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MKH •

UNIVERSITY OF CALIFORNIA
AT LOS ANGELES

THE

COMPLETE WORKS

COUNT RUMFORD.

PUBLISHED BY THE AMERICAN ACADEMY OF
ARTS AND SCIENCES.

VOL. II.

BOSTON.

1873-

UNIVERSITY PRESS : WELCH, BICELOW, & Co.,
CAMBRIDGE.

.

CONTENTS.

PAGE

AN INQUIRY CONCERNING THE WEIGHT ASCRIBED TO HEAT . i

[Read before the Royal Society, May 2, 1799.]

AN INQUIRY CONCERNING THE NATURE OF HEAT AND THE
MODE OF ITS COMMUNICATION 23

[Read before the Royal Society, February 2, 1804.]

EXPERIMENTAL INVESTIGATIONS CONCERNING HEAT . .131

[Read before the National Institute of France, April 9 and 30, and
May 7, 1804, and April 2, 1805.]

REFLECTIONS ON HEAT 166

[Read before the National Institute of France, June 26, 1804.]

HISTORICAL REVIEW OF THE VARIOUS EXPERIMENTS OF THE
AUTHOR ON THE SUBJECT OF HEAT 188

EXPERIMENTS AND OBSERVATIONS ON THE COOLING OF LIQ-
UIDS IN VESSELS OF PORCELAIN, GILDED AND NOT GILDED . 241

[Read before the National Institute of France, August 10, 1807.]

AN ACCOUNT OF A CURIOUS PHENOMENON OBSERVED ON THE
GLACIERS OF CHAMOUNY : TOGETHER WITH SOME OCCA-
SIONAL OBSERVATIONS CONCERNING THE PROPAGATION OF
HEAT IN FLUIDS ,. . 251

[Read before the Royal Society, December 15, 1803.]

AN ACCOUNT OF SOME NEW EXPERIMENTS ON THE TEMPERA-
TURE OF WATER AT ITS MAXIMUM DENSITY . . .258

[Read before the National Institute of France, July 15, 1805.]

347888

iv Contents.

INQUIRIES CONCERNING THE MODE OF THE PROPAGATION OF
HEAT IN LIQUIDS 274

[Read before the National Institute of France, June 9, 1 806.]

EXPERIMENTS AND OBSERVATIONS ON THE ADHESION OF THE
PARTICLES OF WATER TO EACH OTHER .... 290

[Read before the National Institute of France, June 16, 1806.]

CONTINUATION OF EXPERIMENTS AND OBSERVATIONS ON THE
ADHESION OF THE PARTICLES OF LIQUIDS TO EACH OTHER . 300

[Read before the National Institute of France, March 9, 1807.]

OF THE SLOW PROGRESS OF THE SPONTANEOUS MIXTURE OF
LIQUIDS DISPOSED TO UNITE CHEMICALLY WITH EACH OTHER 318

[Read before the National Institute of France, March 29, 1807.]

OF THE USE OF STEAM AS A VEHICLE FOR TRANSPORTING HEAT 324

OBSERVATIONS RELATIVE TO THE MEANS OF INCREASING THE
QUANTITIES OF HEAT OBTAINED IN THE COMBUSTION OF
FUEL. 345

DESCRIPTION OF A NEW BOILER, CONSTRUCTED WITH A VIEW
TO THE SAVING OF FUEL 352

[Read before the National Institute of France, October 6, 1806.]

EXPERIMENT ON THE USE OF THE HEAT OF STEAM, IN PLACE
OF THAT OF AN OPEN FlRE, IN THE MAKING OF SOAP . . 359

[Read before the National Institute of France, October 20, 1 806.]

ACCOUNT OF SOME NEW EXPERIMENTS ON WOOD AND CHAR-
COAL 362

[Read before the National Institute of France, December 30, 1811.]

RESEARCHES UPON THE HEAT DEVELOPED IN COMBUSTION AND
IN THE CONDENSATION OF VAPOURS 370

[Read before the National Institute of France, February 24, and No-
vember 30, 1812.]

Contents. v

Ox THE CAPACITY FOR HEAT OR CALORIFIC POWER OF VARI-
OUS LIQUIDS 425

[Read before the National Institute of France, 1812.]

INQUIRIES RELATIVE TO THE STRUCTURE OF WOOD, THE SPE-
CIFIC GRAVITY OF ITS SOLID PARTS, AND THE QUANTITY OF
LIQUIDS AND ELASTIC FLUIDS CONTAINED IN IT UNDER VA-
RIOUS CIRCUMSTANCES ; THE QUANTITY OF CHARCOAL TO BE
OBTAINED FROM IT; AND THE QUANTITY OF HEAT PRODUCED
BY ITS COMBUSTION . . 435

[Read before the National Institute of France, September 28, and Oc-
tober 5, 1812.]

OF CHIMNEY FIREPLACES . . . . . . 484

, [Essay IV.]

SUPPLEMENTARY OBSERVATIONS CONCERNING CHIMNEY FIRE-
PLACES . ... 559

[Essay XI.]

AN INQUIRY

CONCERNING

THE WEIGHT ASCRIBED TO HEAT.

THE various experiments which have hitherto been
made with a view to determine the question, so
long agitated, relative to the weight which has been
supposed to be gained, or to be lost, by bodies upon
their being heated, are of a nature so very delicate, and
are liable to so many errors, not only on account of the
imperfections of the instruments made use of, but also
of those, much more difficult to appreciate, arising from
the vertical currents in the atmosphere, caused by the
hot or the cold body which is placed in the balance,
that it is not at all surprising that opinions have been
so much divided, relative to a fact so very difficult to
ascertain.

It is a considerable time since I first began to medi-
tate upon this subject, and I have made many experi-
ments with a view to its investigation ; and in these
experiments I have taken all those precautions to avoid
errors which a knowledge of the various sources of
them, and an earnest desire to determine a fact which I
conceived to be of importance to be known, could in-
spire ; but though all my researches tended to convince
me more and more that a body acquires no additional
weight upon being heated, or, rather, that heat has no
effect whatever upon the weights of bodies, I have been

2 An Inquiry concerning

so sensible of the delicacy of the inquiry, that I was for
a long time afraid to form a decided opinion upon the
subject.

Being much struck with the experiments recorded in
the Transactions of the Royal Society, Vol. LXXV.,
made by Dr. Fordyce, upon the weight said to be ac-
quired by water upon being frozen ; and being possessed
of an excellent balance, belonging to his Most Serene
Highness the Elector Palatine Duke of Bavaria; early
in the beginning of the winter of the year 1787, — as
soon as the cold was sufficiently intense for my pur-
pose,— I set about to repeat those experiments, in
order to convince myself whether the very extraordi-
nary fact related might be depended on ; and with a
view, to removing, as far as was in my power, every
source of error and deception, I proceeded in the fol-
lowing manner.

Having provided a number of glass bottles, of the
form and size of what in England is called a Florence
flask, — blown as thin as possible, — and of the same
shape and dimensions, I chose out from amongst them
two, which, after using every method I could imagine
of comparing them together, appeared to be so much
alike as hardly to be distinguished from each other.

Into one of these bottles, which I shall call A, I put
4107.86 grains Troy of pure distilled water, which
filled it about half full ; and into the other, B, I put
an equal weight of weak spirit of wine ; and, sealing
both the bottles hermetically, and washing them, and
wiping them perfectly clean and dry on the outside, I
suspended them to the arms of the balance, and placed
the balance in a large room, which for some weeks had
been regularly heated every day by a German stove,

the Weight ascribed to Heat. 3

and in which the air was kept up to the temperature
of 61° of Fahrenheit's thermometer, with very little
variation. Having suffered the bottles, with their con-
tents, to remain in this situation till I conceived they
must have acquired the temperature of the circum-
ambient air, I wiped them afresh, with a very' clean,
dry cambric handkerchief, and brought them into the
most exact equilibrium possible, by attaching a small
piece of very fine silver wire to the arm of the bal-
ance to which the bottle which was the lightest was
suspended.

Having suffered the apparatus to remain in this situa-
tion about twelve hours longer, and finding no altera-
tion in the relative weights of the bottles, — they con-
tinuing all this time to be in the most perfect equi-
librium, — I now removed them into a large uninhab-
ited room, fronting the north, in which the air, which
was very quiet, was at the temperature of 29° F. ; the
air without doors being at the same time at 27° ; and
going out of the room, and locking the door after me,
I suffered the bottles to remain forty-eight hours, un-
disturbed, in this cold situation, attached to the arms
of the balance as before.

At the expiration of that time, I entered the room,

— using the utmost caution not to disturb the balance,

— when, to my great surprise, I found that the bottle
A very sensibly preponderated.

The water which this bottle contained was com-
pletely frozen into one solid body of ice ; but the
spirit of wine, in the bottle B, showed no signs of
freezing.

I now very cautiously restored the equilibrium by
adding small pieces of the very fine wire of which gold

4 An Inquiry concerning

lace is made, to the arm of the balance to which the bottle
B was suspended, when I found that the bottle A had
augmented its weight by 35^ part of its whole weight
at the beginning of the experiment ; the weight of the
bottle with its contents having been 4811.23 grains
Troy (the bottle weighing 703.37 grains, and the water
4107.86 grains), and it requiring now -£$fa parts of a
grain, added to the opposite arm of the balance, to
counterbalance it.

Having had occasion, just at this time, to write to my
friend, Sir Charles Blagden, upon another subject, I
added a postscript to my letter, giving him a short
account of this experiment, and telling him how "very
contrary to my expectation " the result of it had turned
out ; but I soon after found that I had been too hasty
in my communication. Sir Charles, in his answer to
my letter, expressed doubts respecting the fact; but,
before his letter had reached me, I had learned from my
own experience how very dangerous it is in philosoph-
ical investigations to draw conclusions from single ex-
periments.

Having removed the balance, with the two bottles
attached to it, from the cold into the warm room
(which still remained at the temperature of 61°), the ice
in the bottle A gradually thawed ; and, being at length
totally reduced to water, and this water having acquired
the temperature of the surrounding air, the two bottles,
after being wiped perfectly clean and dry, were found to
weigh as at the beginning of the experiment, before the
water was frozen.

This experiment, being repeated, gave nearly the same
result, — the water appearing when frozen to be heavier
than in its fluid state; but some irregularity in the

tfie Weight ascribed to Heat. 5

manner in which the water lost the additional weight
which it had appeared to acquire upon being frozen
when it was afterwards thawed, as also a sensible differ-
ence in the quantities of weight apparently acquired in
the different experiments, led me to suspect that the
experiment could not be depended on for deciding the
fact in question. I therefore set about to repeat it,
with some variations and improvements ; but before I
give an account of my further investigations relative to
this subject, it may not be amiss to mention the method
I pursued for discovering whether the appearances men-
tioned in the foregoing experiments might not arise
from the imperfections of my balance ; and it may like-
wise be proper to give an account, in this place, of an
intermediate experiment which I made, with a view to
discover, by a shorter route, and in a manner less ex-
ceptionable than that above mentioned, whether bodies
actually lose or acquire any weight upon acquiring an
additional quantity of latent heat.

My suspicions respecting the accuracy of the balance
arose from a knowledge — which I acquired from the
maker of it — of the manner in which it was con-
structed.

The three principal points of the balance having been
determined, as nearly as possible, by measurement, the
axes of motion were firmly fixed in their places, in a
right line, and, the beam being afterwards finished, and
its two arms brought to be in equilibrio, the balance
was proved, by suspending weights, which before were
known to be exactly equal, to the ends of its arms.

If with these weights the balance remained in equi-
librio, it was considered as a proof that the beam was
just ; but if one arm was found to preponderate, the

6 An Inquiry concerning

other was gradually lengthened, by beating it upon an
anvil, until the difference of the lengths of the arms was
reduced to nothing, or until equal weights, suspended
to the two arms, remained in equilibrio ; care being
taken before each trial to bring the two ends of the
beam to be in equilibrio, by reducing with a file the
thickness of the arm which had been lengthened.

Though in this method of constructing balances the
most perfect equality in the lengths of the arms may be
obtained, and consequently the greatest possible accu-
racy, when used at a time when the temperature of the
air is the same as when the balance was made, yet, as it
may happen that, in order to bring the arms of the bal-
ance to be of the same length, one of them' may be
much more hammered than the other, I suspected it
might be possible that the texture of the metal forming
the two arms might be rendered so far different by this
operation as to occasion a difference in their expansions
with heat ; and that this difference might occasion a
sensible error in the balance, when, being charged with
a great weight, it should be exposed to a considerable
change of temperature.

To determine whether the apparent augmentation of
weight, in the experiments above related, arose in any
degree from this cause, I had only to repeat the experi-
ment, causing the two bottles A and B to change places
upon the arms' of the balance ; but, as I had already
found a sensible difference in the results of different
repetitions of the same experiment, made as nearly as
possible under the same circumstances, and as it was
above all things of importance to ascertain the accuracy
of my balance, I preferred making a particular experi-
ment for that purpose.

the Weight ascribed to Heat. 7

My first idea was, to suspend to the arms of the bal-
ance, by very fine wires, two equal globes of glass, filled
with mercury, and, suffering them to remain in my
room till they should have acquired the known tempera-
ture of the air in it, to have removed them afterward
into the cold, and to have seen if they still remained in
equilibrio under such difference of temperature ; but,
considering the obstinacy with which moisture adheres
to the surface of glass, and being afraid that somehow
or other, notwithstanding all my precautions, one of the
globes might acquire or retain more of it than the other,
and that by that means its apparent weight might be
increased ; and having found by a former experiment,
of which an account is given in one of the preceding
papers (that on the Moisture absorbed from the Atmos-
phere by various Substances), that the gilt surfaces of
metals do not attract moisture (see Vol. I. p. 232),
instead of the glass globes filled with mercury, I made
use of two equal solid globes of brass, well gilt and
burnished, which I suspended to the arms of the bal-
ance by fine gold wires.

These globes, which weighed 4975 grains each, being
wiped perfectly clean, and having acquired the tempera-
ture (61°) of my room, in which they were exposed
more than twenty-four hours, were brought into the
most scrupulous equilibrium, and were then removed,
attached to the arms of the balance, into a room in
which the air was at the temperature of 26°, where they
were' left all night.

The result of this trial furnished the most satisfac-
tory proof of the accuracy of the balance ; for, upon
entering the room, I found the equilibrium as perfect as
at the beginning of the experiment.

8 An Inquiry concerning

Having thus removed my doubts respecting the ac-
curacy of my balance, I now resumed my investigations
relative to the augmentation of weight which fluids have
been said to acquire upon being congealed.

In the experiments which I had made, I had, as I
then imagined, guarded as much as possible against
every source of error and deception. The bottles being
of the same size, neither any occasional alteration in the
pressure of the atmosphere during the experiment, nor
the necessary and unavoidable difference in the densities
of the air in the hot and in the cold rooms in which
they were weighed, could affect their apparent weights ;
and their shapes and their quantities of surface being
the same, and as they remained for such a considerable
length of time in the heat and cold to which they were
exposed, I flattered myself that the quantities of mois-
ture remaining attached to their surfaces could not be
so different as sensibly to affect the results of the experi-
ments. But, in regard to this last circumstance, I after-
wards found reason to conclude that my opinion was
erroneous.

Admitting the fact stated by Dr. Fordyce, — and
which my experiments had hitherto rather tended to
corroborate than to contradict, — I could not conceive
any other cause for the augmentation of the apparent
weight of water upon its being frozen than the loss of
so great a proportion of its latent heat as that fluid is
known to evolve when it congeals ; and I concluded
that, if the loss of latent heat added to the weight of
one body, it must of necessity produce the same effect
on another, and consequently, that the augmentation of
the quantity of latent heat must in all bodies and in
all cases diminish their apparent weights.

the Weight ascribed to Heat. 9

To determine whether this is actually the case or not,
I made the following experiment.

Having provided two bottles, as nearly alike as pos-
sible, and in all respects similar to those made use of in
the experiments above mentioned, into one of them I
put 4012.46 grains of water, and into the other an equal
weight of mercury ; and, sealing them hermetically, and
suspending them to the arms of the balance, I suffered
them to acquire the temperature of my room, 61°;
then, bringing them into a perfect equilibrium with each
other, I removed them into a room in which the air was
at the temperature of 34°, where they remained twenty-
four hours. But there was not the least appearance of
either of them acquiring or losing any weight.

Here it is very certain that the quantity of heat lost
by the water must have been very considerably greater
than that lost by the mercury, the specific quantities
of latent heat in water and in mercury having been
determined to be to each other as 1000 to 33 ; but
this difference in the quantities of heat lost produced
no sensible difference on the weights of the fluids in
question.

Had any difference of weight really existed, had it
been no more than one millionth part of the weight of
either of the fluids, I should certainly have discovered
it; and had it amounted to so much as y-jnTVur Part °f
that weight, I should have been able to have measured
it, so sensible and so very accurate is the balance
which I used in these experiments.

I was now much confirmed in my suspicions that the
apparent augmentation of the weight of the water upon'
its being frozen, in the experiments before related, arose
from some accidental cause ; but I was not able to con-

io An Inquiry concerning

ceive what that cause could possibly be, unless it were
either a greater quantity of moisture attached to the
external surface of the bottle which contained the water
than to the surface of that containing the spirits of
wine, or some vertical current or currents of air caused
by the bottles, or one of them not being exactly of the
temperature of the surrounding atmosphere.

Though I had foreseen, and, as I thought, guarded
sufficiently against, these accidents, by making use of
bottles of the same size and form, and which were blown
of the same kind of glass and at the same time, and
by suffering the bottles in the experiments to remain
for so considerable a length of time exposed to the dif-
ferent degrees of heat and of cold which alternately
they were made to acquire ; yet, as I did not know the
relative conducting powers of ice and of spirit of wine
with respect to heat, or, in other words, the degrees
of facility or difficulty with which they acquire the tern-
perature of the medium in which they are exposed,
or the time taken up in that operation, and, conse-
quently, was not absolutely certain as to the equality
of the temperatures of the contents of the bottles at
the time when their weights were compared, I deter-
mined now to repeat the experiments, with such va-
riations as should put the matter in question out of all
doubt.

I was the more anxious to assure myself of the real
temperatures of the bottles and their contents, as any
difference in their temperatures might vitiate the ex-
periment, not only by causing unequal currents in
the air, but also by causing, at the same time, a greater
or less quantity of moisture to remain attached to the
glass.

the Weight ascribed to Heat. n

To remedy these evils, and also to render the experi-
ment more striking and satisfactory in other respects, I
proceeded in the following manner : —

Having provided three bottles, A, B, and C, as
nearly alike as possible, and resembling in all respects
those already described, into the first, A, I put 4214.28
grains of water, and a small thermometer, made on
purpose for the experiment, and suspended in the bot-
tle in such a manner that its bulb remained in the mid-
dle of the mass of water; into the second bottle, B, I
put a like weight of spirit of wine, with a like thermom-
eter ; and, into the bottle C, I put an equal weight of
mercury.

These bottles, being all hermetically sealed, were
placed in a large room, in a corner far removed from
the doors and windows, and where the air appeared
to be perfectly quiet ; and, being suffered to remain
in this situation more than twenty-four hours, the heat
of the room (61°) being kept up all that time with as
little variation as possible, and the contents of the bot-
tles A and B appearing, by their inclosed thermometers,
to be exactly at the same temperature, the bottles were
all wiped with a very clean, dry, cambric handkerchief;
and, being afterwards suffered to remain exposed to the
free air of the room a couple of hours longer, in order
that any inequalities in the quantities of heat, or of
the moisture attached to their surfaces, which might
have been occasioned by the wiping, might be corrected
by the operation of the atmosphere by which they were
surrounded, they were all weighed, and were brought in-
to the most exact equilibrium with each other, by means
of small pieces of very fine silver wire, attached to the
necks of those of the bottles which were the lightest.

12 An Inquiry concerning

This being done, the bottles were all removed into a
room in which the air was at 30°, where they were suf-
fered to remain, perfectly at rest and undisturbed, forty-
eight hours ; the bottles A and B being suspended to
the arms of the balance, and the bottle C suspended, at
an equal height, to the arm of a stand constructed for
that purpose, and placed as near the balance as possible,
and a very sensible thermometer suspended by the side
of it.

At the end of forty-eight hours, during which time
the apparatus was left in this situation, I entered the
room, opening the door very gently for fear of dis-
turbing the balance ; when I had the pleasure to find
the three thermometers, viz. that in the bottle A, —
which was now inclosed in a solid cake of ice, — that
in the bottle B, and that suspended in the open air
of the room, all standing at the same point, 29° F.,
and the bottles A and B remaining in the most perfect
equilibrium.

To assure myself that the play of the balance was
free, I now approached it very gently, and caused it to
vibrate ; and I had the satisfaction to find, not only
that it moved with the utmost freedom, but also, when
its vibration ceased, that it rested precisely at the point
from which it had set out.

I now removed the bottle B from the balance, and
put the bottle C in ts place; and I found that that
likewise remained of the same apparent weight as at the
beginning of the experiment, being in the same per-
fect equilibrium with the bottle A as at first.

I afterwards removed the whole apparatus into a
warm room, and causing the ice in the bottle A to
thaw, and suffering the three bottles to remain till they

the Weight ascribed to Heat. 13

and their contents had acquired the exact temperature
of the surrounding air, I wiped them very clean, and,
comparing them together, I found their weights re-
mained unaltered.

This experiment I afterwards repeated several times,
and always with precisely the same result, — the water
in no instance appearing to gain, or to lose, the least
weight upon being frozen or upon being thawed ;
neither were the relative weights of the fluids in either
of the other bottles in the least changed by the various
degrees of heat and of cold to which they were exposed.

If the bottles were weighed at a time when their con-

O

tents were not precisely of the same temperature^ they
would frequently appear to have gained, or to have
lost, something of their weights ; but this doubtless
arose from the vertical currents which they caused in
the atmosphere, upon being heated or cooled in it, or
to unequal quantities of moisture attached to the sur-
faces of the bottles, or to both these causes operating
together.

As I knew that the conducting power of mercury,
with respect to heat, was considerably greater than either
that of water or that of spirit of wine, while its ca-
pacity for receiving heat is much less than that of either
of them, I did not think it necessary to inclose a ther-
mometer in the bottle C, which contained the mercury ;
for it was evident that, when the contents of the other
two bottles should appear, by their thermometers, to
have arrived at the temperature of the medium in which
they were exposed, the contents of the bottle C could
not fail to have acquired it also, and even to have ar-
rived at it before them ; for the time taken up in the
heating or in the cooling of any body, is, c<eteris paribus.

14 An Inquiry concerning

as the capacity of the body to receive and retain heat,
directly, and as its conducting power, inversely.

The bottles were suspended to the balance by silver
wires about two inches long, with hooks at the ends of
them ; and, in removing and changing the bottles, I
took care not to touch the glass. I likewise avoided
upon all occasions, and particularly in the cold room,
coming near the balance with my breath, or touching it,
or any part of the apparatus, with my naked hands.

Having determined that water does not acquire or lose
any weight upon being changed from a state of fluidity
to that of ice, and vice versa, I shall now take my final
leave of a subject which has long occupied me, and
which has cost me much pains and trouble ; being fully
convinced, from the results of the above-mentioned ex-
periments, that if heat be in fact a substance, or matter,
— a fluid sui generis, as has been supposed, — which,
passing from one body to another, and being accumu-
lated, is the immediate cause of the phenomena we ob-
serve in heated bodies, — of which, however, I cannot
help entertaining doubts, — it must be something so
infinitely rare, even in its most condensed state, as to
baffle all our attempts to discover its gravity. And if
the opinion which has been adopted by many of our
ablest philosophers, that heat is nothing more than an
intestine vibratory motion of the constituent parts of
heated bodies, should be well founded, it is clear that
the weights of bodies can in no wise be affected by such
motion.

It is, no doubt, upon the supposition that heat is a
substance distinct from the heated body, and which is
accumulated in it, that all the experiments which have
been undertaken with a view to determine the weight

the Weight ascribed to Heat. 15

which bodies have been supposed to gain or to lose
upon being heated or cooled, have been made ; and
upon this supposition, — but without, however, adopt-
ing it entirely, as I do not conceive it to be sufficiently
proved, — all my researches have been directed.

The experiments with water and with ice were made
in a manner which I take to be perfectly unexception-
able, in which no foreign cause whatever could affect
the results of them ; and the quantity of heat which
water is known to part with, upon being frozen, is so
considerable, that if this loss has no effect upon its
apparent weight, it may be presumed that we shall
never be able to contrive an experiment by which we
can render the weight of heat sensible.

Water, upon being frozen, has been found to lose a
quantity of heat amounting to 140 degrees of Fahren-
heit's thermometer ; or — which is the same thing — the
heat which a given quantity of water, previously cooled
to the temperature of freezing, actually loses upon
being changed to ice, if it were to be imbibed and
retained by an equal quantity of water, at the given
temperature (that of freezing), would heat it 140 de-
grees, or would raise it to the temperature of (32° -J-
140) 172° of Fahrenheit's thermometer, which is only
40° short of that of boiling water ; consequently, any
given quantity of water, at the temperature of freez-
ing, upon being actually frozen, loses almost as much
heat as, added to it, would be sufficient to make it
boil.

It is clear, therefore, that the difference in the quan-
tities of heat contained by the water in its fluid state
and heated to the temperature of 61° F., and by the
ice, in the experiments before mentioned, was very

1 6 An Inquiry concerning

nearly equal to that between water in a state of boiling,
and the same at the temperature of freezing.

But this quantity of heat will appear much more con-
siderable when we consider the great capacity of water
to contain heat, and the great apparent effect which the
heat that water loses upon being frozen would produce
were it to be imbibed by, or communicated to, any
body whose power of receiving and retaining heat is
much less.

The capacity of water to receive and retain heat —
or what has been called its specific quantity of latent
heat — has been found to be to that of gold as 1000
to 50, or as 20 to i ; consequently, the heat which any
given quantity of water loses upon being frozen, were
it to be communicated to an equal weight of gold at
the temperature of freezing, the gold, instead of being
heated 162 degrees, would be heated 140 X 20 = 2800
degrees, or, would be raised to a bright red heat.

It appears, therefore, to be clearly proved by my ex-
periments, that a quantity of heat equal to that which
4214 grains (or about 9! oz.) of gold would require to
heat it from the temperature of freezing water to be red
hot, has no sensible effect upon a balance capable of indi-
cating so small a variation of weight as that of J-Q-Q^-Q-Q-Q
part of the body in question; and, if the weight of
gold is neither augmented nor lessened by one millionth
•part, upon being heated from the point of freezing water
to that of a bright red heat, I think we may very safely
conclude, that ALL ATTEMPTS TO DISCOVER ANY EFFECT

OF HEAT UPON THE APPARENT WEIGHTS OF BODIES WILL
BE FRUITLESS.

the Weight ascribed to Heat. 17

SU PPLEMENT.

THE foregoing paper having been originally drawn
up for the purpose of being laid before the Royal
Society, my respect for that learned body induced me
to confine my observations to such ^points as I con-
ceived to be new; and I took no notice whatever of a
considerable number of experiments which I had made
in the course of my investigations, because they were
very similar to experiments that had before been made
by other persons ; and because their results did not
appear to me to afford sufficient grounds to form arty
decisive opinion respecting the matter in question.
There were, however, among my experiments, two or
three of which I shall now give an account, which will
probably be thought sufficiently interesting to deserve
being mentioned.

Most of the experiments, from the results of which
philosophers had been induced to form their opinions
respecting the ponderability of heat, had been made by
weighing the same given body at different temperatures.
Thus, solid globes of metal — cannon-balls, for instance
— had frequently been weighed when cold, and then, be-
ing heated red-hot, had been again weighed at that high
temperature, and, from the apparent difference of the
weight of the ball when cold and when red-hot, conclu-
sions had been formed respecting the weight or levity of
heat. But had the numerous causes of error in these
most difficult experiments been less evident than they
are, yet the results of the experiments of this kind which
have hitherto been made by different persons have
. VOL. ii. 2

1 8 An Inquiry concerning

been so various and contradictory that no reliance
whatever can be placed on them.

