Tyndall on the Blue Colour of the Sky, the Polariza-
tion of Skylight, and on the Polarization of Light a
Cloudy matter generally Ae cere

Proceedings of the Royal Institution :—

Dr. A. Crum Brown on Chemical Constitution, and its

Relation to Physical and Physiological Properties ....
On a Mirage in the English Channel, by John Parnell, M.A.,
Ouch, autodata Rae eee ae ean Pincen mire

On the production of a beautiful Patina on Bronzes in large Towns.

On Tyndall’s Cometary Theory, by Mr. E. C: sa we and W. B.

USI OSL LPS be el pi Ney Aue gre 1/8

NUMBER CCLI.—JUNE.

M. A. Willner on the Spectra of certain Gases in Geissler’s
Tubes . :
Mr. J. Dewar on the Motion of a Palladium Plate during the
Formation of Graham’s Hydrogenium ...
Prof. J. Bayma on the Fundamental Pr incipls ‘of Molecular
Physics .
Prof. W. Swan on a Metallic Connector to breplnee the Vulca-
nite Tube used with Bianchi’s Air-pump................
Prof. R. Clausius upon the new Conception of Electrodynamic
Phenomena suggested by Gauss os
Mr. W. Huggins on some Spectrum Observations of Comets. .
rb. J. Mills on Statical and Seanad Ideas in uy
—Part I. Acid, Alkali, Salt, and Base. eae
Proceedings of the Royal Society :—
Mr, F. Guthrie on the Thermal Resistance of Liquids
Piiwoscrore onbliydrofluoric Acig=.) 26... oe. ee.
On the Voltaic Deportment of Palladium, by J. C. Poggendorff.

Vil

Page

. 373

3795

382

383

Vill CONTENTS OF VOL. XXXVII.—FOURTH SERIES.

Page

On the Electrical Polarity and Inequality of the Amalgamated :

Zinc Electrodes in Sulphate of Zine, by E. Patry ........ 475
On a Development of Heat which accompanies the bursting of

the Prince Rupert’s Drops, by M. Dufour >. ..ie73-ee5 8 478

Tidex s.r 48]

PLATE.

Illustrative of Prof. R. Bunsen’s Paper on the Washing of Precipitates.

ea

Phil Mag. Ser.4 Vol 37. PUL.

al

THE

LONDON, EDINBURGH, anno DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

Se

(FOURTH SERIES.]
JANUARY 1869.

I. On the Washing of Precipitates. By R. Bunsen*.
[With a Plate. ]
A PRECIPITATE is washed either by filtration or by decan-

tation: in the former case the portion of liquid not mecha-
nically retained is allowed to drain from the precipitate ; im the
latter it is separated by simply pouring it away, the foreign sub-
stances contained in the precipitate being then removed by the
repeated addition of some washing-fluid, in each successive por-
tion of which the pre ipitate is, as far as possible, uniformly sus-
pended, this process being continued until the amount of im-
purity becomes so minute that its presence may be entirely
disregarded.

Supposing v to represent the volume of the moist precipitate
remaining at the bottom of the vessel after decantation, or upon
the filtrate after filtration, V the volume of wash-water employed
at each successive decantation, m the number of decantations, and

‘Dea : Mt:
- the fraction expressing the proportion of the original amount
a

of impurity still remaining in the precipitate after n decantations,

then
UNA
(Sy) —_— a ° ° ° ° . ° ° (1)

Calling W the total volume of wash-water resulting from n de-

* Translated from the Ann. der Chem. und Pharm. vol. exlviii. [3], by
Mr. T. E. Thorpe, from the proof-sheets kindly furnished by the Author.

Phil. Mag. 8. 4. Vol. 37. No. 246. Jan. 1869. B

2 Prof. R. Bunsen on the Washing of Precipraies.

cantations, then

mnV=W: . 2

wy"
(4 2)
Nv

Ww =ny(./a —l. ..-> Bee (3)

therefore

or

If we differentiate W with respect to n and make the differential
quotient equal to 0, then the minimum value of W becomes,
when n= o,

W=vnat.log.a. .°. >. 2)

Precipitates obtained in the course of chemical analysis may
in all cases be assumed to be sufficiently washed when the im-

purity retained by them amounts to no more than the ——<

part. Making therefore a=100000 and v=1, it results from
equation (4) that the least quantity of fluid required in order to
remove the impurity contained in a precipitate to the ——-l

part, amounts to eleven and a half times the volume occupied by
the precipitate itself in the liquid in which it exists. It 1s evi-
dent, therefore, that the amount of water actually necessary to
wash a precipitate the more nearly approaches this minimum the
oftener we decant, and the smaller the quantity of washing-water
we employ at each decantation.

Since some of the principal sources of error in analytical work
consist in the incomplete or in the too protracted washing of
precipitates, it becomes important to know how to ascertain the
progress of the washing throughout the several stages of the
process. By employing the same volume of water at each suc-
cessive addition, and estimating its relation to that of the preci-
pitate remaining at the bottom of the vessel or upon the filter,
we can find from the following Table, calculated by means of the
formula above given, the number of times it is necessary to de-
cant in order to diminish the amount of impurity in the precip1-

tabestovhe =e ] 1 1 6 eT
160000? 50000? 500002 - 10M Colum

shows the relation between the volume of the precipitate and that
of the washing-water employed for each successive decantation,
column IJ. the number of decantations required to diminish the
amount of impurity to the necessary extent, and column III. the
total volume of water obtained from the several decantations.

Prof. R. Bunsen on the Washing of Precyntates. 3

1 1 | ] 1
100000° | 50000 * | 20000 © 10000 °

Pere ieiel. 41 | 1. ed.) A=) ME i, | WT
Brae (eee | bets oan eee

ist n W. ate heave sl| Ae Ne W. Ne n Ww.
Vv ee Vv aaa 22

05| 28-4 | 14-2 || 05| 26-7 | 13:3 |) 0:5] 24-4 | 12-2 | 0-5] 22-7 | 11-4
1/166 | 1661 | 156 | 156] 1 | 143 | 143/11 | 13-3 | 138
2/105 | 210//2 | 98 | 197] 2) 90] 1802 | 84 | 168
Pee | 249 3 | 78 | 2341] 8 | 71 | 21-413 =|. 66 | 19-9
4] 71 | 286 |14 | 67 | 269] 4] G1 | 2461/4 | 5-7 | 22-9
5 | 64 | 321/15 | 60 | 302] 5 | 55 | 2761/5 | Sl | 25-7 |
6/59 | 355 (16 | 56 | 334] 6 | 51 | 305116 | 4:7 | 284
7\ 55 | 388|/7 | 52 | 364] 7 | 48 | 48317 | 4-4 | 381-0
8 | 52 | 420] 8 | 49 | 394] 8 | 45 | 36118 | 42 | 335
9 | 50 | 450|9 | 47 | 423] 9 | 43 | 387119 | 40 1] 360
10 | 48 | 480/10 | 4:5 | 451/10 | 4-1 | 41-3 10 | 3-8 | 38-4
11 | 46 | 51-0 ll | 4-4 | 47-9 |/11 | 40 | 438 |11 | 3-7 | 408
12 | 45 | 539 12 | 42 | 506/12 | 3-9 | 463 |112 | 3-6 | 43-1
13 | 44 | 564 13 | 41 | 533 113 | 38 | 488 113 | 3:5 | 45-4
14 | 42 | 59-4 lta | 40 | 55-8 |'14 | 3-7 | SLL 14 | 3:4 | 47-5
5 | 42 | 623 (15 | 39 | 585 115 | 3:6 | 536/15 | 33 | 49-8
16 | 41 | 650 16 | 38 | 611/16 | 35 | 560 16 | 3:3 | 53:0
17 | 40 | 67:8 17 | 3-7 | 636 |/17.| 34 | 583/17 | 32 | 54-2
18 | 3:9 | 70-4 18 | 3:7 | 6611/18 | 3-4 | 605 [18 | 3:1 | 563
19 | 38 | 743/19 | 36 | 686/19 | 33 | 628) 19 | 31 | 58-4 |

When the washing-process is performed in a beaker, the rela-
tion between the volume of the precipitate and that of the liquid
may be easily determined by holding a strip of paper along the
side of the vessel and marking upon it the respective heights of
the precipitate and supernatant liquid; then on folding the por-
tion of paper lying between the two marks in such a manner that
each fold corresponds to the height occupied by the precipitate,
the number of folds will give the argument in column I. to
find in column II. the number of decantations needed to wash
to the required extent. If the washing be conducted as in
the ordinary method of filtration, funnels possessing an angle
of 60° must be invariably employed, and the capacities of the
various-sized filters once for all determined by meaus of a bu-
rette. After the precipitate has been brought upon the filter
and allowed to drain, it is mixed as thoroughly as possible
with water from a graduated washing-flask. Call the amount of
water thus necessary to fill the filter vy, and the capacity of the
empty filter ¥, then — = i im column I.; that is, the argu-
ment needed to find in column II. the nunber of times it is ne-
cessary to refill the filter in order to wash the precipitate to the
desired extent.

B2

4, Prof. R. Bunsen on the Washing of Precipitates.

I by far prefer using this Table to employing the method ge-
nerally followed of ascertaining the completion of the washing-
process by evaporating a quantity of the filtrate on platinum-foil,
since in the latter case it is only possible to obtain an infallible
proof when we have to deal with a precipitate possessing an ex-
tremely high degree of insolubility ; if the precipitate be soluble
to any marked extent, the result is completely illusory.

In the process of filtration as hitherto conducted, the time
required is so long and the quantity of wash- water needed so
great that some simplification of this continually recurring ope-
ration is in the highest degree desirable. The following method,
which depends, not upon the removal of the impurity by simple
attenuation, but upon its displacement by forcing the wash-
water through the precipitate, appears to me to combine all the
requisite conditions and therefore to satisfy the need.

The rapidity with which a liquid filters depends, ceteris paribus,
upon the difference which exists between the pressure upon its
upper and lower surfaces. Supposing the filter to consist of a
solid substance, the pores of which suffer no alteration by pres-
sure or by any other influence, then the volume of liquid filtered
in the unit of time is nearly proportional to the difference in
pressure: this is clearly shown by the following experiments,
made with pure water and a filter consisting of a thin plate of
artificial pumice-stone. The thin plate of pumice was hermeti-
cally fastened into a funnel consisting of a graduated cylindrical
glass vessel, the lower end of which was connected with a large
thick flask by means of a tightly fitting caoutchoue cork. The
pressure in the flask was then reduced by rarefying the air by
means of a method to be described upon another occasion; and
for each difference of pressure p, measured by a mercury column,
the number of seconds ¢ was observed which a given quantity of
water occupied in passing through the filter. The following are
the results :—

it;
p- ‘hs pt.
metre. Fh
0-179 Sere 16°4
0:190 81:0 15°4
0-282 52°9 14:9
0-472 33°0 15°6

In the ordinary process of filtration, » on the average amounts
to no more than 0-004 to 0:008 metre. The advantage gained,
therefore, is easily perceived when we can succeed by some
simple practicable and easily attainable method in multiplying
this difference in pressure one or two hundred times, or, say, to
an entire atmosphere, without running any risk of breaking the

Prof. R. Bunsen on the Washing of Precipitates. 5

filter. The solution of this problem is very easy: an ordinary
glass funnel has only to be so arranged that the filter can be
completely adjusted to its sides even to the very apex of the cone.
For this purpose a glass funnel is chosen possessing an angle of
60°, or as nearly 60° as possible, the walls of which must be
completely free from inequalities of every description ; and into it
is placed a second funnel made of exceedingly thin platinum-foil,
and the sides of which possess exactly the same inclination as
those of the glass funnel. An ordinary paper filter is then in-
troduced into this compound funnel in the usual manner; when
carefully moistened and so adjusted that no air-bubbles are
visible between it and the glass, this filter, when filled with a
liquid, will support the pressure of an extra atmosphere without

ever breaking. ?

The platinum funnel is easily made from thin platinum-foil in
the following manner :—lIn the carefully chosen glass funnel is
placed a perfectly accurately fitting filter made of writing-paper ;
this is kept in position by dropping a little melted sealing-wax
between its upper edge and the glass; the paper is next saturated
with oil and filled with liquid plaster of paris, and before the
mixture solidifies a small wooden handle is placed in the centre.
After an hour or so the plaster cone with the adhering paper
filter can be withdrawn by means of the handle from the funnel,
to which it accurately corresponds. The paper on the outside
of the cone is again covered with oil, and the whole carefully
inserted into liquid plaster of paris contained in a small crucible
4 or 5 centims. in height. After the mixture has solidified,
the cone may be easily withdrawn ; the adhering paper filter is
then detached, and any small pieces of paper still remaining
removed by gently rubbing with the finger. In this manner a
solid cone is obtained accurately fitting into a hollow cone, and
of which the angle of inclination perfectly corresponds with that
of the glass funnel.

Fig. 1 (Plate I.) represents the cones. By their help the
small platinum funnel is made. A piece of platinum (fig. 2
shows the natural size) is cut from foil of such a thickness that
one square centimetre weighs about 0°154 grm., and from the
centre a a vertical incision is made by the scissors to the edge
cbhd. The small piece of foil is next rendered pliable by being
heated to redness, and is placed upon the solid cone in such a
manner that its centre a touches the apex of the latter; the sides
a,b,d ave then closely pressed upon the plaster, and the remaining
portion of the platinum wrapped as equally and as closely as
possible around the cone. On again heating the foil to redness,
pressing it once more upon the cone, and inserting the whole
into the hollow cone and turning it round once or twice under a

6 Prof. R. Bunsen on the Washing of Precipitates.

gentle pressure, the proper shape is completed. The platinum
funnel, which should not allow of the transmission of light
through its extreme point, even now possesses such stability
that it may be immediately employed for any purpose.. If de-
sired, it may be made still stronger by soldering down the over-
lapping portion in one spot only to the upper edge of the foil by
means of a grain or two of gold and borax; in general, however,
this precaution is unnecessary. If the shape has in any degree
altered during this latter process, it is simply necessary to drop
the platinum funnel into the hollow cone and then to insert the
solid cone, when by one or two turns of the latter the proper
form may be immediately restored. The platinum funnel is
placed in the bottom of the glass funnel, the dry paper filter
then introduced in the ordinary manner, moistened, and freed
from all adhering air-bubbles by pressure with the finger. A
filter so arranged and in perfect contact with the glass, when
filled with a liquid will support the pressure of an entire atmo-
sphere without the least danger of breaking ; and the interspace
between the folds of the platinum-foil is perfectly sufficient to
allow of the passage of a continuous stream of water.

In order to be able to produce the additional pressure of an
atmosphere, the filtered liquid is received in a strong glass flask
instead of in beakers*. This flask is closed by means of a doubly
perforated caoutchouc cork, through one of the holes of which
the neck of the glass funnel is passed to a depth of from 5 to 8
centimetres (fig. 3); through the other is fitted a narrow tube
open at both ends, the lower end of which is brought ewactly
to the level of the lower surface of the cork, to the other is adapted
the caoutchouc tube connected with the apparatus (fig. 4) de-
stined to produce the requisite difference in pressure: this appa-
ratus will be described immediately. The flasks are placed in a
metallic or porcelain vessel (fig. 3), in the conical contraction of
which several strips of cloth are fastened. This method of sup-
porting the flask has the advantage that, in one and the same
vessel, flasks varying in size from 0°5 to 2°5 litres stand equally
well, and that, by simply laying a cloth over the mouth of the
vessel, the consequences of an explosion (which through inexpe-
rience or carelessness is possible) are rendered harmless.

It is impossible to employ any of the air-pumps at present in
use to create the difference in pressure, since the filtrate not un-
frequently contains chlorine, sulphurous acid, hydric sulphide,
and other substances which would act injuriously upon the me-
tallic portions of theseinstruments. I therefore employ a water

* These flasks must be somewhat thicker than those ordinarily used, in
order to prevent the possibility of their giving way under the atmospheric
pressure.

Prof. R. Bunsen on the Washing of Precipitates. 7

alr-pump constructed on the principle of Sprengel’s mercury-
pump, and which appears to me preferable to all other forms of
air-pump for chemical purposes, since it effects a rarefaction to
within 6 or 12 millimetres pressure of mercury.

Fig 4 shows the arrangement of this pamp. On opening the
pinchcock a, water flows from the tube / into the enlarged glass
vessel 6, and thence down the leaden pipe c. ‘This pipe has a
diameter of about 8 millims., and extends downwards to a depth
of 50 or 40 feet, and ends in a sewer or other arrangement ser-
ving to convey the water away. The lower end of the tube d
possesses a narrow opening; it is hermetically sealed into the
wider tube 0, and reaches nearly to the bottom of the latter. A
manometer is attached to the upper continuation of this tube d
by means of a side tube at d'; at d? is attached a strong thick
caoutchouc tube possessing an internal diameter of 5 millims.
and an external diameter of 12 millims.; this leads to the flask
which is to be rendered vacuous, and is connected with it by
means of the short narrowed tube k. Between the air- pump and
the flask is placed the small thick glass vessel f, in which, when
one washes with hot water, the steam which may be carried over
is condensed. All the caoutchouc joinings are made with very
thick tubing, the internal diameter of which amounts to about
5 millims., the external diameter to about 17 millims. The
entire arrangement is screwed down upon a board fastened to the
wall, in such a manner that each separate piece of the apparatus
is held by a single fastening only, in order to prevent the tubes
being strained and broken by the possible warping of the board.
On releasing the pinchcock a, water flows from the conduit /
down the tube c to a depth of more than 30 feet, carrying with
it the air which it sucks through the small opening of the tube d
in thie form of a continuous stream of bubbles. No advantage
is gained by increasing the rapidity of the flow, since the friction
exerted by the water upon the sides of the leaden pipe acts di-
rectly as a counter pressure, and a comparatively small increase
in the rapidity of the flow is accompanied by a great increase in
the amount of this friction. Accordingly atgis a second pinchcock,
by which the stream can be once for all so regulated that, on
cor-nletely opening the cock a, the friction, on account of the
diminished rate of flow, is rendered sufficiently small to allow of
the maximum degree of rarefaction. Such an apparatus, when
properly regulated once for all by means of the cock g, ex-
hausts in a comparatively short time the largest vessels to within
a pressure of mercury equal to the tension of aqueous vapour at
the temperature possessed by the stream*. The tension exerted

* The time required to obtain the above degree of exhaustion in a flask

of from | to 3 litres capacity ranges from six to ten minutes; the quantity
of water necessary amounts to about 40 or 50 litres.

8 Prof. R. Bunsen on the Washing of Precipitates.

by the water-stream in my laboratory, in which six of these pumps
are used, amounts to about 7 millims. in winter and 10 millims.
in summer. The filtration is made in the following manner :—
The flask standing in the metallic or porcelain vessel (fig. 3) is
connected by means of the slightly drawn-out tube & with the
caoutchoue tube / attached to the pump, the cock a having been
previously opened and the properly fitted moistened filter filled
with the liquid to be filtered. As usual, the clear supernatant
fluid is first poured upon the filter ; in a moment or two the fil-
trate runs through in a continuous stream, often so rapidly that
one must hasten to keep up the supply of liquid, since it is ad-
visable to maintain the filter as full as possible. After the pre-
cipitate has been entirely transferred, the filtrate passes through
drop by drop, and the manometer not unfrequently now shows a
pressure of an extra atmosphere. The filter may be filled (in
fact this is to be recommended) with the precipitate to within a
millimetre of its edge, since the precipitate, in consequence of the
high pressure to which it is subjected, becomes squeezed into a
thin layer broken up by innumerable fissures. As soon as the
liquid has passed through and the first traces of this breaking up
become evident, the precipitate will be found to have been so
firmly pressed upon the paper, that on cautiously pouring water
over it it remains completely undisturbed. The washing is
effected by carefully pouring water down the side of the funnel
to within a centimetre above the rim of the filter: the washing-
flask for this purpose is not applicable ; the water must be poured
from an open vessel. After the filter has in this manner been
replenished four times with water and allowed to drain for a few
minutes, it will be found to be already so far dried, in conse-
quence of the high pressure to which it has been subjected, that
without any further desiccation it may be withdrawn, together
with the precipitate, from the funnel, and immediately ignited,
with the precautions to be presently given, in the crucible.

If the porosity of a paper filter containing a precipitate were
as unalterable as that of a pumice-stone filter, the experiments
above described would show that the times required for filtration,
according to the old method on the one hand, and the new one
on the other, would be inversely proportional to the difference in
pressure in each case; thatis, by using the pump under the full
pressure of about 740 millims., the time needed to wash a pre-
cipitate, occupying by the old process an hour, would at the
utmost not amount’to more than 30 seconds. In using these
pumice filters (about which I will speak presently) to drain
crystals from adhering mother-liquors, or, say, to wash crystals
of chromic acid by means of concentrated sulphuric acid and
fuming nitric acid, the time occupied in the filtration is scarcely

Prof. R. Bunsen on the Washing of Precipitates. 9

longer than that needed to pour a liquid slowly from one vessel to
another. In filtering by means of paper, the precipitate gradually
closes up the pores of the filter, and accordingly such an ex-
traordinary acceleration as this can no longer be expected. But
the followmg examples will show the saving of time and labour
the method effects, even under all unfavourable conditions. For
these experiments I have purposely chosen the hydrated chro-
mium sesquioxide, since it is one of the most difficult of preci-
pitates to wash thoroughly. A solation of chromium chloride
was prepared by acting with fuming hydrochloric acid upon
potassium dichromate; and bymeans of a measuring-vessel, which
allowed the amount of chromium to be estimated to within
0:0001 grm., successive portions of the liquid were withdrawn,
and the chromium oxide contained in them precipitated with the
usual precautions by ammonia. The volume of liquid, the
quantity of ammonia employed, the time occupied in boiling and
in permitting the precipitate to settle, the angle of inclination
possessed by the funnel, and the size of the filter were the
same in all the experiments. All the precipitates were washed
with hot water, and, after burning the filter, ignited over the
blowp:pe for a few minutes; in weighing, the platinum cru-
cible was tared by one of about equal weight, and the posi-
tion of equilibrium of the beam determined by vibrations.

I first attempted to filter one of the precipitates in the or-

, vi
dinary way. 3 amounted to 2; and consequently, from the

Table, 8:4 fresh additions of water were required in order to
wash the precipitate to the ;5)55 part. The times required
were as follows :—

In transferring the precipitate from the 40

beaker and allowing it to drain . .
For the first addition of water to run through. 48
2» second 9 23 70
eet wit hoarel 2 - 80
Total length of time . . . . 238

At this point the experiment was discontinued, as the filtrate
became turbid. A second experiment failed from the same
cause.

Accordingly I attempted to wash the precipitate by decanta-
tion. The volume of the precipitate amounted to about 30 cub.
centims.: the quantity of water required to fill the beaker was seven

times the volume of the precipitate; hence : was 7, and the

10 Prof. R. Bunsen on the Washing of Precipitates.

requisite number of decantations to reduce the amount of impu-

rity to the —-— part was 5:2. The times observed were as
follows :—
II. AL
For the first decantation to run through the filter. 15
a | Second » n ” 12
d9 third 3) 3) 3) 18
29 fourth Be) ye) ” 15
39 fifth 3) 3) 3) ] 38
In transferring the precipitate to the filter . . 30
Time required in washing’ . 7). eda
Weight of the precipitate . . . 0:2458 grm.
Volume of wash-waternV. . . 1050 cub. centims.
III.

Experiment repeated. Number of decantations 7. Other cir-
cumstances the same as in the foregoing determination.

Time required in washing . . . 140!

Weight of the precipitate . . . 02452 grm.

Volume of wash-water . . . . 1200cub.centims.
IV.

After ten decantations.

Time required in washing . . 180!
Weight of the precipitate . . 0°2443 grm. -
Volume of wash-water . . . 1750 cub. centims.

By filtration with the platinum cone and the pump the follow-
ing results were obtained :—

V.
In transferring the precipitate to the filter (17 cub. cen- é
timssiwater) «6 i" 6) cai oe Ar
For the first addition of water (25 cub. cent.) to run through. 2
3) second 3) 3) a) 3
ee ethird 6 ” » 2
3) fourth 3) 33 33 2
3) fifth oP) 33 33 2
In draining the precipitate Me ee fe ee
Time required MEG so, 8 all®
Weight of precipitate . . . . 02485 orm.
Volume of wash-water . . . . 142 cub. centims.

Pressure in manometer . . . 0'576 metre.

_—
—

Prof. R. Bunsen on the Washing of Precipitates.
VI.

In transferring the precipitate and allowing the water oo 4
cub. centims.) to run through . . ia ect:
For the first addition of water (25 cub. cent. ) to run through. 4
3) second 3) 33 33 33 9)
3? third 3) 3 3) 3) 5
op) fourth 3) 33 3) 3) 9)
In draining the precipitate <7 joe
Time required LHe ele deeds ae ee
Weight of precipitate . . . . 02434 grm.
Volume of wash-water .. .. .. .. 118 cub. centims.
POSICCRE ge cs ss we SOO00 metre:

VII.
In transferring the precipitate and allowing the water (20 A
cub. centims.) to run through . -
For the first addition of water (25 cub. cent. ) to run through. 3
” second ” ” ” BP) 3

a third »” ” ” 3
In draining the precipitate Pi ee Ae ae ee:
Time required i SC A i a ON el 5
Weight of precipitate . . . . 02482 germ.
Volume of wash-water . . . . 95 cub. centims.
Erescure: ee eS Oo S4emetre,
VELL.

In transferring with 25 cub. centims. of water. 8
For the first addition of 25 cub. centims. 5
formu through . ... “I

For the second addition of 25 cub. centims.
~ to run through . cid seseat Tip
In draining the precipitate
Time required .
Weight of precipitate. . . 0: 2435, erm.

Ox

P del,

Volume of wash-water . . 72 cub. centims.
Pressures. ae Ye +L 0 OOPOOB anetae!
IX.

In transferring with 15 cub. centims. of water | rf
and allowing it to run through . ;
For a single addition to run through. . . 8
mmdraimine the precipitate 5%...) in 12
dnemequired:., /s:s taco. pasaie yc

Weight of precipitate. . . 0:2489 erm.
Volume of wash-water . . 41 cub. centims.
Pressure. 582325 2 O57 2 metre.

12 Prof. R. Bunsen on the Washing of Precipitates.

X.

i
In transferring the precipitate with 13 cub. | _
centims. of water . .
For a single addition of water (26 cub. ee 8
tims.) to run through.
In draiming the precipitate .

Time required! 2) 7-0 <

Weight of precipitate. . . 0°2439 grm.
Volume of wash-water . . 389 cub. centims.
Pressure ..-.. .- .. < «+. O*>oORmiences

In washing, by means of decantation, in the ordinary manner,
the amounts of chromium sesquioxide found were as follows :—

Il. “0:2458, after 5 decantations, washed to the + part.
PM. 024525, 7 3 ‘ 200000 part.
TWe0:2443 95,10 ;; ¥5 jaoTdene Co
0-2451 mean.
By the use of the pump :—
‘rm.
V. 0:2435, after 5 additions of water.
VI. 02434 jy 4 a
VII. 0:2482 ,, 38 - in

VIII. 0:2485 ,, 2 si MS
IX. 0:2489 ,, 1 addition of water.
XO 2459 ee eae ss mr
0:2436 mean.

Hence the probable amount of chromium sesquioxide con-
tained in the solution, according to the experiments with the
pump, was 0:24:36 grm.; according to the old method of decan-
tation it was somewhat higher, namely 0:2451 grm. This excess
of 1-5 miligramme shows that the adhesion of the soluble mat-
ters to the precipitate and to the filter is, in consequence of the
ereater pressure, more easily overcome in the new method than
in the customary process ; it follows, therefore, that we can ob-
tain a more complete washing by the new method than by the
old. The old process of decantation required 103 minutes and
1050 cub. centims. of water to effect a washing to the -5495
part; the new, on the contrary, only 12 to 14 minutes, and not
more than 89 to 41 cub. centims. of wash-water. If a precipitate
be heated in a platinum crucible immediately after filtration by
the older process, a portion will imevitably be projected out of

Prof. R. Bunsen on the Washing of Precipitates. 15

the crucible. Hitherto, therefore, it has been necessary to dry
the filter and precipitate before ignition. Now to dry a quantity
of hydrated chromium sesquioxide containing 0°2436 grm.
Cr? O? in a water-bath at 100° C. requires at least five hours ; and,
moreover, bringing the dried precipitate into the crucible, burn-
ing the filter, and gradually igniting the mass is in the highest
degree tedious and troublesome. All this expenditure of time
and labour may be saved by employing the new method. By
its means a precipitate is as completely dried upon the filter in
from 1 to 5 minutes as if it had been exposed from 5 to 8 hours
in a drying-chamber; and it can immediately, filter and all,
be thrown into a platinum or porcelain crucible and ignited
without the slightest fear of its spurting. By operating in the
following manner the filter burns quietly without flame or
smoke ; this phenomenon, although remarkable, easily admits of
an explanation. The portion of filter-paper free from precipi-
tate is tightly wrapped round the remainder of the filter in such
a manner that the precipitate is enveloped in from four to six
folds of clean paper. ‘The whole is then dropped into the pla-
tinum or porcelain crucible lying obliquely upon a triangle over
the lamp, and pushed down against its sides with the finger.
The cover is then supported against the mouth of the crucible in
the ordinary way, and the ignition commenced by heating the
portion of the crucible in contact with the cover. When the
flame has the proper size and position, the filter carbonizes
quietly without any appearance of flame or considerable amount
of smoke. When the carbonization proceeds too slowly, the
flame is moved a little towards the bottom of the crucible. After
some time the precipitate appears to be surrounded only by an
extremely thin envelope of carbon, possessing exactly the form
(of course diminished in size) of the original filter; the flame is
then increased, and the crucible maintained at a bright-red heat
until the carbon contained in this envelope is consumed. The
combustion proceeds so quietly that the resulting ash surround-
ing the precipitate possesses, even to the smallest fold, the exact
form of the original filter. Ifthe ash shows here and there a
dark colour, it is simply necessary to heat the crucible over the
blowpipe for a few minutes to effect the complete removal of the
trace of carbon. ‘This method of burning a filter is extremely
convenient and accurate; it is only necessary to give a little
attention at first to the slow carbonization of the paper, after
which the further progress of the operation may be left to itself.

Gelatinous, finely divided, granular, and crystalline precipi-
tates, such as alumina, calcium oxalate, barium sulphate, silica,
magnesium ammonium phosphate, &c., may with equal facility
be treated in this manner; so that even in this particular the

14 Prof. R. Bunsen on the Washing of Precipitates.

work, in comparison with the method generally adopted, is con-
siderably shortened and simplified.

From the above experiments it appears that the time neces-
sary to filter and dry a quantity of chromium sesquioxide,
hitherto requiring about 7 hours, is reduced by the new method —
to 13 minutes. This saving of time is, moreover, proportion-
ately greater in the case of precipitates more easily filtered than
hydrated chromium sesquioxide. Particularly is this so in se-
parating a finely suspended precipitate from a large volume of
water. Under these circumstances the clear fluid runs through
the filter in a continuous stream, so rapidly that it is scarcely
possible to maintain the supply; the entire operation, in fact,
requires scarcely more time than that necessary to pour a liquid
from one vessel to another. Filtration, therefore, may be effected
as quickly through the smallest as through the largest filter.
Moreover the exceedingly small amount of water required to
wash a precipitate completely renders unnecessary the tedious
evaporations which by the older method are almost inevitable
when the filtrate is needed for a further separation. Thus the
introduction of impurities from the action of the liquid upon the
dish in the course of evaporation is prevented ; and also the loss
due to the slight solubility of the greater number of precipitates
in the wash-water is reduced to a minimum. Supposing we
had to analyze an alkaline chromate in which the quantity of
chromic acid is equivalent to 0:2436 grm. chromic sesquioxide,
as in the above described experiments, then to determine the
proportion of alkali we should, by using the older method, re-
quire the preliminary evaporation of about 1050 cub. centims. of
liquid; by the new method the evaporation of 40 cub. centims.
only is necessary.. Now by employing the best form of water-
bath, 7. e. one possessing a constant water-level, such as is used
in my laboratory, it is possible, under favourable circumstances,
to evaporate in a porcelain dish 1 cub. centim. of water in 27 se-
conds. Consequently the evaporation of the filtrate obtained by
the older method would occupy about 8 hours, whilst by the
new 18 minutes only are required. The total length of time
needed to filter the chromium sesquioxide, wash and dry the
precipitate, and evaporate the filtrate is reduced, therefore, from
14 or 15 hours to about 32 minutes.

The experience I have subsequently gained in my laboratory,
where the method has been in general use for the last nine
months, fully confirms the above results. It has shown that, on
the average, three or four analyses can now be made in the time
formerly demanded by a single one.

Another and an inestimable advantage springs from the pecu-
liar condition of a precipitate filtered by this method. It not

Prof. R. Bunsen on the Washing of Precipitates. 15

unfrequently happens, even in the hands of experienced mani-
pulators, in consequence of the agitation it is necessary to give
to the contents of the filter to effect their complete washing,
that the surface of the filter becomes injured and torn, so that
the precipitate becomes mixed with filaments of paper ; this is
particularly the case in using hot water. Supposing the preci-
pitate to consist of mixed hydrates of the sesquioxides (for ex-
ample, iron and alumina), it will be found, on redissolving in an
acid, that the filaments, like tartaric acid, prevent the complete
separation of these substances by subsequent precipitation ; thus
the alumina will contain iron, and on precipitation by means of
ammonium sulphide will be coloured black. On the other
hand, by employing the new method the precipitate coheres so
firmly that the introduction of this source of error is impossible,
even by using common grey filter-paper. The most gelatinous
precipitates, as hydrated ferric oxide, alumina, &c., adhere to the
filter in a thin coherent layer, and may be removed, piece after
piece, so completely that the paper remains perfectly clean and
white. The advantage thus gained where it is necessary to
transfer mixed precipitates to another vessel in order to effect
their subsequent separation is evident.

The filter-pump, moreover, is exceedingly serviceable in sepa-
rating precipitates or crystals from syrupy mother-liquors. Thus
honey-sugar may be so completely separated from the thick
viscid liquid in which it forms by a filter of coarse grey paper,
that it remains only slightly coloured, and by a single crystalli-
zation from alcohol may be obtained in small white shining
needles. And since the bulk of the moist precipitates, particu-
larly that of the more gelatinous, is so much diminished under
the high pressure, the precipitate only occupying one-third to
one-sixth of its bulk under ordinary circumstances, a filter of
one-third to one-sixth of the size usually employed may be
taken, and thus the amount of ash proportionately lessened.

As the water air-pump suffers no injury from the presence of
corrosive vapours or gases, we can equally well employ it to filter
liquids containing nitrous acid, sulphurous acid, fuming nitric
acid, chlorine, bromine, volatile chlorides, &c. In such cases I
use a peculiar filtering arrangement, consisting of a cylindrical
glass vessel, the lower end of which is drawn out before the
blowpipe to the form shown in fig. 5 ; in this drawn-out portion
a thin plate, 1 or 2 millims. in thickness, of artificial pumice,
such as is used by polishers, is packed water-tight by means of
asbestos. This apparatus is arranged for the purpose required
exactly as the funnel in the method of filtration by pressure
above described. In order to have a number of these filters in
readiness, a pumice-stone cylinder of the required diameter is

16 Prof. R. Bunsen on the Washing of Precipitates.

turned in a lathe, and then the thin plates sawn off by means of
a small hand-saw in the small wooden support shown in fig. 6.
The upper surfaces of the plates may afterwards be rendered
perfectly even by a coarse file.

By the aid of these pumice-stone filters many chemical pro-
ducts may be made, the preparation of which has hitherto been
almost impossible. For the sake of example I take the prepa-
ration of pure dry chromic anhydride; in an hour it is easily
possible to filter, wash, and dry crystals of this substance an inch
in length. A solution of 2 parts of potassium dichromate in
20 parts of water mixed with 10 parts of concentrated sulphuric
acid, deposits, after standing about 24 hours, numerous brilliant
needles of chromic anhydride. These may be drained from
adhering mother-liquor upon the pumice filter by means of the
pump, and in a few minutes completely washed by a small quan-
tity of fuming nitric acid free from nitrous acid. A covering of
tolerably strong sheet copper provided with two arms, as shown
in fig. 5, isthen placed round the tube; by hanging lamps upon
the arms the tube may be readily heated to about 60° or 80° C. ;
and by connecting a chloride-of-calcium tube with the upper
end of the glass vessel, a current of dry air may be drawn through
the apparatus by means of the pump, and thus im a compara-
tively short time large and brilliant crystals of chromic anhy-
dride, perfectly dry and free from all impurity, may be easily
obtained.

A single pump of the above description costs, including the
leaden piping, about 8 thalers (24 shillings); and experience
has shown that five or six are amply sufficient for a laboratory
of fifty or sixty students. The apparatus, as may readily be
seen, can be applied in the operation of evaporating in vacuo;
if, however, circumstances will not permit of its being adapted to
this purpose, then a fall of 10 or 15 feet is sufficient to filter a
precipitate according to the above described method, and so far to
dry it that it can be immediately ignited in the crucible. It is
therefore not absolutely necessary to employ an air-pump in this
process of filtration; any apparatus producing a difference of
pressure amounting to a quarter of an atmosphere is sufficient.
The simple arrangement represented in fig. 7 is very useful, and
is frequently employed in my laboratory. It consists of two
equal-sized bottles, a and a, of from 2 to 4 litres capacity, each
of which is provided near the bottom with a small stopcock de-
signed to regulate the flow of water. Suppose a@ filled with
water and placed upon a shelf as high above the ground as pos-
sible and a’ placed empty on the floor, and the two stopcocks
connected by means of caoutchouc tubing ¢, then on allowing
water to flow down the tube the air in the upper bottle be-

Prof. R. Bunsen oa the Washing of Precipitates. 17

comes somewhat rarefied ; and in order to employ the consequent
difference in pressure (amounting to a column of mercury about
0-2 metre in height) for the purpose of filtration, it is only ne-
cessary to connect the mouth of the upper bottle with the tube
of the filter-flask. When the water has ceased to flow, the po-
sition of the bottle is reversed, when the operation recommences.
So small a pressure as 0°2 metre suffices to render the filter and
its contents so far dry that they may be immediately withdrawn
from the funnel and ignited without any other preliminary de-
siccation. The following experiment, made with a portion of the
same solution of chromium used in the former determinations,
will serve to show the saving of time effected by this simple ar-
rangement :—

XI.
Transferring the precipitate with 14 cub. 14
Geutmss of Water... 3 4... *.
For a single addition of 26 cub. centims. -
of wash-water to run through
To drain the precipitate. . . . . . 4
Time required in washing . . . 25
Weight of the precipitate . . 0:2435 grm.
Volume of wash-water . . 40 cub. centims,
Pressure in manometer . . 0'184 metre.

This amount of chromium sesquioxide (0°2435 grm.) differs from
the mean of the former experiments (0°2436 grm.) by one-tenth‘of
a milligramme only, and shows that even by a pressure of 0°184
metre the washing is as complete by the single addition of 26
cub. centims. of water. The duration of the filtermg process in
the former experiments ranged from 12 to 14 minutes under a
difference of pressure amounting to from 0°53 to 0°572 metre ;
in the last experiment it required 25 minutes under a pressure
of 0°184 metre, or about double the length of time. The time
needed to analyze potassium chromate in the former case was
reduced from 14 hours to 82 minutes; by the latter method the
reduction would be from 14 hours to 44 minutes.

The employment of the second method is particularly to be
recommended to beginners in qualitative analysis. The experi-
menter needs only a single funnel, he is obliged to work care-
fully and cleanly, and the great saving of time and work amply
compensates for the little trouble needed to reverse from time to
time the position of the bottles.

I believe that the above-described water air-pump will soon
become an indispensable piece of apparatus in chemical labora-
tories. It not only serves as the most convenient method of

Phil. Mag. 8. 4. Vol. 37. No. 246. Jan. 1869. C

18 Mr. F. A. Paget on a New Form

producing the differences in pressure required to accelerate the
process of filtration, and of obtaining the necessary vacuum for
evaporation ; it is equally adapted to purposes to which neither
the mercury nor the ordinary pumps are in any way appli-
cable. By its aid it is possible to calibrate a thermometer
with the greatest accuracy, and to estimate the vapour-tension
of such corrosive bodies as bromine, chromyl dichloride, &c.
by the simplest method possible, in which the necessary opera-
tions require scarcely more time than an ordinary determina-
tion of a boiling-point.

I purpose returning to these applications of the instrument
in a future communication.

II. On a New Form of Permanent Magnet. By Freprick
A. Paget, C.E.; M. Soc. Ciwil Engineers of France; Corr.
Mem. Franklin Institute ; M. late Government Commission on
Chaincable- and Anchor-proving Establishments*.

yy eo any distinctly given reason, it is taken for
granted in all works on magnetism, and im all the prac-
tical applications of magnetism, that it is impossible to magne-
tize a plate except in the direction of its greatest length.
Michell, in his ‘ Treatise on Artificial Magnets,’ gives a deter-
minate proportion, but without stating any reason, between the
length and the weight of magnets. A magnet, for instance,
2 inches long should weigh one-tenth of a pound. Cavallo re-
commends a width of one-tenth, Fuss one-sixth, Mussche-
broeck and, later, Coulomb one twenty-fourth, of the length. In
all these cases it is assumed that the direction of the poles must
be parallel with the longest dimensions of the sclid bar or plate
to be magnetized, and that it is impossible to regularly magne-
tize a square plate, and still less an oblong plate, in a direction
transverse to its major axis. That this is correct with a solid
continuous plate can be easily proved by experiment; and it is
well known to instrument-makers that it is impossible to per-
manently magnetize a square steel plate. Nodoubt such results
would greatly vary with the constitution and state of the steel
employed, the relations of its different dimensions, the mode
of magnetization adopted; but the only experiment bearing on
the question that I can discover, after much research in scientific
works, is that of De la Bornet, who found, on magnetizing steel
disks, that as long as they were whole they showed no polarity,
and that their polarity only appeared when they were cut in two.
Dr. Lamont, in a paper which first appeared in Poggendorff’s
Annalen (vol. cxii.), and was communicated to the Philosophical

* Communicated by the Author.
+ Pogg. Ann. vol. Ixxu. p. 26.

of Permanent Magnet. 19

Magazine for November 1861 by the Astronomer Royal, inves-
tigated the question of ‘the most advantageous form of mag-
nets,” or that form in which “are united the greatest possible
magnetic moment with the smallest possible mass and the small-
est possible moment of inertia.” In all the forms he experi-
mented upon, the breadth was always less than one-third of the _
length, and generally about one-fifth ; and he does not seem to
contemplate the possibility of magnetizing a square plate, and still
less an oblong plate, in a direction transverse to its greatest
length. Now I find that, by cutting slits nearly up to the
middle of a steel plate, a square plate in one piece can with such
slits be regularly magnetized ; and by this means even an oblong
square plate can be regularly magnetized, and with as many
poles as may be required, in a direction transverse to its greatest
length. I herewith beg to forward a square plate magnetized in
this way. It is of watch-spring steel, 0°0075 inch thick and
% mch x { inch; it has four pairs of slits 4 inch wide cut
from its edges, and leaving a central web } inch wide, uni-
ting the whole. On moving a small needle round this square
plate, it is seen to be regularly magnetized ; and on sprinkling
iron filings on the magnet covered by a sheet of paper, they ar-
range themselves in lines, proving that the magnet really con-
sists of a number of small regular similar magnets arranged
below each other in the same vertical plane. On suspending an
oblong magnet of this kind with its longer axis in the vertical
plane, the needles set themselves to the magnetic meridian ; on
suspending it flatwise, with its longer axis in the horizontal
plane, the longer axis points east and west. As well as can be
judged by. subjecting them to slight shocks, the magnets are as
permanently magnetized as if they were separate from each other.
Only time can prove whether they will lose their magnetism.
The important question as to what form is the best for retaining
magnetism for a length of time is one which, as Dr. Lamont
remarks, no one has yet investigated.

Though I have not yet been enabled to try to magnetize a
parallelopipedon of steel after slotting it vertically and trans-
versely into a number of bars held together by a central web, I
feel very confident that this could be done. ‘The slots could be
cut into the parallelopipedon or cube while in a soft state by a
thin tool worked to and fro in an ordinary engineers’ slotting or
shapimg machine, and the whole magnetized in a powerful elec-
tric spiral, in the way described by Elias. Besides moving the
spiral to and fro, as described by him, no doubt in order to over-
come the resistance to induction, the cube while in the spiral
could also be struck, in order to produce that mechanical vibra-
tion which is so favourable to magnetization and demagnetization.

20 Messrs. KE. T. Chapman and M. H. Smith on the

By pointing the needles, or giving them the rhomboidal form,
it is evident that, in spite of the poles being nearer (as is well
ascertained to be the case in needles of that shape), the ratio of
the magnetic moment to the moment of inertia is still higher than
in the assemblage of oblong needles. Though, for various
reasons, the rhomboid set on its edge is scarcely ever used in
practice, an easy calculation shows that it is the most perfect
form for a moveable magnet. It seems only to have been tried
when lying flat.

Seymour Chambers, Adelphi, W.C.
London, November 20, 1868.

Ill. Action of Dehydrating Agents on Organic Bodies.
By EK. TororpuHron Cuapman and Mires H. Smira*.

ANE-SUGAR, as is well known, yields carbon on treatment
with strong sulphuric acid, which removes the elements
of water. In like manner strong sulphuric acid dehydrates
common alcohol, yielding olefiant gas. Chloride of zinc removes
water from amylic alcohol, yielding amylene. Anhydrous phos-
phoric acid converts acetate of ammonia into acetamide, and
finally to cyanide of methyle. All these are well-known and
characteristic examples of the violent dehydration of organic
substances. The three short notices which follow describe fresh
cases of the action of dehydrating agents.

The first is the instance of nitrate of amyle with phos.
phoric acid: there is very violent dehydration, and pyridine is
produced,

C> H!! NO?—3H?O=C° HEN.

The second is the dehydration of formiate of amylamine by

means of chloride of zinc: there is produced tso-cyanide of amyle,

CH? O? N C? H8—2 H?O0=CN CH?"
The third is a case in which a strong dehydrating agent refused

to perform a violent dehydration, viz. the action of chloride of
zinc on oxalate of amyle. The equation
C2 04 (C5 H"!)?—4H?2O0=C?? H¥
was not realized.
That which actually did happen was as follows :—-

C204 (C5 H")2— H? 0 = C2 02 + 2(C® H22).

I. On the Artificial Production of Pyridine.

Pyridine has been produced by Perkin from azo-dinaphthyl-
diamine (C# H!® N®) by the action of nascent hydrogen. This

* Communicated by the Authors.

Action of Dehydrating Agents on Organie Bodies. 21

reaction has not thrown much light on the structure of the base
in question. The other sources of this body are the destructive
distillation of various nitrogenous matters. It is found in bone-
oil and in the distillate from peat, shale, &c., but im no case is
the rationale of its formation understood.

In a paper read before the Chemical Society and published in
its Journal for August 1866, entitled ‘On the Production of
Acetic and Propionic Acids from Amylic Alcohol” (Chapman),
occurs this passage :—“ Phosphoric acid attacks nitrates as well
as nitrites, though not so easily, and this may prove a method
of obtaining compounds of the same class as picoline.

C® H'! NO$ might give us C°H°N+3H?0.”
—4-— ee a5)

nee
Nitrate of amyle. Pyridine.

This hypothetical equation has been realized exactly in the man-
ner indicated. 3

If excess of dry nitrate of amyle be poured upon anhydrous
phosphoric aeid, at first no reaction appears to take place; but
on long standing or on the application of gentle warmth, the .
phosphoric acid is seen to shrink a little and to change in appear-
ance. This change generally commences at one side of the vessel,
and gradually creeps through the mass. Considerable heat
is produced, but no gas evolved. On treating the mixture
with water no further heat is generated; but the solid mass
in the vessel gradually dissolves, the excess of nitrate separates
and may be decanted off, and the last traces of it may be com-
pletely removed by a few minutes’ boiling. On now adding
excess of potash to the liquid, the smell of pyridine is at once
produced. But though we operated on several ounces of anhy-
drous phosphoric acid, we could not in this manner obtain more
than the slightest traces of the base. A good deal of dark-brown
pitchy matter, possessing apparently feeble basic properties, is
the chief product of the reaction. This substance is probably
intermediate in composition between pyridine and nitrate of
amyle. Acting on this view, we determined to use excess of anhy-
drous phosphoric acid. We here, however, encountered another
difficulty, the reaction between anhydrous phosphoric acid and
nitrate of amyle being, under these circumstances, uncontrollably
violent, though it does not occur until some time after the sub-
stances have been placed in contact, or unless they have beet.
_ gently warmed. We found the only available method of opera-
ting was to take a very long-necked flask, and place in it between
two and three grammes of anhydrous phosphoric acid, together
with from one and a half to two grammes of nitrate of amyle. The
mixture was carefully spread out in a thin layer in the flask.
During this operation it is necessary to keep the flask cool by

22 Messrs. E, T. Chapman and M. H. Smith on the

surrounding it with iced water. A cloth dipped in iced water is
now wrapped round the neck of the flask, and the bulb placed
in the water-bath for a few minutes until the first signs of reac-
tion are visible. It is then removed from the water-bath and
wafted about in the air. As soon as the chief part of the reac-
tion is over, the flask is replaced in the water-bath for a few
minutes. This process is repeated with fresh supplies of mate-
rial in clean flasks. The contents of the flasks are now dissolved |
in water, and the solution so obtained distilled with excess of
potash. This solution is very dark in colour. The alkaline
distillate, which smells strongly of pyridine, is rendered acid with
sulphuric acid, and boiled to expel traces of neutral oily matters.
It is then considerably concentrated by evaporation in the water-
bath, and finally pieces of potash are added. The oily liquid
which rises to the surface is pyridine. Jt was recognized to be
such by its extreme stability, by its odour, and by an analysis of
its chloride, the details of which are subjoined.
Substance taken,
‘4024.

Chloride of silver found, "4992 ;

therefore percentage of Cl, 30°69;

(C° H® NHCl) requires 30°73.

The above process does not yield the full theoretical quantity
of pyridine. Some dark-coloured neutral or slightly alkaline
body is produced in large quantity.

IL. Organic Cyanides.

The question of isomerism amongst the cyanides of the alcohol-
radicals, or nitriles, has acquired a great interest since the pub-
lication of Hofmann’s recent researches on the subject. We must
now recognize two distinct kinds of isomerism amongst the ni-
triles :—first, isomerism dependent on the linking of the carbon
inter se; second, isomerism dependent on the atomicity of the
nitrogen.

As an example of the first kind of isomerism, we may men-
tion cyanide of isopropyle and cyanide of normal propyle or
butyro-nitrile. This kind of isomerism can obviously exist in
nitriles independently of the atomicity of the nitrogen.

We may represent cyanogen in three ways :—

da) NY’ com cu" N", ~~ In this case the two equivalents of
cyanogen which constitute the molecule are held together by the
carbon

Action of Dehydrating Agents on Organic Bodies. 23.

(2) CM Nm ye Ci" Tn this case the equivalents are held
together by the nitrogen.

(3) CM Nm cm Nl" In this case the equivalents are held
together by one carbon and one nitrogen.

If the first of these assumed compounds were to be combined
with a monatomic body, it would yield a compound (M = mon- »
atomic body) of the following constitution, N’’ C"" M, the mon-
atomic body being attached to the C. The second would yield

C!"N” M, “M7”? being attached to the nitrogen. The third
would obviously yield a mixture of the first two in atomic pro-
portions. By assuming the existence of the first two of these
different forms of cyanogen, we are enabled to give an account of
the difference between the two classes of nitriles ; and we think
that some grounds exist for making this assumption.

We find that the action of the iodides of the alcohol-radicals
on different metallic cyanides produce different nitriles. For
example, as Meyer showed many years ago, the cyanide of ethyle
produced by the action of cyanide of silver on iodide of ethyle
yields ethylamine when treated with an acid. Hofmann has
shown that the complementary product in this reaction is formic
acid ; and we, who have also examined this action, can corroborate
the observation. Again, cyanide of mercury under some cir-
cumstances may be made to yield both of the isomeric cyanides
by the action of the alcoholic iodides. We have not completed
the examination of this reaction. A volatile mercury compound
is formed at the same time. As Hofmann has pointed out, the
isomeric nitriles are reproduced when the sulphoyinic salts act
on the metallic cyanides, though not in quantity.

The above facts appear explicable only on the hypothesis of
two distinct cyanogens, or, in other words, on the assumption
that in some cases cyanogen unites by its carbon and sometimes
by its nitrogen. The two cyanides of ethyle would then be re-
presented thus :—

(1) Common cyanide, N!” C!”! C? H®.
(2) Pseudo-cyanide, C!” N” C? HS.

In the first case the carbon of the cyanogen is in union with
the carbon of the ethyle, and remains so when the cyanogen
undergoes its typical alteration by the assimilation of water.

In the second case the carbon of the cyanogen is not in union
with the carbon of the ethyle, and therefore, when the cyanogen
undergoes its transformation by assimilation of water, it does
not combine with the ethyle.

‘ The methods for the production of the common cyanides are
three :—

24 Messrs. E. T. Chapman and M. H. Smith on the

(1) Action of an organic iodide, bromide, or chloride on a
metallic cyanide.

For example, KC!" N!"4+ C? H5T=C? H9CN+KI.

(2) Action of sulphovinates on metallic cyanides.
- For example,

so+{ Go He + KOM N= C2 HCN + S0"1

(3) Dehydration of the ammonia-salts, or the amides of the
acids of the same carbon condensation as the cyanide produced.
For example,

Propionate of ammonia. C? H®O? N H§—2H? O=C? H° CN.
-Propionamide . . . C?H°ON H? — H?0=C? HeCN.

The first two of these methods may also give rise to the so-called
pseudo-cyanides ; or perhaps we should say that analogous opera-
tions on differently constituted metallic cyanides give rise to the
pseudo-cyanides. It proves nothing against this hypothesis
that one and the same metallic cyanide may give rise to both, or
now one and now the other of the cyanides; for the metallic
cyanides themselves may be very liable to change their internal
arrangement in accordance with external circumstances.

The third process gives us but one cyanide—the normal one.

The question naturally arises, is there any analogue of this
last process which will give rise to the pseudo-cyanides ? Perhaps
Hofmann’s method for the preparation of these bodies may be
regarded as to agreat extent analogous. But we find that there
is a much more strictly analogous process; for by dehydrating
the formiates of the amides we obtain the pseudo-cyanides.
The first step in the dehydration of the formiates of the amides
is the difficulty ; but by starting with the formamides no difficulty
is experienced. Nor is there the slightest difficulty in obtaining
the compound formamides; they are produced with remark-
able ease by digesting the compound ammonias with formic
ether. By digesting aniline with formic ether im excess at
130° C. for a few hours, it is completely converted into phenyl-
formamide. Amylamine is converted into amylformamide, even in
the water-bath, when digested with formic ether. Hthylamine
is even more rapidly converted. A little alcohol facilitates the
reaction. These compound formamides may be purified suffi-
ciently by simply heating them to a temperature rather above
that of the water-bath for a short time. If after this treat-
ment they be treated with chloride of zinc (fused and in coarse
powder), the pseudo-cyanides are at once produced, and may
he recognized by their smell and by their decomposition with
acids.

This process can hardly be said to be an available method of

Action of Dehydrating Agents on Organic Bodies. 25

obtaining these cyanides in quantity; or, rather, it is nothing like
so available as Hofmann’s process with chloroform. After ob-
taining these cyanides, we attempted to obtain analogous bodies
from the compound acetamides, but without success. Action
took place fast enough; but charring and other splitting up oc-
curred.

Anhydrous phosphoric acid, by its action on the compound
formamides, also produces the pseudo-cyanides.

The conclusion we draw from the whole of the foregoing is
that the pseudo-cyanides have as much right to be regarded as
cyanides as the common cyanides, and that we must look for the
difference between these classes of cyanides in differences with
cyanogens themselves.

Ilt. Action of Chloride of Zine on the Oxalic Ethers.

The numerous interesting reactions which the oxalic ethers
are known to undergo rendered it probable that the action of
dehydrating agents on these ethers would be worth studying.
We have therefore treated three of the oxalic ethers with chlo-
ride of zinc. These ethers were the oxalates of methyle, ethyle,
and amyle. We expected either that an actual dehydration of
the ethers would take place at the expense of the oxygen of the
oxalic acid and hydrogen of the alcohol radical, or that, simply,
double decomposition would take place, and that we should
obtain oxalate of zinc and chloride of the alcohol radical. Neither
of these two results ensued.

Chloride of Zinc and Oxalate of Ethyl.—When these substances
are heated together, torrents of gas are evolved. This gas is
partially soluble in water. That portion of it which is not so-
luble in water is completely and readily soluble in bromine. It
burns with a luminous flame, and is in fact ethylene. The so-
luble gas is hydrochloric acid. Oxalate of zinc is the solid pro-
duct of the reaction. The reaction consists, therefore, in a double
decomposition of oxalic ether and chloride of zinc ; but instead
of obtaining chloride of ethyle, we have its elements in the form
of hydrochloric acid and ethylene.

Chloride of Zine and Oxalate of Amyle.—The reaction in this
case is exactly similar to the one above described, excepting that
the amylene produced is for the most part polymerized.

Chloride of Zine and Oxalate of Methyle.—When these sub-
stances are heated together, gas is evolved as before, in large
quantities. When this gas is passed through ice-cold water, a
very considerable portion of it is condensed, and an oily layer of
liquid is formed on the surface of the water. On conducting
the non-condensed gases through a U-tube surrounded with ice
and salt, some more light liquid condenses. There is, however,

26 M. O. E. Meyer on the Heating of a

still a residue of gas. This gas is partially absorbed by bro-
mine, not entirely. The residue appears to be chloride of me-
thyle. The liquids condensed both on the surface of the water
and in the U-tube were obviously for the most part olefines. They
began to boil below zero (Cent.), and probably boil at all tempe-
ratures up to about 60°, when the distilling vessel was found to
be dry. They appeared to be a mixture of various olefines.
This reaction apparently resembles closely that with the oxalate

of amyle. |

London Institution.

IV. On the Explanation of Stewart and Tait’s Eaperiments on
the Heating of a Disk rotating ina Vacuum. By Oscar Emin
Meyrr*.

i a previous paper + I have already briefly discussed the expe-

riments on the heating of a disk m an exhausted space
which Messrs. Stewart and Tait laid, in June 1865, before the
Royal Society of Londont ; and I then expressed the opinion that
the agitations which are communicated to the rotating disk by
the wheelwork are the chief cause of the heating. I revert to
the subject once more, because the gentlemen in question have
published another paper on the subject, in which it 1s proved that
the cause of the heating is to be sought neither in terrestrial
magnetism, nor in conduction, nor radiation of heat, nor in the
surrounding air. I think, asI have already said, that the cause
lies in the agitations caused by the wheelwork.

I should not consider it worth while to elucidate this subject
to the readers of the Annalen, if, with the aid of the explana-
tion in question, the experiments did not enable us to calculate
the coefficient of thermal radiation of the disk in absolute measure.
We find in this manner a number which agrees most completely
with a formula which Professor Neumann, of Konigsberg, has
most kindly communicated to me. This formula is based on
the observations of Dulong and Petit on the law of cooling ||,
and an observation which he himself has made. The agreement
between the results obtained in these different ways affords the
conviction not only that the explanation of Stewart and Tait’s
observation is correct, but also that the value in absolute measure
obtained for the thermal radiation is undoubtedly accurate.

* Translated from a separate impression, communicated by the Author,
of a paper published in Poggendorff’s Annalen, vol. exxxv. p. 285.

+ Pogg. Ann. vol. cxxvu. p. 380.

{ Proc. Roy. Soe. vol. xiv. p. 339. Phil. Mag. S. 4. vol. xxx. p. 314.

§ Proc. Roy. Soc. vol. xv. p. 290. Phil. Mag. S. 4. vol. xxxui. p. 224.

|| Ann. de Chim. et de Phys. vol. vu. (1817).

Disk rotating in a Vacuum. 27

The agitations to which I ascribe the heating are communi-
cated to the disk by the wheelwork ; they are due to slight irre-
gularities in the working of the axes and wheels, and are snch
that the rotating disk and its axis, within the play left to it, is
continually moved backwards and forwards.

Such an oscillation cannot escape observation ; for the radius
of the disk amounts to 64 inches = 165 millims. If, therefore,
the axis (which is certainly far shorter) moves only the hun-
dredth of a millimetre in its bearings, there must be a shaking of
the edge, and in rapid rotation an apparent increase in the thick-
ness, of the disk.

Stewart and Tait have, it is true, noticed this phenomenon ;
they observed a rising and sinking of the aluminium disk used
(which was 3!5 inch thick) of 0-015 inch, or 0°38 millim., on
both sides of the edge*. They explain this, it appears, on the
assumption that disk and axis were not fastened to each other
exactly at right angles. I consider it not less probable that
an oscillation of the axis was the cause.

If, however, this assumption is correct, it 1s a necessary con-
sequence that the oscillation must be the stronger the lighter the
disk. This, in fact, was noticed by Stewart and Tait ; for they
found that while the disk of 4, inch thickness deviated by 0:015
inch, that which was half as thick moved up and down as much
as 0:02 inch.

It follows, moreover, from this assumption that the vis viva
which was communicated to the disk by the wheelwork must
have been the same in both cases. The quantities of heat re-
sulting from these equal vires vive must have been equal; that
is, the one of half the thickness must have been twice as hot as
the one which was double. This, however, is exactly what has
been observed by Stewart and Taitt.

After this confirmation of the hypothesis, it seemed worth
while to calculate the magnitude of the vis viva which is changed
into heat by agitations and impulses.

In this calculation we are concerned both with the number of
the impulses and with their strength.

Since the wheelwork runs with constant velocity, the impulses
occur regularly. The axis of the disk rolls, therefore, with re-
gularity within the space which its ends have on their bearings.
The axis describes a kind of conical surface. After each revo-
lution it comes into the same position, or, at all events, into
almost the same position; after each half revolution, into the
opposite one. During each revolution, therefore, it is thrown
once forward and once backward ; or during each turn it expe-
riences two impulses which change its position and direction.

* Article 20 (2). Tt Experiments XIII. and XX. Article 18.

28 M. O. E. Meyer on the Heating of a

At every impulse upon the axis one part of the vis viva pre-e
sent is lost ; for at each impulse the position of the axis of ro-
tation is changed ; hence, of the vis viva present, only that part
remains which corresponds to a rotation about the new axis ; all
the rest of the vis viva is lost, as far as rotation is concerned, and
is used in heating the disk.

From this we can easily calculate the loss of vis viva and the
gain in heat occurring in each second. If we denote the angular
velocity of the disk by yp, the vis viva of the particles at the dis-

tance 7 from the axis is
| bye
for the unit of mass.
At this distance, however, there is an infinitely narrow zone of
the breadth dr, and the thickness of the disk 6, which contains

the mass

2rrdAdr,

if A denotes the density of the disk of aluminium. This zone
has therefore the vis viva

TOAW?r?dr ;

and the entire disk the mtegral of this expression,
oAWRt

where R denotes the radius of the disk, or
4MR*p*

by introducing the mass of the disk,
M=7R6A.

If, now, owing to one of the impulses in question, the axis of
the disk is deviated through the angle yf, the residual vis viva
thereby becomes

IL MR*/* cos? d,
and that which is lost for rotation and changed into heat is
IMR’ sin? ¢.

This loss of vis viva and gain in heat occurs twice during each

rotation—ain the unit of time ae if T denotes the time of one ro-

tation of the disk. The heat produced, therefore, in the unit of
time is equivalent to ae vis viva,

os MR? sin? d;
or, since

20
ya

Disk rotating in a Vacuum. 29
it is
Qa

3

In this expression R sing has a simple meaning; for it is
nothing more than the magnitude of the alternate rising and
sinking of the edge of the disk R, the value of which is 0:015
inch or 0°38 millim. By introducing this value the loss of
vis viva may also be written

Qa?
7s MA?.

This vis viva of motion changed into heat is first of all con-
sumed in raising the temperature of the disk, and is then im-
parted to the surrounding medium by radiation. Since after
some time both the velocity of the rotation and also the excess of
the temperature of the disk over that of the surrounding me-
dium became constant, the heat lost in a second by radiation
must be equivalent to vis viva transformed into heat during the
same time. The first may be calculated from Newton’s law of
cooling, which, owing to the small amount of the heating, may
be unhesitatingly accepted. If the constant excess of the tem-
perature of the disk amounts to ¢ degrees, the quantity of heat
radiated in a second from both surfaces of the disk is

27rhR*t,

if the constant A denotes the heat which is radiated by the unit
of surface for an increase of 1 degree. I obtain the mechanical
work equivalent to this heat by multiplying by Qg, where g is
the accelerating force of gravity, and Q the height to which the
unit of mass can be raised by the unit of heat. The equivalent
in work of that heat is therefore

2TAR*tQg.

The work thus produced corresponds to the vis viva consumed
—that is,

MR? sin? d.

ARAQg= 78 MR.

The first idea suggested by an inspection of this formula is a
circumstance which apparently disagrees with observation. For
Stewart and Tait have observed that the heating of the disk is
inversely proportional to its thickness. From the above equation
we might be tempted to conclude that the heating ¢ increases
proportionally to the mass M, and therefore also to the thickness
of the disk. We must, however, remember that the oscillation
must be the greater the less the thickness of the disk*. The os-

* It is true that the above numbers do not accurately confirm this; but
they are only approximate measurements.

Sy)

0 M. O. E. Mever on the Heating of a

cillation & is therefore inversely proportional to the thickness,
and it follows that the heating of the disk must also increase
inversely as the thickness.

All the magnitudes occurring in the formula are known from
Stewart and Tait’s measurements, or may easily be calculated
from them, including the constant 4 which defines the thermal
radiation. No direct statements have been published; so much
the more interesting, therefore, does it appear to deduce their
value from the observations in question.

If we introduce into the above formula the numerical values

k=0°015 inch =0°38 millim.,
M=10 ounces =810 grms.,
R=6°5 inches =165 millims.,

OO aw:
i 5500 == (ON
Q=423°5 metre,

and for g and 7 their well-known values; and if, finally, we
assume for the heating the mean value

t=0°:84 F. =0°-46 C.,
which holds for the disk coated by lampblack, we get the ther-

mal radiation
h=0:°0017.

This number contains no arbitrary unit of heat, but is con-
nected solely with the so-called absolute units (that is, the milli-
metre and the second of time), as well as the density of water as
unit of specific gravity. It stands as 3 for a surface blackened
by lampblack in a rarefied space in which there is a tension of
0:3 inch or 7°6 millims. of mercury.

An idea is obtained of the meaning of the number thus
found by considering that a blackened surface of 1 square metre,
which has been heated 1 degree above the surrounding rarefied
air, loses in a second a quantity of heat which would raise a kilo-
gramme through 0:72 metre.

The value found for the thermal radiation / is in remarkable
agreement with the result which, with the kind aid of Professor
Neumann of Konigsberg, I was able to deduce from the obser-
vations of Dulong and Petit. 1 take this opportunity of thank-
ing him publicly.

Those philosophers have combined the results of their obser-
vations on the cooling of a heated body in a rarefied space, in
the law that the quantity of heat emitted in the unit of time by
the unit of surface is expressed by the formula

ma>(a'—1)+ np°t?.

Disk rotating in a Vacuum. i a

In this formula 3 denotes the temperature of the surrounding
medium, ¢ the excess of the temperature of the heated body, p the
pressure of the surrounding air; the other signs denote constants.

From the formula adduced, the value of the coefficient of
thermal radiation is obtained by division by the value ¢, assumed
to be very small. We have thus

at —1

j EMpre? E

h=ma*>

From Dulong and Petit’s determination we have, in Centigrade
degrees,

a=1:0077,
b= lao,
ce =0°45.

I have to thank Professor Neumann for the statement that for
a blackened surface
n= 36.3
and the coefficient n, which is independent of the nature of the
surface, in case p is expressed in atmospheres, is for atmospheric
air

n=0:0168.

The first number is deduced from his own observation, the
latter from occasional statements of Dulong and Petit. Both
numbers refer to Paris lines and minutes as units.

Using these values, and taking from Stewart and Tait’s ob-
servation

p=0-010 atmosphere,
t=0°°45 C.,

and putting $= about 20° C., we get from the above formula the
value

h=0:0013,

expressed, again, in millimetres and seconds of time.

The concordance of the value deduced above from Stewart and
Tait’s observation with this directly found is greater than was to
be expected from the multifold uncertainty of the observations.

Another beautiful agreement is also met with. According to
a communication of Professor Neumann, fora metallic surface

m= about 0°5,

that is, about one-seventh that of a lampblack surface. We get
from this for the radiation-constant h of a metallic surface the
value

h=0:000238 ;

32 Mr. S. Newcomb on Hansen’s Theory of the

and it is therefore found that the radiation-coefficient for metals
is about five- or sixfold smaller than that for a blackened sur-
face. Stewart and Tait observed that the aluminium disk with
a pure metallic surface radiated about one-fourth the heat of a
blackened one.

Breslau, September 11, 1868.

V. On Hansen’s Theory of the Physical Constitution of the Moon.
By Stmon NEwcoms*.

HE great reputation of the author has given extensive cur-
rency to the hypothesis put forth by Professor Hansen
some years since, that the centre of gravity of the moon is con-
siderably further removed from us than the centre of figure.
The consequences of this hypothesis are developed in an elabo-
rate mathematical memoir to be found-in the twenty-fourth
volume of the Memoirs of the Royal Astronomical Society. But
the reception of the doctrine seems to have been based rather on
faith in its author than on any critical examination of its logical
foundation+. Such an examination it is proposed to give it.
An indispensable preliminary to this examination is a clear un-
derstanding of what the basis of the doctrine is. Let us then
consider these three propositions :—

(1) The moon revolves on her axis with a uniform motion
equal to her mean motion around the earth.

(2) Her motion around the earth is not uniform, but she is
sometimes ahead of and sometimes behind her mean place, owing
both to the elliptic inequality of her motions and to perturbations.

(3) Suppose her centre of gravity to be further removed from
us than her centre of figure, and so placed that, when the moon
is in her mean position in her orbit, the line joining these cen-
tres passes through the centre of the earth.

Let us also conceive that these two centres are visible to an
observer on the earth. Then a consideration of the geometrical
arrangements of the problem will make it clear that when the
moon is ahead of her mean place the observer will see the two
centres separated, the one nearest him being further advanced
in the orbit; while, when the moon is behind her mean place,

* From Silliman’s American Journal for November 1868.

t Inthis connexion it is curious to notice that on page 83 of his memoir
Hansen appears as the first of the independent modern discoverers of Cag-
noli’s theorem of spherical trigonometry—

cos acos bcos C+ sin asin 6=cos A cos B cos c+sin A sin B.

This was about three years before the above formula was published as new
by Mr. Cayley, and geometrically demonstrated by Professor Airy, in the
Philosophical Magazine.

Physical Constitution of the Moon. 33

the nearest centre will be behind the other.. This apparent oscil-
lation of the two centres is indeed an immediate effect of the
moon’s libration in longitude.

Now the inequalities in the moon’s motion, computed from
the theory of gravitation, are those of a supposed centre of gra-
vity. But the inequalities given by observation are those of the
centre of figure. Hence, in the case supposed, the inequalities
of observation will be greater than those of theory. Also their
ratio will be inversely as that of the distances of the centres
which they represent.

Professor Hansen, in comparing his theory with observations,
found that the theoretical inequalities would agree better with
observation when multiplied by the constant factor 1:0001544..
Supposing that this result could be accounted for on the hypo-
thesis of a separation of the centres of gravity and figure, he
thence inferred that the hypothesis was true. But the result
cannot be entirely accounted for in this way, because the largest
inequality of theory (evection) has a factor (excentricity) which
can only be determined from observation ; and therefore even
the theoretical evection is that of the centre of figure, and not of
the centre of gravity. It must not be forgotten that the excen-
tricity, which is not given by theory, is subject to be multiplied
by the same factor that multiplies the other inequalities. To be
more explicit,—

Let e be the true excentricity of the orbit described by the
moon’s centre of gravity. Then the true evection in the same
orbit will be

ex A,

A being a factor depending principally on the mean motions of
the sun and moon. And on Hansen’s hypothesis, the apparent
evection, or that of the centre of figure, will be

ex Ax 1:0001544:.

On the same hypothesis, the excentricity derived from observa-
tion, being half the coefficient of the principal term of the equa-
tion of the centre, will be

ex 1:0001544,

and the theoretical evection computed with this excentricity
will be
ex 1:0001544 x A,

which is the same with that derived from observation. Hence
The theoretical evection will agree with that of observation, not-
withstanding a separation of the centres of gravity and figure of the
moon.
Phil, Mag. 8. 4. Vol. 37. No. 246. Jan. 1869. D

34 Mr. 8. Newcomb on the Physical Constitution of the Moon.

That Hansen overlooked this point is to be attributed to his
method of determining the lunar perturbations by numerical
computation from the various elements of the moon’s motion, so
that the manner in which the inequality depends on the elements
does not appear. It is only when we determine the perturba-
tions in algebraic form that this dependence appears.

Passing 3 now from the evection, the next great perturbation of
the moon’s motion is the variation, But the value of this per-
turbation has not been accurately determined from observation,
because, attaining its maxima and minima in the moon’s octants,
it is complicated with the moon’s semidiameter and parallactic
inequality. Even if the semidiameter is known, the two inequa-
lities in question cannot be determined separately with precision,
because their coefficients have the same sign in that part of the
moon’s orbit where nearly all the meridian observations are
made. From this cause Airy’s value of the parallactical inequa-
lity from all the Greenwich observations from 1750 to 1830 was
3" in error. And when, in his last investigation*, Airy rejected
the observations previous to 1811, owing to some uncertainty as
to what semidiameter should be employed, the result was still a
second too small. It is therefore interesting to find what value
of the variation will result if we substitute the known value of
the parallactic inequality in Airy’s equations for the determina-
tion of that element. Neglecting those unknowns which have
small coefficients, these equations are, from 1806 to 1851,

1806-15 . . 1066W+ 28:14V=4 17:2 —
1816-24 . . 945 + 30°92 + 24°9
1825-83 . . 9438 + 29°26 + 42:1
1838442 . . 929 + 27°28 + 10°83
1843-51 . . 905 + 23°36 + 79
Sum . . 47:383W-+138°96V= +4102°9

In these equations W x 0":73 represents the correction to the
coefficient of variation, and V x 3"-77 that to the coefficient of
parallactic inequality. We now know from recent special investi-
gations that the latter coefficient is very near 12550. Airy’s
provisional one was 122-10, whence

125"-50—122"-10
Soy.
The sum of the preceding equations gives
W=2°15—2:90V = —0-46.
The resulting correction to the provisional variation (2370"-3)

* Memoirs of the Royal Astronomical Society, vol. xxix.

Mr. R. Edmonds on Extraordinary Agitations of the Sea. 35

is therefore
— 0°46 x 0'°73 = — 0"34,

Making the variation derived from observation . 2369-96
While Hansen’s theoretical valueis . . . . 23869°86
PemelaGayS ~~ fe ue 8 ke a 2369°74:

The differences are too minute to found any theory upon. —

Leaving the evection and variation, the other inequalities are
so minute that their product by Hansen’s coefficient is altogether
insensible.

Summing up the results of our inquiry, it appears that in the
ease of the evection the supposed discordance between theory
and observation would not follow from Hansen’s hypothesis, and
therefore, even if it exists, cannot be attributed to that hypo-
thesis asa cause. In the case of the variation no such discord-
ance has been proved. In the case of the other inequalities the
discordance would be insensible.

The hypothesis is therefore devoid of logical foundation.

VI. On Extraordinary Agiiations of the Sea not produced by
Winds or Tides. By RicHarp Epmonps, /sg.*

Or of those not infrequent agitations of the sea, which are

always accompanied by earthquakes or thunderstorms, or
great maxima of the thermometer, or considerable minima of the
barometer—and sometimes by all these together—but which are
never occasioned by winds or tides, was observed in Mount’s
Bay on the 6th of May, 1867, and another early on the following
morning at Plymouth. ,

At Penzance Pier, on the first of these days, at 5 a.m., a tide-
like “wave 4 to 5 feet high, without a moment’s notice, swept
into the harbour. A vessel in the act of moving from the new
pier to the old was whirled round, and the pilot feared she would
have become unmanageable. The large trawlers were swept
against each other; and the sand at the entrance to the harbour
was washed up, so as to colour the water for a considerable dis-
tance.” The agitation continued nearly two hours; anda friend
to whom I wrote for information replied that he was informed,
by an eye-witness who had watched it for an hour after the first
influx, that the duration of each efflux as well as of each influx
was from three to five minutes. ‘The sky at the time was very
overcast, and at 11] a.m. there was thunder with three or four
flashes of lightning away to the S.H.” The barometer at 9 a.m.
was 29 in., the maximum of the thermometer 64°, which are

* Communicated by the Author, having been read before the Royal Geo-
logical Society of Cornwall on the 3rd of Noyember, 1868.

D2

36 Mr. R. Edmonds on Extraordinary Agitations

respectively lower and higher than on any other day of the year
up to June. The maximum of the thermometer at Plymouth
this day was 74°, the minimum of the preceding night 44°,
showing a range of 30°, whilst at Penzance the contemporaneous
range was only 15°. The weather at Plymouth this forenoon
was very fogey, and of such an unusual character that on going
out of doors into the street I felt as if entering a hothouse. The
above readings of the barometer and thermometer are from the
registers kept at Penzance by Mr. Richards, and at Plymouth
by Mr. Merrifield.

On the following morning, the 7th of May, at the Plymouth
Great Western Docks, when the gatekeeper went to close the
gates at high water about 7.30, he observed to his surprise an
extraordinary current rushing through them into the dock, and
rising to the perpendicular height of one foot above the proper
level of the tide at that time. When it ceased he immediately
closed the gates, and did not wait to see if it were succeeded by
other such currents. The thermometer this day in Plymouth
was 78°, the maximum of the year up to the 11th of June.

I have, in my last paper (read before the Society in 1865*),
described a similar but much greater disturbance of the sea in
Mount’s Bay and Plymouth on the 14th of October, 1862, and
have therein referred to those of the 31st of May and 8th of June,
1811, 5th of July and 30th of October, 1843, 23rd of May,
1847, and the 25th-26th of June and the 4th of October,
1859—which also occurred contemporaneously in those places,
and which I had previously described}, together with the accom-
panying states of the atmosphere.

The only simultaneous disturbance of the sea of this nature
in Mount’s Bay and Plymouth during the last century which I
can find recorded besides those on the days of the two great
earthquakes of Lisbon, is that of the 28th of July, 1761, when
the sea in Mount’s Bay rose six feet above its proper level.
Borlase, after having described it, states that there was “thunder
at times all the day,” and at 8 p.m. the church of Ludgvan, of
which he was the rector, was struck by hghtningf.

Thus have all the recorded extraordinary agitations of the sea
in Mount’s Bay and Plymouth, except those on the days of the
two great earthquakes of Lisbon, which they perfectly and in all
respects resembled, been accompanied with thunderstorms or
great maxima of the thermometer or considerable minima of the
barometer. And because they are always, or almost always,
epee paper appeared in the Philosophical Magazine for January

“if ae my Pamer papers in the ‘Transactions’ of the Society, and my

‘Land’s End District,’ p. 101.
{ Phil. Trans. vol. ln. p. 507.

of the Sea not produced by Winds or Tides. Be

thus accompanied in all parts of the world, whether on sea-coasts
or in lakes, distinguished authors on both sides of the Atlantic
have ascribed them (when unaccompanied with known earth-
quakes) to storms or unusually great and sudden augmentations
or diminutions of the atmospheric pressure on the surface of the
water. But this hypothesis is quite at variance with known facts,
and so are all the other hypotheses hitherto advanced by geolo-
gists, as 1 have shown in the printed Transactions of this Society
and elsewhere.

My attention was first drawn to this subject by having wit-
nessed one of these disturbances in Mount’s Bay more than
twenty-five years since, which I described first in a letter printed
in the Literary Gazette of the 15th of July, 1848, and after-
wards more fully in the paper which I read before this Society
in the same year. During this long period every fact I have
met with connected with the subject confirms me in the opinion
that the hypothesis which I then, and in subsequent years, sub-
mitted to this Society is the only one capable of reconciling all
the observed facts—that hypothesis being that all these extra-
ordinary agitations (of which each efflux, as well as each influx,
occupies generally about five minutes, and never more than ten
on our coasts) are produced hy local submarine shocks of earth-
quakes without any upheaving, subsidence, dislocation, or frac-
ture of the submarine ground. The way, too, in which they are
produced on shores or submarine ground sloping outward, I
have also fully explained, viz. by the continually repeated dash-
ings seaward of the surface of the water by the vertical and rapid
vibrations of the submarine ground, until a very broad, but not
high, wave is raised, and much of the shore is consequently left
dry. When the vibrations have ceased, the dashed-off waters
return shoreward to find their level, and move up and down on
the shore like a pendulum until the equilibrium is restored.
That a shock does generally consist of a rapid succession of
countless vibrations is evident, not only from its being felt at
sea “like the letting out of a cable,” and on land “like a wagon
rushing over a paved road,” but by its very names of earthquake,
tremblement de terre, and seismos.

These tide-lke movements of the sea are totally unlike the
agitations produced by storms. Of these latter agitations we
had a memorable example on the 24th of April last at the Scilly
Isles and along the southern coasts of Cornwall and Devon, when
the waves rose so enormously, and their spray ascended to such
an unusual height, that no one who witnessed the spectacle can
ever forget it. The master of the Great Western Docks in Mill-
bay, Plymouth, informed me that, as the huge waves rolled in
and the vessels outside the docks mounted over them, great parts

38 Mr. R. Edmonds on Eavtraordinary Agitations

of their keels were out of water, and he could see under them ;
and at high water the waves swept over the gates into the docks,
a thing never known before. The cause of this unusual disturb-
ance was no doubt a storm from the south-west, some hundreds
of miles off in the Atlantic, which never reached us. These huge
breakers would have commanded the attention of every one, how-
ever unobservant, who happened to be near and in sight of them.
But the tide-like currents which I have described, when occur-—
ring on an open shore would not attract the attention of any one,
however observant, even if he were close to them, unless he
watched them for some time, or unless he knew whether the or-
dinary tide were then coming or going, and saw that this extra-
ordinary current was moving in an opposite direction. This
quiet tide-like motion of the water up and down an open beach
was strikingly shown during one of the extraordinary agitations
of the sea in 1848, by the conduct of some children, who were
then amusing themselves on the beach and rocks, near the
Chimney Rock in Penzance, and had been there long enough to
observe that the sea was flowing in and out very differently
from usual, and at intervals of about ten or fifteen minutes.
Instead of running home at once and telling thew parents
what an extraordinary thing they had seen, they preferred
making use of their knowledge for some new kind. of play;
and accordingly, when they were joined on the beach by other
children who had not been present long enough to make the
same discovery as themselves, they told them to go out on the
rocks to see something. These new comers, therefore, suspecting
nothing, and observing, as they thought, that the tide was going
and had left the rocks dry, and not dreaming that there was any
possibility of the sea coming in again for some hours, went on
the rocks as they were told by their playfellows ; and before they
could return, the current surroundedthem. After:waiting a few
minutes in a great fright lest they should be drowned, the sea
began again to ebb, and in a few minutes more they reached the
beach in safety.

P.S.—These phenomena commence generally with an efflux
or retirement of the sea.’ And it appears from the newspapers
that those accompanying the great earthquake of the 15th of
August last along the western coasts of South America began
with an efflux, as did also those on the same day in New Zealand,
when “the sea rushed out and in with extraordinary violence,
and in some places in the South Island great damage was done
by the sea going far over the usual high-water mark.” This
rushing out and in of the sea in New Zealand and on the South-
American coast was in all probability occasioned in each place
by local submarine shocks in the way I have above described.

of the Sea not produced by Winds or Tides. | 389

But because no earthquake shock was felt on that day in Call-
fornia, nor in New Zealand until a day or two afterwards, the
writer of the article in the ‘Times’ of the 3rd of November,
beginning with .‘‘There are earthquakes in divers places,”
boldly states, without referring to any authority, that “on the
15th of August the most terrible earthquake ever known wrecked
and then drowned many hundreds of miles of the South-Ame-
rican coast, sending a wave as far north as California, and right
across the Pacific (8000 miles) to our own countrymen in New
Zealand.” This untenable hypothesis I have already fully dis-
proved in my last paper above referred to, which I wrote in
answer to a similar hypothesis advanced by ‘Mr. Mallet, who in
the ‘Quarterly Journal of Science’ for January 1864 (p. 68)
states that “the great sea-wave of translation rolls in often hours
after the shock has done its work of destruction, or portions of
it may roll in upon shores that have felt no shock at all. Thus
in the great earthquake. at Japan, which a few years ago wrecked
a Russian frigate in one of the harbours there, the great sea-
wave produced in the deep sea near those islands hours after-
wards reached the opposite shores of the Pacific at St. Diego and

Francisco.”

_ The writer in the ‘ Times’ would, I think, have given a much
more credible explanation of the recent agitations on the shores
of the Pacific, had he said that the great earthquake of the 15th
of August was not confined to America, but appears to have ex-
tended under the Pacitic to New Zealand, where, although it was
not perceived on dry land, its submarine shocks produced move-
ments of the sea similar to those on the American coasts, com-
mencing, too, like them, with a retirement of the sea.

In agreement with what I have above stated, is the following
extract from the ‘Times’ of December 2, 1868, from its own
correspondent’s letter, dated Melbourne, October 13 :—“ In a
recent letter I referred to the great tidal wave which at various
hours of the 15th of August last rolled in on different parts of
Australia and New Zealand, doing some damage at Chatham
WSland. 2... <. Mr. Ellery of the Melbourne Observat tory, the
President of our Royal Society, a very scientific man, last evening
in answer to a question from Professor Wilson . ... said he had
been asked to offer a few notes on the great tidal wave. ... The
time of the wave was recorded at Sydney to a few seconds. It
was also pretty accurately taken at Newcastle and in New Zea-
land. He had reduced the time taken at those places to Mel-
bourne mean time; and according to that reckoning the first indi-
cation of the wave was at about half-past 2 of the morning of the
15th of August, the mdication being only by the self- registering

40 Mr. R. Edmonds on Extraordinary Agitations of the Sea.

tide-gauge ; but the great wave was not observed until twenty-
four minutes past 7 on the same morning. ‘The first indication
at Newcastle was at two minutes past 7 in the morning; two
hours afterwards a pretty full wave was noticed, and five hours
afterwards was the greatest disturbance of all. On the coast of
New Zealand the time extended from about 5 a.m. of the 15th
of August to nearly an hour after noon.”

All this very strikingly coincides with the agitations in the ~
Scilly Isles, Mount’s Bay, Falmouth, and Plymouth on Whit-
sunday, the 23rd of May, 1847. That in Mount’s Bay was
noticed as early as 5 a.m., and continued all day with varying
magnitude, the rise and fall having been from 38 to 5 feet or more
perpendicularly. In the night preceding, a slight tremor of the
earth was felt in Mount’s Bay by two coastguardsmen while
standing on the cliff between Newlyn and Mousehole; and “a
strange noise as if underground was heard” at Scilly about the
time of the oscillation of the sea there. The disturbance was at
its maximum in Mount’s Bay at 5 p.m., and in Plymouth be-
tween 8 and 9 p.m., and did not cease until the following day,
when a more fearful movement of the sea, lasting several hours,
occurred in Peru in the harbour of Callao; and “a furious sub-
marine earthquake was felt by the captain of the American whale
frigate ‘Acushuett’ about sixty miles W.S.W. from the island
of San Lorenzo, at 3 a.m. of the 24th’*, These extraordinary
oscillations of the sea in the west of England twenty-one years
ago appear, therefore, in duration, magnitude, and varying mag-
nitude, to bear a very close resemblance to those of the present
year in Australia and New Zealand.

Having already shown how these extraordinary disturbances
of the sea may be produced by local submarine shocks, I will
now state how they may, during their continuance, become of
greater magnitude at one time than at another. This may result
from a subsequent shock coinciding with one of the effluxes,
and thus making that efflux considerably greater than it would
otherwise have been. The following influx would therefore
rise proportionally higher on the beach than did the influx which
preceded it.

It thus appears that the recent extraordinary agitations of the
sea in Australia and New Zealand, as well as in Peru and Cali-
fornia, were all produced, not by any great disturbance of any
kind in mid-ocean, but by local shocks of the submarine ground
upon or near which, in each locality, the agitated waters had
previously rested.

Plymouth, December 1868.

* British Association Report for 1850, (Sections) p. 82.

Losaie atagl

VII. Experimental Proof that the Electric Spark is an Electro-
motor. By HK. Eptunp*.

a former papers} I have proved that by the mechanical work

which the voltaic current exerts in disintegrating the poles in
producing the electric light, an electromotive force results which
sends a current in a direction opposite to that of the principal
current. <s, in an electric discharge, when sparks are formed in
the air there is also a disintegration of the polar surfaces, the idea
readily suggested itself that the electric spark, like the voltaic
arc, might possibly be an electromotor. To investigate this point
more minutely, I have, in common with Dr. Lemstrom of Helsing-
fors, made the following experiments.

A Holtz’s machine, made by Ruhmkorff of Paris, was used in
the investigation. The rotating glass disk hada diameter of 55
centims., and each of the jars belonging to the apparatus had a
coated surface of 42 square centims. The copper galvanometer
wire was | millim. in diameter, and was surrounded by a layer
of gutta percha 2 millims. in diameter. The entire thickness of
the wire, the insulating layer included, amounted to 5 millims.
This wire was coiled in forty turns round a wooden frame. The
aperture inside the frame, in which the needle was suspended by
a cocoon-thread, was 5 centims. in length and 38 centims. high.
To protect the needle from draughts, the instrument was enclosed
In a glass jar.

2. If the voltaic current which, it is assumed, is produced in
the electric spark, is to be investigated by the aid of the galva-
nometer, the spark must be connected with the galvanometer by
a closed circuit. This necessary condition was satisfied, after
many vain attempts, in the following manner :—

In the following figure, A B represents the rotating disk, and ab
the two combs. An insulated copper wire ac is directly con-
nected with a, while the insulated wire de terminates in a brass
knob d in the neighbourhood of 6. From ¢ and e insulated wires
pass to the knobs fand g. Two other conducting-wires lead
from the points c and e to the galvanometerG. Atm a rheostat
is introduced, which consists of an insulated thin German-silver
wire. Ifthe machine is charged and the disk A B put in rota-
tion, andif moreover the resistance at m and the distance between

the knobs fg and bd is suitably adjusted, sparks pass simulta-

* Communicated by the Author, as a separate copy of a paper pub-
lished in Poggendorff’s Annalen, July 1868, having been read before the
Swedish Royal Academy of Sciences on the 13th of May 1868.

+ Poggendorff’s Annalen, vol. cxxxi. p. 586, and vol. exxxiv. p. 250.
Phil. Mag, vol. xxxv. pp. 103 & 441.

4.2 Prof. H. Edlund’s Eaperimental Proof that

neously between f and g and between
band d. If the wires are connected
in the simple manner represented by
the figure, a difficulty is met with
which at first I could not entirely
remove. The electric discharge does
not, of course, entirely pass through
the spark fg, but part passes through
the galvanometer G. The galvano-
meter-wires coated with gutta percha
acquire thus an electric charge which
acts electroscopically upon the mag-
netic needle and draws it onone side.
This charge was retained for some
time after the machine was at rest,
and caused a deflection. It is possible
that this charge might have been
avoided if the galvanometer had been
differently constructed, and the con-
ducting wire had been otherwise in-
sulated. The charge in question
was ultimately quite removed, and the position of equilibrium of
the needle made quite independent of it, by directly connecting
the points 7 and & with each other by a German-silver wire which
could be lengthened or shortened at pleasure. The point k was
moreover directly connected with the water-pipes of the house
by the wire /, by which it was placed in conducting communica-
tion with the earth. Part of the electric charge passed now
through A instead of through the galvanometer, and the electri-
city of either one kind or the other which might have been in
excess passed to the earth through /. After these wires had been
introduced, no charge was observed in the galvanometer. In all
these experiments the jars belonging to the electrophorus ma-
chine were used. Without these there was mdeed an electrical
discharge between b and d; but it was impossible to produce
sparks between f and g, however great was the resistance at m.
It is well known that the electric discharge of a battery acts
upon the magnetic needle and produces a deflection which in-
creases with the quantity of electricity. The direction in which
the deflection of the magnetic needle occurs is the same as if the
magnetic needle were surrounded by a voltaic current which went
from the positive to the negative coating. If, then, the knobs f
and g are so far apart that no discharge ensues between them,
the magnetic needle must make a deflection when the disk 1s
turned. This was always the case; and when the disk rotated
with a constant velocity, the sparks between 4 and d followed

the Electric Spark is an Electromotor. 43

-each other so closely that the equilibrium of the needle was con-
stant. The position of equilibrium could not, of course, be di-
rectly observed, because the needle constantly oscillated ; but a
knowledge of it was attained by observing the points on the scale
towards which the needle turned. If the positive electricity
passed from the comb a to the conduction, the deflection of
the magnetic needle was always towards the left of the scale.
When now the knobs f and g were pushed so close together that
sparks ensued between them, the deflection ought to have been less
than before, because part of the current would pass through the
conduction cfge. If the spark at fg were only a conductor of
electricity, this must have been the case. But instead of this the
deflection was from fifteen to twenty times as much as before.
The deflection was in the same direction as if no sparks had been
formed between f andg. When the positive current starts from
a it divides at c; part flowsthrough the spark at fg, and another
part through the galvanometer in the same direction as indicated
by the dotted arrows. Now, if there is in the electric spark, as
there is in the voltaic arc, a galvanic current in a direction op-
posed to that of the discharge, it will traverse the conductors
in the direction indicated by the arrows; hence there must be
deflections of the magnetic needle in the same direction as the
discharge; and this was always the case. From this the con-
clusion must be drawn that in the electric spark there is an
electromotive force which sends a current in an opposite direction
to the discharge which the spark causes.

To test more completely the correctness of this conclusion, the
connexion between the spark-apparatus and the conducting wires
was altered as follows. This apparatus was removed from the
bridge between c and eand inserted at n instead. In the bridge
between c and e the rheostat was inserted which had hitherto
been at m. As is at once seen, the galvanic current of the spark
must now produce a deflection in the magnetic needle in a di-
rection the reverse of that of the original current; the experi-
ments showed also that this was always the case. The magni-
tude of the deflections depends in all these cases mainly on the
distance between the knobs fand g; the resistance in the rheo-
stat m, as well as that in h, must therefore be so great that sparks
pass between f and g, even if the distance between them is some-
what greater.

3. It seemed also interesting to ascertain whether the voltaic
spark could produce chemical decompositions. For this purpose
the conductions to the galvanometer were removed, and instead
of the rheostat wire a voltameter was inserted between i and k.
The voltameter contained, as usual, dilute sulphuric acid. But
a certain proof of the decomposition of water could not thus be

44 Prof. E. Edlund’s Experimental Proof that

obtained. Thereupon the same experiment was made with a.
battery of a few Bunsen’s elements, after so great a resistance
had been interposed in the conduction that the deflection of the
galvanometer was about as great as that produced by the voltaic-
spark current. But just as little with this current was there a
certain proof of the decomposition of water. The currents in
both cases were too feeble to produce distinct ascending gas-
bubbles; the gas which is produced by so feeble a current is so
small in quantity that it is partially retained by the platinum
disks and partially absorbed by the liquid. It was next attempted
to ascertain whether the voltaic-spark current was sufficiently
strong to produce a polarization in the platinum disks. With this
view a glass vessel was filled with water containing sulphuric acid,
in which were placed two pieces of platinum-foil, one connected
with z and the other with k. While the electrophorus disk was
turned, the conducting-wires of the galvanometer were separated
from 7 and k, but by means of a commutator could be again joined
with these points as soon as the comb a was connected by means
of a brass rod with the comb 6 and therefore all flow of electri-
city to the polarization-vessel ceased. If the discharge was now
allowed to pass through the polarization-vessel for a given time
while the knobs g and f were so far apart that no sparks ensued
between them, a feeble polarization-current was always obtained
when the galvanometer was connected with zandk. If, on the
contrary, sparks passed between f and g while the machine was
at work, after connecting the galvanometer-wires with 2 and k,a
polarization-current was obtained which was much stronger than
before. The deflection took place towards the proper side, and
the current gradually diminished till it entirely ceased. If
the machine was for some time in activity, the polarization-cur-
rent was so powerful that the scale of the telescope was inad-
equate to measure the first deflection.

4. The knobs used in the spark-apparatus were of iron, brass,
and tin, and all of the same magnitude, namely 17 millims. dia-
meter. The position of equilibrium of the needle was determined
by observing points on the scale where the needle turned, and
taking the mean of two observations belonging to the saine os-
cillation. For a single oscillation the needle required about
eleven seconds. The electrophorus disk was turned with as
uniform a velocity as possible. As the disk, when it once began
to move, could not at once be brought to rest, the machine, when
it was necessary to do so, was rendered inactive by connecting the
two combs by a metal rod. The following are a few of the
observations made :—

the Electric Spark ts an Electromotor. 45

Series 1.
Knobs of iron at fg.
Experiment 1. The knobs were at a distance of 3 millims.
from each other; and no formation of sparks ensued between
them.

Position of equilibrium when the machine was—

A. At work. B. At rest.
— 260-0 301°5
261:0 302°5
264°5 Mean . 302:0
263:0
Mean . 262°1

For the sake of brevity, the first position of equilibrium is de-
noted by A, and the second by B.

Experiment 2. The knobs were just so far apart that the for-
mation of sparks ceased.

A. ’ B.
297°3 299°7
297°3 299°7
297°9 Mean . 299:7

Mean . 297°4
Experiment 3. Like experiment 1.

A. B.
257°5 300°5
2580 300°5
209° Mean . 3800°5
Mean .. 258°3

Experiment 4, The knobs were at a distance of 1:5 millim.
Formation of sparks.

A. B.
269-0 296-0
270°8 296-0
270°5 Mean . 296-0

Mean . 270°1
Experiment 5. Distance between the knobs very small. For-
mation of sparks.

A. B.
289:0 295°8
289°3 295°8
283°0 Mean . 295°8

Mean . 288°8

When there was a formation of sparks between the knobs f and
g, and these were 3 millims. apart, a mean constant deflection was

46 Prof. E. Edlund’s Experimental Proof that

obtained of 41:1 divisions. When, on the contrary, there was
no discharge between fand g, the deflection only amounted to
2-3 divisions. Moreover the deflection diminished when the dis-
tance between the knobs was lessened.

Series 2.

Knobs of brass at f g.
Experiment 6. The knobs at a distance of 3 millims. Forma-

tion of sparks.

A B.

263°5 300-0

264:5 999°5

265°0 Mean . 299-7
Mean . 264°3

Experiment 7. The knobs removed from each other. No
formation of sparks.

A. B.
297-0 299:0
297-0 299°3
2973 Mean . 299°2
Mean . 29771
Experiment 8. Like experiment 6.
A. B.
267:0 299°5
263°5 299°5
262°0 Mean’ 2 9299-3
Mean . 2642

The deflection obtained with brass knobs (35:4 divisions) was
thus somewhat smaller than when the knobs were of iron. The

deflection obtained when there was no formation of sparks be-
tween f and gy was, on the contrary, as ought to be the case, the
same as before.

Series 3.

Knobs of tin at fg.
Experiment 9. The knobs ata distance of 3 millims.
tion of sparks.

Forma-

A. B.
266°5 299:0
264-0 208°5
eae Mean . 2988
263°3

Mean . 265°7

the Electric Spark ts an Klectromotor.
Experiment 10. Like the preceding.

AT

A. B.
265'5 299-0
261-0 298°6
ABT Mean . 298°8
263°5
Mean . 264°4
Experiment 11. The knobs so far apart that no spark formed.
A. B.
295°8 297°5
295°8 291-3
299°9 Mean . 297°5

Mean . 295°7

Experiment 12. The eanbs at a distance of 15 millim. For-

mation of sparks.

A. B.
271°8 297°5
271-0 297-5
2743 Rican Oas

Mean . 272°4

Experiment 13. The knobs removed apart from each other.

No formation of sparks.

A. B.
295-0 297°0
295:0 297°0
Mean . 295:0 Mean . 297:0

When the distance between the knobs amounted to 3 millims.,
the mean deflection was 33:7 divisions, and therefore somewhat
smaller than when brass knobs were used.

Series 4.

Both the knobs f and g were removed from the bridge between
ce and e and inserted at n instead; c and e, on the contrary, were
joined by the rheostat wire of German silver, which had pre-
viously been at m. The deflections thus obtained were now to
the right of the scale, instead of to the left as the others had been
—a deportment which can only be explained on the assumption
that the spark is electromotive.

48 Prof. E, Edlund’s Experimental Proof that

Experiment 14. Knobs of iron.

i B.
313:0 29405
313°0 294:°5
313°0 Mean . 294°5
315°3

Mean . 313°6

The deflection amounted therefore to 19°1 divisions.

Experiment 15. Knobs of tin.

A. B.
813°5 295'8
314:0 296-0
318°5 Mean . 295:9
Mean . 313°7

The deflection amounted thus to 17°8 divisions.

The reason why the deflections were smaller than before was,
that the resistance in the bridge only consisted of the rheostat
wire m, in consequence of which the greater part of the electric
discharge took this path. The distance between the knobs must
therefore be small if the sparks are to jump across.

Series 5. Polarization of platinum disks.

A polarization-vessel was introduced between 7 and & instead
of h. While the disk was beg turned, and the current there-
fore passed through the liquid in the vessel, the galvanometer G
was removed. After a definite time the machine was made in-
active by directly connecting the combs a and 6. Thereupon the
galvanometer-wire was connected as rapidly as possible with the
polarization-vessel, and the successive positions of equilibrium of
the magnetic needle were observed.

Experiment 16. No sparks formed between f and g. The
position of equilibrium of the needle before the experiment
=219°0. The successive positions of equilibrium after polariza-
tion were 215°0, 217°5, 217:5, 218:0. The greatest deflection,
therefore, was =4 divisions.

Experiment 17. Formation of sparks between fand g. The
position of equilibrium of the needle before the experiment was
=219-0. The successive positions of equilibrium after the po-
larization were 192-5, 209-0, 213°0, 214°5, 215°5, 215°6, 215-5,
216'5, 217°0. The first observed position of equilibrium, after
connecting the platinum disks with the galvanometer, was at
26:5 divisions.

the Electric Spark is an Electromotor. 49

Series 6.

To obtain a measure for the magnitude of the electromotive
force, the conducting-wires of a battery were interposed between
e and m. When a spark passed between f and g, the voltaic cir-
cuit was closed by the conducting spark, but was open in the
other case ; and the current which formed in the spark had to
pass through the voltaic battery. Both currents had therefore
to traverse the same circuit, and both only existed during the
time in which the spark passed between f and g. The ratio be-
tween the deflections which each current produced in the galva-
nometer must be equal to the ratio between their electromotive
forces. By means of a commutator the current of the battery
might be reversed ; so that it either went in the same direction as
the spark-current, or in the one opposite to it. If the deflection
of the galvanometer from the spark-current is 2, and that from the
battery-current y, we have in one case + y and in the other r—y.
From this, z and y may be easily calculated, as well as the ratio
between them, by which the electromotive force of the battery-
current is known. In order that this method may be regarded
as perfectly correct, the conducting-power of the spark must not
vary with the direction of the battery-current. This is undonbt-
edly the case ; for the battery-current in its passage through the
spark is so enfeebled, that it can have no perceptible influence
on the conducting-power. In all the following experiments the
battery consisted of ten Bunsen’s elements. The specifie gravity
of the nitric acid was 1°32. In order that the deflections of the
battery-current might be greater than in the preceding experi-
ments, the resistances m and / were altered.

Experiment 18. The knobs fand g were of iron, at a distance
of 3 millims. Formation of sparks between them. The posi-
tion of rest of the needle when no current traversed the galva-
nometer =244:0,

Position of rest when the currents went in epposite direc-
tions :—

v-Y.
179°5
1745
Position of rest when the currents went in the same direction: —
V+y.
148-0
150°5
1515
Mean 72 7 Lo0:0
Phil, Mag. 8S. 4. Vol. 37. No. 246. Jan. 1869. EK

50 Prof. E. Edlund’s Haperimental Proof that

Position of rest when the currents went in opposite direc-
tions :—
L—-Y.
178-0
178-0

The mean of the first two and last two observations is =177°5.
From this we get

2t+y=940, e—y=665, 7=80°3, y=13'8, and 7a 8.

As the battery consisted of ten elements, the electromotive
force of the spark was equal to that of 58:2 Bunsen’s elements.
It must here be at the same time remarked that the deflection
x is not exclusively caused by the spark-current, but part de-
pends on the electrical discharge of the machine. To obtain at
any rate a limiting value for this part the following experiments
were made :—
Experiment 19. The knobs so far apart that no sparks were
formed.
Position of equilibrium when the machine was at rest: —
231°5
231°3
Position of equilibrium when the machine was at work :—
225°0
2247
The battery-current was reversed by the commutator :—
225°0
225°0
Position of equilibrium when the machine was at rest;—

231:0
231:0
Mean of the first two and last two observations =2381°2.
From this experiment it follows that the battery-current has
no infiuence on the magnitude of the deflection—a natural con-
sequence of the circumstance that its circuit is open when no
sparks are formed between the knobs f and g. The discharge-
current, however, brings a deflection of 6°3 divisions. This de-
flection cannot, of course, be so great if sparks are formed between
fand g; for part of the discharge passes then through the path
of the sparks. That part, therefore, of the deflection x which is
caused by the current forming in the spark fg cannot be less
than 80°3—6'3=74:0 divisions. We thus find that the elec-
tromotive force of the spark cannot be less than that of 53°6
Bunsen’s elements.

the Electric Spark is an Electromotor. o1

Experiment 20. Distance between the iron knobs 0°5 millim.
Formation of sparks.

r—y. x+y. L—Y.
220°5 202°0 220°5
221:0 201°8 220°0

200-0
201°3

Mean of the first two and last two observations. . =220°5.
Position of equilibrium when the machine was at rest =243:1.

From this we obtain
a+y=41'8, r—y=22'6, r=32-2, y=9'6, and — =3°35.

The electromotive force was thus now equal to that of 33°5
Bunsen’s clements. If from x=82°2 we subtract 6°3, it is
found that the same force cannot be less than that of 27 elements.

Experiment 21. The knobs were of tin. Distance 3 millims.
Formation of sparks. Position of equilibrium of the magnetic
needle =242°5.

a—Y. x+y. L—Y.
169°5 136-0 174°5
169°5 141:0 173°0
135°5
137°5

Mean of the first two and last two observations = 171-6.
From this we obtain

x+y=105-0, e—y=70°9, «=88-0, y=17'1, and als.

The electromotive force amounts therefore to 51°5 elements.
if 6:3 is subtracted from 88:0, we get as the limiting value for
the same force that of 47:8 elements.

Experiment 22. The distance between the tin knobs 0°5 millim,
Formation of sparks. Position of equilibrium of the magnetic
needle =241°5.

L— Ye L+Y. Tlie
225°0 208:0 221°)
2240 209-0 226°5

210°0

Mean. ., -209:0

The mean for «—y=225°5.
From this we obtain

v+y=82'5, e—y=160, 7= 243, y=8'3, and 793.
E2

52 Prof. EK. Edlund’s Experimental Proof that

Thus the electromotive foree = that of 29°3 elements, and its
limiting value = that of 21:7 elements. |

Experiment 23. The knobs were of brass. Distance 3 millims.
Formation of sparks. Position of equilibrium of the magnetic
needle =288°5.

L—Y. e+y. LY
165°5 129-0 163°5
161-:0 185°0 | 162°5
162-0 128°0
1375
128°5
Mean. . 181°6

Mean of the first and last observations =162°:9.
From this we obtain

a+y=106-9, e—-y=75'6, v=91°3, y=15°7, and = =5°815.

The electromotive force in this case = that of 58°15 elements,
and its limiting value = that of 54°14 elements.

Experiment 24. The distance of the brass knobs 0°5 millim.
Formation of sparks. Position of equilibrium of the magnetic
needle 238°7.

Th Uy L+Y. L—Y.
224:0 206°5 218-0
223°9 203°0 219°0

209-0

Mean. . 206°2

The mean for x—y is 2211.
From this we get

2+y=82'5, e—y=17°6, =25-02, y=7-45, and — =3°36.

Consequently the electromotive force =33°6, and its limiting
value that of 25-2 Bunsen’s elements.

The electromotive force in the electric spark appears unexpec-
tedly great if it is compared with the electric force in the voltaic
arc. From a former determination, this, when the poles were of
brass, was about equal to that of 15 elements; but in the
electric spark, from what has been above said, it amounts to from
50 to 60 elements; and yet the disintegration of the poles with
the Juminous arc appears to be very much stronger than with
the spark.

Two circumstances must here be taken into account. In the
first place, the voltaic arcis continuous and the spark discontinuous.
The duration of the spark, as is well known, depends on several
circumstances. Under the circumstances of the present experi-

the Electric Spark 1s an Electromotor. . 53

ments it cannot be more than the 0:0001 of second. The num-
ber of sparks which passed in each second did certainly not ex-
ceed 10. With this assumption we arrive at the conclusion that
the passage of sparks from one pole to the other does not occupy
more than 0:001 of the time during which the machine is being
worked. Moreover it must be considered that each spark, as
Feddersen has shown, is no continuous whole, but consists of
a number of partial sparks. In order to compare the mechanical
activity of the luminous arc and that of the current of sparks as
regards the disintegration of the polar surfaces, we must on these
assumptions first multiply that of the latter by 1000; and it is
possible that in fact a still larger number must betaken. And,
secondly, the metallic polar surfaces on the luminous arc have
so a high temperature that they are often near their fusing-point,
while with the spark they are only slightly warmer than the sur-
rounding medium. Hence in the latter case the disintegration
requires much more work than in the former. Taking into con-
sideration this circumstance, the difference between the mecha-
nical work in the luminous are and that in the spark is quite
different from what might at first have been supposed.

5. In the previous experiments for determining the electro-
motive force the distance between the knobs 6 and d was un-
changed. To determine the infiuence which a change in this
distance might produce, the followimg experiments were made :-—

Experiment 25. The battery consisted this time also of ten
Bunsen’s elements. The distance between the knobs 6 and d
was about 8 millims. Formation of sparks between f and g.
Position of equilibrium of the magnetic needle =231°7.

L—Y. “+y. L—Y.
150-0 A es 158:0
150° 106:0 1530

101-0
1130
Mean = > dl07-9

Mean for e—y=152'8.
From this we obtain

x +y=123'8, e—y=789, x=101'3, y=22'5, and 7 = 4°50,

The electromotive force, therefore, is equal to that of 45
elements.

Experiment 26. Distance between the knobs 6 and d about
16 millims. In other respects no change. Position of equili-
brium of the needle =231-0.

54. Mr, H.Wilde on a Property of the Magneto-electric Current.

L—Ye a+y. L—Y.
190'5 167°0 185°5
188°5 164°0 189-0

160:0

Mean. . 168°7
Mean for z—y=188°4.
From this we get

e+y=67'3, e—y=42°6, v=5495, y= 12°35, and 7 = 4°45.

The electromotive force is equal to that of 44°5 elements.

From the last two experiments it follows that the electromo-
tive force is independent of the distance between the knobs 6
and d. As isat onceseen, y represents the conducting-power in
the entire circuit; and this depends principally on the conduct-
ing-power in the sparks at f and g, and on their number. In ex-
periment 25, y was almost twice as great as in experiment 26.
Yet this is easily explained if we consider that the sparks in the
first case followed each other much more rapidly than in the latter.

The subject I have here undertaken to treat is by no means
completely exhausted by the experiments adduced. Several
questions which are in the closest connexion with it require fur-
ther investigation. It is only after these questions have been
answered that it can be settled whether the electromotive force
may in the future find a practical application.

VIII. Ona Property of the Magneto-electric Current to control and
render Synchronous the Rotations of the Armatures of a number
of Electromagnetic Induction Machines. By H. Witpn, Hsq.*

ae discovery of the property which I am about to describe

arose out of the efforts which have been made, during the
last two years, to reduce the internal heat generated in an Bleeee
magnetic machine by the induction-currents set up in the eleec-
tromagnet and armature by the rapid magnetization and demag-
netization of the latter. This heating of the armature (as 1s well
known) was first observed by Dr. Joule in 1848, as the result of
a delicate investigation on the quantitative relation existing be-
tween ordinary mechanical power and heat+. In the electro-
magnetic machines of my invention this phenomenon unfortu-
nately manifests itself on an alarming scale, so much so that
the armature of the 10-inch machine rises in the course of a few
hours to 800° F. and upwards; and were the action of the ma-
chine to be continued for any lengthened period, the insulation
of the armature-coils would be in great danger of being destroyed.

* Communicated by the Author, having been read at a Meeting of the

Literary and Peon Soviety of Manchester, December 15, 1868.
+ Phil. Mag. S. 3. vol. xxiii. p. 264.

Mr. H. Wilde on a Property of the Magneto-electric Current. 55

One method of mitigating this evil was to construct the ma-
chine of smaller dimensions, so as to afford greater facilities for
the dissipation of the heat by radiation and conduction. But
even in the smaller machines an inconvenient residuum of heat
still remained when the machines were worked continuously for
a considerable time, such as to render it desirable to adopt some
means for abstracting the heat more rapidly. By means of a
current of water circulating in the hollow brass segments which
form part of the magnet-cylinder, Mr. Charles E. Ryder, the skil-
ful manager at the works of Messrs. Elkington and Co., has
happily succeeded in so far reducing this heating as to perinit
of the machines being worked for days and nights together with-
out intermission, and without any sensible flere crn a the
power of the current.

The machines which have been found to be the most ee
and economical in their working are those which have armatures
from 34 to 4 inches in diameter. The armatures are driven at
about 2000 revolutions per minute ; and the water, after having
passed through the magnet- cylinder, is used for supplying the
boilers which furnish the power for driving the machines.

I have already shown elsewhere that the current from a small
magneto-electric or electromagnetic machine is sufficient to ex-
cite the great electromagnet of the 10-inch machine ; and it has
been further found, by my friend Mr. G. C. Lowe, that the cur-
rent from one small machine is sufficient to excite simultaneously
the electromagnets of several small machines. In a number of

3-inch machines which have been constructed under my direc-
tion for Messrs. Eikington and Co., for the electrodeposition of
copper on a large scale, the currents from two 34-inch electro-
magnetic machines are made to excite the electromagnets of
twenty similar-sized machines to a degree sufficient to bring out
the maximum dynamic effect of each machine. The electromag-
nets of the two 33-inch exciting machines are charged by the
current from a small 24-inch magneto-electric machine; but I
have found that nearly as good a result may be obtained from
the twenty machines by dispensing with the small magneto-
electric machine, and employing the residual magnetism of the
two 34-inch exciting machines in a manner similar to that de-
scribed, almost simultaneously, by Mr. Farmer*, Messrs. Var-
leyt+, Mr. Siemens {, and Sir Charles Wheatstone §.

* Letter to the Author, November 9, 1866, Salem, Mass. U.S., Pro-
ceedings of the Literary and Philosophical Society of Manchester, Febru-
ary 19, 1867.

T Specification filed at the Office of the Commissioner of Patents, De-
cember 24, 1866.

{ Specification filed at the Office of the Commissioner of Patents, Janu-
‘ary 31, 1867. /

§ Proceedings of the Royal Society, February 14, 1867.

56 Mr. H. Wilde on a Property of the Magneto-electric Current.

So far I have adverted principally to the means by which a
very serious defect in the practical working of the new induction
machine was remedied, a defect which many of my friends, who
were unacquainted with the efforts which have been made to over-
come it, have considered to be fatal to the success of what seemed
likely to be a useful invention. But while the difficulty arising
from the heating was now obviated, the subdivision of the mate-
rials of one large machine into a number of small ones gave rise
to another defect which it was also found necessary to overcome ;
for although the armatures of several machines might be driven
nominally at the same speed from the same driving-shaft, by
means of straps, yet when the combined direct current from
several commutators was required, the want of perfect synchro-
nisin in the revolution of the armatures operated to produce a
diversion of the currents of some of them through the coils of
others, which were at the neutral point of their revolution; and
consequently the maximum useful effect of the combined cur-
rents could not be obtained.

As the high speed at which the machines were driven precluded
the employment of toothed gearing, the only method which
seemed at all feasible for producing the requisite synchronism of
the armatures was to place a number of the machines in a straight
line, and connect them together by means of a clutch fixed on the
end of each armature-spindle. The chief objection to the carry-
ing out of this arrangement was the difficulty of providing the
requisite means for preserving the synchronism of the system,
when any of the intermediate machines were disabled by accident,
or stopped for repairs; so that, practically, it would not have been
found convenient to work more than two machines geared toge-
ther in the manner described.

It was while experimenting with a pair of machines so geared
together, that I first observed the phenomenon which forms the
subject of this communication. These machines were arranged
for producing the electric light, with a view to their application
to lighthouse illumination. The armatures were 4 inches in dia-
meter, and each of them was coiled with a copper-wire conductor
280 feet long and } of an inch in diameter. The currents
were taken from the armatures by means of copper brushes rub-
bing against metal rmgs connected respectively with the ends of
the armature-couls, and were therefore in alternate directions. It
has been found that alternating currents are much better adapted
for the production of a constant electric hght at a fixed point in
space than the current which has been rectified by means of a
commutator.

The clutch, by which the armatures were connected, consisted
of two iron disks about 4 inches in diameter, having, in the face of

Mr. H. Wilde on a Property of the Magneto-electric Current. 57

me, two iron pins which could be guided into two corresponding
holes in the face of the other. These disks could be engaged or
disengaged either when the machines were at rest or in motion.
The relative positions of the pins and holes in the disks were
such that the armatures might be engaged in reversed positions
of half a revolution when required.

Each of these 4-inch machines, when making about 2000 re-
volutions per minute, was of itself capable of producing a very
efficient electric light ; and when the two armatures were clutched
together in such a position that the united positive currents
from both machines proceeded from one polar terminal simulta-
neously with the united negative currents from the other polar
terminal, the sum of the currents of the two machines was ob-
tained. On the other hand, when the armatures were clutched
together in the reverse position without any change being made
in the armature connexions, no current was produced outside the
two machines.

These experiments, besides exhibiting the necessity of syn-
chronous rotation, further showed that the armatures must also
occupy the same relative position in the magnet-cylinders in
order that the combined current from the two machines might
be obtained. It now occurred to me to see to what extent the
want of synchronism in the armatures would affect the magni-
tude of the current. The armatures were therefore unclutched
and allowed to revolve independently of each other, in the same
manner as when the attempt was made to take the combined
direct current from the commutators. After the alternating
current had been transmitted through the electric lamp for some
tine, I was surprised to find that there was no perceptible dimi-
nution in the amount of light produced from the carbon points,
and that the current would melt very nearly the same quantity
of iron wire as when the armatures were clutched together. On
examining into the circumstances attending this unexpected phe-
nomenon, I first observed that, whenever the machines were
stopped, the pins and holes in the respective disks were exactly
opposite each other, and that, while the armatures were revol-
ving, the two disks could at all times be engaged and disengaged
with the greatest facility. Moreover, even when, before starting
the machine, the disks were set a quarter or half a revolution
out of the position in which the maximum amount of current
was obtained, it was found that, after the armatures had been
revolving for a few moments, the disks resumed their normal
position with respect to each other (as indicated by the action of
the clutch) —thereby exhibiting not cnly the synchronous rota-
tion of the armatures, but also that the machines contained a
principle of self-adjustment to the position in which the maxi-

58 Mr. H. Wilde on a Property of the Magneto-electric Current.

mum effect of the combined current was obtained. It will there-
fore be evident that this property of the current, to maintain the
synchronism of the armatures, renders it unnecessary to employ
mechanical gearing of any kind for that purpose.

Proceeding further in this investigation, I found that, in order
to produce synchronous rotation, it was not at all essential that
the circuit which conveyed the combined currents for producing
the light should be completed, provided that the ends of the
coils of each armature were connected respectively with the same
metal plates which formed the polar terminals of the machines.
In this case the armatures adjusted themselves to their normal
positions even more readily than when the current was produ-
cing the light. The accompanying diagram will assist in ex-
plaining these observations moré fully.

i
ote aaa

Let D and D represent the two armature-coils, which, though
each 280 fect long, may virtually be represented by a single
turn; EE the two outer extremities of the coils, both connected
by means of the metal rings and brushes with the metal termi-
nal plate F; GG the inner extremities of the same coils, simi-
larly connected with the terminal plate H. The synchronous ro-
tation of the armatures and coils D and D, as I have said, occurs
either when the light is produced by the combined currents
transmitted from the polar terminals }' and H, or when the cir-
cuit which conveyed these combined currents is broken.

The synchronism, however, is no longer preserved when a
short circuit is made between the terminals F and H by substi-
tuting a good conductor for the carbon points, or for the long
piece of iron wire which was melted. Nor, again, was this syn-
chronism preserved when contact between the metal plate H and
one of the ends (G) of the coil was broken. In the latter case
it was observed that, whenever contact between G and H was
made and broken, a bright spark appeared at the point of dis-
junction so long as the rotation was not synchronous; but when
the synchronism was reestablished, only a trifling residual spark
was visible.

Although the synchronous rotation was preserved when the
terminals F H, from which the combined current was trans-
mitted, were disconnected from the electric lamp, yet it will be
seen, from an inspection of the diagram, that a complete metallic
circuit was in fact always formed between these terminals through

Mr. H. Wilde on a Property of the Magneto-electric Current. 59

the coils themselves. Now, when the coils D D happen to be
at the same moment in that position during their revolution in
whieh they are producing the maximum and minimum amount
of current respectively, as must often be the case where there is
no synchronism, that current which is at the maximum rushes
through the coil whichis producing the minimum current, as is
shown by the spark at the pomt where contact is broken be-
tween Gand H. The effect of this passage of the current from
one coil to the other is to accelerate or retard the rotation of the
armature (according to the direction of the current) until syn-
chronism is established.

That this influence of one coil upon the other operates in the
manner described was easily shown by the following experi-
ment :—The driving-strap of one of the armatures was removed,
so that only one of the armatures should be producing a current,
while the magnetism of the electromagnets of both machines
was, as usual, maintained to the same degree. On placing the
stationary armature with its coil ina suitable position in relation
to the magnet-cylinder for producing electromagnetic rotation,
and setting the other armature in motion, the stationary arma-
ture with its coil oscillated rapidly im ares of very small ampli-
tude, the oscillations corresponding in number with the alterna-
tions of the current. As the amplitude of the oscillations in this
experiment was limited by the vis inertze of the armature, and in
order that the effect of one pulsation only on the armature might
be observed, contact was made and broken suddenly between the
plate H and the end G of the coil by a sort of tapping motion,
when the stationary armature was suddenly jerked round nearly
a quarter of a revolution, sometimes in the direction in which it
would have been driven by the strap, and at other times in the
opposite direction, according as the alternating electrical wave
which happened to be passing at the instant of making contact
was positive or negative.

We have now seen, in the results obtained with the rotating
and stationary armatures, a cause sufficient to account for their
synchronism when revolving together,—the absence of synchro-
nism observed when the terminals F and H were bridged over
by a conductor having comparatively little or no resistance beg
occasioned by the controlling current traversing the short cireuit
established between the terminals F and H, mstead of the 280
feet of resistance presented by either of the coils when approach-
ing the neutral point of their revolution. The absence of syn-
chronism observed when the direct current was taken from the
machines by means of commutators, is caused by the direction of
the current being coimcident with that which they would receive
by induction from the electromagnets, and consequently opposite

60 Mr. H. Wilde on a Property of the Magneto-electric Current.

to that which tends to impart an accelerating or retarding im-
pulse to the armatures.

Having obtained the full effect of the combined alternating
currents from the two machines without any mechanical gearing,
it yet remained to obtain the combined direct currents from the
machines in the same manner. A pair of rings and a commu-
tator were therefore fitted upon one of the armature-spindles,
which was made sufficiently long for the purpose, and metallic
connexion was established between the rings of each machine
and the commutator on the prolongation of the armature-axis.
As the commutator necessarily revolved synchronously with the
two armatures, it was found that the combined alternating cur-
rents were rectified just as if they had proceeded from only one
machine, and were consequently available for electrodeposition,
or for any other purpose for which a direct current might be
required.

Although this property of synchronous rotation has as yet
been observed only in the case of several pairs anda triple com-
bmation of machines, yet there is no reason for supposing that
it may not be extended to any number of machines that may be
conveniently worked together from the same prime mover. It is
necessary, however, to observe that as the controlling power of
the current is only calculated to correct such minute deviations
from synchronism as it is beyond the power of mechanical skill
to prevent, the driving and driven pulleys should be respectively
as nearly as possible of the same diameters, as the correction of
any considerable difference in the number of the revolutions of
the armatures, caused by differences in the diameters of the
pulleys, must necessarily be attended by a corresponding dimi-
nution of the useful effect of the current outside the machines.

Before concluding this communication I wish to direct atten-
tion to an important property of the magneto-electric circuit
which renders the commonly accepted theory, by which the ge-
neration and propagation of the electric influence in voltaic cir-
cuits is explained, inapplicable to those circuits which are entirely
metallic. Reference to this property is all the more called for
at the present time, as I find that a want of acquaintance with
it has given rise to no small amount of misconception on the
part of several eminent mathematicians and electricians who
have examined my experiments on the electric condition of the
earth, and the method by which I have thought proper to esti-
mate the magnitude of powerful induction-currents*.

The intensity of a voltaic current, as represented by the ma-
thematical theory of Ohm, is equal to the electromotive force di-

* Philosophical Magazine, August 1868.

Mr. H. Wilde on a Property of the Magneto-electric Current. 61

vided by the internal resistance of the battery; and from this
theory it is inferred that an electromotor, in order to overcome
a great external resistance, must itself possess a correspondingly
great internal resistance. A further consequence deduced from
this theory is, that the maximum useful effect of a given electro-
motor is obtained when the external and internal resistances are
equal.

Now this mode of estimating the magnitude of an electric
current does not apply to the circuits on the armatures of my
machines. Taking for example the results obtained from the
quantity-armature of a 10-inch machine :—The dimensions of the .
coil of this armature may be represented by a bar of pure cop-
per, 67 feet long, and having a sectional area of 1°6 square inch;
so that the resistance which this circuit presents to the passage
of a current, when compared with that of the liquids in a voltaic
battery, is practically null. When the coil is in full action it
will melt 15 inches of thin iren wire *035 of an inch in dia-
meter, or the same length of 4-inch iron rod with equal certainty,
and will electrolyze acidulated water in at least 16 voltameters in
series ; so that the resistance outside the circuit, whether esti-
mated by the 15 inches of thin wire melted or by the number
of electrolyzing-cells in series, is more than a hundred times as
great as that of the coil in which the current is generated.

Moreover I have found that whenever a voltaic battery and a
magneto-electrie machine will melt an equal length of wire, the
power which these electromotors have to overcome external re-
sistance, as measured by the number of voltameters in series, is
also equal. And, generally,the power of an electromotor (whether
voltaic or magneto-electric) to overcome external resistance is
directly proportionate to the length of wire which it will melt.

From a consideration of these results, it will be seen that one
of the fundamental elements which enters into the theory of Ohm
is found wanting when that theory is applied to the estimation
of the magnitude of currents generated in circuits entirely me-
tallic.

MM. Jamin and Roger, in a recent Number of the Comptes
Rendus of the Academy of Sciences*, have also pointed out the
discrepancy here referred to in the application of Ohm’s theory
to magneto-electric circuits. Jam, however, by no means pre-
pared to admit the correctness of the views advanced by these
physicists in their endeavours to reconcile the facts observed with
established theory; besides which, other anomalies present
themselves when the customary formule are applied to magneto-
electric circuits, a consideration of which must ultimately lead

* Philosophical Magazine, October 1868.

62 Notices respecting New Books.

to the enunciation of laws much more general in their applica-
tion than those with which we are at present familiar.

Manchester.

P.S.—Since this paper was read, it has occurred to me that
a comparison might be attempted to be drawn between the con-
trolling power of the magneto-electric current over the rotations
of a number of armatures, and that of the voltaic current over
the oscillations of a number of pendulums. Beyond the fact
that synchronism is produced in both cases through the agency
of an electric current, there is no further resemblance between
the two actions. In the case of the armatures the synchronism
is produced by the mutual action of several rotating bodies upon
one another, or by the dominant influence of several bodies upon
one; whereas in the case of the pendulums the synchronism of
the system is produced by the influence of one body alone upon
several. Again, the synchronism of a number of pendulums is
only accomplished by the skilful adaptation of means to an end,
while the synchronous rotation of a number of armatures is a
phenomenon which exhibits itself without the exercise of any
ingenuity whatever; and, so far as I have studied this peculiar
electromechanical action, no amount of mgenuity can produce
the synchronous rotation of the armatures by means of the vel-
taic current, as magneto-electric currents and circuits seem ab-
solutely essential to the attainment of this result.

IX. Notices respecting New Books.

A Manual of Elementary Chemistry, Theoretical and Practical. By
GrorcE Fowness, F.R.S., late Professor of Practical Chemistry
in University College, London. ‘Tenth Edition, London, Churchill:
1868. (Pp. xxviii & 1020.)

The Elements of Heat and of Non-metallic Chemistry. specially
designed for Candidates for the Matriculation Pass Examination of
the University of London. By Frepuricx Guturiz, B.A. (Lond.),
PhD. F.RS.E., F.CS., late Professor of Chemistry and Physics,
Royal College, Mauritius. London, Van Voorst: 1868. (Pp. x
& 210.)

1S different chemical manuals which appear from time to time
seem to be written from two distinct points of view—the author
desiring either to display some original mode of considering his sub-
ject, or to make an average statement of the chemical knowledge
which is accepted, ina given year, as useful to the student. Manuals
of the former class are, from their nature, not very frequently
written; while those belonging to the latter constitute the great
majority of such publications. ‘To each kind a special merit apper-

Notices respecting New Books. 63

tains; but while the one has the narrower limit of an individual
effort, it is included in the other, which hands down to the historian
the general character of a time.

The present edition of Fownes’s ‘ Manual of Chemistry’ has the
curious property of blending both these distinctions. It does this
by adhering to the design of the late Professor Fownes, which, if
interpreted from the first edition and preface, was to lead to the prin-
ciples of chemistry by an inductive ascent, and convey as complete
an impression of the entire range of the science as could fairly be
expected. Hence we find a special place allotted to the analytical
characteristics of the elementary bodies, brief notices of laboratory
operations, of higher researches, of the relations of chemistry to —
physics and biology. Such a plan was not then a novelty abroad ;
but no students’ book of this kind had, so far as we are aware, ap-
peared in this country. The sale of nine editions in twenty-four
years, and the almost universal approval of English teachers, are
gratifying proofs both of the value of the original conception and of
the manner in which it has been carried out at subsequent intervals.

Though succeeding editions have thus been invariably prepared
upon the primitive model, the progress of science has made con-
siderable readjustments and amendments necessary to them; and
the influence of all the great ideas which have arisen in chemistry
since 1844 may be readily observed here at the appropriate epoch.
But, unfortunately, in this process the modest octavo of less than six
hundred pages has so far overgrown as to contain at present more
than a thousand. We cannot help thinking that some part of this
growth is excessive, and that means might be taken to repress it with
advantage. The physical introduction, for example, is no longer jus-
tifiable, when physics is beginning to be taught (even in elementary
schools) by a distinct official, or asa distinct subject from chemistry.
If that were omitted, about one-eighth of the entire volume (or one
hundred and twenty-five pages) would be removed, referring to sub-
jects which, as their very able writer occasionally admits, cannot be
satisfactorily treated in so smalla compass. For the electricity and
crystallography afterwards described, and occupying about thirty
pages, the student might also be referred to other and appropriate
quarters. Most of the Tables, too, at the end of the book are usu-
ally sought for in larger works, and seldom noticed in their present
position. An additional reason for this curtailment is to be found in
the increased length of the sections which are devoted to chemistry
proper. On account of the growing attention which is now paid to
inorganic chemistry, there is much fresh matter to summarize and
record in that department. Still, the number of those who pur-
sue organic research preponderates ; and it is here consequently that
we notice the greatest enlargement in the size of the manual.

The best mode of treating the multitudinous detail which the
science continues to produce is a point upon which chemists either
doubt or disagree. ‘The philosopher laments a dreary desert of facts
fruitless and even dangerous for want of law; the teacher bewails
each serious trifle that he is compelled to read, as adding only to the

64 Notices respecting New Books.

dust and effort of his pilgrimage. It is to be hoped that something
may be done in the next decade to disencumber chemistry of the in-
convenience and reproach of want of generalization. Meanwhile,
however, a contrivance which has been frequently resorted to of late
years has a certain temporary value; we allude to the statement of
general formule for series of bodies, followed by the particular de-
scription of the constituent members. ‘This is the method pursued
in the organic part of the work now before us, and adds much to its
clearness of exposition ; but it is impossible to avoid feeling that
there is a great deal of matter given which the average student never
reads and never will be called upon to read with advantage. ‘There
is scarcely a single group of substances of whose individuals it is
desirable or necessary for him’ to know more than a few; and an
excess of information has the demerit of making chemistry positively
less accessible to him. Accordingly the removal or abridgment of
one or several paragraphs in the description of the various series
would, in our opinion, render Fownes’s manual a much more useful
aid to learning. ‘lhe inorganic part, though of course admitting of
very little seriation, would obviously allow of considerable curtail-_
ment of a like nature.

The chapter on the General Principles of Chemical Philosophy has
been very carefully rewritten, and is as compact and lucid an ex-
pression of the prevailing views as could be desired. The reader’s
attention is frequently called to such matters in connexion with
special instances which subsequently occur; and, in the organic sec-
tion more particularly, characteristic reactions of groups are pointed
out with exemplary copiousness and accuracy. Such is the case
under ‘‘Alcohols,’”’ ‘‘Aldehydes,”’ ‘‘ Ketones,” &c. The manner in
which this task is performed is one of the best criterions by which to
estimate the value of a manual, and the care and talent of its writer ;
for here he is performing his highest duty, namely, developing the
idea of a chemical function. We do not remember any book of the
kind where that duty has been so well fulfilled as in the present
instance.

Among the novelties in this edition we notice Erlenmeyer’s judi-
cious definition of an equivalent (a definition which did not appear
too early), with the consequent division of the elements into “‘ mono-
genic and polygenic.’’ The primary classification of the elements is
of course based on their “ equivalence or atomicity ;’’ but the secon-
dary classification seems to have been made on the natural-history
principle. The nomenclature employed in this manual partakes
quite appropriately of both of the existing usages; so that we find
such names as ‘‘ sodium phosphate” (taken from the mode advocated
by Harcourt and Roscoe) and ‘‘ ferric chloride ” (from the far pre-
ferable Berzelian nomenclature lately revived by Williamson).

Fownes’s manual undoubtedly owes its success in recent times
chiefly to its representative character, which has rendered it, perhaps,
the most popular and useful cf its class. On no other occasion has
the editorial work been better executed than in the present edition,
which contains a large amount both of new matter and fresh arrange-

Royal Society. 65

ment. We shall not, we trust, be deemed to exceed our legitimate
province when we say that, while the entire volume has received
admirable supervision from both of the gentlemen to whose care it
nas been entrusted, most of the labour has fallen to the share of Mr.
Watts, a chemist whose long experience and high literary ability
have conferred on the work a completeness and finish it could not
otherwise have possessed. The result of his attention is a faithful
portrait of modern dogmatic chemistry. Hereafter (when dynamical
theory shall have displaced or greatly modified the atomic and other
statical speculations.) we may look upon this picture with regret, but
its truth we shallnever be ableto deny. The science is a prisoner in
the enchanted castle of the Absolute, and still awaits some knight
to rescue and deliver her.

The object of Professor Guthrie’s little book is sufficiently evident
from its titlepage, and does not call fora lengthy notice on our part.
The writer’s aim has been to produce a students’ manual which shall
** contain all (and but little more than all) that is required” for the
chemical branch of the Matriculation Pass Examination of the Uni-
versity of London. We have already commented upon the associa-
tion of physical with chemical subjects in the same volume, and can-
not but believe that, at no distant date, the subject of Heat will be
placed in its true position among the subjects selected for that ex-
amination by the Senate. That it is not so placed at present, con-
stitutes, however, Professor Guthrie’s justification for the course he
has pursued. The work itself is concise, decided, and clear. The
nomenclature (“chloride of silver,” ‘‘ carbonate of calcium,” &c.) in
the chemical part is open to objection as not being sufficiently mo-
dern; and the mode of calculation under ‘‘ Expansion” (§ 18) in
the physical part might undoubtedly have been simplified. But
these blemishes do not seriously affect the general character of the
manual, which, as we have said, possesses the characteristics which
are most valued in such publications.

X. Proceedings of Learned Societies.

ROYAL SOCIETY.
(Continued from vol. xxxvi. p. 394.]
June 18, 1868.—Lieut.-General Sabine, President, in the Chair.

r Paes following communications were read :—

«An Account of certam Experiments on Aneroid Barometers,
made at Kew Observatory, at the expense of the Meteorological
Committee.” By B. Stewart.

In judging of the value of an instrument such as an aneroid, it is
not the mere extent of difference between its indications and those of

Phil, Mag. 8. 4. Vol. 37. No. 246. Jan. 1869. F

65 Royal Society :-—

a standard barometer that ought to guide us, but it is rather the
constancy of its indications under the various circumstances to which
it may be subjected that determines its value.

An aneroid may differ from a standard barometer at the ordinary
pressure, and to a greater extent at other pressures; but, provided
these differences can be well ascertained and remain constant,
such an instrument ovght to be regarded as valuable, just as much
as a chronometer of known constancy, but of which the rate is
wrong.

The circumstances which may be supposed to affect the indica-
tions of an aneroid may be classed under three heads, namely :—

(1) Time.
(2) ‘Temperature.
(3) Sudden variations of pressure.

(1) Time.—Of the influence of time I am not able to say much ;
Captain Henry Toynbee has allowed me to examine the various read-
ings of an aneroid which he carried about with him ,for many
years in his voyages, and constantly compared with a standard
barometer.

This aneroid (which I shall call No. 1) was between 4 and 5 inches
in diameter, and was compensated for temperature.

In July 1860, as compared with a standard barometer, it read 0°025
in. too low. In September 1862 it read (at the same temperature)
about 0°012 in. too low; while in March 1864 (still at the same
temperature) it read about 0°020 in. too low.