When a hot body is suspended in the air to the arm
of a balance in order to its being weighed, as it con-
tinually gives off heat to the fluid in contact with it,
this communication of heat occasions a strong ascend-
ing current of air to be formed over and by the sides
of the hot body, which current cannot fail to affect the
result of the experiment, and render the conclusions
drawn from it fallacious. To prevent, if possible, these
causes of error, the following experiments were con-
trived.

The hot body to be weighed, which was a small
metallic ball, heated red-hot, was placed in the scale of
the balance in a small hemispherical porcelain cup,
which had a slender foot, or stand, about one inch
high ; and this cup, with the hot ball in it, was covered
over by a porcelain coffee-cup, turned upside down,
which, without touching the hot ball, confined the
heated air which surrounded it. This coffee-cup and
the porcelain stand were very exactly balanced, by
weights in the opposite side, before the ball was intro-
duced.

The following experiment was made at Munich on
the 2oth of April, 1785. The weather being cloudy,
with intervals of sunshine, the thermometer in my
room stood at 52° F., and the barometer 26 inches 4
lines, French measure.

At 30 minute* after noon, a small bullet, or grape-
shot, of cast-iron, very well formed, and apparently
solid, having been well washed and cleaned by scouring
with sand, and thoroughly dried, was exposed in a
clean vessel of porcelain in the midst of a mixture of

the Weight ascribed to Heat. - 19

pounded ice and sea salt, till it had acquired the tem-
perature of 25° F. (7 degrees below the point of freez-
ing water), when it was carefully weighed, and found
to weigh very exactly 773 Jf- grains Troy.

At i h. 30/72. P. M., the same bullet having been ex-
posed 30 minutes in a clean, dry vessel of porcelain,
placed in a sand heat, at the temperature of 212° F., or
that of boiling water, was again weighed, while yet hot,
and found to weigh no more than 773^ grains.

At 2 h. o m. P. M., the bullet having now been ex-
posed 15 minutes, in a clean new Hessian crucible,
well covered, to the heat of a strong charcoal fire, and
being thoroughly red-hot, was found to weigh 773 f£
grains.

The bullet, being yet red-hot, was put again into the
crucible, and being once more exposed to the fire, which
now burned very bright, at ih. 20 m. it had acquired a
white heat, and began to show signs of melting, some
small bubbles appearing upon its surface. In this state
it was taken from the fire, and very carefully weighed
sixteen times successively, at different intervals, when
it was found to weigh as follows : —

Time when weighed. Was found to weigh.

2h.
2
2
1

20 m.

21
23 . . . '.
26

773$£ grai
773*f "
773H '

2

2
2
2

29 •»'•..'
32

43 • • • • •

46

773M '
77381 '

774^ '

2
2
2

49
52

56 ,. . .

774*1 "
774** "
774^-2 "

2

q8

774#J "

2o An Inquiry concerning

Time when weighed. Was found to weigh.

At3h. im 774$ J grains.

3 18 774M "

* 3 25 . . . . . . 774M "

6 15 774H "

Immediately after this last-mentioned weighing of
the bullet, the whole of the apparatus appearing to have
acquired the temperature of the air in the room (60° F.),
the bullet was taken away, and the porcelain stand and
cup were again balanced in the scale, when it appeared
that they had lost \ of a grain in weight during the
preceding experiment. This apparent loss of weight I
could ascribe to nothing but to the thorough drying of
the cups in the experiment with the red-hot bullet, and
to the drying of the silk cords by which the scale con-
taining the cup and stand was suspended to the arm of
the balance.

This weight = \ of a grain, which was required to
balance the scales at the end of the experiment, being
added to the apparent weight of the bullet at 6 h. 1 5 m.
— 774ei> *ts true weignt at that time appears to have
been 775 J£.

The weight of the bullet at I h. 30 m. having been no
more than 773^- grains, and at 6 h. 15 m. it being found
to weigh 775jf grains, it appears that it had gained in
weight by being heated red-hot 775J-f — 773 e6* = 2i
grains.

This augmentation of weight doubtless arose from
the partial oxidation of the iron. It certainly did not
arise from the heat, for it remained after the bullet had
become cold.

* Just before this weighing, the coffee-cup which covered the bullet in the scale
had been removed for a moment to look at the bullet, and then immediately re-
placed. What it was that escaped on this occasion I will not undertake to say, but
certain it is that its weight amounted to -£•% of a grain, at the least;

the Weight ascribed to Heat. 21

An Account of an Experiment made with a Bullet of Fine Gold.

Munich,, i^d April, 1785. — Weather cloudy, with
intervals of sunshine ; thermometer in my room at
65° F ; barometer at 26 inches 4 lines.

A small bullet of fine gold, equal in value to 10 Ger-
man ducats, which I procured from the master of the
mint, being weighed in the open air of my room, was
found to weigh 477^ J grains.

The small open china cup, in which the bullet was
weighed, was exactly counterbalanced by a weight =
44°lf! grains.

At 10 h. 5 m. A. M. the bullet, heated to a clear red
heat approaching to whiteness, and weighed in the cup,
open to the air, the bullet and the cup together were
found to have lost of their weight J|J of a grain.

Removing the bullet immediately, I found that the
cup, or rather the cup and the scale in which it was
placed, together had lost in weight ^-f f parts of a grain.

Consequently, the bullet must have lost of its weight
by being heated red-hot ; or it appeared to be lighter
when red-hot than when cold by ^|F parts of a grain,
or fc-yj-g- part of its whole weight.

Upon repeating the experiment I had nearly the
same result ; but upon varying it, by covering the
heated bullet in the scale, in different ways, I found
such variations in the results as convinced me that the
apparent diminution of weight above mentioned might
easily have arisen from currents in the atmosphere,
and consequently that no dependence can be placed
in experiments of that kind for deciding the fact rela-
tive to the weights of heated bodies, or the ponder-
ability of heat.

22 An Inquiry concerning the Weight ascribed to Heat.

I afterwards contrived an apparatus for making the
experiment in a different and more unexceptionable
manner. I provided three hollow globes of brass, very
thin, and one larger than the other, and which being
made to open in the middle, like a tobacco-box, could
be placed one within another. In the centre globe I
intended to place a solid bullet of pure gold, red-hot.
Between the centre globe and that next it, I proposed
to leave a space equal to the diameter of the heated
bullet, filled with air ; and the space between the sec-
ond globe and the third I meant to have filled with
pounded ice; and I proposed to have made the ex-
periment at a time when the heat of the atmosphere
should be just equal to that of freezing water; and in
this manner I conceived that I should be able to avoid
the currents in the air, whose effects I had found so
distressing in my former experiments. But when I
considered that the whole of the heat contained by the
red-hot bullet would not be sufficient to thaw one half
of the ice which surrounded it, and that, when the bul-
let should be cooled to the temperature of the ice, the
whole mass of metal, of ice, and of water, would still
remain at the -point of freezing ; and, moreover, that
weighing the water produced by the ice would, in fact, be
weighing the heat which before existed in the red-hot
bullet, it first occurred to me that the point in question
might much more readily be determined by simply
weighing a quantity of ice at the temperature of freezing,
and weighing the same again when changed into water.

I therefore left my apparatus unfinished, and turned
my whole attention to the experiments of which an
account has been given in the former part of this paper.

[This paper is printed from Rumford's Philosophical Papers,
pp. 366-383.]

AN INQUIRY

CONCERNING THE

NATURE OF HEAT, AND THE MODE OF ITS
COMMUNICATION.

HEAT is employed in such a vast variety of differ-
ent processes, in the affairs of life, that every
new discovery relative to it must necessarily be of real
importance to mankind ; for, by obtaining a more inti-
mate knowledge of its nature and mode of action, we
shall no doubt be enabled not only to excite it with
greater economy, but also to confine it with greater
facility, and direct its operations with more precision
and effect.

Having many years ago found reason to conclude
that a careful observation of the phenomena which at-
tend the heating and cooling of bodies, or the communi-
cation of heat from one body to another, would afford
the best chance of acquiring a farther insight into the
nature of heat, my view, in all my researches on this
subject, has been principally directed to that point ;
and the experiments of which I am now to give an
account may be considered as a continuation of those
I have already, at different times, had the honour of
laying before the Royal Society, and of presenting to
the public in my Essays.

In order that the attention of the Society may not be

24 Inquiry concerning the Nattire of Hcat>

interrupted unnecessarily by description of instruments
in the midst of the accounts of interesting experiments,
I shall begin by describing the apparatus which was
provided for these researches ; and, as a perfect knowl-
edge of the instruments made use of is indispensably
necessary in order to form distinct ideas of the experi-
ments, I shall take the liberty to be very particular in
these descriptions.

The thermometers, four in number, which were used
in these experiments, were constructed under my own
eye, and with the greatest possible care ; and, after
every trial I have been able to make with them, in
order to ascertain their accuracy, they appear to be very
perfect.

They are mercurial thermometers, graduated accord-
ing to Fahrenheit ; their bulbs are cylindrical, 4 inches
long, and -j4^- of an inch in diameter ; and their tubes
are from 15 to 16 inches long. The mercury with
which they are filled is quite pure, and they are freed
from air. Their scales were divided with the greatest
care; and, by means of a nonius, they show eighth
parts of a degree very distinctly; they are graduated
from about 10 degrees below the freezing point to 5
or 6 degrees above the point of boiling water. Their
bulbs are quite naked; their scales ending about i
inch above the junction of the bulb with its tube. The
freezing point is situated about 5 inches above the
upper end of the bulb. The reason for placing it so
high will be evident from the details of the experiments
in which these instruments were used.

The instrument I contrived for ascertaining the
warmth of clothing is extremely simple ; it is merely a
hollow cylindrical vessel made of thin sheet brass. It

and the Mode of its Communication. 25

is closed at both ends, and has a narrow cylindrical
neck, by which it is occasionally filled with hot water.

This vessel, being covered with a garment made to
fit it, composed of any kind of cloth or stuff, or other
warm covering, is supported in a vertical position on a
wooden stand, which is placed on a table in a large
quiet room ; and one of the thermometers above de-
scribed being placed in the axis of the vessel, the time
employed in cooling the water, through the clothing
with which the instrument is covered, is observed and
noted down.

Now, as the time of cooling through any given inter-
val of the scale of the thermometer (or from any given
degree above the temperature of the air of the room to
any other given lower degree, but still above the tem-
perature of the air of the room) will be longer or
shorter as the covering of the instrument is more or
less adapted for confining heat, it is evident that the
relative warmth of clothing of different kinds may
be very accurately determined by experiments of this
sort.

I provided four instruments of this kind, all very
nearly of the same dimensions. Their cylindrical bodies
are each 4 inches in diameter and 4 inches long; and
their cylindrical necks are about T87 of an inch in diam-
eter, and 4 inches in length. This neck is placed in
the centre of the circular flat top, or upper end, of the
vertical cylindrical body ; and opposite to it, in the
centre of the flat bottom of the body, there is a hollow
cylinder, T8^ of an inch in diameter and 3 inches long,
projecting downwards, into which a vertical cylinder of
wood is fitted, on the top of which the instrument is
supported, in such a manner that the air has free access

26 Inqiiiry concerning the Nature of Heat,

to every part of it. This cylinder of wood constitutes
a part of the wooden stand above mentioned.

As the thermometer is placed in the axis of the cylin-
drical vessel, and as its bulb is just as long as the body
of this vessel, it is evident that it must ever indicate
the mean temperature of the water in the vessel, however
different the temperature of that water may be at differ-
ent depths.

The thermometer is firmly supported in its place by
causing a part of the lower end of its scale to enter the
neck of the cylindrical vessel, and to fit it with some
degree of accuracy, but not so nicely as to be in danger
of sticking fast in it.

The lower end of the bulb of the thermometer does
not absolutely touch the bottom of the vessel, but it is
very near touching it.

Figure i (Plate I.) will give a clear idea of this
instrument placed on its wooden stand, which is so con-
trived that the instrument may be placed higher or
lower at pleasure.

The foregoing description of this instrument is so
particular that the figure will be easily understood
without any further illustration. The cylindrical vessel
is represented placed on the stand, with its thermome-
ter in its place.

As, in some of the first experiments I made with this
instrument, I found it difficult to apply the coverings
which I used to the ends of the body of the instru-
ment, I endeavoured, by covering up those ends with a
permanent and very warm covering, to oblige most of
the heat to pass off through the vertical sides of the
instrument, to which it was easy to fit almost any kind
of covering, and more especially coverings of various

PLATE I

fSiy'J.

and the Mode of its Communication. 27

thicknesses of confined air, the relative warmth of
which I was very desirous of ascertaining.

The means I employed for covering up the ends of
the instrument were as follows. Having provided two
thin cylindrical wooden boxes (like common pill-boxes,
but much larger), something less in diameter than the
body of the instrument, and 2-J- inches deep, I dried
them as much as possible ; and, after having varnished
them within and without with spirit varnish, I covered
them within and without with fine wove writing-paper,
and then gave the paper three coats of the same varnish.
I then perforated the bottoms of these boxes with
round holes, just large enough to admit the neck of the
instrument, and the cylindrical projection at its bot-
tom ; and then inverted them over the two ends of the
instrument, filling the boxes at the same time with
eider-down.

These boxes were fixed and confined in their places
by means easy to be imagined ; and, in order to con-
fine the heat still more effectually, each of the boxes
was covered on the outside with a cap of fur, as often
as the instrument was used; as was also that part- of
the neck of the instrument which projected above the
box.

Two of the instruments, which I shall distinguish by
the numbers i and 2, were covered up at their ends in
this manner; the other two instruments, No. 3 and
No. 4, were left in the state represented by the Figure
i ; that is to say, the ends of their cylindrical bodies
were not covered with permanent coverings.

In each experiment, two similar instruments (No. i
and No. 2, for instance, or No. 3 and No. 4) were
used, the one naked^ and the other covered; and, as the

•28 Inquiry concerning the Nature of Heat.,

naked instrument always served as a standard, with
which the results of the experiments made with the
other were compared, it is evident that this arrange-
ment rendered the general results of the experiments
much more satisfactory and conclusive than they could
possibly have been, had the experiments made on differ-
ent days and with various kinds of covering been
made singly, or unaccompanied by a fixed and invari-
able standard.

The experiments were made and registered in the
following manner: The two instruments used in the
experiment, placed on their wooden stands, being set
down on the floor, were filled to within about \\ inch
of the tops of their cylindrical necks with boiling hot
water ; and, a thermometer being put into each of them,
they were placed at the distance of three feet from each
other, on a large table, in a corner of a large quiet
room,* where they were suffered to cool undisturbed.
Near them on the same table, and at the same height
above the table, there was placed another thermometer
(suspended in the air to the arm of a stand), by which
the temperature of the air of the room was ascertained
from time to time.

No person was permitted to pass through the room
while an experiment was going on ; and in order to
prevent, as far as it was possible, all those currents of
air in the room which were occasioned by partial heat,
produced by the light which came in at the windows,
the window-shutters were kept constantly shut ; one of
them only being opened for a moment, now and then,
just to observe the thermometers, and note down the
progress of the experiment.

* This room, which is adjoining to my laboratory, in my house at Munich, is 19
feet wide, 24 feet long, and 13 feet high.

and the Mode of its Communication. 29

The results of each experiment were entered on a
separate sheet of paper ; which paper was previously
prepared for that use by being divided into separate
vertical columns by lines drawn with a pen, and ruled
in parallel horizontal lines with a lead-pencil.

" Experiments on Heat, made at Munich, nth March, 1803. The
large cylindrical Vessels, No. I and No. 2 (made of thin sheet brass),
were filled with hot Water, and exposed to cool in the Air of a large
quiet Room. The Ends of both these Instruments were well covered
with warm Clothing, Furs, &c. The vertical polished Sides of
No. I were naked. The Sides of No. 2 were covered with one
Thickness of fine white Irish Linen, which had been worn,
strained over the metallic Surface."

Time.

Temperature

Tem-
perature
of the
Air.

Time.

Temperature

Tem-
perature
of the
Air.

h.

min.

of No. i,
naked.

of No. 2,

covered.

h.

min.

of No. i,

of No. 2,

covered.

10

IO .

o
126}

o
126

0

4

o

O

o

43i

30

IO9j

io6£

43^

3°

59^

52

. .

45

105

loof

432

5

3°

57

49|-

44

II

IQlJ

942

44

6

55i

49 \

. . 2\

94

30

54i

48J

IS

94

9°4~

. .

7

. .

53&

47^

42

. .

3P

94

86 £

8

. .

54

46 \

. .

39

. .

84

9

. .

5°

45 1

. .

45

94

82^

. .

IO

. .

49

45

. .

12

88 ^

79$

8

1 2th Mar. 43

42

40

. .

IS

85 i

76

. .

The instruments were now removed into

25

84"

8

2

43

42

62

. .

3°

. .

74i

. .

32

44j

44|

62^

45

80 70

47

46

46*

63

I

. .

78 68 i

. .

9

24

48

49 i

. .

3°

74i

644

IO

5°

52

2

64

43!

. .

41

54

53|

3°

68 ^

SSI | 43 i

12

54

56^

3

. .

65!

562 ! . .

12

26

54i 57

3°

63i

S4| |. -•

An end was now put to the experiment.

The above is an exact copy of one of these regis-

30 Inquiry concerning the Nature of Heat,

ter-sheets, and contains the results of an actual and very
interesting experiment, which lasted 26 hours.

Though it was easy to discover, by a single glance at
the register, whether a covering which was put over
one of the instruments prolonged the time of its cool-
ing or not; yet, in order to compare the results of dif-
ferent experiments, and particularly of such as were
made on different days, so as to determine with pre-
cision how much warmer one kind of covering was than
another, it was necessary to fix on some particular in-
terval in the scale of the thermometer, or number of
degrees, commencing at some certain invariable number
of degrees above the temperature of the 'air by which
the instrument was surrounded, in order that the
warmth of the covering, or its power of confining heat,
might with certainty be estimated by the time employed
in cooling through that interval.

By the results of a great number of experiments I
found that the same instrument cooled through any
given (small) number of degrees (10 degrees, for in-
stance) in very nearly the same time, whatever was the
temperature of the air of the room ; provided always,
that the point from which these 10 degrees commenced
was at the same given number of degrees above the
temperature of the air at the time being.

The interval I chose for comparing the results of my
experiments is that which commences with the fiftieth,
and ends with the fortieth, degree of Fahrenheit's ther-
mometer above the temperature of the air in which the in-
strument is exposed to cool When, for instance, the air
was at 58°, the interval commenced at the io8th degree,
and ended at the 98th. When the air was at 64^°, it
commenced at 114^°, and ended at 104!°.

and t/ie Afode of its Communication. 31

That the same instrument, exposed to cool in the
air, does in fact cool the same number of degrees in the
same time, very nearly, when the given interval of the
scale of the thermometer is reckoned from the same
height, or given number of degrees above the tempera-
ture of the air at the time when the experiment is made,
will appear from the following results of 1 1 different
experiments, made on different days, and when the air
in which the instrument was exposed to cool was at dif-
ferent degrees of temperature.

The large cylindrical vessel, No. i, having its two
ends well covered up with eider-down, furs, &c., its
vertical sides being exposed naked to the air, in a large
quiet room, was found to cool 10 degrees, viz. from the
5Oth to the 4Oth degree above the temperature of the air
in which it was exposed, as follows : —

44

. from 94 to 84

45*

.

95i to 85^

48

"

98 to 88

5!i

ii

ioii to 91^

52

"

102 tO 92

54

"

104 to 94

44

"

94 to 84

42*

M

92^ to 82^

45

"

95 to 85

46

"

96 to 86

44

M

94 to 84

55 minutes.

551 ««
55 "

.. 56

. 55

The fact which these experiments are here brought
to prove has likewise been confirmed by other experi-
ments, made with other instruments, and at times when
the temperature of the air has been as high as 64°; but
I will not take up the time of the Society by giving a
particular account of them in this place.

32 Inquiry concerning the Nature of Heat,

As it sometimes happened, though very seldom, in
the course of an experiment (which commonly lasted
several hours) that I was called away, and was not pres-
ent to observe the thermometer at the moment of the
passage of the mercury through one or both of those
points of its scale which formed the limits of the given
interval chosen as the standard for a comparison of the
results of the experiments with each other, it became a
matter of considerable importance to find means for
supplying these accidental defects, and ascertaining the
points in question by interpolation.

In order to facilitate the means of doing this, I en-
deavoured to investigate the law of the cooling of hot
bodies in a cold fluid medium ; and I found reason to
conclude,

M

That if, on the right line AB, a perpendicular CD be
taken, equal to the difference of the temperatures of the
hot body and of the colder medium, expressed in de-
grees of the thermometer ; and, after a certain given
time, represented by CE, taken on the line AB at the

and the Mode of its Communication* 33

point E, another perpendicular EF be erected, and EF
be taken equal to the difference of the temperatures
after the time represented by CE has elapsed; and if
the perpendiculars GH and LM be drawn, representing
the difference of the temperatures after the times EG
and GL have elapsed, a curved line PQ drawn through
the points D, F, H, M, will be the logarithmic curve;
or, if it vary from that curve, its variation, within
the limits answering to a change of temperature amount-
ing to a few degrees (especially if they be taken when
the temperature of the hot body is about 40 or 50
degrees above that of the medium), will be so very
small that no sensible error will result from a supposi-
tion that it is the logarithmic curve, in supplying, by
computation, any intermediate observations which hap-
pen to have been neglected in making an experiment.

These computations are very easily made, with the
assistance of a ta"ble of logarithms, in the following
manner.

Supposing CD, CG, and GH, to have been deter-
mined by actual observation ; and that it were required
to ascertain, by computation, the absciss CE, corres-
ponding to any given intermediate ordinate EF, or
(which is the same thing) to determine at what time the
cooling body was at any given intermediate temperature
(= EF) between that (= CD) which it was found by
observation to have at the point C, and that (= GH)
which it was found to have after the time represented by
the line GC had elapsed ;

It is log. CD — log. GH is to CG as i to m
(= modulus = the subtangent of the curve at the point
D.)* And CE = m X log. CD — log. EF.

* The subtangent shows in what time the instrument would cool down to the tem-
VOL. II. 3

34 Inquiry concerning the Nature of Heat,

If, for instance, in the experiment of the nth March,
(the details of which have just been given) the time
when the instrument No. 2, in cooling, passed the
important point of 94° had not been observed, this
neglect might have been supplied, by computation, in
the following manner.

It is CD = 94f°, the nearest observed temperature
higher than EF (= 94°), and GH = 9oJ, the nearest
observed temperature below that of 94° ; and CG = 15
minutes, or 900 seconds = the time elapsed between
the two observations.

It is log. 94! = 1.9765792
And log. 90^ — 1.9554472

Log. CD — log. GH = 0.021 1320

And 0.0211320 is to 900 (= CG) as i to 42590 = m.

And again, log. 94! — 1.9765792
Log. 94 = 1.9731279

Log. CD — log. EF = 0.0034513

42590 X 0.0034513 (=mX log. CD — log. EF) =
147 seconds = 2 minutes and 27 seconds; which dif-
fers very little from 2j minutes, the observed time.

If, from the temperature observed at nh. 30 min. =
86J°, and the temperature observed at nh. 45 min. =
82^°, and the time which elapsed between these two

perature of the air in which it is placed, were its velocity of cooling at the point D to
be continued uniformly from that point; and, as the subtangent of the logarithmic
curve is constant, if PQ were the logarithmic curve, it would follow that the velocity
with which a hot body cools in a fluid medium is everywhere such, that, were that
•velocity to be continued uniformly, the body would be cooled down to the temperature
of the medium in the same time, whatever might be the excess of the temperature of
the hot body above that of the medium, at the moment when its velocity of cooling
became uniform.

and the Mode of its Communication. 35

observations (= 15 minutes), we were to determine by
computation the time when the instrument was at the
temperature of 84° (the lower point of the standard
interval of 10 degrees answering to the temperature of
the air, = 44°, in which the instrument was cooled), it
will turn out, 8 minutes and 55 seconds after nh.
30 min. The observed time was nh. 39 min. ; which
differs from the computed time no more than 5 seconds.

If it were strictly true, as a very great philosopher
and mathematician has advanced, that the velocity with
which a hot body, exposed to cool in a cold fluid me-
dium, parts with its heat is as the difference of the tem-
peratures of the body and of the medium, it is most cer-
tain that the curve PQ could be no other than the loga-
rithmic curve. Perhaps it may be so in fact, and that
the variations from it which my experiments indicated
were owing solely to the imperfection of the divisions
of our thermometers. If it be so, it is not impossible
to divide the scale of a thermometer in such a manner
as to indicate with certainty equal increments of heat, as
thermometers ought to do ; but this is not the proper
place to enlarge on this subject. I may perhaps return
to it hereafter.

Passing over in silence a number of experiments I
made in order to get thoroughly acquainted with my
new instruments, and to assure myself that the results
of similar experiments made with them were uniform
and might be depended on, I shall now proceed to give
an account of several experiments made with pointed
views, the results of some of which were very inter-
esting.

Experiment No. i. — The large cylindrical vessel No. i,
with its ends covered with warm clothing, in the man-

36 Inquiry concerning the Nature of Heat,

ner before described, and its vertical sides (which were
polished, and very clean and bright) exposed naked to
the air, was filled with water nearly boiling hot, and
placed on its wooden stand, on a table, in a large quiet
room to cool ; the air of the room being at the tem-
perature of 45° Fahrenheit.

Another cylindrical vessel, No. 2, in all respects like
No. i, and with its ends covered in the same manner,
but with its vertical sides covered with a single covering
of fine Irish linen (such as is sold in London for about
4 s. per yard), closely applied to the body of the instru-
ment, was filled with hot water at the same time, and
placed on the same table to cool.

This experiment lasted many hours ; and, in that
period, the temperature of the water in each of the
instruments was carefully observed and noted down a
great number of times.

The result of this experiment (the details of which
have already been given) was very remarkable.

While the instrument No. i, whose sides were naked,
employed 55 minutes in cooling from the point of 94°
to that of 84°, the instrument No. 2, whose sides were
covered with linen, cooled through the same interval in
36! minutes.

Hence it appears that clothing may, in some cases,
expedite the passage of heat out of a hot body, instead
of confining it in it.

Desirous of seeing whether the same covering would,
or would not, expedite the passage of heat into the in-
strument, after having suffered both instruments to
cool down to the temperature of about 42°, I removed
them into a warm room, in which the air was at the
temperature of 62°; and I found that the instrument

and the Mode of its Communication. 37

No. 2, which was clothed, acquired heat considerably
faster than the other, No. i, which was naked.*

The discovery of these extraordinary facts surprised
me, and excited all my curiosity ; and I immediately
set about investigating their cause.

As it is well known that air adheres with consider-
able obstinacy to the surfaces of some solid bodies, I
conceived it to be possible that the particles of air in
immediate contact with the surface of the cylindrical
vessel No. I, might in fact be so attached to the metal
as to adhere to it with some considerable force ; and, if
that were the case, as confined air is known to consti-
tute a very warm covering, it appeared to me to be
possible that the cooling of the vessel No. i might
have been retarded by such an invisible covering of
confined air; which covering, in the experiment with
the vessel No. 2, had been displaced and in a great
measure driven away by the colder covering of linen
by which the body of the instrument was closely em-
braced.

I conceived that the linen must have accelerated the
cooling of the instrument, either by facilitating the
approach of a succession of fresh particles of cold air,
or by increasing the effects of radiation; and, with a
view to elucidate that important point, the following
experiments were made.

Experiment No. 2. — Removing the linen with which
the instrument No. 2 was clothed, I now covered the
sides of that instrument with a thin transparent coat-
ing of glue ; and, when it was quite dry and hard,
I again filled the two instruments (No. i and No. 2)

* The details of this experiment (which was made on the nth of March, 1803)
may be seen on page 29.

347888

38 Inquiry concerning the Nature of Heat,

with hot water, and observed the times of their cooling
as before.

Result, or time of cooling 10 degrees, reckoned from
the 50th to the 4Oth degree above the temperature
of the air in which the instruments were exposed to
cool : —

Instrument No. I, sides naked, . . . . -55 min-
Instrument No. 2, sides covered with one coating of glue, 431 "

When we consider this experiment with attention,
we shall find reason to conclude, that if it were by facili-
tating the approach and temporary contact of a succes-
sion of fresh particles of the cold air of the room to the
surface of the glue (which was now in fact become the
surface of the hot body), that the cooling of the instru-
ment was accelerated, the metal being as completely
covered, and the air, supposed to be attached and fixed
to its surface, as completely excluded by one coating of
the glue as it could be by two or more, two coatings
could not possibly accelerate the cooling of the instru-
ment more than one ; but if, on the other hand, the
cooling of the instrument in this experiment was ac-
celerated, not by facilitating and accelerating the mo-
tions of the circumambient cold air, but by facilitat-
ing and increasing those radiations which are known to
proceed from hot bodies, I conceived that two coat-
ings of the glue might possibly accelerate the cooling
of the vessel more than one. In order to put this con-
jecture to the test, I made the following decisive experi-
ment.

Experiment No. 3. — I now gave the instrument No. 2
a second coating of glue; and, when it was thoroughly
dry, I repeated the experiment last mentioned, with the

and the J\lode of its Commiinication. 39

above variation ; when I found the results to be as fol-
lows : —

Time of cooling

the 10 degrees

in question.

The instrument No. I, naked metal, . . . . 55^ min.
The instrument No. 2, covered vi\\h. two coatings of glue, 37^ "

Finding that two transparent coatings of glue facili-
tated the cooling of this instrument even more than
one coating, I washed off all the glue with warm water ;
then, making the instrument as clean and bright as pos-
sible, I covered its sides with a coating of very fine,
transparent, and colourless spirit varnish ; and, after
this coating of varnish had become quite dry and hard,
I repeated the experiment above mentioned ; and, find-
ing that this covering, like that of glue, expedited the
cooling of the instrument, I first added a second coat-
ing of the varnish, and repeated the experiment again,
and then added two coatings more, making four in all.
Finding that the cooling of the instrument was more
and more rapid; as the thickness of the varnish was
increased, I now added four coatings more, making
eight coatings in the whole, giving time for each new
coating to dry thoroughly before the next was applied ;
but I found, on repeating the experiment with this
thick covering of varnish, that I had passed the limit
of thickness which produced the greatest effect.

In order that the result of these experiments with
coatings of different thicknesses of spirit varnish may
be seen at one view, I shall here place them all to-
gether ; and I shall place by the side of each the result
of the standard experiment, which was made at the same
time with the instrument No. I, the sides which were
naked.

40 Inquiry concerning the Nature of Heat,

Time employed in cooling through
the given interval of 10 degrees.
Instrument Instrument

No. i, No. 2,

varnished. naked.

Experiment No. 4. — I coating of varnish, 42 min. 55^ min.

Experimented. 5. — 2 coatings, . • 35t " 55i "

Experiment No. 6. — 4 coatings, . . 30^ " 55! "

Experiment No. 7. — 8 coatings, . . 34^ " 55 "

Experiment No. 8. — Desirous of finding out what
effect colour would produce, I now painted the sides of
the instrument No. 1 black, with lamp-black mixed up
'with size (this paint being laid upon the eighth coating
of the varnish), and, repeating the experiment, its re-
sults were as follows : —

Time employed in

cooling through the

given interval.

The instrument No. I, naked, . . . . • 55i rnin.
The instrument No. 2, covered with 8 coatings of var-
nish, and painted black, . . . . . 34 "

Experiment No. 9. — Finding that the painting of this
thick coating of varnish black rendered the covering
still colder, or accelerated the cooling of the instrument,
I now washed off the black paint with warm water;
then washing off all the varnish with hot spirit of wine,
I painted the metallic sides of the instrument of a black
colour with lamp-black and size ; and when the paint
was quite dry, I repeated the experiment so often men-
tioned, when the results were as follows : —

Time employed in

cooling through the

given interval.

The instrument No. I, sides naked, . . . . 55^ min.
The instrument No. ^, painted black, . . . 35 "

Experiment No. 10. — In order to find out whether
the black colour had any particular efficacy in expediting
the cooling of the instrument, or whether another colour-
ing substance would not produce the same effect, when

and the Mode of its Communication. 41

mixed up with the same size, I now washed off the
black paint and painted the sides of the instrument
white y with whiting mixed up with size ; and, on repeat-
ing the experiment, the results were as follows : —

Time of cooling through
the given interval.

The instrument No. I, naked, . . . . • 55a nrin.
The instrument No. i, painted white, . . . 36 "

As in both the two last experiments it was found
necessary to paint the body of the instrument three or
four times over, in order to cover the polished metal so
completely as to prevent its shining through the paint ;
this, of course, occasioned the surface of the metal to be
covered with a thick coating of size, which, no doubt,
affected very sensibly the results of the experiment, and
rendered it impossible to determine, in a satisfactory
manner, what the effects really were, which were pro-
duced by the different colours used in the two experiments.

Experiment No. 1 1 . — With a view to throw some more
light on this interesting subject, having washed off the
paint from the instrument No. 2, I now rendered its
sides of a perfectly deep black colour, by holding it over
the flame of a wax candle ; and, repeating the usual ex-
periment, the results were as follows : —

Time of cooling through
the standard interval.

The instrument No. I, naked, 55! min.

The instrument No. 2, blackened, . 36^ "

In order to ascertain the quantity of matter which
composed this black covering, I weighed a small piece
of clean and very fine linen ; and, having wiped off
with it all the black matter from the body of the instru-
ment No. 2, in such a manner that the whole of it re-
mained attached to the linen, I weighed it again, and

42 Inquiry concerning the Nature of Pleat,

by that means discovered that the whole of this black
substance, which had so completely covered the sides
of the instrument (a surface of polished brass = 50
superficial inches) that the metal did not shine through
it in any part, weighed no more than T^ of a grain
Troy.

How this very thin covering, which, if the specific
gravity of the black matter were only equal to that of
water, would amount to no more than ?-£$-§ of an inch
in thickness, could expedite the cooling of the instru-
ment, in the manner it was found to do, is what still
remains to be shown ; but, before I proceed any farther
in these abstruse inquiries, I shall make a few observa-
tions relative to the results of the foregoing experi-
ments.

Although we may with safety presume, that the ve-
locities with which the heat escaped through the sides of
the instruments * were nearly as the times inversely taken
up in cooling through the given interval of 10 degrees ;
yet, as. some heat must have made its way, in the course
of the experiment, through the ends of the instrument,
notwithstanding all the care that was taken to prevent
it by covering them up with warm clothing, it is
necessary, in order to be able to compare the results of
the preceding experiments in a satisfactory manner, to

* I have found myself obliged in this, as in many other places, to make use of lan-
guage which is far from being as correct as I could wish. I do not believe that heat
ever makes its escape in the manner here indicated ; but I could not venture to use
uncommon expressions in pointing out the phenomena in question, however well
adapted such expressions might be to describe the events which really take place. If
it should be found that caloric, like phlogiston, is merely a creature of the imagination,
and has no real existence (which has ever appeared to me to be extremely probable),
in that case, it must be incorrect to speak of heat as making its escape out of one body,
and passing into another ; but how often are we obliged to use incorrect and figurative
language, in speaking of natural phenomena !

and the Mode of its Communication* 43

find out how much of the heat made its escape through
the covered ends of the instruments, during the time
the instruments were cooling through the interval in
question.

In order to determine that point, I now removed the
covering from the ends of the instrument No. i ; and,
when it was quite naked, I found, on making the ex-
periment, that it cooled through the given interval in
45^ minutes.

When its two ends and its cylindrical neck were cov-
ered up with warm clothing, I found, by taking the
mean of the results of several experiments, that it re-
quired 55J minutes to cool through the same interval.

On measuring the instrument with care, I found its
dimensions as follows : —

Inches.

Diameter of the body of the instrument, . . = 4.03
Length of the body, .'.»,. ss 3.96

Diameter of the neck of the instrument, . . = 0.8
Length of the neck, . . . . . = 4-

The superficies of the different parts of the instru-
ment are therefore as follows : —

Superficies of the vertical sides of the body (= 4.03

X 3-HJ59 X 3-96) — S°-136 inches.

Superficies of the flat circular bottom of the instru-
ment, (—4.03 X 3-I4I59 X ^) = 12.755 inches; de-
ducting nothing for that part which is covered by the
end of the tube, which serves as a support for the
instrument.

Superficies of the flat circular top of the instrument
(after deducting 0.502 of a superficial inch for the cir-
cular hole in its centre, made to receive the lower end
of the cylindrical neck) = 12.253 inches.

44 Inquiry concerning the Nature of Heat,

Superficies of the cylindrical neck of the instrument
(= 0.8 X 3.HI59 X 4) = 10-051 inches.

Supposing, now, that the heat passes with equal ve-
locity through the surface of all the different parts of the
instrument, when the instrument is naked, we can deter-
mine the quantity of heat which escaped through the
ends and neck of the instrument in the experiments in
which those parts of the instrument were covered with
warm clothing.

The whole of the metallic surface exposed to the air,
in the experiments made with the instrument when it
was quite naked, amounted to 85.195 superficial inches,
namely : —

Inches.

Surface of its vertical sides, . . . . =50.136
Surface of its lower end, . . . . =12.755
Surface of its upper end, . . . . = 12.253

Surface of its neck, .....= 10.051

Total surface, =85.195

When the instrument was exposed quite naked to the
air, it was found to cool through the standard interval
of 10 degrees in 45^- minutes.

Assuming, now, any given number as the measure of
the whole quantity of heat given ofT by the instrument
during the period above mentioned, we can ascertain
what part or proportion of that quantity passed off
through the sides of the instrument ; and what part of
it must have made its escape through its ends, and
through the sides of its neck.

As the quantities of heat given off are supposed to
have been as the quantities of surface exposed to the
air, if we suppose the whole quantity of heat lost by
the instrument to be = 10,000 parts, the quantity which

and tlie Mode of its Communication. 45

passed through the vertical sides of the instrument in
45! minutes, in the experiment, must have amounted
to 5885 parts. For, the whole of the surface of the
instrument, = 85.195 superficial inches, is to the whole
of the heat given off, = 10,000, as the surface of the
vertical sides of the instrument, = 50.136 superficial
inches, to the quantity of heat which must have passed
off through that surface in the given time, = 5885.

Now, as we may with safety conclude that the quan-
tity of heat which passes off through a given surface
must be as the times elapsed, all other circumstances
being the same, we can determine how much of the heat
given off by the instrument, in those experiments in
which its ends were covered, passed through the sides
of the instrument ; and, consequently, how much of it
must have made its way through its ends and neck, not-
withstanding their being covered:

The instrument with its ends and neck covered up
with eider-down, furs, &c., was found to cool through
the standard interval of 10 degrees in 55! minutes.
Now, as only 5885 parts of heat were found to pass
through the naked vertical sides of the instrument in
45 \ minutes, no more than 7015 parts could have
passed through the same surface in 55^ minutes ; con-
sequently, the remainder of the heat lost by the instru-
ment in the experiment in question, amounting to
2985 parts, must necessarily have made its way through
the covered ends and neck of the instrument in the
given period, 55} minutes.

Taking it for granted that these computations are
well founded, we may now proceed to a more exact de-
termination of the relative quantities of heat which
made their way through the sides of the instrument

46 Inquiry concerning the Nature of Heat,

No. 2, when its sides were exposed naked to the air,
and when they were covered with the different sub-
stances which appeared to facilitate the escape of the
heat.

In the experiment No. n, when the sides of the in-
strument were made quite black by holding it over the
flame of a wax candle, the instrument cooled through
the standard interval of 10 degrees in 36^ minutes.

In that time a quantity of heat = 1942 parts must
have passed off through the covered ends and neck of
the instrument; for, if a quantity = 2985 parts could
pass off that way in 55-! minutes, the quantity above
mentioned (= 1942 parts) must have escaped in 36^
minutes.

This quantity, = !942 parts, taken from the whole
quantity, = 10,000 parts, lost by the instrument in
cooling through the interval in question, leaves 8058
parts for the quantity which made its escape through
the sides of the instrument in the experiment in
question.

Now, if a quantity of heat = 7015 parts, requires
55^- minutes to make its way through the naked sides
of the instrument (as we have just seen), it would
require 63 f minutes for the quantity in question, =
8058 parts, to pass off through the same surface.

But, when that surface was blackened over the flame
of a candle, that quantity of heat passed off through it
in 36^ minutes.

Hence it appears, that the velocity with v/hich heat is
given off from the naked surface of a heated metal ex-
posed to cool in the air, is to the velocity with which it
is given off by the same metal when its surface is black-
ened in the manner above described, as 36^ to 63!, or

and the Mode of its Communication. 47

as 5654 to 10,000, very nearly ; for the velocities are as
the times of cooling, inversely.

Again, in the experiment No. 6, the sides of the in-
strument No. i being covered with four coatings of
spirit varnish, the instrument was found to cool through
the given interval of 10 degrees in 30^ minutes.

In that time, a quantity of heat = 1627 parts, must
have made its way through the covered ends of the in-
strument ; and the remainder, = 8373 parts, must have
made its way through its varnished sides.

This quantity, = 8373 parts, would have required
66| minutes to have made its way through the naked
sides of the instrument ; and, as it actually made its
way through the varnished sides of the instrument in
30^ minutes, it appears that the velocity with which
the heat was given off from the naked metallic surface,
was to the velocity with, which it was given off from
the same surface covered with four coatings of spirit
varnish, as 66 \ to 30^, or as 10,000 to 4566.

Without pursuing these computations any farther at
present, and without stopping to make any remarks on
the curious facts they present to us, I shall hasten to
experiments, from the results of which we shall obtain
more satisfactory information. But, before I proceed
any farther, I must give an account of an instrument I
contrived for measuring, or rather for discovering, those
very small changes of temperature in bodies, which are
occasioned by the radiations of other neighbouring
bodies, which happen to be at a higher or at a lower
temperature. ,

This instrument, which I shall take the liberty to
call a ther mo scope ^ is very simple in its construction.
Like the hygrometer of Mr. Leslie (as he has chosen

48 Inquiry concerning the Nature of Heat,

to call his instrument), it is composed of two glass
balls, attached to the two ends of a bent glass tube; but
the balls, instead of being near together, are placed at
a considerable distance from each other ; and the tube
.which connects them, instead of being bent in its mid-
dle, and 'its two extremities turned upwards, is quite
straight in the middle, and its two extremities, to which
its two balls are attached, are turned perpendicularly
upwards, so as to form each a right angle with the mid-
dle part of the tube, which remains in a horizontal
position.

At one of the elbows of this tube there is inserted a
short tube of nearly the same diameter, by means of
which a very small quantity of spirit of wine, tinged
of a red colour, is introduced into the instrument ; and,
after this is done, the end of this short tube (which is
only about an inch long) is sealed hermetically ; and all
communication is cut off between the air in the balls
of the instrument and in its tube and the external air
of the atmosphere.

A small bubble of the spirit of wine (if I may be
allowed to use that expression) is now made to pass
out of the short tube into the long connecting tube ;
and the operation is so managed that this bubble
(which is about f of an inch in length) remains station-
ary, at or near the middle of the horizontal part of the
tube, when the temperature (and consequently the elasticity}
of the air in the two balls, at the two extremities of the tube,
is precisely the same.

By means of a scale of equal parts, attached to the
horizontal part of the connecting tube, the position
of the bubble can be ascertained, and its movements
observed.

and the Mode of its Communication. 49

If now, the bubble being at rest in its proper place,
one of the balls of the instrument be exposed to the
calorific rays which proceed in all directions from a hot
body, while the other ball is defended from those rays
by a screen, the air in the ball so exposed to the action
of these rays will be heated ; and, its elasticity being
increased by this additional heat, its pressure will no
longer be counterbalanced Dy the elasticity of the colder
air in the other ball, and the bubble will be forced to
move out of its place and to take its station nearer to
the colder ball.

By presenting two hot bodies at the same time to
the two balls of the instrument, taking care that each
ball shall be defended from the action of the hot body
presented to the opposite ball, the distances of these
hot bodies from their respective balls may be so regu-
lated that their actions on those balls may be equal,
however the temperatures of those hot bodies may
differ, or however different may be the quantities or
intensities of the calorific rays which they emit.

The instrument will show, with the greatest certainty,
when the actions of these hot bodies on their respective
balls are equal ; for, until they become unequal, the
bubble will remain immovable in its place.

And, when the actions of two hot bodies on the
instrument are equal, the relative intensities of the rays
they emit may be ascertained by the distances of the
bodies from the balls of the ;nstrument.

If their distances from their respective balls are equal,
the intensities of the rays they emit must, of course, be
equal.

If those distances are unequal, the intensities will
probably be as the squares of the distances, inversely.

VOL. II. 4

5O Inquiry concerning the Nature of Heat,

A distinct and satisfactory idea may be formed of the
instrument I have been describing, from Fig. 2 (Plate 1 1.).

AB is a board, 27 inches long, 9 inches wide, and i
inch thick, which serves as a support for the bent tube
CDE, at the two extremities of which the two balls are
fixed. The two projecting ends of the tube, C and E,
which are in a vertical position, are each 10 inches
long ; and the horizontal part D of the tube, which is
fastened down on the board, is 17 inches in length.

The balls are each 1.625 inches in diameter. The
diameter of the tube is such, that i inch of it in length
would contain 15 grains Troy of mercury.

The pillar F, which, by means of a horizontal arm
projecting from it, serves for supporting the circular
vertical screen represented in the figure, is firmly fixed
in the board AB.

This circular screen (which is made of pasteboard,
covered on both sides with gilt paper) serves for pre-
venting one of the balls of the instrument from being
affected by the calorific rays proceeding from a hot body
which is presented to the opposite ball.

Besides the circular screen represented in the figure,
several other screens are used in making experiments ;
for the instrument is so extremely sensible, that the
naked hand presented to one of the balls, at the dis-
tance of several inches, puts -the bubble in motion ; and
it is affected very sensibly by the rays which proceed
from the person who approaches it to make the experi-
ments, unless care be taken, by the interposition of
screens, to prevent those rays from falling on the balls.
These screens can be best and most readily made by
providing light wooden frames, about two feet square,
and half an inch in thickness, and covering them on

:>&CO.

and the Mode of its Communication. 51

both sides, first with thick cartridge paper, and then
with what is called gilt paper; the metallic substance
(copper) with which one side of the paper is covered
being on the outside.

To support a movable screen of this kind in a ver-
tical position, it must of course be provided with a foot
or stand. Those I use are fastened to one side of a
pillar of wood by two screws, one of which passes
through the centre of the screen where the cross-bars
belonging to the frame of the screen meet, and the
other through the middle of the piece of wood which
forms the bottom of the screen. This pillar of wood,
which is turned in a lathe, is I2-|- inches high, and
is firmly fixed, at its lower end, in a piece of wood
8 inches square and i inch thick, which serves as a stand
or foot for supporting it.

As, in making experiments with this thermoscope, it is
frequently necessary to remove the hot bodies that are
presented to it farther from it or to bring them nearer
to it, in order that this may be done easily and expedi-
tiously by one person, and without its being necessary
for him to remove his eye from the bubble (which he
should constantly have in his view), I make use of a
simple machine, which I have found to be very useful.

It is a long and shallow wooden box, open at both
ends. It is 6 feet long, 12 inches wide, and 5 inches
deep, measured on the outside ; its vertical sides are
made of ij-inch deal; its bottom and top, of inch deal.
A part only of the top or cover of this box is fixed
down on the sides, and is immovable. The part of
the cover which is fixed, and on which the thermoscope
is placed, occupies the middle of the box, and is 13
inches in length. On the right and left of this fixed

52 Inquiry concerning the Nature of Heat,

part, the top of the box is covered by a sliding board,
1 feet 3 inches long, which passes in deep grooves, made
to receive it, in the sides of the box. A rack is fixed
to the under side of each of these sliding boards ; and
there is a small cog wheel in the box, the axis of which
passes through the sides of the box, and is furnished
with a winch in the front of the box. By turning round
these wheels by means of their winches (both of which
can be managed by the same person, at the same time),
the sliders may be moved backwards and forwards at
pleasure.

In order to ascertain with facility and dispatch the
distances of the hot bodies from their respective balls,
the top of the front side of the wooden box is divided
into inches on each side of the fixed part of the cover
of the box ; and there is a nonius belonging to each of
the sliders, which is placed in such a manner as to indi-
cate, at all times, the exact distance of the hot body
from its corresponding ball.

The level of the upper surface of that part of the
cover which is fixed is about J of an inch higher than
the level of the upper surface of the sliders, in order
that, when a thermoscope longer than this fixed part is
placed on it, the sliders may pass freely under its two
projecting ends without deranging it.

It is evident, from this description, that by placing
the thermoscope on the fixed part of the cover of the
box, with its two balls in a line parallel to the axis of
the box, and by placing the two hot bodies presented
to the two balls of the instrument (elevated to a proper
height) on stands set down on the s-liders, an observer,
by taking the two winches in his hands, keeping his
eye fixed on the bubble, may, with the greatest facility,

and the Mode of its Communication. 53

so regulate the distances of the hot bodies from their

O

respective balls that the bubble shall remain immov-
able in its place.

In order to be able to ascertain precisely the tem-
peratures of the hot bodies presented to this instru-
ment, and in order that their surfaces might be equal,
two equal cylindrical vessels, of thin sheet brass, with
oblique cylindrical necks, were provided, of the form
represented in Figure 3 (Plate II.).

This cylindrical vessel, which is placed in a horizon-
tal position in order that its flat bottom may be pre-
sented in a vertical position to one of the balls of the
thermoscope, is so fixed to a wooden stand, of a pecu-
liar construction, that it may be raised or lowered at
pleasure. This is necessary, in order that its axis may
be in the continuation of a line passing through the
centres of the two balls of the thermoscope.

This cylindrical vessel is 3 inches in diameter and 4
inches in length, and its oblique cylindrical neck is
O.86 of an inch in diameter and 3.8 inches in length.

The neck of this vessel is inserted obliquely into its
cylindrical body, in order that the water with which it
is occasionally filled may not run out of it, when the
body of the vessel is laid down in a horizontal posi-
tion, in the manner represented in the above-mentioned
figure.

A thermometer, with a cylindrical bulb 4 inches in
length, being inserted into the body of this vessel,
through its neck, shows the temperature of the con-
tained water.

Care is necessary, in constructing a thermoscope, to
choose a tube of a proper diameter; if its bore be too
small, it will be found very difficult to keep the spirit

54 Inquiry concerning the Nature of Heat,

of wine in one mass; and if it be too large, the little
horizontal column it forms (which I have called a bub-
ble) will be ill defined at its two ends, which will ren-
der it difficult to ascertain its precise situation. After
a number of trials I have found that a tube, the bore
of which is of such a size that I inch of it in length
contains about 15 or 18 grains Troy of mercury, an-
swers best. For a tube of that size the balls may be
about i J inch in diameter; and they should both be
painted black with Indian ink, which renders the in-
strument more sensible.

I have an instrument of this kind, the tube of which
is quite filled with spirit of wine, excepting only the
space occupied by a small bubble of air, which is in-
troduced into the middle of the horizontal part of the
tube; but it does not answer so well as those which
contain only a very small quantity of that liquid, suf-
ficient to form a small bubble.

But, without enlarging any farther, at present, on
the construction of these instruments, I now proceed to
give an account of the experiments for which they were
contrived.

Having found abundant reason to conclude, from the
results of the experiments of which an account has
already been given, that all the heat which a hot body
loses when it is exposed in the air to cool is not given
off to the air which comes into contact with it, but that
a large proportion of it escapes in rays, which do not
heat the transparent air through which they pass, but,
like light, generate heat only when and where they are
stopped and absorbed, — I suspected that in every case
when, in the foregoing experiments, the cooling of my
instruments was expedited by coverings applied to their

and the Mode of its Communication. 55

metallic surfaces, those coverings must, by some means
or other, have facilitated and accelerated the emission
of calorific rays from the hot surface.
' Those suspicions implied, it is true, the supposition
that different substances, heated to the same tempera-
ture, emit unequal quantities of calorific rays ; but I
saw no reason why this might not be the case in fact ;
and I hastened to make the following experiments,
which put the matter beyond all doubt.

Experiment No. 11. — Two equal cylindrical vessels,
made of sheet brass, and polished very bright, each
3 inches in diameter and 4 inches long, suspended by
their oblique necks in a horizontal position (being
placed on their wooden stands), were filled with water at
the temperature of 180°; and their circular flat bottoms
were presented in a vertical position to the two balls
of the thermoscope, at the distance of 2 inches.

When the two hot bodies were presented, at the same
moment, to the two balls of the instrument, or, what
was still better, when two screens were placed before
the two balls, at the distance of about an inch, and,
after the hot bodies were placed, these screens were
both removed at the same instant, the small column of
spirit of wine, which I have called a bubble., remained
immovable in its place, in the middle of the horizontal
part of the tube of the instrument.

If one of the hot bodies was now brought nearer the
ball to which it was presented (the other hot body re-
maining in its place), the bubble immediately began to
move from the hot body which was advanced forward,
towards the opposite ball to which the other hot body
was presented.

If, instead of advancing one of the hot bodies nearer

56 Inquiry concerning the Nature of Heat,

the ball to which it was presented, it was drawn back-
ward to a greater distance from it, the action of its calo-
rific rays on the ball was diminished by this increase of
distance ; and, being overcome by the action of the rays
from the hot body presented to the opposite ball (at a
smaller distance), the bubble was forced out of its
place, and obliged to move towards the ball which had
•been drawn backward.

When one of the hot bodies only was presented to
one of the balls, the bubble was immediately put in
motion, and by bringing the hot body nearer to the
ball, it might be driven quite out of the tube into the
opposite ball ; this, however, should never be done, be-
cause it totally deranges the instrument, as it is easy to
perceive it must do.

Having, by these trials, ascertained the sensibility
and the accuracy of my instrument, I now proceeded to
make the following decisive experiment.

Experiment No. 13. — Having blackened the flat cir-
cular bottom of one of the cylindrical vessels by hold-
ing it over the flame of a wax candle, I now filled both
vessels again with water at the temperature of i8o°F.,
and presented them, as before, to the two opposite balls
of the instrument at equal distances.

The bubble was instantly driven out of its place by
the superior action of the blackened surface, and did
not return to its former station till after the vessel
which was blackened had been removed to more than 8
inches from the ball to which it was presented ; the
other vessel, which had not been blackened, remaining
in its former situation, at the distance of 2 inches from
its ball.

The result of this experiment appeared to me to

and t/M Mode of its Communication. 57

throw a new light on the subject which had so long
engaged my attention, and to present a wide and very
interesting field for farther investigation.

I could now account, in a manner somewhat more
satisfactory, for those appearances in the foregoing ex-
periments which were so difficult to explain, — for the
acceleration of the passage of the heat out of my instru-
ments, which resulted from covering them with linen,
varnish, &c. ; and .1 immediately set about making a
variety of new experiments, from which I conceived I
should acquire a farther insight into those invisible
mechanical operations which take place when bodies are
heated and cooled.

Finding so great a difference in the quantities of calo-
rific rays which are thrown off by the polished surface
of a metal when exposed naked to the cold air and
when blackened^ I now proceeded to make experiments to
ascertain whether or not all those substances with which
the sides of my cylindrical vessels had been covered, and
which had been found to expedite the cooling of those
instruments, would also facilitate the emission of calo-
rific rays from the surfaces of the instruments I pre-
sented to the balls of my thermoscope ; and I found
this to be the case in fact.

As the results of all these experiments proved, in the
most decisive manner, that all the substances which,
when applied to the metallic surfaces of my large cylin-
drical vessels, had expedited their cooling, facilitated and
expedited the emission of calorific rays, I could no
longer entertain any doubts respecting the agency of
radiation in the heating and cooling of bodies. Many
important points, however, still remained to be investi-
gated before distinct and satisfactory ideas could be

58 Inquiry concerning the Nature of Heat,

formed respecting the nature of those rays and the
mode of their action.

I had hitherto made use of but one metal (brass) in
my experiments ; and that was not a simple, but a com-
pound metal. The first subject of inquiry which pre-
sented itself, in the prosecution of these researches, was
to find out whether or not similar experiments made
with other metals would give similar results.

Experiment No. 14. — Procuring from a gold-beater a
quantity of leaf goid and leaf silver about three times
as thick as that which is commonly used by gilders, I
covered the surfaces of the two large cylindrical vessels,
No. i and No. 2, with a single coating of oil varnish ;
and, when it was sufficiently dry for my purpose, I gilt
the instrument No. i with the gold leaf, and covered the
other, No. 2, with silver leaf. When the varnish was per-
fectly dry and hard, I wiped the instruments with cotton,
to remove the superfluous particles of the gold and sil-
ver, and then repeated the experiment, so often mentioned,
of filling the instruments with boiling-hot water, and
exposing them to cool in the air of a large quiet room.