This instrument, which was well cared for, and which, being used
chiefly on the surface of the ocean, was subjected neither to a very
great nor to a very sudden change of pressure, must be allowed to
have retained its character with great constancy.

This is the only definite information regarding the effect of time
on these instruments which I have received.

(2) Temperature.—A good aneroid is generally compensated by
its maker for the effects of temperature; and the question to be in-
vestigated is, to what extent such compensations are trustworthy. I
record the results (obtained at the Kew Observatory) of subjecting
six aneroids, each 43 inches in diameter, made by two different
makers, to a very considerable range of temperature.

Mr. B. Stewart on certain Haperiments on Aneroid Barometers. 67

NGLof Correction at

instru-

me econ! | OH peo | 88°F goo
ae —"105 | —"135 | —‘140 | —*145 | —"145
2. —"055 | —‘o9o | —"o95 | —‘095 | —‘I00
4. —'095 | —"095 | —‘095 | —‘o80 | —*o60
5 —"r06 | —"106 | —‘111 | —‘1Ir | —‘1II
6 —"Ior | —‘11zr | —‘1r1r | —*106 | —*106
7 Se Oe OOM ec OOK a "OOMm || .O41F

These results are, on the whole, very satisfactory, and appear to
show that a well-made compensated instrument has its indications
comparatively little affected by a very considerable temperature-
change.

- It ought always to be borne in mind that an aneroid is not capable
of being read to the same accuracy as a standard barometer, and that
the ;1, of an inch is a very small quantity. These temperature ex-
periments were made at the ordinary atmospheric pressure.

I am unable to say what effect a change of temperature would
have at a diminished pressure.

(3) Sudden changes of pressure.—A preliminary investigation,
made at the request of Mr. De La Rue, into the behaviour of an
aneroid belonging to the Italian Government, seemed to show con-
siderable error at low pressures. For the purpose of investigating
the influence of sudden changes of pressure upon the indications of
aneroids, I then applied to some of the best known makers of these
instruments, for the loan of several, and through their courtesy in
lending mea sufficient number, and for a sufficiently long time, I have
been enabled to investigate this influence at some length.

In the following experiments the instruments were, to begin with,
suspended vertically, at the usual atmospheric pressure. They were
tapped before being read. The pressure was then lowered an inch,
and the instrument allowed to remain ten minutes at this pressure
before being read, after having again been well tapped.

The pressure was thus reduced an inch every time, being allowed
to remain ten minutes at each stage ; the instrument was always well
tapped before being read, by means of an arrangement contrived for
this purpose by Mr. R. Beckley. The exhaustion was carried down-
wards to 19 inches in the case of those instruments in which the
scale was sufficiently great, and the instrument was allowed to remain
an hour and a half at its lowest pressure; the air was then admitted
an inch at a time, the previous arrangement as to time and tapping

_ being followed.
F 2

Royal Society

68

MOU ‘SY

Surpeed oy} Jnq : opeul jou sv WOTsNeYXe B10Foq vAnssod

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d ATeuIpIO oY} 4B 1OA1004 OY]} UL UOIJLAdesgoO o[SUIS ¥B s}uOUTItedxe esoyy Ut APJUO}toApeUT x

sem oanssdid Sty} yea

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‘Logt qsnsny|soyour V) Sr | “x
“Logt aung|‘soyoursb| “br | o
‘Logit . Ajng|‘soyour z| -€x iS
“Logit Ajnplsoyour Z| *zr oe
"Logt Ayng|soyour’e| sr1 a
‘Logt oung\'soyoutrz| -or | —
Logt = fynglperay puz| °6 fe
“Logt Ane Tey put] °g a0)
"Logi sung|soyour sh) 6 i
“Loge ting |'soyour <b) *g ©
a
————_—. om
|
Sie des 5 lea S
“Logr oun |" =f, a
49 flsoyour z| *Z41 | 6
“49gr oung)seqourgz) -gt | re
4ogr ysnsny|soyout >| “Sr S
r49gr oung) soyout Sh) “rr S
rZogr Alnplsoyout z| “fr |S
rZogr Aynelseyout z| ‘zr | 7
‘Logt Ajnglsoyour%z| “11 | ©
rZogt oun) soqourez|) ‘or
‘Logr = Ayng|pery puz| °6
“Logi = ATne|"Te114y puz| *g
‘Logit aung|sayourSy) °6
‘Logit ounp|soyour ft) °g

“plod
-dUue
Jo'on

|

“IZ10

This Table may be bett

hes)—that is to say, by correcting each instru-
We thus obtain

inc

gs, and by supposing each aneroid right to start with

Mr. B. Stewart on certain Experiments on Aneroid Barometers. 69
y, right at 29

ment for index-error.

down readin

(sa

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|

‘soyout 6z 4e yysia posoddns “Ty epqey, Jo sprosouy oY} JO Sduipvat UMO(T Of} LOZ UOTJOOIIO_

‘T] Fav,

70

Royal Society :-—

If now we separate the results of Table II. into two sets, one com-
prising large (4 to 43 inch) aneroids and the other small instruments,
we snali find the mean down correction for large aneroids to be as

follows.

Mean correction for
largeaneroids, gra-
duated to 1 @) lal, 5

ee ee oe oe

23 in.

29 in.| 28 in,| 27 in. 26 in.) 25 in.
"00 "00 |-+'02 |+°03 |-+'04
©O |—‘O2 |-+."02 |-+°03 |+-"04

24 in.| 23 in.

|+-04|+"07
+:08|+ ‘10

22 in.| 21 in.| 20 in,

+11 |+°14 {+19

In like manner we shall find for small aneroids, supposed right at 29
inches, the following mean correction :—

Mean correction for
smallaneroids,gra-
duated to1gin. ..

ee ese 08 ee

29 1N./ 28 in.] 27 in.| 26 1n.| 25 in.
<©O |=-°0r |4>"02 |--"03 |-- 707
‘oo |+:03}-+'07 |+-12 |+°16

241n.

= Oy
+20

2.3 in.| 22 in.

+"09 |-- "12

aay

21in.|20in

+17 4°25

It will be seen that there are two instances in which the same
instrument has been twice experimented on.
mean of the two experiments represents the true correction for eac
of these instruments, we find :—

ee

No. 8.
Mean correction,
deduced from two

experiments ....

Mean minus first
determination

29 1n. | 28 in.| 27 in.| 26 in.
"00 |—"or |-+ 02 |+°%o2
"00 |-+ ‘or }+-02 |+-02

In like manner :—

24.1n.

Assuming that the

2.3 1:

+1i

+-o1r

22 “sl 21 in 201

$15 |+'18 |+'2

+’or)j+’or |+-o1

IN@; Ge
Mean of two ex-
periments ..

Mean minus first.
determination

7108

29 in. |28 in.| 27 in.
“00 |+ "OI |-+ "02 |-+-03
700 |+:'or /+:02 |-+--02

| --*o2

20in

°O2

Mr. B. Stewart on certain Experiments on Aneroid Barometers. 71

We see from these results, if aneroids, right to begin with, be:
subjected to a decrease of pressure similar to that to which they were
subjected in these experiments :—

(1) That a well-constructed large aneroid will not go far wrong
down to 24 inches ; but after that pressure its reading will be consi-
derably lower than that of a standard barometer, so that a large
positive correction will have to be applied.

(2) That small aneroids are less trustworthy than large ones, and
probably cannot be trusted below 26 inches.

(3) That if previous experiments are made upon an aneroid, we
are enabled by this means to obtain a table of corrections which,
when applied to future observations with the same instrument, will .
most probably present us with a much better result than had we not
verified our instrument at all, and that by this means we may use
our instrument down to 19 inches with very good results.

Let us now consider the up readings of these instruments, and let
us Suppose that each instrument is right to begin with—that is to
say, while remaining an hour and a half at its lowest reading.

These corrections and up readings are exhibited in the following

Table :—

Tas._e III.

Correction for the up readings of the aneroids of Table I. supposed right |

T ;
No. of with standard at lowest reading.

ane-
roid. to
19 in.|20 in.

| | | {
20 lee in.|23 in./24 in.}25 in.|26 in.|27 1n./28 in./29 1n.{30 in. |
"00 ~|+°03|+°03 Sok +05 |+'02 |+'o1 |—"03 (tO On | ae |—-18 |
"oo «|+'05 |+°06 |+°06 |-++04 |+'06 |+°06 |+°05 |+'05 | +01 |—"02 |—‘o2
"eo |+°02|/+"01] ‘co |-+:ce2/—'or |—-03 |—"06 |—"11 |—"15 |—"16 |—"19
"00 {+ °03 |+°03 |—‘o1 |-+°01 |+"02 +02 |+'04 Tole) — "OR |—/06 —'o6
‘OO "00 | +°03 | +04. |+'03 |-+'07 |-+'05 |+°02| ‘oo|—'o5 |—‘o8$ |—"11

8

Y)

8

9

10

rie

12 —
13. | 700 |+°05}-+°05 |+°06 |+-°05 |+-°05 |+ "05 | +05 |
14. ih Nae BK Mate —
15

16

17

(OGM O4))||— "02 | "OO |-—"O2 |—"as |—"06)|—" 11 | —"14|—"19)|— "16 |— "14
"00 «|+ "or |—*o2 |—*o2 |—"11 |—*12 | —"12 |— "14 |—"21 |—"20 | —"24 | —"26
aCe Oia —aonn | ——— 14.

OO | -7OO Na e ft Rare if o7 503) | 02

"00 | —"o1 |—°06 |—°06 |—-08 |—"og | — ‘06 | —‘08

"00 | "02 |-+°03| ‘co |—*03 |—*04 |—*07 —-06 |

°OO)|-- "OL |—"021|—"o4, |— "11 | —" 59) |——-2.5 | — "38

Hence we find the mean up correction for large aneroids :-—

Ig 1M.) 201.) 271.) 22 1N.| 23 1n. ZG pUn cS) in.| 26 in. 27 in. 28 1n.! 29 10.) 30 1n.

_ —|}

Supposedright
at Ig in.....| ‘oo |+°03 |+'03 |-+°03 |+'03|++'02 |4+"o1| ‘00 |—-03 |—"06 |—-08 |—"11

See, 2A. 1s... Sc ae - 50 "00 |-+- "04 |-+-°03 | °03 |-4-"o1 |—"o1 |—o2 —H OR

72 : . Reyal Society :—

Tn like manner for small aneroids we have the following result :—

|
|

|
. . . . . . °

Ig in.| 20in.] 21 in.| 22 in.) 23 in.| 24. in.| 25 in.) 26 in.) 27 in.| 28 in.| 29 in. 30 in.
Right atIgin. ..| ‘oo | ‘oo |+ ‘01 |-+’02 |—"o1 |—-o1 |—*02 |—-o4 |—"07 |—"10 |—"15 |—"16
!
‘Rizht at 23in. .-| .. 46 - * "oo |-+'o1| ‘co|—‘o2 |—"07 |—"11 |—*12 |—"19

As before, there are two instances in which the same instrument was
twiee tried ; assuming the mean of the two trials to represent the truth, we

find—
1g in.| 20in.) 21 in| 22 in. 23 in.| 24 in. 25 In. 26 in.| 27 in.| 28 in.| 29 in.| 30 in
Besa * a ea =| = a 2|\24 ee 24S sat a
No. 8.
Mean correction..| ‘oo |+*o2 }+:02}+'02) +703) ‘co —’ol |—*o4 |—*07 |—"I1|—"12 ;—"18
Mean minus first | | | |
determination ..| ‘oo |—-‘o1r|—‘o1 |—‘03 —‘o2 |—‘02 |—‘o2 |—"o1 |—"03 |—"03 |—"o1| -00
In like manner—
19 in.| 201n.| 21 in./ 22 in| 23 in./ 24 im.| 25 In.| 26 in.| 27 in. 28 in| 29 in.| 30 in
Sees =| = = = =| ae —e Ee Ee si
|
No. 9.
Mean correction..| ‘oo |+°04|+°04 |-++'03 |+°03 | +°04 | +04 |+"04 |--°02 |—"or |—"04 |—"04
Mean minus first |
determination ..| ‘oo |—‘o1 |—‘o2 |—‘03 |—‘o1 |—-°02 |— ‘02 |—-o1r |—"03 |-—-"02 |—‘o2 |—-o2

We may learn from these results, if aneroids which have been
subjected for at least one hour and a half to the lowest pressures
which they register have the pressure increased by means of the
gradual introduction of air into the receiver (after the manner already
described) :—

(1) That a well-constructed large aneroid will not go far wrong for
about 8 inches above the lowest pressure.

(2) That in this respect small aneroids are somewhat less trust-
worthy than large ones.

(3) That if the mstrument read be sneonely tested and its cor-
rections ascertained, we may consider it trustworthy (making use of
these corrections) for up readings throughout a greater range than
if it had not been so tested.

I come now to consider whether a rapid change of pressure affects
an anercid after the experiment has been completed.

The following Table will exhibit the results obtained in this ee
tion :—

Mz. B. Stewart on certain Experiments on Aneroid Barometers. 73

Taste IV.
ist Ex.)1st Ex.|2nd Ex. 2nd Ex.
3. 9. Sr |) 9: IO. IY, 12. 13. 14.
Correction before
experiment .| —"10o | —"12 | —"13 | —"0g | —"32 | —*11 | —"13 | —*47 | —"04
Immediately after |
experiment co | +°03 | +:06 +707 | +706 | —'03 "oo | —"19 | +706
18 hours after ex-
periment paomerstat SHE or) WW eezeyl, pia der — 10) |'—"07 | —°34) | --°o1
48 hours after ex-
periment .. .| —'08 | —'04 | —'03 —°37
3 days after ex-
periment ...... =—Oo) |) O05 eu
3 weeks after ex-
periment ...... =") |) Sess | oe | — II —"O7 |

It thus appears that if an instrument reads correctly before it is
put into the receiver it will read too low immediately afterwards,
and that it may be some considerable time before it recovers its pre-
vious reading. ‘The instrument cannot, therefore, be safely trusted
for absolute determinations if it has been recently exposed to rapid
changes of pressure.

The experiments hitherto recorded, in which an inch of pressure
has been taken away or added every ten minutes, are perhaps analo-
gous to ascents in a balloon, or descents from a mountain; they are
not, however, precisely analogous to mountain-ascents, since a longer
time than 10 minutes is usually taken to produce a change of pressure
equal to 1 inch.

. At the suggestion of Mr. Charles Brooke, a couple of aneroids
were tested in April 1868, with the view of rendering the experiment
more analogous toa mountain-ascent.

The pressure was reduced by half an inch at a time and at inter-
vals of 30 minutes, the aneroids being well tapped.

The following corrections were obtained for down readings (instru-
ments supposed right at 30 inches).

TABLE V.

| At No. 8 No. 9. At No. 8. | No. 9. |

| inches | inches.

bee ‘co CO 23°95 | +08 | —-o02
29°5 ere) = 04 23 +11 Og
29 ele) — ley 22°5 mele On
28°5 Tele) S18 22 Scie "00
28 "00 aan 21°5 +:16 +02
275 *20 8S A 25 aie +°04
27 S646 a Sulipee 2On5 +20 +°06
26°5 "00 OD eel aaa +'22 +'07
26 a —— opal +°25 +°'c9
Ze +04 OF, 49 +:27 +'11
25 Oy — "04 |

hacer +:06 —"'o2 |

bene +°05 "or || |

ste
‘ 10)
Un

74 Royal Sectety.

These results, when compared with the previous determinations for
these same instruments, would seem to show that a somewhat better
result is obtained when the exhaustion is carried on more slowly, and
hence that the corrections depend, to a considerable extent, on the
nature of the treatment received. No. 8 seems to be more constant
under different treatment than No. 9.

From all these experiments we may perhaps conclude as follows :—

(1) A good aneroid of large size may be corrected for temperature,
by an optician, so that the residual correction shall be very small.

(2a) If an anercid correct to commence with be used for a bal-
loon- or mountain-ascent, it will be tolerably correct for a decrease of
about 6 inches of pressure.

(2) A large aneroid is more likely to be correct than a small one.

(2 y) The range of correctness of an instrument used for mountain-
ascents may be imereased by a previous verification, a table of cor-
rections being thus obtained.

(3a) Ifan aneroid have remained some time at the top of a moun-
tain, and be supposed correct to start with, then it will give good
results for about 8 inches of increase of pressure.

(33) A large aneroid is more likely to be correct than a small one.

(3y) If the aneroid has been previously verified, it is likely to give
a better result.

(4) After being subjected to sudden changes of pressure, the zero
of an aneroid gradually changes ; so that under such circumstances it
ought only to be used as a differential and not as an absolute instru-
ment—that is to say, used to determine the distance ascended, making
it correct to begin with, or to ascertain the distance descended, ma-
king it correct to begin with—it being understood that the instrument
ought to be quiescent for some time before the change of pressure is
made.

Before concluding I ought to mention that most of the experi-
ments herein described were undertaken and executed in a very careful

manner by Mr. T. W. Baker.

“On an Easy Method of measuring approximately the Intensity
of Total Daylight.” By Roger J. Wright, Esq.

An easy method by which the amount of light may be at any time
measured and registered appears to be still wanting. I would sug-
gest the following plan, by which | believe the desired object may
be attained.

A Bisa rod of solid metal, terminated by a heavy base, which
keeps the rod in a perpendicular position. CD is a hollow tube,
blackened inside, of such a diameter as exactly to fit and side over
AB. The extremity, B, of the rod AB is painted of a snowy white,
with a jet-black spot in the centre, as shown in the figure. On AB
is marked the scale, beginning with zero at A. The tube is pushed
over the rod till the extremity C coincides with the zero line at A.

The method of using this instrument is as follows:— Draw the
tube gently up the rod, at the same time looking steadily at the
black spot before mentioned. It will be found, as the tube ascends,

Intelligence and M gee unEnes Articles. fo

- that the black spot will gr “gaits disappear, and ultimately vanish
in the gloom ; it will also ‘be found that on different days, and differ-

woe B
on | Fil iH

SC mw Jem

ent hours of the same day, the point at which the black spot vanishes
will vary with the intensity of the light. This point is read off on
the graduated scale, and thus we are enabled to measure the inten-
sity of the light at any required time. In taking an observation, it
would be well to state whether that portion of sky round the zenith
from which the cone of rays proceeds be clear or cloudy.

It will be seen that the result obtained by this method is not sczen-
tifically correct, as it will be affected by the eyesight of the person
who makes the observation, but only in a slight degree. The me-
thod of measuring light, as just described, has been known to me for
upwards of three years. The hope that I should some day be en-
abled to make the instrument scientifically correct has hitherto pre-
vented me from making it public. As I understand that it is highly
desirable to have some means of estimating the changes in the light
which will occur during the total eclipse of the sun in August next,
I no longer feel justified in keeping in the background an instrument
which may possibly be of some slight assistance.

XI. Intelligence and Miscellaneous Articles.

ON THE DISPERSIVE POWER OF GASES AND VAPOURS.
BY M. CROULLEBOIS.

ae measurement of the dispersive power of gases, which has long

been obscurely foreseen, has not yet been supplied by any phy-
sicist by the aid of a convenient and accurate experimental method.
The illustrious mathematician Cauchy, in the month of August
1836, even sent to the Academy a memoir which concluded, as a
necessary consequence of his able theory of light, that this dispersion
had no existence. Arago announced that in this there was an error
of fact, and he promised to publish a memoir on this subject con-
taining numerous delicate measurements; but this memoir never
appeared, and it has not been met with in his papers. We are lost
in conjectures as to the method employed by this illustrious physicist
to measure the dispersion of colours in elastic fluids. Doubtless

76 Intelligence and Miscellaneous Articles.

Arago had no absolute confidence in the measurements obtained by
his then method, and sought a more delicate process for the obser-
vation of such delicate phenomena than the one he had used. This
opinion gains in plausibility when we consider that it was by a sub-
sequent discovery that he became possessed of a method of observa-
tion (that of interference) which has never been equalled in delicacy.
I have been able to apply this process to the measuring the dis-
persive power of gases by two different methods. In both cases the
interference-fringes were produced by means of M. Billet’s seimi-
lenses.

first method.—When the ordinary apparatus are used for produ-
cing fringes, the experimenter finds that the determination of the dis-
persion is impossible if, working with white light, a central zone is
discriminated, in reference to which everything is symmetrical, and
which can be sighted. The number of fringes becomes considerable
when a decidedly homogeneous light is used; a central region is no
longer distinguished ; the fringes of the system resemble each other ;
every point of comparison has disappeared, and we no longer know
which of the fringes to stop at on the cross wires of the telescope.
To measure dispersion it is necessary, therefore, to obtain with ho-
mogeneous light a system of fringes limited in number—a condition
which has been realized by very simply modifying the semilenses.

To reduce the number of fringes, we cover by any suitable method
(by a small plate or by the removal of the interposed tubes) the in-
terior edges of the semilenses. (A lens which, cut, has undergone a
loss of matter produces this result in a third manner. ) Then the
part which is in common, instead of extending indefinitely, may
become defined, and the region which succeeds ‘ie plane of the maxi-
mum of the fringes may terminate in only giving one fringe, as
takes place in the region preceding this plane of the maximum.
But to observe these fringes the lens alone cannot be employed ;
the screen of ground glass must be used, through which they are
viewed. ‘This was Fresnel’s old method. ‘lo compensate the retar-
dation, I used M. Billet’s compensator, graduated for each colour
by a very simple method, which consists in determining for each of
them the zero of the instrument, which is variable.

Two differential tubes containing dry gases were placed in front
of the semilenses, behind a collimating lens which had the slit for
focus.

In a special memoir I shall publish the numerous precautions to
be taken in the arrangement of the apparatus. In the case of air,
the two tubes were filled with dry air under the same pressure, and
the air in one of the tubes was gradually rarefied. It was merely
necessary to measure (1) the pressures H and H’ of the gases,
(2) the temperature, (38) the graduation of the compensator.

For one of the colours investigated the index of the gas was given

by the formula
Noma [14 100 REED E DS a

Intelligence and Miscellaneous Articles. Vif

E is the common length of the tubes. N may be known for every
temperature and under every pressure. For other gases than air
one of the tubes was filled with dry air, the other with the gas to
be investigated; the index of this latter was given by the formula

Nyaa / 14s ™{ xs—14 Baten, }

We must know ¢, H, m; m is positive or negative according as the
gas to be investigated is more or less refracting than air.

To have a colour of a known wave-length, a pure spectrum was
produced, and one of the three lines C, E, G was made to fall on
the slit which illuminated the apparatus.

Second method.—The idea of this method was suggested by the
consideration of the formula (1).

In fact, let us conceive an arrangement of apparatus by which we
can measure for each value of \ the number of fringes removed corre-
sponding to the ditference H—H’ of the pressures in the two tubes.

The difference of pressure is measured by a kind of voluminometer;
and while the mercury fiows out as the elastic force of the gas in one
of the tubes diminishes, the experimenter counts the number of
fringes removed. In this method, singularly enough, the compen-
sator has but a secondary part, and most frequently its use may
even be suppressed.

These two methods, which were intended to control each other,

have given the same results. It will moreover be understood that
the first method admits of numerous means of verification.
- Vapours.—These two methods of experimentation may be applied
to vapours. I had intended to apply these methods to all those
whose elastic forces are furnished by M. Regnault’s Tables. But
time and sunlight having failed me, my investigations im this direc-
tion could only be extended to bisulphide of carbon, to ether, and
chloride of ethyle; and as the results obtained with these two latter
compounds seem to leave something to be desired, I shall not adduce
them here.

Gases.
1. Air.—Index of white light : 1:0092944.
inc O) aera ot eeNio— A OOO ioe
Termes Wee seta Papuite eee sa (ac Ne—1-0003042.
TnerGoe erg gu cis eet Ne M0008 157.

The dispersion is therefore
Ng—Nr=9'0000115; Ng—Nc=0:'0000582.
2. Carbonic Acid.—Index of white light : 1:000449.

lines Repeat te e NG=1- 000895.
letives Ein tent(o haere es, a N= 1000456.
Heiney Gases eee ses oo NG= 1000496:

78 Tatelligence and Miscellaneous Articles.

The dispersion therefore 1s
Ne—Ne=0:000014 ; Neg—Nc=0'000115.

3. Oxygen.—Mean index : 10002719.

Nc=1:000255 ; N,=3°000294; Ng=1°000300.

4. Hydrogen.—Mean index : 1:000138.

No=1:000129; Ne=1:000140; Ng=1-000153.
5. Nitrogen.—Mean index : 1:0003019.
Nop=1:000258; Nz=1:000302; Ng=1:000321.

6. Chlorine.-—Mean index : 1:000774.

No=1-000699 ; Ne=1:000792; Ng=1-000840.

7. Cyanogen.— Mean index : 1:000829*.

No=1-000804 ; N,=1:000834; Ng=1:000895.
8. Sulphuretted Hydrogen.—Mean index : 1:000639.
No=1°000599; N,=1:000647; N.=1°000691.
9. Ammonia.—Mean index : 1:000390.
N,=1:000374; N,=1°000399; N.=1°600444.
10. Carbonie Oxide.—Mean index : 1:000344.
N,=1-000301 ; Ne=1:000350; Ng=1:000391.
11. Olefiant Gas.—Mean index: 1:000669.
N,=1'000652; N,=1°000694; Ng=1-000702.
12. Marsh-gas.— Mean index : 1000449.
No =1°000412; N,z=1°000471; Ng=1'000502.
Vapours.
Bisulphide of Carbon.—Mear index : 1:001592.
Nce=1:°001489 ; N,=1:001609 ; Ng=1:001795.
The dispersion is
Ng—Nco=0'000306 ; Ne—N,=0'000186.

It will be remembered that M. Le Roux has recently found that
through the vapour of iodine the spectrum is reversed. I propose
to ascertain whether the dichroism noticed by M. Le Roux is met
with in the vapour of bromine ; but this investigation presents diffi-
culties, and requires a knowledge of physical constants which have
not yet been determined.

The subject of these researches, which tends to fill up a void in
science, was suggested to me in the laboratory of investigation in
the Sorbonne by Professor Jamin. Ihave been fortunate enough to
be able to execute them in the physical laboratory of the Faculty of
Sciences at Dijon, and under the eyes of Professor Billet, who has

aided me by his advice, which is so valuable to all who are engaged
in optical researches.— Comptes Rendus, October 5, 1868.

* We find for this gas an appreciable difference between Dulong’s num-
ber and that which we have obtained.

Intelligence and Miscelianeous Articles. 79

ON THE GENERATION OF OZONE IN OXYGEN AND IN AIR UNDER
THE IN¥LUENCE OF THER CONDENSED ELECTRICAL SPARK. BY
MM. L’HOTE AND ST.-EDME.

Some time ago Mr. Ladd devised an electrical condenser which he
proposed as capable of producing large quantities of ozone by elec-
trifying oxygen. ‘This apparatus consists of a wooden box 14 by 7
inches by 13 inch, inside which are six glass plates coated inside
with tinfoil, arranged so that the spark furnished by an induction coil
whose poles are connected with the two extreme plates sweeps by
condensation all the intermediate spaces. Itis known that oxygen
which traverses Ladd’s apparatus at the moment of discharge ac- |
quires a powerfulodourof ozone; hence the inventor has proposed the
use of the apparatus for injecting electrified oxygen into the ventilation
passages of large buildings—amphitheatres, hospitals, theatres, &c.

The interest attaching to such a producer of ozone has increased
since General Morin called attention to the utility which the addition
of suitable quantities of ozone in ventilation might have as a de-
stroyer of miasmata.

MM. Becquerel and Fremy have determined the proportion of
ozone which the electric spark produces when it strikes directly be-
tween two platinum wires fused in a glass tube full of pure oxygen.
Tt is also known that under these circumstances the air becomes
charged with nitrous products; but we are quite ignorant of the
extent to which a spark from a powerful induction-coil, striking in
a cascade condenser like Ladd’s apparatus, modifies the gas in con-
tact with its multifold surfaces.

We began by arranging Ladd’s apparatus so that it could rigo-
rously retain the pressure of the gas to be investigated, and then we
estimated the proportion of ozone formed in equal volumes of oxygen
and air circulating with the same velocities in the condensing-appa-
ratus, and under the influence of a spark of the same force (20 to 25
centims. in air).

It has been established that the modified gas (oxygen or air) does
not attack tin. Solution of iodide of potassium is immediately
attacked in both cases; silver is oxidized. It is difficult to ob-
serve any difference between the odours of oxygen and of air.

The measurements were made in the following manner :—The
gas emerging from the condenser passed through a Will’s apparatus
containing a pipette of sulphuric acid in which was 0:061 grm. of
monohydrated acid, to which was added a cubic centimetre of solution
of neutral iodide of potassium containing 0'1 gr. of iodide. ‘The quan-
tity of ozone was determined alkalimetrically from the proportion of
potash formed. The following are the results obtained :—

(1) The oxygen which passes into the condenser is pure and dry.
Six estimations gave for 10 litres of gas the proportions of ozone—

milligrammes. milugrammes.
28°77 26°3
29:0 16°8
26°9 15°9

In other experiments the odorant gas was collected, on emerging
» from the condenser, m a small gasometer containing distilled water.

80 Intelligence and Miscellaneous Artteles.

For 10 litres of odorant gas the proportions of ozone found were—

milligrammes.
36°00
3°90
9:00
(2) The same experiments made in air prove that no nitrous com-
pounds are formed in the atmosphere which emerges from Ladd’s
condenser.
The proportion of ozone formed is less than with pure oxygen.
For 10 litres the numbers found are—
miligrammes.

38

2°7

The successive diminution in the numbers quoted is due to the
decrease in the intensity of the electrical source, since the results of
experiments made near each other are almost identical. In a subse-
quent research we shall give the relation which may exist between
the degree of ozonization of the atmosphere and the length of the
spark. We can even now Say that the discharge of a coil far smaller
than that used for the above experiments (producing a spark of 3 cen-
tims. instead of 20) communicatesalmostasstrong an odour to the gas.

This point is the more interesting to clear up, since experiments
prove that this condenser is a continuous source of ozone for air tra-
versing it; and since this air does not become charged with any trace of
nitrous compounds, the detrimental influence of which on the organs
of respiration is well known, this czonized atmosphere, therefore,
would not be at all injurious if it were introduced by ventilation.

We propose to decide by other experiments how far the difference
of chemical activity may extend which at present seems to exist be-
tween the direct spark and that of condensation.— Comptes Rendus,
September 21, 1868.

NEW METHOD OF ESTIMATING MINUTE TRACES OF METALS, SPE-
CIALLY DESIGNED FOR WATER-ANALYSIS. BY J. ALFRED
WANKLYN, PROFESSOR OF CHEMISTRY IN THE LONDON INSTI-
TUTION, AND ERNEST THEOPRON CHAPMAN.

In the concluding chapter of our short treatise on water-analysis,
we made mention of the possibility of the presence of very minute
quantities of metals in drinking-water exercising a considerable in-
fluence on the health of the community. A method of detecting
and measuring these minute traces of metals was wanted. We are
now able to supply the want.

Availing ourselves of the circumstance that sulphuretted hydrogen
does not precipitate, but simply colours avery dilute solution of cer-
tain metals (the depth of coloration following the quantity of metal
present in the solution), we have devised and practised a method of
titration which is for certain metals much what the Nessler-titration
is for ammonia. In this way we have measured the amount of lead
in a specimen of Manchester water.

The practical details of the process, together with examples, will
be published on a future occasion. ,

THE
LONDON, EDINBURGH, ann DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

‘FOURTH SERIES.]

FEBRUARY 1869.

XII. Remarks on Affinty. By M. Dumas*.

HAT is the force which causes simple substances to unite

with other simple substances to form compounds—acids

with bases to form salts, quicklime with water to form slaked
lime, carbon to burn in air, iron to become covered with rust ?

This force we do not know. We are merely aware that it is
only exerted when bodies are in apparent contact, that it be-
comes inappreciable when the distance of the bodies is appreci-
able, that, although the mass of bodies may come into play in
the phenomena which it produces, their nature exerts the pre-
ponderating action. We designate it as affinity.

I do not propose to retrace here the history of affinity since the
first appearance of this word in the doctrines of chemistry, now
more than two centuries ago. I have explained elsewhere the
successive interpretations which have been given toit by Barchu-
sen, who first used it, Boerhaave, who fixed the meaning, Geof-
froy, who thought he had discovered the laws, and Berthollet, who
did really formulate them for a great number of phenomena.

I should even not have allowed myself to place before the
Academy this fragment borrowed from the exposition of the last
researches of French chemists, if, in order to show their import,
I had not been led to place them in parallel with the principles
established by Newton at the close of the long researches to
which he devoted himself to account for the nature of chemical
reactions.

* Translated from the Comptes Rendus, September 21, 1868.
Phil. Mag. 8. 4. Vol. 37. No. 247. Feb. 1869. G

82 M. Dumas’s Remarks on Affinity.

But having, for my own part, been led to pay homage to the ~
power and accuracy of his chemical knowledge, it seemed to me
that at the moment in which they have been brought to the atten-
tion of scientific men by our illustrious dean, when he communi-
cated to the Academy his very interesting philosophical studies,
I might anticipate by a few weeks a publication in which they
play an important part.

Newton, it is known, had made numerous chemical experiments
which have been jost. The conclusions which he had drawn
from them have been summed up by himself. They served as
basis for the chemical doctrine. of Bergmann and for that of
Buffon, who, by a premature use of Newton’s principles, have not
a little contributed to prevent chemists from according to them
the respect they merit. Thus the name of Newton has disap-
peared from treatises on chemistry; and I think, with M. Chevreul
as well as M. Trouessart, that it ought to be restored, as he
was the first to comprehend the nature of affinity.

Lavoisier, contemporary with Buffon, but more reserved with
regard to a subject with whose difficulties he was better ac-
quainted, never expressed himself definitely on the subject of
affinity. He even considered this branch of science too high
for the reach of the chemists of his time; and he recommended
them, before busying themselves with it, to settle on a solid basis
the elements of chemistry, in the same manner, says he, that we
fix with certainty the principles of elementary geometry before
approaching the difficulties of the higher geometry.

Lavoisier, therefore, postponing the investigation of the force
which pr oduces chemical phenomena, had concentrated his atten-
tion on the part which ponderable matter plays. He had doubt-
less considered the heat disengaged or absorbed in the reactions
of bodies a fundamental phenomenon, the measurement of which
was as necessary for their explanation as the determination of the
weights of the substances employed and of the substances ob-
tained ; but we do not see that he regarded this heat as an ex-
pr ession of the chemical force.

Ponderable matter, heat, molecular attraction are the three
terms to which Therneteien had recourse, and with which he con-
tented himself for the explanation of chemical phenomena. He
meusured most exactly and delicately matter and heat in their
displacements. He left attraction on one side as a notion inac-
cessible to experiment, and as only pviving rise in his time to use-
less hypotheses.

_ Lavoisier, then, had assumed chemical attraction, affinity, but
had not endeavoured to explain it. In that respect he agreed
with Newton. This great man, almost a century before, enun-
ciated in the followitie terms the result of his labours and his

M. Dumas’s Remarks on Affinity. 83

reflections on chemical phenomena, showing by the accuracy of
his details and the depth of bis views that the humble practical
investigations of the laboratory were as familiar to him as the
most elevated conceptions of celestial mechanics* :—

“ Have not the small particles of bodies certain powers, virtues
or forces by which they act at a distance not only upon the rays of
light for reflecting, refracting, and inflecting them, but also upon
one another for producing a great part of the phenomena of
nature? Tor it is well known that bodies act upon one another
by the attractions of gravity, magnetism, and electricity; and.
these instances show the tenour and course of nature, and make
it not improbable but that there may be more attractive powers
than these. For Nature is very consonant and conformable to
herself. How these attractions may be performed | do not here
consider.

“ What I call attraction may be performed by impulse, or by
some other means unknown to me. I use that word here to
signify in general any force by which bodies tend towards one
another, whatsoever be the cause. For we must learn from the
phenomena of Nature what bodies attract one another and what
are the laws and properties of the attraction, before we inquire
the cause by which the attraction is performed.

“The attractions of gravity, magnetism, and electricity reach
to very sensible distances, and so have been observed by vulgar
eyes; and there may be others which reach to so small distances
as hitherto escaped observation; and perhaps electrical attrac-
tion may reach to such small distances even without being ex-
cited by friction.”

Newton explains by this attraction the property which certain
salts possess of absorbing water from the air, and the difficulty of
separating this water from them by heat ; he also thus explains the
absorption of aqueous vapour by sulphuric acid, and the heat
developed by mixing this acid with water :—

““When spirit of vitriol poured upon common salt or saltpetre
makes an ebullition with the salt and unites with it, and in dis-
tillation the spirit of the common salt or saltpetre comes over
much easier than it would do before, and the acid part of the
vitriol stays behind, does not this argue that the fixed alkali of
the salt attracts the acid spirit of the vitriol more strongly than
its own spirit, and not being able to hold them both, lets go
its own ?

* [As M. Dumas does not mention whence he has taken Newton’s
statements, the passages in the text are taken from the ‘ Optics,’ Book III.
(vol. iv. p. 242 et seq. of Horsley’s edition of Newton). In some rases M.
Dumas appears to have summed up in his own language Newton’s views.
Where it could be done without undue length the corresponding original
passage has been given.— EDs. |

G2

84: M. Dumas’s Remarks on Affinity.

** When salt of tartar per diliquium (potash) being poured into
the solution of any metal precipitates the metal and makes it
fall down to the bottom of the liquor in the shape of mud, does
not this argue that the acid particles are attracted more strongly
by the salt of tartar than by the metal, and by the stronger
attraction go from the metal to the salt of tartar? And so when
a solution of iron in aqua fortis dissolves the lapis calaminaris
and lets go the iron, or a solution of copper dissolves iron im-
mersed in it and lets go the copper, or a solution of silver dissolves
copper and lets go silver, or a solution of mercury in aquafortis
being poured upon iron, copper, tin, or lead dissolves the metal
and lets go the mercury, does not this argue that the acid par-
ticles of the aqua fortis are attracted more strongly ky the lapis
calaminaris than by iron, and more strongly by iron than copper,
and more strongly by copper than by silver, and more strongly
Ey mon copper, tin, or lead than by mercury?”

. And when metals corroded with a little acid turn into
rust, alneh | is an earth tasteless and indissolvable in water, and
this earth imbibed with more acid becomes a metallic salt, and
when some stones, as spar of lead, dissolved in proper men-
struums become salts, do not these things show that salts are
dry earth and watery acid united by attraction, and that the
earth will not become a salt without so much acid as makes it
dissolvable in water.”

I think that no chemist contemporary with Newton had such
just and sound notions of chemistry as are summed up in these
lines. It is doubtful whether any one at that time understood
their force and import.

We may then regard the following considerations of Newton
not as vain hypotheses, but as the fruit of a very advanced expe-
rience, of long and substantial studies :—

“‘ Now the small particles of matter may cohere by the strong-
est attractions and compose bigger particles of weaker virtue ;
and many of these may cohere and form bigger particles whose
virtue is still weaker; and so on for divers successions, until the
progression end in the biggest particles, on which the operations
in chemistry and the colours of natural bodies depend, and
which by adhering compose bodies of a sensible magnitude.

“If the body is compact and bends or yields to pression with-
out any sliding of its parts, it is hard and elastic, returning to its
figure with a force rising from the mutual attraction of its parts.
If the parts slide upon one another, the body is malleable or soft ;
if they slide easily and are of a fit size to be agitated by heat,
and the heat is big enough to keep them in agitation, the body
is fuid; and if it be apt to stick to thingsit is humid; and the
drops of every fluid affect a round figure by the mutual attrac-

M. Dumas’s Remarks on Affinity. 85

tion of their parts, as the globe of the earth and sea affects a
round figure by the mutual attraction of its parts by gravity.

“Since metals dissolved in acids attract but a small quantity
of the acid, their attractive force can reach but to a small dis-
tance from them. And as in algebra, where affirmative quanti-
ties vanish and cease there negative ones begin, so in mechanics,
where attraction ceases, there a repulsive virtue ought to succeed.
And thus Nature will be very conformable to herself and very
simple, performing all the great motions of the heavenly bodies
by the attraction of gravitation which intercedes these bodies,
and almost all the small ones of their particles by some other
attractive and repelling power which intercedes the particles.

“There are in nature agents capable of uniting the particles
of bodies, and it is the province of experimental - philosophy to
discover these agents.”

Newton proceeds: —‘‘All these things being considered, it seems
probable to me that God in the beginning formed matter in
solid, massy, hard, impenetrable, moveable particles, of such sizes
and figures and with such other properties and in such propor-
tion to space as most conduced to the end for which he formed
them ; and that these primitive particles being solids, are incom-
parably harder than any porous bodies compounded of them,
even so very hard as never to wear or break in pieces.”

In the same way that it would be difficult to define molecular
attraction (to which chemical affinity is referred) better than New-
ton did, im like manner the definition which he gives of atoms
would even now be the best introduction to the statement of the
ideas which it 1s possible to form of the atoms of modern che-
mistry, which are identical with the particles which he calls pri-
migenal, Chemists of the present time elude, it is true, the dif-
ficulty by leaving in vagueness whatever concerns the nature of
affinity or that of atoms. They thus obey their praiseworthy
habits of mind, preferring to pass over in silence subjects on which
certainty cannot be obtained. ‘This reserve, however, is not
without inconvenience ; for those commencing the study of che-
mistry naturally attempt to supply the silence of their masters
on these subjects, the only ones which the beginner can attack
in the absence of laboratories, and when he is not led to fix all his
attention on.the details of experiments and the management of
apparatus. It is unnecessary to add that they go astray, and
that one of the principal obstacles to the diffusion of sound prin-
ciples in chemistry arises probably from the ignorance in which
the beginner is left as to the nature of the forces at work, and on
that of the atoms it is concerned with.

“Tt seems to me further,” adds Newton, “ that these particles
have not only a vis znerti@ accompanied with such passive laws

86 M. Dumas’s Remarks on Affinity.

of motion as naturally result from that force, but also that they
are moved by certain active principles, such as is that of gravity,
and that which causes fermentation and the cohesion of bodies.”

I will conclude these quotations by a few lines in which New-
ton states the true philosophy of science :—

“To tell us that every species of things is endowed with an
occult specific quality, by which it acts and produces manifest
effects, 1s to tell us nothing ; but to derive two or three general
principles of motion from phenomena, and afterwards to tell us
how the properties and actions of all corporeal things follow from
those manifest principles, would be a great step in philosophy,
though the causes of those things were not yet discovered; and
therefore I scruple not to propose the principles of motion above
mentioned, they being of very general extent, and leave their
causes to be found out.”

Without solving the question propounded by Newton, Ber-
thollet subsequently discovered one at any rate of the general
principles of motion, the application of which to the fundamental
reactions of salts upon each other, of acids and of bases on salts,
constitutes what are known as Berthollet’s laws.

If, for instance, we mix nitrate of lime and sulphate of soda,
both in aqueous solution, sulphate of lime is deposited and ni-
trate of soda remains in solution.

Berthollet justly ascribes the exchange of the base and of the
acid which has taken place, not to more energetic affinities, but
to the deficient solubility of sulphate of lime. He shows that, in
general, when two saline solutions are mixed, and one of the
four salts capable of being formed is insoluble, this one is formed,
deposited, and thus determines the production of the corre-
sponding complementary salt.

Berthollet assigns the greater cohesion of the insoluble salt
as the cause which dCi eriines its formation; but if we en-
deavour to define by what signs he ascertains whether the cohe-
sion of a salt is greater or less, we are forced to accept solubility
and insolubility themselves as the only indications of the weak-
ness or the intensity of the cohesion. Thus, in the statement of
Berthoilet’s laws, we have long been content to say that, in the
mixture of two saline solutions, if the possible insoluble salt is
formed and is deposited it is because it 1s insoluble.

Ihave shown, however, that Newton with wonderful precision
had indicated the greater or less force of union of the parts as
one of the determining causes of fluidity or of fixity; for what
Berthollet calls cohesion consists really in a diminution of volume,
in an increase of density, as my investigations on atomic vo--
lumes prove.

If, for instance, we compare magnesia, lime, strontia, and

M. Dumas’s Remarks on Affinity. 87

baryta as regards their combinations with sulphuric acid, we find
that the condensation of the elements increases from sulphate of
magnesia to sulphate of baryta. It is least in sulphate of mag-
nesia, that of these four sulphates which water dissolves easily ; it
is greatest in sulphate of baryta, which is quite insoluble.

In this respect all soluble sulphates are comparable to sul-
phate of magnesia; sulphate of lead, which is insoluble, resem-
bles, on the contrary, sulphate of baryta.

The same relation is observed between chloride of silver, calo-
mel, chloride of lead, and corrosive sublimate. The condensa-
tion of the elements is greatest in the first of these bodies, which
is the most insoluble, and least in the last, which is most soluble.

Todide of silver is more condensed than bromide, and this,
again, than the chloride of the same metal—which agrees with
their respective solubilities in liquid ammonia.

In the case of an acid soluble in water, the salts which it
forms with bases, for the same state of saturation, are the more
soluble the less the acid is removed from its primordial condition
—that is, the weaker the condensation; and they are less so-
luble the stronger it is.

The phenomena of double decomposition are always deter-
mined by the production of the most condensed compound and
by its precipitation.

Thus a greater force of union: between the parts, the measure
of which is their approximation (that is, their condensation), is
a sign of insolubility, as Newton foresaw, a proof of increase in
cohesion and a cause of double decomposition, as Berthollet
taught.

But why is this condensation greater in the sulphates of baryta
and lead, and less in the sulphates of magnesia and of copper?
Why are the phosphates generally insoluble, while all the ni-
trates and all the acetates are soluble? We do not know; and
if, to answer such questions, it 1s not, perhaps, necessary to arrive
at an absolute knowledge of the nature of affinity, we must at
any rate penetrate more deeply into its laws.

Lavoisier never stated fully his opinion on the subject of affi-
nity. Newton wished, before mvestigating its nature, to make
a thorough investigation of the laws which it obeys. But the
restricted point of view chosen by these two great men gave place
at the beginning of this century to a new point of view. They
each of them compared chemical or molecular attraction to ge-
neral attraction; Davy, Cirsted, Ampere, Berzelius, our col-
league M. Becquerel, and their imitators endeavoured to connect
it specially with electrical attractions, or even to identify it with
these forces.

An electrochemical theory which could account for the effects

88 M. Dumas’s Remarks on Affinity.

of affinity would have seemed impossible so long as statical elec-
tricity alone was known to physicists; but Volta’s discovery and
the investigation of the properties of dynamical electricity opened
out a new path. It seemed natural to suppose, for example, that
there was a close connexion, for instance, between the force of the
spark which determines the combinaticn of oxygen and hydrogen
in the formation of water, and that of the battery which, effecting
in silence and without intermission the decomposition of this
liquid, transfers hydrogen to the negative and oxygen to the
positive pole.

Reversing the decomposing mode of action of the pile, should
we not obtain the most natural representation of the attractive
force which unites the elements of water?

Davy was the first to endeavour to give by means of electricity
an explanation of the permanent effects due to chemical attrac-
tion, and of the transitory phenomena which accompany the com-
bination of bodies. He supposed that at the contact of an acid
and a base their particles become charged withcontrary electricities,
and that at the moment of combination these electricities suddenly
reunite. The compound formed, the light or the heat developed
at the moment of combination are readily explained on this hy-
pothesis. Davy supposes, then, that it is attraction which unites
the particles of bodies, but that placing in contact sulphur and
copper, for instance, they take opposite electrical conditions,
that by heating them the electrical tensions are increased, that,
lastly, the two electrical fluids acquire so high a tension that
they attract one another and unite, producing heat and light,
while the sulphur and the copper, being approximated by this
contact, remain united by the attraction and thus form sulphuret
of copper.

Ampere, modifying this hypothesis, regards the atoms as
being endowed with an electricity of their own, and as being
surrounded by an electrical atmosphere of the opposite kind.
These electrical atmospheres, when they neutralize one another,
produce heat and light; the electricities peculiar to the atoms
produce the combination by their mutual action. Ampére has
thus no need to bring into play general attraction; he refers to
the operation of a single force both the transient and permanent
phenomena of chemical action. But Ampére would willingly
have sought in electricity the cause of universal attraction itself.

Berzelius, finally, regards the molecules as being not merely
electrified but polarized.

These various conceptions have had only one single practical
consequence. Davy, convinced that the force which united the
elements of compound bodies was of electrical origin, concluded
that, by opposing to the electricity of combination the electricity

M. Dumas’s Remarks on Affinity. 89

of decomposition furnished by the battery, ail bodies might be
analyzed. Increasing, therefore, the voltaic power at his disposal,
he succeeded in isolating the metals of the alkalies, those of the
earths, boron, and silicon.

Since this great event electrochemical theories have taught
nothing which could at all guide chemists either as to the nature
of affinity, or the laws which regulate its influence in the forma-
tion or in the destruction of bodies.

It has been simply proved that every chemical action is ac-
companied by a movement of electricity, and that every con-.
ducting chemical compound may be disjoined when it is placed
between the two poles of a battery. The metals are always libe-
rated at the negative, and the oxygen at the positive pole, and
other substances at one or the other pole, according to the nature
of the compounds in which they are engaged.

When two bodies combine, electricity is disengaged ; and when
two bodies separate, electricity is absorbed.

How much electricity is produced when two bodies combine?
How much is consumed in the separation of the same bodies ?
These two questions have been attentively examined; the disco-
veries of Faraday and of M. Edmond Becquerel on this important
point, as well as Favre’s researches in the same direction, have
thrown a new light on them by defining in a precise manner
electrical equivalents, but they have not furnished chemists with
a doctrine of affinity.

Having perceived that the hope of representing affinity in
its cause and in its effects as a purely electrical action was not
realized, and led to no practical conception, I returned, in the
last course which I had the honour of giving at the Faculty of
Sciences, to the following point of view.

Accepting affinity as a fact, I proved:—(1) that combination
seemed possible only in case the bodies placed in juxtaposition
would disengage heat in acting on each other, but that in pro-
portion as the combination became more complicated the heat
disengaged became less; (2) that in order to separate com-
bined substances, the heat must be restored which they had lost
in combining.

Thus, taking as an example the formation and destruction of
alum, I compared the following facts :—

Potassium and oxygen = potash ie a

j Brisk heat and

bright light.

Sulphur and oxygen = sulphurous | Hee edaleise.
or sulphuric acid) -. . -: e

Aluminium and oxygen = alumina

90 M. Dumas’s Remarks on Affinity.

Potash and sulphuric acid = sul-
phate of potash. . . .
Alumina and sulphuric acid = sul- Heat.
phate of alumina
Sulphate of potash and sulphate of Lite Ps
alumina = alum .
Alum and water = crystallized Ob fecble nate

iui Me ae ea eae

Heat.

Beyond this term combination becomes impossible, as we
know ; and crystallized alum appears the last product which can
be realized with this order of compounds.

Conversely :—

Crystallized alum heated to 120° becomes anhydrous.

Anhydrous alum heated to redness is converted into sulphu-
rous acid, oxygen, alumina, sulphate of potash.

Sulphurous acid, sulphate of potash, and alumina, when raised
to extreme temperatures, are themselves converted into oxygen,
sulphur, potassium, and aluminium.

The elements which combine lose heat. Therefore the ele-
ments of a chemical compound which separate must be raised
to a temperature which is higher the greater the heat they have
emitted in combining.

Heat being regarded as motion, combination would consist in
a diminution of this motion; it would cease to be possible when
the molecules of the compound had no more heat to lose.

Whatever be the manner in which this heat intervenes in the
formation and destruction of chemical compounds, we must see
in it the sum and the expression of all the forces put in play in
the successive production of the various agglomerates of a com-
pound, or for their disaggregation. And it was with a grand
perception of the true nature of chemical phenomena that La-
voisier in his equations placed heat in the same rank as matter,
and that he attached such great importance to the calorimetrical
investigations which so long occupied him.

The extension which M. Regnault has given them, as regards
specific heats, and that which they have received from M. Favre
in all that concerns the disengagement of heat at the moment
of combination, prepare chemistry for passing from the epoch
in which it only considered matter to that in which it will take
force into consideration.

The new researches to which the mechanical theory of heat
has given rise have recalled the attention of chemists to the me-
chanical theory of heat stated by Jules Robert Meyer. This
profound physicist considers chemical phenomena due to an
attractive force which precipitates atoms against each other.

M. Dumas’s Remarks on Affinity. 91

Their shock at the moment of contact would produce heat, light,
electricity. The union of atoms once produced, in order to se-
parate these, molecular forces must intervene capable of separa-
ting them and carrying them to the limit at which attraction, be-
coming null or even negative, would cease to act or be changed
into repulsion.

Thus we are led to the simple views of Newton and of Lavoisier.
Chemical combination takes place between ponderable bodies ;
the permanent cffects are due to attraction; its transitory
effects are due to the losses of motion which the atoms experi-
ence at the moment of their union.

However, general attraction being admitted as a necessary
and sufficient representation of the force which determines che-
mical combinations, are we not led to efface the line of sepa-
ration which has been assumed to exist between cohesion and
affinity? Is it not convenient to see one and the same force
varying its effects in the three states of aggregation—cohesion,
solution, and chemical combination ?

Not that we should confound them ; for, their first cause being
the same, it would be none the less indispensable to modify its
application in these three circumstances, each of them having its
own distinct and persistent character. Just as it would always be
necessary to distinguish between general and molecular attrac-
tion, it would be none the less necessary to maintain the dis-
tinction between the three forms of molecular attraction. Ihave
no doubt that, if once we knew the cause of affinity itself, we
should recognize in its mode of acting on bodies well-marked
modifications, as M. Chevreul long ago suggested.

Yet, if chemical action, the force of solution, and cohesion are
mere modifications of general attraction, if they do not consti-
tute so many special and distinct forces, ought we not to expect
that the affinity of chemists more profoundly investigated would
lose its special character, become more mechanical, approach
little by little first its two congeners, and finally planetary at-
traction itself ?

But cohesion and the force of solution, resembling in this re-
spect general attraction, form continuous phenomena ; the atomic
theory, on the contrary, ranges affinity amongst discontinuous
phenomena.

Berthollet, guided doubtless in this respect by Laplace, him-
self familiar with Newton’s philosophy, maintained for a long
time, as we know, that bodies can combine in all proportions.
He would willingly have applied to chemical phenomena, and
to the forces which determine them, Linneus’s axiom, Natura
non facit saltus, which is true of organized beings; and if his
opinion had been confirmed, affinity would have been attached
more closely to cohesion and general attraction.

92 M. Dumas’s Remarks on Affinity.

Proust, who maintained the contrary, succeeded in establishing
his view. Dalton’s atomic theory, soon confirmed by Gay-Lus-
sac’s laws of gaseous combination, by Wollaston’s experiments
on salts in various degrees of saturation, by Berzelius’s immense
researches, and especially by the simple and constant ratios which
he pointed out, in salts of the same acid and in the same state
of saturation, between the oxygen of the base and that of the
acid—all these striking events have powerfully contributed to
lead chemists to continue to regard affinity as having a character
of its own and as having almost nothing to borrow from general
attraction ; for, in fact, what links are to be established between
general attraction (acting directly as the masses and inversely
as the square of the distance, obeying without discontinuity
all changes in mass, all changes in distance) and chemical
affinity ?

Viewed with regard to masses, affinity does not admit that
combination can neither be effected below a certain minimum
nor above acertain maximum. Between these two extreme limits
the atomic theory, confirmed in this respect by the universal ex-
perience of chemists, just as little allows that combinations may
be indefinitely multiplied ; far from that, it limits the number,
and only admits those which are represented by atoms united in
simple ratios, represented by whole numbers, as 1:1, 1:2, 2:3,
DO

If it be true that the experiments of MM. Marignac and De-
bray have rendered certain the existence of compounds formed
in accordance with more complex ratios, even in mineral che-
mistry, still nothing indicates that their formation takes place
according to a law of continuity, and that in this respect they
disaccord with the fundamental principle of the atomic theory.

Thus the reciprocal action exerted by the atoms of bodies,
attractive at inappreciable distances, less so as they separate,
becoming zero, or even repulsive when the sign is changed—
this, according to Newton, is the most faithful image of affinity.

But to make the effects agree with the incontestable results on
which the atomic theory is founded, we must add, with Newton,
that the figure of the atoms should be taken into consideration.
It is not difficult to understand, in fact, that the action exerted
by the peculiarities in the shape of the atoms may limit the pro-
duction of their compounds, and restrict them to uniting in
simple ratios expressed by whole numbers.

Ampérein his youth had proposed to the chemists of his time
a doctrine of chemical combination which both appealed to the
principles of the Newtonian attraction and the laws of erystallo-
graphy: it excited but little interest ; it represented neither the
absolute ideas of affinity as then understood, nor the ideas of
chemical dualism as the interpreters of Lavoisier understcod it,

M. Dumas’s Remarks on Affinity. 93

or at any rate those who, giving to his nomenclature all the
force of a doctrine, had seen, in the creation of a language made
to aid the memory by logic, a real representation of the intimate
constitution of compound bodies.

Such, in fact, is the power of the forms of language, that it is
necessary to make an effort over one’s self to understand that in
an oxide or in a sulphuret, for instance, it may be that the
metal is not the body overcome, conquered, subordinated, and
that oxygen and sulphur are not the dominant bodies. In the
same way in salts. The French nomenclature, irreproachable
so far, that it limits itself to making known the nature of bodies
united to form a compound, has never attempted to define the
arrangement they affect in the combination once it is formed.
To give it this meaning is to falsify it and destroy its real use.

The French nomenclature was intended to interpret a natural
classification. It first discriminated elements and compound
bodies. In the latter it has formed genera, and characterized
species. ‘The genera have been defined by the element common
to all the species—oxygen for oxides, sulphur for sulphurets,
carbonic and nitric acids for carbonates or nitrates; the species
by the substance which forms the complement of the com-
pound :—oxide of iron, of zinc; sulphuret of lead, of silver ; car-
bonate of lime, nitrate of potash.

The French chemists have proceeded as naturalists; and as
they created a new language, they have been able to make the
names of the genera singularly significant by varying the ter-
minations.

But there is nothing, either in this new language or in the
interesting exposition of it in which Lavoisier has laid down its
origin and its principles, to indicate that on his part and that of
his co-workers there was any other object than that which has
been mentioned—to range together compounds which have an
element in common, to indicate what substances enter into each
combination, and in what proportion. The idea of a molecular
arrangement, of an intimate constitution, of the compound was
never entertained.

At the present time we should be disposed to admit that the
theory of chemical combination proposed by Ampere agrees best
with the general laws of mechanics, for it depends upon uni-
versal attraction—and with the special laws of chemistry, for it
brings in as the determining and characteristic element of the
constitution of bodies the shape of their molecules, which would
contain at least four atoms each where they are tetrahedral, and
as many as fifty atoms for other solids.

It would be unjust to omit the mention of M. Gaudin’s name
by the side of that of Ampére. The efforts of this ingenious

94, M. Dumas’s Remarks on Affinity.

philosopher, whatever idea be entertained on the subject of their
import and of their future, have had at any rate this result,
that they have led chemists to take into account certain laws of
symmetry in arranging the formule of compound bodies. The
eee based on them, proposed by M. Gaudin forty years

go, have been confirmed by experiment; they have paved the
oe for the rearrangement of the formule of all compounds of
carbon or of silicon—that is to say, of all compounds of organic
origin, and of almost all those the investigation of which cousti-
tutes mineralogy properly so called.

The absolute defence of dualism retained no partisans after
the last struggles which Berzelius maintained with singular bril-
hancy towards the end of his life in the interest of this doctrine.

It is to be observed that the electrochemical theory, regarding
the elements of bodies as obeying the two electrical forces, and
the materials of every compound as uniting in twos to form by
successive agglomerations, and always two by two, gradually
more complicated combinations, proceeded in harmony with
the French nomenclature. It is not, therefore, surprising that
the use of the molecular system proposed by Ampére, modified
by M. Gaudin, and generally adopted with divers variations by
the chemists who, being occupied with organic chemistry, are
obliged to take account of the phenomena of substitution, has
both rendered less ardent the pursuit of a precise electroche-
mical theory, and less confident the too absolute interpretation
of the French nomenclature.

We are thus led to conclude that, on the one hand, the search
for an electrical theory of affinity now occupies but few—although
beautiful and useful applications of electro-chemistry have been
accomplished of late years, and are pursued with great success;
on the other hand, that it is no longer possible to represent by
means of the dualistic nomenclature the multitudinous che-
mical compounds which the molecular system registers daily.

We are thus more and more led towards the experimental in-
vestigation of chemical types as a basis of the classification of
compounds, apart from any hypothesis on the internal arrange-
ment of their elements,—which constitutes the true foundation of
the French nomenclature properly understood.

At the same time we are led towards the idea which attri-
butes to the molecules of compound bodies a more complex con-
stitution than would be derived from the binary nomenclature,
and which makes of them planetary or crystallographical systems
presenting sev eral centres of force—mobile in the first case, fixed
in the second.

We finally revert to the thought which would directly connect
affinity with universal attraction.

M. Dumas’s Remarks on Affinity. 95

In recent times the views of Newton have met with an unex-
pected and remarkable support in the beautiful and important
researches which our eminent colleague M. Henri St.-Claire De-
ville has devoted to the phenomenon of dissociation—one of the
greatest acquisitions, not only of chemistry, but of natural phi-
losophy.

Nothing, in fact, is more in accordance with the laws of me-
chanics than to say that a volatile liquid placed in connexion with
a free space fills it with its vapour, and that the tension of this
increases or decreases regularly in a continuous manner accord-
ing as the temperature rises or falls. |

But to say that carbonic acid separates from lime in the same
manner, to establish that there is a tension of decomposition
analogous to the tension of vapours, and that the evaporation of
a liquid and the decomposition of a carbonate take place in virtue
of the same laws, and present the same phenomenon of continuity,
is to connect chemical combination with cohesion, is to prove
that under certain conditions the laws which regulate the aggre-
gation or the separation of molecules of the same kind are also
applicable in the case ur molecules of different kinds.

Without affirming that in all cases the dissociation of com-
pounds presents the character of a continuous phenomenon, it is
enough that the case is frequent (as is proved by the researches
of our eminent compeer and those of his pupils), to justify our
assimilating the purely physical molecular separations and the
chemical molecular separations, and to give us the right hence-
forth to unite cohesion and affinity the one to the other, and
both to universal attraction.

It follows from this brief summary :—

(1) That Newton gave of chemical affinity a notion to which
nothing has been added, when he connected it with general
attraction and showed how, at acertain distance from the centres
of molecular action, it may become zero, or even repulsive.

(2) That Ampére has given the complement to this view by
showing that the shape of the components limits the number of
combinations which two elements may produce, and that it de-
termines the ratios according to which they may unite, and even
enables us to predict the ready replacement of one element in a
complex molecule by another without its stability being com-
promised.

(3) That Meyer has shown how the impact of molecules,
striking against each other with extreme velocity to produce
combination, may give rise to the phenomena of heat, of light,
and of electricity which accompany chemical action.

(4) That M. Henri St.-Claire Deville, in discovering the ca-
pital phenomenon of dissociation, has opened a new way to science

96 M. Dumas’s Remarks on Affinity.

by closely connecting chemical combinations with the purely phy-
sical phenomenon of the formation of vapour.

(5) Finally, that the doctrines with the aid of which it has been
attempted to explain chemical phenomena by a distinct unknown
cause, or by electricity, have yielded no fruit ; while those which
tend to bring it under the laws of universal attraction consoli-
date themselves, approach more and more to the facts, and indi-
cate better and better the path of progress.

It would then be natural, just, and useful that Newton’s
name, and the definitions he gives, both of molecular attraction
and of chemical atoms, should be retained in works imtended for
instruction in chemistry. In my opinion (but I give it with all
the reserve which such subjects demand), heat is the real measure
of chemical energy, while light and electricity may for the pre-
sent be regarded by the chemist either as agents of which he
makes use, or as phenomena whose appearance he ascertains.

Matter and heat would still be, as in Lavoisier’s time, the de-
finition of the two objects to which the thoughts of chemists
should especially be directed.

The time will doubtless come when, the laws which molecular
attraction obeys being themselves known, we shall be able to
predict or explain the formation of compounds, their destruc-
tion, the preferences and the choice of elements in the formation
of combinations, the special affections which acids or bases exhibit
in the production of salts; but before attacking this last and
difficult problem, we must know otherwise than by suppositiens
the bond which connects the shape of the crystals of one chemical
species with the arrangement of the atoms the grouping of which
constitutes the molecules which are the materials of these
crystals.

I hope the Academy will pardon my having so long occupied
it with these historical considerations, and that it will understand
the interests attached to them.

My object would be attained if, on the one hand, I had con-
tributed still more vividly to direct the attention of chemists to the
relations which connect the motions of heat with the transfor-
mations of matter, and if, on-the other, I had shown that the
principle of the French nomenclature is not unsuited to the
classng and naming the compounds of organic or molecular
chemistry.

Lavoisier, in proposing the new nomenclature, stated that the
Commission, of which he was the eloquent organ, “ had been un-
willing to devote itself to great discussions on the constituent
principles of bodies and on their elementary molecules—that it
had severed itself from the systematizing chemists, who are always
ready to accompany facts by an apparatus of reasoning in which

On the Heating of a Disk by rapid rotation in vacuo. 97

the fact itself disappears, and in whose hands science becomes
an edifice raised by their imagination.”

He declared, finally, that the Commission “had sought to ap-
ply to chemistry the logic which belongs to all sciences—the
name of class or genus recalling, in the natural order of ideas,
properties common to a great number of individuals, and that of
species properties peculiar to certain individuals.”

I do not know whether I am deceiving myself; but it seems to
me, moreover, that this duel of antagonist molecules which is
met with in all the phenomena of chemistry, and which the pre- —
sent nomenclature expresses so well, remains incontestable, and
that we should not give up depicting it until we are forced to do
so. But the act of combination once accomplished, the duel ter-
minated, the French nomenclature does not pretend to say that
the two bodies which have acted on each other have retained their
distinctive character in the molecule formed and are not con-
founded in a complex system. It is in this respect that Berze-
lius, going beyond Lavoisier’s idea, exaggerated the meaning.

It is not without a legitimate satisfaction that we have the
right to say in this circle, that, notwithstanding the progress
which has metamorphosed the field of chemistry, the Academy
has nothing to regret, either as regards doctrine or language, of
what our illustrious predecessors had founded with so much
prudence, wisdom, and even genius.

XIII. On the Heating of a Disk by rapid rotation in vacuo.
To the Editors of the Philosophical Magazine and Journal.

GENTLEMEN,
TITH reference to the paper of Herr O. HE. Meyer, which
you translated in the last Number of the Philosophical
Magazine, we desire to make the following remarks.

There was no assumption (Annahme) whatever in our statement
of the small but unavoidable deviation of the axis from perpendi-
cularity to the disk. The amount of this bias was, in each case,
directly measured by turning the disk so slowly that no flexure
could possibly be produced by the rotation ; and the amount thus
determined was not visibly exceeded even at the highest speeds.
The length of the axis is nearly 4°5 imches (cr more than two-
thirds of the radius of the disk) ; and it lies in two bearings which
fit it as tightly as is consistent with free rotation. The utmost
amount of deflection of the edge of the disk due to slackness of
these bearings cannot possibly be nearly as great as 0-001 inch.

Herr O. KE. Meyer supposes, contrary to the usual principles
of ordinary dynamics, that a change of position of the instanta-

Phil. Mag. 8. 4. Vol. 37. No. 247. Feb. 1869. H

98 Prof. W. A. Norton on the Fundamental —

neous axis of the disk necessarily implies loss of vis viva, and he
calculates the supposed loss in a very peculiar manner. What he
means by saying that vis viva lost by impact of the axle on its
bearings is employed in heating the disk (alle tibrige lebendige
Kraft geht fiir die Rotation verloren und wird zur Erwarmung
der Scheibe verwandt) we cannot pretend to understand. Such a
statement, if meant to be understood literally, would appear to be
contrary to the fundamental principles of thermodynamics. If,
however, though he certainly does not say so, Herr Meyer means
that impact of the axle on the bearings may produce vibrations of
the disk which in time will by viscosity be frittered down into heat,
he merely repeats one of many objections, long ago perceived by
ourselves, and also pointed out to us by others, an objection which
we have already at least partially met by experiment and calcu-
lation. [It may be well to say here that Professor Helmholtz,
nearly two years ago, very kindly detailed to us his objections,
making several valuable suggestions by which we have since en-
deavoured to profit, and which will be duly acknowledged when
we are in a position completely to answer these objections. This
will, we hope, soon be the case, as extensive additional apparatus
is now in course of construction. |

There are various other parts of Herr Meyex’s paper to which
we might easily take exception, especially the calculation he
makes (even supposing his assumptions to be correct) as to the
absolute amount of radiation to be expected; but it would be
foreign to our present object to enter into such details. The
determination of radiation in absolute measure is an inquiry of
great importance, and we are glad to hear that it has been taken
up by Professor Neumann ; we believe that Sir W. Thomson
also has been working at it ; so that the question is now in good
hands, and will no doubt soon be definitely answered.

We are, Gentlemen,
Yours &c.,
B. Stewart,
P. G. Tait.
January 1869.

XIV. Fundamental Principles of Molecular Physics.
By Professor W. A. Norton*.

i a recent work by Joseph Bayma, S. J., Professor of Philo-
sophy, Stonyhurst College, England, in which a new theory
of Molecular Mechanics is ably set forth, I find a brief critique
of my theory of Molecular Physics, published originally im Silli-
man’s Journal, and republished in the London and Edinburgh

* From Silliman’s American Journal for September 1868.

Principles of Molecular Physics. 99

Philosophical Magazine. To this I propose to reply, and at the
same time to remark incidentally upon some of the fundamental
principles of the theory advanced by Professor Bayma. This
can be most briefly and effectively done by taking up the differ-
ent objections urged by him in due order, and commenting upon
them in succession, having a care not to dissociate remarks that
should properly be presented together. The quotations made
will be indicated to the eye by being printed in smaller type.

A great number of scientific men, to give an explanation of calo-
rific, electric, and luminous phenomena, assume that ether pervades
all ponderable bodies; whence many of them have come to the con-
clusion that every molecule of a body is surrounded by an ethereal
atmosphere, the action of which is considered to be the source of
those phenomena. Professor W. A. Norton, in a series of interesting
articles published in the American Journal, gives a theory of mole-
cular physics, of which the fundamental principle is that each mole-
cule is formed by an atom of ponderable matter surrounded by two
ethereal atmospheres of a different kind. I give his words.

“‘ The established truths and generally received ideas which form
the basis of the theory are as follows :—

‘1st. All the phenomena of material nature result from the action
of force upon matter.

*©2nd. All the forces in operation in nature are traceable to two
primary forces, viz. attraction and repulsion.

“3rd. All bodies of matter consist of separate indivisible parts
called atoms, each of which is conceived to be spherical in form.

«‘ 4th. Matter exists in three forms essentially different from each
other. These are (1) ordinary or gross matter, of which all bodies
of matter directly detected by our senses either wholly or chiefly
consist. (2) Asubtile fluid, or ether, associated with ordinary mat-
ter, by the intervention of which all electrical phenomena originate or
are produced. ‘This electric ether, as it may be termed, is attracted
by ordinary matter, while its individual atoms repel each other.
(3) Astill more subtile form of ether, which pervades all space and
the interstices between the atomsof bodies. ‘his is the medium by
which light is propagated, and is called the luminiferous ether, or the
universal ether. ‘The atoms, or ‘ atomettes’ of this sether mutu-
ally repel each other; and it is attracted by ordinary matter, and is
consequently more dense in the interior of bodies than in free space.

“5th. Heat, in all its recognized actions on matter, manifests
itself as a force of repulsion.

“The corner stone of a physical theory of molecular phenomena
must consist in the conception that is formed of the essential consti-
tution of a single molecule—understanding by a molecule an atom
of ordinary matter, endued with the properties and invested with the
arrangements which enable it to exert forces of attraction and repul-
sion upon other molecules. In seeking for this, the most philoso-
phical course that can be pursued is to follow out to their legitimate
conclusions the general principles already laid down...... The

100 Prof. W. A. Norton on the Fundamental

conception here formed of a molecule involves the idea of the opera-
tion of the two forces of attraction and repulsion: a force of attrac-
tion is exerted by the atom upon each of the two atmospheres sur-
rounding it, and a force of mutual repulsion between the atoms of
each atmosphere. These we regard as the primary forces of nature,
from which all known forces are derived.”

These are the capital points of Professor Norton’s ingenious
theory. But we think that such a theory contains a great deal of
arbitrary assumption. And indeed on what evidence are we to
grant that matter exists in three forms essentially different from each
other? Then how can we know the existence of atoms of gross
matter having a spherical form, and therefore extended though indi-
visible? Why should we admit two ethereal fluids, which are both
repulsive and only differ in subtilty? All this the learned Professor
assumes without proof, apparently because it consists of ‘‘ established
truths and generally received ideas.’’ But we say that no one has
up to this day established the proof of such propositions. As for
‘received ideas,’ every one knows how often questionable notions
have been and are received without serious examination, especially
when expressed by professors in a very dogmatic style. Are not a
thousand hypotheses received? and do they cease to be hypotheses,
although he who makes use of them for building a theory adorns
them with the high name of principles ?

This is all very plausible, but the objections urged are desti-
tute of any real force. We will first consider the general intima-
tion that the theory rests upon ‘a great deal of arbitrary
assumption.”” No theory of molecular physics can, in the
nature of things, have any other foundation than general prin-
ciples to be regarded as hypotheses that have been rendered
more or less probable, either by inductions from observation or
by @ priori reasonings. Molecular physics cannot be erected,
like mathematics, upon a foundation known from the first to be
eternally sure, that of self-evident truths. Mechanical axioms
may exist as mere figments of the mind, and have often risen
like bubbles in the minds of speculative philosophers, shone with
an evanescent splendour, and suddenly burst at the touch of a
hard fact. Our author is another instance of a learned philo-
sopher who has faith in such unsubstantialities, and thinks to
substitute them as a proper basis for a theory of molecular me-
chanics, in place of the general conceptions to which the pro-
gress of science leads, and by which aione its highest inductions
find any explanation—regards the latter as arbitrary assump-
tions, and his own mental convictions of what matter must be
and how it must act as the only reliable foundation upon which
to build. It is true that he takes exception to Principles 3rd and
Ath from the inductive point of view. Upon this ground (the
only legitimate one to be occupied) I am quite ready to meet

Principles of Molecular Physics. 101

him; but I wish to enter here, at the outset, a demurrer against
the virtual claim of the superiority of his own @ priori method of
establishing his fundamental principles. Such a claim is implied
in the intimation that “no one has up to this day established the
truth of such propositions,” as will be best appreciated by those
who have read Professor Bayma’s book. Having proved, as he
conceives, his propositions, and clinched each one of them with
a Q. E. D., he insists that obvious intimations of nature are to
be discarded because the stamp of infallibility cannot be put upon
them at once, before the test of availability in the explanation of —
phenomena has been applied. It was evident from the tenor of
my exposition of the subject that the ‘established truths” re-
ferred to were merely regarded as having been virtually estab-
lished, or rendered highly probable, by the inductions of science.
The claim implied in Professor Bayma’s criticism, that they re-
quire a higher confirmation, in fact a demonstration of their
truth, is not to be admitted.
He asks:

On what evidence are we to grant that matter exists in three
forms essentially different from each other ?

A sufficient answer to the critic himself is, that, pursuing a
systematic course of deduction from his leading principles and
his assumptions of the essential nature of matter, he actually
proves to his own satisfaction that matter does in fact exist in
essentially three different forms. He reaches the conclusion
that every primitive molecule consists of an attractive nucleus
surrounded by a repulsive envelope. My own position is that
every primitive molecule consists of an attractive atom of gross
matter surrounded by a repulsive atmosphere of electric ether.
The atom of gross matter answers to his attractive nucleus, the
electric ether to his repulsive envelope. The difference of doc-
trine, from the present point of view, is in name only. In an-
other connexion he elaborately undertakes to prove that ether
(i. e. the ether of space) is a “special substance.” Thus he
makes out that there are three essentially different forms of
matter.

But to reply to others who may be disposed to adopt the ob-
jection urged. .No one will deny the existence of gross or pon-
derable matter, or of something which has all the mechanical
attributes of matter. That an ether exists in space and within
transparent media we may certainly regard as abundantly estab-
lished by optical phenomena. As to the electric ether, the evi-
dence of its existence is that the great body of electric and mag-
netic phenomena, it is generally conceded, admit of satisfactory
explanation on the hypothesis of an electric fluid or ether inti-

102 Prof. W. A. Norton on the Fundamental

mately associated with matter, and that no successful attempt
has yet been made to account for the simplest of these phenomena
on any other hypothesis. Some physicists, it is true, are stri-
ving to do away with the supposed electric fluid—prompted by
the conjecture that nature must operate by some simpler method,
and work out all her wonderful diversity of phenomena by one,
or at most two forms of matter. Shall we wait until these
physicists have realized their aspirations, at their discouraging
rate of progress? or, guided by the indications of nature, strive
to link all natural phenomena together by a few recognized
principles? A theory that shall accomplish this is the great de-
sideratum. Even should sucha theory not rest upon the highest
and fewest possible mechanical principles, still the generalizations
embodied in it must have their counterparts in certain physical
truths, to the knowledge of which it will be likely to lead. It
is by following the ascending grade of generalizations that spe-
culative science has hitherto progressed. Preconceived notions
of what matter must be in its essential nature, or by what form
of matter or varieties of method nature must operate, have thus
far contributed little to its advancement ; and in fact, when we
consider that we positively know and can know nothing @ priori
with regard to the essential nature and condition of matter, and
its means and mode of operation, such notions are entitled to
little credit.

Our author implies in the remarks above quoted that the ex-
istence of an electric ether is not only not an “ established truth,”
but is to be ranked among those questionable notions that have
been received without serious examination. This implication is
obviously unjust. Besides, the serious examination that he has
given the subject only leads him to confirm the substantial truth
of what he would here seem to discredit ; for, as we have already
seen, his “repulsive envelope” is essentially my “ electric at-
mosphere.”’

Why should we admit two ethereal fluids which are both repul-
sive and only differ in subtilty ?

Professor Bayma and myself agree in admitting the existence
of two kinds of matter, attractive and repulsive; and, as we have
seen, three forms of matter. Is it inherently any less probable
that two of these should be repulsive and one attractive, than, as
he assumes, that two should be attractive and one repulsive ?
viz. gross matter and the ether of space attractive, and the
elements of the “repulsive envelope” repulsive. In the
supposition that the two ethereal fluids differ in subtilty,
nothing more is essentially implied than that a considerable
number of atoms of the one occupy the interstices between the

Principles of Molecular Physics. 103

atoms of the other. Professor Bayma assumes equally great
differences to subsist between his two attractive forms of mat-
ter. He remarks, “the distinction of such a medium” (a me-
dium for the transmission of light) “from any peonderable sub- »
stance is not an hypothesis, but a necessary inference drawn
from observed facts ;” and again, “I do not see how such a
fact ” (that light can pass undisturbed through air notwithstand-
ing the immense number of air-particles it encounters) “ can be
accounted for if zther is not immensely denser than atmospheric
air.” The reason for the conclusion is groundless ; but it is
the conclusion itself that we have here to notice. He adds, —
“ with this great density sther possesses also a very great sub-
tilty.”’

i might also reply to Professor Bayma by asking him why we
should admit, in order to explain electric and optical phenomena,
two substances so distinct as the repulsive envelope of molecules
and the attractive luminiferous ether. The evidence of their
similarity is much greater than of their dissimilarity.

In speaking of the two ethers as subtile, it was meant that a
large number of their atoms occupied the interstices between the
atoms of gross matter. It was also, of course, recognized that
the velocity of propagation of a wave is much greater through
either of the ethereal fluids than through a mass of ordinary
matter. The only apparent force in the question under consi-
deration is derived from the fact that a vague conjecture is apt
to be raised by it, that a single ether may be equal to all the
duty now assigned to both.

To proceed with our quotations:

What we have said on the constitution of molecules demonstrates
indeed the necessity of granting to each molecule of ponderable
matter a repulsive atmosphere, which we have called the molecular
envelope. But this envelope is not of ether, since ether is not
repulsive. >

That is, is not of the same substance as his luminiferous ether,
which he regards as attractive. But the “atmosphere ” which
corresponds in its direct operation with Professor Bayma’s
“molecular envelope” is composed of electric matter, and this
is repulsive. It is true that I conceive the interstitial spaces of
this electric matter and the space between it and the central
atom to be pervaded by the ether of space ; but the mechanical
part chiefly played by this condensed universal xther consists in
its being the medium in which pulses are originated that con-
stitute the force of heat-repulsion.

Had Professor Norton known the impossibility of continuous mat-
ter, he would have found out that what he calls an atom of gross

104 Prof. W. A. Norton on the Fundamental

matter comprises already not only the central element of a molecule,
but its nuclei and its envelope ; and consequently is already endued
with the properties and invested with the arrangements which
enable it to exert forces of attraction and repulsion upon other mole-
cules, without requiring any new and special atmosphere of elec-
tric or luminiferous ether.

That is, in other words, as already shown, Professor Bayma’s
nucleus and envelope are in all outward relations precisely cor-
respondent to my central atom and electric atmosphere. The
only essential point of difference between us lies in the fact that
I conceive that the interstitia! lumimiferous ether is condensed
around the central atom, and is concerned in the production of
some of the phenomena. It is not easy to see how Professor
Bayma escapes the conclusion that his interstitial ether, which
is attracted by the central nucleus, is condensed around it ; stall
it is plain that he imagines that all natural phenomena are pro-
duced by the mutual actions of molecules composed of a central
nucleus and a single repulsive envelope without the mtervention
of any ether, except the luminiferous in the case of the pheno-
mena of light and radiant heat. This will appear from the fol-
lowing quotation :—

As for the examples by which he illustrates the theory, they con-
sist of a series of phenomena of different kinds, the explanation of
which does not show that the theory is not at fault. For it must be
remarked that those explanations do not imply the existence of ex-
tended atoms or of two distinct ethereal substances; and therefore
the theory assumes more than is necessary for, or guaranteed by, the
explanation of phenomena.

When he has shown this to be true of even the ordinary calo-
rific and electric phenomena, we will admit that his objection to
a second ethereal atmosphere interpenetrating the first may
have some force. He has given no hint of the general manner
in which he supposes electric phenomena to be evolved. Heat
he conceives to originate in the vibrations of the molecules of
bodies; but it can be proved, almost to a demonstration, that
heat cannot originate in this manner.

Our author proceeds as follows :—

>

The atoms of gross matter being “‘ indivisible’? cannot be extended,
and cannot be conceived to be ‘‘ spherical in form ;” for if they were
extended and indivisible they would be so many pieces of continuous
matter, which we have already proved to be impossible.

To this I have the following replies to offer :—

1. Professor Bayma assumes that every point of matter acts
instantaneously upon every other point at all distances, however
great or small, with a force having the same character at all dis-

Principles of Molecular Physics. 105

tances, and inversely proportional to the square of the distance.

This may seem probable, but is not self-evident ; and in fact no
reason can be assigned why one material point having no extent
should act upon another with a force decreasing with the dis-
tance, according to any law whatever. The law of inverse
squares is a consequence of wave propagation, or of radiations
along definite lines, received on a molecule of definite size, and
cannot be predicated of a force that acts instantaneously between

two mathematical points. To suppose such a law is an arbitrary
assumption. ,

2. If matter consists of material points, as supposed by Pro-
fessor Bayma, it is no more difficult to conceive of an atom of
continuous matter than of the space coextensive with it.

3. It is not more difficult to conceive of an indivisible atom
acting as a whole upon another atom with a certain energy, than
of a mere point acting upon another point, and causing it to
change its place, at the same time transferring to a new point all
the properties it possesses.

4. If the occult nature of the force of action of one material
point on another be such that the intensity becomes indefinitely
small at indefinitely small distances, instead of infinitely great as
imagined by Professor Bayma, then a collection of an infinite
number of material points may form one invariable atom,
since the size of the atom may in every instance be so imappre-
ciable in comparison with the distance between the nearest
atoms that there may never be any inequality of extraneous action
on different points of the same atom, imparting different velo-
cities to them, and so tending to break up the continuity of the
matter. Besides, we have already seen that no inequality of
elementary action, by reason of a difference of distance, is legiti-
mately deducible from Professor Bayma’s premises.

5. In speaking of atoms of gross matter as “ indivisible,” no
other ground was intended to be taken than that each atom was
indestructible from any possible action of another atom, and es-
sentially invariable in form. This does not preclude the idea
that the atom may be an aggregation of a finite number of
material points; for it may be that the mutual action of two
attractive pomts passes into a repulsion at excessively minute
distances, and so that an atom of ordinary matter may be a
system of material points in either a statical or dynamical equi-
librium. Indivisibility, taken in the only sense in which the
term can properly be used, does not, then, necessarily imply
continuity, as maintained by Professor Bayma.

6. The assumption that each atom is “spherical in form,”
was adopted merely as the simplest embodiment of the funda-
mental principles that the action of the atom was equal in all

106 . Prof. W.A. Norton on the Fundamental

directions, and that the attractive action upon an atom of ether
was neutralized at minute distances by the resistance developed
at the point of contact. The existence of such a resistance
necessarily implies that the elementary parts of the attractive
atom, whether finite or infinite in number, act repulsively at
very minute distances. But another conception may be formed
of the mode of operation of an atom of gross matter, which
involves no other supposition than that it acts equally outward
in all directions from a centre, and takes no account of its geo-
metrical extent. This is, that the effective attraction of the atom
for the ether of space is due to the existence of a repulsion less
than would be exerted by the one or more atoms of ether that
would naturally occupy its place. ‘The result would be the con-
densation of an atmosphere of ether around the atom, without
the exertion of any direct attractive force, or of any additional
force of resistance. We may conceive the molecular atmosphere
of electric ether to originate in a similar way; but as the op-
portunity of examining and testing this idea sufficiently has not
yet been obtained, I shall continue to regard the electric ether’
as directly attracted by the atom of gross matter, and that the
antagonistic force of resistance is furnished by the repulsion of
the luminiferous ether condensed around the atom.

If, mm accordance with these views, we seek for a possible
origin of gravitation, we can find it in a primary attraction sub-
sisting between atoms of gross matter. This must be excessively
feeble in comparison with “ molecular forces,” and modify the
effect of those forces only by creating a slight additional pressure
of contiguous molecular atmospheres. Should we assume the
primary actions between atoms of all kinds to be wholly repul-
sive, and the effective attraction of the gross atom for both its
zethereal atmospheres to be a mere consequence of imequalities
of repulsion, it is conceivable that the attraction of gravitation
might result from ethereal waves, as maintained by Professor
Challis, these waves having their origin in a dynamical equili-
brium of the atmosphere of universal ether condensed around
each atom.

Another critical remark is the following :—

Again, «xthereal substance, according to the author, is repulsive ;
now this is inconsistent with astronomical facts, as we have suffici-
ently shown.

The principal astronomical fact here referred to is that the
planets do not encounter any sensible resistance in their motion
through space. The evidence of an ethereal resistance afforded
by Encke’s comet, Professor Bayma strives to explain away with-
out success. The fact that no sensible resistance is experienced

Principles of Molecular Physics. 107

by the planets does not necessarily imply, as he supposes, that
the ether is not repulsive. For, in the first place, if the mole-
cules of the planetary mass have the constitution I have attri-
buted to them, the impinging ether must take effect upon either
the zthereal or the electric atmospheres of the molecules, and
so may be mostly expended in the generation of heat and elec-
tric currents. I have in fact undertaken to show, in my paper
on Molecular Physics, that the earth may derive its magnetic
condition and a certain portion of its heat from the impact of
the ether of space. Again, if the action of gravity be not.
instantaneous, it will take effect in a direction slightly inclined
to the radius vector, and, in the existing state of the planetary
system, the tangential component resulting from this inclination
may be in equilibrium with the feeble overplus of resistance
from the ether. Besides, the supposed difficulty is not removed
by substituting an attractive for a repulsive ether. It is true
that when a molecule of the earth’s mass encounters an atom of
the zther on the line of its advance, it will, upon Professor
Bayma’s idea, pass through it and leave it behind; but he has
failed to note the fact that during the approach of the two their
relative velocity will be equal to the sum of the velocity of the earth
and that due to their mutual attraction, and during their separa-
tion will be equal to the difference of the same velocities, and
hence that the atom of ether will continue to attract the molecule
during a longer interval of time while the two are separating
than while they are approaching. The molecule will therefore
on the whole be retarded by the action of the atom. If the at-
tractive ether be “immensely denser than atmospheric air,” the
resistance should certainly not be less than that of a subtile re-
pulsive ether. If Professor Bayma should still hold to the
same line of argument, I do not see but he must abolish the
ether of space altogether.
He continues :

Moreover the writer, after having assumed that the electric and
luminiferous ethers are both made up of atoms that repel each other,
assumes also that electric ether attracts luminiferous ether; for he
admits that a molecule is formed of an atom of gross matter with two
atmospheres, of which the first, consisting of condensed luminiferous
xther, is attracted by the ether which consists of electric ether.
Now, if the atoms of electric ether are repulsive, how can they
attract? So, then, we must conclude that Professor Norton’s theory,
as presented by him, in spite of the talent and learning ofits author,
cannot be adopted in science.

Professor Bayma has here entirely misunderstood me, and re-
presented what I threw out as a possible and perhaps probable

108 Prof. W. A. Norton on the Fundamental

conception, to be a fundamental principle of my theory. The
real fundamental principle was that the atoms of electric ether
repelled each other; and it was merely conjectured that this re-
pulsion might be due to atmospheres of luminiferous ether
condensed around the electric atoms, instead of being a repulsive
action. It is a little singular, in view of this distinct state-
ment ofthe manner in which the repulsion might result from a
possible attraction, that our author should ask the question,
“‘ Now, if the atoms of electric «ether are repulsive, how can they
attract ?’? and thereupon intimate the existence of a discrepancy
fatal to the theory. It is, im fact, altogether immaterial whether
the mutual repulsion of electric atoms is indirect as conjectured,
or direct.

It has now been made sufficiently apparent that the objections
urged against my theory of molecular physics have no real force,
and that its fundamental principles have not been disturbed.
Whether it will ultimately be “adopted in science” or not must
depend upon its availability in rendering a satisfactory account
of phenomena, and its ability to withstand the test of a detailed
comparison with the entire range of physical facts. If life and
health are granted me, I shall endeavour in good time to show,
to the satisfaction of every candid mind, that the natural pheno-
mena and experimental results, with their laws and features of
diversity, that make up the different departments of physics are
legitimately deducible from the fundamental principles of the
theory, and that it presents claims to acceptance superior to
those which can be urged in favour of any other theory.

The attempt to deduce the existing constitution of things and
prominent phenomena by Professor Bayma from his fundamental
ideas, so far as made, has certainly failed at several important
points. ‘To specify one or two of these. He obtains a curve of
molecular action that represents a repulsion at the smallest dis-
tances succeeded by an attraction at greater distances. This
can only be made to represent the three states of bodies by con-
ceiving the molecules of a gas to be in such a condition that, if
it were entirely freed from pressure, it would expand into a
liquid. We know that many gases can be compressed into a
liquid, but it is altogether gratuitous to suppose that they could be
brought into a similar condition by a diminution of pressure.
Experiment has given no indication of such a result or tendency.

Heat and light he conceives to originate in vibrations of gross
molecules; but against this notion, as I shall take another occa-
sion to show, insuperable objections may be urged. If this be
given up, his explanation of the changes of the state of bodies
must also be abandoned.

The doctrine that “transparent bodies transmit rays of light

Principles of Molecular Physics. 109

by the motions of their own molecules” will hardly be accepted,
we think, by physicists. It would be a waste of time to argue
against it.

- Again, the notion that a certain substance radiates light of a
certain colour because its molecules are made to vibrate in unison
with the ray of that colour, will not stand; for the results of
spectral analysis show that the parts of a body which are capable
by vibration of giving out any colour are precisely those which
absorb and stifle that colour. This fact, we may add, also proves
conclusively that the rays cannot be transmitted by the motion of
the molecules. Though so radically at variance with Professor
Bayma’s theoretical views, it is in entire accordance with my
own ; for, according to these, light originates in certain vibratory
movements of the atoms of the electric atmospheres of molecules,
and when these vibrate naturally in unison with the ray of any
colour that falls upon them, they take up its ws viva, and so the
ray is transformed into a molecular electric current.

As to the “leading principles” laid down by the author, they
may in the main be conceded; but these by no means cover the
whole ground upon which his theory is raised. We find, for
example, that he assumes that all elements or material points of
the same form of matter act, under similar circumstances, with
the same intensity. Now if this principle be admitted, what
theoretical basis have we for the existence of distinct primitive
molecules for every different substance, the number of elements
associated together being exactly the same for each primitive
molecule of each substance, and different for primitive mole-
cules of different substances? The natural tendency would be
to a fortuitous association of elements in an endless variety of
numbers into groups. No controlling principle by which uni-
formity would be evolved from chaotic confusion is furnished by
the theory. The Hand ofthe Creator must be supposed to have
miraculously interfered, and guided each element to its precise
place in the formation of every molecule of matter. The objec-
tion here urged derives still greater force from the consideration
that both the nucleus and envelope of each specific molecule are
assumed to have a regular geometrical form, different for each
substance. To assume the existence of such molecules is to
make an incalculable number of arbitrary assumptions. No
such exception can be taken to the views I have advocated ;
for primarily each specific atom of gross attractive matter must
appropriate to itself, from the universally diffused repulsive
zethers, its electric and its ethereal atmosphere, each of a certain
definite extent. Upon the relations of these specific atmospheres
to the central atom and to one another, all the different proper-
' ties of each specific molecule must depend.

110 Prof. W. A. Norton on Molecular Physics.

We have already seen that the principle that one material
point acts upon another instantaneously, without the interven-
tion of any medium, is opposed to the fundamental idea that the
force exerted is inversely proportional to the square of the dis-
tance. This law, to say the least, is an arbitrary assumption in
the premises. The author also conceives that the mutual action
of two material points is in no degree and under no circum-
stances intercepted by another intervening point. But we know
that, in the case of the molecular forces, the amount of vis viva
expended in imparting motion to one particle is abstracted from
the force in action ; and, according to Professor Bayma, the mo-
lecular forces are of the same nature as the forces subsisting
between the material elements. The force of gravity, it is true,
is not sensibly intercepted; but this does not prove that a ten-
dency to interception does not exist; for, upon the supposition
of a wave-transmission of the force, the effective attraction of
any molecule may be the mere differential of the actual force
transmitted, and, besides, in the circular revolution of a planet
the distance from the sun remains unchanged.

My own doctrine is that the molecular forces, mcluding the
heat-repulsion, are dynamical forces transmitted by wave-pro-
pagation and developed by the primary forces of attraction and
repulsion subsisting between the atoms of gross matter and those
of the electric matter and the ether of space. The primary
forces determine the electric and ethereal atmospheres of mole-
cules, originate the molecular forces proper, and also, when an
inequality of electric condition is produced on two contiguous
molecules or bodies by molecular actions, gives rise to the spe-
cial forces of electric attraction and repulsion. The waves of
heat and light originate in the ethereal atmospheres of mole-
cules, and are developed by vibrations of the atoms of the elec-
tric atmospheres toward and from the centre of each molecule
and the region of zthereal disturbance. By reason of the vary-
ing conditions of equilibrium, the rate of vibration increases, and
its intensity or vis viva decreases, in proportion as the electric
atom is more remote from the centre of the molecule. Thus of
the different coloured rays the red proceeds from the lowest
depth in the electro-zthereal atmosphere. The obscure heat-
rays originate at a still lower depth. Heat and light may also
originate in the space between two molecules in the act of com-
bination, or near approach, by reason of the condensation of the
interstitial electric ether toward the line of the centres, resulting
from the oblique attractive action of the molecules. In this
condensation of the electric «ther between molecules that are
urged nearer to each other, and the expansion of the same
when they are separated, we find the key to the explanation of

M. H. St.-Claire Deville on the Temperature of Flames. 111

the different modes of electric excitation (that of the galvanic
current included). The secret of the intimate relations between
electricity and heat and light is obvious in view of what has
been stated.

The ethereal atmospheres of molecules, besides playing the
part already signalized, are the chief determining cause of the
diverse phenomena that attend the transmission of light through
transparent media. Thus refraction is chiefly due to the retar-
dation attending the propagation of the ray around from one
side to the other of the molecular atmospheres ; dispersion of
the rays in the spectrum to the fact that the rays of the greatest
intensity and slowest rate of vibration penetrate to the greatest
depth in the molecular atmospheres, pass around in smaller
circles, and thus suffer the least retardation; and double refrac-
tion to the fact that the atmospheres have a spheroidal form,
owing to unequal molecular compression on different sides.

XV. On the Temperature of Flames, and its relations with the
Pressure. By M. H. St.-Ciarre Devitie*,

T is impossible not to be greatly struck by the numerous

consequences which may be deduced from the experiments
. recently published by Professor Frankland, and of which he has
given an account in an article in the Comptes Rendus of the 12th
of last Octobert. I will ask leave from the Academy to develope
here some ideas which this magnificent research has suggested
to me, and to deseribe a plan of investigation commenced some
time ago in my laboratory, the direction of which has been a
little changed by the new facts discovered by the illustrious
English chemist.

Professor Frankland (to sum up in brief his principal experi-
ments) proves that the higher the pressure of an oxyhydrogen jet
burning in a compressed atmosphere, the more brilliant and lu-
minous{ does its flame become, which under the ordinary pres-
sure is scarcely visible. At a high pressure a flame is obtained
whose intensity may be compared to that of a wax candle. This
single fact is sufficient to show the importance of such results,
which may be said to have been as unforeseen as they are clearly
and definitely established.

Professor Frankland finds the best explanation of this great

¥ From the Comptes Rendus, November 30, 1868.

+ [See also Phil. Mag. for October, 1868, p. 309.]

{ To make a flame brilliant, it is sufficient that its rays, if they are
simple and belonging to a monochromatic light, possess great intensity.
That a flame shall be Juminous in the ordinary acceptation of this word, it
must possess almost all the rays of the solar spectrum; it must be white,
or as nearly so as possible by approximating to sunlight.

112 M. H. St.-Claire Deville on the Temperature of Flames,

fact in the mere increase of density which necessarily accom-
panies the compression of the gas. He also draws conclusions
which seem to invalidate the classical ideas introduced into
science by Sir Humphry Davy, and which withdraw from the
theory of flame a basis which has always appeared beyond the
reach of attack. I confess that on this latter point I do not |
share Professor Frankland’s ideas; and I base my opinion on
certain facts as yet imperfectly investigated, but which I shall
describe before long, when I shall have given them that demon-
strative form which they want, and which in the present state
of science must be given to all our speculations.

I shall not attack with the same firmness the questions relative
to the influence of density on the luminous power of flames. I
propose here to develope an idea the germ of which I find in the
last paragraphs of Professor Frankland’s communication. Our
colleague ascribes the want of illuminating power im the flame of
phosphorus burning in chlorine to the slight elevation of tem-
perature which a combustion accompanied by so small a disen-
gagement of heat must obviously produce. I believe this to be
the real and only reason.

Let us first inquire what is the principal condition for lumino-
sity ina flame. If we take an obscure but hot flame like that of
a Bunsen’s burner, and introduce common salt into it, every
one knows that we obtain a light of feeble intensity and which is
monochromatic ; for the prism does not decompose it into a spec-
trum, and only produces one bright band. But if we increase
the temperature of this flame (by adding oxygen, for instance),
the lustre immediately revives, the number of lines increases, and
hence approximates to a complete spectrum. The experiments
of M. Fizeau and of MM. Wolf and Diacon are remarkably de-
finite from this point of view. But suppose we use M. Debray’s
apparatus, by which, for spectroscopic experiments, a very high
temperature (one of about 2500°) can be obtained. In this
flame the spectrum of sodium spreads out and becomes com-
plete; it may be assumed, then, that the great number of bril-
lant lines which the spectrum contains merge into each other
to form a whole which seems continucus. An observation of
the same kind is made when large quantities of sodium are burnt
in alr or oxygen, or when lithium is set on fire: the flame of
sodium, which is ordinarily yellow and monochromatic, that of
lithium, which is usually red, both become white ; they then
contain all the rays or, we may say, all the brilliant lines of every
refrangibility. They thus become luminous when the metal
burns at a high temperature.

This observation is exact also for the invisible rays—for the
chemical rays whose lines crowd and multiply in the spectrum in

and its relations with the Pressure. Hs

proportion as luminous sources at higher temperatures are used
to produce them. This is a cardinal observation due to M.
Mascart. Thus the number of lines increases in the proportion
in which the temperature rises in the flames which produce them ;
and when the temperature attains a certain intensity, these lines
merge into one another and give a continuous spectrum. The
flame then necessarily becomes white, brilliant, and luminous.

A fact of the same kind is produced in Professor Frankland’s
experiment. The lines increase in number and in intensity in
the hydrogen flame in proportion as the pressure on the explosive
mixture within and without the blowpipe itself increases. What
more rational conclusion cau be drawn than that the tempera-
ture itself increases in the flame in proportion as the pressure in-
creases? This is a prime fact, the demonstration of which may
seem sufficient ; but it is full of consequences so important that
direct verifications should still be demanded. I shall revert sub-
sequently to the consequences and the methods of verification
which I think of using; but I desire to show at once that these
considerations, deduced from spectrum-analysis, will explain the
fact of the great illuminating power of arseniuretted hydrogen—
a power that Davy’s theory, which I think is incomplete from
this point of view, can only explain by the supposed presence of
a solid body in the flame. It is sufficiently evident that gases
in burning give lines. If these lines are brilliant and numerous
for reasons depending on the special nature of the substances
observed, it is clear that the flame of these gases will be brilliant
and the more luminous the greater the difference in the refran-
gibility of the lines these spectra contain. Here we have to do
with a phenomenon belonging to arsenic in vapour contained in
the flame of arseniuretted hydrogen ; and in the explanation of
such a fact it seems to me useless to bring in the consideration
of densities, invalidated moreover by the objection urged by
Professor Frankland himself in the case of the flame of phos-
phorus burning in chlorine.

Thus the illuminating power of an entirely gaseous flame is a
specific property connected with the production of lines furnished
by the substances it contains; it is as inexplicable as the specitic
properties of the bodies themselves—the density, colour, &c.
Professor Frankland’s idea, moreover, relative to the production
in ordinary flames of very dense carburetted hydrogen seems to
me difficult to rest on experiment. We know, im fact, that all
these carburetted hydrogens decompose at the lowest tempera-
tures into hydrogen andcarbon—the latter hydrogenized, itistrue,
but opaque*. I think, then, that Davy’s theory remains intact.

* I have proved (Legons sur la Dissociation, p. 317, Lecons de la Société
Chimique. Paris, Hachette, 1866) that in strongly heated carbonic oxide

Phil. Mag. 8S. 4. Vol. 37. No. 247. Feb. 1869. I

114 M. H. 8t.-Claire Deville on the Temperature of Flames,

I have said that if the flame of hydrogen becomes luminous
under a high pressure, it arises from the temperature of the flame
increasing in proportion as the pressure at which the combus-
tion takes place itself increases. Let us now see what are the
consequences of this fact, supposing it to be well established.

M. Debray and I have proved that the temperature of combi-
nation of hydrogen and oxygen, under the ordinary pressure,
is 2500°. We determined this fixed point by throwing into water
a kilogramme of melted platinum raised to the highest tempera-
ture which could be produced in a lime- furnace, taking into
account the increase in the temperature of the water, the specific
heat of platinum and the law of its increase given by M. Pouil-
let, along with its latent heat as determined by M. Person. We
should have liked to control so important a result by a great
number of tests, and to fix it, as far as the data of calculation
permitted, m an incontestable manner. For that purpose it
would have been necessary to use large masses of platinum, and
to protect ourselves against very serious accidents, terrible ex-
plosions, of which we narrowly escaped being the victims. We
were closely occupied with the solution of this question when
Professor Bunsen published his beautiful memoir on the tempe-
rature of combustion*. The excellence of the method invented
by the great Heidelberg physicist made it unnecessary for us to
recur to a tedious and dangerous method, the more so as the
numbers obtained by Professor Bunsen are in the most com-
plete agreement with our own. Professor Bunsen gives 2800°
as the temperature of combination of the two gases purified
and intreduced in a state of absolute dryness into his valve-
eudiometer. Allowing for the moisture of the gases used in our
experiments, and for the nitrogen brought into the gasholder by
the water which displaced the gas, a number is obtained very
near 2800°, which I shall adopt for the future as the true tem-
perature corresponding to this phenomenon.

Taking the number 2500°, I obtained the fraction 0°447 to
represent the portion of the gases which really combine at the

dissociation took place with the production of oxygen and of a yellow
pulverulent and light carbon, to which, according to all appearance, is due
the blue tint of the flame. M. Cailletet has observed that, in withdrawing
and suddenly cooling the gases from the tuyére of a blast-furnace by means
of my hot and cold tubes, these gases, produced by a carbon absolutely
destitute of volatile matters, were rendered almost opaque by a sort of
thick brownish fog, which after the lapse of some time was resolved into a
blackish-yellow deposit of extremely finely divided carbon.

* Pogg. Ann. vol. cxxxi. p. 161; Phil. Mag. S. 4. vol. xxxiv. p. 489.

t Compare Lec¢ons de la Socitté Chimique (de la Dissociation), p, 290
(Paris, Hachette, 1866).

and its relations with the Pressure. 115

moment when (the heat of the mixture being a maximum) the
dissociation of water corresponding to this temperature presents
an obstacle to the complete union of its elements. Adopting
the new number 2800°, we see that the part combined or not
dissociated of the flame of hydrogen and of oxygen is really 0°50,
or half the total mass.

Bunsen’s valve-eudiometer enabled him to investigate the tem-
perature of combustion when the total pressure of the oxygen
and hydrogen is diminished and 1s brought below the atmospherie
pressure. It is sufficient for this purpose if a certain quantity ~
of an inert gas be added to the explosive mixture. Under these
circumstances Professor Bunsen observed that this temperature
rapidly decreased in proportion as the partial tension of the ex-
plosive gases was made to decrease. Consequently the quantity
of matter dissociated, or the tension of dissociation of water in
the flame, decreases with the temperature.

What would take place if we investigated the temperature of
combination under a higher pressure than that of the atmo-
sphere? This is obviously shown by Professor Frankland’s ex-
periments,

To acquire absolute certainty on this point a striking verifica-
tion is required, which may be obtained either by melting pla-
tinum in an artificially condensed atmosphere, or by repeating
Bunsen’s experiments with the valve-eudiometer.

I am about to commence experiments of this kind ; they will
be made in a laboratory with iron walls capable of resisting a
pressure of at least three atmospheres—a pressure which the ex-
periments made at the bridge of Kehl show is quite innocuous.

It is easy to understand the practical consequences which may
flow from a series of experiments made under pressure with the
ordinary combustibles. They lead to a direct trial of furnaces
fed with air forced under a pressure equal to the pressure of the
vapour in the generator. These furnaces, especially if they are
fed with the mineral oils, the use of which is already beginning
to be recommended, and which leave no residue—these boilers
where the products of combustion compressed to five atmospheres,
for instance, would move through the tubes with one-fifth the
velocity of our present apparatus, would doubtless enable the sur-
face of heating.to be considerably diminished. It is owing to the
interest that investigations of this kind may have in furnishing
naval engineers with the data necessary for calculating the
results, that the Emperor has been good enough to order that
these experiments be made in the laboratory of the Ecole Nor-
male. A large cylindrical chamber capable of holding the ope-
rator and his apparatus, and of supporting a considerable pres-
sure of air furnished by a steam-pump, will form a laboratory

I

116 M. H. St.-Claire Deville on the Temperature of Flames.

where all the manipulation necessary for determining the tem-
perature produced by flames and solid combustibles may be
effected without danger.

If, as is almost already demonstrated by what I have said and
by almost all the observations made by engineers and by physi-
cists in chambers containing compressed air, the temperature
of combustion rises at the same time as the pressure increases,
that would be one analogy more to be added to the number of
those I have indicated between the phenomena of combination
and of decomposition on the one hand, and the phenomena of the
condensation of vapours and of volatilization on the other hand.

We may in fact give the name greatest temperature of conden-
sation of vapour to what is improperly known as the bozling-
point of a liquid. This temperature is no other than that com-
mencing from which a vapour no longer condenses on the surface
of a cold thermometer, which is merely heated by means of the
latent heat yielded to it by the vapour in which it is immersed.
The boiling-point, or temperature of condensation, rises, as we
know, when the pressure above the liquid which produces the va-
pour is increased.

The combination of bodies, and particularly that of oxygen
and hydrogen in the oxyhydrogen blowpipe, is apparently a more
complex phenomenon, but corresponds perfectly to the act of the
condensation of vapours.

Assuming that the temperature of the combination of hydro-
gen and oxygen is 2800°, the quantity of water formed under
a pressure of 760 millims. will be in the flame, at the hottest
part *,

637 + (2800 — 100) 0°475
3833

that is to say, only half the oxygen and hydrogen will be com-
bined under a pressure of 760 millims.

But if we increase the pressure, the temperature of the flame
increasing also, it will be seen from the preceding formula that
the proportion of substance combined or of aqueous vapour
formed will increase as the pressure increases—just as the tension
of asaturated vapour increases in proportion as the temperature
increases. Lastly, the temperature of combination of a gaseous
mixture, like the greatest temperature of condensation (or boil-
ing-point) of a vapour, increases with the pressure.

The substance combined in a flame plays the same part as the
substance condensed im a space full of vapour the temperature
and pressure of vane are varied so that the vapour is always
saturated.

* Vide Lecons de Chime, given in 1864 and 1865, p.290 (Hachette, 1866).

—=1\) 15) 9

On EKthylate of Sodium and Eihylute of Potassium. 117

It is clear from this that the quantity of substance uncom-
bined or dissociated in the flame diminishes as the pressure in-
creases. It may therefore be supposed that there is a pressure
at which a mixture of hydrogen and oxygen would produce in
combining the unimaginable temperature of 6800° which corre-
sponds to total combination. But it is no more possible to make
a serious hypothesis on this subject, than to ask whether there
be a pressure at which water could no longer boil, whatever tem-
perature were applied to it.

I hope the Academy will excuse my having so long dwelt upon -
a mere programme of researches in course of execution; but
they will be long and tedious, and I have been anxious to pre-
serve the right of pursuing them if any one more fortunate than
myself should sooner reach the object I am desirous of attaining.
If the general consideratiuns developed in this communication
should facilitate the solution of a problem which I propound for
the first time, and which I seek by paths which, if complicated,
are yet rational, I shall be happy to have prepared the way.

XVI. On Ethylate of Sodium and Ethylate of Potassium.—Part 1.
By J. Aurrep Wanxuyn, Professor of Chemistry in the Lon-
don Institution*.

| Ni Kthylates of the Alkali-metals have been very imper-

fectly studied, and are well deserving of a minute investi-
gation. Almost every one who has had occasion to prepare
ethylate of sodium must have observed that the quantity of metal
capable of being easily made to act on alcohol is comparatively
small; from being very energetic, as it is at first, the action be-
tween the sodium and the alcohol soon becomes sluggish, and
ceases long before so much as one equivalent of metal has de-
composed one equivalent of alcohol. Nevertheless I believe that
chemists usually regard the beautiful crystals which form when
sodium is allowed to react upon alcohol as being ethylate of so-
dium, and as having the formula C? H®O Na.

The crystals are in reality a compound of ethylate of sodium
with alcohol. A note by A. Geuther and EH. Scheitz shows that
they consist of NaC? H®O,2(C?H°QO). (I quote from the
Chemical News of January 8, 1869, which quotes the note on
Ethylate of Sodium from the Jena Zevztschrift f. M. und N.
vol. iv. p. 16).

According to my own experiments, the crystals contain even
more alcohol, viz. three molecules of alcohol to one molecule of
ethylate of sodium, as will presently be described. It will alse

* Communicated by the Author.

118 Prof. J. A. Wanklyn on Ethylate of Sodium

appear that the absolute ethylates of the alkali-metals are en-
dowed with an extraordinary degree of stability, bemg among
the most permanent compounds belonging to organic chemistry.

Passing on to the description of my research :—A small glass
retort, of 75 cubic centims. capacity (see figure), was cleaned,
dried, and weighed. Into it was put
some freshly cut sodium, the weight
of which was ascertained. (Sodium
admits of being accurately weighed,
the thin film of oxide with which it
so soon becomes covered being of
insignificant weight.) Anhydrous
alcohol was next poured into the
retort, and the reaction between it and the sodium allowed to
take place. The apparatus was then heated in the water-bath
as long as any alcohol distilled over, and then cooled, dried, and
weighed. The apparatus wasa second time placed in the water-
bath and subsequently cooled, dried, and weighed. The follow-
ing are the numbers given by two experiments :—

ie II.

Weight of sodium employed .. . 2°2 grm. 1:160
Quantity of absolute alcohol poured in, about 30 cub. centims.
Weight of the solid product after heating | 4q. ;

Sor arek a Weede 19:95 11-192
Weight of the same after second heating 19°75

toplOO we swe, Wass. }
Calculated into percentage, we have—

Found.

EHEOny for we at 3(C? H®O). — Hi ———_,

a I. ae

Na Daaes 88 Ws 165 11°14 10°37
Cle. 9G
Pe ee P28
Ot 60 264

206 100-00

The crystals therefore consist of Na C? H® O, 3(C? H® O), and
will bear a temperature of 100° C. without losing alcohol. They
are in a state of complete fusion at 100° C., and so long as the
air is excluded remain quite colourless. A very slight exposure
to the air tinges them with brown—a remark which is applicable
to the absolute ethylate about to be described. They are not
very soluble in ether; in a mixture of acetic ether and ether
they appear to be more soluble.

On exposing them to temperatures above 100° C. these crys-
tals give off alcohol, but they require a very considerable appli-
cation of heat to drive off all the alcohol from them.

and Kihylate of Potassium. — 119

The 11°192 grms. of Na C? H® O, 3(C? H® O) of experiment II.
were gradually heated to 130° C. in the oil-bath, maintained at
that temperature, and then raised to 140° C. The following are
the numbers :—

aa grms.
Weight of sodiumemployed . . 1-160
Weight of product at 100°C. . 11:192

Weight of product at 140°C. . 4°466

from which is deduced, percentage of sodium in product at
140°=25:°98. The theory for absolute ethylate is, percentage -
of sodium = 83°82. It appears, therefore, that there was still
about 23 per cent. of alcohol in the product; and from this cir-
cumstance it may be concluded that the retention of alcohol by
ethylate of sodium is very obstinate.

On raising the temperature considerably higher the expulsion
of alcohol is complete, and absolute ethylate remains behind, as
is shown by the following :—

elk
Weight of sodium employed. . 2 0584
Weight of product of action on aleohol after heating 1-694
for some time from 190° to 205°

In a second experiment, in which the temperature of the oil-
bath was high but not measured, the quantities were :—

erm.

Sodiumitaken’..)..°. . ,O:498
Ethylate obtained . . . 1:°453
We have, therefore,
Exp. I. Percentage of sodium in product = 34°48
Exp. IT. = 34°28
Theory for INFO O 20. | Pk gets

At about 200° C., therefore, pure absolute ethylate of sodium
may be obtaimed from the crystals. This result was confirmed
by an observation of the degree of alkalinity of the product
which had been exposed to a temperature of 200°C. The 1:694
germ. which had been obtained from 0°584 grm. of sodium
(Exp. I.) was placed in water, which of course resolved it into
alcohol and caustic soda. It was then titrated with normal sul-
phuric acid. It saturated 25°5 cubic centims. of the acid, show-
ing 0°5865 grm. of sodium in a state of causticity. All the
sodium, therefore, was caustic; no organic acid, therefore, had
been produced by the action of the high: temperature on the
ethylate of sodium. A still more severe test of the stability of
the ethylate at 200° C. is afforded by the following experiment.

1:3285 grm. of sodium was dissolved in absolute alcohol, and

120 Prof. J. A. Wanklyn on Ethylate of Sodium

the resulting ethylate of sodium maintained for some time at
about 200° C. Weight of the product 3°862 grm.

Found, Na percent. . . =384°40
Dheory sg cce 6. mee

The amount of alcohol given on distillation with water was
next estimated. Added 50 cubic centims. of water and distilled
off 32°713 grms., which had a specific gravity of 0-9868 at 16° C.,
and which therefore consisted of 8:0 per cent. alcohol. Weight of
alcohol obtained =2°616 grms. Therefore the quantity of alco-
hol yielded by 100 parts of the substance is 67°7 parts. The
theory for ethylate of sodium requires 67°65 parts.

Further experiment has also shown that even a temperature of
290° C. is sustained by ethylate of sodium without decomposition.

When ethylate of sodium is very strongly heated, viz. up to
dull redness, having ceased to evolve alcohol, it evolves no ap-
preciable quantity of liquid product, but carbonizes with evolu-
tion of a certain quantity of gas. A rough examination of the
gas showed the absence of olefines and of carbonic oxide. The
gas was of low specific gravity, and burnt with a not very Jumi-
nous flame. It was apparently marsh-gas, or marsh-gas and
hydrogen. The residual solid product contained (as was made
out by titration) all the sodium in the state of metal, caustic, or
carbonate ; therefore no stable acid had resulted.

The presence of free metallic sodium, or possibly carbide of
sodium, in the residue was proved by the very violent efferves-
cence which the addition of water to the residue occasioned.
The presence of a considerable amount of carbonate was proved
by the evolution of carbonic acid which took place on making
the titration with standard acid. A considerable quantity of
black carbon separated on dissolving the product in water.
Weighings were made of the amount of sodium which was con-
verted into ethylate, and also of the total solid product left after
the heating to redness, as follows :—

grms.
Sodium taken = 0:792 grm., equivalent to are
to ethylate of sodium, C? He NaO : Te
Residual solid product . . . wk = 1588

‘Rherefore volatile product... ss. name = ‘754

A weighing was made of the black carbon got on treatment of
the solid residue with water and test acid, and after subsequent
washing and drying.

Black carbon =0:216 grm.

(There had been a slight loss of the black carbonaceous matter,
so that the number is only a rough approximation.)

and Kihylate of Potassium. \21

Absolute ethylate of soda (NaC? H®O) is a perfectly white
amorphous solid. It is non-fusible, differmg totally from the
crystals. Its specific gravity is very low ; it swims inether. It
is almost insoluble in ether, 1000 parts of ether not dissolving
more than 2 or 3 parts of the ethylate. As has been hinted, it
becomes brown on exposure to the air; otherwise it may be
heated to a very high temperature, 275° C. (and probably much
higher), without losing its whiteness.

With acetic ether or valerianic ether it behaves in a very in-
teresting manner. There is, first of all, combination, and after- |
wards, between 100° and 200° C., an abundant disengagement
of alcohol.

Ethylate of sodium. Acetic ether.
C? H* NaO H+ C? H°O C? H?O
New compound.

——__ Alcohol.
= He Nal" O16 Ho O-- €* He @,

The new compounds (in the case of acetic ether an isomer of
butyrate of soda, and in the case of valerianic ether an isomer of
cenanthylate of soda) are being investigated. ‘They appear to
yield alcohol and a salt of soda on being treated with water,
thus :—

Isomer of butyrate of soda.
—_——~ Aleohol. Acetate of soda.
a2 rH Nal’O'C? HC O+ H? O=C? H®O+ NaO C? H3 O.

Potassium and Alcohol.

Potassium reacts with extreme violence on alcohol. It forms
a compound consisting of ethylate of the metal and alcohol; the
number of molecules of alcohol in combination with the ethy-
late has not been determined ; but the existence of a compound
of the kind is made out. At a high temperature, towards
200° C., the absolute ethylate is produced. During the expul-
sion of the alcohol there is a marked difference in appearance
between the potash- and the soda-compound, the potash-com-
pound remaining fusible at a much higher temperature than the
soda-compound.

London Institution,
January 21, 1869.

Fs 223

XVII. On the Relation of Hydrogen to Palladium.
By Tuomas Granam, F.R.S., Master of the Mint*,

Dig often been maintained on chemical grounds that hy-

drogen gas is the vapour of a highly volatile metal. The
idea forces itself upon the mind that palladium with its occluded
hydrogen is simply an alloy of this volatile metal, in which the
volatility of the one element is restrained by its union with the
other, and which owes its metallic aspect equally to both consti-
tuents. How far such a view is borne out by the properties of
the compound substance in question will appear by the following
examination of the properties of what, assuming its metallic cha-
racter, would have to be named Hydrogenium.

1. Density.—The density of palladium when charged with eight
or nine hundred times its volume of hydrogen gas is perceptibly
lowered ; but the change cannot be measured accurately by the
ordinary method of immersion in water, owing to a continuous
evolution of mimute hydrogen bubbles which appears to be de-
termined by contact with the liquid. However, the linear dimen-
sions of the charged palladium are altered so considerably that
the difference admits of easy measurement, and furnishes the
required density by calculation. Palladium in the form of wire
is readily charged with hydrogen by evolving that gas upon the
surface of the metal in a galvanometer containing dilute sulphuric
acid as usual+. The length of the wire before and after a charge
is found by stretching it on both occasions by the same moderate
weight, such as will not produce permanent distention, over the
surface of a flat graduated measure. The measure was graduated
to hundredths of an inch, and by means of a vernier the divi-
sions could be read to thousandths. The distance between two
fine cross lines marked upon the surface of the wire near each of
its extremities was observed.

Exp. 1.—The wire had been drawn from welded palladium, and
was hard and elastic. The diameter of the wire was 0:462 mil-
lim. ; its specific gravity was 12°38, as determined with care.
The wire was twisted.into a loop at each end and the mark made
near each loop. The loops were varnished so as to limit absorp-
tion of gas by the wire to the measured length between the two
marks. To straighten the wire, one loop was fixed, and the
other connected with a string passing over a pulley and loaded
with 1:5 kilogramme, a weight sufficient to straighten the wire
without occasioning any undue strain. The wire was charged
with hydrogen by making it the negative electrode of a small
Bunsen’s battery consisting of two cells, each of half a litre in

* Read before the Royal Society January 7, 1869.

+ Proceedings of the Royal Society, vol. xvi, p. 422 (1868). [ Phil. Mag.
Ser. 4. vol. xxxvi. p. 63.]

On the Relation of Hydrogen to Palladium. 123

capacity. The positive electrode was a thick platinum wire
placed side by side with the palladium wire, and extending the
whole length of the latter within a tall jar filled with dilute sul-
phuric acid. The palladium wire had, in consequence, hydrogen
carried to its surface, for a period of 1} hour. A longer exposure
was found not to add sensibly to the charge of hydrogen acquired
by the wire. The wire was again measured and the increase in
length noted. Finally the wire, being dried with a cloth, was
divided at the marks, and the charged portion heated in a long
narrow glass tube kept vacuous by a Sprengel aspirator. The
whole occluded hydrogen was thus collected and measured ; its
volume is reduced by calculation to Barom. 760 millims., and
Therm. 0° C.

The original length of the palladium wire exposed was 609°144:
millims. (23°982 inches), and its weight 1°6832 grm. The wire
received a charge of hydrogen amounting to 936 times its volume,
measuring 128 cubic centims., and therefore weighing 0°01147
erm, When the gas was ultimately expelled, the loss as ascer-
tained by direct weighing was 0°01164 grm. The charged wire
measured 618°923 millims., showing an increase in length of
9°779 millims. (0°385 inch). The increase in linear dimensions
is from 100 to 101°605, and in cubic capacity, assuming the
expansion to be equal in all directions, from 100 to 104°908.
Supposing the two metals united without any change of volume,
the alloy may therefore be said to be composed of

By volume.
Paladin) 4. . 100 or 95°32
Hydrogenium . . 4°908 or 4°68
104°908 100

The expansion which the palladium undergoes appears enormous
if viewed as a change of bulk in the metal only, due to any con-
ceivable physical force, amounting as it does to sixteen times the
dilatation of palladium when heated from 0° to 100° C. The
density of the charged wire is reduced by calculation from 12:3
to 11°79. Again, as 100 is to 4°91, so the volume of the palla-
dium, 0°13858 cubic centim., is to the volume of the hydrogenium
0006714 cubic centim. Finally, dividing the weight of the hy-
drogenium, 0:01147 grm., by its volume in the alloy, 0-006714.
cubic centim., we find
Wencity of hydrogenium . . . 1°'708

The density of hydrogenium, then, appears to approach that
of magnesium, 1°743, by this first experiment.

Further, the expulsion of hydrogen from the wire, however
caused, is attended with an extraordinary contraction of the latter.
On expelling the hydrogen by a moderate heat, the wire not only

124 Mr. T. Graham on the Relation of

receded to its original length, but fell as much below that zero
as it had previously risen above it. The palladium wire first
measuring 609°144 millims., and which increased 9°77 millims.,
was ultimately reduced to 599°444 millims., and contracted 9°7
millims. The wire is permanently shortened. The density of
the palladium did not increase, but fell slightly at the same time,
namely from 12°38 to 12°12; proving that this contraction of
the wire is in length only. The result is the converse of exten-
sion by wire-drawing. The retraction of the wire is possibly
due to an effect of wire-drawing in leaving the particles of metal
in a state of unequal tension, a tension which is excessive in the
direction of the length of the wire. The metallic particles
would seem to become mobile, and to right themselves in pro-
portion as the hydrogen escapes; and ‘the wire..cateniets in
length, expanding, as appears by its final density, in other di-
rections at the same time.

A wire so charged with hydrogen, if rubbed with the powder
of magnesia (to make the flame luminous), burns like a waxed
thread when ignited in the flame of a lamp.

Exp. 2.—Another portion of the same palladium wire was
charged with hydrogen in a similar manner. ‘The results ob-
served were as follows :—

Length of palladium wire . . . + 488°976 millims.
The same with 867-15 volumes of occluded eas 495°656 _,,
Linear elongation . . OO GS z
Linear elongation on. 100 2... . ( eeeGGsmae
Cubic expansion on 1006.2 2%. ee
Weight of palladium-wire . . ; ~~ >290)EOGE7term:
Volume of palladium wire . . . . . . 0:08072 cub.c.
Volume of occluded hydrogen gas si te: ye aie
Weightiotsane. pene. oie te oe ORO Ose: erm.
Volume of hydrogenium. . . .'. . = @00s00Ment ce
From these results is calculated

Density of hydrogenium . .. . 1°898.

Exp. 3.—The palladium wire was new, and on this occasion
was well annealed before being charged with hydrogen. The
wire was exposed at the negative pole for two hours, when it had
ceased to elongate.

Length of palladium wire. . . . 556°185 millims.
Same with 888°303 volumes hydrogen 563°652 __,,
Linear elongation . . ba! “(ATi
Linear elongation on 100. . . . 1324
Cubie-expansionion 100-1 2-2. > 4:025— ee

Weight of palladium wire pete bel 0/05) ero

Hydrogen to Palladium. 125

Volume of palladium wire’ . . . 00949 cub. centim.
Volume of occluded hydrogen gas . 84°3 cub. centims.
Weight of same. . fo 3. OOO 7ans erm.
Volume of hydrogenium as) 2. .O'008820 cub: centim-

These results give by calculation
Density of hydrogenium . . . . 1°977.

It was necessary to assume in this discussion that the two
metals do not contract nor expand, but remain of their proper
volume on uniting. Dr. Matthiessen has shown that in the for-
mation of alloys generally the metals retain approximately their
original densities *.

In the first experiment already described, probably the maxi-
mum absorption of gas by wire, amounting to 935°67 volumes,
1s attained. The palladium may be charged with any smaller
proportion of hydrogen by shortening the time of exposure to
the gas (329 volumes of hydrogen were taken up in twenty mi-
nutes), and an opportunity be gained of observing if the density
of the hydrogenium remains constant, or if it varies with the
proportion in which hydrogen enters the alloy. in the follow-
ing statement, which includes the three experiments already re-
ported, the essential points only are produced :—

TABLE.
; Linear expansion in
eanbed millimetres. Density of
NCENGCd Guest sso | es Te Se hydrogenium.
From To
329 496:189 498-552 2-055
462 493-040 496°520 1:930
487 370°358 373°126 1-927
745 305°538 511°303 1:917
867 488-976 495:656 1-898
888 556°185 563-652 1:977
936 609-144 618-923 1:708

If the first and last experiments only are compared, it would
appear that the hydrogenium becomes sensibly denser when the
proportion of it is small, ranging from 1708 to 2055. But the
last experiment of the Table is perhaps exceptional ; and all the
others indicate considerable uniformity of density. The mean
density of hydrogenium, according to the whole experiments, ex-
cluding that last referred to, is 1951, or nearly 2. This unifor-
mity is in favour of the method followed for estimating the den-
sity of hydrogenium.

On charging and discharging portions of the same palladium

* Philosophical Transactions, 1860, p. 177.

126 Mr. T. Graham on the Relation of

wire repeatedly, the curious retraction was found to continue,
and seemed to be interminable. The following expansions,
caused by variable charges of hydrogen, were followed on expel-
ling the hydrogen by the retractions mentioned :—

Elongation. Retraction.
lst Experiment 9°77 milliims. . . 9°70 millims.
2nd 5 D700 os |. 2 ORO
ord a 236" %,, ala
Ath = 3°482__,, . Sao ie
23°99

The palladium wire, which originally measured 609:144 mil-
lims., has suffered, by four successive discharges of hydrogen from
it, a permanent contraction of 23°99 millims.; that is, a reduc-
tion of 3:9 per cent. on its original Jength. The contractions
will be observed to exceed in amount the preceding elongations
produced by the hydrogen, particularly when the charge of the
latter is less considerable. With another portion of wire the
contraction was carried to 15 per cent. of its length by the effect
of repeated discharges. The specific gravity of the contracted
wire was 12°12, no general condensation of the metal having
taken place. The wire shrinks in length only.

In the preceding experiments the hydrogen was expelled by
exposing the palladium placed within a glass tube to a moderate
heat short of redness, and exhausting by means of a Sprengel
tube; but the gas was also withdrawn im another way, namely,
by making the wire the positive electrode, and thereby evolving
oxygen upon its surface. In such circumstances a slight film of
oxide of palladium is formed on the wire, but it appears not to
interfere with the extraction and oxidation of the hydrogen. The

wire measured
Difference.

Before charge . . 448°25 millims.
With hydrogen . . 449°90 _,, +6°65 millims.
After discharge . . 4387:31 _,, ta a

The retraction of the wire therefore does not require the con-
currence of a high temperature. This experiment further proved
that a large charge of hydrogen may be removed in a complete
manner by exposure to the positive pole (for four hours in this
case) ; for the wire in its ultimate state gave no hydrogen on
being heated zn vacuo.

That particular wire which had been repeatedly charged with
hydrogen, was once more exposed to a maximum charge, for the
purpose of ascertaining whether or not its elongation under hy-
drogen might now be facilitated and become greater in conse-
quence of the previous large retraction. No such extra elonga-

Hydrogen to Palladium. - 127

tion, however, was observed on charging the retracted wire more
than once; and the expansion continued to be in the usual pro-
portion to the hydrogen absorbed. The final density of the wire
was 12°18.

The wire retracted by heat is found to be altered in another
way, which appears to indicate a molecular change. The metal
gradually loses much of its power to take up hydrogen. The
last wire, after it had already been operated upon six times, was
again charged with hydrogen for two hours, and was found to
occlude only 320 volumes of gas, and in a repetition of the ex- |
periment 330°5 volumes. The absorbent power of the palladium
had therefore been reduced to about one-third of its maximum.

The condition of the retracted wire appeared, however, to be
improved by raising its temperature to full redness by sending
through it an electrical current from a battery. The absorption
rose thereafter to 425 volumes of hydrogen, and in a second ex-
periment to 422°5 volumes.

The wire becomes fissured longitudinally, acquires a thready
structure, and is much disintegrated on repeatedly losing hy-
drogen, particularly when the hydrogen has been extracted by
electrolysis in an acid fluid. The palladium in the last case is
dissolved by the acid to some extent. The metal appeared, how-
ever, to recover its full power to absorb hydrogen, now conden-
sing upwards of 900 volumes of gas.

The effect upon its length of simply annealing the palladium
wire by exposure in a porcelain tube to a full red heat, was ob-
served. The wire measured 556:075 millims. before, and 555°875
millims. after heating; or a minute retraction of 0:2 millim.
was indicated. Ina second annealing experiment, with an equal
length of new wire, no sensible change whatever of length could
be discovered. There is no reason, then, to ascribe the retraction
after hydrogen, in any degree, to the heat applied when the gas
is expelled. Palladium wire is very slightly affected in physical
properties by such annealing, retaining much of its first hardness
and elasticity.

2. Tenacity.—A new palladium wire, similar to the last, of
which 100 millims. weighed 0:1987 grm., was broken, in expe-
riments made on two different portions of it, by a load of 10 and
of 10°17 kilogrammes. Two other portions of the same wire,
fully charged with hydrogen, were broken by 8°18 and by 8°27
kilogrammes. Hence we have—

Tenacity of palladium wire . . . 100
Tenacity of palladium and hydrogen 81:29

The tenacity of the palladium is reduced by the addition of hy-
‘drogen, but not to any great extent. It is a question whether

128 Mr. T. Graham on the Relation of

the degree of tenacity that still remains is reconcilable with any
other view than that the second element present possesses of
itself a degree of tenacity such as is only found in metals.

8. Electrical Conductwity—Mr. Becker, who is familiar with
the practice of testing the capacity of wires for conducting elec-
tricity, submitted a palladium wire, before and after charging
with hydrogen, to trial, in comparison with a wire of German
silver of equal diameter and length, at 10°°5. The conducting-
power of the several wires was found as follows, being referred to
pure copper as 100 :—

Pure copper 4." wi

Palladium: 727 3.04 8:10
Alloy of 80 copper +20 nickel . 6°63
Palladium + hydrogen . . . 5:99

A reduced conducting-power is generally observed in alloys; and
the charged palladium wire falls 25 per cent. But the conduct-
ing-power remains still considerable, and the result may be
construed to favour the metallic character of the second consti-
tuent of the wire. Dr. Matthiessen confirms these results.

4. Magnetism.—lIt is given by Faraday as the result of all his
experiments, that palladium is “feebly but truly magnetic ;”
and this element he placed at the head of what are now called
the paramagnetic metals. But the feeble magnetism of palla-
dium did not extend toits salts. In repeating such experiments,
a horseshoe electromagnet of soft iron, about 15 centims. (6 inches)
in height, was made use of. It was capable of supporting 60
kilogs. when excited by four large Bunsen cells. This is an
induced magnet of very moderate power. The instrument was
placed with its poles directed upwards; and each of these was
provided with a small square block of soft iron terminating la-
terally in a point, lke a small anvil. The palladium under
examination was suspended between these points in a stirrup of
paper attached to three fibres of cocoon silk, 3 decimetres in
length, and the whole was covered by a bellglass. A filament
of glass was attached to the paper, and moved as an index on a
circle of paper on the glass shade divided into degrees. The
metal, which was an oblong fragment of electro-deposited palla-
dium, about 8 millims. in length and 3 millims. in width, being .
at rest in an equatorial position (that is, with its ends averted
from the poles of the electromagnet), the magnet was then charged
by connecting it with the electrical battery. The palladium was
deflected slightly from the equatorial line by 10° only, the mag-
netism acting against the torsion of the silk suspending thread.
The same palladium charged with 604°6 volumes of hydrogen
was deflected by the electromagnet through 48°, when it set

Hydrogen to Palladium. 129

itself at rest. The gas being afterwards extracted, and the pal- —
ladium again placed equatorially between the poles, it was not
deflected in the least perceptible degree. The addition of hy-
drogen adds manifestly, therefore, to the small natural magnetism
of the palladium. To have some terms of comparison, the same
little mass of electro-deposited palladium was steeped in a solu-
tion of nickel, of specific gravity 1:082, which is known to be
magnetic. The deflection under the magnet was now 35°, or
less than with hydrogen. The same palladium being afterwards
washed and impregnated with a solution of protosulphate of iron ~
of specific gravity 1:048, of which the metallic mass held 2°3 per
cent. of its weight, the palladium gave a deflection of 50°, or
nearly the same as with hydrogen. With a stronger solution of
the same salt, of specific gravity 1:17, the deflection was 90°,
and the palladium pointed axially.

Palladium in the form of wire or foil gave no deflection when
placed im the same apparatus, of which the moderate sensitiveness
was rather an advantage in present circumstances; but when
afterwards charged with hydrogen, the palladium uniformly gave
a sensible deflection of about 20°. A previous washing of the
wire or foil with hydrochloric acid, to remove any possible traces
of iron, did not modify this result. Palladium reduced from the
cyanide and also precipitated by hypophosphorous acid, when
placed in a small glass tube, was found to be not sensibly mag-
netic by our test; but it always acquired a sensible magnetism
when charged with hydrogen.

It appears to follow that hydrogenium is magnetic, a property
which is confined to metals and their compounds. This mag-
netism is not perceptible in hydrogen gas, which was placed
both by Faraday and by M. E. Becquerel at the bottom of the
list of diamagnetic substances. This gas is allowed to be upon
the turning-point between the paramagnetic and diamagnetic
classes. But magnetism is so liable to extinction under the in-
fluence of heat, that the magnetism of a metal may very possibly
disappear entirely when it is fused or vaporized, as appears with
hydrogen in the form of gas. As palladium stands high in the
series of the paramagnetic metals, hydrogenium must be allowed
to rise out of that class, and to take place in the strictly mag-
netic group, with iron, nickel, cobalt, chromium, and man-
ganese.

Palladium with Hydrogen at a high Temperature.—The ready
permeability of heated palladium by hydrogen gas would imply
the retention of the latter element by the metal even at a bright
red heat. The hydrogenium must in fact travel through the
palladium by cementation, a molecular process which requires
time. The first attempts to arrest hydrogen im its passage

Phil, Mag. 8. 4. Vol. 37. No. 247. Feb. 1869. K

130 On the Relation of Hydrogen to Palladium.

through the red-hot metal were made by transmitting hydrogen

gas through a metal tube of palladium with a vacuum outside,
rapidly followed by a stream of carbonic acid, in which the
metal was allowed to cool. When the metal was afterwards ex-
amined in the usual way, no hydrogen could be found in it.
The short period of exposure to the carbonic acid seems to have
been sufficient to dissipate the gas. But on heating palladium
foil red-hot in a flame of hydrogen gas, and suddenly cooling
the metal in water, a small portion of hydrogen was found
locked up in the metal. A volume of metal amounting to 0-062
cubic centim., gave 0°080 cubic centim. of hydrogen; or, the
gas, measured cold, was 1°306 time the bulk of the metal.
This measure of gas would amount to three or four times the
volume of the metal at a red heat. Platinum treated in the
same way appeared also to yield hydrogen, although the quantity
was too small to be much relied upon, amounting only to 0:06
volume of the metal. The permeation of these metals by hy-
drogen appears therefore to depend on absorption, and not to
require the assumption of anything like porosity in their stucture.