The time of cooling through the given interval of
10 degrees was just the same as it was before, when the
natural surface of these brass vessels was exposed naked
to the air. 1 repeated the experiment several times,
but could not find that the difference in the metals
made any difference in the times of cooling.

Experiment No. 15. — Not satisfied to rest the deter-
mination of so important a point on a trial with three
metals only, — brass, gold, and silver, — I now provided
myself with two new instruments, — the one made of
lead, and the other covered with tinned sheet-iron, im-
properly, in England, called tin.

and the Mode of its Communication. 59

As the conducting power of lead, with respect to heat,
is much greater than that of any other metal, I con-
ceived that, if the radiation of a body were any way
connected with its conducting power, the cooling of the
water contained in the leaden vessel would necessarily
be either more or less rapid than in a vessel constructed
of any other metal.

The result of this experiment, as also the results of
several others similar to it, showed that heat is given
off with the same facility, or with the same celerity,
from the surfaces of all the metals. '

Is not this owing to their being all equally wanting
in transparency ? And does not this afford us a strong
presumption that heat is in all cases excited and com-
municated by means of radiations, or undulations, as I
should rather choose to call them ?

I am sensible, however, that there is another and
most important question to be decided before these
points can be determined ; and that is, whether bodies
are cooled in consequence of the rays they emit or by
those they receive.

The celebrated experiment of Professor Pictet, which
has often been repeated, appears to me to have put the
fact beyond all doubt, that rays, or emanations, which,
like light, may be concentrated by concave mirrors,
proceed from cold bodies ; and that these rays, when so
concentrated, are capable of affecting, in a manner per-
fectly sensible, a delicate air thermometer.

One of the objects I had principally in view, in con-
triving the before-described instrument, which I have
called a thermoscope, was to investigate the nature and
properties of those emanations, and to find out, if pos-
sible, whether they are not of the same nature as those

60 Inquiry concerning the Nature of

calorific rays which have long been known to proceed
from hot bodies.

My first attempts, in these investigations, were to
ascertain the existence of those emanations universally,
and to discover what visible effects they might be made
to produce independently of concentration by means
of concave mirrors.

Experiment No. 16. — My two horizontal cylindrical
vessels of sheet brass (of the same form and dimen-
sions), having been made very clean and bright, were
fixed to their stands ; and, being elevated to a proper
height to be presented to the balls of the thermoscope,
were set down near that instrument (which was placed
on a table in a large quiet room), where they were suf-
fered to remain several hours, in order that the whole
of this apparatus might acquire precisely the same tem-
perature.

Daylight was excluded by closing the window-shut-
ters ; and, in crder that the thermoscope might not be
deranged by the calorific rays proceeding from the person
of the observer on his entering the room to complete
the intended experiments, screens were previously placed
before the instrument in such a manner that its balls
were completely defended from those rays.

Things having been thus prepared, I entered the
room as gently as possible, in order not to put the air
of the room in motion, and, approaching the thermo-
scope, presented first one and then the other cylin-
drical vessel to one of the balls of the instrument ; but
it was not in the least degree affected by them, the bub-
ble of spirit of wine remaining immovably in the same
place.

Experiment No. 17. — Having assured myself, by these

and the Mode of its Communication. 61

previous trials, that the instrument was not sensibly
affected by a bright metallic surface being presented to
it, provided the temperature of the metal and that of
the instrument were the same, I now withdrew one of
the cylindrical vessels, and, taking it into another room,
I filled it with pounded ice and water.

Entering the room again, I now presented the flat
vertical bottom of this horizontal cylindrical vessel,
filled with ice and water, to one of the balls of the ther-
moscope at the distance of four inches.

The bubble of spirit of wine began instantly to
move with a slow, regular motion towards the cold
body ; and, having advanced in the tube about an inch,
it remained stationary.

On bringing the cold body nearer the ball to which it
was presented, the bubble was again put in motion, and
advanced still farther towards the cold body.

Experiment No. 18. — Although the result of the fore-
going experiment appeared to me to afford the most
indisputable proof of the radiation of cold bodies, and
that the rays which proceed from them have a power of
generating cold in warmer bodies which are exposed to
their influence, yet in a matter so extremely curious,
and of such high importance to the science of heat, I
was not willing to rest my inquiries on the result of a
single experiment.

In order to vary the substance, or species of matter,
presented cold to the instrument, and at the same time
to remove all suspicion respecting the possibility of the
effects observed being produced by currents of cold air
occasioned in the room by the presence of the cold
body, I now repeated the experiment with the following
variations.

62 Inquiry concerning the Nature of Heat,

The thermoscope was laid down on one side, so that
the two ends of its tube, to which its balls were attached,
instead of being vertical, were now in a horizontal posi-
tion ; and the cold body, instead of being presented
to the ball of the instrument on one side of it, and on
the same horizontal level with it, was now placed di-
rectly under if, and at the distance of 6 inches.

This cold body, instead of being a metallic substance,
was a solid cake of ice, circular, flat, and about 3 inches
thick, and 8 inches in diameter. It was placed in a
shallow earthen dish, about 9 inches in diameter below,
12 inches in diameter above, at its brim, and 4 inches
deep. The cake of ice being laid down on the bottom
of the dish, the top of the dish was covered by a circu-
lar piece of thick paper, 14 inches in diameter, which
had a circular hole in its centre, just 6 inches in di-
ameter.

This earthen dish, containing the ice, and thus cov-
ered, was placed perpendicularly under one of the balls
of the thermoscope, at such a distance that the centre
of the upper surface of the flat cake of ice was 6 inches
below the ball.

The result of this experiment was just what might
have been expected : the ice was no sooner placed under
the ball of the instrument than the bubble of spirit of
wine began to move towards that side where the cold
body was placed ; and it did not remain stationary till
after it had advanced more than an inch in the tube.

Experiment No. 19. — Desirous of discovering whether

, the surface of a liquid emits frigorific or calorific rays,

as solid bodies have been found to do, I now removed

the cake of ice from the earthen dish, and replaced it

with an equal mass of ice-cold water.

and the Mode of its Communication. 63

The result of this experiment was, to all appearance,
just the same as that of the last. The bubble moved
towards the cold body, and took its station in the same
place where it had remained stationary before. I found
reason, however, to conclude, after meditating on the
subject, that although the last experiment proves, in a
most decisive manner, that radiations actually proceed
from the surface of water^ yet the proof of the radiation
from the surface of ice, afforded by the preceding ex-
periment, is not equally conclusive ; for, as the tem-
perature of the air of the room in which these experi-
ments were made was many degrees above the freezing
point, it is possible, and even probable, that the surface
of the ice was actually covered with a very thin, and
consequently invisible, coating of water during the
whole of the time the experiment lasted.

Finding reason to conclude that frigorific rays are
always emitted by cold bodies, and that these emana-
tions are very analogous to the calorific rays which hot
bodies emit, I was impatient to discover whether all
cold bodies, at the same temperature, emit the same
quantity of rays, or whether (as I had found to be the
case with respect to the calorific rays emitted by hot
bodies) some substances emit more of them and some
less.

With a view to the ascertaining of this important
point, I made the following experiments.

Experiment No. 20. — Having found that a metallic
surface, rendered quite black by holding it over the
flame of a wax candle, emits a much larger quantity of
calorific rays when hot, than the same metal, at the
same temperature, throws ofF when naked, I was very
curious to find out whether blackening the surface of

64 Inquiry concerning the Natiire of

a cold metal would or would not increase, in like man-
ner, the quantity of frigorific rays emitted by it.

Having blackened, in the manner already described,
the flat bottom, or rather end, of one of my horizontal
cylindrical brass vessels with an oblique neck, I rilled it
with a mixture of ice and common salt ; and, filling
another vessel of the same kind, the bottom of which
was not blackened, with the same cold mixture, I pre-
sented them both, at the same instant, and at the same
distance, to the two opposite balls of my thermoscope.

The result of this experiment was perfectly conclu-
sive : the bubble of spirit of wine began immediately to
move towards the ball to which the blackened cold body
was presented ; indicating thereby that that ball was
more cooled by the frigorific rays which proceeded from
the blackened surface than the opposite ball was cooled
by the rays which proceeded from an equal surface of
naked metal, at the same temperature.

As this experiment appeared to me to be of great
importance, I repeated it several times, and always with
the same results ; the motion of the bubble, which con-
stituted the index of the instrument, constantly show-
ing that the frigorific rays from the blackened surface
were more powerful in generating cold than those
which proceeded from the naked metal.

The bubble, it is true, did not move so far out of its
place as it had done in the experiments in which hot
bodies were presented to the balls ; but this was not to
be expected, for though I had taken pains, by mixing
salt with the ice, to produce as great a degree of cold as
I conveniently could, yet still the difference between
the temperature of the balls and that of the bodies pre-
sented to them was much greater when the hot bodies

and the Mode of its Communication. 65

were used than when the experiments were made with
the cold bodies ; and it is evident, that the distance to
which the bubble is driven out of its place must neces-
sarily be greater or less in proportion as that difference
is greater or less.

In those experiments in which the horizontal cylin-
drical vessels were filled with hot water, and then pre-
sented to the balls of the instrument, the temperature
of the circular flat surfaces was that of 180°, while the
temperature of the air of the room in which those ex-
periments were made, and consequently that of the
balls, was about 60°; the difference amounts to no less
than 1 20 degrees of Fahrenheit's scale; but, in these
experiments with cold, the difference of the tempera-
tures at the moment when the cold bodies were first
presented to the instrument did not probably amount
to more than 40, or at the most 50 degrees; and in a
very few seconds it must have been reduced to less
than 30 degrees, in consequence of the freezing of
the water precipitated by the air of the atmosphere
on the surface of the vessel containing the cold mixt-
ure.

This precipitation of water by the surrounding air
was so copious that the brilliancy of the polish of the
metallic surface was almost instantly obscured by it,
and the vessels were very soon covered with a thick
coat of ice. These accidents, which were not to be
prevented, affected in a very sensible manner the results
of the experiment. The bubble, instead of remaining
stationary for some time after it had reached the point
of its greatest elongation, as it had done in the experi-
ments with hot bodies, had no sooner reached that
point than it began to return back towards the place
VOL. ii. 5

66 Inquiry concerning the Nature of Heat,

from which it had set out ; and, as often as I wiped off
the ice from the surface of the flat end of the vessel
which was not blackened, and presented it clean and
bright to the ball of the instrument, the bubble began
again to move towards the opposite side, — which, by
the bye, shows that ice emits a greater quantity of frigo-
rific rays than a bright metallic surface, at the same
temperature.

Having frequently observed, on presenting my hand
to one of the balls of the thermoscope, that the instru-
ment was greatly affected by the calorific rays which
proceeded from it, apparently much more so than it
would have been by a much hotter body of the same
quantity of surface, but of a different kind of substance,
placed at the same distance, I was extremely curious to
find out whether animal substances do not emit calorific
(and consequently frigorific) rays much more copiously
than other substances, and whether living animal bodies
do not emit them in greater abundance than dead ani-
mal matter.

The first experiment I made, with a view to the
investigation of this particular point, was as simple as
its result was striking and conclusive.

Experiment No. 21. — Having procured a piece of
gold-beater's skin (which, as is well known, is one of
the membranes that line the larger intestines in cattle,
and is exceedingly thin), I moistened it with water; and,
applying it, while moist, to the flat circular end of one
of my horizontal cylindrical vessels, it remained firmly
attached to the surface of the metal when it became
dry. I now filled this vessel, and another, of equal
dimensions, the end of which was not covered, with
hot water (at the temperature of 180°), and presented

and the Mode of its Communication. 67

them both, at the same moment, to the two balls of the
thermoscope, and at the same distance.

The bubble of spirit of wine was immediately driven
out of its place to a great distance; and did not return
to its former station till after the vessel whose end was
covered with gold-beater's skin had been removed to a
distance from the ball to which it was presented which
was five times greater than the distance at which the
other vessel was placed from the opposite ball.

I was induced to conclude, from the result of this
interesting experiment, that an animal substance emits
25 times more calorific rays than a polished metallic sur-
face of the same dimensions, both substances being at
the same temperature.

Experiment No. 22. — Having emptied both the ves-
sels used in the last experiment, and refilled them with
pounded ice and water, I now presented them again to
the thermoscope, at equal distances from their respec-
tive balls.

The result of this experiment confirmed the conclu-
sion I had been induced to draw from a former experi-
ment of the same kind (No. 13), the motion of the
bubble towards the vessel whose surface was covered
with gold-beater's skin showing that the rays which
proceeded from that animal substance were considerably
more efficacious in producing cold than those which
proceeded from the naked metal.

The radiation of cold bodies appearing to me to have
been proved beyond all doubt by the preceding experi-
ments, I now set about to investigate a very important
point which still remained to be determined : I en-
deavoured to find out whether the intensity of the
action of the frigorific rays which proceed from cold

68 Inquiry concerning the Natzire of Heat,

bodies, or their power of affecting the temperatures of
other warmer bodies, at equal intervals of temperature^ is,
or is not, equal to .the intensity of the action of the
calorific rays which proceed from hot bodies. To as-
certain this point, I made the following very simple
and decisive experiment.

Experiment No. 23. — Having placed the thermoscope
on a table, in the middle of a large quiet room, at the
temperature of 72° F., I presented to one of its balls, at
the distance of 3 inches, the flat circular end of one of
the horizontal cylindrical vessels (A) above described,
with an oblique cylindrical neck, this vessel being filled
with pounded ice and water ; and, at the same moment,
an assistant presented to the opposite side of the same
ball of the thermoscope, at the same distance (3 inches),
the flat end of the other similar and equal cylindrical
vessel (B), filled with warm water at the temperature
of 112° F., the opposite ball of the thermoscope being
hid and defended, by means of screens, from the actions
of the bodies presented to the other ball, as also from
the calorific rays which proceeded from the bodies of
the persons present.

From this description it appears, that while one of
the balls of the thermoscope was so defended by screens
that it could not be sensibly affected by the radiations
of the neighbouring bodies, the other ball was exposed
to the simultaneous action of two equal bodies, at equal
distances (two vertical metallic disks, 3 inches in di-
ameter, placed on opposite sides of the ball, at the
distance of 3 inches) ; one of these bodies being at the
temperature of 32° F., or 40 degrees below that of the
ball, while the other was at 112° F., or 40 degrees
above the temperature of the ball.

and the Mode of its Communication. 69

I knew, from the results of former experiments, that
this ball would, at the same time, be heated by the calo-
rific rays from the hot body and cooled by the frigo-
rific rays from the cold body ; and I concluded that if
its mean temperature should remain unchanged under
the influence of these two opposite actions, that event
would be a decisive proof of the equality of the inten-
sities of those actions.

The result of the experiment showed that the inten-
sities of those opposite actions were in fact equal ; the
bubble of spirit of wine, which, by its motion, would
have indicated the smallest change of temperature in
the ball of the thermoscope to which the hot and
the cold bodies were presented, remained at rest.

On removing the cold body a little farther from the
ball, — to the distance of 3} inches, for instance, — the
hot body remaining in its former station, at the distance
of 3 inches, the bubble began immediately to move to-
wards the opposite ball of the thermoscope, indicating
an increase of heat in the ball exposed to the actions of
the hot and the cold bodies ; but, when the hot body
was removed to a greater distance, the cold body re-
maining in its place, the bubble indicated an increase of
cold.

The celerity with which the ball of the thermoscope
acquired heat or cold might be estimated by the ve-
locity with which the bubble of spirit of wine advanced
or retired in its tube ; but, on the most careful and
attentive observation, I could not perceive that it
moved faster when the ball was acquiring heat than
when it was acquiring cold, provided that the hot and
the cold bodies from which the calorific and frigorific
rays proceeded were at the same relative distances.

70 Inquiry concerning the Natiire of Heat,

From these experiments, which I lately repeated at
Geneva, in the presence of Professor Pictet, Mons. de
Saussure, M. Senebier, and several other persons, we
may venture to conclude, that, at equal intervals of tem-
perature, the rays which generate cold are just as real,
and just as intense, as those which generate heat ; or,
that their actions are equally powerful in changing the
temperatures of neighbouring bodies.

On a superficial view of this subject, it might appear
extraordinary that so important a fact as that of the
frigorific radiations of cold bodies should have been so
long unnoticed, while the calorific radiations of hot
bodies have been so well known ; but, if we consider
the matter with attention, our surprise will cease.
Those radiations by means of which the temperatures
of neighbouring bodies are gradually changed and equal-
ized are not sensible to our feeling unless the intervals
of temperature be very considerable ; and the constitu-
tion of things is such, that, while we are often exposed
to the influence of bodies heated several thousand de-
grees (as measured by the thermometer) above the
mean temperature of the surface of the skin, it is very
seldom that we have opportunities of experiencing the
effects of the radiations of bodies much colder than
ourselves, and we have no means of producing degrees
of cold which bear any proportion to the intense heats
excited by means of fire.

From the result of the experiment of which an ac-
count has just been given, it is evident that we should
be just as much affected by the calorific rays emitted by
a cannon bullet at the temperature of 160 degrees of
Fahrenheit's scale (= 64 degrees above that of the
blood) as by the frigorific rays of an equal bullet, ice

and the Mode of its Communication. 7 1

cold, placed at the same distance ; and that a bullet at
the temperature of freezing mercury could not affect us
much more sensibly, by its frigorific rays, than an equal
bullet at the temperature of boiling water would do
by its calorific rays ; — but at these comparatively small
intervals of temperature, the radiations of bodies are
hardly sensible, and could never have been perceived,
much less compared and estimated, without the assist-
ance of instruments much more delicate than our or-
gans of feeling. Hence we see how it happened that
the frigorific radiations of cold bodies remained so long
unknown. They were suspected by Bacon ; but their
existence was first ascertained by an experiment made
at Florence towards the end of the seventeenth century.
And it is not a little curious, that the learned academi-
cians who made that experiment, and who made it with
a direct view to determine the fact in question, were so
completely blinded by their prejudices respecting the
nature of heat that they did not believe the report of
their own eyes ; but, regarding the reflection and con-
centration of cold (which they considered as a negative
quality) as impossible^ they concluded that the indica-
tion of such reflection and concentration which they
observed must necessarily have arisen from some error
committed in making the experiment.

Happily for the progress of science, the matter was
again taken up, about twenty years ago, by Professor
Pictet ; and the interesting fact, which the Florentine
academicians would not discover, was put beyond all
doubt. But still, this ingenious and enlightened phi-
losopher did not consider the appearances of a reflection
of cold, which he observed in his experiments, as being
real; nor was he led by them to admit the existence of

72 Inquiry concerning the N attire of Heat,

frigorific emanations from cold bodies, analogous to
those calorific emanations from hot bodies which he
calls radiant heat. He everywhere speaks of the reflec-
tion of cold (by metallic mirrors) as being merely appar-
ent ; and it is on that supposition that the explanation
he has given of the phenomena is founded.

On a supposition that the caloric of modern chemists
has any real existence, and that heat, or an increase of
temperature in any body, is caused by an accumulation
of that substance in such body, the reflection of cold
would indeed be impossible ; and the supposition that
such an event had taken place would be absurd, and
could not be admitted, however striking and convincing
the appearances might be which indicated that event.
But, to return from this digression : —

Having found that the intensity of the calorific rays
emitted by a hot body, at any given temperature, de-
pends much on the surface of such body, — that a pol-
ished metallic surface, for instance, throws off much
fewer rays than the same surface, at the same tempera-
ture, would emit if painted, or blackened in the smoke
of a lamp or candle, — I was desirous of finding out
whether the frigorific rays from cold bodies are affected
in the same manner, by the same means, and in the
same degree.

It was to ascertain that point that the experiment
No. 20 was made ; and although the result of that ex-
periment afforded abundant reason to conclude that
those substances which, when hot, throw off calorific
rays in the greatest abundance, actually throw off great
quantities of frigorific rays when they are cold, yet, as
the relative quantities of these rays could, not be ex-
actly determined by that experiment, in order to ascer-

and the Mode of its Communication. 73

tain so important a fact I had recourse to the following
simple contrivance.

Experiment No. 24. — Having found, by the result
of the last experiment (No. 23), that the calorific ema-
nations of a circular disk of polished brass, 3 inches in
diameter, at the temperature of 112° F., were just
counterbalanced by the frigorific emanations of an equal
disk of the same polished metal, at the temperature of
32° F., placed opposite to it, so that one of the balls of
the thermoscope placed between these two disks, at
equal distances, was just as much heated by the one as
it was cooled by the other, I now blackened the two
disks, by holding them over the flame of a wax candle,
and repeated the experiment with them so blackened.

I knew, from the results of former experiments, that
the intensity of the calorific radiations from the hot
disk would be very much increased, in consequence of
its surface being blackened ; and I was certain that, if
the intensity of the frigorific radiations of the cold disk
should not be increased in exactly the same degree, the
ball of the thermoscope, exposed to the simultaneous
actions of these two disks, could not possibly remain at
the same constant temperature, that of 72°.

The result of the experiment was very decisive ; the
bubble of spirit of wine remained at rest, — which proved
that the intensities of the rays emitted by the two disks
still continued to be equal at the surface of the ball
of the thermoscope, which, at equal distances, was ex-
posed to their simultaneous action.

Hence we may conclude, that those circumstances
which are favourable to the copious emission of calorific
rays from the surfaces of hot bodies are equally favour-
able to a copious emission of frigorific rays from similar
bodies when they are cold.

74 Inquiry concerning tlie Nature of Heat,

But it is time to consider these emanations in a new
point of view. What difference can there be between
calorific rays and frigorific rays ? Are not the same
rays either calorific or frigorific according as the body at
whose surface they arrive is hotter or colder than that
from which they proceed ?

Let us suppose three equal bodies, A, B, and C,
(the globular bulbs of three mercurial thermometers,
for instance,) to be placed at equal distances (3 inches)
in the same horizontal line ; and let A be at the tem-
perature of freezing water, B at the temperature of 72°
F., and C at that of 102° F. The rays emitted by B
will be calorific in regard to the colder body A, but in
respect to the hotter body C they will be frigorific;
and, from the results of the two last experiments, we
have abundant reason to conclude that they will be
just as efficacious in heating the former as in cooling
the latter.

Before I proceed to give an account of the experi-
ments which were made with a view to determine the
relative quantities of rays emitted from the surfaces of
various substances, from living animals, dead animal
matter, &c. (which I must reserve for a future com-
munication), I shall lay before the Society the results
of several experiments, of various kinds, which were
made with a view to the farther investigation of the
radiations of hot and of cold bodies, and of the effects
produced by them.

Experiment No. 25. — Having found, from the re-
sults of the experiments No. 21 and No. 22, that great
quantities of rays are thrown off from the surface of the
animal substance used in those experiments (gold-beat-
er's skin), I now covered the whole of the external sur-

and the Mode of its Communication. 75

face of one of my large cylindrical passage thermom-
eters (No. 4) with that substance ; and, filling it with
boiling-hot water, exposed it to cool gradually in the
air of a large quiet room, in the manner often described
in former parts of this paper; another similar naked
standard instrument (No. 3 ) being filled with hot water at
the same time, and exposed to cool in the same situation.
The temperature of the air of the room being 51 J°,
the instruments were found to cool through the stand-
ard interval of 10 degrees, namely, from IOI-J- to 91^,
in the following times : —

No. 4, covered \\\\k gold-beater's skin, . in 27! minutes.
No. 3, which was naked, ... in 45 "

Experiment No. 16. — Being desirous of finding out
whether or not the covering of animal matter, which
had so remarkably facilitated the cooling of the instru-
ment No. 4, would be equally efficacious in facilitating
the passage of heat into the instrument, I suffered both
instruments to remain in the cold room all night ; and,
entering the next morning, at half an hour past seven
o'clock, I found the temperature of the water in the
naked instrument, No. 3, to be 50^°; that in the instru-
ment No. 4, which was covered with gold-beater's skin,
was 49!"° ; while the air of the room was at 48°.

At 7 h. 30 m. A. M. I removed both instruments into
a warm room, and observed the times of their acquiring
heat to be as expressed in the following table.

Observed Temperature. Temperature

imes when the obser- No. 3, No. 4. of the air of

vations were made. naked. covered, the room.

At 7 h. 30 rn. . . 50^° . . 49^° . . 64°

7 45 - 5'i 5»4 • 64*

8 .. . . 5** • • 53* ' • 6*

8 15 • 531 S4i

j6 Inquiry concerning the Nature of Heat,

Observed Temperature. Temperature

Times when the obser- No. 3, No. 4, of the air of

vations were made. naked. covered. the room.

At 8h. 3011). . . 54$ . 56 ...

8 45 • 55i . 57i

9 ... , 564 . . 58£ . ...
93° • 57^ • 60

10 ... . 58* . . 6i£ . ...

10 30 . 591- . 62^

11 . . .• . 6oJ . -63 . ...
ii 30 . 6 1 63' . 641

The results of this experiment, and of several others
similar to it, showed, in a manner which appeared to
me to be perfectly conclusive, that those substances
which part with heat with the greatest facility, or celer-
ity, are those which also acquire it most readily, or with
the greatest celerity.

If we might suppose that the temperatures of bodies
are changed, not by the rays they emit, but by those
they receive from other neighbouring bodies, this fact
might easily be explained ; but, without stopping to
form any hypothesis for the explanation of these appear-
ances, I shall proceed in my account of the various
attempts I have made to elucidate, by new experiments,
those parts of this interesting subject which still ap-
peared to be enveloped in obscurity.

As the cooling of hot bodies is so much accelerated
by covering their surfaces with such substances as emit
calorific rays in great abundance, or with such as are
much affected by the frigorific rays of the colder bodies
by which they are surrounded, it seems to be highly
probable that a comparatively small part of the heat
which a body so cooled actually loses is acquired by
the air ; a much greater proportion of it passing off
through that transparent fluid, under the form of calo-
rific rays, without affecting its temperature.

and the Mode of its Communication. 77

If this supposition should turn out to be well founded,
the knowledge of the fact would enable us to explain
several interesting phenomena, and particularly that
most curious process by means of which living animals
preserve an equal temperature, notwithstanding the vast
quantities of heat that are continually generated in the
lungs, and notwithstanding the great variations which
take place in the temperature of the air in which they
live.

It is evident, that the greater the power is which an
animal possesses of throwing off heat from the surface
of his body, independently of that which the surround-
ing air takes off, the less will his temperature be affected
by the occasional changes of temperature which take
place in the air, and the less will he be oppressed by
the intense heats of hot climates.

It is well known that negroes and people of colour
support the heats of tropical climates much better than
white people. Is it not probable that their colour may
enable them to throw off calorific rays with great facil-
ity, and in great abundance ; and that it is to this cir-
cumstance they owe the advantage they possess over
white people in supporting heat ? And, even should it
be true, that bodies are cooled, not in consequence of
the rays they emit, but by the action of those frigorific
rays they receive from other colder bodies (which I
•much suspect to be the case), yet, as it has been found
by experiment that those bodies which emit calorific
rays in the greatest abundance are also most affected by
the frigorific rays of colder bodies, it is evident that in
a very hot country, where the air and all other sur-
rounding bodies are but very little colder than the sur-
face of the skin, those who by their colour are prepared

78 Inquiry concerning the Nature of Heat,

and disposed to be cooled with the greatest facility will
be the least likely to be oppressed by the accumulation
of the heat generated in them by respiration, or of that
excited by the sun's rays.

With a view to throw some light on this interesting
subject, I made the following experiments.

Experiment No. 27. — Having covered the flat ends
of both my horizontal cylindrical vessels with gold-
beater's skin, I painted one of these coverings (of this
animal substance) black, with Indian ink; and then,
filling both vessels with boiling-hot water, I presented
them, at equal distances, to the two opposite balls ' of
the thermoscope.

The bubble of spirit of wine was immediately driven
out of its place by the superior efficacy of the calorific
rays which proceeded from the blackened animal sub-
stance.

On repeating this experiment a great number of
times, and when the water in the vessels was at different
degrees of temperature (the temperature being the same
in the two vessels in each experiment), the results uni-
formly indicated that calorific rays were thrown off
from the black surface in greater abundance than from
the equal surface which was not blackened.

Although the results of these experiments appeared
to me to be so perfectly conclusive as to establish the
fact in question beyond all possibility of doubt, yet, in
so interesting an inquiry, I was desirous, by varying
my experiments, to bring, if possible, a variety of
proofs to support the important conclusions which
result from it.

Experiment No. 28. — Having covered the two large
cylindrical vessels, No. 3 and No. 4, with gold-beater's

and the Mode of its Communication. 79

skin, I painted one of them black, with Indian ink;
and, filling them both with boiling-hot water, I exposed
them to cool, in the manner already often described, in
the air of a quiet room.

No. 4, which was blackened, cooled through the stand-
ard interval of 10 degrees in 23 1- minutes; while the
other, No. 3, which was not blackened, took up 28
minutes in cooling through the same interval.

In a former experiment (No. 25), the instrument
No. 4, covered with gold-beater's skin, but not black-
ened, had taken up 27! minutes in cooling through
the given interval, as we have before seen.

The results of these experiments do not stand in
need of illustration ; and I shall leave to physicans and
physiologists to determine what advantages may be
derived from a knowledge of the facts they establish,
in taking measures for the preservation of the health of
Europeans who quit their native climate to inhabit hot
countries.

All I will venture to say on the subject is, that were
I called to inhabit a very hot country, nothing should
prevent me from making the experiment of blackening
my skin, or at least of wearing a black shirt, in the
shade, and especially at night ; in order to find out if,
by those means, I could not contrive to make myself
more comfortable.

Several of the savage tribes which inhabit very cold
countries besmear their skins with oil, which gives
them a shining appearance. The rays of light are re-
flected copiously from the surface of their bodies. May
not the frigorific rays, which arrive at the surface of
their skin, be also reflected by the highly polished sur-
face of the oil with which it is covered ?

8o Inquiry concerning the Nature of Heat,,

If that should be the case, instead of despising these
poor creatures for their attachment to a useless and
loathsome habit, we should be disposed to admire their
ingenuity, or rather to admire and adore the goodness
of their invisible Guardian and Instructor, who teaches
them to like, and to practise, what he knows to be use-
ful to them.

The Hottentots besmear themselves, and cover their
bodies, in a manner still more disgusting. They think
themselves fine, when they are besmeared and dressed
out according to the loathsome custom of their country.
But who knows whether they may not in fact be more
comfortable, and better able to support the excessive
heats to which they are exposed ? From several experi-
ments which I made, with a view to elucidate that
point, (of which an account will be given to this Soci-
ety at some future period,) I have been induced to con-
clude that the Hottentots derive advantages from that
practice exactly similar to those which negroes derive
from their black colour.

It cannot surely be supposed that I could ever think
of recommending seriously to polished nations the
filthy practices of these savages. That is very far in-
deed from being my intention, for I have ever consid-
ered cleanliness as being so indispensably necessary to
comfort and happiness that we can have no real enjoy-
ment without it ; but still I think that a knowledge
of the physical advantages which those savages derive
from such practices may enable us to acquire the same
advantages by employing more elegant means. A
knowledge of the manner in which heat and cold are
excited would enable us to take measures for these
important purposes with perfect certainty ; in the mean

and the Mode of its Communication. 81

time, we may derive much useful information by a
careful examination of the phenomena which occasion-
ally fall under our observation.

If it be true that the black colour of a negro, by
rendering him more sensible to the few frigorific rays
which are to be found in a very hot country, enables
him to support the great heats of tropical climates with-
out inconvenience, it might be asked how it happens
that he is able to support, naked, the direct rays of a
burning sun.

Those who have seen negroes exposed naked to the
sun's rays, in hot countries, must have observed that
their skins, in that situation, are always very shining.
An oil exudes from their skin, which gives it that shin-
ing appearance ; and the polished surface of that oil
reflects the sun's calorific rays.

If the heat be very intense, sweat makes its appear-
ance at the surface of the skin. This watery fluid not
only reflects very powerfully the calorific rays from the
sun which fall on its polished surface, but also, by its
evaporation, generates cold.

When the sun is gone down, the sweat disappears ;
the oil at the surface of the skin retires inwards ; and
the skin is left in a state very favourable to the admis-
sion of those feeble frigorific rays which arrive from the
neighbouring objects.

But I shall refrain from pursuing these speculations
any farther at present.

I shall now proceed to give an account of several ex-
periments, of various kinds, which were made with a
view to a farther investigation of the radiations of cold
bodies.

Having found, by several of the foregoing experi-

82 Inquiry concerning the Nature of Heat,

ments, that the radiations of cold bodies affected my
thermoscope very sensibly, even when placed at a con-
siderable distance from it, and in situations where cur-
rents of cold air could not be suspected to exist, I was
desirous of rinding out whether the cooling of a hot
body would or would not be sensibly accelerated by
those rays. To determine that point, I made the fol-
lowing experiment.

Experiment No. 29. — Having provided two conical
vessels, made of thin sheet brass, each 4 inches in diam-
eter at the base, and 4 inches high, ending above in a
cylindrical neck, 0.88 of an inch in diameter, I enclosed
each of them in a cylinder of thin pasteboard, covered
with gilt paper, and then covered them up with rabbit-
skins, which had the hair on them, in such a manner that
no part of these vessels, except their flat bottoms, was
exposed naked to the air. I then covered their bottoms
with gold-beater's skin, painted black with Indian ink,
in order to render them as sensible as possible to calo-
rific and frigorific rays.

This being done, I suspended these two vessels in
an erect position, or with their bottoms downwards, to
the two opposite horizontal arms of a wooden stand,
provided for the experiment; and I placed under each
of them a pewter platter, blackened on the inside by
holding it over a lighted wax candle.

Each of these platters was 12 inches in diameter,
and they were supported on the top of two shallow
earthen dishes, each of which was 1 1^ inches in diameter
at its brim ; these earthen dishes being supported on
circular wooden stands 10 inches in diameter.

A circular piece of thick drawing-paper, i2| inches
in diameter, with a circular hole in its centre, just 6

and the Mode of its Communication. 83

inches in diameter, was placed on each of the platters,
and served as a perforated cover to it.

The stands on which the platters were supported
were of such a height that the upper surface of the flat
bottom of each of the platters was elevated just 40
inches above the level of the floor of the room ; and
the horizontal arms of the wooden stand which sup-
ported the conical vessels were of such a height that
the flat bottoms of these vessels (which were placed per-
pendicularly over the centres of the platters) were just
4 inches above the flat horizontal surface of the bottoms
of the platters.

One of the platters was at the temperature of the air
of the room (63° F.), but the other was kept constantly
ice-cold, during the whole of the time the experiment
lasted, by means of pounded ice and water, which was
put into the earthen dish, over which, or rather in
which, this platter was placed.

Each of the platters was just I inch deep, measured
from the level of the top of its brim to the level of the
upper surface of the flat part of its bottom ; this flat
part was about 8 inches in diameter.

The £wo conical vessels were now filled with boiling-
hot water, and the times of their cooling were carefully
observed.

From the above description of the apparatus used in
this experiment, it is evident that the vessel which was
suspended over the ice could not be reached by any
streams of cold air that might be occasioned by that ice,
or by the cooled sides of the vessel which contained
it ; for the air which, coming into contact with the sides
of that vessel, was cooled by it, becoming specifically
heavier than it was before, naturally descended, and

84 Inquiry concerning the Natiire of Heat,

spread itself out on the floor of the room ; and the per-
forated circular sheet of paper, which was laid down
horizontally on the platter, effectually prevented any of
the air so cooled from being thrown upwards against
the bottom of the conical vessel (placed immediately
over the platter), by any occasional undulation of the air
in the room.

To preserve the air of the room in a state of perfect
quietness, not only the doors and windows, but even
the window-shutters of the room were kept shut ; so
much light only being admitted occasionally as was
necessary to observe the thermometers which were
placed in the conical vessels.

In order to guard still more effectually the bottoms
of the vessels which were cooling from the effects of
occasional undulations in the air of the room, over each
of these vessels there was drawn a cylindrical covering
of very fine thin post paper, the lower open end of
which projected just half an inch below the horizontal
level of the flat bottom of the vessel. These cylin-
drical coverings of post paper were made to fit as ex-
actly as possible the cylinders of pasteboard by which
the sides of the conical vessels were covered and de-
fended from the air ; and the warm coverings of fur
(rabbit-skins) were put over all.

To confine the heat still more effectually, a quantity
of eider-down had been introduced between the outside
of each conical vessel and its cylindrical neck, and the
inside of the hollow cylinder of pasteboard in the axis
of which it was fixed and confined.

The result of this experiment was very conclusive.
The conical vessel which was suspended over the ice-
cold pewter platter cooled through the standard interval

and the Mode of its Communication. 85

of 10 degrees (namely, from the point of 50 degrees to
that of 40 degrees above the temperature of the air of
the room) in 33 minutes and 42 seconds ; whereas
the other vessel, which was not over ice, required 39
minutes and 15 seconds to cool through the same in-
terval.

Experiment No. 30. — On repeating this experiment
the next day, the air of the room still remaining at 63°,
the times of cooling through the given interval were as
follows : —

Min. Sec.

The vessel suspended over the ice-cold platter, in . 33 15
The other vessel, in 39 3°

From the results of these experiments (which were
made with the greatest possible care) it appears that
the radiations of cold bodies act on warmer bodies at a
distance, and gradually diminish their temperatures.

It will likewise be evident, when we consider the
matter with attention, that the cooling of the vessel
which was suspended over the ice-cold platter was in
fact considerably more accelerated by the frigorific radia-
tions from that cold surface than it appears to have
been when we estimate the effects produced simply by
the difference of the times taken up in the cooling of
the two vessels, without having regard to any other
circumstance.

These times are, no doubt, inversely as the velocities
of cooling ; but, as all the heat lost by the vessels dur-
ing the time of their cooling did not pass off through
their flat bottoms, and as the rays from the cold sur-
face fell on the bottom only of the vessel which was sus-
pended over it, without at all affecting its covered sides,
the velocity with which the heat made its way through

86 Inquiry concerning the Nature of Heat,

the covered sides of the vessels was the same in both ;
consequently, more heat must have passed that way,
and of course less through the bottom of the vessel,
when the time of cooling was the longest, that is to say,
in the vessel which was not p aced over ice.

As the cooling of these vessels is a complicated pro-
cess, I will endeavour to elucidate the subject still
farther.

As the two conical vessels were of the same form and
dimensions, and contained equal quantities of hot water,
the quantities of heat they parted with, in being cooled
the same number of degrees, must of course have been
equal.

Expressing that quantity by the algebraic symbol a,
and putting x =. the quantity of heat which passed off
through the covered sides of the vessel which was sus-
pended over ice during the time it was cooling through
the given interval of 10 degrees, and jy = the quantity
which passed off through the covered sides of the other
vessel during the time that vessel was coo ing through
the same interval, the quantity of heat which passed
off through the bottom of the vessel which was placed
over ice during the time it was cooling through the
given interval must have been = a — x3 and that
which passed off through the bottom of the other ves-
sel during the time of its cooling through the same
interval = a — y.

But, as the velocities of the heat through the covered
sides of both vessels must have been equal, the quanti-
ties of heat which passed off that way must have been
as the times of cooling.

The times of cooling in the last-mentioned experi-
ment (No. 30) were as follows : —

and the Mode of its Communication. 87

Min. Sec. Seconds.

Of the vessel suspended over ice, . . 33 15=1995
Of the other vessel, . . . . 3930=2370

x is therefore tojy, as 1995 to 2370; consequently,

x = '-Sr = 0.841 77 y;

And, substituting for x its value = 0.84177^, the
quantities of heat which passed off through the bottoms
of the two vessels, in the experiment in question (No.
30), must have been = a — 0.84177 y for the vessel
which was suspended over ice, and = a — y fort he
other vessel.

And, asjy is greater than 0.84177 jy, consequently^ —
0.84177 y is greater than a — jy, or the quantity of heat
which passed off through the bottom of the vessel which
was cooled the most rapidly was greater than that
which passed off through the bottom of the other vessel ;
and hence we perceive that the effect produced by the
frigorific rays from the cold surface, in the experiments
in question, was greater than it appeared to be at first
sight, when it was estimated by the times of cooling.

To determine exactly how much the cooling was ac-
celerated by the presence of the cold body, it is neces-
sary to find out how much heat actually passed off
through the bottoms of the two vessels, in the experi-
ments in question. This we will endeavour to do by
comparing the results of those experiments with the re-
sults of some other experiments of a similar nature.

In the experiment No. 28, a cylindrical vessel of thin
sheet brass, 4 inches in diameter, and 4 inches in height,
covered with gold-beater's skin painted black with In-
dian ink, being filled with hot water and exposed to
cool in the air of a large quiet room, cooled from the
point of 50 degrees to that of 40 degrees above the
temperature of the air of the room in 23 \ minutes.

88 Inquiry concerning the Nature of Heat,

The quantity of surface by which this vessel was ex-
posed to the cold air was = 74.5581 superficial inches,
exclusive of its neck, which was well covered up with
fur.

The quantity of surface which was exposed to the air,
in the foregoing experiments with the conical vessels, or
the area of the bottom of each of the vessels, was (4 X
3.14159) = 12.4263 superficial inches.

As the diameters and heights of the conical and cylin-
drical vessels were equal, the contents of the former
must have been to the contents of the latter as i to 3 ;
and the quantities of heat which they lost in cooling
were .as their contents.

If now the cylindrical vessel lost a quantity of heat
= 3 in 23^ minutes, it would have disposed of a
quantity = I (equal to that which the conical vessel
lost) in one third part of that time, or in 7 minutes
and 50 seconds.

But the quantity of surface exposed to the air in the
experiment with the cylindrical vessel was to that so
exposed in the experiment with the conical vessel as
74.5581 to 12.4263, or as 6 to i.

Now, as the time in which any given quantity of heat
can pass out of any closed vessel into or through any
cold fluid medium by which the vessel is surrounded
must be inversely as the surface of the vessel, other
things being equal, if a quantity of heat = i could
pass out of the cylindrical vessel in 7 minutes and 50
seconds, it would require 6 times as long, or 47 min-
utes, to pass out of the conical vessel through its fiat
bottom, supposing no heat whatever to escape through
the covered sides of that vessel.

If now the whole of the heat which the conical vessel

and the Mode of its Communication, 89

actually lost would have required 47 minutes to have
passed through the bottom of that vessel, it is evident
that the quantity which actually passed through that
surface, in the experiment in question (No. 30), could
not have been to the whole quantity actually lost in a
greater proportion than that of the times, or as 39}
to 47.

Assuming any given number — as 10,000, for instance
— to represent the whole of the heat lost in the experi-
ment, we can now determine what part or proportion
of it passed off through the bottom of the conical ves-
sel, and consequently how much of it must have made
its way through its covered sides.

If the whole quantity, = 10,000, would have re-
quired 47 minutes to have passed through the bottom
of the vessel, the quantity which actually passed through
that surface in 39^ minutes could not possibly have
amounted to more than 8404, = a — y.

For it is 47 minutes to 10,000, as 39! minutes to
8404. The remainder of the heat, = 10,000 — 8404
= 1396 parts, (= y) must have made its way through
the covered sides of the vessel.

And, if a quantity of heat =1396 required 397} min-
utes to make its way through the covered sides of one
of the conical vessels, the quantity which made its way
through the covered sides of the other in 33 ' j- minutes
could not have amounted to more than 1175 parts ; and
the remainder of that which was actually disposed of in
the experiment = 10,000 — n?5 — 8825 (==" a —
#,) must have passed off through the bottom of the in-
strument.

Hence it appears, that the quantity of heat which
actually passed off through the bottom of the conical

90 Inquiry concerning the Nature of Heat,

vessel which was placed over ice, in 33^ minutes, was
to that which passed off in 39^- minutes through the
bottom of the other vessel as 8825 to 8404; and con-
sequently, that the velocity with which the heat passed
through the bottom of the vessel which was exposed to
the frigorific rays from the surface of the cold platter
was to the velocity with which it passed through the
bottom of the other vessel in the compound ratio of
8825 to 8404, and of 39^ to 33^; or as 10,000 to
8025, which is as 5 to 4, very nearly.

From these experiments and computations it appears
that the cooling of the hot body which was placed over
the ice-cold platter was sensibly, and very consider-
ably, accelerated by the vicinity of that cold body, —
may we not venture to say, by the frigorific rays which
proceeded from it ?

I made several other experiments similar to those
just described, and with similar results ; but I shall not
take up the time of the Society by giving a detailed
account of them. I may, perhaps, at a future time
find occasion to mention some of them more particu-
larly.

In the two last-mentioned experiments, as the conical
vessels were suspended in an erect position, and had a
circular band or hoop of fine post paper, by which the
lower end of each of them was surrounded, and which
projected downwards half an inch below the horizontal
level of the bottom of the vessel, and as the air which
came into immediate contact with the bottom of the
vessel, and received heat from it (though it became
specifically lighter than it was before), could not make
its escape upwards into the atmosphere, being confined
and prevented from moving upwards by the thin pro-

and the Mode of its Communication. 91

jecting hoop of paper, there is no doubt but that the
time of cooling was prolonged by this arrangement ;
for, there being much reason to believe that the propa-
gation of heat downwards, in air, from one particle of
that fluid to another, is either quite impossible or so ex-
tremely slow as to be imperceptible, as a succession of
fresh particles of cold air was prevented from coming
into contact with the bottoms of the vessels, but very
little heat could have been given off immediately to the
air in those experiments.

In order to be able to form some probable conjecture
respecting the quantity so given off in cases where the
succession of fresh particles of air is free and uninter-
rupted, I made the following experiment.

Experiment No. 31. — The two conical vessels used
in the last experiment (which I shall now distinguish
by calling the one No. 5 and the other No. 6) being
left suspended in the air to the two horizontal arms of
their wooden stand, at the height of 44 inches above
the floor of the room (the pewter platters, the earthen
dishes, and the stands on which they were placed being
removed), both the vessels were again filled with boiling
hot water, and exposed to cool in the air.

The vessel No. 5 remained in a vertical position, or
with its flat bottom in a horizontal position, as before ;
but the vessel No. 6 was now reclined, so that its axis,
and consequently the plane of its flat bottom, made an
angle with the plane of the horizon of 45 degrees. In
this position of the vessel No. 6, it is evident that the
air, heated by coming into contact with its bottom, had
full liberty to escape upwards, and to make way for
other particles of colder air to come into contact with
the hot surface and be heated, rarefied, and forced up-

92 Inquiry concerning the Nature of Heat,

wards in their turns ; and under these circumstances
it might reasonably be expected that as much heat as
possible would be communicated immediately to the air
by the hot body, and that the heat so communicated
would of course accelerate the cooling of that vessel.

It was in fact cooled in a shorter time than the other,
No. 5, which was suspended in a vertical position ; but
the difference of the times of cooling was very small ;
which indicates, if I am not mistaken, that a compara-
tively small quantity of the heat a hot body loses
when it is cooled in air is communicated to that fluid,
much the greater part of it being sent off through the
air, to a distance, in calorific rays.

The vessel No. 5 was found to cool through the
standard interval of 10 degrees in 38-^ minutes; and
No. 6, which was in a reclined position, in 37^ min-
utes.

It will no doubt be remarked that the vessel No. 5
cooled somewhat faster in this experiment than it had
done in the two preceding experiments (No. 29 and
No. 30), when it stood over a pewter platter which (at
the beginning of the experiment at least) was at the
same temperature as' the air of the room.

The calorific rays from the bottom of the vessel heat-
ing the platter in some small degree, and still more,
perhaps, the upper surface of the perforated sheet of
paper which covered it, the frigorific rays from these
bodies were, on that account, somewhat less powerful
in lowering the temperature of the neighbouring hot
body ; and the time of its cooling was consequently a
little prolonged.

In one of the preceding experiments it cooled through
the given interval in 39^- minutes, and in the other in

and the Mode of its Communication. 93

minutes ; but in this experiment it took up only
38 J minutes in cooling through it, as we have just seen.

Supposing now (what appears to me to be not im-
probable) that all, or very nearly all, the heat lost by
the instrument No. 5 passed off in rays through the air,
we can ascertain what part of the heat lost by the instru-
ment No. 6 was communicated to the air which came
into contact with its surface.

Putting the total quantity of heat lost by each of the
instruments in cooling through the given interval =
10,000, as we have just seen that a quantity of heat
= 1396 passes through the covered sides of each of
these instruments in 39^- minutes, the quantities so lost
in this experiment must have been as follows : By
the instrument No. 5, in 38^ minutes, = 1081 ; by
No. 6, in 37 J minutes, = 1046 ; and, deducting these
quantities so lost (through the covered sides of the in-
struments) from the total quantity lost by each (=
10,000), we shall find out how much heat passed off
through the bottom of each of the instruments.

For the instrument No. 5 it is . 10,000 — 1081 = 9919
And for " No. 6 . 10,000 — 1046 = 9954

If now the whole of the heat lost through the bot-
tom of the instrument No. 5 passed off through the air
in rays, as there is no reason to suppose that a less
quantity passed off in the same time, in the same way,
through the bottom of the instrument No. 6, it ap-
pears that this last-mentioned instrument must have
lost by radiation, or in rays which passed through the air,
a quantity of heat = 9597.

For it is 38 J minutes to 9919 as 37 J minutes to

9597-

94 Inquiry concerning the Nature of Heat,

And if of the total quantity of heat which passed off
through the bottom of the conical instrument No. 6, =
9954, a quantity = 9597 passed off through the air in
calorific rays, the remainder only (9954 — 959?) , which
amounts to no more than 357 parts, could have been
communicated to the air.

Hence it would appear that when a hot body is
cooled in air ^V Part on^y °f tne neat which it loses is
acquired by the air; for 357 is to 9597 as i to 27, very
nearly. But I shall refrain from enlarging farther on
this subject at present.

One of the objects which I had in view in the last ex-
periment was to find out whether the cooling of a hot
body in air is or is not sensibly accelerated or retarded
by the greater or lesser distance at which the body is
placed from other neighbouring solid bodies, when these
neighbouring bodies are at the same temperature as the
air; and, as a comparison of the result of this experi-
ment with the results of the two preceding experiments
so strongly indicated that the cooling of the conical ves-
sel in the preceding experiments had in fact been re-
tarded by the vicinity of the pewter platter over which it
was suspended, I was now induced to repeat these ex-
periments with some variations.

These investigations appeared to me to be of the
more importance, as I conceived that the results of them
might lead to a discovery of one of the causes of the
warmth of clothing.

Experiment No. 32. — I now placed the pewter platters
once more in their former stations, perpendicularly under
the bottoms of the two conical vessels, but at the dis-
tance of 3 inches only ; that which was under the vessel
No. 5 being at the temperature of the air of the room

and the Mode of its Communication. 95

(62°), while that placed under the vessel No. 6 was kept
ice-cold, by means of pounded ice and water, which was
put into the earthen dish on the brim of which it was
supported.

The times of the cooling of the vessels, through the
standard interval of 10 degrees, were as follows : —

No, 5 ...... in 40^ minutes.

No. 6, which was over ice, . in 33^ "

Experiment No. 33. — I repeated this experiment once
more, but varied it by bringing the pewter platters still
nearer to the bottoms of the conical vessels. The flat
horizontal part of each of the platters was now only 2
inches below the flat surface of the bottom of the con-
ical vessel which was suspended over it. Both the plat-
ters still remained covered by their flat circular perforated
covers of paper ; but it should be remembered that the
circular hole in the centre of each of these covers was no
less than 6 inches in diameter, and consequently that a
large portion of the flat part of the bottom of the platter
was in full view (if I may use that expression) of the
bottom of the vessel which was suspended over it.

The times of cooling in this experiment were as fol-
lows : —

No. 5 cooled through the given interval in 42^ minutes.
No. 6, which was over ice, . . in 32^ "

The results of these experiments show (what indeed
might have been expected, especially on the supposition
that the heating and cooling of bodies is effected by
means of radiations) that, although the cooling of the hot
body suspended over a surface kept constantly cold by
artificial means was accelerated by being brought nearer
to that cold surface, yet, in a case where the cold surface

96 Inquiry concerning the Nature of Heat,

was less intensely cold, and where its temperature could
be sensibly raised by the calorific rays from the hot body,
the cooling of the hot body was retarded by a nearer
approach of that cold surface.

From the results of these experiments we may safely
conclude that, if the hot body, instead of being a conical
vessel covered up on all sides except its flat bottom,
had been a globe, and if this hot globe had been sus-
pended in the centre of another larger thin hollow sphere
(this last being, at the beginning of the experiment, at
the same temperature as the air and walls of the room),
the vicinity of the surface of this hollow globe to the
surface of the hot body would have retarded the cooling
of the hot body in the same manner as the cooling of
the conical vessel No. 5 was retarded in the foregoing
experiments ; and if, instead of inclosing the hot body
in the centre of a single hollow sphere of any given
thickness, it were placed in the common centre of a
number of much thinner concentric spheres, of different
diameters, the time of cooling would be still more re-
tarded.

By tracing the various operations which would take
place in the cooling of the hot body in this imaginary
experiment, we shall become acquainted with the nature
of those which actually take place when the cooling of a
hot body is prolonged by means of warm clothing.

From the results of several of the foregoing experi-
ments we may conclude that, supposing the thin con-
centric hollow spheres in which the hot body is confined
to be made of metal, the cooling will be slower if the sur-
faces of these spheres are polished than if they are unpol-
ished or blackened ; and hence we might very naturally
be led to suspect (what is probably true in fact) that the

and the Mode of its Communication. 97

warmth of any kind of substance used as clothing, or its
power of preventing our bodies from being cooled by
the influence (frigorific radiations) of surrounding colder
bodies, depends very much on the polish of its surface.

If, with the assistance of a microscope, we examine
those substances which supply us with the warmest cov-
erings, — such, for instance, as furs, feathers, silk, &c., —
we shall find their surfaces not only smooth, but also very
highly polished ; we shall also find that, other circum-
stances being equal, those substances are the warmest
which are the finest, or which are composed of the great-
est number of fine polished detached threads or fibres.

The fine white shining fur of a Russian hare is much
warmer than coarse hair; and fine silk, as spun by the
silkworm is warmer than the same silk twisted together
into coarse threads ; as I found by actual experiments,
an account of which has already been laid before this
Society and published in the Philosophical Transactions.

I formerly considered the warmth of natural and ar-
tificial clothing as depending •principally on the obstacle
it opposes to the motions of the cold air by which the
hot body is surrounded ; but, by a patient and careful
examination of the subject, I have been convinced that
the efficacy of radiation is much greater than I had sup-
posed it to be.

From the result of the experiment No. 31, we might
be led to conclude that a very small part only of the
heat which a hot body appears to lose when it is cooled
in air is in fact communicated to that fluid, a much
greater portion of it being communicated to other sur-
rounding bodies at a distance ; and, in one of my for-
mer experiments, a hot body was cooled, though it was
placed in a Torricellian vacuum.

VOL II. 7

98 Inquiry concerning the Nature of Heat,

These researches appear to me to be the more inter-
esting, as I have long been of opinion that it must be
by experiments of this kind (showing in what manner
the temperature of bodies are affected reciprocally at
different degrees of temperature and at different dis-
tances) that the hypothesis of radiation must be estab-
lished or proved to be unfounded.

When I speak of heat as being communicated to air
immediately by a 'hot body which is cooled in it, I mean
only that it is not first communicated to other neighbour-
ing bodies, and then given by them to the particles of air
with which they happen to be in contact. In this last-
mentioned way much of the heat, no doubt, which a hot
body loses when cooled in air is ultimately communi-
cated to that fluid.

I am far from supposing that the particles of air
which, coming into contact with a hot body, are heated
in consequence of that near approximation receive heat
in any other manner than that in which other bodies at a
greater distance receive it. If in the one case it be gen-
erated or excited by the agency of calorific rays or un-
dulations caused by the hot body, it must, I am per-
suaded, be excited in the same manner in the other.