The highest velocity of permeation observed was in the expe-
riment where four litres of hydrogen (3992 cubic centims.) per
minute passed through a plate of palladium | millim, in thick-
ness, and calculated for.a square metre in surface, at a bright
red heat, a little short of the melting-point of gold. This is a
travellmg movement of hydrogen through the substance of the
metal with the velocity of 4 millims. per minute.

The Chemical Properties of hydrogenium also distinguish it
from ordmary hydrogen. . The palladium alloy precipitates
mercury and calomel from a solution of the chloride of mercury
without any disengagement of hydrogen; that is, hydrogenium
decomposes chloride of mercury, while hydrogen does not.
This explains why M. Stanislaus Meunier failed to discover
the occluded hydrogen of meteoric iron by dissolving the latter
im a solution of chloride of mercury ; for the hydrogen would
be consumed, like the iren itself, in precipitating mercury. Hy-
drogen (associated with palladium) unites with chlorine and
iodine in the dark, reduces a persalt of iron to the state of
protosalt, converts red prussiate of potash into yellow prussiate,
and has considerable deoxidizing powers. It appears to be the
active form of hydrogen, as ozone is of oxygen.

The general conclusions which appear to flow from this in-
quiry are that in palladium fully charged with hydrogen (as in
the portion of palladium wire now submitted to the Royal
Society) there exists a compound of palladium and hydrogen in
a proportion which may approach to equal equivalents*; that

* Proceedings of the Royal Society, 1868, vol. xvi. p. 425. [Phil. Mag.
July 1868, p. 66. ]

On some Phenomena of Binocular Vision. 13]

both substances are solid, metallic, and of a white aspect ; that
the alloy contains about 20 volumes of palladium united with 1
volume of hydrogenium, and that the density of the latter is
about 2, a little higher than magnesium, to which hydrogenium
may be supposed to bear some analogy; that hydrogenium
has a certain amount of tenacity, and possesses the electrical
conductivity of a metal; and, finally, that hydrogenium takes
its place among magnetic metals. The latter fact may have its
bearing upon the appearance of hydrogenium in meteoric iron,
in association with certain other magnetic elements.

I cannot close this paper without taking the opportunity to
return my best thanks to Mr. W. C. Roberts for his valuable co-
operation throughout-the investigation.

XVIII. On some Phenomena of Binocular Vision. By Josrru
LrConte, Professor of Chemistry and Geology in the Uni-
versity of South Carolina *.

I. Adjustments of the Eye.

a kinds of ocular adjustment take place in every volun-
tary act of sight, viz. (1) a proper convergence of the optic
axes so that they shall meet on the object of sight, and (2) an
adjustment of each eye so that the diverging pencil of rays which
enters the pupil shall be brought to perfect focus, and therefore
produce ‘a perfect image on the retina. The first or binocular
adjustment is necessary for single vision ; the second or focal ad-
justment is necessary for distinct vision. The first is distinctly
sensible for all distances within 100 yards, and perhaps for much
greater distances; the second is scarcely, if at all, sensible for
distances beyond two yards.

To the two adjustments mentioned above may be added a
third, viz. contraction of the pupil. The design of the contrac-
tion of the pupil is probably to increase the clearness of defini-
tion of the retinal image by cutting off the most divergent rays
from very near objects, and thus to decrease the spherical aber-
ration which is not entirely corrected in the eye by the form of
the lens. The pupil, however, also contracts involuntarily under
the stimulus of strong hght, without regard to distance. This
must be carefully distinguished from the adjustive contraction,
which is (to some extent at least) voluntary.

These three adjustments of the eye, viz. binocular or axial
adjustment, focal adjustment, and contraction of the pupil, are
associated in every voluntary act of sight. They are accom-
plished by one act of volition. They are so intimately associ-
ated that they cannot be voluntarily separated. It is usually

* From Silliman’s American Journal for January 1869.

K 2

132 Prof. J. LeConte on some Phenomena

impossible to converge the optic axes on any point without at
the same time adjusting the lens and contracting the pupil in
a manner suitable for perfect vision at that distance. Such
inseparably associated movements are called consensual move-
ments.

The binocular adjustment is well understood ; there is no dif-
ference of opinion as to its necessity, nor the means by which it
is accomplished. But in regard to the focal adjustment, there
has been much difference of opinion among the best physiolo-
gists and physicists. Some have denied altogether the necessity,
and therefore the existence, of any adjustment—attributing the
phenomena which are usually explained by this means to mere
transference of attention from near to distant objects, or vice
versd. The large majority of the best physicists and physiolo-
gists, however, have for a long time regarded focal adjustment
as an optical necessity, and therefore a fact ; but the real nature
of this adjustment, and the means by which it is accomplished,
has been a question in doubt. It has been attributed by some tothe
elongation of the eye by the action of the recti muscles, by others
to the change in the convexity of the cornea, by others to the
structure of the crystalline lens combined with contraction of the
pupil, by others to the pulling forward of the erystalline lens
by the ciliary muscle so as to elongate the chamber behind the
lens, and by still others to the change of form of the lens by
the action of the ciliary musele. Recent very ingenious obser-
vations by Donders, Cramer, and Helmholtz upon the images of
external objects made by reflection from the anterior surface of
the crystalline lens, and the changes in form and size which they
undergo when the eye is adjusted for near objects, have definitely
settled the question in favour of a change in the curvature of the
lens. The mechanism by which this change 1s effected is not
clearly known ; but it is probable that it is effected by the action
of the cihary muscle,

Before giving some experiments which bear upon the question
of adjustment, I will state that my eyes are perfectly normal.
In youth and early manhood the natural distance for distinct
vision of small objects was eight inches ; but with effort I could
see perfectly distinctly at five inches. At the present time my
natural distance for fine print 1s ten inches, though with effort I
see distinctly at eight inches. Beyond this there is for me no
limit of distinct vision. My eyes define the edge of the moon
as perfectly as they do an object at the distance of ten inches.
Moreover, by long practice I have acquired considerable, and
perhaps very unusual facility in making experiments on binocu-
lar vision and in analyzing my visual impressions. ‘The follow-
ing experiments, which I have practised from boyhood, are in-

of Binocular Vision. 133

teresting, not only as a beautiful illustration of the laws of
binocular vision, but, I believe, as throwing some light on the
subject of adjustment, and also upon the difficult subject of the
horopter.

If a plane surface checkered or otherwise figured in regular

pattern, such as an oil floor-cloth, a tessellated pavement, or a
papered wall, be placed before the eyes at the distance of several
feet and the optic axes be then voluntarily converged (the eyes
crossed) upon some point in space nearer than the surface, the
figures will of course be all seen double. If, now, the conver- ~
gence be steadily increased until two contiguous similar images,
one belonging to the right eye and one to the left, are made to
coincide perfectly, and the eyes be then held steadily in this po-
sition for some time, the patterned surface will be distinctly seen
In exquisite miniature, not at its proper distance, but between
the real object and the eye, at a distance depending upon the
interval between the centres of the contiguous similar figures of
the pattern. If the pattern be very regular, the illusion is com-
plete; we actually seem to
be looking at a real object. Fig. 1.
In this experiment the po-
sition of the eyes is such
that, of two contiguous si-
milar figures, the right eye
is directed toward the left
figure and the left eye to-
ward the right figure ; and
the image is seen at the
crossing of the visual lines.
Thus if one eye be directed
toward a (fig. 1) and the
other toward 0b, a perfect
image or these two figures
will be seen ata’. So also
6 and c will be united and
seen at c’ anda and dat d',
and so on for all the figures
ofthe pattern. The dotted line d! a’ c' will be the position of the
image-surface. - The image thus obtained may be a little indi-
stinct at first, but it gradually grows perfectly clear. As soon
as the image is distinctly seen and the outlines of the figures
well defined, it may be retained without any difficulty; for we
seem to be looking at a real object, and therefore retain the ne-
cessary convergence of the optic axes with ease. The eyes may
now be turned m every direction, viewing this extensive image-
surface precisely as if 1t were a real surface.

a el 6 e

134 Prot. J. LeConte on some Phenomena

If, now, while viewing the image in the last experiment, we
repeat upon it the same experiment, 7. e. if by increasing the
convergence of the optic axes we bring again the two contiguous
figures into coincidence, a new image is formed between the last
and the eye, and is seen in still smaller miniature. In this case
the position of the optic axes is such that the eyes crossing are
directed, not toward contiguous figures of the real object, but to
figures separated by an intervening one. Thus in the figure
(fig. 2) a and c will be combined and seen at a’, d and 0 at d",
and 6 and e at e”.

Upon this second image the same experiment may be repeated
so as to make a third image still smaller and nearer the eye at
de and: trom. tthe ves
third even a fourth and Hes
still smaller image ma
be formed ate”. The
positions of these succes-
sive planes are indicated
by the dotted lines ; but
in this figure the posi-
tion of the axes is only
adapted to vision on
plane No. 2. For the
higher planes, the optic
axes must converge still
more. For the fourth
plane Le and [Id will
represent the visual —@ a & € é
lines. Standing erect
and looking down upon the regularly checkered carpet on the
floor of my room, the figures of which are 44 inches from centre
to centre, I can with the greatest ease bring out successively
four distinct images one above the other, the nearest being but
seven inches from my eyes, and the figures (which are 2 inches
in diameter in the carpet) reduced to about } inch in diameter.
If while looking at the image on the fourth plane the conver-
gence of the optic axes be suddenly relaxed, the image drops and
may be caught on No. 3. Again, by relaxing the convergence
it may be dropped and caught on successive planes until it falls
to its natural position.

I have made similar experiments on a great variety of patterns
of wall-papering, oil-cloths, calicoes, &c. with the same results.
Of a regularly checked oil-cloth in my hall, the lozenge-shaped
figures of which are 10:2 inches across, I make successively
three perfectly distinct images, the nearest being but 44 inches
from the eyes.

of Binocular Vision. 135

Those who are not accustomed to experiments of this kind
can probably most easily succeed as follows. If we look on the
floor and place the finger between the eye and the floor, the
finger will of course be seen double. Now move the finger up
or down until we find a place in which the two images of the
finger will exactly fall on contiguous figures of the pattern ; the
finger now indicates the position of the first plane. Now look
steadily at the finger instead of the floor until the image of the
floor rises to it and becomes distinct, then withdraw the finger.
To get the second plane, look again at the floor and raise the
finger until its images fall upon figures separated from one an-
other by an intervening figure and then Jook steadily at the
finger. The other planes may be obtained in a similar manner.
The position of the several planes may also be easily calcu-
lated—the data being the interocular line, the distance of the
object, and the interval from centre to centre of the figures.
Both by measurement and calculation I determined the planes
in the case of the carpet to be 21°5, 13°05, 9°37, and 7°3
inches respectively. In the case of the oil-cloth they were 11°8,
6°54, and 4°5 inches.

If the distance between the centres of contiguous figures
be less than the mterocular line, then still other images may
be seen beyond the real object and very much enlarged. The
position of the eyes and the place of the image in this case also
is easily. explained. If dabc (fig. 3) be the plane of the real

object, and the eyes I and II be directed toward contiguous”
figures a and 6 but not crossed, then the image of a and 8 will
combine and be seen at a’, the imtersection of the visual lines.

136 Prof. J. LeConte on some Phenomena

So also a and d will be seen at d', and 6 and c¢ at c!, and the
dotted line will represent the position of the image-plane.. In
order to make this image, we must gaze through and beyond the
pattern until we observe the double images come together and
coincide, and then fix the eyes steadily. The enlarged image
gradually becomes distinct.

This experiment is much more difficult than the preceding.
The pattern should not be too small, otherwise the difficulty is
very great. In former years I had often performed the experi-
ment with perfect success ; but the wall-papering I had used for
this purpose had been destroyed, and I found difficulty in again
obtaining a suitable pattern. I therefore constructed a pattern
by ruling black lines on a large sheet of paper so as to make
perfectly equal squares 14 inch wide. With this simple diagram
my success in all the preceding experiments was really marvel-
lous. The coloured patterns before used form far more beautiful
images ; but for scientific purposes the ruled diagram is far pre-
ferable. With this diagram standing upright before me at the
distance of sixteen inches, I got with great ease seven successive
images on this side of the object, and one beyond. All the
images on this side were defined with great ease and perfect dis-
tinctness, although the nearest both by measurement and by
calculation was but three inches from my eyes, 7. e. far within
the limits of my distinct vision. With great effort I could ob-
tain others still nearer. The nearest I actually retained and
measured was but 11 inch from the root of the nose; but I after-
wards found that there was no limit except the root of the nose
itself. Within three inches, however, the images were no
longer perfect, not from any want of distinctness of the lines,
but because the horizontal lines of the two images were no
longer parallel, but crossed one another, as shown in the figure
(fig. 4), and therefore could not be made to coalesce perfectly.

Fig. 4.

ay

The explanation of this will be given in its proper place.
The still nearer images, as, for instance, those within 14 inch,
could not be retained ; the strain on the interior recti muscles
of the eye was too great.

The image beyond the object is much more difficult to obtain
with clearness, especially if the object be near the eyes. At the

of Binocular Vision. 137

distance of two feet from the object 1 obtained the image very
clearly and without much difficulty; but on approaching to
within ten or twelve inches it was only by patient trial for some
time that it could be brought out with perfect distinctness.
When the object was twelve inches from the eyes, the image, by
calculation, was found to be about thirty inches distant. By
turning the diagram so that the diagonals were horizontal, and
similar points therefore more than two inches apart, the image
was seen at the distance of about six feet. It had the exact ap-
pearance of a tessellated marble pavement made up of squares
nine inches on a side.

In all these experiments the least irregularity in the pattern
shows itself very conspicuously in the image, not by indistinct-
ness of outline of the figures, but by apparent inequality in the
plane of the image. Thus in the carpet it shows itself by an
apparent wrinkle, in the lined diagram by some of the lines
rising like black threads stretched above the general surface of
the image. This phenomenon is a familiar one in stereoscopy,
and is used for detecting the slightest difference in two appa-
rently similar patterns, as, for instance, between a genuine and
a forged bank-bill.

I believe any one, and particularly any young person with
good eyes, can with pr actiée succeed in all the experiments de-
tailed above. Several of my family have tried them with success.
Yet in all cases it requires some practice to succeed well. Ican,
even yet, always detect some difficulty on first trial after an in-
terval of a few days. But after several hours’ practice the illu-
sion is so complete that it is almost impossible to dispelit. The
image is so real, that in attempting to recover the real object
by relaxing the convergence of the optic axes, the doubling of
the lines causes the eyes instinctively to return to their former
position, and thus to restore the image. I have sometimes

been actually obliged to look away in order to recover the real
object.

The experiments detailed above have an important bearing on
some points in the theory of vision. It is the universally ac-
cepted doctrine among physiologists that the axial and focal ad-
justments of the eye cannot be dissociated. Helmholtz, speaking
of the consensual movements of the eyes, says, “ We cannot
turn one eye up and the other down; we cannot move both
eyes at the same time outward; we are obliged to combine
always a certain degree of Seeoatiodacion of the eye to distance
[focal adjustment], with a certain angle of convergence of the
axes [axial adjustment]”*. He proceeds, however, to give cer-

* Helmholtz, Croonian Lecture, Proc. Roy. Soc. April 1864.

138 Prof. J. LeConte on some Phenomena

tain peculiar conditions under which the first two laws may be
violated, but none in which the last is violated. For many
years I regarded these experiments as confirming the ordinary
doctrine. I had observed in my first experiments on the carpet
that each successive plane became more and more indistinct.
I accounted for this by supposing that both the optic axes and
the lenses were adjusted for vision on the plane of the image,
while the hght diverged from the floor five feet distant. It
seemed to me acrucial experiment, proving the necessity of focal
adjustment and the inseparable association of it with axial ad-
justment. On recommencing these experiments a few weeks
ago, however, I was struck with the fact that the figures of the
images were far more distinct than the real figures were when a
small object was viewed in the position of the images. To test
this point fairly, | placed two bone buttons in similar posi-
tions and on similar spots on the pattern, and then brought their
images into coincidence. At first the united image was indistinct,
but gradually it became perfectly defined, every thread-hole as
clear and distinct as it is possible to conceive. I succeeded,
though with greater difficulty, in getting a perfectly distinet
image of the buttons on all the planes. It was evident there-
fore that the indistinctness of the figures of the image on the
higher planes was not the result of the want of focal adjustment,
but of imperfection in the pattern. The subsequent experi-
ments with the ruled diagram proved this beyond the possibi-
lity of doubt. The images in this case were obtained with
much more ease, and the lines were defined with the most per-
fect sharpness, even when the image was brought nearly to the
root of the nose.

In all cases, however, the image when first obtained was a
little indistinct, and then gradually became clear. With un-
practised eyes this interval of indistinctness 1s considerable, but
becomes shorter and shorter with practice, until it almost dis-
appears. When the image once becomes clear it remains s0 ;
but there is then a sense, while looking at the image, of gazing
beyond it ; or rather perhaps there is a difference between the
image and the real object which we cannot account for, but
which is not a difference of distinctness. There is evidently
an unnatural condition of the eyes, which produces stram and
fatigue.

There is but one possible explanation of these phenomena,
viz. that the optic axes and the lenses are adjusted to entirely dif-
ferent distances. The three adjustments of the eye, viz. the
axial adjustment, the focal adjustment, and the contraction of
the pupil, have been so associated through successive genera-
tions, and the association so confirmed and strengthened in each

of Binocular Vision. 139

individual by constant practice from the earliest childhood, that
a single act of velition accomplishes them all. Under ordinary
circumstances they are so indissolubly associated that neither
can be accomplished without the others. But the experiments
described above prove that under certain circumstances the first
two at least may be completely dissociated. In these experiments,
when the image is first obtained, the optic axes, the lenses, and
the pupil are all consensually adjusted for vision at the distance
of the image; and hence the image must be indistinct, for the
rays diverge from an entirely different distance. But gradually
the lenses adjust themselves to the actual divergence, 7. e. for
rays diverging from the real object, while the optic axes remain
adjusted for the distance of the image. The difficulty experi-
enced in dissociating these two adjustments causes the interval
of indistinctness. The perception of the difference between the
image and a real object is the sense of this dissociation. Con-
sensual movements have been perhaps brought about by the ne-
cessities of single and distinct vision; Helmholtz has shown*
that other consensual movements may be dissociated when the
necessities of single vision require it; these experiments show
that the consensual adjustments of the eye may be dissociated
when the necessities of distinct vision require it.

I was now anxious to determine what part was taken by the
pupil. Is the contraction of the pupil more intimately associated
with the axial or the focal adjustment ? This question has been
discussed by E. H. Weber, Cramer, and Donders+. Weber be-
lieves it is directly associated with the axial: adjustment, Cramer
and Donders with the focal adjustment. To test this question,
while I was obtaining the image and making it clear, an assist-
ant standing behind and a little to one side observed my pupil
reflected in a small mirror conveniently placed. After gazing
intently at the real object until the pupil was steady, as soon as
I converged the optic axes so as to obtain the image No. 1, the
pupil was observed to contract decidedly, but as the image became
clear it again expanded to its original size. Again, at the moment
of obtaining the second image the pupil contracted still more
strongly, but as soon as the image became clear it again ex-
panded nearly, if not entirely, to its original size. The same
phenomena were observed for each of the images, only that in
the nearest images, when the convergence of the optic axes was
extreme and the first contraction very great, the pupil did not
return entirely to its original dimensions.

I then made similar experiments on the image beyond the

* Proc. Roy. Soc. April 1864.
t+ Donders, “ Accommodation and Refraction of the Eye,’ Transactions,
p. 574.

140 On some Phenomena of Binocular Vision.

real object. As before, I looked intently first on the real object
at the distance of twelve inches until the pupil became steady.
So soon as I gazed beyond the object the pupil of course ex-
panded; but as soon as the image became clear, it again con-
tracted to nearly its original size. In this last experiment the
pupil is apt to be unsteady. This might have been expected ;
for, as we have already said, it is much more difficult to obtain
this image clear, or to retain it when obtained.

There is no doubt of the fact, therefore, that the contraction
of the pupil 1s most intimately associated with the focal ad-
justment.

I believe that this principle of dissociation of consensual
adjustments explains perfectly certain phenomena of the stereo-
scope. It is well known that many persons experience diffi-
culty in seeing stereoscopic pictures distinctly even when the
two pictures are brought into perfect coincidence; and I be-
lieve all persons experience some fatigue to the eyes in look-
ing at stereoscopic pictures for a considerable length of time.
I have often felt both the difficulty and the fatigue, though
to a much less degree than most persons. The explanation
of this difficulty is as follows. We judge of distance, as is
well known, by the axial adjustment. If, then, the two pic-
tures are so taken that, in order to bring them together, the
visual lines must meet at a certain distance, say, fifty yards,
then the picture will be seen at that distance, and of course very
much enlarged. But in order to see the picture clearly, the
rays must come to the eye as if they diverged from the same
distance ; for the eyes are adjusted for that distance. To fulfil
this condition lenses are always used; but it is obvious that a
given pair of lenses are suitable for one distance only. For all
other distances or degrees of optic convergence there must be
some degree of dissociation of the two adjustments ; and this is
both difficult and fatiguing to most persons.

I have found that observations upon the images of the ruled
diagram area most delicate means of determining both the rota-
tions of the eye and the position of the horopter. I hopein my
next communication to take up this most difficult subject.

|To be continued. |

oes Es

XIX. Notices respecting New Books.

Elementary Lessons in Astronomy. By J. Norman Lockyer, F.R.A.S.
London and Cambridge : Macmillan and Co.

eye schools of our country are much indebted to the author of
this little work both for the substance and the shape of the in-
formation which he has given them.

The amount of thought which he has bestowed upon the arrange-
ment of his materials has not been thrown away, but has produced
a work which will give the young student (as well as children of a
larger growth) a clear and more complete idea of that great whole
called the universe than most works of greater pretensions.

The custom hitherto has been for writers on astronomy to direct
their readers’ attention rather to the instruments by which observa-
tions are made, and to the principles according to which they are
discussed, than to invite them to begin by taking a bird’s-eye view
of the Cosmos. We are told how to adjust a transit, and how to
measure the sun’s distance from the earth ; but our energies are so
much used up in understanding these things, that we have little
strength left to contemplate as a whole the grand reality which they
disclose.

But our author adopts a different method, and beginning with
what we see, and first of all with the stars, we have a series of les-
sons in which the reader has clearly put before him a view of the
magnitudes and distances of these bodies, as well as an account of
their occasional peculiarities, such as colour and variability. Inthe
nebular hypothesis, which is then described, we receive a hint of the
process by which matter has been wrought from the state of pri-
meval chaos into a sun or star.

When the reader has by this means become properly impressed
with the magnitudes with which we deal in astronomy, one particular
star is singled out for especial consideration. Our own star or sun
is that one of all the host of heaven with which we are most inti-
mately acquainted. His appearance and habits are therefore de-
scribed, and we receive an insight into his chemical constitution.

Still proceeding downwards from greater to lesser magnitudes, we
are next invited to consider the minor bodies of the solar system ;
and just as the sun was singled out as the type of the stars, so the
earth is singled out as the type of the planets. Astronomers have
been fond of drawing attention to the adaptation implied in the
fact that the gravitating centres of the various systems are also
the centres of light and heat; but it is only of late years that
we have come to recognize that both these facts can be explained
by the operation in two different ways of one and the same law.
Accordingly we have another definition of planets, and one to which
the author has given considerable prominence, namely that planets
are cold while suns are hot, just as truly as that they are wandering
while suns are fixed.

142 Royal Socrety :—

In clearness of diction, in comprehensiveness, in heauty of illus-
tration this little volume is all that can be desired. In Lesson
XLIV. we have an extremely useful summary of the methods by
which the true positions of the heavenly bodies are obtained; and
at the end of the volume we have a very complete and withal ex-
tremely intelligible account of the law of gravitation.

XX. Proceedings of Learned Societies.
ROYAL SOCIETY.

[Continued from p. 75.]

November 19, 1868.—Lieut.-General Sabine, President, in the
Chair.
fs lie following communications were read :—
“On the Lightning Spectrum.” By Lieut. John Herschel, R.E.

I have had two or three opportunities of seeing this spectrum to
advantage of late. The storms at the period of the setting in of the
south-west monsoon here are very frequent, and supply for a time
almost incessant flashes, many of which are of course very brilliant.
The first time I examined the light in the spectroscope I had no idea
of measuring, but was content to realize the principal facts of a con-
tinuous spectrum crossed by bright lines; but subsequently I made
several attempts (with some success) to obtain measures. That I was
unable to do more in this line is due partly to the difficulty of utili-
zing the short-lived appearance, partly to that fascination of waiting
for ‘one more” bright flash to verify the intersection, which can
only be thoroughly appreciated by the aid of a similar experience.

The principal features of the spectrum are a more or less bright
continuous spectrum crossed by numerous bright lines, so numerous
indeed as to perplex one as to their identity. This perplexity is
increased by the constantly changing appearance due to a variable
illuminating-power. This variable character of the appearances is
unquestionably the peculiar feature of the spectrum. It is not that
the whole spectrum varies in brightness in the same degree, but that
the relative intensities are variable, not only among the various lines,
but between these and the continuous spectrum. The latter is some-
times very brilliant ; and when that is the case, the red portion is
very striking, though in general the spectrum seems to end abruptly
at D+0°34 (E=D+1°38, Kirchhoff’s 120°7=D-+0°55).

There is one principal line which I found equal to D+ 2°20 as the
result of five independent measures. The probable error of this
value is about +°02. The general mean of all my measures of the
principal nebular line (obtained from twelve different nebulz) is 2°18,
with a probable error of about +°02. I have therefore very little
doubt that these are the same, viz. the nitregen line identified in
the case of nebule by Mr. Huggins. This line in the lightning
spectrum is narrow and sharply defined, and is conspicuously the
brightest, except as noted below.

Mr. J. N. Lockyer on the Spectrum of a Solar Prominence. 143

The next in prominence is situated about D+3°58 (F=D+2°73,
Kirchhoff’s 232°5=D+3-'50). It is broader and less vivid, and not
so well defined at the edges.

There are several other conspicuous lines, but none comparable
to the first. I noticed a sharp line in the red, but did not get a
measure.

I said that at D+ 0°34 the continuous spectrum ends abruptly.
A faint continuation, hewever, is frequently seen in bright flashes,
very bright ones bringing out a brilliant red end crossed by a bright
line. :

The whole of the ordinary spectrum seems green and blue, or
rather greenish blue; but as the usual prismatic order of colours is
recognizable in bright flashes, it is to be inferred that the region from
E, to F is so much brighter as to give the character in question.
What strikes one most, however, is the varying relative brightness
of the continuous and linear spectra; sometimes the lines are
scarcely seen, and sometimes very little else is seen. ‘This may be
nothing more than an illusion; but in the absence of any certainty
that it is so, the impression left on the mind is worth recording.

The difficulty of discriminating between the many less prominent
lines 1s immensely increased by the momentary character of the
phenomenon. Before the mind has selected an individual, the feeble
impression on the retina has vanished; and before another flash
succeeds, the memory of the half-formed choice has vanished with
it, and there is nothing on which to found a selection. Otherwise
it would be easy enough to measure many more lines.

‘«“ Notice of an Observation of the Spectrum of a Solar Prominence.”
By J. N. Lockyer, Esq., in a Letter to the Secretary.

October 20, 1868.

Sir,—I beg to anticipate a more detailed communication by in-
forming you that, after a number of failures, which made the attempt
seem hopeless, I have this morning perfectly succeeded in obtaining
and observing part of the spectrum of a solar prominence.

As a result I have established the existence of three bright lines in
the following positions :—

I. Absolutely coincident with C.
II. Nearly coincident with F.

III. Near D.

The third line (the one near D) is more refrangible than the more
refrangible of the two darkest lines, by eight or nine degrees of
Kirchhoff’s scale. I cannot speak with exactness, as this part of
the spectrum requires remapping.

I have evidence that the prominence was a very fine one.

The instrument employed is the solar spectroscope, the funds for
the construction of which were supplied by the Government-Grant
Committee. It is to be regretted that its construction has been so

long delayed.
I have, &c.,
J. Norman Lockyer.

The Secretary of the Royal Society.

144 Royal Society.

Supplementary Note. Received Nov. 5, 1868.

Str,—I have the honour, in continuation of my letter of the
20th ultimo, to inform you that I have this morning obtained evi-
dence that the solar prominences are merely the expansion, in certain
regions, of an envelope which surrounds the sun on all sides. I
may add that other facts observed seem to point out that we may
shortly be in a position to determine the temperature of these cir-
cumsolar regions.

J. Norman Lockyer.

* Spectroscopic Observations of the Sun.”’—No. II. By J. Nor-
man Lockyer, F.R.A.S. (This paper was concluded on November 26).

The author, after referring to his ineffectual attempts since 1866
to observe the spectrum of the prominences with an instrument of
small dispersive powers, gave an account of the delays which had
impeded the construction of a larger one (the funds for which were
supplied by the Government-Grant Committee early in 1867), in
order that the coincidence in time between his results and those
obtained by the Indian observers might not be misinterpreted.

Details are given of the observations made by the new instrument,
which was received incomplete on the 16th of October. ‘These ob-
servations include the discovery, and exact determination of the lines,
of the prominence-spectrum on the 20th of October, and of the fact
that the prominences are merely local aggregations of a gaseous
medium which entirely envelopes the sun. The term Chromosphere
is suggested for this envelope, in order to distinguish it from the
cool adsorbing atmosphere on the one hand, and from the white
light-giving photosphere on the other. The possibility of variations
in the thickness of this envelope is suggested, and the phenomena
presented by the star in Corona are referred to.

It is stated that, under proper instrumental and atmospheric con-
ditions, the spectrum of the chromosphere is always visible in every
part of the sun’s periphery; its height, and the dimensions and
shapes of several prominences, observed at different times, are given
in the paper. One prominence, 3’ high, was observed on the 20th
October.

Two of the lines correspond with fraunhofer’s C and F; another
lies 8° or 9° (of Kirchhoff’s scale) from D towards E. There is an-
other bright line, which occasionally makes its appearance near C,
but slightly less refrangible than that line. It is remarked that the
line near D has no corresponding line ordinarily visible in the solar
spectrum. The author has been led by his observations to ascribe
great variation of brilliancy to the lines. On the Sth of November
a prominence was observed in which the action was evidently very
intense ; and on this occasion the light and colour of the line at F
were most vivid. This was not observed all along the line visible in
the field of view of the instrument, but only at certain parts of the
line, which appeared to widen out.

The author points out that the line F invariably expands (that the

Geological Society. 145

band of light gets wider and wider) as the sun is approached, and
that the C line and the D line do not; and he enlarges upon the
importance of this fact, taken in connexion with the researches of
Plucker, Hittorf, and Frankland on the spectrum of hydrogen—
stating at the same time that he is engaged in researches on gaseous
spectra which, it is possible, will enable us to determine the tempe-
rature and pressure at the surfaces of the chromosphere, and to give
a full explanation of the various colours of the prominences which
have been observed at different times.

The paper also refers to certain bright regions ia the solar spec-
trum itself.

Evidence is adduced to show that possibly a chromosphere is,
under certain conditions, a regular part of star-economy ; and the
outburst of the star in Corona is especially dwelt upon.

GEOLOGICAL SOCIETY.

[Continued from vol. xxxvi. p. 234.]

May 20th, 1868.—Prof. T. H. Huxley, LL.D., F.R.S., &c.,
President, in the Chair.

The following communications were read :—

1. ‘ On the Eruption of the Kaimeni of Santorin.”’ By Dr. J.
Schmidt.

The eruption to which this paper referred commenced in January
1866, and continued uninterruptedly up to the close of the year 1867.
Probably years may elapse before the volcanic energy has died cut.

The eruption of the Nea-Kaimeni originated on the south side of
the island, and extended towards the west. The tendency of the lava-
current was southwards, and the extension, after about two years was
from 1200 to 1400 yards southward, and 1800 yards from east to
west. On account of the great depth of the water and the continual
access of the open sea, the temperature of the water has not been
remarkably elevated, varying from 77° to 122° F. The old George
harbour has been greatly improved by the upheaval of the southern
and western sides, while the channel between Nea and Micra
Kaimeni has been shallowed, so as to be passable only for boats.

The author then described the George volcano, and stated that
an eruption of stones and ashes, accompanied generally with sharp
explosions, took place about every seven minutes. Immediately
atter these stone-showers hissing columns of white steam succeeded,
and these were followed by faint-yellow noiseless issues from the
central fumarole. None of the stones were thrown more than 400
feet above the water. It is impossible to predict anything with
regard to the cessation of the eruption, although it has diminished
in intensity since 1866.

Capt. Spratr pointed out that this was only one of the many
- peaks in the large crater of Santorin which have risen up since the
historical period. In the position in which he had anchored but six
or seven years ago there is now a hill upwards of 300 feet in height.

Sir Ropericx Murcuison referred to the communications to the

Phil, Mag, S. 4, Vol. 37. No, 247, Feb, 1859. L

146 Geological Society :—

French Academy relative to the chemical products of the eruption,
and their relation to those of Vesuvius and other volcanoes. |
Mr. Forzss directed attention to the fact alluded to in the late
President’s anniversary address, that the lavas of this volcanic out-
burst were, at its commencement, trachytes, or of highly silicated
character, but afterwards were basic lavas—thus proving that rocks
of totally different characters and chemical composition (respec-
tively analogous to the granitic and trappean rocks of former
periods) might proceed from a volcanic focus during an eruption.
Prof. Ansrep called attention to the probable connexion of the
eruptions in these islands with those of Vesuvius and Htna, and
mentioned that Baron von Waliershausen had presented to the
Society photographs of his magnificent original drawings of the
whole region of Etna, which were upon the table, of which only
three copies were taken on a larger scale than the published maps.

2. * On the Structure of the Crag-beds of Norfolk and Suffolk,
with some observations on their Organic remains.—Part II. The
Red Crag of Suffolk.” By Joseph Prestwich, Esq., F.R.S., F.G.S.

The superposition of the Red Crag to the Coralline having been
clearly shown by previous writers, the author confined his paper to
those questions on which differences of opinion still exist, namely,
the structure of the Red Crag, its affinities with the Coralline, and
its exact relation to the Mammaliferous Crag of Norfolk. The
Red Crag of Suffolk was described as occupying an excavated area
in the Coralline, wrapping round the isolated reefs of the latter,
filing up the hollows between them, and occupying a similar, and
sometimes a rather lower level than the summits of these older reefs.
it forms such an extremely variable series of beds, that the author
had been unable to observe any definite order of succession in the
greater part of it; but he remarked that oblique lamination is most
strongly developed in the lower and central portions, and that
almost everywhere there occurs at the base a bed of phosphatic
nodules, although deposits of that nature are by no means confined
to one level. Old sea-cliffs of Coralline Crag, and remains of old
sea-beaches at their base, were described by Mr. Prestwich as oc-
curring at Sutton; and he also gave detailed descriptions of nume-
rous pits in the Red Crag of Suffolk, where the phenomena which
he described may be observed. Dividing the Red Crag into an
upper, frequently unfossiliferous, member (the fossils of which, being
most frequently in the position in which they lived, may be re-
garded as truly representing the fauna of the period), and a lower
fossiliferous portion (in which the shells are found mostly in a broken
and comminuted state and mixed largely with fossils derived from
the older Coralline Crag), the author described their distribution in
Suffolk, and their mode of occurrence on the eroded Coralline Crag,
referring more especially to the difficulty in drawing the line be-
tween them in many cases.

In treating of the Organic Remains of the Red Crag, Mr. Prest-
wich gave lists of the shells found at the different localities, which
had been prepared with the aid of Mr. Gwyn Jeffreys. Taking

Mr. J. Prestwich on the Red Crag of Suffolk. 147

the local conditions into consideration, eliminating the extraneous
fossils of the Red Crag of Sutton, Butley, &c., and excluding the
freshwater fossils of the more northern districts, the author regarded
the remaining fossils of the two divisions of the Red Crag as being
so closely related that the whole group must paleontologically be
treated as one. Mr. Searles Wood had given the total number of
species of its mollusca as 239; to these Mr. Gwyn Jeffreys has
added six additional species ; on the other hand, he regarded ninety-
nine of them as varieties and extraneous fossils, leaving 146 species
belonging to the Red Crag. Of these Mr. Jeffreys has identified
138, or 92 per cent., with living species, 115 still being inha-
bitants of British seas, 15 being found in more northern seas, and
3 in more southern.

From the Mammaliferous Crag of Norfolk and the Red Crag of

Suffolk never having been found in superposition, from the circum-
stance that just at the point where the latter ceases the former
begins, as well as from the community of so many species of
organic remains, the author regarded the two deposits as equivalent ;
and he attributed their distinctive characters partly to the extra-
neous fossils in the Red Crag, and partly to the difference in the
conditions which prevailed in the two areas at that time, and espe-
cially to the more littoral and brackish-water conditions which pre-
vailed in the Norfolk area. In conclusion, Mr. Prestwich gave a
sketch of the physical history of the Red-Crag period, describing
the mode in which the various phenomena he had noticed had been
produced.
_ The Rev. Mr. Guny, in opposition to the view of the Forest-bed
being placed above the Chillesford clay, mentioned that at Easton
Bavent, where the latter has been supposed to occur in the cliff, he
had seen the Forest-bed exposed on the shore. He instanced other
cases where the Forest-bed, in his opinion, underlay the Chillesford
clay and sands, and supported his views by the evidence of the
Mammalian remains of the different beds, and especially the suc-
cession of the Mastodon Arvernensis, the Klephas meridionalis, HE. an-
tiquus, and EH. primigenius. He regretted the absence of any men-
tion of the Mammals of the Red Crag.

Mr. Gwyn Jrerrreys made some remarks on the subject of spe-
cies, and explained how, from a comparison of a large number of
specimens, he had in many instances been led to reduce what had
formerly been considered distinct species into mere varieties of the
same species. He corroborated the views of the author as to the
presence in the Red Crag of numerous fossils of the Coralline Crag.

Dr. Cozzo tp stated that, from a microscopic examination of the
phosphatic nodules, he had established the existence in them of
Radiolarize and Diatomacex, and especially of Arachnoidiscus coc-
coneis, the Radiolariz being chiefly of the division Acanthometre,
_all three forms being purely marine.

Mr. CuarLEeswortTH commented on the remarkable fact that in a
few thousand square feet of Coralline Crag we have a fauna as ex-
tensive as the whole British molluscan fauna. He considered that
at present the attempt to solve the question of the age of the Red

L2

148 Geological Society :—

Crag was hopeless, mainly from the difficulty of recognizing ex-
traneous fossils. He expressed his disappointment at the fish-fauna
of the Red Crag not having been noticed by the author. The
teeth which were common to the Eocene and Red Crag had usually
some phosphatic matter adherent. ‘Those, on the contrary, which
only occur in the Crag, have never any phosphatic matter attached.
He therefore regarded the former class as derivative, but the latter
as belonging to the deposit in which they occur.

Mr. Szartes Woop, Jun., denied that the Red Crag was the
one homogeneous deposit divided into two beds represented by
Mr. Prestwich; he protested against the Walton and Butley de-
posits being regarded as one and the same—the former bearing more
affinity to the Coralline Crag, and being therefore probably the older.

Mr. Prestwicu, in reply, explained that he did not intend to
omit the lists of mammalian remains of the Red Crag, Tables of which
were appended to the paper, the greater part of them, however,
he regarded as derivative. With regard to the relation of the
Chillesford beds to the Forest-bed, he had never seen a section in
which the latter underlay the former; the Chillesford beds at
Easton Bavent were underiain by sandy beds referable to the Nor-
wich Crag. He considered that some division in the lower bed, as
suggested by Mr. Searles Wood, was to be found.

June 8rd, 1868.—Prof. T. H. Huxley, LL.D., F.R.S., &c., President,
in the Chair.

The following communications were read :—

1. ‘“‘ On some Genera of Carboniferous Corals.”’ By James Thom-
son, Esq. ;

Mr. Thomson gave a résumé of the diagnostic peculiarities of
Cyathophyllum, Goldfuss, Clisiophyllum, Dana, Aulophyllum, Milne-
Edwards and Jules Haime, and Cyclophyllum, Duncan and 'Thom-
son. The author then noticed that the separation of these genera
was inevitable and necessary, from the ordinary rules of the classi-
fication of the Zoantharia. He concluded by remarking upon the
evident structural distinctions between Clistophyllum, Aulophyllum,
and Cyclophyllum.

Dr. Duncan said that the existence of a columella was a generic
distinction in recent and mesozoic corals, that the type of the pale-
ozoic Cyathophyllide was reflected in the Lower-Liassic coral-fauna
of South Wales and the west of England, and that there was a
necessity for the same principles of classification in the paleozoic
and in the recent coral-fauna. ‘There was a gradation from the
Rugosa to the Aporosa.

Prof. Huxtey remarked that the structure of the specimens of
the different genera proved that there were great difficulties in ac-
cepting Agassiz’s opinion that these old forms were not Zoantharia.

2. ** On the Pebble-beds of Middlesex, Essex, and Herts.” By
S. V. Wood, Jun., Esq., F.G.S.

The author described some pebble-beds in the counties of Mid-
dlesex, Hertford, and Essex, which, in the MS. memoir deposited

Mr.W.Topley on the Cretaceous Rocks of the Bas-Boulonnais. 149

in the Society’s Library, he had described and referred to the age
of the Bagshot sands. Premising that there could be no mistake as
to the beds under discussion, as Mr. Hughes and the author had
found their lines of the Middle Glacial gravel (termed “ gravel of
the lower plain” by the former geologist) to coincide, Mr. Wood
described the distribution of the gravels which he regarded as of Bag-
shot age, and gave an account of the physical phenomena which he
conceived had led to their deposition and subsequent denudation.
He objected to Mr. Hughes’s view, that the pebble-bed termed
*‘oravel of the higher plain’? by Mr. Hughes belongs to a period
anterior to the gravel of the lower plain, as it involves the admission
that there has been a period intermediate between that of the Bag-
shot pebble-beds and the Glacial, during which the sea occupied
these counties and deposited the gravel of the higher plain—an ad-
mission which would be fatal to his view of the Bagshot age of the
pebble-beds described in this paper.

Mr. Prestwicu was inclined to regard some of the beds referred
by the author to the Bagshot series rather as local drifts derived
mainly from those beds than as the beds themselves.

Mr. Wairaxer saw a difficulty in classing the pebble-beds at
Brentwood and elsewhere among the Bagshot beds, as in the London
district, at all events, no such pebble-beds occur in the Bagshot
series.

Mr. Evans pointed out the difficulty in supposing that the
gravels at the high level could have been deposited at a later period
than those of the low level without, at the same time, overlying the
latter.

Mr. Srarxtes Woop considered that there was not that broad
line of distinction to be drawn between the gravels of the higher
and lower level; he maintained that the pebble-beds when truly zn
situ were free from Quartzite, and truly of the Bagshot age.

3. ‘On the Cretaceous Rocks of the Bas-Boulonnais.” By
William Topley, Esq., F.G.S., of the Geological Survey of England
and Wales.

After a résumé of previous notices on the subject, the author
described the Physical Geography of the district and the Cretaceous
beds below the chalk, comparing them with their English equi-
valents.

Each great division of the Kentish series was stated to be repre-
sented in the Boulonnais, although, in every case, in diminished
thickness. ‘The Upper Greensand and Gault were shown to sur-
round the district at the base of the chalk hills; and a fossiliferous
phosphatic bed was described at the bottom of the Gault, as in Kent.
This bed was regarded by the author as a passage between Gault
and Lower Greensand, as nodules with fossils often occur in the
sands below; and it was shown to be frequently impossible in
- sections to mark off accurately the Lower Greensand from the Gault.
The marked change in the faunz of these formations was regarded
by the author as due to the complete change in the conditions of
deposit.

The sands which occur below the Gault were shown to belong

150 Geological Society :—

partly to the Folicestone beds (or highest division of the Lower Green-
sand) and partly to the Wealden—the intermediate stages being
absent, although well developed where last seen on the Kentish
coast. ‘The ferruginous sands, with variegated clays and iron-ore,
which cap the hills in the interior of the Bas-Boulonnais, were re- —
ferred by the author to the Wealden series, as were also the pebble-
beds of St. Etienne and elsewhere, hitherto regarded as “ drift.”

The Wealden beds were shown to rest upon the Portland around
Boulogne, and upon lower members of the Oolites in the west and
north; while in the north-west corner they fll ‘‘ pipes” in Paleo-
zoic limestones. The Wealden beds, thus proved to be unconform-
able to those below them, were shown to underlie conformably the
remaining Cretaceous beds above, thinning away, however, against
the old ridge, where, by overlapping the Lower Greensand and finally
the Gault, they rest immediately upon the Paleozoic rocks.

The paper was illustrated by a map, showing the probable out-
crop of the Cretaceous rocks beneath the English Channel.

Sir RopErick Murcuison, without doubting the correctness of
the author’s views, wished that fossil evidence had been forthcoming
to identify more conclusively the Wealden strata of the Boulonnais
with those of England, and suggested their correlation with the
Beauvais beds. |

The Rev. Mr. Wittsuire remarked that in Kent the Ammoniies
mammillaris was contained in large nodules, and occurred only
below the lower phosphatic band.

Mr. Wuiraxer, who had been with the author in the Boulonnais,
had been, contrary to his predilections, compelled to regard the beds
referred to the Wealden as belonging to that formation, and not to
the Lower Greensand.

4. ‘* Note on the Mendip Anticlinal.”” By C. H. Weston, Esq.,
F.G.S.

The author called attention to the discovery of igneous rocks in
the north-western portion of the Mendip Hills long previous to Mr.
Moore’s discovery of them in the south-east ; and he stated that this
fact left no doubt about the persistence of this upheaving agent
throughout the entire anticlinal of the Old Red and Carboniferous
series.

June 17th, 1868.—Prof. T. H. Huxley, LL.D., F.R.S.,
President, in the Chair.

The following communications were read :—

1. “On the Distribution of Stone Implements in Southern India.”
By R. Bruce Foote, Esq., F.G.S8., of the Geological Survey of India.

The chipped stone implements of Southern India are found in,
or associated with, two formations—the coast-laterite, whichis a
marine formation, and a freshwater deposit, occurring inland at
greater elevations above the sea. Most of them have been found
either in situ in the laterite of the eastern coast, or distributed over
its surface; several have been collected off the surface of older
rocks, in places where the laterite had been removed by denudation ;
others have been discovered on the surface at great elevations in

Mr. B. Foote on Stone Implements in Southern India. 151

other parts of the country, where no distinct traces could be seen of
the formation from which they had weathered out, and which had a
different origin (possibly freshwater) from that of the marine coast-
laterite; while a few have been obtained from unquestionably
fluviatile deposits. None have been collected from formations
known to be either younger or older than the coast-laterite.

The author inferred that during the latter part of the laterite-
period the land was raised to the extent of 500 or 600 feet, that
this elevation was followed by a period of quiescence during which
the laterite was extensively denuded, that this epoch was succeeded
by a period of depression during which the recent coast-alluvium
was formed, and that a subsequent elevation brought the land into
its present position.

The PresipEnt referred to the evidence of physical geography
to prove that the Deccan was once an island, and to ethnological
data to prove that the people who made the quartzite implements
were probably not the original Aryans, but were the ancestors of
the Hill tribes, whose nearest affinities are with the aboriginal Aus-
tralians of the present day. He was of opinion that the two popu-
lations were once nearly or quite continuous, having been sub-
sequently cut into segments by geological changes, and that the
makers of the quartzite implements came from the same stock as
both these recent tribes, which present the most rudimentary civi-
lization known.
~ Prof. Rupert Jones called attention to the similarity in the type
of these quartzite implements to that of the flint implements of
Europe. .

Sir Roperick Murcuison doubted whether the laterite was a
marine formation, as neither in it nor in the lacustrine deposits
alluded to had any organic remains been found.

M. pz Normanp stated that Obsidian knives, like Mexican types,
were found by him, with domestic implements cut out of volcanic
stone, under 70 feet of tuff of the primitive volcano of Santorin ;
and he considered that before the formation of the first volcano
ceramic pottery was brought to Santorin from foreign shores,
and, of course, by sea.

Dr. Meryown remarked that the occurrence of the same type of
implement in Europe and Asia proved a dispersion of the human
race in very ancient times, and that man originated from one centre ;
while in later times a divergence of type in the worked objects was
a result of the dispersion.

Mr. Presrwics was inclined to believe that greater physical
changes had occurred in India since the Pliocene period than in
Europe. ‘The implements were so like those of Europe, that their
fabricators seemed to have been taught in the same school.

Mr. Foors, in reply, stated that he regarded the laterite as a
marine formation, because it occurred all round the coast. All the
implements were quartzite, with perhaps one doubtful exception,
which was formed of basalt. Stone circles and kistvaens had been
found on the surface of the laterite in some localities.

152 Geological Soctely :—

2. On worked Flint fiakes from Carrickfergus and Larne.” By
G. V. Du Noyer, Esq.

These flakes have been found by the author in two very distinct
positions, namely :—the older in the marine drift (sand and gravel)
skirting the shores of the county Antrim and county Down, the
maximum elevation being about 20 feet above the sea; and the more
recent in the subsoil clay at all elevations up to 600 feet, near Bel-
fast, Carrickfergus, Larne Lough, and Island Magee. The former
are of the rudest forms, highly oxidized or white on their entire
surface, but, though imbedded in marine drift, having the chippings
around the sides and angles generally sharp. ‘The latter have a
comparatively fresh look, though still possessing the characteristic
porcellanous glaze; they are regarded by Mr. Du Noyer as possibly
the rough materials out of which the historic races in Ireland manu-
factured the spear- and arrow-heads which are found with their
sepulchral and other remains.

3. “On the Diminution in the volume of the sea during past
eeological Epochs.” By Andrew Murray, Esq., F.L.8.

In opposition to Sir Charles Lyell, the author submitted that, instead
of the proportion of dry land to sea having always been the same,
and its volume above the level of the sea a constant quantity, they
are constantly increasing, while both the mean and extreme depths
of the sea are constantly diminishing, the cause being the extreme
affinity which water has for the constituent elements of minerals.
In illustration of his view, he quoted the so-called upheaval of coral-
islands as being really caused by a diminution in the volume of
the sea.

4, “Has the Asiatic Elephant been found in a fossil state?”
By A. Leith Adams, M.B., F.G.S. With a Note by G. Busk, Esq.,
Reno EEG.

An elephant’s tooth in the possession of Dr. Fischer, of St. John,
New Brunswick, which had been found in Japan at a distance of
40 miles from the sea-shore, between Kanagawa and Jeddo, and at
the base of a surface ccal-bed, appeared to the author referable to the
Asiatic elephant; and he accompanied his description of it by a
drawing and plaster cast. In his note appended to the paper, Mr.
Busk gave some further details of the characters exhibited by the
cast, and agreed with Dr. Leith Adams in regarding it as probably
referable to Hlephas Indicus rather than EH. Armeniacus, a fossil
molar of which had been found in China; but he concluded that it
was the antepenultimate upper left molar, and not the penultimate, as
inferred by Dr. Leith Adams.

5. ** On the Characters of some new fossil Fish from the Lias of
Lyme Regis.” By Sir Philip de M. Grey Egerton, Bart., M.P.,
F. R. Noeae de G. S.

The species described in this paper were the following :—

1. Osteorachis macrecephalus, gen. et spec. nov.—A Sauroid fish,
chiefly remarkable for the massive dimensions and complete ossifica-
tion of the hedies of the vertebre, and characterized by the large
size of the heed and the multiplicity of the teeth.

Sir P. G. Egerton on Fish from the Lias of Lyme Regis. 153

2. Isocolum granulatum, gen. et spec. nov.—For elegance of form
this fish can vie with the salmon of modern times, its contour being
very similar. It bears the greatest resemblance to the Sauroid genus
Caturus, but in the absence of the teeth it cannot be assigned with
certainty to any particular family.

3. Holophagus gulo, spec. nov.—A ccelacanth fish, remarkable
for its resemblance, especially in the contour of the head, to the
Cretaceous genus Macropoma, and for substantiating Prof. Huxley’s
demonstration of the persistence of type presented by this family,
which ranged from the Coal-measures to the Chalk.

4. Eulepidotus sauroides, gen. et spec. nov.—'Lhis first represents
a genus uniting the Lepidoid and Sauroid families of Agassiz’s
Ganoid order—the teeth and the tail being Sauroid in character,
while the fins are Lepidoid, and the scales partake of the characters
of ae structures in both families.

6. “ Note on the Geology of Port Santa Cruz, Eaeomee By
oa T. Baker, Lieut. Royal Naval Reserve.

This note accompanied some specimens of fossil shells obtained
by the author from the cliffs of the western arm of the river Santa
Cruz, the stratification of which he described. ‘The shells are for
the most part referable to the Tertiary species from Patagonia pre-

viously obtained by Mr. Darwin.

7. “On the Jurassic deposits in the N.W. Himalaya.” By Dr.
F. Stoliczka, F'.G.8., of the Geological Survey of India.

The author described the following strata as composing the
Jurassic rocks in the north-west Himalayas :—

. a. Lower Tagline limestone.
Lema b. CED Tagling limestone.
ce. Jurassic slates.
a. Dee ‘a Spiti shales.
3. Malm? — e. Gieumal sandstone.

The object of the paper was to show, in opposition to Mr. Tate’s
assertion to the contrary, that the Indian Jurassic formation could
clearly be subdivided, and that in some measure the subdivisions
correspond with those of the European Jura.

8. On a true Coal-plant (Lepidodendron) from Sinai.” By J.
W. Salter, Esq., A.L.S., F.G.S.

The fossil described was received by Sir R. I. Murchison some
years ago. ‘The author regarded it as an infallible indication of the
pesence of the true northern Coal-formation, with species like
those from the Erekli coal. The proposed name of the species is
Lepidodendron mosaicum.

9. “On some Fossils from the Menevian Group.” By J. W.
Salter, Hsq., A.L.S., F.G.S., and H. Hicks, Esq.

The authors, after describing the localities and stratigraphical
relations of the Menevian group, proceeded to describe the following
species :—

Paradowides aurora, Salter, represented by a few imperfect heads,
unattached pleure, &c. Localities, Porth-y-rhaw and St. Davids.

P. Hicksii, Salter. This species presents a singularly inter.

—

154 Geological Society -—

mediate character, reminding us equally of Paradowxides and Ano-
polenus. ,

Conocoryphe bufo, Hicks, represented by a few separate heads and
one with six body-rings attached. Localities, Porth-y-rhaw and
St. Davids. We

C. applanata, Salter. Young specimens show all the metamor-
phoses observed by Barrande. ‘The characters of such genera as
Agnostus and Microdiscus are as clearly seen in the embryo of Cono-
coryphe as in the adult state of those genera. Localities, Porth-y-
rhaw, St. Davids, Maentwrog, and Dolgelly.

C.(?) numerosa, Salter. Of this species, a part of the head and
six thoracic rings have been found. These, however, show cha-
racters sufficient to indicate that it is specifically, if not generically,
distinct from the others. Localities, Porth-y-rhaw and St. Davids.

10. “On Harthquakes in Northern Formosa.” By H. F. Holt,
Esq., H.M. Consul at Tamsuy.

The first shock felt in the northern end of the island took place
on the morning of the 18th of December, 1867. Many buildings
were destroyed and many lives lost in Tamsuy. About fourteen
minor shocks were felt during the same day, and on the 20th
another violent shock occurred.

At Kelung the whole harbour was left dry, and the water return-
ing in one vast wave rushed into the town itself. Large landslips
have taken place, and several villages between Kelung and Tamsuy
have been destroyed.

11. “ Memorandum on the Coal-mines of Iwanai, Island of Yesso,
Japan.” By A. B. Mitford, Esq. |

The mines lie about two miles inland from the village Kaianoma.
Four seams of coal have been discovered, which are from one to six
feet thick. The coal is soft, yields from ten to twelve per cent. of
ash, and from thirty to thirty-five per cent. of gas. It sends out
thick black smoke when first lighted, but afterwards burns with a
clear strong flame, and leaves no clinker.

12. ‘On a new species of Fossil Deer from Clacton.” By W.
Boyd Dawkins, Esq., M.A., F.R.S., F.G.S., &e.

This species (named Cervus Brownii by the author) is unlike any
other species excepting C.dama, to which it is closely allied. ‘The
antlers, however, have the third tyne present on the anterior portion,
while in the Fallow deer it is entirely absent. From the presence
of Rhinoceros Merkii and Hlephas antiquus in the Clacton deposit,
and from the absence of Arctic species, the author regarded it as
forming a term in the series of strata to which the Lower Brick-
earths of the Thames valley belong, and as deposited before the
immigration of Arctic animals into Great Britain.

13. “On a new species of Fossil Deer from the Norwich Crag.’
By W. Boyd Dawkins, M.A., F.R.S., F.G.S8., &c.

Cervus Faiconeri, Dawkins, spec. nov. ‘The brow tyne differs
from that of C. dama and of C. Brownii in being removed from the
base, and situated in a different plane from. the second and third

Dr. Nicholson on the Graptolites of the Coniston Flags. 155

tynes; in this it-is allied to C. tetraceros. The straightness of
the beam separates it from the species to which he had compared it ;
and it is further separated from C. tetraceros by the absence of deep
wrinkles. The small amount of palmation in C. Falconeri is greatly
increased in C. Brownii, and reaches its maximum in C. dama.

14. “Notes to accompany a section of the Strata from the Chalk
to the Bembridge Limestone at Whitecliff Bay, Isle of Wight.” By
T. Codrington, Esq., F.G.S.

In these notes the author described in detail the beds which are
comprised in the section exhibited in Whitecliff Bay, and which he
had carefully measured at low water. Comparing it with the Alum-
Bay section measured by the officers of the Geological Survey, he
found the total thickness of the beds from the chalk to the base of
the fluviomarine series to be the same in both, although the thick-
nesses of the component formations differ considerably.

15. ‘‘ On the Graptolites of the Coniston Flags, with notes on the
British species of the genus G‘raptolites.” By H. A. Nicholson, D.8c.,
M.B., F.G.S., d&e.

The author, after remarking upon the prevalent differences of
opinion regarding the stratigraphical position of the Coniston Flags,
proceeded to describe the following species :—

Diplograpsus palmeus, Barr. Graptolites Sedgwickii, Porti.
D. folum, Zs. G. fimbriatus, Nich.
D. angustifolius, Hail. G. Nilssoni, Barr.

D. confertus, Nich. G. tenuis, Portl.

D. tamariscus, Nich. G. discretus, Nich.

D. pristis, His. G. Bohemicus, Barr.

. priodon, Bronn.

. colonus, Barr.

. Sagittarius, Linn.

. turriculatus.

. Sedgwick, Poril.

, var. spinigenis, Nich.

Retiolites perlatus, Nich., noy. sp.
Rastrites Linnei, Barr.
Climacograpsus (Diplograpsus) |
teretiusculus, His.
Rastrites peregrinus, Barr.
Graptolites lobiferus, M‘Coy.

C2 92 G2 C2 42

16. “On the ‘ Waterstone Beds’ of the Keuper, and on Pseudo-
morphous Crystals of Chloride of Sodium.” By G. W. Ormerod,
Ksq., M.A., F.G.S.

Between Salcombe Mouth and the River Sid, and between Bud-
leigh-Salterton and Littleham Bay, several beds of ripple-marked
«* Waterstone’”’ occur, and also pseudomorphous crystals of chloride
of sodium. A small fragment of Waterstone exhibited apparently
traces of reptilian remains. In conclusion, the author drew atten-
tion to the fact that pseudomorphs occur over the greater part of the
Triassic area in England.

17. “On the discovery of the remains of Pteraspidian Fishes in
Devonshire and Cornwall, and on the identity of Steganodictyum
Cornubicum, M‘Coy, with Scaphaspis (Archeoteuthis) Dunensis,
Roemer.” By E. Ray Lankester, Esq.

A specimen labelled ‘“* Pteraspis,” from the Lower Devonian slates
of Mudstone Bay, in the collection of the late Mr. Wyatt-Edgell,

156 Intelligence and Miscellaneous Articles.

was at once referred by Mr. Salter to the Steganodictyum of M‘Coy ;
and on further research he concluded that M‘Coy’s supposed sponge
is actually the cephalic plate of a Pteraspidian fish. ‘The author
fully endorsed Mr. Salter’s determination, and inferred that the
specimens of Steganodictyum Cartert are really head-plates of true —
Cephalaspis.

18. “ On the Geological peculiarities of that part of Central Ger-
many known as the Saxon Switzerland.” By the late Capt. James
Clark.

The author described in detail the rocks of which the district
under consideration is composed, namely :—1, the Upper Quader
Sandstone; 2, Planer Limestone; 3, Planer Marl; 4, Lower Quader
Sandstone; and gave a list of their chief fossils.

The peculiarities of this region consist, first, in the abrupt and
marked variations of altitude without any corresponding inclination
or dislocation of the strata; secondly, in the remarkable regularity
of the fissures by which the rocks are divided, which cross them at
right angles; thirdly, in the phenomena observable along the
line of separation between the Quader and the Lusatian granite,
the Quader being overlain by the granite and syenite; fourthly, in
the disposition of the basalt, which rises through the granite and
the stratified rocks above, indurating the latter, but not contorting
them.

XXI. Intelligence and Miscellaneous Articles.

ON THE TEMPERATURE OF FLAMES AND DISSOCIATION.
BY E. VICAIRE.

URING the combustion of a gaseous mixture in an enclosure

which is impermeable to heat, the heat evolved is employed

solely in heating the mass, and we may easily calculate the tempe-

rature which it will have attained after the combustion of a certain
fraction of the combustible element.

Supposing this combustion to be complete, we obtain the ordinary
formule of the temperatures of combustion. But these formule
furnish results far higher than the temperatures which are actually
observed, and the beautiful investigations of M. H. Sainte-Claire
Deville clearly show us the reason of this; it is, that aftera certain
point the elevation of the temperature places anobstacle in the way
of a more complete combustion, because no combination can take
place without causing a dissociation which exactly compensates it.

If we have determined the temperature by experiment, we easily
deduce from it the quantity of gas that has been burnt, by the same
equation which, if we knew the quantity burnt, would give the tem-
perature.

But this equation, which I establish in a rather more general
manner than has hitherto been done, does not take the place of the
old formule of combustion: it does not allow us to foresee the tem-

Intelligence and Miscellaneous Articles. 157

perature of combustion of a given mixture ; for it includes two mag-
nitudes which are equally unknown beforehand—the quantity burnt,
and the temperature.

To determine these two magnitudes for a given mixture is the
problem which I have set myself, assuming the phenomenon of dis-
sociation to be known in all its details. Although this assumption
is far from having been realized, the solution of this problem pos-
sesses henceforth a certain amount of interest, inasmuch as it enables
us to account for the cireumstances which may influence the tempe-
rature of combustion, and the direction of this influence. It will be
seen, moreover, that it suggests various means of studying dissocia-
tion experimentally.

Let us take, in the first place, a mixture of equal equivalents of
oxygen and hydrogen; let us call c the specific heat of the mixture,
ce! that of ayueous vapour, and let k, at a given moment, be the frac-
tion of the mixture which is not yet burnt ; we then easily establish
the proportion

[ke+(1—A)c']t=(1 —4)3240,

whence _ 3240—c't Q)
3240+(c—e)t ’

Taking ¢ as the abscissa and & as the ordinate, this equation is
that of an hyperbola each point of which, in the part with positive
coordinates, represents one of the states through which the mixture
would successively pass if the combustion could become complete.
The ordinate defines the composition of the mixture, the abscissé
gives the temperature.

‘On the other hand, let us consider aqueous vapour brought to a
gradually increasing temperature. Let wu be the tension of dissocia-
tion at agiven moment—that is to say, the fraction which has been
transformed into a mixture of chemical equivalents of oxygen and
hydrogen; if we suppose the pressure constant, w will be a function
of the temperature alone, or

US Oe Toe Ah @Mponwn, Meeeg Ang C)

This equation will be that of a curve which will also represent the
successive states of the aqueous vapour.

From the position of the points where the curves (1) and (2) inter-
sect the axis of the ¢’s and the horizontal k=1, they must of necessity
intersect each other between these two lines.

The point of intersection corresponds to a moment at which the
gaseous mass in combustion is identical in composition and tempe-
rature with dissociated water. Now this is ina state of equilibrium
which it is incapable of modifying of itself; this is therefore the case
with the gaseous mass; that is to say, always supposing it in an en-
closure impermeable to heat, it must remain indefinitely in the same
state. Here, therefore, we have the stationary condition, and the
corresponding temperature is the actwal temperature of combustion.

158 Intelligence and Miscellaneous Articles.

Thus this temperature will be given by the equation

3240—c't |
SSS, ESS bs e ° ° Siete e ° 3
3240+ (c—c' )t IO (3)
If the gaseous mixture, instead of being originally at zero, con-
tained more than at zero, a quantity of heat, v, positive or negative,
the equations would become

3240+v—clt _
= 3040 EGE “jah eee ce, (ED

If, instead of being dry, the mixture, before any combustion, con-
tained a fraction g of its weight in the state of water, we should have

_ 82400.1—g)+u—ct _
fous 3240+ (c—e')é HIE Gea ek)

In these various cases nothing is ever present but aqueous vapour
and explosive gas; if we suppose the former to be always the same,
the dissociation will only change from one case to the other by the
effect of temperature. The function f(¢) is therefore always the
same. If, therefore, we place ourselves successively in different cases,
varying v and gq (that is to say, the initial temperature and humidity),
and observe the temperature of combustion, we shall deduce there-
from different values of f(t) ; that is to say, we shall get the law
which connects the tension of dissociation with the temperature
under the pressure in question.

The equations (4) are equally true at any moment that the quan-
tity of heat v is added or deducted. They agree therefore, suppo-
sing v to be negative, with the successive states of the mass when it
cools from the maximum of temperature. We are thus led to an-
other method of obtaining values of /(¢),—namely, observing
simultaneously, during the cooling of the mass, the quantities of
heat which it abandons and the temperatures through which it
passes.

If each kilogramme of more or less hot and moist explosive gas
were mixed with a weight p of a gas not capable of entering into re-
action, and of specific heat c’’, we should have

_ 8240(1—g) +u—(e'+-pe")t _
i 3240+ (c—c')é =f).

IT here introduce this new function f(t), because we may assume,
until the contrary is proved, that the presence of a foreign gas modi-
fies the dissociation.

It is evident that, by varying only v and g, we may determine the
function f,(¢). By subsequently varying the nature and the quan-
tity of the intermixed gas, we shall see how these conditions modify
the dissociation.

Assuming the identity of /(¢) and f(£), «we easily see that if we
compare two mixtures for which the temperature of total combustion
(that given by the ordinary formule) is the same, but one dry and
containing a foreign gas such as nitrogen, the other with no

k

Intelligence and Miscellaneous Articles. 159

foreign gas, but humid, the real temperature of combustion wil) be
less for the latter.

It is clear that these formule apply to oxide of carbon with mere
numerical modifications. They likewise suit, whatever be the pres-
sure, provided this is constant in each case.

Without trying prematurely to indicate the arrangements by
which [ hope to realize some, at least, of the cases under consider-
ation, I pass to the examination of a recent memoir by M. Bunsen
on the present question.

M. Bunsen detonates gaseous mixtures in a valved eudiometer,
and caleulates the temperature from the pressure which is developed
at the moment of the explosion. This case differs in two points
from those which we have considered: in the first place, we must
introduce into the formulee specific heats at constant volumes, and
not at constant pressures ; and then the pressure does not remain
constant, but it increases up to the moment of the maximum of
temperature. These two circumstances tend to augment the real
_temperature of combustion, at leastif we assume that pressure tends
to diminish the tension of dissociation.

It will thus be understood how M. Bunsen finds for the gas of the
pile 2800°, and M. Deville, operating under the ordinary pressure,
only 2500°.

I next discuss M. Bunsen’s theoretical conclusion, according
to which dissociation is not a continuous phenomenon, but one
varying suddenly at certain temperatures, in the interval of which
it remains constant, varying moreover in such a manner that there
is always a simple proportion between the dissociated part and that
which is not dissociated. I show that this conclusion has but litle
probability a priori ; for this instantaneous production of a phenome-
non which induces an evolution or an absorption of heat, when the
exchange of heat with surrounding bodies is necessarily continuous,
must cause sudden variations of temperature such as we do not
observe.

M. Bunsen shuns the difficulty by assuming that, during the pas-
sage from one simple proportion to another, the temperature remains
constant. But we ought to observe this period of constancy. Thus
in the flame of a blowpipe with mixed gases, of which the various
parts offer precisely the successive conditions of a mixture in com-
bustion which is cooling, we ought to observe a very appreciable
space during which the temperature would be constant. Now the
accurate experiments of M. Deville upon the blowpipe with oxide of
carbon indicate a.continuous decrease of both the temperature and
the dissociation.

Moreover, during this period of invariable temperature, which
should represent a very noticeable fraction of the total duration of
the refrigeration, there would be a gradual, and not a sudden, passage
from one simple proportion to another. The simple proportion
would therefore not be an absolute natural law.

Finally, even the discussion of the experiments leaves, at least,
much doubt as to the legitimacy of the conclusion.— Comptes Rendus,
December 28, 1868, vol. lxvii. pp. 1848-1352.

Peter ey ae ee

160 Intelligence and Miscellaneous Articles.

ON A FRICTION AND INDUCTION ELECTRICAL MACHINE.
BY F. CARRE,

The author exhibited to the Academy of Sciences a new generator
of electricity founded upon statical induction reduced to its simplest
expression, the action of which he considers may aid in more clearly —
defining this phenomenon.

It consists of the friction-plate of the old electrical machine turn-
ing slowly between two cushions; above and parallel to this plate
turns a larger disk of non-conductive matter, in such a position that
the superior and inferior sectors of the two plates reciprocally cover
from two-fifths to three-fourths of each other’s radii.

The inferior plate fulfils the function of an inductor, the charge of
which is kept constant by its continuous passage between the two
cushions ; it acquires positive electricity. In front of the inferior
sector of the induced disk is a vertical comb connected with a con-
ductor which becomes charged with positive electricity ; a second
comb placed diametrically collects the negative electricity which is
poured out upon the disk by the lower comb.

From the direct action of the inductive plate at its maximum of
charge, the apparatus is but slightly sensitive to the humidity of the
atmosphere, and the induced disk furnishes an abundant “evolution
of electricity of considerable tension. Sparks of 15 to 18 centimetres
may be obtained with a machine having plates 38 and 49 centi-
metres in diameter; and the interposition of a condenser increases
their length.—Comptes Rendus, December 28, 1868, p. 1341.

ON THE SHAPE OF THE FLAME OF A BUNSEN’S BURNER.
; BY A. POPPE.

On closely viewing the flame of an ordinary Bunsen’s burner, we
are at once struck by the peculiar flickering or pulsation of the flame,
to which any definite rhythm seems wanting. I investigated the
cause of this phenomenon, and the true form of the flame, by the me-
thod which Magnus used in his investigation on the constitution of
the jet of water. Between the eye and the flame is interposed a
circular disk, in which is cut a narrow slit in a radial direction, so
that the whole length of the flame is seen when the slit is parallel
to it. On rotating the disk, when the velocity has acquired a cer-
tain rapidity it will be observed that that flickering is due to an un-
dulatory motion, which consists in a very rapid and regular succes-
sion of enlargements (loops) and contractions (nodes) of the flame.
If the disk makes one rotation in the time required for the succeed-
ing wave to take the place of the preceding one, the flame appears
immoveable, and the true form of the flame, which is that of an un-
duloid with a circular section, is at once plain. From the measu-
rable distance of the two loops, and the given velocity of rotation of
the disk, the actual velocity of propagation of the wave-motion may
be calculated.—-Poggendorti’s danalen, No. 10, 1868.

ited

ee

THE
LONDON, EDINBURGH, saxo DUBLIN
PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

[FOURTH SERIES.]
MARCH 1869.

XXII. Historical Notes on some Phenomena connected with the
Boiling of Liquids. By Cuarues Tomuinson, F.R.S.*

1. W HEN water is heated to that temperature at which its

tension equals the whole pressure of both air and va-
pour on its surface, and it begins to emit steam not only from
its surface (as it did before), but from all parts of its depth, it 1s
said to be boiling. The boiling-point of any liquid means,
therefore, the temperature at which its evaporating tendency
equals the pressure of the atmosphere at the time—or the lowest
temperature at which its vapour can have the elasticity of com-
mon alr.

2. During many years after the invention of the barometer,
and the consequent discovery of atmospheric pressure, it was
supposed that the above statements contained a sufficient account
of boiling. It was not until the irregular shifting of the boil-
ing-point in thermometers under a constant pressure had been
insisted on by such men as De Luc, Shuckburg, Horsley, and
Cavendish, that steps were taken to determine the conditions
on which that instrument should be constructed. The Royal

* Communicated by the Author.

[In preparmg the paper “ On Boiling Liquids ” recently read before the
Royal Society, ‘L was led to consult a good many books and memoirs, and
to accumulate a number of historical details which, though not adapted to
the ‘ Proceedings’ of a Society whose chief object is to assist the progress
of living science, may yet, if briefly stated, be acceptable in the Philosophical
Magazine, which performs the useful functions both of critic and of observer.
_ The insertion of these historical details may serve to correct some errors
that have crept into our text-books. |

Phil. Mag. 8. 4. Vol. 87. No. 248. Mar. 1869. M

162 Mr. C. Tomlinson’s Historical Notes on some

Society gave the sanction of its high authority to a Report on
the subject prepared by some of its most distinguished mem-
bers, and published in the Transactions for the year 1777. In
this Report the want of fixity in the boiling-point of water under
a constant pressure is noticed, and the cause is referred to the
depth of water in the vessel, which causes it to boil in gusts. It
was found, however, that the elasticity of the steam from boiling
water fairly represents the atmospheric pressure, and it was re-
commended that the water be boiled in a metal vessel constructed
so as to allow the bulb, and nearly the whole of that part of the
stem that contained mercury, to be surrounded by the steam.

8. IT am not aware that in this Report, or in the results pre-
viously published that led to it, it 1s anywhere stated that the
nature of the vessel influences the boiling-pomt. That fact was
distinctly brought forward by M. Achard in 1785*. Distilled
water was boiled in a brass cylindrical vessel by means ofa spirit-
lamp, the thermometer-bulb being within half an inch of the
bottom. Under these conditions the temperature was constantly
varying, although the water appeared to boilequably. Blowing
on the side of the vessel, opening and shutting a door, or any-
thing that produced an agitation in the air caused a fall in the
thermometer of 1:12° R. When the water was boiled in a ma-
trass of white glass, there was no variation in the boiling-point
as indicated by the thermometer. Achard performed a large
number of experiments on the boiling-point of water in vessels
of silver, brass, porcelain, earthenware, glass, &c., many of them
being articles in domestic use; and he gives drawings of them in
three folding plates, with measurements of their dimensions, to
justify his conclusion (afterwards found to be erroneous) that in
vessels of the same material the temperature of boiling water
varies according to the size of the opening. There is no doubt,
however, as to the influence of the vessel on the boiling-point.
He says:—“Le degré de chaleur de eau en ébullition dans dif-
férens vases est different pour la méme pression atmosphérique
quoique les vases soient chauffés de la méme manieére et qu’ils se
trouvent dans le méme bain de-sable.’? His idea was, that, metal
being a good conductor, the heat readily escaped from it when the
air was agitated, while glass retained its heat, and hence the oscil-
lation of the mercury in the one case and its fixity im the other.
He concludes his memoir with the remark ‘‘ that the experiments
prove that the degree of heat of boiling water under an equal

* Nouveaux Mémoires de ? Académie Royale de Berlin for 1785, pub-
lished in 1787. The following is the title of the memoir :—“‘ Expériences
faites dans la vue de s’assurer sile degré de chaleur de l’eau pure bouillante
est un degré fixe et invariable, indépendant de toute autre circonstance que
de la pression de latmosphére.”

‘ Phenomena connected with the Boiling of Liquids. 1638

pressure of the atmosphere is not a fixed term, but that many
circumstances cause it to vary; that it is much more inconstant
in vessels of metal than in vessels of glass; and that the action,
more or less direct, of the external air on the sides of the vessels,
especially when of metal, as upon the surface of the water, pro-
duce considerable changes in the degree of heat that it may
receive in boiling. As the construction of the thermometer
depends on the fixity of the boiling-point, it is not surprising
that thermometers made on this supposition, with the greatest
possible care, should not always agree.”

4. I have given these details at some length, because French
and English writers of authority assign to Gay-Lussac the merit
of Achard’s discoveries. Biot seems to have led the way in this
respect. Writing in 1816*, he says, in reference to the boiling
of water, “Il y a aussi quelques différences dans le degré de
Pébullition selon la nature des vases que l’on emploie, et selon
celle des substances qui se trouvent mélées a Peau, méme quand
elle ne peut les dissoudre. Cette remarque est due a M. Gay-
Lussac.”

5. The effect of insoluble substances on the boiling-point was
also first noticed by Achard, in 1784+. The water was boiled in
a glass vessel; and when the mercury in the thermometer was
steady, a drachm of the solid to be tried was thrown in, and the
effect noted in tenths of a degree on Réaumur’s scale. When the
temperature had again become steady, a second drachm of the
substance was thrown in, and so on until no further effect was
apparent. A large number of substances were tried in this
way, aud the results are given in Tables occupying fourteen
quarto pages. Each Table contains six columns, for recording
the name of the substance, the height of the barometer, the
boiling-point of the water before the addition, the weight of the
water, the weight of the substance added, and, lastly, the effect
on the thermometer in tenths of a degree Réaumur. Thus 1
drachm of iron-filings lowered the thermometer ten tenths, or
—10as Achard writes it; a second drachm had no further effect ;
copper-filings —8, tin-filings —13, white sand 0 to —8, eale-
spar —13, quicklime —9, rosewood —11, limestone in powder
—13, the same in a lump —8, bismuth in powder —12, the
same in fragments —8,and so on. Achard does not pretend to
offer any satisfactory explanation of these results, but he di-
stinctly claims the merit of having originated them.

6. The effect of soluble substances on the boiling-point was

* Traité de Physique, vol. i. p. 42.

Tt Berlin Memoirs, 1784, published 1786. The following is the title of
the memoir :—“ Sur l’effet produit par Paddition de différens corps 4 l’ eau,
relativement au degré de chaleur dont elle est susceptible dans |’ébullition.”

2

— waa -

164 Mr. C. Tomlinson’s Historical Notes on some :

clearly made out during the fine experiments undertaken by Dal-
ton, Watt, Robison, Southern, and others for determining the
pressures of saturated steam at different temperatures above and
below the standard boiling-point. It was noticed that if a mi-
nute portion of soda, or of some salt soluble in water and not
capable of rising in vapour with it, be allowed to ascend to the
top of the mercury, the column rises, thereby indicating a dimi-
nished pressure of steam, although the soda has not touched it,
but remains covered by the layer of water on the top of the mer-
cury. This shows that the elasticity depends not merely on the
temperature and the nature of the vapour, which are both un-
changed, but on the nature of the liquid. The adhesion of the
soda to the water tends to restrain the water from evaporating,
and this tendency is a measurable force and here measured ; for it
partly balances the tension of the water, or its tendency to emit
steam, and thus makes the steam-emitting tension of a soiution
of soda measurably less than that of pure water at the same tem-
perature. As the difference remains at all temperatures, the
solution must always be made hotter than pure water in order
to give steam of the same elasticity.

7. The effect of air dissolved in the water on the boiling-point
was noticed in minute detail by De Luc* in 1803, not indeed
for the first time; for in his previous works, published in 1772
and 1786+, he had described the principal experiment on which
his remarkable theory was based. He says:—“ Le phénoméne
de Pébullition est produit par des bulles d’air que la chaleur
dégage du liquide ....; quand on a préalablement purgé l’eau
de tout lair qu’elle contenoit, elle ne peut plus bouillir; et la
raison en est que les vapeurs ne peuvent se former qu’a des
surfaces libres. Les bulles d’air qui se rassemblent dans son
sein y produisent des solutions de continuité; c’est-a-dire, ces
surfaces libres nécessaires ; mais quand Veau est purgée d’air les
vapeurs he peuvent se former qu’a sa surface extérieure ” (Iniro-
duction, &e. vol. 1. page 247). De Luc hadalready described, in
1772, with great minuteness of detail an experiment in which a
matrass containing water, and also a small thermometer, had the
upper part of its tube drawn out into a capillary bore, and, the
matrass being heated in hot water, the air as it accumulated in
the fine tube was got rid of by an ejection of steam, and the
tube was sealed. ‘The tube was also subjected to percussion
during a long time, and the process of heating was continued

* Introduction a la Physique terrestre par les Fluides expansibles.
Paris, 1803.

t+ Recherches sur les Modifications de ’ Atmosphere. Geneva, 1772. See
chapter 10 of the Supplement to vol. 11. Recherches sur les Variations de la
Chaleur de V Eau bowllante. Idées sur la Météorologie. London, 1786.

Phenomena connected with the Boiling of Liquids. 165

until more air got into the fine tube, when it was opened and the
air expelled. After continuing these operations of shaking and
heating the tube in order to get rid of the air, the tube was
raised to 212°; and the point being broken so as to reestablish
atmospheric pressure, the water was further heated to 2344° F.
without boiling*.

8. Proceeding in the order of time, we come to Gay-Lussact.
While engaged in his experiments on solubility, he seems to
have rediscovered the two facts respecting the imfluence of the
vessel on the boiling-point, and also of the effect of an insoluble
body in lowering the boiling-point. But it is remarkable that
in both his papers Gay-Lussac refers to Achard’s results, or
rather to his faulty conclusions, with a view to contradict them,
without giving him credit for those points that were true. It is
quite possible that Achard’s fame was more injured by his friends
than his opponents, since an attempt had been made by Gmelin
and others, in answer to Gay-Lussac’s paper of 1812, to show
that in a number of vessels of different material, all sunk to the
same depth in a sand-bath, water boiled at the same temperaturet;
while in 1817 Muncke stated§ that copper-filings appeared to
have no influence in lowering the boiling-point, and that sand did
so only to the extent of one-tenth of a degree. Gay-Lussac in 1817
noticed these papers, and reasserted the original facts with even
more decision than he had done in 1812. But even in this his
first notice of the subject, his language is not to be mistaken.
His paper is on Deliquescence, and he says :—‘ In determining
the boiling-poimt of saline and acid liquids I observed a very
singular phenomenon which deserves to be known. Water or
any other liquid boils later in a glass vessel than in a metallic
one, except when we put into the former some turnings of iron,
copper, or other metal, or carbon in powder, or pounded glass.
The difference in the case of water may amount to 1°3° C. and
upwards.” In 1817 he states|| that water boils later in glass
and earthenware (fatence) than in metal vessels. He does not
give the measure of the difference, but believes it to vary with the
nature of each body, and, with the same substance, according to
the nature of its surface: “car il est probable quelle dépend a

* De Luc also dropped water into oil heated to 82° or 90°, and even 100° R.;
but he was by no means satisfied that the water ever attained this tempe-
rature. He says :—“ Ces gouttes d’eau, renfermées dans l’huile, pouvoient
étre dans un état particulier’ (see paragraph 993 of the Recherches). That
is, they were probably in what would now be called the ‘‘ spheroidal state,”
which De Luc understood and accurately describes in § 1007.

ft Annales de Chimie, vol. \xxxii. p. 171.
{ Schweigger’s Journal, vol. xxvu. p. 27.
§ Gilbert’s Annalen, vol. lvuu. p. 215.
_ || Ann. de Chim. et de Phys. vol. vii. p. 307.

166 Mr. C. Tomlinson’s Historical Notes on some

la fois et de la propriété conductive pour le calorique et du poli
des surfaces.” When a flask half full of water is in a state of
ebullition, a peculiar noise shows that the boiling goes on with
difficulty ; large bubbles of steam proceed from certain points
ouly of the surface, and a thermometer plunged into the water
shows frequent variations. In a tinned-iron vessel, on the con-
trary, the bubbles of steam are not so large, but they are more
numerous, the variations of the thermometer are less consider-
able, and the boiling point is not so high. If, however, water
be boiled in a glass vessel and a few pinches of iron. filings be put
into the vessel, the boiling instantly goes on as in a metal vessel.
In the absence of this aid, the quantity of steam formed is pro-
portional to the excess of the temperature of the water over that
of its boiling-pomt. The temperature falls to 100° C. with a
sort of explosion, the steam having to overcome the cohesion of
the liquid and its resistance to change of state. This cohesion,
or viscosity of the liquid, must exert a great influence on its
boiling-point, since the steam has to overcome not only the
atmospheric pressure, but also the cohesion of the liquid mole-
cules. Then, again, the adhesion of the liquid to the vessel
must be a force analogous to its viscosity. The conducting-
power of the vessel for heat and the nature of its surface must
also exert considerable influence on the boiling-point of water.
Water boils more easily in a glass vessel into which powdered
glass has been thrown, than in a glass containimg nothing but
water.

9. Gay-Lussac illustrates the greater or less ease with which
steam escapes from boiling water by referring to the readiness

with which carbonic acid escapes from fermented liquors, such as
bees or champagne, especially when a bit of paper or a crust of
bread, &c., is introduced, or simply by stirring. Carbonic acid is
mostly disengaged f from the sides of the vessel, andl especially from
parts containing asperities. The bubbles increase in size in traver-
sing the liquid, because they establish in it a solution of continuity
which is very favourable to the disengagement of the gas. It is
easy to explain by these facts the phenomena of soubresauts or
“jumping ebullition,” or “kicking.” ‘When the liquid is above
the boiling-pomt, it 1s im a forced state; and in an instant a
burst of steam 1s formed, the liquid 1s thrown out, and the vessel
itself raised. This 1s especially the case in distilling sulphuric
acid; butif some pieces of platinum wire be put into the retort,
the distillation then becomes easy.

10. It is impossible to read this paper without being struck
with the large amount of suggestion contained init. Indeed
Gay-Lussac’s imagination was so lively that it seldom left him
satisfied with one explanation when he had to discuss some new

De
‘\

Phenomena connected. with the Boiling of Liquids. 167

point, and the varied suggestions thrown out by him have each
served as a basis for further inquiry by subsequent observers.
But the difference between him and some of them consists in
this, that he would originate an idea, examine, and discard it
when seen to be no longer tenable; they clung to the idea even
though it carried them into the region of error. It is the dis-
tinction between genius and talent, that the one originates capital,
and the other trades with it. :

11. In 1825 Dr. Bostock published some facts respecting the
boiling-point of ether*. Ether (spec. grav. 0°755) in a matrass
over aspirit-lamp boiled at 112° I’.; but in a test-tube put into
hot water it did not begin to boil until it had reached 150°,
and on one occasion 175°. Some bits cf cedar-wood were put
into the ether, and it boiled at 110°; the wood was covered
with bubbles, until it got soaked and sank. Bits of quill, feather,
wire, pounded glass, &c. also lowered the boiling-point consider-
ably. After stating that copper-filings, chips of wood, &c. ap-
peared to produce ebullition in the ether after it had ceased to
boul, Dr. Bostock says, ‘‘ Plunging a thermometer into ether
caused the production of the bubbles at a temperature many
degrees below the point at which ebullition took place without
the thermometer; but the effect of the thermometer after a short
time was no longer perceptible, and I observed that by alter-
nately plunging the thermometer into the ether and removing it
from the fluid, the bubbles were produced at each immersion.”
The various nuclei above referred to are said to act by carrying
down air into the ether, and as soon as the air is discharged they
cease to act.

12. Dr. Bostock’s interesting paper called attention to some
processes in the useful arts adopted with a view to facilitate the
process of boiling. Thus Mr. Bald+ notices a practice among
the engine-keepers of Scctland, when the ordinary supply of
steam cannot be raised from the boiler, of throwing in about a
bushel of the radicles of barley, separated during the process of
cleaning the malt and called “ comings.””? When steam is again
raised, the effect is immediately apparent ; “for not only is there
a plentiful supply of steam for producing the full working speed
of the engine, but an excess going to waste at the safety-valve.
This singular effect will continue several days.” So also in dis-
tilling ardent spirits on a large scale, when converting the fer-
mented wash into “low wines,” it is usual to throw a bit of soap
into the still every time it is charged. This causes the steam to

rise more quickly, and to be freer from the residual matter of the

process.

* Annals of Philosophy, N.S. vol. ix. p. 196.§
y+ Edinb. Phil, Journ. vol. i. p. 340.

168 _ Mr. C. Tomlinson’s Historical Notes on some

13. Attention was also called to a conclusion arrived at by
(Ersted*, that gas resulting from chemical decomposition is never
disengaged from a liquid except in contact with some solid body ;
and he proposes to apply this principle to the disengagement of
vapours. He says:—‘‘If a metallic wire be suspended in a
boiling fluid, it instantly becomes covered with bubbles of va-
pour.” To show the application of this fact, ten pounds of brass
wire, one-fifth of a line in diameter, were put into a still contain-
ing ten pints of brandy; seven pints came over at a heat which
without the wire would have sent over only four.

14. In 18385 Le Grand+ remarked that “ when water is boiled
in a glass vessel the boiling goes on at first regularly, with the
production of numerous bubbles, and without noise; but as soon
as the water has lost the greater part of the air that it held in
solution matters become changed; the ebullition takes place in
intermittent bursts,accompanied with noise, and the thermometer
experiences considerable oscillations. This 1s known as bdump-
ing. Many salts in small quantity prevent it im a remarkable
manner. Others favour it highly, especially the neutral tartrate
of potash. Platinum is generally used to prevent it, on account
of its unalterable character; but this is a mistake; for the mo-
ment a small quantity of platinum-filings 1s added, ebullition is
facilitated, on account of the air introduced; but as soon as this
air is disengaged the bumpings are resumed.”

15. In 1887 some curious experiments were recorded by
Schénbein f, in which the effect of gas generated in the midst of
water near the boiling-point wasshown. For this purpose 1 per
cent. of sulphuric acid was added to the water, and when it was
boiling the lamp was removed and some bits of iron or zine wire
were thrown into the flask. Ebullition set in again immediately,
and continued during some seconds. If the wire was first rolled
up into a coil before being thrown in, the effect was so consider-
able that a portion of the contents of the flask was thrown out.
Metals that do not disengage hydrogen, and from whose surface
the adhering film of air has been removed by dipping them into
boiling water (such as platinum, gold, silver, &c.), will not dis-
engage any vapour from water near the boiling-point.

16. Schonbein’s explanation of the effect of zinc in the acid
water did not depend, as we should have supposed, on the effect
of air or gas in diminishing the cohesive force of the liquid par-
ticles, but his theory rested entirely on the principle of heat
overcoming pressure. He reasons in this way :—Hydrogen on
being liberated has the same pressure as the atmosphere; the

* Gehlen’s Journal fiir Chemie, vol. 1. pp. 277-289.
+ Ann. de Chim. et de Phys. vol. lix. p. 426.
t Pogg. Ann. vol. xl. p. 391.

Phenomena connected with the Bowling of Liquids. 169

elasticity of the vapour of water that has just left off boiling we
may suppose to be one-hundredth less than the pressure of the
air; hence 1 volume of hydrogen and 99 volumes of vapour
would produce a mixture equal in elasticity to the atmospheric
pressure *, |

17. Some of the German text-books+ on physics assign to
Rudberg the honour of an important observation made in 18387,
namely, that although water boils at a higher temperature in a
glass than in a metal vessel, yet the temperature of the steam is
in both cases the same, the pressure being the same. This fact
was known to Cavendish and the other eminent men who pre-
sented the Report on Thermometers to the Royal Society already
referred to (2). |

18. In 1842 Marcet published a long memoir “ On certain
circumstances that influence the Boiling-point of Water”t. The
condivions of the case are thus stated :—Boiling takes place in
any liquid at the moment when the repulsive force of heat is
sufficient to overcome the effect of cohesion among the particles
of the liquid plus the atmospheric pressure. But if the liquid is
in a vessel of which the adhesion of the sides to the particles of
the liquid is more than the cohesion of the latter among them-
selves, this adhesion must be overcome, and more heat will be re-
quired than if the simple cohesion of the particles were concerned.

19. Marcet considers that iron, zinc, and other substances
tend to lower the temperature of boiling water, because they
have a less molecular adhesion for water than glass has. If the
vessel be coated with a thin layer of sulphur, gum-lac, or any
similar substance that has no sensible adhesion for water, the
boiling-point is lowered, and the temperature of the water and
of the steam are identical. In such case the boiling-point may
be lower by some tenths of a degree than in metal vessels. The
boiling-poimt varies m flasks made of the same glass, and even in
the same flask at different times, irrespective of pressure. Differ-
ences were also noticed between flasks fresh from the maker and
those that had been used for experiments. In such as had held

* Schonbein repeats Bostock’s experiments, of course without being
aware of it. He says, “bits of wood are remarkably active so long as
their pores are full of air, but not at all when this is expelled.” And
again :—‘ ‘All bodies that contain air or liberate it, set air or gas free from
their solutions.”’ This is precisely the theory of M. Gernez, ‘‘ On the Dis-
engagement of Gases from their Supersaturated Solutions,” as given in the
Comptes Rendus for November 19, 1866, pp. 883-887, and examined by
me in the Philosophical Magazine for August 1867.

ft See Eisenlohr, Physik, 1860, p. 356. Rudberg’s paper is on the
Construction of Thermometers. It 1s imserted in Poggendorff’s Annalen,
_ vol. xl. p. 49, and is more modest in its claims for originality than the
books referred to.

{ Annales de Chimie et de Physique, ser. 3. vol. v. p. 449.

170 Mr. C. Tomlinson’s Historical Notes on some

sulphuric acid the boiling-point of water rose to 106° C.; so
much had the internal surface of the glass become modified by
the acid; but by simply heating the flask to 300° or 400° C. a
similar result was obtained. The conclusion arrived at was that
“the effect was due to a species of molecular modification of the
surface of the glass, brought about by the acid, of such a nature
as to increase the adhesion of the water and so delay its boiling.”
In other words, the glass was made chemically clean. Still,
however, the author does not catch this idea; he goes on con-
triving new experiments which again bring him “to some slight
modification in the physical texture of the glass by the action of
the sulphuric acid, or by destroying the impalpable dust retained
between the molecules of the glass. A new flask, however clean
in appearance, always has more or less of such dust on its sur-
face. This kind of dust or varnish (vernis) not only adheres
to the surface of glass, but forms part of its very substance,
imprisoned between its molecules, and the adhesion of glass for
water is diminished thereby.” Heating the glass to redness
“may destroy foreign matter on the glass, or up to a certain
point modify the molecular condition.” In the last page of his
memo Marcet is still referring to these “ molecular changes ”
(so powerful was the influence cf Gay-Lussac on scientific opi-
nion) (10); and it is only in summing up the conelusions “ drawn
from his inquiry, still very mcomplete (encore fort imcomplet) , that
he makes use of the expression “ perfectly clean glass vessels.”
In them, he says, “‘ water and alcohol may be raised to a higher
temperature than has hitherto been known.”

20. In 1844 Magnus*, in the course of some observations on
the elasticity of steam, has some remarks on the cohesion and ad-
hesion of water during the boiling. Ifthe walls of the vessel had
an infinitely stronger adhesion for the water than the liquid par- ~
ticles had of cohesion among themselves, or if the walls of the
vessel were of water, we might obtain a measure of the cohesive
force, because in such case the water would only attain a boiling-
point at which the elasticity of the steam was sufficient to overcome
the pressure of the air and thecohesion of the water. But in a vessel
whose sides have less achesion for the water than the liquid mole-
cules have of cohesion among themselves, a less force is required
to overcome the adhesion than the cohesion. Hence the boiling-
point is lower in proportion as the adhesion of the sides or of
any foreign insoluble substance in the water is small. It is sup-
posed that a smooth metal surface to which the water-particles
adhere more strongly than they cohere, must raise the boiling-
point—although experiment shows the contrary. Ifa perfectly
clean metal surface be dipped into water so as to wet it com-

* Poggendorfi’s Annalen, vol, |x. p. 248.

Phenomena connected with the Boiling of Liquids. 171

pletely, points will be found where the water does not adhere,
where in fact the adhesion is less than the cohesion of the liquid
molecules. The same is true of glass, though cleaned with boil-
ing sulphuric or nitric acid. In a platinum vessel cleaned first
with fused caustic potash and then with sulphuric acid, the boil-
ing-point of water was higher than the temperature of the steam,
but not so high as in a glass vessel; but in this the boiling-point
was not so high as in Marcet’s experiments (19). The reason
probably was that the platinum vessel used was much worn, and
contained cracks and scratches (Risse und Schrammen) which
probably acted like puiverulent bodies in lowering the boiling-
point.

21. In 1843 Donny published a paper* in which the influence
of the air or of gases dissolved in the liquid is made of first-rate
importance in studying the phenomena of ebullition. M. Donny’s
results have been estimated so highly that most subsequent
writers have not only adopted them, but have promoted further
investigations with reference to them. Whether it be true or
not that the dissolved air is so important has been considered in
another place+; but the idea that it is so 1s by no means new,
as already noticed (7), (11), (14), &c.

22. According to Donny, boiling is not an inherent property
of liquids; they only boil when they contain air—that is, when
they are not pure. Heat liberates bubbles of air nearest to the
source of heat: each air-bubble presents to the liquid molecules
surrounding it a surface which promotes the vaporization of these
molecules; and when the tension of the vapour is sufficient to
counterbalance the pressure to which these bubbles are submitted,
nothing further opposes the development of this vapour, which
then forms currents that traverse the liquid and give rise to
ebullition. Hence, according to this view, ebullition is a kind
of evaporation extremely rapid, which operates upon those inte-
rior surfaces of the hquid which limit a bubble of some aériform
fluid f.

23. Ifthe quantity of air im the liquid be small, the boiling-
point may rise ; but the boiling-point is constant only when the
liquid contains air. It is difficult, if not impossible, to get rid
of the dissolved air; after a burst of vapour a bubble of air may
often be seen adhering to the vessel. ‘The boiling-point is also
singularly influenced by the forces of cohesion and adhesion—the

* «Sur la Cohésion des liquides, et sur leur adhérence aux Cozps
solides,” Mémoires couronnés par l Académie Royale de Bruxelles, 1843 &
1844, vol. xvii. published 1845. See also Annales de Chimie et de Physique
for 1846, ser. 3. vol. vi. p. 167.

+ Proceedings of the Royal Society, January 21, 1869.

{ These views are the same as those put forth by M. De Luc(7).

BLS SPST EE PANE ELIT,

172 Mr. C. Tomlinson’s Historical Notes on some

cohesion of the molecules of water being superior to a pressure
of three atmospheres, or a column of water of 380 metres. This
conclusion was arrived at by heating water ina chemically clean
tube in a bath of chloride of calcium as high as 138° C.
(280°°4 F.). The tube was 8 millims. in diameter (;% or 7344 —
inch), curved at an angle of 100° at the end where the water
was heated, the other end being furnished with two bulbs. The
water was first boiled so as to expel the air, and the extreme bulb
was then sealed. ‘The portion of the column of water contained
in the short covered end was then put into the chloride-of-calcium
baths, of which there were four, one at 118° C., another at 121°,
a third at 128°, anda fourth at 132°, and this rose to 188°, at
which temperature the water suddenly burst into steam and con-
densed in the bulbs at the other end of the tube.

24. From 1843 to 1863 it was considered a settled point in
physico-chemistry that, in proportion as water is deprived of air,
the character of its ebullition changes, becoming, as it does,
more and more abrupt, and boiling, like sulphuric acid, with fre-
quent soubresauts, and that between every two bursts of vapour
the water reaches a temperature above its boiling-pomt. To
effect this, according to Mr. Grove*, it 1s necessary that the
water be boiled in a tube with a narrow orifice, through which
the vapour issues ; if it be boiled in an open vessel, it continually
reabsorbs air and boils in the ordinary way. Mr. Grove de-
scribes an experiment in which water covered with oil was boiled
in a tube: the water also contained some wire, which was plati-
nized for the purpose of presenting more points for the ebullition
and for preventing soubresauts as muchas possible. The boiling
was continued for hours and even for days; the steam condensed
in the oil, and there was always found with it a minute bead of
nitrogen gas. It is contended that in this and another similar
experiment there was no pure boiling of water, no rupture of
cohesion of the molecules of water itself, but the water was boiled
by evaporation against a surface of gas. The conclusion 1s suffi-
ciently startling, viz. ‘‘ that no one has yet seen the phenomenon
of pure water boiling, 7. e. the disruption of the liquid particles
of the oxyhydrogen compound so as to produce vapour which
will, when condensed, be a water leaving no permanent gas.”

25. In 1861 M. Dufourt published an account of an experi-
ment in which water is said to have been raised to the tempera-
ture of 178° C. (852°4° F.) without boiling. For this purpose
the water, previously raised to 80° or 90° C., was suspended in

* «On some Effects of Heat on Fluids,” Journal of the Chemical So-
ciety for 1863, 2nd series, vol. i. p. 263.

+ Archives de la Bibliotheque Uniwverselle de Genéve. See also Ann. de
Chim. et de Phys. for 1863, ser. 3. vol. Ixviil. p. 378.

Phenomena connected with the Boiling of Liquids. 178

a mixture of oil of cloves and linseed-oil, and this was gradually
raised to 110° or 115°; and the water did not burst into vapour
unless it touched the sides of the vessel or the thermometer.
The smallest globules of water bore the higher temperatures
best: those of 10 millims. diameter were raised to 120° or
130° C.; while those of from 1 to 3 millims. were raised to 178°,
when the vapour has an elastic force of 8 or 9 atmospheres*.
26. Solids brought into contact with the globules liberated
vapour with a hissing noise. Porous bodies, such as wood,
chalk, cotton, paper, &c., produced this effect best. A glass rod
or a metallic wire did not always act in this way. A platinum
wire by frequent use appeared to lose the power of causing sud-
den vaporizationt. Porous bodies act best because they carry
down air in which the globule begins to evaporate and expand.
27. M. Dufour rejects the theory which attributes the retar-

dation in boiling to the adhesion of the liquid to the sides of the’

vessel. The contact of solids may prevent the liquid from rising
above its boiling-point. The real explanation is to be found in
the molecular relations of liquids—in a sort of internal cohesion.
When a liquid is near the boiling-point, these molecular influ-
ences act as excitants to change of state. The adhesion to the
sides of a vessel also excites a peculiar molecular condition in
the liquid, and it is at the sides that this molecular equilibrium
is disturbed and boiling takes place. But when the aqueous
globule is immersed in a fluid with which water does not mix
and is raised to a high temperature, it is the contact of a solid
that disturbs the mechanical structure of the globule and induces
change of state. Heat alone, acting on water protected from the
air, contact of solids, and other disturbers of the molecular con-
dition, cannot produce change of state, except very much above
the temperature usually recognized as the boiling-poimt. But
M. Dufour admits that the molecular influences or disturbers
unfortunately present so many irregularities, that they have hi-
therto escaped the controlling action of any regular law. He
thinks there must be some other force besides cohesion that

* T have no doubt that the globules were in the spheroidal state, as in
De Luc’s experiment (7, note *, p 165). More than thirty years ago I pub-
lished in my ‘ Student’s Manual of Natural Philosophy,’ p. 553, an'account of
some experiments in which water, alcohol, ether, and_ some other liquids
were gently delivered from a dropping-tube to the surface of a fixed oil
heated to 450° or 500° F. The liquid drops rolled about on the surface in
the spheroidal state ; and in some cases, when a drop slipped beneath the
surface, it exploded and scattered the oil about; but in other cases it was
shot up again to the surface, where it continued to roll about as before.

Tt Dufour says in another part of his memoir that glassis less active as a
. promoter of vaporization than metal.. “{l semble que le fréquent usage
d'une pointe de platine contribue 4 ’amener a cette sorte de passivité.”

174 On some Phenomena connected with the Boiling of Liquids.

delays the boiling of a liquid; “ but these and numerous other

phenomena which depend on mechanical molecularity are in a
deplorable state of obscurity.” He thinks that Gay-Lussac (8)

uses the word cohesion in a wider sense than that which opposes

the separation of particles. ‘ We must simply conceive that the
force which prevents the vapour from forming is an internal
force due doubtless to cohesion of the liquid, which the vapour

must overcome, and that resistance to change of state which it is
more difficult to analyze.”

28. In 1864 and the following year M. Dufour published
two further memoirs* on the phenomena of boiling water, in
which he shows that under certain conditions the retardation of
the boiling-poimt takes place at reduced pressures and under
atmospheres of hydrogen, street gas, and carbonic acid. As to
the action of solids in prometing boiling, he has no doubt that
it is due to the air adhering to them, and they become inactive
when this air is removed by the boiling water—and that when
the boiling-point of water rises by repeated boiling, the effect is
due to the expulsion of air (1]). Bits of dry pine-wood, paper,
filaments of cotton, &c. lowered the boiling-point. ‘* Soustraits
depuis longtemps au contact de Vair, fréquemment et longue-
ment chauffés dans |’eau, ils avaient fini par devenir absolument
imactifs: jamais une bulle de vapeur ne se produisait plus sur
leur surface, et des retards considérables d’ébullition pouvaient
se manifester’”’ (p. 210).

29. It will be seen from these historical notices that much im-
portance is attached to the influence of dissolved air upon the
boiling of liquids, as pointed out by De Luc (7) nearly a century
ago, and more recently insisted on by Donny (21) and others.
It is generally admitted in our text-books (1st) that as soon as this
dissolved air has been expelled by heat, liquids boil with difficulty,
or produce only sudden flashes of steam; (2nd) that those liquids
which have only a weak affinity for air, such as sulphuric aeid,
aleohol, ether, &c., boil with the greatest difficulty ; (6rd) that the
mutual cohesion of the molecules of the quid, and the adhesion
of the liquid to the sides of the vessel, influence the boiling-point,
but the adhesion varies with the nature of the vessel and the con-
dition of its sides as to roughness or smoothness; (4th) that the
action of solid substances in promoting tranquil boiling and in
preventing soubresauts is by carrying down air.

30. My reasons for dissenting from these conclusions are
eiven in my paper published in the Proceedings of the Royal
Society (21, note), to which I beg to refer.

* Archives des Sciences, Bib, Univ, vol, xxi. p. 201; vol. xxiv.

fr 175 J

XXIII. On the Compounds of Ethylene-sodium and of its Homo-
logues. By J. Atrrep Wanktiyn, Professor of Chemistry
in the London Institution*.

‘5 inede reaction described at the end of my former paper + in-

dicates very distinctly that the absolute ethylate of so-
dium got by heating the well-known crystals is in reality hydrated
oxide of ethylene-sodium, the substances arising from the action
of the ethers on this compound being the different salts of the
new organo-metal ethylene-sodium. |

((C? H4)" Nal’)! = Hthylene-sodium (radical).

2174
(C* H* Na) iy }O= Hydrated oxide of ethylene-sodium.
2174
(C ie Ho tO= :Acetate of ethylene-sodium.
2174
(C - HO yO= loinc of ethylene-sodium,
(C? H4 Na)!

C7 H2O O= Benzoate of ethylene-sodium.
((C® H!°)" Na!”)' = Amylene-sodium (radical).

5 TT10

(C°H a ? Lom Hydrated oxide of amylene-sodium.
5 [10

(C re aa O=Acetate of amylene-sodium.
C5 H!9Na

C5 HS 5 }O= Valerianate of amylene-sodium.

The foregoing is a list of the formule of such compounds of
ethylene-sodium and of amylene-sodium as have been already
produced, to which are added the formule of the radicals them-
selves.

Ethylene-sodium and Amylene-sodium (radicals).

It will of course be understood that should these radicals be
capable of existing in an isolated state, their formule in that
tafe must be double of that which represents them in a state of
combination. Thus we should have :—

214 Na)!
ice a Nay f = free ethylene-sodium.

Very great difficulties will have to be overcome before the
free radicals can be actually prepared. Passing in review the
history of the isolation of the organo-metallic radicals, it will be

* Communicated by the Author.
+ Phil. Mag, vol. xxxvii. p. 117.

176 Prof. J. A. Wanklyn on the Compounds of

understood that the methods which have answered in the in-
stances already known are not likely to answer in the present
case. Kakodyle was obtained from chloride of kakodyle by
driving out kakodyle by means of zinc. Supposing, however,
that I had got the chloride of ethylene-sodium, what metal could |
I expect to be capable of driving out ethylene-sodium ?

Zincethyle was obtained by the distillation of the double zinc-
compound of iodine and ethyle, when, as is well-known, zinc-
ethyle distils over. The non-volatility of ethylene-sodium is a
bar to the establishment of a parallel process.

The only hope which I have at present of isolating the new
radical is the hope of finding it among the products of the de-
structive distillation of the double compound of sodium-ethyle
and zinc-ethyle, not, however, in the distillate, but in the resi-
due, along with the finely divided zine and sodium which results
from the destructive distillation i question.

With respect to the chemical constitution of ethylene-sodium,
there are two modes of representation which will commend
themselves to the chemical mind, viz. :—

((C? H4)"Na!)', and ((C? H4)!" Nal")!,

Against the first, and in favour of the second formula (that
to which I have given the preference) may be urged the fact
that sodium appears to be a trivalent metal; and also that the
first method of representation would necessitate the assumption
that in the hydrated oxide there existed oxygen not in direct union
with sodium, whilst the second formula represents the sodium as
directly combined with oxygen. Another reason for giving the
preference to the second formula will be mentioned on a future
occasion.

In support of the statement that sodium is a tri-valent metal,
a statement which will be looked upon as a chemical heresy
in certain quarters, I would bring forward the cases of the
double zinc-sodium-ethyle and of sodium-triacetyle.

The analysis of the first of these compounds led to the em-
pirical formula (Na C? H°+ Zn(C? H*)?)*, as will be seen on
reference to my paper on the subject. It will also be remem-
bered that I altogether failed to effect a separation between the
sodium-ethyle and the zinc-ethyle. The real constitution of the
compound is :—

Nall!—_C2 #15
Fa
nee re
Zn!'—C? H®

-Na—2o, “i 00.

Ethylene-sodium and of its Homologues. 1V@

Sodium-triacetyle, asI pointed out at the last Meeting of the
British Association (vide also the January Number of Liebig’s
Annalen), is obtained by the action of sodium on acetic ether.
Although its formula may be represented in another way, still
tne most elegant representation is Na!”(C? H? O)3,

In the common sodium-salts I regard the sodium as having
united with itself; thus common salt is looked upon as being

NaCl

|
Na"'—Cl

In fine, I regard sodium as being an analogue of nitrogen and
arsenic rather than of hydrogen.

Hydrated Oxide of Ethylene-sodium.

This compound was described in my last paper under the
name of the absolute ethylate of sodium, and is obtained by
heating the well-known crystals which are the product of the
action of sodium on alcohol. It is also formed by the action of
sodium on the ethyle-ethers of the fatty acids.

It is a snow-white amorphous solid, non-fusible, and of remark-
ably low specific gravity. There are difficulties in the way of
taking its specific gravity with great precision. It appears to
be lighter than ether, in which it swims. There is just the pos-
sibility that this extreme lowness of specific gravity may be to
some extent simulated, and that the floating in ether may be
due to adherent gas (hydrogen).

Whether or not the specific gravity is lower than that of ether
must be determined by further experiment ; but that the specific
gravity does not exceed that of water has been shown by a de-
termination.

As has already been described, this substance possesses the
property of withstanding a very high temperature without de-
composition. It will bear being heated to 290° C.; possibly it
will bear a much higher temperature; but, as might have been
expected, it will not bear a low red heat without carbonizing.*

In contact with excess of water, it gives caustic soda and
alcohol, the latter, as I showed in my last paper, being obtained
in the theoretical quantity from product which had undergone
heating to 200° C. Heated with an insufficient quantity of
water to convert all of it into caustic soda and alcohol, the reac-
tion is still of the same kind, a quantity of water liberating an
equivalent of alcohol, thus :—

2444 '
2 $0420? 0=207 18 0 + Na? (110)?

Phil. Mag. 8. 4. Vol. 37. No. 248. Mar, 1869. N

178 Prof. J. A. Wanklyn on the Compounds of

The numbers given on experiment were :—

Quantity of water added to a weighed tan am :

quantity of the substance . .
Loss on heating the substance and
water to 270° C. and 280° C bee —— ee
Therefore by experiment, ratio of water to alcohol produced
=O = 27309).
Theory requires
1:00 : 2°55.

This experiment shows very plainly that there is no forma-
tion of anhydrous soda. If Na*O were formed, double the
quantity of alcohol should have been given. Furthermore,
experiment with alcohol shghtly moist, 7. e. containing 3 per
cent. of water, has shown that the new compound is very sen-
sitive to the presence of traces of water, the smallest quantity
of water effecting an equivalent decomposition according to the
equation just given.

With iodide of ethyle:—It is well known that an alcoholic
solution of potash or soda, as also the crystals contaiming alco-
hol and ethylate of sodium, effects an easy decomposition of
iodide of ethyle into ether and iodide of the allcali-metal.
The hydrate of ethylene-sodium behaves in a very different
manner. I took 5:849 grms. of the hydrate and 10 cubic cen-
tims. of iodide of ethyle and heated very gradually up to 210° C.
in a small retort open to the air; 9 cubic centims. of iodide
of ethyle distilled over, and were condensed and measured.
The product was subsequently weighed and found to be 5:948
erms., showing that there had been no sensible action, the small
difference of 0-1 erm. being only that which would be occasioned
by the difference of weight between the apparatus partially
filled with vapour of iodide of ethyle and the apparatus filled
with air. In this experiment, although the temperature of the
oil-bath was 210° C., still the temperature of the interior of
the retort must have kept very low, owing to the evaporation
of the iodide of ethyle until near the end of the experiment.
The conclusion to be drawn is that there is no rapid action
between iodide of ethyle and hydrated oxide of ethylene-sodium
at moderate temperatures. Under similar circumstances, either
the crystals or alcoholic solution of potash or soda would have
decomposed a very considerable quantity of iodide of ethyle.

When iodide of ethyle and the hydrated oxide of ethylene-
sodium are sealed up together and heated up to between 120° C.
and 150° C. for an hour or two, there is very complete decom-
position.

Ethylene-sodium and of its Homologues. 179

- 1°25 grm. sodium was dissolved in alcohol, and the product
dried at 196° C., 3 cubic centims. of iodide of ethyle added to it
and sealed up with it. The whole was then heated to from 120° C.
to 150° C. for about two hours. On opening the tube there
was a slight escape of gas. Water was then added to the pro-
duct, whereupon about 2 cubic centims. of light oil separated.
This oil proved to be common ether, boiling at 36° C., and
boiling to dryness at 40° C. The aqueous liquid was distilled,
and the distillate redistilled. To the second distillate a httle
dry carbonate cf potash was added, whereupon there formed two
layers, viz. an aqueous layer of carbonate and an oil. This oil
had the smell of the secondary alcohols, and was, I suppose,
secondary butylic alecohel*.

With the ethers of the fatty acids there is produced alcohol
and a salt of ethylene-sodium, e. g.

C? H4 Na C? i° C2 EAN C*
an }O+ ca180 fO= cn0 f° i fO:

A reaction of this kind has been observed with acetate of
ethyle, acetate of amyle, valerianate of ethyle, and benzoate of
ethyle. An analogous reaction has also been observed between
the hydrated oxide of amylene-sodium and valerianate of amyle.
There is every reason to believe that this reaction is perfectly
general, applicable to the hydrated oxides of all the olefine com-
pounds of sodium or potassium, and all the fatty and aromatic
ethers.

Acetate of Hthylene-sodium.,

As just mentioned, this salt is prodaced by the action of
acetic ether on the hydrated oxide of ethylene-sodium. The re-
action appears to take place slowly even at 100° C.+ At higher

* Should further experiment confirm the indication here given, a very
important step in organic synthesis will have been taken—from ethylic to
isobutylic alcohol ; and in like manner a regular ascent of the series should
be practicable.

+ Owing to the occurrence of this reaction at 100° C., the attempts
made by various chemists to render acetic ether free from any alcohol with
which it might be contaminated by distilling it off sodium, have had the
reverse result, and, continually producing aleohol, have rendered the ether
more impure. By the action of sodium on acetic ether there is produced
sodium-triacetyle and hydrated oxide of ethylene-sodium, which latter at-
tacks excess of acetic ether slowly at water-bath temperatures. A sample
of acetic ether which, from the mede of its preparation, must have been
originally almost, if not quite, free from alcohol, became, after several dis-

tillations off a small quantity of metallic sodium, charged with aleohol ta
the extent of 15 per cent. This circumstance, which really no one can be
blamed fornot expecting and providing against, has probably led Geuther,
Frankland, and Duppa astray.
N 2

‘i
H

ne

FSS SE REST ERI ETE IS

180: Prof. J. A. Wanklyn on the Compounds of

temperatures it proceeds more rapidly. At temperatures ap-
proaching to 200° C. it is rapid. |

The most satisfactory way of preparing the compound appears
to consist in sealing up hydrated oxide of ethylene-sodium with
twice its weight of pure acetic ether, and heating for some
time to 150°C. (at which temperature the materials form a clear
fluid), and afterwards opening the tube and distilling off the
alcohol and excess of acetic ether in the oil-bath.

It is very easy to effect a partial transformation of the
hydrated oxide into the acetate, but not easy to complete the
reaction.

Acetate of ethylene-sodium is a white solid, non-fusible at
200° C., but apparently readily soluble at 150° C. in acetic
ether. Its characteristic reaction is the giving of aleohol and
acetate of soda* by action on water.

2144
2. oaHsG, pO+ 2H? O
= Na*(C* B® 07)? 4-202 hee:
It is isomeric with butyrate of soda. The circumstance of its
furnishing alcohol and acetate of soda with water shows that the
ethylene is associated with the metal and not with the acid part
of the salt.

With iodide of ethyle it reacts in a very interesting manner.
It combines with the iodide in the first instance, forming a
solid. On the addition of water to this solid (which dissolves in
the water, forming a solution of iodide of sodium), there sepa-
rates a considerable quantity of oily liquid. This liquid does
not contain any sensible quantity of common ether. I am
engaged in the investigation of it.

Valerianate of Ethylene-sodium.

Preparation.— Hydrated oxide of ethylene-sodium and pure
valerianate of ethyle are heated in a retort placed in the oil-bath.
Owing to the high boiling-point of valerianate of ethyle, it is
unnecessary to make a preliminary digestion in sealed tubes, as
in the instance of the acetate just descrited. The temperature
of the oil-bath is to be gradually raised up to the boiling-
point of valerianate of ethyle, and then taken up gradually to
200° C. During this operation abundance of alcohol has been

* The fact that this substance really does give alcohol and an acetate,
and not the salt of any higher fatty acid, was established by treating some
of it with water, and then distilling off the alcohol and estimating it in the
distillate, and subsequently rendering the residue acid with dilute sulphurie
acid and distillmg. The distillate was then saturated with carbonate of
baryta, and the resulting baryta-salt analyzed. It contained 53°34 per
cent. of barium, Acetate contains 53°73.

Ethylene-sodium and of its Homologues. 181

observed to distil over; the valerianate of the ethylene-sodium
remains behind as a white mass.

Valerianate of ethylene-sodium gives alcohol and valerianate
of soda with water, thus :-—

2 T74
2EEN Lo oHlon QAM Lorre Cl Lo,

Benzoate of Hihylene-sodium.
Formed like the salts just described. The high boiling-point

of benzoic ether makes this a very convenient instance for the
demonstration of the production of alcohol during these reac-
tions. There is moreover no difficulty in effecting a tolerably
complete transformation of a quantity of the hydrate into the
benzoate. I subjoin the details of an experiment.

2°0555 grms. of sodium were dissolved in alcohol, and the
resulting crystals heated up to 220° C., and maintained for some
time between 220° C. and 230°C. Weight of the hydrate of
ethylene-sodium =5°528 grms. Added 17:455 grms. of pure
benzoic ether and heated to 200° C. for about an hour, and just
at last raised the temperature to 240°C. There distilled over a
-liquid, of which 2°9 grms. were collected and weighed. This
proved to be absolute alcohol; it boiled to dryness sharply at
80° C. The weight of the solid residue was 19°486 grms., and
the loss in weight by heating consequently was equal to 3-497
erms. ‘The theoretical loss which the quantity of hydrated
oxide of sodium-ethylene experimented on should have sustained
is 4111 grms., showing that in the above experiment the action
had been nearly complete.

The benzoic ether used in the above experiment was quite
pure, being neutral to test-paper, and having given correct
numbers on titration with alkali.

Hydrated Oxide of Amylene-sodium.

This compound is obtained like the corresponding ethylene-
compound, viz. by the action of heat upon the product got on
dissolving sodium in amylic alcohol. It is also formed m a very
interesting way by the action of amylic alcohol on the hydrated
oxide of ethylene-sodium :—

eT }O+ vy fos ee }o4 + y bO.

The salts of amylene-sodium are parallel with those of ethy-
lene-sodium. ‘The acetate and valerianate have been prepared 5
the latter is particularly distinguished from the ethylene-sodium
salts by being readily fusible. In the preparation of these salts

PERE LS ESTE EL Sa

182 Prof, J. Bayma on the Fundamental ~
amylic alcohol is the complementary product, thus:—

(ce H!9 Na) Cé Hl! (C® H!9 Na)! C5 Hl
| i) bO+ CH o } O= cn 0 OF ae

Like . corresponding ethylene-compounds, these salts of
amylene-sodium react on water, giving amylic alcohol and a
common soda-salt of the acid they contain.

Some of the most striking and easiest to verify of the ex-
perimental facts of which the foregoing is the scientific expres-
sion are the following :—

(1) That hydrated oxide of ethylene-sodium (absolute ethy-
late of sodium) and different ethers of the fatty and aromatic
acids furnish alcohol on being heated to about 200° C.

(2) That the weight of the product obtained on heating these
materials'is much less than the weight of one molecule of
hydrated oxide of ethylene-sodium and one molecule of the ether
of the fatty acid.

(3) That a// the alcohol radical employed, both in the state
of hydrated oxide of ethylene-sodium or hydrated oxide of amy-
lene-sodium, and in the state of ether of fatty or aromatic acid,
is to be recovered after the reaction in the state of aleohol—
alcohol distilling over before, and alcohol distilling over after the
addition of water to the solid product.

(4) That the fatty acid found after the reaction is the same as
that employed at the beginning.

With regard to (1), it will be comprehended that by the use
of an absolute ethylate charged with some caustic soda, arising
from moisture in the aleohol, or by the employment of an ethy-
late containing alcohol in combination (such as the imperfectly
decomposed erystals), the production of alcohol would be si-
mulated. The author of this paper has specially guarded against
these sources of fallacy, and has made sure that more alcohol
is given than could be accounted for in any such manner.

XXIV. Fundamental Principles of Molecular Physics.
By Professor J. Bayma, S. J., of Stonyhurst College.
To the Kditors of the Philosophical Magazine and Journal.

GENTLEMEN,
‘e the last Number of the Philosophical Magazine (February

1869, pp. 98-111) I find an article by Professor W. A.
Norton, entitled “Fundamental Principles of Molecular Phy-
sics,” intended to be an answer to certain remarks which I made
in my ‘Elements of Molecular Mechanics’ (pp. 186-189), on
his theory of molecular physics. My remarks were designed
to show that some of the principles of the learned Professor did

Principles of Molecular Physics. 183

not rest upon sufficient proof, and contained a good deal of
arbitrary assumption. Professor Norton, of course, is not of
my opinion, and argues that my objections “are destitute of
any real force.” This was his undoubted right; and, had he
confined himself to the defensive, I should have deemed a reply
unnecessary; but, as he goes on to attack my own theory with
arguments which “have a plausible appearance, I think it worth
while submitting his article to examination.

The contents of his ably written paper may be summarized,
as it appears to me, in the three following propositions :—

1st. That in molecular science all our general principles are
but probable hypotheses.

2nd. That his own principles are not arbitrary assumptions.

drd. That lin my ‘ Elements of Molecular Mechanics’ assume
principles destitute of sufficient proof.

To these three propositions I beg leave to offer a short reply,
which, I hope, will be of interest to all who are engaged, either
directly or indirectly, in promoting molecular science.

fe

And to begin with the first proposition, Professor Norton
says :

‘“No theory of molecular physics can, in the nature of things,
have any other foundation than general principles to be regarded as
hypotheses that have been rendered more or less probable, either by
induction from observation, or by @ priori reasonings. Molecular
physics cannot be erected, like mathematics, upon a foundation
known to be eternally sure, that of self-evident truth.”

These words express an opinion, which is by no means un-
common among physicists, for the obvious reason that they
cannot, by the help of physics alone, undertake to establish
fundamental principles ; a work, which requires a higher know-
ledge of speculative science, than it is the fashion for them to
acquire. Hence I do not wonder that mere physicists, even
with their hands full of good scientific materials, can build only
hypothetical theories. The cement, which alone can keep
together the stones of a scientific building , 1s an article which
cannot be prepared by the skill of the chemist, but only
by the application of general philosophy to experimental truth ;
and only in proportion as physicists are conversant with general
philosophy can they hope to build theories of a character truly
scientific, viz. independent of hypotheses ; for hypothesis begins

_there only, where real science ends. I do not wish to develope
this point at greater length. I am satisfied that this mere hint
will suffice for those whose judgment is of any weight in matters
of this sort. They will see at once that I had good reasons for

|
t
|
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184 Prof. J. Bayma on the Fundamental

saying (‘Molecular Mechanics,’ p. 2) that a work which was
intended to lay down the very first foundation of a molecular
theory, could not possibly rest on hypothetical ground, and that I
had embodied in the work, as principles of molecular mechanics,
those propositions only which were evident, or which I thought £
had the power of rigorously demonstrating from known laws of
nature; a proposition which seems to have amazed Professor
Norton. But even he will allow, I hope, that, in my capacity
of Professor of Philosophy, I can aspire to something better than
those hypotheses which are the lot of mere experimentalists.

And now to come to his 4ssertion.- I would observe in the
first place that, if “no theo. ‘of molecular physics can have any
other foundation than gener. ‘rinciples to be regarded as hypo-
theses,” then no physical t..cory can lead to any other than
hypothetical conclusions; and as hypothetical conclusions can-
not be called “established truths” in any true sense of- the
words, it follows that neither Professor Norton’s theory nor its
principles are “ established truths.” And this would suffice to
justify my stricture that his theory rests upon “a great deal of
arbitrary assumption.”

But I must add secondly, in justice to molecular science, that
Professor Norton’s opinion of it is far from being accurate.
Molecular science is not without established principles : it is not
a pure heap of hypotheses. That material substance is endowed
with active power, passivity, and inertia, for causing, receiving,
and conserving local motion: that no natural. cause can com-
municate a finite velocity to a body in an infinitesimal unit of
time: that m the impact of bodies no communication of motion
can be made by means of a true and immediate contact of matter
with matter: that an increase or decrease of intensity in motion
is always due to a real production or extinction of velocity: that
material substance acts, ceteris paribus, with different intensity
on bodies placed at different distances: that material substance
is not prevented by intervening bodies from acting on other
bodies placed at a greater distance: that the primitive com-
ponents of molecules are unextended elements: that these
primitive elements obey the Newtonian law of action: and
other points of the hke nature, with all their corollaries, are not
mere hypotheses, but “ established truths,” about which I think
that the readers of the ‘ Hlements of Molecular Mechanics’ can
entertain no doubt. And whilst we must admit that we cannot
by means of these truths alone attain to a knowledge of all the
secrets of molecular science, we do nevertheless affirm that we
have in them a solid foundation to build upon. So false is it
that molecular science has no established principles, that even
Professor Norton’s theory, of which some fundamental prin-:

Principles of Molecular Physics. — 185

ciples are, in my opinion, not sufficiently probable, contains
undoubtedly a great deal of “established truth.”

But “molecular physics,” says he, ‘‘ cannot be erected, like
mathematics, upon a foundation known from the first to be
eternally sure, that of self-evident truth.” This remark of my
learned critic does not show that molecular physics cannot be
erected on certain truth, but only that physical science, whether
molecular or not, does not deal, like mathematics, with truths
which consist of necessary relations, but with truths dependent
upon contingent facts. ‘The first are known mainly by reason,
the secondly mainly by observation: and no one demurs to
physical certainty on the ground that it is not mathematical.

Professor Norton adds:

** Mechanical axioms may exist as mere figments of the mind, and
have often risen like bubbles in the minds of speculative philosophers,
shone with an evanescent splendour, and suddenly burst at the touch
of a hard fact.”

I do not deny that axioms may exist as mere figments in the
minds of ‘ speculative” philosophers ; but the learned Professor
has surely forgotten that all philosophers, who build theories,
are “speculative” philosophers. Otherwise how is it possible
that he should write atheory of molecular physics, and yet be so
hard on speculative philosophers amongst whom his work places
him?

But Professor Norton apparently wishes to designate as
“speculative philosophers” a particular school of philosophers,
whose speculations have their origin in @ priori reasonings in-
stead of natural facts. If so, I may safely reply that such a
school (to which he imagines me to belong) has never existed.
There has indeed been a school of philosophers, whose physical
speculations are now known to have been in most instances
illustrious failures ; nevertheless, that school notoriously abided
by facts; and their failure was caused by misinterpretation of
facts, not. by any desire of substituting @ priori grounds for @
posteriori arguments. In. what does modern speculation differ
from that of the ancients? We possess, to be sure, a greater
number of experimental data; but this advantage (which does
not change the nature of scientific speculation) is frequently coun-
terbalanced im a great measure by the vagueness and shallow-
ness of our philosophical acquirements. "acts and laws are only
materials for speculation: something more is needed for building
sound physical theories: and this something is not so much the
power of imagining new hypotheses, as the art of reasoning and
an intimate acquaintance with those speculative principles which
apply to the imterpretation of facts. Such principles are the

SET Poe rf

186 Prof. J. Bayma on the Fundamental

supreme test of scientific hypotheses: and if our men of science

were less afraid of speculative knowledge than they appear to

be, we should be less familiar with the sight of “ bubbles shining

with an evanescent splendour, and suddenly bursting at the touch

of a hard fact,” or, let me add, of a still harder principle.
Professor Norton thus continues:

«‘Our author is another instance of a learned philosopher, who
has faith in such unsubstantialities, and thinks to substitute them,
as a proper basis for a theory of molecular mechanics, in place of the
general conceptions, to which the progress of science leads, and by
which alone its highest inductions find any explanation—regards the
latter as arbitrary assumptions, and his own mental convictions of
what matter must be and how it must act as the only reliable foun-
dation upon which to build.”

This passage is made up of assertions which may easily be
retorted against my critic. But to answer directly. The pro-
gress of science leads without doubt to general conceptions,
which are sometimes very good, and at other times very ques-
tionable, according as those who deal with the matter are more
or less conversant with the principles of speculation and the
highly important art of reasoning. But the question les not
in this: it lies in the ¢ruth or falsehood of the assertion that I
* substituted ” unsubstantialities for those general conceptions.
Now, I think that everyone who has read my ‘ Hlements of
Molecular Mechanics’ can bear witness to the gratuitousness of
the assertion. What Professor Norton calls “ unsubstantialities”
(probably because he cannot touch them with his finger) are
considerations which have not been substituted in the place of
the general conceptions to which the progress of science leads,
but have been added, for the greater satisfaction of a class of
readers, under the form of scholia, to the theorems by which
those general conceptions are shown to be legitimate results of
the progress of science: and have been appended not to prove
those theorems (which had no need of a second demonstration)
but to meet the “ unsubstantialities” of some metaphysicians,
who are yet to be reconciled with modern science in certain
matters: and, lastly, they have been printed in a smaller type,
lest the reader should mistake them for the substance of the work,
and engage unawares in the awful mysteries of philosophical spe-
culation (Introd. p. G). Let Professor Norton read again the
first pages of my work: I do not doubt but that he will discover
his mistake.

He states likewise that I regard those general conceptions (to
which the progress of science leads) as arbitrary assumptions,
and my own mental convictions as the only reliable foundation
upon which to build. Surely, Professor Norton himself relies

Principles of Molecular Physics. 187

upon his own mental convictions, and considers as arbitrary
assumptions those conceptions which clash with them: and he
may easily understand that I cannot but do the same. But
such mental convictions as he attributes to me are quite impos-
sible; for if a man, in matters dependent on facts and laws of
nature, should disregard ‘‘ the general conceptions to which the
progress of science leads,” how could he ever find a ground on
which to rest his mental convictions ?

The truth is that Professor Norton has failed to realize to
himself the spirit in which my ‘ Elements of Molecular Mecha-
nics’ were written. He is mistaken in his assumption that I
virtually claimed for my method a superiority which he is not
ready to recognize. The geometrical method, which I adopted,
has its own advantages, independently of the writer who employs
it, as everyone must allow: but I was so far from claiming any
superiority for the method as employed in my work, that I ex-
plicitly declared the contrary. As the employment of the geo-
metrical method may have given to the work an air of dogmatism
in questions regarding which there are great differences of opinion
among philosophers, I beg to say once for all that I have merely
stated my own views, without pretending to make further discussion
unnecessary (p. 10). Professor Norton has apparently failed to
notice these words.

But the whole passage in which [ am thus attacked deserves
to be here inserted :

«It is true that he takes exceptions to Principles 3rd and 4th
from the inductive point of view. Upon this ground (the only legi-
timate one to be occupied) I am quite ready to meet him: but I wish
to enter here, at the outset, a demurrer against the virtual claim of
the superiority of his own ad priort method of establishing his funda-
mental principles. Such a claim is implied in the intimation that
‘no one has up to this day established the truth of such proposi-
tions’ as will be best appreciated by those who have read Professor
Bayma’s book.”

My American critic acknowledges that I argued against two
of his principles ‘‘ from the inductive point of view.” Hence
my intimation that no one had yet established the truth of such
propositions, was obviously drawn “from the inductive point of
view.” How could then my learned critic construe it into a
virtual claim of the superiority of any @ priori method ?

The learned Professor shows a great hostility to what he
rather invidiously styles “my @ priori method.” But a method
in which arguments are presented under a syllogistic form, is
not necessarily an @ priort method. Professor Norton seems to
~ remember only two methods, the @ priori and the inductive. He
seems to have forgotten that there is a third, the a@ posteriort

188 On the Fundamental Principles of Molecular Physics.

and deductive, which consists of reasoning based on observation.
This is the method which I followed in establishing the funda-
mental principles of molecular mechanics. The a@ priori method
would have been absurd. Professor Norton may consequently
show his horror of the @ priori method as much as he likes:
after all, it is only a matter of taste, about which I am not
concerned.
He continues:

“Having proved, as he conceives, his propositions, and clinched
each one of them with a Q. E. D., he insists that obvious intimations
of nature are to be discarded, because the stamp of infallibility can-
not be put upon them at once, before the test of availability in the
explanation of phenomena has been applied.”

This language is rather severe. Let the learned Professor
show, if he can, in the first place, that I have not sufficiently
proved my fundamental propositions. I should consider it a
great favour, as I love nothing more than truth. Secondly, let
him bring forward, if he can, a single passage in my ‘ Elements
of Molecular Mechanics’ to establish his statement that “I insist
that obvious intimations of nature are to be discarded.” As for
the “stamp of infallibility’” I need not say that it is a merry
invention of my American critic.

He then adds:

“It was evident from the tenor of my exposition of the subject,
that ‘the established truths’ referred to were merely regarded as
having been virtually established, or rendered highly probable by
the inductions of science. The claim implied in Professor Bayma’s
criticism, that they require a higher confirmation, in fact a demon-
stration of their truth, is not to be admitted.”’

I was perfectly well aware that Professor Norton regarded his
drd and 4th Principles as having been only virtually established.
But, as to the fact itseif, I was not of his opinion. Hence the
claim implied in my criticism was not precisely that those prin-
ciples “required a higher confirmation, in fact a demonstration
of their truth,” but that they had yet to be “virtually esta-
blished ” in the sense in which Professor Norton uses the word. |
I adduced reasons to prove this point. Unless my critic suc-
ceeds in answering those reasons (as he endeavours to do in the
next part of his paper), I maintain that my claim is too reason-
able not to be admitted.

» [To be continued. |

[ 189 ]

XXYV. On the Theory of Sound. By R. Moon, M.A., Honorary
Fellow of Queen’s College, Cambridge*.

eae transmission of sound through air confined within a

cylindrical tube, when the axis of the tube is the direction
of transmission, may be represented by a single partial differen-
tial equation, which in its rudest form is of a very simple cha-
racter.

If, when the air is undisturbed, # denote the distance from
the origin of an element of the thickness dx made by planes per-
pendicular to the axis, if y be the same distance at the time ¢
after disturbance, p the pressure at the time ¢ at the point whose
ordinate is y, and D denotes the density of equilibrium, then, the
pressure at the time ¢ on the one side of the element being p
and on the other side being p + ® aa, the moving force on the

: ; : d
element, estimated without reference to sign, will be A dx; and

dividing this last by Ddz, the mass of the element, we get
= : = for the accelerating impressed force acting on the element

at the time ¢.
The corresponding effective force on the element will of course

2
be = ; hence equating these in accordance with D’Alembert’s

principle, account being now taken of signs, we get for the dif-
ferential equation of motion,
age Ltidp
Ure DR gs. ee (1)
If we assume that Mariotte’s law, which has been proved to
hold very approximately in the case of equilibrium, holds also

when the air is in motion (observing that ; = 2 and therefore
=!
a—ap—ao. D). ay) , where p denotes the density), (1) be-
comes am
re d*y : dy —2 d?y
G= eae ie ge ony ey scat e )
- When the motions are small, (2) reduces to
d*y oy
O= diz — ee op tn ctenet tLe. Yi6h tha 2 Fe (3)

from which approximate equation the theoretical value of the

* Communicated by the Author,

190 Mr. R. Moon on the Theory of Sound.

velocity of sound has been calculated to be 916°322 feet per
second*, the true velocity being about one-fifth greater.

The discrepancy thus evinced between the results of theory
and of experiment was long supposed to have been removed by
the celebrated correction of (3) on account of temperature pro-
posed by Laplace, by means of which the theoretical and the as-
eertained values of the velocity of sound were conceived to have
been brought within a very small fraction of each other.

- A most competent judget has pronounced, however, that the
experimental processes of Clément and Desormes, and of Gay-
Lussac and Welter, upon which this supposed coincidence has
been founded, are worthy of no confidence whatever; “ de sorte
que l’explication de Laplace n’est encore aujourd’hui qu’une
hypothése, trés-ingénieuse sans doute, mais qui a besoin d’étre
confirmée par lexpérience.”

A further and decisive objection may be taken also to La-
place’s correction in the form in which it is actually presented to
us on the following ground.

The correction depends upon the assumption that “for very
small condensations the rise of temperature will be proportional
to the increase of density” (Hncyc. Met. No. 72).