The reason why the particle of air which is in imme-
diate contact with a hot body is heated, while other par-
ticles near it are not affected by the calorific rays from
the hot body which are continually passing by them
through the air, is, I conceive, because the particle
heated is at the surface of the fluid (air), where these rays
are either reflected, refracted, or absorbed ; but when a
ray has once passed the surface of a transparent fluid, it
proceeds straight forward, without being farther affected
by it, and consequently without affecting it, till it conies to

and the Mode of its Communication. 99

the confines of the medium, or to the surface of some
other body.

If this hypothesis of the communication, or rather
generation, of heat and of cold by radiation be true,
it will enable us to explain, in a satisfactory manner,
what has been called the non-conducting power of trans-
parent fluids with respect to heat ; for, if heat be real-
ly communicated or excited in the manner above de-
scribed, it is quite evident that a perfectly transparent
fluid can receive heat only at its surface, and, conse-
quently, that heat cannot be propagated in such a fluid
by communication from one particle of the fluid to an-
other.

By a transparent fluid I mean such an one as admits
the calorific and frigorific rays emitted by hot and by
cold bodies to pass freely through it without obstruct-
ing their passage or diminishing their intensities.

Whether any of the fluids with which we are ac-
quainted be perfectly transparent in this sense of the
word or not, I will not pretend to say ; but there is
reason to think that pure water and air and most other
fluids which are transparent to light, possess a high de-
gree of transparency in regard to calorific and frigorific
rays, or that they give a very free passage to them when
they have once passed their surfaces.

An even or polished surface has been found to facili-
tate very much the reflection of the rays of light. May
it not, in all cases, have an equal tendency to facilitate
the reflection of calorific and frigorific rays ?

In the experiments with the large cylindrical vessels,
where they were exposed naked to cool in the air, their
surfaces were polished, and they were a long time in
cooling. But, when the surface of the vessel was black-

TOO Inquiry concerning Ike Nature of Heat,

ened or covered with other substances, the vessel was
found to cool much more rapidly.

A large proportion of the frigorific rays from the sur-
rounding colder bodies were, in the former case, reflected
at the polished surface of the metallic vessel ; but, in
the latter case, more of them were absorbed.

When a large drop of water rolls about without being
evaporated upon the flat surface of a piece of red-hot
iron, the surface of the drop is polished; and, the calo-
rific rays being mostly reflected, the water is very little
heated, notwithstanding the extreme intensity of the heat
of the iron and its nearness to the water.

If the iron be less hot, the water penetrates the pores
of the oxide which covers the metal, the drop ceases to
have a polished surface, acquires heat very rapidly, and
is soon evaporated.

If a drop of water be placed on the clean and polished
surface of a metal not so easily oxidable as iron, it will
retain its spherical form and polished surface under a
lower degree of temperature than on iron ; and conse-
quently will be less heated, and less rapidly evaporated
by a moderate heat.

If a large drop of water be put carefully into a clean
silver spoon, previously heated very hot (that is to say,
so hot as to give a loud hissing noise when touched with
the wetted finger, but much below the heat of red-hot
metal), the drop will support, or rather resist, this heat
for a considerable time ; but after the spoon has been
suffered to cool down nearly to the temperature of boil-
ing water a drop of water put into it will be evaporated
instantaneously.

It appears, from the results of these experiments, to
be probable that under high temperatures air is attracted

and the Mode of its Communication. 101

by metals so much more strongly than water that even
the weight of a drop of water is not sufficient to force
away the stratum of air which covers and adheres to the
surface of a metal on which the drop reposes; but at
lower temperatures this does not seem to be the case.

The following experiment, which I made several
months ago with a view to investigate the cause of the
slow evaporation of drops of water placed on hot metals,
will, I think, throw much light on this subject.

Experiment No. 34. — Taking a clean polished silver
spoon, I blackened the inside of it by holding it over
the flame of a wax candle ; then, putting a large drop of
water into it, I found, as I expected, that the drop took
a spherical form, and rolled about in the spoon without
wetting its blackened surface.

I now held the spoon over the flame of a candle, and
attempted to make the water boil ; but I found it to be
absolutely impossible. The handle of the spoon became
so very hot that I could not hold it in my hand without
being burnt, though it was wrapped up in three or four
thicknesses of linen ; but still the drop of water did not
appear to be at all affected by this intense heat. If the
bowl of the spoon were touched with the finger, a hissing
noise announced that it was extremely hot ; but still the
water remained perfectly quiet in the spoon without be-
ing evaporated.

Having in vain attempted to make this drop of water
boil, and not being able to hold the spoon over the
flame of the candle any longer on account of the heat of
its handle, I now poured the drop into the palm of my
hand. I found it to be warm, but by no means scald-
ing hot.

By holding the spoon with a pair of tongs over the

IO2 Inquiry concerning the Nature of Heat,

flame of the candle for a longer time, I found that a
drop of water in the spoon gradually changed its form,
became less, and was at length evaporated ; from be-
ing spherical and lucid, it gradually took an oblong form,
and its surface became obscure ; and when it was evap-
orated it left a kind of skin behind it, which was evident-
ly composed of the particles of black matter which had
by degrees attached themselves to its surface, and which
probably had contributed not a little to its being at last
heated and evaporated.

The change in the form of the drop of water, and
more especially the gradual loss of its lucid appearance,
made me suspect that it had turned round during the
experiment. If it really did so its motion must either
have been extremely rapid or very slow, for, though I
examined it with great attention, I could not perceive
that it had any rotatory motion.

I will take the liberty to mention another little exper-
iment which I have often made to amuse myself and
others, though it may perhaps be thought too trifling to
deserve the attention of the Royal Society.

Experiment No. 35. — If a large drop of water be
formed at the end of a small splinter of light wood
(deal, for instance), and this drop be thrust quickly in-
to the centre of the flame of a newly snuffed candle,
which burns bright and clear, the drop of water will re-
main for a considerable time in the centre of the flame
and surrounded by it on every side, without being made
to boil, or otherwise apparently affected by the heat ;
and if it be taken out of the flame and put upon the
hand, it will not be found to be scalding hot.

If it be held for some time in the flame, it will be
gradually diminished by evaporation ; but there is much

and the Mode of its Communication. 103

reason to think that the heat which it acquires is not
communicated to it by the flame, but by the wood to
which it adheres, which is soon heated by the flame, and
even set on fire.

I cannot refrain from just observing that it appears to
me to be extremely difficult to reconcile the results of
any of the foregoing experiments with the hypothesis
of modern chemists respecting the materiality of heat.

Deeply sensible of the insufficiency of the powers of
the human mind to unfold the mysteries of nature and
discover the agents she employs and their mode of ac-
tion in her secret and invisible operations, and being,
moreover, fully aware of the danger of forming an at-
tachment to a false theory, and of the folly of wasting
time in idle speculation, I have ever, in my philosoph-
ical researches, been much more anxious to discover
new facts, and to show how the discoveries of others
may be made useful to mankind, than to invent plau-
sible theories, which much oftener tend to misguide than
to lead us in the path of truth and science.

There are, however, situations in which an experi-
mental inquirer sometimes finds himself, where it is
almost impossible for him to abstain from forming or
adopting some general theory for the purpose of ex-
plaining the phenomena which fall under his observa-
tion, and directing him in his future researches.

Finding myself in that situation at this time, I beg
the attention and, above all, the indulgence of the Society
while I endeavour to explain the conjectures I have
formed respecting the nature of heat and the mode of
its communication.

Hot and cold, like fast and slow, are mere relative
terms ; and, as there is no relation or proportion be-

IO4 Inquiry concerning the Nature of Heat,

tween motion and a state of rest, so there can be no
relation between any degree of heat and absolute cold,
or a total privation of heat ; hence it is evident that
all attempts to determine the place of absolute cold, on
the scale of a thermometer, must be nugatory.

It seems probable that motion is an essential quality
of matter, and that rest is nowhere to be found in the
universe.

We well know that all those bodies which fall under
the cognizance of our senses are in motion ; and there
are many appearances which seem to indicate that the
constituent particles of all bodies are also impressed
with continual motions among themselves, and that it is
these motions (which are capable of augmentation and
diminution) that constitute the heat or temperature of
sensible bodies.

The only effects of which we have any idea result-
ing from the action of one body on another are a change
of velocity or a change of direction, or both. We per-
ceive, it is true, that certain bodies have a power of
affecting certain other bodies at a distance; but this is
no proof that the effects produced are essentially differ-
ent from those which result from collision ; for, if an
elastic body be interposed between the two bodies, their
actions on each other may be communicated through
such intermediate elastic body, which, when the action
is at an end, and the effects resulting from it on the
two bodies have taken place, will be in the same state
precisely in which it was before the action began.

If a bell or any other solid body, perfectly elastic,
placed in a perfectly elastic fluid, and surrounded by
other perfectly elastic solid bodies, were struck and
made to vibrate, its vibrations would by degrees be

and the Mode of its Communication. 105

communicated, by means of the undulations or pulsa-
tions they would occasion in the elastic fluid medium,
to the other surrounding solid and elastic bodies. If
these surrounding bodies should happen to be already
vibrating, and with the same velocity as that with which
the bell is made to vibrate by the blow, the undulations
in the elastic fluid occasioned by the bell would neither
increase nor diminish the velocity or frequency of the
vibrations of the surrounding bodies ; neither would
the undulations caused by the vibrations of these bodies
tend to accelerate or to retard the vibrations of the
bell. But if the vibrations of the bell were more fre-
quent than those of the surrounding bodies, the undu-
lations it would occasion in the elastic fluid would tend
to accelerate the vibrations of the surrounding bodies ;
on the other hand, the undulations occasioned by the
slower vibrations of the surrounding bodies would re-
tard the vibrations of the bell, and the bell and the
surrounding bodies would continue to affect each other
until, by the vibrations of the latter being gradually
increased and those of the former diminished, in con-
sequence of their actions on each other, they would all
be reduced to the same tone.

Supposing now that heat be nothing more than the
motions of the constituent particles of bodies among
themselves (an hypothesis of ancient date, and which
always appeared to me to be very probable), if for the
bell we substitute a hot body, the cooling of it will be
attended by a series of actions and reactions exactly
similar to those just described.

The rapid undulations occasioned in the surrounding
ethereal fluid, by the swift vibrations of the hot body,
will act as calorific rays on the neighbouring colder solid

io6 Inquiry concerning the Natiire of Heat,

bodies, and the slower undulations, occasioned by the
vibrations of those colder bodies, will act as frigorific
rays on the hot body ; and these reciprocal actions will
continue, but with decreasing intensity, till the hot
body and those colder bodies which surround it shall,
in consequence of these actions, have acquired the same
temperature, or until their vibrations have become iso-
chronous.

According to this hypothesis, cold can with no more
propriety be considered as the absence of heat than a
low or grave sound can be considered as the absence of
a higher or more acute note ; and the admission of rays
which generate cold involves no absurdity and creates
no confusion of ideas.

On a superficial view of the subject, it may perhaps
appear difficult to reconcile solidity, hardness, and elas-
ticity with those never-ceasing motions which we have
supposed to exist among the constituent particles of all
bodies ; but a patient investigation of the matter will
show that the admission of that supposed fact, instead
of rendering it more difficult to form distinct and satis-
factory ideas of the causes on which those qualities of
bodies depend, will rather facilitate those abstruse re-
searches.

Judging from all the operations of nature, of the causes
of which we are able to form any distinct ideas, we are
certainly led to conclude that the force of dead matter
(and perhaps of living matter also), or its power of
affecting, that is to say, of moving other matter, or of
resisting its impulse, depends on its motion.

If, therefore, solid (or fluid) bodies have any powers
whatever, either of impulse or of resistance, it appears
to me to be more reasonable to ascribe them to the

and the Mode of its Communication. 107

living forces residing in them — to the never-ceasing
motions of their constituent particles — than to sup-
pose them to be derived from their want of power, and
their total indifference to motion and to rest.

No reasonable objection against this hypothesis (of
the incessant motions of the constituent particles of all
bodies), founded on a supposition that there is not
room sufficient for these motions, can be advanced ;
for we have abundant reason to conclude that if there
be in fact any indivisible solid particles of matter
(which, however, is very problematical), these particles
must be so extremely small, compared to the spaces
they occupy, that there must be ample room for all
kinds of motions among them.

And whatever the nature or directions of these inter-
nal motions may be among the constituent particles of
a solid body, as long as these constituent particles, in
their motions, do not break loose from the systems to
which they belong (and to which they are attached by
gravitation), and run wild in the vast void by which
each system is bounded (which, as long as the known
laws of nature exist, is no doubt impossible), the form
or external appearance of the solid cannot be sensibly
changed by them.

But if the motions of the constituent particles of any
solid body be either increased or diminished, in conse-
quence of the actions or radiations of other distant
bodies, this event could not happen without producing
some visible change in the solid body.

If the motions of its constituent particles were dimin-
ished by these radiations, it seems reasonable to con-
clude that their elongations would become less, and
consequently that the volume of the body would be

1 08 Inqziiry concerning the Nature of Heat.,

contracted ; but if the motions of these particles were
increased, we might conclude, a •priori, that the volume
of the body would be expanded.

We have not sufficient data to enable us to form dis-
tinct ideas of the nature of the change which takes place
when a solid body is melted ; but as fusion is occa-
sioned by heat, that is to say, by an augmentation (from
without) of that action which occasions expansion if
expansion be occasioned by an increase of the motions
of the constituent particles of the body, it is, no doubt,
a certain additional increase of those motions which
causes the form of the body to be changed, and from
a solid to become a fluid substance.

As long as the constituent particles of a solid body
which are at the surface of that body do not, in their
motions, pass by each other ^ the body must necessarily
retain its form or shape, however rapid those motions
or vibrations may be ; but as soon as the motion of
these particles is so augmented that they can no longer
be restrained or retained within these limits, the regular
distribution of the particles which they acquired in
crystallization is gradually destroyed, and the particles
so detached from the solid mass form new and inde-
pendent systems, and become a liquid substance.

Whatever may be the figures of the orbits which the
particles of a liquid describe, the mean distances of
those particles from each other remain nearly the same
as when they constituted a solid, as appears by the
small change of specific gravity which takes place when
a solid is melted and becomes a liquid ; and, on a sup-
position that their motions are regulated by the same
laws which regulate the solar system, it is evident that
the additional motion they must necessarily acquire, in

and the Mode of its Communication. 109

order to their taking the fluid form, cannot be lost, but
must continue to reside in the liquid, and must again
make its appearance when the liquid changes its form
and becomes a solid.

It is well known that a certain quantity of heat is
requisite to melt a solid, which quantity disappears or
remains latent in the liquid produced in that process ;
and that the same quantity of heat reappears when this
liquid is congealed and becomes a solid body.

But before I proceed any farther in these abstruse
speculations, I shall endeavour to investigate some of
the consequences which would necessarily result from
the radiations of hot and of cold bodies, supposing
those radiations to exist, and their motions and actions
to be regulated by certain assumed laws.

And first, it is evident that the intensity of the rays
emitted by a luminous point, in a perfectly transparent
medium, is everywhere as the squares of the distance
from that point inversely ; for the intensity of those
rays must be as their condensation ; and their con-
densation being diminished in proportion as the space
they occupy is increased, if we suppose all the rays
which proceed in all directions from any point to set
out at the same instant and to move with the same
velocity in right lines, these simultaneous rays (or un-
dulations) will in their progress form a sphere, which
sphere will increase continually in size as the rays ad-
vance ; and as all the rays must be found at the surface
of this sphere, their intensity or condensation must
necessarily be as the surface of the sphere inversely, or
as the squares of the distance inversely from the centre
of the sphere, or, which is the same thing, from the
luminous point from which these rays proceed ; the

no Inquiry concerning the Nature of Heat,

surfaces of spheres being to each other as the squares
of their radii.

Supposing now (what, indeed, appears to be incontro-
vertible) that the intensity of the rays which hot and
cold bodies emit, in a medium perfectly transparent,
follows the same law, we can determine what effects
must be produced by the largeness or smallness of the
confined space (of a room, for instance) in which a hot
body is placed to cool.

To simplify this investigation, we will suppose this
confined space to be a hollow sphere of ice 9 feet in
diameter, at the temperature of freezing water ; and the
hot body to be a solid sphere of metal 2 inches in
diameter, at the temperature of boiling water, placed in
the centre of it ; and we will suppose, farther, that this
hollow sphere is void of air, and that the cooling of the
hot body is effected solely by the frigorific rays from
the ice.

The question to be determined is, in what manner
the cooling of the hot body would be affected by in-
creasing the diameter of this hollow sphere of ice.

Let us suppose its diameter to be increased to 18
feet. Its internal surface will then be to the surface of
a sphere 9 feet in diameter as the square of 18 to the
square of 9, that is to say, as 324 to 8 1, or as 4 to i.
And as the quantity of frigorific rays emitted are, c<eteris
•paribus, as the surface from which they proceed, the
quantity of rays emitted by the internal surface of the
larger sphere will be to the quantity emitted by the.
internal surface of the smaller as 4 to I.

But the intensities of these rays at the common cen-
tre of these spheres (where the hot body is placed) be-
ing as the squares of the distances from . the radiating

and the Mode of its Communication. 1 1 1

points inversely, the intensity of the rays from the
internal surface of the smaller sphere must be to the
intensity of the rays from the internal surface of the
larger sphere as 4 to i, at the common centre of those
spheres.

Now, as the time of the cooling of the hot body will
depend on the quantity of frigorific rays which arrive at
its surface, and on the intensity of their action, and as
the intensity of the rays from the internal surface of the
sphere at its centre is diminished in the same propor-
tion as the surface of the sphere is augmented when its
diameter is increased, it follows that a hot body placed
in the centre of a hollow sphere at any given constant
temperature below that of the hot body, will be cooled
in the same time, or with the same celerity, whatever
may be the size of the sphere.

If this conclusion be well founded (and I see no rea-
son to suspect that it is not so), it will follow, from the
principles assumed, that the hot body will be cooled in
the same time, in whatever part of the hollow sphere it
be situated. And as the cooling of the body is not
affected, that is to say, accelerated or retarded, either by
the greater or smaller size of the enclosed space in
which it is confined, or by its situation in that confined
space, so it cannot be in any manner affected either
by the form of that hollow space or by the presence of
a greater or less number of other solid bodies; provided
always, that all these surrounding bodies be at the same
constant temperature.

If, however, any of these surrounding bodies, the
temperature of which is liable to be sensibly changed
during the experiment by the calorific rays emitted by
the hot body,, be placed very near that body, the cooling

1 1 2 Inquiry concerning the Nature of Heat,

of that hot body will be retarded, the rays from this
neighbouring body, so heated, being less frigorific than
those from other bodies at a greater distance, which it
intercepts.

The results of all my experiments on the cooling
of bodies tended uniformly to confirm the above con-
clusions.

Admitting that the cooling of a hot body is effected
solely by the rays which proceed from colder bodies,
and that these rays, like those of light, are reflected,
refracted, and concentrated, according to certain known
laws, by the polished surfaces of mirrors and lenses, it
might perhaps be imagined that the cooling of a hot
body might be accelerated or retarded by giving it
some peculiar form ; or by placing near it, and in cer-
tain positions with respect to it, two or more highly
polished reflecting mirrors.

As these conjectures, if well founded, might lead to
experiments from the results of which the truth or false-
hood of the hypothesis in question might be demon-
strated, it is of much importance that this matter should
be thoroughly investigated. I shall therefore beg the
indulgence of the Society while I endeavour to examine
it with that careful attention which it appears to me to
deserve.

When different solid substances, heated to the same
degree of temperature, are exposed in the air to cool,
those among them which appear to the touch to be the
hottest are not those which cool the fastest, or which
send off calorific rays through the air in the greatest
abundance.

As polished metals reflect a great part of the rays
from other bodies which arrive at their surfaces, and as

and the Mode of its Communication. 1 1 3

they are neither heated nor cooled by the rays so re-
flected, their temperatures are slowly changed by the
actions of the surrounding bodies at a different tem-
perature.

When a hot polished metallic body is exposed in the
air to cool, surrounded by other bodies at the same
temperature as that of the cold air, most of the rays
from the surrounding bodies are reflected at the pol-
ished surface of the hot body ; it is evident, then, that
two sorts of rays must proceed from the surface of that
body, namely, those calorific rays which it emits, and
those other rays (which with regard to the surround-
ing bodies are neither calorific nor frigorific) which it
reflects.

On a cursory view of the subject, one might be led
to imagine that, as the rays which proceed from the hot
metallic body are of two kinds, the energy of the calo-
rific rays, which properly belong to the hot body, might
be diminished by those other reflected rays by which
they are accompanied, and with which they may be said
to be mixed ; but a more careful examination of the
matter will show that this cannot be the case, that is
to say, as long as all the surrounding bodies continue
to be at the same temperature. If the temperature of
the surrounding bodies be different, such of them will
be affected by the reflected rays as happen to be of a
temperature different from that from which the ray
originated ; but still the effects produced by the rays
emitted by the hot body will be the same, or their
power of effecting changes in the temperatures of other
(hotter or colder) bodies will remain undiminished and
unchanged.

The reason why their effects are not more powerful

VOL. II. 8

H4 Inquiry concerning the Nature of Heat,

than they are found to be, is not because they are mixed
with other reflected rays, but because they are few, the
greater part of the rays which the hot body actually
emits being reflected and turned back upon itself by the
reflecting surface by which it is immediately surrounded.

The reflecting surface at which the rays of light which
impinge against the polished surface of any solid or
fluid body are turned back and reflected is actually situ-
ated without the body, and even at some distance from
it ; this has been proved by the most decisive experi-
ments ; and there are so many striking analogies be-
tween the rays of light and those invisible rays which
all bodies at all temperatures appe.ar to emit, that we
can hardly doubt of their motions being regulated by
the same laws.

Perhaps there may be no other difference between
them than exists between those vibrations in the air
which are audible and those which make no sensible im-
pression on our organs of hearing.

If the ear were so constructed that we could hear all
the motions which take place in the air, we should, no
doubt, be stunned by the noise ; and if our eyes were
so constructed as to see all the rays which are emitted
continually, by day and by night, by the bodies which
surround us, we should be dazzled and confounded by
that insupportable flood of light poured in upon us on
every side.

Taking it for granted that these invisible radiations
exist, we will endeavour to trace the effects which must
necessarily be produced by them, and see if these in-
vestigations will not lead us to a discovery of the causes
of some appearances which have hitherto been envel-
oped in much obscurity.

and the Mode of its Communication. 1 1 5

Suppose two concave reflecting mirrors, of highly
polished metal, each 18 inches in diameter, and 18
inches focal distance, to be placed opposite to each
other at the distance of 10 feet, in a large quiet room,
in which the air and the walls of the room remain con-
stantly at the same temperature (that of freezing water,
for instance), without any variation.

If we suppose the floor, ceiling, walls of the room,
and doors and windows, to be lined with a covering of
ice, at the temperature of freezing water, we can then,
without any difficulty, conceive that the temperature of
the room may remain the same, notwithstanding the
presence of hotter bodies, which are brought into it for
the purpose of making experiments.

Let us now suppose one of the mirrors to be at the
temperature of freezing, and the other at that of boiling
water ; and let us see what effects they would produce
on each other by their radiations.

And first, with respect to the hot mirror, it is evi-
dent that it will be cooled, not only by the frigorific
rays which proceed from the cold metal of which the
opposite mirror is constructed, but also by such of the
frigorific rays from the sides of the room as, impinging
against the polished reflecting surface of the cold mir-
ror, and being reflected by that surface, happen to fall
on the surface of the hot mirror without being reflected
by it.

But, as the quantity of rays which the cold mirror
reflects is greater in proportion as the reflecting surface
is more perfect, while the quantity of rays emitted by
this cold mirror is less in proportion as its reflecting
surface is more perfect, it is extremely probable that the
total quantity of frigorific rays (emitted and reflected)

1 1 6 Inquiry concerning the Nature of Heat,

which, coming from the surface of the cold mirror, im-
pinge against the surface of the hot mirror, will be the
same, whatever may be the degree of polish, or reflect-
ing power, of the cold mirror. And, if this be the case,
we may conclude that the presence of this mirror will
have no effect whatever on the hot mirror ; or that it
will no more expedite its cooling than any other body,
of any other form, would do, at the same distance and
occupying the same space.

It might perhaps be imagined that the form of the
cold mirror might concentrate the rays it emits and
reflects, and, by such concentration, produce a greater
effect on the opposite mirror than if its surface were
flat, or of any other form ; but a more attentive exami-
nation of the matter will show that no such concentra-
tion actually takes place : for, with regard to those rays
which are emitted by this cold body, as they proceed
from each point of its surface in all directions^ it is per-
fectly evident that these are not concentrated ; and with
respect to those which are reflected, it is equally certain
that they are not concentrated, because, in order to
their being concentrated, they must arrive at the surface
of the mirror in parallel lines, and in the direction of
the axis of the mirror, which, under the given circum-
stances, is evidently impossible.

Hence we see that the presence of the cold mirror
will not tend, in the smallest degree, either to accelerate
or to retard the cooling of the hot mirror; that is to
say, provided its temperature be not raised by the calo-
rific rays from the hot mirror.

If its temperature be raised by those rays, it will
tend to retard the cooling of the hot mirror ; but, even
in this case, it will not retard it more than any other

and the Mode of its Communication. 1 1 7

polished metallic body would do, of any other form,
having the same area or quantity of surface opposed to
the hot mirror, and being placed at the same distance
from it.

By a similar train of reasoning it may be shown that
the form of the hot body (that of a concave mirror) will
contribute nothing to the effect it will produce on the
cold mirror, in heating it by the calorific rays it emits ;
and that it will itself be cooled neither faster nor slower
on account of its peculiar form.

Let us now suppose both mirrors to be at the tem-
perature, precisely, of the room (that of freezing water),
and that a bullet, or other small body of a spherical
form, at the temperature of boiling water, be placed in
the focus of one of the mirrors, which mirror we shall
call A.

As the rays emitted by this hot body are sent off in
right lines, in all directions, in the same manner as
light is emitted by luminous bodies, all those rays which
fall on the concave polished surface of the mirror A
will be reflected (as is well known) in lines nearly paral-
lel to the axis of the mirror ; they will consequently
fall on the concave polished surface of the opposite
mirror B, and, being there again reflected, they will be
concentrated at the focus of the second mirror.

If now a sensible thermometer, at the temperature of
the room, be placed in this focus, it will immediately
begin to rise, in consequence of the heat generated in it
by the action of these calorific rays, so accumulated in
that place.

If, instead of being placed in the focus of this second
mirror, the thermometer be placed at a very small dis-
tance from that focus, on one side of it, the instrument,

1 1 8 Inquiry concerning the Nature of Heat,

however sensible it may be, will not be apparently-
affected by the rays from the hot body.

This experiment, which is of ancient date, has often
been made, and always with the same results.

Let us now suppose the hot body to be removed
from the focus of the mirror A, and that a colder body
be substituted in place of it. And, in the first place,
we will suppose the temperature of this- colder body to
be that of freezing water, or just equal to that which
reigns in the room.

As the rays which bodies at the same temperature
send off from one to the other have no tendency to
increase or to diminish the temperature of those bodies,
the concentration of rays in the focus of the mirror B,
proceeding from the ice-cold body placed in the focus
of the mirror A, can have no effect on a thermometer,
at the same temperature, which is exposed to their
action.

If heat be a vibratory motion of the constituent par-
ticles of bodies, and if the rays which sensible bodies
send off in 'all directions be undulations in an ethereal
elastic fluid by which they are surrounded, occasioned
by those motions ; as the pulsations in this fluid must
be isochronous with the vibrations by which they are
occasioned, these pulsations or undulations can neither
accelerate nor retard the vibrations of other bodies at
the surfaces of which they arrive, provided the vibra-
tions of the constituent particles of such bodies are, at
that time, isochronous with the vibrations of the con-
stituent particles of the body from which these undula-
tions proceed. But to return to our experiment.

Suppose now that, instead of this ice-cold body,
another much colder — at the temperature of freezing

cr.d the Mode of its Communication. 1 1 9

mercury, for instance — be placed in the focus of the
mirror A, and that a thermometer at the temperature
of freezing water be placed in the focus of the mirror B ;
what might be expected to be the result of this experi-
ment ? — That the thermometer would fall, in conse-
quence of its being cooled by the accumulation of frigo-
rific rays proceeding from this very cold body.

Now this is what actually happened in the celebrated
experiment of my ingenious friend, Professor Pictet, of
Geneva.

Several attempts have been made to explain the result
of that experiment, on the supposition that caloric has
a real or material existence, and that radiant heat is that
substance, emitted and sent off in right lines in all direc-
tions from the surfaces of hot bodies. But none of
these explanations appear to me to be satisfactory. One
of the most plausible of them is that which is founded
on a supposition that caloric is emitted continually,
under the form of radiant heat, by all bodies, at all
temperatures, but in greater abundance by hot bodies
than by such as are colder; and that a body, at the
same time that it sends off radiant caloric in all direc-
tions to the bodies by which it is surrounded, receives
it in return, in greater or less quantities, from all those
bodies ; that in all cases where a body, in any given
time, receives more radiant caloric than it gives off, an
accumulation of caloric in the body takes place, in
consequence of which accumulation it becomes hotter,
but when it gives off more caloric in any given time
than it receives, its quantity of caloric is gradually di-
minished and it becomes colder; and that a constant
temperature results from the quantities of caloric emit-
ted and received continually being equal. But besides

1 2O Inquiry concerning the Nature of Heat,

the difficulty of explaining how, or by what mechanism,
it can be possible for the same body to receive and
retain, and reject and drive away, the same kind of sub-
stance, at one and the same time (an operation not
only incomprehensible, but apparently impossible, and
to which there is nothing to be found analogous, to
render it probable), many other reasons might be brought
to show that this hypothesis of the supposed continual
interchanges of caloric between neighbouring bodies is
very improbable; and, among the rest, there is one which
appears to me to be quite conclusive.

As the point in dispute seems to be of great impor-
tance to the science of heat, I shall endeavour to ex-
amine it with all possible attention; and, in order to
put the hypothesis in question to the test, we will see
if it will accord with the results of some of the fore-
going experiments,^ which, in order to their being more
easily comprehended and examined, I shall elucidate by
figures.

Let the two opposite ends of the cylinders A and B
(Plate III. Fig. 4) represent the two vertical metallic
disks of equal dimensions, which were presented at the
same time to the ball of the thermoscope C, in the ex-
periment No. 23.

In that experiment the disk A being at the tempera-
ture of 32° F. (that of freezing water), and the disk B
at 112° F., while the ball of the thermoscope C and all
other surrounding bodies were at 72°, it was found that
the temperature of the thermoscope was not changed by
the simultaneous actions of these two bodies, the one
hot and the other cold.

In order to account for this result on the hypothesis
before mentioned, we must begin by supposing that the

PLATE III.

A FiaJ\

V B

/ly

V/ B

and the Mode of its Communication. 121

ball of the thermoscope gives off radiant caloric con-
tinually in all directions, and receives it in return from
the surfaces of all the bodies by which it is surrounded.

With regard to all these surrounding bodies (ex-
cepting the disks A and B), as they are at the same
temperature as the ball of the thermoscope (that of 7.2°),
they will give continually to that instrument just as
much radiant caloric as they receive from it, and no
change of temperature will result from these equal
interchanges.

But in respect to the disk A, as that is colder than
the ball of the thermoscope, it returns to it a smaller
quantity of radiant caloric than it receives from it ;
consequently the thermoscope receives continually less
than it gives : it would of course be gradually exhausted
of caloric and become colder were it not for the com-
pensation it receives for this loss from the disk B. This
disk, being hotter than the thermoscope, gives to it
continually more radiant caloric than it receives from
it ; and were it not for the simultaneous loss of caloric
which the instrument sustains in its interchanges with
the cold disk A, its quantity of caloric would be aug-
mented, and it would become hotter.

Now, as the temperature of the ball of the thermo-
scope is an arithmetical mean between that of the disk
A and that of the disk B, it is reasonable to suppose
that the thermoscope receives just as much more caloric
from B than it gives to it as it gives to A more than it
receives from it ; and if that be the case in fact, it is evi-
dent that the simultaneous actions of the two disks on
the ball of the thermoscope (or the traffic which they
carry on with it in caloric) can neither tend to increase
nor to diminish the original stock of that substance be-

122 Inquiry concerning tfie Nature of Heat,

longing to that instrument ; consequently the instru-
ment will neither be heated nor cooled by these inter-
changes, but will continue invariably at the same con-
stant temperature.

This explanation is plausible, but, before the hypoth-
esis on which it is founded can be admitted, we must
see if it will agree with the results of other experi-
ments, — for the greatest care ought always to be used in
the admission of hypotheses in physical researches, and
in no case can it be more indispensably necessary than
where an hypothesis has evidently been contrived for
the sole purpose of explaining a single experiment, or
elucidating a new fact.

When the surface of the metallic disk B was black-
ened by holding it over the flame of a candle, the in-
tensity of its radiation at the given temperature (that
of 112°) was found to be very considerably increased;
and when (being so blackened) it was again presented
to the ball of the thermoscope at- the same distance as
in the last-mentioned experiment, and the cold disk A
(at the temperature of 32°) was placed opposite to it at
an equal distance, as represented in Fig. 5, the thermo-
scope, instead of continuing to retain its original tem-
perature (that of 72°), was now gradually heated.

There is nothing, it is true, in that event, which ap-
pears difficult to explain on the assumed principles; for,
if the quantity of radiant caloric emitted by the disk B
be increased by blackening its surface, the quantity re-
ceived from it by the ball of the thermoscope must be
increased also, and that additional quantity must, of
course, tend to raise the temperature of the instrument.
But here is an experiment which cannot be explained on
those principles.

and the Mode of its Communication 123

The surface of the cold disk A having been black-
ened as well as that of the hot disk B, when both disks
(blackened) were again presented at equal distances to
the ball of the thermoscope, as represented in Fig. 6, it
was found that the original temperature of the thermo-
scope remained unchanged.

The result of this most interesting experiment proves
that the ball of the thermoscope was just as much
cooled by the influence of the cold blackened disk as it
was heated by the hot blackened disk.

Now, as it was found by experiment that the intensity
of the radiation of the disk B was increased 'by the black-
ening of the surface of that disk, we must conclude
that the intensity of the radiation of the disk A was
likewise increased by the use of the same means ; but if
those radiations be caloric, emitted by those bodies
(which the hypothesis in question supposes), how did it
happen that the ball of the thermoscope, instead of being
more heated by the additional quantity of caloric which
it received in consequence of the blackening of the disk
A, was actually more cooled?

It may perhaps be said by the advocates for the hy-
pothesis in question, that the blackening of the surface
of the disk A caused a greater quantity of caloric to be
sent off to it by the ball of the thermoscope. Without
insisting on an explanation of the mode of action of the
cause which is supposed to produce this effect (which I
might certainly do, as the supposition is perfectly gra-
tuitous), I will content myself with just observing that
as the surface of the opposite disk was also blackened,
this supposed augmentation of the q.uantity of caloric
emitted by the ball of the thermoscope, occasioned by
the blackening of the surfaces of the bodies presented to it,

1 24 Inquiry concerning the Nature of Heat,

can be of no use in explaining the phenomena in ques-
tion.

The results of the two last mentioned experiments
appear to me to be very important ; and I do not see
how they can be reconciled with the opinions of modern
chemists respecting the nature of heat.

In order to simplify our speculations on this ab-
struse subject, we have hitherto supposed that difference
of temperature depends solely on the difference of the
times of the vibrations of the component particles of
bodies. It is possible, however, and even probable,
that it depends principally on the 'velocities of those
particles ; for it is easy to perceive that, the more rapid
the motions of those particles are, the greater their elon-
gations must be in their vibrations, and the more, of
course, will the volume of the body they compose be
expanded.

It is well known that the pulsations occasioned in an
elastic fluid by the vibrations of an elastic solid body
proceed from that body in all directions, and that these
pulsations are everywhere (that is to say, at all distances
from the body) isochronous with the vibrations of the
solid body ; it is known, also, that the mean velocity of
any individual particle of the fluid is less in proportion
as the distance of the particle is greater from the centre
from which these pulsations proceed.

In the case of the pulsations occasioned in the air by
the vibrations of sonorous bodies, those pulsations are
everywhere isochronous with the vibrations of the sono-
rous body, and the time, or frequency, of these pulsa-
tions, determines the note ; but it is the velocity of the
particles of the air, or the breadth of the wave, on
which the force or strength of the sound depends ; and

and the Mode of its Communication. 125

this velocity becoming less as the distance from the
sonorous body increases, the sound is weakened in the
same proportion.

There are several circumstances which might lead us
to suspect that colour depends on the frequency of those
pulsations which have been supposed to constitute
light ; and that the heat produced by them is in pro-
portion to their force.

If this supposition should be well founded, a knowl-
edge of that important fact might perhaps enable us to
explain several very interesting phenomena, — the com-
bustion of inflammable bodies, for instance, and the great
intensity of the heat which is produced by the concen-
tration of calorific rays.

There are several well-known experiments with burn-
ing-glasses which show that the intensity of the heat
generated by the concentration of the solar rays is not
simply as the condensation of those rays, but in a higher
proportion ; and that it depends much on their direc-
tion^ being greater as the angle is greater at which they
meet at the focus of the lens.

That fact is certainly very remarkable. It has often
been the subject of my meditations, and it has contrib-
uted not a little to the opinion I have been induced to
adopt respecting the nature of light and of heat. I
never could reconcile it with the supposition that heat
is caused by the accumulation of anything emitted by the
sun, or by any other body which sends off calorific
radiations.

Reserving for a future communication an account
of the sequel of my inquiries respecting the subject
which I have undertaken to investigate, I shall conclude
this long paper with some observations concerning the

126 Inquiry concerning the Nature of Heat,

practical uses that may be derived from a knowledge of
the facts which have been established by the results of
the foregoing experiments.

In all cases where it is designed to -preserve the heat
of any substance which is confined in a metallic vessel,
it will greatly contribute to that end if the external sur-
face of the vessel be very clean and bright ; but if the
object be to cool anything quickly in a metallic vessel,
the external surface of the vessel should be painted, or
covered with some of those substances which have been
found to emit calorific rays in great abundance.

Polished tea-urns may be kept boiling hot with a
much less expense of spirit of wine (burnt in a lamp
under them) than such as are varnished ; and the cleaner
and brighter the dishes and covers for dishes are made,
which are used for bringing victuals on the table, and
for keeping it hot, the more effectually will they answer
that purpose.

Saucepans and other kitchen utensils which are very
clean and bright on the outside may be kept hot with a
smaller fire than such as are black and dirty ; but the
bottom of a saucepan or boiler should be blackened, in
order that its contents may be made to boil quickly, and
with a small expense of fuel.

When kitchen utensils are used over a fire of sea-coal
or of wood, there will be. no necessity for blackening
their bottoms, for they will soon be made black by the
smoke ; but when they are used over a clear fire made
with charcoal, it will be advisable to blacken them, —
which may be done in a few moments by holding them
over a wood or coal fire, or over the flame of a lamp or
candle.

Proposals have often been made for constructing the

and the Mode of its Communication. 127

broad and shallow vessels (flats), in which brewers cool
their wort, of metal, on a supposition that the process
of cooling would go on faster in a metallic vessel than
in a wooden vessel ; but this would not be found to be
the case in fact, a metallic surface being ill calculated
for expediting the emission of calorific rays.

The great thickness of the timber of which brewers'
flats are commonly made is a circumstance very favour-
able to a speedy cooling of the wort ; for, when the flats
are empty, this mass of wet wood is much cooled, not
only by the cold air which passes over it, but also and
more especially by evaporation ; and when the flat is
again filled with hot wort a great part of the heat of
that liquid is absorbed by the cold wood.

In all cases where metallic tubes filled with steam are
used for warming rooms or for heating drying-rooms,
the external surface of those tubes should be painted or
covered with some substance which facilitates the emis-
sion of calorific rays. A covering of thin paper will
answer that purpose very well, especially if it be black,
and if it be closely and firmly attached to the surface of
the metal with glue.

Tubes which are designed for conveying hot steam
from one place to another should either be well cov-
ered up with warm covering or should be kept clean
and bright. It would, I am persuaded, .be worth while,
in many cases, to gild them, or at least to cover them
with what is called gilt paper, or with tin foil, or some
other metallic substance which does not easily tarnish
in the air.

The cylinders and principal steam-tubes of steam-
engines might be covered first with some warm cloth-
ing, and then with thin sheet brass kept clean and

128 Inquiry concerning the Nature of Heat,

bright. The expense of this covering would, I am con-
fident, be amply repaid by the saving of heat and fuel
which would result from it.

If garden walls painted black acquire heat faster when
exposed to the sun's direct rays than when they are not
so painted, they will likewise cool faster during the
night; and gardeners must- be best able to determine
whether these rapid changes of temperature are, or are
not, favourable to fruit-trees.

Black clothes are well known to be very warm in the
sun ; but they are far from being so in the shade, and
especially in cold weather. No coloured clothing is so
cold as black when the temperature of the air is below
that of the surface of the skin, and when the body is
not exposed to the action of calorific rays from other
substances.

It has been shown that the warmth of clothing de-
pends much on the polish of the surface of the substance
of which it is made; and hence we may conclude that,
in choosing the colour of our winter garments, those
dyes should be avoided which tend most to destroy that
polish ; and, as a white surface reflects more light than
an equal surface, equally polished, of any other colour,
there is much reason to think that white garments are
warmer than any other in cold weather. They are uni-
versally considered as the coolest that can be worn in
very hot weather, and especially when a person is ex-
posed to the direct rays of the sun ; and if they are well
calculated to reflect calorific rays in summer, they must
be equally well calculated to reflect those frigorific rays
by which we are cooled and annoyed in winter.

I have found, by direct and decisive experiments (of
which an account will hereafter be given to this Soci-

and the Mode of its Communication. 129

ety), that garments of fur are much warmer in cold
weather when worn with the fur or hair outwards than
when it is turned inwards. Is not this a proof that we
are kept warm by our clothing, not so much by confin-
ing our heat as by keeping off those frigorific rays which
tend to cool us ?

The fine fur of beasts, being a highly polished sub-
stance, is well calculated to reflect those rays which fall
on it ; and if the body were kept warm by the rays
which proceed from it being reflected back upon it,
there is reason to think that a fur garment would be
warmest when worn with the hair inwards ; but if it
be by reflecting and turning away the frigorific rays
from external (colder) bodies that we are kept warm by
our clothes in cold weather, we might naturally expect
that a pelisse would be warmest when worn with the
hair outwards, as I have found it to be in fact.

The point here in question is by no means a matter
of small importance; for until the principles of the
warmth of clothing be understood, we shall not be able
to take our measures with certainty, and with the least
possible trouble and expense, for defending ourselves
against the inclemencies of the seasons, and making
ourselves comfortable in all climates.

The fur of several delicate animals becomes white in
winter in cold countries, and that of the bears which
inhabit the polar regions is white in all seasons. These
last are exposed alternately, in the open air, to the most
intense cold and to the continual action of the sun's
direct rays during several months. If it should be true
that heat and cold are excited in the manner above de-
scribed, and that white is the colour most favourable to
the reflection of calorific and frigorific rays, it must be

VOL. II. 9

1 30 Inquiry concerning the Nature of Heat.

acknowledged, even by the most determined sceptic,
that these animals have been exceedingly fortunate in
obtaining clothing so well adapted to their local circum-
stances.

The excessive cold which is known to reign, in all
seasons, on the tops of very high mountains and in the
higher regions of the atmosphere, and the frosts at night
which so frequently take place on the surface of the
plains below in very clear and still weather in spring
and autumn, seem to indicate that frigorific rays arrive
continually at the surface of the earth from every part
of the heavens.

May it not be by the action of these rays that our
planet is cooled continually, and enabled to preserve the
same mean temperature for ages, notwithstanding the
immense quantities of heat that are generated at its sur-
face, by the continual action of the solar rays ?

If this conjecture should be well founded, we should
be led to conclude that the inhabitants of certain hot
countries who sleep at night on the tops of their houses,
in order to be more cool and comfortable, do wisely in
choosing that situation to pass their hours of rest.

[This paper is printed from the Philosophical Transactions of the
Royal Society, XCIV. (1804), pp. 77 - 182.]

EXPERIMENTAL INVESTIGATIONS
CONCERNING HEAT

SECTION I. — Short Account of a new Experiment on Heat.

I HAVE lately made a new experiment, the result
of which appears to me sufficiently interesting to
deserve the attention of the Class.

Having found, by experiments often repeated, that
metallic bodies, exposed in the free air of a large apart-
ment, are much more speedily heated and cooled when
their surfaces have been blackened (over the flame of a
candle, for example) than when they are clean and pol-
ished, I was curious to know whether the same phe-
nomena would take place when, instead of exposing
these bodies in the open air, they should be placed in
close metallic vessels, surrounded by a certain thickness
of included air, and these vessels should be then plunged
in a large mass of hot or cold water. In order to clear
up this important point, I made the following experi-
ment : —

A cylindrical vessel of brass, three inches in diame-
ter and four inches long, was enclosed in another larger
cylindrical vessel, in the centre of which it was sus-
pended by its neck, so as to touch it in no other part,
leaving on all sides an interval of one inch between the
vessels.

The external vessel, as well as the smaller one in-
cluded within it, is made of thin sheets of brass; its

132 Experimental Investigations

diameter is five inches, and its height six. It is one
inch and a half in diameter, and six inches high. Its
neck is one inch and a quarter in diameter, and two
inches and a half long.

The interior vessel is suspended in the centre of the
external one by a stopper of cork. This stopper is
adjusted to the neck of the external vessel, and there is
a cylindrical hole of three quarters of an inch diameter
through the cork, and having the same axis ; which per-
foration receives the neck of the interior vessel, and
retains it in its place.

The interior vessel was introduced and fixed in its
place before the bottom of the exterior vessel was sol-
dered in.

At the centre of the bottom of the great vessel is a
small metallic tube, of three quarters of an inch diame-
ter and one inch and a half long, by means of which
this instrument is attached to a solid heavy foot of
metal, which supports it in 'a vertical position when the
whole instrument is submerged in a vessel of water.

This instrument, which greatly resembles that de-
scribed in my seventh Essay on the Propagation of
Heat in Fluids, which I have called the passage ther-
mometer* may be used to make a number of interesting
experiments on the cooling of bodies through different
fluids. In the present experiment I employed it in the
following manner : —

The interior vessel was entirely filled with hot water
to the height of half an inch in its neck, and a good
thermometer, having its cylindrical bulb four inches
long, was inserted therein. The instrument was then
plunged in a mixture of pounded ice and water, and

* See Vol. I. p. 237.

concerning Heat, 133

the time was noted by means of the thermometer,
during which the hot water in the small vessel became
cold.

I was careful to plunge the instrument in this frigo-
rific mixture, so that the large vessel was completely
submerged, except the upper extremity of its neck ; and
I added, from time to time, a sufficient quantity of
pounded ice to keep the frigorific mixture constantly
and throughout at the temperature of melting ice.

The following were the' results afforded by two simi-
lar instruments, employed at the same time : —

These two instruments, which I shall distinguish
respectively by the letters A and B, are of the same
form and dimensions ; there is no difference between
them but in the state of their surfaces. In the instru-
ment A the exterior surface of the small vessel and the
interior surface of the great vessel which encloses it
are bright and polished ; but in the instrument B
the exterior surface of the small* vessel and the inte-
rior surface of the large vessel are black, having been
blackened over the flame of a candle, before the bottom
of the great vessel was soldered in its place.

Having filled the interior vessel of each of these in-
struments with boiling water till the water rose to the
height of half an inch in the neck, I placed a ther-
mometer in each ; and then plunging both instruments
at the same time into a tub filled with cold water, mixed
with pounded ice, I observed the course of their refrig-
eration during several hours.

Each of the instruments was completely submerged
in the frigorific mixture, excepting about one inch of the
superior extremity of the neck of the exterior vessel,
and I was careful to add new quantities of pounded ice,

134 Experimental Investigations

from time to time, in order to keep the frigorific mix-
ture constantly at the precise temperature of melting ice.

As the specific gravity of water at the temperature of
three or four degrees of the thermometer of Reaumur
is greater than that of melting ice, the water which lies
at the bottom of a vessel containing a mixture of water
and pounded ice is usually warmer than the fluid which
occupies the upper part of the vessel. To remedy this
inconvenience, my refrigeratory for the frigorific mixture
was a tin vessel, supported on 'three feet of one inch in
length; and I placed this first vessel in a larger one of
wood, containing a certain quantity of ice surrounding
the bottom and part of the sides of the metallic vessel.

As in the first moments of the experiment the ther-
mometers descended too quickly to be observed with
precision, I waited till each of them had arrived at the
55th degree of Reaumur ; after which I carefully ob-
served the number of minutes and seconds employed in
passing through each interval of five degrees of the lower
part of the scale of the thermometer to the fifth degree
above zero.

Degrees of the Time employed in cooling

thermometer. By the instrument A. By the instrument B

From

55 to

50 . ' .

1 1

6

• . : •'•• • 7

5°

"

50 «

45

13

'5

8

"10

"

45 "

40 .

• 15

12

. . 9

5

"

40 "

35

19

10

10

5°

"

35 "

30 .

. 22

24

. 12

18

"

30 «

25

27

5°

. 15

to

M

•7 r "

/T

1 5

«

2O "

'5

54

15

28

"

15 «

10

. 80

25

V . . . 4«

25

"

10 "

5 • •

. 183

45

. . . 85

15

Time employed in cooling | g
from 55° to 5°, j 47

254 5

concerning Heat.

135

The foregoing table exhibits the depression of the
thermometers during eight hours employed in the ex-
periment.

It is evident, from the results of this experiment,
that the blackened body is constantly cooled in less
time than the polished body ; but it appears, by the
course of the thermometers, that the difference between
the quickness of cooling of these two bodies varies,
and that this difference was less considerable in propor-
tion as the temperature of the bodies was more elevated
in comparison to that of the medium in which they were
exposed to cool.

In cooling from the 55th degree to the 5oth above
the temperature of the surrounding medium, the pol-
ished body employed 1 1 minutes and 6 seconds, and
the blackened body employed 7 minutes and 50 sec-
onds to pass through the same interval. But from the
loth to the 1 5th degree above the temperature of the
medium, the polished body employed 183 minutes and
45 seconds, while the blackened body employed only 85
minutes and 15 seconds; but it is extremely probable
that this difference between the proportion of the times
employed in cooling the two bodies at different tem-
peratures is only apparent, and that it depends on the
greater or less time required for the thermometers in
the vessels to arrive at the mean temperatures of th«»
masses of water which surround them.

In order to compare the results of this experiment
with those I made last year with metallic vessels, pol-
ished and blackened, and left to cool in the undisturbed
air of a large chamber, it is necessary to ascertain how
much time the two bodies in question employed in cool-
ing from the 5oth to the 4Oth degree of Fahrenheit

136 Experimental Investigations

above the temperature of the medium. Now, I found,
by observation, that the polished vessel A employed
39 minutes and 30 seconds to pass over that interval
of cooling, while the blackened vessel B employed only
11 minutes. These times are in the proportion of
10,000 to 5810. By one of my experiments, made last
year, I found that the times employed in passing through
the same interval of cooling in the open air by a clean
polished metallic vessel, and another of the same form
and capacity, but blackened without, were as 10,000 to

5654-

Reflecting on the consequences which ought to result
from the radiations of bodies, on the supposition that
the temperatures of bodies are always changing by
means of these radiations, I was led to the following
conclusion : If the intensity of the action of the rays
which proceed • from a body be universally as the
squares of the distances of bodies inversely, which is
extremely probable, a hot body exposed to cool in a
close place, or surrounded on all sides by walls, ought
to cool with the same celerity, or in the same time,
whatever may be the magnitude of this enclosure, pro-
vided the temperature of the sides or walls be at a
constant given temperature; and the results of the
experiment here described, in which the hot body was en-
closed in a vessel of a few inches diameter, compared with
those of several experiments made last year, in which
the heated bodies were exposed to cool between the walls
of a large chamber, appear to confirm this conclusion.

As to the effect produced by the air in cooling a
heated body exposed to cool in a close place filled with
that fluid, I have reason to believe that it is much less
considerable than has been supposed.

concerning Heat. 137

I have shown, by direct and conclusive experiments,
that bodies cool and are heated, and that with consider-
able celerity, when placed in a space void of air ; *
and by experiments made last year, with the intention
of clearing up this point, I found reasons to conclude
that when a hot body cools in tranquil air, not agitated
by winds, one twenty-seventh only of the heat lost by
this body (or, to speak more correctly, which it excites
in surrounding bodies) is communicated to the air,
all the rest being carried to a distance through the air
and communicated by radiation to the surrounding solid
bodies.

SECTION II. — Experiments on cooling Bodies.

It is only by careful observation of the phenomena
which accompany the heating and cooling of bodies,
that we can hope to acquire exact notions of the nature
of heat and its manner of acting.

Many experiments have been made by different per-
sons, at different times, with a view to determine what
has been called the conducting quality of different sub-
stances with regard to heat. I have myself made a con-
siderable number ; and it is from their results, often no
less unexpected than interesting, that I have been gradu-
ally led to adopt the opinions on the nature of heat which
I have presumed to submit to the judgment of this
illustrious assembly. The flattering attention with
which the Class has honoured the three Memoirs I
have lately presented encourages me to communicate the
continuation of my researches.

All philosophers are agreed in considering glass as
one of the worst conductors of heat which exists ; and

* In my Essay on the Propagation of Heat in various Substances. See Vol. I.
p. 401.

138 Experimental Investigations

when it is proposed to confine the heat in a body, of
which the temperature has been raised, or to hinder its
dissipation as much as possible, care is taken to sur-
round the heated body with substances known to be
bad conductors of heat.

The results of many of my experiments having led
me to suspect that the cooling of bodies is not effected
in the manner which is generally supposed, I made the
following experiment, with the intention of clearing up
this interesting part of the science.

I procured two bottles, nearly cylindrical, of the same
form and the same dimensions when measured exter-
nally, — one being of glass, and very thick, and the
other of tin or tinned iron, which was very thin. Each
of them is three inches ten lines in diameter, very
nearly, and five inches in height ; and each has a neck
one inch three lines in diameter, and one inch two lines
in height. The glass bottle weighs 13 ounces, i gros,
and 1 8 grains poids de marc; and the other thin me-
tallic vessel weighs only 5 ounces, i gros, and 65 grains.

Having very exactly weighed the bottle of tinned
iron, I found its exterior surface to be 54.462 inches,
which give 0.21142 of a line for the thickness of
its sides, taking the specific gravity of the metal ac
7.8404.

The mean thickness of the sides of the glass bottle
is more than six times as great, as may be easily de-
duced from a calculation founded on the weight of the
bottle, the quantity of its surface, and the specific grav-
ity of glass.

Having filled these two bottles with boiling water,
I hung them up by slender strings in the midst of
the tranquil air of a large chamber, at the height of

concerning Heat. 139

five feet from the floor, and at the distance of four feet
asunder.

The temperature of the air of the chamber, which
did not vary a quarter of a degree during the .whole
time of the experiment, was 9! degrees of Reaumur's
scale.

An excellent mercurial thermometer, with a cylindri-
cal bulb, of four inches long and two lines and a half
in diameter, suspended in the axis of each of these
bottles, indicated the temperature of the contained
water ; and the time employed in its cooling for every
five degrees of Fahrenheit's thermometer was carefully
observed, during eight hours.

The glass being considered as a very bad conductor
of heat, and the sides of the bottle being so thick, who
would not have expected that the water in this bottle
would have been more slowly cooled than that in the
very thin bottle of tin ?

The contrary, however, was the event ; the bottle
of glass was cooled almost twice as quickly as that of
tin.

While the water included in the bottle of tinned
iron employed 56 minutes to pass through a cer-
tain interval of cooling, — namely, through ten degrees,
between the 5oth and 4Oth degree of the thermometer
of Fahrenheit above the temperature of the air of the
chamber, — the water in the glass bottle employed only
30 minutes for the same change.

It appears to me that the result of this experiment
throws great light on the mysterious operation of the
communication of heat.

If we admit the hypothesis that hot bodies are
cooled, not by losing or acquiring some material sub-

140 . Experimental Investigations

stance, but by the action of colder surrounding bodies,
communicated by undulations or radiations excited in
an ethereal fluid, the results of this experiment may
be easily explained ; but, if this hypothesis be not
adopted, I cannot explain them.