Now if + denote the excess of temperature at the time ¢
above the mean temperature, it is clear that in any case of mo-
tion the value of 7 at a given time and place must be known, 2. e.
we must have

== tunet. (7,2);
and if s denote the condensation and v the velocity at the time ¢
at the point whose ordinate is y, we shall have in like manner

ee “s=chunet.(y50)s

v= funct. (y, 0).
Hence, eliminating y and ¢ between the last three equations, we
have

7— tuner, (60);
and since it is evident that 7 will not become infinite when either

s or v vanishes, we are warranted in concluding that, when the
motions are small,

T=A.s+B.2,
where A and B are constants ; and we are not warranted in assu-
ming that r=A.st,

as in effect has been done by Laplace and Poisson.

* Encyc. Met. art. Sound, No. 66.
+ M. Regnault, see Mém. de ? Acad. vol. xxiv. p. 40 (1862).

{ The comparative success which had attended the bold hypothesis of
the uniformity of the law of pressure in the cases of motion and of equili-

Mr. R. Moon on the Theory of Sound. 19]

But the objections to the principle upon which equations (2)
and (3) have been obtained are not confined to the failure of the
latter equation to givea calculated velocity of sound reconcilable
with the experimental velocity.

The principle in question, viz. that the equation p=a?p holds
in all cases irrespective of the state of rest or motion of the fluid,
is a pure assumption, having no basis of fact or argument to rest
upon. ‘This will appear most clearly as follows.

In any case of motion under the circumstances we are consi-
dering, the pressure at a given point at a given time must be
known: the same may be said of the velocity; the same of the
density ; so that we must have

P— TURCE. (Yet).
v= funet. (y, 2),
A tunct. (7. ¢).

Eliminating y and ¢ between these three equations, and solving
the result with respect to p, we shall get

PUBCON oO). 2 = oe Sew

It is evident that this last equation affords no more proof of
the truth under all circumstances of the equation

: p=a’p a ° e ° e e Py e (5)
than the fact that the series
A+A,v+A,2?+ &e. in inf.

becomes A when z=0 affords that the same series has the value
A whatever be the value of z.

If the substitution for the general equation (4) of its parti-
cular case (5) enabled us to escape from difficulties which other-
wise are insurmountable, the continuing to adopt such substitu-
tion could be readily understood. The truth is, however, that
the exact contrary is the fact.

All efforts hitherto have failed to elicit a solution of the pro-
blem of adequate generality from (2), which is what (1), the
true indisputable equation of motion, becomes when (5) is taken
to represent the law of pressure, the most general solution hi-
therto so obtained (that of Poisson) involving only one arbitrary

brium naturally tempted Laplace to hazard the corresponding and equally
unwarranted assumption with regard to the temperature. At a time like
the present, when the principles of the mechanical theory of heat are gene-
rally diffused and recognized, a suggestion that the law of temperature in

a fluid is irrespective of the fluid’s state of rest or motion could hardly be
entertained.

192 Mr. R. Moon on the Theory of Sound.

function*. On the other hand, I have elsewhere + shown that,
adopting for the pressure the only expression which the facts of
the case authorize us to assume (that, namely, embodied in (4)),
a solution can be obtained possessing a degree of generality not
merely equal to all that had been considered requisite, but even
greater than had been conceived to be attainable.

_ The solution to which I refer is contained in the three follow-
ing equations, viz. :—

Peon |
a i, | | ete
a tf(ot av et 5. pe |

where « is an arbitrary constant; y, ¢, and ¥ are arbitrary
functions ; and the form of fis defined by the equation

| du
Tes (a Fla

For the details of the method by which this result has been
obtained I must refer to my former paper. Its general cha-
racter may be described as follows.

Equation -(4) enables us to put (1) under the form

eck d*y a(Z: dp dp dv

~

~ dt? ' Dido dx dv da)’

dy dy
or, since v= 7 and p=D. a ;

ony Le, ty ba ty Gg
al? DD" dy dxdt de dads a

| oo (7) simply as a partial differential equation between

Bit, Ys a a requiring solution, the most obvious mode of treating

it is to attempt its solution by Monge’s method. I have shown
that, in order that (7) may admit of two integrals of the kind
given by Monge’s method, two equations of condition must be
satisfied involving p, p, and v only; both of which are satisfied
by the relation between p, p, and v contained in the first of
equations (6). When that relation holds, (7) will have for first
integrals the last two equations of the same group.

* It would be easy to point out the cause of this failure. Upon this
branch of the subject, however, I do not propose to enter at present.
+ See the Philosophical Magazine for August 1868.

Mr. R. Moon on the Theory of Sound. 198

That equations (6) constitute a true solution of the problem
(and therefore ¢he true solution unless the possibility be enter-
tained of there being other solutions possessed of the requisite
degree of generality) may be verified as follows.

Eliminating ¢ from the second of equations (6) by differen-
tiation in the usual manner, we get

iidv__ « dp i a dp
0= Feat D Ja Fo de) ea,
The first of apes (6) gives us
dp _ #° dp (av — « dp

We have also the til condition

aan dt atae

dy dy _D
or, since v= 7, and ame
ey ae
dz” gp dt

Substituting this value of 2 in (9), it becomes

dp S a dp Ge ae dp)
ee ea) XT Nae” Be
Dividing this last equation by D and subtracting from (8) we get
do 1 dp
dé ' Dda
which is identical with (1), the true equation of motion.
The same mode of treatment, with the same result, may be
applied to the third of equations (6).
I shall now proceed to draw certain conclusions from the fore~

going formule in the case where the motions are small.
The first of (6) gives us

a? a
p=——+ (vt “)
B p x p
Es ot ot
= tov Fa( vt *) + (v+"
s(t)
= tav-+ m(v+ “)
Phil. Mag. 8. 4. Vol. 37. No. 248. Mar. 1869. 0

Oo=

194 Mr. R. Moon on the Theory of Sound.

suppose, where 7 denotes an arbitrary function. Therefore

we +a +n(v + )
dv
dp et Obes ly )
gd, pac sit
io. oe Cr)
and substituting these values in the equation of motion (7), we get
Lye 4 oe d?y ayy tay,
0= hy a Ce =) ate Ea ee
and putting v=0 and D=p in the coefficients of —— ee
: Re dad? du?’ **

we may do when the motions are small, we get, observing that

dx -
Set \7 (F)tabs ee a -7(5)- 52 10)

If we consider the case of a disturbance confined to a portion
of the tube defined by planes perpendicular to the axis, and in
which the law of continuity is preserved (that is, which offers no
sudden changes of velocity or density), it is clear that the values
of p at the boundaries of the disturbance will follow Mariotte’s
law; so that we shall have

(are oa

and

Substituting this value, (10) becomes
td 2y, « D\ d*y 9d*y
0= Fe t(p- 8a) ae
where a and D are known and a is an unknown constant; or we
get, finally, for the approximate equation of motion,

dy d*y
OF ae ee ae dx?,

where e is a constant the value of which must be determined by
experiment.

(11)

Mr. R. Moon on the Theory of Sound. 195

We have here, in effect, two equations of motion*, of which
the first, viz. i -
ari ie +200 TF pas
has for its general integral
y=${x—a(et+ V1+e%)t} +{e—a(e— V1 +e)#} ;
or if ae be small in comparison with a,
y=o{x—a(l+e)t} + {z+a(1—e)t} ;
whence we have

of"y
dx?

(12)

)
= —UL+e)p! {e~ all +6)¢} +a(l—oyteta(l—o}

. (18)
= g{e—a(L+e)t} + {a+a(l—e)z}. |
If F(z), f(x) be the respective values of = = when ¢=0, we
shall have
F (2) = —a(1 +6) $!(a) +a(1—e)p'(2),
f(z) = 9 (2) +" (2) 5

whence we get

¢! (27) = — ae F(x) —(1—e)f(z) \ ;
(2) = a: F(x) + (1+e) f(x)

Substituting these values in (13), and neglecting terms involving
e?, we get
pe dy 1 [ (l+e)F{z—a(1 +e)t} Rede tied

dt 2 + (L—e)F {x +a(1—e)é} + af {e+ a(1—e)tt
iF 5
oe “B{2—a(l +e)é} + (l—e)f{a—a(1+e)t} |

I.
| + GF ieta(l—e)t} +(1+e)f{ata(l—e)g} "
Suppose that when ¢=0 the disturbance is confined to the length
¢ measured from the origin to the right, then
F(z) =0, if 2 >J or <0,
f(@)=1.

* Whether of the two is to be adopted as representing the motion in
any particular case will hereafter be explained,

NS he

196 Mr. R. Moon on the Theory of Sound.

If x be measured positively to the right, we shall have at all
points to the right of the original disturbance

Ffa+a(l—e)i}=0, f{e+a(1—e)t} =],

whatever be the value of ¢; so that for all points to the right
of the original disturbance the motion will be represented by.

v= T° Pea +6) ett + 5 (1—-f{2—a(1+e)¢}], (14)

d 1 1

=~ 9, F{e—all ae gj [l+e+(1—elffa—a(l + e)t}] |
Moreover, for all points to the right of the original disturbance

we shall have

F{e—a(l+e)t}=0, f{ew—a(l+e)i}=1

for all values of ¢ between zero and that value of ¢ which gives
“x—a(l+e)i=l,

aay in other words, at a point &
to the right of the original disturbance there will be neither ve-
locity nor condensation until ¢ has attained the latter value, at
the same time that when ¢ has that value the velocity and con-
densation immediately begin to have significance..

It follows, therefore, that the disturbance has taken the time
x—l
a(1 +e)

the right with the velocity a(1 +e).
Multiplying (14) by 1—e, and neglecting terms in the result
involving e?, we get

(l—e)v= 3 F fz—a(l+ eth ge! Tl pee L+eit]( ].(16)

1. e. between =O and t=

to traverse the space «—/, having been propagated to

Also, since
dy DD DE
dé =p > Ds) = aie

substituting in (15) this value of Ss we get, multiplying by a,

w= 40 fo—all +o + UE (fa —a(l + ef];

therefore

as=(Il—ely. 3s) eee lia))

Hence, when the motion is represented by the differential equa-
tion (12), we shall have a disturbance propagated to the right with

Mr. R. Moon on the Theory of Sound. 197

the velocity a(1 +e), which is represented by the equations (16)
and (17). The disturbance so propagated will retain the same
invariable form ; and (17) shows that it will be either a conden-
sation or rarefaction, according as v is positive or negative.

We have hitherto been considering what takes place to the
right of the original disturbance when the motion is represented
by (12), # being supposed positive when measured to the right.

For points to “the left of the original disturbance we shall have

x—a(l+e)t <0,
and therefore
Ffe—a(l+e)t}=0, f{z—a(1+e)s}=1

for all values of ¢.
Hence the motion to the left of the original disturbance will
be represented by the equations

ZR fetal—ot} 30 —ffo tale} 1

7 on F {z+ a(1—e)t} + 5Ul—e+ (L+e)ffeta(l—e)t} J;

and adopting a mode of treatment similar to that employed in
the former case, we shall find that when the equation (12) 1s ap-
plicable to the motion, there will be propagated with the velocity
a(1—e) to the left of the original disturbance a disturbance re-
presented by the equations

(1 +ejo= $F {z+ a(l—e)é} — nee

—as=(l+e)v;

[1 -—f{e+al—e)t ‘|,

from which last it results that the disturbance so propagated will
consist of a rarefaction when v is positive, and vice versd ; which
is the opposite of what obtains with regard to the disturbance
propagated to the night.
If in (11) we take the lower sign, we get the alternative equa-
tion of motion,
SOD) d*y ON
Oa an eee, oe FEE Be Bo ak anc (18)
The results which occur when this equation is applicable to the
motion will obviously be found by changing the sign of e in the
results obtained on the assumption that (12) is the differential
equation applicable to the motion.
In this case, therefore, we shall have a disturbance propagated

198 Mr. R. Moon on the Theory of Sound. .
to the right with the velocity a(1 —e) represented by the equations
i .
(l+e)u= gF {a—a(l—e)th + ae [l1—f{e—a(l—e)i},
as=(l+e)v;

while to the left will be propagated, with the velocity a(1+e), a
disturbance represented by

(l—ejv=$F fa+a(l+e)é} —

—as=(1—e)v.

-

J —ffata(l eet,

It only remains, therefore, to determine dina what circumstances
(12), ‘and under what circumstances (18) is to be taken as the
equation of motion.

Comparing (11) with (1), we get

Leap... dv ad dy
D a. SER “da da’
or, since

dy Dah
dz D es) tame
dp dv

= Da oe
i eee

p= + 2Daev + Da’s + const.
= 12Daer+ Dar(i+ts)) 2 eee)

Now it is obviously impossible that im any particular case of
motion p should have two values. We have therefore to deter-
mine in each particular case of motion which of the above values
is to be taken.

Suppose that we have at a given epoch, in two different tubes,
exactly the same kind of disturbance, with this difference, viz.
that the velocity at each point of the one is in the opposite di-
rection to that at the corresponding point of the other. Ata
point in each for which the values of v and s are identical except
as regards the sign of the former, it is clear that the pressure
must have the same absolute value; but it is equally clear that
the expression for the pressure must differ in the two cases.

If in the one case, the particle-motion being to the right, and
#% being measured positively in the same direction, the pressure
is represented by

p= +2Daev+ Da?(1 4-s),

Mr. R. Moon on the Theory of Sound. 199

then in the other case, the particle-motion being to the left, x
being measured as before, the pressure must be represented by

p= —2Daev+ Da?(1 +s),
and vice versd.

The occurrence of the double sign in the value of p and in
the (11) is thus at once accounted for. It still remains to
be determined, however, whether, when the particle-motion at a
given point is to the right, the coefficient of v in the expression
for the pressure should have a positive or negative sign affixed
to it.

Suppose that, the air being of uniform density and at rest, a
disturbance is suddenly impressed upon a limited portion of it
of this kind, viz. a velocity which beginning at zero gradually
increases till it attains the value v,, and thence diminishes by the
same gradations till it finally vanishes, the density throughout
being unaffected. According to the formula (19), we shall have
under these circumstances,

p=Da?+2Daer,

i. e. the pressure will be either increased or decreased by the
impressed velocity.

The sign to be attributed to the coefficient of v in the
last expression, equally with the numerical value of the con-
stant e, is a proper subject for experiment; nevertheless I think
we may conclude with perfect certainty that the lower sign is to
be taken (in other words, that the effect of the impressed velo-
city is to diminish the pressure in the portion of the air affected
by it), on the following grounds.

We have before us the following alternative. For the sake of
perspicuity, assuming that the particle-motion thus supposed to
be impressed tends to the right, we must either have the pres-
sure gradually increasing as we move from the left of the dis-
turbance till we reach its middle point, and thence gradually
diminishing until it again assumes at the right-hand extremity
the value of equilibrium, or else the pressure will diminish from
the left-hand extremity up to the middle point, and will thence
increase till it ultimately regains the value of equilibrium.

But in either case we shall have in the first half of the dis-
turbance (beginuing from the left) the particles in each element
flying from each other, the tendency, by reason of the impressed
velocity, being to expansion ; while in the second half the parti-
cles in each element are moving towards each other, the ten-
dency in this latter case beg towards compression.

200 Mr. R. Moon on the Theory of Sound.

It appears, therefore, that we have to choose between two things,
viz. on the one hand a diminished pressure where there is
throughout a tendency to expansion, and an increased pressure
where there is throughout a tendency to condensation; or, on
the other hand, an increased pressure where there is throughout
a tendency to expansion, and a diminished pressure where there
is throughout a tendency to condensation. That this latter
alternative should be true appears incredible. We may with
safety conclude, therefore, that when the motion is to the right,
x being measured positively in that direction, the lower sign is
to be taken in (19), and vice versd.

Applying this conclusion to the results previously obtained, it
follows that, when the motion is represented by (12), the par-
ticle-motion is to the left, and vis negative ; so that any disturb-
ance propagated to the right of the original disturbance will be
a rarefaction, and its velocity of propagation will be a(1+e) ;
while any disturbance propagated to the left must be a condensa-
tion, whose velocity of propagation will be a(1—e).

On the other hand, when the motion is represented by (18)
the particle-motion takes place to the right, 1. e. v 1s positive ;
so that any disturbance propagated to the right of the original
disturbance will in this case be a condensation, whose velocity of
propagation is a(1—e); while any disturbance propagated to
the left must be a rarefaction, and its velocity of propagation
will be a(1 +e).

It results on the whole, therefore, that waves of condensation
are propagated with the velocity na e), which is less than
what has hitherto been regarded as the calculated velocity apart
from temperature; while waves of rarefaction are propagated
with a velocity a(1+e), which is just as much greater than such
calculate velocity. -

If it be asked whether is ¢ so small that the difference between
these two velocities is imperceptible to the human ear under all
circumstances, or are two perceptibly distinct waves in fact pro-
pagated ? I answer that e is not so small as that the difference
between a(1+e) and a(1—e) cannot be distinctly appreciated.
‘Two waves will in fact be propagated, one of which (the slower)
the human ear is so constructed as to suppress. The proof of
this I reserve for a future communication.

6 New Square, Lincoln’s Inn,
February 16, 1869.

26g

XXVI. On the Physical Cause of the Motion of Glaciers.
By Jamus Crout, of the Geological Survey of Scotland*.

i HAVE just seen an abstract of a most interesting paper
H by the Reverend Canon Moseley “On the Mechanical
Possibility of the Descent of Glaciers by their weight only,”
which was read before the Royal Society on the 7th of January
last +. In that memoir he arrives at the conclusion that, owing
to the great resistance offered by the solid ice to shearing, it is
impossible that glaciers can descend by their weight alone.

“ All the parts,” he remarks, “of a glacier do not descend
with a common motion; it moves faster at its surface than
deeper down, and at the centre of its surface than at its edges.
It does not only come down bodily, but with different motions
of its different parts; so that if a transverse section were made
through it, the ice would be found to be moving differently at
every point of that section...... There is a constant displace-
ment of the particles of the ice over one another and alongside
one another, to which is opposed that force of resistance which
is known in mechanics as shearing-force.”

He determines by calculation the amount of shearing-force
which must not be exceeded if the displacement of the particles
is to be effected by the weight of the ice alone. In the case of
the Mer de Glace at the Tacul, the shearing-force of the ice must
not exceed 1°3193 lb. per unit surface of one square inch, if that
glacier descends merely by its weight, at the rate observed by
Professor Tyndall. From experiments which he has made,
he finds that the actual shearing-force of ice per unit surface is
about 75 lbs. Consequently he concludes it is impossible that the
motion of the glacier can be due to its weight alone; there must
be some other force in addition to the weight impelling the ice
forward. And he calculates that the amount of work performed
by this unknown force is thirty-four times the amount performed
by the weight of the glacier.

This is a most important conclusion. It is quite decisive
against the generally received opinions regarding the descent of
glaciers by their own weight.

But although it is thus demonstrated that glaciers cannot de-
scend by means of their weight alone in the manner generally
supposed, still, I venture to think that, notwithstanding the

demonstration, gravitation after all may be the only force moving
the ice.

* Communicated by the Author.
t+ Proceedings of the Royal Society, vol. xvii. p. 202. [See p. 229 of
our present Number, Ep. Phil. Mag. |

202 Mr. J. Croll on the Physical Cause

The correctness of the above conclusion, that the weight of the
ice is not a sufficient cause, depends upon the truth of a cer-
tain element taken for granted in the reasoning, viz. that the
shearing-force of the molecules of the ice remains constant. If
this force remains constant, then Canon Moseley’s conclusion is
undoubtedly correct, but not otherwise ; for if a molecule should
lose its shearing-force, though it were but for a moment, if no
obstacle stood in front of the molecule, it would descend in virtue
of its weight.

The fact that the shearing-force of a mass of ice is found to
be constant does not prove that the same is the case in regard
to the individual molecules. If we take a-mass of molecules in
the aggregate, the shearing-force of the mass taken thus collec-
tively may remain absolutely constant, while at the same time
each individual molecule may be suffering repeated momentary
losses of shearing-force. This is so obvious as to require no further
elucidation. The whole matter, therefore, resolves itself into this’
one question, as to whether or not the shearing-force of a crys-
talline molecule of ice remains constant. In the case of ordinary
solid bodies we have no reason to conclude that the shearing-force
of the molecules ever disappears, but in regard to ice it is very
different. |

If we analyze the process by which heat is conducted through
ice, we shall find that we have reason to believe that while a mo-
lecule of ice 1s in the act of transmitting the energy recewed (say
from a fire), 1t loses for the moment its shearing-force if the tempe-
rature of the ice be not under 32° F. Ifwe apply heat to the end
of a bar of iron, the molecules at the surface of the end have
their temperatures raised. Molecule A at the surface, whose
temperature has been raised, instantly commences to transfer to
B a portion of the energy received. The tendency of this pro-
cess 1s to lower the temperature of A and raise the temperature
of B. B then, with its temperature raised, begins to transfer the
energy toC. The result hereis the same; B tends to fall in tem-
perature, and C to rise. This process goes on from molecule to
molecule until the opposite end of the bar is reached. Here in
this case the energy or heat applied to the end of the bar is
transmitted from molecule to molecule under the form of heat or
temperature. The energy applied to the bar does not change its
character ; it passes right along from molecule to molecule under
the form of heat or temperature. But the nature of the process
must be wholly different if the transference takes place through
a bar of ice at the temperature of 32°. Suppose we apply the
heat of the fire to the end of the bar of ice at 32°, the molecules
of the ice cannot possibly have their temperatures raised in the
least degree. How, then, can molecule A take on, under the form

of the Motion of Glaciers. 203

of heat, the energy received from the fire without being heated
or having its temperature raised? The thing is impossible. The
energy of the fire must appear in A under a different form from
that of heat. The same process of reasoning is equally applicable
to B. The molecule B cannot accept of the energy from A under
the form of heat; it must receive it under some other form.
The same must hold equally true of all the other molecules
till we reach the opposite end of the bar of ice. And yet,
strange to say, the last molecule transmits in the form of heat
its energy to the objects beyond ; for we find that the heat ap-
plied to one side of a piece of ice will affect the thermal pile on
the opposite side. ,

The question is susceptible of a clear and definite answer.
When heat is applied to a molecule of ice at 32°, the heat applied
does not raise the temperature of the molecule, it is consumed
in work against the cohesive forces binding the atoms or par-
ticles together into the crystalline form, The energy then must
exist in the dissolved crystalline molecule, under the statical
form of an affinity—crystalline affinity, or whatever else we may
eall it. That is to say, the energy then exists in the particles as
a power or tendency to rush together again into the crystalline
form, and the moment they are allowed to do so they give out
the energy that was expended upon them im their separation.
This energy, when it is thus given out again, assumes the dyna-
mical form of heat; in other words, the molecule gives out heat
in the act of freezing. The heat thus given out may be employed
to melt the next adjoining molecule. The ice-molecules take on
energy from a heated body by melting. That peculiar form of
motion or energy called heat disappears in forcing the particles
of the crystalline molecule separate, and for the time being exists
in the form of a tendency in the separated particles to come
together again into the crystalline form.

But it must be observed that although the crystalline molecule,
when it is acting asa conductor, takes on energy under this form
from the heated body, it only exists in the molecule under such
a form during the moment of transmission; that is to say, the
molecule is melted, but only for the moment. When B accepts
of the energy from A, the molecule A instantly assumes the
crystalline form. B is now melted; and when C accepts of the
energy from B, then B also in turn assumes the solid state. This
process goes on from molecule to molecule till the energy is
transmitted through to the opposite side and the ice is left in its
original solid state. This is the rationale of Faraday’s property
of regelation.

This is no mere theory or hypothesis; it is a necessary conse-
quence from known facts. We know that ice at 32° cannot take

\
i
ia
yee
k

es
v
t

204, Mr. J. Croll on the Phusical Cause

on energy from a heated body without melting; and we know
also equally well that a slab of ice at 32°, notwithstanding
this, still, as a mass, retains its solid state while the heat is being
transmitted through it. This proves that every molecule resumes
its crystalline form the moment after the energy is transferred
over to the adjoining molecule.

This point being established, every difficulty regarding the
descent of the glacier entirely disappears; for a molecule the
moment that it assumes the fluid state is completely freed from
shearing-force, and can descend by virtue of its own weight with-
out any impediment. All that the molecule requires is simply
room or space to advance in. If the molecule were in absolute
contact with the adjoining molecule below, it would not descend
unless it could push that molecule before it, which it probably
would not be able to do. But the molecule actually has room
in which to advance ; for in passing from the solid to the hquid
state its volume is diminished by about ;1,, and it consequently
can descend. ‘True, when it again assumes the solid form it will
regain its former volume; but the question is, will it go back to
its old position? If we examine the matter thoroughly we shall
find that it cannot. If there were only this one molecule affected
by the heat, this molecule would certainly not descend; but all
the molecules are similarly affected, although not all at the same
moment of time.

Let us observe what takes place, say at the lower end of the
glacier. The molecule A at the lower end, say, of the surface,
receives heat from the sun’s rays; it melts, and in melting not
only loses its shearing-force and descends by its own weight, but
it contracts also. B immediately above it is now, so far as A
is concerned, at liberty to descend, and will do so the moment
that it assumes the liquid state. A by this time has become
solid and again fixed by shearing-force; but it 1s not fixed in its
old position, but a little below where it was before. If B has
not already passed into the fluid state in consequence of heat de-
rived from the sun, the additional supply which it will receive from
the solidifying of A will melt it. The moment that B becomes
fluid it will descend tillit reaches A. B then is solidified a little
below its former position. The same process of reasoning is in
a similar manner applicable to every molecule of the glacier.
Kach molecule of the glacier consequently descends step by step
as it melts and solidifies, and hence the glacier, considered as a
mass, Is in a state of constant motion downwards. ‘The fact ob-
served by Professor Tyndall that there are certain planes in the
ice along which melting takes place more readily than others
will perhaps favour the descent of the glacier.

We have in this theory a satisfactory explanation of the origin

of the Motion of Glaciers. 205

of “crevasses” in glaciers. Take, for example, the transverse
crevasses formed at the point where an increase in the inclina-
tion of the glacier takes place. Suppose a change of inclination
from, say, 4° to 8° in the bed of the glacier. The molecules on
the slope of 8° will descend more rapidly than those above on
the slope of 4°. A state of tension will therefore be induced at
the point where the change of inclination occurs. The ice on
the slope of 8° will tend to pull after it the mass of the glacier
moving more slowly on the slope above. The pull being con-
tinued, the glacier will snap asunder the moment that the cohe-
sion of the ice is overcome. ‘The greater the change of inclina-
tion is, the more readily will the rupture of the ice take place.
Every species of crevasse can be explained upon the same
principle.

This theory explains also why a glacier moves at a greater rate
during summer than during winter; for as the supply of heat to
the glacier is greater during the former season than during the
latter, the molecules will pass oftener into the liquid state.

As regards the denuding power of glaciers, I may observe
that, though a glacier descends molecule by molecule, it will
grind the rocky bed over which it moves as effectually as. it
would do did it slide down in a rigid mass in the way generally
supposed ; for the grinding-effect is produced not by the ice of
the glacier, but by the stones, sand, and other materials forced
along under it. But if all the resistances opposing the descent
of a glacier, internal and external, are overcome by the mere
weight of the ice alone, it can be proved that in the case of one
descending with a given velocity the amount of work performed
in forcing the grinding materials lying under the ice forward
must be as great, supposing the motion of the ice to be molecular,
in the way I have explained, as it would be supposing the ice de-
scended in the manner generally supposed.

Of course, a glacier could not descend by means of its weight
as rapidly in the latter case as in the former; for in fact, as
Canon Moseley has shown, it would not in the latter case de-
scend at all; but assuming for the sake of argument the rate of
descent in both cases to be the same, the conclusion I have
stated would follow. Consequently whatever denuding- effects
may have been attributed to the glacier, according to the ordi-
nary theory, must be equally attributable to it according to the
present theory.

This theory, however, explains, what has always hitherto ex-
_ cited astonishment, viz. why a glacier can descend a slope almost
horizontal, or why the ice can move off the face of a continent
perfectly level.

Canon Moseley suggests that heat passing into the ice might

206 Mr. R. Peacock on Geological Time, and the probable

by its mechanical energy, together with the weight of the glacier,
be sufficient to account for the motion. But the mechanical
energy of heat is not required to push the glacier forward ;
gravitation alone, as we have just seen, will suffice. Besides,
heat entering ice could not produce a mechanical pressure that
would move the glacier ; for heat produces contraction of volume,
not expansion. ‘True, heat no doubt destroys the crystalline
structure of the ice-molecule by tearing the constituent particles
separate ; but nevertheless the volume of the mass is diminished
by this process, for ice in losing its crystalline structure, or, in
‘other words, in passing from ice to water, decreases in volume.

XXVII. On Mr. J. Croll’s paper “ On Geological Time, and the
probable Date of the Glacial and the Upper Miocene Period”*.
By R. A. Peacock, CLE.+

HE writer hereof believes that Mr. Croll’s paper is of great

value; and if a few remarks are ventured upon below on

small points of detail, they no more detract from the general

value of the paper than a few “ striz” or scratches would detract
from the value of a good painting.

“The only evidence which we can now reasonably expect to
find in the stratified rocks of the existence of land-ice of former
epochs, is the presence of erratic blocks which may have been
transported by icebergs and dropped into the sea. But unless
the glaciers of that epoch reached the sea or the sea was frozen,
we could not possibly have even this evidence. Traces in the
stratified rocks of the effects of land-ice of former epochs must,
from the very nature of things, be rare indeed” (p. 364).

On the contrary, might we not have striation on the stratified
rocks pretty often in this way? When we remember the fre-
quent oscillations of land by sinkings and risings in every part
of the globe since the commencement of the glacial period (assu-
ming that to have commenced 240,000 years ago and to have
lasted 160,000 years), the following may often have happened.
Suppose (as must have been the case) many glaciers to have
been making each its way down its own valley in the usual
manner, bearing its lines of moraines, as in Switzerland at pre-
sent. The glaciers would then striate the stratified rocks of every
valley. Such striations would continually go on increasing as
long as the glaciers existed. And considering the vast tract of
the earth which must have been thus operated on during 160,000

* Philosophical Magazine, November 1868.
+ Communicated by the Author.

Date of the Glacial and the Upper Miocene Period. 207

years, we may be quite sure that by means of sinkings of land
many such striated rocks have become sea-bottom; the conse-
quences of which would be that the glaciers would have melted,
and the stratified rocks would retain their striations, which would
be well protected by the thousands of feet of sea-water they
might have above them. Their moraines of erratic blocks would
be sure to be deposited at the sea-bottom also. And the ground
may have risen again since, and even in some cases risen and
sunk again and again. Denudation would, I fully agree, oblite-
rate all striations which were exposed to it long enough in sub-
aérial situations. Again :—

“ But do icebergs striate the rocky bed of the ocean? Are they
adapted for such work? It seems to be almost universally as-
sumed that they are. But I have been totally unable to find any
rational grounds for such a belief. Clean ice can have but little
or no erosive power, and never could scratch a rock” (p. 366).

I must dissent from the words I have italicized. As often
as floating icebergs happen to touch a rocky bottom during
storms, when they are making way through the water like ships,
since they often weigh many thousands of tons, they will still
striate the bottom-rocks, although their own bottom parts will
be ground to powder by the operation. Such bottom parts
would do something in the way of striation, as Mr. Croll admits
(p. 367), by the mere force of concussion; for all their force
would not necessarily be expended in tearing up loose and dis-
jointed rocks, nor in hurling loose materials to a distance.

In Jersey there are some remarkable striations or flutings on
the face of the metamorphic clayslate rock, which is nearly per-
pendicular, as you enter the village of ?Etacq from the east, on
the right (2. e. the north) side of the road. They were first ex-
posed when the road was widened some eight or ten years ago.
Previously they were covered up with earth, grass, or other
rocks, I do not know which. I have heretofore spoken of these
as “ slickensides ;” but as they are horizontal, it is at least pos-
sible that they may have been striated by a glacier, as they are
at the side of a valley :—

\<~ | Metamorphic-clay-slate section; the

og length 20 or 30 feet.
i, EZ 3 8
ws

208 Prof. A. Lielegg on the Spectra of the

The flutings ab, bc, &c. (of which there are about ten or ee
are about 4 inches broad and an inch deep.

On page 368 it is stated that “an iceberg 100 feet in thick-
ness will exert just as much pressure as one a mile in thickness.”
This cannot be so. An iceberg 100 feet thick when afloat will
displace water weighing (suppose) 100 tons, but one a mile
thick will displace water weighing (suppose) 10,000 tons. These
quantities are equal to the respective weights of the icebergs
while afloat. Now let it be supposed that the two icebergs are
each propelled by a storm at the rate of three miles an hour, and
‘it must be evident that, when they each come in contact with a
rocky bottom, the latter will exert 100 times as much force as
the former and produce strie far greater.

Jersey, January 25, 1869.

XXVIII. Contributions to the Knowledge of the Spectra of the
Flames of Gases containing Carbon. By ANDREW LiELEGE,
Professor at the National Upper Practical School at St. Pol-
ten, Austria*.

AC the time when I was making my observations on the .
spectrum of the Bessemer-flamet, I conceived the idea of
investigating what similarity or difference existed between this
spectrum (which is, in fact, that of the flame of oxide of carbon)
and the spectra of the flames of other gases which contain carbon.
It seemed to me that data might also thus be obtained for the
solution of the question, whether all spectra of gases containing
carbon are really to be regarded as spectra of carbon, or whether
every such gas has its own peculiar spectrum.

With this object in view, I undertook to examine the spectra
of light carburetted hydrogen, of olefiant gas, and of cyanogen,
and came thus to the knowledge, concerning the two former
gases, of some details which, in the greater works already be-
fore us on this subject, have either HE been noticed at all, or
at least have not been described as seen in the manner in which
I have had the opportunity of observing them. In communi-
cating, then, im the following pages, these details as contribu-
tions to our knowledge of the spectra of ignited bodies, I give
also the results which I have been able to obtain from a compa-
rison of the Bessemer-spectrum with the spectra of other flames.

* Translated and communicated by W.'T. Lynn, B.A., F.R.A.S., of the
Royal Observatory, Greenwich, having been read at. ‘the Meeting of the
Vienna Academy of Sciences on April "16, 1868,

+ See my translations of Professor Lielego’ s papers on that subject in
the Philosophical Magazine, vol. xxxiv. p. 302—W. T. L

Flames of Gases containing Carbon. 209

Spectrum of Coal-gas.

When Swan published* his investigations on the prismatic
spectra of the flames of compounds of carbon and hydrogen,
which are remarkable for their completeness in the then (1855)
state of our knowledge in spectrum-analysis, the only known
observations were those of Fraunhofer, Brewster, and Draper
on the spectrum of the cone of the blowpipe-flame, and those
of Fraunhofer, Herschel, and others on the spectrum of a wax-
or oil-flame; moreover the means of making this kind of ob-
servation had not at that time attaimed its present high degree

of perfection. Under these circumstances, the service rendered

by Swan must not be underestimated—in examining the spec-
tra of the flames, not’ only of carbon combined with hydro-
gen, but of the various compounds of carbon, hydrogen, and
oxygen, in doing this with an accuracy not surpassed even in
recent times, and in arriving at conclusions which are still con-
sidered true in their fundamental principles, viz. (1) that the
position of the bright Jines in the spectra of the different com-
pounds of carbon and hydrogen is mdependent of the relative
proportion of those two substances contained in them and is n
all cases the same, and (2) that compounds which contain
oxygen as well as carbon and hydrogen give spectra identical
with those of compounds of the latter two substances only.
Since the time to which I refer, this subject has been again
investigated ; and particularly Plucker and Hittorf +, as well as
H. C. Dibbitst, have annexed to their publications very excel-
lent drawings; those indeed of the last-named investigator
leave nothing to be desired im their repetition. But not one of
these authors has mentioned, in treating of the spectrum of
coal-gas or olefiant gas obtained by combustion with oxygen, a
group of five red lines, which I, in my oft-repeated experi-
ments, have always been able to observe with uniform distinct-
ness, and which decidedly belong to the spectrum of coal-gas.
For the production of this spectrum, I made use of a Daniell’s
cock of the ordinary construction, with an escape-aperture, nar-
row in bore compared with that of the tubes by which the coal-
gas and oxygen are brought into communication, regulating the
quantity of the gases to be combined in such a manner thatI ob-
tained a small, nearly globular flame, only narrowing into a very
short point at the top, which was of a faint bluish-white colour
' and an intense brilliancy. A flame thus produced, and brought

* Transactions of the Royal Society of Edinburgh, vol. xxi. part 3,
p. 411.

f* Phil. Trans. vol. cly. part. J. p. 15.

{ De Spectraal-Analyse, Akademische Proefschrift: Rotterdam, EK. H.
Tassemeyer, 1863.

Phil. Mag. 8. 4. Vol. 37. No. 248. Mar. 1869. le

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it
me

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i
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210 Prof. A. Lielegg on the Spectra of the

as near as possible to the slit in the apparatus, exhibited the
spectrum of coal-gas with extraordinary sharpness and brilliancy
of colour, and furnished the means of observing the five red
lines spoken of with great distinctness,

The successive development of the spectrum of coal-gas,
which can be easily proved by comparing the spectra which are
produced by a Bunsen’s gas-burner, then by coal-gas with
oxygen in small quantity, and lastly by coal-gas with oxygen in
sufficient quantity to create combustion, leads to the conclu-
sion, which has now been known for some length of time, that
increase in the temperature of the flame causes a great change
in the form of the spectrum; that is to say, continued aug-
mentation of the supply of oxygen adds more and more lines,
whilst at the same time greater intensity of light and brilliancy
of colour is shown throughout, and this without any percepti-
ble appearance of change of an opposite character. Beginning
with the flame of a Bunsen’s gas-burner, and passing on to the
hottest gas-flame inflamed by oxygen, a series of spectra may
be followed which show no essential difference, since the dif-
ferent degrees of their development cannot be considered such ;
for the lines which are produced by Bunsen’s gas-burner
preserve their position unchanged, other groups being as it
were filled in, so that this successive completion of the spec-
trum can be distinctly followed as the temperature is increased.

It can only be ascribed to this gradual change of the spec-
trum of coal-gas proceeding from a change of temperature that
the group of five lines mentioned above has never before been
observed and described as it is in this paper. The flame must
be brought, by a sufficient supply of oxygen, to the maximum
of its temperature and intensity of light; this group then ap-
pears as sharp and distinct as those in the green and blue parts
of the spectrum, which become visible at a considerably lower
temperature ; in general character also its correspondence with
the latter is complete.

In order to obtain a means of reference, in regard to the
position and also the breadth of the red lines and those of the
spaces between them, to those of the other lines of the spec-
trum, I made a determination of their relative position by
means of an illuminated Steinheil’s scale, which divides the
space between K & and K @ into 255 equal parts. The breadth
given to the slit was such that that of the sodium-line just filled —
up the interval between two divisions; this breadth is also that
of nearly all the lines which form groups. The apparatus thus
employed* (the same which I used in my earlier works) has

* From the manufactory of mathematical and scientific instruments, by
Starke and Kammerer, at the Imperial Polytechnic Institute of Vienna.

Flames of Gases containing Carbon. 211

two prisms, which were inserted at the minimum of deviation
for D, and a telescope magnifying six times. The following are
the results of the readings, with the addition also in the proper
places of those of the lines of potassium, sodium, and lithium :—

304 Ka.
285 Extreme red.
270. Lia.
260>
257 |
a< 254 + Group of five red lines.
| 252 |
(250)

246 Sodium-line.

| 225

oo
230
B 25 [ Group of five yellowish-green lines.
R222

201) Group of three pea-green lines, to which also fol-
y 4 198 lows a fourth, when the intensity of light of the
195 flame is especially great.
“160
sJ157| gq ve eae
155 ¢ Group of four right-blue lines.
153

107 middle, and becoming gradually fainter towards
the edges.

103 Narrow bright-violet line.

101°5 | Boundaries of a bright dark-violet band, brightest
98 im the middle (100).

82 Violet end.

It is thus seen that the group of five red lines is situated
between the lithium and the sodium line; the three first lines
are at equal distances from each other, and are sensibly of
equal breadth ; the distance of the third line from the fourth,
and of the fourth line from the fifth is somewhat less, as is also
their breadth, though in a degree less evident to the sight. As
regards intensity of light, this group is circumstanced like the
others; that is to say, the first or least-refracted line is the
brightest, whilst each succeeding line is fainter, the last being
faintest of all; this diminution of brightness, however, is not
so striking as it is, for example, in the lines of the group y, and
may perhaps even be regarded as merely the effect of con-
trast.

oe Boundaries of a broad blue band, brightest in the

P2

Pass a ee =

prerees aS SSeS
$Eeese ees — apica - = 2
a ree =

$$$ — -——- - --——

as 3

'

212 Prof. A. Lielege on the Spectra of the

The pea-green line, 201 of the group y, and the last violet
band, 101°5-98, which (as is well known) nearly coimcide with
Fraunhofer’s lines C and G, are also those lines which are
always visible if we use as a source of light a flame of spirit of
wine, or the lowest non-luminous blue part of the flame of a
wax-light, or the spherical light of the gas-flame of a Bun-
sen’s burner; in the two latter there can also usually be di-
stinctly observed, under favourable circumstances, the second
line (198) of the group ¥, the first line (233) of the group 8, and,
lastly, the whole group 6; only the individual lines of the latter
are not to be distinguished, the whole group appearing to stand
out from the background as a faint broad band.

It is moreover to be remarked that, when the combustion of
the coal-gas takes place with an insufficient quantity of oxygen,
the group of five red lines cannot be even momentarily discerned,
and the red and yellow part of the spectrum generally is not
perceptible, the space corresponding to it being quite dark up to
the first line of the group @.

Spectrum of Olefiant Gas.

If we burn olefiant gas with oxygen in the same manner as
we have described for coal-gas, we obtain a spectrum which
agrees perfectly with that of coal-gas, and presents only in the
development of the extreme violet part (appropriately called by
Briicke* lavender-grey) a form quite peculiar, in that it is in-
tersected by a great number of strong black lines, which are
arranged near each other in the dark violet part fine and narrow,
but in this lavender-grey part, immediately following it, become
increasingly broader, and also are separated by longer intervals,
until, again approaching nearer, they at last terminate in a broad
dark streak, succeeded by a lavender-grey one of equal breadth,
at which the visible part of the spectrum ends.

The extent and appearance of this part of the spectrum, which
comes immediately after that of the coal-gas, will be at once
understood by an inspection of the following results of the mea-
sures made of it :—

95 | Blue-violet space intersected by fine black lines, the light

71 f constantly decreasing in intensity towards 71.

sy } Dark space, black at 61.
J *eontinaty intersected by many black lines, which
50

continually increase in breadth, as well as the inter-
7 spaces, and in the last third of the whole space again
become gradually narrower, but in a less degree+.

* Poggendorff’s Annalen, vol. lxxiv. p. 461.
+ The violet potassium line K £ has the position 49.

Flames of Gases containing Carbon. 213

5 Middle of a broad black line.
2 Middle of a lavender-grey band*.
1 End.

This peculiarity of the spectrum, which imparts to its most
refrangible part a character of quite an opposite kind to that of
the remaining parts, could never be distinctly observed in the
spectrum of coal-gas, although in the latter also fine black lines
are perceptible in the dark-violet end. In other respects this
spectrum agrees perfectly (as has been already stated) with that
of coal-gas; for the appearance of a fourth line in the group y,
as well as of a group of four faint lines between y and 4, to
which the values 186, 183, 181, and 170 of our scale corre-
spond, in no way affects the distinctive type of this spectrum,
and is only seen under circumstances especially favourable to
the observation.

The agreement which is indubitably apparent on a comparison
of the spectra which are obtained by a flame of spirit of wine,
by a flame of a wax-light in the blue part, by coal-gas ignited
with atmospheric air or oxygen, and by olefiant gas with oxygen,
justifies the assertion that it is entirely the greater or smaller
quantity of the luminous particles combined with the higher or
lower temperature that produces the gradually seen difference
in these spectra, and that all must be in themselves of the very
same quality. Whether the luminous particles of disintegrated
carbon are in the condition of vapour, as has been repeatedly
assumed, and whether the opinion first expressed by Attfield f,
that the spectra of all combinations of carbon are to be consi-
dered as spectra of carbon itself, will be confirmed, or whether
every gas contaiing carbon has its own peculiar spectrum,—
these are questions which, in regard to the spectra of flames,
the present state of our knowledge does not enable us to decide.
If, however, we are careful to use only facts in our discussions
of the problem, and remember that the presence of carbon in a
gaseous condition is only an hypothesis, and even those cases in
which this hypothesis appears justifiable, as in Geissler’s tubes,
manifest relations of so different a nature that reasoning from
them is an madmissible process—and if, moreover, we take
into consideration the great difference shown by the spectra of
cyanogen and carbonic oxide compared with those of coal-gas
and other kindred substances, we shall not be able to adopt the
view that all spectra of flames of compounds of carbon can be
regarded as spectra of carbon itself. In addition to this, the in-

* The bright lines of the most refracted group of the cyanogen-spec-
trum, which ‘also are of a lavender- -grey colour, correspond ‘precisely with

this position.
+ Edinburgh Phil. Trans. vol. xxii. p. 224.

(214 Prof. A. Lielegg on the Spectra of the

teresting investigations also of Frankland *, according to which
the intensity of light of a flame depends upon the density of the
ignited vapours, cannot but lead us to hesitate in supposing
carbon to exist in a state of vapour in such flames; so that it
appears simpler to refer the flame-spectrum of the compounds
of carbon with hydrogen, and of oxygen with carbon and hy-
drogen, to the ignited vapours of carbon combined with hydrogen
than to those of carbon alone.

Since, then, it would seem that no independent spectrum of
carbon exists, and that, instead of this, every gas contaming
carbon has its own peculiar spectrum, and since the quantitative
proportions of any compound have no effect upon the character
of the spectrum, we have a sufficient explanation why it is that
the flames of spirits of wine, wax-lights +, coal-gas, and olefiant
gas exhibit the same spectrum, whilst, on the contrary, cyanogen
and carbonic oxide, in which bodies of a different nature become
the sources of ight, manifest an essential difference in their spectra.

In support of this view, similar cases may also be adduced in
combinations which have a different nature in their chemical
constitution—for instance, the spectra of the compounds of
copper with chlorine, bromine, and iodine, observed by A. Mits-
cherlich t and, on account of their characteristic differences,
proposed by him to be applied to analytical purposes. There
is no question that these spectra are due, not to the copper,
but to the combinations in question, and that the difference
shown by them is produced by the substance united with the
copper, as in the combinations of carbon it is produced by hy-
drogen, oxygen, and nitrogen.

Spectrum of Carbonic Oxide.

When combustion of carbonic oxide with atmospheric air or
with oxygen is produced, a continuos spectrum is obtained
without bright or dark lines, iv which 12 gre.. and blue parts
are especially well developed. A flame, however, of carbonic
oxide, caused by the combustion of charcoal in a blast-furnace,
in which carbonic oxide is consumed at a tolerably high tem-
perature, shows in the continuous spectrum some bright Imes ;
the higher the temperature of the carbonic oxide the more lines
appear; and it is evident that the conditions, under which the
formation and combustion of the carbonic oxide takes place
during a “charge” in the Bessemer-process, are particularly
favourable for the production of a spectrum with complete lines.

* Polytechnic Journal, vol. clxxxv. p. 279.

+ The lowest blue part of the flame of a wax-light shows, ifa cold body
be held in it, a white border.

{ Fresenius, Zeitschrift fiir analytische Chemie, 1865, p. 153, [ Phil. Mag.
Dec. 1865, p. 449. ]

Flames of Gases containing Carbon. 215

_ Having already described this in my previous papers on this
subject, I will only add here those remarks which are suggested

by a comparison with other spectra of gases containing carbon ;

they may be summed up in the following points :—

1. The lines of a flame of carbonic oxide (Bessemer-flame)
appear on a continuous spectrum, and contain several groups of
bright lines and some dark absorption-streaks, which are irre-
gularly distributed from the red up to the violet end.

2. The groups of lines coincide neither with those of coal-gas
and olefiant gas, nor with those of cyanogen.

3. The strongest lines are situated, as in the spectrum of
coal-gas, in the green and blue-violet part.

4. The increase in ‘the intensity of light of the individual
lines of the groups, when such an increase is perceptible at all,
takes place always in the same direction: but this 1s the oppo-
site direction to that observed in all other spectra of gases con-
taining carbon; for the most refrangible line of each group is
the brightest, and those succeeding it invariably become fainter.

5. The spectrum shown by a Geissler’s tube filled with car-
bonic oxide is not the same as that of the flame of carbonic
oxide, since both the position and the distribution of the bands
and lines are different.

The spectrum, then, of a flame of carbonic oxide is such that it
must unquestionably be considered as one peculiar to itself—the
spectrum of ignited carbonic oxide.

Spectra of the flames of compounds of carbon and hydrogen,
of cyanogen and of carbonic oxide, never show the lines of hy-
drogen relatively to those of nitrogen and oxygen; but from
this we can only infer either that the lines of these last-named
gases do not appear on any ground of such a kind (as is the case
in the spectrum of chloride of potassium, in which also the po-
tassium lines alone are visible), or that the molecules of the
three first-named kinds of gas as such form the luminous matter
when in the state of most intense ignition. Now, as the spectra
are of different characters, they cannot be referred to a common
origin, namely, to the carbon alone; and from this we are enti-
tled to argue that every gas has its own peculiar spectrum, in
so far as it possesses a difference of quality in regard to its con-
stitution.

Lastly, as to the comparison of the spectra of the flames of
gases with the spectra given by them when in the condition of
greatest rarefaction and made luminous by the induced electrie

current, I believe 1 ought not to conceal my opinion that it is
really madmissible; if the electric current is able to decom-
pose so many bodies in their natural condition of density, how
much more must it be able to do so when that density is so

Y
hi

=a
=e

216 Mr. D. Vaughan on the Secular Effects

greatly diminished ! the mass, being so very small in proportion,
will follow completely the impulse of the motion produced by the
electric current, and be decomposed in quick succession into its
constituents, which are afterwards again united. ‘Therefore tubes
filled with combinations of carbon and hydrogen show the lines
of carbon and those of hydrogen; tubes filled with carbonic
oxide or carbonic acid gas show those of carbon and oxygen,
giving, in fact, a spectrum of carbon, because the extremely
small pressure and the high temperature cooperate im reducing
the carbon to a gaseous condition. Tubes filled with cyanogen
are not adapted for the observation, because the capillary tubes
become immediately blackened by decomposed carbon, by which
means observation is prevented.

[Professor Lielegg’s paper is accompanied by a Plate contain-
ing diagrams of the solar spectrum with the more important of
Fraunhofer’s lines, the spectrum of olefiant gas and of coal-gas
(which are identical, except that the latter terminates at 82),
and the spectrum of the Bessemer-flame. These, however, are
not essential to the paper, and are here omitted.—W. T. L.].

XXIX. The Secular Effects of Tidal Action.
By Daniut Vaueuan, Esq.*

N tracing the mutual relations between the physical forces, it is
important to show that the occurrence of tides, while attended
with friction and with a consequent development of heat, must
involve some permanent alteration in the momentum of the vast
orbs which are concerned, either in exciting or in restraining the
great movement of the liquid domain. An estimate of the
amount of the minute changes which this cause may slowly oc-
casion in planetary motion is also intimately connected with
some of the great problems of practical astronomy. The earth
and the moon have been found to differ slightly in recording
time since the earliest astronomical observations; and much of
this difference is now generally ascribed to a gradual reduction
in the diurnal velocity of our planet as its watery envelope is
alternately elevated and depressed by lunar attraction. The
vast tidal force which some of the satellites of Jupiter and Saturn
must feel, in consequence of the powerful attraction of the pri-
maries, would be sufficient to cause perpetual oscillations even
in the solid matier of these subordinate worlds, if they were not
secured by some special means against such desolating effects
from the great disturbance. But it is reasonable to suppose
that the motion of the satellite would change in proportion to

* Communicated by the Author.

of Tidal Actiou. 214

the amount of heat generated by these oscillatory movements ;
and more exact investigations show that the changes which take
place under such circumstances would ultimately cause these
second-rate planets to occupy the same time in their rotation
and in their orbital revolution, while the axis of each would
become nearly, if not exactly, perpendicular to the plane of its
orbit. On the surfaces of bodies having their motions so ad-
justed in the course of time, gravity, though not uniform in dif-
ferent localities, would be exempted from any material periodical
changes, and the repose of the planetary structure could not be
seriously affected by the centrai disturbance. From the evidence
of the telescope, it would appear that this peculiar arrangement
for keeping the same side of a moon always turned to its primary
invariably prevails in all secondary systems of celestial bodies ;
and it may justly claim much interest from astronomers, whether
it be regarded as a beneficent provision for preventing excessive
tides, or as the result of tidal action during past ages.

Though the great disturbance to which satellites are exposed
in narrow orbits, and which, in the absence of certain conditions,
is capable of producing commotions even in the most stubborn
solid matter of which they may be composed, has been the main
object of my researches in this department of science, I think it
advisable to introduce a few items in regard to the tides on our
own globe. In a paper published in the twenty-seventh volume
of the Reports of the British Association for the Advancement
of Science, I gave a popular exposition of the mode in which the
vast tidal wave on our oceans must permanently alter the mo-
tions of the earth and the moon. I have since learned that the
views I then presented respecting the loss of terrestrial motion
were not entirely new; and as I understand that the subject is
already receiving much attention from some eminent astrono-
mers, I do not think it proper to treat on it at a greater length
than the main object of my researches demand. I shall accord-
ingly take up only the more simple cases of this kind of action,
as they will be sufficient to show how the secular changes with
which the tides on our oceans must be attended are divided be-
tween our earth and its satellite.

For the source of the slow changes in question, we may first
look to the effects of the attraction between the moon and the
portion of water which swells, by her influence, above the mean
level of the ocean. The presence of so large an amount of pro-
tuberant matter on opposite sides of the terrestrial spheroid must
produce a slight deviation in the direction of gravity between the
earth and the moon, and thus lead to permanent changes in their
movements. ‘To determine the relative rates at which motion is
slowly lost to each body from this cause, and to show how far one

218 Mr. D. Vaughan on the Secular Effects

can be depended upon for correcting the time kept by the other, 1s
not difficult if the moon’s orbit is supposed to be an exact circle.
The centrifugal forces arising from the movement of the earth and
the moon around the common centre of gravity between them,
must have a resultant in a line passing through the centre of gra- _
vity of our planet. In the absence of tides, the resultant of the
attraction between the two great bodies would, in its mean posi-
tion, meet the earth’s axis which passes through the same centre ;
for though it may be caused to deviate from this position by the
influence of mountains or by irregularities in the density of ter-
restrial strata, the deviation would take place to an equal extent
on opposite sides of the axis, and would have its effect evenly
compensated in the course of every period of rotation. But the
influence of the swollen tidal waters causes the attractive force
of the earth on the moon to act in a line passing a little east of
the terrestrial axis; and it is on this slight deviation from the
axis that the permanent change of motion in both orbs depends.
Let D denote the distance between the centres of the earth and
the moon, R the measure of the attraction between both bodies,
and / the shortest distance between the earth’s axis and the line
which marks the direction of this attractive force; then R may
be resolved into three components—one coinciding in direction
with centrifugal force which it balances, a second depending on
the ellipticity of our planet, and serving to produce the preces-
sion of the equinoxes and the nutation of the earth’s axis, while
the third, much smaller in magnitude, depends on the attraction
of the tidal waters on the moon. If the last component (which
acts in the direction of lunar motion) be represented by f, then
from the principles of the resolution of forces it will appear that
R/

fe pi oe!
From the theory of rotation it may be also easily inferred that if
f' denote the force exerted in changing the earth’s rotation by
the action of R, then

Ricos s

r

He 3 ee e our) © Gea hic: (2)

where r stands for the earth’s equatorial radius, and s for the
moon’s declination.

ee D coss
From these expressions it follows that j! is equal to f : at

and the changes of momentum resulting from f and /! in the
same time, being proportional to the forces themseives, must have
one to the other the ratio of r to Deoss. In this we may
observe a conformity to the principle of the preservation of areas
and moments. Laplace has shown that a similar relation sub-

of Tidal Action. 219

sists between the changes which the spheroidal form of the earth
occasions in lunar and terrestrial motion.

It is easy to estimate with more accuracy than is common to
this department of science the ratio between the minute errors
of the earth and the moon in recording mean time, and thus to
derive important information respecting the portion of ue
errors discoverable by observation. As the moon, while only 7
of the earth in respect to mass, moves in its orbit with about : ot
times the diurnal velocity of our equator, our planet, supposing
it to be homogeneous, would derive from its rotation about fifteen
times the momentum which the moon owes to her orbital motion.
Now, the action to which each body is exposed from tidal move-
ments being in the ratio of sixty to one, our globe must lose four
infinitesimal parts of its angular velocity from the disturbance
while the moon guined one, the mean distance between both
orbs being regarded as immutable. But it is well known that
if the moon’s velocity were increased | per cent., there would be
an augmentation of 2 per cent. in the size of her orbit, and of 3
per cent. in the time of her periodical revolution. From this it
foliows that the relative change in the mean motion of our satel-
lite, from the occurrence of the tides, is about three-fourths of
that which the length of the day must experience from the same
cause, and that only one-fourth of the permanent change thus
occasioned in the rotation of our planet would be revealed by a
comparison of ancient and modern eclipses.

This result, however, requires some corrections, not only for
the inequalities of density in terrestrial matter, but also for the
ever varying declination of the moon. ‘To correct for declina-
tion, put L for the moon’s longitude, I for the inclination of its
orbit to the plane of the equator, M for the mass of the earth,
and K for its radius of gyration, and dw for the amount of the
secular change in its angular motion in a given time. ‘Then in
Mk*dédo

dt

principles of dynamics, and for cos s its equal “1—sin? Lsin®I,
extracting the square root of the latter in a series and reducing,
we obtain

equation (2) substituting for f'in conformity with the

MK*ddo — R/ sin?I sin? I cos2L

iD seein (1- 4 7 eee. @
Now if L be expressed in terms of the time ¢, and I for the pre-
sent be regarded as constant, the terms containing I will disap-
pear on integration, and the last equation will yield the following:

2
MK*8o=5-(1— *) BNE. 8 (A)

If the moon moved in the plane of the ecliptic, this formula

fee
j
he
’
F
f
!

220 Mr. D. Vaughan on the Secular Effects

would indicate a reduction of nearly 4 per cent. in the estimate
deduced for the earth’s loss of diurnal motion, on the supposition
that the lunar orbit coincides with the plane of the equator.
Had we taken the actual case, in which the moon’s path has a
small inclination to the plane of the ecliptic, | should be regarded |
as variable, and the investigation would be more complicated ;
yet it may be easily seen that the result would not materially
differ from that given in formula (4).

While the inclination of the moon’s orbit to the equator re-
duces the change in the earth’s diurnal motion 4 per cent., an
opposite effect arises from the increasing density of the matter
towards the central region of our world. . The law to which the
variable density of terrestrial strata conforms is not at present
sufficiently well defined to serve as a basis for an accurate mathe-
matical investigation ; but judging from the effects of this cause
on the form of the earth and the precession of the equinoxes, we
may safely state that it cannot add more than 12 per cent. to
the secular loss which the tides occasion to the motion of our
globe ; and accordingly a little less than one-third of this loss
would be made known by a comparison of the observations on
the moon in ancient and modern times. How far these results
are liable to be vitiated from the action of a resisting medium in
the celestial space, or from the slow contraction of our globe as
it constantly parts with internal heat, is a question which cannot
be embraced in the present inquiry.

To obtain from the preceding equations a numerical estimate
of the extent to which lunar and terrestrial motions are affected
by tidal action, it is necessary that the value of 7 should be
known. The most reliable data for determining this value might
be derived by observing the small amount of deviation which
the position of the moon or the swelling of the tides occasions in
the direction of plumblines extending from the top to the bot-
tom of deep mines in various localities. But for obtamimg such
an estimate from the results of observations already made on the
tides a different mode of investigation must be adopted. This
I shall now present in the most simple form, my object being
not so much to determine how much the length of the day or
the path of the moon has changed during long periods of time,
as to afford the means for showing the manner in which the.
power which the tides supply comes indirectly from the immense
stores of force which our globe and its satellite derive from their
ereat velocities.

I shall take first the least complicated case, in which the ter-
restrial waters are supposed to be confined to a uniform channel
encircling the earth at the equator, the plane of which I shall
regard as coincident with that of the lunar orbit. Let M and m

of Tidal Action, =~ 22]

represent the masses of the earth and the moon, 7 the equatorial
radius of the former, D the distance between the centres of both
bodies, A the difference of terrestrial longitude between the crest
of the tide-wave and that place where the moon is vertical, ¢ the
difference of longitude between the crest of the wave and any
point in the channel; and let y be the variable height of the
tide at this point ; while the breadth of the channel is denoted
by 5, and is supposed to be small in comparison to the earth’s
dimensions. Then drd¢ will express the magnitude of the infi-
nitesimal portion of the water which rises above the proper geo-
metrical boundary of the terrestrial spheroid, and its attractive
force on the moon will be
k?gbyrdd :
D?—2Dr cos (A—¢) +7? cos? (A—¢)’ ~~ 9)
in which g measures the attraction exerted at the distance k by
a volume of water assumed as the unit of matter and having a
spherical form. Of the force represented by formula (5), the
component acting horizontally and tending to change the direc-
tion of terrestrial gravity on the moon will be
kbgyr? sin (A— ¢) dh (6)
(D?—2Dr cos (A—¢) +7? cos? (A—¢) )e
Making this expression equal to df, transforming it into a series
of which it-is necessary to retain only the first two terms, and
putting C for k®gb, there results
_, Cyr?sin (A—¢)dd , 8Cyr? sin2(A—¢)dp (7)
df= D3 Wr 9D4 :
The value of the force f which occasions the secular change in
the lunar movement may be obtained by integrating the last
equation ; but for this purpose y must be expressed in terms of
¢; and in ascordance with the theory of the tides and the laws
of periodicity in their movements, y may be assumed equal to
heos2h+h'sin2¢; h and h' being two constant quantities, the
latter small in comparison to the first, and depending on the
effect of friction. Equation (7) becomes, on the substitution of

this value of y,
_ Chr?sin (A+¢)db Chr* sin (86—A)dh 4

uf 2D3 2D
8Chr?sin2Adb __ 8Chr*sin(46—2A) dd
4D4 44 [
Chir?cos(A-+¢)dp Ch'r?cos (86—A)dp {+ (8)
si 2D2 2D3

3CHr3 cos 2Adp _ 38CH'r*cos(4—2A)dd |
4.D4 4.14 J

222 Mr. D. Vaughan on the Secular Effects

Now, on integration within the limits of 6=0 and 6=27, the
terms containing this variable angle disappear; and since A is
constant, there results

Bs

f= aps (isin 2A +2) cos 2A ae ae

If the waters of our globe, instead of being confined to the
vicinity of the equator, were made to occupy a number of regular
channels ranging with the parallels of latitude, and if dr denote
the breadth of one of these channels, O the polar distance of its
middle part, while the notation already given is retained for the
remaining items, the tidal swelling of the fluid confined under
the given parallel will have its tangential action on the moon ex-
pressed by

37k? gbr? sin? O

2D4

This may be easily found by using in the foregoing investigation
rsin QO, the radius of the parallel of latitude, instead of r the
radius at the equator. Now instead of the complicated case
which our terraqueous world presents, I shall, like most writers
on the tides, take an equivalent one in which the entire globe is
supposed to be covered with water having a depth equal in all
places, or varying regularly with the latitude according to some
obvious law. We may suppose this hypothetical ocean divided
into watery zones or canals by partitions parallel to the equator ;
as the number of these divisions become infinite, the breadth of
each will be represented by rdO, and its tangential force on the
moon by df. From formula (10) there is thus obtained

__ 82rk*gr4 sin? OdO
7 2D4

The angle A may without much error be regarded as constant
for all latitudes ; but it is proper to consider the greatest height
of the tide-wave as depending on the distance from the equator ;
and supposing it proportional to the cosine of the latitude, we
must substitute for 2 and A’in the last equation AsinO and
h'sinO. Making this substitution and integrating within the
limits of O=0 and O=90°, we obtain

Q rp Dn
P= 297" (asinQA+Meoos2A). . . (12)

Some idea of the small effect of the tides on lunar motion may
be derived from a numerical estimate of the value of F in the
last equation, supposing the angle A to be 45°, and the greatest
height of the tides equal to three feet. For this purpose it will
be most convenient to take for the unit of attracting matter a

(Asn 2A+A/'cos2A). . (10)

d¥ (Asm 2A+/'cos2A). (11)

of Tidal Action. 223

sphere equal to the earth in size and having the density of water ;
k would then be equal to 7; and according to the most recent

estimates of the earth’s density g would indicate a velocity of five
4
feet a second generated in a second of time. Now 7, is nearly

equal to +59e¢h 000) and the product 7?k*h sin 2A will represent
a quantity of matter which, with the unit of measure I have as-
sumed, will be s55h55y5- ‘The velocity due to the force F in a
second of time will be expressed by the following fraction of a
foot per second :

J poh

27648000000000°

This significant force acting on the moon for three millions of
years would change her velocity a little more than 1 per cent. ;
and through the indirect influence on her orbit an increase of
about 3 per cent. would be then occasioned in her period of re-
volution around our planet. If in this estimate I have assigned
too low a value for the height of the equatorial tides, there is
an ample compensation for the error by giving to the angle A
the value necessary for producing a maximum effect.

The relation already exhibited between the change in lunar
and terrestrial motion may be also deduced by investigating the
loss in the earth’s rotation from the reciprocal attraction of the
moon on the protuberant tidal waters in a channel either coinci-
dent with the equator or parallel to it. To arrive at an approxi-
mate estimate of this loss, in the first case the tangential force
proceeding from lunar attraction must, with the notation already

412 asi oe:
used, be expressed by ee ee ; and the momentary
decrease in the momentum of terrestrial matter from the action
of this force on the small portion of the fluid represented by
brydd will be
dk*gbyr2m sin 2(A— jd dt
Ds PD AD Alsi ACT a)

On making the substitutions already employed for y and kgf,
the formula becomes

3Chmr? cos 2¢ sin 2(A — h) dd dt =
3
me » (14)
3CH! mr? sin 2¢ sin 2(A—¢)dd dt
f 203

Reducing and integrating with reference to dd, taking the limits
of 6=0 and ¢=2r7, there results

37Chmr? sin 2Adt 382Ch'mr? cos 2Adt

BO RMI UE DS josie: cata

224 On the Secular Effects of Tidal Action.

This is the loss of terrestrial momentum in the instant of time
dit; and the loss must fall on the water alone if its movements
were wholly umimpeded by friction. It thus appears that the
waste of motive force is sixty times as great to the earth as to
the moon, as may be seen by comparing the last formula with
equation (9) after multiplying the latter by m. The same con-
formity to the law for the preservation of areas may be shown
for zones of water parallel to the equator in every latitude.

While the enlargement of the moon’s orbit through tidal in-
fluence converts her apparent gain into an actual loss of velocity,
a corresponding result of indirect action would be exhibited in
our liquid domain if no friction retarded its movements. Were
the terrestrial waters confined to regular channels ranging with
the equator or the parallels of latitude, the constant loss of mo-
tion would serve to increase the gravity and the pressure of the
fluid. But if an ocean of uniform depth covered the entire
earth, and if its bottom were perfectly smooth, its waters, though
losing some velocity by tidal movements, would have their velo-
city of rotation increased by retiring towards the polar regions
as the centrifugal force declmed. In the aqueous envelope of
the earth there would accordingly be a gain of momentum, while
a loss occurred to the moon on a corresponding scale and from
the same cause. But the result is much modified by friction,
which makes the oceanic waters partake of the velocity of our
planet, and occasions a consumption of motion proportional to
the calorific energy of the tides.

The effects of the impediments to the great movement of our
seas may be readily understood from what is known to attend
the collision of imperfectly clastic bodies. If a large meteorite
moving from west to east directly over the equator, and having
a circular orbit coincident with the verge of our atmosphere,
were to have its planetary career arrested by striking a very high
mountain, the collision would occasion no loss of momentum ;
for whatever the body parted with must be gained by the earth ;
but the sum of the living forces which the earth and the me-
teorite possess, and which are measured by the masses multiplied
by the square of the velocities, would be diminished in proportion
to the amount of heat developed as the meteorite struck the
mountain or incorporated with our planet in any other way.
There is a similar destruction of living force and a corresponding
development of heat from the rolling of the vast bodies of water
over the asperities in the bed of the ocean; and motion is ever
annihilated in giving birth to calorific energy. Yet nothwith-
standing the effects of friction, much of the velocity which the
moon gives the liquid domain is retained for some time and ex-
hibited in the production of oceanic currents; but as the force

On an Equation in Differences of the Second Order, 225

of these currents is called into requisition for the works of nature
or of art, and the water is made to partake of the velocity of the
bed on which it rests, the store of force in our planet must be
wasted and the length of our day augmented.

A more definite relation between the destruction of force in
this manner and the consequent change in planetary motion may
be shown by investigating the extent to which a satellite revol-
ving close to its primary has its orbit altered by tidal action
arising from the eccentricity of the ellipse whick it describes,
supposing the rotation adjusted for keeping the same side always
turned to the central body. To this problem other solutions
may be given besides that which I presented in the Philoso-
phical Magazine for December 1851. To seek for evidence of
the correlation of forces by physical inquiries of cases hitherto
untried or relating to phenomena presented in distant systems
is as legitimate as the course pursued by Newton and his
followers, who applied all the vast resources of mathematics,
not for calculating the course of projectiles near the earth’s sur-
face, but for determining the orbits which solar attraction would
give bodies moving with immense velocities through the distant
realms of space.

Cincinnati, January 21, 1869.

[To be continued. ]

XXX. The Story of an Equation in Differences of the Second
Order, By J. J. Syuvesrer*.

M* recent researches into the order of the various systems
of equations which serve to determine the forms of redu-
cible cyclodes have led me to notice an equation in the second
order of differences which I imagine is new, and possesses a pe-
culiarly interesting complete integral.
If we call
iG (w?— a?)' (a? —b2) (a2 —¢2)! Say
and (7,7, k,... &c. being given) determine 5D, Cy)0 = Co SO1AS
to make (fx)? + (f'x)* a complete square, and if we suppose the
indices 2,7, k,... to consist of X integers of one value, « inte-
gers of a second value, y of a third, and so on, the number of
solutions of the problem will in general depend not on i,j, 4, but
on the derived integers A, pw, v,.. -; and we may denote the
maximum value of this number by the type [A, p, v,.. ai
* Communicated by the Author.
eee. Or. A.
fe= (2-0)? —b a —e)(e—@y,
the type is [1, 1, 1, 1], of which the maximum value is 9; but if the sum

Phil, Mag. 8. 4. Vol. 37, No. 248. Mar. 1869.

226 On an Equation in Differences of the Second Order.

Now I have been able to establish the following theorem of
derivation as a particular case of a more general one of which
the clue is in my hands :—

[1, A, fv, o+-] =[A, o, vy...) + S(A2—A)f, A—2, we v,.. |
+2>2Arp[1,4—1, w—1,y,...].
Suppose now that A, uw, v,... all become unity, and that we call
[es <3 60 7 terms) eee
then the theorem above stated gives the relation
On = On + (n—1) (n— 2) On _2.

But by virtue of the form of the equations for finding fz, I
know independently that ©, 1s the product of terms of the pro-
gression

t, 1,°2,/23.5) 3p oe

Hence we have one particular solution of the above equation in
differences. To find the second,if we make Q, and Q,, 1 and 2
respectively instead of 1, 1, it will be found that the nth term
becomes the product of » terms of the analogous progression
1,2,2,4,4,6,6.... Thus, then, we are in possession of the com-
plete integral of the equation

Ue 41 = Uy + (a? —&) Uy 4,
VIZ.
Us, =C.1?.3?.5?...(Q2a—1)? 4+ K2?, 42, ... (22) 2a,
ogg = CO. 1?. 37.5... 2e—1)?(2r+ 1) = 22 eee)

Writing u,=1.2.3...(¢—1)v,, the above equation takes the
remarkably simple form

UV» *k
Vg41 ~~ Uz-1 = — °

of any two of the quantities 7, 7, k, 7 happens to become equal to the sum
of the other two, the order sinks and is either 8 or 7; Iam not quite cer-
tain which at present, although it is more probably the former.

* Whether taken under this or the original form, the equation will be
found to he outside the cases of integrable lmear difference of equations of
the second order with linear or quadratic coeflicients given by the late Mr.
Boole in his valuable treatise on finite differences. In the second form the
solution ought by Laplace’s method to be representable by a definite inte-
gral, HKxpressed under the more ordinary form the integral is as follows:

Bob 2r- 1) 4 2 26 eee

5 =O poe cele
is 2 A765", (22-2) 195. eee
ye eC orb Tes (Qe=1) |, 2.4.6...(2=2)
tal OA 4 (On—2) 1325 1e2=3

Royal Society. 227

The romance of algebra presents few episodes more wonderful
than this specimen of the way in which the determination of the
degree of an equation resulting from elimination can be made to
contribute a new and by no means obvious fact to the Calculus
of Differences.

Athenzeum Club,
February 23, 1869.

XXXI. Proceedings of Learned Societies.
ROYAL SOCIETY.

[Continued from p. 145.]

December 17, 1868.—Captain Richards, R.N., Vice-President, in
the Chair.

| Mae following communication was read :—
“On the Measurement of the Luminous Intensity of Light.”
By William Crookes, F.R.S. &e.

The measurement of the luminous intensity of a ray of light is a
problem the solution of which has been repeatedly attempted, but
with less satisfactory results than the endeavours to measure the
other radiant forces. The problem is susceptible of two divisions,
the absolute and the relative measurement of light.

A relative photometer is one in which the observer has only to
ascertain the relative illuminating powers of two sources of light, one
of which is kept as uniform as possible, the other being the light
whose intensity is to be determined. It is therefore evident that one
great thing to be aimed at is an absolutely uniform source of light. In
the ordinary process of photometry the standard used is a candle,
defined by Act of Parliament as a “ sperm of six to the pound, burn-
ing at the rate of 120 grains per hour.”’ This, however, is found to
be very variable, and many observers have altogether condemned the
employment of test-candles as light-measures.

The author has taken some pains to devise a source of light which
should be at the same time fairly uniform in its results, would not
vary by keeping, and would be capable of accurate imitation at any
time and in any part of the world by mere description. The ab-
“sence of these conditions seems to be one of the greatest objections
to the sperm-candle. It would be impossible for an observer on
the continent, ten or twenty years hence, from a written description
of the sperm-candle now in use, to make a standard which would
bring his photometric results into relation with those obtained here.
Without presuming to say that he has satisfactorily solved all diffi-
culties, the writer believes that he has advanced some distance in the
right direction, and pointed out the road for further improvement.

A glass lamp is taken of about 2 ounces capacity, the aperture
in the neck being 0°25 inch in diameter; another aperture at the
side allows the liquid fuel to be introduced ; this consists of alcohol

Q2

ak be Royal Society :—

of sp. gr. 0°805, and pure benzol boiling at 81° C., waich are mixed
together in the proportion of five volumes of the former and one of
the latter. The wick-holder consists of a platinum tube, and the
wick is made of fifty-two pieces of platinum wire, each 0°01 inch in
diameter. The flame of this lamp forms a perfectly shaped cone,
the extremity being sharp, and having no tendency to smoke; with-
out flicker or movements of any kind, it burns when protected from
currents of air at a uniform rate of 136 grains per hour.

There is no doubt that this flame is very much more uniform than
that of the sperm-candle sold for photometric purposes. ‘Tested
against a candle, considerable variations in relative illuminating
power have been observed; but on placing two of these lamps in op-
position, no such variations have been detected.

The instrument devised for measuring the relative intensities of
the standard and other lights is next described ; it has this in com-
mon with that of Arago described in 1833, as well as with those
described in 1853 by Bernard, and in 1854 by Babinet, that the
phenomena of polarized light are used for effecting the desired end*.
But it is believed that the present arrangement is quite new, and it
certainly appears to answer the purpose in a way which leaves little
to be desired. The instrument cannot be described without the aid
of drawings, which accompany the original paper ; but its mode of
action may be understood by the following description.

The standard lamp being placed on one of the supporting pillars
which slide along a graduated stem, it is moved along the bar to
a convenient distance, depending on-the intensity of the light to be
measured. The light to be compared is then fixed ina similar way
on the other side of the instrument. On looking through the eye-
piece two brightly lumimous disks will be seen, of different colours.
One of the lights must now be slid along the scale until the two disks
of light, as seen in the eyepiece, are equal in tint. Equality of illu-
mination is easily obtained; for, as the eye is observing two adjacent
disks of light which pass rapidly from red-green to green-red, through
aneutral point of no colour, there is no difficulty in hitting this point
with great precision. Squaring the distance between the flames and
the centre will give inversely their relative intensities.

The delicacy of this instrument is very great. With two lamps,
each about 24 inches from the centre, it is easy to distinguish a
movement of one of them to the extent of one-tenth of an inch to
or fro; and by using the polarimeter an accuracy exceeding this can
be attained. :

The employment of a photometer of this kind enables us to com-
pare lights of different colours with one another. So long as the
observer, by the eyepiece alone, has to compare the relative inten-
sities of two surfaces respectively illuminated by the lights under
trial, it is evident that, unless they are of the same tint, it is im pos-

* Since writing the above, I have ascertained that M. Jamin had previously
devised a photometer in which the principle adopted in the one here described

is employed, although it is carried out in a different and, as I believe, a less
perfect manner.—W. C., Dec. 16, 1868,

The Rev. H. Moseley on the Descent of Glaciers. 229

sible to obtain that absolute equality of illumination in the mstrument
which is requisite for a comparison. By the unaided eye one cannot
tell which is the brighter half of a paper disk illuminated on one side
with a reddish, and on the other with a yellowish light; but by using
the photometer here described the problem becomes practicable.
When the contrasts of colour are very strong (when, for instance,
one is a bright green and the other scarlet) there is difficulty in
estimating the exact point of neutrality; but this only diminishes
the accuracy of the comparison, and does not render it impossible,
as it would be according to other systems.

January 7, 1869.—Lieut.-General Sabine, President, in the
Chair.

The following communication was read :—

“On the Mechanical Possibility of the Descent of Glaciers by
their Weight only.’ By the Rev. Henry Moseley, M.A., Canon of
Bristol, F.R.S., Instit. Imp. Sc. Paris, Corresp.

All the parts of a glacier do not descend with a common motion ;
it moves faster at its surface than deeper down, and at the centre of
its surface than at its edges. It does not only come down bodily,
but with different motions of its different parts; so that if a trans-
verse section were made through it, the ice would be found to be
moving differently at every point of that section.

This fact*, which appears first to have been made known by M.
Rendu, Bishop of Annecy, has since been confirmed by the mea-
surements of Agassiz, Forbes, and Tyndall. There is a constant dis-
placement of the particles of the ice over one another, and alongside
one another, to which is opposed that force of resistance which is
known in mechanics as shearing force.

By the property of ice called regelation, when any surface of ice
so sheared is brought into contact with another similar surface, it
unites with it, soas to form, of the two, one continuousmass. ‘Thus
a slow displacement of shearing, by which different similar sur-
faces were continually being brought into the presence and contact
of one another, would exhibit all the phenomena of the motion of
glacier ice.

Between this resistance to shearing and the force, whatever it
may be, which tends to bring the glacier down, there must be a
mechanical relation, so that if the shearing resistance were greater
the force would be insufficient to cause the descent. The shearing

* The remains of the guides lost in 1820, in Dr. Hamel’s attempt to ascend
Mont Blanc, were found imbedded in the ice of the Glacier des Bossons in 1863.
“* The men and their things were torn to pieces, and widely separated by many
feet. Allaround them the ice was covered in every direction for twenty or thirty
feet with the hair of one knapsack, spread over an area of three or four hundred
times greater than that of the knapsack.” ‘“ This,” says Mr. Cowell, from whose
paper read before the Alpine Club in April 1864 the above quotation is made,
* is not an isolated example of the scattering that takes place in or on a glacier,
for I myself saw on the Theodule Glacier the remains of the Syndic of Val Toui-
nanche scattered over a space of several acres.”

230 Royal Society :-—

force of cast iron, for instance, is so great that, although its weight
is also very great, it is highly improbable a mass of cast iron would
descend if it were made to fill the channel of the Mer de Glace, as
the glacier does, because its weight would be found insufficient to
overcome its resistance to shearing, and thus to supply the work
necessary to those internal displacements, of which aglacier is the
subject, or even to shear over the irregularities of the rocky channel.
The same is probably true of any other metal.

I can find no discussion which has for its object to determine this
mechanical relation between what is assumed to be the cause of the
descent of a glacier, and the effect produced—to show that the work
of its weight (supposing that alone to cause it to descend) is equal
to the works of the several resistances, internal and external, which
are actually overcome in its descent. Itis my object to establish such
a relation.

The forces which oppose themselves to the descent of a glacier
are:—Ist. The resistance to the sliding motion of one part of a piece
of solid ice on the surface of another, which is taking place continu-
ally throughout the mass of the glacier, by reason of the different
velocities with which its different parts move. This kind of resist-
ance will be called in this paper (for shortness) shear, the unit of
shear being the pressure in lbs. necessary to overcome the resistance
to shearmg of one square inch, which may be presumed to be con-
stant throughout the mass of the glacier.

2ndly. The friction of the superimposed laminee of the glacier
(which move with different velocities) on one another, which is
greater in the lower ones than the upper.

3rdly. The resistance to abrasion, or shearing of the ice, at the
bottom of the glacier, and on the sides of its channel, caused by the
roughnesses of the rock, the projections of which insert themselves
ito its mass, and into the cavities of which it moulds itself,

Athly. The friction of the ice in contact with the bottom and
sides so sheared over or abraded.

If the whole mechanical work of these several resistances in a
glacier could be determined, as it regards its descent, for any rela-
tively small time, one day for instance, and also the work of its
weight in favour of its descent during that day, then, by the prin-
ciple of “virtual velocities”’ (supposing the glacier to descend by its
weight only), the aggregate of the work of these resistances, opposed
to its descent, would be equal to the work of its weight, in favour of
it. It is, of course, impossible to represent this equality mathema-
tically, in respect to a glacier having a variable direction and an
irregular channel and slope; but in respect to an imaginary one,
having a constant direction and a uniform channel and slope, it is
possible.

Let such a glacier be imagined, of unlimited length, lying on an
even slope, and having a uniform rectangular channel, to which it fits
accurately, and which is of a uniform roughness sufficient to tear
off the surface of the glacier as it advances. Such a glacier would

The Rev. H. Moseley on the Descent of Glaciers. 231

descend with a uniform motion if it descended by its weight only,
because the forces acting upon it would be uniformly distributed and
constant forces*. The conditions of the descent of any one portion
of it would therefore be the same as those of any other equal and
similar portion. The portion, the conditions of whese descent it
is sought in this paper to determine, is that which has descended
through any given transverse section in a day; or, rather, it is one
half this mass of ice, for the glacier is supposed to be divided by a
vertical plane, passing through the central line of its surface, it being
evident that the conditions of the descent of the two halves are the
same. ‘The measurements which have been made of the velocities
of the surface-ice at different distances from the sides make it pro-
bable that the differences of the spaces described in a given time
would be nearly proportional to the distances from the edge ina
uniform channelt, and the similar measurements made on the velo-
cities at different depths on the sides that, under the same circum-
stances, the increments of velocity would be as the distances from the
bottom. ‘This law, which observation indicates as to the surface
and the sides, is supposed to obtain throughout the mass of the
glaciers. Any deviation from it, possible under the circumstances,
will hereafter be shown to be such as would not sensibly affect the
result.

The trapezoidal mass of ice thus passing through a transverse
section in a day is conceived to be divided by an infinite number of
equidistant vertical planes, parallel to the central line, or axis of the
glacier, and also by an infinite number of other equidistant planes
parallel to the bed of the glacier. It is thus cut mto rectangular
prisms or strips lying side by side and above one another. If any
one of these strips be supposed to be prolonged through the whole
length of the glacier, every part of it will be moving with the same
velocity, and it will be continually shearing over two of the similar
adjacent strips, and being sheared over by two others. The position
of each of these elementary prisms in the transverse section of the
glacier is determined by rectangular coordinates; and in terms of
these, its length, included in the trapezoid. The work of its weight,
while it passes through the transverse section into its actual position,
is then determined, and the work of its shear, and the work of its

* It is supposed that the weight is only just sufficient to cause the descent.

+ Prof. Tyndall measured the velocity of the surface of the Mer de Glace at a
series of points in the same straight line across it at a place called Les Ponts.
The distances of these points in feet along the line up to the point of greatest
velocity are set off to a scale in fig. 1; and the space in feet through which each
point would pass in thirty-six days, ifits velocity continued uniformly the same,
is shown by a corresponding line at right angles to the other. The extremities
of these last lines are joined. It will be seen that the line joining them is for
some distance nearly straight ; if it were exactly so, the law stated in the text
would, in respect to this ice, be absolutely true. Fig. 2 shows in the same manner
the spaces described in thirty-six days by points at different depths on the side
of the Glacier du Géant, as measured by Prof. Tyndall at the Tacul. See Phil.
Trans. Royal Society, vol. cxlix. part 1, pp. 265, 266. [The figures referred to
in this note accompany the MS. of the paper.]

232 Royal Society :— :
friction. A double integration of each of the functions, thus-repre-

senting the internal work in respect to a given elementary prism,
determines the whole internal work of the trapezoid, in terms of the
space traversed by the middle of the surface in one day, the spaces
traversed by the upper and lower edges of the side, and a symbol
representing the unit of shear. Well-known theorems serve to de-
termine the work of the shear and the friction of the bottom and
side in terms of the same quantities. All the terms of the equation
above referred to are thus arrived at in terms of known quantities,
except the unit of shear, which the equation thus determines. The
comparison of this unit of shear (which is the greatest possible, in
order that the glacier may descend by its weight alone) with the
actual unit of shear of glacier ice (determined by experiment), shows
that a glacier cannot descend by its weight only ; its shearing force
is too great. The true unit of shear being then substituted for its
symbol in the equation of condition, the work of the force, which
must come in aid of its weight to effect the descent of the glacier, is
ascertained. :

The imaginary case to which these computations apply, differs from
that of an actual glacier in the following respects. The actual
glacier is not straight, or of a uniform section and slope, and its
channel is not of uniform roughness. In all these respects the re-
sistance to the descent of the actual glacier is greater than to the
supposed one. But this bemg the case, the resistance to shearing
must be less, in order that the same force, viz. the weight, may be
just sufficient to bring down the glacier in the one case, as it does in
the other. The ice in the natural channel must shear more easily
than that in the artificial channel, if both descend by their weight
only; so that if we determine the unit of shear necessary to the
descent of the glacier in the artificial channel, we know that the
unit of shear necessary to its descent by its weight only in the na-
tural channel must be less than that.

A second possible difference between the case supposed and the
actual case lies in this, that the velocities of the surface-ice at differ-
ent distances from the edge, and at different heights from the bottom,
are assumed to be proportional to those distances and heights; so
that the mass of ice at any time passing through a transverse section
may be bounded by plane surfaces, and have a trapezoidal form.
This may not strictly be the case. Al] the measurements, however,
show that if the surfaces be not plane, they are convex downwards.
In so far therefore as the quantity of ice passing through a given
section in a day is different from what it is supposed to be, it is
greater than it. A greater resistance (other than shearing) is thus
opposed to each day’s descent, and also a greater weight of ice
favours it; but the disproportion is so great between the work of
the additional resistance to the descent, and that of the additional
weight of ice in favour of it, that it is certain that any such con-
vexity of the trapezoidal surface would necessitate a further reduction
of the unit of shear, to make the weight of the actual glacier suffi-
cient to cause it to descend.

The Rev. H. Moseley on the Descent of Glaciers. 233

A third difference between the actual glacier and the imaginary
one, to the computation of whose unit of shear the following formulze
are applied, is this—that the formulee suppose the daily motion of
the surface of the glacier and the daily motion of its side to have
been measured at the came place, whereas there exist no measure-
ments of the surface motion and the side motion at the same place.
The surface motion used has been that of the Mer de Glace at Les
Ponts, and the side motion that of the Glacier du Géant at the
Tacul—both from the measurements of Prof. Tyndall. This error
again, however, tends to cause the unit of shear, deduced from the
case of the artificial glacier, to be greater than that in the actual
one; for the Glacier du Géant moves more slowly than the Mer de
Glace. The quantity of ice which actually passes through a section
at Les Ponts is therefore greater than it is assumed in the computa-
tion to be, whence it follows, as im the last case, that the computed
unit of shear is greater than the actual unit of shear.

To determine the actual value of (the unit of shear in the case
of ice) the following experiment was made. ‘Two pieces of hard
wood, each three inches thick and of the same breadth, but of which
one was considerably longer than the other, were placed together, the
surfaces of contact being carefully smoothed, and a cylindrical hole,
13 inch in diameter, was pierced through the two. The longer piece
was then screwed down upon a frame which carried a pulley, over
which a cord passed to the middle of the shorter piece, which rested
on the longer. ‘There were lateral guides to keep the shorter piece
from deviating sideways when moved on the longer. The hole in
the upper piece being brought so as accurately to coincide with that
in the lower, small pieces of ice were thrown in, a few at a time,
and driven home by sharp blows of a mallet on a wooden cylinder.
By this means a solid cylinder of ice was constructed, accurately fit-
ting the hole. Weights were then suspended from the rope, passing
over the pulley until the cylinder of ice was sheared across. As by
the melting of the ice, during the experiment, the diameter of the
cylinder was slightly diminished, it was carefully measured with a
pair of callipers.

Ist experiment.—Radius of cylinder °65625 in., sheared with 98 lbs.

2nd experiment.—Radius of cylinder -703]2 im., sheared with
119 lbs.

By the first experiment the shear per square inch, or wait of shear,
was 72°433 lbs.; by the second experiment it was 76°619 lbs. The
main unit of shear of ice, from these two experiments, is therefore

3 lbs.

Now it appears by the preceding calculations, that to descend by —

its own weight, at the rate at which Prof. Tyndall observed the ice
of the Mer de Glace to be descending at the Tacul, the unit of shear-
ing ferce of the ice could not have been more than 1°3193 lb.*

* By an experiment on the shearing of putty, similar to that which was made
on the shearing of ice, its unit of shear was found to vary from 1 Ib. to 3 lbs.,
according to its degree of hardness. If ice were of the same weight per unit of

234: | } Royal Society.

To determine how great a force, in addition to its weight, would
be necessary to cause the descent of a glacier of uniform section and
slope, such as has been supposed in the calculations, let w represent,
“1 inch-lbs., the work of that force in twenty-four hours. Then
assuming the unit of shear (u) in glacier ice to be 75 Ibs., it follows,
by the principle of virtual velocities, that

u= 94134000 + 1012560 — 2668400
— 92478160 inch-Ibs.=7706513 foot-lbs.*

This computation has reference to half only of the width of the
glacier, and to 23-25 inches of its length. The work, m excess of
its weight, required to make a mile of the imaginary glacier, 466
yards broad and 140 feet deep, descend, as it actually does descend
per twenty-four hours, is represented by the horse-power of an engine,
which, working constantly day and night, would yield this work, or by

2x 7706513 x 5280 x 12
“—883°78 h. p.
3-9 x 24 X 60 X 33000 fee

The surface of the mass of ice, on which the work w is required
to be done, in aid of its weight, to make it descend as it actually
does, is 124771°5 square inches. The work required to be done
on each square inch of surface, supposing it to be equally distributed
{706513 270ee
fe Ola
1247715

These 61°76 foot-lbs. of work are equivalent to ‘0635 heat-units,
or to the heat necessary to raise ‘0635 lb. of water by one degree of
Fahrenheit. This amount of heat passing into the mass of the gla-
cier per square inch of surface per day, and reconverted into mecha-
nical work there, would be sufficient, together with its weight, to

over it, is therefore, in foot-lbs.,

25
bring the glacier down.

The following considerations may serve to disabuse some persons
of the idea of an unlimited reservoir of force residing somewhere in
the prolongation of a glacier backward, and in its higher slopes, from
which reservoir the pressure is supposed to come which crushes the
glacier over the obstacles in its way.

Let a strip of ice one square inch in section, and one mile in
length, in the middle of the surface of the imaginary glacier, be con-
ceived to be separated from the rest throughout its whole length, ex-
cept for the space of one inch, so that throughout its whole length,
except for that one inch, its descent is not retarded either by shear
or by friction. Let, moreover, this inch be conceived to be at the
very end of the glacier, so that there is no glacier beyond it. Now
it may easily be calculated that this strip of ice, oue inch square and
one mile long, lying on a slope of 4° 52', without any resistance to

volume as soft putty, and its consistency about the same, it would descend by its
weight only, without the aid of any other force. It would not, however, be pos-
sible to walk on such ice.

% Thus the work to be done in aid of the weight is thirty-four times the work
of the weight.

Intelligence and Miscellaneous Articles. LY S86

its descent, except at its end, must press against its end, by reason
of its weight, with a force of 194°42 lbs. But the cubical inch of
solid ice at its extremity opposes, by the shear of its three surfaces
whose attachment to the adjacent ice is unbroken, a resistance of
3X75 l|bs., or 225 lbs. That resistance stops therefore the descent
of this strip of ice, one mile long, having no other resistance than
this opposed to its descent, by reason of its detachment from the
rest*. It is clear, then, that it could not have descended by its
weight only when it adhered to the rest, and when its descent was |
opposed by the shear of its whole length; and the same may be
proved of any number of miles of strip in prolongation of this.
Also, with obvious modifications, it may be shown, in the same way,
to be true of any other similar strip of ice in the glacier, whether
on the surface or not, and therefore of the whole glacier.

It results from this investigation that the weight of a glacier is
insufficient to account for its descent; that it is necessary to con-
ceive, in addition to its weight, the operation of some other and
much greater force, which must also be such as would produce
those internal molecular displacements and those strains which are
observed actually to take place in glacier ice, and must therefore be
present to every part of the glacier as its weight is, but more than
thirty-four times as great.

XXXII. Intelligence and Miscellaneous Articles.

FORMATION OF AN ARTIFICIAL SPECTRUM WITH ONE
FRAUNHOFER’S LINE. BY A. WULLNER.

ee ING to Kirchhoff’s explanation of Fraunhofer’s lines,

they are formed by an absorption in the ignited gas sur-
rounding the solid core of light of particular wave-lengths emitted
from the core. If the solar atmosphere alone sent us light, these
lines, assuming that the intensity of the light proceeding from the
atmosphere was great enough, must appear bright upon a dark
ground. ‘This inversion may possibly be observed at the total
eclipse of next August.

I may be allowed to communicate an experiment which shows the
phenomencn with a terrestrial source of light, in the same manner as
Kirchhoff has concluded for the sun from the absorption of light in
flames.

If the discharges of a Leyden jar of about a square foot of coated
surface, and a small striking-distance, be passed through a Geissler’s
spectrum-tube of the usual form by the aid of a Holtz’s machine, the
tube being held before the slit of a spectrometer, the spectrum of
the gas enclosed in the tube is first seen as on the passage of a pow-
erful induction-current. If the striking-distance be only a little in-

* If, however, the glacier were inclined at 35° 10’, instead of 4° 52', and a
strip were detached from its surface, as described above, it would equal tke shear
of one eubic inch at its lower end, if it were 300 yards long, and if the glacier
were vertical, when it was 172°8 yards long.

236 Intelligence and Miscellaneous Articles.

creased, the sodium-line is added to the spectrum of the gas, as it
is seen that while using the induction-current the capillary part
of the spectrum-tube in front of the slit is heated. With a suitable
striking-distance, the sodium-line is so bright that it far exceeds in
intensity the lines of the gas-spectrum if a hydrogen-spectrum tube
has been taken. If the striking-distance be slightly increased, the
bright lines of the calcium-spectrum occur with a beauty and preci-
sion which can scarcely be obtained in any other way. Passing he-
yond the striking-distance which has furnished this spectrum, the
entire phenomenon changes. ‘The luminous line in the spectrum-
tube is of such dazzling brightness, that even looked at by daylight
it leaves a long-continued after-image in the eye. ‘This luminous
line, looked at in the spectrometer, shows a considerably bright con-
tinuous spectrum, in which, however, the position of the sodium-line
appears quite dark ; we thus obtain an artificial spectrum with one
dark line, or, since the mode of formation is the same, with one Fraun-
hofer’s line.

That this line is formed in the same manner as, according to
Kirchhoff, Fraunhofer’s are in the solar spectrum, is at once seen on
Icoking at the tube after the experiment; the inside of the capillary
tube is seen to be very strongly corroded by detached glass splinters,
so that after the experiment has been often made the glass has be-
come quite dull. ‘These glass particles, which each discharge de-
taches, are at the same time raised to incandescence, and the light
of these ignited solid particles furnishes the bright continuous spec-
trum. These solid particles glow, however, in an atmosphere of
sodium-vapour, and this holds back the same light which was ob-
served before the solid- particles were detached; hence where this
light ought to be in the spectrum there is a dark part. There is here
seen in its individual stages the formation of Fraunhofer’s line ; for the
discharge of the Leyden jar first produces the ignited atmosphere, and
then the far more brightly glowing core in it. With the formation
of the glowing solid core the bright line furnished by the atmosphere
becomes obscure.

It might be expected that, besides the scdium-line, the calcium-
line and that of the gas would appear dark. Ihave been unable
to perceive these lines; the reason doubtless is that calcium-vapour
is not sufficiently dense to allow the absorption of the light corre-
sponding to it to be so strong that the inversion can occur.—Poggen-
dorff’s Annalen, No. 9, 1868.

ON THE QUANTITY OF ELECTRICITY PRODUCED BY THE ELEC-
TROPHORUS MACHINE EXPRESSED IN ABSOLUTE MEASURE.
BY ¥F. KOHLRAUSCH,.

The working of Holtz’s electrophorus machine has been investi-
gated by means of the unit-jar, and particularly as compared with
that of the friction machine. An absolute measurement in this way
would be attended with the greatest difficulties. If we restrict our-

Intelligence and Miscellaneous Articles. 237

selves to the limiting case in which the conductors are in metallic
contact (which in some cases might possibly be applied instead of
voltaic electricity), the quantities of electricity produced are easily
obtained in absolute measure if the magnetic actions of the current
they form are observed. The reduction of the measurements of the
intensity of the current to mechanical units, which my father and
Weber executed, renders it easy to express quantities of electricity
in electrostatic units.

The machine investigated was constructed by Schultz of Berlin, .
according to the pattern described by H. Holtz in vol. xxx. of this
Magazine. ‘The fixed disk has two coatings; the moveable one has
a diameter of 400 millims. Where it is not otherwise expressly
mentioned, only two of the four combs which were opposite the coat-
ings were at work.

By velocity of rotation is understood the number of turns of the
handle in a second, one of which corresponds to six turns of the
glass disk.

The two conductors were connected (a moist thread being inter-
posed) with the ends of the wire of the same multiplier as was ar-
ranged for the research of Weber and my father, and which is de-
scribed in the fifth volume of the Proceedings of the Royal Academy
of Saxony, pp. 259 & 289. The 5635 turns of its wire, amounting
to about three miles, were completely protected against the forma-
tion of short circuit by careful insulation.

The intensity of the current which flows through the coils of this
multiplier and deflects the needle through , is in absolute magnetic
measure

—————— o

= F691 98»
or, with the present value of the horizontal intensity of terrestrial
magnetism for Gottingen T=1°'844,

i=0-00704 log @.

In what follows, the distance of the scale from the mirror of the
magnet was =1400 divisious ; hence, if p represents the deflection of
the needle in parts of the scale, for small values of p we can put

. 0:00704
2800

The very powerful damper completely stopped the needle after a few
minutes ; and with a little practice it was possible so to regulate the
velocity of rotation by a seconds’ watch, that the deviations only
amounted to a few divisions.

It was surprising to find the working of the machine as good as
constant on different days. Although the absolute moisture of the
air in the room of observation was between 9 and 14 germs. of water
in a cubic metre, and the relative varied between 0°42 and 0°58,
and the greatest length of spark was subject to great variations, as is
usual with these machines, yet the inequalities observed in the in-

p=0'00000251 .p.

238 Intelligence and Miscellaneous Articles.

tensity of the current were within the errors of observation. If, for
instance, the mean be taken of the sets of observations on the 16th,
17th, and 18th of July, and those on the 25th and 26th of July, the
deflections, in parts of a scale, are—

Velocity of rotation .4555- =s ~ 4 =

16th, 17th, and 18th of July =30'2 42°96 “892 ia7e

25th and 26th of a, woe = 29°78 872
Mean: ..:.-4-..... =30°0 » 437) Serer ae

The differences are similarly small if the mean be taken of other
groups.

It is, secondly, remarkable that the electricity furnished is, within
the limits prescribed by the dimensions of the machine, as good as
independent of the distance between the combs and the rotating
plate, as follows from the following numbers, which also represent
the mean values of several experiments :—

Velocity of rotation...... =F 4 41 3
4 millims. 30°5 45:2 90°7. + 1389°4
Distance of the combs } 19 __,, 30°0 “460 “892s itet-7.
from the glass disk*) 27 <a 30°5 47°0 882 1¥30°0
San he 30°99 46:0 > 8/7) aaiaG;s

The working with a slow rotation remained unchanged; with the
greatest velocity the diminution is only about 7 percent. Hence for
a velocity of the particles of glass of 3 metres in a second, the dis-
charge and charge are as complete when the distance of the points is
34 millims. as it is whenitis 4millims. With a velocity of 6 to 9
metres the discharge would only be incomplete—a point which, like
any motion of electricity for which a measurable time is required,
would deserve further examination. (The above observations are
less trustworthy, owing to the greater variations which always ac-
companied the further removal of the combs. <A few times a sudden
decrease in activity set in which extended to total cessation.)

It is seen, thirdly, that there is an almost exact proportionality
between the intensity of the current and the velocity of rotation, for
which purpose it is sufficient to compare the numbers given above.
After introducing a small correction for magnitudes which are pro-
portional to the tangent of the angle of deflection, we have, in the
mean,—

Velocity of rotation .... = 4 4 + 3

Deflection .... =30'0 43°l 88°7 136°6
while, assuming proportionality, we calculate

Detection Sit... = 29°9 A478 89:7 134°5

The productiveness of Holtz’s machine was further compared with
that of a very good friction machine (made on Winter’s plan by
Apel) which has a disk of 600 millims., and under fayourable cir- »

Intelligence and Misceilaneous Articles. 239

cumstances yields sparks of 15 inches. Here also the quantity of
electricity was almost proportional to the velocity of rotation;
for—

Velocity of rotation .... = a i 3
Deflection 45 0s es os =9°7 14°7 26°F 40°5
Cakemlateies .4. iiss ==9°9 137 27°5 41-2

As both machines can be turned with the same velocity, Holtz’s
is more productive in the ratio 10: 3.

In reducing the current to absolute magnetic measure, the deflec-
tion must be multiplied with 0:00000251. Owing to agitations, the
greatest velocity observed, of three turns in two seconds, would be
almost the maximum for continuous use with the above machine.
If instead of the deflection 137 we take as the maximum 150 divi-
sions, the intensity of the current in magnetic measure is

150 x 0:0000025 1=0:000376.
Changed into mechanical measure, we have
0:000376 x 155370 x 10°=58 million

units of positive electricity in a second, or a little more than one
charge of the small Leyden jar used in the méasurements of Weber
and my father.

Yet how small this quantity is as compared with that set in mo-
tion by voltaic se is seen from the fact that the current 0°000376

ly decompose me of wat or that, in order
only decomposes ——— ws of a milligramme of water,

to obtain a cubic centimetre of explosive mixture, the strongest cur-
rent of our electrophorus machine would have to be passed for about
forty hours through water.

I have incidentally found the electromotive force of a Grove’s ele-
ment in absolute measure to be =17°9, assuming the magnetic as
unit of current-intensity, and Siemens’s as unit of resistance. H.
von Waltenhofen* finds, expressed in the same unit, Daniell=11°4;
- and Bosscha in the same manner finds Daniell=10°8; from which
Grove
Daniell
tained by direct comparison. The current 0:000376 of our ma-
chine is therefore produced by a single Grove’s element in a conduc-

= 1°57 or 1°66 respectively, which is about the number ob-

tion of SER =48000 mercury-units, or in a telegraphic com-
munication of about 3800 miles.

To obtain an idea of possible medical or physiological applications,
I determined the resistance of the human body, which from hand to
hand (the hands being immersed in dishes containing liquid) in four
persons amounted to between 1600 and 3600 mercury-units, the
- mean being 2200. Putting the polarization as equal to the electro-
motive force of one Grove’s element, which for feeble currents is far
too high, a battery of two elements would furnish the current

* Poge. Ann, vol, cxxxill. p, 462,

240 Intelligence and Miscellaneous Articles.

one =0:0081, or twenty-two times the current produced by the

machine in the human body.

Such numbers lead to the conclusion that, though far more pro-
ductive machines than the above may, and probably will, be con-
structed by increased velocity of rotation, a larger number of places
of decomposition, and of combs, yet they cannot be thought of as a
substitute for constant currents, or in general for actions which are
proportional to the intensity. Itis different with actions which are
proportional to the square of the intensity, like the thermal actions
observed by Holtz and Poggendorff, or with the physiological which
are produced by intermittent currents, and depend upon the rapidity
of the change of current. By the possibility of resolving the mean
current of the machine, by means of an interposed layer of air, into
parts of greatly increased intensity, actions may be obtained which,
under certain circumstances, may approach to galvanic ones.—Pog-
gendorff’s Annalen, No. 9, 1868.

ON THE INTERFERENCE OF LIQUID WAVES.
* BY M. LISSAJOUS.

The interference of liquid waves may be demonstrated by means
of an apparatus which is both simple and easy to construct. It
consists of two horizontal “diapasons fixed to the same support in
such a manner that the four branches are in the same horizontal
plane. Each diapason is provided with a vertical point; these two
dip at a distance of a few centimetres in a bath of mercury or
water.

If one of them be made to vibrate, the disturbances communicated
to the liquid produce waves which are propagated with greater or
less rapidity, according to the nature of the liquid. If both be si-
multaneously disturbed, a system of fixed waves is formed between
the two points which are perfectly distinguishable by the play of
light which they produce.

When the two diapasons are not in perfect unison, the waves are
seen to be slowly displaced; andit can readily be proved that they
move towards the lowest one.

Thus, by means of the eye, not merely the discordance of two
vibrating apparatus may be recognized, but also its direction.

This second experiment furnishes an ocular demonstration of the
cause of beats.

It is also possible to use this method for comparing the velocity
of the propagation of waves on the surface of different liquids.
—Compites Kendus, December 24, 1868.

THE

LONDON, EDINBURGH, ann DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

Fe 3 a AIR
:FOURTH SERIES.]

a

APRIL 1869.

XXXIIT. On Cometary Theory.
By Joun Tynvatt, F.R.S. &c.

To the Editors of the Philosophical Magazine and Journal.

GENTLEMEN,

N the 8th of this month, in a lecture delivered before the
Cambridge Philosophical Society, I ventured to enunciate
a speculation regarding the origin and deportment of visible co-
metary matter. I had been led to reflect on the subject by those
experiments, on the decomposition of vapours by light, which I
have already described in abstract in the Proceedings of the
Royal Society. The speculation was introduced and communi-

cated to the Philosophical Society in the following words :—
“In the course of my experiments on actinic action I have
been often astonished at the body of light which a perfectly infi-
nitesimal amount of matter, when diffused in the form of a cloud,
can discharge from it by reflection. I have been repeatedly per-
plexed and led into error by the action of residues so minute as
to be simply inconceivable. In order to get rid of these residues,
my experimental tubes, after having been employed for any va-
pour, are flooded with alcohol, sponged out with soap and hot
water, and finally flooded with pure water. Let me give you
some idea of the quantities of matter that here come into play.
The tube before you, which is 3 feet long and 3 inches wide,
was so thoroughly cleansed that when filled with air, or with the
vapour of aqueous hydrochloric acid, no amount of exposure to
an intense light produced the least cloudiness. Having thus
assured myself of the perfect purity of the tube, I took a small

Phil. Mag. 8. 4. Vol. 37. No, 249. April 1869. R

242 Prof. Tyndall on Cometary Theory.

bit of bibulous paper, rolled it up into a pellet not the fourth
part of the size of a small pea, and moistened it with a liquid
possessing a higher boiling-point than that of water. I held the
pellet in my fingers until it had become almost dry, then intro-
duced it into a connecting-piece and allowed dry air to pass over it
into this tube. The air charged with the modicum of vapour thus
taken up was subjected to the action of light. A blue actinic
cloud began to form immediately, and in five minutes the blue
colour had extended quite through the experimental tube. For
some minutes this cloud continued blue, and could be completely
quenched by a Nicol’s prism, no trace of its light reaching the
eye when the Nicol was in its proper position. But its particles
augmented gradually in magnitude, and at the end of fifteen mi-
nutes a dense white cloud filled the tube. Considering the
amount of the vapour carried in by the air, the appearance of a
cloud so massive and luminous seemed like the creation of a
world out of nothing.

“ But this is not all; the pellet of bibulous paper was removed,
and the experimental tube was cleared out by sweeping a current
of dry air through it. This current passed also through the con-
necting-piece in which the pellet of bibulous paper had rested. The
air was at length cut off and the experimental tube exhausted.
Fifteen inches of hydrochloric acid were then sent into the tube
through the same connecting-piece. Now it 1s here to be noted
(1) that the total quantity of liquid absorbed by the pellet in
the first instance was exceedingly small, (2) that nearly the
whole of this small quantity had been allowed to evaporate be-
tween my fingers before the pellet was placed in the connecting-
piece, (3) that the pellet had been ejected and the tube in
which it rested rendered for some minutes the conduit of a
strong current of pure air. It was part of such a residue as
could linger in the connecting-piece after this process, that was
carried into the experimental tube by the hydrochloric acid and
subjected there to the action of light.

“One minute after the ignition of the electric lamp a faint
cloud showed itself; in two minutes it had filled all the anterior
portion of the tube and stretched a considerable way down it ; it
developed itself afterwards into a very beautiful cloud-figure ;
and at the end of fifteen minutes the body of light discharged by
the cloud, considering the amount of matter involved in its pro-
duction, was simply astounding. But though thus luminous,
the cloud was far too fine to dim in any appreciable degree ob-
jects placed behind it. The flame of a candle seemed no more
affected by it than it would be by a vacuum. Placing a page of
print so that it might be illuminated by the cloud itself, it could
be read through the cloud without any sensible enfeeblement.

Prof. Tyndall on Cometary Theory. 243

Nothing could more perfectly illustrate that ‘ spiritual texture’
which Sir John Herschel ascribes to a comet than these actinic
clouds. Indeed the experiments prove that matter of almost
infinite tenuity is competent to shed forth light far more intense
than that of the tails of comets. The weight of the matter which
sent this body of light to the eye would probably have to be
multiphed by millions to bring it up to the weight of the air in
which it hung.

« And now will you bear with me for five minutes while I en-
deavour to apply these results to cometary theory ? Iam encou-
raged to do so by a remark of Bessel’s, who said that had any
theory preceded his observations on Halley’s comet, by fixing
his attention either upon its verification or its confutation, it
would have enabled him to return from his observations with a
greater store of knowledge than he had actually derived from
them. If time permitted, I should like to lead you by an easy
gradient up to the view that I wish to submit to you; but time
does not permit of this, and therefore the speculation must suffer
from the baldness arising from the absence of such preparation.

“You are doubtless aware of the tremendous difficulties which
beset cometary theory. The comet examined by Newton in
1680 shot out a tail sixty millions of miles in length in two
days. The comet of 1843, if I remember aright, shot out in a
single day a tail which covered 100 degrees of ‘the heavens. This
enormous reach of cloudy matter is supposed to be generated in
the head of the comet and driven backwards by some mysterious
force of repulsion exerted by the sun. Bessel devised a kind of
magnetic polarity and repulsion to account for it. ‘ It is clear,’
says Sir John Herschel, ‘that if we have to deal here with matter
such as we conceive it, viz. possessing inertia, at all, it must be
under the dominion of forces incomparably more energetic than
gravitation, and quite of a different nature.’ And in another
place he states the difficulties of the subject in the following re-
markable words :—

“«¢ There is beyond question some profound secret and mystery
of nature concerned in the phenomenon of their tails. Perhaps
it is not too much to hope that future observation, borrowing
every aid from rational speculation, grounded on the progress
of physical science generally (especially those branches of it
which relate to the ethereal or imponderable elements), may ere
long enable us to penetrate this mystery, and to declare whether
it is really matter, in the ordinary acceptation of the term, which
is projected from their heads with such extravagant velocity, and
if not impelled, at least directed in its course by a reference to
the sun as its point of avoidance. In no respect is this ques-
ticn as to the materiality of the tail more forcibly pressed on us

R 2

244: Prof. Tyndall on Cometary Theory.

for consideration than in that of the enormous sweep which it
makes round the sun in perthelio, in the manner of a straight
and rigid rod, in defiance of the law of gravitation, nay, even of
the received laws of motion, extending (as we have seen in the
comets of 1680 and 1843) from near the sun’s surface to the
earth’s orbit, yet whirled round unbroken—in the latter case
through an angle of 180° in little more than two hours. It
seems utterly incredible that in such a case it is one and the
same material object which is thus brandished. [I would espe-
cially invite the reader’s attention to these words in reference to
the following theory.—J. T.] If there could be conceived such
a thing as a negative shadow, a momentary impression made
upon the luminiferous ether behind the comet, this would re-
present in some degree the conception such a phenomenon irre-
sistibly calls up.’

“ T now ask for permission to lay before you a speculation which
seems to do away with all these difficulties, and which, whether
it represents a physical verity or not, ties together the pheno-
mena exhibited by comets in a remarkably satisfactory way.

“|. The theory is, that a comet is composed of vapour decom-
posable by the solar light, the visible head and tail being an
actinic cloud resulting from such decomposition ; the texture of
actinic clouds is demonstrably that of a comet.

“2. The tail, according to this theory, is not projected matter,
but matter precipitated on the solar beams traversing the come-
tary atmosphere. -It can be proved by experiment that this
precipitation may occur either with comparative slowness along
the beam, or that it may be practically momentary throughout
the entire length of the beam. The amazing rapidity of the
development of the tail would be thus accounted for without in-
voking the incredible motion of translation hitherto assumed.

“3. As the comet wheels round its perihelion, the tail is not
composed throughout of the same matter, but of new matter
precipitated on the solar beams, which cross the cometary atmo-
sphere in new directions. The enormous whirling of the tail
is thus accounted for without invoking a motion of translation.

“4. The tail is always turned from the sun for this reason :—
Two antagonistic powers are brought to bear upon the cometary
vapour,—the one an actinic power tendimg to produce preci-
pitation, the other a calorific power tending to effect vaporiza-
tion. Where the former prevails, we have the cometary cloud ;
where the latter prevails, we have the transparent cometary va-
pour. As a matter of fact, the sun emits the two agents here
invoked. There is nothing whatever hypothetical in the assump-
tion of their existence. That precipitation should occur behind
the head of the comet, or in the space occupied by the head’s

Prof. Tyndall on Cometary Theory. 245

shadow, it is only necessary to assume that the sun’s calorific rays
are absorbed more copiously by the head and nucleus than the
actinic rays. This augments the relative superiority of the ac-
tinic rays behind the head and nucleus, and enables them to
bring down the cloud which constitutes the comet’s tail.

‘5. The old tail, as it ceases to be screened by the nucleus, is
dissipated by the solar heat; but its dissipation is not instan-
taneous. The tail leans towards that portion of space last
quitted by the comet, a general fact of observation being thus
accounted for.

“6. In the struggle for mastery of the two classes of rays a
temporary advantage, owing to variations of density or some
other cause, may be gained by the actinic rays even in parts of the
cometary atmosphere which are unscreened by the nucleus. Oc-
casional lateral streamers, and the apparent emission of feeble
tails towards the sun would be thus accounted for.

“7. The shrinking of the head in the vicinity of the sun is
caused by the beating against it of the calorific waves, which dis-
sipate its attenuated fringe and cause its apparent contraction.

“Throughout this theory I have dealt exclusively with true
causes, and no agency has been invoked which does not rest on
the sure basis either of observation or experiment. It remains
with you to say whether in venturing to enunciate it I have
transgressed the limits of ‘ rational speculation.’

“Tf I have done so, surely I could not have come to a place
more certain to ensure my speedy correction. If the theory
be a mere figment of the mind, your Adams and your Stokes
(both happily here present), to whom I submit the speculation
with the view of having it instantly annihilated by astronomy
and physics, if it merit no better fate, will, I doubt not, effec-
tually discharge that duty, and thus save both you and me from
error before it has had time to lay any serious hold on our ima-
gination.””

The leniency with which this speculation was received at Gane
bridge induces me to submit it to the critical judgment of the
readers of the Philosophical Magazine*.

I remain, Gentlemen,

Royal Institution, Your obedient Servant,

March 15, 1869. JoHN TYNDALL.

* There may be comets whose vapour is undecomposable by the sun,
or which, if decomposed, is not precipitated. This view opens out the pos-
sibility of invisible comets wandering through space, perhaps sweeping
over the earth and affecting its sanitary condition without our being other-
wise conscious of their passage. As regards tenuity, I entertain a strong
persuasion that out of a few ounces (the possible weight assigned by Sir
John Herschel to certain comets) of iodide-of-allyl vapour, an actinic cloud

of the magnitude and luminousness of Donati’s comet might be manu-
factured.

Pa:

XXXIV. Remarks on the Luminous, Thermal, cna Feustic Phe-
nomena attending the Fallof Meteorites. By Chevalier W. von
HaIpDINGER*.

1. ETEORIC falls in the course of the year 1868.—The first

: of these falls in 1868 brought to the notice of the scientific
world was that at Pultusk, near Warsaw, January 30. Next to it
camethe falls of Villanova and Motta dei Conti, near Casale (Pied-
mont), February 26, between 10.30 and 10.45 a.m., of Slavetic
(Croatia), May 22, and of Ornans (Département du Doubs), July
- 11. The detonation of a fifth meteor was heard at Salzburg in

the night of September 27-28, without having (at least as far as hi-
therto known) left any tangible traces. A fragment of the Ornans
meteorite, weighing 39 grms., has come into possession of the
Imperial Museum of Vienna through the kind intervention of the
eminent geologist, M. Joachim Barrande. The fall of Villanova
was preceded by a number of detonations; no igneous globe,
only a small cloud with internal motion and in rapid progression,
was observed. ‘The meteor passed from N.W. or W.N.W. to
S.E. or E.S.E. at a small angle to the horizon. Two stones,
the one weighing 6°700 grms., the other 1°920 grm., have been
preserved ; a third, whose weight may have amounted to from
300 to 500 grms. was broken by the violence of its fall.

2. M. Stanislas Meunier has published ‘Géologie comparée:
Etude descriptive théorique et expérimentale sur les Météorites,’
Paris, 1867, a book highly commended by Madame Cat. Scar-
pellini. In one passage (p. 18) the author says, “A great num-
ber of circumstances attending meteoric falls have as yet re-
mained without explanation. The causes of the explosions,
especially when repeated, and of the incandescence, are still un-
known.” So it may be inferred that he had no knowledge of
the notices on these questions published by von Haidinger in
the Proceedings of the Vienna Academy (vol. xl. p. 380, vol.
xlvi. sect. 2. pp. 283-298). M. Meunier, quoting the Nou-
velles Archives du Muséum, vol. ii. p. 1, 1867, says, further,
(p. 29), ‘‘ Generally the crust is not uniformly spread over the
whole surface of the meteorites, showing seams and wrinkles, the
form of which in certain cases may indicate the position kept by
the meteorite during its flight through the air. These circum-
stances have been duly noticed by M. Daubrée in his remarks on
the Meteorite of Orgueil.”” The late Director Schreibers, in a
book published in 1820, and von Haidinger, in several papers
published in the Vienna Academy’s Proceedings (vol. xi. p. 525,
and vol. xlv. p. 791), had, long before Professor Daubrée, de-

* Abstract of a memoir read before the Imperial Academy of Vienna,
Oct. 8, 1868, for which we are indebted to Count Marschall, For. Corr. G.S.

Chevalier W. von Haidinger on the Fall of Meteorites. 247

scribed, figured, and discussed these “‘ seams and wrinkles” as

they appear on the crust of the meteorites of Stannern (Moravia,
1808).

3. Professor A. Daubrée has greatly added to our knowledge
of meteorites, both by enlarging the collection of the Muséum
d’ Histoire Naturelle (somewhat neglected in this respect pre-
viously *), and by his theoretical investigations on this subject,
especially by experiments concerning the artificial production
of meteoroid substances. He has lately published his notices
on the meteoric fall of Orgueil (May 14, 1864), communicated
to the Paris Academy at eight meetings, between May 16 and
November 14, 1864, together with notices on those of Tourinne-
la-Grosse (December 7, 1863), of Aumale in Algeria (August
25, 1865), of St. Mesmin (May 30, 1866), and of Setif in
Algeria (June 9, 1867). It must, however, be remarked that
the learned Professor of the Jardin des Plantes never men-
tions von Haidinger’s observations or views about meteorites,
except (p. 8) where he quotes, verbo tenus, a passage concerning
the means of discerning the position of meteorites during their
course through cosmical space.

4. Comparison of theoretical views——Von Haidinger distin-
guishes two periods in the existence of any meteorite: (1) from
its primordial formation down to the completion of the body en-
tering the terrestrial atmosphere ; (2) from its entering into the
atmosphere down to its fall on the earth’s surface. This last
period, being the subject of direct observation, must be especially
treated here, although the former, still to be studied in many
respects, cannot be left entirely out of discussion.

5. A. Phenomena connected with meteorites.—No qualities of
matter or forces except those known at present can be admitted
in explaining these phenomena. As early as March 14, 1861,
von Haidinger distinguished the consecutive phases as fol-
lows :—

(1) A fragment pursuing its way meets the upper limit of the
terrestrial atmosphere.

(2) Its cosmical velocity meets a resistance, and, in conse-
quence, suffers diminution.

(3) Meantime pressure developes light and heat, the meteorite
rotates, and an enamelled crust forms on its surface.

(4) The heated stratum of air agglomerates to an “ igneous
globe ” behind the meteor.

(5) The meteor having reached the term of its cosmic course
- becomes stationary.

(6) The development of light and heat ceases; the surround-

* On December 15, 1863, the Museum specimens numbered 86 from dif-
ferent localities ; on March 31, 1868, the number had increased to 203.

a

248 Chevalier W. von Haidinger on the Luminous, Thermal,

ing air suddenly rushing into the vacuum — the igneous
globe causes a detonation.

(7) A compensation of temperature takes place between the
cold internal nucleus and the external surface.

(8) The meteorite, now subject to the laws of gravitation,
falls on the surface, its temperature standing in direct proportion
to the thermo-conductive power of its substance.

Ad i. A fragment in its course meets the upper limit of the
terrestrial atmosphere.—The existence of but one single frag~
ment detached from a larger body is supposed, in order to
simplify the reasoning. Two or more fragments moving in the
same direction under the impulse of the same force, either
in Immediate contact or with a greater or less distance be-
tween them, may as well be supposed to enter at once the ter-
restrial atmosphere. Professor Daubrée expresses a different
opinion, saying (p. 16), ‘* Nothing entitles us to admit, as it has
been asserted, that the different meteorites of the same fall tra-
verse cosmical space separated from each other and, as it were,
in swarms;” and (p. 14), “So in general the bolides leave
us parts of their substance in three different ways: (1) by
combustion, vaporization, or gasification; (2) by bemg dis-
persed into ‘dust, the fall of which generally escapes observation,
and which may be analogous to the dust gathered after certain
meteoric falls; (3) by dispersion of the fragments detached at
the moment of the explosion.” Further, ‘‘ The proceedings are
such as if the greatest portion of the meteoric mass would pass
from the atmosphere to continue its cosmical course, leaving be-
hind only some particles whose velocity has been lessened in
consequence of the explosion.” Professor Daubrée admits still
another supposition, saying (p. 10), ‘There is no proof that,
besides this sudden exhalation, these small planetary bodies are
not endowed with an atmosphere of their own, which indeed
they absorb soon after their entrance into our atmosphere.
These gaseous substances, whatever may be their origin, may, by
their combustion, increase the splendour of the meteor ; how-
ever, as they Suid burn away in continuity, they leave unex-
plained the fact of the explosion preceding any fall of meteo-
rites.’ If Professor Daubrée, having entered into the most mi-
nute distinctions and called in to aid several very objectionable
suppositions, concludes with acknowledging the want of satis-
factory explanations for the explosions, it must not be wondered
at that M. St. Meunier speaks of their cause as “ absolutely un-
known.” In fact, an “explosion” exists not, and therefore
neither admits nor wants explanation. The term itself is im-
proper; and if instead of it the term “ detonation” is used (as
it ought to be), an inaccurate presupposition is eliminated and

and Acoustic Phenomana attending the Fall of Meteorites. 249

explanation made easier. The first proposition may be expressed
more precisely thus: A fragment (or a group of fragments) in tts
course meets the limits of the terrestrial atmosphere.

Ad 2. The cosmical velocity of the fragments meets resistance,
and consequently is diminished—This proposition is certainly
not subject to any objection.

Ad 8. Together with the diminution of velocity, the compres-
sion of the air developes light and heat, the meteorite takes a rota-
tory movement, and an enamelled crust forms on its surface.

Ad 4. The heated stratum of awr, due to the pressure of the me-
teorite deprived of its cosmical velocity, is pushed forward in pro-
portion to the initial force of movement, and agglomerates behind it
in an “ igneous globe.”

a. Luminous Phenomena.—The ideal diagrams (figs. 1 and 2)
may assist in the explanation of these phenomena. Pressure pro-
duces a centre of expansion in front of the meteorite. The com-

Fig. 1.

D
pressed air is forced out of it radially in every direction. The re-
sistance remains equal against this luminous disk; only at some
distance in the direction of the line of course it overcomes the lu-
minous and incandescent stratum of air, pressing it at last behind
the course of the meteorite. Movement is transmuted into light
and heat—a proposition frequently enunciated of late years, and

250 Chevalier W. von Haidinger on the Luminous, Thermal,

perfectly applicable to the process here in question. The cele-.
brated Professor G.V. Schiaparelli announces it im these terms:
“While the meteoric substance is dispersed through the atmo-
sphere, this vis viva, being transformed into heat and light, is |
entirely destroyed.” This explanation is rejected by Professor
Daubrée, who says (p. 8), “The recent investigations as to the
mechanical production of heat have induced some to suppose the
heat of meteorites to be the consequence of their loss of vis viva.
This supposition is in contradiction to the carbonaceous meteo-
rites, which, instead of being hot as far as their centre, as they
ought to be according to this supposition, include substances
liable to be altered or dispersed by a slight increase of tempera-
ture.” He has not, however, considered this transformation as
proceeding not suddenly, but by degrees, in proportion to the at-
mospheric resistance, and only on the surface where the air is
in contact with the meteoric nucleus. He supposes likewise the
meteorites to come cold out of cosmical space on account of their
composition being easily destructible by heat, although he does
not mention the extremely low temperature which must be sup-
posed to exist in cosmical space. The learned Professor, when
ascribing (p. 9) the thermal phenomena observed in meteorites
to the development of electricity provoked by violent friction, is
rather commenting on than contradicting von Haidinger’s views.
It may be a question what idea is to be conceived of the
dispersion of a swarm of meteors, different in size, without de-
tonation and at the moment of quietly entering the atmosphere.
Director Julius Schmidt has witnessed this phenomenon at
Athens, October 18, 1863, and sketched it in the diagram, fig. 3
(reproduced from memory; part of the luminous tail spreading

Fig. 3.

—— ae) West

Athens, Oct. 18, 1863, 14 h. 55 m. Course of the meteor E. to W.

eastward behind the meteor is left out for want of space). The
atmospheric resistance acts more powerfully on bodies of compa-
ratively greater surface, while the larger and heavier ones move
forward. The most minute particles remain behind in form of
a tail. The telescope has dissolvca into a group what seemed to
be a single meteor; itis as possible that bodies nearly approach-
ing each other, and even wrapped up in the same meteoric enve-
lope, may proceed in common. The ideal sketch, fig. 4, may

and Acoustic Phenomena attending the Fall of Meteorites. 251

illustrate such a supposition. The largest fragment possesses,
of course, the greatest amount of momentum ; although pressed
backward it still leads in the van, the smaller ones being likewise

Fig. 4.

pressed backwards. Those next to the larger ones cannot totally
remain behind, as the larger leading fragments have determined
the elements of the igneous globe by producing a centre of elas-
ticity (C) before it. All of them (HE, F, G, H) must move for-
ward within the anterior portion of the igneous globe, each single
fragment in rotation on its own axis and around the axis of
the line of course, and thus probably frequently come into mu-
tual contact, by which their enamelled crust is damaged, as at
Kuyahynia, where nearly all the specimens collected were found
more or less damaged. Of course the smaller fragments will
_ follow the largest mass—although instances of several groups fol-
lowing each other have been frequently observed.

Ad 5. The meteor, having reached the term of its cosmical
course, becomes stationary.

Ad 6. The development of light and heat ceases ; the surround-
ing air, suddenly rushing into the vacuum within the igneous globe,
causes a detonation.

The igneous globe becomes stationary the moment the action
of the vis viva of the movement has reached its term. At the
same moment its equivalent has occurred to our senses. We
have perceived the last seconds of the movement, together with
the great display of ight and heat into which it has been trans-
muted. Electricity has not been mentioned, as its presence has
not yet been ascertamed by direct observation, although its
action may be supposed. Lightning itselfis but “a transmuta-
tion of electricity into light ;” and the late Professor Pliicker,

252 Chevalier W.“von Haidinger on the Luminous, Thermal,

certainly an authority in physical questions, expressly asserts,
with reference to the phenomena in Geissler’s tubes, that “ there
is no electrical light in the abstract sense of the term,” and that
“the particles of the gaseous substances become incandescent.” |

At the moment when the cosmical velocity, as well as light
and heat, is exhausted, the tension of the vacuum within the
igneous globe, entirely depending on this velocity, comes to an
end, and the meteor obeys only the law of gravitation, causing it
to fall on the earth’s surface.

b. Acoustic Phenomena.—The sudden irruption of the sur-
rounding atmosphere into the vacuum of the igneous globe
causes a violent sound, in the same way as when gunpowder
explodes, or whenever longitudinal oscillations take place. One
or more detonations are heard, sometimes at intervals, the last
one being the most intense. If previously masses, or groups
of meteoric swarms, have separated from each other, repeated
detonations may be expected. At all events these phenomena
still require repeated and close observation before general con-
clusions can be founded on them. As we have seen above, Pro-
fessor Daubrée (p. 16) declared it impossible for him to give a
sufficient explanation of the detonations, and acknowledged the
special difficulty offered by successive detonations, suggesting the
idea of successive discharges and “recharges” of what he terms
the “appareil explosif.”” It is, indeed, impossible to explain a
phenomenon having no real existence; the subject of explana-
tion can only be the “ detonations” connected with the fall of
meteorites that have reached the terrestrial atmosphere, the
term of their cosmical career. |

Ad 7. Compensation of temperature takes place between the
internal nucleus and the external surface.

Without doubt the meteorites, before reaching the terrestrial
atmosphere, take their course through a space of intensely cold
atmosphere*. Professor Daubrée (p. 8) explams by this cir-
cumstance how the meteorites of Orgueil, containing substances
easily alterable by heat, could reach the terrestrial surface with-
out alteration of their chemical constitution. The incandescence
of the enamelled crust during its formation is likewise not to be
doubted. The efficient cause of this high temperature ceases as
soon as the meteorite has become stationary. During its sub-
sequent fall to the surface time is left for a compensation between
the melting temperature of its crust and the intense cold of
its nucleus; and generally fallen meteorites are warm, but not
incandescent. Some meteoric irons (as at Caritas Paso in Cor-
rientes, 1844) have been found incandescent in their interior—
an apparent exception, to be explained by the high thermal con-

* Von Haidinger in Vienna Acad. Proc. vol. xxxiv. p. 11, January 7, 1859.

and Acoustic Phenomena attending the Fall of Meteorites. 253

ductive power of iron. In the report on the meteoric fall of
Dhurmsala (India) some fragments are said to have been “in-
tensely cold.” Conceivable as this fact may be, meteorites
having undergone the intense cold of cosmical space before their
arrival in the earth’s atmosphere, it is a new proof with what
caution facts must be ascertained and asserted by future obser-
vers: in the first, superficial reports on the fall of Knyahynia
in Hungary (July 9; 1866), the meteorites were said to have
been as cold as ice; further inquiries elicited that the few speci-
mens collected immediately after the fall had been of no higher
temperature than any other stones exposed to the sun for some
time would be.

Ad 8. The meteorite, now subject to the law of gravitation,
falls on the surface, its temperature being in direct proportion to
the thermo-conductive power of its substance——This proposition,
being a necessary corollary of proposition 7, requires no special
discussion.

The enamelled crust of meteorites offers some peculiarities,
among which one is important enough to deserve special notice.

c. Seams of enamelled crust.—These seams are eminently
conspicuous on the meteorites of Orgueil and of Stannern.
Von Haidinger* admits that any meteoric fragment of some-
what regular figure, having entered the limit of the terres-
trial atmosphere, persists in one and the same direction, de-

termined by its figure, during the period whilst its enamelled —

crust is forming, and that the differences shown by this crust
depend on the position of the surface-planes of the meteorite—
the anterior plane being surrounded by a characteristic seam
of enamelled crust, distinguishing it from the lateral and
posterior planes. Professor Daubrée acknowledges also two
forms of crust, which, as he says (p. 6), may serve to indicate
the direction of the meteorite’s course ; but he submits (p. 7) that
“the meteorites showing both varieties of crust have undergone
two successive superficial fusions during their atmospheric course
—at first a general one of the whole substance, perhaps connected
with the heat attending the explosion, then a greater degree of
fusion on the portion pressing before it the air with an intensity
proportional to the enormous velocity of movement.” He sup-
poses evidently an explosion to be the first cause of the forma-
tion of a crust; while von Haidinger thinks the detonation indi-
ceative of the final moment, when the meteorite, with its crust com-
pletely formed, becoming stationary, and the emission of light
having ceased, falls to the surface of the earth just as any other

* Acad. Vienna Proc. vol. xl. pp. 525-536, April 19, 1860, and vol.
xliv. (2) pp. 790-795, May 16, 1862.

254 Chevalier W. von Haidinger on the Luminous, Thermal,

heavy body. M. Daubrée (p. 7) observes that ‘the air thus
pressed away acts as a flame from a blowpipe on the anterior
portion of each splinter,”’ thus giving to understand that he con-
siders the meteorite in question to be rather a fragment detached
from a larger body than an individual object. Two consecutive
formations of crust are hardly admissible within the brief period
of some few seconds. ‘The meteorites of more or less discoid
form have given rise to a remarkable difference of opinions. Von
Haidinger* concluded, from the position of the seams of ena-
melled crust on a discoidal fragment from Stannern, that the
broadest plane rotating around the axis of movement must have
necessarily been opposite to the resisting atmosphere. A por-
tion of the wis viva of rectilineal movement is changed into
rotatory movement in consequence of atmospheric resistance ;
and rotation may be increased so far as to produce disruption, as
in the meteoric falls of Quenggouk in Pegu, December 27, 1857,
according to Dr. T. Oldham’s report +, and of Knyahynia, where
the largest fragment had been dug out of a depth of 11 feet,
evidently in a state of disruption. The large meteorite of Or-
gueil, figured by Professor Daubrée (plate 1. figs. 1 & 1 bis), is
also characteristically discoidal, and is commented upon by the
author (p. 9) in the following terms :—“ This splinter, resem-
bling a thick shell detached from a curved surface, instead of
traversing the air in the direction of its breadth, as a flat stone
thrust with violence would have done, has pursued its course
with its large surface turned forward .... the fragment has
been projected at the moment of the explosion with a celerity
too great to allow it to change its initial position for one offering
less resistance.’ These views may be applied to a heavy body
(such as a stone) intentionally thrust by a thinking being, but
not to a mass of inorganic substance acted on by a vis viva pro-
pelling it at the rate of four geographical miles per second until
it is superseded by atmospheric resistance. The position with
the broad surface forward is a necessary one. The supposition
of a determined “explosion” (at least in the proper sense of the
term) rests on insufficient ground. Professor Daubrée puts
the question (p. 13) “whether a portion of the bolide’s mass
leaves the atmosphere after the explosion ”—a question to be
affirmed with some probability, according to his views, as he says
(p. 15), “ Consequently matters proceed as if the greater portion
of the meteoric mass left the atmosphere to continue its cos-
mical course, leaving behind only some few particles whose ve-
locity had been diminished in consequence of the explosion.” This
supposition is not applicable to the totality of the meteoric phe-

* Vienna Academy Meeting, May 15, 1862.
+ Vienna Acad. Proc. vol. xliv. p. 637.

and Acoustic Phenomena attending the Fall of Meteorites. 255

nomena hitherto observed. The fall of Knyahynia, July 9, 1866,
may serve for an example. The meteor approached the terres-
trial surface with only 6° zenithal distance, in a direction N. 76°
30/ E. to 8. 76° 30’ W. It iscertainly not to be supposed that,
subsequently to the explosion, a portion of the meteor would
have left the atmosphere under the same angle; nor is such a
supposition admissible in the fall of Orgueil, as described by
Professor Daubrée. The following data are taken from his
communications to the Academy of Paris*: fig. 5 is the plan

Fig. 5.
19° \Ferroast

Kilometres.
a0 6 40 20 309 40 SO 60 7O 80 ¢0 i6a
Lisl 1 I { 1 | ! l { ]

19° Ferro Last

of the region within which the phenomenon was observed. M.
Laussedat’s report to Professor Daubrée gives the important
fact that the meteor was seen falling down “vertically” at Ichoux
(Département des Landes). The line BC in fig. 5 represents con-
sequently the projection of the meteor’s course on the surface of
the earth. M. Lajous’s report to M. Petit, dated from Rieumes
(Haute Garonne), supplies the following data :—Beginning, azi-
muthN. 24° W., altitude 22°; final term, azimuth N. 20°H.,alti-
tude 164°; and hence we have, in fig.6, AB=29-49 kiloms. (8-973
German geographical or 17°81 English miles), CD =17-77 kiloms.
(2°394 geogr. or 11:24 English miles). Light first appeared at an
altitude of 29°49 kiloms. (3°973 geogr. or 17°18 English miles) ;
and the phenomenon ended above Orgueil and Nohic at an altitude
of 17°77 kiloms. (2°394 geogr. or 11°24 English miles). The fall

* May 30, 1864, Comptes Rendus Acad. Se. vol. lviii.

256 Chevalier W. von Haidinger on the Luminous, Thermal,

of the meteor in a distance of 58 kiloms. (7:815 geogr. or 36°68
English miles) amounted to 11°72 kiloms. (1:579 geogr. or 9-332
English miles). The obliquity of the course towards the surface
is therefore =11° 26’, and the zenithal distance of the fall =
78° 34!. The meteorites of Orgueil, their cosmical velocity
having been annihilated by atmospheric resistance, fell down as
any other heavy body would have done. Had they pursued
their course to the last, they would have touched the ground
about 90 kiloms. (12°12 geographical or 56°92 English miles)
further off, at all events still W. of Montpellier. Such a
course would be quite incon- Fig. 6.

celvable if supposed to have
been pursued by the greater
portion of the meteorite’s nu-
cleus, after the extinction of
the light concomitant with
the transmutation of the vis
viva of movement. M. Bagel
remarked that after extinc-
tion of the brightest light the meteor seemed to pursue its way
for a brief time, emitting a feeble reddish hght: this may indeed
have taken place during the brief moment in which the in-
candescent crust fell to red-hot temperature. A bird or any
creature organized for flight and endowed with volition may
change the direction of its movement at its own choice ; but this
is not the case with an inorganic body.

6. B. Primordial formation of Meteorites.—It must be ad-
mitted as a fundamental principle that, from the first moment
of their existence, the material elements possessed no other
properties, and the vis viva acted according to no other laws,
than those which we know to exist at present. The first
consequence of creation (an act quite above human comprehen-
sion) must therefore have been aggregations of pulverulent sub-
stances spread about in the intensely cold cosmical space. The
successive phases of formation may be supposed thus :—

(1) Creation, matter i statu nascentt.

(2) Cosmic bodies in the state of aggregations of pulverulent
matter.

(3) Increase of temperature by pressure of the superficial
strata against the deeper ones, and by natural pressure of homo-
geneous and heterogeneous particles, the interior of the cosmical
body against its superficial crust *.

(4) Formation of a solid crust, the innermost space still pro-
gressing in solidification.

(5) Explosion of the cosmical body in consequence of the dif-

* Humboldt, Cosmos, vol. i. p. 209.

and Acoustic Phenomena attending the Fall of Meteorites. 257

ference of internal and external expansive tension ; the fragments
thrown out in every direction pursue their course through cos-
mical space.

The effective formation of the mass of meteorites falls entirely
within the third period; it can, however, only proceed very
gradually. At the moment of a destructive catastrophe many
substances, different in nature or in progress of evolution, may
coexist, all of them, however, impressed with a common cha-
racter. Soft or hard meteorites, non-crystalline and more or
less distinctly crystallized ones, bear the mark of more or less
advanced evolution; all of them, however, show a distinct
tufaceous structure and a breccia-like formation, the meteoric
iron, partly emineuitly crystalline, representing veins included in
a more solid matrix. Traces of gradual formation occur every-
where ; nor do the meteorites of Orgueil prove an exception to
this rule. Although composed of substances of rarer occurrence,
they show the general tufaceous type. Professor Daubrée says
(p. 3), “They [the common meteorites] seem indeed to have
been formed at once; it seems this was not the case with the
mass of which the Orgueil meteorites are fragments.” And,
speaking of the common meteorites, he says (p. 4), “ whose ge-
neral character is to be capable of being produced vid siccd
under the action of high temperature.” Certainly the experi-
ments of.the distinguished author concerning artificial produc-
tion of meteoroidal substances have thrown considerable light
on their mode of formation ; it must, however, be stated that
the more crystallized these bodies are, the more remote they
stand in the scale of evolution from the primordial pulverulent
condition of their substance. It cannot be doubted that the
varieties of meteorites, between dust and highly crystalline iron
and stone-like substances, indicate distinct terms of evolution,
the pulverulent agglomerates in the intensely cold cosmical space
bemg heated by progressing solidification and pressure to the
end of their existence as cosmical bodies. The simultaneous
presence of heterogeneous particles within a body of notable
dimensions may well be supposed*.

The lines, in the interior of meteorites, identical in com-
position with the enamelled crust, although of inferior forma-
tion, deserve some attention. Their formation probably coin-
cides with the consecutive and far advanced process of soli-
dification. As in telluric rocks, progressive evolution and mo-
bility of particles, even of solid substances, certainly takes
place in the interior of meteoric bodies, although not assisted
_ by the dissolving power of water. In places where pres-
sure and temperature come to their maximum, partial fusion

* See Vienna Acad. Proc. vol. xl. (1861) pp. 489-526.

Phil. Mag. 8. 4. Vol. 37. No. 249. April 1869. S

238 Chevalier W. von Haidinger on the Luminous, Thermal,

may begin, at first where the larger separate portions of the
whole are pressing on each other. Vein-like strata, occasionally
with sliding lamine of iron (the first beginning of iron-veins),
form. In ancther paper* Professor Daubrée insists again on
the possibility ofa meteoric body, after the fall of a comparatively —
minute portion of its substance, continuing its course from the
terrestrial atmosphere into cosmical space. ‘The altitude of the
Orgueil meteor at the moment it entered the atmosphere is said
(doe. cit.) to have been about 65 kiloms.; while according to the
geographical distance, communicated by M. Lajous and pub-
lished by Professor Daubrée (see above, p. 255), it cannot have ex-
ceeded 29°49 kiloms. Professor Daubrée says, further (p. 2),
that the fall of meteorites is immediately -preceded by their
‘nearly horizontal” course. In fact the inclination towards
the horizon was observed to be about 11° 26! for the meteorite
of Orgueil, 44° (according to Professor Galle) for that of Pul-
tusk, and 84° for that of Knyahynia (according to von Hai-
dinger).

7. The Professors of Casate—MM. Goiran, Zannetti, Ber-
tolio, and Musso, in their report on the fall of Villanova and
Motta dei Contit, admit, as an undoubted fact, the fall ‘of a
whole group” of meteorites (p. 83). Ina further passage { the
existence of a single body, broken into larger and smaller frag-
iments by “one or more explosions attended with a detonation,”
is asserted. This explosion is explaimed, without any iurther
proof, by admitting an “elevation of temperature, imparting to
the large proportion of gaseous substances included in these
bodies an amount of elastic power sufficient to produce an ex-
plosion” (p. 66). The authors$ admit the entrance of a
“eroup ”” of meteorites into the terrestrial atmosphere, as the
formation of a complete crust could not be accounted for by any
other supposition. :

8. M. Leymerie.—In a letter dated from Toulouse, June 10,
communicated by Professor Daubrée to the Academy of Paris in
the Meeting of May 30, 1864, M. Leymerie says, “ Allow me
to insist on the circumstance that all the separate pieces (ten in
number) which I had occasion to see offered a distinct form
and were wholly covered with ‘ vernice’ (enamelled crust). It is
evident to me that all these pieces, agglomerated closely to each
other, formed but one whole, a ‘swarm,’ to use M. Haidinger’s
term. ‘After the explosion they were separated and dispersed,
no fracture having taken place.”

* Nouvelies Archives du Muséum, tom. i. p. 1 (1866).

+ Bolletino dell’? Osservatorio Meteorol. di Moncalierz, vol. i. Nos. 3, 4,
6, and 8, Suppl. hk

t Now7yp. Go. § No. 8, Suppl. p. 90.

' cateoe= etc
er

and i... Phenomena attending the Fall of Meteorites. 239

_ 9. Professor J. G. Galle.-—This distinguished astronomer has
published a paper on the meteoric fall of Pultusk, January 30,
1868, in the Transactions of the Silesian Society for 1868.
The views of the celebrated Director of the Breslau Observatory
are, In many particulars, concordant with those of von Haidin-
ger, as he says (p. 28), “The mode of expression generally used,

by which the division of a meteor at the moment of extinction is
designated by the terms ‘ explosion’ or ‘ diffraction,’ 1s, for rea-
sous , subsequently to be discussed, improper and inadequate to
the real fact. We can only admit a dispersion of the meteoric par-
ticleswhich have arrwed as separate bodies at the puint of extinction.

This sappoagion alone admits an explanation of the acoustic
phenomena and of their peculiar series, beginning with one or

more chief detonations.” The meteorites of Pultuats fell near ly .

vertically from the point of dispersion. The inclination of their
cosmical course to the horizon was 44°. Compared with fig. 6,
the altitude of the entrance into the atmosphere A 8, the aiti-
tude at the term of the cosmical course C D (C being the point
of dispersion), the distance B D, the inclimation of the cosmical
course C A H, stand in the following proportion :—

AB. CD. BD. CAE.
Paltusk . . 40 54 25 44°
Orenciks: . 3 G/5 2394 7°815 14° 28

Geographical miles.

Professor Galle says about the origin of meteorites, “ What
may have been the origin of such a metvoritic swarm entering
the solar system with a velocity of one to two miles per second,
is a problem siill more difficult to solve than the origin of the
periodical swarms of falling stars, whose connexion with the
comets has been ascertained by Professor Schiaparelli’s brilliant
discovery, and which, on account of their nearly parabolical
orbit, may be considered to be cosmical clouds, endowed with a
small power of movement, and coming at some point or other
within the solar sphere of attraction.” And as to their velo-
city, “It is at least one or two miles per second less than the
average velocity of falling stars, as admitted by Professor Schia-
parelli ; the orbit - through the solar system is therefore an hy-
perbola.”

10. Dr. G. vom Rath has published a notice concerning the fall
of Pultusk, especially with regard to the chemical and mineralo-
gical constitution of the meteorites, of which he had occasion to
examine above 1200 single specimens, and to compare them
with those preserved in ‘the museums of Bonn and Berlin.
Fig. 1 a, 6, c of this notice reproduces the anterior surface of a
meteorite weighing 870 grms., on which the author (p. 4) com-

S 2

a

ere

260 Chevalier W. von Haidinger on the Luminous, Thermal,

ments thus: “ The anterior portion of our meteorite is charac-
terized beyond any doubt by the presence and the direction of the
seams of enamelled crust, by means of which the position of the
stone during its telluric course before its fall may be ascertained.” |
According to Dr. vom Rath (p. 6) the meteorites of Pultusk
cannot be considered to be the results of the diffraction of one
single cosmical body, but must rather be supposed to be a swarm
of larger or smaller planetary individuals that had come within the
sphere of terrestrial attraction and having most of them under-
gone diffraction, although the strongly flattened cosmical figure
could still be traced on some of them. As von Haidinger re-
marks, seams of enamelled crust could not be formed on meteo-
rites of quite irregular form, whose position necessarily changes
‘at every moment of their course. During its cosmical course
a swarm could remain in repose; but as soon as it enters the
terrestrial atmosphere, the individuals composing it, in collision
with each other, must undergo loss of substance. During the
continuation of the cosmical course through the atmosphere, the
conditions for incrustation constantly remained extant, and frag-
ments of secondary origin could be incrusted again. From
the moment of detonation the incrusted meteorites, having
reached their point of dispersion, fall down individually in more
or less vertical direction; they may thus damage each other,
but no new incrustations take place. Figs. 7a and 7 6 in Dr.
vom Rath’s paper (p. 9) deserve particular attention, represent-
ing a completely incrusted meteorite with an aggregation of
thirty to forty minute fragments which had evidently adhered
to it during its course when its velocity began to suffer diminu-
tion. An analogous circumstance has been observed by von
Haidinger on a meteorite from Stannern; it is, however, cha-
racteristic of those from Pultusk. Dr. vom Rath says, further,
(p. 27), “ The meteorites, not quite dissimilar to telluric rocks,
although for the most part so different from them, indicate con-
ditions of formation as they were never found united within the
known portion of the terrestrial crust ;” and (p. 12), “The ex-
planation of the surfaces clothed with metallic or sulphuretted iron
(metallische Harnische) presents great difficulties; at all events,
they are of cusmical origin, while the lines and surfaces of fusion
are of telluric origin.” This last assertion appears to von Hai-
dinger not to be quite unobjectionable. The enamelled crust,
formed during the course,.may, under peculiar circumstances,
penetrate here and there into the substance of the meteorite ; it
must, however, be admitted that the internal clefts and fissures,
partly filled up with a black enamel-like substance, have origi-
nated during the cosmical period of the mass, before its being
broken into pieces which immediately began their course through

and Acoustic Phenomena attending the Fall of Meteorites. 251

cosmical space. A specimen from Pultusk in the Imperial Mu-
seum of Vienna shows, in a breadth of about 2 inches, seven
planes of separation filled up with enamel-like substance*. M.
von Fritsch has published a valuable notice of the chemical
constitution of the Pultusk meteorites in No. 5, pp. 92-94 of
the Proceedings of the Imperial Geological Institute for 1868.
11. Professor G. V. Schiaparelli—This illustrious astronomer
of Milan kas published (1867) ‘‘ Notes and Reflections on the
Astronomical Theory of Fallmg Stars” in the Memorie di Ma-
tematica e Fisica della Societa Italiana delle Scienze, ser. 8,
vol. 1. part 1, p. 153. The author treats only collaterally of
the formation of meteorites and the phenomena connected with
their fall, his chief purpose being the development of his re-
markable discovery concerning the concordance of the course
ef meteoric currents with the orbits of some comets. This
subject, merely alluded to with great reserve by that noble pa-
triarch of science, Alex. von Humboldt, in his ‘Cosmos?’ (vol.1.
p- 142), could only be discussed by way of numerical com-
parison subsequent to the preparatory investigations of MM.
Leverrier and H. A. Newton. Professor Schiaparelli (p. 198)
admits the transmutation of the vzs viva into heat and light, and
alludes (p. 255) to the probability of the meteoric iron having
at first been gaseous, as the existence of crystals of olivme in
the interior of the “ Pallasian iron” could not be explained
by means of any other supposition. Alexander von Humboldtt
declares inadmissible, even in the regions of mere probability,
any unproved arbitrary opinion; and, indeed, those who have
specially studied the substances composing the solid crust of our
globe will explain the fact here in question rather by the mobi-
hty of the minutest particles of even solid substances in the
course of their successive development than by ascribing to matter
such proprieties as they are not known to possess at present.
12. Dr. E, Weiss begins his paper “‘ On Falling Stars” { with
the words, “It can no longer be doubted that the igneous phe-
nomena connected with falling stars owe their existence merely
to the resistance of the atmosphere.”” He assumes that every year
the earth gives to innumerable meteors a direction which takes
them out of the solar system into the region of the fixed stars.
The contrary process may likewise take place, as Professor Galle
(see above) has proved the meteoric swarm of Pultusk to have en-
tered the solar system with a velocity of at least one or two geogra-
phical miles per second. Dr. E. Weiss supposes the nuclei of the
fallmg-star meteors to be small, without determining their size ;

* See Vienna Acad. Proce. vol. lvii. sect. 2. p. 1, March 12, 1868.
+ Cosmos, vol. 1. p. 137.
t Vienna Acad. Proe. vol. lv. sect. 2, pp. 281-342, January 19, 1868.

262 Chevalier W. von Haidinger on the Luminous, Thermal,

but, indeed, applied to cosmical bodies, the conception of magni-
Fane will always be relative. He concludes, further, from the
more intense emission of light in higher atmospherical strata, that
such meteors have a greater amount of velocity than those appear- .
ing with less splendour in the lower regions of the atmosphere.
Director Julius Schmidt came to the same conclusion from his
observations of the meteors in the course of 1851*. These
observations induced Haidinger+ to suppose a connexion between
the accelerated formation of the luminous envelope in the pro- —
gress of motion and the tenuity of particles of agglomerations
of cosmical pulverulent substance, in conformity with the views
expressed in Mr. A. 8. Herschel’s letter on the nature of pla-
netary corpuscles, addressed to Abbé Moignot. Dr. E.Weiss has
still some doubts about the explanations of the prevalence of fall-
ing stars or of meteors, according as the meteoric bodies and the
tcrrestrial globe are moving in the same or in opposite directions.

13. Messrs. R. P. Greg and A. 8S. Herschel published in 1867
an ‘ Atlas of Charts of the Meteor-tracks contained in the Bri-
tish-Association Catalogue of Observations of Luminous Meteors,
extending over the years 1845 to 1866.2 This Atlas compre-
hends twenty-two celestial charts of Bede (three for January,
August, and September, two for February, April, October, and
November, and one for each of the five other months), on which
are entered the dates of the phenomena, the limits of their
duration, the position of the points of radiation, their denomi-
nation as proposed- by MM. Heis and Greg, and their peculiar
characters with regard to all general and special meteoric cur-
rents hitherto observed in the northern hemisphere. An appen-
dix contains a synoptic ‘Table of the pomts of radiation in the
northern hemisphere from January 1 to June 30, and from
July 1 to December 31, and another, for each day of the year,
of the radiations of fifty-one epochs of meteoric currents, as de-
termined by Professor Heis. A paper published in the ‘ Scien-
tific Review,’ London, June 1, 1868, has added twelve new points
of radiation of meteoric currents to the sixty points already
known. Mr. Greg has undertaken the laborious task of redu-
cing above one thousand new observations made by M. Jezioli at
Bergamo. An enormous amount of observations is also trea-
sured and systematically arranged in Messrs. J. Glaisher, R. P.
Greg, E. W. Brayley, and A. 8. Herschel’s ‘‘ Reports of Observa-
tions of Luminous Meteors,” addressed to the British Association
for the Advancement of Science§. Mr. A. Herschel’s spectrum-

* See Vienna Acad. Proc. vol. xxxvu. pp. 803-820.

t Vienna Acad. Proc. vol. xlix. sect. 2, pp. 6-61, January 8, 1864.
+ See Les Mondes, 1° annee, tom. ii. liv. 14, Nevember 5 1863.

§ See Report of Brit. Assoc. 1866 & 1867.

and Acoustic Phenomena attending the Fall of Meteorites. 203

observations of several meteors, and his discovery of the spectrum-
hne of scdiwm as distinct as in the spectrum from a gas-flame of
a Bunsen’s burner or of a monochromatic flame richly fed with
common salt, together with his observations on the forms and
modifications of the luminons remains of meteors, deserve special
attention, as they seem to confirm the supposition of a gaseous
envelope forming around the progressing nucleus. Mr. Her-
schel says*, “‘ Hach new acquisition of knowledge, however un-
foreseen may be its origin, tends to support the theory of Chladm,
and to confirm the belief that shower-meteors and shooting-
stars are actually aérolites of small dimensions. In whatever
manner aérolites and shooting-stars are related to each other in
their astronomical and other peculiarities, they will evidently
Tequire a vast number of future experiments to unfold their real
source.” ‘The meteor telescopically observed by Mr. H. Christ
at Basle, June 11, 1867, 8.30 to 9 p.m., and pursued in its
further course, N.W. to 8.., by Professor H. Hagenbach-Bischof
at Basle and by M. de Fonvielle at Paris, excited likewise a great
deal of interest.

14. Professor J. J. Omalius d’ Halloy, 1 in the eighth edition of
his Précis élémentaire de Géologie, has devoted a special chapter
to meteorites and the phenoniena attending their apparition,
in which he briefly expounds von Haidinger’s views on the
subject. He says (p. 118), “As to the light manifested by
bolides in their course through the atmosphere, and the vitrifi-
cation undergone by their crust, M. Haidinger explains both
‘these circumstances by the de evelopment of heat and light re-
sulting from the compression of the air m consequence of the
rapidity of the meteors: falling towards the terrestrial surface ;
and he aseribes the detonations attending their fall to the irrup-
tion of the ambient air rushing into the vacuum left by the
passage of the bolide—that is, of the solid body and the portion
of compressed air around it.”

15. Conclusion.—The facts at present ascertained, together with
the conclusions derived from them, allow us to distinguish four
consecutive periods in the existence of meteorites: (1) primor-
dial formation; (2) progressive movement through cosmical
space ; (3) fall to the terrestrial surface ; (4) the fallen substances
themselves now become subjects of scientific investigation. They
are at once subjects of investigation and meditation for the mine-
ralogist,the chemist, the physicist, the meteorologist, the geologist,
the geographer, and the astronomer. The English translation
of von Haidinger’s “‘ Considerations on the Phenomena attend-
ing the Fall of Meteorites on the Earth,” read before the Im-
perial Academy of Vienna, March 14, 1861, was: published

* Report to the Brit. Assoc. 1866, p. 146.

264 Prof. How on the Mineralogy of Nova Scotia.

in the November and December Numbers of the Philosophical’
Magazine for 1861. Other notices by. the same author were
communicated and commented upon by Mr. R. P. Greg at the
Manchester Meeting of the British Association. Meantime the
Imperial Museum had received specimens of the Tula iron from
Dr. Auerbach, and a rich collection of East-Indian meteorites]
through Dr. Thomas Oldham’s kind intervention ; and Messrs.
Laurence Smith, B. V. Marsh, H. A. Newton, Baron Reichen-
bach, and others had published their theoretical views on me- ff
teorites. Dr. Buchner had lectured on the same subject at the
thirty-sixth Meeting of German Naturalists at Spire, 1861.9
Another paper by von Haidinger had been communicated to the fj
Academy of Paris by M. Ele de Beaumont*. The collections §
of meteorites have been greatly augmented since then. The Mu-
seum of Munich numbers (March 1, 1868) twenty-two localities
of iron or of lithoid meteorites; the University Museum of Got-
tingen (July 1, 1868) 176 localities, 99 of lithoid meteorites, 77
of meteoric iron; the Museum of the Geological Survey of India
in Calcutta (December 1867) 254 localities, 159 of lithoid me-
teorites, 95 of meteoric iron.

XXXKV. Contributions to the Mineralogy of Nova Scotia. By
Professor How, D.C.L., University of King’s College, Wind-
sor, N.S.

[Continued from vol. xxxv. p. 41.]

IV. Lignite—Semibituminous Coal—Cannel Coal —Turgite—
Delessite—Fahlunite—Silicoborocalcite.

IGNITE.—In the eastern part of the province there are
found in the carboniferous districts, but apart from the

beds of coal, sulphides of metals associated with coaly matter
having the characters of lignite. The sulphides are relatively
large in quantity, and frequently consist of iron and copper py-
rites, with a very rich sulphide of copper, apparently vitreous,
though called grey. The enclosing rock of such specimens of
these copper ores as I have seen is sandstone, and it is generally
more or less impregnated with green carbonate. In one instance
galena occurs with iron pyrites in a conglomerate of limestone
and siliceous pebbles. The masses composed of the carbonaceous
and metallic minerals generally exhibit the form of branches and
trunks of trees; and Dr. Dawson points out + that those con-
taining copper result from the action of vegetable matter on
waters containing sulphate of the metal. The formation of

* See Comptes Rendus, vol. li. (1861) pp. 456-461.
+ Acadian Geology, p. 327.

Prof. How on the Mineralogy of Nova Scotia. 265

galena would involve some secondary action. The deposits are
not thought to be of mining-importance, except in two instances,
in which the ores of copper are considered to exist in promising
quantities: in one of these, indeed, lately discovered there is
said to be a bed some feet thick; a sample of the ore sent me
gave 29°5 per cent. metallic copper.

I have not been able to find more than one complete ultimate
analysis of a lignite; this is one of the fourteen analyses given
by Dana*. Ina minority only of the others is the existence of
nitrogen mentioned ; the quantity is given in no case but that re-
ferred to, the analysis of Vaux, who found 0°57 per cent. From
this result and the following ultimate analysis of a lignite from
one of the deposits above mentioned, for which I am indebted
to Professor Anderson of Glasgow, it appears that the quantity
of nitrogen is somewhat less in this mineral than in black coal.

The lignite selected for examination occurs in the carbonife-
rous district of Pictou county, with copper ore and common iron
pyrites. It is nearly black, and retains on some faces a fine-
grained woody structure, not very obvious to the naked eye, but
distinct under a glass: these surfaces are dull; those at right or
oblique angles are black, of almost resinous lustre, and without
structure: it is sectile, and easily broken into angular fragments
which receive polish under the burnisher. The mineral evidently
belongs to the variety of brown coal called jet. Boiled in potash,
it scarcely colours the fluid. Ignited, it gives a transient feeble
yellow flame, and afterwards glows for a considerable time, evol-
ving the greasy odour often observed with lignite; in a closed
tube the product is chiefly water with a little yellowish matter ;
the vapours have an alkaline reaction. Ultimate analysis gave :—

Garon et dy iat fcc no
Hivdrogen’ . }. 4. . 43
Nigroven. 45 so 1-0
Oxyecniteyy el) by LOd
Ash AE eae eT Ce

100-0

It does not appear that any inquiry has been made as to
whether lignites vary in composition according to their geolo-
gical age. As the circumstances under which they were formed
must have been analogous, the only differences to be expected at
the corresponding stages of conversion are those depending on
variations in the original material. Hence nothing like strict
comparison can be made; the following, however, is not without
interest. The large deposits of brown coal found in Germany

* Mineralogy, 5th edit. p. 758.

266 Prof. How on the Mineralogy of Nova Scotia.

are of tertiary age; and Liebig has shown* that there is a nota-
ble difference among these in chemical composition. The more
complete the obliteration of the woody structure, the greater the
departure from the relative proportions of the organic elements |
in the original material. ‘The wood-coal from Ringkuhl, near
Cassel, is seldom found with the structure of wood, and is there-
fore more comparable with the Pictou lignite than any in which
this is retained ; its composition is given as—

Carbon ~'.. . & sOe7ea

Mydrogen pee

Oxygen: . ..)'° 2 om

Ash. A ae ee

100-00
and the approximate formula (old notation)
(82 15 C9
is added as deduced from these numbers: for comparison’ sake I
have calculated a corresponding approximate formula from the
analysis of the Pictou lignite; it is
(32 H}2 O8.

Hence, as compared with wood, for which Liebig gives the
formula

C36 F122 Olt,
there is a further loss of one atom of water and two atoms of
hydrogen, marking the difference between the carboniferous and
the tertiary ignites in question.

As I have before pointed out}, the true ratio of carbon to
hydrogen, in such minerals as contain these elements together
with exygen, is only brought out after deducting the amount of
hydrogen equal to that of the latter element present. In the
case of the two lignites just spoken of, the ratio stands thus :—

. Pictou. Ringkuhl.
Lomo deducting Lio0 5-77 100: 7-52

Ratio of C to H after deducting
He Opreent |... yp lOUe ei eamaniaaee 50

The effect of this deduction is obvious enough; at the same
time a very close accordance is exhibited in the ratio between the
remaining elements. How much this differs from that existing
in bituminous coals is seen by the following comparisons. While
numerous coals of the province have been submitted to prismatic

* Agricultural Chemistry, 4th American edit. p. 368 ef seq.
+ Mineralogy of Nova Scotia, p. 25.

ae
Te ee ae

Prof. How on the Mineralogy of Nova Scotia. 267

Per Pee

analysis*, one only has had its ultimate composition determined,

that, namely, found at Springhill, Cumberland county. All the

true coals of the province are bituminous, and they would, no ;
doubt, give results comparable with those from the Springhill ,
coal below and the bituminous coals now selected as represen-

tatives from among those analyzed by myself during the British

Admiralty Coal-Inquiryt.

| Percentages.

hydrogen.
Bituminous coals. OS

Ratio of carbon to |

Authority. |
Car- |
bon.

Hydro-| Oxy- | By ana- | On deduct-
gen. | gen. lysis. | ing H=O.

Nova- ete eo. 72-00 | 5:02 7-26 100: 6:97 100 : 5-72 { Woodhouse

Scotian. | Cum). co. & Jeffcozke
Duffryn ...... 88:26| 4:66 | 0:60 |100: 5:28) 100:5:18 | HI. How.
Welsh. | Newsd nie | 84-71! 5:76 | 3:52 1100:6°79| 100:6-28 | __,,
Ebbw Vale ...| 89°78; 5:15 | 0:39 |100:5-73) 100:5°67 | __,,
Scotch, [ Gtangemouth.| 79°85 5:28 | 8:58 '100:6 61) 100:5-27 5
Ree || Fordels........ 79°58| 5°50 | 838 |100:6-93 100:5:73 | __,,
aay peed Hill ...] 81-70, 6:17 | 4:37 |100:7-55| 100:6-88 | __,,
eemLydney '...... 73°52, 5°69 | 648 |100:7:73, 100:6-63 | __,,

|

Semibituminous Coal.—On the line of railway between Truro
and Pictou, about twenty miles from the former town, a curious
“vein” is found between slaty walls, consisting of black lustrous
mineral formed into a sort of network by the intersection of nu-
merous cross veins of fibrous ferriferous carbonate of lime, the
whole being two or three inches thick. The black mineral looks
something like graphite,is rather hard, H.=2-5, and very brittle;
ignited, it gives a luminous white flame, exfoliates, smells strongly
of sulphurous acid, and burns with some difficulty to a reddish
ash. In a closed tube it does not melt, scarcely changes its
form, gives but a small quantity of smoke and oil; the fumes are
very acid. For the carbon- and hydrogen-determinations which
follow I am indebted to Professor Anderson. Ultimate analysis
gave i—

DAGON hoy vs hws) Gu kes 4), 4 | BOLO
I ATOLEM, er. 1 64) sities Pane gs vst 4°99
Sulphur, nitrogen, and oxygen . 4°70
PMS steed, i siige punt hr spall AOS

100-00

Proximate analysis afforded me :—

Volatile matters . . . 10°90
Residue, or “coke” . . 89:10

———

100-00

* Loc. cit. p. 33, and Dawson’s ‘ Acadian Geology.’
+ First Parhamentary Report by Delabeche and Playfair.

268 Prof. How on the Mineralogy of Nova Scotia.

The residue, or “ coke,”’ consisted of a powder unchanged in ap-
pearance from that put into the crucible. |

The foregoing results indicate a semibituminous coal: the
mineral differs widely from the bedded coals of the province,
which, as before mentioned, are bituminous; some, indeed, are
so in rather a high degree. The mode of occurrence of this coal
(the only one I have met with here approaching anthracite) is
curious, and worth further investigation.

Cannel Coal.—A specimen “ from an 18-inch seam at Little
Glace Bay, Cape Breton,” had the appearance of cannel coal,
gave a brown powder and a brownish-black streak, burned alone
when well heated in a flame. in a closed tube gave much volatile
matter, and left a rounded swollen coke. Proximate analysis
gave me :—

Moisture ois: | ise 2 ee
Volatile combustible matter . 30°07
Fixed carbon...) «ss See
Ashi Asn %- ow) Oe es

100:00

The amount of ash here, though considerable, is smaller than
that in the well-known Scotch cannel from Capeldrae, which
gives, according to Fyfe, 25°40 per cent. The volatile combus-
tible matter is evidently high enough, in proportion to the fixed
carbon, to mark the class of minerals to which the specimen be-
longs. This is the first example of Nova Scotian cannel coal yet
examined, unless, as would be right according to some authorities,
now perhaps diminishing in number, the remarkably rich oil-coal
which I have called stellarite * is made to belong tothe class.

Turgite—This well-defined species may be recorded among
the minerals of iron met with in the province. It occurs with
brown hematite at Terry Cope, and at another locality, probably
in the same county of Hants, according to my own examination
of specimens sent me, and it will doubtless be found frequently
elsewhere in the same association. Both the specimens in ques-
tion afforded red powder, gave water on ignition, and decrepitated
violently in the forceps before the blowpipe. The mineral from
the last-mentioned locality was mixed with siliceous and calca-
reous matters; when these were deducted, the constituents of
the air-dried substance were :—

Wiatet. sues). | oe enn
Peroxide of tron -. . . Q4A9

100-00
The formula of turgite, 2 Fe? 0?+HO, requires 5:32 per
* Mineralogy of Nova Scotia, p. 24.

Prof. How on the Mineralogy of Nova Scotia. 269

cent. water ; hence there can be no doubt as to the nature of the
species.

Delessite ?—-There are frequently seen in the amygdaloidal
traps of the western part of the province masses of a soft, dark
green, chlorite-like mineral ; or perhaps there are more species
than one having these characters, sometimes filling rock-cavities
more or less completely, and occasionally coating or partly com-
posing zeolites, as, for example, analcime, which in different loea-
lities has its colour thus made to vary through all shades to dark
green. At one place, Two Islands, in the Basin of Minas, I
observed, several years ago, large crystals of this species lying
loose in a cavity of the trap above high-water mark, like speci-
mens on the shelf of a cabinet. I could not get as many of
these as I wished, nor examine the nature of the cavity, on account
of the rapidly rising tide. Some of the crystals were colourless ;
one was most curiously composed: nearly half of the upper por-
tion consisted of white partly transparent analcime ; the rest,
including the whole base, was almost entirely made up of a soft
dark-green mineral like chlorite. The crystal had the form of
analcime ; it was about an inch and a quarter in diameter. I
made no analysis of the green mineral in this case; but I examined
a specimen of similar soft, green, greasy-looking mineral from
cavities of trap on the Bay of Fundy. It was very dark in colour,
opaque to the naked eye, translucent under the microscope, very
soft, fusible on the edges to a black glassy bead before the blow-
pipe. It dissolved partially in slightly warmed hydrochloric
acid, to which it gave both protoxide and peroxide of iron in
large quantity. Water was lost on ignition and was so estimated ;
the amount obtained in this way, however, would be rather below
the truth, owimg to the absorption of oxygen by the protoxide
of iron. Alkalies were not sought for. Analysis of the air-
dried mineral gave :—

SICARAR SAMMrt) eta) Gd? AOS
Metalhiepron, 2 co). 1250
Ala an er sl O95
Hhimaes FN Ge adh tae GROW
Macniesias jira 4 wi iat 4 del
Ganener adalat ictaieee tp 287.
Water (byignition) . . 13:10
Oxygen andloss . . . 9°38

100-00

These results appear to place the mineral between Delessite
and epichlorite, which have the following composition* :—

* Dana’s ‘ Mineralogy,’ 5th edit. pp. 493, 497.

270 Prof. How on the Mineralogy of Nova Scotia.

Epichlorite. Delessite from Mielen.

Silica Ee ate Wee Mee REO ROS 31:07
Alpmina (3. eis.) 2% .« LO2Sm 15°47
Peroxide of iron . 8:72 17°54
Protoxide of iron . 8:96 4°07
Marnesia (i. <oO00 19°14
Wianies .,: Gicede ae OOS 0°46
Water ion oe Sets SLOULS 11:55

160°38 99°30

As epichlorite occurs in veins in serpentine, and Delessite is
found coating and filling the cavities of amygdaloid, the mineral
now described is probably the latter, perhaps mixed with some
free silica.

Fahlunite-—On the road between Windsor and Chester gra-
nite is found, at some point not mentioned to me, containing
crystals which present the characters of chlorophyllite, or one of
the varieties of Fahlunite. They are many- (perhaps 12-)sided
prisms, sometimes half an inch across, greenish brown and dull
externally ; the distinct basal cleavage shows faces of a grey
colour and vitreous lustre ; weathered surfaces of this kind have
the appearance of mica; hardness of the fresh faces about 3;
streak grey andearthy. The mineral fuses before the blowpipe
on the edges to a black slag, yields a little water on ignition,
gives abundance of protoxide of iron to cold hydrochloric acid
on standing for some time, and a very small quantity of peroxide ;
by fusion with alkaline carbonate its other constituents are found
to be silica, alumina, manganese, a trace of lime, and a little
magnesia. | made no quantitative analysis; but it is evident the
mineral belongs to the species Fahlunite, which results from the
alteration of iolite*.

Silicoborocalcite in a new locality.—It is an interesting fact
that this new mineral, which was first described in the last part
of these “‘ Contributions’’+, and which Dana has since called
Howhitet, has recently been found in gypsum in a new locality
some thirty or forty miles N.E. of Brookville near Windsor,
whence it was first obtained. The quantity is said to be by no
means inconsiderable ; and as I have shown§ that the mineral
will probably admit of a special application, just as it occurs, in
enamelling iron, it may prove to be a valuable addition to the
already large and varied mineral resources of the province. The
specimen by which I identified the species recently found was in

* Dana’s ‘ Mineralogy,’ 5th edit. p. 484.
+ Phil. Mag. Jan. 1868.

~ Mineralogy, Sth edit. p. 598.

§ Mineralogy of Nova Scotia, p. 141.

Dr. Paalzow on the Galvanic Resistance of Liquids. 271

the powdery form described in the paper referred to above. The
mineral is reported to be most abundant in a “ black band” of
gypsum, and to be met with in nodules which are sometimes
very much larger than any seen by myself near Windsor ; a good
deal is said to have been thrown away by the quarrymen as being
of no value compared with the plaster; this is worth about 90
cents a ton, shipped, while the borate would probably realize
nearly as many dollars, or, roughly, be a hundred times as
valuable. It was mentioned in the paper already twice alluded

to, that, from what I had observed, the lowest beds of gypsum -

would probably afford the largest quantity of this mineral and
its fellow borate: the new locality, as I understand, is one of
those where the lowest members of the carboniferous series con-
taining beds of gypsum are found.

XXXVI. On the Galvanic Resistance of Liquids.
By Dr. Paauzow%.

HE first trustworthy values for the galvanic resistance of a
liquid (that of sulphate of zinc) are contained in a paper
by Beetzt+. The paper also contains the reasons for placing no
confidence in previous statements obtained by other methods.
It is only by the combination of zinc with sulphate of zinc, which
Beetz made use of, that it is possible to avoid polarization and
other changes of the electrodes as well as of the adjacent elec-
trolytes.

I proposed to determine the resistance of other liquids as well
as of sulphate of zinc, retaining, however, unpolarizable elec-
trodes and their advantages.

In order more clearly to detect a possible influence of the
chemical nature of the hquid on the resistance, I made the solu-
tions of the acids and salts under investigation in chemical equi-
valents ; for it may be reasonably supposed that such an influ-
ence exists, as the conduction of electricity in liquids is always
accompanied by chemical decomposition.

I then also examined the resistances of mixtures of saline
and acid solutions in water with equal equivalents of water, in
order to decide whether the current divides in accordance with
Ohm’s law.

In order, moreover, to ascertain whether there is with elec-
trolytes, as with metals, a connexion between the conduction for
heat and for electricity, | imvestigated the conducting-powers
for heat of certain liquids whose galvanic resistances were known.

* Translated from the Berlm Monatsbericht, July 1868.
+ Poggendortff’s Annalen, vol. cxvu. p. 1.

Sh ee
= 2h aera

272 ~=Dr. Paalzow on the Galvanic Resistance of Liquids. -

The fundamental idea which regulated the construction of the
apparatus was the following. In order to limit a defined quan-
tity of the liquid investigated, a siphon tube had to be filled
with it, and this connected with the electrodes and the conduct-
ing liquids, so that the values for the resistance of the liquid in
the siphon tube were as great as possible in comparison with
the resistance of the conducting liquids and the inequality and
polarization of the electrodes. But to exclude these latter un-
avoidable magnitudes in each individual experiment, a second
siphon tube had to be connected with the electrodes in the same
manner, the dimensions of this second tube being either consi-
derably greater or smaller than those of the first tube. The re-
sistance of the liquid alone could be determined from the differ-
ence of the two numerical values, provided that in the time which
elapsed between two observations no alteration had occurred in
the electrodes or in the conducting liquids. The resistances had
to be referred to mercury as unit.

Two wide glass vessels were filled with a concentrated solu-
tion of sulphate of zinc, and as large electrodes as possible of
amalgamated zinc placedin them. Over these electrodes porous
cells were placed, which were connected by a siphon tube. Both
cells and siphon tube were filled with the liquid to be inves.
tigated.

The zine electrodes of the apparatus were connected with the
conducting-wire of one branch of a Wheatstone’s bridge, while
in the other bridge a normal resistance-coil of 0-1 to 50000
Siemens units was introduced. Such a proportion of this re-
sistance was introduced that the terminal of the wire of the
bridge was as near the middle as possible.

When the observation for the first siphon tube was ended,
the first siphon was replaced by a second, and, for control, fre-
quently by a third. Beginning with the largest, the second was
filled with the liquid contained in the first, the third with that
in the second; so that almost exactly the same quantity of
liquid was retained. After inserting suitable resistances, the
numbers were read off on the measuring-line.

By preliminary experiments the resistance of the mercury was
measured which filled the siphon tubes, and the difference of
the mercurial resistances of every two tubes calculated once
for all.

In order then to obtain the resistance of the liquid referred
to mercury as a unit, the difference of the resistance of the
liquid had only to be divided by the difference of the mercury-
resistance of every two siphon tubes. With three siphon
tubes, therefore, the three possible quotients must give the
same numbers. But even with two siphon tubes a simple control

Dr. Paalzow on the Galvanic Resistance of Liquids. 273

was possible ; for, from the difference of the liquid resistances, by
the aid of the mercurial resistances the entire resistances of the
liquids in the siphon tubes could be calculated without the
accessory magnitudes. Deducting these resistances from the
observed values, the difference represented the magnitude which
was due to the resistance of the conducting vessels and the in-
equality and polarization of the electrodes. In one and the same
experiment this magnitude must be the same for all the siphon
tubes used.

By this method I have investigated aqueous solutions of
sulphuric acid, sulphates of zinc, copper, and magnesium, and
hydrochloric acid. J am indebted to Dr. Rudorff for the che-
mically pure solutions of known strength. The observations
were made at the temperature of the rcom.

Sulphuric Acid.
Temperature. Resistance as compared
with mercury.
H? SO¢ 15 C. 96950
H’*SO*+ 14H?0O 19 14157 | ye:
H*SO*+ 13H?0 22 13510) iain
H*SO*+499H?O- 22 184773

Sulphate of Zinc.

Zn SO*+ 38H?0 236: 194400
Zn SO*+ 24H’?O 23 191000 | yy.
Zn SO*+107 H’ O 23 354000,

Sulphate of Copper.

202410
339341

22 C.
22

CuSO*+ 45H? O
CuSO*+105 H? O

Sulphate of Magnesium.

MegSO‘+ 34820 22 C. 199180

MgSO‘+ 107 H? O 29 324600
Hydrochloric Acid.

HCl+ 15H?0 23 C. 13626

HC1+500H? 0 23 86679

Although I have examined the acids and salts in question
Phil. Mag. S. 4. Vol. 37. No. 249. April 1869. i

74 Dr. Paalzow on the Galvanic Resistance of Liquids. -

mixed with many other proportions of water (in which I have
had the kind aid of M. Patry of Geneva), I only give the present
numbers, as I intend to repeat and extend the observations at
constant temperatures. |
In reference to the resistance of the mixture of two liquids,

assuming that the liquids do not act chemically upon one another,
we may either expect the arithmetical mean, or, if the current
traverses both liquids separately and therefore divides between
them, we may have

2K

eae
m

W=

where W is the resistance of the mixture, R the resistance of one
liquid, m a number which expresses how much greater is the
resistance of the second liquid over that of the first, assuming
that equal volumes have been taken of both liquids. If, as for
example in the case of sulphuric acid and water, m is very large,
the resistance of the mixture can at most be double the resist-
ance of the best conductor.

The experiments agree with neither supposition. I mixed, of
the liquids to be investigated, first those which were dissolved in
equal equivalents of water, and obtained the following results :—

Resistance haa 2R

of the | Arithmeti-; ~— 1 | Observed.
individual | cal mean. ae

liquids.

Zn SO*+50H?O 232600 |
CuSO*+50H20 | 213932 | 228216 | 222840 | 193920

ZnSO*+50H?O | 232600
H?SO!-+50 H2O 95775 | 129187 46300 64800

CuSO!+50H? O 213832
H? SO#+.50H?2O 25775 119803 45900 63460

Zn SO*+ 23H? O 194400 if
CuSO!+55 H? O 995254 209827 208700 192430

ZnSO*+ 23H?O;} 194400

The numbers, which might have been somewhat (but not
much) different if they had been observed at constant tempera-
tures, show that the resistance of mixtures of two liquids is
nearer that of the best conductor.

With reference to the connexion between the conduction of

On the Fundamental Principles of Molecular Physics. 275 |

electricity and heat, experiments which I shall detail m another
place show that it does not exist. I investigated mercury, water,
sulphuric acid (specific gravity 1:25), concentrated solutions of
chloride of sodium, sulphates of zinc and of copper. I find the
following series, in which the better conductor precedes :—

Conduction for heat. Conduction for electricity.
Mercury. Mercury.
Water. Sulphuric acid.
Sulphate of copper. Solution of chloride of sodium.
Sulphuric acid. Sulphate of zinc.
Sulphate of zinc. Sulphate of copper.

Solution of chloride of sodium. | Water.

XXXVII. Fundamental Principles of Molecular Physics.
By Professor J. Bayma, S. J., of Stonyhurst College.

[Continued from p. 188.]
EF.
NG prepared his ground for the defence and for the

attack, Professor Norton comes to my objections against
his third and fourth principles, which the reader will find in the
Philosophical Magazine (February 1869, p. 99).

Three forms of matter.—I had asked: On what evidence are we
to grant that matter exists in three forms essentially different
from each other? The learned Professor gives two answers.
The first is that such forms of matter are admitted even by me,
though in different words. And to prove this, he remarks that
I, in my ‘ Molecular Mechanics,’ admit these three things :—
(1) the nucleus of a molecule, (2) the envelope of the nucleus,
(3) the universal ether: and from this he infers that the differ-
ence of doctrine between us, from the present point of view, is
in name only. I am sorry to say that the difference lies not in
the name only, but in the thing also.

According to my doctrine, the matter of which the nuclei (I
say nuclei, not nucleus; for there are many in each molecule) are
made is exactly of the same form as the matter of which the
envelope is composed and the matter which is to be found in
luminiferous ether. For in the doctrine of simple elements,
which I have advocated, the matter in each element is a single
unextended point: and unextended points cannot differ in form.
_ If however Professor Norton in his notion of matter implies
the force also (which I doubt, as he in his first principle speaks
of matter and force as of distinct things), then the form of matter
would be its principle of activity, which is the formal constituent
of material substance. In this case [ am ready to allow that

£2

276 ~ Prof. J. Bayma on the Fundamental

there are two forms or kinds of matter, attractive and repulsive.
But this can hardly be his meaning: as he distinguishes kind
from form, and says the kinds are two, whilst he maintains that
the forms are three.

Lastly we might understand the word form as meaning the
result of a kind of composition. But if we accept this meaning,
the forms of matter cease to be three, and they become as many
as there are primitive compounds in nature. And thus the as-
sumption of three forms of matter can find no explanation in my
doctrine, whatever the meaning we attach to the word form.

This shows well enough how much Professor Norton is mis-
taken when he says that I “ proved to my own satisfaction that
matter does in fact exist in three essentially different forms.”
I had said indeed that luminiferous ether is “a special sub-
stance,”’ in the same sense as I say that oxygen and carbon are
special substances, but I never said nor implied that zther was
“a distinct form of matter ;” I rather taught the contrary by
stating (Molecular Mechanics, p. 174) that ether, though a spe-
cial substance, was not “a new specific matter.”

Professor Norton’s second answer runs as follows:

“« But to reply to others who may be disposed to adopt the objec-
tion urged. No one will deny the existence of gross or ponderable
matter, or of something which has all the mechanical attributes of
matter. ‘That an ether exists in space and within transparent media
we may certainly regard as abundantly established by optical pheno-
mena. As to electric ether, the evidence of its existence is that the
great body of electric and magnetic phenomena, it is generally con-
ceded, admit of satisfactory explanation on the hypothesis of an
electric fluid or ether intimately associated with matter, and that no
successful attempt has yet been made to account for the simplest of
these phenomena on any other hypothesis.”

I beg leave to say that this answer is not to the point. The
assertion to be proved was “that matter exists im three forms
essentially different.” Now, in the whole passage the word form
is not even to be found: and that which has no place in the pre-
misses, cannot find place in the conclusion.

It is not my intention to deny that there is something in
nature which corresponds to what Professor Norton calls “ gross
matter :” yet I believe that the name of gross matter is calcu-
lated to engender misconceptions with regard to a subject about
which men are already too much biased by the common preju-
dices of infancy. Gross matter! What is it? It is said to be
that which possesses “all the mechanical attributes of matter.”
I will not say the contrary: but I may remark that material
substance as such has no other mechanical attributes besides
activity, passivity, and inertia: and these are to be found in ether

Principles of Molecular Physics. 277

also. Why then should we make a distinction between gross
matter and ether, as if the matter of the one had attributes not
shared by the matter of the other?

The author will say that Ads “ gross matter” has other mecha-
nical attributes besides the three mentioned. True: but I main-
tain that these other attributes are not attributes of matter itself
as such, but of a mechanical compound of material parts. [for it
is only on account of its mechanical composition that the so-called
“oross matter” possesses different properties in different sub-
stances—it being evident that it is a difference either in the
number and nature of the components or in the mode of their
composition that entails a difference in the constitution, atomic
weight, and other properties of molecules. On the contrary, if
gross matter were only one form of primitive matter, how could it
possibly have different attributes in different substances ? Gross
watter, according to Professor Norton, is attractive: and yet
possesses all the mechanical attributes of matter, and therefore
impenetrability, viz. reactivity against pressure; an attribute
which implies repulsive powers. Now, the learned Professor
acknowledges that attractive matter and repulsive matter are two
kinds of matter. He must therefore acknowledge that gross
matter is not a primitive form of matter, but a compound of
primitive elements, some attractive, and others repulsive. This
remark would seem sufficient to expose the fallacy of Professor
Norton’s argument. He calls “gross matter”? that which is
not a primitive unit, but a number of material units: and then
concludes that such gross matter having special properties must
be “‘an essentially different form of matter.” We might as well
say: Let a company of men be called “gross man ;” then, as
such a gross man has some attributes which are not predicable
of each individual, let us conclude that “ gross man” is an essen-
tially different form of man.

Something remains to be said about the two ethers, the elec-
tric and the luminiferous, which are, according to the author,
two other distinct forms of matter. The learned Professor him-
self remarks that “some physicists are striving to do away with
the supposed electric fluid.” This fact, which is perfectly true,
would tend to prove that the existence of electric ether asa spe-
cial form of matter is not yet “an established truth.” But Pro-
fessor Norton adds :

**Qur author implies in the remarks above quoted that the exist-
ence of an electric zther is not only not an established truth, but is
to be ranked among those questionable notions that have been re-
ceived without serious examination. This implication is obviously
unjust. Besides, the serious examination that he has given the sub-
ject only leads him to confirm the substantial truth of what he would

278 Prof. J. Bayma on the Fundamental

here seem to discredit; for, as we have already seen, his repulsive
envelope is essentially my electric atmosphere.”

My preceding remarks about the three forms of matter make
any further answer unnecessary. I may, however, add (1) that
my repulsive envelope is a most essential part of the molecule,
no less indeed than the nuclei: it therefore essentially belongs,
according to my views, to what Professor Norton calls “ gross
matter’? or ponderable matter. Then, how could the learned
Professor find it to be essentially “his electric ether,” which, as
he maintains, must be another form of matter essentially dif-
ferent? (2) That my argument was not directed against the ex-
istence of some agency on which electric phenomena must depend:
such an agency every one is compelled to admit. The point in
question was whether the explanation of phenomena required
the existence of a special form of matter essentially different from
that of gross matter and of luminiferous ether. It is the asser-
tion alone of the existence of such a special form that I implied
to be not only not an established truth, but a very questionable
assertion. It may he that the assertion was made by Professor
Norton after ‘ serious examination :” yet from what I have stated
it would appear that his examination might have been more
serious.

I conclude this point by repeating the question which had to
be answered: On what evidence are we to grant that matter ex-
ists in three forms essentially different from each other? Has
Professor Norton given such evidence? The reader will decide.

Two ethers—My next question was: Why should we admit
two ethereal fluids which are both repulsive, and only differ in
subtlety ? He answers thus:

*« Professor Bayma and myself agree in admitting the existence of
two kinds of matter, attractive and repulsive ; and, as we have seen,
three forms of matter. Is it inherently any less probable that two of
these should be repulsive and one attractive, than, as he assumes,
that two should be attractive and one repulsive ?”’

I think I have already made it sufficiently clear that I do not
agree with him about the existence of his three forms of matter.
I therefore cannot be bound to admit either that two forms are
attractive and one repulsive, or that two forms are repulsive
and one attractive. He on the contrary who teaches the exist-
ence of three forms of matter and pronounces it to be “an esta-
blished truth,” must be competent to enlighten us as to the
grounds on which that truth has been established. In like
manner, when the learned Professor tells us that there are two
ethereal fluids both repulsive, and we ask: Why two, since one
might suffice? we should be thankful to obtain a clear and posi-

Principles of Molecular Physics. 279

tive answer from him. Unluckily he did not give one: at least,
I look in vain for it. In its stead he gives some short com-
ments upon the differences which I admit to subsist between
what he wrongly calls my “two attractive forms of matter,” and
especially upon my opinion on the density of luminiferous ether.
Yet the point at issue was not whether I have succeeded or not
in establishing the great density of luminiferous zther, but how
it can be proved that two ethers both repulsive must be ad-
mitted in nature.

He then says:

“T might also reply to Professor Bayma by asking him why we
should admit, in order to explain electric and optical phenomena,
two substances so distinct as the repulsive envelope of molecules and
the attractive luminiferous ether. The evidence of their similarity is
much greater than of their dissimilarity.”

Why should we admit them? The answer is plain. We
should admit the “repulsive envelope,” because we have proved
its existence as an essential part of the molecule (Molecular Me-
chanics, p. 147): and we should admit an “ attractive luminife-
rous ether,” because we have also proved its existence by the
consideration of natural facts (Ibid. pp. 176-180). Had Pro-
fessor Norton done the same with regard to his three forms of
matter, I should never have thought of putting him the ques-
tion Why should we admit them?

From this answer the author will perceive that it 1s not pre-
cisely or solely in order to explain electric and optical phenomena,
but in order to account for all other phenomena, that the repul-
sive envelope of molecules and the attractive luminiferous ether
are to be admitted. The repulsive envelope however does not
deserve the name of a special substance; for it has not an inde-
peudent and complete constitution of its own, and belongs as a
constituent part to the molecule of which it is the envelope.

As to the evidence of its similarity to luminiferous ether,
where is it ?

‘The learned Professor concludes his answer by these words:

«The only apparent force in the question under consideration is
derived from the fact that a vague conjecture is apt to be raised by

it, that a single ether may be equal to all the duty now assigned to
both.”

Be it as he wills. Yet even a vague conjecture would have
no little weight against an assertion which, as we have shown, is
itself at the best only another vague conjecture.

What Professor Norton adds immediately after has no need of
special reply. He says that my molecular envelope ‘is com-
posed of electric matter,” and that the universal ether condensed,

280 Prof. J. Bayma on the Fundamental

as he believes, around each molecule, is “ the medium in which
pulses are originated that constitute the force of heat repulsion.”
These views, which in the present controversy have only a se-
condary importance, I will not now discuss, as much remains to |
be said upon points of greater moment.

A molecule-—One of my remarks about Professor Norton’s.
theory was that “‘ Had Professor Norton known the impossibility
of continuous matter, he would have found out that what he
calls an atom of gross matter comprises already not only the
central element of a molecule, but its nuclei and its envelope; -
and consequently is already endued with the properties and in-
vested with the arrangements which enable it to exert forces of
attraction and repulsion upon other molecules, without requiring
any new and special atmosphere of electric or luminiferous
ether.” To this he answers:

‘* That is, in other words, as already shown, Professor Bayma’s
nucleus and envelope are in all outward relations precisely corre-
spondent to my central atom and electric atmosphere. The only
essential point of difference between us lies in the fact that I con-
ceive that the interstitial luminiferous ether is condensed around the
central atom, and is concerned in the production of some of the phe-
nomena. It is not easy to see how Professor Bayma escapes the
conclusion thut his interstitial ether, which is attracted by the cen-
tral nucleus, is condensed around it.”

Here the learned Professor intends to show that his theory is
in a manner implied in mine, and mine in his, the only difference
between us being a difference of words. I heartily wish that
such may be the case, as I should deem myself highly honoured
by concurring in the views of a man whom I regard as a good
authority in science. Unfortunately our present question is not
so much one of physics as of philosophy ; our different manner
of speaking proceeds in fact from a wide difference of principles.
Professor Norton endeavours to attenuate such differences as far
as he can: yet they cannot disappear; they remain a sufficient
obstacle to our mutual agreement. He speaks of my molecular
“nucleus” in the singular, whilst I always speak of molecular
nuclei” in the plural; the “ nucleus” is for him “ gross mat-
ter” ora special form of matter essentially different from that of
his electric ether, whilst my “nuclei”? are not a special form of
matter essentially different from that of the molecular envelope :
his “ nucleus” is one piece of continuous matter, my “nuclei”
are systems of discrete material points: his “nucleus” is all
attractive, my “nuclei” are some attractive and others repulsive,
as it appears from the molecular formulas which I give passam
in my ‘ Molecular Mechanics.’ Now these differences are too
substantia! and too radical to be passed over in silence. On the

Principles of Molecular Physics. 281

contrary, should we differ only in the question whether or net
luminiferous ether is condensed around a central atom (or rather
around the nuclei) the difference would be comparatively unim-
portant, asit would bear simply on a point of detail.

Accordingly, when Professor Norton states that this last point
is ‘the only essential point of difference between us,” I must
deny the truth of a statement which tends to shift the ground
of our discussion and to substitute a question of facts for a ques-
tion of principles. I have shown that the point touched upon
by the learned Professor is not the on/y point of difference: and
moreover I do not consider it an essential point in the present
controversy whether I can or cannot ‘‘ escape the conclusion that
my interstitial ether, which is attracted by the central nucleus,
is condensed around it.’? Ofcourse, I am confident that I can
escape the conclusion ; for I have never admitted the existence of
any interstitial ether between the nuclei and the envelope of a
molecule. But to proceed.

I had expressed my opinion that the examples by which Pro-
fessor Norton illustrates his theory “do not imply the existence
of extended atoms or of two distinct zthereal substances.” To
this he answers thus:

“When he has shown this to be true of even the ordinary calorific
_ and electric phenomena, we will admit that his objection to a second
zethereal atmosphere interpenetrating the first may have some force.”

But this is nota sufficient reply. The onus probandi evidently -
rests with him who makes positive assertions, not with him who
asks for a proof of them. Now, it is Professor Norton that
started his theory by positively affirming that the existence of his
three forms of matter was an established truth. If then we hap-
pen to find nothing hke a sufficient ground for his affirmation,
it is not for us to prove that we have found no grounds; it is for
him to point them out.

He adds:

«‘He has given no hint of the general manner in which he sup-
poses electric phenomena to be evolved. Heat he conceives to ori-
ginate in the vibrations of the molecules of bodies ; but it can be
proved, almost to a demonstration, that heat cannot originate in this
manner.”

Electricity is a branch of science scarcely a century old, and
electric theories are as yet, as everyone knows, obscure and un-
certain. Such being the case, I did not think it convenient to
devote to conjectures more or less probable space in a book of so

positive a character as | intended my ‘Elements of Molecular
Mechanics’ to remain. Hence it is perfectly true that I gave
no hint of the evolution of electric phenomena. But the state-

282 Prof. J. Bayma on the Fundamental

ment that I conceive beat “to originate ” in the vibrations of the
molecules of bodies is not equally correct. I said indeed that
“the first cause of calorific motion is to be found in the very
constitution of molecules . . . . which are always subject to vibra-
tory motion”? (Molecular Mechanics, p. 264): but the first
cause is only one out of many, as nothing is called first without
reference to asecond. On the other hand, when speaking of
vibrativity, to which I trace the phenomena of heat, I state that
vibrativity, as a general property of bodies, implies the capability
of making vibrations determined “ by an extrinsic agent” (Ibid.
p. 171). In fact, I conceive heat ¢o consist, though not to origi-
nate, in certain vibrations of the molecules of bodies, and these
vibrations to depend first on the molecular constitution of bodies,
secondly on any extrinsic causality that is brought to bear on
their velocity and intensity. If Professor Norton proves ‘ almost
to a demonstration ”’ that this view is untenable, I shall be thank-
ful to learn in what his proof consists. Should he however, as
Iam afraid he will, argue from the supposed existence and work-
ing of universal ether between the molecules of bodies, I would
tell him beforehand that such a proof, besides other considerable
objections, might admit of a reply drawn from the well-known
law of calorific capacities.

Luminiferous ather.—One of my objections against Professor
Norton’s theory was that luminiferous zther, according to him,
was a repulsive and resisting medium, which I had shown to be
irreconcilable with astronomical facts. He answers:

‘‘The principal astronomical fact here referred to is that the
planets do not encounter any sensible resistance in their motion
through space. The evidence of an ethereal resistance afforded by
Encke’s comet, Professor Bayma strives to explain away without
success.”

I give to the reader the opportunity of judging for himself of
this point of our controversy, by transcribing the passage referred
to by the learned critic. ‘‘ How do we know that Encke’s comet
cannot possibly have suffered a change in its orbit, unless it
moves through a resisting medium? Have we any evidence, or
even any ground whatever for a probable conjecture, that there
is absolutely nothing in interplanetary spaces, except the medium
and those bodies which we have hitherto observed? To dis-
courage such a supposition it would suffice to mention Le Ver-
rier’s discovery. I do not say that we shall hereafter discover
any new celestial body by whose action to account for the modi-
fication of the orbit of Encke’s comet: there are perhaps thou-
sands of bodies in the solar system of which we have no notion,
and never shall have, on account of their being unobservable. I

Principles of Molecular Physics. 283

say only that with the scanty knowledge we have of the bodies
that move in heavenly spaces, and after the discovery of so many
new planets, the existence of which had never been suspected
before, it would be too rash on the part of a man of science to
pronounce that no other cause exists in the heavens to which we
can trace the change of Encke’s comet course, except a resisting
medium. The more so, since Encke’s comet shows a regular acce-
leration of its motion, instead of a retardation. Now acceleration
does not proclaim, but refute, the theory of a resisting medium ;
and therefore Encke’s comet and all the other celestial bodies with
one loud voice proclaim, and witness in fact, the absolute non-
existence of a resisting medium” (Molecular Mechanics, pp. 178,
179).

Professor Norton goes on arguing:

‘The fact that no sensible resistance is experienced by the pla-
nets does not necessarily imply, as he supposes, that the ether is not
repulsive. For, in the first place, if the molecules of the planetary
mass have the constitution I have attributed to them, the impinging
sether must take effect upon either the ethereal or the electric atmo-
spheres of the molecules, and so may be mostly expended in the ge-
neration of heat and electric currents. I have in fact undertaken to
show, in my paper on Molecular Physics, that the earth may derive
its magnetic condition and a certain portion of its heat from the
impact of the ether of space.”

In this argument the learned Professor assumes (1) that the
molecules of the planetary masses have the constitution which he
has attributed to them, and (2) that the impinging ether spends
the greatest part of its impetus in producing heat and electric
currents. The first of these assumptions has been examined
sufficiently, I believe, in the preceding pages. With regard to
the second (which apparently would not stand without the first)
I may add that, in my opinion, no possible production of heat
and electric currents affords a sufficient ground for assuming a
reduction of resistance and retardation. Impact is a mechanical
fact, the first, direct, immediate result of which is not a produc-
tion of heat or of electric currents, but simply a communication
of motion in a certain direction. Accordingly the impact of
ether on a planet primarily and directly tends to check its velo-
city of translation through space: and only inasmuch as the
effect of this effort cannot instantaneously be transmitted from
the surface of the planet, where it is exerted, to the remaining
molecules of the planetary mass, it gives rise to intermolecular
motion. In other words, the generation of heat or of electric
currents depends upon the actual diminution of the velocity of
translation as a previous condition, intermolecular motion being
the result of a preceding change in the mutual relation of mole-

284 Prof. J. Bayma on the Fundamental

cules, of a change by which the conditions of the molecular
equilibrium have been violated. Hence, before we speak of a
possible generation of heat and electric currents in the move-
ment of a planet through a resisting medium, we must admit -
the full efficiency of the impact in retarding the motion of the
molecules directly exposed to the resistance of the medium.
The generation of heat and electric currents may, or even must,
follow, according to the assumption: but that which follows can-
not entail the least decrease of intensity in the retardation which
precedes, and of which it is the result.
Professor Norton here employs a second argument. He says:

“‘ Again, if the action of gravity be not instantaneous, it will take
effect in a direction slightly inclined to the radius vector, and, in the
existing state of the planetary system, the tangential component
resulting from this inclination may be in equilibrium with the feeble
overplus of resistance from the ether.”

To this I answer (1) that, if luminiferous zether is supposed to
be repulsive, the study of the phenomena of light leaves no
room whatever for any hypothesis implying that such zther op-
poses a feeble resistance. This I have proved in my ‘ Molecular
Mechanics’ (pp. 176-180). As to the everplus, I have shown
just now that it would be the whole of the resistance. (2) That
the hypothesis concerning the successive propagation of the action
of gravity is utterly false, as I have fully shown in my work
(pp. 63-65), and has no other foundation than the confusion of
two things perfectly different, viz. action and motion, cause and
effect. (3) That, independently of the two preceding remarks,
and granting (only for the sake of the argument) that the said two
assumptions might be admitted, it would still be false that the
action of gravity “ will take a direction slightly inclined to the
radius vector’? and have ‘‘a tangential component.”” The case
of gravitation is not parallel to that of the aberration of light, as
Professor Norton’s argument seems to imply. Gravitation in-
vests continually the whole mass of the planet, and its resultant
passes through the centre of it: hence no tangential component
of gravitation is conceivable consistently with the received prin-
ciples of general mechanics.

The learned Professor, after the two arguments hitherto ex- —
amined, gives a third which consists of a retorsion of my diffi-.
culty against my own explanation :

‘« Besides, the supposed difficulty is not removed by substituting
an attractive for a repulsive ether. It is true that when a molecule
of the earth’s mass encounters an atom of the ether on the line of its
advance, it will, upon Professor Bayma’s idea, pass through it and
leave it behind; but he has failed to note the fact that, during the

Principles of Molecular Physics. 285

approach of the two, their relative velocity will be equal to the sum
of the velocity of the earth and that due to their mutual attraction,
and, during their separation, will be equal to the difference of the same
velocities, and hence that the atom of ether will continue to attract
the molecule during a longer interval of time while the two are se-
parating than while they are approaching. The molecule will there-
fore on the whole be retarded by the action of the atom. If the
attractive zther be ‘immensely denser than the atmospheric air,’
the resistance should certainly not be less than that of a subtile re-
pulsive ether.”

This argument has one great defect : it is based on a false alle-
gation. It is not “my idea,” nor has it ever been, that a mole-
cule of the earth’s mass ‘passes through the atom of ether and
leaves it behind. The earth in its path beats back and carries
before it the whole mass of ether upon which it impinges: and
the reason why it finds no resistance is not because it leaves the
zether behind, but because the ether itself is destitute of all re-
pulsive powers. ‘This is a sufficient answer to the learned Pro-
fessor’s objection. He will see that ‘‘ by still holding to my line
of argument” I cannot be compelled, as he believes, “ to abolish
the ether of space altogether.’

Electric ether.—I had proposed two other questions on the
fundamental principles of Professor Norton’s theory: the one
regarded the material continuity of gross matter, to which he
made a long reply, which I intend to examine in a future paper.
The other regarded the nature of his electric ether. I had
pointed out that this ether, being repulsive, could not attract
luminiferous ether; and yet the author seemed to hold this

contradiction.
He replies thus : .

‘« Professor Bayma has here entirely misunderstood me, and re-
presented what I threw out as a possible and perhaps probable con-
ception to be a fundamental principle of my theory.”

To this I have only to answer that I did not represent his con-
ception as a fundamental principle of his theory. I argued on
the contrary that this conception could not agree with the fun-
damental principles of his theory. A reference to my ‘ Molecular
Mechanics’ (p. 188) will convince the reader of the truth of my
statement. As for misunderstanding him, I regret the fact if
true: of course Professor Norton is better qualified than I to
explain his own meaning. He says:

The real fundamental principle was that the atoms of electric
ether repelled each other; and it was merely conjectured that this
‘repulsion might be due to atmospheres of luminiferous ether con-
densed around the electric atoms, instead of being a repulsive
action.”

286 On the Fundamental Principles of Molecular Physics.

Very well: but if the conjecture is “a possible and perhaps
probable conception,” the action of electric zther (prescinding
- from the surrounding luminiferous ether) is not yet proved to_
be repulsive. Then the electric ether itself, as distinct from
luminiferous ther, might be attractive. What then becomes
of the “ established truth” and of “ the real fundamental prin-
ciple” that the atoms of electric ether repel each other? Pro-
fessor Norton will say that the word “electric zther”’ includes
not only the atom, but also the atmosphere of luminiferous
eether condensed around it. But how then is electric ether one
special form of matter, since it implies two ?

All this I did not and do not yet understand: and such
being the case, I must confess that it was simply impossible for
me to guess at any other meaning that Professor Norton’s words
might consistently bear, except that which I ventured to ex-
press in my objection.

The learned Professor adds :

‘Tt is a little singular, in view of this distinct statement of the
manner in which the repulsion might result from a possible attrac-
tion, that our author should ask the question, ‘ Now, if the atoms of
electric ether are repulsive, how can they attract?’ and thereupon
intimate the existence of a discrepancy fatal to the theory.’’

Professor Norton will at any rate acknowledge that my ques-
tion will cease to be singular, if I modify it in the following
manner :—“ If electric ether is of itself possibly attractive, how
can we assume as an established truth and a fundamental prin-
ciple that the two ethers differ on/y in subtlety and are both re-
pulsive ?”

He concludes :

“Tt is, in fact, altogether immaterial whether the mutual repulsion
of electric atoms is indirect as conjectured or direct.”

I reply that the difference is very material in a theory which
teaches the existence of two repulsive forms of matter. For if
the electric atoms repel only indirectly, viz. by the help of an
atmosphere of luminiferous ether, such repulsion is due to lu-
miniferous zther alone. Accordingly the electric zther would
not be a second repulsive form of matter. This mference can-
not be regarded as immaterial by one who maintains the exist-
ence of two repulsive ethers differing only in subtlety as an es-
tablished truth.

To sumup. Ihave shown, I believe, that Professor Norton’s
attempt towards solving my objections has proved unsuccessful.
Accordingly, though he says in his concluding statement: “ It
has now been made sufficiently apparent that the objections
urged against my theory of Molecular Physics have no real

M. O. E. Meyer on the Heatiny of a Disk rotating 1n vacuo. 287

force, and that its fundamental principles have not been dis-
turbed,” I am sorry to think that I am still justified in main-
taining the contrary. I leave it to a man of his thoughtful
mind to weigh the reasons which compel me, however reluct-
antly, to differ from hin.

[To be continued. |

XXXVIII. Further Remarks on the Explanation of Stewart and
Tait’s Haperiments on the Heating of a Disk rotating in vacuo.
By Oscar Emtt Meyer*.

wie reference to the paper ‘On the Explanation of

Stewart and Tait’s Experiments” contained in one of
the previous Numbers of the Philosophical Magazinet, the gen-
tlemen in question have published a reply | which I cannot leave
unanswered, although I should prefer doing so, for I fear it may
lead to a protracted controversy about trifles.

They consider “the assumption that a change of position of
the instantaneous axis of the disk necessarily implies loss of vis
viva”’ to be “ contrary to the usual principles of ordinary dyna-
mics.” I consider it to be an application, that was perhaps not
indicated clearly enough, of Carnot’s theorem, that every sud-
den change in motion is accompanied by loss of vis viva.

Messrs. Stewart and Tait think the calculations based on this
assumption “ very peculiar,” and a little further on they confess
“that they cannot pretend to understand them.” For this
reason they ask for an explanation of the manner in which vis
viva is transformed into heat. They ask especially whether I
“‘mean that impact of the axle on the bearings may produce vi-
brations of the disk which in time will by viscosity be frittered
down into heat.”

I have not expressed my opinion on this point, because I think
it to be quiteimmaterial. The principle of vires vive has the ad-
vantage of holding goud quite independently of any considera-
tion as to the mode of the transition. of vires vive out of one state
into another. It is.sufficient to know the amount of vis viva at
the commencement and at the end.

If mechanical force be transformed into heat either by means
of sonorous or non-sonorous vibrations, by compression, by elec-
tricity, by chemical combination, or by any means whatever, in
all these cases the law holds good, namely, that the heat gene-

* Communicated by the Author. |

t Pogg. Ann. Oct. 1868, vol. exxxv. p. 285. Phil. Mag. Jan. 1869,
vol. xxxvul. p. 26.

t Pogg. Ann. Jan. 1869, vol. exxxvi. p. 165. Phil. Mag. Feb. 1869,

vol. xxxvu. p. 97.

288 M.O.E. Meyer on the Heating of a Disk rotating in vacuo.

rated is equivalent to the loss of ws viva. The question, there-
fore, is without any bearing upon the present dispute.

Nevertheless I shall not keep back my opinion, as Messrs.
Stewart and Tait wish for it. In answer to the question put to
me I answer simply, yes. But I do not admit the following
statement to be correct :—“ he merely repeats one of many ob-
jections long ago perceived by ourselves, and also pointed out to
us by others, an objection which we have already at least partially
met by experiment and calculation.” No, not even partially;
because there is a difference between my objection and that of
Messrs. Stewart and Tait*. They refer to the 250 vibrations per
second, which correspond to the fundamental note of their disk.
The agitations and impacts I refer to correspond to 2 x 2500 vi-
brations in 30 seconds, or to 83 vibrations to and fro per second.
The corresponding note would be of a lower pitch than the fun-
damental one; and asit would consist simultaneously of longitu-
dinal and transversal vibrations, it cannot exist, and therefore
must appear as heat.

The reply of Messrs. Stewart and Tait contains only a single
positive argument against my explanation of the experiment.
Placing too implicit confidence in the accuracy of a figure ad-
joined to one of the paperst, I made a mistake as to the length
of the axis. This may invalidate my supposition that the vibra-
tions were produced by impacts of the axle upon the bearings.
But this supposition is not essential. What is essential to my
explanation is only the conception of impulses occurring periodi-
cally and twice during each revolution of the disk. The irregu-
larity in the rotation ‘of the disk can be explained just as well
by supposing that the axle hada slight bend, or that the pinion
attached to it was slightly excentric. Such irregularities produce
by impulses sudden changes in the speed of the rotation. Alter-
nately the velocity increases and decreases ; the excentric wheels
and pinions striking one another and then again being thrown
asunder. My assumption, therefore, of impulses occurring pe-
riodically backwards and forwards, remains intact, as also the
calculation ; and I maintain that my explanation, in spite of the
error mentioned, is still correct.

On the other hand I admit, without reserve, that my explana-
tion is not positively proved. Still it can be very easily verified,
for instance by repeating the observations with a different velo-
city of rotation. And as both gentlemen are about to make new
experiments with regard to the objections raised by Professor
Helmholtz, I would request them kindly to take into considera-

* Art. 20 of the third paper. Proc. Roy. Soc. vol. xv. p. 295. Phil.
Mag. S. 4. vol. xxxin. p. 230.
+ Proc. Roy. Soc. vol. xiv. p. 339. Phil. Mag. &. 4. vol. xxx. p. 314.

On the Falsetto or Head-sounds of the Human Voice. 289

tion my objection as well. Should the experimental test decide
against me, I will willingly retract my calculations, the more
so because they are only approximately correct. This may be
brought about either by the new experiments of Messrs. Stewart
and Tait, or by Sir Wiliam Thomson’s promised determination
of the radiation of heat in absolute measure. But so long as this
experimental test is wanting it would be idle to continue a dis-
pute about an unproved hypothesis.

Breslau, February 13, 1869.

XXXIX. On the Fulsetto or Head- Sounds of the Human Voice. By
Wiriiam Marcet, M.D., F.R.S., Assistant Physician to the
Hospital for Consumption and Diseases of the Chest, Brompton*.

HE consideration of the cause of the head-notes of the
human voice is of much interest, not only in a physiolo-
gical point of view, with the object of accounting for the produc-
tion of those wonderfully soft and penetrating sounds in which
Swiss and Tyrolese singers are so remarkably proficient, but also
for the purpose of explaining certain morbid changes of the hu-
man voice not unfrequently met with. Let me premise that, by
means of the laryngoscope (a small mirror so constructed as to
allow the observer to view the imside of the larynx and the action
of its various parts in the production of sound), the phenomenon
of phonation can be investigated with great minuteness. There
are, moreover, certain changes of form the larynx undergoes in
the act of phonation, and bearing on the subject of the present
communication, which can be determined by external observa-
tion, much in the same way as we can ascertain by looking and
feeling, that the windpipe is raised in the act of swallowing.

The vocal apparatus consists of two folds of the mucous mem-
brane of the larynx, supplied at their free edge with bands of
elastic tissue. These folds are opposite each other in a horizontal
plane, and in the antero-posterior axis of the larynx. Their lips
or free edges may be brought so close as to touch one another,
while at the same time they may be subjected to a certain degree
of tension; if under these circumstances air be blown out from
the lungs, these laryngeal folds or vocal cords will be made to vi-
brate, emitting a sound.

It is considered by J. Miller and others that the human chest-
sounds are owing to the whole breadth of the laryngeal mem-
branes entering into vibration, while the head-sounds are due
‘to the vibrations being confined to the margins or mere edges
of the membranes. Helmholtz thinks the head-sounds are caused

* Communicated by the Author.
Phil. Mag. 8. 4. Vol. 37. No. 249. April 1869. U

290 — Dr. W. Marcét on the Falsetto or

by the removal of the mucus which constantly moistens the rim
of the cords ; their edges thus become sharper and their weight
less, while, their elasticity remaining the same, they are shaken
into more rapid tremors* The observations I have had the op- §]
portunity of making appear to show that the head- or falsetto
sounds are really caused by the vibrations being confined to the
rim of the cords; and I have been able to determine with the
laryngoscope the conditions of the larynx which give rise to
these sounds.

When the larynx is examined with the laryngoscope during
the act of phonation, the vocal cords are seen to approach each
other throughout their whole length and parallel with each other,
till they appear in contact, or very nearly so. Any circumstance
which interferes with this mutual approximation of the cords, such
as weakness of certain of their muscles, as shown by Dr. Morell
Mackenzie, or swelling of some parts of the larynx, causes the
voice to become very weak or entirely suppressed ; and this is a
frequent source of aphonia. When the cords do not meet in
their entire length, either an anterior or posterior portion of one
of them remaining apart, a sound is produced, but instead of a
fair chest-note we have a falsetto or head-sound.

If a finger be applied to the throat, a depression will be felt
between the thyroid and cricoid cartilages ; now on singing the
notes of the scale, beginning with the lowest, this depression will
be felt to contract, on account of one of the cartilages ap-
proaching the other, until with the highest notes it has entirely
disappeared—this being due to the action of two of the laryngeal
muscles (the crico-thyroid), which tightens the cords, thereby
raising the sound of the notes. If, however, in imitation of
the Swiss and Tyrolese singers, a chest-note should be followed
by the same note sung in a falsetto tone, the space on which the
finger rests will be found to have undergone little or no con-
traction, notwithstanding the pitch of the head-sound being no
less than one octave higher.

My attention was drawn to the present subject by the remark-
able condition of the voice of one of my patients at the Con-
sumption-Hospital. He spoke in a sharp clear head-voice, which
consisted entirely of “harmonic” sounds. His larynx, of which
I obtained a good view with the laryngoscope, exhibited this very
peculiar appearance—that the left cord was bent at about the
middle, its anterior half coming in contact with the correspond-
ing half of the other, while the posterior half remained aside, so
that the vibrating-power of the blast from the chest was exclu-
sively exerted on the anterior halves of the cords. On applying
certain solutions to the cords with a camel-hair brush, I succeeded

* Tyndall, ‘ Lectures on Sound.’

Head-sounds of the Human Voice. 291

in bringing back immediately a fair chest-sound, the difference
being so remarkable that anybody in the next room could not
have believed the same person was speaking; an inspection of
the larynx now showed both cords to meet well throughout their
whole length. For some time, however, my patient did not re-
tain his chest-voice; so that I had several opportunities of con-
firming the correctness of this observation. I then lost sight of
him for some weeks, during which time his voice remained good ;
but he finally again applied to me, his speech having relapsed
into the falsetto sound. I now observed with the laryngoscope
that the anterior half of the left cord was at fault, a chink re-
maining visible between the anterior portions of the cords during
the act of phonation. On the application to the larynx of a so-
lution of iodine in olive-oil, the chest-voice was again brought
back, and both cords were seen to come into mutual contact
throughout their whole length. The cause of this relapse was due
to a swelling of the left side of the larynx (left false cord), extend-
ing to the true cord and interfering with its movements. I find
in Sir Duncan Gibbs’s book on diseases of the throat the ac-
count of two cases of what he calls double voice, apparently due
to a similar circumstance. In one of them the motion of the
left vocal cord was sluggish, slowly coming into action, approxi-
mation beginning more at its posterior third. In the other the
left vocal cord was narrowed and contracted near its attachment
to the arytenoid cartilage, and did not meet its fellow at that
situation during phonation.

A case of cracked voice, due toa state of swelling of the cords,
has also come under my notice; but the falsetto sound was not
so well marked as it had been in the other instance.

I now thought of inspecting the throat of a professional Ty-
rolese singer while singing falsetto or head-notes; and one
of the well-known Tyrolese artists now giving concerts at St.
James’s Hall, and possessed of the power of singing head-notes
ina high degree of perfection, kindly acceded to my request
to submit himself to a laryngoscopic examination. I had a
fair view of his larynx; but the irritability of his throat pre-
vented me from making so close an examination as I should
have liked. His vocal cords were beautifully developed, and the
action of his laryngeal muscles was full and rapid; he had some
little difficulty, as might have been expected, in singing with
the laryngeal mirror in the mouth; still he succeeded with

his head-notes. I could then see the cords considerably short- -

ened and applied tightly against each other throughout the
whole of their length; this was attended with a rapid play of
the laryngeal muscles.
How are we now to apply the facts reported in the present
U2

Ne a a eee

292 On the Falsetto or Head-sounds of the Human Voice.

communication to the explanation of the mode of formation of
head-sounds ?

We must first admit that clear falsetto or head-notes are har: :
monic sounds ; then we must consider how harmonic notes can
be produced by the laryngeal instrument. |

If the vocal cords be regarded in the same light as the vi-
brating ‘tongue ” of a reed-instrument, their nodes* must be
parallel to their edges ; when the whole breadth of the cords
vibrates, the harmonics are not heard, and the sound emitted is
said to be from the chest ; but if the cords meet only on a por-
tion of their length, then the vibrating-power of the blast will be
entirely spent in distributing the vibrations in a longitudinal
direction to those portions of the cords which are kept apart.
Hence the edges only of the cords will vibrate; the vibrating-
body may then be regarded as a narrow strip of elastic mem-
brane included between the edge of the cords and one of the nodes
nearest and parallel to that edge. An harmonic note, or a head-
or falsetto sound, will be the result of these vibrations. Now this
head-sound may be clear, sharp, and well defined, or it may be
cracked and even painful to hear. This appears to me due to
the circumstance that the vocal apparatus, being reduced to a
narrow strip lmited on one side by its edge and on the other
by a node, becomes a true vibrating cord with nodes im a longi-
tudinal direction. Ifthe cords meet in such a way as to limit
the direct action ofthe blast to the distance between two of their
corresponding ends and two of their corresponding nodes, an
harmonic sound will be emitted. In fact there will then be a
combination of the two harmonics, viz. the one belonging to the
vocal cord considered as a membrane, the other to the cord con-
sidered as a true cord; the result will be the emission of a fine,
clear, sharp head-note.

But if the cords do not meet in such a way as to limit the
direct action of the blast, as stated above, then the sound pro-
duced will be the same as that obtained when the exact spot to
bring out the harmonic of a violoncello-cord, for instance, is
not detected at once, the shrieking disagreeable sound of the
instrument showing the performer’ s skill to be open to much
improvement.

The act of singing at will head-notes equally esuity in the
emission of harmonic sounds; but its mechanism is not quite
the same as in the former case. I could not satisfy myself, as
I should have wished, as to the muscular action which brought
about the shortening and tight approximation of the vocal cords

* Tt is hardly necessary for me to observe that the “nodes ” of a vibra-
ting-cord are the places on the cord which, when lightly pressed with a
finger, yield harmonic sounds.

M. H. Wild on the Absorption of Light by the Air. 298

of the Tyrolese singer; but I believe it can be due to no other
cause than the close apposition of the arytzenoid cartilages through
the action of a special muscle, the arytenoideus proprius; and
this would account for the formation of harmonics. ‘The vocal
cord may be regarded as fixed to these two cartilages poste-
‘riorly, which in some measure act as parts of the cords ; so that
these two bodies, by pressing against each other, will reduce the
length of the cords, very much in the same way as when a finger
is applied lightly to a vibrating violoncello-cord. The skill of
the singer who wishes to pass very quickly from a chest- toa
head- note, and to strike the right clear sharp falsetto sound, will
be an acquired dexterity of regulating the motion of the arytenoid
cartilages so as to cause the air from the chest to act on the length
of the cords required for one of their harmonics. If he should
im any way miss the exact spot, a cracked sound will be emitted.
This will account for the present mode of singing requiring a
great deal of practice to be done in perfection. The fact that
‘the cricoid and thyroid cartilages remain nearly motionless, on
passing from a chest- to its corresponding falsetto note, would
appear to show that falsetto-singing is not due to increased ten-
sion of the cords*.

I have cbserved that the mere swelling of the vocal cord may
produce a harsh head-note; this appears to me to be due to the
lessened vibrating-property of the cords, the vibrations being
prevented from reaching the whole of their breadth. I believe
this is not an unfrequent cause of cracked voice from inflamma-
tion of the larynx, and that it is not an affection difficult to cure.

XL. On the Absorption of Light by the Air.
By H. Wixpt.

ae ee ERIC air, like other ponderable bodies, is not to

be considered a perfectly transparent substance, but, espe-
cially in strata of some thickness, exerts an appreciable absorp-
tion on transmitted light. Daily experience teaches that this
absorption is very different at different times. Distant objects
sometimes appear indistinct and hazy in their outlines, as if they
were covered with a veil; sometimes their details are seen so
clearly defined that we are unavoidably led to regard them as
brought nearer to us. The first phenomenon is generally ob-

* It is not impossible, however, that a combined action of the arytznoi-
_ deus proprius and posterior crico-arytznoid muscles should add to the ten-
‘sion of the vocal cords im falsetto singing.
t Translated from Poggendorfi’s Annalen, No. 8, 1868, having been read
before the Naturforschende Gesellschaft of Bern.

peg
Rate

294 — -M. H. Wild on the Absorption of Light by the Air.

served in continuously dry weather, while increased transpa-
rency is regarded as a sign of approaching wet weather.

With these facts and observations are connected the two prin-
cipal views which at different times have been propounded as to
the greater or less transparency of theair. A. De la Rive ascribes
the Jess transparency of the air in dry weather to the presence of
opaque dust and vegetable germs. If the air becomes moist by
south-west winds setting in, these corpuscles become more trans-
parent, and at the same time heavier, owing to the absorption of
aqueous vapour, so that they fall to the ground more rapidly,
which is more completely the case when the rain begins; the air
thereby becomes purified and at the same time more transparent.
Marshal Vaillant, on the contrary, assigns as the chief reason
for the different degrees of transparency in the air in north-east
and south-westerly winds, the circumstance that during the pre-
valence of the latter, owing to the uniformity in the temperature
of the ground and the air, local vertical currents are far less than
with north-easterly winds. Disturbed air, however, is far more
opaque, because at the boundary of warmer and colder layers of air
multifold reflections and irregular refractions of light take place.

We will add no new hypotheses to these, but at once inquire
how far this question as to the various degrees of transparency
of the air and the absolute magnitude of the absorption of light
may be experimentally answered.

Saussure was the first who attempted to measure the trans-
parency of the air. He devised for this purpose a simple mstru-
ment, which he called the diaphanometer*. It consists of a black
circle in the centre of a white circle of three times its diameter.
In determining the transparency of the air two such disks are
necessary, one of which has a considerably greater (twelve times,
for instance) diameter than the other. If either of these disks be
gradually moved away from the eye, a point is ultimately reached
at which the black central spot disappears. This will be the
case when the visual angle of the black circle has become less than
the limiting angle of distinct vision, which amounts to about 50".
If we were merely concerned with this limiting angle, the black
spot of the larger disk would obviously disappear at twelve times
the distance of the smaller disk from the observer. If, then, as is
actually the case, the spot of the larger disk disappears at even
a smaller distance, the brightness of the white background has an
influence on this disappearance, and the deviation in the ratio of
the two distances at which the black circles of the smaller and the
larger disks disappear, from the ratio 1 : 12, may serve as a mea-
sure for the transparency of the air. From known photome-
trical principles, the two white disks uniformly illumimated by

* Mémoires de Académie de Turin, vol. iv. (1789) p. 425. |

M. H. Wild on the Absorption of Light by the Air. =.295

the sun or diffused light should appear equally bright to the eye
of the observer at all distances; if, therefore, the more distant
one is less bright, this arises from an enfeeblement of the light
in passing through a layer of air twelve times as thick. The
more strongly the air absorbs, the more will the ratio of the
distances differ from the true theoretical one of 1: 12.

Beer was the first to give a theory of the diaphanometer based
on the principles of photometry*. He assumes that the pheno-
menon would not be materially altered if the disks consisted of
white circles on a black ground, and that in this case the two
different-sized white spots would send an equal amount of light
to the eye at the moment of their disappearance. In fact,
according to this view also, the disk twelve times as large would,
at twelve times the distance, send to the observer’s eye the
same amount of light as the smaller one, and disappear simulta-
neously with this, only if the air were quite transparent. If
it is not so, the light which is lost by absorption in the thicker
layer of air must be compensated by a greater apparent diameter
of the disk. On this assumption the coefficient of transparency +
a of the air (that is, the fraction of the incident light which tra-
verses a layer of air of the unit thickness) may, according to Beer,
be calculated from observations with the diaphanometer by the
formula

in which d and D are the diameters of the two disks, e and E
the distances at which their spots just disappear.

By this formula Beer has calculated the coefficient of transpa-
rency of the air at two different heights, from observations made
on the Tyrolese Alps by H. Schlagintweit with a Saussure’s
diaphanometer{. He finds that, referred to a unit of length of
1000 Paris feet, at

2300 feet above the sea . . . a=0:9029
12000 ca ee oe a 0-095

The development of the above formula of Beer necessitates two
suppositions which call for a more minute discussion. It is as-

* Grundriss des photometrischen Calculs, by A. Beer: Brunswick, 1854,
pp. 91-93.
__ + Both here and afterwards I designate as the coefficient of transparency
what is usually called coefficient of absorption. The first designation ap-
pears more convenient and more in accordance with general usage, because
for greater values of this coefficient the transparency and not the absorption
increases.

t Poggendorff’s Annalen, vol. Ixxxiv. p. 298.

(796M. H. Wild on the Absorption of Light by the Air.

sumed, first, that the two disks are just equally illuminated, and
then that the apertures of the pupils of the observer’s eyes are
equal in looking at both disks. The first condition can in fact only
_ be realized by taking extraordinary precautions ; and the second
is, strictly speaking, never fulfilled. It is one of the oldest ob-
servations in reference to the accommodation of the eye, that the
pupil becomes narrower when accommodated for near objects, and
enlarged on looking at a distance. Allowing for this alteration
of the pupil, the above formula becomes more exactly

2
wR.
0=(5, AJ 8
where 6 is the diameter of the aperture of the pupil on looking

at the nearer disk, and A that for the more distant one. In
order to ascertain the approximate value of the factor of correc-

2
=e

tion (z)° » I estimated the alteration in the pupillary aper-

ture on passing from the accommodation to an object at a distance
of 200 feet to one at 2000 feet, and I found that the diameter
changes about 0°6 millim. If, therefore, we put S=2:4 mil-
lims., A=8 millims. Introducing these numbers into the above
equation, in calculating the coefficient a from the observation at a
height of 2000 feet we get, instead of the above value a=0°9029,

a=0°7225.

The influence of the alteration in the pupil is therefore consi-
derable.

These circumstances, as well as the uncertainty in ascertaining
the exact point of disappearance of the black circle, diminish the
value of the diaphanometer as a measuring-instrument so mate-
rially that it no longer comes up to the present requirements of
science.

A. De la Rive has recently again taken up the investigation of
the transparency of the air, and followed the only rational path—
that of endeavouring to determine photometrically the ratio of
the transparency of two objects at different distances from the
observer. The instrument in question was exhibited at the
Meeting of the Swiss Naturalists in Geneva in August 1865 ;
and at the same time the above theory of the causes of the varying |
degree of transparency of the air was propounded*, De la Rive
has not, however, as yet published any results of observation.

Before I knew of De la Rive’s work, having become possessed
of some long wide tubes for other investigations, I made on the

* Compare Phil. Mag. S. 4. vol. xxxiv. p. 241.

M. H. Wild on the Absorption of Light by the Air. 297

8th of March, 1866, a long projected experiment for measu-
ring the absorption of the air by means of my photometer, which
gave, however, a negative result. I shall subsequently revert to
it. I at first concluded from it that the transparency of the
alr was so great that the enfeeblement of the light im a layer a
metre in thickness was below the limit of the delicacy of my in-
strument—that is, did not amount to ,,)5 of the incident light.
I therefore determined to make measurements in the open air at
far greater distances. After some preliminary experiments which
indicated the precautions to be taken, the definitive observations
were made on the 6th to the 10th of July 1866, first in my garden,
and afterwards in an open street in the neighbourhood of my
house. ‘Two paper screens, consisting of square wooden frames
respectively 0°6 metre and 1:2 metre in the side, over which was
stretched paper from the same roll, were first put up side by side at
a distance of 6 metres from the two apertures in my photometer*
by which hght enters, and the ratio of their brightness was
determined. Without altering the position of the smaller one, I
first placed the larger screen at a distance of 21 metres and then
of 36 metres from the photometer, again determined the relative
brightness by its means, which operation was once more repeated
after the screens had been again placed at equal distances. The
mean of the first and last measurements (with an equal distance
of the screens), compared with the results of the second observation
(when the screens were respectively 15 and 30 metres apart), ren-
dered it possible to determine the coefficient of transparency a of
the air. For if we designate by e the constant distance of the
small screen from the photometer, and the varying one of the
larger screen by H, if, further, the brightness of the small screen
be called 2 and that of the larger one J, looking from the photo-
meter, the ratio of brightness of the two is

The same ratio of brightness of the two screens may be calcu-
lated from the angle of neutralization v, read off on the photo-
meter, from the formula

= Cr tane,

in which C is a constant depending on the position of the prisms,
which is unknown, and has therefore first to be determined by
Bexperiment. We have thus now the equation

“* Poggendorff’s Annalen, vol. exviii. p. 193.

298 M.H. Wild on the Absorption of Light by the Air.

or

J
ae—-E— 7°& . tan v? ;

and in this case the two unknown magnitudes C and ; are de-

fined or eliminated by our placing both disks at the same distance
(that is, makng H=e), on the assumption that the removal

of the larger screen does not alter the ratio z If the angle of

neutralization observed in this position is v,, we have for this case
J
i 70 . tan v,?.
This equation, divided by the pele; gives

tan*v,
tan*v

On the above-mentioned days I succeeded in obtaining seven
complete observations uninterrupted by any disturbing influ-
ences. The unexpectedly large difference in the angles of neu-
tralization v and v, (about 2° when the screens were at the
greater distance 30 metres apart, while I had only expected
about 4°) led me to fear that there might have been some dis-
turbing reflection from the house-walls on one of the screens.
Hence on the 10th of July the measurements were repeated on
the open road (one, that 1s to say, bounded on both sides by
meadows) ; these, however, only confirmed the previous results.
Introducing the values obtained for v and v,, and the correspond-
ing ones for E—e, into the above formula, we get as the mean of
all observations for the coefficient of transparency of air, referred
to 1 metre as the unit of thickness,

a=0°9061,

with a probable error of +0:0005. This number refers to white
light (that is, to the brightest rays in it, the colours that are be-
tween Fraunhofer’s lines D and E of the solar spectrum), fora
mean temperature of the air =24° C., relative moisture =0°55,
and a mean pressure of 722 millims. The layer of air was about
1:2 metre above the ground.

Before making any further observations on this result, I must
briefly mention the precautions which are indispensable for ac-
curate observations. It is first of all necessary that during an

peat

I Maa ene a 5
experiment the relative illumination —~ of the screens remain

J
exactly equal. For this purpose the larger screen must always
be moved quite parallel, which is best effected by fixing a sight

M. H. Wild on the Absorption of Light by the Air. 299

to its frame. The sky must also be almost cloudless ; at any rate
there must be no mist in the neighbourhood of the sun. Owing
to small clouds which passed over the sun, I had frequently to
break off observations which had been commenced ; for irregular
and sometimes very considerable changes ensued in the relative
brightness of the two screens. It was also impossible to observe
when the wind was at all powerful; for the larger screen more
especially was altered in its position and in its illumination.
Reflection from adjacent objects, too, which affects the two
screens differently, must be carefully avoided.

The above values, when reduced by Beer’s formula, and by my
modification of it, to the unit of 1000 Paris feet, and, on the
other hand, to the unit I have adopted of 1 metre, give us the
comparison—

For 1000 Paris feet. For 1 metre.
Schlagintweit-Beer . a=0°9029 a=0:9997
Schlagintweit-Wild . a=0°7525 a=0°9990
Rs i oe a= 0°2801 a=0'9961

Our comparatively much smaller coefficient of transparency of
the air is partially to be explained by the circumstance that in
our observations all those influences which are usually consi-
dered to favour absorption were represented. On the days of
observation a north-east wind prevailed which at times was pow-
erful; the air was very dry and its temperature high, so that
undoubtedly local ascending currents set in, and abundant dust
and vegetable germs were met with in the lower layers.

How great is the influence of dust in transparent liquids on
their power of absorption has been already shown by my deter-
minations of the absorption of water*. According as the water
was more or less freed from admixed dust by filtration through
various kinds of paper, were different values obtained for its
coefficient of transparency. Reduced to 1 metre as unit of path,
we get from these determinations for the coefficient of transpa-
rency of water after filtration through

Coarse filtering-paper . . 0°5368
Medium fine) 3.) eS (O'G491
J NTGSIS Bi STO a ie Neal lad UCAS

These numbers differ, therefore, comparatively far more than
those for air for the same unit of path. It must, on the other
hand, be taken into account that in our determinations of the
coefficients of transparency of air in the open the particles
of dust are also illuminated, and thus not only act as absorbents

* Poge. Ann. vol. xcix. p. 272.

300 M. H. Wild on the Absorption of Light by the Air.

but also as illuminators, while when air or liquids are enclosed
in tubes their absorptive action alone comes into play.

The unexpected magnitude of the absorption of the air as de- |
duced from my measurements led me to investigate whether the
transparency of the air for different colours could not be experi-
mentally determined in an analogous manner. With this view the
relative brightness of the two screens while at a distance of 80 me-
_tres was determined—in one case for red light by placing a deep-
red glass in front of the ocular of the photometer, in the other
case for blue light by the use of a combination of a cobalt with a
bluish-green glass. Twosets of observations made in this man-
ner, on the 9th and 14th of September, showed that red light 1s
absorbed less strongly than blue, or that the coefficient of transpa-
rency of the aw for red light ts greater than for blue. I do not
give the numerical values for the coefficients, as they are only very
approximately determined, and may be essentially modified by
later, more accurate, and more complete observations.

I was prevented by pressing business from resuming these
observations; and only in August 1867 could I proceed to attempt
to make them by a new method of observation, which was more
in accordance with that which I had first chosen. With the deli-
cacy of my photometer and the unexpected magnitude of the
absorption of the air, it seemed that I ought to be able to de-
monstrate it by means of tubes of about 2 metres in length.

The apparatus which I used consisted of an oiled transparent
paper disk of 30 centims. diameter, which was placed near a
window only illuminated by diffused daylight, and which, in
order to obtain as uniform illumination as possible, was rotated
by an axis passing through its centre which was moved by clock-
work. At right angles to-the face of this disk, on a horizontal
diameter of it, and with their centres opposite, two horizontal
sheet-metal tubes were placed of 2°4 metres length and 0-1
metre diameter. They were provided throughout their entire
length with twelve diaphragms, each with an aperture of 0-06
metre, and were moreover closed at the ends with plate glass.
Each had two smaller lateral apertures, which im the case of
one tube were constantly open; while one of the apertures in
the second was closed, and the other connected with an air-pump
by means of a caoutchouc tube with an enclosed spiral. The
photometer was placed in front of the ends of the tubes furthest
from the paper disk, in such a manner that the light from the
two halves of the paper disk could pass through both tubes into
the two apertures of the prism apparatus. The chief difficulty
and uncertainty in this form of the experiment arises from its
being almost impossible to keep the two halves of the disk at a
constant ratio of brightness. I could only effect this for the

M. H. Wild on the Absorption of Light by the Air. 301

duration of the same series of observations by shortening them as
much as possible, and choosing days when the cloudiness did not
much vary. The position of neutralization was observed in only
one quadrant, and first of all when one tube was exhausted and
the other filled with air, and then after air had been allowed
rapidly to enter again. The results to be obtained from these
observations are therefore only to be regarded as first approxi-
mations. This comparison, moreover, of the ratio of the lumi-
nous intensity when the tube was full in one case and in the
other exhausted, merely gives us the ratio of the coefficient of
transparency of rarefied air, and of air of ordinary density.

The series of observations on the 29th of August gave as the
mean angular difference of the two positions on the photometer
21', which corresponds to a ratio of the coefficients of transpa-
rency of the air for pressures of 85 and 720 millims., referred to
a length of 1 millim.,

“35 — 1-01023.
Q790

This result, however, is uncertain, because on this day during
the time of observation the clouds, and therewith the illumina-
tion of our disk, greatly varied.

On the 31st of August, when the sky was almost Beran
and the illumination almost constant, for four successive series of
observations the mean angular difference in the two positions
of the photometer was 8'-5, the pressures being 715 and 100
millims. From this we get

“00 — 1-00413.

o7is

It is here assumed that the increase in the luminosity when
the tube was exhausted was exclusively due to diminished -ab-
sorption, and was not due to a simultaneous diminution of the
enfeeblement of the light owing to its passage through the en-
closing plates. Fresnel’s formule of intensity show in fact that
transmitted light is not materially altered in its intensity when
the glass plates are bounded on one side by a vacuum instead of
on both sides by air.

The above numbers may also be used to cnlealate the coeffi-
cients of transparency of air of ordinary density.

: ainy-dol
The coefficient of transparency of air whose density is = that

_ of ordinary air is obviously

302 M. H. Wild on the Absorption of Light by the Air.

and since the densities are as the pressures, we shall have

P
n= —
Pp
if P represent the original pressure, and p the pressure of the

rarefied air; thus we have also
P
Ap=Ap?,
where a, and ap represent the coefficients of transparency of the
air for the respective pressures p and P.
If we put the ratio determined by our previous experiments, of

oe. =2, we have also ia 8

ap ap=2 P—p

Introducing z, P, and p, the above values, we get, referred to a
unit of path of 1 metre,

Aro =0°98935 August 29.
&7,=0°99521 ws Male

The latter, which from the reasons stated is the more reliable
result, almost agrees within the limits of error with that previously
ascertained. Without prematurely attributing too great weight
to this agreement, we may draw the conclusion that by means of
my photometer it ts possible to determine the absorption of air in
tubes of no great length, those, for instance, which can be set up
in an ordinary room.

From the previous observations it follows with certainty that
air in the lower layers is far less transparent than is ordinarily
assumed. In the case of air only half saturated with aqueous
vapour and heated to about 24° C., the absorption near the
ground is so considerable, that after traversmg 300 metres the
luminous intensity has been diminished to about one-third.
However paradoxical and large this absorption of air may seem,
it is infinitely small compared with that of water. From the
above numbers we find that, after traversing the same distance in
water as pure as possible, the luminous intensity would only
amount to one quintillionth (that is, absolute darkness would
set in), and that, to diminish the intensity to only one-third, its
path in water need not be more than 5 metres. From my ob-
servations I can also deduce with certainty a greater degree of
transparency for red than for blue light, though I cannot yet
consider the quantitative difference definitely settled. This sup-
ports the ordinary explanation of morning and evening red ; yet
only further detailed observations can show whether Clausius’s
theory of morning and evening red, as well as of the blue colour
of the sky, which has been accepted by most physicists, is cor-
rect or not.

M. H. Wild on the Absorption of Light by the Air. 303

Appendix.

In close connexion with the preceding investigation is another,
of which I wish here to communicate a preliminary result. It
refers to the difference in the colour of the waters of lakes and
rivers in summer and winter, as well as of the warm and saline
water of the Gulf-stream as compared with the surrounding
water. I consider that the darker or deeper and more vivid
colour in summer, and in the Gulf-stream, is not to be ascribed
to a greater quantity of salt, but essentially to the higher tem-
perature. It is well known that in most bodies absorption in-
creases with increase of temperature. To decide whether this
is also the case with water, I first determined the coloration of
a paper surface illuminated by the sun, when looked at through a
layer of water 2°4 metres in thickness. To judge the colour
the better, the tube was only half filled, so that the uncoloured .
white paper above was visible. Ordinary well-water cooled to
7° C. gave a bright greenish-white tone, and at 50° C. a de-
cidedly deeper bright green coloration; distilled water, too, at
20° C. exhibited a bright bluish-green colour, which at 58° C.
passed into a deeper and greener colour.

The transparency of water at two different temperatures was
directly measured. Between the photometer and the ground-
glass pane of a front window, at one aperture two glass tubes
(each closed by glass plates) of 50 millims. and 200 millims.
length were placed, at the other aperture of the photometer two
other such tubes of 100 millims. and 150 millims. length.
The relative intensities with the empty and the partially filled
tubes were ascertained; in one case the tubes of 50 millims. and
150 millims., and in the other those of 100 millims. and 200
millims. were filled with distilled water filtered through coarse
filtermg-paper. The temperature of the water, of about 6° C.,
was obtained by cooling the entire room to this temperature ;
with the higher temperature of 25° C., the room was at a tempe-
rature of 16°C. From the experiments made on the 4th and
5th of January, 1867, the following values were obtained for the
coefficient of transparency of distilled water filtered through
coarse paper :—

At 24°4 C. a=0-91790,

At 62 C. a=0°94769,
referred to 1 decim. as unit of path. My former experiments in
Konigsberg had given for the same paper and a temperature of

about 17° C., and referred to the same unit of path, the value

: 17° C. a=0'93968,
which agrees well with the above. Hence the transparency of
water at low temperatures is in fact greater than at higher ones.

[ 304 ]

XLI. Notices respecting New Books.

An Introduction to Scientific Chemistry ; designed for the use of
Schools and Candidates for University Matriculation Examina-
tions. By F. 8. Barrr, M.A. London: Groombridge. (Pp. xv
and 315.)

(see appearance of this book may be regarded as one of the im-

mediate results of the recent impulse in favour of teaching ex-
perimental science, which has been felt in almost every school in this
country. Two or three years ago common class instruction in che-
mistry or physics could only be obtained in a few institutions of the
larger and more expensive kind ; but itis now understood that these
subjects can be beneficially taught to boys, nay, that they are essen-
tial elements in a liberal education. Acting upon this belief (in
which he has our hearty concurrence), the schoolmaster is naturally
exposed to two dangers, which are not inconsiderable, and really
deserve his serious attention.

The first danger which the schoolmaster has to encounter is, that
he does not, as a rule, appreciate the real value of what he is about
to undertake. - His own learning has been, for the most part, ac-
quired from books and disseminated by the pen; the methods of
accurate observation and of analytical and synthetical reasoning
with which experimental science is specially associated, appear to
him to have been much overestimated. It will be more economical,
and quite as salutary, if, after the little study that may be necessary,
he teach the new branches himself. Need we say that such a plan
must inevitably end in failure? Yet it is one that has been adopted
on several occasions by teachers who would be ashamed to meet a
class in mathematics, for example, without being far more than ade-
quate to their duty. It is evident that a science can only be pro-
perly taught by some one who is as conversant with it as can fairly
be expected from a teacher in any other subject; and care ought to
be taken that no one should be employed for this purpose who can-
not give proof of at least two years’ exclusive attention to the study
of the science he professes. We must add that, in addition to a
properly qualified instructor, a laboratory is indispensable. ‘To say
nothing of the intense delight with which most boys regard labora-
tory work, it is reasonable to believe that they will miss the very aim
of their efforts unless they learn in a practical way that which de-
rives its chief advantage from being practical.

But the twin peril advances from another quarter. If it is true
that the average schoolmaster is not sufficiently serious and appre-
ciative, it is no less certain that physicists, and especially chemists,
have provided very badly for the event of his becoming so. When
he anxiously asks us for the class-book which is to tell as plain and
simple a story as he already possesses in the ‘Geography’ or ‘ Arith-
metic’ he uses (or a dozen others that he might as well use), he puts,
it must be admitted, a very puzzling question. Weare compelled to
confess that, even including the manuals which have been expressly

Notices respecting New Books. 305

written with this design, there are scarcely any that we can recom-
mend as a school-book. Too often devoted to the exposition of the
fancies or whims*of the hour, or to a wonderful confusion of the
creeds of independent apostles, most of our manuals of chemistry
are like copies of some manuscript legend in which the original
sentences have been repeatedly misplaced and rendered almost un-
intelligible by the intervening conjectures of successive readers. Is
this the romance of nature? So much censure certainly does not
attach to the current physical manuals; but they are almost all far
above a boy’s level, and in a form unavailable for a teacher.

Bearing these considerations in mind, we shall better be able to
understand the great merit of Mr. Barff’s little book. His object
has been to write for boys an Introduction to Chemistry which,
while never rising above a matriculation standard, can condescend
to touch on many of the minorand petty difficulties which such pu-
pils always feel. Confining himself exclusively to this humble
region, and using throughout the personal address of a teacher, he
is able to enforce the matter of instruction with largely increased
effect. His work is, moreover, characterized by extreme simplicity
both in style and plan. ‘he reader will not find anywhere in Part I.
(206 pages) a single symbol, formula, or reference to the atomic
theory. Even in Part II. (where these matters are considered) only
the most direct and intelligible methods of interpretation are cau-
tiously employed, it being the author’s conviction that ‘“ young
minds are often apt to espouse warmly views of a certain school, and
to regard as facts what are nothing more than assumptions.”
Throughout the first part of the work the combining proportions
(and minimum weights generally) are given in non-symbolic num-
bers and quite dogmatically ; and it is not until a large amount of
exercise in calculation has been traversed that the student is allowed
to formulate anything whatever. Another excellent feature is the
set of questions which occurs at the end of each chapter, and the
collection of actual matriculation problems at the close of Part II.:
many of these are worked out as examples. ‘The ‘advice to stu-
dents under examination ”’ is also excellent.

We shall not, of course, be supposed to intimate that this book is
free from defects. It is quite impossible that an effort of the kind,
unique as it is, should have been unattended with some taint of the
sins of modern chemistry. ‘There is, however, quite enough in the
manual to console -us for such blemishes and aid us to forget them.
Mr. Barff’s ‘ Introduction’ will be of the greatest value to schools,
and is a most serviceable contribution to chemical literature. ‘The
modesty and simplicity of its purpose, its freedom from theoretical
partialities, and (what is not unimportant) its moderate price will
ensure it a deserved and hearty commendation.

Phil. Mag. 8. 4. Vol. 87. No. 249. April 1869. x

[ 306 ]

XLII. Proceedings of Learned Societies.
ROYAL SOCIETY. 8
[Continued from p. 235.]
Jan. 7, 1869.—Lieut.-General Sabine, President, in the Chair.

(hee following communication was read :—

** Notes of a Comparison of the Granites of Cornwall and De-
vonshire with those of Leinster and Mourne.” By the Rev. Samuel
Haughton, M.D., D.C.L., F.R.S., &c.

The granites of Mourne are eruptive, and can be proved to con-
tain albite as their second felspar.

The granites of Leinster are also eruptive ; and although albite has
never yet been actually found to occur in them, its existence can be
inferred with considerable probability.

During the past summer (1868) I have succeeded in proving
that the second felspar that occurs in the granites of Cornwall is
albite. I found this mineral as a constituent of the granite at Tre-
wavas Head, where it has the following composition :—

I. Albite, var. Cleavelandite (Trewavas Head).

SGA iy oste o\s a oie ean ee ae 65:76
AM aiminal tide. ple nee Ya ee
PIMC Sc 8 Sie! cote 0:89
eee Pr ae trace
Soda. . Woks ae 9°23
Potash ; 1°76
Waterss. os oe eee eee 0°40

99°76

This albite is opaque, cream-coloured, lamellar, and associated
with quartz and orthoclase, which has the following composition :—

Il. Orthoclase (Trewavas Head).

No. 1*. No. 2t.
OTTCA cote nae. cslldae Mises ole tet oi are eam 63°20
Alumina ecbet. ie: pac oer 21:04 21°00
Iron and manganese oxides .... _ trace trace
Dimer ssise Jey hice, bees 0-90 0-68
Magnesia 4 ose; Set. 4e geese trace trace .
Sadar ai. tu. te eee eee ee 3°08 2°79
Potashiy . ie ei ight 9°91 10°30
Water, can't eye ascicak be Gener 0:40 0°40

98°93 98°33

The granites of Cornwall and Devon contain two micas, white and
black. I was fortunate enough to obtain, through my friend Mr. W.
J. Henwood, F.R.S., of Penzance, a sufficient quantity of white mica
from Tremearne, near Trewavas Head, to determine accurately its
composition, which proves to be highly interesting. It differs essen-

* From veins at foot of cliff associated with Cleavelandite albite.
+ From the granite at summit of cliff.

Royal Society.

307

tially from the white mica of Leinster and Donegal, and proves to be

a variety of lepidolite.

Ill. White Mica, Lepidolite es near Trewavas Head).
Silica (Si0,) .
Fluosilicon (SF, 3
ATuminas. ... .

Iron peroxide
Manganese protoxide ...

Lime

Potash.. -..

See CO) Cle) eens) 6.8, vo es

This lepidolite is white, pearly, and occurs in rhombic tables of 60°
and 120°. Its oxygen-ratios are, reckoning for the fluorine its equi-

valent of oxygen :—

Silica ....
Fluosilicon
Alumina

Iron peroxide

Oxygen-Ratios.
: 24°714

Manganese protoxide
LS ee
Se

Botash.-.....

oS) ee Be 06

8°9

4°8

1:00

This corresponds with a dicoretioal formula in which the oxygen

of the silica is to that of the bases as 3: 2.

The Black Mica of the Cornish granites seems to be more abundant

than the White Mica already described.

I found a sufficient quan-

tity of it at Coron Bosavern, near St. Just, to enable me to make the

following analysis :—

IV. Black Mica, Lepidomelane (Coron Bosavern, near St. Just).

Silica (Si0,)
Fluosilicon (Sif,)
Alumina
Iron peroxide
Tron, protoxide -- 2... :

Manganese protoxide ....

Lime

Magnesia
Potash eps he. oe cies aie

Soda

Thehiniee

eeoerere eevee ese

aa) ONG) 8) 6) else) e) e

xa) |e) [et (ee) oe) 8) @) (ey (od! (8) 10

OO ee

308 | Royal Society.

The Black Mica of St. Just is of a blackish-bronze colour and
metallic lustre, and occurs in rhombs of 60° and 120° angles. Its
oxygen-ratios are,reckoning for the fluorine its equivalent of oxygen,—

Oxygen-Ratios.

Dey Ce Me ne cee eee 2 20°727 :
Eitcuilicon eee ene a:
ANU eos eke es ee 10°692 :
from peroxide). 25. ae A604 ken
Iron protoxide ........ 0°514 \
Manganese protoxide.... °310

Wine ees 6 Rios pe
Magnesia ........ ... O'427 > 4-292
Potash) sa. +255 0 eee

SOA ook cess dn. ted se ee

ih a oo os oe ose Oe

The oxygen-ratio of this iron-potash Mica (which is undoubtedly
a lepidomelane) for silica and bases is

216: 194, or 1:1.

The granites of Cornwall and Devon, which have been frequently
examined by me during the last sixteen years, appear all to con-
tain the two felspars and the two micas above analyzed. In a future
communication I hope to describe their composition in detail, and to
give a comparison of this composition with that of the granites of
Treland.

The following generalizations will be found, I believe, capable of
root.
: (1) The granites of Ireland may be divided into two distinct
classes, marked by characters both geological and mineralogical.

(2) The First Class of granites consists of Eruptive rocks, of ages
varying from the Silurian to the Carboniferous periods. To this
class may be referred the granites of Leinster and Mourne, and the
granites of Cornwall and Devon.

(3) The first class of granites is characterized by the presence of
orthoclase and albite, and by the absence of all the Lime Felspars.

(4) The Second Class of granites consists of Metamorphic rocks,
of unknown geological age, but probably subsequent to the Lauren-
tian period. To this class may be referred the granites of Donegal
and Galway, and the granites of Scotland, Norway, and Sweden.

(5) The second class of granites is characterized by the presence
of orthoclase and oligoclase, or Labradorite, or some other of the
Lime Felspars, and by the absence of albite.

Geolugical Society. 309

GEOLOGICAL SOCIETY.
[Continued from p. 156.]

Nov. 11th, 1868.—Prof. 'T. H. Huxley, LL.D., F.R.S.,
President, in the Chair.

The following communications were read :—

L. “ Note comparing the Geological Structure of North-western
Siberia with that of Russia in Europe.” By Sir R. I. Murchison,
Barts, K.C.B., G.C.St.8., F.R.S., V.P.G.8., &.

Count A. von Keyserling had communicated to the author the
following facts :----The district between the rivers Lena and Jenissei
is occupied by Upper Silurian rocks of the same type as those found
in the region of Petchora, and by Carboniferous rocks containing
seams of coal. The chief Secondary deposits are of Oolitic or
Liassic age, and agree with those of the Petchora region, which is
the next adjacent tract on the west to the Siberian region in ques-
tion. Similar rocks are found in Spitzbergen. The banks of the
Jenissei are covered with Postpliocene accumulations similar to
those found near Archangel. It is thus seen that the vast, slightly
undulating, and to a great extent horizontal and unbroken forma-
tions, each of which occupies so wide an area in European Russia,
are repeated on the eastern side of the Ural Mountains. In this
range of mountains only are to be found igneous and erupted rocks.

In conclusion, Sir Roderick referred to the discovery of fossili-
ferous white chaik in parts of the great Sarmatian plain by M.
Grewinck.

Sir Roperick Murcuison, in explanation of the paper, referred to
a geological map of Russia, and gave a general sketch of the bearing
of the paper on the previously known geology of that country. He
mentioned the discovery by M. Grewinck of beds of brown coal
containing amber, and overlying true chalk. The amber in the
Baltic had been supposed to have been washed out of beds beneath
the sea; but Count Keyserling has suggested that the amber may
have been brought down by the rivers from the interior, and depo-
sited in the Baltic. Sir Roderick also called attention to the ab-
sence of igneous rocks in Russia to the west of the Ural Mountains.

2. “On a Section of a Well at Kissingen.” By Prof. Sand-
berger, For.Corr.G.S.

Taking as a starting-point a bed of dark-blue limestone, the
author proceeded to describe the various beds passed through in
sinking the Schénbern well, both as regards their petrological cha-
racters and chemical constitution. He considered that this bed is
on the same horizon as the uppermost Plattendolomite of the Zech-
stein formation in the Harz and Thuringia. Above this lie the
lowermost beds of the Bunter (containing dolomites), and below it
the upper part of the Zechstein formation. Below the Plattendolo-

310 Geatngteal Society:—

mite of the Zechstein, from the depth of 1740 feet to 1884 feet,
follow the saliferous beds.

3. “On the Formation of Deltas; and on the Evidence and
Cause of great Changes in the Sea-level during the Glacial Period.”’
By Alfred Tylor, Esq., F.L.8., F.G.S., &.

The first portion of this paper was devoted to a comparison of the
delta-deposits of the Po, Ganges, and Mississippi. The surfaces of
these deltas and the alluvial plains above them were compared
together ; and it was stated that a parabolic curve drawn through the
extremities of each river, and through one point in its course,
nearly represents its longitudinal section—the greatest deviation
being 30 feet in some of the largest deltas.

The littoral deposits around Great Britain described by Mr. God-
win-Austen were next investigated, to ascertain whether the hypo-
thesis of a fall of 600 feet in the sea-level is tenable. The ice-cap
at the poles was also alluded to as a probable cause of a great reduc-
tion of the sea-level during the Glacial period.

The upper 600 feet of deposits in the Pacific Ocean, made by coral-
zoophytes, were quoted as cases which might be explained as well by
oscillations in the sea-level as by the received hypothesis of the sub-
sidence of the sea-bottom.

Prof. E. Forbes’s investigations into the origin of the fauna and
flora of the British Isles were next alluded to, and the author con-
sidered that the hypothesis of a fall in the sea-level better accords
with the facts of migration than Forbes’s suggestion of changes of
the level of the land ‘and sea- bottom.

The origin and age of the English Channel was discussed at some
length; and the occurrence of the Crag and fossiliferous gravels
and raised beaches near the same level, although of different ages,
together with the evidence afforded by the dredging up of fresh-
water and littoral shells in the North Sea and English Channel,
were adduced in support of the theory of the depression of the sea-
level.

The parabolic curve not only represents the curve of deposition ;
for the author had measured other sections, and found that the
curves of denudation and deposition approximate often to that of
the parabola.

Discussion.

The Presrpent called attention to the fact that in the neighbour-
hood of coral reefs the dead corals extend to such a vast depth
that, supposing them all to have been formed near the surface, and
that surface only lowered by abstraction of water to the Poles,
the accumulation of ice must have been so great as to become in-
credible.

Sir Cuartes Lyrrxi had already suggested to Mr. Croll that, as-
suming the accumulation of ice at the Pole depressing the centre of
gravity of the earth, the submergence that would have resulted had

Mr. A. Tylor on the Formation of Deltas. dll

the quantity of water in the sea remained the same would, to some
extent, be counteracted by the reduction in volume consequent on
the formation of the ice. With regard to the delta of the Missis-
sippi, the data on which he argued had considerably altered since
first he wrote on the subject, inasmuch as recent calculations had
doubled the estimated volume of water flowing into the sea, and
thus it was capable of producing the same effect in half the pre-
viously calculated time. The progress of the delta at any spot was
of necessity variable, as the position of the mouth changed. The
American engineers had allowed only 40 feet as the depth of the
fluviatile deposits, whereas from boring Sir Charles had concluded
it to be at least 500 or 600 feet. There was now reason to suppose
that it was much more, possibly as much as 1500 fect. This
being the case, notwithstanding the amount of work done by the
river being doubled, his calculation as to the time required for the
formation of the delta might not after all be so excessive.

Mr. Prestwicn suggested that Mr. Croll’s theory only involved a
transfer of ice from one Pole to the other, and not a diminution of
volume of the sea. The raised beaches round the coast of Britain
varied considerably, and were not on one uniform horizon, as they
would have been had they resulted from a lowering of the sea.
The elevation of the old sea-beds during the Glacial period were not
accounted for by any supposition of the mere alteration in the
volume of the sea.

Mr. Evans pointed out that, the Cyrena being a freshwater shell,
its position at a certain level was not connected directly with the
height of the sea. He doubted the curve of the rivers being in all
cases parabolic.

Mr. Matzer had already remarked that the beds of rivers,
especially near their sources, appeared to assume curves closely
allied to a parabola. He considered that the form was due rather
to the elevatory forces than to erosion. He doubted, however,
whether they were really parabolic curves, or indeed any other ma-
thematical curve.

Mr. Tytor replied that he had not found definite evidence as to
the extension of corals downwards to such a depth as that men-
tioned by the President. With regard to oscillation, he had merely
treated of the southern part of England. The opening of the Straits
of Dover would account for the existence of beaches above the pre-
sent level, as the. tides would have previously risen higher. The
parabolic curve was that which, by actual comparison, coincided
most closely with the longitudinal section of the banks of the rivers
Po, Mississippi, and Ganges.

elas

XLII. Intelligence and Miscellaneous Articles.

ON THE COLORATION OF PEROXIDE OF NITROGEN,
BY M. SALET.

(THE vapour of peroxide of nitrogen (hyponitric acid) has several

remarkable properties. Its density rapidly decreases up to 43°;
the decrease then becomes slower, and it ceases at 150°*. It is
at the same time observed that the colcur of the vapour gradually
deepens; from yellowish brown it becomes reddish brown and then
deep red.

It may be asked whether the same cause cannot explain these two
peculiarities.

Wurtz supposes that the molecule of peroxide of nitrogen at a low
temperature contains N?O!= 2 vols., and that on being heated it is
gradually dissociated into 2 molecules, NO?, each occupying two
volumes (Chimie Moderne, p. 156). This decomposition, which is
the inverse of polymerization, is not without examples in chemistry ;
the cases of cyanic acid, styrolene, &c. may be adduced.

Supposing that NO? and N20! expand regularly, it is easy to cal-
culate the composition of a mixture of these two bodies which for a
given temperature would have the density found for peroxide of
nitrogen,

Let D be this density referred to hydrogen (that is, the weight of
the volume of peroxide of nitrogen equal to that of H); let a and }
be the quantities in weight of NO and N? 0‘ contained in this vo-
lume. As we have 2(NO?)=23 and 3(N? O*)=46 for the theore-
tical densities of NO? and N? U! referred to hydrogen, the following
relations may be established :

a+b6=D, —+4— =];

whence
a=D—46, b6=2D—46.

Table A gives the values of - ; that is, the proportion in weight

of NO? calculated from the experimental densities determined with
so much accuracy by MM. St.-Claire Deville and Troostt. It will
be observed that these latter numbers are a little too high, corre-
sponding to an experimental density a little weaker than the theo-
retical.

Uhis being granted, we may reason as follows :—Since peroxide
of nitrogen is colourless at a temperature at which its density pro-
bably corresponds to N?0‘, and its colour is deeper the nearer
we approach the temperature at which the molecular condensation
corresponds to the formula NO?, let us assume that N? O* is colour-
less and NO’ coloured, and investigate the consequences of this hy-
pothesis.

* MM. H. St.-Claire Deville and Troost.
+ Comptes Rendus, vol. Ixiv. p. 237,

Intelligence and Miscellaneous Articles. 313

Table A will serve to construct Table B; this latter gives the
length 2 which a column of nitrous vapour at 26°°7 must have, on
our hypothesis, to present the same degree of colour. as a column
of vapour of constant length and equal to unity but of varying tem-
perature. It is calculated by the formula
ail P

D 3:1214 x 20°26
in which P is the weight of the unit of volume of peroxide of ni-
trogen at ¢ degrees. It will be seen from an inspection of this Table
that the coloration at first rapidly increases with the temperature—
that it then attains a maximum, because the increase in specific co-
loration is balanced by a decrease in density—that, finally, the effect
of this decrease predominates, so that the coloration itself decreases
indefinitely.

Se) Sonessca oes ce I a 2

uv

A. Be
Tempera- -

ture, | Weight of | Proportion in Theoretical

be a litre of Weight of N O?, coloration, Experimental

vapour, | = a wile . | numbers.
D D 3:1214 x 20-26
°

26-7 | 31214 20°26 per cent. | 1 ]

35:4 2°8975 25:8 ee 1-182 1-18

39:3 | 27745 | 296 ” 1-299 128

49-6 | 24793 | 405 ” 1-588

60-2 2-1980 53°3 3 1°852 1:9

70:0 1:9768 66:1 ee 2-066

80°6 | 1:7973 | 769 | 2-185 | 22

900 | 16744 | 851 ” 2-253

1001 | 1:5892 | 897 2-254 | 28
111-3 15144 93-3 a 2-234 2-25
121°5 1:4519 96-6 Ls 2-218 2-24
135-0 1:3814 99-1 i 2-165 2-2
154-0 | 13082 [101-7 » 2-104 2-12
FAS NT ie ea 1-9 1:95
2 pad Je |) oes da ee oe 1:8
aU RUA ce i Tose ze iy
MMA BGR 7 | <4 ye cwcanece. 1-6 16
SUD I Seal aaa ee een 1-56 1°52

nN ee

These consequences of our hypothesis have been experimentally
verified. By means of a special calorimeter we determined the values
of x with a sufficient degree of approximation; the means of the
experiments are met with in the last column of Table B. We
have carried the experiment beyond the temperatures for which the
vapour-density has been determined by MM. Deville and Troost;
we have assumed with these chemists that the density is then normal.

Our apparatus consists of two prisms for total reflection, which
send the light of the zenith through two horizontal tubes closed by
glass plates and placed in the same right line. These tubes contain
vapours under the ordinary atmospheric pressure ; they are heated

314 Intelligence and Miscellaneous Articles.

in an air-bath ; and one of them may be lengthened or shortened at
pleasure. Inthe space between them two other prisms for total re-
flection are placed, which send the two coloured beams parallel, so as"
to form two tangential images as in the saccharometer. ‘The tube of
fixed length is gradually heated; and equality in colour is obtained
by varying the length of the second tube, which is kept at a tempe-
rature of 26°°7.

It was previously ascertained that the principle of compensation
adopted was applicable; for two columns of vapour, the one hot and
short, and the other cold and long but presenting the same colour to
the eye, gave the same spectrum when the same image was examined
by a direct-vision spectroscope the refracting edges of which were
horizontal.

Spectroscopic examination showed that the colour of a column of
nitrous vapour cannot be compensated by that of a column of liquid
peroxide of nitrogen. ‘The spectrum of this latter does not present
bands of absorption, only a maximum of intensity in the reddish yel-
low.—Comptes Rendus, August 8, 1868.

ON THE MAGNETISM OF CHEMICAL COMPOUNDS.
BY PROFESSOR WIEDEMANN.

The magnetic deportment of chemical compounds of magnetic me-
tals is highly interesting, inasmuch as the metals in them frequently
retain to a greater or less extent the magnetism which they possess in
the free state, and thus, by a determination of this magnetism, conclu-
sions may frequently be drawn in reference to the properties of the’
metals themselves in their combinations. From this point of view
the author had determined in a former investigation the degrees of
magnetism of various oxygen and haloid salts of the magnetic me-
tals, and had found that in analogous salts of the same metal the product
of the atomic weight with the temporary magnetism excited by the unit
of magnetizing force in the unit of weight of the salt (that is, the
magnetism of an atom of these salts) is almost constant. If this atomic
magnetism for ferric-oxide salts is 466, its mean value for chromic-
oxide salts is 190°8, and for protosalts of manganese, iron, cobalt,
and nickel the numbers respectively 468, 307, 313, and 142.

I. Recent investigations, made by an entirely analogous method to
the former, have shown that the same deportment also prevails in the
oxygen and haloid salts of cerium, didymium, and copper. Retain-
ing the former unit, we have for the atomic magnetism in aqueous
solutions the numbers—

Didymium sulphate .......- 104°4
a WMIGLACE As ees eee 104°2
ms acetate. oe). oe Oa

a chloride >. 225.0 Oa

Intelligence and Miscellaneous Articles. 315

Cergus nitrates O20 Soe. 48°7
Certum chloride: .....:.... 47°6
Pupricysulphate:, 4..3,..3 +... 49°5
* Chil eS Sa 50°7
ue elilonidets os 2. bcs. 48°9
ee VOM: 6 eos Sels ew wore 47°7
* BE CUAGC Eo ico aigiee Ke 48:0

II. In the solid salts, too, almost ‘i same values are obtained,
especially when they contain water of crystallization. Thus the
atomic magnetism for

Crystallized didymium sulphate is ... 107°2
Crystallized cupric sulphate is ...... 49-6

If, however, the solid salts are anhydrous, their atomic magnetism
is in general somewhat less, as has been found in a previous investi-
gation in the case of cobaltous sulphate, ferrous oxide, and ferrous
chloride.

Thus the atomic magnetism of anhydrous cerous sulphate is 44:9.

These diminutions in the atomic magnetism of anhydrous copper salts
are considerable, even when they are combined with ammonia, It is,
for

Euuydrous cupric sulphate’ ......0..2..... 42:2
Me eT 1... le, oe ae ee ose eS: 43°5
2CuSO*+NH?.. BO oS RAR RA Sc |
sO? + ONE? +aq)... 0.0.0... fe 481
eae INET. ee oe, ESR AN, SY 44:6
Cupric chloride (anhydrous) ............ 40:0
. a saturated with ammonia..: 37°l
= dissolved in water ........ si °2
pp eeromide (anhydrous) 0.995%... oe 24-0
$5 a saturated with ammonia.... 41°l
sts x dissolved in water ...... 48:0

A similar deportment is exhibited by the solid scab salts. While
the mean atomic magnetism of the dissolved salts is 142, that of

Crystallized nickel sulphate is .... 1389°2
Anhydrous nickel sulphate........ 131:0
Ammonium nickel sulphate ...... 135°6

The solid anhydrous chlorides of nickel and of cobalt exhibit a
higher atomic magnetism (156 and 378-395 respectively ).

These variations obviously depend upon the different densities,
and are especially prominent with very dense salts—for example,
cupric bromide (specific gravity =4°38). Ifthe connexion between
the particles of the salts is diminished by the intervention of water,
asin the case of the hydrates or of ammonia (as in the ammoniacal
copper salts), the atomic magnetismi s at once diminished, and still
more so by dissolving the salts.

III. The magnetism of the copper salts is very remarkable, and

=

316 Intelligence and Miscellaneous Articles.

particularly that of cupric bromide, a salt both whose constituents
(copper and bromine) are feebly but decidedly diamagnetic, as direct
determinations show. Two diamagnetic elements can thus by their.
combination give a magnetic compound. 4

That this magnetism of copper salts is to be ascribed to the copper
itself is proved by its constancy in various salts, even when, as in the
double cyanides, the magnetism of the simple or compound radical
united with it is changed.

IV. In other investigations two solutions of known magnetism,
M, and M,, which change their constituents by double decomposition,
were mixed in a glass and the magnetism M,, of the mixture investi-
gated. Among others the following solutions were mixed :—

M,+M,. Mn.
Ferric chloride and potassium ferrocyanide .... 20°4 7p Mea
Ferrous sulphate as i +e. pee, petal 40°3
Cupric sulphate i 3s Bene 77 08
Nickel sulphate J 2One 22°5
Ferric chloride and potassium sulphoeyanide . omboel 14°6
Manganous suiphate and potassium ferrocyanide. 71°8 70°2

The solid form in which one of the salts formed by double decom-
position is frequently precipitated exercises in only a few cases any
disturbing influence.

Hence, if we miz two salts whose constituents change by double elec-
tive affinity, the total magnetism of the solutions is the same after
double decomposition as before.

We can draw from this with great probability the following con-
clusion :—That the magnetism of a binary compound is made up by
simple addition of the magnetisms of both its constituents in their re-
spective conditions ; and that these constituents, when they enter into
other binary compounds without changing their constiiution or atomic
grouping, retain their atomic magnetism without alteration.

V. From the equality of the atomic magnetism of solid potassium
ferrous oxalate with the atomic magnetism of other ferrous salts, as
well as of potassium ferric oxalate and of potassium iron alum in a solid
form with that of the other ferric salts, we can prove, in opposition to
the views based on the peculiar colour of the salts*, that in these salts
in the solid form the iron is contained in the same manner as in other
ferrous and ferric salts. The constancy of the atomic magnetism
proves that in the different coloured chromic salts the magnetic
atomic group retains its properties unchanged. It also remains un-
changed if anhydrous copper or nickel salts combine with water, an
observation which does not agree well with Graham’s views on the
constitution of the ammoniacal copper salts. On the other hand,
luteocobaltic chloride and purpureocobaltic chloride are diamagnetic ;
so that, unlike the copper salts, they are not to be regarded as simple
cobaltic salts united with ammonia; the atomic group containing
the metal and determining the atomic magnetism must be es entially
different from what it is in the simple salts.

* Compare Haidinger, Pogg. Ann. vol. xeiv. p. 246,

Intelligence and Miscellaneous Articles. 317

VI. If uv, stand for the atomic magnetism of the dissolved salts of
the magnetic metals, the atomic magnetism wu, of their hydrated
oxides freshly precipitated from their solutions is as follows :—

Hydrated nickel monoxide .... u, = 1°004u;
ne cobalt monoxide <....... 112
A FERTOUS ORIG. ok 2 ns ates © it?
manganous oxide ..... . 0°85
3 emiie OXIME! 2 2 7)./ntn x te OAS
a2 chromic: oxide 2.02)... 22.3- O95
ies ferric oxide ...... : 0°69-1°18

Thus the atomic magnetism of the Riis of the magnetic metals
is partly equal to, and partly smaller or somewhat larger than that of the
corresponding salts ; so that, having regard to the influence of density,
it may be assumed that the group “which determines the magnetism
in them has the same constitution as in the corresponding salts.

VII. On precipitating ferric hydrate from its salts, the atomic
magnetism of the precipitated oxide rapidly rises from 0°67 to
1°129u, ; this is probably due to the circumstance that in the first
few moments the ferric hydrate is still partially dissolved in the col-
loidal condition.

The colloidal dissolved ferric oxide has an atomic magnetism
(100°2) which is only about 0-2 that of the ferric salts. In like
manner the feeble atomic magnetism of ferric acetate under different
circumstances (114 to 147) shows that in this case also a great part
of the ferric oxide is dissolved in the colloidal state. In any case
the magnetic atomic group in this colloid ferric oxide is different from
what it is in the precipitated ferric hydrate and in the ferric salts.

This difference is not met with in the chromic oxide dissolved in
potash, where the chromium both before and after coagulation has
the same atomic magnetism as in the salts. In like manner the

atomic magnetism of nickel monoxide dissolved in ammonia is the same
as that of the hydrate.

VIII. The magnetism of the oxides of the magnetic metals is far
less than that of the salts; yet it is different according to the mode

of preparation and the density. The atomic magnetism was found
to be, for

Freshly ignited nickel monoxide Seite or a ob cee 66°4

“ SOPOT NATED. 11 (SUN PRE E eee eA 55°0

3 Asie da GUTELC ORTIG Biotic cg hoe ole ssuersnycyiegs 10°5

Seg DNAPANOUS OXRIGE oc fons oats cieys cues clean

ss aoe CHROMIC OKIGCH 7, cof wt < a hy an. the, 8

e », Chromic oxide cag tes ice Sor 107
with alumina

ES SAW METS SEO RTS To Ce Se an

5 » ferric oxide precipitated aa 256
WEUM, AMINA | ee ee sk cae. «

It cannot yet be determined whether the magnetism of the oxides,

318 Intelligence and Miscellaneous Articles.

which is so small in comparison with the magnetism of the hydrates,
depends on an alteration in the density of the whole mass, or only
on an alteration of the magnetic atomic group itself.

IX. The sulphur compounds corresponding to the salts of the mag-
netic metals investigated are, with the exception of sulphide of man-
ganese, very feebly magnetic.

X. Nickel cyanide and cobalt cyanide have an atomic magnetism
which is only about 0°4 to 0°6 of the atomic magnetism of the other
salts of nickel and cobalt. When these cyanides are dissolved in solu-
tion of cyanide of potassium, their magnetism almost entirely disap-
pears. This cannot arise from the formation of a simple double
salt; for the magnetic constituents in the double salts retain their
atomic magnetism unchanged; the magnetic atomic group must
rather have itself changed. The salts formed have probably the
composition 2 KCy, CoCy’, and 2KCy, NiCy’, corresponding to their
electrolytic deportment. The analogous magnetic deportment of
potassium ferrocyanide and potassium ferridcyanide favours this view.
’ From the experiments on the decomposition of magnetic salts by
double elective affinity, the potassium can be replaced by the magnetic
metals, which thereby retain their atomic magnetism unchanged as in
the ordinary oxygen and haloid salts. From the analogy with the
latter they would also have to be regarded as consisting of an equi-
valent of potassium combined in potassium ferrocyanide with a dia-
magnetic atomic group (Cy+43FeCy), by which the salt itself is dia-
magnetic, and in potassium ferridcyanide with a magnetic atomic
group (Cy+Fe2Cy), by the addition of which the salt becomes

magnetic.

XI. The atomic magnetism of the three salts of manganese, iron,
and cobalt corresponding to potassium ferridcyanide is, both when in-
vestigated in the solid and in the liquid state, for one equivalent of
the magnetic metal (for instance Fe =28, &c.),—

Potassium manganicyanide.......... 145°4
se ferrocyanide 42:72 pee one
tn cobalticyanide..... ben" 3°5

As in the oxygen and haloid salts of the three metals, the atomic
magnetism of potassium ferrocyanide is the mean between that of potas-
sium manganicyanide and potassium cobalticyanide; and the three
atomic magnetisms of these salts are less by almost an equal amount
than the magnetisms of the oxide salts of the same metal, as if a
strong diamagnetic atomic group had been joined to the magnetic
metals in them. In the sulphocyanides the metal has the same
magnetic properties as in the simple salt of the same metal.—Ber-
liner Monatsberichte, July 1868.

ON THE LATENT HEAT OF VOLATILIZATION OF SAL-AMMONIAC.
BY M. C. MARIGNAC.
Sal-ammoniac when volatilized occupies double the volume re-
quired by a theory which of late years has had numerous partisans.
Is this to be ascribed to an anomaly in the physical constitution of

Intelligence and Miscellaneous Articles. 319

its vapour, or should it be explained by the dissociation of the
elements ?

We owe to M. H. St.-Claire Deville an ingenious experiment
which proves that in all cases the decomposition of sal-ammoniac is
nut complete. Ammoniacal gas and hydrochloric acid gas heated
to 360°, and brought together in a space kept at this temperature,
would manifest their combination by a disengagement of heat which
would raise the thermometer beyond 390°. It is therefore impos-
sible to assume that in the vapour of sal-ammoniac at 360° the
elements are quite in a state of liberty. But it isnot thereby proved
that at this temperature there is not a partial decomposition, which
may reach an amount sufficient both to explain the disengagement
of heat arising from the mixture of the two gases, and the low den-
sity of sal-ammoniac.

Among the experiments which might throw some light on this point,
if not solve it, one of the most important would be a determination
of the latent heat of sal-ammoniac. For if this volatilization is due
toa simple change of state, it ought only to absorb a quantity of heat
analogous to that required to produce this same physical modification
in other compounds. If, on the contrary, it is accompanied by a
more or less complete chemical decomposition, it should require a
far greater quantity of heat, not greatly different from that which
results from the chemical combination of ammoniacal gas and hydro-
chloric acid.

These considerations have led me to attempt this determination ;
but it presents such difficulties that I can only offer my results as a
rough approximation, sufficient, however, for the object in view.

The method usually employed for the determination of the latent
heats of vapours is inapplicable in the present case; for it is im-
possible to transport the vapour of sal-ammoniac from the vessel
where it is formed to the calorimeter. When it is no longer in con-
tact with surfaces heated to 350°, it condenses and soon stops up
even the widest tubes.

I have endeavoured to invert the problem, and to measure the
quantity of heat used in volatilizing the salt in the open air, as com-
pared with that required for the volatilization of water under the
same circumstances.

The apparatus I used consists of a massive cast-iron cylinder in
which three cavities are perforated symmetrically about the axis; in
one of these is an air-thermometer, in the two others the substance
to be volatilized.

The cylinder heated to redness is transferred to a box with badly
conducting sides, in such a manner that its upper face is exposed to
the air.

_The substance to be volatilized, contained in thin glass or silver
tubes, is placed in the cavities of the cylinder the moment it attains
a given temperature (500° for instance). The tubes are withdrawn
when the thermometer indicates 420°; the loss of weight they have
experienced gives the amount volatilized.

On the other hand, an investigation of the cooling of the appara-
tus, made by numerous experiments both when it contained no sub-

320 Intelligence and Miscellaneous Articles.

stance in the interior and when part of its heat was used in volati-
lizing either water or some volatile substance, enables us to calculate,
not exactly, perhaps, but at all events with sufficient approximation,
_ the quantity of heat consumed in each case.

For the details of the method I must refer to the memoir which I
shall publish on the subject, and I limit myself here to indicating the
principle of the method.

I find that the heat of volatilization of 1 gramme of sal-ammoniac
is 706 thermal units, with a great probability that its real value is
between the limits 617 and 618. .

The magnitude of this number, compared with that of the various
compounds for which it is known, and, on the other hand, its agree-
ment with that for the heat of combination of ammoniacal and hy-
drochloric acid gases*, make it highly probable that sal-ammoniac is
indeed partially decomposed into its elements when it is vaporized.

To strengthen this conclusion, and to be certain that the high
numbers are not solely due to the imperfection of the method used,
I have endeavoured to apply it to determining the latent heats of
some other substances; but having only made a few experiments
in each case, I shall cite the results without attaching any other im-
portance than that of showing that my method does not necessarily
lead to high results in the case of bodies which approach sal-ammo-
niac in their physical properties (boiling-point or solid state).

Mercury, 103 to 106.—This must be regarded as a minimum ;
for a considerable quantity of mercury condenses at the orifice cf the
tubes and falls in the interior in droplets.

Mercurous chloride, 72 to 131, according as we do not, or do,
allow for the portion of salt vaporized in the tubes, but condensed
at their orifice. This difficulty does not occur in the case of sal-am-
moniac, the fumes of which, being very light, are easily carried
away by the motion of the air.

Mercuric chloride, 28 to 45.—These numbers comprise both the
latent heat of fusion and that of volatilization.

Monohydrated sulphuric acid, 292 to 342.—These high numbers
seem to justify the hypothesis of the dissociation of this acid as-
sumed by Messrs. Wanklyn and Robinson. It may, moreover, be
remarked that this heat of volatilization would exactly agree with
the heat of combination of anhydrous sulphurie acid and water.

I must, in conclusion, remark that when I speak of the dissocia-
tion of sal-ammoniac or of sulphuric acid, I attach to this term the
meaning which M. St.-Claire Deville has given to it—that of a par-
tial decomposition, the resultant of a state of equilibrium, varying
with the temperature, between the elements of a body and the com-
pound they tend to form. The principle of my experiments, and
the uncertainty which prevails as to their results, do not justify us
in concluding that there is a complete decomposition, which, more-
over, seems impossible within the limits of temperature attained in
my experiments.—Comptes Rendus, November 2, 1868.

* This heat of combination, according to MM. Favre and Silbermann, is

743°5 thermal units at the ordinary temperature; it would be 715 at a
temperature of 350°.

THE
LONDON, EDINBURGH, ann DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

[FOURTH SERIES.]

MAY 1869.

XLIV. Researches in British Mineralogy.
By Davip Forsss, F.R.S. &c.*

iE

Native Gold.

. the first part of these researches, which appeared in 1867
in the November Number of this Magazine, I communi-
eated the results of my investigations into the chemical composi-
tion and geological occurrence “of the native gold which is met
with in the quartz lodes and alluvial river- deposits of North
Wales. Since that time the recent discoveries of gold in the
north of Scotland have attracted much attention, and rendered
the subject of the occurrence and distribution of the noble metal
in the British Isles one of somewhat more than ordinary inter-
est—a circumstance which has induced me to extend this in-
quiry into an examination of the native gold from all the British

localities whence I am able to procure authentic specimens.
Although it will be found that, even from the most ancient
eriods in English history, statements of discoveries of gold have
been from time to time recorded as having been made in nume-
rous places throughout England from north to south, none of
them seem to have at any time led to a practical or successful
result ; and certainly the majority of such accounts do not upon
scrutiny appear to be entitled to any confidence being placed
either in their correctness or veracity ; in fact the only districts
in England where unquestionable evidence of the presence of

native gold can be obtained are Devonshire and Cernwall.

* Communicated by the Author.
Phil. Mag. 8. 4. Vol. 37. No, 250. May 1869. Y

322 Mr. D. Forbes’s Researches in

It must be remembered, however, that gold in minute quan-
tity is undoubtedly contained in some of the English lead and
copper ores, especially when these ores are strongly argentiferous,
as will be hereafter noticed. Stili the total amount of gold
present in such cases is so extremely insignificant as neither to
entitle them to the appellation of gold ores proper, nor even, in
most if not all cases, sensibly to augment the value of the ore
itself, since, as a rule, its value would scarcely be found to cover
the expense of its extraction or separation from the other metals
with which it 1s associated in the ore as it comes from the mine.

In Devonshire the Poltimore mines at North Molton are tra-
ditionally reported to have been worked for gold by the Romans
during their occupation of Britain; and in 1853 the brown and
red ‘‘ gossans”’ forming the substance of this lode at its surface-
outcrop or “backs,” as it is called by the miners, were treated
as gold ores, and stated to yield between one and two ounces of
fine gold per ton of “ gossan.” Still, although a not meonsider-
able amount of gold was extracted from them, the final result of
the adventure did not prove remunerative. The chemical exami-
nation of these “ gossans,” made by myself in 1854, indicated
that they were a product of the decomposition of slightly aurife-
rous metallic sulphides (principally iron), due to oxidation and
other atmospheric influences; and whilst it proved that these
gossans did contain a small amount of gold, it at the same time
showed that the actual amount present in them was much less,
and much more irregularly disseminated throughout the mass,
than had generally been reported. |

Native gold along with stream-tin ore (cassiterite) has also
been washed out of alluvial deposits at Shepstor in Dartmoor,
which have no doubt been formed from the débris arising from
the disintegration of the granitic rocks of that district.

Natwe Gold from Cornwall.

In this district the occurrence of gold im situ in its original
rock-matrix is extremely rare; but it is reported to have been
found in a cross course in Huel Sparnon, and the gossan of the
Nangiles mine is said to be auriferous. In the British Museum
a specimen of gold in quartz along with argillaceous or possibly
chloritic slate 1s exhibited ; but as no locality is given besides
Cornwall, I am uncertain as to whether it is to be regarded as
thoroughly authentic or not.

In a recent visit to the north of Cornwall I found that the
argentiferous tetrahedrite (Freibergite), chalcopyrite, and galena
from a lode at Bound’s Cliff near St. Teath, contained a minute
bui distinct amount of gold; but I have as yet not been able to
determine its amount quantitatively.

British Mineralogy. | 328

It has long been known, however, that the alluvial deposits in
the beds of many of the Cornish rivers contain native gold in the
form of nuggets and small rounded or flattened grains or scales;
and it appears not improbable that the gold forming the orna-
ments of prehistoric origin frequently found in Cornwall and
the neighbouring counties may have been derived from this source.
A nugget of gold from these alluvial deposits in the collection of
the late Sir Charles Lemon weighs more than one ounce, and
the largest nugget recorded is stated to have weighed 2 ozs,
3 dwts.; but these are quite exceptional instances, as in general

_the weight of the particles does not exceed a few grains.

Most frequently the gold is found associated with the so-called
stream-tin (cassiterite or oxide of tin) ; and when the stream-
works were, as anciently, an important source of the tin-production
of Cornwall, a not inconsiderable quantity of native gold seems
to have been obtained during the washing of the alluvial deposits
for tin ore. As these deposits have now been nearly, if not alto-
gether, exhausied, it has become extremely difficult to meet with
authentic specimens of Cornish gold at the present time.

In the British Museum may be seen a specimen of stream-tin
ore with gold from the Carnon stream-works ; and Messrs. Greg
and Lettscm mention gold being found at the Crow Hill stream-
works at Trewarda, Kenwyn, at Llanlivery near Lostwithiel, and
at Laddock near Grampound.

As no analysis of native gold from Cornwall is to be met with
in any of the works of mineralogy which I have examined, I
have for several years been endeavouring to secure an authentic
specimen for the purpose of determining its chemical composi-
tion, but only succeeded last month, when Mr. W. J. Henwood,
F.R.S., kindly sent me a specimen, obtained through Mr. Pe-
therwick of St. Austell, from St. Austell Moor.

The gold thus obtained was of a rather deep gold-colour, but
ef a dingy lustre, the surface of the particles being worn and
rounded by attrition; it consisted of nine minute nuggets of very
irregular forms, the largest of which weighed 2°1 grains, whilst
their aggregate weight was only 5°46 grains.

The specific gravity, determined upon the entire quantity at
disposal, was found to be 16°52 at 60° Fahr. ; and the chemical
analysis gave the following numbers as the percentage composi-
tion of the gold itself :—

Golds 6 yeMeain? els oe sees eo 9O12

pul wer ns |!/s-/t12 : sas) +9205
Silica with sesquioxide Gumont = = O33
100-00

¥2

O24 Mr. D. Forbes’s Researches in

results which closely approximate to the composition of the gold
from the Clogau mine in North Wales previously examined by
me, and which correspond to the formula Au® Ag, which by cal-
culation requires 90°88 per cent. gold to 9:12 per cent. silver.

The geological age of the appearance of this goldis, I believe,
identical with that of the intrusion of the stanniferous and auri-
ferous granites of Cornwall, which appears to be some time be-
tween the Silurian and Carboniferous periods; and it seems not
improbable that the greater portion of both, the stream-tin ore
as well as the native gold, was originally disseminated through-
out the mass of the granite itself, and subsequently, through
its disintegration, became set free and washed down into the
alluvial deposits formed by the rivers.

late Gold, Wicklow, Ireland.

To the good offices of Mr. F. Jennings I am indebted for two
small nuggets of gold from the Wicklow alluvial deposits, which
have enabled me to determine their composition.

The specimens were rounded irregular masses, and evidently
contained internal cavities, so that the determination of their
specific gravity is not to be relied upon.

Their colour was a rather brassy golden hue, whilst the ex-
ternal surface of the gold was abraded and possessed a very
dingy lustre.

The specific gravity of the one nugget was found to be 15-07,
whilst that of the other was only 14°34——probably owing to the
existence of internal cavities or quartz particles. |

The analysis was conducted upon the first-mentioned of these
nuggets (spec. grav. 15:07), and in precisely the same manner
as described in the case of the gold from the Clogau mine in the
first part of these researches.

The results obtained gave the following percentage compo-
sition :—

Gold’). 232 2) See Geom

Silver oc.) 2) Sse aoe
Quartz: <2 4. 0c). eae
100:00

These results do not coincide with the analysis of Mr. W.
Mallet, published in the Journal of the Geological Society of
Dubha, vol. iv. p. 271, but are almost identical with those ob-
tained by Mr. R. Scott, published in Sir W. Wilde’s ‘ Catalogue
of the Gold Antiquities in the Collection of the Royal Irish
Academy,’ 1862, when the amount of iron obtained by him is
subtracted*.

* Mr. Scott informs me that this was probably due to entangled pyrites,
and that he also found a trace of copper present.

British Mineralogy. 325

The results of these two analyses are given as follows :—

Mallet. Scott.
Cold Be. 6 «9202 89:0
SEven 3. <.. 6:17 Sal
MEM se cs OTS. Dal
99°27 99:2
Specific gravity . 16°342 ?

Several large nuggets of the gold from the washings on the
river on the north-east side of the mountain Croghan Kinshela
in the county of Wicklow, on the borders of Wexford, are to be
seen in the British Museum; and the largest nugget known to
have been obtained is stated to have weighed twenty-two ounces.

The minerals associated with this gold are as follows :—

Cassiterite (tinstone), magnetite, hematite, pyrite, titanoferrite,
wolfram, wad, chalcopyrite, galena, molybdenite, garnet, chlo-
rite, felspar, and mica—as well as, according to Mr. Mallet,
topaz, sapphire, zircon, and native platinum.

This gold is, without doubt, derived from the disintegration
of the granite of the district, which appears to be what I have
elsewhere described as a normal auriferous granite composed of
orthoclase, quartz, and mica, similar to the Cornish rock, and,
like it, both stanniferous and auriferous.

That the gold along with the cassiterite and wolfram really
exists as a constituent of the granite itself, or, in other words,
is disseminated throughout its mass, is in accordance with the
conclusions arrived at by Mr. Weaver, who, with Messrs. Mills
and King, was appointed Director of the Government gold-wash-
ings on the Ballinvally stream at Croghan Kinskela in 1796.
The observations of Mr. Weaver are contained in the report on
the geological relations of the east of Ireland, published in the
Transactions of the Geological Society, vol. v. p. 211; and he
mentions therein that the total gold obtained during the period
that the washings were worked on aceount of the Government
amounted to 944 ozs. 4dwts.15 grs., or in value £3675 7s. 114d.,
and that up to the time of the Irish Rebellion in May 1798 the
gold obtained had not only fully reimbursed the advances made
by the Government, but had, besides defraying its expenses, left
a surplus in hand.

Native Gold, Sutherlandshire.

In the sixteenth century gold is said to have been discovered
in some quantity, and worked, at Durness on the north coast of
Sutherlandshire ; and in 1840 a solitary nugget of more than one
ounce in weight is reported to have been found in the river of

326 Mr. D. Forbes’s Researches in

Kildonan. It was only, however, towards the close of last year
that the localities which now are being somewhat extensively
explored were discovered by a Mr. Gilchrist, a native of Suther-
landshire, who had but recently returned from Australia, where
he had been engaged in the gold-diggings for a number of years.
The consequent rush of adventurers to these auriferous deposits
has led to finding gold in the beds of many of the neighbouring
streams; but as yet no authentic information has been received
as to the occurrence of gold in situ in the rocks of this district.

The first find was made in the Kildonan Strath, about ten
miles inland from Helmsdale, and a little later at Siesgill Burn,
about two miles above Kildonan. At the commencement of this
year a further discovery of gold was made in the Strath of Dun-
beath in Caithness-shire , about the end of January, in two dif-
ferent burns between Ben Smesral and Gordonbush, and subse-
quently in Auldtoun Burnand at Kilcomikill (about six miles from
Brora), in a tributary of the river Brora.

Mr. James Haswell of Hdinburgh kindly put me in communi-
cation with Mr. P. G. Wilson* of Inverness, who has furnished
me with specimens of the gold produced from the Kildonan
washings, and thus enabled me to submit them to a chemical
examination.

The gold from the Kildonan diggings, as they are called, which
I received from Mr. Wilson, was in ‘the form of minute erains
more or less flattened, and varying in size from the smallest
speck up to that of a split pea, the largest of them weighing
about 5 grains. I understand, however, that lumps of much
greater size have been occasionally met with, and, amongst others,
that the original discoverer (Mr. Gilchrist) had in his possession
five nuggets varying in weight from one quarter of an ounce up
to one ounce troy.

The colour was an extremely beautiful pure golden yellow, very
much resembling that of the South American alluvial gold; and
from its appearance it would be judged much richer in gold than
it actually proved to be upon assay.

The specific gravity of the gold was determined upon 39°97
grains, carefully selected so as to be free from any visible mineral
impurity, and was found to be 15°799 at the temperature of
60° Fahr.

The analysis was conducted in precisely the same manner as
described in the first part of these researches when treating of
the Welsh gold; but it was found, owing to the large amount of
silver present, that considerable difficulty was experienced in
getting the whole of the gold into solution; even when the gold

* In aletter from Mr. Wilson, dated the 8th of April, he informs me
that he has already purchased gold from the diggers to the amount of £431.

British Mineralogy. 327

had previously been flattened out extremely thin on an anvil, it
became instantly coated with a firmly adherent film of chloride
of silver, which effectually protected it from the further action of
the acid; and it was only after repeatedly removing this film by
dissolving it off with ammonia, that the entire amount of gold
could be converted into the state of chloride.

Two analyses were made, and afforded respectively the follow-
ing percentage results :—

Bee. Ge 81:27
PECs by cals» det 18°47
Silica (quartz)). . O44 0:26

100-00 100-09

From these numbers it will be seen that the composition dif-
fered very considerably from either the Clogau, Wicklow, or
Cornish gold previously examined, and that it was alloyed with
much more silver than even the stream-gold from the washings
in the river Mawddach near Dolgelly, which by analysis afforded
as much as 13°99 per cent. of silver.

The associated minerals, as far as I have been able as yet to
verify, are :—quartz, which frequently is entangled in even the
very small particles of gold; garnets, the iron alumina variety or
almandine, of a pale red or rather pink-red colour, often crystal-
lized in dodecahedrons and about the size of pins’ heads; mica,
iron glance, titanoferrite, magnetite, and iron pyrites.

Upon washing the gold from the lighter substances, there in-
variably remains a quantity of black sandy particles mixed with
grains of quartz and garnets in fragments as well as in minute
rounded dodecahedrons: upon treating this with a magnet the
greater part of the black particles are removed; but there remain
a number behind, which consist of black iron glance along with
apparently non-magnetic titanoferrite. The black particles taken
up by the magnet were examined and found to possess a specific
gravity of 5:08 at 60° F., and to give a blackish-grey streak. On
analysis they were proved to be composed of

Oxidewoe ron 2). 6 9126

Titamevaci 2 eo 54) 8:03
Siieas arent ites es that OZ |:
100-00

s0 that | imagine that the sand consists principally of grains of
magnetite along with a little Ilmenite, or some other variety of
titanoferrite.

Although the native gold from Sutherlandshire has as yet only
been obtained from washing the alluvial deposits which have ac-

828 Mr. D. Forbes’s Researches in

cumulated in the beds of the rivers, and not been mined out of
the solid rock, the geological structure of the surrounding dis-
trict furnishes evidence as to its origin. A glance at the maps
published by Mr. Cunningham and Sir Roderick Murchison
shows that the country is composed of slates, schists, and other
highly metamorphosed rocks, now considered to be the represen-
tatives of the Lower Silurian formation, and further indicates that
these strata are in many places broken through and disturbed by
bosses and veins of eruptive granites.

Mr. Haswell informs me that his correspondents from Kildo-
nan write him that the main rock is slate traversed by granite,
and that china-clay is found along the banks of the burn, which
appears to have been produced from the decomposition of the
felspar in these granites; so that it may be inferred that the
auriferous granite and the quartz and other dykes which invari-
ably are connected with its intrusion have been the cause of the
appearance of the gold itself, which most probably is of the same
geological age as in Cornwall, Wicklow, and many other parts of
both hemispheres.

Babingtonite.

This mineral species, which is essentially a silicate of iron and
lime, is of extremely rare occurrence, perfectly authentic speci-
mens having only been procured from its original locality (Aren-
dal in Norway); and there it is but very rarely met with, as small
crystals, associated with epidote and garnet in the iron mines.
It is said to have been found in quartz in the Shetland Islands,
and at Massachusetts on epidote; but in the latter case Dana,
in the Supplement to the last edition of his ‘ Mineralogy,’ p. 794,
states that the angular measurements are not identical.

In 1854 I received from the late Mr. 8. Blackwell a mineral
which had been discovered in a railway-cutting im Devonshire
in such quantities as to be used extensively as an iron ore, with
the request that I should assay it for iron. The sample in
question was found to contain 20°24 per cent. metallic tron along
with 48°26 per cent. silica. The mineral, which looked much
like a variety of hornblende, appeared to me to be worthy of
further examination; but as I shortly after started for my
foreign travels, I have been unable until lately to complete its
examination.

The mineral itself occurs as an aggregate of groups of radia-
ting crystalline fibres which curve in towards their centres of
development, and possess a decided dark blackish-green colour ;
its lustre is vitreous, and in very thin splinters it is trans-
lucent; it 1s somewhat dichroic, and gives green and brown
tints when examined by Haidinger’s dichroiscope ; fracture im-

British Mineralogy. 329

perfect and hackly ; brittle; hardness 5:5, scratching apatite,
but scratched by orthoclase.

The specific gravity, determined by weighing a larg, ‘ge specimen
(2024°5 gers.) out of and in distilled water, was found to be 3-431.
Another determination, made upon 38: 26 grains in the powdered
state, gave 3°436 spec. grav. at 60° F. Afterignition for some
time at a red heat, the mameek which had lost 0°729 per cent.,
was found to possess a specific gravity of 3-474.

The blowpipe characters were found to be as follows :— Heated
in a close or open tube it remains unaltered in appearance, but
evolves a little water, which is probably only hygroscopic; if in
larger fragments, it occasionally decrepitates. After heating, it
reacts alkaline to reddened litmus and turmeric test-papers
moistened with distilled water.

Heated alone in the blowpipe-flame, either in the platinum
forceps or on charcoal, it melts at a pretty strong heat under 3
of Von Kobell’s scale, quietly, without intumescence, to a brilliant
black globule which is not magnetic; with soda alone in the re-
ducing flame it also fuses with escape of gas toa black non-mag-
netic globule; on platinum-foil with soda and nitrate of potash
in the oxidating flame it affords the characteristic green reaction
of manganese.

With borate on platinum wire in the oxidating flame it dissolves
completely to a clear reddish-yellow glass, which becomes colour-
less on cooling, and in the reducing flame on charcoal produces a
greenish lass. With phosphate “it gives the same colour-reac-
tions as with borate, both in the oxidating and reducing flames; but
in this case a skeleton of silica remains in the glass undissolved
by the phosphate.

It is not, or at least very imperfectly, decomposed by acids.
The chemical analysis was conducted as follows :—The amount
of ignition loss was determined upon 88°40 grs., and after heat-
ing for twenty minutes to redness found to be 0°28 gr., equivalent
to 0°729 per cent. 20-01 gers. of the mineral in fine powder
were fused in a platinum crucible with 80 grs. carbonate of soda
n potash; a strong manganese reaction was observed. The
fused mass was decomposed by hydrochloric acid, evaporated in
a water-bath to dryness, and then heated in an air-bath to render
the silica insoluble; the silica, after being weil washed and ig-
nited, weighed 7°83 grs., or 49°12 per cent. of the mineral; its
purity was tested by being dissolved, ina silver basin, in a solu-
‘tion of carbonate of soda, when only an inappreciable trace of
oxide of manganese was found to remain insoluble.

The filtrate was thrown down by ammonia, and the alumina
separated from the oxides of iron and manganese by potash ;
after reprecipitation and ignition it weighed 0:33 gr., equal to

330 Mr. D. Forbes’s Researches in

1604 per cent. The oxides of manganese and iron were then
separated by carbonate of barytes and determined as usual, the
sesquioxide of iron obtained amounting to 4°82 grs., and the
manganosomanganie oxide to 0:27 gr., equivalent to 1:25 per
cent. protoxide of manganese in the mineral. The solution, after
separating the alumina and oxides of iron and manganese, was
now precipitated by oxalate of ammonia, and the resulting oxa-
late of lime converted into carbonate by gently heating to red-
ness with the subsequent employment of carbonate of ammonia.
The amount of carbonate obtained was 7°46 grs., equal to 4°17
grs. lime, or 20°87 per cent. lime in the mineral. From the fil-
trate the magnesia was separated by addition of ammonia and
then phosphate of ammonia, and the precipitate converted into
pyrophosphate of magnesia by ignition; it weighed 2°04 grs.,
equal to 0°73 magnesia, or 3°67 per cent.

As it was found that the iron contained in the mineral was
present im the state of both protoxide and sesquioxide, it
became necessary to determine their respective amounts. Tor
this purpose a separate portion of the mineral was employed and
treated as follows :—A portion of the mineral finely powdered
was mixed with four times its weight of the carbonates of soda
and potash, and placed at the bottom ofa platinum bottle (beaten
out ofa single piece without soldering) about 34 inches deep and
1} inch in diameter ; asmall porcelain tube like the stem of a to-
bacco-pipe was then suspended halfway down the interior of the
platinum bottle, and through it a current of dry carbonic acid gas
was kept passing, provided by a suitable apparatus; the mixture
of the mineral! and carbonates was then heated until fully decom-
posed in this atmosphere of carbonic acid gas; and after allowing
it to cool, the fused mass was decomposed by the addition of sul-
phuric acid uatil all the iron was brought into complete solution,
whilst during the whole of the operation the stream of carbonic
acid gas was kept passing continuously through the apparatus,
so as effectually to prevent oxidation. The contents of the bottle
were now rapidly poured out into a beaker containing water
which had been previously boiled to expel all air, and the bottle
itself well rinsed with boiling water into the same solution, which
was at once titrated by a normal solution of permanganate of
potash in order to determine the amount of protoxide of iron
present.

Two separate determinations were made in this manner, and
the amount of sesquioxide of iron corresponding to the quantity
of protoxide indicated was then subtracted from the total amount
obtained in the course of the analysis, as before described.

The results of the analysis thus executed, when tabulated
showed the composition of the mineral to be as follows :—

British Mineralogy. 301

Oxygen.
Pe beers fe ve ». 40°12 26°19
Pmt, ieee sg, 2 1260 hal 3.68
Beaquioxide.of iron. . . 9°78 2°93

PImioxide Of 1ron. .. .. . 12°87 2°36
Protoxide of manganese . 1°25 0°28 10°57
Tie 5 OS a0 04 5:96

Magnesia . Cae 3°57 1:47
PeceOuienition., .» .» ,. O73

99°39 40°44,

Upon calculation it will be found (when the smaller amounts
of alumina, protoxide of manganese, and magnesia are taken into
consideration, along with respectively the sesquioxide of iron,
protoxide of iron, and lime) that we have 12 equivalents of silica,
1 of sesquioxide of iron, 3 of protoxide of iron, and 6 of lime;
and taking the atomic numbers of these substances at Si0?= 30,

Fe? O?=80, FeO =36, and CaO =28, we should have :—

eae. OE SOU 50°28
bese Pc BO ba he
ea ET TOS 15°08
Seager = 2 168 23°47

716 160-00
These numbers, which approximate closely to those found by
actual analysis as above stated, indicate the mineral to be com-
posed of
6CaO S8i0?+ 3 FeO Si0?-+ Fe? 0? $102,
or 9(CaFe}O, Si02+ Fe? 0% Si0?,
giving the generai formula
9RO Si0? + R? O03, 3 8i0?, |
in which the protoxides are those of iron, manganese, lime, and
magnesia, whilst the sesquioxides are alumina and sesquioxide
of iron.
In the analysis of the Babingtonite from Arendal, spec. grav.
3°366, Rammelsberg * obtained thefollowing percentage results :—
: . Oxygen.
Silica, 6 ne, 1 O22 26°59
Sesquioxide of iron . . 11:00 3°30
Protoxide of iron. . . 10°26 2°28 RasS
Protoxide of manganese. 7:91 1:78 ae
Piticmmt ce Vaniee LOB? d°52
Waenesia /. Sac O77 0-31
WomitionlOss..j54 5 > 6. O44 ;
100-92
* Handbuch der Mineralchemie, p. 477.

332 Prof. R. Ball’s Lecture Experiments to

from which he also deduced the same formula,

9RO Si0? + Fe? 0%, 38102,
being
49CaO
94FeO +S8i0?+ Fe? 0? 8102.
MnO

The minerals are also perfectly identical in constitution, the
only difference beg that the percentage of manganese in the
English Babingtonite is considerably less than in the specimen
from Arendal analyzed by Rammelsberg, which also contained
no alumina, The Arendal Babingtonite, however, appears to
vary considerably in composition in different specimens ; for its
analysis by Arppe* afforded him only 1°8 per cent. protoxide of
manganese along with 0-3 per cent. alumina, whilst another
analysis by Thomson+ showed as much as 6°48 per cent. alumina
and 10°16 per cent. protoxide of manganese. As, however,
neither of these chemists had determined the state of oxidation
of the iron in the mineral, the numerical results of their analyses
are useless for the purpose of determining the constitution or
formula of the mineral itself.

Children announced that titanic acid was a constituent in this
mineral, which I could not*confirm ; and Arppe’s explanation,
that some of the Arendal crystals contained minute particles of
titaniferous magnetite, no doubt accounts for this statement,
since, after extracting all magnetic particles from the powdered
mineral before analyzing it, Arppe found that no titanic acid
could then be detected in the purified silicate.

XLV. Lecture Experiments to illustrate the Laws of Motion.
By Professor Ropert Bari, A.M ft

] HAVE found the arrangements described in this paper

effective in demonstrating to an audience a tew elementary
properties of gravitation and the laws of motion. It is certainly
true that a clear appreciation of the truth of these laws, so es-
sential for properly studying dynamics, requires some experi-
mental illustration to beginners. However satisfactory may be
the multitudes of indirect proofs of these laws with which the
more advanced student is familiar, it will hardly be denied that
it is a little difficult to demonstrate them directly. So far are
they from being axiomatic, that for centuries they were not be-

lieved at all.
* Berzelius, Jahrbuch, vol. xxii. (1842).
fT Phil. Mag. vol. xxvii. p. 123.
+ Communicated by the Author.

illustrate the Laws of Motion. 333

The apparatus which is described in works on physics as
available for the purpose of proving them, consists merely of a
very few instruments, among which Atwood’s machine is that
most commonly referred to. This meagreness contrasts strangely
with the profusion of apparatus which has been devised for the
illustration of the elements of other branches of science (electri-
city, for example); yet surely it would be as desirable to prove
to a student the second law of motion by direct experiment, as
it is to demonstrate experimentally the laws of electrical induc-
tion. I have communicated this paper, thinking that any contri-
bution, however small, to the list of apparatus available for
this purpose might prove useful to others, as it has been to
myself.

A certain principle should always be borne in mind by the
arranger of an experiment which is to be used for purposes of
elementary instruction. A law A is required to be proved; and
an experiment is performed which demonstrates the fact B; it
is then shown by logical inference that the truth of the fact B
necessitates the truth of the fact A. Thus A has been proved by
two distinct steps—(1) the experiment proving B, (2) the chain
of reasoning connecting A with B. For the instruction of a
class of beginners, it is essential that the experiment be so se-
lected that the second step be reduced to a minimum, or, if pos-
sible, totally dispensed with. ‘To take an illustration from the
subject with which we are engaged. Suppose it be required to
prove that a body will fall sixteen feet in the first second. The
distance may, of course, be determined most accurately by find-
ing the time of vibration of a pendulum; but the subsequent
chain of reasoning would be quite unintelligible. Atwood’s
machine might be made to give some approximation to the value ;
but it likewise does not indicate the direct result, but rather
something from which the direct result is to be inferred by cal-
culation. ‘This appears to me one of the defects in Atwood’s
very beautiful machine: it possesses neither great accuracy nor
great simplicity in the interpretation of its results; and one or
the other, if not both, of these features should characterize every
experiment. Besides, in its ordinary form Atwood’s machine is
quite unadapted for use in the lecture-theatre.

The arrangements now to be described have been designed
with a view of proving the points required as directly as possible
and with the minimum amount.of subsequent reasoning.

It should be mentioned that whatever has been necessary for
_ the purpose of supports and framework has been constructed out
of the very beautiful system devised by Professor Willis, and de-
scribed in his ‘ System of Apparatus for the use of Lecturers and
Experimenters in Mechanical Philosophy’ (Weale and Co.).

Ba4 Prof. R. Ball’s Lecture Experiments to

The convenience of this apparatus for every kind of mechanical
appliance in a lecture-room is wonderful.

All bodies fall through the same height in the same time.
This was Galileo’s experiment from the top of the tower of Pisa ;
it can be repeated on a small scale in the lecture-room in a stri-
king manner.

A scaffolding is built up with the stool, beds, and bolts of the
system; and thus at the height of 24 feet from the floor a pul-
ley is supported through which passes a rope. A piece of wood
the shape of an equilateral triangle, 9 inches each side, has two
electromagnets, each 3 inches long, attached to its base, the wire
being contmuous round the two magnets. The triangle is at-
tached by its vertex to the rope, and can therefore be easily
raised to 24 feet, or any less height, and lowered again at
pleasure. The two wires communicating with the electromag-
nets are sufficiently long to allow of the triangle and magnets
being hoisted up while the other ends of the wires are attached
to a battery of a few cells, a contact-breaker beg mtroduced
into the circuit.

The mode of experimenting will be easily understood. Sup-
pose it is desired to prove that a heavy iron ball and a light
one will fall through the same height in the same time. The
circuit being complete, the balls are attached one to each of the
electromagnets, care having been taken to interpose a piece of
paper between each of the balls and the corresponding magnet,
as this ensures their beg disengaged simultaneously. The
piece of wood and its freight are then hoisted up 24 feet (or
less), and the two balls are in the same horizontal line, sup-
ported, of course, merely by the attraction of the magnets. At
a signal the current is broken and the balls fall together; they —
are disengaged simultaneously ; and the line joining them is
easily seen to be horizontal throughout their entire descent,
though, of course, they are perfectly free fromeach other. The
iron balls used were ] inch and 14 inch in diameter respectively.

An iron ball (15 inch) and a cork ball (24 inches) can be
likewise tried. A flat-headed nail driven into the cork affords
sufficient holding-ground for the magnet. It 1s a most unex-
pected result to find that when they reach the ground, or rather
the cushion placed to receive them, the cork ball is only a few
inches behind its weighty companion. That even this difference
is due to the resistance of the air is shown in the next experi-
ment, by lowering down the triangle, again affixing the cork
ball, and likewise the iron bail, with a small parachute of card-
board attached to it. Raising up the triangle and again break-
ing the current, the cork is seen this time to reach the ground
before the iron.

illustrate the Laws of Motion. 335

The next experiment is to prove that a body fails sixteen feet
in the first second. The apparatus already described is em-
ployed for this purpose, but into the same circuit two other parts
are introduced whick will require a few words of explanation.

The contrivance on which the arrangement principally depends
is the contact-breaker, the action of which will be understood
from the annexed diagram (fig. 1). To a block of wood, AB,a

Fig. 1.

SAF
WY RAY . NX \
\ \ AAA

WN

brass pillar P is screwed. ‘This pillar is 3 inches high, and has
a binding-screw attached to it to receive the current. - Near the
top of the pillar a very slender spring is rivetted ; this spring is
of brass wire slightly flattened, and is 8 inches long ; at the point
T, five inches from P, it bears what may be called a saddle.
This consists of a piece of ordinary tin plate cut into a rectangle
of 1 inch by 3 an inch, soldered lengthways on the upper sur-
face of the spring and then bent down on each side, so that its
section is similar to what is represented in fig. 2. The object of
this will presently appear. The other end of the Fig. 2:
spring is free, but it bears against a screw, X,

which turns in a brass piece, Q, likewise screwed foO~N

to the block of wood AB. The spring being

weak enough, the slightest touch will depress the end of it from
X, to which, however, it immediately returns on the relaxation
of the pressure. When the spring (along which the current tra-
vels) touches X the circuit is complete, and it is of course inter-
rupted when the spring is depressed.

A seconds-pendulum is suspended from a suitable portion of
the framework by a spring in the usual manner. No clock-
escapement is used ; indeed, if the bob be heavy, the pendulum
once set in motion will vibrate for some minutes without requi-
ring an additional impulse. Underneath the pendulum the con-
tact-breaker is to be placed in such a manner that its spring 1s
normal to the plane of vibration of the pendulum ; and the height
of the pendulum must be so adjusted that when the bob is in its
lowest position, a point attached to it shall just touch the saddle
in passing over it. The final adjustment, however, is incon-
venient to make by moving the point of suspension of the heavy

336 Prof. R. Ball’s Lecture Experiments to

pendulum ; so, for the sake of making this with the necessary
delicacy,- the screw X has been introduced into the contact-
breaker, by raising or lowering which the limiting position of,
the spring and therefore of the saddle is raised or lowered.
By this means the amount by which the pendulum depresses
the spring in its transit over it can be arranged with the great-
est nicety. After the pendulum has received an impulse, and at
the bottom of its swing comes into contact with the saddle, the
current is broken owing to the depression of the spring from X.
After the point has passed the saddle the spring returns to its
bearing, and the current flows again until the return of the
pendulum to the lowest point, when the current is broken again ;
and if the contact-breaker have been nicely adjusted, exactly a
second will have elapsed between these two breakings. Thus at
the completion of each second the current is interrupted. The
apparatus being nicely adjusted, the amount of vis viva lost by
the pendulum in depressing the spring is so small that it will
make, after having received an impulse, upwards of two hun-
dred breakings before it requires another push.

An electromagnet acting on a bell is introduced into the cir-
cuit, so arranged that at each interruption of the current the bell
is struck. The simple arrangement necessary for this need not
be described. At every oscillation of the pendulum the bell
rings, the sounds of which may therefore be regarded as the tics
of the pendulum rendered easily audible to the whole room.

The reason why the spring or middle of the saddle of the con-
tact-breaker should be placed exactly under the point of suspen-
sion of the pendulum can: now be easily seen. It is in order
that the intervals of two consecutive strokes of the bell shall be
exactly equal. If the spring have not the correct position, then
there will be two intervals, one as much greater as the other 1s
less than a second, and these intervals will alternate. + Krrors
which arise from the want of perfect adjustment of this position
are fortunately rendered insensible by the fact that at its lowest
point the pendulum has its maximum velocity.

It will be noticed that with this contact-breaker the interval
between the strokes is independent of the are of vibration.

I am not aware that this mode of breaking contact has been
used before, and therefore I have given the details. It ap-
pears convenient, efficient, accurate, and not lable to derange-
ment, and is free from the troubles (in my experience unavoidable)
arising from using mercury or other fiuids for the same purpose.

The mode of proving that a body falls sixteen feet in a second
is then easily seen. A large scale divided into feet is attached
to the upright support of the pulley. One or both of the elec-
tromagnets belonging to the triangle, the contact-breaker, and

illustrate the Laws of Motion. 337

the bell are all included in a battery of a few cells. The pendu-
lum being held-to one side (for in its position of rest the point
keeping down the saddle breaks the current), the current passes.
An iron ball is attached to the electromagnet, which is then
hoisted to the height of sixteen feet (as pointed out by the scale)
above the surface of a cushion on which the ball is to fall, so as
to deaden the sound. The eyes of the audience are to be directed
to the cushion, while their ears listen for the bell. When the
pendulum is released, the first break rings the bell and drops the
ball together; the second break rings the bell again, and, as
nearly as the eye and ear can judge of simultaneity, identically
at the same moment as the ball reaches the cushion. If the ball
be hoisted to the height of eighteen feet, it is seen to be too late ;
if lowered to fourteen feet, itis seen to be too soon. From this
may be inferred the amount of accuracy of which the experiment
is capable. It must be remembered that the arrangement is one
for illustrating a certain quantitative result to an audience, and
not for determining in the cabinet an important natural constant.

The next experiment may perhaps claim greater accuracy than
that just described, as there is always more or less of difficulty
(more, apparently, with some persons than others) in perceiving
the identity of time of two phenomena presented to two different
senses simultaneously. This arrangement depends only on the
sense of sight; and the law which it demonstrates may be thus
enunciated.

“A body projected in a horizontal direction with any velocity
whatever, will take the same time to reach the ground as a body
let fall vertically through the same height.”

This clearly is an important truth to impress on a beginner
endeavouring to understand the second law of motion. It will
teach him that, in at all events one very important case, the
effect of the same force acting for the same time does not in the
least depend upon the circumstance as to whether the body on
which it acts is at rest or in motion; and perhaps this is the
least self-evident of the truths that are wrapped up in Newton’s
concise enunciation of his law.

The arrangement consists of two parts, and the assistance of
electricity as a rapid messenger is again called in. ABCD
(fig. 3) is a piece of wood 14 inch thick; AC is an are ofa
circle of two feet radius, the tangent to which at C is horizontal,
AC being about a foot long. °A ball being intended to run
down this piece, it is grooved ; and A C is one “of the edges of the
groove, the other being of course at a distance of 14 inch on the
other side of the wood. The ball which rolls down the groove
is a sphere of 24 inches in diameter, made of wood and neatly
covered over with tinfoil. The two edges of the groove are each

Phil, Mag. 8. 4. Vol. 37. No. 250. May 1869. Z

338 Prof. R. Ball’s Lecture Experiments to

likewise covered with a piece of tinfoil, which pieces, however,
must at no place communicate with one another. Hach edge is

EF 1)

furnished with a binding-screw, to which a wire is attached.
Whenever the ball rests on the groove, the tinfoil enclosing it
touching each edge completes the electric connexion between
the two binding-screws, the ball acting as a bridge along which
the current passes. At D, and the similar poimt on the other
side, the two ends of a piece of india-rubber spring are fastened
so that the ball can be grasped by the spring. When the ball
is pulled up along the groove and then released, the force of the
spring pulls it down and it darts off with a horizontal velocity.
This piece of apparatus may be about seven feet from the ground.
At precisely the same vertical height as C, and at a distance of
some feet, an electromagnet, M, is to be supported. One wire
from this goes to the battery, the other is fastened to one of the
binding-screws on one edge of AC, the second edge bemg con-
nected with the other pole of the battery.

As long as the tinned ball P is on the groove, the cireuit Bei
complete, the electromagnet, M, will sustain a second ball R; but
the moment P leaves the groove, R is released. Drawing back P
and the spring which embraces it and then releasing it, P main-
tains the circuit until it arrives at C ; im fact a good contact is
ensured by the double circumstance that both the spring and the
centrifugal force of P conspire to keep it in close contact with
the tinned edges. After leaving C the ball darts off in the tra-
jectory indicated in the figure; but directly it is free R is like-
wise free, and the two can be seen with the greatest exactness to.
reach the ground together.

By stretching the sprmg more or less, any amount (owiehe
reasonable limits) of horizontal velocity can be communicated to
P; and it is a most striking result to observe in all cases the
perfect simultaneity with which the two balls reach the ground.

illustrate the Laws of Motion. 339

For demonstrating the particular point in question, this arrange-
ment apparently leaves little to be desired.

“The path of a projectile is a parabola.” The method of de-

monstrating this is indicated in M. Daguin’s Traité de Physique
(vol. i. p. 94). The arrangement for the lecture-room based
upon it is simple enough. A quadrant (fig. 4) of two feet ra-
dius is made of wood 14 inch thick,
and grooved as in the preceding ex- Fig. 4.
periment. This is to be very firmly [Oo
supported parallel to the wall and
about two inches distant from it, and io
six or seven feet from the ground.
Down this a wooden ball 24 inches ) nie,
is to roll, and it is proposed to prove :
that the path it follows after leaving
the groove is a parabola. That the
ball after rolling down shall describe
precisely the same path each time, it
is necessary that the direction of projection be perfectly constant ;
this is ensured by fixing the quadrant very firmly; and then the
direction of projection is the tangent at the base, which for con-
venience is horizontal, or nearly so. It is no less necessary that
the velocity of projection be constant ; this is provided for by
allowing the ball always to start from the same position on the
quadrant. ‘To secure this, a small ledge is fastened at the top,
and the ball is, before each descent, brought home against the
ledge, and thence allowed to fall. By this means the same
trajectory can be reproduced as often as desired.

To show that this is a parabola, the following simple plan is
employed. A number of little arches are made from slips of
cardboard 1 inch wide; these arches are about 4 inches across and
6 inches high, something the shape of the letter U turned upside
down. They are fastened to the wall by drawing-pins or other-
wise all along the constant path traversed by the ball, as shown
in the figure. The mode of placing them ‘is easy. First, one
is arranged so that after each descent the ball goes through its
centre ; then the next is similarly placed, and so on until ten or
thereabouts have been affixed, through all of which, and without
touching any, the ball will pass, after leaving the curve, finally’
falling into a basket placed to catch it.

- By joining the centres of the arches along the wall by a curve,
the position of the focus and directrix of the parabola will be

_ easily found, and the nature of the trajectory consequently de-
monstrated.
Royal College of Science for [reland,
Stephen’s Green, Dublin,
March 25, 1869.

Z2

[ 340 ]

XLVI. On Shadow Optometers. By Joun C. Dovetas, East-
India Government Telegraph Dapariment*.

NHE well-known experiment of Father Sheiner, in which a
smail object is regarded through two small orifices, is the
principle upon which almost all optometers are constructed.
The distance obtained is generally considered the mean distance of
distinct vision. Repeated experiments do not give similar results
with the same person; and the use of the principle is stated to
be only possibly of value when great practice has given the fa-
culty of altering accommodation}. The variation between the
results of several determinations is not such as to destroy the
value of these results; a variation might be expected. The ob-
jection most fatal to its employment appears to me to be the
indefinite nature of these results. In using Sheiner’s method to
examine the nature and position of images on the retina, and to
find the conjugate foci under different conditions of accommoda-
tion and refraction, the interposition of the diaphragm is a con-
dition which removes the circumstances of the case from the
conditions of natural vision. I venture to propose the following
as far preferable to Sheiner’s experiment for optometric purposes.
If a small object be moved to and fro between the eye and
two or more luminous points not having conjugate foci on the
retina, and subtending a small angle with each other at the eye,
as many objects or rather shadows will be seen as luminous
points employed, except at a particular distance, at which the
object appears single: pin-holes in a card held before a lamp or
distant street-lamps may be used to furnish the luminous points,
and a common pin or pen-nib may be employed as the object.
The cause of this multiplication cf the object is evident; the
objects seen are shadows of the object employed, one shadow
being given by each hight. As there is only one object, if this
were placed in a focus of the eye having its conjugate on the
retina, it would appear single and distinct. Of the infinite
number of parallel planes of the pencils between the eye and the
sources of light only one is at a focus having its conjugate on
the retina in any given state of accommodation. If the object be
in this plane, as the section of the pencils through this plane is
accurately reproduced on the retina, the images of the several
shadows will coincide and one only be seen; but if the object be
placed on any other plane the several shadows will no longer co-
incide on the retina, and a separate shadow due to each light will
be seen. A method is thus furnished for finding for what dis-
tance the eye is accommodated without the disturbance due to the
interposition of a diaphragm between the object and the eye.

* Communicated by the Author, Tt Donders.

Mr. J. C. Douglas on Shadow Optometers. 341

If A be a convex lens, Ba focus of diverging rays, C an opaque
object interposed between B and A, and 1, 2, and 3 a screen

I yt 2 3

ed ed
4

receiving images at the different positions shown, it will be appa-
rent on inspection of the diagram that if the object C be moved in
the direction of the dotted line, the shadow will on 1 move in
the same direction as the object, and cn 8 in an opposite direc-
tion, while on 2 no shadow will be thrown, but the luminous
point B will be reproduced diminished in intensity. If the lens
be replaced by the refracting media of the eye*, and 1, 2, and 3 be
positions of the retina, it will be evident that with the retina too
near A for distinct vision of B, (1) the motion of the shadow will be
seen in the opposite direction to that of C; and with the retina
too distant (8), it will appear to be in the same direction: with
the retina at 1 the shadow of C will appear inverted with respect
to C; with the retina at 3 it will appear erect. The different
relative positions of the retina may be due to any cause altering
either the refracting media or the figure of the eye, or both, the
diagram being a convenient mode of representation only: e. g.
transfer of the retina to 1 may represent a diminution of the re-
fractive power of A, the retina not moving, &c.

Applying this to optometric purposes, a method 1s afforded of
determining the effect of accommodation and refraction at any
moment with reference to any Juminous point B. To find if the
retina is too near or too distant from the lens for distinct vision,
pass a pin or pen-point past the eye close to the cornea; if no
shadow is seen, the eye is accurately adjusted ; if a shadow is
seen and moves in the same direction as the object, the retina is
too far from the lens ; if the shadow be inverted and move in the
opposite direction, too near; if the luminous point be far enough
distant for the rays to be considered parallel, the three cases are
emmetropia, myopia, and hypermetropia respectively.

_ The degree of myopia or hypermetropia may be measured by
interposing lenses until the shadow is no longer seen, or lenses
may be applied and the luminous point approached or withdrawn
until the shadow is no longer seen; myopia may be measured
by merely approaching or withdr awing the luminous point with-

* A diagrammatic eye for simplicity.

342 Mr. J. C. Douglas on Shadow Optometers. .

out the interposition of a lens; but hypermetropia cannot be so
measured, there being no positive distance at which vision -is
perfect. Ifa graduated series of lenses be not at hand, it must |
be first overcorrected by a lens, and then the distance of the
focus of incident rays adjusted until the shadow is no longer seen.
If two or more luminous points be used, they are removed
until the shadows are erect and move in the same direction as
the object (a convex lens being employed in hypermetropia). The
object being held near the eye, as many shadows are seen as
lights employed; the object is now removed until one shadow
only is seen; the distance at which this occurs, and the effect
of any lens introduced being known, the distance required may
be at once arrived at.
_ On comparing the methods last referred to with Father Shei-
ner’s method, I found in my own case a difference of one inch in
favour of the proposed method in determining the far point—
Sheiner’s method giving rather more than seven, and the mul-
tiple-shadow method proposed more than eight inches. I found,
in Sheiner’s experiment, that practice enabled me to render the
object confused after it had apparently reached the far point, and
that it became again distinct after further removal; but this dis-
tance was that referred to above, and was not the far point; for
on regarding an approaching point of light, I found the distance
thus obtained agreed with the shadow indication, and exceeded
therefore the distance given by Sheiner’s experiment. In some
hundreds of experiments Sheiner’s method invariably gave a
shorter distance; the interposition of a concave Jens removed
the far point obtained by the shadow method to twelve inches;
but that obtained by Sheiner’s method under the same circum-
stances was about an inch less than this distance.
The method proposed appears to have the following advan-
tages over Father Sheiner’s experiment: it appears more accu-
rate; vision is natural, not beg modified by the introduction of
a diaphragm ; it 1s at once seen what kind of correction is required ; -
and the far pomt may be more readily found. Most persons ac-
commodate for their far point only when actually viewing a dis-
tant object ; and the conditions of Sheiner’s experiment are there-
fore unfavourable to the determination of the far pomt; but no
unfavourable conditions are introduced in the methods proposed,
a distant object being viewed. It also appears superior to the
use of test-types, being more accurate, showing more certainly
(to unscientific persons at least) the existence of confusion and
the kind of correction required. In the last two respects it is
superior to the method recommended by Donders, viz. view-
ing a point of light through lenses, the passing of the object
showing at once if perfect adjustment has been arrived at, and,

Mr. J. C. Douglas on Shadow Optometers. 343

if not, the kind of correction required, both of which, without
the application of the shadow method, must be left to trial and
the opinion of the observer, which (particularly in the case of his
being mexperienced) must render the process tedious and the
result more or less inaccurate.

_ As the methods described depend on the passing of a shadow
over the field, and are thereby distinguished from other methods
of determination in which the object is regarded directly, I have
called them shadow methods; and I suggest the name Shadow
Optometer as appropriate to such instruments constructed on
these principles. The purposes to which the principles described
and explained are applicable, and the manner of applying them,
are evident; the special arrangements in any particular case
(upon which the accuracy of any method must in a measure de-
pend) will depend on the ingenuity of the experimenter. Pos-
session of a pen-nib and a set of lenses would enable any ordi-
narily intelligent person to find the kind of spectacles he re-
quired (if any) with great exactitude by viewing a distant street-
lamp in the manner indicated.

After completing the above, I found the inversion of a small
object placed near a hole in a card held near the eye had been
described by M. le Cat in his Traité de Sens (Brewster’s Edin-
burgh Journal of Science, vol. iv. p. 89); but his description
is incomplete as given in Brewster’s Journal of Science, and
his explanation appears to me erroneous. It is stated the pin
and hole must be near the eye (ibid.), whereas any luminous
point may replace the hole in the card, and the phenomenon
depends on the distance of the card being less than the focus of
the eye haying its conjugate on the retina at the time of experi-
ment. The explanation given is, that the shadow of the pin is
seen, and the inversion is due to the fact that the light from the
lower part of the white wall or window, which furnishes the light
in M. le Cat’s experiment, passes by the upper part of the pin,
and that from the upper part passes by the lower part of the pin ;
hence the shadow is inverted with reference to the wall or win-
dow. I consider the correct explanation is that given by me,
and that inversion of the light from the wall or window with
regard to the pin has nothing to do with inversion of the sha-
dow, which is produced equally well if a luminous body replace
the hole in the card. I have not noticed that the shadow ap-
peared to be on the opposite side of the card to the eye; andthe
diagram given in the notice referred to (ibid.) is evidently in-
_ correct; it removes any possibility of the explanation given being
that given by me. The enlargement of the shadow is due to the
same cause as would enlarge any shadow modified by the effects
of refraction, and not to any circumstances peculiar to this case,
as shown in the diagram referred to.

Calcutta, Feb. 7, 1868,

po B44]

XLVIT. On the Cause of a Pink Colour in White-Lead Corrosions.
By WiittraM Baker, F.C.S., Associate of the Royal School
of Mines, London*.

i some contributions to the metallurgy of lead, published in

the Philosophical Magazine in 1862, I attributed a certain
pink tint, occasicnally seen in white-Jead corrosions, to the pre-
sence of small quantities of copper. As the results of any expe-
riments upon the corrosion of lead by the combined action of
fermenting bark, acetic-acid vapour, and atmospheric oxygen
can only be arrived at after the expiration of ten weeks or three
months, the progress of further investigation in this matter has
been necessarily slow. I have been unable to isolate the colour-
ing-matter ; but I wish to correct the statement that the pink
colour is due to copper, and to detail some conclusive proofs that
it is caused by finely divided silver.

Having obtained many tons of lead which contained only
traces of copper, I found in several instances the pink colour
still quite evident in the corrosions. By the method which had
been employed for refining the metal, there could be only silver
left as an impurity in any perceptible amount. I therefore
sought for evidence that this substance could produce such a
result. Upon analyzing 5000 grains of a perfectly white corro-
sion, and one which was distinctly and uniformly pink, the
result showed that the composition of the two samples differed
mainly in the amount of silver :—

CuO. FeO. NiG: Ag.
White corrosion . ‘0050 :0022 trace ‘0005 per cent.
Pink corrosion. . ‘0060 :0022 ‘0018 ‘0058 ,,

A small quantity of silver was then added to a portion of the
lead which had produced the white corrosions, and this was again
submitted to the corroding action. The result was a decided
pink carbonate. This synthetical experiment was repeated many
times with a hke result upon various samples of lead which had
before produced a white carbonate; and I find that the pink
colour begins to show at the edge of the metallic portion left
uncorroded when the silver amounts to more than 4 oz. per ton
of lead. A decided colour, which is uniform throughout the
mass of the corrosion, is obtained when the silver amounts to
about 15 oz. per ton. A fracture cf a dense corrosion often
shows the crystalline character of the metallic lead, which is de-
fined to some extent by the pink cclour—as if the silver had

* Communcated by the Author.

M. L. Soret on the Colour of the Lake of Geneva. 345

segregated out at certain faces of the lead crystals. By the ad-
dition of a small quantity of arsenic or antimony the pink colour
was replaced by adull purple; and a clear pink tint was only ob-
tained when all the oxidizable metals had been removed.

I come now to the discussion of the state in which the silver
exists to cause a pink or reddish reflection of light. Silver does
not oxidize under the conditions of exposure to acetic-acid vapour
and oxygen of the air. Moreover oxide of silver and silver car-
bonate are themselves decomposed and reduced to a metallic

state by a heat below that attaimed in the stacks of fermenting
tan. The silver must consequently be in the metallic state. As
confirming this statement I made the following experiments :—
Silver carbonate was triturated with white lead and water and
then dried. Upon increasing the temperature, a delicate pink
tint became visible upon the reduction of the oxide of silver. If
a small quantity of silver carbonate be precipitated along with
lead carbonate, the colour upon drying and heating is more uni-
form, and it may be obtained exactly resembling the tint seen on
white-lead corrosions.

The colour of the photographs obtained by means of silver-
salts is also evidence in favour of the metallic state of the silver;
and I may also adduce the fact that aray of light, when reflected
ten times from a polished silver surface, is distinctly of a reddish
colour.

Collegiate Laboratory, Sheffield,
April 19, 1869.

XLVIII. On the Colour of the Lake of Geneva. By Lh. Sonet*®,

My prEar TYNDALL, Geneva, March 31, 1869-

®t thanking you for your letter and the pamphlet you sent
me, I take the opportunity of communicating to you an
observation which may interest yon.

Whilst dealing with a different subject, I was led to consider
whether the blue colour and the absorption of certain rays of light
by water are due to the liquid itself or to the therein suspended
solid particles. This question has been often discussed by others,
as well as by yourself in your work ‘The Glaciers of the Alps.’
Your memoirs on the polarization of the blue light of the sky
have suggested to me the idea that if the blue colour of the
water be due to suspended solid particles, phenomena of polari-
_ zation will be produced analogous to those observed by you on
the light of the sky.

The water of the Lake of Geneva, owing to the well-known

* Communicated by Professor Tyndall, F.R.S.

346 M. L. Soret on the Colour of the Lake of Geneva.

beauty of its colour, is very favourable to investigations of this
kind.

- For this purpose I had a very simple apparatus constructed.
It is a kind of telescope; a flat plate of glass with parallel sur-
faces, fitted hermetically at its one end, serves as ‘object-glass.
The instrument, therefore, can be immersed in water without the
latter being able to enter it. The eyepiece consists of a Nicol’s
prism. It is easy to understand that, by immersing the tele-
scope in the water, the eye receives the blue rays of light emana-
ting from the water, and that this hight can be analyzed by.
turning the Nicol.

By proceeding in this manner, I found that the water of our
lake really exhibits phenomena of polarization comparable to
those observed on the light of the sky; only their observation is
more difficult, and up to this time I have not been able to study
them as well as I could have wished.

Supposing the surface of the water N N perfectly plane, which

TL

R

is the case in time of perfect calm, a beam of solar light incident
with the direction S I will be deviated to I R after the refraction.
Now from a boat the telescope can always be placed in the ver-
tical plane passing through thesun. It the telescope be inclined
in such a manner that its axis becomes perpendicular to I R, then
the light received by the eye is emitted perpendicularly to the di-
rection of the solar rays in water. This arrangement is analo-
gous to that where the maximum of polarization of the light of
the sky appears—that is, when one 1s looking at a right angle
from the sun.

_ In this manner I made a series of observations on the Lake
of Geneva in a place where the water was sufficiently deep not
to allow the ground to be seen; and I was able to perceive a
marked polarization. The plane of polarization was coincident
with the plane of incidence.

M. L. Soret on the Colour of the Lake of Geneva. 347

--If the telescope, always in the same vertical plane passing
divouch the sun, be inclined in any other direction, then the po:
larization is the less marked the more the direction of the tele-
scope differs from the perpendicular to IR. If the direction of
the telescope be vertical, so that one is looking downwards, no
trace of polarization appears.

If the telescope be placed in a vertical plane perpendicular to
the former one (that is, at 90° to the sun), the polarization is
the more distinct the more the direction of the telescope becomes
horizontal, and the plane of polarization passes through the direc-
tion of the telescope and the sun.

I have not been able as yet to prove that the maximum of po-
larization corresponds exactly to the position of the telescope
where its axis is at aright angle to the direction of the solar rays.

It cannot escape your attention that the phenomena are more
complicated in the case of water than in the case of the firmament.

In the first place, it is evident that, if the surface of the water
is agitated, the solar rays cannot remain parallel after the refrac-
tion. The phenomenon, therefore, is the less distinct the more
agitated the water is. This is exactly what I observed. When
I tried my apparatus for the-first time, the water was agitated,
and I remarked no appreciable polarization—although this may
be attributed as well to the fact that, for some days before, we
had strong northerly winds and the water was not perfectly
transparent. On two other days, when the water was only
slightly agitated, an appreciable polarization could be observed.
On a very fine and calm day at last, the polarization was as
marked as that of the sky, which, however, was not very blue at
the time.

In the second place, the solar rays entering the water are
already partially polarized by refraction ; but when the telescope
is placed in the vertical plane passing through the sun (that is,
in the position most favourable for observation), it is easy to see
that the rays already polarized must be extinguished (exactly as
in the experiment where you produce a blue cloud with a pencil
of light already polarized).

Finally, the direct solar ight is not the only light that enters
the water. There are scattered rays of diffused lhght, which,
impinging upon the water from all directions, produce after
refraction a blue non-polarized light, or, properly speaking, an
infinite number of rays polarized with different planes of polari-
zation. I have satisfied myself that, when the sky is covered,
no appreciable polarization is observed.

As I know of no prior description of this phenomenon, and as
peculiar circumstances prevent for some time my pursuing this
investigation, | communicate to you these results, although I

348 Prof. J. Bayma on the Fundamental

regret that I was not able to finish the series of observations,
and to repeat them with the use of artificial light.
| Yours &ce.,
L. Soret,

I hope my friend Soret will compare the action of the water
of the Lake of Geneva upon hight with that of other waters. By
intensifying his illuminating beam he may be able to operate
upon small masses. His method of experiment holds out a pro-
mise of a definite solution of a much discussed and still open
question. |

An elaborate memoir, “ Sur la Polarisation Atmosphérique,”’
published in 1864 by Dr. Rubenson of Upsala, has just reached
me. I promise myself much instruction from the perusal of this
essay.

Royal Institution, J. TYNDALL,
April 21, 1869.

XLIX. Fundamental Principles of Molecular Physics.
By Professor J. Bayma, S. J., of Stonyhurst College,

[Continued from p. 287. ]
Ill.

ie his paper on the “ Fundamental Principles of Molecular

Physics ” Professor Norton undertakes not only to answer
my objections against his theory, but also to show, as far as he
can, that some of my own views on the same subject are question-
able, and others inadmissible. Having in my last article exa-
mined briefly his system of defence, I come now to a rapid re-
view of his means of attack.

The reader, if he has watched attentively the progress of our
controversy, will have already noticed the striking ability dis-
played by my learned opponent in framing arguments out of
objections. The last example of such tactics I have reserved for
this part of my reply as a natural introduction to what I shall
say concerning his other arguments.

Bulk of atoms.—As Professor Norton had assumed the atom
of “gross matter” to be indivisible and spherical in form, I
took the liberty to object that atoms “ indivisible” cannot be
either extended or spherical in form ; for ‘if they were extended
and indivisible, they would be so many pieces of continuous
matter, which we have already proved to be impossible.”

To this the learned Professor gives no less than six distinct
replies, which I am now going to examine. ‘The first is as
follows :

Principles of Molecular Physics. 349

‘< Professor Bayma assumes that every point of matter acts instan-
taneously upon every other point at all distances, however great or
small, with a force having the same character at all distances, and
inversely proportional to the square of the distance. This may be
probable, but it is not self-evident ; and in fact no reason can be as-
signed why ove material point having no extent should act upon
another with a force decreasing with the distance according to any
law whatever. ‘The law of inverse squares is a consequence of wave-
propagation, or of radiation along definite lines, received on a mole-
cule of definite size, and cannot be predicated of a force that acts in-
stantaneously between two mathematical points. ‘To suppose such
a law is an arbitrary assumption.”

I beg leave to make some remarks upon the few expressions
which I have italicized. Ist. The werd assumes should be
changed into proves. (See Molecular Mechanics, pp. 31, 32, and
53-65.) 2nd. It is not self-evident : of course; and therefore
it was made evident by the help of special proofs. 3rd. No rea-
son can be assigned: and yet many were assigned, and others are
still assignable. 4th. Wave-propagation is a propagation of
motion, and has nothing to do with elementary action, which
cannot be propagated (Molecular Mechanics, pp. 63-65). 5th.
On a molecule of definite size. Continuous or not? If conti-
nuous, then the reply confirms my objection: if not, then the
action is received on single material points, contrary to the as-
sertion of my learned critic. 6th. Cannot. Why not? 7th.
Mathematical points : mathematical does not here exclude phy-
sical. 8th. An arbitrary assumption: here the learned Profes-
sor gives himself the innocent pleasure of applying to me, by
way of retaliation, what I ventured to say and to prove of some
of his fundamental principles. Fortunately however those who
have read my ‘ Molecular Mechanics’ know that I have done
enough not to deserve the compliment. I wish my learned op-
ponent had done as much.

But, even setting aside all these imperfections, the reader will
undoubtedly see that this first answer of the learned Professor
is not calculated to meet my objection. Accordingly I consider
all further discussion of it as unnecessary.

His second answer is the following :

“Tf matter consists of material points, as supposed by Professor
Bayma, it is no more difficult to conceive of an atom of continuous
matter than of the space coextensive with it.’

This second answer I cannot well understand. Surely, the
learned Professor does not mean that, if matter (as I have not
only supposed, but proved) consists of separate material points,
then continuous matter can be more easily conceived. Yet what
else is the natural sense of his conditional proposition? How-

350 Prof. J. Bayma on the Fundamental

ever this may be, he wishes us to know that he, irrespectively of
what I may have said to the contrary, conceives continuous
matter as easily as the space coextensive with it. Now, nothing
that is impossible is conceivable, and therefore contmuous matter
is not impossible.

The argument, if unexceptionable, would fairly meet my ob-
jection. But I may be allowed to express my conviction that
the fact is not exactly what Professor Norton imagines. The
difference between matter and space, with regard to continuity,.
is such as to allow of no assimilation between them. Dimen--
slons In mere space are mathematical relations only, whilst in:
matter they would of necessity be physical: moreover space is
not a compound made up of a formal infinite multitude of ma-
terial parts, whilst continuous matter would be such, as it would
imply so many distinct parts of matter as can be marked out by
endless division: space is vacuity, continuous matter would be
fulness: space 1s only virtually continuous, inasmuch as it
allows and makes possible continuous motion, whilst matter
would be materially and formally continuous, as is evident. It
is useless to enlarge on other such marks of perfect opposition :
those mentioned suffice to show the impossibility of intellectually
conceiving matter and space as possessing any common pro-
perty. The learned Professor, reconsidering the subject, will, I
hope, acknowledge that it is ‘infinitely more difficult “ to con-
ceive of an atom of continuous matter, than of the space coex-
tensive with it.” Any one who has a true and philosophical no-
tion of space must own that, whatever may be the phantasma-
gory of our imaginations, it is simply impossible for the intellect
to conceive continuous matter as an imitation of continuous
space.

But as these considerations might lead us too far into the re-
gion of Metaphysics, whither Professor Norton is perhaps little
inclined to follow me, I will dismiss the idea of space altogether
and fall back on the purport of my objection concerning the
continuity of matter. In that objection I said indeed that con-
tinuous matter is an impossibility: this was the shortest way of
proving that the existence of extended and indivisible atoms
was not “an established truth.” But to prove this last point it
is not necessary to argue from the very impossibility of continu-
ous matter: and therefore, even though it were true that Pro-
fessor Norton conceives continuous matter as easily as the space
coextensive with it, the assumption of the existence of oe
ous matter in nature would not become “ an established truth,”
but would remain “an arbitrary assumption.’ I say wbirreee
because no science whether speculative or experimenial, whether
inductive or deductive, whether ancient or modern, affords any

Principles of Molecular Physics. — 351

foundation on which to build an argument proving directly or
indirectly the truth of the assertion. Let Professor Nurton

make the attempt: he will then be convinced of what I say.
He adds:

“Tt is not more difficult to conceive of an indivisible atom acting
as a whole upon another atom with a certain energy, than of amere
point acting upon another point, and causing it to change its place,
at the same time transferring to a new point all the properties it
possesses.”

This is his third reply. I doubt whether it has much to do
with my objection. Professor Norton is endowed with a very
ereat facility both of conceiving everything he likes and of turn-
ing his own conceptions into realities : accordingly he conceives
* of an indivisible atom acting as a whole,” and silently invites
us to conclude from this that the existence of continuous matter
is an established truth. But is he certain of the fact of his
conception? The action of matter is calculated to cause local
motion : it therefore must have intensity and direction. But
direction is taken from a mathematical point to a mathematical
point. Therefore the action must proceed from a mathema-
tical point, and cannot be conceived to proceed from an ex-
tended atom acting as a whole, viz. by a single action which is
not a resultant of other distinct actions. (See Molecular Me-
chanics, p. 31.)

Yet I have no need of insisting on this point. My objection
was that Professor Norton’s “ gross matter” being a piece of
continuous matter did not exist in nature, and was already
proved to be impossible. The right answer would have been
to deny either that gross matter is continuous, or that conti-
nuous matter has been proved to be impossible. ‘The first alter-
native would hardly have been consistent with his doctrine
(though he will try it m his fifth answer), because it would have
stripped matter of its essential epithet “‘gross:” the second
would have obliged him to demolish my proofs (Molecular Me-
chanics, pp. 27-31): and this he has not done as yet, though
it was the best course he could have followed in order to con-
vince his readers of the merit of his theory. Thus my objection
still remains unanswered.

His fourth attempt at a solution of the objection is quite ori-
ginal. He says:

“Tf the occult nature of the force of action of one material point
on another be such that the intensity becomes indefinitely small at
indefinitely small distances, instead of indefinitely great, as ima-
gined by Professor Bayma, then a collection of an infinite number
of material points may form one invariable atom, since the size of

B52 Prof. J. Bayma on the Fundamental

tlie atom may in every instance be so inappreciable in comparison
with the distance between the nearest atoms, that there may never
be any inequality of extraneous action on different points of the .
same atom, imparting different velocities to them, and so tending to
break up the continuity of the matter. Besides, we have already
seen that no inequality of elementary action, by reason of a differ-
ence of distance, is legitimately deducible from Professor Bayma’s
premisses.”’

According to this process of reasoning, the nature of the force
of action is supposed, for the sake of the cause to be defended,
to be occult; then, for the sake of the same cause, it 1s supposed
to be such that the intensity becomes indefinitely small at inde-
finitely small distances: lastly it is inferred that, if this suppo-
sition be admitted, ‘“‘gross matter” will be possible, and will
consist of an infinite number of points invariably united. But
Ist. The nature of the active powers of matter is by no means
so occult as to allow of our inventing any law of action we may
be pleased with. 2nd. If the nature of the active powers be
occult, then the new law of action imagined by Professor Norton
has no ground whatever in the nature of things; and on this
account it must be, even in his opinion, ‘ an arbitrary assump-
tion.” 38rd. Such a new law is irreconcilable with all mole-
cular and non-molecular science: and on this account it is eyi-
dently antiscientific, as it tends ‘to discard the obvious intima-
tions of nature” and violates the exigencies of the “ inductive
method.” 4th. The same hypothetic law leads to the avowed
conclusion that “gross matter”? would consist of an znfinite
number of material points: which conclusion implies not only
that continuous extension can be made up of unextended points
(a proposition openly and notoriously false), but also that a
finite being, almost an infinitesimal being, an atom whose size
is Inappreciable even in comparison with molecular distances,
which are themselves almost inappreciable, would consist of an
infinity of beings: a proposition, which, I make bold to say, not
even Professor Norton, who can conceive so many things, will
be able to realize. 5th. In the same supposition the material
points of which the atom of gross matter is said to be made up
would not be invariably united, being all compelled to move
towards the centre of the atom, and to vibrate to and fro, For
those material points are all supposed to be attractive, and actu-
ally to attract one another; hence they must approach one
another and move all around a central point. And therefore
the atom of gross matter would not be invariable. 6th. Let us
grant the supposition as possible, however much our reason may
revolt against it: even so, gross matter would be only an hypo-
thesis as arbitrary as the new law of action supposed, Isit thus

Principles of Molecular Physics. 353

that Professor Norton proves that his fundamental doctrine is
not an “ arbitrary assumption” and deserves the name of “ esta-
blished truth” ?

What he says about the “ size” of his atom is directed against
an argument by which I proved the impossibility of imparting
motion to a globule of continuous matter (Molecular Mechanics,
pp- 28, 29). Of course, if the size of the atom were smaller
than any assignable finite size, my argument would cease to be
applicable: but then such an atom would be a mere material
point, and gross matter an unreality and an empty name. But,
if the size of Professor Norton’s atoms remains finite, my argu-
ment remains unanswered. For there will be a finite amount
of inequality in the intensity of the extraneous actions (espe-
cially moiecular) on different points of the same atom, inipart-
ing to them yelocities, the difference between which will be
finite and appreciable, and so “ tending to break up the conti-
nuity of matter.”

In my ‘ Molecular Mechanics’ | had given (pp. 30, 31) a se-
cond and, I think, very conclusive proof of the imposstbility of
continuous matter. The learned Professor says nothing of it,
probably because he thought it to consist of what he had pre-
viously called “ unsubstantialities.” Yet the more unsubstan-
tial, the easier should have been the task of its refutation.

As to his saying “‘ We have already seen that no inequality
of elementary action, by reason of a difference of distance, is
legitimately deducible from Professor Bayma’s premisses,” the
reader needs not to be informed that this is one out of the many
gratuitous assertions to which the learned Professor has already
accustomed us. He does not even take care to make his as-
sertion credible. He says “‘ We have already seen,” and speaks
of my “ premisses,” when no premisses have been quoted by
him, and therefore nothing could possibly have been seen to be
either legitimately or illegitimately deducible from them.

The fifth answer of my American critic dwells on the word
“indivisible,” which I understood to convey the notion of abso-
lute indivisibility. He does not admit my interpretation. He
says:

«Tn speaking of atoms of gross matter as indivisible, no other
ground was intended to be taken than that each atom was inde-
structible from any possible action of another atom, and essentially
invariable in form. This does not preclude the idea that the atom
may be an aggregation of a finite number of material points; for it
-may be that the mutual action of two attractive points passes into a
repulsion at extremely minute distances, and so that an atom of or-
dinary matter may be a system of material points in either a statical
or dynamical equilibrium. JIndivisibility, taken in the only sense

Phil. Mag. 8. 4. Vol. 37. No. 250. May 1869. a &

354 Prof. J. Bayma on the Fundamental

in which the term can properly be used, does not, then, necessa-
rily imply continuity, as maintained by Professor Bayma.”’

Tam sorry that I interpreted the word “ indivisible” contrary —
to the now expressed intention of the learned Professor. Cer-
tainly, if “‘ gross matter” is to be considered as an aggregation of
a finite number of material points beimg in either a statical or a
dynamical equilibrium, I allow that its mdivisibility will not
imply continuity. Yet if “ gross matter” is an aggregation of
a finite number of material poznts, why is it to be called gross?
Andif such material points can be in dynamical equilibrium, how
can Professor Norton say that the aggregation of them is “ es-
sentially znvariable in form” ? No aggregation of distinct ma-
terial points can be invariable in form, unless these points be,
by some reason or other, immoveable: and an essential invariability
in the form of the aggregation cannot exist unless those points
be essentially immoveable. Iesteem Professor Norton too much
to suppose that he can ever dream of admitting material points
essentially immoveable, especially as he holds that these same
points may be in a dynamical equilibrium ; for such equilibrium
is not essentially inviolable.

This, to my mind, being the case, I was obliged to assume
that Professor Norton’s atoms “ essentially invariable in form ”
could by no means be considered as an aggregation of a finite
number of distinct material points. But when the idea of such
an ageregation has been discarded, no other idea remains which
can be adopted, except that of continuous matter: and there-
fore I was compelled to consider the asserted indivisibility and
essential invariability of the atom as implying its continuity.

If however Professor Norton now chooses to admit that his
atoms of “ gross matter” are not continuous matter, I shall be
glad to interpret the word “ indivisible ” according to the mean-
ing now intended by him: yet, even so, my objection will not
be nullified ; only instead of being based on the indivisibility of
the atom, it will be drawn from the essential invariability of
its form. Instead of saying: The atom is a whole indivisible ;
therefore it 1s a piece of continuous matter, I shall say: The
atom is a multitude of distinct material points substantially
independent ; therefore it cannot be essentially invariable in
form.

As to the possibility of a change of attractive into repul-
sive action at extremely minute distances between primitive
elements (1 say elements, not molecules, whose action is a re-
sultant variable according to special laws) I will say nothing in
this place, as I have refuted such a view at some length and, I
believe, quite sufficiently in my ‘ Molecular Mechanics’ (pp. 49-
52), where I gave also three direct proofs of the contrary. I

Principles of Molecular Physics. 355

mention this in order to make up for Professor Norton’s silence
on this point.

The sixth and last answer by which the learned Profes-
sor strives to weaken the force of my objection is an explana-
tion of the words “spherical in form” applied by him to
his atom of gross matter. To say that “all bodies of matter
consist of separate indivisible parts called atoms, each of which
is conceived to be spherical in form,” as Professor Norton says
in his 3rd principle, was virtually to say that such atoms were
pieces of continuous matter. Such at least was my impression.
But he answers :

«‘The assumption that each atom is spherical in form was adopted
merely as the simplest embodiment of the fundamental principles
that the action of the atom was equal in all directions, and that the
attractive action upon an atom of ether was neutralized at minute
distances by the resistance developed at the point of contact. The
existence of such a resistance necessarily implies that the elementary
parts of the attractive atom, whether finite or infinite in number, act
repulsively at very minute distances.”

I have already allowed that, when Professor Norton himself
explains the meaning attached by him to his own words, J am
not entitled to contradict him. It is strange, however, that the
expression “spherical in form” which is drawn from geometry,
and conveys the clear notion of something geometrical only,
should have been in need of an interpretation drawn from me-
chanical considerations. However this anomaly may be ex-
plained, let us take notice first that Professor Norton, in giving
this interpretation, reveals to us a new “ fundamental principle.”
The principle is this: “The attractive action upon an atom of
zether is neutralized at minute distances by the resistance deve-
loped at the point of contact.” Is this principle true? I
think not.

I have rigorously proved in my ‘ Molecular Mechanics’ (I
quote my own book for the excellent reason that no other book
to my knowledge has yet appeared in which the same subject
has been regularly and philosophically developed) that in the
true and immediate contact of matter with matter no action is
possible (pp. 14, 15). So long as this theorem holds good, I
cannot admit that any resistance is developed “ at the point of
contact’ of two atoms. Moreover, if the attractive action of
the so-called “ gross matter?’ upon an atom of ether is neutra-
lized “at minute distances,” surely repulsion must prevail at
such minute distances: but when two atoms are at a minute
distance, they are not in contact ; and therefore, if the attractive
action is neutralized at minute distances, the resistance deve-
lopes before the two atoms reach the point of contact : and

Sea Awe

356 Prof. J. Bayma on the Fundamental

therefore the new “ fundamental age ” to say the fede is
incorrect.

But face if, according to another view of the learned Pro-
fessor already noticed, the intensity of action ‘‘ becomes indefi-
nitely small at indefinitely small distances,” we must come to
the conclusion that, according to the same view, the intensity of
action at the very point of contact will become null. There-
fore, if that view is adopted, no resistance will be developed at
the point of contact, and the ‘ fundamental principle” will be
false, at least hypothetically. Such is the accuracy with which
some physicists set down what they call “fundamental princi-
ples” and “established truths.”

Yet, after all, if an atom of gross matter is more than a ma-
terial point, the assumption that each atom is spherical in form
cannot be the mere embodiment of mechanical principles. An
- atom which is more than a material point, and possesses “a
size’ however inappreciable in comparison with the atomic dis-
tances, must have a surface: and this surface must have a geo-
metric form either regular or irregular. Tf it be spherical in
form, then it would seem that Professor Norton has tried in
vain to discard my gecmetrical interpretation of his words:
whilst, if the geometrical form is not spherical, Professor Nor-
ton’s own interpretation collapses; as the action of the atom
cannot be conceived ‘ equal in all directions,’’ unless the form
of the atom itself be uniformly equal all around, viz. un-
less the atom be a sphere. The learned author has one means
only of avoiding the horns of the dilemma, viz. by allowing that
his atoms are systems of discrete material points; his interpre-
tation of the words “spherical in form ”’ will then be substan-
tially correct, though rather unusual; and his theory of mole-
cular physics, disembarrassed of gross matter and its difficulties,
without losing anything worth regretting, will then be able to
recommend itself more strongly to a philosophical mind.

In the passage now under examination Professor Norton en-
deavours also to establish ‘‘a change of attractive into repulsive
action at very minute distances.” As I have fully refuted this
view, and the arguments by which Boscoyich strove to defend it,
in my ‘Molecular Mechanics,’ I will now only say that the
inference drawn by Professor Norton is not legitimate. The
existence of a resistance between his atom of gross matter and
the atom of ther does not necessarily imply that the elementary
parts of the attractive atom act repulsively at very minute dis-
tances. It implies simply that the so-called gross matter is a
dynamical system of elements of which some are attractive and
others repulsive, the attractive always attracting, the repulsive
always repelling, and the effect of their exertions being a re-

Principles of Molecular Physics. 357

sultant attractive or repulsive according as the atoms acted on
‘are supposed to be placed beyond or within the limits of their
molecular distance of equilibrium. This is the only inference
that can be drawn legitimately from the impenetrability of mo-
lecules. |

I might dispense with all remarks on what the writer adds
about a conception which he himself as yet hesitates to adopt.
The idea however is calculated by its novelty and_brilliancy
to fascinate a mind devoted to physical speculation, and de-
serves a short notice. The author says:

“But another conception may be formed of the mode of opera-
tion of an atom of gross matter, which involves no other supposition
than that it acts equally outwards in all directions from a centre,
and takes no account of its geometrical extent. This is that the
effective attraction of the atom for the ether of space is due to the ex-
astence of a repulsion less than would be exerted by the one or more
atoms of ether that would naturally occupy its place. The result
would be the condensation of an atmosphere of ether around the
atom, without the exertion of any direct attractive force, or of any
additional force of resistance. We may conceive the molecular at-
mosphere of electric ether to originate in a similar way; but as the
opportunity of examining and testing this idea sufficiently has not
yet been cbtained, I shall continue to regard the electric ether as
directly attracted by the atom of gross matter, and that the antago-
nistic force of resistance is furnished by the repulsion of the lumini-
ferous ether condensed around the atom.”

This conception, however plausible it may be, is exposed to
many serious objections, which however I am not ready to treat
in this paper, as I must confine myself to the questions already
raised. The least that I can say of this new theory is that it is
quite unnecessary, and that, no matter how much talent may be
spent in building it, it will never be more than an d priorz as-
sumption ; for in the whole multitude and variety of natural
facts nothing has yet been found which can serve as a basis for
its future demonstration. Professor Norton himself says that
the opportunity of examining and testing this idea sufficiently
has not yet been obtained: I rather think that the idea has not
even begun to be tested, and never will, unless the question be
of testing its inadmissibility. For, though there are no facts in
nature supporting the hypothesis, there are facts strongly con-
tradicting it, as for instance molecular cohesion and gravitation.
Moreover, this new hypothesis would not have for its result “the
- condensation of an atmosphere of ether around the atom without
the exertion of any direct attractive force,’ as assumed by Pro-
fessor Norton. ‘The hypothesis that the atom of gross matter
repels less than the zther which would naturally occupy its

358 Prof. J. A. Wanklyn on some Reactions of

place, would lead us to this result only, that the atoms of ether
would from every side approach nearer the atom of gross mat-
ter, without however becoming closer amongst themselves, that —
is, without condensation. But, as it is not my intention to dis-
cuss an incidental question about which Professor Norton has
not yet formed a definite opinion, I will say no more on this
subject.

I trust that the reader in the preceding pages will have found
sufficient evidence as to whether my criticism on Professor Nor-
ton’s theory was well founded or not. It only remains for me
to answer the objections which he advances against some views ©
put forward in my ‘ Klements of Molecular Mechanics... When
this has been done, I shall consider the present controversy as
closed.

j [To be continued. |

SS

Li. On some Reactions of Hydrated Oxide of Ethylene-sodium.
By J. Atrrep Wankiyn, Professor of Chemistry in the Lon-
don Enstitution™.

Ae described in former papers+, hydrated oxide of ethylene-

sodium is obtamed by allowing metallic sodium to act on
ten times its weight of perfectly absolute alcohol and heating the
product to rather over 200° C., maintaining it at that tempera-
ture so long as alcohol distils off. In this manner a perfectly
white pr oduct may be obtained having accurately the composition

NaC?H°O. This substance 1s hydrated oxide of ethylene-

sodium. It is characterized by its reaction with the ethers of the

fatty acids and the ether of benzoic acid, with which it gives
alcohol and a salt of ethylene-sodium, Dis: —
Hydrated oxide of Acetate of

ethylene-sodium. Acetic ether. ethylene-sodium. Alcohol.
C? H4 Na) gu Ce «C24 oe C2 FSO.
H sot C?H? 0 = O2H8 0

It has oe been poh that I do not regard sodium as
inono-valent, but as tri-valent in these compounds, the radical
ethylene-sodium being

CC H4) I Nal”)!

The following reactions, which I have lately studied, tend in

favour of this view of the atomicity of sodium.

Sulphuretted Hydrogen and Hydrated Oxide of Ethylene-sodium.
Experiment I. 1:3815 grm. of sodium was dissolved in 15 grms.
of absolute alcohol, and the product heated in the oil-bath up to

* Communicated by the Author.
+ Phil. Mag. vol. xxxvii. pp. 117 & 175.

Hydrated Oxide of Ethylene-sodium. 359

above 200° C. The product was then cooled and weighed. Its
weight was 44645 grms., being a little above the weight of
the product completely freed from alcohol. (The theoretical
quantity of Na C? H°O is 4:0844.) It was not considered ne-
cessary to drive off the last trace of alcohol in this instance. A
current of dry sulphuretted hydrogen was next transmitted over
the product, no external heat being applied, but considerable
heat being generated by the action of the gas on the substance.
After a while the passage of the gas was stopped, and the appa-
ratus with its contents cooled and subsequently weighed. Weight
of contents =5:76erms. The gas was again trausmitted, and again
generated heat by its action on the substance. Again the appa-
ratus was cooled and weighed. Weight of contents =6°175 grms.
Again sulphuretted hydrogen was transmitted, this time there
being no generation of heat. Weighed again: weight = 6°137
grms., showing that the action of the sulphuretted hydrogen was
complete.

This experiment indicates that one molecule of sulphuretted
hydrogen combines with one molecule of hydrated oxide of ethy-
lene-sodium.

Nal] Oy +H" S—NaC?2H780.

By experiment, 1:3815 grm. of sodium have yielded 6°137
grms. of product; therefore the percentage of sodium in this
product equals 22°51. The theoretical percentage of sodium in
Na C? H7S8 O is 22°55.

The compound Na C? H7S§ O, anearly white solid, the formula

of which I write thus,
C2 ie
Nal’. H
SE

is endowed with considerable stability, having during the process
of its formation undergone a considerable spontaneous heating
without damage. At 100° C., however, it is gradually decom-
posed into alcohol and sulph-hydrate of sodium, thus:—

O C? H® '
and =o }04 Nae PS
SH :

_ The 6137 germs. of product, on being heated to 100° C. in
the water-bath for some time, lost alcohol (2 grms. of which was
condensed and weighed), 3-901 grms. of solid residue remaining.
This residue was lastly heated up to 200° C. for some time,
when it lost more alcohol and ultimately weighed 3-459 grms.
Calculating the percentage of sodium in the 3:459 grms. of pro-

360 Prof. J. A. Wanklyn on some Reactions of

duct which was produced by 1°3815 grm. of sodium, we have -

_Na per cent. =39°94.
Na per cent. =41-07, theory for NaHS.

Experiment II. In this instance the sulphuretted hydrogen
was passed into the hydrated oxide of ethylene-sodium at an ele-
vated temperature, viz. at about 200° C.

3990 grms. of sodium were dissolved in 60 grms. of absolute
alcohol and the product dried at 225° C. Weight = 11-642
germs. Calculating the percentage of sodium from these data,
Na per cent. = 34°27. The theory for NaC? H°O is Na per
cent. =33'82.

Next, a slow stream of sulphuretted hydrogen was passed over
the substance at 210° C. for about two hours. Durmg the
passage of the gas there distilled out a quantity of liquid which
was condensed in a Liebig’s condenser having a narrow tube.

The distillate was weighed at intervals,

(1) 6:5 grms.

(2) 73 ,,
(3) 0k
(4) 745 ,,

until it became constant. The solid residue was also weighed.
Weight of solid residue =9°772 grms.

On referring to the foregoing, it will be seen that this 9°772
germs. of product was made from 3°990 germs. of sodium. There-
fore Percentage of sodium found =40°83.

Theory for NaHS . . =41:07.

The distillate (7-45 grms.) was examined. It was alcohol,
and boiled at 77° C. with the utmost constancy quite to dryness.
The theoretical yield of alcohol, according to the equation

Na C? H78SO=NaH8+C?H°O,

requires that 7°98 grms. should have been obtained. The quan-
tity 7-45 grms. got in the above experiment is a very good ap-
proximation to it, regard being had to the inevitable loss imse-
parable from a determination of this kind.

Hydrochloric Acid Gas and Hydrated Oxide of Ethylene-sodium.
There is very energetic action between these materials, the
generation of heat being so great that 1t 1s necessary to cool the
apparatus with cold water.
The resulting solid, which is white and amorphous, is tolerably
stable.
Naemployed:;. . .. . = 3820jeumes
WaiC>H> O produced: , =10475 jee
HCl+ NaC? H°O given =16:148 __,,

Hydrated Oxide of Ethylene-sodium. 361

From which it follows that the percentage of sodium found in
the hydrated oxide of ethylene-sodium = 84°28. Theory re-
quires 33°82.

The gain of HCl is, in percentage,

100 parts of product gain 159-97 of HCI.

The theory for NaC? H°O+ HCl is
LOO”: 158°7.
_ The resulting compound, NaC? H®°C1O, breaks up between
100° and 150° into alcohol and hydrochloric acid; after heating
the above compound up to 200° C. it weighed 9°218 grms., which
contain 3°5820 grms. of sodium.

Chloride of Acetyl and Hydrated Oxide of Ethylene-sodium.

These substances act very energetically, developing much heat.
Apparently the compound NaC? H®O, C? H3 OC is formed.
On heating this compound above 100° C., it is resolved into
chloride of sodium and acetate of ethyle.

Action of CO? on Hydrated Oxide of Ethylene-sodium.

It was a matter of interest to ascertain whether or not carbonic
acid and the hydrated oxide of ethylene-sodium would give lac-
tate of soda. Experiment im which the materials were brought
together at 180° C. showed that there is no formation of any
fixed acid.

2-1 grms. of sodium were dissolved in absolute alcohol and sub-
sequently heated to 180° C. in a-current of dry carbonic acid.
In this instance the product was not weighed, but treated with
water and subsequently distilled to drive off the aqueous alcohol.
The distillate, consisting of weak alcohol, measured 14°5 cubic
centims., and its specific gravity at 16° C. was 0°9670. It con-
tained therefore 3°48 grms. of absolute alcchol. The residue
left after the distillation of the weak alcohol was titrated with
standard acid. It saturated 91:5 cubic centims. of normal acid,
and therefore contained 2°1045 grms. of sodium uncombined
with any permanent acid. During the progress of the titration
the observation was made that the sodium was fully saturated
with carbonic acid. Collecting these data,

INartakem is, karat yeh ants <yie LO-erms:
Na found unneutralized . =2:1045 ,,
Aleohol obtained «. . . =8'48

No special care was bestowed on this determination of alcohol.
The close correspondence between the unneutralized sodium
after the experiment and that taken for experiment is demonstra-
tion of the non-formation of any lactate of soda during the action

oP)

362 On some Reactions of Hydrated Oxide of Ethylene-sodium.
of CO? on NaC?H*°O at high temperatures. Carbonic acid

therefore only forms carbonate of ethylene-sodiam when made
to act on the hydrated oxide of ethylene-sodium.

Action of Oxide of Carbon, CO.

It is stated in many of the chemical handbooks that carbonic
oxide and ethylate of sodium give propionate of soda. What the
authority may be for this statement I have never been able to
ascertain. Some years ago several chemists, including myself,
made the crystals of so- called ethylate of. sodium and subjected
them to the action of oxide of carbon at 100° C. We were un-
able to observe any formation of propionate of soda. Another
statement respecting the action of these substances is that they
give a pseudo-propionate of soda, which on treatment with water
gave formiate of soda and alcohol.

I have therefore studied the action of aunboree oxide on the
hydrated oxide of ethylene-sodium with the special object of as-
certaining whether or not there was formation of a soda-salt.

IT employed 2-032 grms. of sodium, which was dissolved in
absolute alcohol, and the resulting product heated up to 220° C.
for some time in a current of dry carbonic oxide. The weight
of the product after this exposure to the action of the gas was
5°898 grms., bemg only the unaltered hydrated oxide of ethy-
lene-sodium. Calculating the percentage of sodium in the pro-
duct from these data, we have Na per cent. = 34°45. The
theory for hydrated oxide of ethylene-sodium is Na per cent.
=33°82. Therefore no absorption of CO takes place even at
220° C. In further confirmation of this result, water was added
to the product and a titration made with normal acid. It satu-
rated 82°5 cubic centims. of normal acid, and therefore con-
tained 1°897 grm. of sodium in the caustic state—a result
which confirms the statement that there is no action between
carbonic oxide and hydrated oxide of ethylene-sodium.

Action of Ammonia.

A quantitative experiment showed that at 240° C. there is no
action between hydrated oxide of ethylene-sodium and ammonia.
The following new compounds have been deseribed in this

paper :—
: O C? He
Nal’2 H
S Hi.

oc?rpe
Nall H
Ch,

Canon Moseley on the Descent of Glaciers. 363
O°C?
Nal! C2 H3 O
Cl.

The large amount of heat evolved during the formation of these
compounds proves them to be genuine cases of chemical combi-
nation, and not merely instances of juxtaposition of molecules.

Ll. On the Mechanical Impossibility cf the Descent of Glaciers
by their Weight only. By Henry Moserzy, M.A., Canon of
Bristol, F.R.S., Instit. Imp. Sc. Paris, Corresp.*

lide following is the mathematical discussion of the condi-

tions of the descent of a glacier of unlimited length and
uniform rectangular section and slope, from which I have de-
duced the conclusion that it is mechanically impossible the Mer
de Glace should descend as it does by its weight only, ina paper
of which an abstract was read before the Royal Society on the 7th
of January, and published in the Proceedings of the Society and
in your Magazine for March.

Let ABCD represent part of the surface of a glacier of

uniform slope and uniform width and depth, A D being a por-
tion of the central line of the surface, and BC of the edge, and
AB at right angles to AD and BC. Also let abed bea part
of the floor of the glacier, and A Bda@ a section perpendicular to
the floor and the surface of the glacier and to the direction of its
motion, and let AadD and BécC be planes perpendicular to
the surface and floor, but parallel to the direction of the motion
of the glacier. Let AD be the space traversed by a particle in
the central line of the surface in any given time, BC that de-
scribed by a particle in the edge of the surface in the same time,
-andadand bc spaces similarly described by points in the centre
and edge of the bottom of the glacier. Imagine the trapezoidal
solid Ac to be intersected by an infinite number of planes pa-

* Communicated by the Author.

364 Canon Moseley on the Mechanical Impossibility of —

rallel to AadD, and equidistant from one another, and let
PpqQ be one of these planes. Imagine it, too, to be similarly
intersected by planes parallel to A B CD. Let the intersections
of these planes m n be the edge of one of the rectangular strips
into which the solid will thus be divided. If we suppose the
strip mn to be prolonged indefinitely both ways, every particle
of ice in it will be moving with the same velocity, the glacier
being supposed to be of indefinite length and uniform dimen-
sions and slope. The strip mn will therefore sustain no pres-
sure downwards from its upward prolongation, nor resistance
upwards from its downward prolongation; and supposing the
weight of the glacier to be the only force tending to bring it
down, the work of the weight of every particle of ice in mn must
be equal to the work of the resistances which oppose themselves
to its uniform descent; and since all the particles of mn may be
assumed to have equal weights and to sustain equal resistances,
what is true of a single particle is true of the whole elementary
strip of ice mn. The resistances to the descent of mn are, first,
the shear of its surfaces on the surfaces of similar contiguous
strips above and below and on each side of it, and, secondly, its
friction on the strips below and above it. Besides these resist-
ances, to which its elements, such as mn, are subjected by reason
of the different velocities with which its parts move, and which
consume the work of its weight internally, there 1s the work ne-
cessary to move the whole solid Ac over its floor ab ed, and to
overcome its adhesion to its side BbcC. Let it be supposed
that the floor and sides of the channel of the glacier are so
rough that it is necessary to shear the ice over them.

Let « = the shear of the ice in lbs. per-unit of surface.
¢ = inclination of floor of glacier to horizon.
J = coefficient of friction of ice upon ice.
w = weight of ice per solid unit.

AB=a, iVije==ilb), bp=—a, pm=y,
AD=a, (BC—6) be=y, ad= al

p
U sins = whole work of the weight of solid Ac in unit of time.
U,« = whole work of internal shear of solid A cin unit of time.
U,m = work of external shear of bottom abcd in unit of time.
U3; = work of external shear of side B dcC in unit of time.

U, fcose= work of internal friction of solid A c in unit of time.
U; feose= work of friction on floor of channel in do.

Then, by the principle of virtual velocities,

U sns=U,w+U.4+U,u4+ U,feose+Usfeoss, . (1)

the Descent of Glaciers by their Weight only. 365

_ Usine—(U,4+U,) feos (1)
=" Sg as | ae | SS ae MS

BP a

yx (AD— BO) =8+ £(8—a) =
Let the motion of the bottom of the glacier in the centre be

supposed to bear the same proportion to the motion at the top

in the centre that that of the bottom of the sides does to the top

ad be ay

at the sides. Or let AD = BG? whence ad= B?

aB+a(a—B)

a

Pa BCs

. pg=bet+ cs (ad—be)=y+ - “(2 -7)=4 on Y [a8 +x(a—8)];
*, PQ—pq= snare) ia 7 [a8 + x(a —P)|
a ap + a(a—B) |
es *) a :
*. mn=pyt 5 7 (PQ—pa) = 5, [eB +a(e—-8)]

ai 7 =)

3

1 ee et 3)

a Bet x—B)]lby+y(8—y)],

abe

Weight of prism mn=w . mn dx dy.
Work of the weights of the particles descending mn while m
descends from m to n = weight of prism x 4 mnsine;

si page AE: Cy SUM bs 2 CON os. siintsbe 302!)
yp Lab +2(e—8) 2Tby+y(B—y) |?
= Ue lana WE WL ae dy,
2laB+a2(a— by + 4(8 =
er ( oe =I dx dy,
Ow

y 2b B99"),
188? (2 —8)(8—y)
wab

U= 13g + +a8+?)(0?+By+y’). eae Cie (2)

366 Canon Moseley on the Mechanical Impossibility of

Let m'n' be the elementary ee which rests eas on
mn. Drawon 3. pendicular to m'n'. Then is on! the distance
through which mn! is sheared over mn. Moreover the resist-

ance to this shearing is the constant quantity yw mn dz;

~.*. work of the horizontal shear of mn=yw.mn. on’. dx.
dmn
But on’ =m!r!—mn= Re dy ;
y

*, work of horizontal shear of mn

=~

=n a dy es ee eo)

[a8 + x(a—B)][by+y(B—)]

But mn = abe :
_ dmn _ (8—y)[aB+a(e—B)] |
eda ab ‘

.. work of horizontal shear of mn

= ge [a8 + 2(e—8)]* [by +y(B— yee dy.

Whole work of internal horizontal shear of trapezoid Ac

Megs A 4 (a8 2—B))*Lby+ 98a) de dy
poe 8 (Coy)
68?(«—B)

In the same manner it may be shown that work of vertical
shear of mn

= pin 2 dandy ou. Vib Sa. 1s RE SE een reece)

= SSF [by +yl8 7) [ob + 2(2—6)] de dy,

Whole work of internal vertical shear of trapezoid A c

=" (4, [oy +y(B— /)? [a8 + #(a—8) |de dy
peb(a*—B"*) (8° — 9") ,

66°(8 —y)

the Descent of Glaciers by their Weight only. 367

**, whole work of internal shear of trapezoid A c

es | 8) (Cy) OB 7 )(a? — 8?)
= Saas ana

Uy= ggelad?—7°) (02 +48 + 6°) +0(0? 6%) (+B y+7°)]. (8)

If we suppose the bottom acd of the trapezoid Ac to be di-
vided into an infinite number of equal elements, they will have
been sheared over different parallel distances as the trapezoid
moves into its present position, and the work of the shear of each
element will be represented by the shear multiplied by the cor-
responding distance, so that the whole work of the shear of this
displacement will be represented by the sum of these products.
But the sum of these products is equal to the sum of the shears
(that is, the whole shear of the base of the trapezoid) multiplied

by the distance which the centre of gravity of the base has tra-

versed in the act of displacement.
This distance is represented by

alee y a eso
6 aly+y')
oye

Also the whole shear of the base

_valyt+y),
2

*, work of shear of base
a oO
=pU = (y+ y+).

But y/= is

U.= =t(v+% 4%),
U.= ha (B+ ab +a). eee Rat YA)

Yn the same manner it may be shown that work of shear of the
side BdcC of the trapezoid

pU3= se (8° +98 +y"),

b
= 6 (8°+ By +’). Jct ETM Ly Ys (03)

368 Canon Moseley on the Mechanical Impossibility _
Weight of vertical lamina P mn 1Q= Lw(PQ +mn)Pin de.

Normal pressure of weight on mn = weight x cose.

Friction of weight of Pmn Qon mn = fweight x cost.
Distance traversed by m’ n! over mn = ss dy.
Work of friction of Pmn Qon mn

= Lufcose(PQ+ mn)Pm

PQs mn tee B) |, ek ee eel

(5)

a abB
_ [a8 +2) (6+ 1)0+ 98-1,
on abB
dmn _(@—y)[aB+2(a—8)] |
dy abB 3

-, work of friction of PmnQ on mn

= LO GTe [ab +2(a—8)]°18-+1)0+ (C— yy] Ode dy

+ Uy f com nae { [ob tele UE +

+ (B—y)y](6—y da dy,

U,f cos pS WA args LA l [4 (a?a3 — a3?) [3 (B+ y¥)03

| +4(6—y)6*) |,
U,f cos s= wabf{B — y)(a*—B) (28 +7)

186°(a—8) oe
U,fcos t= ews ae (a ean) Cosi. « (O)

Work of friction of lamina Pp gq Q on pq
= weight PpgQ x cosex fx 4 pg,
weight PygQ = wPp.4 PQ+pq dz
ee peels +a(a—B) (B+) 7
av ‘
bpq= 5° (ob +2(«—8)].

of the Descent of Glaciers by their Weight only. 369
Work of friction of Pp g Q on pg
__ A\12
EE aU cos r= why f(b +7) [aB + #(a—8)]? cos ¢ pi

4.a°B?
Def cost= ee at (eb + «(a —8) ]*da,
_ why f(B+y)cose [4 (aa? —a?B)
U; feos v= 4ag? PHeceto))
b a? — B?

U,fcost= eB CINCY as SR i ee : 6) COS t | Fe

_wabyf(B+y)(e?+eB+B%) f -

= pg eee ce a cos ‘|

Substituting these values of U, U,, U,, Us, U,, U; in equa-

tion (1) and reducing,

2 (6? EY) Suri Dae is \fcose. 8)
aB*(a* + a8 + 8°) +ba*(B?+ By + 7%)
By the measurements of Professor Tyndall on the Mer de
Glace,
*a= 699, *O—= 1350'S, ta—1°9375, +6 ="b4d 6".
iy=-elso, jw= 62:5, §f=-022, b=2 4° 52!.
Substituting which values, we obtain
Equation (2), U sinv=2657583 sino.
Equation (3), U,= 89836.
Equation (4), U,= 18262:
Equation (5), Ve—a toe.
Equation (6), U,fcose= 54028 cose.
Equation (7), U;fcose= 380656 cos.
Equation (1),
_ Usins—(U,+U;) feost 2657583sintc—84684.cos¢ 9
eM ULeU. 7 omoR
In the case of the Mer de Glace, .=4° 52’;
_ _ _, 220458 — 84380
Se OAT

w= hawab (a? + «8 + 6°)

=1:3489. ~ . (10)

* Phil. Trans. vol. exlix. pp. 265 & 266.

+ Tyndall’s ‘Glaciers of the Alps,’ p. 292.

{ The specific gravity of glacier-ice is assumed equal to that of water.
§ By the experiments of Mr. G. Rennie.

Phil, Mag. 8. 4. Vol. 37. No, 250. May 1869. 2B

370 Canon Moseley on the Uniform Motion

Now the unit of shear in ice is at the least 75* lbs. per square
inch. It is therefore mechanically impossible that the Mer de
Glace should descend by its weight only. Some other force in
addition to its weight must act upon it to cause it to descend.
This foree must, moreover, be such as would produce those
molecular displacements and strains which are observed actually
to take place in glacier-ice, and must therefore be, as its weight
is, present to every part of the glacier, but more than thirty-four
times as great.

LIL. On the Uniform Motion of an Imperfect Fluid.
By Henry Moseztry, F.R.S. &c.t

IBS? a perfect fluid I understand a fluid to the displacement
of whose parts among one another no resistance is opposed
either of shearing or friction; and by an imperfect fiuid one to
the displacement of whose parts among one another there is op-
posed the resistance of shearing but not of friction. All fluids
are perhaps in this sense imperfect fluids.

Let AadB represent half a transverse section of an im-

SS AEE. S36 igen \ -—3

ye ee N
SS ‘ Ss \
: \e ees SE ;
So rr
a F

perfect fiuid descending in a straight channel, having a uni-
form slope and a rectangular section everywhere of the same di-
mensions. Conceive the plane surface D dec C to be replaced by
a curved surface, and let A DdcCB (bounded in front by this

* The unit of shear in soft putty is from 1 Ib. to 3 lbs. per square inch.
The Mer de Glace would therefore descend by its weight only if it were of
the same degree of hardness as that substance and of the same specific gra-
vity. Although the resistance to shearing in ice is great enough to stop
effectually the descent of a glacier by its weight, yet it is probably less than
the resistance to shearing of any other solid. The unit of shear in wrought
iron is 50,000 Ibs. per square inch; in cast iron 27,000 lbs.; in oak 2300
Ibs. ; in ash and elm 1400 Ibs. ; in larch 970 to 1700 lbs. ; in spruce 600
Ibs.; and in red pine from 500 to 800 lbs.

+ Communicated by the Author.

of an Imperfect Fluid. 371

curved surface) represent the mass of fluid which passes through
the section Aad B in a unit of time.

Representing by Xu the work of any system of forces other
than the weight of the fluid which tends (with its weight) to
cause it to descend, and adopting in other respects the same
symbols as in the last article and the same reasoning, we have
by equation (1’), observing that in this case f=0,

o(U,+U,+U,)=U sine + zu ;
where
f/= the unit of shear.

Usinv= the work of the weight of the finid which passes
through the transverse section AaéJ in a unit of
time.

U,u = the zternal work of the shear of the same fluid.
U,mu = the work of the shear of the same fluid on the bot-
tom of its channel.
U,m= the work of the shear of the same fluid on the
sides of its channel.
By equation (2’),

U=3 w (rm dex dy =4 w {2 dx dy ;
by equations (3/, 4’),
Ue \ {im dmn 1. {Vie din ay
BU = pb et a de
dz dz
pU,=p \{(- a +2 =) dx dy,

BU, = 3 liad (# dx,

where z, is any value of z for which y=0, or which is measured
on the bottom of the channel.

MUs= 4 pea,

where 2, is any value of z for which #=0, or which is measured
on the sides of the channel ;

dz od |
. ul \(c 2 +2 ie dy + be ete su (=u

=tw sine ¥ \ 2*dx dy LS

12 Be

372 On the Uniform Motion of an Imperfect Fluid.

Differentiating successively in respect to z and y, and observing
that /zidx is not a function of y, nor f23dy of 2,

dz UNS co du “<)
ire ne =1lwsine2? + > ae

If the fluid descends by its weight only, — = 0
dz = ea
ae + dy = 3W2 sin b.

Tet eee ww Sin ys
af

— + dy —= ae

The general primitive of this partial differential equation is

readily found by the method of Lagrange to be
ge Cem*tby—*) ,

or, since # and y enter symmetrically,
— CemytGe—y),

where ¢@ is an arbitrary function of (e—y). A complete primi-

tive is found by the method of Charpit to be
mz Ac™* ah Bey,

The whole volume Q of the fluid discharged in a unit of time
through a rectangular portion of the transverse section repre-
sented by xy is

Q= { { z dx dy= at ae (Ac™" + Be”) dx dy,

: Q= 12 {Ay(e""—1) + Baler"—1)},

Or, substituting the value of m,

Qh w sin w sine

go — SAs 2 4 Bea ie SOIR 1)

W SIN 6

w sine sin t

Q= (7H) say(ese * —1) 4 Bale}. . @)

In equation (1) z represents the velocity of the stream at the
point zy. This equation only applies to one-half the section—
from one side to the centre. The whole discharge is therefore
to be determined by substituting @ for x and 6 for y in equation
(2) and taking twice the result.

Mr. J. J. Sylvester on the Quadrature of the Circle. 370

The values of the constants w, A, B may be determined by ob-
serving the quantities Q,, Q., Qs; of fluid discharged through the
same channel with three different supplies, and therefore three
different depths of the fluid in the channel or values of 0.
These constants bemg determined, the velocities z, and zg at
the bottom and sides are known from equation (1). ‘hat
equation shows the velocity to increase from the bottom to the
surface and from the sides to the centre, which corresponds with
observation.

LIII. Note ona new Continued Fraction applicable to the Quadra-
ture of the Circle. By J. J. Syuvester*,

| fe a recent note inserted by the author in the Philosophical
Magazine it was virtually shown, and indeed becomes almost

self-evident as soon as stated, that the equation u,i1)= = SLi) ane

possesses two particular integrals, «,, 6,, which are the products
of # terms of the respective progressions

—[L, it; 3, us 2, Ii Ber css |'3
BG eM Se ite Ds cel

5?
Now any continued fraction whose partial quotients are
Ae os
2 REY ehiwite
values of uw, in the above equation, 2. e. of two linear functions of
ez, By; and in especial when k= 1 it will be found very easily that
Br— ty

Ay

- will be equal to the ratio of some two particular

this fraction is

But, on supposing 2 infinite, = becomes equal to the well-

&

. TT .
ee Poe ,* ae 2.2.4. 4.6
known factorial expression for g? Vie 7-3-5 +5 + Goee Hence
; =
we may deduce the following value for 5 under the form of a
wo

continued fraction, viz.

1

— 1

1+ a 1
ae fs ee 43 ad infinitum.

Reverting to pure integers, the above equality may be written

7
5 alt

* Communicated by the Author.

374: Mr. J.J. Sylvester on the Quadrature of the- Circle.

as follows,

Tee

6
1+— ae
1 + 7 ad infinitum,

++

the denominators of the partial fractions being all units, and the
denominators (after the first) the doubles of the natural series of §}
triangular numbers 1, 3, 6,10.... This is obviously the sim-
plest Shea of continued fraction for a that can be given, and yet,
strange to say, has not, [ believe, before been observed. Truly
wonders never cease !

At first.sight it might seem as if the above-stated continued
fraction were incapable of teaching anything that cannot be got
direct out of the Wallisian repr esentation itself that has become
transformed into it. Thus, ex. gr., the convergent

L2G. A
Tad VAS ea
2.2.4.4.

is identical with the corresponding factorial prodig ne STE

14+ —

But I think a Aubeeaagl difference does arise in favour of the
continued fraction form, inasmuch as it indicates a certain obvious
correction to be applied i in order that the convergence may be-
come more exact. For if we call

n(n+1) (n+1)(n+2)
1+ 1+ me

net n
I Un+1
when n becomes infinite ; for then w,1, would also be finite, and
consequently u” would be a finite fraction of infinity, which is a
contradiction in terms.

Hence ‘ultimately

. ad infinitum Un,

we have u,= This shows that uw, cannot remain finite

Nps Une =n> +n, I. Ce Un — 2;
or, in other words,

Le : ane ad ad onfnaee

ed ee et ee) a
converges (and, it may be shown, always in an ascending direction)
towards unity as its limit when 2 converges towards infinity.
Thus we may write when n is very great,

On the Theory of Rectifiable Compound Logarithmic Waves. 375

Bay pO eT Og ee
mete Ve Te os ey
Ex. gr., when n=4, - approximately equals
mec sy th 2181-5802,

(2 (ieee seers ee
352 ,
and. when n=5, will be found to be 595 OF 1:5644. The un-
corrected convergent corresponding to the former of these is, as

64 . 384 ae
» aE? OF 14222; and the next is 395° 1:7056,

the true value of = being 15708. The errors given by the

we have seen

uncorrected factorial values are -1486 and *1348 respectively (of
course with opposite signs), whereas the errors corresponding to
the corrected values are only ‘0094 and ‘0064; the approxima-
tion being this more than fifteen and twenty-one times bettered
for the fourth and fifth convergents respectively by aid of the
correction.

Athenzum Club,
April 1869.

LIV. On two remarkable Resultants arising out of the Theory of
Rectifiable Compound Logarithmic Waves. By J. J. Syu-
VESTERT.

HE fruitful mvestigations in which I have been for some

time past engaged concerning reducible cyclodes and recti-

fiable compound logarithmic waves have led me znter alia to

notice a problem of elimination which from its elegance and

peculiarity is, I think, worthy of being offered in a detached
form to the Philosophical Magazine.

* This comes to the same thing as saying that for the purposes of cal-
culation the continued fraction should be always considered as ending with

: 1 | et TS
a numerator, 1, and not with a denominator, zk Ex. gr. 1+ Te * &9

7 eo ae 1
is a good deal nearer to 3 than panera 2. €. 3, 183 and so 1+ Ts
2+1,
or is much nearer to it than 1+ u Jj a. € 16 is
5» 1+ 2. 3? e e OF °
By taking the mean between two consecutive corrected convergents, or,
still better, the mean between two such consecutive means, and so on, a few

terms will serve to give a very close approximation indeed to the limit >
+ Communicated by the Author.

3876 Mr. J.J. Sylvester on two remarkable Resultants arising
Suppose any number of equanions (to fix the ideas say four)

of the form which follows:

U=ax +by +cz +dt =0,

V=az? + by? + cz? 4+ di?=0,

W =a2x° + by? +c2°+d°=0,

O= ax’ + by’ +z? + dt? =0.
If these be regarded as surfaces, they can only be made to inter-

sect in one or another of a definite number of points.
For in the case of intersection we must evidently have

A el Se rae

2
aa 1..€.GLG(@%, se ste
| 26 y6 26 76
€ being the symbol which expresses the product of the differences
of the quantities which it affects. Hence
e+y=0 ‘or ¢+z=0 or yt2=0 or 2470 oe
Or gary 0) Op v0)
Hence it will easily be seen by substitution and successive reduc-

tion that the points of intersection are confined to those herein-
under stated and their analogues, viz.

amt een,

Gea,

r= 0; =e 2).
the total number of points in the group being

2344. 224+6.24-4, ie. ae
and so in general for n such equations the number of possible
points of intersection will be —
As regards the resultant, we have
ig | Merial
x? sy? 2? | O+(.)W+(.)V+(-)U Saga? gine).
xt yt 24

Hence the resultant of U, V, W, © is the same as that of
U, V, W, dé. O(x?, y?, 2?, @),
divided by the resultant of
U, NP W, O(a, OP aay

out of the Theory of Rectisiable Compound Logarithmic Waves. 377

2. e. 18 the resultant of
U, V, W, dt (a? —7?) (y?— 2?) (2?—7”).
This enables us to see that the required resultant is the product

of all the resultants of the systems that can be formed by the in-
terchange of a, b, c after the pattern of the system

(atdje +(btdy +(cte)z,
(atd)a?+ (b+d)y? + (ctd)z3,
(atd)x’+ (btd)y?+ (exd)z
(the signs in the coefficients of the same column being alike, but
independent as between column and column), multiplied by the
resultant of
ax +by +cz,
aa? + by? + cz,
ax? + by? + cz°,
multiplied by

nk 03.5 =
and by continuing this process it is obvious that the required
resultant will be made up exclusively of factors of the form

a, (dto)","; (dtetb)", (dtetd+a)".

So in general for n equations, it may be shown in like man- ~

ner that the resultant is the product of factors of the form

(a, + ay-+05... +a)",
where w,,; 1s a function of n andzto be determined. But by
aid of the method of reduction above indicated, and fixing his
attention on those factors of the resultant only in which the

single coefficient retained in the substituted equation appears,
the intelligent reader will find no difficulty in ascertaining

(i thaw, j=l. a0... (a— Bb),
(2). that tn, == (t-— 1) ea: g1-
These two conditions furnish us with the following Table of
double entry :—
w= «(cd CY, 5; 4, 5, 6

i 1

== 1 ean

=e) egal mNGP

== et on nea O
= 1 Oar, ton Gh G24

=6 | 945 105 30 18 24 120

378 Mr.J. J. Sylvester on two remarkable Resultants arising

which, of course, may be indefinitely extended. Thus, ex. gr.,

when n=3, the resultant is

(abc)? (a2 —b?)(a? —c°)(b? —c*) (a* + 644 ct+— 2a7b? —2a?c? —26'c?)?. |
The above investigation leads as a corollary to the following

arithmetical theorem. :

Call 1.3.5... (22—1)=Q, and 1=@7. hes

2a! + 2a(2x —2) Te? 4 2a(20—2)(Re—d) oe 4+...

Qo A ee 1

7
Ex. gr. lf x=4,
aoe) 1.3 Le i
8 9 +8.6. ri +8.6.4.64+8.6.4.2.¢
—60 +86+4+32+48=176.
So, too,

o'5.711.5.74+1.8.7/44.9, 00a

The value of w,,;18, of course, Ti(¢—1)Q,-:.-

There is a more elaborate system of 2n equations, the result-
ant of which can be made to depend on that of the system of n
equations just ascertained. Thus, take 2n=6, and consider the

system

ax -+by +cz +dt +eu those ty tee tees

aa? + by? +cz2 + dP + ew + fv? ; Pt+P+2+h+w+e ;

aa® + by? + cz° + dt? + eu? + for e+y+e+P+uP+v" ;
the order of the resultant of this system in the letters a,b,c,d,e, f
is obviously 1.3.5(1.54+1 .5+38.5).

Now pair the six variables in every possible manner ; the num-

ber of such pairs is 1.3.5.
Let x, y, 2, t, u, v be any one such set of pairs. Make

e+ty=0, z+t=0, ut+v=0;
then the latter set of three functions become zero, and the

former three may be made zero with right assignments OL, 2; Ga
provided the resultant of

(a—b)2 + (c—d)z + (ef)
(a—b) 2° + (c—d) 28 + (ef),
(a—b)a°+ (c—d)2+ (e—f)v

out of the Theory of Rectifiable Compound Logarithmic Waves. 379

is zero. Hence the required resultant will contain the product
of the resultants of the 1.3.5 systems formed after the above
pattern ; and as this product will be of 1.3.5(1.8+1.5+438.5)
dimensions in the constants, it must be not merely contained in,
but identical with, the required resultant. Thus the new set of
functions regarded as hyper-loci (like the former set) can only
be made to intersect in one or another of a fixed group of points.
Moreover, passing to the case of 2n equations, it is obvious that
the resultant of such system will be made up exclusively of fac-
tors of the form

7 ee
(a, + d,+ hae! aie gy ——— (17 p06 © — Ap; ) n, i
where J,,,; 1s a function of m and z to be determined. The value

OF Up, i, Which has been found above, leads to this without diffi-
culty. By an obvious method of calculation it may be shown that

n.(n—lL n—itl
ees 5). (en—1)) See ee
s- {28-n=V) 22 @a—di41) 184, GID.W EY

we 21 2 eee te. 1
ey ee Ih a
Tights oe er i—1 ))?Q,=i- Qn

ee bras
We thus obtain the following Table for finding the frequency
Jn,;0f any given form of factor :—
cee oS 84d, Oy) A Ue
earns ee eee

= 5 9 2 j2
SA O25 1S 12 144
=5 | (105)? 450 108 140 2880

_ The resultant thus determined is the coefficient of the leading
term of an equation of the degree 1?. 8° ..5*. . . . (2n—1)?, upon
which eee the determination of a set of 2n quantities ae
E,...., &,, so chosen as to make the are of the curve whose equa-
tion i 18

y=a, log (x?—€;) + dg log (a? — £2)... + don log (x? — & )

equal to
! —£,

n log ————
@t+é, Pat a By + Ean

* Tt will, of course, be understood that @,, a,,a3, &c. are written above
in place of a, b, c, &e.

— Eon

2+a, log =

380 Mr. J. J. Sylvester on two remarkable Resultants arising

GQ); Ag,+++ Aon being 2m given unequal quantities. It follows
from the above that the number of distinct solutions is
1? 37... (2u~—1)?, unless one group of 7 of the coefficients a and
a second group of z other of them can be found such that the sum
of the one group is equal to the sum of the other; in that case,
and in that case only, the number of solutions undergoes a re-
duction. A similar conclusion can be extended to the case of
an odd number (2n+1) of the parameters (a), in which case
the number of solutions is 1*.3?... (2n—1)?(2n+1), except
when, as above, two sets of parameters can be found the same
in number and equal in amount, in which case the number
of solutions undergoes a reduction as before. |

I mention these facts with the view of making it understood
that the problems of elimination herein proposed and solved are
not mere idle dreams and speculations of the fancy, but have a
real ontological significance in connexion with a great algebraico-
Diophantine problem of the Integral Calculus.

P.S. Suppose v to be any positive integer, even or odd, and
that the curve or compound symmetrical logarithmic wave

6=1 (0) 2
Y= Zo_ Ao log (2 — &4)
is to be made subject to the relation are minus abscissa

6=1 a—E, 3
==, _% log ee
Then the a coefficients (or form-parameters) being given, the &
quantities (or asymptotic distances from the Y axis of the loga-
rithmic wavelets) depend on the solution of an algebraical equa-

tion whose degree is the product of v terms of the series
1, opwds 25; 0 eee

When v=2n, the coefficient of the leading term of this equa-
tion is the resultant of the system, or rather double system, of
2n functions of 2n variables which has been already discussed.

When v=2n-+1, the coefficient of the leading term is the re-
sultant of a system of 2 +1 functions of 2n +1 variables: (n+ 1)
of them of the form Sv, >2?,...2v"t!; n of them of the form
Da, Lar. ae respeckively.

To obtain this last-named resultant we may pair the variables
(leaving one out) in every possible way, then make the sum of
each pair and also the solitary or unpaired one zero, and finally,
substituting in the m equations last stated (which come down to
the form of a system of n equations between n variables discussed
at the outset of this paper), calculate its resultant*. The product

* Regarded as loci, the y functions can only interset in one or another

of an invariable system of points independent of the particular values of
the coefficients. The equations to any one of these pomts (from what has

out of the Theory of Rectifiable Compound Logarithmic Waves. 881

of all the resultants so found will be the resultant required, as
may be proved by counting its order in the given coefficients,
which is easily ascertained to be

=——</1 1 1 ~ =~
1.3.5...2041(; 4+ gt ---g yz) (1-8-5..-20—1),
as it ought in order to be the complete resultant. It will be seen
then that this complete resultant, like the former one, is still
made up of linear factors of the form

(@,+dg+ 02. 4O;—Aj41 —Aj4o.+. — ay),
and it only remains to ascertain the frequency of each such factor.
By a calculation precisely similar in nature to that indicated for
the case of y=2n, it will be found that for this case of vy=2n+1
the frequency in question
=I1(2-—-1)IIz. Qin—2)Q(n—7i +1).

For v=2n it has been already proved to be

II (¢—1) TiC Q(n— 0) be
Thus we obtain the complete double-entry Table of Frequency
underwritten :

i ie a 3, A, 5, 6
y= 2 1
= 4 1 2
= 5 3) 2
= 6 a 2 12
= 8 225 18 12 144,
= a Loves, 90 36 144,
=) 11025 450 108 144 2880
=—J] 99225 3150 540 482 2880
— 13 | 893025 22050 2700 1296 2880 3628800

This Table, although obtained by two slightly varying pro-

been shown in the text) will easily be seen to be of the form
LS UQg=.. SLA — M2} 41S — Ugji2=...= —ly,
Fop8 == 0, Ly4+9=0, so ty =0.

Hence by a simple enough combinatorial calculation it may be deduced
that the number of these fixed possible points of intersection, or, so to say,

AS
_ ganglions of the system a = E which is, of course, always an

« . . . . . 3Y
Integer; or, more briefly, the ganglionic exponent is the integer part of =

382 Notices respecting New Books.

cesses according as v is even or odd, forms, and ought to be re=
garded as, an organic whole. 3
To prevent misconception, I ought to add that when y is suf-
ficiently great, the compound symmetrical logarithmic wave
Sa log («?—£*) admits of other rectifiable cases besides those of
“a—§

the form 2a log ( 2) above adduced.

It remains to study the relation between the frequency of
each factor and the nature of the corresponding contact between
the functions (regarded as Joc?) into whose resultant it enters.
I have reason to hope that Dr. Olaus Henrici, who has
done such valuable work in the theory of Discrimimants and
Resultants, may be disposed to take up this interesting and
pregnant question.

LV. Notices respecting New Books.

Physical and Historical Evidences of vast Sinkings of Land on the
North and West Coasts of France, and South-western Coasts of
England, within the Historical Period. Collected and com-
mented on by R.A. Peacock, Esg., C.H. 8vo. London and
St. Helier, 1868. .

i studying the Geology of Jersey, the author was struck by the

strong evidences of subsidence in thé sea about that island and the
neighbouring coasts ; and turning his attention to the subject, and
being already strongly imbued with notions respecting the existence
of cavities in the earth admitting of, and conducive to, infallings, he
took up the matter with energy, and, gathering information from
the autiquary, astronomer, engineer, naturalist, geologist, geogra-
pher, historian, and philologist, he has compiled and digested the
great number of facts and statements carefully arranged in this
closely printed and very interesting book, which is illustrated by
three outline maps. ‘These collected evidences prove that within
the last nineteen centuries, and even so late as the beginning of the
fifteenth century, large tracts of land and sea-bottom have sunk,
even more than a hundred feet at some places, along the coasts of

Western Prussia, Holland, and Belgium, from the Elbe to near

Nieuport; along the coasts of North Somerset, and of Devon and

Cornwall, north and south; in the bed of the English Channel ;

amongst the Channel Islands; along the ccast of Normandy and

Brittany, from the Seine to Portrieux ; on the north coast of Brit-

tany, from about Lannion to the north-west angle of Brittany ;

around the Isle of Sein, on the west of Brittany; and probably also
along the French coast in the Bay of Biscay; whilst possibly the
land around Rochelle has risen a few feet since the commencement
of the twelfth century. The rich store here accumulated of evi-
dences of loss of land, particularly among the Channel Islands and
on the north and west coasts of France, has been carefully gleaned

Notices respecting New Books. 383

by observation, correspondence, and reading, from all available
sources, especially from geography and history, ancient, medieval,
and modern.

Nowadays most educated people can understand to some extent,
and are prepared to believe in, oscillations of the land, and can even
master the idea of the English Channel and the German Ocean having
enlarged their areas by subsidence within some appreciable period of
time; such a book as the present gives them proofs enough of this
having occurred, and supplies much other matter for useful thought.
The geologist, of course, can accept the facts and conclusions
readily ; for he knows that these changes which have happened in
the relative level of land and water during historic times are but
modern repetitions of movements that have long affected this por-
tion of the earth’s crust. Some of the results of these normal dis-
turbances of level, in the prehistoric and pliocene periods, have been
described with scientific accuracy by Mr. R. Godwin-Austen (in the

‘Journal of the Geological Society of London, in 1849-51), well
known among geologists for his mastery of the geography of the past,
and as a delineator of the old hydrographical conditions of the earth’s
surface, altered again and again by heavings and sinkings of the
land. Thanking Mr. Peacock most heartily, therefore, for the valu-
able repertory of facts his book presents, we need not be at all
astonished at the changes that have occurred in North-western
Europe in the last few centuries, whether ten, twenty, a hundred,
or more; for already we have learnt from Godwin-Austen’s good
geological observation and reasoning “ that the area of the present
English Channel was in the condition of dry land previous to its
occupation by the waters of the Pleistocene sea, or during the period
of the Pliocene (Crag) accumulations of the German basin, and that,
together with a‘large area beyond, it served to connect the British
Islands with France on the south, and Ireland on the west, into a
tract which had a far greater amount of elevation than any portion
of it has at present.” Books and parchments are wanting for these
long-past pre-historic times, but kitchen-middens and flint imple-
ments, and even human bones, have already supplied some indica-
tions of early man and his occupation of Europe and Britain when at
an elevation greatly differing from what now exists; and much more
is still to be learnt of this highly interesting subject by careful work
in the line of research. that has been followed by Mr. Peacock among
engineers and by Mr. Godwin-Austen among geologists.

On Steam as the Motive Power in Earthquakes and Volcanoes, and on
Cavities in the Earth’s Crust. By R. A. Peacock, Esq., C.E:
8vo. Jersey, 1866.

Bound up with the foregoing, and accompanied with a Preface
dated 1867, is a tract with the title given above. In it the
well-known fact that the vapour of water is the cause of volcanic
explosions and other phenomena is enthusiastically insisted upon.
The many quotations from observers and writers brought forward in
illustration of this long-accepted theory would delight Woodward,

884 Royal Society :—Prof. Tyndall on the Blue Colour

Mitcheli, and the other old vaporists, were they to rise now amongst
their successors and take part in discussions on the earthquake
question. " %

The author offers a new formula for calculating the temperature
of high-pressure steam, and some carefully worked-out tables of tem-
peratures and pressures of high-pressure steam. and says (in his
Prospectus), “‘it has been ascertained that, within known limits at
least, the force of saturated steam increases as the 43-power of the
temperature, this being an enormously rapid ratio of increase. For
example, the 43-power of the number 10 is equal to 31,622 and
a fraction. In this way we may understand how melted lava, which
has a temperature of about 3000° Fahr., may, when water gains
access to it, produce steam sufficiently powerful to account for the
greatest effects of earthquakes and volcanoes.” Mr. Peacock’s
studies on the properties of steam are useful adjuncts to the extensive
researches of Davy, Daubeny, Scrope, Daubrée, and others on the
part played by water in the reaction of the interior of the earth
against its crust ; but when, led into those subterranean regions of hy-
pothesis where cavities or no cavities, solid nucleus or no nucleus, hot
centre or cool centre, are the vexed and vexing questions of the scien-
tific physicist, mathematical amateur, and general newspaper-reader,
he gives the usual compilation of facts and fancies, we can only hope
that some at least of his observations will be of use to somebody—
that he will enlarge his reading in the modern literature of the
subject —not mix up the little superficial caverns of limestone, lava,
and such like with the larger cavities in the earth’s crust, for the
existence of which he judiciously argues—and, lastly, that he will
take into consideration the conditions and effects of Dana’s theory of
the horizontal crumpling of mountain-masses and other strata by
lateral crush or contraction, before he allows everything to be ab-
sorbed by hypothetic cavities.

*

LVI. Proceedings of Learned Societies.

ROYAL SOCIETY. —
[Continued from p. 308.]
Jan. 14, 1869.—Lieut.-General Sabine, President, in the Chair.

(| Uns following communication was read :—

“On the Blue Colour of the Sky, the Polarization of Skylight,
and on the Polarization of Light by Cloudy matter generally.” By
John Tyndall, LL.D., F.R.S.

Since the communication of my brief abstract “On a new Series
of Chemical Reactions produced by Light,” the experiments upon
this subject have been continued, and the number of the substances
thus acted on considerably augmented. New relations have also been
ee between mixed vapours when subjected to the action of
ight.

I now beg to draw the attention of the Royal Society to two

of the Sky, and on the Polarization of Light. 585

questions glanced at incidentally in the abstract referred to—the blue
colour of the sky, and the polarization of skylight. Reserving the
historic treatment of the subject for a more fittitig occasion, I would
merely mention now that these questions constitute, in the opinion
of our most eminent authorities, the two great standing enigmas of
meteorology. Indeed it was the interest manifested in them by Sir
John Herschel, in a letter of singular speculative power, that caused
me to enter upon the consideration of these questions so soon.

The apparatus with which I work consists, as already stated to
the Society, of a glass tube about a yard in length, and from 24 to 3
inches in internal diameter. The vapour to be examined is introduced
into this tube in the manner described in my last abstract, and
upon it the condensed beam of the electric lamp is permitted to act
until the neutrality or the activity of the substance has been declared.

It has hitherto been my aim to render the chemical action of light
upon vapours visidle. For this purpose substances have been chosen,
one at least of whose products of decomposition under light shall have
a boiling-point so high that as soon as the substance is formed it
shall be precipitated. By graduating the quantity of the vapour,
this precipitation may be rendered of any degree of fineness, forming
particles distinguishable by the naked eye, or particles which are
probably far beyond the reach of our highest microscopic powers.

I have no reason to doubt that particles may be thus obtained
- whose diameters constitute but a very small fraction of the length of
a wave of violet light.

In all cases when the vapours of the liquids employed are suffi-
ciently attenuated, no matter what the liquid may be, the visible
action commences with the formation of a blue cloud. I would guard
myself at the outset against all misconception as to the use of this
term. The blue cloud to which I here refer is totally invisible in
ordinary daylight. ‘To be seen, it requires to be surrounded by dark-
ness, it only being illuminated by a powerful beam of light. This
blue cloud differs in many important particulars from the finest ordi-
nary clouds, and might justly have assigned to it an intermediate po-
sition between these clouds and true cloudless vapour.

With this explanation, the term ‘‘ cloud,” or ‘‘ incipient cloud,” as
I propose to employ it, cannot, I think, be misunderstood.

I had been endeavouring to decompose carbonic acid gas by light.
A faint bluish cloud, due it may be, or it may not be, to the residue
of some vapour previously employed, was formed in the experi-
mental tube. On looking across this cloud through a Nicol’s prism,
the line of vision being horizontal, it was found that when the short
diagonal of the prism was vertical the quantity of light reaching the
eye was greater than when the long diagonal was vertical:

- When a plate of tourmaline was held between the eye and the
bluish cloud, the quantity of light reaching the eye when the axis
of the prism was perpendicular to the axis of the illuminating beam
was greater than when the axes of the crystal and of the beam were
parallel to each other.

This was the result all round the experimental tube. Causing the
erystal of tourmaline to revolve round the tube, with its axis perpen-

Phil, Mag. 8. 4. Vol. 37, No. 250, May 1869, 2C

386 Royal Society :—Prot. Tyndall on the Blue Colour

dicular to the illuminating beam, the quantity of light that reached.
.the eye was in all its positions a maximum; when the crystallogra-
phic axis was parallel to the axis of the beam, the quantity of light
transmitted by the crystal was a minimum. i

From the illuminated bluish cloud, therefore, polarized light was
discharged, the direction of maximum polarization being at right an-
gles to the illuminating beam; the plane of vibration of the polarized
light, moreover, was that to which the beam was perpendicular*.

Thin plates of selenite or of quartz, placed between the Nicol and §
the bluish cloud, displayed the colours of polarized light, these co-
lours being most vivid when the line of vision was at right angles to
the experimental] tube. The plate of selenite usually employed was
a circle, thinnest at the centre, and augmenting uniformly in thick-
ness from the centre outwards. When placed in its proper position
between the Nicol and the cloud, it exhibited a system ef splendidly
coloured rings.

The cloud here referred to was the first operated upon in the
manner described. It may, however, be greatly improved upon by
the choice of proper substances, and by the application in proper
quantities of the substances chosen. Benzol, bisulphide of carbon,
nitrite of amyl, nitrite of butyl, iodide of allyl, iodide of isopropyl, and
many other substances may be employed. I will take the nitrite of
butyl! as illustrative of the means adopted to secure the best result
with reference to the present question. |

And here it may be mentioned that a vapour, which when alone,
or mixed with air in the experimental tube, resists the action of light,
or shows but a feeble result of this action, may, by placing it in
proximity with another gas or vapour, be caused to exhibit under
light vigorous, if not violent action. The case is similar to that of
carbonic acid gas, which diffused in the atmosphere resists the de-
composing action of solar light, but when placed in contiguity with
the chlorophyl in the leaves of plants has its molecules shaken
asunder.

Dry air was permitted to bubble through the liquid nitrite of butyl
until the experimental tube, which had been previously exhausted,
was filled with the mixed air and vapour. The visible action of light
upon the mixture after fifteen minutes’ exposure was slight. The
tube was afterwards filled with half an atmosphere of the mixed air
and vapour, and another half atmosphere of air which had been ©
permitted to bubble through fresh commercial hydrochloric acid.
On sending the beam through this mixture, the action paused barely —
sufficiently long to show that at the moment of commencement the
tube was optically empty. But the pause amounted only to a small
fraction of a second, a dense cloud being immediately precipitated
upon the beam which traversed the mixture. :

* T assume here that the plane of vibration is perpendicular to the plane of
polarization. This is still an undecided point ; but the probabilities are so much ~
in its favour, and it is in my opinion so much preferable to have a physical image
on which the mind can rest, that I do not hesitate to employ the phraseology
in the text. Even should the assumption prove to be incorrect, no harm will b
done by the provisional use of it. :

of the Sky, and on the Polarization of Light. 387

This cloud began blue, but the advance to whiteness was’so rapid
as almost to justify the application of the term instantaneous. The
‘dense cloud, looked at perpendicularly to its axis, showed scarcely
any signs of polarization; looked at obliquely the polarization was
‘strong.

The experimental tube being again cleansed and exhausted, the
mixed air and nitrite-of-butyl vapour was cee to enter it until
the associated mercury column was depressed 1, of an inch. In
other words, the air and vapour, united, exercised a pressure not ex-
ceeding =|, ofan atmosphere. Air passed through a solution of hy-
‘drochloric acid was then added till the mercury column was depressed
three inches. The condensed beam of the electric light passed for
‘some time in darkness through this mixture. There was absolutely
nothing within the tube competent to scatter the light. Soon,
however, a superbly blue cloud was formed along the track of the
‘beam, and it continued blue sufficiently long to permit of its thorough
examination. The light discharged from the cloud at right angles
to its own length was perfectly polarized. By degrees the cloud be-
came of a whitish blue, and for a time the selenite colours obtained by
looking at it normally were exceedingly brilliant. The direction of
maximum polarization was distinctly at right angles to the illumina-
ting beam. This continued to be the case as long as the cloud
Maintained a decided blue colour, and even for some time after the
-pure blue had changed to whitish blue. But as the light continued
‘to act the cloud became coarser and whiter, particularly at its centre,
where it at length ceased to discharge polarized light in the direction
of the perpendicular, while it continued to do so at both its ends.

But the cloud which had thus ceased to polarize the light emitted
normally, showed vivid selenite colours when looked at obliquely.
‘The direction of maximum polarization changed with the texture of
the cloud. This point shall receive further illustration subsequently.

A blue, equally rich and more durable, was obtained by employ-
ing the nitrite-of-buty] vapour in a still more attenuated condition.
Now the instance here cited is representative. In all cases, and
with all substances, the cloud formed at the commencement, when
the precipitated particles are sufficiently fine, is b/we, and it can be
made to display a colour rivalling that of the purest Italian sky. In
all cases, moreover, this fine blue cloud polarizes perfectly the beam
which illuminates it,. the direction of polarization enclosing an angle
of 90° with the axis of the illuminating beam.

It is exceedingly interesting to observe both the perfection and the
decay of this polarization. For ten or fifteen minutes after its first
appearance the light from a vividly illuminated incipient cloud,
looked at horizontally, is absolutely quenched by a Nicol’s prism
with its longer diagonal vertical. But as the sky-blue is gradually

_ rendered impure by the introduction of particles of too large a size—in
-other words, as real clouds begin to be formed, the polarization begins
to deteriorate, a portion of the light passing through the prism in all
its positions. It is worthy of note that, for some time after the ces-
‘sation of perfect polarization, the residual light which passes when
the Nicol is in its position of minimum transmission is of a gorgeous

2C2

3888 Royal Society :—Prof. Tyndall on the Blue Colour

blue, the whiter light of the cloud being extinguished*. When the
cloud-texture has become sufficiently coarse to approximate to that
of ordinary clouds, the rotation of the Nicol ceases to have any sen-

sible effect on the quality of the light discharged normally:

The perfection of the polarization in a direction perpendicular tof
the illuminating beam is alsoillustrated by the following experiment.
A Nicol’s prism large enough to embrace the entire beam of the
electric lamp was placed between the lamp and the experimental
tube. A few bubbles of air carried through the liquid nitrite of butyl
were introduced into the tube, and they were followed by about 3
inches (measured by the mercurial gauge) of air which had been
passed through aqueous hydrochloric acid. Sending the polarized
beam through the tube, I placed myself in front of it, my eye being
on a level with_its axis, my assistant, Mr. Cottrell, occupying a
similar position behind the tube. The short diagonal of the large
Nicol was in the first instance vertical, the plane of vibration of the
emergent beam being therefore also vertical. As the light continued
to act, a superb blue cloud visible to both my assistant and myself was
slowly formed. But this cloud, so deep and rich when looked at
from the positions mentioned, utterly disappeared when looked at
vertically downwards, or vertically upwards. Reflection from the
cloud was not possible in these directions. When the large Nicol
was slowly turned round its axis, the eye of the observer being on the
level of the beam, and the line of vision perpendicular to it, entire ex-
tinction of the light emitted horizontally oceurred when the longer
diagonal of the large Nicol was vertical. But now a vivid blue cloud
was seen when looked at downwards or upwards. ‘This truly fine
experiment was first definitely suggested by a remark addressed to
me in a letter by Prof. Stokes.

Now, as regards the polarization of skylight, the greatest stum-
blingblock has hitherto been that, in accordance with the law of
Brewster (which makes the index of refraction the tangent of the
polarizing-angle), the reflection which produces perfect polarization
would require to be made im air upon air; and indeed this led
many of our most eminent men, Brewster himself among the num-
ber, to entertain the idea of molecular reflection. I have, however,
operated upon substances of widely different refractive indices, and
therefore of very different polarizing-angles as ordinarily defined, but
the polarization of the beam by the incipient cloud has thus far
proved itself to be absolutely independent of the polarizing-angle.
The law of Brewster does not apply to matter in this condition ; and it
rests with the undulatory theory to explam why. Whenever the pre-
cipitated particles are sufficiently fine, no matter what the substance
forming the particles may be, the direction of maximum polarization
is at right angles to the illuminating beam, the polarizing angle for
matter in this condition being invariably 45°. This I consider to
be a point of capital importance with reference to the present questionf.

* This seems to prove that particles too large to polarize the blue, polarize
perfectly light of lower refrangibility.

tT The difficulty referred to above is thus expressed by Sir John Herschel :—

“The cause of the polarization is evidently a reflection of the sun’s light upon
something. The question is, On what? Were the angle of maximum polarization

of the Sky, and on the Polarization of Light. 389

_ That water-particles, if they could be obtained in this exceedingly
fine state of division, would produce the same effects, does not admit
of reasonable doubt. And that they must exist in this condition in
the higher regions of the atmosphere is, I think, certain. At all
events, no other assumption than this is necessary to completely ac-
count for the firmamental blue and the polarization of the sky*.

Suppose our atmosphere surrounded by an envelope impervious to
light, but with an aperture on the sunward side through which a pa-
rallel beam of solar light could enter and traverse the atmosphere.
Surrounded on all sides by air not directly illuminated, the track of
such a beam through the air would resemble that of the parallel
beam of the electric lamp through an incipient cloud. The sunbeam
would be d/ue, and it would discharge laterally light in precisely the
same condition as that discharged by the incipient cloud. In fact
the azure revealed by such a beam would be to all intents and pur-
poses that which [ have called a “ blue cloud” rf.

But, as regards the polarization of the sky, we know that not only
is the direction of maximum polarization at right angles to the track
of the solar beams, but that at certain angular distances, probably
variable ones, from the sun “ neutral points ” (or points of no polari-
zation) exist, on both sides of which the planes of atmospheric polari-
zation are at right angles to each other.

I have made various observations upon this subject which I reserve
for the present ; but, pending the more complete examination of the
question, the following facts and observations bearing upon it are
submitted to the Royal Society.

The parallel beam employed in these experiments marked its way
through the laboratory-air exactly as sun-beams are seen to do in
the dusty air of London. I have reason to believe that a great por-

76°, we should look to water or ice as the reflecting body, however inconceivable
the existence in a cloudless atmosphere on a hot summer’s day of unevaporated
molecules (particles?) of water. But though we were once of this opinion, careful
observation has satisfied us that 90°, or thereabouts, is a correct angle, and that
therefore, whatever be the body on which the light has been reflected, if polarized
by a single reflection, the polarizing angle must be 45°, and the index of refraction,
which is the tangent of that angle, unity ; in other words, the reflection would
require to be made in air uponair!” (‘ Meteorology,’ par. 233).

* Any particles, if small enough, will produce both the colour and the polari-
zation of the sky. Butis-the existence of small water-particles on a hot summer’s
day in the higher regions of our atmosphere inconceivable? It is to be remem-
bered that the oxygen and nitrogen of the air behave as a vacuum to radiant
heat, the exceedingly attenuated vapour of the higher atmosphere being therefore
in practical contact with the cold of space.

+ The opinion of Sir John Herschel, connecting the polarization and the blue
colour of the sky, is verified by the foregoing results. ‘‘’The more the subject [the
polarization of skylight] is considered,” writes this eminent philosopher, “ the
more it will be found beset with difficulties; and its explanation, when arrived at,
will probably be found to carry with it that of the blue colour of the sky itself
and of the great quantity of light it actually does send down to us.” ‘“* We may
observe, too,” he adds, “that it is only where the purity of the sky is most absc-
lute that the polarization is developed in its highest degree, and that where there
is the slightest perceptible tendency to cirrus it is materially impaired.” Th.is
applies, word for word, to the ‘‘ incipient clouds.”

890 Royal Society :—Prof. Tyndall on the Blue Colour

tion of the matter thus floating in the laboratory-air consists of organic
_ germs, which are capable of imparting a perceptibly bluish tint to the
air. This air showed, though far less vividly, all the effects of po-
larization obtained with the incipient clouds. The light discharged
laterally from the track of the illuminating beam was polarized,
though not perfectly, the direction of maximum polarization being at °
right angles to the beam.

- The horizontal column of air thus illuminated was 18 feet long,
and could therefore be looked at very obliquely without any disturb-
ance from a solid envelope. At all points of the beam throughout its
entire length the light emitted normally was in the same state of po-
larization. Keeping the positions of the Nicol and the selenite con
stant, the same colours were observed throughout the entire beam
when the line of vision was perpendicular to its length.

I then placed myself near the end of the beam as it issued fain
the electric lamp, and, looking through the Nicol and selenite more
and more obliquely at the beam, observed the colours fading until
they disappeared. Augmenting the obliquity, the colours appeared
once more, but they were now complementary to the former ones.

Hence this beam, like the sky, exhibited its neutral point, at op-
posite sides of which the light was polarized in planes at right Joe
to each other.

Thinking that the action observed in the laboratory might be
caused in some way by the vaporous fumes diffused in its air, I had
a battery and an electric lamp carried to a room at the top of the
Royal Institution. ‘The track of the beam was seen very finely in the
air of this room, a length of 14 or 15 feet being attainable. This
beam exhibited all the effects observed with the beam in the labora-
tory. Even the uncondensed electric light falling on the floating mat-
ter showed, though faintly, the effects “of polarization*.

When the air was so sifted as to entirely remove the visible fioat=
ing matter, it no longer exerted any sensible action upon the light,
but behaved like a vacuum.

I had varied and confirmed in many ways those experiments on
neutral points, operating upon the fumes of chloride of ammonium,
the smoke of brown paper, and tobacco-smoke, when my attention
was drawn by Sir Charles Wheatstone to an important observation
communicated to the Paris Academy in 1860 by Professor Govi,
of Turm+. His observations on the light of comets had led M.
Govi to examine a beam of light sent through a room in which was
diffused the smoke of incense. He also operated on tobacco-smoke.
His first brief communication stated the fact of polarization by such
smoke ; but in his second communication he announced the discovery
of a neutral point in the beam, at the opposite sides of which the
light was polarized in planes at right angles to each other.

But, unlike my observations on the labor atory-air, and unlike the
action of the sky, the direction of maximum polarization in M.
Govi’s experiment enclosed a very small angle with the axis of the
illuminating beam. The question was left in this condition, and I

* T hope to try Alpine air next summer.
+ Comptes Rendus, tome li. pp. 360 & 669.

of the Sky, and on the Polarization of Light. 391

am not aware that M. Govi or any other investigator has pursued it
further.

- I had noticed, as before stated, that as the clouds formed in the
experimental tube became denser, the polarization of the light dis-
charged at right angles to the beam became weaker, the direction of
maxinium polarization becoming oblique to the beam. Experiments
on the fumes of chloride of ammonium gave me also reason to sus-
pect that the position of the neutral point was not constant, but that
it varied with the density of the illuminated fumes.

The examination of these questions led to the following new and
remarkable results :—The laboratory being well filled with the fumes
of incense, and sufficient time being allowed for their uniform diffu-
sion, the electric beam was sent through thesmoke. From the track
of the beam polarized light was discharged, but the direction cf
maximum polarization, instead of being along the normal, now en-
elosed an angle of 12° or 13° with the axis of the beam.

A neutral point, with complementary effects at opposite sides of
it, was also exhibited by the beam. The angle enclosed by the axis
of the beam, anda line drawn from the neutral point to the observer’s
eye, measured in the first instance 66°. ;

The windows of the laboratory were now opened for some minutes,
a portion of the incense smoke being permitted to escape. On again
darkening the room and turning on the beam, the line of vision to
the neutral point was found to enclose with the axis of the beam an
angle of 63°.

The windows were again opened for a few minutes, more of the
smoke being permitted to escape. Measured as before, the angle
referred to was found to be 54°.

This process was repeated three additional times ; the neutral point
was found to recede lower and lower down the beam, the angle be-
tween a line drawn from the eye to the neutral point and the axis
of the beam falling successively from 54° to 49°, 43°, and 33°.

The distances, roughly measured, of the neutral point from the
lamp, corresponding to the foregoing series of observations, were
these :— ;
lst observation, 2 feet 2 inches.

2nd 33 2 bP) 6 33
3rd os acre eae
Ath 33 3 33 2 bP)
5th 33 3 33 7 33
6th 33 4 33 6 33

At the end of this series of experiments the direction of maximum
polarization had again become normal to the beam.

The laboratory was next filled with the fumes of gunpowder. In
_ five successive experiments, corresponding to five different densities
of the gunpowder-smoke, the angles enclosed between the line of
vision to the neutral point and the axis of the beam were 63°, 50°, 47°,
42°, and 38° respectively. .

After the clouds of gunpowder had cleared away, the laboratory was
filled with the fumes of common resin, rendered so dense as to be

392 Royal Society :—Prof. Tyndall on the Blue Colour

very irritating to my lungs. The direction of maximum polarization
enclosed in this case an angle of | 2°, or thereabouts, with the axis of
the beam. Looked at, as in the former instances, from a position near
the electric lamp, no neutral point was observed throughout the entire
extent of the beam.

When this beam was looked at normally through the selenite and
Nicol, the rig system, though not brilliant, was distinct. Keeping
the eye upon the plate of selenite and the line of vision normal, the
windows were opened, the blinds remaining undrawn. The resinous
fumes slowly diminished, and as they did so the ring system became
paler ; it finally disappeared. Continuing to look along the per-
pendicular, the rmgs revived, but now the colours were complemen-
tary to the former ones. The neutral point had passed me in its
motion down the beam consequent upon the attenuation of the fumes
of resin.

With the fumes of chloride of ammonium substantially the same
results were obtained as those just described. Sufficient, I think,
has been here stated to illustrate the variability of the position of the
neutral point. ‘The explanation of the results will probably give new
work to the undulatory theory*.

Before quitting the queeiies of the reversal of the polarization by
cloudy matter, I will make one or two additional observations.
Some of the clouds formed in the experiments on the chemical action
of light are astonishing as to form. The experimental tube is often
divided into segments of dense cloud, separated from each other by
nodes of finer matter. Looked at normally, as many as four rever-
sals of the plane of polarization have been found in the tube in pass-
ing from node to segment, and from segment to node. With the
fumes diffused in the laboratory, on the contrary, there was no change
in the polarization along the normal; for here the necessary differ-
ences of cloud-texture did not exist.

Further, by a puff of tobacco-smoke or of condensed steam blown
into the illuminated beam, the brilliancy of the colours may be greatly
augmented. But with different clouds two different effects are pro-
duced. For example, let the ring system observed in the common
air be brought to its maximum strength, and then let an attenuated
cloud of chloride of ammonium be thrown into the beam at the
point looked at; the ring system flashes out with augmented bril-
liancy, and the character of the polarization remains unchanged.
This is also the case when phosphorus or sulphur is burned under-
neath the beam, so as to cause the fine particles of phosphoric acid
or of sulphur to rise into the light. With the sulphur-fumes the
brilliancy of the colours is exceedingly intensified ; but in none of
these cases is there any change in the character of the polarization.

But when a puff of aqueous cloud, or of the fumes of hydro-
chloric acid, hydricdic acid, or nitric acid is thrown into the beam,
there is a complete reversal of the selenite tints. Each of these clouds

* Brewster has proved the variability of the position of the neutral point
foe “aig with the sun’s altitude. Is not the proximate cause of this revealed
by the foregoing experiments?

of the Sky, and on the Polarization of Light. 393

twists the plane of polarization 90°. On these and kindred points
experiments are still in progress*.

- The idea that the colour of the sky is due to the action of finely
divided matter, rendering the atmosphere a turbid medium through
which we look at the darkness of space, dates as far back as Leonardo
da Vinci. Newton conceived the colour to be due to exceedingly
small water particles acting as thin plates. Goethe’s experiments in
connexion with this subject are well known and exceedingly instruc-
tive. One very striking observation of Goethe’s referred to what is
technically called “chill”? by painters, which is due no doubt to
extremely fine varnish particles interposed between the eye and a dark
background. Clausius, in two very able memoirs, endeavoured to
connect the colours of the sky with suspended water vesicles, and to
show that the important observations of Forbes on condensing steam
could also be thus accounted for. Brticke’s experiments on preci-
pitated mastic were referred to in my last abstract. Helmholtz has
ascribed the blueness of the eyes to the action of suspended particles.
In an article written nearly nine years ago by myself, the colours of
the peat-smoke of the cabins of Killarney} and the colours of the
sky were referred to one and the same cause, while a chapter of the
‘Glaciers of the Alps,’ published in 1860, is also devoted to this
question. Roscoe, in connexion with his truly beautiful experiments
on the photographic power of sky-light, has also given various in-
stances of the production of colour by suspended particles. In the
foregoing experiments the azure was produced in azr, and exhibited a
depth and purity far surpassing anything that I have ever seen in
mote-filled liquids. Its polarization, moreover, was perfect.

In his experiments on fluorescence Professor Stokes had conti-
nually to separate the light reflected from the motes suspended in
his liquids (the action of which he named “false dispersion’) from
the fluorescent light of the same liquids (which he ascribed to “ true
dispersion”’). In fact itis hardly possible to obtain a liquid without
motes, which polarize by reflection the light falling upon them, truly
dispersed light being unpolarized. At p. 530 of his celebrated me-
moir ‘On the Change of the Refrangibility of Light,” Prof. Stokes
adduces some significant facts, and makes some noteworthy remarks,
which bear upon our present subject. He notices more particularly
a specimen of plate glass which, seen by reflected light, exhibited a
blue which was exceedingly like an effect of fluorescence, but which,
when properly examined, was found to be an instance of false dis-
persion. ‘It often struck me,”’ he writes, ‘‘ while engaged in these
observations, that when the beam had a continuous appearance the
polarization was more nearly perfect than when it was sparkling, so

* Sir John Herschel has suggested to me that this change of the polarization
_ from positive to negative may indicate a change from polarization by reflection to
polarization by refraction. This thougkt repeatedly occurred to me while looking
at the effects; but it will require much following up before it emerges into
clearness.

+ 1 have sometimes quenched almost completely, by a Nicol, the light dis-
charged normally from burning leaves in Hyde Park. The blue smoke from the
ignited end of a cigar polarizes also, but not perfectly.

394. . Royal Society.

as to force on the mind the conviction that it arose merely from
motes*. Indeed in the former case the polarization has often appeared
perfect, or all but perfect. It is possible that this may im some
measure have been due to the circumstance that, when a given quan-
tity of light is diminished in a given ratio, the illumination is per-
ceived with more difficulty when the light is diffused uniformly than
when it is spread over the same space but collected into specks.
Be this as it may, there was at least no tendency observed towards
polarization in a plane perpendicular to the plane of reflection when
the suspended par ticles became finer, and therefore the beam more
nearly continuous.’

Through the courtesy of its owner, I have been permitted to see
and to experiment with the piece of plate glass above referred to.
Placed in front of the electric lamp, whether edgeways or trans-
versely, it discharges bluish polarized light laterally, the colour being
by no means a bad imitation of the blue of the sky.

Prof. Stokes considers that this deportment may be invoked to
decide the question of the direction of the vibrations of polarized
light. On this point I would say, if it can be demonstrated that
when the particles are small in comparison to the length of a wave
of light the vibrations of a ray reflected by such particles cannot be
perpendicular to the vibrations of the incident hght, then assuredly
the experiments recorded in the foregoing communication decide the
question in favour of Fresnel’s assumption.

As stated above, almost all liquids have motes in them sufficiently
numerous to polarize sensibly the light; and very beautiful effects
may be obtamed by simple artificial devices. When, for example,
a cell of distilled water is placed in front of the electric lamp, and
a slice of the beam permitted to pass through it, scarcely any po-
larized light is discharged, and scarcely any colour produced with
a plate of selenite. But while the beam is passing through it, if a
bit of soap be agitated in the water above the beam, the moment
the infinitesimal particles reach the beam the liquid sends forth late-
rally almost perfectly polarized light ; and if the selenite be employed,
vivid colours flash into existence. A still more brilliant result is ob-
tained with mastic dissolved in a great excess of alcohol.

The selenite rings constitute an extremely delicate test as to the
quantity of motes in a liquid. Commencing with distilled water, for
example, a thickish beam of light is necessary to make the polariza-
tion of its motes sensible. A much thinner beam suffices for common
water; while with Bricke’s precipitated mastic, a beam too thin to
produce any sensible effect with most other liquids suffices to bring
out vividly the selenite colours.

* The azure may be produced in the midst of afield of motes. By turning the
Nicol, the interstitial blue may be completely quenched, the shining and appa-
rently unaffected motes remaining masters of the field. A blue cloud, moreover,
may be precipitated in the midst of the azure. An aqueous cloud thus precipi-
tated reverses the polarization; but on the melting away of the cloud the azure
and its polarization remain behind.

Royal Institution. 395

ROYAL INSTITUTION OF GREAT BRITAIN.

March 19, 1869.—‘* On Chemical Constitution, and its Relation
to Physical and Physiological Properties.” By Dr. A. Crum Brown,
F.R.S.E.

Chemists have long endeavoured to answer the question, What
is the relation in which the constituents stand to one another ina
compound? and numerous hypotheses, more or less ingenious, have
been devised for this purpose. Two of these modes of representing
chemical phenomena occupy so prominent a place in the history of
the science as to merit special notice, even in so slight and hurried
a sketch as this must be. These are, lst, the Electro-chemical and
Radical Theory; and 2nd, the Theory of Atomicity and Chemical
Structure.

The first was the product of the genius, learning, and laborious
research of Berzelius; it was soon adopted by all chemists, and
formed for many years the foundation of all chemical teaching and
the guide in all chemical work. The point of view from which it
regards chemical phenomena is that of combination and decomposi-
tion, of the union of elements to form compounds, and the separa-
tion of compounds into elements. A very important form of
chemical decomposition is electrolysis, or the breaking up of a com-
pound by means of current electricity. From the nature of the case
electrolysis gives rise to a dichotomous decomposition; and this
duality was extended to all cases of combination and decomposition.
Elements combine with each other in pairs; these pairs may again
combine in pairs, forming compounds of the second order, and so on.
Thus calcium combines with oxygen to form lime, sulphur combines
with oxygen to form sulphuric acid, and sulphuric acid combines
with lime to form sulphate of lime. This union of compounds with
compounds was not supposed to depend on a union of the con-
stituents of the one with the constituents of the other, but to bea
combination of the one as a whole with the other as a whole—not
a combination of the calcium of the lime with the sulphur or with
the oxygen of the sulphuric acid, or of the sulphur of the sulphuric
acid with the oxygen of the lime, but of the lime as such with the
sulphuric acid as such.

This view may be illustrated by a reference to the relations of
human life. Individuals unite to form partnerships or corporations ;
and these may again enter into alliances, although the members of
the one allied corporation may be altogether unacquainted and
unconnected with the members of the other.

But the progress of discovery brought to light facts which seemed
to contradict this view of binary combination. Cases were observed
‘In which a compound of two elements united directly with an
element ; and to meet this new class of facts the theory was modified
by the introduction of the notion of Radicals. A radical was a
compound which acts like an element.

The simile introduced above may be used to illustrate this exten-
sion of the theory. Some combinations of men (corporations) can
be treated as individuals, can enter into legal relations with indivi-

396 Royal Institution :—

duals, while others cannot ; so some compounds can unite with ele-
ments, while others have not this capability.

The Theory of Atomicity regards chemical phenomena from an

altogether different point of view. In it the various substances are
considered as modifications of one another rather than as compounds.
The rise of this mode of viewing chemical phenomena may be traced
from the early papers by Dumas, and by Laurent, on Substitution.
It appears more prominently in the position given to double de-
composition as the representative of all chemical action, by Laurent
and Gerhardt, in the types of Gerhardt and Williamson, in Frank-
land’s theory of the organo-metallic bodies, and in its extension by
Kolbe to the compounds of carbon. It was reserved, however, for
Kekulé to combine these ideas into a consistent theory*. The
theory has been further elaborated by Butlerow (to whom we owe
the name ‘‘Chemical Structure’’), by Erlenmeyer, and by many
others ; and it has been adopted and applied with slight modifications
by almost all chemists engaged in organic research.
; According to this theory the typical form of chemical action is
what we may call the chemical exchange. ‘To illustrate this idea we
may consider the simplest case, that of double decomposition,
where two molecules act on one another to produce two new
molecules.

Chloride of sodium, for instance, acts on nitrate of silver, produ-
cing chloride of silver and nitrate of sodium. Comparing chloride
of sodium and chloride of silver, we at once see that, while there are
important respects in which the sodium and the silver differ as to
the nature of their union with chlorine (thus the amount of work
required to separate the metal from the chlorine is very different in
the two cases), still from one point of view (and that is the point of
view taken by the atomicity theory) the silver may be said to re-
place or to be substituted for the sodium. In the same way, a cup
filled with mercury is very different from the same cup filled with
water ; and the relation of the mercury to the cup differs in many
respects (such as pressure and adhesion) from the relation of the
water to the cup; but they agree in this, that the cup is filled in
both cases. In the same way, the chlorine is said to he saturated
by the sodium or the silver, although the intimacy or firmness of the
combination is not the same in the two cases.

We may also consider this double decomposition from the other
side. As the silver and sodium have changed places, so the chlo-
rine has changed place with the rest of the nitrate of silver, with
what in the nitrate of silver is not silver; or, representing the action
in symbols (NaCl+ AgNO,=Ag Bee 3)» Cl and NO, have
changed places.

In this example we have one Aon or group replacing one other
atom or group; but all cases of double decomposition are not of
so simple a kind. Thus, when water is treated with pentachloride

* It is right to observe that although Kekulé has used this theory with the
most eminent success, both in the explanation of facts already known, and in the
discovery of new chemical relations, he does not exclude the possibility of the
union of compounds with each other to form compounds of a second order.

Dr. A. Crum Brown on Chemical Constitution. 397

of phosphorus, we find that one atom of oxygen (from the water) re-
places, and is replaced by two atoms of chlorine from the penta-
chloride ; thus PCl,+ H,O=PCl,0+2HC1; so that while the two
atoms of hydrogen were formerly united to one atom of oxygen
and formed with it one molecule, they are, after the change, each
united to a separate atom of chlorine and form with them two mo-
lecules.

Oxygen, therefore, in this case (and, as far as we know, in all
cases) enters into two relations, while hydrogen, chlorine, silver,
and sodium only enter into one. In a similar way it has been
shown that the different elements have different ‘‘atomicities,” or
enter into different numbers of relations. It is to this “ polyatomi-
city,” or multiple-relatedness, that the complexity of compounds
is due; for it is obvious that by the union together of several mul-
tiply related atoms a very complicated structure may be produced.

In the case of a compound containing only two atoms, such as
chloride of sodium, there is clearly only one way in which it can
break into residues; but a complex substance, containing many
atoms, may, and generally does, break in different ways when acted
on by different substances ; and it is by the study of these ways of
decomposition of a substance, and by the study of the ways in
which, by means of double decomposition, it can be produced, that
we arrive at a knowledge of its structure—that is, of the mutual
relation of its atoms.

But the multiple-relatedness of some atoms produces a further
complication, producing a kind of chemical action which, while still
a chemical exchange, cannot be called doubie decomposition. In
double decomposition we saw that each molecule breaks into residues
which change places with the residues of the other molecule, and
that this breaking into residues results from the rupture of one or
more relations between pairs of atoms. But where we have multi-
ply related atoms, it may happen that such a rupture takes place
without a separation of the residues, these being retained in combi-
nation by some other relation of their multiply related atoms. ‘To
illustrate this we may compare the action of anhydrous potash, K,O,
and of anhydrous lime, CaO, on water.

Using graphic formule, we have in these two cases :—

aa . @©-O—-®
+ Ee oN Cate

and
a
O © + ©1@© =
e <_O+-@

Here the dotted lines indicate the relations ruptured ; and it will
be seen that, while in the first case the rupture produces a separa-
tion into two residues, in the second case it does not, what would
otherwise be residues remaining united on account of the double
relatedness of the calcium sigh |

398 ‘pues “Royal Institutton:—- = * =

From this examination of chemical exchange, it will be obvious
that no operation of this kind can produce a change in the ‘‘ atomi-
city’’ of an atom; for every relation ruptured a new one is en.
tered into. But we have no reason to suppose that all chemical
action is of this kind; and there are numerous phenomena which it.
is very difficult to explain, except by the assumption that there is an-
other kind of chemical action, in which the number of relations of
an atom is increased or diminished. Such actions are those by
which we pass from one series of compounds to another. Thus the
ferrous salts are connected together by processes of exchange ; but
it is only by making new hypotheses that we can thus explain the
passage from the ferrous to the ferric salts. Similar relations exist
between the manganous salts, the manganic salts, the manganates,
and the permanganates, where a consideration of each group, apart
from the others, would lead us to a different atomicity for manga-
nese; and many other examples might he given of the same kind.
The speaker considered it, in the eee! to be better to regard
each such series separately rather than by an attempt to bring all
chemical processes under one class to endanger the stability of the
theory of chemical structure, which, while St is probably not de-
stined, in its present form, to remain as a permanent part of the great
edifice of the science, is certainly a most convenient scaffolding, not
easy to replace, and not hastily to be thrown down.

Having thus seen what is meant by chemical structure, and ery
we aniive at a knowledge of it by a study of the history of the sub-
stance, of the ways in which it may be formed and in which it may
be decomposed, we may now glance at the relations which exist
between the chemical structure of a substance and its physical and
physiological properties. We shall consider specially two of the
physical characters of matter, volatility and colour, and examine in
what way these are modified by the performance upon the substance
of certain specified chemical operations. The volatility of a sub-
stance depends upon two things:—lst, the temperature at which
the substance boils under a particular pressure ; and 2nd, the change
of boiling-point produced by a change of pressure. In order, there-
fore, fully to know the volatility of a substance, its boiling-point
must be determined through a very great range of pressure. This
involves great labour; and only a few substances have been thus
fully examined. Almost all we know on this interesting question
is due to the ingenious and patient experiments of Reenault. These
do not, as yet, furnish us with sufficient data to enable us to deduce
anything hkealaw. They show us, however, that a mere com-
parison of boiling-points under an arbitrarily selected pressure
(such as 760 millimetres, which happens to be the mean pressure of
the atmosphere) cannot lead us to a law, as the boiling-points of two
substances are frequently changed very unequally by a change of
pressure.

Such comparisons “of boiling-points have been made, and oe
them have been deduced, especially by Kopp, a series of very ins
teresting and certainly not fortuitous coincidences. That dis-
tinguished chemist and physicist has shown that, in a very large

Dr. A. Crum Brown on Chemical Constitution. 399

number of instances, the change of chemical structure produces
nearly the same change of boiling-point. These ‘“laws’’ of Kopp
are only approximate, and are not even approximate in the cases
where the boiling-points of the substances compared are very dif-
ferently changed by change of pressure.

Turning to the other physical character which has been mentioned,
namely, colour, we see at once a marked regularity. As a rule,
substances belonging to the same series differ from one another in
degree rather than in kind of colour; while in passing from one
series to another, we observe that the colour undergoes a total change
of character. ‘This is well illustrated by comparing the colours of
substances belciging to such series as the ferrous salts, the ferric
salts, the ferrates—the manganous salts, the manganic salts, the
manganates and the permanganates—the cupreous and cupric salts,
the chromous and chromic salts, the chromates and perchromic acid.
Possibly such changes of colour as we see in the transformation of
rosaniline and its derivatives into leukaniline and analogous bodies,
and of blue into white indigo, may be cases of the same kind. It is
also interesting to note that, while the nitro-substitution products
of the aromatic series are generally yellow, all the known substances
of the same kind in the fatty series are colourless.

These considerations of colour would naturally incline us to re-
gard the operations which lead from one series to another as dif-
ferent in kind from those which lead from one member to another of
the same series ; and when we examine the physiological action of
bodies of the same and of different series, this impression is greatly
strengthened.

The speaker described in some detail a few of the observations
made within the last two years by Dr. T. R. Fraser and himself,
pointing out the similarity of the action of substances belonging to
the same series, and the remarkable change of physiological action
produced by those chemical changes which lead from one series to
another. ‘The illustrations were drawn from the natural alkaloids
(a group of substances containing trebly related nitrogen), and those
derivatives of the alkaloids which contain fivefold-related nitrogen,
It was shown that the salts of the alkaloids, although containing
fivefold-related nitrogen, were not adapted for this comparison, on
account of the readiness with which they lose acid in the presence
of alkaline substances, their nitrogen thus returning to the trebly
related condition. [hé bodies formed by the addition of a com-
pound of methyl have not this disadvantage; and as the nitrogen
in them is permanently fivefold-related, their physiological action
may be satisfactorily compared with that of the alkaloids them-
selves.

The experiments leading to a knowledge of the action of strychnia
and of the salts of methyl-strychnium were described; and it was
shown that while the former acts by exciting the origins of the motor
nerves in the spinal cord, the latter act by diminishing the action and
ultimately paralyzing the terminations of the same nerves in the
muscles. Similar relations exist between brucia and methyl-brucium,
thebaia and the salts of methyl-thebaium, morphia and the salts of

400 Intelligence and Miscellaneous Articles.

methyl-morphium, &c. Indeed it may be stated generally that, as
far as observation goes, compounds of trebly related nitrogen exert
an action totally different in kind from similar compounds of five-
fold-related nitrogen, that a similar difference exists between the
triatomic and pentatomic compounds of other members of the nitro-
ecn family, and that this principle appears to be of still wider, and
probably general application.

The speaker, in conclusion, drew attention to the peculiar interest
attaching to those regions of science which lie on the frontiers be-
tween two distinct departments, as on their successful exploration
would depend the ultimate fusion of all physical sciences into one,
the science of dynamics, the science which treats of matter and
energy and their relations to one another. Such a fusion is pro-
bably very remote; but we now see in the border-land between
chemistry and physics that slow process of absorption going on
which has already converted the once independent sciences of sound,
light, heat, electricity, and magnetism into more or less completely
subjugated provinces of the great empire of applied mathematics.
If we believe in the unity of the plan of creation, we must believe
that this process will advance and ultimately triumph.

LVI. Intelligence and Miscellaneous Articles.

ON A MIRAGE IN THE ENGLISH CHANNEL.
BY JOHN PARNELL, M.A., F.R.A.S.*

EV ING had the good fortune to witness an extraordinary mirage
at Folkestone on the 13th of April in the present year, I ven-
ture to think that the following description of the phenomenon, so
far as it passed under my observation, may not be uninteresting.
During the morning, and up to 2 o’clock p.m., a dense fog had
hung over the sea; but apparently it was not very deep, as the sun’s
rays penetrated it pretty freely. At the hour above mentioned the
fog opened towards the S.E., disclosing the cliffs on the French
coast; and in the course of a few minutes the fog had disappeared,
leaving the atmosphere in a state of unusual transparency. ‘The
French cliffs were apparently so lofty and with every indentation so
clearly visible, that one might easily have imagined that they were
but ten miles distant. On examining the objects in view through
a small telescope with a 25-power, it was at once apparent that this
arose from something more than common looming. 'The French
coast could be seen from near Calais towards the E. to far away and
many miles beyond Boulogne towards the 8.W., the land in the
latter direction being ordinarily invisible, as it is situated below the
horizon. Immediately under the erect image of the coast was an
inverted one, of about double the height of the former. The light-
house at Cape Gris Nez gave five images in a vertical line ;—the
lowest erect but somewhat magnified; above that and separated
from it a pair of images of the centre and highest portion of the
building only, one erect and the other inverted; and over these an-
other pair, the inverted image being like the former one, but the

* Communicated by the Author.

Intelligence and Miscellaneous Articles. 401

erect image showing the whole building. Over Boulogne, in the
air, were two images of the double funnels and the mast of a tug-
boat, the lower image being erect and the upper inverted, the two
lines of smoke bending, the one upwards and the other downwards,
and both towards the W., till they joined together. The only tug-
boat near Boulogne at the time, so far as I could learn, was in the
harbour. The cathedral was plainly visible, but only gave a single
image. Towards the S.W., and beyond the French coast, some
fishing-luggers were observed hull down, so that the position of the
horizon could be ascertained ; up to 3 o’clock they presented no un-
usual appearance ; but over these were pairs of images of vessels
which ordinarily would have been invisible. In some instances
three and even four pairs could be observed placed in a vertical line,
the lower image in each pair being inverted. With the exception
of the uppermost pair, the images seemed to represent the maintop-
gallant sail only, and that considerably elongated; but the highest
erect image showed the mizen- and the fore masts and the jib, but
in no instance could the hulls be seen. In all cases the inverted
images were of about twice the height of the erect. Soon after 3
o’clock vessels between the observer and the horizon began to be
affected. The Varne light-ship, which is about 83 miles from the
English coast, had her mast-flagstaff and stanchions elongated to
some three times their proper length : this effect lasted for about ten
minutes, when they shrank to less than half their usual size, and
the hull began to rise till it was nearly as high as it was long, and
formed a most conspicuous object even to the naked eye. I then
looked towards Dover: the pier seemed completely disorganized ;
it appeared to be divided in half longitudinally, with the sea in the
midst, and the stone coping moved as if huge waves were agitating
it. A steam-boat entering Dover harbour was shrunk to less than
half her proper vertical dimensions, but elongated horizontally.
Captain Paull, of the 8.E.R. steam-boat ‘ Napoleon III.,’ crossed the
Channel between the hours of 2 and 4; and he told me that he saw
Beachy Head during the passage, a circumstance which had never
previously occurred during the many years that he has been on the
Folkestone and Boulogne route.

At 4 o'clock the atmosphere had returned to its normal condition.
The place of observation was about 30 feet above high-water
mark. The barometer on the day in question stood at 30°33 in., ther-
mometer 58° F.; wind S.W., very light at 2 o’clock and dropping
to a calm; the electricity of the air unusually high, 185 by a
Thomson’s portable electrometer (with which five cells of Grove
give a potential of 3); and the ozone was 7 of Negretti’s scale.

Hadham House, Upper Clapton.
April 20, 1869.

ON THE PRODUCTION OF A BEAUTIFUL PATINA ON BRONZES IN
LARGE TOWNS.
In almost all large towns, especially in those in which coal is used
as a combustible, it has been found that bronzes exposed in public
places, instead of becoming coated witha patina (vert antique), have

Phil. Mag. 8. 4. Vol. 37. No. 250, May 1869. 2D

402 . Intelligence and Miscellaneous Articles.

a dark and dirty appearance like that of cast iron. ‘The desire to
remedy this led the Berlin Verein zur Beforderung des Gewerbfleisses
to cause comparative experiments to be made with a view to find, if |
possible, a remedy.

First of all the question had to be solved, whether the production
of a beautiful patina is dependent upon the composition of the
bronze. For this purpose ten samples of bronzes, remarkable for
their beautiful patina and taken from different places, were ana-
lyzed. Each of the samples was divided into two, and intrusted to
two different chemists. The results were given in the Proceedings
of the Verein for the year 1864. They showed that the bronzes in-
vestigated were of very varying composition. ‘The proportion of
copper varies between 94 and 77 per cent. ‘The quantity of tin
amounts in one to 9 per cent., in others to only four ; while others,
again, only contain 0°8 per cent., but up to as much as 19 per cent.
of zinc. The other accidental admixtures, such as lead, iron,
nickel, vary in like manner. With the most different composition
these bronzes have all avery beautiful green patina. The com-
position may:possibly have some influence on the time requisite for
the production of the patina; but the experiments leave no doubt
that it ensues even with the most different composition.

To ascertain the effect of other influences, a number of bronze
busts were placed in a part of the town in which particularly
unfavourable exhalations take place, and in which various bronze sta-
tues in the neighbourhood are destitute of any trace of patina, but
have the above-mentioned unpleasant black exterior.

It was observed that, on several monuments in places accessible to
the public, the parts liable to be handled had, if nota green, an
otherwise beautiful patina, while all the other parts were black and
unsightly. This led the Commission to the idea that grease pro-
bably influenced the production of the patina. Hence one of the
busts was rinsed every day, with the exception of rainy days, and
was, moreover, once a month painted over with bone-oil, which was
immediately rubbed off with woollen cloths. Another bust was
washed daily with water, but was not oiled. A third, which was
also cleaned daily with water, was only oiled twice a year. The
fourth was left unpurified, and, indeed, was not at all touched.

The first- and the last-named bust have been set up since 1864,
and treated in the manner described ; the second and third since
1866. ‘The supposition as to the action of the fat has been most
completely confirmed.

The one which has been oiled once a month possesses a dark
green patina, which is considered to be very beautiful by all con-
noisseurs. The one whichis only rubbed twicea year does not look
so well; and that only cleansed with water has none of the beau-
tiful appearance which bronzes obtain by the deposit of patina.
The one which was not at all cleansed is quite dull and black.

Hence we may expect that if a bronze exposed in the open air,
after being purified, be rubbed down with oil, it will assume a beau-
tiful patina.

How far this rubbing, which in many cases will be difficult to

Intelligence and Miscellaneous Articles. 403

perform, may be restricted is to be decided by continued expe-
riments which have already been commenced. ‘The Verein has also
exposed two bronzes which have been artificially patinated by che-
mical means, in order to ascertain how they are influenced by similar
treatment.

How the oil works in the formation of the patina, cannot
with certainty be stated. Experiments have shown that any excess
of oil is to be avoided, and that which has been painted on must
be rubbed off as much as possible. If excess of oil remains, the
dust deposits on it, and the bronze acquires an unsightly appear-
ance. It cannot be assumed that the residual small quantity of
oil enters into a chemical combination with the layer of oxide,
especially as bone-oil acts just as well as olive-oil in the expe-
riments. Probably the film of oil only acts in preventing the ad-
herence of moisture, by which dust adheres, gases and vapours are
absorbed, and in which vegetation forms. Whatever be the mode
of action, the experiments leave no doubt that the fat is essen-
tially connected with the formation of the patina.

It is probable that in other respects it will be advantageous.
It has been observed that bronzes covered with a beautiful patina,
in those parts where water trickles down assume a white, opaque,
chalky surface, which in course of time is more and more washed
away by the water. Proper treatment with oil will doubtless pre-
vent the formation of these chalky places; yet only long-continued
experiments can settle this point.

In any case this use of oil justifies the hope that for the future
we may retain beautifully patinated monuments even in large towns.
Where coal is the only combustible, they will not be bright, but
dark green, and perhaps even black; but they will have the other
beautiful property of the patina, the peculiar transparent condi-
tion of the surface.—Poggendorff’s Annalen, April 1869.

TYNDALL’S COMETARY THEORY.
To the Editors of the Philosophical Magazine and Journal.

GENTLEMEN, Streatham Hill, April 8, 1869.
Professor Tyndall’s interesting cometary theory, which appeared
in your last Number, turns on an assumption which is hardly com-
_ patible with the laws of motion. His assumption is that the tail of
a comet is ‘‘ matter precipitated on the solar beams traversing the
cometary atmosphere.” If so, the linear dimensions of a comet
must exceed the length of its tail—that is, in some cases 60 millions
of miles or more. Now it seems utterly incredible that such a butk of
vapour can whirl round the sun at the perihelion passage unbroken.
A very slight modification of Tyndall’s theory avoids this difficulty, and
equally well explains all the observed appearances. If there be an
extremely attenuated solar atmosphere extending considerably fur-
ther than the earth’s orbit, and if, when a comet approaches the sun
and is therefore exposed to intense heat, its volume becomes compa-
rable with the volume of the sun, the heat of the sun will be shut off
from that portion of the solar atmosphere in the shade of the comet
(which though transparent te light is opaque to heat), and actinic

404. Intelligence and Miscellaneous Articles.

clouds will be formed in the solar atmosphere, thus giving the appear-
ance of a tail to the comet. If the shape of the comet be irregular
there may be more than one tail. The comet after its perihelion |
passage recedes from the sun and at the same time gradually cools
and contracts; the tail therefore ought to be greatest and brightest
at or shortly after the perihelion, and then slowly diminish and fade
away. This is in accordance with observation.
Your obedient Servant,
Ernest CARPMAEL,
Scholar of St. John’s College.

GENTLEMEN,

In the last Number of the Philosophical Magazine Professor Tyn-
dall has propounded the theory that the visible head and tail of a
comet is an actinic cloud, resulting from the decomposition of vapour
by the solar light. This theory accounts for the extreme tenuity of
comets, their polarization, and the motion and development of their
tails.

Now if all our knowledge of comets were derivable from observa-
tions with the unassisted eye, this theory would account for the ob-
served phenomena; and, as it is, it is valuable by increasing our
knowledge of matter which, if not cometary matter, at all events has
striking analogies with it; but I do not think it affords any explana-
tion of cometary phenomena as observed by the telescope.

In the first place, immediately behind the nucleus, where, accord-
ing to this theory, we should expect a very luminous region, we
commonly have a dark space. Also the matter which forms the tail
usually streams out from the head towards the sun; this was especi-
ally noticed in Halley’s comet in 1836. Bond also, speaking of
Donati’s comet, says, ‘‘ the material, after being thrown off from the
nucleus, instead of at once being driven into the tail, formed a dense
cloud of nebulosity into which the luminous matter continued for
some time to stream. This cloud extended itself on the sunward side,
remaining in its vicinity for several days. When it had acquired a
certain stage, the discharge took place mainly from the corners or
cusps on either side in two streams, which, coalescing with those
issuing from other envelopes, formed the two branches of the tail.”
Then, too, we have several series of envelopes which rise up towards
the sun. In Donati’s comet seven were detected; in the great
comet of 1861 no less than eleven were noticed: the force which
causes the ascent of these is mtermittent and finally dies away.
Mr. Webb, in 1861, noticed the descent of the envelopes on the nu-
cleus; also Herschel and Schroeter noticed the same in the comet
of 1811. |

From these facts I am disposed to think that although Professor
Tyndall’s hypothesis accounts for some of the phenomena, yet the
true theory is still to be discovered.

I am, Gentlemen,

Talfourd Road, Peckham, Your obedient Servant,

April 18, 1869. W. B. Grsss, F.R.A.S.

THE
LONDON, EDINBURGH, ann DUBLIN

PHILOSOPHICAL MAGAZINE

AND

JOURNAL OF SCIENCE.

[FOURTH SERIES.]
JUNE 1869.

“LVIIL. On the Spectra of certain Gases in Geissler’s Tubes.
By A. WULLNER*.

I. Hydrogen.
ee spectrum which hydrogen enclosed in Geissler’s tubes,

under very small pressure, exhibits when the current from
a small Ruhmkorff’s coil passes through it consists, as Pliicker
first showed}, essentially of three bright lines, which he has de-
signated as Ha, HS, Hy. H eis a brilliant red line which takes
the place of Fraunhofer’s line C; H 8 is a bright bluish-green
line exactly corresponding to the dark line F ; and H ya bluish-
violet line which,corresponds to a delicate dark line just in front
of G; this M. Angstrom{ also designated as belonging to hy-
drogen. Besides these there is a further violet line H 6, the posi-
tion of which, owing to its feeble light, cannot be accurately de-
termined.

Besides these bright sharp lines there is seen in many tubes a
feebly bright field traversed by dark lines, in the neighbourhood
of the sodium-line in the place corresponding to the dark line
D of the spectrum. This bright field begins about 0°8 of the
space between « and D in front of D, and extends beyond D so
far that the part on that side is about half as broad as that on
the other side of D. Looked at with a flint-glass prism of 60°

* Translated from Poggendorft’s Annalen, December 1868.
Tt Pogg. Ann. vol. evi. pp. 506 & 518.

{ Pogg. Ann. vol. exxiil..

Phil. Mag. 8. 4, Vol. 37. No. 251. June 1869. 2 i

4.06 M. A. Willner on the Spectra of

refracting angle with great dispersive power, and through a tele-
scope of about twelvefold magnifying-power, this field is resolved
into about from fourteen to sixteen bright dark-edged and beau-.
tifully shaded bands, which are red, orange, yellow to yellowish
green. With different hydrogen-tubes this part is seen of differ-
ent degrees of brightness, so that Pliicker originally ascribed it to
the last traces of air still present in the tubes.

Plucker subsequently recognized that this part of the spectrum
also belonged to hydrogen. In an investigation made with M.
Hittorf on the spectra of ignited gases and vapours*, they
show that several elements, as nitrogen and sulphur, have two
different spectra—a continuous one with shaded bands, and one
consisting of bright lines separated more or less by dark spaces ;
these are designated by them as spectra of the first and of the
second order. In this investigation they describe this bright field
as a special spectrum of hydrogen of a peculiar character. Plucker
says there, in reference to this spectrum :—“ In an old spectrum-
tube which contained very rarefied hydrogen, the ground against
which the three characteristic lmes stand out is not always of the
same degreeof darkness; sometimes new and brilliant lines appear,
especially near the sodium-line. We confirmed the existence of
a new hydrogen spectrum, which corresponds to a lower tempe-
rature, but exhibits no similarity to all the other spectra of the first
order, those of nitrogen, sulphur, &c. In this spectrum, of a pe-
culiar character, we observed, when it was fully developed, a great
number of well-defined lines, almost too numerous to be counted
or drawn, but bright enough to be investigated with a magni-
fying-power of 72.”

That this spectrum is peculiar to hydrogen was further con-
firmed by pansies the discharge of a Ruhmkorfi’s apparatus
through a tube 4 to + inch wide, which contained hydrogen
under a pressure of 5 to 10 millims.; a bluish-white line was
then observed in its axis. Analyzed with the prism, it exhibited ©
the spectrum in question, especially numerous bright lines be-
tween red and yellow. Along with these lines neither H « nor
Hy appeared, only Hf, but feebler than many other lines. When a
Leyden jar with an iner easing charge was interposed, all the lines
were brighter, H 6 most so, Ha appeared beautifully, H y more
feebly.

2. About two years ago I observed a third additional spectrum
of hydrogen, which neither in its appearance nor in its formation
agreed with those already described; for especially in its green
part the spectrum has decidedly the character of one of the first
order, and at first I considered it belonged to nitrogen, from
which, however, more accurate comparison showed that it differed

* Plucker and Hittorf, Philosophical Transactions, 1865, part 1.

certain Gases in Geissler’s Tubes. 407

essentially at the blue end which is so characteristic of nitrogen.
The first observation, which I communicated in 1866 at the May
meeting of the Niederrheinische Gesellschaft fiir Natur- und
Heilkunde, was an accidental one. In an experimental investi-
gation on the relation between the refractive indices and the
densities of bodies, I used in determining the refractive indices
the spectrum of ignited hydrogen consisting of the three bright
lines. On this occasion a hydrogen-tube, which had previously
been used for frequent measurements, became one day suddenly
altered: its previous beautiful red light became white ; the violet
line disappeared in the spectrum ; and instead of the former
Spectrum a continuous one was formed which, especially in the
green, was most beautifully shaded. The first supposition, that
the tube had begun to leak and had admitted some air, was seen
to be erroneous on making a comparison with the spectrum of
nitrogen, and in further experiments which had for their object
@ more accurate investigation of the spectrum; for the tube
just as suddenly assumed its previous red colour, and exhibited
as spectrum the three well-known bright lines only. Hence it
was established that, under circumstances which as yet were not
determinable, hydrogen could furnish a continuous spectrum.

Shortly afterwards I obtained from Dr. Geissler of Bonn a
number of new hydrogen-tubes. One of them was found on in-
vestigation to undergo just such a change; it suddenly became
white, and yielded the continuous spectrum observed in the first
tube. This tube, which is an ordinary one with platinum elec-
trodes, still shows this Spectrum when the induction-current
merely passes through it. The spectrum is so rich and beautiful
in its shading that it is difficult to describe, and still more diffi-
cult to delineate*,

. . . . e =
accordingly coincide with the second hydrogen-spectrum de-

* Illustrations of this and of the other hydrogen-spectra as well as of
hose of aluminium, after drawings by Dr. Bettendortf, are given in the
estschrift der niederrheinischen Gesellschaft fiir Natur- und Heilkunde
ur OOjahrigen Jubelfeier der Universitit Bonn. Bonn: Marcus, 1868,

2H 2

/

408 M. A. Wiillner on the Spectra of —

To the reddish-yellow part succeeds, first of all, a feebly illu-
minated green field bounded on the right by a brighter green
band. The follows, as far as the line H B, which always remains
visible, a beautiful green multifariously shaded field, which by its
shading and the bright bands standing out from the darker back-
ground, four of them being particularly bright, makes quite a
stereoscopic impression. ‘The character of this partis so hke
that of the green in the first nitrogen-spectrum, that only a
closely detailed comparison makes the difference perceptible.

From H 8 on the blue side, the spectrum reaches to about the
middle of the space between H 8 and Hy; and here also against
the faint blue ground four brighter bands stand out, of which
the second and the fourth are the brightest. Hy can only be
occasionally faintly seen.

I have since then observed just the same spectrum in a tole-
rable number of other hydrogen-spectrum-tubes when, after
being for a long time used with a well-working imduction-appa-
ratus, they were illuminated by a feebler current.

The observation of MM. Plicker and Hittorf, that continuous
spectra of the first order belong to a lower temperature than the
spectra of the second order (consisting of dividual bright lines),
led to the supposition that this spectrum also belonged to a
lower temperature, which might result from the circumstance
that, after lengthened use (perhaps through partial melting of
the electrodes), the induction-current on entering the gas met
with a greater resistance. If this supposition were correct, the
method already adopted by Plucker and Hittorf for producing
the second spectra (the simultaneous interposition of a Leyden
jar into the current of the induction-apparatus) must also again
produce the spectrum of hydrogen consisting of the characteristic
lines. This supposition was so far confirmed that, on introdu-
cing a Leyden jar, the above-mentioned spectrum-tube exhibited
a flickering, alternately red and white hight, and that, viewing
the flickering up of the red light with the spectrometer, the well-
known three lines were observed.

The change of the continuous spectrum into that consisting
of the three lines was effected with the aid of Holtz’s machine.
If the current of such a machine without a condenser was allowed
to pass through the hydrogen-tubes, their light appeared white,
and, viewed with the spectrometer, the continuous spectrum ap-
peared, though faint, yet distinct, especially in the green. If
the condenser was laid upon the machine, so that the spark tra-
versed the tube in individual! discharges, the light of the tube at
once became red and exhibited only the characteristic lines. The
same was of course seen when, by means of a Holtz’s machine,
the discharges of a small Leyden jat with a small striking-dis-

certain Gases in Geissler’s Tubes. 409

tance were allowed in quick succession to pass through the tube.
By these discharges the resistance in the tube appeared even to
be permanently diminished ; for shortly afterwards the simple
induction-current of the small Ruhmkorff, passed through, again
produced the red light of hydrogen, which, however, again
changed into the white one with a continuous spectrum when
the current had passed for about a quarter of an hour through
the tube.

3. After it had thus been established that the light of ignited
hydrogen, according to its different temperatures, which depend
on the mode of discharge, might be different, it was to be ex-
pected that there would be a similar difference when, with the
same discharge, the density of the gas in the tube varied. To
test this conclusion I made some experiments in conjunction
with Dr. Bettendorff, which not only confirmed it, but also gave
a new spectrum quite different from the preceding ones.

The arrangement of the apparatus was as follows :—In front
of the slit of the spectrometer a spectrum-tube was fixed, which
near each electrode was provided with a small lateral tube that
could be closed by means of a Geissler’s stopcock. The upper
of these lateral tubes was connected with the horizontal arm of a
Sprengel’s pump* constructed by Dr. Bettendorff; the lower
one was connected with an apparatus for decomposing water, a
tube filled with anhydrous phosphoric acid and a bulb-apparatus
containing concentrated sulphuric acid being interposed. Over
the platinum electrodes of the apparatus for decomposing water
tolerably wide glass tubes provided with stopcocks were placed,
which at the same time served as gasometers. In preparing the
hydrogen, the oxygen was allowed to issue from the tube over the
Esitive electrode, so as not to contaminate the hydrogen with
oxygen dissolved in the watery.

After the tube and the pump had been dried by heating and
the continued passage of air, the spectrum-tube was exhausted
and then filled with hydrogen from the decomposition-apparatus,
again exhausted and filled, and this repeated until, at a pres-
sure of from 8 to 10-millims., only the characteristic lines of the
hydrogen-spectrum could be seen on the passage of the current.
The tube was then again filled with hydrogen, and the light
produced by a Ruhmkorff’s coil investigated while the tube was

* Journal of the Chemical Society, 8. 2. vol. ii. p. 9.

+ The necessity for this precaution was indicated by the observation that
the spectrum of the hydrogen-tube exhibited oxygen-lines when the oxygen
was collected and thus the acidulated water saturated with oxygen was
allowed to press out of the tube surrounding the anode and mix with the
other liquid. The absorbed oxygen which then, diffused throughout the

entire apparatus, escaped over the cathode was quite enough to produce 3 in
the spectrum the most distinct oxygen-lines.

A10 M. A. Wiillner on the Spectra of

being gradually exhausted, the pressure of the enclosed gas being
read off on the mercurial column of the pump.

In this way it was found that the current of the small induc- |
tion-coil can, under a pressure of 1385 millims., strike across the
tubes, the electrodes of which are 1°4 decim. apart; the tube
shines with a white light, the intensity of which is too small to
analyze it prismatically.

When the pressure of the enclosed gas is diminished, the
brightness of the ght steadily increases, and under a pressure
of 100 millims. it is bright enough to be investigated with the
prism. Under this pressure the hght of the tube is bluish
white, and sometimes it appears for a moment reddish-tinged..
It gives a continuous spectrum, upon which, when the light ap-
pears reddish, the bright lines H « and H @ distinctly stand out.

Under a pressure of 70 millims. the ight of the gas is reddish
white, and in the spectrometer the continuous hydrogen-spec-
trum is seen as above described. It shows first of all He; as
far as half the distance between H & and D the field of view is
dark ; then follows a reddish-yellow to a greenish-yellow part,
consisting of a series of beautifully shaded bands; then another
dark one, and then as far as H 6 a feebly bright green field, on
which four brighter green bands stand out. Behind H 8, as far
as Hy, the field of view is illuminated by a feeble blue light, in
which two bands stand out more brightly—the first at 0-3 of
the distance H 8 to Hy behind H £, the second in the middle
between these lines.

if the pressure be further diminished, the light in the tube
increases in brightness, the colour becomes redder, and the spec-
trum continually more beautiful. Even under a pressure of 52
millims. the spectrum is developed just as has been already de-
scribed; it becomes brighter and more beautiful as the gas is
still further rarefied, until the pressure amounts to about 80 mil-
lims., at which the spectrum appears extremely brilliant.

On further rarefaction the brightness of the continuous spec-
trum decreases, while the three hydrogen- Imes become continually
brighter. Under a pressure of 21 millims. the limes Ha, H8,
H y were very beautiful, the reddisheyellow part of the continuous
spectrum also beautiful, but the green part of the spectrum much
enfeebled, only the bright bands in them being visible. Near
H 8, towards the more refrangible side, only the two brightest
lines could be recoginzed.

Under a pressure of 10 millims. the reddish-yellow part could
still be seen in its brightest bands; in the green, individual
bands were still faintly Saieanen é beyond H @ scarcely a band
was visible.

Under a pressure of 6 millims. the reddish-yellow part was Just

certain Gases in Geissler’s Tubes. 411

visible, besides the characteristic hydrogen-lines; at two places
in the green a bright glow was to be seen; and also between H 8
and Hy the two previously mentioned bright bands were vi-
sible.

On further rarefaction to 8 or 2 millims. the characteristic
lines retained the same brightness, and everything else disap-
peared almost entirely from the spectrum; yet, with a simulta-
neous enfeeblement of the bright lines, part of the continuous
spectrum reappeared in the green, in the form of about five bright
fields, when the gas was rarefied to fractions of a millimetre pres-
sure. These observations show that the hydrogen-spectrum de-
scribed belongs, in fact, to a lower temperature than that consist-
ing of the three lines ; for with increasing density of the gas in the
spectrum-tube the temperature must become lower, since the
induction-current experiences a greater resistance in the denser
gas, and a larger quantity of the gas has to be heated. But,
just as a great density of the gas does not permit the full inten-
sity of the current to be developed, so the current is also enfeebled
by great rarefaction ; for by adequate rarefaction the current ina
spectrum-tube may be completely stopped. The occurrence,
therefore, of the continuous spectrum both with greater density
and with greater tenuity of the gas proves that it belongs toa
lower temperature.

4. By the experiments communicated in the preceding, the proof
has been furnished that the continuous hydrogen-spectrum be-
longs to a lower temperature ; and the question arises how it hap-
pens that Geissler’s spectrum-tubes, which contain hydrogen
under a pressure of from 5 to 10 millims. (a pressure favourable,
therefore, for producing the line- gees yet after some time,
after lengthened use, may yleld the continuous spectrum. The
observation that this spectrum is especially seen when, after
lengthened use, the tube is exposed to the action of a feebler
eurrent, led to the supposition that (possibly owing to a super-
ficial melting of the electrodes) greater resistance was offered to
the passage of the induction-current. That such a fusion of the
electrodes has an influence of that kind was established by a
series of experiments. In the extreme degrees of exhaustion
mentioned above, and which are to be subsequently discussed,
the resistance in the spectrum-tubes was so great that the whole
of the positive electrode became incandescent. It thereby be-
came quite bent, and after some time was partially fused, so that

_ it looked like a series of small pearls ona thread. After this de-

formation of the electrodes had occurred, the tube, on gradual ex-
haustion of the hydrogen, always exhibited the continuous spec-
_ trum, even under pressures at which the green light was other-
wise scarcely visible. The continuous spectrum was extremely bril-

412 M. A. Wiillner on the Spectra of

lant under a pressure of 30 millims., 21 millims., 16 millims. ;
and even under a pressure of 8 millims. it was doubtful whether
the continuous part was really fainter, or whether it only ap- —
peared so in comparison with the dazzling lustre of the lme H @.

Several observations which we made on a phosphorus-tube and
a sulphur-tube, prepared by Dr.Geissler, favour, I think, the view
that the nature of the electrodes exerts an influence on the pro-
duction of the continuous spectrum. These tubes also contained
hydrogen. Ifthe induction-current was allowed to pass without
heating the tubes to the melting-point of phosphorus or of sul-
phur, they exhibited a beautiful continuous spectrum exactly as
has been previously described ; the spectrum of phosphorus or
sulphur only appeared on stronger heating. In these tubes the
electrodes are always more or less covered with phosphorus or
sulphur, by which, since these substances do not conduct, the
resistance to be overcome is greater, and therefore the intensity
of the current must be less.

5. It has already been mentioned, in § 3, that when the pres-
sure of the gas in the tube only amounted to fractions of a milli-
metre the continuous spectrum of hydrogen was again formed,
particularly in the green. Ifthe tube was then still further
exhausted by means of the Sprengel’s pump, the light in the
tube first became feebler and its colour paler; and in the spec-
trum, while all the rest was weakened, the green part stood out
still more beautifully. It appears in the form of six beautifully
shaded bright bands, which are connected with each other by less
bright intermediate spaces. In the brightest parts of the blue
in the continuous spectrum bright fields also appear, of which
that in the middle between H 8 and Hy is seen as columnar
grouped lines.

On further pumping, the light in the tube suddenly becomes
of a splendid green like the hight of a thallium-flame, and the
spectrum is quite changed; the red line He can scarcely be
seen; the reddish-yellow part of the spectrum has completely
disappeared ; and in the green six splendid groups of lines appear
on an almost black ground. Repeated measurements gave for
the least deflection of these groups the following values* :—

(1) Middle bright line of the first group, consist-
ing of three bright lines, this being the brightest

e) Se ‘ a the second Carn ieee | 10 15

* The flint-glass prism used for these measurements has a refractive
angle of 60° 2’ 00"; its refractive indices are, for Ha 1°743355, for
H 8=1°772210, for H y=1-790564: the measurements were made with a
Meyerstein’s spectrometer with a circle divided to 10",

dos 47 40

certain Gases in Geissler’s Tubes. 413

(3) Second brightest line of the third group, con-
sisting of two bright lines .

(4) First bright line of the fourth eroup, consist-"
ing of two very closely adjacent lines

(5) Middle line of the fifth group, consisting of
three bright lines: this line is the brightest, >64 92 20
and is more than aslitinbreadth . , .

(6) Middle bright line of a ae of at least Sasi 64 88 40
individual lines . : : -

(7) H8 still faintly vicialcsad wa i adin 4 dental, GAG

These groups, as is evident, corresponding to the green co-
lour of light, all he in the green part of the spectrum; in the
red and yellow part there is nothing to be seen. Besides these
measured groups, at the boundary of the green towards the yellow
a feebly bright part was seen, between the first and second groups
two feebly bright lines, and between the fourth and fifth groups
about three faint lines. About as far to the right of HP as
the sixth group is to the left of @, there is a feebly bright line,
too obscure, however, to be measured. Then at about 65° 20!
there is a faint blue field bounded on both sides by two beauti-
fully shaded bright bands; and behind this, after a perfectly
dark space about half as broad as the field just mentioned, there
is a faint field of considerable breadth; at times there is in the
neighbourhood of Hy, at 67° 10/, a faint lustre.

This spectrum occurs whenever the gas in the tube has attained
the extreme degree of rarefaction attainable with a Sprengel’s
pump. The resistance in the tube is here so great that the posi-
tive electrode becomes quite incandescent, bends, and appears to
consist of a series of fused globules. That this deformation at
the same time seriously hinders the passage of the current, as
before mentioned, follows from the fact that on its entrance the
current no longer started from the point of the electrode of
aluminium wire, but from the part of it which lay against the
platinum wire melted into the glass of the tube, where such a
fusion could not be perceived.

If the extreme rarefaction which furnishes the spectrum just
described is maintained for some time with closed stopcocks, the
hehkt of the tube again assumes a white colour and again shows
the continuous spectrum, the reddish-yellow part is again seen,
the six groups of lines again disappear, and the green appears once
more. But the density of the gas in the tube is not changed ;
for if the stopcock be opened which connects the tube with the
air-pump, the position of the mercury remains quite unchanged.
Notwithstanding this, renewed pumping again produces the line-
spectrum.

Another means of again evoking the line-spectrum is the si-

63 29 20
63 46 25

414 M. A. Wiillner on the Spectra of

multaneous interposition of a Leyden jar in the circuit of the
induction-current. <A brilliant bright-green light is then ob-
tamed in the tube, and the six groups of lines become truly
splendid. At the same time the parts lying between the groups
of lines become brighter, yet not to such an extent as to change
the character of the spectrum. The tube then afterwards ex-
hibits the same spectrum even without a Leyden jar.

This spectrum is also obtained with the extremest degree of
rarefaction if the spark of Holtz’s machine with a condenser be
caused to pass, orif a small Leyden jar with a short striking-dis-
tance be discharged through it. | Care must at the same time be
taken not to have the striking-distance too great; otherwise the
calcium-spectrum, or the continuous spectrum of ignited glass
with the dark line D, occurs.

With a tube once arranged I have frequently observed this
spectrum for fourteen days together and compared it with others ;
so accurately closed were Dr. Geissler’s glass stopcocks.

6. The phenomenon of a hydrogen-tube at its extreme ex-
haustion furnishing a third spectrum essentially different from the
earlier ones observed is so surprising, that the question must be
considered whether this spectrum belongs in fact to pure hydro-
gen, or is not due to other elements standing in connexion with
the tube. It might be believed that it was a spectrum of alumi-
nium, of which the electrodes consisted, or of mercury, of which,
perhaps, vapours had distilled over into the tubes, or of phos-
phorus or sulphur, as the gas was dried with phosphoric and sul-
phuric acids, or, finally, that some of the fat with which the
stopcocks were slightly coated had evaporated and had entered
the tubes, and thus that the lines belonged to the spectrum of
carbon.

As regards carbon, the description which Plucker gives of the
spectra of this element* shows that none of the groups of lines
of the kind described occur in them; and im an investigation of
the spectrum in a tube filled with carbonic acid, we found it of
the same character as Plucker describes.

In reference to the sulphuric-acid spectrum, Plicker+ states
that it is one of the most beautiful spectra and at the same time
most rich in colour, it consists of bright lummous bands on a
black ground; and he then counts three red, one orange, one yel-
low, four green, nine blue and viclet bands. He mentions at the
same time that, using anhydrous sulphuric acid, this spectrum
can only be obtained with the large induction coil. All this
proves that the spectrum described cannot be due to sulphuric

* Philosophical Transactions for 1865.
Tt Poge. Ann. vol. exil.

certain Gases in Geissler’s Tubes. A415

acid, even if we were to assume that along with the hydrogen
some sulphuric-acid vapour had entered the tube.

Our spectrum cannot be confounded with that of phosphorus
or mercury, as follows from Plicker’s descriptions, and as we
have convinced ourselves by experiments. Phosphorus exhibits
in the green only one group of bright lines, about 8! broad, the
most refrangible of which has the minimal deviation of 63° 38’.
The mercury-spectrum consists of a series of bands, of which a
yellow one is particularly characteristic ; moreover , In a tube
containing mercury, this spectrum is only formed when the tube
is consider ably heated.

To compare the spectrum in question with that of aluminium,
wires of this metal were fastened to the ends of the wires leading
to the induction-apparatus, and the induction-spark was allowed
to strike between these, which were placed in front of the slit of
the spectrometer. It was then observed that, according to the
distance of the electrodes, the aluminium-vapour might have two
essentially different spectra. When the distance of the electrodes
was only about two millims., the spectrum consisted of four
green splendidly shaded fields. The fields are brightest on the
more refrangible side, and gradually diminish towards the less
refrangible side; at distances of 5 minutes these fields are tra-
versed by sharp bright lines, and these give quite the appear-
ance of fluting to the fields. The mght limit of these fields was
found, in the minimum deflection, at :—

st Habis). < 63 24 10 patteea:
OES hia) ocx re os) (4010-20 0 46 10
BEE bohtew iss oy 14) O404, 40 0 44 20
HOH f50 ons, ress > 80, 40-00 0 45 20

The measured distances of the fields (that is, of their right
boundaries) are so nearly equal that their differences may hp 26-
garded as errors of observation, since the adjustment is not per-
fectly accurate; the breadth of the fields is about 30'; so that
this spectrum of aluminium consists of four equidistant almost
equally broad groups of flutings.

When the distance of the two wires between which the sparks
passed was increased to 10 millims. and more, a totally different
_ spectrum was obtained, both with the use of the small Ruhm-
korff and with that of Holtz’s machine with superposed con-
denser; the four fluted fields disappeared, and instead of them a
number of bright lmes and groups of lines started out upon
a feebly illuminated background. With the minimum deflec-
tion the positions of these lines were :—

4.16 M. A. Willner on the Spectra of

(1) Beautiful bright double lime. . . so P ReReAe
(2) Position of the first of three faint lines, raf 0
which the second is nearer the first than the third
(3) Brightband 7 ea eae 63 51
(4): Bright lines). 2° 2 6 4) 24,2 ee
(5) Bright band .5° 38%". Ls) oe
(6) Faintly brightline . . 65 5
(7) Middle, brightest, of an entire e group 0 of lines. 65 47
(8) Bright ilnene re 66 41
(9) Faintly bright lime .- .. .. » ye

The two aluminium-spectra stand in the same relation to
one another as the spectra of the first and second order which
MM. Plicker and Hittorf have represented for nitrogen, sulphur,
&c.; the formation of the second at a greater striking-distance
and with the use of a Holtz’s machine with a condenser proves
that it belongs to the higher temperature.

A comparison of this second aluminium-spectrum with the
hydrogen-spectrum described in § 5 shows that they are quite
different. Hence it must be assumed that the spectrum con-
sisting essentially of the measured six groups of lines is peculiar
to hydrogen.

7. The spectra of hydrogen described in the preceding are es-
sentially different. One is not formed from the other by the de-
velopment of new lines or new colours as the temperature rises ;
but quantities of light disappear which are present at a lower
temperature, or on a previously continuously illuminated space
bright lines stand out at a higher temperature on an almost
black ground; for, from the mode of formation of the spectra, it
cannot be doubted that the continuous spectrum belongs to
the lowest temperature, since the spectrum consisting of three
lines, as well as that consisting of six groups of lines, takes the
place of the continuous one when the discharges of a Leyden jar
are passed through the gas, from which undoubtedly a much
greater heating results than from the simple discharge of an in-
duction-current. These spectra may, itis true, be formed by the
simple current of induction, but only under circumstances which
favour such an increase of temperature. The first spectrum is
formed if the gas has such a density that the current 1s best and
most completely developed—the six-group spectrum if only mi-
nimal quantities of gas are present for the conduction, which can
then be raised to the highest temperature, like the particles de-
tached from the carbon-points in the electric light.

This difference of temperature must, in the case of hydrogen,
be regarded as the sole cause of this phenomenon ; for a decompo-
sition into further elements is not to be thought of. It follows,

certain Gases in Geissler’s Tubes. 417

then, from these observations that the emissive power of a sub-
stance may materially alter with the temperature.

If. Oxygen.

8. The spectrum which a Geissler’s tube filled with pure oxy-
gen gives consists, according to Plicker’s* description, of a
series of bright lines, the least refrangible of which lies in the red-
orange, and which, more or less close, extend thence to the violet.
Pliicker described only this one spectrum, and in the subsequent
Investigation, made in common with M. Hittorf, obtained only
the same. In communicating these experiments he says} :—
“We obtained only one spectrum of oxygen working in the
same manner as with nitrogen, with this difference, that under
the same circumstances an equally brilliant spectrum was only
obtained with a stronger discharge. He further states that,
especially in oxygen, the gradual appearance of the bright lines is
noticeable—that at first the least refrangible show themselves, and
at last as the temperature rises the most refrangible come out—
that a drawing, therefore, which represents as simultaneously
appearing those lines which are only successively formed, gives an
ideal picture of the spectrum rather than accords with nature.

The experiments previously communicated on the spectra of
hydrogen, the observation that the spectrum may materially alter
with the density of the gas and the mode of discharge, led me to
investigate oxygen in this direction.

The method of experiment was the same as that described in
§3. The lateral tube of such a spectrum-tube as is there de-
scribed was connected with the tube placed over the anode of the
apparatus for decomposing water. In order to dry the oxygen
supplied, a tube containing phosphoric acid and a bulb filled with
strong sulphuric acid were interposed. The production of a per-
fectly pure oxygen-spectrum, however, is almost always attended
with great difficulties; the three characteristic lines of hydrogen
were almost always observed, arising from the moisture condensed
on the inside of the spectrum-tube. It could, however, be ex-
pelled by strongly heating the spectrum-tube and then repeat-
edly drawing pure oxygen through it. When the tube had thus
been dried so that with oxygen under a pressure of from 5 to 10
millims. it no longer showed any hydrogen-lines, it was filled with
_ oxygen under the ordinary pressure, then gradually exhausted
by the Sprengel’s pump as described in § 3, and the spectrum
investigated which the gas gave at different densities.

9. It was first found that, using a spectrum-tube of exactly the

* Poge. Ann. vol. evil.
f Philosophical Transactions for 1865, part 1, p. 23.

418 M. A. Willner on the Spectra of

same dimensions as had been used for the experiments with hy-
drogen, the density of the gas had to be much smaller to allow
the current of the same induction-coil to pass through when the
same number of elements were used. While hydrogen allowed
the current to pass even under a pressure of 135 millims., several
experiments showed that with oxygen continuous passage only
took place when the pressure was diminished to 45 or 4:7 millims.
The hght is whitish, but far too weak for a spectrum-imvestiga-
tion; this was only possible when the density was diminished to
28 or 80 millims. The light appears even then whitish-coloured.
The spectrum presents six bright lines—a red line (the flesh-red
one characteristic of oxygen and designated by Plucker Oa),
two green and two blue lines, and a violet one. The brightest
have then the following positions of least deviation :—

Ow, the flesh-redline . . . 61 54 30
Thesecond gréen’one’ ..) =) )) (doze
The violet 2°)}e 4. 00 2 Soe

After a longer passage of the current, the second red line in-
dicated by Plucker is recognized.

When the pressure is diminished to 25 millims. the tube still
shines with a whitish hight, the brightness of which, however, has
greatly mcreased. Besides those previously observed, there are
seen in the spectrum. three fainter green lines, at about 64° least
deviation. Under a pressure of 18 to 20 millims. the colour of
the light somewhat passes into violet, the brightness is increased ;
there appear besides the former lines two orange-coloured ones,
two very faint yellowish green, a faint blue, at about 65° 10/,
and a faint violet line at the end of the spectrum.

The pressure being diminished to 6 millims., some new lines
occur—a bluish green, and a violet which is somewhat further
deflected than those previously mentioned.

At the same time the background on which the lines stand
out no longer appears quite dark, but here and there distinctly
continuously illuminated. Such a continuous field probably
forms the background against which the previously mentioned
three faint green lines at about 64° are formed.

Without these lines disappearing, the continuously illuminated
fields stand out more distinctly when the pressure is further di-
minished ; and when it only amounts to fractions of a muilli-
metre, the background of the spectrum has become changed into
a spectrum of the first order, consisting of several beautifully
shaded fields. The colour of the light has become more green ;
and in accordance with this the continuously illuminated parts
he in the green and in the blue.

The first, very faint yellowish part appears just on the right

certain Gases in Geissler’s Tubes. 419

of Oa. Separated from this by a dark space, a green field is
seen, sharply defined on the left, and gradually shading off on the
right, among the yellowish-green lines which appear under a
pressure of 20 millims.

On the right of the bright-green line at 63° 28/, and sepa-
rated from this by a dark space, there is a splendid green field
consisting of several beautifully shaded bands. It has a simi-
larity to the violet part of the nitrogen-spectrum, inasmuch as its
individual parts are brightest and most sharply defined on the
left, while on the right they gradually shade off. The field ex-
tends to the third of the above-mentioned three fait green
lines. Then follows a beautifully shaded blue field, the left limit
of which is at about 64° 56’, which continues in strongly shaded
parts into the violet.

On continuing the rarefaction, when the pressure can no longer
be measured the character of the spectrum suddenly changes,
just in the manner described for hydrogen: the continuously
illuminated fields disappear ; and in their places, or near them,
splendid groups of lines stand out. These perfectly sharp
bright lies on a dark ground lie preferably in the green and
blue, corresponding to the bluish-green colour of the lght
which the tube emits.

The spectrum observed does not agree with that described by
Plucker, and drawn on plate 2 in the Philosophical Transactions
for 1865; for the groups of lines are in other positions than
those given by Pliicker ; and where Pliicker draws entire groups
of lines, nothing or only individual lines are met with. The
spectrum shows five groups of lines, the first two of which are
the brightest and broadest. The first of these groups is just in
the middle between the positions corresponding to Ha and HB
of hydrogen, and extends from 68° 11! to 63° 20'. The second
group (the broadest of all) extends from 63° 48! to 64° 9!; it
thus les about in the middle between the first group and H £.
The third group has a breadth of 6’, its middle is at 64° 42/.
Then follows, separated by a feebly bright field, a narrow group
- consisting of five lines, the right limit of which is at 65°4!/. The
fifth, very narrow group is at the beginning of the blue, at 65° 40.
In the violet only three lines appear, at 66° 44!, 67° 2', 67° 8! 30";
and then a very faint line at 67° 36’, which bounds the spec-
- trum on the most refrangible side.

10. The phenomena described are seen in the above order, if
the current of the small induction-apparatus is passed through
the spectrum-tube filled with oxygen. In that case the last-
mentioned spectrum is obtained when, after the appearance of the
continuous spectrum, it is attempted still further to exhaust the
tube. The line-spectrum is more easily obtained by adopting

420 M. A. Willner on the Spectra of

the method proposed by Plicker for producing spectra of the
second order—that is, by connecting a Leyden jar with the in-
duction-apparatus; the continuous spectrum then passes at once
into that consisting of groups of lines.

11. The best means, however, of investigating the two new spec-
trais Holtz’s machine: by its means the continuous spectrum is ©
obtained without the bright lines of the oxygen-spectrum de-
scribed by Pliicker; and it can thus be demonstrated that the
spectrum consisting of lines is essentially different from the con-
tinuous one—that is, that the latter spectrum emits light which
is different from that emitted by the former.

If the current of a Holtz’s machine without its condenser be
passed through the tube filled with extremely rarefied oxygen,
the light has a sea-green colour, and in the spectrometer only the
continuous spectrum is seen without bright lines. Besides a
faint reddish field, four beautiful bright fields are first seen,
which are sharply bounded and are brightest on the less refran-
gible side, and gradually shade off towards the more refrangible
side, so that the limits cannot there be sharply defined. For the
position of the less refrangible limit, numerous measurements,
which only differed by fractions of a minute, gave the following
values :—

(1) Boundary of a yellowish-green field . . 62 50 380
(2) Boundary ofa greenfield .« . ~. « » 6a 42900

This field has the greatest brightness.

(3) Boundary of a greenish-blue field . . . 64 56 00

The brightness of this field decreases pretty rapidly in the first
quarter; the followimg three quarters are almost of the same
brightness. The breadth of the entire field is about 40!.

(4) Boundary of a blue-violet field which on yf 66 18 40

more refrangible side shades off most beautifully

Besides these four fields, a few other less bright ones are seen,
which could only be partially measured, and partly were estimated
in their position relatively to the brightest fields.

Between the red field at Oa and the first green one two nar-
row yellowish-green bands were seen, at 62° 25! and 62° 35!

Between the fields called above (1) and (2) there is from about
63° 20! a feebly bright field, which also 1s brightest on the less
refrangible side, and gradually shades off towards the more re-
frangible side.

At 64° 15! there is a feebly bright field about 10! broad, shaded
off in bands.

From 65° 52! to the bright field (4) the field of view is feebly

certain Gases in Geissler*s Tubes. 421

illuminated with a brightness which only slightly diminishes
towards the more refrangible side.

A very feebly illuminated field appears then at 66° 54’; it is
of small breadth.

12. If the condenser be placed upon Holtz’s machine, the conti-
nuous spectrum changes at one stroke into the line-spectrum :
groups of lines stand out in places which were previously dark ;
the bright fields split up; and on the field (2), for instance, bright
lines start out right and lett of the brightest part, while the
brightest part itself becomes dark.

The colour of the light becomes bluish green.

The positions of the individual groups of lines are, from several
concordant measurements, the following :—

Ist group of lines, left boundary . .. . 63 11 20
rn Tight boundary... . 6a 19 30

The right boundary is formed by a very bright line about 3!
distant from the preceding.

_ 2nd group of lines, left boundary . . « 65°47 30
In the middle a very large bright Gib line. 638 58 OO
Right boundary ee. Gam OP aw

This group is formed from the green field which was before
designated as (2) ; it gives the impression that the brightest part
has been torn asunder at the left limit and separated into indi-
vidual lines. |

3rd group, of six lines . . between 64° 37! and 64° 46!
The right boundary is the brightest.

Ath group of lines. It starts from the field
designated in the preceding section as (38),
yet in such a manner that the brightness of
the lines increases towards the more refran-
gible side; the brightness has thus a distvi-
bution the reverse of what it has in the con-
tinuously illuminated field. The left limit of
this group cannot, therefore, be quite sharply
determined ; several measurements furnished
values between 64° 58’ and 65°; so that the
beginning of this group does not coincide
with that of the bright field. The nght

foley

boundary is at. 65 4. 40
Sth group of lines, in the blue, ‘three ‘bright

limes... eee aon 65° 40! 10" to 65 44 00

6th. The ae field which, without the condenser, begins at
66° 18! 40", disappears entirely when it is added, Instead
Plul. Mag. 8. 4. Vol. 37, No, 251, June 1869. 2F

422 M. A. Willner on the Spectra of

of it several lines stand out on each side of this place, which,
however, cannot be arranged in groups, and are not of great
brightness. 3

7th. In the violet part of the spectrum there are—

A bright violet lime . . . at 66 45 00
A feebly bright group 6! broad, ‘from 67° 3! to 67 9 00
A bright violet ine . . . at67 36 30

If the discharges of a small hei jar be passed through a
Geissler’s tube filled with highly rarefied oxygen, just the same
spectrum is obtained; with a stronger charge it becomes more
brilhant without otherwise changing.

When the spectrum obtained with a Holtz’s machine is com-
pared with that described in § 9 as obtaimed with the Ruhmkorfi’s
coil, itis at once seen that both are identical, although, owing to
the greater brightness in individual groups with the Holtz’s
machine, a few lines become visible which could not be seen in the
former case.

It therefore follows that in this case, as also with hydrogen,
three distinct spectra may be obtained with induction-currents,
according as the gas in the tube has greater or less density. That
this difference in the spectra is solely due to the different tem-
peratures of the gas follows from the experiments with the Holtz’s
machine. The same considerations which in § 7 led to the
continuous spectrum being regarded as that corresponding to
the lower temperature, and that consisting of groups of lines as
corresponding to the highest temperature, lead here to the same
conclusion. The continuous spectrum belongs to the lowest
temperature (although it 1s not seen with gas of great density),
because it is formed by the continuous discharge of the Holtz’s
machine. The spectrum described by Plicker, which with gas of
suitable density may also be produced in its essential features
with the small Ruhmkorff’s apparatus, belongs to a higher tem-
perature. The last mentioned, which is attained with gas of the
least density by the aid of the Ruhmkorff’s coil and of a Leyden
jar, belongs therefore to the highest temperature.

IIL. N¢trogen.

13. In investigating the spectra of nitrogen, Geissler’s tubes
were filled with dry air, after what Plicker states had been con-
firmed, that dry air furnishes the same spectrum as pure nitro-
gen. W ith air in Geissler’s tubes no traces of oxygen-lines are
seen; and there is here no difficulty in getting the spectrum
free from hydrogen-lines ; the tube need only be filled a few
times with air which has been dried by sulphuric and phospho-
ric acids,

certain Gases in Geissler’s Tubes. 423

Using the same induction-apparatus as in the previous expe-
riments, the current just began to pass through the tube filled
with air when the pressure was 94 millims; yet the light was
not continuous. A continuous passage of the current only oc-
curred when the pressure was diminished to 64 millims, though
the luminous intensity was so small that a prismatic investiga-
tion of the light was not possible. Ona further diminution of
the pressure, the brightness of the light gradually increases ; and
under a pressure of 46 millims. the luminous intensity is ade-
quate for spectrum-investigation. The less refrangible parts of
the spectrum in the red and yellow are barely visible; only from
the green is the spectrum distinctly present ; most beautiful are
the violet parts, which are so characteristic of the nitrogen-
spectrum.

The red and yellow parts occur first under a pressure of 30
millims.; but they are so faint, that the shaded bands which
Pliicker has described in the nitrogen-spectrum of the first order
are at most scarcely perceptible. The green part with its rich
shading stands out more; but the blue and the violet are the
most beautiful ; in them the individual flutings are completely
developed.

Under a.further diminution of pressure by 5 millims., red and
yellow come out more, and the beautiful shaded bands of the
complete nitrogen-spectrum are visible. Under a pressure of
18 millims. the spectrum is completely developed; it quite
corresponds to the description which Plucker has given of it*,
and to what a spectrum-tube filled with pure nitrogen exhibits.

The brightness and beauty of the spectrum increases as the
pressure diminishes; under a pressure of about 5 millims. it
is developed most brilhantly, and remains so until the pres-
sure of the gas is less than 1 millim. Only when the pres-
sure is so far diminished that it can scarcely be measured by
Sprengel’s pump does the brightness become less, the darker
parts being first extinguished, and finally only the brightest
parts visible. In its appearance the spectrum approximates to
one of the second order, without, however, changing into one,
for no new bright lines appear.

With a simple Ruhmkorff’s apparatus, then, only one spec-
trum can be exhibited in a tube filled with nitrogen; a differ-
ence in density is only of influence so far, that the spectrum is
more or less complete and appears of eveater or less brightness.

Using, too, a Holtz’s machine without superposed condenser,
the nitrogen-spectrum of the first order was seen as with an in-
duction-apparatus. Using the condenser or a small Leyden jar,
the spectrum of the second order described by Plucker occurred.

* Pliicker and Hittorf, Philosophical Transactions for 1865.
22

424 Mr. J. Dewar on the Motion of a Palladium Plate.

Even when the exhaustion had reached its utmost limit the ap-
pearance was quite unchanged.

14, Nitrogen thus only furnishes the two known spectra; and
without using a Leyden jar the first spectrum cannot be
changed into the second. Hence there is a considerable differ-
ence between the behaviour of hydrogen, oxygen, and nitrogen.
With the first two gases the same mode of discharge can yield
entirely different spectra in the enclosed gas, according to its
density. Hence this difference can have no other reason than
the higher or lower temperature to which the gas has been
heated, and which, as mentioned in § 7, depends on the different
density of the gas. It must be assumed that the emissive power
of both gases does indeed essentially vary with the temperature.
The case is different with nitrogen: the difference in tempe-
rature produced by the different density of the gas is not suffi-
cient to change the spectrum; the mode of discharge must be
changed. Nitrogen can only be brought into the condition in
which it yields a spectrum of the second order, by the sudden
passage of large quantities of electricity, obtamed by simul-
taneously interposing a Leyden jar in the circuit of the induc-
tion-coil, or by passing the discharge of a Leyden jar with the
Holtz’s machine. Hence we may speak of an allotropic condi-
tion of nitrogen, which furnishes the second spectrum, and which
is formed by the sudden discharge of large quantities of electri-
city, which, however, returns to the ordinary form as soon as the
temperature diminishes. ‘To be sure, no explanation is thus
given of the difference in deportment of nitrogen ‘and other
gases; this can only be expected from further experiments,
which will be reported upon in due course.

Bonn, August 1868.

LIX. On the Motion of a Palladium Plate during the Formation
of Graham’s Hydrogenium. By Jamus Duwar, F.R.S.H.*

RAHAM, in continuing his exhaustive researches on diffu-
sion, has recently examined the relation of gases to various
colloid septa. The remarkable discovery of Deville and Troost
of the permeability of platinum and iron by hydrogen at a red
heat, he has expanded into a general examination of the relative
rates of passage, at high temperatures, of the various gases
through different metallic septa. Further, he has proved that
different metals have a specific occluding power over certain
gaseous elements, retaining them in combination at low tempe-
ratures, although the absorption took place at a red heat. Of

* Communicated by the Author, having been read before the Royal
Society of Edinburgh, March 1, 1869.

during the Formation of Graham’s Hydrogenium. 425

the many astonishing discoveries made during the course of
these investigations, probably the most remarkable is the occlu-
sion of hydrogen by palladium. This metal, whether in the form
of sponge or hammered foil, when heated and cooled in an atmo-
sphere of hydrogen, absorbed between six and seven hundred
times its volume, increasing to the enormous occlusion of 982
volumes when the metal used had been deposited by voltaic
action. This occlusion of hydrogen, Graham has shown, can be
easily effected at low temperatures by making palladium the
negative electrode during the electrolysis of water. He has
also shown that the metal charged with hydrogen increases
greatly in volume, and that its physical properties are entirely
modified. So marked is the change in the physical, electrical,
and magnetic properties of the combination, that the only class
of compounds we can compare it with are the metallic alloys. In
the occluded state the chemical intensity of hydrogen is increased,
many reactions being effected by its agency beyond the power of
the element in the free state. Graham, as a general result of hig
experiments, considers the occluded gas to exist in the form of
a solid, with all the physical properties of a metal. During the
course of an experimental exhibition of Graham’s discovery, I
noted several phenomena associated with the occlusion of hy-
drogen by palladium when it is made the negative electrode
during the electrolysis of water; and as they illustrate in a new
form the results already arrived at by the Master of the Mint,
with his permission I am induced ‘to bring them before the
Society.

If a palladium plate, used as the negative electrode during the
decomposition of water, be arranged at right angles instead of
parallel to a similar platinum plate, the hydrogen in a short
time is evolved at the edge of the palladium plate nearest to the
platinum electrode, no trace of hydrogen coming from any other
part of the plate. Gradually, as the saturation takes place, the
hydrogen seems to travel slowly along the plate, and only after
saturation is it freely evolved from the whole surface of the elec-
trode. If we now reverse the current, so as to evolve oxygen at
the palladium plate, immediately the nearest edge begins to
evolve gas, the rest of the plate remaining tranquil ; the evolution
of oxygen moves along the plate in a gradual manner. This
gradual transference depends on the time necessary to effect the
occlusion, and on the relative intensity of the lines of force.

When a palladium plate charged with hydrogen is brought
into contact with a platinum electrode freely evolving oxygen,
evolution of gas is immediately arrested over the entire surface
of the electrode. The same plate, free from hydrogen, when
brought into contact with a platinum electrode evolving hydrogen,

426 Mr. J. Dewar on the Motion of a Palladium Plate

shifted the evolution of gas only on the same side on which it
was firmly pressed. In order to examine the action of mixed
electrodes, the palladium plate was welded with a similar plati-
num plate into a V-shaped electrode, when the apex of the com-
bination could be placed in or out of the liquid. If the platino-
palladium electrode is made the negative pole, hydrogen makes
its appearance immediately on the platinum plate; no gas is
evolved by the palladium for some time. If, after saturation,
by reversing the poles oxygen is thrown on the mixed electrode,
no gas is evolved from the platmum ; and when the gas began to
be evolved, it appeared simultaneously on both plates. The
same result 1s observed whatever may be the position of the com-
pound plate relatively to the other pole in the liquid, relative
distance from the other pole having no effect. This proves that
the whole of the oxygen that ought to be evolved on the platinum
is transferred by a polar chain through the liquid on to the pal-
ladium plate, so long as this plate contains occluded hydrogen.
The presence of the strong electric current is shown by connect-
ing the hydrogenized palladium with a platinum plate im an acid
liquid, the circuit containing a galvanometer. If the apex of
the V electrode 1s placed in the acid hquid, additional phenomena
are witnessed, depending upon which side of the compound elec-
trode is next to the other electrode. Ifthe platinum side of the
V electrode is firmly clipped in a stand, a glass rod keeping the
apex in the same position in the liquid, and if the palladium
plate is next to the positive electrode, we observe the following
change during the course of the hydrogenation. The angle of
the V continually diminishes by the motion of the palladium
towards the perpendicular, the hydrogen evolved coming only
from the outer surface of the compound plate. After some time
the plate returns to its original position, and would curve beyond
it if the action were continued. If oxygen is now evolved on the
compound plates the first effect of the oxygen is to curve it be-
yond its first position, or to diminish the angle of the V. If the
palladium plate is furthest from the positive electrode, the first
effect of the hydrogenation is to increase the angle of the com-
pound plate by the palladium moving outwards; after some time
it returns. Similar observations with the palladium clipped
in a stand, but made with the junction out of the liquid, showed
a decided movement depending on the relative position of the
plates. Seeing the palladium moved, although firmly clipped in
a socket out of the liquid, it was evident the motion could be
examined without the use of compound plates.

After devising several arrangements in order to examine with
ease the motion of the plate, the following plan was found to be
the best im practice :—

during the Formation of Graham’s Hydrogenium. 427

The electrodes of palladium and platinum were firmly clamped
im the little vice represented by D, and arranged as shown in the

SL
7 QV
i’,

| Yi
Y, Yf
Y/, Wf
WY Yj]

figure, where A represents the palladium and B the platinum.
To the lower edge of the palladium plate a narrow strip of the
same metal is fused by the oxyhydrogen blowpipe; the strip is
of such a length as to project above the level of the acid liquid
when the plate is immersed. ‘To the end of the strip of palla-
dium a thread of glass is fused so as to have a radius in all of 40
or 50 centims.; the are ofa divided circle of the same radius on
a piece of cardboard is supported by a stand at the extremity of
the index. By this apparatus the small deflection of the palla-
dium plate is greatly magnified, and the direction of motion well
defined. Suppose the palladium plate A in the figure is con-
nected with the negative pole of the battery, the glass index,
after a short time, begins to move from left to right on the plane
of the diagram to the extent of 8 or 10 centims. on the scale.
As the saturation goes on, the index begins to move backwards
from its first position, going towards the left, even to a greater
extent than its first deflection towards the right. Continuing
the action, it again returns to near its original position. The
power of being able to return to the position it had at starting
seems to depend on the condition of the plate, as regards the

428 Mr. J. Dewar on the Motion of a Palladium Plate |

distribution of tensile strain produced by rolling; at least after
repeated use the plate lost the power of returning after having
passed towards the left. If the plate after saturation is connectd
with the positive pole of the battery, the first effect on the index
is to move quickly towards the left, then to return to where it
was, this double motion taking place before any gas makes its
appearance on the palladium. If the platimum electrode B is
placed on the opposite side of A and the saturation of the plate
repeated, the index goes through the same series of positions, but
the direction of motion is reversed. The direction of motion
depends, therefore, on the relative positions of the electrodes,
but is constant for the same position. This is easily shown by
allowing the index to commence its motion, say, from left to right;
then by moving the positive electrode to the other side of the
palladium plate, the motion immediately commences in the op-
posite direction, although the saturation was far from being com-
plete. The motion of the index when oxygen is thrown on the
hydrogenized plate depends also on the position of the electrodes.
The index has also a motion at right angles to the plane of
the scale, the resultant motion being compounded of the separate
flexures of the plate. Many other devices could be used to show
the motion, such as a plate bent into the form of a cylinder with
a narrow channel left between the two edges, which would shut
and open alternately, or vice versd, according to whether the po-
sitive electrode were without or within the cylinder.

Graham has shown that the formation of the alloy of hydro-
genium and palladium is attended with an enormous increase in
the volume of the metal. He found that a wire of palladium
100 millims. in length became 101°5 millims. when saturated
with hydrogen. Now, if a uniform hydrogen atmosphere sur-
rounds a symmetrical piece of palladium, there is no reason why
it should penetrate with a greater rapidity one surface rather
than any other. But if the absorption is not uniform on all the
surfaces, from want of uniformity in the hydrogen atmosphere,
the surface absorbing must produce a flexure of the plate from
the expansion of the metal. Ifa thin plate of this rigid metal
can be so arranged as to induce absorption on one side rather
than the other, then, as a necessary consequence, the plate will
become convex on the side where the greatest relative absorption
is taking place ; and as the saturation approaches uniformity,
the convexity should disappear, the plate regaining its original
form if the elasticity of the metal is not changed durmg the
action. <A plate of palladium, when it functions as the negative
pole during the electrolysis of water, is subjected during the
course of the action to the supposed non-uniformity of the gaseous
atmosphere, if the surface of the plate is parallel to a similar

during the Formation of Graham’s Hydrogenium. 429

platinum electrode. The amount of chemical action effected by
the unit-surface of the electrode, and its distribution, depend
upon the position of the plate relatively to the lines of force
emanating from the poles. Now, of the two surfaces of the pal-
ladium plate, the surface next to the positive pole has the greatest
concentration of the lines of force; and therefore the greatest
evolution of hydrogen takes place on this surface, so that the
quantity of alloy formed in the first instance is in excess of the
amount produced on the other side. The plate, from the great
expansion on the outer side, becomes convex, until the progres-
sion of the action on the other side is able to compensate this
flexure by a corresponding expansion, thereby bringing the plate
to its original form. But I have already explained how this
backward motion goes beyond the original position, producing
a flexure in the opposite direction, only in some cases returning
to its normal shape. This, in all probability, arises from the
combined effect of expansion and compression. Graham has
shown that the tenacity of the alloy is considerably diminished
as compared with that of the palladium, so that in the first
flexure of the plate the expansion has to compress the rigid pal-
ladium, whereas, when it begins to return, the compression is
effected on the less rigid hydrogenium already formed on the
other side, the elasticity of form being also probably relatively
small. This is the general explanation of the motion of the
plate ; but it must be remembered that the smaller flexures
produced by different forms and positions of the electrodes are
the result of non-homogeneity or excessive strain. There is one
position, at least, of the palladium relatively to the other elec-
trode, where the plate should have no lateral motion—that is,
when it is at mght angles to the surface of the positive plate;
but all the attempts made with the small palladium plate at
my disposal failed to prevent Jateral motion, probably from
want of uniformity of surface producing different rates of pene-
tration.

Effect on the Current during the Formation of the Hydrogenium.

In order to determine the effect on the current during the oc-
clusion of the hydrogen and its reoxidation, two Bunsen’s cells
were connected, through a tangent-galvanometer, with a plate of
palladium and platinum as poles m a cell containing acidulated
_water. The intensity of the current was determined, first, during
the decomposition of the water when the palladium pole evolved
oxygen, then during the absorption of hydrogen (when the cur-
rent was reversed), and lastly when the oxidation of the occluded
hydrogen was taking place.

430 Mr. J. Dewar on the Motion of a Palladium Plate.

Palladium | Palladium | Hydrogenium
Positive pole. |Negative pole.| Positive pole.

Angles on tangent- 2 O °
galvanometer see gre = 40°3
Danwents).tcscees.s 75: 0°4348 0°3939 0°8541

The diminution in the intensity of the current during the
formation of the hydrogenium arises from the strong current
generated in the decomposing-cell by the secondary polarity of
the electrodes, acting in the opposite direction, whereas the oxi-
dation of the hydrogenium produces a current acting in the
same direction as the battery. The intensity of the current
during the oxidation of the hydrogenium is nearly doubled ; so
that if we consider the resistance in the circuit to remain con-
stant, the additional electromotive force added by the oxidation
of the hydrogen is equivalent to two cells of Bunsen. The great
increase in the intensity of the current during the oxidation of
the hydrogenium may be shown in the following manner :—Use
two palladium plates in the decomposing-cell with index to show
the motion of the plate attached to each, as in the figure formerly
given, and include in the circuit a commutator and a fine spiral
of platinum wire. During the occlusion of hydrogen the plati-
num spiral may be made of such a length as to remain dark, the
motion of the index proving the absorption of hydrogen. Re-
verse now the direction of the current, and the spiral of platinum
will become red-hot, the index moving rapidly back to its original
position, while the index of the other plate will begin to move.
The oxidation of the occluded hydrogen is the limit to the
brightness of the platinum spiral, so that a reversal of the cur-
rent produces a renewed brightness. By this arrangement we
keep both indices moving along the scale, and the platinum
spiral alternately bright and dark. If the electromotive force
is really equal to a Bunsen’s cell, this arrangement must pro-
duce a current far more intense than any similar gas-battery
where oxygen and hydrogen are the reacting elements; but as
the resistance in the circuit might vary, several indirect experi-
ments were made. When a palladium plate saturated with hy-
drogen was associated with a platinum plate in an acid solution
of permanganic acid and connected through a voltameter, the
arrangement could decompose water. A similar result was ob-
tained when a platinum plate coated with platinum-black satu-
rated with oxygen was employed; but the action in this case
was very slow, and sometimes did not succeed. A platinum

On the Fundamental Principles of Molecular Physics. 4:31

plate covered with peroxide of lead was opposed to the hydroge-
nium; the combination decomposed water with facility. Grove
found that two pairs of his gas-battery could effect a slow decom-
position of water, and a single pair did as well if the oxygen was
replaced by peroxide of lead. (The intensity of the palladium
and peroxide-of-lead combination must render it particularly well
adapted to form secondary piles of great intensity, by substitu-
ting it instead of a lead plate in the arrangement devised by M.
G. Planté.) The transformation of gaseous hydrogen into the
occluded state would seem to have little effect in reducing its
total chemical energy, so that the occluded hydrogen must re-
tain a relatively large proportion of the total gaseous energy
in a potential form. If we compare the occlusion of gases to
work done on the gas, the elaborate researches of Joule and
Thomson on the “Thermal Effects of Fluids in Motion”
would lead us to believe that hydrogen, of all gases, would in
this new condition retain the greatest amount of its original
store of energy. But before a just comparison can be made
with the results of Joule and Thomson, careful determinations
must be made of the electromotive force, latent heat, &c. of
hydrogenium. Professor Tait has determined by a new process
the electromotive force of platinum and palladium covered with
oxygen and hydrogen; and the result will be communicated
to the Society im a short time.

LX. Fundamental Principles of Molecular Physics.
By Professor J. Bayma, S. J., of Stonyhurst College.

[Concluded from p. 358. |
ROFESSOR NORTON convinced as he was that he had

fully answered all my objections and that his fundamental
principles required no further vindication, felt himself free at
last to ponder over my shortcomings, and proceeded directly
to criticise five items of my molecular doctrine, viz. the curve of
molecular action, the production of heat and light, the transmis-
sion of rays, the constitution of molecules, and the transmission
of force.
Curve of molecular action.—The learned Professor begins
thus:

“The attempt to deduce the existing constitution of things and
prominent phenomena by Professor Bayma from his fundamental
ideas, so far as made, has certainly failed at several important points.
To specify one or two of these. He obtains a curve of molecular
action that represents a repulsion at the smallest distances succeeded
by an attraction at greater distances. This can only be made to

EE EE ee ee

432 Prof. J. Bayma on the Fundamental

represent the three states of bodies by conceiving the molecules of a
gas to be in such a condition that, if it were entirely freed from
pressure, it would expand into a liquid. Weknow that many gases
can be compressed into a liquid, but it is altogether gratuitous to
suppose that they could be brought into a similar condition by a di-
minution of pressure. Experiment has given no indication of such
a result or tendency.”

This is a mistake. My curve of molecular action does not
require the molecules of a gas to be in such a condition that, if
entirely freed from pressure, it would expand into a liquid.
What I said is this. ‘If hydrogen, or any other gas, were freed
from pressure, it would expand as much as its constitution re-
quires, viz. to a certain determinate bulk only ; for there must
be a limit of expansivity for all permanent substances. Then
it would remain at rest in the same manner as if it were a liquid.
Its molecules would then be at the distance of equilibrium: and
its difference from known liquids would only be that, whilst
other liquids do not allow themselves to be sensibly reduced in
bulk, hydrogen would allow of a very sensible reduction”’ (Mo-
lecular Mechanics, p. 195). Such is my real doctrine. But
Professor Norton seems to have thought that a thing, which can
remain at rest 7 the same manner as if it were a liquid, must
needs be a liquid: and it is on the strength of such a brillant
discovery that he proceeded to pronounce that I have “ certainly
failed”? in this first of several “ important ”’ points.

But, again, my curve of molecular action in his judgment
“cannot represent the three states of bodies,’ unless the
gaseous molecules are of the condition already described. I
reply that my curve of molecular action has been drawn from
the consideration of bodies in general, without descending to
those special conditions which must be verified in the case of
gases. Hence Professor Norton is perfectly free to remove,
even indefinitely if he likes, the intersection of the curve with
the axis, viz. the poimt where repulsion ceases and attraction
begins. In this case the actions represented by the ordinates
of the curve will easily become repulsive all throughout to his
full satisfaction: only it might be difficult, after this change,
to say what body in nature we could point out as possessing
the properties indicated by the curve so boldly stripped of its
inferior branch.

As for‘the limit of expansivity of the gaseous molecules, its
necessity 1s not gathered from the curve of molecular action, nor
from the nature of the gaseous state, but from the permanency
of the gaseous substance. That it 1s not deduced from the
curve of molecular action is quite evident—since the curve is
only the expression of facts already established, and represents

Principles of Molecular Physics. 433

under a general aspect a law of action already recognized. The
nature of the gaseous state, on the other hand, is in no need of
a limit of expansion; for if we grant, out of deference to Pro-
fessor Norton’s opinion, that the molecules of hydrogen instead
of having a limit of expansion can expand indefinitely, what in
the world would prevent such hydrogen from being a highly
gaseous substance? Surely, it would not cease to be an expan-
sive gas for the sole reason that its expansivity would have no
limit. The only reason why primitive gases have a limit of ex-
pansion is an @ posteriori reason, viz. because they are perma-
nent substances, having a constitution which cannot be destroyed
by external action whether mechanical or chemical. Such sub-
stances, though expansive, must have a limit of possible dilata-
tion ; otherwise they would tend of themselves to their own dis-
solution ; in other words, they would cease to be permanent.
(See Molecular Mechanics, p. 145.) This is the reason why I
have admitted that a gas freed from all pressure would expand
to a determinate bulk only, and then remain at rest in the same
manner as if it were a liquid. Professor Norton cannot hold
the contrary, unless he holds either that primitive gases are not
permanent substances, or that their molecules, though perma-
nent, must. repel each other at all great distances. The first
hypothesis would lead to the conclusion that the gaseous mole-
cules have no sufficient constitution of their own, but depend
for their existence on all sorts of exterior agencies: which view
is too unscientific to be adopted by the learned Professor. The
second hypothesis would entail the impossibility of any chemical
combination of gases; for if the gaseous molecules, though per-
manent, repel each other at all great distances, their absolute
power of repelling is certainly greater than their absolute power
of attracting: and thus chemical affinity between two gases will
become an impossibility. This suffices to show that Professor
Norton’s criticism on this first “important point” is wholly
without foundation.

Fleat and light—My second “ failure,” according to Pro-
fessor Norton’s statement, regards the origin of heat and light.

He says:

“Heat and light he conceives to originate in vibrations of gross
molecules; but against this notion, as I shall take another occasion
to show, insuperable objections may be urged. If this be given up,
his explanation of the changes of the state of bodies must also be
-abandoned.”

I have already stated somewhere that I conceive heat to consist
rather than ¢o originate in vibrations of molecules. Of course,
I do not say in vibration of “ gross ” molecules; because “ gross

FT cre Re I a i Lhe NC CT ie A

4S Prof. J. Bayma on the Fundamental

matter” has nothing to do with my conceptions, and is the ex-
clusive property of my learned critic, as I have made clear on a
previous occasion. If however by gross molecules he means —
molecules of ponderable bodies having the constitution which I
pointed out in my treatise, then I allow (though protesting
against the epithet “ gross”’) that the heat of such bodies con-
sists in vibrations of such molecules. I do not know just now
what “ insuperable objection” the learned Professor will urge
against this view on another occasion: when those objections
arrive, we may think of them. Meanwhile an objection which
my opponent, I fear, will not solve is the followmg. The
learned critic, while defending his three forms of matter, de-
clared emphatically that my repulsive envelope is essentially his
“electric ether,” and consequently that my repulsive envelope is
not his “gross matter.” If therefore in my theory the mole-
cular envelope is the sole agent directly concerned in the com-
munication of heat from molecule to molecule, it is evident that
heat in my theory does no¢ originate in the vibrations of gross
matter. Now such is exactly the case. He may read in my
treatise that ‘ calorific motion is communicated from molecule
to molecule mainly through their respective envelopes, which
are in the best condition for strongly influencing one another.
The rest of the molecular masses, 7. e. the nuclei, move in con-
sequence of the motion to which the respective envelopes have
been subjected, according to the nature of the molecular con-
stitution ; and therefore the difficulty of communicating calorific
motion to a body does not depend, except in a very secondary
degree, on the inner part of the molecules (Molecular Mechanics,
p- 205). This mner part is what my critic assumes to be
‘“esross”’ matter. So long as this objection remains unanswered
I have reason to question the exactness of Professor Norton’s
statement and the conclusions drawn therefrom.

And now with regard to light. Is it true that I conceive
light “to originate in vibrations of gross molecules?” I need
not repeat that gross matter has nothing whatever to do with my
conceptions. What I had said was this: “Luminous bodies -
cannot excite luminous undulations of a certain period in the
surrounding ether, unless they themselves move at the same
period and make as many undulations. With regard to non-lu-
minous bodies, they either transmit or reflect hght; and there-
fore although they are incapable of setting themselves into spon-
taneous vibrations suitable to make a sensible impression on our
organ of vision, yet they are prepared, when acted upon by impin-
ging rays, to take up the same kind of vibratory motion, at their
surface at least, if they are opaque” (Molecular Mechanics,
p- 209). This view we are now going to examine.

Principles of Molecular Physics. 435
Transmission of rays.—My critic says:

“The doctrine that transparent bodies transmit rays of light by
the motion of their own molecules, will hardly be accepted, we
think, by physicists.”

The author knows, I assume, that Mr. Grove, who is an eminent
physicist, holds in his ‘ Correlation of Physical Forces’ that the
phenomena of light can be explained without any intervention of
zether, and consequently by the vibratory motion of ponderable
matter. And although I think, as I have remarked in my
“Molecular Mechanics,’ that Mr. Grove has failed to establish
the non-existence of ether as a special substance, his arguments
have still sufficient weight in the case of the transmission of
light through solid bodies, as the reader will see in my treatise
(pp. 190-192).

The author adds that it would be “a waste of time” to argue
against this view. I cannot subscribe to his opinion, nor pro-
bably would Mr. Grove. A view unsupported by reasons may
be passed over without arguing, as it might be a waste of time
even to mention it: but when reasons are adduced, a critic
should at any rate mention the fact of their existence and bear-
ing, before he decides that arguing against them is a waste of
time: a decision which should rather be left to the reader him-
self. ‘The principal reason adduced by me in support of my
view was that “in the hypothesis that the ray is transmitted by
the motion of the ether intercepted between the molecules, the
regular arrangement of these would not explain the fact of the
transmission of a ray in any other direction than that deter-
mined by molecular interstices in a straight line. Now the ray
is in fact transmitted in all other directions. Accordingly we
maintain that the transparent bodies transmit the rays of light
by the motion of their own molecules, not by the motion of in-
tercepted ether”? (Molecular Mechanics, p. 191). Had Pro-
fessor Norton transcribed this argument, and then declared his
repugnance “to waste time” about it, the reader would have
been able to judge of the matter: but my opponent did not give
the reader any such satisfaction, although, I venture to say, this
would not have been a waste of time.

Professor Norton adds:

«The notion that a certain substance radiates light of a certain
colour, because its molecules are made to vibrate in unison with the
. ray of that colour, will not stand; for the results of spectral analy-
sis show that the parts of a body which are capable by vibration of
giving out any colour are precisely those which absorb and stifle that
colour. This fact, we may add, also proves conclusively that the
rays cannot be transmitted by the motion of the molecules.”

436 Prof. J. Bayma on the Fundamental

I confess that I cannot see the conclusiveness of this proof: first
because the fact referred to regards incandescent substances
only, whilst the molecules to which the author alludes in this —
conclusion are not supposed to be incandescent; and therefore
he has not the right of applying to the second the law of the
first phenomenon: secondly because spectral light is a light
elicited from the substance which is being burnt or made self-
luminous, whilst the light simply transmitted is a light received
from without ; and it is obvious that what is truly said of a self-
luminous body with regard to its own light cannot be said truly
of a non-luminous body with regard to a light which it receives
from without. These two reasons flow from one fundamental
fact that heat alters, at least for a time, the molecular constitu-
tion of bodies by causing a change in the relation of molecular
radii, an increase of vibratory motion, and a modification of mo-
lecular distances. Such alterations evidently cannot take place
without a proportionate modification of the optical properties of
the body. Thus, for instance, hyponitric acid is almost colour-
less at the low temperature —20° C., becomes yellow at the
temperature O° C., orange at 15° C., and intensely red when
transformed into vapours. It is evident therefore that the
period of the luminous vibrations depends on the temperature of
the body and changes with it. Accordingly the period of the
vibrations of an incandescent body and the quality of the spec-
tral ght radiated by it while existing in such a violent condi-
tion cannot be assumed to indicate the period of vibrations and
the quality of the light transmitted or reflected by a body exist-
ing in opposite conditions.

Professor Norton concludes in the following words:

“This fact... . though so radically at variance with Professor
Bayma’s theoretical views, is in entire accordance with my own.
For, according to these, light originates in certain vibratory move-
ments of the atoms of the electric atmospheres of molecules, and
when these vibrate naturally in unison with the ray of any colour
that falls upon them, they take up its vis viva, and so the ray is
transformed into a molecular electric current.”

The reasoning expressed in this passage comes to this. A
substance when ignited and incandescent absorbs and stifles
such and such rays; therefore such and such rays are always
absorbed and stifled by the same substance, even though it be
not ignited and incandescent: and the theory which authorizes
us to draw such a conclusion is therefore more scientific than
any opposite doctrine. The reader will be able to judge for
himself of the value of this argument. On the other hand when
the atoms of the electric atmospheres of molecules (my molecu-
lar envelope) vibrate naturally in unison with the ray of any

Principles of Molecular Physics. 437

colour that falls upon them, and take up its vis viva, is it neces-
sary to conclude that the ray will be “transformed into a mole-
cular electric current?” or is it not more natural to maintain
that the ray will remain a ray and undergo no transformation
at all? A transformation must have a cause calculated to sub-
stitute one form for another, and therefore to destroy the form
of the ray and to introduce the form of an electric current.
Now the cause which destroys a kind of motion must be con-
trary to that kind of motion: if it were in unison with it, it
would propagate instead of destroying it. And therefore, if
the atoms of the electric atmospheres vibrate im unison with
the ray, we must conclude that the ray is transmitted or pro-
pagated, not transformed into a molecular electric current.
But to proceed.

Elements and molecules.—Professor Norton allows that my
leading principles “‘ may in the main be conceded :” a conces-
sion for which I feel obliged; but then he thinks that such
principles “by no means cover the whole ground upon which
the theory is raised.” The thing is quite possible, as my ‘ Mo-
lecular Mechanics’ contains suggestions and hints which are
not strictly and solely derived from such “leading ”’ principles ;
yet they are few in number, and of so secondary an importance
that I do not consider them as a substantial part of the theory*.
But even so, those suggestions are not gratuitous, and cannot
be discarded without a fair examination of the reasons by which
they are supported.

Professor Norton to prove his assertion points out that I as-
sume “that all elements or material points of the same form of
matter act, under similar circumstances, with the same inten-
sity.” I wonder how this can be true, since in my book I ex-
plicitly stated the contrary. Isaid: “ One might ask: Is there
any material element possessing a greater power than any other?
This question cannot be answered in the present state of science.
Still it would be rashness on our part to assume, without neces-
sity or indication of any kind, that all elements have equal
power ” (Molecular Mechanics, p. 69). It is strange that my
American critic should have read the opposite, especially when
we consider that all the molecular formulas contained in the
book take into account the different intensity with which ele-
ments can act under the same circumstances. The allegation is
therefore a clear mistake.

Then my critic argues in the following strain:

* I take this opportunity to acknowledge the impropriety of an example
- given in my book (p. 171), where I stated that the sun exercises no sen-

sible influence in the production of tides. Professor Haughton of Trinity
College, Dublin, kindly pointed out the inaccuracy of the statement.

Phil. Mag. 8. 4. Vol. 87, No. 251. June 1869. 2G

—

438 Prof. J. Bayma on the Fundamental

_ Now, if this principle be admitted, what theoretical basis have
we for the existence of distinct primitive molecules for every differ-
ent substance, the number of elements associated together being
exactly the same for each primitive molecule of each substance, and
different for primitive molecules of different substances? The na-
tural tendency would be toa fortuitous association of elements in an
endless variety of numbers into groups. No controlling principle
by which uniformity would be evolved from chaotic confusion, is fur-
nished by the theory. The hand of the Creator must be supposed
to have miraculously interfered, and guided each element to its pre-
cise place in the formation of every molecule of matter.”

I have brought in this passage, though I have no necessity of
giving it a reply, only because it shows what style of reasoning
is sometimes adopted by men of scientific merit. Professor
Norton starts from the assertion that my elements act, under
the same circumstances, with equal intensity : and the assertion
is false. He then draws a conclusion; which accordingly has
no foundation. He assumes that the conclusion must be rejected
in order to give a theoretical basis to molecular science, and
does not reflect that the existence of distinct primitive molecules
is in no need of a theoretical basis @ priori, it being quite sufi-
ciently established as a matter of fact by a posteriort reasonings.
He imphes gratuitously that elements must have existed in a
previous state of dissociation ; and therefore considers them as
having a natural tendency to a fortuitous association, and speaks
of chaotic confusion with no controlling principle. He comes
to the consequence that “ the Creator must be supposed to have
miraculously interfered ;” and seems either to regret the neces-
sity of the fact, or to imagine that in the work of creation there
has been nothing miraculous. Lastly he supposes that the
Creator must have interfered “ by guiding each element to its
precise place,” as if the elements could not have been created in
those precise places without any need of a miraculous guidance.

To strengthen this first argument, he adds:

“‘The objection here urged derives still greater force from the
consideration that both the nucleus and envelope of each specific
molecule are assumed to have a regular geometric form, different
for each substance. ‘To assume the existence of such molecules
is to make an incalculable number of arbitrary assumptions.”

The reader already knows how in my criticism on Professor
Norton’s “fundamental principles ” I had ventured to say, and
to prove, that his theory contained a great deal of arbitrary as-
sumption. It is not surprising then, that the learned Professor
should now and then indulge, to his own relief, in an attempt
at retaliation, and that here, at the end of his paper, should make
a décharge générale of an “incalculable number” of projectiles.

Principles of Molecular Physics. 439

Thus far there is no harm. But is it true that the nuclei and
envelope of each specific molecule are “ assumed ” by me to have
a regular geometric form? The question is one of fact: every
one may easily satisfy himself that I in my ‘ Molecular Mecha-
nics’ have not simply assumed, but proved the regularity of mo-
lecules in general, and clinched the demonstration by those
symbols Q. HE. D., which Professor Norton has so well discerned
on a previous occasion (see Molecular Mechanics, pp. 150-
152). The critic may discuss my proofs if he likes; but I deny
that he has the right of dissembling their existence.

Again, have I assumed, as the learned Professor says, that
the geometric forms of molecules are “different for each differ-
entsubstance?” This is another question of fact; and the fact
is quite the reverse of the statement. Not only I never affirmed
what Professor Norton imagines, but on the contrary I went so
far as to maintain that the molecules of oxygen, nitrogen, chlo-
rine, sulphur, iodine, are all of the same geometric form, though
they belong to different substances (see Molecular Mechanics,
pp. 236-243). Moreover, as there are from sixty to seventy differ-
ent primitive substances, it was as impossible for me to admit that
each different substance had a different regular geometric form,
as it would have been to discover from sixty to seventy different
regular polyhedric forms.

Transmission of force.—I hasten to say a word about the last
“failure” pointed out by Professor Norton in my ‘ Elements
-of Molecular Mechanics.’ He says:

“We have already seen that the principle that one material point
acts upon another instantaneously, without the intervention of any
medium, is opposed to the fundamental idea that the force exerted
is inversely proportional to the square of the distance. This law,
to say the least, is an arbitrary assumption in the premisses.”

I look in vain for the page m which “ we have already seen ”
what my able critic here advances. What we have seen is only
his assertion that “the law of mverse squares is a consequence
of wave-propagation ;” but he gave no proof of it for the case
of elementary action, and I defy him to give one. Wave-pro-
pagation is propagation of motion, and regards only the pro-
gressive development of a series of effects and of their condi-
tions, not of their causality. Physicists indeed often say that
actions are conveyed through a material medium; but this ex-
pression means only that a material medium is indispensable
. for the progressive development of the aforesaid series of effects,
as I have shown in my work (p. 64). As for the “ arbitrary
assumption in the premisses” I need only remark that Pro-
fessor Norton neither brought forward my premisses, nor said
in what they consist. The reader will find them in my book

2G2

440 Prof. J. Bayma on the Fundamental

(p. 63), and will soon be convinced that they are not arbi-
trary assumptions, as advanced by the learned Professor.

He then adds:

«The author also conceives that the mutual action of two mate-
rial points is in no degree and under no circumstances intercepted
by another intervening point. But we know that, in the case of
the molecular forces, the amount of vis viva expended in imparting
motion to one particle is abstracted from the force in action; and,
according to Professor Bayma, the molecular forces are of the same
nature as the forces subsisting between the material elements. The
force of gravity, it is true, is not sensibly intercepted ; but this does
not prove that a tendency to interception does not exist; for upon
the supposition of a wave-transmission of the force, the effective at-
traction of any molecule may be the mere differential of the actual
force transmitted, and, besides, in the circular revolution of a planet
the distance from the sun remains unchanged.”

The statement that in my opinion mutual action is never
intercepted by intervening matter is perfectly true: only the
writer might have noticed that I never confound action with
motion, and therefore though I hold that action cannot be in-
terfered with by mtervening matter, I hold nothing of the sort
regarding motion. Had he made the same important distinc-
tion, he would have seen that his objection is a mere sophism.
We know indeed that “the amount of vis viva expended in im-
parting motion to one particle is abstracted from the force in
action ” or more exactly from the body in motion; but we do not
know that it 1s abstracted from the active power of the element
or from its action. V2s viva is a function of velocity ; and velo-
city is neither action nor active power, as I have shown at length
in my treatise (pp. 19-25, also pp. 44, 45). The body in mo-
tion will therefore, by a loss of vis viva, lose motion, not action,
nor active power.

The other statement, that, according to me, “the molecular
forces are of the same nature as the forces subsisting between
material elements,” may be true or false, according as the word
“forces”? is assumed to mean active powers or the result of their
combined exertions. In the first case the statement is true, be-
cause the action of the whole molecule proceeds from the same
powers which constitute the molecular system. In the second
case the statement is false, because the nature of the resultant
depends not only on the nature of the active powers, but also
on the nature of the actual composition or mechanical state of
the molecule: so that the resultant of their actions (which is
considered as the action of the molecule) widely differs from the
action of each element, and, unlike it, does not follow the New-
tonian law at molecular distances, as is well known.

Principles of Molecular Physics. 441

Finally Professor Norton insists that, though the force of
gravity is not sensibly intercepted “ this does not prove that a
tendency to interception does not exist : ” and to prove the exist-
ence of this tendency he argues from “the supposition of a
wave-transmission of the force.” To this I reply that nothing
proves the existence of the slightest tendency to the interception
of the action of gravity or any other action. Such an intercep-
tion can moreover be demonstrated to be absurd, as there is no
power in nature which is calculated to intercept action. As for
the “ supposition ” (the author seems here as elsewhere to accept
suppositions as proofs) I reply that it is only a supposition :
which moreover has nothing to do with the exertion of active
power ; since the propagation of waves is a phenomenon of mo-
tion, not of its causality with which alone we are here concerned.
But. my critic, who employs the indefinite word “ force ” instead
of * action,” could not help confounding the exertion of power
with the consequent motion and its propagation.

Out of fairness to Professor Norton, I must quote a short
passage that I find in one of his articles (Phil. Mag. vol. xxvi.
pp. 277, 278) where he gives his reason for admitting the inter-
ception of action. He says:

*« If two-molecules are in equilibrium under their mutual actions,
the attractive and repulsive impulses exerted by each upon the
central atom of the other must be equal, and therefore no effective
action, either attractive or repulsive, can be transmitted to other
most distant particles on the same line. Under these circumstances,
one molecule in receiving the action of another, intercepts the action

that would otherwise talce effect upon other most distant molecules.
This being admitted” &c.

I recommend this curious reason to the consideration of phy-
sicists, of those especially who deal most with dynamics. As
for myself, I have italicized the word therefore, but shall not
stop now to give a special answer; as the passage is not taken
from the paper to which I intended to reply. On the other
hand, the author must himself solve his argument in the case of
gravity, which, as he allows, is not sensibly intercepted. To
conclude. What I have said suffices, in my opinion, to show
that Professor Norton has been unsuccessful both in his an-
swers to my objections and in his arguments against some
of my conclusions. The cause of his ill-success les almost
wholly in his too great facility to take a stand upon gratui-
tous hypotheses and mere conceptions, which he also con-
founds too frequently with “established truths.” iis fact is
now so evident that I might be allowed to consider his last
paper not as an answer to, but as a striking confirmation of,
my previous objections.

442. Prof. Swan on a Metallic Connector to replace

I cannot end without sincerely thanking the learned author
for the honour which he has bestowed on me by condescend-
ing to criticise my ‘Elements of Molecular Mechanics.’ The
more so, as his criticism, whilst impugning a few points of
secondary importance, contains what to my great satisfaction
I consider to be a virtual approbation of my leading princi-
ples. Nothing can be more gratifying to the author of a scien-
tific work than to find his fundamental views shared by men
of such accomplishments in science as Professor Norton is
known to be, whatever’ unavoidable differences may remain in
some matters of detail.

LXI. On a Metallic Connector to replace the Vulcanite Tube used
with Bianchi’s <Air-pump. By Witiiam Swan, LL.D.,
F.RS.E, &c., Professor of Natural Philosophy in the Univer-
sity of St. Andrews*.

| ks the air-pumps constructed by M. Barthélemi Bianchi of
Paris, which are driven with a continuous motion of rotation,
the cylinder C (fig. 1), like that of an oscillating steam-engine,
vibrates on trunnions, T, U, through a considerable are. The
trunnion T is pierced to form an air-passage, to which a tube (A)

Fig.l
. 0
Ih KO App
ray
i i

AUD [| ears
gn AT ipa A
a im] uo =

i mime e 0) |
Mei \\\

EB

* Communicated by the Author, having been read before the Literary
and Philosophical Society of St. Andrews, April 17, 1869.

the Vulcanite Tube used with Bianchi’s Air-pump. 4.43

is screwed on air-tight. In order that the cylinder shall be
free to oscillate, it is evident that the tube A does not admit of
being rigidly attached to any fixed piece of apparatus; and ac-
cordingly, to connect A with the tube B communicating with
the pressure-gauge and air-pump plate, M. Bianchi employs a
flexible tube of vulcanite, which is prevented, by a helix of wire
inside, from collapsing with the pressure of the atmosphere when
the pump is working.

Such a vulcanite connector, when of the quality furnished by
M. Bianchi and when new, answers its end most satisfactorily ;
but, like all other vulcanite tubes, in course of time it becomes
brittle, and, especially where it is attached to the metal tubes
A and B, it begins to leak. Thus it happens, when an experi-
ment is to be made, that the pump, in every other respect in
perfect order, may be found to be useless until the vulcanite has
had its ends cut off and is again attached, or until it is replaced
by a new tube. I believe all who have been in the habit of usmg
this form of air-pump must have experienced the inconvenience
thus arising, and will agree with me in thinking that, although
the use of a vulcanite tube may sometimes be convenient, the
necessity of employing it always is the only objectionable feature
of Bianchi’s otherwise most excellent instrument.

In order to remedy this defect, I have recently constructed a
metallic connector for the Bianchi air-pump belonging to the
Natural-Philosophy Museum of the United College, St. An-
drews. This consists of a brass tube, H (fig. 1), about 6 feet
long, + of an inch bore, and + of an inch outside diameter,
coiled into a helix of three and a half turns about 6 inches in
diameter. To the air-tubes, A of the pump and B of the pres-
sure-gauge and pump-plate, are attached, by soldering, tubes
with conical ends. That which is soldered into the air-tube A
is carefully centered. It is represented at D (fig. 2). The
D are fitted air-tight, by grinding, into hollow conical pieces,
HE, F, attached by soldering to the ends of the connecting helix H.
_ To prepare the pump for working, the cones D having been
slightly oiled, the piece E of the connector is slipped on to the
cone D of the pump at A; andthe pump-plate and gauge are slid
on the table on which they stand towards the pump until the
conical tube D at B (not seen in the figure) entering the hollow
piece F’, takes its seat and slightly compresses the helix H length-
wise. The helix of brass tube, although quite rigid enough from
point to point to preserve its shape, yet possesses ample elasticity
as well as flexibility to keep the cones D in their places, notwith-
standing any joltmg motion which may occur, even when the
pump, for rapid exhaustion, is driven with the utmost speed.
It need scarcely be further explained that the cone D at A turns

AAA, Prof. Swan on Bianchi’s Azr-pump.

freely within the hollow piece H, and thus the cylinder C has
perfect liberty to oscillate without necessarily twisting the con-
necting tube H, although, owing to the unavoidable friction
between the rubbing surfaces, at each stroke of the pump a slight
torsion of the connector actually does take place. In order to
ensure the connexions remaining perfectly air-tight, oil-cups, O,
are placed on fthe pieces H, I’, and a groove, G (fig. 2), is cut
round each of the cones D,so that when a little oil is dropped
into the cups it runs down into the grooves and effectually pre-
vents the passage of air. In the apparatus as constructed,
wings, W, w, were added at the ends of the connector, and also
placed on the tubes A and B with the intention of stretching
vulcanite bands over the wings to maintain the connexions until
such time as the atmospheric pressure, owing to the progress of
the exhaustion, should of itself be sufficient for that end. ‘'The
wings have proved convenient in handling the connector; but it
has not been found necessary in practice to make use of vulca-
nite bands. A pair of stops might be.attached to the pump-
stand immediately below and im contact with the wings, W, so as
effectually to hinder their oscillation. Thus, were it deemed de-
sirable, the slight torsion of the tube H, already noticed, might
be prevented. It is indeed quite possible that, failing this pre-
caution, in course of time the tube may become brittle by con-
tinued twisting. Not only the wings, but, I believe, the oil-cups
also, or at least that at B, might be dispensed with; but I am.
not disposed to advise that either of the cups be omitted.

The apparatus, as described, which has been exceedingly well
constructed by Messrs. Kemp of Edinburgh, was designed by
me for use with a moveable air-pump which is placed on the
floor, while the pump-plate stands on a table. If the air-pump
be permanently screwed to a lecture-table, which, where room
can be spared, is a good plan, the apparatus might advantageously
be simplified. The helix might probably be made of a shorter
tube, and the fastening at B might be permanent. A straight
tube might even perhaps replace the helix, or a tube bent at
right angles, where the table does not admit of the pump-
plate standing in front of the pump. Im either case suffi-
cient play might be given to keep the cone D im its place
while the pump is working, if the pump-plate were mounted
on a board with small castors or rollers; and, if necessary,
vulcanized bands might be stretched over the wings on the
tubes A, E, to draw them together. With a permanently fixed
pump, I would also suggest that, by making the helical connector
long enough, the connexions at A and B might be made abso-
lutely rigid and permanent, the oscillatory motion of the cylinder
being rendered possible simply by the torsion of the helix. Per-

On Gauss’s Conception of Electrodynamic Phenomena. 445

haps in this construction it would be necessary to employ a tube
of tempered steel, but probably one of brass or copper might
suffice.

I will only further add that the moveable connector which I
have described has been found to work most satisfactorily. It
can be mounted or dismounted in an instant; and if at any time
it be desirable to revert to the use of a vulcanite connector, all
that is needed is to pull the vulcanite over the cones D on to the
tubes A and B.

In conclusion I cannot omit the opportunity now afforded me
of warmly recommending, with or without the new connector,
Bianchi’s most elegant and useful air-pump. Owing to the very
great rapidity with which, by its use, a vacuum can be obtained,
it is particularly well adapted for lecture-experiments. The
pump-cylinder and nearly all the apparatus being made of cast
iron, is not liable to suffer corrosion from oil, and will therefore,
I have no doubt, last much longer than a brass air-pump. I
have found a glass case very effectual in preventing external
rusting; and the instrument is so beautifully finished as well
to deserve such protection. M. Bianchi has adopted in his
air-pumps Babinet’s ingenious arrangement for double exhaus-
tion. By turning a stopcock, one end of the barrel of the pump
is made to exhaust the other; and thus a very perfect vacuum,
as is well known, can be obtained.

LXII. Upon the new Conception of Electrodynamic Phenomena
suggested by Gauss. By R. Crausivs*.

i a letter written by Gauss in 1845 to W. Weber, the brief

remark occurs that he considered the corner stone of elec-
trodynamics to be the deduction of the accessory forces (which are
superadded to the reciprocal action of electrical particles at rest)
not from an instantaneous action, but (as is the case with light)
from one requiring time for its propagation. Based upon this
remark, three very interesting papers, by Riemann, C. Neumann,
and Betti, have lately appeared. All three authors arrive by dif-
ferent ways at the result that the forces which two currents
exert upon each other are explicable on the assumption that a
certain time is necessary for the propagation of electrical actions.

I have read these researches with the greatest interest, but
must confess that [ am not satisfied with them; and I think
_that both the well-deserved reputation which these authors possess
in the scientific world, and the importance of the subject, amply
justify me in stating my objections. The fact that three distin-

* Translated from a separate impression, communicated by the Author,
from Poggendorff’s Annalen for December 1868.

446 Prof. R. Clausius on the new Conception of

guished mathematicians, by pursuing three different methods of
investigation, have obtained what is virtually the same result,
would seem to furnish a guarantee for the accuracy of the inves-
tigation ; and perhaps many physicists will thereby be led to con-
sider the matter settled. Under these circumstances a publication
of the reasons on the other side can only have a useful effect, by
giving rise to further investigations made probably from other
points of view.

The most complete of the above investigations is that of C.
Neumann, which appeared, under the title Principles of Electro-
dynamics,” as a publication on the occasion of the Jubilee of the
University of Bonn, after a preliminary notice of the results had
been published in the Proceedings of the Gottingen Royal Aca-
demy of Sciences. I will first discuss this.

Neumann starts from the consideration of two points, which
move under their reciprocal action. If the potential of one of
these points, (for greater accuracy we will at once say) the point
m,, is to be determined in reference to the point m, the time ne-
cessary for the propagation of the action must be taken into
account, which is done by Neumann in the following manner.

The potential which the point m, exerts at the time ¢ he calls
the emissive potential, and denotes it by 7. Assuming Newton’s
law in reference to the reciprocal action of the two points, namely
that the force is inversely as the square of the distance, we have,
according to Neumann, for the determination of the emissive
potential the equation

m My
r

T= )
in which rv denotes the distance of the two points at the time 7.
This potential requires some time to reach the point m, and
hence arrives there not at the time ¢, but somewhat later. If,
on the contrary, we want the potential arriving at the time ¢ in
the point m, which Neumann calls the receptive potential, we
must take for it that potential which the poimt m, emitted at a
certain earlier time ¢—A?¢. Denoting the distance which the
two points had at this previous moment by r—Ar, and choosing
for the receptive potential the sign w, according to Neumann we
must put
elegy
~ r—Ar
Replacing the denominator by a series progressing by powers of
At, we have

@

Sani ehh eimisetinn it
oO= Ale Aree |. ap emma)
PO Gb WL oa Enon

Electrodynamic Phenomena suggested by Gauss. 447

As regards the difference of time At, it is the time which the
potential requires to traverse the distance between the two points;
and denoting by ¢ the velocity of propagation of the potential,
Neumann puts

A — it ° ° . . ° € . ° p
i=" (2)
The previous equation thereby passes into
mm,
—— ——————_—_—_—_——————— S| e e e .
iad Fah agen Be). (3)

&e.

~T— en —_- —_—_——_ —
cat 2c? dt?
Developing this expression in a series, and, inasmuch as ¢ is
very great, neglecting all members which have in their denomi-
nator higher powers of it than the second, we obtain

_ min, E Lode ppck (2). . =| (4)
ere Pe ie hoe ai dl iaah | ae
From this expression Neumann separates that part which may
be represented in the form of a differential coefficient according
_ to the time, viz.
De ee gl ae
NGF dt 82 a
and calls it the ineffective potential. The other members form
then the effective potential. Denoting this by w, he finally ob-
tains the equation

mm 1 /dr\?
ee) ee

In this statement I think I have accurately reproduced that
part of Neumann’s investigations with which we are concerned
for our present purposes, and we will now inquire whether this
reasoning can be allowed to be correct in all points.

If the action of the point m, on the point m is presupposed to
be momentary, both the emissive and the receptive potential of

mm
F

m, in reference to m must be represented by the fraction ’

in which 7 is the distance which the two points possess at the
time ¢. In order to express that a duration of time is needed
for the propagation of the potential, and that thus the potential
which arrives at the time ¢ on the point m was exerted from the
point m, at an earlier time ¢— Az, Neumann puts in the receptive
potential the value »—Ar as the denominator of the fraction
instead of , by which he understands that distance which the
points had at the time ¢—A?¢. But if we assume that the
action is propagated similarly to light from the point m, to

44.8 Prof. R. Clausius on the new Conception of

the point m, it seems to me that we must take as denominator
of the fraction neither the distance which the points have at the
time ¢, nor that which they had at the time ¢— Ad, but must take
into account another quantity—that is, the distance between the
position where the point m, was at the time t—At (at the moment
of emission) and the position where the point m is at the time t
(the moment of reception). This distance may be denoted by
rt AG):

To determine this distance, itis convenient, besides the above-
used differential coefficients of the distance 7, in which the mo-
tions of the two points are simultaneously taken into account, to
bring in two other kinds of differential coefficients of this mag-
nitude—those, that is to say, which only refer to the motion of the
point m, and those which only refer to the motion of m,. We have
now to do with the latter, and will distinguish them by an index

dr ar
added to the d, thus, Be a
then be expressed by the following series,
At dr | AP dir
Ledt “Ne 2idig
Putting this value into the denominator of the fraction which is

to represent the receptive potential, we obtain instead the follow-
ing expression,

&c. The distance in question may

r(¢— Af, t)=r— &e.

mm,

Ned yr. At? dir
at ie see i

This expression is essentially different from Neumann’s. If it
be applied to two constant currents, presupposing that in each of
the two conductors there is everywhere an equal quantity of posi-
tive and negative electricity, we obtain zero for the potential of
the two currents on each other.

Besides iat has here been said, there is another objection
which I think I must make against Neumann’s analysis. To
determine the difference of time A¢ which the potential requires to
pass from the point m, to the point m, Neumann uses equation (2),

: (1a)
— &e.

Y

that is, he regards in this determination the distance 7, which
the two points have at the time /, as the path traversed by the
potential. But this is obviously not the real path ; this we must
again consider to be the above-discussed distance-—that ts, the —
distance of the position of the point m, at the moment of emission,
from the position of the point m at the moment of arrival.

Electrodynamic Phenomena suggested by Gauss. 449

Hence, instead of the previous equation, we must put

Ap Abd),

c
or if we take for r(¢— At, t) the above-mentioned expression,

2
At=*(r— Adie Nt dir ke).

Cc

en aie
From this equation we get for Az, the following series,

ag ee pot ee ee hwy Or n™..6 owt (2a)
Reverting to equation (1a), if we replace A? by the series just
found, we obtain instead of (8) the equation

mm,

s= re. tome

Bae ay |e ay, PA he i
c dt an 202 dt? i

and from this we get the following equation instead of (4),

_ mn, iar ee a)
ox 14-2 — 55). eer imc ne (4a)

This expression for the receptive potential is distinguished from
that in (4), not only by the complete differential coefficients of
r being replaced by partial differential coefficients, but’ also by
the fact that the principal member of Neumann’s formula (that
containing the square of the first differential coefficient) is wanting.

It appears to me to follow indubitably that Neumann’s ana- |

lysis, by means of which he deduces his potential formula from
the assumption mentioned in the mtroduction to his paper (that
the potential, like light, is propagated through space with a cer-
tain constant velocity), cannot in all respects be admitted as con-
clusive. Whether perhaps that formula may be arrived at by
different assumptions as to the mode of propagation of the po-
tential, or by the help of other points of view, is, of course,
still undecided.

I turn now to Riemann’s paper, which appeared in Poggen-
dorfi’s Annalen, vol. cxxxi. p. 237*, after it had been presented
to the Gottingen Royal Society in 1858, but subsequently with-
drawn by Riemann.

Riemann endeavours to deduce an expression for the potential
of a constant galvanic current S, in reference to another constant
- galvanic current 8’, from the same assumption, namely, that the
potential requires time for its propagation through space.

He first of all considers two small quantities of electricity, ¢

* Phil. Mag. 8, 4. vol. xxxiv. p. 368,

450 Prof. R. Clausius on the new Conception of

and e!, moving in the two conductors. The distance from each
other he calls 7; but from the first he makes the distinction that
jn determining r he considers the two quantities of electricity at
different times. The distance between the position of ¢ at the
time ¢ and the position of ¢’ at the time 7@' he denotes by r(é, 7’).
If thus we wish to determine the potential emitted from e¢ at the
time t— At, and which arrives at é! at the time ¢, we have, as
before, to denote by 7(¢— Az, z) the value of r which then comes
into play.: Thus the potential of e upon e’ (if, with Riemann,
we use the minus sign, since similar electricities repel each
other) is she:

ee!

~ r(¢—At,t)

In calculating with this expression, he distinguishes between the
differentiations which refer to the motion of e from those which
refer to the motion of e', by denoting the first by d and the
latter by d’.

For the sake of greater convenience, he introduces the func-
tional sign F with the meaning

ih

— ae

nts t') ( ) i),
by which the expression for the potential passes into

—eel (¢—At, ¢).
Using this functional sign, he distinguishes between the deduc-
tions which refer to e and those referring to ¢! by affixing to F
' either an accent or an index, that is, either by F” or by F,.

So far nothing can be urged against Riemann’s expressions ;
but in the further treatment points occur with which I cannot
agree.

First of all, in determining AZ he proceeds just like Neumann.
Denoting the velocity of propagation of the potential by a, he
puts

&

At= =,
a
in which 7 is the distance of the quantities of electricity e and ¢!

at the time ¢. His expression for the potential accordingly

becomes :
—eB(¢— Ea ‘).
a

But to carry out logically his own distinction of the various dis-
tances, he ought to put

r(t—At, 2)
Aft= SS ee.

a

Electrodynamic Phenomena suggested by Gauss. 451

which, neglecting the higher members, gives

In accordance with this the expression for the potential should be
Se)
ce Bt a oe dt’ 8:

In the further course of Riemann’s calculations there occurs

another very essential oversight. To prove this I will follow his
own developments further, merely remarking that wherever in

the sequel the fraction - occurs, the somewhat altered value
‘aie hak should be inserted.
a a dt

In order to deduce from the potential of the individual elec-
trical masses ¢ and ¢! the potential of the entire electrical cur-
rents § and S!, he considers the summations executed in reference
to all the quantities of electricity in the two conductors. Hence
from this the potential of S upon S! would be

—3Xee F(t s t).

But, for the transformations which he intended, it was necessary
to have the time in the formula differently from the manner in
which it occurs; and he therefore considers the potential not
merely at the time ¢, but during an interval of time from 0 to ¢;
and the expression thus formed he considers to be the potential of
the forces exerted from the time 0 to the time ¢. If this poten-
tial be denoted by P, we get

pa—|‘s3eR(r—7, rr. =. is geen

; Bye : r
develope the function occurring in the expression according to —.
a

Then, neglecting higher members, there would have been obtained
t Lr 72
ee f EE e!| F(x, 2) — Pr, 7) + 5 M(x, 2) | ar,

or, otherwise written,

This expression, in which occur only differential coefficients which
refer to the motion of e, becomes equal to zero if the summation

To calculate this magnitude P, it would have been simplest to.

|
}
|

et A, aE i it ae

a a 5

a rn gn rr er ee i ey om er pre eee

452 Prof. R. Clausius on the new Conception of

be effected of the quantities of electricity ¢! in the conductor of
the current S!, which are so distributed that there is everywhere
the same quantity of positive and of negative electricity. It
follows thence that the expression (6), proposed by Riemann
for the potential, is not fitted to explain the action of two cur-
rents upon each other.

An expression which is to fulfil this object must necessarily
contain a member in which a differentiation in respect to the
motion of ¢ as well as one in reference to the motion of ¢
occurs—a member, that is, which contains either the product

‘C)e

— or the differential coefficients of the second order,

ig Var
dl! E)
oa Nae s
dt dr

To introduce such a member into his expression, Riemann effects
a peculiar operation,
He first writes

tas “, r) = F(¢, r) -{Pe-«, "ae

If we introduce the difference which stands here on the right-
hand side into the expression (6), it divides into two members,
the first of which, containing I'(7, 7), becomes zero by summing
all the quantities of electricity e and ¢’, owing to the uniform distri-
bution of positive and negative electricity. Hence there remains

pa ( assed (*Pe—o, 2d. ee ae
0

0
Riemann now changes the order of the integrations by writing

Pua Go
P= >dee! ( al dvi" (7 —o,7) eee eo)
e/ 0 0
In this he puts t+ for 7, by which he gets

< t—o
P= | ‘dof dr¥'(r,7+0).
0 —o

If in this expression the limits —o and t—o of the second in-
tegral are to be replaced by the limits 0 and ¢, to the integral
thus changed another must be added which goes frem —o to 0,
and another from ¢—o to ¢ subtracted from it. But Riemann
shows subsequently that the members resulting from these two

Electrodynamic Phenomena suggested by Gauss. 453

integrals are infinitely small ; hence instead of the preceding we
may write

PaESee! (“do dP(@, 7-40), Lea |)
0 0

This expression is distinguished from that given under (8)
by the altered form of the function; and after this change has
been effected, Riemann again alters the order of the integrations
and. thereby obtains

if

u re
B= axed | dalla, tas) a2, ae 8 (LO)
0 0
From this point the further calculation is very simple. If the
function under the second integral sign is developed according
to o, we get, neglecting the higher members,

Ue

P= [assee(“de [E"(7, T) is of" (r, colile

0
or, by performing the second integration,

} ' 2
p={ dt Zee! E I(r, 7) + 53 P(r, 7) | ;

This expression resolves into two members, of which that con-
taining I" (7, r) disappears when the summation is performed with
respect to ¢’, and there remains

t 2
b=, drSSed 5 F(z, 7) 5 oh eevee rteell ear ole)
0

1
re (da'(=)
P= I ede www (12
: Ze 20 drdr 2)
This is the expression deduced by Riemann, which represents
the electrodynamic action of the two currents upon each other.
That which I consider to be incorrect in this analysis is the
manner in which Riemann exchanges the integrations in order
to pass from equation (7) to equation (8), and afterwards from
(9) to (10). This exchange would only be admissible in case the

or, differently written,

lors (ee mn
magnitude — which forms the upper limit of one integral, were
a

independent of the time 7, according to which the other integra-
tion is to take place. This, however, is not the case, but, if the
quantities of electricity « and ¢’ move, their distance 7 is variable
with the time. Hence the equations which are obtained by
Phil, Mag. 8. 4. Vol. 37. No. 251, June 1869. 2H

ee a es ie to oe aoa SS | Se

ABA Prof. R. Clausius on the new Conception of

these changes cannot be regarded as correct consequences of
the earlier equations.

I believe that Riemann subsequently convinced himself of this
error, and that this was the reason why he withdrew his paper.
Yet its publication has not been without use for science; for
though it has not yet solved the question as to the origin of elec-
trodynamie forces, it has contributed to moot this question afresh,
and to give to it a heightened interest ; so that at present several
physicists and mathematicians have had their attention directed
to it, and a solution may perhaps thereby be attained.

Of the above-mentioned three papers, there remains to be con-
sidered that of Betti, which appeared in the Nuovo Cimento,
vol. xxvii.

Betti figures to himself as follows the two constant currents
whose potential on each other he wishes to determine. He sup-
poses the closed curves traversed by the currents to consist of
elements which are periodically polarized, and therefore act upon
each other as if they were magnetic elements whose axes are pa-
rallel to the tangents of the curves. He assumes that the periods
of the changes are the same in both currents, so that they can
only be distinguished by their phases. He adds to this idea the
assumption that, for the propagation of the action of an element
of one current to an element of another, a certain time is neces-

sary which he calls =; r being the distance of the two elements

from each other. He thus obtains for the potential of the two
currents upon each other the same expression as that known. in
electrodynamics.

It might seem that the assumptions made had been fully con-
firmed, and that thus the question as to the nature of the electro-
dynamic forces had been solved in a different manner from that
attempted by Riemann and Neumann. Yet it may be shown
that here, apart from an improbability inherent in the mode of
representation, upon which I will not enter, there is an oversight
in the mathematical development which is of essential influence
upon the result.

To show this, it is not necessary to follow the entire investi-
gation, but itis sufficient to consider that part in which it occurs.

In order to express mathematically the periodical changes of
the polarized elements, Betti introduces a function of the time
@(¢) which has the property of regularly altering its value in
very short intervals. The duration of the periods he designates
by p. Of this function the value is to be determined which it

assumes if ¢ is replaced by ¢+o0— - in which o may be any mag-

nitude between O and p, and - the above-mentioned time which

Electrodynamic Phenomena suggested by Gauss. 455
Is necessary for the propagation of the action. To determine
this value, Betti developes the function in powers of o — and

limits himself to the first powers by putting 7
Buys —"\g+(o—2) #0,
B(+o—T)=$(y +(o— "pn +(o—2 :
The limitation to the first two powers he justifies on the ground

Cs :
that o and ~ are small magnitudes. But, according to his own
c

assumption, the duration of a period of the function represented
by $(¢) is also very small, and in the course of his deduction
there is even the following passage :—“ Now let the duration p
of a period be very small as compared with the time in which
the electrical action propagates itself through the unit of length,
so that o (the magnitude lying between 0 and p) may be neg-

° : . VT 33
lected in comparison with ~
Cc

If the function (2) has so short a period, and its value there-
fore changes so rapidly as is here presupposed, it must have
very great differential coefficients. If such a function is to be

: ogi
developed in reference to a magnitude which contains -, and in
c

comparison with which the duration of a period is very small, it
is impossible to neglect in this development all higher powers
than the second. To see this, since Betti has named no special
conditions as regards the nature of the periodical functions, it is
sufficient if we consider any given function whose period has the
duration p. Let it be the following :

sin sl t.
P
Putting in this ¢+P in the place of ¢, and developing with re-
spect to powers of P, we have 7

2 Q
sin = (¢4. P) = sin £4. Pe cog e™ “es =o Sips
p p p 1.2
PF 72r\3 = Ir
ie pr ona “— ngs t+ &e.

Tn this series we see at once that when the magnitude p in
the denominator is small as compared with the magnitude P in
the numerators, we must not think of restricting ourselves to
the first three members.
Since in Betti’s paper the entire further calculation depends
upon the development of that series in which all members higher
: 2H 2

456 Mr. W. Huggins on some Spectrum

than the second power are omitted, members are wanting in the
result which should not be omitted; and therefore this result
cannot, until otherwise proved, lay claim to any validity.

I think I have thus shown that all the investigations cited at
the outset of my paper, however cleverly they otherwise treat the
matter, contain certain faults which make it impossible to admit
that the results are correctly deduced, and that the solution of
the problem of referring electrodynamic forces to known electro-
static forces has not been attained in these investigations.

Wurzburg, October 20, 1868.

LXIII. On some Spectrum Observations of Comets.
By Witu1am Hueerns, F.R.S.*

6 ae is another class of heavenly bodies distinct from the

objects we have considered—the comets. Of the nature
of the phenomena presented by these strange masses of light of
constantly changing form we possess but little certain informa-
tion. It is doubtless to spectrum analysis that we must look for
any important increase of our positive knowledge of the consti-
tution of those bodies, and of the true nature of the remarkable
changes which take place in them under the actionof the solar rays.

A not unimportant earnest of the more complete information
which the prism will doubtless exact from the next brilliant comet
has been already gained by the examination of five faint comets.
One of these was examined by Donati in 1864+. Two of these,
which were excessively faint, | observed in 1866 and 1867%.
The others, which were in a small degree brighter, I examined
in the summer of last year.

These observations showed that the greater part of the light
from the heads of comets is very different from solar light, and
therefore cannot be the sun’s light sent to us by ordinary re-
flection from the cometary matter.

In the case of the very faint comets of 1866 and 1867, I was
not able to determine more than-that the light of the brightest
part of the coma consisted for the most part of green rays of the
refrangibility between 6 and F of the solar spectrum. Further,
as far as such very faint objects would permit of observation, I
suspected that the margin ofthe coma and the tail gave a conti-

* From the Rede Lecture, delivered at Cambridge, May 18, 1869.
Communicated by the Author.

t+ Astronomische Nachrichten, No. 1488; and Monthly Notices of the
Royal Astronomical Society, vol. xxv. p, 490.

{ Proceedings of the Royal Society, vol. xv. p. 5.

§ Monthly Notices of the Royal Astronomical Society, vol. xxvii. p. 288.

Observations of Comets. 457

nuous spectrum, and was probably solar light sent to us by ordi-
nary reflection.

Previous telescopic observations had shown that in several
bright comets the light of the head differed from solar light in
having a decided blue tint*. In this part of the comet the po-
lariscope has generally given but feeble indications of the pre-
sence of reflected light. ‘These characters are in accordance
with the spectroscopic examination of the light of this part of
comets.

I will now describe the more complete analysis of the blue
cometary light which the brighter comets of last summer enabled
me to make.

One of these was Brorsen’s comet at its return in 1868, the
other a comet discovered by Winnccket.

Winnecke’s comet (Comet II. 1868) presented in the telescope
a nearly circular coma surrounding a bright nebulous spot, where
probably a true nucleus existed. The faint nebulosity from the
margin of the coma could be traced for more than a degree, and
formed a tail which was sharply defined on the following edge,
but faded away so gradually on the opposite side that no limit
could be perceived. In the spectroscopic observations the slit
was placed across a diameter of the head.

The spectrum of this comet, and also that of Brorsen’s comet,
consisted of three bright bands in similar but not identical parts
of the spectrum. The circumstance that the bands were nar-
rower than those of the other comet might be due to the smaller
intensity of the light of this comet, in consequence of which the
bands could not be traced so farin the instrument. If this pos-
sible explanation of the difference in breadth of the bands be
admitted, there will remain the difference of refrangibility in
the strongly marked beginning of the middle bands of the two

* Sir William Herschel described the head of the comet of 1811 to be
of a greenish or bluish-green colour, while the central point appeared to be
of a pale ruddy tint. The representations of Halley’s comet at its appear-
ance in 1835 by the elder Struve are coloured bluish green, and the nucleus
on October 9 is coloured reddish yellow. He describes the nucleus on that
day thus:—‘ Der Kern zeigte sich wie eine kleine, etwas ins gelbliche
spielende, gliihende Kohle von langlicher Form” (Beobachtungen des Hal-
ley’schen Cometen, p. 41). Dr. Winnecke describes similar colours in the
bright comet of 1862 :—‘ Die Farbe des Strahls erscheint mir gelbrothlich,
die des umgebenden Nebels (vielleicht aus Contrast) mattblaulich.....
Die Farbe der Ausstrémung erscheint mir gelblich; die Coma hat blau-

~ liches Licht”? (Mémoires de Académie Impériale des Sciences de St. Péters-

bourg, vol. vii. No. 7).

Tt For a more detailed account of the observations of these comets and
diagrams of their spectra, the reader is referred to papers by the lecturer in
the Proceedings of the Royal Society, vol. xvi. p. 386; and Phil. Trans.
1868, p. 555.

458 Mr. W. Huggins on some Spectrum

comets—a difference sufficiently great to support the conclusion
that the conditions in the two comets by whick the light was
furnished were not identical. The first band occurs about half-
way from D to E of the solar spectrum; the second band begins
about 5 and extends nearly to F. ‘The third band presents itself
between F and G.

The three broad cometary bands differ greatly in refrangibility
and in character from the sharply defined narrow lines of the
-nebul, and appear to show a constitution distinct from that
of the nebule.

The morning after I had made the observations of Winnecke? S
comet, I was much interested to find that the comet’s spectrum
appeared to be identical with one of a series of the spectra of
carbon, as obtained from the decomposition by the induction-
spark of several compounds of carbon which I had prepared
some years before.

The modification of the spectrum of carbon, which appeared
identical with the cometary spectrum, presented itself when the
spark was taken in olefiant gas and some other compounds of car-
bon, and differs from the apparently more perfect spectrum which
is obtained by the decomposition of cyanogen and olive-oil, &c.,
in the one circumstance alone that the three bands in the bright
parts of the spectrum are not resolved into distinct narrow lines,
but the light in each band becomes gradually fainter without suf-
fering any break in its continuity.

I believe we have a right to consider this peculiar spectrum,
containing the three bright bands, to be the spectrum of the
vapour of carbon and not that of any stable hydrocarbon, for the
reason that I obtained the same spectrum when I used olive-oil,
the vapour of Persian naphtha in hydrogen, and other hydrocar-
bons, as when I employed cyanogen. In one case the spectrum
was accompanied by the lines of hydrogen, in the other by the
known complex spectrum of nitrogen. A spectrum essentially
the same, though less complete, was obtained, together with the
known lines of oxygen, when carbonic acid and carbonic oxide
were employed.

In the evening of the same day I compared the spectrum of
the comet directly with the spectrum of olefiant gas, the two
spectra being juxtaposed in the instrument. Careful compari-
sons made on that evening, when my friend Dr. W. Allen Miller
observed with me, and on two subsequent nights, showed that
in every particular of refrangibility and of relative intensity, the
spectrum of the comet was similar to that of carbon.

The obvious and apparently well-founded conclusion from
these observations would be that the cometary matter from which
this light comes consists of the luminous vapour of carbon.

Observations of Comets. 459

- It must not be overlooked that on this supposition a formi-
dable difficulty presents itself in the insufficiency of the degree of
solar heat to which this comet was subjected for the conversion
of carbon into vapour. We cannot, for several reasons, suppose
that the solar heat was supplemented by the heat of chemical
action which it called forth. The suggestion, however, that car-
bon may possibly exist in an allotropic state in which it may be
much less fixed, and so capable of passing into vapour at a com-
paratively low temperature, is not perhaps inconsistent with our
positive knowledge of other elements. LHven if this suggestion
were true to fact, a diffieulty would remain; for, so far as we
know, vapour in the non-luminous state, though it would not trans-
mit light of the refrangibilities which it would emit when heated,
would not give them back by reflection, so as to reflect light si-
milar to that which is peculiar to it in the luminous condition*.

It may be well to consider for a moment the principal pheno-
mena which usually present themselves when a comet approaches
the sun.

(1) Under the influence of the solar force the nucleus throws
out luminous jets which frequently assume the form of luminous
envelopes about itt.

_ (2) The jets or envelopes rise, in the first instance, towards
the sun.

(3) The envelopes are frequently separated from the head,
and from each other, by invisible spaces.

(4) At the boundary of the head the envelopes behave as if
_ they had become subject to an intense force of repulsion from
the sun.

(5) The matter of the envelopes appears to be driven from the
sun on all sides of the head, and in this way to form a hollow
conical tail.

Though the feeble light of the comets hitherto subjected to
spectrum analysis has permitted them to be but imperfectly in-
vestigated, we have learned that the matter which emanates
from the nucleus, and is distinguished by a blue tint, gives a
light which the prism shows to be identical with that emitted
by the vapour of carbon. It is certain, therefore, that the light
which has the blue colour is not due to reflection from a cloud
of which the particles are too small to reflect the longer waves of
the less refrangible colours.

* It might be possible that a spectrum of bright bands would be given by
- a gas in a fluorescent state; but the circumstance of the coincidence of the
cometary spectrum with that of carbon would remain unexplained.

+ Of these phenomena see a graphical account by Sir John Herschel,
_*Famihar Lectures on Scientific Subjects,’ p. 115; also the “ Account of

the Great Comet of 1858,” by G. P. Bond, which forms vol. iii. of the
* Annals of the Observatory of Harvard College.’

460 On some Spectrum Observations of Comets.

The invisible spaces between the envelopes may possibly cor-
respond toa condition of the vapour too cool to emit light, and
yet not condensed so as to reflect light.

The exterior parts of the coma and the tail, which have been
found to be polarized in a plane, showing the light to come from
the sun, may be supposed to consist of the vapour of the nu-
cleus condensed into widely scattered particles of great mi-
nuteness.

The remarkable phenomenon of the great rapidity with which
the tail is seen to extend itself to enormous distances in a direc-
tion from the sun remains unexplained. It may be suggested
that the instant at which the matter appears to come under the
influence of repulsion from the sun, may be that at which the
vapour is condensed into discrete particles, and be in some way
connected therewith*.

Many years since Benedict Prevét+ suggested the following
hypothesis. The head of the comet by the sun’s heat is con-
verted into vapour which is invisible, and expands toa great dis-
tance from the head in all directions. Behind the head, where
the vapour is sheltered from the sun’s heat, it is condensed into
cloud, which reflects light and appears as the tail. This cloud
passes back into invisible vapour as, by the comet’s motion, it
becomes exposed again to the solar beams.

This theory is obviously inconsistent with the observed ap-
pearances and forms of the tails, and especially with the rays
which are frequently projected in a direction different from that
of the tail, with the absence of tail immediately behind the head,
and with the different degrees of brightness of the sides of the
tail.

I should not refer to this almost-forgotten hypothesis, but
for the circumstance that the same theory essentially forms part
of the recent ingenious speculations of Professor Tyndall on the
nature of comets, with the difference, however, that clouds
formed in the cool shade of the comet’s head are supposed by
him to be due to chemical action which can then take place, and
not, as in Prevét’s theory, to a lower temperature alone.

For further positive knowledge of the nature of cometary
phenomena we must doubtless wait until the searching method
of analysis by the prism can be applied to the series of changes
presented by a brilliant comet.

* Phil. Trans. 1868, p. 563.
t+ Arago, ‘ Popular Astronomy,’ translated by Smyth and Grant, vol. 1.
p- 623.

[ 461 ]

LXIV. On Statical and Dynamical Ideas in Chemistry.—Part I.
Acid, Alkali, Salt, and Base. By Komunp J. Miuts, D.Sc.,
F.C.S.*

iN ple history of chemistry exhibits, in one respect, a re-

markable parallel to the history of philosophy ; for no
“other sciences have transmitted to the present epoch so many
unresolved and kindred controversies. The question of the One
and the Many, for example, is allied to that in which the unity
of matter is challenged by the variety of elements; discussions
as to Absolute and Infinite resemble those which have reference
to the divisibility of matter; Kosmos reappears in the law of
Definite Proportions ; and the contest about general principles
was an echo of the battles of realism. Of the attempts to de-
cide satisfactorily upon philosophical disputes, Ferrier considered
his own + the best and purest; and it is a masterpiece among its
kind: but I believe that no chemist has ever proposed an enter-
prise like that of the philosophert. Nevertheless there are pro-
bably but few chemists who, amid the assault and confusion of
modern theories, would decline a criterion by which to estimate
the multitudinous claims so pertinaciously presented for their
allowance. Such a criterion seems attainable by the following
considerations.

Adopting the primitive procedure of reason itself (which con-
sists In comparing one object with another), inductive science has
uniformly selected the analogical method as the basis of her
progress. In this manner, the notion of comparability has con-
ferred upon scientific reasoning a peculiar character, and made
it, for the most part, a process of convergence. The history of
the different sciences may, indeed, be compared to a group of con-
verging series having a common |imit—that limit being the law,
for ever to be desired, from which all phenomena may be de-
duced. Such is the point towards which analogy, by compari-
son, and by abstracting differences, 1s ceaselessly making an ad-
vance. Ifthis be admitted, a criterion of scientific progress
becomes possible; and that criterion is the most general idea
existing at a given time as a factor in every branch of science.
An idea is, for this purpose, preferable to a law, because ideas
always determine the form of contemporary laws. Now it will
probably be conceded that the criterion at present required is at-

* Communicated by the Author.

+ Institutes of Metaphysic, first edition, p. 63.

{ Fremd’s work, entitled ‘““Chymical Lectures: In which almost all the
Operations of Chymistry are Reduced to their True Principles and the Laws
of Nature” (London, 1737), must not be supposed to have been written
with the intention above indicated.

462 Dr. E. J. Mills on Statical and

tained in the idea of motion, such motion being understood of itself
—that is (in ordinary language), without reference to anything
moved. This criterion will sufficiently enable us t6 decide upon
the relative value of most of the current theories, of chemistry
especially. I purpose in this paper to apply it to the contro-
versy about acid, alkali, base, and salt; but the following histo-
rical digression is a necessary preface to the argument*.

2. The word acid was probably used at first only in a concrete
sense, signifying vinegar. The solvent properties of what we
now call acids were noticed by Geber. ‘Tachenius (an iatro-
chemist) defines them as forming salts with alkalies, to which
they have a certain oppositeness or antagonism. Boyle and
others noticed that they reverse the colorific effects of alkalies.
Freind testifies to the general acceptance of the Tachenian doc-
trine during the first third of last century, and strongly protests
against it; the corrosive, colorific, and fermentative properties
are, he states, often shared by acids and alkalies alike, “ and
what in respect to one body is named alkali, is, if compared
with some other, by the very same writers call’d an acid. So
that in vain we endeavour to fix the boundaries which separate
each kind.”

Various opinions have been proffered as to the source of the
acid properties. Becher and Stahl ascribed them to the pre-
sence of the universal acid, Sylvius to a fiery matter, Meyer
to an “acidum pingue ”—the last two bemg supposed to be
common also to alkalies. Lemery assured himself of the sharp-
ness of the constituent particles of acids; Mayow, Scheele, and
Lavoisier ascribed acidity to oxygen. Davy, on the other hand,
first considered hydrogen-as the acidifying principle; but he
afterwards discarded the notion of a principle, and held, if I may
so illustrate his view, that the acidity of any substance is a kind
of resultant whose direction ishydrogen. ‘lhe doctrine that “ an
acid is a salt of hydrogen” may be assigned to Dulong and
Gerhardt (the former especially).

A question of nomenclature has arisen recently with reference
to this subject. Professor Williamson maintainst that the words
ACID and BASE “were introduced to describe bodies of oppo-
site properties which are more or less completely lost in the salt
or compound of acid and base” (p. 423), or “belong to the
idea of compounds of fundamentally opposite properties which
unite to form one or more molecules of a comparatively neutral

* The following historical details have been purposely compressed as
much as possible. Authority for many of them will be found im Kopp’s
Geschichte der Chemie, or in Watts’s ‘ Dictionary of Chemistry ;’ but they
are partly supported by original research.

+ Chem. Soc. Journ. vol. xvii.

Dynamical Ideas in Chemistry. 4.63

compound” (p. 424); and he proposes to revert to this usage,
confining the word acid to what Gerhardt called “ anhydrides.”
Certain bodies which resemble hydric, ferrous, and ferric chlo-
rides are termed “ normal salts” and ‘acid in their properties.”
Dr. Williamson also remarks that “ chemists might just as well
limit the word acid to the salts of lead, calling the acids them-
selves ‘‘ anplumbates,” as say with Gerhardt, that hydrogen-
salts are the only acids, and that the real acids are not acids, but
only anhydrides ;”” and he adds that “the hydrogen-salts can-
not with any consistency be called acids.” Professor Foster*
defends the common application of the word “acid.” He shows
that, for some little time prior to the definition of Gerhardt, the
term included both hydric salts and hydrides; but that, as a
matter of fact, “‘in perhaps ninety-nine cases out of a hundred,
when an acid was spoken of as taking part in, or resulting from,
a reaction, it was a hydrogen-salt, and not an anhydrous acid,
that was meant.” On the whole, however, he is disposed to
think that the word “indicates a distinction to which we now
know that no real difference corresponds,”’ and advocates term-
ing acids “hydric salts,” and the anhydrides, what they really
are, merely “ oxides.”

Alkali originally signified crude potash. Van Helmont,
Sylvius, Lemery, and Boerhaave applied it in a general sense to
bodies’ which effervesce with acids; but Boyle recognized as
alkalies certain substances which do not act in that manner.
The iatro-chemists noticed that they neutralize the effects of
acids. Kunkel limited the name to what also might, as he be-
lheved, be transformed into acids; ready union with acids was
the characteristic advocated by Stahl. When alkalies came to
be divided into causTIc and EFFERVESCENT, it was assumed that
the action of lime in transforming the latter into the former
kind consisted im a transference of one of its own constituents
to the effervescent alkali. This constituent was supposed by
Lemery and others to consist of igneous particles; Kunkel as-
signed to it both weight and acid properties. Stahl supposed
that alkalies contain a minimum of the primitive acid, of which
common acids and neutral and alkaline salts are also partakers.
Black, by an admirable series of inductive experiments carried
out quantitatively, showed that rixED AIR is the cause of loss or
diminution of causticity. Meyer controverted this conclusion ;
and a train of reasoning, which we may still admire for its sub-
- tlety and system, led him to refer causticity to the acidum pingue
—an igneous matter of acid nature. So ably did Meyer support
this theory, that two of the most eminent contemporary che-
mists gave it special refutation.

* Phil. Mag. S. 4. vol. xxi. p. 262;

464, Dr. E. J. Mills on Statical and

The term sal¢ was likewise concrete in its primitive significa-
tion, having been from time immemorial applied to culinary salt.
Aristotle denoted by it the evaporated lixivium of wood-ash ;
Dioscorides and Pliny seem to have called crude soda by this
same name, the latter naturalist using it generally for substances
which could be recovered from water by evaporation. Such per-
haps was the practice of Geber and certain alchemists of the
west. Basil Valentine classified the vitriols apart as metallic
salts ; and from his time the word saur had, as one of its mean-
ings, that of a constituent indestructible by ignition. This, ac-
cording to Paracelsus, may be found in all bodies; moreover
alum and the vitriols are salts. Other chemists of the sixteenth
century understood by salts substances which im taste and solu-
bility resemble common salt. Palissy included sugar in the
list. In the seventeenth century Lemery defined a neutral salt
(sel salé) as an alkali charged with acid ; Van Helmont observed
that salts are composed of two opposite constituents ; Tachenius
stated that all salts are decomposable into acid and alkali. Ac-
cording to Becher, a salt contains elementary earth and water ;
according to Stahl, acids, alkalies, and salts are transmutable
inter se, and consist of the same ingredients. Newton called
water a salt. In the next century Boerhaave defined salts as
soluble in water, fusible, and sapid; the vitriols he excepted, as
being semimetals. “Bergmann and Kirwan depended especially
upon taste and solubility in a certain proportion of water.

Rouelle (whose example was followed by Trommsdorf and La-
voisier) regarded a salt as a compound of an acid and a base.
But, as analytical knowledge advanced, it was found that the
definition required to be amended in order to include sodic chlo-
ride and its analogues; and accordingly we find Berzelius, in the
year 1825, arranging a new and matured classification of salts, and
specifying electrochemical indifference as the appropriate idea to be
connected with them. Gerhardt defined a salt as a binomial
(‘corps binome”’), prone to double decomposition ; and Griffin
understood by it ‘a compound of two radicals.”

The idea represented by the term Base is much older than the
word. Thus, in Lemery’s conception of a salt, it 1s the alkali
which comes first, and is “cloyed or filled with acid.” Stahl
also, referring to the substance which, in common salt, he sup-
posed to be united with hydric chloride, calls it “ materia illa
quee sali corpus preebet.”” Duhamel, Rouelle, and others in the
last century used the name base to express “that which gives a
concrete or solid form” to a salt. In this century it has been
chiefly used to signify an oxidized body, having properties com-
plementary to an acid; at present it stands in a generic relation
to the word alkali.

Dynamical Ideas in Chemistry. 4.65

In the year 1809 Avogadro published a most remarkable me-
moir, entitled “ Idées sur l’Acidité et ’Alkalinité”*, which ap-
pears to have hitherto almost escaped the attention of chemists ;
yet it embraces, with marvellous skill and simplicity, the whole
of this interesting question. After pointing out the well-known
difficulties which stood in the way of the oxygen theory of acids,
he shows that the idea of acidity involves two factors—namely, an
antagonist force (reciprocated by alkalies), and a great tendency
to unite with bodies in general. The latter seems to depend
chiefly on a certain state of aggregation, which may either allow
full play to the former or almost entirely prevent its action ;
hence this state of aggregation is not a cause, but the condition
of acidity. ‘Such being the case, all the phenomena are easily
explained if we consider acid and alkaline antagonism as purely
relative properties, only becoming somewhat absolute when re-
ferred to a middle term fixed arbitrarily in the scale of acidity
and alkalinity ; so that the same substance A which, with refer-
ence to B, has the acid antagonism, may possess the alkaline
antagonism with reference toa third substance, C; whence what
we term absolutely acids and alkalies are merely bodies which
have the acid or alkaline antagonism in respect of certain others
whose position in the scale is approximately indicated by certain
properties, such as inability to affect vegetable blues, though
their state of aggregation be suitable for the purpose.” The
degree of acidity or alkalinity of a compound depends on the
degree of those properties in its constituents. Thus considered,
“of two substances in the act of combination, one always plays the
part of acid and the other of alkali; and it is this antagonism
which constitutes tendency to combination, or AF¥INITY properly
so called.”

Bodies might thus be arranged in a series, the position of each
marking its true affinity to any successor. Oxygen and sulphur
would probably come first, and the neutral salts in the middle ;
while hydrogen, carbon, and the like would occupy the other
extremity. The measure of chemical antagonism is electric he-
terogeneousness ; its appropriate name is oxygenicityt. Oxygen
is the most oxygenic of bodies; and a substance is evidently
more oxygenic the less it is oxidizable. Avogadro concludes by
recommending (as Professor Foster did subsequently) the disuse
of the word acid, on account of its representing, as commonly
received, a merely accidental property. It will suffice, he
thinks, to employ the nomenclature of oxides (e. g. higher or

* Journ. de Phys. p. 142 et seq.

+ Llectricity and electric are obviously the pattern words for oxygenicity
and oxygenic. Avogadro seems to have proposed the latter on account of
their reference to chemistry.

466 Dr. E. J. Mills on Statical and

lower oxide) or salts as a case may require. These views, it may be
added, were fully retamed by their author when (two years later)
he wrote his celebrated ‘ Essai.’

3. The preceding historical survey is sufficient to show that
some of the inadvertencies of chemical thinking have been for
hundreds of years precisely the same as those of ordinary think-
ing, and consequently abundantly exemplified in our daily life.
In our habitual (and for the most part uncritical) mood the mind
is 1n a fixed attitude, and its object 1s a sedentary image ; it re-—
sembles a mirror in an unoccupied apartment. If not purely
receptive, it either postpones inquiry, or soon bounds that in-
quiry with the kind of limit that is known as belief. In this
manner statical ideas arise. On the other hand, a mind in which
every event is criticised on its occurrence, by the sum total of its
predecessors, can only evolve dynamical ideas. Doubt is the
popular representation of such a condition. Now neither of these
states 1s ever exclusively realized; but history and common ex-
perience show that, of the two, the former accurately describes
the greater part of our intellectual existence, the latter designates
its occasional or unsystematic life. Nevertheless it is this which
it is advantageous to make uniform; the abandonment of sta-
tical ideas necessarily follows from the criterion of motion.

Acid, alkah, and salt have had, it appears, very varying but
kindred significations. They all at first were names for one con-
crete substance respectively. They were all at times generically
used for bodies whose properties were explained by universals ;
of which the ‘universal acid” of Stahl, the “acidum pingue ”
of Meyer, and the “igneous particles ” of Lemery are examples,
and from which the “acidifying principle” of Lavoisier only
differed by being isolated, These universals were supposed really
to exist im bodies and to constitute part of them. The finest
conception of this kind was the primitive acid of Stahl, supposed
to be common to acids, alkalies, and salts; few men have so
closely approached a dynamical theory as he did and yet failed
to reach it.

Tachenius was undoubtedly the first to give a clear statement
of the dualistic doctrine respecting salts. But if, as Freind as-
serted, his doctrine led to this result, namely, that acids and
alkalies have only a relative existence, Tachenius deserves a
nobler monumené than obscurity ; for he must be credited with
one of the first dynamical theories in chemistry. The transition
from this to certain later views is easy. Davy’s experiments in
electrolysis suggested to Avogrado the idea of a chemical force
polar at the moment of action, and presiding not onty over the
union of acid with alkali, but over every chemical change. Ber-
zelius afterwards announced that salts are electrochemically in-

Dynamical Ideas in Chemistry. 467

different ; and Laurent, Graham, and Brodie have successively
contributed (each from his own point of view) to the furtherance
of the idea of polarity.

One result of these dynamical doctrines has been, that we have
now current among us a tolerably pure idea of a salt—as a sub-
stance prone to double decomposition. The term base (now
including the ancient alkali) is admitted on all sides to in-
volve an idea complementary to that of acid.. This last word is
still under discussion. According to the prevailing definition,
an acid is a salt of hydrogen ; according to Professor Williamson
it is what was called by Gerhardt an anhydride. Neither of
these is in accordance with the criterion; for they both agree in
calling acid something particular. Now if we really mean to
assign to acids properties which are opposite to those of bases, it
follows that hydric sulphate and hydric acetate are, with sul-
phurie teroxide and diacetylic oxide, equally acids. Thus, in
the equations

KHO + H? S04 = KH 80*+ H?0,

KHO +80? Sse
KHO+C?H40?. =KC? H®0?+ H?0,
KHO + (C? H? 0)?O= KC? H3 0?+ HC? H3 02,

the four bodies indicated are alike antagonistic to hydropotassic
oxide. Again, the reactions

As? 0?+-6HCl] =3 H?0+2 As Cl
and
As? 0?+ 2KHO= H? O-+ K? As O4

prove either (1) that arsenious oxide is both a base and an acid,
or (2) that hydric chloride and hydropotassic oxide are both acids
or both bases. Such are the contradictions which must neces-
sarily ensue as long as we attempt to carry out in practice a sta-
tical definition on a dynamical understanding.

The value of the idea of motion as a criterion in chemical
theory has, I trust, been indicated in the preceding paper. As
a criterion, however, it really has a far wider usefulness than I
have here assigned it; for it throws light into every branch of
knowledge. Several advanced problems (more especially in
ethics) yield remarkable results on its application, and | intend
to take an early opportunity of again referring to its efficacy.

[ 468 ]
LXV. Proceedings of Learned Societies. :

ROYAL SOCIETY.
[Continued from p. 394. ]

Jan 21, 1869.—John Peter Gassiot, Esq., Vice-President, in the
Chair.
HE following communication was read :—
“Qn the Thermal Resistance of Liquids.’ By Frederick
Guthrie.
_ The memoir of which the following is an abstract gives an account
of some experiments made by the author with the object of deter-
mining the laws according to which heat travels by conduction
through liquids.

After pointing out the importance of the subject, and briefly re-
capitulating the methods previously used and the results obtained
by other experimenters, the ‘‘ Diathermometer”’ is described.

This instrument, which may be employed for the examination
of the thermal resistance or conducting power of solids as well as
liquids, has the following form. A hollow brass cone, having a pla-
tinum base, is screwed with its apex downwards into a tripod stand
which rests upon adjusting screws. The apex of the cone is tu-
bular, and carries a cork, through which passes a vertical glass
tube graduated and dipping into water. The level of the water in
the tube is nearly as high as the apex of the cone. By means of
a micrometer screw, a second cone, exactly similar and equal to
the first, having its apex upwards, may be brought to any required
distance from the lower cone. The brass cones and their platinum
faces are highly polished, and the latter are cleaned by washing
successively with hot nitric acid, caustic soda, alcohol, and water.
The upper surface of the lower cone is brought into an exactly hori-
zontal position, and the upper cone is lowered to any required dis-
tance from it. ‘There is thus formed between the platinum faces
a cylindrical interval of known height or thickness, and diameter,
and having its opposite faces parallel and horizontal. This wall-less
chamber receives the liquid whose thermal resistance has to be mea-
sured. <A liquid, introduced by means of a strangulated pipette of
known capacity (equal, say, to the interstitial space when the cone-
faces are 1 millim. apart) between the cones, remains there by means
of its adhesion and cohesion. A description is given of the method
used to get a constant current of water of uniform and known tem-
perature to pass through the upper cone. When such a current
passes, the platinum face of the upper cone becomes heated; it
communicates its heat to the liquid in contact with it. The heat
passes downwards through the liquid, heats the upper surface of the
lower cone, expands the air therein, and depresses the level of the
water in the tube attached to the lower cone.

A description is given of the most prominent sources of error of
this instrument, and the means which were employed to eliminate
them. It is concluded, from direct experiments (1st by measuring

Prof. F. Guthrie on the Thermal Resistance of Liquids. 469

the time required for the production of the first heat-effect in the
lower cone, 2ndly by showing the smallness of the difference caused
by the introduction of athermanous disks), and from comparison
with recent results of Magnus, that the effect of radiation in all the
cases tried is negligible if not nothing.

By measuring resistance rather than conductivity, several sources
of experimental error are eliminated, If the two cones are brought
into actual contact, and water of a known temperature is led for a
given time through the upper cone, a certain thermal effect is pro-
duced in the lower one. _ If the cones be then separated, anda liquid

before be led for the same time as before through the upper cone,
a less thermal effect is produced. The difference between the two
effects is a measure of the resistance of the liquid. Resuits so ob-
tained have to be corrected for the varying pressure to which the air
in the lower cone is subjected as the water in the glass tube sinks.
To find the absolute results in thermal units, we have to take into
account the diameter of the surface of the lower cone, its capacity,
and the specific heat of the air which js in it.

(1) The connexion, in the instance of water, between the thickness
and the time required for the first heat-effect.

(2) The connexion between the temperature and the time required
for the first heat-effect. It is shown that hotter water conducts heat
better than ‘colder, and that the hotter the conducting-water the
greater is the difference in rate,

(3) The connexion between the entire quantity of heat passing in
a given time and the thickness and temperature of the conducting-
water.

(4) The effect of the solution of various salts in altering the
thermal resistance of water. Every salt tried was found, when dis-
solved in water, to increase its thermal resistance. The author sub-
mits that the effect of the dissolved salt is chiefly, perhaps wholly, due
to the displacement of a portion of the water by a substance having
greater resistance, and to the modification in the specific heat of the
liquid caused by the introduction of the salt.

(5) The resistance of the liquids in the following list was ex-
amined under precisely similar circumstances. The thickness was
in each case 1 millim. he initial temperature of the liquid was
20°°17 C., and the temperature-difference, AT, was 10°C. That is,
the platinum surface of the upper cone was maintained at 30°-17(.
The duration of the experiment in each case was 1/. The numbers
show the specific resistance under the above circumstances—that is,
the ratio between the quantities of heat arrested by the several
liquids and that arrested by water.

Phil. Mag. 8. 4. Vol. 87. No. 251. June 1869. 9 T

4.70 Royal Society :—

ee Specific red Specific
Lena eta ePnget segues!

MAGGI 55 cankico.ceewmtode ecuatemntee iL: Acetate of amyl, civwqssheceepenn 10-00
Glycerine | spay -es-e-cenedansenee ee 3° O4 | Amylamity . sncvaee seen uneeeaneee 10:14
Acetic acid (glacial) ............ 8°38 | Antylic-aleohol ce-cossscueeeeee 10:23
Acetone acs ee sss tnecanaecerece 8:51 | Oil of turpentine Site. eeeeeree 11°75
Oxalate of ethyl. .c..4.0 sssseees, 8:85 | Nitrate of butyl .......s.ses.c.c0- 11:87
Perm =O yep se seenseeseeaeee dees 88) | ~Chloroform:.s, cecesct-ge-eeaeeeeee 12°10
a WKc(0) dolly Sai eb scoe Tat abe or 9:08 | Bichloride of carbon ............ 12°92
Acetate of ebhiyl <...2.<5.%ss.ntere 9:08 | Mercury, amiyl<.ccceesasees tenn 12-92
INI ERODEN70) nen aeesee sens scceceeaee 9°86 | Bromide of ethylen ............ 13:16
Oxalate of amyl weeieeh. et 10°06 | Lodide of amyl") Pes aeetees 13:27
Butylic alcohol. s2si27. Ate. es 10-00 | Iodide of ethyl ......0.......0005 (?)

The more salient points of these results are pointed out, such as
the preeminently small resistance of water and of bodies containing
a large proportion of the elements of water (potential water), the
possible connexion of this fact with the results of Magnus concern-
ing the conductivity of hydrogen, the increased resistance accompa-
nying increased molecular complexity in the case of isotypic liquids
as exemplified by the alcohols and their derivatives, the great re-
sistance shown by the liquids containing halogens. The results ob-
tained by Tyndall in regard to relative diathermancy are shown to
be in accord with the author’s results concerning resistance. 4
highly diathermanous liquid invariably offers great resistance to
conducted heat. 'The relation between electrical and thermal resist-
ance in the case of liquids is also briefly discussed.

Jan. 28.—Lieut.-General Sabine, President, in the Chair.
The following communication was read:—

“On Hydrofluoric Acid.” By G. Gore, F.R.S.

A. Anhydrous Hydrofluoric Acid.

This paper contains a full description of the leading physical and
chemical properties of anhydrous hydrofluoric acid, and also an ac-
count of various properties of pure aqueous hydrofluoric acid. The
author obtained the anhydrous acid by heating dry double fluoride of
hydrogen and potassium to redness in a suitable platinum apparatus
(shown by a figure accompanying the paper), and states the conditions
under which it may be obtained in a state of purity.

The composition and purity of the anhydrous acid are shown and
carefully verified by various methods of analysis, both of the double
fluoride from which it was prepared and of the acid itself; and par-
ticulars are given of all the circumstances necessary to insure reliable
and accurate results. Nearly all the operations of preparing, puri-
fying, analyzing, and examining the properties of the acid were con-
ducted in vessels of platinum, with lutings of paraffin, sulphur, and
lampblack ; articles of transparent and colourless fluor-spar were also
employed in certain cases. Nearly all the manipulations with the
acid were effected while the vessels containing it were immersed in a
strong freezing-mixture of ice and crystallized chloride of calcium.

The pure anhydrous acid is a highly dangerous substance, and

Mr. G. Gore on Hydrofluorie Acid. 471

requires the most extreme degree of care in its manipulation. It is
a perfectly colourless and transparent liquid at 60° Fahr., very thin
and mobile, extremely volatile, and densely fuming in the air at or-
dinary temperatures, and absorbs water very greedily from the atmo-
sphere. It was perfectly retained in platinum bottles, the bottle
having a flanged mouth with a platinum plate secured with clamp-
screws, and a washer of paraffin.

A number of attempts were made, finally with success, to deter-
mine the molecular volume of the pure anhydrous acid in the gaseous
state, the acid in these cases being prepared by heating pure anhy-
drous fluoride of silver with hydrogen in a suitable platinum apparatus
over mercury. Particulars are given of the apparatus employed and
of the manipulation. The results obtained show that one volume of
hydrogen, in uniting with fluorine, produces not simply one volume
of gaseous product as it does when uniting with oxygen, but two
volumes, as in the case of its union with chlorine. The gaseous
acid transferred to glass vessels over mercury did not corrode the
glass, or render it dim in the slightest degree during several weeks,
provided that moisture was entirely absent.

The author concludes that the anhydrous acid he has obtained is
destitute of oxygen, not only from the various analyses and experi-
ments already referred to, but also, 1st, because the double fluoride
from which it was prepared, when fused and electrolyzed with pla-
tinum electrodes, evolved abundance of inflammable gas at the ca-
thode, but no gas at the anode, although oxides are by electrolysis
decomposed before fluorides; 2nd, because the electrolysis of the
acid with platinum electrodes yielded no odour of ozone, whereas
the aqueous acid of various degrees of strength evolved that odour
strongly ; and, 3rd, because the properties of the acid obtained from
hydrogen and fluoride of silver agree with those of the acid ob-
tained from the double salt. He considers also that the acid obtained
from pure fluor-spar and monohydrated sulphuric acid heated to-
gether in a platinum retort is free from oxygen and water.

The specific gravity of the anhydrous liquid acid was several times
determined, both in a specific-gravity bottle of platinum, and also by
means of a platinum float submerged and weighed in the acid. Con-
cordant and reliable results were obtained; the specific gravity found
was 0°9879 at 55° Fahr., that of distilled water being=1:000 at the
same temperature. |

The anhydrous acid was much more volatile than sulphuric ether.
Its boiling-point was carefully determined in a special apparatus of
platinum, and was found to be 67° Fahr. Not the slightest sign of
freezing occurred on cooling the acid to —30° Fahr. (= —34°5 C.);
and it is highly probable that its solidifying temperature is a ver
great many degrees below this. Its vapour-tension at 60° Fahr.
_ was also approximately determined, and was found to be =7°58 lbs.
per square inch. On loosening the lid of a bottle of the acid at
60° Fahr., the acid vapour is expelled in a jet like steam from a
boiler ; this, together with the low boiling-point, the extremely dan-
gerous and corrosive nature of the acid, and its great affinity for

212

472 Royal Society :—

water, illustrates the very great difficulty of manipulating with it and
retaining it in a pure state. Nevertheless, by the contrivances de-
scribed, and by placing the bottles in a cool cellar (never above a
temperature of 60° Fahr.), the author has succeeded in keeping the
liquid acid perfectly, without loss and unaltered, through the whole
of the recent hot summer.

The electrical relations of different metals &c. in the acid were
found to be as follows at 0° Fahr. :—zine, tin, lead, cadmium, in-
dium, magnesium, cobalt, aluminium, iron, nickel, bismuth, thallium,
copper, iridium, silver, gas-carbon, gold, platinum, palladium.

Numerous experiments were made of electrolyzing the anhydrous
acid with anodes of gas-carbon, carbon of lignum-vite and of many
other kinds of wood, of palladium, platinum, and gold. The gas-
carbon disintegrated rapidly ; all the kinds of charcoal flew to pieces
quickly ; and the anodes of palladium, platinum, and gold were cor-
roded without evolution of gas. The acid with a platinum anode con-
ducted electricity much more readily than pure water; but with one
of gold it scarcely conducted at all. ‘These electrolytic experiments
presented extreme difficulties, and were conducted in a platinum
apparatus (shown by a figure) specially devised for the purpose.
The particulars of the conditions and results obtained are described
in the paper. Various mixtures of the anhydrous acid with mono-
hydrated nitric acid, with sulphuric anhydride, and with monohy-
drated sulphuric acid were also electrolyzed by means of platinum
anodes, the particulars and results of which are also described.

To obtain an idea of the general chemical behaviour of the pure
anhydrous acid, numerous substances (generally anhydrous) were
immersed in separate portions of the acid in platinum cups, kept at
a low temperature (0° to —20° Fahr.). The acid had scarcely any
effect upon any of the metalloids or noble metals; and even the base
metals in a state of fine powder did not cause any evolution of hy-
drogen. Sodium and potassium behaved much the same as with
water. Nearly all the salts of the alkali and alkaline-earth metals
produced strong chemical action. Various anhydrides (specified)
dissolved freely. Strong aqueous hydrochloric acid produced active
effervescence. The alkalies and alkaline earths united strongly with
the acid. Peroxides gave no effect. Numerous oxides (specified)
produced strong chemical action, some of them dissolving. Some
nitrates were not chemically affected ; others (those of lead, barium,
and potassium) were decomposed. Fluorides generally were un-
changed; but those of the alkali metals and of thallium produced
different degrees of chemical action, those of ammonium, rubidium,
and potassium uniting powerfully. Numerous chlorides were also
unaffected, whilst those of phosphorus (the solid one only), antimony
(the perchloride), titanium, and of the alkaline-earth and alkali me-
tals, were decomposed with strong action, and generally with effer-
vescence. ‘The chlorates of potassium and sodium were also decom-
posed with evolution of chloric acid; the bromides of the alkaline-
earth and alkali metals behaved like their chlorides. Bromate of
potassium rapidly set free bromine. Numerous iodides were unaf-

Mr. G. Gore on Hydrofluoric Acid. 473

fected; but those of the alkaline-earth and alkali metals were strongly
decomposed, and iodine (in some cases only) set free. —The anhydrous
acid decomposed all carbonates with effervescence, and those of the
alkaline-earth and alkali metals with violent action. Borates of the
alkalies also produced very strong action. Silico-fluorides of the
alkali metals dissolved with effervescence. All sulphides, except
those of the alkaline-earth and alkali metals, exhibited no change ;
the latter evolved sulphuretted hydrogen violently. Bisulphite of so-
dium dissolved with effervescence. Sulphates were variously affected.
The acid chromates of the alkali metals dissolved with violent action
to blood-red liquids, with evolution of vapour of fluoride of chro-
mium. Cyanide of potassium was violently decomposed, and hydro-
cyanic acid set free. Numerous organic bodies (specified) were also
immersed in the acid; most of the solid ones were quickly disin-
tegrated. The acid mixed with pyroxylic spirit, ether, and alcohol,
but not with benzole; with spirit of turpentine it exploded, and
produced a blood-red liquid. Gutta percha, india-rubber, and
nearly all the gums and resins were rapidly disintegrated and ge-
nerally dissolved to red liquids. Spermaceti, stearic acid, and myrtle
wax were but little affected, and paraffin not at all. Sponge was
also but little changed. Gun-cotton, silk, paper, cotton-wool, calico,
gelatine, and parchment were instantly converted into glutinous
substances, and generally dissolved. The solution of gun-cotton
yielded an.inflammable film on evaporation to dryness. Pinewood
instantly blackened.

From the various physical and chemical properties of the anhydrous
acid, the author concludes that it lies between hydrochloric acid and
water, but is much more closely allied to the former than to the latter.
It is more readily liquefied than hydrochloric acid, but less readily
than steam; like hydrochloric acid it decomposes all carbonates ;
like water it unites powerfully with sulphuric and phosphoric anhy-
drides, with great evolution of heat. The fluorides of the alkali
metals unite violently with hydrofiuoric acid, as the oxides of those
metals unite with water; the hydrated fluorides of the alkali metals
also, like the hydrated fixed alkalies, have a strongly alkaline reac-
tion, and are capable of expelling ammonia from its salts. It may
be further remarked that the atomic number of fluorine lies between
that of oxygen and chlorine; and the atomic number of oxygen,
added to that of fluorine, nearly equals that of chlorine.

B. Aqueous Hydrofluoric Acid.

Under the head of the aqueous acid the author enumerates the
various impurities usually contained in the commercial acid, and
describes the modes he employed to detect and estimate them, and
to estimate the amount of HF in it. The process employed by
him for obtaining the aqueous acid in a very high degree of purity
from the commercial liquid, is also fully described. It consists es-
sentially in passing an excess of sulphuretted hydrogen through the
acid, then neutralizing the sulphuric and hydrofluosilicic acids pre-
sent by carbonate of potassium, decanting the liquid after subsidence

Ai7 4: Intelligence and Miscellaneous Articles.

of the precipitate, removing the excess of sulphuretted hydrogen by
carbonate of silver, distilling the filtered liquid in a leaden retort
with a condensing-tube of platinum, and, finally, rectifying.

The effect of cold upon the aqueous acid was briefly examined, the
result being that a comparatively small amount of hydrofluoric acid
lowers the freezing-point of water very considerably.

The chemico-electric series of metals &c. in acid of 10 per cent.
and in that of 30 per cent. were determined. In the latter case it
was as follows :—zinc, magnesium, aluminium, thallium, indium,
cadmium, tin, lead, silicon, iron, nickel, cobalt, antimony, bismuth,
mercury, silver, copper, arsenic, osmium, ruthenium, gas-carbon,
platinum, rhodium, palladium, tellurium, osmi-iridium, gold, iridium.
Magnesium was remarkably unacted upon in the aqueous acid. The
chemico-electric relation of the aqueous acid to other acids with pla-
tinum was also determined.

Various experiments of electrolysis of the aqueous acid of various
degrees of strength were made with anodes of platinum. Ozone
was evolved, and, with the stronger acid only, the anode was cor-
roded at the same time. Mixtures of the aqueous acid with nitric,
hydrochloric, sulphuric, selenious, and phosphoric acids were also
electrolyzed with a platinum anode, and the results are described.

LXVI. Intelhgence and Miscellaneous Articles.

ON THE VOLTAIC DEPORTMENT OF PALLADIUM.
BY J. C. FOGGENDORFF. ,

ji! his remarkable research on hydrogenium, Mr. Graham has shown,

among other things, that palladium when it takes up hydrogen
expands, and, when the hydrogen escapes, contracts apparently more
strongly than it had previously expanded. A palladium wire which
originally measured 609'144 millims., and by absorbing hydrogen
had become longer by 9°77 millims., after the hydrogen had been
expelled, was found to measure 599°444 millims., and had therefore
shortened to the extent of 9°7 millims.

Where no exact numerical determinations are required, both phe-
nomena may be very strikingly demonstrated if palladium is charged
with hydrogen by electrolysis, a very thin plate being used. I used
a plate which was 118 millims. long by 23 millims. broad, and only
1 millim. thick, placed at a distance of 8 millims. from a platinum
plate in dilute sulphuric acid.

If this be connected witha small Grove’s battery of two elements,
so that the palladium becomes charged with hydrogen, the following
is observed.

Even after afew minutes the palladium plate begins to bend away
from the platinum, and gradually becomes greatly curved. After
about a quarter of an hour this has reached its maximum. A cur-
vature then commences in the opposite direction, so that the plate
first becomes straight, and then curves towards the platinum, which

Intelligence and Miscellaneous Articles. 475

ina short time goes so far that the plates come into contact, by which
the electrolytic process, of course, is stopped.

These curvatures are obviously due to the fact that the sides of
the palladium plate are successively saturated with hydrogen, and
therefore expand, just as does a Breguet’s spiral by an alteration in
temperature.

Just as the expansion of palladium by absorbing hydrogen may be
rendered obvious by this experiment, so the contraction of the metal
by the escape of the gas may be shown even more strikingly.

For this purpose the palladium plate, after having attained the
maximum of its first curvature, is removed from the liquid, washed,
dried, and brought into a spirit-lamp flame. As soon as it is suffi-
ciently hot, it curves in the opposite direction with extreme rapi-
dity, and so much that it seems to be regularly rolled up.

In these contractions and expansions of the plate its other dimen-
sions also undergo change. When the process of charging a plate
with hydrogen, and afterwards expelling it by heat, has been fre-
quently repeated on the same plate, it can be distinctly seen that
it has not only become shorter, but also narrower and thicker.
After the process had been repeated six times my plate was 8 mil-
lims. shorter and 1°5 millim. narrower, but at the same time was
quite 0:1 millim. thicker. That dimension, therefore, which is com-
pressed by rolling expands, and the two others, by which the metal
is stretched, crumple up when the hydrogen is expelled. Graham
has already shown, by the decrease of its specific gravity, that a
palladium wire is thicker when it becomes shorter.

Jt may, in conclusion, be remarked that, although Graham and
Wurtz have not succeeded in preparing a hydride of palladium by
purely chemical processes, such a compound appears to be formed
by the electrolytic process; for the dilute sulphuric acid in which
this process is performed becomes of a brown colour, without be-
coming turbid or depositing anything. A solution of caustic pot-
ash or ammonia in which, according to an old observation of mine,
tellurium used as negative pole produces a beautiful and deep wine co-
loration, remains quite clear with palladium.—Poggendorff’s Annalen,
March 1869.

ELECTRICAL POLARITY AND INEQUALITY OF THE AMALGAMATED
ZINC ELECTRODES IN SULPHATE OF ZINC. BY E. PATRY.

In a series of experiments on the galvanic resistance of liquids,
in which I assisted Dr. Paalzow, polarization and galvanic ine-
quality of the so-called unpolarizable electrodes were met with as
sources of error. I was thereby led to examine this subject speci-
ally, in which I had the advantage of his counsel.

Unpolarizable electrodes are obtained by using amalgamated zine
and sulphate of zinc. When I used zinc and commercial zinc
vitriol, I found that the polarization and inequality were very di-
stinct as soon as the resistance of the circuit was not very great. [
observed that a number of gas-bubbles were liberated at the surface

476 Intelligence and Miscellaneous Articles.

of the electrodes; and a flame kindled these bubbles, which showed
that the gas in them was hydrogen. Assuming that free sulphuric
acid was present in the solution, I saturated it with carbonate of
zinc by adding this to the solution, which I kept boiling for two or
three hours. Thisis necessary; for experiment showed me that a sim-
ple addition has but a slight action. The filtered solution contained
sulphate of zinc, an extremely small quantity of carbonate of zinc,
and basic sulphate of zinc, which had been formed during the boil-
ing. This mixture gave a far smaller polarization.

I then compared the polarization and the inequality which occur
in ordinary sulphate of zinc and those which are exhibited by the
solution I had treated with carbonate of zinc, and measured these
various values.

I took for this purpose glass troughs 80 millims. in length, 30
millims. in breadth and in height. The zinc electrodes measured
75 by 18 millims. By means of a tongue on the zinc plate the con-
ducting-wire could be fastened outside the liquid.

By means of a commutator this trough could be inserted in a cir-
cuit consisting of a mirror-galvanometer and of a Wheatstone’s
bridge. The same commutator placed the electrodes in connexion
when the apparatus was outside the circuit.

The resistance of the galvanometer was 694 Siemens’s units, that
of the trough only 3 to 4. The latter could be neglected as com-
pared with the former.

On the other hand, the Daniell’s element which fed the bridge
was provided with a rheostat of 162 units, by which the variations
in the battery (the resistance of which amounted to about 1 unit)
could be neglected. This rheostat and the position of the slider
were so arranged that the battery could only yield a hundredth of its
electromotive force.

Some preliminary experiments showed me that the battery was
sufficiently constant.

First experiment. Crude sulphate of zinc.—

The inequality gave the following numbers for the deflections of the
mirror :—

millims. minutes.

18 after 1
20) ae 4)
23 554 AO
155455 30)
12) Be QO
Lae 40
12:9 3,G0

The number 12 may be regarded as constant after the lapse of a
certain time. We shall then further see how the electromotive force
may be deduced from this number.

Polarization.—The current passed first through the trough, and
then directly gave, first, the force of the current minus the polari-
zation and, according to the direction, plus or minus the inequality ;
secondly, the current alone.

Intelligence and Miscellaneous Articles. 477

Let C be the current, P the polarization, and I the inequality ;
the current gave the following results :—

millims.
C—P—I=—498
C=519}. (1)
therefore P-I= 21
The current sent in the other direction,
C—P+I1=487
C=484 |. (2)
I—P= 38
Combining (1) and (2) we obtain
millims.
Eneqiaalityi: sic 208 12
Palarization...o2y.' 220): 9

These experiments thus confirm the result found above for the
inequality.
Second experiment. Sulphate of zinc treated with carbonate of zinc.
—I gives very quickly
I=3 millims. = constant ;
upon this the current passed

C—P+I=462,
C=459.
In the opposite direction,
C—P—I=466,
C=469,
from which
I=3, P=0.

Calculation of the electromotive force resulting from the inequality,
and of that from the polarization of the electrodes.

We have acircuit in which three electromotive forces may be in-
troduced. ‘They are proportional to the deflection produced by each
of them. If 500 millims. is the mean deflection produced by the
hundredth of the battery, the electromotive force corresponding to one
millimetre will be 0°00002.

We conclude from this that the electromotive force arising from
the inequality is, in the case of the first solution,

0:00024 of a Daniell’s cell,

and with the second solution

0:00006.
_ The electromotive force resulting from the polarization is in the first
Cape 0:00018,

and in the second case null.
The same method, applied to sulphuric acid of 1:08 at 27° C. and
to amalgamated zinc electrodes, gives

I1=25 millims. and C=15 millims.

478 Intelligence and Miscellaneous Articles.

Since the battery produces a deflection of 480 millims., the elec-

tromotive forces are
95

Sy 2 eo onose:
48000

Sonoma:
48000

We thus see that, using amalgamated zinc electrodes, sulphate of
zine gives considerable inequality and polarization if it contains free
sulphuric acid and the resistances are small, but that the former is
reduced to a quarter and the latter to zero if the free acid is neutra-
lized with carbonate of zinc.—Arch. des Scienc. Phys. et Nat. Nov.
1868.

ON A DEVELOPMENT OF HEAT WHICH ACCOMPANIES THE
BURSTING OF THE PRINCE RUPERT’S DROPS. BY M. DUFOUR.

The bursting of a Prince Rupert’s drop is accompanied by a vio-
lent projection of the substance of the glass. A molecular repul-
sion seems to be produced in the interior of the body, which is strong
enough to impart to the separating particles a great velocity. At
the moment of explosion there is a considerable development of vis
viva, quite out of proportion to the feeble mechanical effort consumed
in bursting the point. From the latter point of view, the Rupert’s
drops suggest a problem concerning the mechanical theory of heat ;
and it is natural to inquire whether the work which accompanies
this explosion is not accompanied by calorific phenomena.

At first sight it would seem as if there were some analogy be-
tween the separation of the vitreous particles in a bursting drop
and the sudden dilatation of a gas which expands after compression.
The small amount of work which consists in opening a stopcock
renders possible a considerable amount of work in the expanding
gas, just as the small effort necessary to break the point of a tear
gives rise to the reduction to powder and the projection of a large
mass of glass. Yet between these facts, the analogy of which I
point out, there are so many differences of an essential character,
that we cannot predict whether the explosion of the Rupert’s drops
is accompanied by thermal phenomena like those which accompany
the expansion of a gas.

This thermomechanical problem, which is difficult to discuss
a priori, appeared important enough to merit some investigation ;
and I have endeavoured to ascertain whether the. explosion is ac-
companied by a change in temperature of the substance of the
glass.

In a first series of experiments a thermo-electric apparatus was
used, to ascertain whether there was any difference of temperature
between the drops and the powder they produce. All the results
agreed, and showed a heating of the substance of the glass; the
method employed did not enable me to measure with accuracy the
increase of temperature, which, moreover, was very slight.

In a second series of experiments the drops were broken in a small
brass vessel containing oil of turpentine, which received the powder

Intelligence and Miscellaneous Articles. 479

after explosion. ‘The usual precautions were taken to avoid the
influence of the surrounding temperature, and to measure the quan-
tity of heat produced in the vessel*. The observations, properly
calculated, have shown that the powder had always a temperature
higher by 0°°18 to 0°°45 than that of the drops before the explo-
sion. By this method it was impossible to avoid a very violent
agitation of the liquid, produced by the contact of the bursting tears ;
the results thus obtained are therefore liable to important errors.

In a third series of experiments the drops were placed in a sort
of truncated cone of cardboard, the axis of which was almost verti-
cal; the base of the cone was uppermost, and was closed by a sheet
of caoutchouc. ‘The points just projected through this sheet far
enough to be seized with a pair of nippers and broken. The vitre-
ous powder fell into avery thin cylinder of brass, suitably placed
below the cone, and containing some grammes of oil of turpentine.
The temperature of the drops before bursting was observed, as well
as that of the turpentine before and after the fall of the powdered
glass. ‘The apparatus was protected, of course, against the effects
of the surrounding temperature; and the observations were calcu-
lated so as to furnish the difference between the temperature of the
fragments of glass and that of the drops which produced them. All
the results indicate an increase in the temperature of the glass on its
bursting ; the results, which are in better agreement than those of
the preceding series, are comprised between 0°°26 and 0°35.
Control experiments were made with the view of proving that the in-
crease of temperature could not be due either to the mere fall of the
glass into the oil, or to some capillary action between the liquid and
the powder of the solid.

All the experiments made authorize the following conclusions :—

(1) At the time of the explosion of the drops the glass powder
which is produced has a higher temperature than that of the drops
themselves at the time of the explosion.

(2) A series of six experiments (third method) made with eighteen
drops having a mean weight of 4°8 grms. indicated a mean eXcess
of 0°30.

This heating probably derives its origin from the molecular
motion which accompanies an explosion; and | think it can be
brought into connexion with the phenomena produced when metallic
wires, having been elongated (without exceeding the limit of elasti-
city), suddenly resume their original length. Mr. Joule has shown+
that wires become cooler when drawn out, and then heat again when
they resume their original volume. In a recent memoir{ M. Edlund
has published similar results, obtained by drawing out wires of dif-
ferent metals, and then allowing them to cool.

* The details of these experiments will be found in a memoir in an early
Number of the Archives des Sciences Physiques et Naturelles de Geneve.

+ Phil. Trans. for 1858. Phil. Mag. vol. xv. p. 538.

t Ann. de Chim. et de Phys. vol. Ixiv., and Pogg. Ann. 1865. Sir W.
Thomson has given a formula, deduced from the mechanical theory of heat,
by which these variations of temperature may be calculated.

480 Intelligence and Miscellaneous Articles.

In the preparation of a Rupert’s drop the sudden cooling solidi-
fies the external coating of the glass while the interior is still liquid.
This layer surrounds, therefore, a volume greater than the volume of
the cooled glass will occupy. During cooling, the internal mass is
connected by adherence to the outside layer already formed. ‘The
glass cannot, therefore, undergo its normal contraction ; it undergoes
a traction which tends to keep its volume larger, and its condition
must greatly resemble that of a metallic bar elongated by an ex-
ternal effort. A Rupert’s drop may be regarded as a rigid en-
velope, inside which bars raised to a high temperature have been
fixed to the sides, these bars being in considerable numbers, inter-
lacing one another, and connected by countless solderings. During
cooling, all these bars in contracting would undergo a traction on the
part of the rigid envelope, they would be drawn out; and the whole
system would be ina condition of unstable equilibrium. In a Rupert’s
drop the infinitely small and infinitely numerous particles of the
glass play the part of the bars in question, and they contract at the
moment of breaking. The contraction of these particles, like that
of the metal wires in the experiments of Messrs. Joule and Edlund,
is accompanied by very small molecular displacements, to which a
state of repose quickly succeeds. Vis viva disappears, and it is to be
expected that at the same time a certain quantity of heat will ap-
pear. This is doubtless the origin of the heat observed in the expe-
riments above described.

But the return to the condition of stable equilibrium in a Rupert’s
drop is accompanied by this remarkable and sudden projection of the
particles of glass, which gives the phenomenon the appearance of an
explosion. ‘This is a very curious phenomenon, and one difficult to
explain in a satisfactory manner. It may perhaps arise from parti-
cles of glass only attaining their volume and their form of stable
equilibrium after some oscillations resembling those which a spring
performs when suddenly let go. When an elastic body is in vibra-
tion, it impels with more or less velocity foreign bodies in contact
with it. If the spring itself is moveable and it strikes against fixed
bodies, the reaction will send it in the opposite direction. If a
considerable number of small elastic fragments undergo vibrations
and are, moreover, in contact, they strike against and mutually
repel each other. Ina Rupert’s drop it may be supposed that at
the time of rupture the particles of glass, till then drawn out, vi-
brate also for a short time before attaining their position of stable
equilibrium. The mutual shocks which are thus produced are per-
haps the cause of the remarkable projection suffered by the débris
of an exploded drop.

Moreover, whatever may be the immediate cause of this projection,
it is probable that the motion thus produced in the glass consumes a
portion of the internal heat, a fraction of which is partially regenerated
in the fragments when they are stopped by external resistances.—
Comptes Rendus, February 15, 1869.

481

INDEX to VOL. XX XVII.

AFFINITY, observations on, 81.

ee the absorption of light by the,
293:

Air-pump, on a metallic conductor to
replace the vulcanite tube used
with Bianchi’s, 442.

Aneroid barometers, experiments on,

5

Babingtonite, analysis of, 328.

Baker (W.) on the cause of a pink
colour in white-lead corrosions,
344,

Ball (Prof. R.) on lecture experiments
to illustrate the laws of motion,
332.

Bayma (Prof. J.) on the fundamental
principles of molecular physics,
182, 275, 348, 431.

Bianchi’s air-pump, on a metallic con-
nector to replace the vulcanite tube
used with, 442.

Books, new:—Fownes’s Manual of
Elementary Chemistry, 62; Guth-
rie’s Elements of Heat and of Non-
metallic Chemistry, 65; Lockyer’s
Elementary Lessons in Astronomy,
141; Barft’s Introduction to Sci-
entific Chemistry, 304; Peacock’s
Evidences of vast Sinkings of Land
&c., 382; Peacock’s Steam as a
motive power in Karthquakes and
Volcanoes, 383.

Bronzes, on the production of a beau-
tiful patina on, 401.

Bunsen (Prof. R.) on the washing of
precipitates, 1.

Carbonic oxide, on the spectrum of,
214.

Carpmael (E.) on Tyndall’s cometary
theory, 403.

Carré (F.) on a friction and induc-
tion electrical machine, 160.

~ Chapman (E. T.) on the action of de-

paueineg agents on organic bodies,

Chemical compounds, on the magne-
tism of, 314.

constitution and its relation to

physical and physiological proper-

ties, on, 395.

Chemistry, on statical and dynamical
ideas in, 461 .

Circle, on a new continued fraction
applicable te the quadrature of the,
373.

Clausius (Prof. R.) on the new con-
ception of electrodynamic pheno-
mena suggested by Gauss, 440.

Coal-gas, on the spectrum of, 209.

Cometary matter, on the origin and
deportment of visible, 241,403,460.

Comets on some spectrum observa-
tions of, 456.

Copper salts, on the magnetism of,
315.

Croll (J.) on the physical cause of the
motion of glaciers, 201.

Crookes (W.) on the measurement
of the luminous intensity of light,
227

Croullebois (M.) on the dispersive
power of gases and vapours, 79.

Crum Brown (Dr. A.) on chemical
constitution, and its relation to
physical and physiological proper-
ties, 395.

Cyanides, on isomerism amongst the
organic, 22.

Daylight, on a method of measuring
the intensity of total, 74.

Delessite, analysis of, 269.

Deville (H. St.-Claire) on the tempe-
rature of flames, and its relations
with the pressure, 11].

Dewar (J.) on the motion of a palla-
dium plate during the formation of
hydrogenium, 424.

Diathermometer, description of a, 468.

Dissociation, observations on, 156.

Douglas (J. C.) on shadow-optome-
ters, 340.

Dufour (M.) on a development of
heat which accompanies the burst-
ting of Prince Rupert’s drops, 478.

Dumas (M.) on affinity, 81.

Edlund (E.) on the electromotive
force of the electric spark, 41.

Edmonds (R.) on extraordinary agi-
tations of the sea, 35.

Electric spark an electromotor, 4].

482

Electrical machine, on a friction and
induction, 160.

Electrodes, on the electrical polarity
and inequality of the amalgamated
zinc, in sulphate of zine, 475.

Electrodynamic phenomena, on the
new conception of, suggested by
Gauss, 445.

Electrophorus machine, on the quan-
tity of electricity produced by the,
expressed in absolute measure,

36.

Equation in differences of the second
order, on an, 225.

Ethylene-sodium, on the compounds
of, and of its homologues, 117, 175;
on some reactions of hydrated ox-
ide of, 358.

Flame of a Bunsen’s burner, on the
shape of the, 160.

Flames, on the temperature of, and
its relations with the pressure,
111; on the temperature of, and
dissociation, 156.

Fluid, on the uniform motion of an
imperfect, 370.

Forbes’s (D.) researches in British
mineralogy, 321.

Gases, on the dispersive power of,
75; on the spectra of the flames
of, containing carbon, 208 ; on the
spectra of certain, in Geissler’s
tubes, 405.

Gauss, on the new conception of
electrodynamic phenomena sug-
gested by, 445.

Geological Society, proceedings of
the, 145, 309.

time, and the probable date of
the glacial period, on, 206.

Gibbs (W. B.) on Tyndall’s cometary
theory, 404.

Glaciers, on the physical cause of the
motion of, 201, 229, 363.

Gold, analyses of native, 521.

Gore (G.) on hydrofluoric acid, 470.

Graham (T.) on the relation of hydro-
gen to palladium, 122.

Granites, on a comparison of the, of
Cornwall and Devon with those of
Leinster and Mourne, 306.

Guthrie (Prof. F.) on the thermal re-
sistance of liquids, 468.

Haidinger (W. von) on the luminous,
thermal, and acoustic phenomena
attending the fall of meteorites,
246.

Haughton (The Rey. 8.) on the gra-

“INDEX.

nites of Cornwall and Devon, Lein-
ster and Mourne, 306.

Heat, on the production of, by the
rotation of a disk in vacuum, 26,
97, 287; on a development of,
which accompanies the bursting of
Prince Rupert’s drops, 478.

Herschel (Lieut. J.) on the lightning-
spectrum, 142.

How (Prof.) cn the mineralogy of
Nova Scotia, 264.

Huggins (W.) on some spectrum ob-
servations of comets, 456.

Hydrofluorie acid, researches
470.

Hydrogen, on the spectra of, 405.

Hydrogenium, observations on, 122 ;
on the motion of a palladium plate
during the formation of, 424,474.

Kohlrausch (Prof. F.) on the quan-
tity of electricity produced by the
electrophorus machine, expressed
in absolute measure, 236.

LeConte (Prof. J.) on some pheno-
mena of binocular vision, 131.

L’Hote (M.) on the generation of
ozone in oxygen and in air under
the influence of the electric spark,

on,

Lielegg (Prof. A.) on the spectra of
the flames of gases containing car-
bon, 208.

Light, on the measurement of the
lumimous intensity of, 227 ; on the
absorption of, by the air, 293; on
the polarization of, by cloudy mat-
ter, 384.

Lightning-spectrum, on the, 142.

Lignite, analysis of, 265.

Liquid waves, on the interference of,
240.

Liquids, on some phenomena con-
nected with the boiling of, 161; on
the galvanic resistance of, 271; on
the thermal resistance of, 468.

Lissajous (M.) on the interference of
liquid waves, 240.

Lockyer (J. N.) on the spectrum of a
solar prominence, 43; on spectro-
scopic observations of the sun, 144.

Logarithmic waves, on two remark-
able resultants arising out of the
theory of rectifiable compound,
375.

Magnet, on a new form of permanent,
18

Magnetism of chemical compounds,
on the, 314,

INDEX.

Magneto-electric current, on a pro-
perty of the, 54.

Marcet (Dr. W.) on the falsetto or
head-sounds of the human voice,
289.

_ Marignac (Prof. C.) on the latent
heat of volatilization of sal-ammo-
niac, 318.

Metals, on a new method of estima-
ting minute traces of, 80.

Meteorites, on the luminous, thermal,
and acoustic phenomena attending
the fall of, 246.

Meyer (Dr. E.) on the heating of a
disk rotating in a vacuum, 26, 97,
287.

Mills (Dr. KE. J.) on statical and dy-
namical ideas in chemistry, 461.
Mineralogy of Nova Scotia, contribu-
tions to the, 264; researches in

British, 321.

Mirage in the English Channel, on a,
400.

Moon, on Hansen’s theory of the
physical constitution of the, 32.
Moon (R.) on the theory of sound,

189.

Moseley (Canon) on the mechanical
impossibility of the descent of gla-
ciers by their weight only, 229,363;
on the uniform motion of an im-
perfect fluid, 370.

Motion, lecture experiments to illus-
trate the laws of, 332.

Newcomb (S.) on Hansen’s theory of
the physical constitution of the
moon, 32.

Nitrogen, on the coloration of per-
oxide of, 312; on the spectra of,
422.

Norton (Prof. W. A.) on the funda-
mental principles of molecular phy-
sics, 98.

Olefiant gas, on the spectrum of,
Pal bee

Optometers, on shadow-, 340.

Organic bodies, on the action of de-
hydrating agents on, 20.

Oxalic ethers, on the action of chlo-

ride of zine on the, 25.

Oxygen, on the spectra of, 417.

Ozone, on the generation of, in oxy-
gen and in air under the influence
a the condensed electrical spark,

o:

Paalzow (Dr.) on the galvanic resist-

ance of liquids, 271. .

483

Paget (F. A.) on a new form of per-
manent magnet, 18.

Palladium, on the relation of hydro-
gen to, 122; on the voltaic deport-
ment of, 474.

Parnell (J.) on a mirage in the En-
glish Channel, 400.

Patry (E.) on the electrical polarity
and inequality of the amalgamated _
zinc electrodes in sulphate of zine,
475.

Peacock (R. A.) on geological time,
and the probable date of the gla-
cial period, 206.

Photometer, description of a new, 293.

Physics, on the fundamental princi-
ples of molecular, 98, 182, 275,348,
431.

Poggendorff (Prof.) on the voltaic
deportment of palladium, 474.

Poppe (A.) on the shape of the flame
of a Bunsen’s burner, 160.

Precipitates, on the washing of, 1.

Pyridine, on the artificial production
of, 20.

Royal Institution, proceedings of the,
395.

Royal Society, proceedings of the, 65,
141, 227, 306, 384, 468.

Rupert’s drops, on a development of
heat which accompanies the burst-
ing of, 478.

St.-Edme (M.) on the generation of
ozone in oxygen and in air under
we influence of the electric spark,
iJ.

Sal-ammoniac, on the latent heat of
volatilization of, 318.

Salet (M.) on the coloration of per-
oxide of nitrogen, 312.

Sea, on extraordinary agitations of
ae produced by winds or tides,

Silicoborocaleite, on a new locality
for, 270.

Sky, on the blue colour of the, 384.

Smith (M. H.) on the action of de-
esis agents on organic bodies,

Soret (L.) on the colour of the Lake
of Geneva, 345.

Sound, on the theory of, 189.

Spectra of the flames of gases contain-
ing carbon, on the, 208.

Spectrum, on the formation of an ar-
une with one Fraunhofer’s line,

484

Spectrum observations of comets, on

some, 456.

Stewart (B.) on certain experiments
on aneroid barometers, 65; on the
heating of a disk by rapid rotation
in vacuo, 97.

Sun, spectroscopic observations of the,
144.

Swan (Prof. W.) on a metallic con-
nector to replace the vulcanite tube
used with Bianchi’s air-pump, 442.

Sylvester (J.2J.) on an equation in
differences of the second order, 225.
on a new continued fraction appli-
cable to the quadrature of thecircle,
373; on two remarkable resultants
arising out of the theory of rectifi-
able compound logarithmic , waves,
375.

Tait (Prof. P. G.) on the heating of

a disk by rapid rotation in vacuo, 97.

Tidal action, on the secular effects of,
216.

Tomlinson (C.) on some phenomena
connected with the boiling of h-
quids, 161.

Turgite, analysis of, 268.

Tyndall (J.) on cometary theory, 241;
on the blue colour of the sky,
the polarization of skylight, and on
the polarization of light by cloudy
matter, 384.

Vapours, on the dispersive power of,

5

INDEX.

Vaughan (D.) on the secular effects
of tidal action, 216.

Vicaire (E.) on the temperature of
flames and dissociation, 156.

Vision, binocular, on some pheno-
mena of, 131.

Voice, on the falsetto or head-sounds
of the human, 289.

Wanklyn (Prof. J.) on a new method
of estimating minute traces of me-
tals, 80; on ethylate of sodium and
ethylate of potassium, 117; on the
compounds of ethylene-sodium and
of its homologues, 175; on some
reactions of hydrated oxide of ethy-
lene-sodium, 358.

Water, on the blue colour of, 345.

White-lead corrosions, on the cause
of a pink colour in, 344.

Wiedemann (Prof.) on the magnetism
of chemical compounds, 314.

Wild (H.) on the absorption of light
by the air, 293.

Wilde (H.) on a property of the mag-
neto-electric current, 54.

Wright (R. J.) on a method of mea-
suring the intensity of total day-
light, 74.

Willner (A.) on the formation of an
artificial spectrum with one Fraun-
hofer’s line, 235; on the spectra of
certain gases in Geissler’s tubes,
405.

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CONTENTS or N° 246.— Fourth Series.

I. On the Washing of Precipitates. By R. Bunsen. (With a
EEE) ge 2 RSIS ARIS oe oR TO oe A Oe cic ee Daa REM tee est 3 page 1
II. On a New Form of Permanent Magnet. By Freperickx A.
Paget, ©C.E., M. Soc. Civil Engineers of France; Corr. Mem. Franklin
Institute; M. late Government Commission on Chaincable- and Anchor-

preteen Pua MUSHMGRtS) 5 6) 20) es yee eo a wee aca wip eso evee aed 18
III. Action of Dehydrating Agents on Organic Bodies. By HE.
Turopsron Cuapman and Mizes H. Smita .........+.-..--.5-: 20
IV. On the Explanation of Stewart and Tait’s Experiments on the
Heating of a Disk rotating in a Vacuum. By Oscar Emin Meyer .. 26
V. On Hansen’s Theory of the Physical Constitution of the Moon.
Perio INE WCOMB Ss ofc ls cc bo os iote o Siwne'e Bled weg 2 Pies, oer 32
VI. On Extraordinary Agitations of the Sea not eae by Winds
or Tides. By RicHarp Epmonps, Esq. ......... . 35

VII. Experimental Proof that the Electric Spark is an Gta es
PEELED ee ey Ns cakk we Spec teeta ew nl toes 4]

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render Synchronous the Rotations of the Armatures of a number of
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Royat Society :—Mr. B. Stewarrt’s Account of certain Ex-
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On the Generation of Ozone in Oxygen and in Air under the in-
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OTSA at sake eR aks = 2 op ictal duere’skalere awe a0) aariee ek kes 80

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JOURNAL OF SCIENCE.

Being a Continuation of Tilloch’s ‘ Philosophical Magazine,’
Nicholson’s ‘Journal,’ and Thomson’s ‘ Annals of Philosophy.’ |

Cc
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4

oe

ae
CONDUCTED RY wie 34 ao

SIR ROBERT KANE, LL.D. F.R.S: M.R.LA. F.C.S.
AUGUSTUS MATTHIESSEN, Pu.D. F.R.S. F.C.S.

AND

WILLIAM FRANCIS, Pu.D. F.L.S. F.R.A.S. F.C.S.

FOURTH SERIES.

N° 247.— FEBRUARY 1869.

Printers and Publishers to the University of London.

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CoNTENTS.

I. On Polyzonal Curves, otherwise the Curves VU+V V4 &e. =0. By Pro-
fessor CAYLEY. Communicated by Professor Tait.

II. On the Motion, Equilibrium, and Forms of Liquid Films. By the late Sir
Davip Brewster, K.H., D.C.L., &c. (With two Plates.) Communicated by
Francis Deas, Esq., LL.B. |

III. On the Temperature of the Common Fowl (Gallus domesticus). By the late
Dr. Joun Davy, F.R.SS. Lond and Edinb. Communicated by Professor Allman.

IV. On the Burning Mirrors of Archimedes, with some Propositions relating to
the Concentration of Light produced by Reflectors of different forms. By JoHN
Scorr, Esq., Tain. (With a Plate.) Communicated by Professor Kelland.

¥V. On the Connexion between Chemical Constitution ‘and Physiological Action.
—Part. I. On the Physiological Action of the Salts of the Ammonium Bases,
derived from Strychnia, Brucia, Thebaia, Codeia, Morphia, and Nicotia. By
Dr. A. Crum Brown and Dr. THomas R. FRASER.

VI. On the Products of the Destructive Distillation of Animal Substances.
Part V. By Tuomas ANDERSON, Professor of Chemistry in the University of
Glasgow.

VII. On Vortex Motion. By Professor Sir W. THomson.

Edinburgh: R. Grantiand Son. London: Williams and Norgate.

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PROCEEDINGS OF THE METEOROLOGICAL SOCIETY.
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CoNnTENTS :—

On the Rainfall .of Cobham and Chiswick. By G. Dines, Esq.

On an exceptionally Heavy Rainfall in the Colony of Natal in August 1868.
By R. J. Mann, Esq., M.D.

November Meteors, 1868. By the Editor.

A Journal of Natural Appearances and Occurrences in Farming from 1808 to
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GEOLOGY.—KING’S COLLEGE, LONDON,

Prof. TENNANT, F.G.S., will commence a Course of LECTURES on GEO-
LOGY, on Friday, Jan. 22, at 9 a.m. They will be continued on each succeeding
Wednesday and Friday at the same hour. A shorter Course will be given on
Thursday Evenings from 8 to 9; First Lecture, Jan. 21. Text-book, Lyell’s
‘Blements of Geology.’ Prof. TENNANT accompanies his Students to the Public
Museums and to places of geological interest in the country. He gives private
Instruction in Mineralogy and Geology at his Residence, 149 Strand, W.C.

A Course of Lectures on PRACTICAL GEOLOGY. will be given at King’s
College, after Haster, having especial reference to the Application of the Science
to Engineering, Mining, Architecture, and Agriculture.

‘TO GEOLOGISTS AND MINERALOGISTS.
For Sale.

Two handsome Cabinets, measuring 9 feet 3 inches long, 2 feet 4 inches wide, and 3 feet
10 inches high; each containing 45 drawers, with a Glass Case on the top of each Cabinet,
4 feet 11 inches high, and 15 inches from back to front. One Cabinet is filled with
Minerals, the other with Fossils.

They are at present in a room at King’s College, which is required as an additional class-
room. Mr. TENNANT has received notice to remove them, and would like to dispose of
them at once. Any person wishing to become practically acquainted with the interesting
and important study of Mineralogy or Geology, or both, will find this a good opportunity to
obtain an instructive and valuable Museum.

The Collection contains upwards of two thousand specimens, many very select. The first

' Gold Nugget received from Australia, which was exhibited in the Exhibition of 1851, is in
the Collection, and cost £37; it contains about 8 ounces of gold. The specimens have
been frequently used to illustrate the Lectures on Mineralogy and Geology at King’s Col-
ege, and at the Royal Military Academy, Woolwich*. Price

TWO THOUSAND GUINEAS.
Mr. Tennant has other Collections, at one thousand, five hundred, one hundred, down to
Students’ Collections at twenty, ten, five, and two guineas each.
149 Strand, London, W.C., January 1869.
* Mr. TenNANT held the appointment of Lecturer on Geology and Mineralogy at Wool-
_ wich for seventeen years; 'the Lectures were discontinued in December 1867, Lectures on
| Military History being substituted.

DIAGRAMS TO ILLUSTRATE LECTURES ON GEOLOGY.
A Colotred Lithographic Print (size 34 by 28 inches) of B. WaTernousr Hawaus'’s,
_ELS.,&c., Restoration of the Exrincr Animats of the Drirr- and Cave-rertop. Price 12s.
Jusr pusuisuep, a Chart of the characteristic British Tertiary Fossils, stvatigraphically
arranged, containing 800 figures, compiled and engraved by J. W. Lowry. -Price, mounted
| on linen to fold in case, or mounted on rollers and varnished, 10s.
A New Chart of Fossiz Crustacea, illustrated by upwards of 490 Figures, and accom-
panied by a Descriptive Catalogue. Designed and drawn by J. W. Satren, F:G.S., and

H. Woopwarp, F.G.S. Engraved by J. W. Lowry, F.R.G.S. Price 10s. 6d.

Six DracRAMs or GENERIC ForRMS OF FoRAMINIFERA. Size, three feet by two feet.
Price 18s. for the Six Diagrams, either on paper or linen. They contain Eighty-two Figures.

Mr. Tuomas Hawkrns’s “Great Sra-Dracons.” Containing ’80 folio Plates (which
form good school diagrams) of the Remains of Ichthyosaurus ‘and Plesiosaurus from the Lias.
The Original Specimens are in the British Museum. Price 25s., published at £2 Ts.

SOPWITH’S GEOLOGICAL MODELS IN WOOD,
To illustrate the nature of Stratification; of Valleys of Denudation; Succession of Coal-
seats ‘in the Newcastle'Coal-field ; Strata of adjacent Lead-mine Districts; the effects pro-
duced ‘by Faults or Dislocations; Intersections of Mineral Veins, &c.3 accompanied with a
letterpress description, which -can be had-separately, price 1s. 6d., by T. Sopwarn, C.E. &c.
Sold in Case, bound and lettered to resemble a large folio volume.

Twelve Models, 4 inches square...........- £5 0

—"Te

A Catalogue of 2000 of the most common Fossils found in the British Isles, being a list
-of those in the private collection of J. TENNANT, F.G.S. Price 2s.

A descriptive List of Fuint Imptemenrs found at St. Mary Bourne ; with Illustrations of
the principal types. By Joserpn Stevens, Memb. Roy. Coll. Physicians, Lond.'&c. Price 2s.

All the recent Works relating to Mineralogy, Geology, Cunchology, and Chemistry ; also
Geological Maps, Models, Diagrams, Hammers, Blowpipes, Magnifying Glasses, Platina
Spoons, Electrometer and Magnetic Needle, Glass-top Boxes, Microscopic Objects, Brass
and Steel Forceps, Acid Bottles, &c., can be supplied to the Student in these interest.ng
ranches of Science by

Se ee a oa ee kn er mer 8 ag aM Mane CAT OS

CONTENTS or N° 247.—Fourth Series.

XII. Remarks on Affinity. By M. Dumas .............. page

XIII. On the Heating of a Disk by rapid rotation in vacuo. By
Messrs. B. Stewart and P.G. Tair. .0. a 22

XIV. Fundamental Principles of Molecular Physics. By Professor
WA. NORTON Oo es Seine Code ee

XV. On the Temperature of Flames, and its relations with the
Pressure. By M. H.S7.-Crarre Devirue® 2 ee

XVI. On Ethylate of Sodium and Ethylate of Potassium.—Part. I.
By J. Atrrep Wank Lyn, Professor of Chemistry in the London In-
SLILHTION (Ls ee oe Ce eles oe eee oe eae cae

XVII. On the Relation of Hydrogen to Palladium. fe THOMAS
Grauam, F.R.S., Master of the Mint :

XVIII. On some Phenomena of Binocular Vision. By . JOSEPH
LeConre, Professor of See and neaetie in the ene of
South Carolina. . z

XIX. Notices ening New Books:—Mr. J. N. Locxyer’s
‘Elementary Lessons in Astronomy’............. Sigs ie aaa.

XX. Proceedings of Learned Societies :—

Royat Sociery:+—Lieut. J. Herscuer on the Lightning Spec-
trum; Mr. J. N. Lockyer on the Spectrum of a Solar Pro-
minence; and Spectroscopic Observations of the Sun .. 141

GroLocicaL Society :—Dr. J. Scumipt on the Eruption of the
Kaimeni of Santorin; Mr.J. Prestwics on the Structure of the
Crag-beds of Norfolk and Suffolk; Mr. J. THomson on some
genera of Carboniferous Corals; Mr. 8. V. Woop, Jun., on
the Pebble-beds of Middlesex, Essex, and Herts; Mr. W.
Torey on the Cretaceous Rocks of the Bas-Boulonnais ;
Mr. R. B. Foote on the Distribution of Stone Implements in
Southern India; Sir Puitip pe M. Grey Ecerton on some
new fossil Fish from the Lias of Lyme Regis; Mr. J. W.
SALTER on a true Coal-plant from Sinai, and on some Fossils
from the Menevian Group; Mr. W. B. Dawkxrns on a new
Species of Fossil Deer from Clacton and the Norwich Crag ;
Mr. E. R. Lanxester on the remains of Pteraspidian Fishes

in Devonshire and Cornwall ©. 2230. 0. So ee ee

XXI. Intelligence and Miscellaneous Ancee. =
On the Temperature of Flames and Dissociation, by E. Vicaire.
On a Friction and Induction Electrical Machine, by E. Carré, .
On the Shape of the Flame of a Bunsen’s Burner, by A. Poppe .

81
97
98

111

117

122

13]

14]

—145

156

156%

160
160

** It is requested that all Communications for this Work may be addressed, —
post-paid, to the Care of Messrs. Taylor and Francis, Printing Office, Red —

Lion Court, Fleet Street, London.

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ee SOMARCH ise), No. cae,

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eS = meee

2 LONDON, EDINBURGH, AND DUBLIN

| PHILOSOPHICAL MAGAZINE,
| - AND

JOURNAL OF SCIENCE.

Being a Continuation of Tilloch’s « Philosophical Magazine,’
Nicholson’s ‘Journal,’ and Thomson’s « Annals of Philosophy.’

—_—_——____

CONDUCTED RY

SIR ROBERT KANE, LL.D. F.R.S. M.R.I.A. F.C.S.
AUGUSTUS MATTHIESSEN, Pu.D. F.R.S. F.C.S.

AND

WILLIAM FRANCIS, Pu.D. F.L.S. F.R.AS. F.C.S.
re ee eee eet ee oe a
FOURTH SERIES.

N° 248.—M ARCH 1869.

lc foaee aare e

LONDON:

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Dublin :—and Putnam, New York,

Now ready, in post 8vo, with 86 Diagrams, price 7s. 6d.

THE THEORY OF OCULAR DEFECTS AND OF SPECTACLES.

Translated from the German of Dr. HERMANN SCHEFFLER by ROBERT
BRUDENELL CARTER, F.R.C.S. (Exam.), Fellow of the Royal Medical
and Chirurgical Society, Consulting Surgeon to the Gloucestershire —
Eye Institution.

With Prefatory Notes and a Chapter of Practical Instructions.

London: Longmans, Green, and Co., Paternoster Row.

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to February lst, 1869.

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392 pp. 8vo, 15s.,
THE MECHANICAL THEORY OF HEAT,
With its APPLICATIONS to the STEAM-ENGINE and to the PHYSICAL —
PROPERTIES OF BODIES.

By R. CLAUSIUS,
Professor of Physics in the University of Zurich.

Edited by T. ARcuER Hirst, F.R.S.,
Professor of Mathematics in University College, London.

With an Introduction by Professor TyNDALL.

First English Edition. Post 8vo, cloth, 10s. 6d.
A MANUAL OF INORGANIC CHEMISTRY.

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ADVERTISEMENTS continued on 3rd page of Cover.

I
ne’

GEOGRAPHERS and TOURISTS derive additional pleasure in their rambles

| pts acquainted with Minrrats, Rocks, and Fosstns. Mr. TENNANT,
e

Sele

ologist, 149 Strand, London, has had thirty years’ experience in giving PRAC-
TICAL INSTRUCTION to Ladies and Gentlemen; and from his extensive Col-

tection, comprising many thousand specimens, persons are enabled in a dozen or

twenty lessons to acquire sufficient knowledge to identify all the ordinary compo-
nents of crystalline and volcanic rocks, and most of the minerals and metals used
in the Arts.

A Course of Lectures on PRACTICAL GEOLOGY will be given at King’s
College, after Waster, having especial reference to the Application of the Science

to Engineering, Mining, Architecture, and Agriculture.

; .

TO GEOLOGISTS AND MINERALOGISTS.
For Sale.
Two handsome Cabinets, measuring 9 feet 3 inches long, 2 feet 4 inches wide, and 3 feet
10 inches high; each containing 45 drawers, with a Glass Case on the top of each Cabinet,
4 feet 11 inches high, and 15 inches from back to front. One Cabinet is filled with

. Minerals, the other with Fossils.

They are at preseut in a room at King’s College, which is required as an additional class-
room. Mr. Tennant has received notice to remove them, and would like to dispose of
them at once. Any person wishing to become practically acquainted with the interesting
and important study of Mineralogy or Geology, or both, will find thisa good opportunity to
obtain an instructive and valuable Museum.

The Collection contains upwards of two thousand specimens, many very select. The first
Gold Nugget received from Australia, which was exhibited -in the Exhibition of 185], is in
the Collection, and cost £37; it contains about 8 ounces of gold. The specimens have
been frequently used to illustrate the Lectures on Mineralogy and Geology at King’s Col-
lege, and at the Royal Military Academy, Woolwich*. Price

TWO THOUSAND GUINEAS.
Mr. Tennant has other Collections, at one thousand, five hundred, one hundred, down to
Students’ Collections at twenty, ten, five, and two guineas each.
* Mr. Tennant held the appointment of Lecturer on Geology and Mineralogy at Wool-
wich for seventeen years; the Lectures were discontinued in December 1867, Lectures on

Military History being substituted.

DIAGRAMS TO ILLUSTRATE LECTURES ON GEOLOGY.
A CoJoured Lithographic Print (size 34 by 28 inches) of B. Warernovsz Hawkns’s,

_F.LS.,&c., Resroration of the Extrncr AntmAts of the Drirr- and CAvE-rERIOD. Price 12s,

iy

Just PuBLISHED, a Chart of the characteristic British Tertiary Fossils, stratigraphically

_ arranged, containing 800 figures, compiled and engraved by J. W. Lowry. Price, mounted
on linen to fold in case, or mounted on rollers and varnished, 10s.

A New Chart of Fossir Crustacea, illustrated by upwards of 490 Figures, and accom-

panied by a Descriptive Catalogne. Designed and drawn by J. W. Satrer, F.G.S., and

H. Woopwarp, F.G.S._ Engraved by J. W. Lowry, F.R.G.S. Price 10s. 6d.
Six Diacrams or Generic Forms or ForRAMINIFERA. Size, three feet by two feet.

Price 18s. for the Six Diagrams, either on paper or linen. They contain Eighty-two Figures.

Mr. Taomas Hawkxrns’s “ Great Sea-Dracons.” Containing 80 folio Plates (which
form good school diagrams) of the Remains of Ichthyosaurus and Plesiosaurus from the Lias.
The Original Specimens are in the British Museum. Price 25s., published at £2 10s.

SOPWITH’S GEOLOGICAL MODELS IN WOOD,
To illustrate the nature of Stratification; of Valleys of Denudation; Succession of Coal-
seams in the Newcastle Coal-field; Strata of adjacent Lead-mine Districts; the effects pro-
duced by Faults or Dislocations; Intersections of Mineral Veins, &c.; accompanied with a

letterpress description, which can be had separately, price ls. 6d., by T. Sorwirn, C.E. &c.

Sold in Case, bound and lettered to resemble a large folio volume.
Twelve Models, 4 inches PHAROS el, PA: £5 0

: Se LER APE Shree ae

A Catalogue of 2000 of the most common Fossils found in the British Isles, being a list
of those in the private collection of J. TENNANT, F.G.S. Price 2s,

A descriptive List of FLint ImpitemeEnts found at St. Mary Bourne; with Illustrations of
he principal types. By JoserpH Stevens, Memb. Roy. Coll. Physicians, Lond. &c. Price 2s.
; All the recent Works relating to Mineralogy, Geology, Conchology, and Chemistry ; also

eological Maps, Models, Diagrams, Hammers, Blowpipes, Magnifying Glasses, Platina
poons, Electrometer and Magnetic Needle, Glass-top Boxes, Microscopic Objects, Brass
nd Steel Forceps, Acid Bottles, &c., can be supplied to the Student in these interesting
ranches of Science by

JAiM&S TENNANT, Mineralogist to Her Majesty, 149 Strand, W.c.
March 1869.

CONTENTS or N® 948,—Fourth Series.

XXII. Historical Notes on some Phenomena connected with the .
‘Boiling of Liquids. By Cuarzes Tomurnson, F.R.S..-..-++- yage 161

XXIII. On the Compounds of Ethylene-sodium and of its Homo-
logues. By J. AnFRep Wawnxuyn, Professor of Chemistry in the .
London Institution ......--+:-- wale clucisie t'00 5 bake olen) site iam 175

XXIV. Fundamental Principles of Molecular Physics. By Pro-

fessor J. Bara, S.J., of Stonyhurst College ...---- vere eeress 182
XXV. On the Theory of Sound. By R. Moon, M.A., Honorary
Fellow of Queen’s College, Cambridge .... ----s¢s0) =e: 8eras 189
®x-xVI. On the Physical Cause of the Motion of Glaciers. By .
James Crout, of fhe Geological Survey of Scotland - (2) ese meee 201°

XXVII. On Mr. J. Croll’s paper “ On Geological Time, and the
probable Date of the Glacial and the Upper Miocene Period.” By R.
A. Pracock, O.By s..--0 047 reste ss a 206 —

XXVIII. Contributions to the Knowledge of the Spectra of the
Flames of Gases containing Carbon. By AnpREw LIELEGG, Professor

at the National Upper Practical School at St. Pélten, Austria...... 208 —
XXIX. The Secular Effects of Tidal Action. By DaniEL VAUGHAN,

Bag. 26 eho seee be a es eee VG ‘
XXX. The Story of an Equation in Differences of the Second ‘
Order. By J.J. SYLVESTER...--- Spe oie aa Ps ne 225 @

XXXI. Proceedings of Learned Societies :—

Roya Socrery :—Mr. W. Crookes on the Measurement of the
Luminous Intensity of Light ; Canon Mossxey on the Mecha-
nical Possibility of the Descent of Glaciers by their Weight

227-235 |

only. feeb tyes oem CRRA” ois ae eee ee awe
XXXII. Intelligence and Miscellaneous Articles :—

Formation of an Artificial Spectrum with one Fraunhofer’s Line,

by A. Willner 62.012 s20+ +) 07-7 2s (ones le 235 |

On the Quantity of Electricity produced by the Electrophorus

Machine expressed in Absolute Measure, by F. Kohlrausch. . 236

On the Interference of Liquid Waves, by M. Lissajous ..---- 240,

——

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post-paid, to the Care of Messrs. Taylor and Francis, Printing Office, Red
Lion Court, Fleet Street, London. 4

PHILOSOPHICAL MAGAZINE,

1. 37. | APRIL 1869. No. 249.

Published the First Day of every Month.—Price 2s. 6d.

THE
LONDON, EDINBURGH, ann DUBLIN

AND

JOURNAL OF SCIENCE. A

Being a Continuation of Tilloch’s ‘ Philosophical Magazine,’
Nicholson’s ‘Journal,’ and Thomson’s * Annals of Philosophy.’

CONDUCTED RBY

SIR ROBERT KANE, LL.D. F.RS. M.RIA. FOS
AUGUSTUS MATTHIESSEN, Pu.D. F.R.S. F.C.S.

AND

WILLIAM FRANCIS, Pu.D. F.LS. F.R.AS. F.C.

FOURTH SERIES.

N° 249.—APRIL 1869.

LONDON:

PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET,
Printers and Publishers to the University of London.

Sold by Longmans, Green, Reader and Dyer; Kent and Co.; Simpkin, Marshall and
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Dublin :—and Putnam, New York.

aus QUARTERLY J OURNAL OF pean
No. XXII. April 1869. - Price 5s. |

I. The Malay Archipelago. With Two Woodcuts.
II. The Projected Mersey Tunnel and Railway from Liverpool to Tekeatead:
By Sw Cuarues Fox. With Page Plate. —

III. Vesuvius.
IV. The Artificial Production of Ice and Cold. By Dr. B. H. Pav. With

Four Woodcuts.
VY. On some Recent Spectroscopic Researches. By W1iLLIAM Hueens,
F.R.S.. With Page Plate and Three Woodcuts.
VI. The Future Water Supply of London. By C. W. Heaton, F.C.S.,
Charing Cross Hospital. ee i:
~CHRONICLES of SCIENCE; includmg the Proceedings of Learned So-
cieties at Home and Abroad, and Neues of Recent Scientific Literature.

Books Reviewed (amongst others) :—

Wa.uace’s ‘ Malay Archipelago.’ LosBiry’s ‘ Vesuvius.’

Bickmore’s ‘ East Indian Archipe- | Stmonin’s ‘ Underground Life.’
lago.’ JORDAN’S ‘ Vis Inertiz in the Ocean.’

PHILLIPS’s ‘ Vesuvius.’ LANGE’s ‘ Agate Industry.’

London: Longmans, Green, and Co., Paternoster Row.

This day, crown 8vo, price 6s.
A HISTORY OF CHEMICAL THEORY.
From the Age of Lavoisier to the present Time.
By AD. WURTZ. Translated by HENRY WATTS, F.R.S.

Macmillan and Co., London.

TO PHILOSOPHICAL INSTRUMENT MAKERS.

The Advertiser is desirous of engaging a thoroughly practical Workman in the
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only, addressed X. Y. Z, care of Mr. Boore, 54 Strand.

UNIVERSITY OF LONDON.

Just published, Price 4s.
THE CALENDAR FOR THE YEAR 1869;

Contaming the Regulations for each Examination, the Examination Papers
set durmg the past year, and other information.

Price 2s. 6d.

THE GENERAL REGISTER OF GRADUATES AND
UNDERGRADUATES,
to February Ist, 1869.

Taylor and Francis, Printers and Publishers to the University,
Red Lion Court, Fleet Street.

ADVERTISEMENTS continued on 3rd page of Cover

PRACTICAL GEOLOGY, KING’S COLLEGE, LONDON.

' PROFESSOR TENNANT, F.G:S., will give a COURSE OF LECTURES ON GEO-
LOGY, having especial reference to the Application of the Science to ENGINEERING,
“MINING, ARCHITECTURE, and AGRICULTURE. The Lectures will commence on
| Friday, April 9, at 9 a.m. They will be continued on each succeeding Wednesday and
| Friday at thesame hour. Fee £1 11s. 6d. Professor Tennant accompanies his Students
to the Public Museums and to places of Geological interest in the country. He also gives
PRIVATE INSTRUCTION in Mineralogy and Geology at his residence, 149 Strand, W.C.

GEOGRAPHERS and TOURISTS derive additional pleasure in their rambles
| by being acquainted with Miverats, Rocks, and Fossirs. Mr. TENNANT, Geolo-
| gist, 149 Strand, London, has had thirty years’ experience in giving PRACTICAL
INSTRUCTION to Ladies and Gentlemen; and from his extensive collection, comprising
many thousand specimens, persons are enabled in a dozen or twenty lessons to acquire
sufficient knowledge to identify all the ordinary components of crystalline and yolcanic
‘rocks, and most of the minerals and metals used in the Arts. om

TO GEOLOGISTS AND MINERALOGISTS.

For Sale.

Two handsome Cabinets, measuring 9 feet 3 inches long, 2 feet 4 inches wide, and 3 feet
10 inches high; each containing 45 drawers, with a Glass Case on the top of each Cabinet,
4 feet 11 inches high, and 15 inches from back to front. One Cabinet is filled with
Minerals, the other with Fossils.

They are at present in a room at King’s College, which is required as an additional class-
room. Mr. TENNANT has received notice to remove them, and would like to dispose of
them at once. Any person wishing to become practically acquainted with the interesting
and important study of Mineralogy or Geology, or both, will find this a good opportunity to
obtain an instructive and valuable Museum.

The Collection contains upwards of two thousand specimens, many very select. The first
Gold Nugget received from Australia, which was exhibited in the Exhibition of 185], is in
the Collection, and cost £37; it contains about 8 ounces of gold. The specimens have
been frequently used to illustrate the Lectures on Mineralogy and Geology at King’s Col-
lege, and at the Royal Military Academy, Woolwich*, Price

TWO THOUSAND GUINEAS,
Mr. TENNANT has other Collections, at one thousand, five hundred, one hundred, down to
Students’ Collections at twenty, ten, five, and two guineas each.
* Mr. Tennant held the appointment of Lecturer on Geology and Mineralogy at Wool-
wich for seventeen years; the Lectures were discontinued in December 1867, Lectures on
Military History being substituted.

DIAGRAMS TO ILLUSTRATE LECTURES ON GEOLOGY.

A Coloured Lithographic Print (size 34 by 28 inches) of B. WaTrernousr HAwkuns’s,
FE.LS.,&c., Restoration of the Extinct Animats of the Drirr- and Cave-Periop. Price 12s.

JUST PUBLISHED, a Chart of the characteristic British Tertiary Fossils, stratigraphically
arranged, containing 800 figures, compiled and engraved by J. W. Lowry. Price, mounted
on linen to fold in case, or mounted on rollers and varnished, 10s.

A New Chart of Fossiz Crustacza, illustrated by upwards of 490 Figures, and accom-
panied by a Descriptive Catalogue. Designed and drawn by J. W. Satren, F.G.S., and
H. Woopwarp, F.G.S. Engraved by J. W. Lowry, F.R.G.S. Price 10s. 6d.

Srx Diacrams or GENERIC Forms oF FoRAMINIFERA. Size, three feet by two feet.
Price 18s. for the Six Diagrams, either on paper or linen. They contain Eighty-two Figures.

Mr. Toomas Hawxins’s “Great SEA-Dracons.” Containing 30 folio Plates (which
form good school diagrams) of the Remains of Ichthyosaurus and Plesiosaurus from the Lias.
The Original Specimens are in the British Museum. Price 25s., published at £2 10s.

SOPWITH’S GEOLOGICAL MODELS IN WOOD,
To illustrate the nature of Stratification; of Valleys of Denudation; Succession of Coal-
seams in the Newcastle Coal-field; Strata of adjacent Lead-mine Districts; the effects pro-
duced by Faults or Dislocations; Intersections of Mineral Veins, &c.; accompanied with a
letterpress description, which can be had separately, price ls. 6d., by T. Sorwirn, C.E. &c.
Sold in Case, bound and lettered to resemble a large folio volume.
Twelve Models, 4 inches square............ £5 0

A Catalogue of 2000 of the most common Fossils found in the British Isles, being a list
of those in the private collection of J. TENNANT, F.G.S. Price 2s.

A descriptive List of Fuint ImpLeMENTs found at St. Mary Bourne; with Illustrations of
the principal types. By Josepu Stevens, Memb. Roy. Coll. Physicians, Lond. &e. Price 2s.

All the recent Works relating to Mineralogy, Geology, Conchology, and Chemistry ; also
Geological Maps, Models, Diagrams, Hammers, Blowpipes, Magnifying Glasses, Platina
Spoons, Electrometer and Magnetic Needle, Glass-top Boxes, Microscopic Objects, Brass
and Steel Forceps, Acid Bottles, &c., can be supplied to the Student in these interesting
branches of Science by

JAMES TENNANT, Mineralogist to Her Majesty, 149 Strand, W.C.

XXXII. On Cometary Theory. By Joun frspan, © R. Ss. &c. page 241

_ XXXIV. Remarks on the Luminous, Thermal, and Acoustic Phe-.
nomena attending the Fall of Meteorites. By Chevalier W. von

‘HAIDINGER

XXXV. Contributions to the ee 2 of Nova Scotia. By
Professor How, D.C.L., University of King’s College, Windsor, N.S.

XXXVI. On the Galvanic Resistance of Liquids. By Dr, Paatzow.

XXXVII. Fundamental Principles of Molecular Physics. By Pro-
fessor J. Baya, 8. J., of Stonyhurst College

ese @e ese © ® ese @e + & ©

XXXVIII. Further Remarks on the Explanation of Stewart and
Tait’s Experiments on the Heating of a Disk rotating in vacuo. By
Oscan Emini MEYER? joo et iis yes oi dee ie ie elles dala rag Sees

XXXIX. On the Falsetto or Head-sounds of the Human Voice.
By Wiiu1am Marcet, M.D., F.R.S., Assistant Physician to the
Hospital for Consumption and Diseases of the Chest, Brompton ....

XL. On the Absorption of Light by the Air. By H. Wizp

XLI. Notices respecting New Books :—An Introduction to Scien-
tific Chemistry ; designed for the use of Schools and Candidates for
University Matriculation Examinations. By F. S. Barrr,M.A.....

XLII. Proceedings of Learned Societies :—

Roya Society:—The Rev. 8S. Haveuton’s Notes of a Compa-
rison of the Granites of Cornwall and Devonshire with those
of Leinster and: Mourne®. 6...) .-4 ieee aie

GrotoaicaL Society :—Sir R. I. NMowonee on fi Gelso
Structure of North-western Siberia; Prof. SANDBERGER on a
Section of a Well at Kissingen; Mr. A. Tyxor on the Forma-

246

ac NE Sit os

264
271 3m

275

287

289

. 293

304

306

fiom, of Deltas... | uct cieen. Pee 309-311 j

XLIII. Intelligence and Miscellaneous Articles :—
On the Coloration of Peroxide of Nitrogen, by M. Salet......
On the Magnetism of Chemical Compounds, by Professor Wiede-
DART es aie nee eo etate Se) tie nt he ec ee ya's ahonareiars
On the Latent Heat of Volatilization of Sal-ammoniae, by M.C.
Marignac .. 6554066 s co ee es te boa nee ae ree

312

*,.* It is requested that all Communications for this Work may be addressed,

post-paid, to the Care of Messrs. Taylor and Francis, Printing Office, Red

Lion Court, Fleet Street,-London.

La MAY 1869. | No. 250.

Published the First Day of every Month.—Price 2s. 6d.

THE
LONDON, EDINBURGH, ann DUBLIN

PHILOSOPHICAL MAGAZINE,
AND

JOURNAL OF SCIENCE.

Being a Continuation of Tilloch’s ‘Philosophical Magazine,’
Nicholson’s ‘Journal,’ and Thomson’s ‘ Annals of Philosophy.’

CONDUCTED RY

SIR ROBERT KANE, LL.D. F.R.S. M.R.I.A. F.C.S.
AUGUSTUS MATTHIESSEN, Pu.D. F.R.S. F.C.S.

AND

WILLIAM FRANCIS, Pua.D. F.L.S. F.R.A.S. F.C.S.

FOURTH SERIES.

N° 250.—M AY 1869.

LONDON:

PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET,
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HABIT AND INTELLIGENCE.

In their connexion with the Laws of Matter and Force. A Series of Scientifie
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By JOSEPH JOHN MURPHY.

Recently published, 8vo, 14s.

FORCE AND NATURE: ATTRACTION AND REPULSION.

The Radical Principles of Energy graphically discussed in their Relation to —
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By C. F. WINSLOW, M.D.

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in ena Ma
“SILLIMAN’S JOURNAL.”
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[Two Volumes Annually, 450 pp. 8vo.]
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April 1863.

ADVERTISEMENTS. continued on 3rd page of Cover.

wee OF the first GOLD NUGGET received from Australia in 1851. The
original is in the possession of J. TENNANT, Mineralogist to Her Majesty,
and contains about Eight Ounces of Gold. Price of the Model 3s. 6d., with glass-
topped box to hold it, Is. 6d.,—together, 5s.
Model of the “ Welcome” Gold Nugget, being the largest brought to England
from Australia : it contained Gold to the value of £8,376. Price of the Model £3 35.

ee pete. GEOLOGISTS AND MINERALOGISTS. For Sale.

Two handsome Cabinets, measuring 9 feet 3 inches long, 2 feet 4 inches wide, and 3 feet
10 inches high; each containing 45 drawers, with a Glass Case on the top of each Cabinet,
4 feet 11 inches high, and 15 inches from back to front. One Cabinet is filled With
Minerals, the other with Fossils.

Any person wishing to become practically acquainted with the interesting and important
study of Mineralogy or Geology, or both, will find this a good opportunity to obtain an
instructive and valuable Museum.

The Collection contains upwards of two thousand specimens, many very select. The first
Gold Nugget received from Australia, which was exhibited in the Exhibition of 185], is in
the Collection, and cost £37 ; it contains about 8 ounces of gold. The specimens have
been frequently used to illustrate the Lectures on Mineralogy and Geology at King’s Col-
lege, and at the Royal Military Academy, Woolwich*. Price

TWO THOUSAND GUINEAS,

Mr. TENNANT has other Collections, at one thousand, five hundred, one hundred, down to
Students’ Collections at fifty, twenty, ten, five, and two guineas each,

* Mr. Tennant held the appointment of Lecturer on Geology and Mineralogy at Wool-
wich for seventeen years; the Lectures were discontinued in December 1867, Lectures on
Military History being substituted.

ee eee TS SS Faw An a
DIAGRAMS TO ILLUSTRATE LECTURES ON GEOLOGY.

A Coloured Lithographic Print (size 34 by 28 inches) of B. Warernousr Hawarna’s,
F.L.S.,&e., Restoration of the Extinct Anmats of the Drirr- and Cavz-prerrop. Price 12s.

JUST PUBLISHED, a Chart of the characteristic British Tertiary Fossils stratioranhiag My
arranged, containing 800 figures, compiled and engraved by J. W. Lowry. Price, meuntaci
on linen to fold in case, or mounted on rollers and varnished, 10s.

A New Chart of Fossiz CrusTacra, illustrated by upwards of 490 Figures, and accom-
panied by a Descriptive Catalogue. Designed and drawn by J. W. SALTER, F.G.S., and
H. Woopwarp, F.G.S. Engraved by J. W. Lowry, F.R.G.S. Price 10s. 6d.

Six Dracrams or Generic Forms or ForRAMINIFERA. Size, three feet by two feet.
Price 18s. for the Six Diagrams, either on paper or linen. They contain Eighty-two Figures.

Mr. Thomas Hawxrns’s “ Gruat Sra-Dracons.”’ Containing 30 folio Plates (which
form good school diagrams) of the Remains of Ichthyosaurus and Plesiosaurus from the Lias.
The Original Specimens are in the British Museum. Price 25s., published at £2 10s.

SOPWITH’S GEOLOGICAL MODELS IN WOOD,

To illustrate the nature of Stratification; of Valleys of Denudation; Succession of Coal-
seams in the Newcastle Coal-field; Strata of adjacent Lead-mine Districts; the effects pro-
duced by Faults or Dislocations; Intersections of Mineral Veins, &c.; accompanied with a
letterpress description, which can be had separately, price ls. 6d., by T. Sorwirn, C.£. &c.
Sold in Case, bound and lettered to resemble a large folio volume.
Twelve Models, 4 inches square............ £5 0
oben Se Sa eee
A Catalogue of 2000 of the most common Fossils found in the British Isles, being a list
of those in the private collection of J. Tennant, F.G.S. Price 2s.
A descriptive List of Fuinr IMPLEMENTS found at St. Mary Bourne; with Illustrations of
he principal types. By Josern Stevens, Memb. Roy. Coll. Physicians, Lond. &c. Price 2».
All the recent Works relating to Mineralogy, Geology, Conchology, and Chemistry; also
eological Maps, Models, Diagrams, Hammers, Blowpipes, Magnifying Glasses, Platina
poons, Electrometer and Magnetic Needle, Glass-top Boxes, Microscopic Objects, Brase
nd Steel Forceps, Acid Bottles, &c., can be supplied to the Student in these interesting
ranches of Science by

JAMES TENNANT, Mineralogist to Her Majesty, 149 Strand, W.c.
May 1869, 7

CONTENTS “or N° 250.—Fourth Series.

XLIV. Researches in British Mineralogy. By Davip Forsgs,
PRIS: Ce soe ‘bac | Sapa geek
XLY. Lecture Hserrcents to sl aeeate the Lae e Motion. By.”
Professor Ropert Bat, A.M. .. ieee
XLVI. On Shadow Oe “By ion ae) ‘Dower East-
India Government Telegraph Department .......--+---++++:: aah
XLVII. On the Cause of a Pink Colour in White-Lead Corrosions.
By Wii11aM Baker, F.C.S., Associate of the ae School of Mines,
London oboe heen
XLVIII. oe the Golo ae fhe lake " lecnera By L. Soret... 345
XLIX. Fundamental Principles of Molecular Physics. By Pro-
fessor J. Bayma, S.J., of Stonyhurst College .... 348
L. On some Reactions of Hydrated Oxide of Ethylene dodian
By J. Aurrep Wang yn, Professor of Chemistry in the London In-
stitution ..... 358
LI. On the Medianieal Teapocb ily, a te Dene a Glace xe
their Weight only. By Henry Mosetey, M.A., Canon of Bristol,

F.R.S., Instit. Imp. Sc. Paris, Corresp....... 6+ ++ sess ress stee ss 363
LILI. On the Uniform Motion of an Imperfect Fluid. By Henry

Mosanry, FiR.Se &e. . hie ne liens nb = tare one ere 370 |
LIII. Note on a new Continued maevicn aac: to the Quadra-

ture of the Circle. By J.J. SyLVESTER .... eR pak 373

LIV. On two remarkable Resultants arising out a the Theary +: ii
Rectifiable Compound Logarithmic Waves. By J.J. SYLVESTER .. 375
LV. Notices respecting New Books :—Physical and Historical

Evidences of vast Sinkings of Land on the North and West Coasts of
France, and South-western Coasts of England, within the Historical
Period. Collected and commented on by R. A. Puacock, Esq., C.E.
_—On Steam as the Motive Power in Earthquakes and Volcanoes, and
on Cavities in the Earth’s Crust. By R.A. Peacock, Esq., C.H. 382-384
LVI. Proceedings of Learned Societies :—
Bovan Socrery:—Prof. Tyxpauz on the Blue Colour of the Sky,
the Polarization of Skylight, and on the Polarization of Light
by Cloudy matter generally...........--¢ cess ce eeeeees 384
RovaL Institution :—Dr. A. Crum Brown on Chemie Con-
stitution, and its Relation to Physical and Physiological Pro-
PELtIES .. 2 seen eects see ce eu ee tena ie meet 393
LV{i. Intelligence and Miscellaneous Articles :—
On a Mirage in the English Channel, by John Parnell, M.A.,
BURGAS. 20 eee ee ee oo 400
On the production of a beautiful Patina on Bronzes in large Towns. 401 ©
On Tyndall’s a Theney he: Mr. E. a and W. B.
Gibbs, F.R.A.S. ese ees weteee es 408 |

*,* I¢ is requested that all Communications for this Work may be addressed, —
post-paid, to the Care of Messrs. Taylor and Francis, Printing Office, Red
Lion Court, Fleet Street, London. |

a

Tol. 37. JUNE 1869.

Wo: 251.

Published the First Day of every 1 fonth.—Price 2s. 6d.

ia ee THE
GH, ann DUBLIN

PHILOSOPHICAL MAGAZINE,

ad
7 AND

~ JOURNAL OF SCIENCE.

oe Being a Continuation of Tilloch’s ‘ Philosophical Magazine,’
- Nieholson’s ‘Journal,’ and Thomson’s ¢ Annals of Philosophy.’

CONDUCTED RY

SIR ROBERT KANE, LL.D. F.R.S. M.R.LA. F.C.S.
AUGUSTUS MATTHIESSEN, Pu.D. F.R.S. F.C.S.

AND

WILLIAM FRANCIS, Pu.D. F.LS. F.R.A.S. F.C.S.

FOURTH SERIES.

N° 251.—J UNE 1869.

LONDON:

PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET,
Printers and Pubiishers to the University of London,

Sold by Longmans, Green, Reader and Dyer; Kent and Co.; Simpkin, Marshall and
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Thomas Clark, Edinburgh; Smith and Son, Glasgow:—Hodges and Smith,

_ Dublin :—and Putnam, New York.

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RELIQUIZ AQUITANICA,
Being Contributions to the Archeology and Paleontology of Périgord and the
adjoining Provinces of Southern France.
By EDOUARD LARTET and HENRY CHRISTY.
Edited by T. RUPERT JONES,
Professor of Geology &c., Royal Military College, Sandhurst.
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No. 42 for March 17, 1869, just published, price 2s. contains :—

On the Storm of February 12, 1869. By James Glaisher, Esq.

On Comparative Observations of Solar Radiation. By the Rev. Fenwick W.
Stow.

On the Meteorology of England during the years 1867 and 1868. By James
Glaisher, Esq.

On the Rotation of the Wind between oppositely directed currents of Air in
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Taylor and Francis, Red Lion Court, Fleet Street, E.C.

ADVERTISEMENTS continued on 3rd page of Cover.

GEOLOGICAL EXCURSION.—Professor Tennant will accompany his Students
on Wednesday next, June 2, to Maidstone to examine the Wealden, Greensand, Gault, and
Chalk of the district, under the direction of Mr. Bensted. Professor TENNANT will be glad
to see any former Student.

GEOGRAPHERS and TOURISTS derive additional pleasure in their rambles
by being acquainted with Minerrats, Rocks, and Fossius. Mr. TENNANT, Geolo-
gist, 149 Strand, London, has had thirty years’ experience in giving PRACTICAL
INSTRUCTION to Ladies and Gentlemen; and from his extensive collection, comprising
many thousand specimens, persons are enabled in a dozen or twenty lessons to acquire
sufficient knowledge to identify all the ordinary components of crystalline and volcanic
rocks, and most of the minerals and metals used in the Arts.

TO GEOLOGISTS AND MINERALOGISTS. For Sale.

Two handsome Cabinets, measuring 9 feet 3 inches long, 2 feet 4 inches wide, an feet
10 inches high; each containing 45 drawers, with a Glass Case on the top of each Cabinet,
4 feet 11 inches high, and 15 inches from back to front. One Cabinet is filled with
Minerals, the other with Fossils.

Any person wishing to become practically acquainted with the interesting and important
study of Mineralogy or Geology, or both, will find this a good opportunity to obtain an
instructive and valuable Museum.

The Collection contains upwards of three thousand specimens, many very select. The first
Gold Nugget received from Australia, which was exhibited in the Exhibition of 1851, is in
the Collection, and cost €37; it contains about 8 ounces of gold; also a fine series “of
Coloured Diamonds, illustrating crystalline form and colour. The specimens have been fre-
quently used to illustrate the Lectures on Mineralogy and Geology at King’s College, and
at the Royal Military Academy, Woolwich*. Price

THREE THOUSAND GUINEAS,

Mr. TENNANT has other Collections, at one thousand, five hundred, one hundred, down to
Students’ Collections at fifty, twenty, ten, five, and two guineas each.

* Mr. Tennant held the appointment of Lecturer on Geology and Mineralogy at Wool-
wich for seventeen years; the Lectures were discontinued in December 1867, Lectures on
Military History being substituted.

Mr. TENNANT is commissioned to sell several highly interesting Collections, viz. the ex-
tensive Collection of MrnerRAts, Rocks, and Fossrts collected by the late Lord Farnham ;
a Cabinet of Precious Stones and Pearls, and several others. Particulars can be had at 149
Strand.

SOPWITH’S GEOLOGICAL MODELS IN WOOD,

To illustrate the nature of Stratification; of Valleys of Denudation; Succession of Coal-

seams in the Newcastle Coal-field; Strata of adjacent Lead-mine Districts; the effects pro-

duced by Faults or Dislocations; Intersections of Mineral Veins, &c.; accompanied with a

letterpress description, which can be had separately, price 1s, 6d., by T. Sopwiru, C.E. &c.
Sold in Case, bound and lettered to resemble a large folio volume.

Twelve Models, 4 inches square............ £5 0

‘A Catalogue of 2000 of the most common Fossils found in the British Isles, being a list
of those in the private collection of J. Tennant, F.G.S. Price 2s.

A descriptive List of Fuinrt ImpLements found at St. Mary Bourne; with Illustrations of
the principal types. By JosepH Stevens, Memb. Roy. Coll. Physicians, Lond. &c. Price 2s.

All the recent Works relating to Mineralogy, Geology, Cunchology, and Chemistry; also
Geological Maps, Models, Diagrams, Hammers, Blowpipes, Magnifying Glasses, Platina
Spoons, Electrometer and Magnetic Needle, Glass-top Boxes, Microscopic Objects, Brass
and Steel Forceps, Acid Bottles, &c., can be supplied to the Student in these interesting
branches of Science.

ODEL of the firss GOLD NUGGET received from Australia in 1851. The

4¥4 original is in the possession of J. TENNANT, Mineralogist to Her Majesty,

d contains about Hight Ounces of Gold. Price of the Mod 3s. 6d., with glass-
opped box to hold it, ls. 6d.,—together, 5s.

Model of the “ Welcome” Gold Nugget, being the largest brought to England

om Australia : it contained Gold to the value of £8,376. Price of the Model £3 3s.

JAMES TENNANT, Mineralogist to Her Majesty,149 Strand, W.cC.
May 31, 1869.

CONTENTS on N° 251.— Fourth Series.

“2

LVIII. On the ay of certain Gases fe Geissler s Tubes. By
A: WULLNER | 8 ok teen ool. sare 405

LIX. On the Motion of a Palladium Plate duos the Formation of
Graham’ s Hydrogenium. By James Dewar, F.R.S.E. ........ 424

2

LX. Fundamental Principles*af Molecular Physics. By Professor
J.$Bayma, S.J.,; of Stonyhurst College ..:.....220.. i Neg 431

LXI. Ona Metallic Connector to replace the Vulcanite Tube used
with Bianchi’s Air-pump. By Wittiam Sway, LL.D., F.R.S.E. &c.,
Professor of Natural Philosophy in the University of St. Andrews >... 442

LXII. Upon the new Conception of Electrodynamic Phenomena
suggested by Gauss. By R.Cnausius ........-....-.......- 445

al

LXIII. On some Spectrum Observations of Comets. By Witi1am
Huecins, BRS. eee eee ee te ce eee ae Bane a ea 456

LXIV. On Statical and Dynami¢al Ideas in Chemistry.—Part I.
Acid, Alkali, Salt, and Base. By Epmunp J. Mitts, D.Sc., F.C.S. 461

LXV. Proceedings of Learned Societies :— a j
Royan Society :—Mr. F. GuTHRIE. on the Thernal Pee oJ
of Giquids: Mr. G. Gorz on Hydrofluoric Acid ...... 468-474
LXVI. Intelligence and Miscellaneous Articles:— .
On the Voltaic Deportment of Palladium, by J. C. Poggendorff ee. «fe
On the Electrical Polarity and Inequality of the Amalgamated Zinc
Electrodes in Sulphate of Zinc, by BE. Patty .. 72 475
Ona Development of Heat which accompanies the bursting of the

Prince Rupert’s Drops, by M: Dufour :...2.7,.3099 ee 478

With Title-page, Contents, &c.

* It'is requested — at all Gout ener for this Work may be addressed, |
post-paid, to the Care of Messrs. Taylor and. Francis, oe Office, Red

~ Lion Court, Fleet poe London, Nae ‘

: 6. Rarey oD. bale 2
me

4
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’
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