It might, perhaps, be suspected that the air attached
by a certain attraction, but with unequal forces, to the
surfaces of the two bottles, might have been the cause
of this remarkable difference in the time of their cool-
ing ; but those who will take the trouble to reflect
attentively on the results of the experiments I have
described in a preceding Memoir, which were made with
a view to clear up this point, with a metallic vessel first
naked, and afterwards with one, two, four, and five coat-
ings of varnish, will be persuaded that this cause is not
sufficient to explain the facts.

By a course of experiments made at Munich, last
year, of which the details are given in a Memoir sent to
the Royal Society of London,* I have found that a
given quantity of hot water, included in a metallic ves-
sel of a given form and capacity, always cools with the
same quickness in the air, whatever may be the metal
employed to construct the vessel ; provided always that
the external surface of the vessel be very clean, and the
temperature of the air the same.

In order that the cooling shall be effected in the same
time, nothing more is required than that the external
surface of the vessel be truly metallic, and not covered
with oxide, or other foreign bodies.

On the inquiry, what quality all the metals might
have in common, and possess in the same degree, to
which this remarkable equality of their susceptibil-

* See p. 23.

concerning Heat. 141

ity of cooling might be attributed, I found it in their
opacity.

The rays which cannot penetrate the surface of a
body must necessarily be thrown back, or reflected ;
and as the rays of light, which have much analogy with
the invisible calorific or frigorific rays, easily penetrate
glass, though they are reflected, at least for the greatest
part, by metallic surfaces, I suspected beforehand the
result of the experiment with the two bottles, — one of
glass, and the other of tinned iron.

The state of a heated body, or a body which con-
tains a certain quantity of caloric, has been compared
to that of a sponge which contains a certain quantity of
water. Supposing this comparison to be just, we might
compare the loss of heat by the emission of the ca-
lorific rays to the loss of water by evaporation. Let
us try if this comparison can supply us with the means
of throwing some light on the interesting subject of our
researches.

Instead of the sponge filled with water, let us substi-
tute the earth, and suppose, for a moment, that the
earth is everywhere equally heated, and its surface, in
all parts, covered with a bed of the same kind of soil,
equally moist.

As a square league in a mountainous country contains
more surface, or more superficial acres than a square
league situated in the plain, it is evident that more
water would be evaporated from the whole surface of
the earth in a given time, if the earth were covered with
mountains than if its surface were an immense plain,
and, consequently, that more caloric ought to be pro-
jected from the surface of any solid body broken with
asperities, than from the surface of another body, of the

142 Experimental Investigations

same form and dimensions, which is smooth or well
polished.

This reasoning appears to me to be just, and, if I
am not deceived, the conclusions which may be drawn
from the facts in question, well confirmed by experi-
ment, ought to be considered as demonstrative. I
have taken every possible care to establish these facts ;
and the results of all my experiments have constantly
shown that more or less perfect polish, or the greater or
less brightness of the surface of a metallic vessel, does
not sensibly influence the time of its cooling.

I took two equal vessels of brass, and polished the
external surface of one of them as highly as possible ;
and I destroyed the polish of the other by rubbing it
in all directions with coarse emery. When these two
vessels were filled with hot water, I did not find that
the unpolished vessel employed more or less time in
cooling than that which was polished.

I was careful to wash the surface of the unpolished
vessel effectually with water, before the experiment ; as
I knew that if I did not take the precaution of remov-
ing all the dirt which might be lodged in the asperities
of the surface, the presence of these small foreign bod-
ies would influence the result of the experiment in a
sensible manner.

We ought carefully to distinguish those surfaces
which appear unpolished to our eyes, but which in
fact are not so, from those which reflect little or no
light.

It is more than probable that the surface of a metal
is always polished, and even always equally so in all the
cases wherein the metal is naked and clear and clean,
notwithstanding all the mechanical means which may

concerning Heat. 143

be used to scratch its surface and break the glare of its
lustre.

Let us return to the comparison of the evaporation
of water from the surface of the earth, with the emis-
sion of caloric radiating from the surface of a heated
body, and let us suppose, for an instant, that the evapo-
ration of the water from the surface of the earth does
not depend on the heat of the earth itself, but that it is
caused merely by the influences of surrounding bodies,
— as, for example, by the rays of light received from
the sun. It is evident that, in this case, the evapora-
tion could not be sensibly greater in a mountainous
country than in the plain ; and by an easy analogy we
see that if hot bodies be cooled, not in consequence of
the emission of some material substance from their sur-
faces, but by the positive action of rays sent to them
by colder surrounding bodies, the more or less perfect
polish of their surfaces ought not sensibly to influence
the rapidity of their cooling.

This is precisely what all my experiments concur to
prove.

I have long sought, and with that patience which the
love of the sciences inspires, to reconcile the results of
my experiments with the opinions generally received
concerning the nature of heat and its mode of action,
but without being able to succeed.

It is in the hands of two of the most illustrious
bodies of learned men that ever existed that I have
thought it incumbent on me to deposit my labours, my
discoveries, my doubts, and my conjectures.

I am earnestly desirous of engaging the philosophers
of all countries to turn their attention towards an ob-
ject of inquiry too long neglected.

144 Experimental Investigations

The science of heat is not only of great curiosity, from
the multitude of astonishing phenomena it offers to our
contemplation, but it is likewise extremely interesting
from its intimate connection with all the useful arts, and
generally with all the mechanical occupations of human
life.

Without a knowledge of heat, it is not possible either
to excite it with economy or to direct its different opera-
tions with facility and precision.

SECTION III. — Experiments tending to show that Heat is
communicated through solid Bodies, by a Law which
is the same as that which would ensue from Radiation
between the Particles.

Having made a considerable number of experiments
on the passage of heat through fluids, and through dif-
ferent substances in the state of powder, I was curious
to ascertain the laws of its propagation through solid
bodies, particularly metals.

I hoped this discovery would furnish some additional
data to confirm or refute the opinions I had adopted
concerning heat and its manner of acting ; and it will
be seen by the results that my expectations were not
frustrated.

Having procured two cylindrical vessels of tin, each
six inches in diameter and six inches high, I fastened
them together, by means of a solid cylinder of copper,
six inches long and an inch and a half in diameter,
which was fixed horizontally between the two tin ves-
sels. The extremities of the cylinder passed through
two holes, an inch and a half in diameter, made for
the purpose in the sides of the vessels, midway be-

concerning Heat. 145

tween the bottom and top, and were soldered fast in
them.

Each of the vessels was made flat on the side where
the copper cylinder was fastened, so that the extremity
of the cylinder did not project into the vessel, but was
level with the flattened part.

This instrument was supported at the height of eight
inches and a half above the table on which it stood, by
means of three feet, — two fixed to one of the vessels,
and one to the other.

One of these vessels being filled with boiling water,
the other with water at the freezing point, as the two
extremities of the cylinder were placed in immediate
contact with these two masses of fluid, a change of
temperature must necessarily take place by degrees in
all the interior parts of the cylinder. For the pur-
pose of observing this change, three vertical holes were
made in the cylinder, into which were introduced the
bulbs of three small mercurial thermometers. One
of the holes was in the middle of the cylinder, the
others midway between the centre and either extrem-
ity.

Each of these holes is four lines in diameter, and
eleven lines and a half deep ; so that the bulbs of the
thermometers, which are three lines in diameter, were
all in the axis of the cylinder.

When the thermometers were put in their places, the
holes were filled with mercury, in order to facilitate the
communication of heat from the metal to the bulb of
the thermometer.

To keep the hot water constantly boiling, a spirit-
lamp was placed beneath the vessel containing it; and
to keep the cold water constantly at the temperature of

146

Experimental Investigations

melting ice, fresh portions of ice were added to it, from
time to time.

The thermometers are graduated to Fahrenheit's
scale, the freezing point being marked 32°, and that of
boiling water 212°.

As the first and most important object I had in view
was to learn at what temperature the three thermome-
ters would become stationary, I did not very carefully
notice the progress of the thermometers toward this
point ; but as soon as they appeared nearly stationary,
I observed them with the greatest attention for near
half an hour.

To distinguish the three thermometers, I shall call
that nearest the boiling water B, that in the centre C,
and that nearest the cold water D.

The following are the progress and results of an ex-
periment made the 28th of April, 1804, the tempera-
ture of the air being 78° of Fahrenheit.

Time.

Temperature
of the hot water.

Temperature
marked by the
thermometer B.

Temperature
marked by the
thermometer C.

Temperature
marked by the
thermometerD.

Temperature of
the cold water.

h. m. s.

Degrees.

Degrees.

Degrees.

Degrees.

Degrees.

I 52 15

212

1 60

130

J05

32

— 53 30

160^

131

i°5£

— 55

161

ttt|

1 06

— 56 3°

I6i|

I32

io6|

— 58

162

134

107

2 O O

162

I32f

107^

— I 30

162

133

l°?i

— 4

162

»3*l

io6|

— 6

—

162

132

1 06

— 9

162

I32|

ic6£

— ii

162

I32j

io6£

— 28

162

i3£f

t*|

Before I proceed to examine more minutely the re-
sults of this experiment, I. will endeavour to show

concerning Heat. 147

those results which it ought to have exhibited, on the
supposition that heat is propagated, even in the interior
of solid bodies, by radiations emanating from the sur-
faces of the particles composing these bodies.

On this supposition, we must necessarily consider
the particles that compose bodies as being separate from
each other., and even by. pretty considerable distances,
compared with the diameters of these particles ; but
there is nothing repugnant to the admission of this sup-
position ; on the contrary, there are many phenomena
which apparently indicate that all the solid bodies with
which we are acquainted are thus formed.

To see now by what law heat would be propagated
in a solid cylinder, let us represent the axis of this cylin-
der by a right line A E, Plate IV. Fig. i ; and let
us begin with supposing that the cylinder consists of
three particles of matter only, ACE, placed at equal
distances in that line.

Let us farther suppose that the extremity, A, of the
cylinder is constantly at the temperature of boiling water,
while its other extremity, E, remains invariably at the
freezing point.

By an experiment, of which I have already given an
account to the Class,* I found that when two equal
bodies, A B, one hotter than the other, are isolated and
placed opposite each other, the intensities of their ra-
diations are such, that a third body, C, placed in the
middle of the space that separates them, will acquire a
temperature, by the simultaneous action of these ra-
diations, which will be an arithmetical mean between
those of the two bodies A and B.

From the result of this experiment we have ground

* See the preceding paper.

148 Experimental Investigations

to conclude that if the cylinder were composed of three
particles of matter only, A, C, E, the particle C, which
is in the middle of the cylinder, must necessarily have
the arithmetical mean temperature between that of A
and that of E, which are at the two extremities of the
cylinder; that is to say, between 212° and 32° of Fah-
renheit, which is 122°.

Now let us interpose between the particles A, C, and
E, two other particles, B, D, and see whether the intro-
duction of these two particles will make any change in
the temperature of the particle C that occupies the mid-
dle of the cylinder.

If the particle B be placed in the middle of the space
comprised between the extremity, A, of the cylinder and
its middle, C, it ought to acquire a mean temperature
between that of the extremity, A, of the cylinder, and
that of the point C, namely that of 167°, the mean be-
tween 212° and 122°; and if the particle D be placed in
the midst of the space comprised between the middle
of the cylinder and its other extremity, E, this particle
ought to acquire a mean temperature between that of
the middle of the cylinder and that of its extremity, E ;
it ought then to have the temperature of 77°.

From this new arrangement, the particle C, situate
in the middle of the cylinder, will find for its neigh-
bours, on one side the particle B, at the temperature of
167°, and on the other the particle D, at that of 77°.
The point in question is, whether the presence of these
two particles will make any change in the temperature
of the particle C, or not.

In the first place, it is evident that if the calorific in-
fluences of the particle B on the particle C be as effica-
cious in heating it as the frigorific influences of the

concerning Heat. 149

particle D be in cooling it, the temperature of the particle
C ought not to be changed. But experience has shown
that, at equal distances and equal intervals of tempera-
ture, the calorific influences of hot bodies and the frigo-
rific influences of cold bodies are exactly equal ; and as
the distance from B to C is equal to the distance from
D to C, while the interval of temperature between B
and C, = 45°, is the same as that between D and C,
= 45°, it is evident that the temperature of the par-
ticle C, which is in the middle of the cylinder, can be
no way affected by the introduction of the intermediate
particles B and D.

By the same way of reasoning may be proved, that
the introduction of an indefinite number of interme-
diate particles would produce no change in the tempera-
ture of the middle of the axis of the cylinder, or in any
part of it; and if the introduction of an indefinite num-
ber of intermediate particles make no change in the state
of a thermometer placed in the middle of the axis of
the cylinder, we may conclude that the thermometer
would remain equally stationary if the number of inter-
mediate particles were increased till they had that prox-
imity to each other which is necessary to constitute a
solid body. If, instead of a single row of particles in a
right line, there were a bundle composed of an indefinite
number of such rows placed side by side, forming a
solid cylinder, the temperature in the different parts of
the line A E would remain the same.

From this reasoning we may infer that the tempera-
tures of the different parts of the cylinder should de-
crease in arithmetical progression from one extremity
of the cylinder to the other.

But it is evident that this law of decrement of tern-

150 Experimental Investigations

perature could take place only in the single case of the
surface of the cylinder being completely isolated, so as
to be no way affected by the action of surrounding
bodies, which is absolutely impossible.

The circumstances under which the experiments were
made are very different from those here taken for
granted. The bodies we subject to experiment are con-
stantly surrounded on all sides by the air and other
bodies which act on our instruments continually, and
often in a very perceptible manner ; and we can never
hope to isolate a cylinder so completely that the appar-
ent progress of heat in its interior shall perceptibly
obey the law we have just discovered. In common
cases it deviates widely from this law.

As the causes of this deviation are well known, we
will see whether there be no means of appreciating their
effects.

The surface of the cylinder being surrounded by the
atmospheric air and other bodies, all which are of a
known and sensibly constant temperature, we may de-
termine the comparative effects of these bodies on the
different parts of the surface of the cylinder.

In those parts of the cylinder which are hotter than
the air and other surrounding bodies, the surface of the
cylinder will be cooled by the action of these bodies ;
but if one of the extremities of the cylinder be colder
than the atmospheric air, those parts of the cylinder
which are colder than the circumambient fluid will be
heated by its influence and that of the surrounding
bodies.

We will begin with examining the case where the
coldest extremity of the cylinder is at the same tem-
perature as the surrounding air. Let us suppose,

concerning Heat. 151

then, that the experiment with boiling water at the one
end and freezing at the other be made when the tem-
perature of the air is at the freezing point, or 32° of
Fahrenheit.

In this case it is evident that the surface of the cyl-
inder must everywhere be cooled by the influence of the
surrounding atmosphere. The question, then, is to
determine the comparative effects, or the relative quan-
tities of refrigeration or loss of heat, that must take
place in the different farts of the cylinder ; and, in the first
place, it is clear that the hotter a given part of the cyl-
inder is, the more heat it must lose in a given time, by
the influence of the surrounding cold bodies; whence
we may conclude that the refrigeration of the surface of
the cylinder by the influence of the air and other sur-
rounding cold bodies must necessarily diminish from
the extremity of the cylinder, A, which is in contact with
the hot water, to its extremity, E, which is in contact
with the cold.

From reasoning which appears incontrovertible, and
which the results of a great number of experiments
appear to confirm, it has been concluded that the celer-
ity with which a hot body placed in a cold medium is
cooled is always proportional to the difference between
the temperature of the hot body and that of the me-
dium. Considering this conclusion as established, we
may determine a •priori what ought to be the gradation
of temperatures in the interior of a given solid cylinder
surrounded by air, one extremity of which is in contact
with a considerable body of boiling water, while the
other is similarly in contact with cold.

We have seen that, if the surface of the cylinder were
perfectly isolated, the decrease of temperature from the

152 Experimental Investigations

hottest extremity of the cylinder, A, to its other extrem-
ity, E, which is in contact with cold water, would be in
arithmetical progression^ and it has just been shown that
the decrease must necessarily be accelerated by the ac-
tion of the air and other surrounding cold bodies.

But the acceleration of the decrease of temperature in
those parts of the cylinder which are toward the cold
extremity, depending on the action of the air and sur-
rounding bodies, must be continually diminishing in
proportion as the temperature of the surface of the cyl-
inder approaches nearer and nearer that of the air ; and
hence we may conclude that, if a given number of points,
at equal distances from each other, be taken in the axis
of the cylinder, the temperatures corresponding with
these points will be in geometrical progression.

We may represent the progress of the decrease of
temperature by Plate IV. Fig. 2.

In a right line A E, representing the axis of the cylin-
der, if we take the three points B, C, and D, so that
the distances A B, B C, C D, and D E shall be equal,
and, erecting the perpendiculars A F, B G, C H, D I,
EK, take A F = the temperature of the cylinder at
its extremity A, B G = its temperature at the point B,
and so of the rest; the ordinates A F, B G, &c. will
be in geometrical progression, while their corresponding
abscisses are in arithmetical progression ; consequently
the curve, P Q, which touches the extremities of all
these ordinates, must necessarily be the logarithmic curve.

We will now see whether the results of experiment
agree with the theory here exhibited, or not.

To form our judgment with ease and, as it were, at a
single glance, of the agreement of our theory with the
results of the experiment of which I gave an account

concerning Heat. 153

at the beginning of this Memoir, we have only to repre-
sent these results by a figure in the following manner.

On the horizontal line A E, Fig. 3, representing the
axis of the cylinder employed in the experiment, we will
take three points, B, C, and D ; one, C, in the middle
of the axis, being the situation of the central thermom-
eter, the other two, B and D, at the intermediate points
which the other two thermometers occupied between
the middle of the axis and its two extremities.

Erecting the perpendiculars A/, B gy C /z, D /, and
E k, on the points A, B, C, D, and E ; and taking the
ordinate Af= 212, the temperature of boiling water,
B g = 162, the temperature indicated by the thermom-
eter B, C h = 132!, the temperature indicated by
the thermometer C, D / = io6-|, the temperature given
by the thermometer D, and lastly, E k = 32, the tem-
perature of water mixed with pounded ice, — a curve,
P Q, passing through the points /, g, h, i, k, ought to
be the logarithmic; that is, supposing the temperature
of the surrounding air to be constantly at the tempera-
ture of melting ice during the experiment.

But the experiment in question was made when the
temperature of the air was at 78° F. ; consequently,
reckoning from a certain point, taken in the length of
the cylinder, where the temperature was at 78°, to the
extremity, E, the influence of the surrounding air, in-
stead of cooling the surface of the cylinder, heated it ; and
it is evident that the curve, P Q, must necessarily in this
case have a point of inflection.

In fact, it appears on a simple inspection of the figure,
that the curve, P Q, has a point of inflection ; but we see,
likewise, that this curve is not regular. That branch
which is concave toward the axis of the cylinder is not

154 Experimental Investigations

similar to the adjoining portion of the curve, of equal
length, which is convex toward that axis, as it ought to
be according to our theory ; and even the part of the
curve which is convex toward the axis, A E, differs sen-
sibly from the logarithmic, particularly toward its ex-
tremity, P.

It ought necessarily to differ from this curve as far
as the divisions of our thermometers are defective ; but the
deviation between the ordinates, A /and B g, indicated
by the results of the experiment in question, appears to
me much too considerable to be ascribed to the imper-
fection of our thermometers.

To see how far the curve, P Q, differs from the loga-
rithmic, we have only to draw a logarithmic curve, R S,
through the points g and /, and we shall find, that the
ordinates corresponding to the points

A, B, C, D, E,

o o o o o

Instead of being 212.00 162 132^ io6j 32.00
Will be 199-55 J6z 131 io6£ 86.35

Difference — I2-45 ° — 'i ° +54-35

The very great difference that exists between the tem-
perature of cold water and that indicated by the results
of the experiment for the extremity of the cylinder
which was in contact with this water led me to suspect
that it was owing to the quality possessed by water in
common with other fluids, which renders it a very bad
conductor of heat.

If it be true, as I believe I have elsewhere proved,
that there is no sensible communication of heat be-
tween the adjacent particles of a fluid, from one to
another, and that heat is propagated through fluids
only in consequence of a motion of their particles, re-

concerning Heat, 155

suiting from a change in their specific gravity, occa-
sioned by their being heated or cooled ; as the specific
gravity of water is very little altered by an inconsidera-
ble change of temperature when this fluid is near the
freezing point, it might have been foreseen that a solid
body a little heated, and plunged into cold water, would
be very slowly cooled.

The result of the following experiment, which I
made with a view to elucidate this point, will put the
fact out of all doubt.

The three thermometers being stationary, one, B, at
162°, the second, C, at ijsf0, and the third, D, at
io6J°, the water in contact with one of the extremities
of the cylinder being still boiling, while the water mixed
with pounded ice, which was in contact with the other
extremity, was constantly at the temperature of melting
ice, I began to stir this mixture of ice and water pretty
briskly with a little stick, and I continued to stir it
uninterruptedly and with the same velocity for 22
minutes.

I had scarcely begun this operation when I had a
proof that my conjectures were well founded. The
mercury in the three thermometers immediately began
to descend, and did not stop till it had fallen very con-
siderably.

The thermometer B fell from 162° to 152°; C from
132!° to inf°; and D from io6J° to 78}°.

On comparing these numbers, we find that, in con-
sequence of the agitation of the cold water for 22
minutes, the thermometer B fell 10° of Fahrenheit's
scale, the thermomete C 21°, and the thermometer D
28°.

As soon as I had ceased to stir the cold water the

156 Experimental Investigations

three thermometers began to rise, and at the end of a
quarter of an hour they had all reached the points from
which they set out at the beginning of this operation.

To facilitate the comparison of the results of these
two experiments, — one made with cold water at rest, the
other with the same water in a state of constant agita-
tion, — I have represented them in Fig. 4.

In the first place, we shall learn several very interest-
ing facts by simple inspection of this figure ; we shall
see, —

i st. That the progress of refrigeration — or, to speak
more properly, the decrease of temperature — was every-
where much more rapid when the cold water in contact
with the extremity, E, of the cylinder was agitated than
when it was at rest.

2dly. That the extremity of the cylinder in contact
with this water was constantly near jo° colder 'in the
first case than in the second.

^dly. We shall see that the progress of refrigeration
was everywhere, and in both the experiments, such
nearly as our theory points out.

The decrease of temperature toward the middle of the
cylinder was so regular that it is more than probable
the apparent irregularities toward the two extremities
were occasioned solely by the difficulty which a body of
water finds in communicating its mean temperature to
a solid with which it is in contact.

The boiling water being in continual motion, owing
to its ebullition, it had a great advantage over the cold
water, which was at rest, in communicating its tempera-
ture to the extremity of the cylinder it touched; but I
have found, notwithstanding this, that by agitating the
boiling water strongly with a quill, and particularly

concerning Heat. 157

when with the quill I made a rapid friction against the
end of the cylinder immersed in the boiling water, I
occasioned all the thermometers to rise several degrees.

It may perhaps be imagined, at first sight of the re-
sults of the experiment, that as the three thermometers,
which occupied the parts about the middle of the axis
of the cylinder, did not indicate a decrease perfectly
agreeing with the theory, the theory itself cannot be
true ; but a moment's reflection will show that this in-
ference would be too hasty, and that the difference be-
tween the theory and the results of our experiments, far
from proving anything adverse to the theory, serve on
the contrary to render it more probable.

The results of such experiments can never agree with
the theory, except the divisions of our thermometers be
perfectly accurate; but it is well known to everyone
who has any knowledge of natural philosophy that the
divisions of our thermometers are defective.

One of the objects I had in view in the experiments
of which I have just given an account to the Class, and
in several others which I intend to make without delay,
is to improve the division of the scale of the thermom-
eter, in order to render this valuable instrument of
greater utility in the delicate investigations of natural
philosophy.

It appears certain that the increase of the elasticity
of air by heat is much more nearly proportionate to the
increase of temperature than the dilatation of mercury
or any known fluid ; consequently, it is the air thermom-
eter we ought to endeavour to improve, and which
must ultimately afford us the most accurate measure of
heat that it is possible for us to procure.

158 Experimental Investigations

SECTION IV. — The Heat produced in a Body by a given
Quantity of solar Light is the same whether the Rays be
denser or rarer, convergent, parallel, or divergent.

In all cases where the rays of the sun strike on the sur-
face of an opaque body without being reflected, heat is
generated and the temperature of the body is increased;
but is the quantity of heat thus excited always in pro-
portion to the quantity of light that has disappeared ?
This is a very interesting question and has not hitherto
found a decisive solution.

When we consider the prodigious intensity of the
heat excited in the focus of -a burning mirror or a lens,
we are tempted to believe that the concentration and
condensation of the solar rays increase their power of
exciting heat ; but, if we examine the matter more
closely, we are obliged to confess that such an augmen-
tation would be inexplicable. It would be equally so
on both the hypotheses which natural philosophers
have formed of the nature of light ; for if light be analo-
gous to sound, since it has been proved, both by calcu-
lation and experiment, that two undulations in an
elastic fluid may approach and even cross each other
without deranging either their respective directions or
velocities, we do not see how the concentration or con-
densation of these undulations can increase their force of
impulse; and if light be a real emanation, as its velocity
is not altered either by the change of direction it under-
goes in passing through a lens or by its reflection from
the surface of a polished body, it seems to me that the
power of each of these particles to excite or impart
heat must necessarily be the same after refraction or
reflection as before, and consequently, that the heat

concerning Heat. 159

communicated or excited must be, in all cases, as the
quantity of light absorbed.

I have just made some experiments which appear to
me to establish. this fact beyond question.

Having procured from the optician Lerebours two
lenses perfectly equal, and of the same kind of glass,
4 inches in diameter, and of nj focus, I exposed them
at the same time to the sun, side by side, about noon,
when the sky was very clear ; and by means of two
thermometers, or reservoirs of heat, of a peculiar con-
struction, I determined the relative quantities of heat
that were excited in given times by the solar rays at dif-
ferent distances from the foci of the lenses.

The two reservoirs of heat are a sort of flat boxes of
brass filled with water. Each of these reservoirs is
3 inches ioj lines in diameter, and 6 lines thick, well
polished externally on all sides except one of its two
flat faces, which was blackened by the smoke of a
candle. On this face the solar rays were received in
the experiments.

Each of these reservoirs of heat weighs when empty
6850 grains, folds de marc (near a pound troy), and
contains 1210 grains of water (about 2 oz. 2 dwts.).

Taking the capacity of brass for heat to be to that
of water as i to n, it appears that the capacity of
the metallic box weighing 6850 grains is equal to the
capacity of 622 grains of water; and, adding this quan-
tity of water to that contained in the box, we shall have
the capacity of the reservoir prepared for the experi-
ments equal to that of 1832 grains of water.

Each reservoir is kept in its place by a cylinder of
dry wood, one of the extremities of the cylinder being
fixed in a socket in the centre of the interior face of the

160 Experimental Investigations

reservoir ; and each reservoir has a little neck, through
which it is filled with water, and which after receives
the bulb of a cylindrical thermometer, that reaches com-
pletely across the inside of the box in the direction of
its diameter.

The two reservoirs of heat, with their two lenses, are
firmly fixed in an open frame, which being movable in
all directions by means of a pivot and a hinge, the ap-
paratus is easily directed toward the sun, and made to
follow its motion regularly, so as to keep the solar
spectra constantly in the centres of the blackened faces
of the reservoirs.

In order that the quantities of light passing through
the two lenses should be perfectly equal, a circular plate
of well-polished brass, in the centre of which is a circu-
lar hole 3! inches in diameter, is placed immediately
before each of the lenses.

When the reservoirs of heat are placed at different
distances from the focuses of their respective lenses, the
diameters of the solar spectra which .are formed on the
blackened faces of the reservoirs are necessarily differ-
ent ; and as the quantities of light are equal, its density
at the surface of each reservoir is inversely as the square
of the diameter of the spectrum formed on that surface.

Experiment No. I. — In this experiment the reservoir
A was placed so near the focus of the lens, between
the lens and the focus, that the diameter of the solar
spectrum falling on it was only half an inch, or 6 lines,
while the reservoir B was advanced so far before the
focus that the spectrum was 2 inches in diameter, or
24 lines.

As the quantities of light falling on both were equal,
the density of the light at the surface of the reservoir

concerning Heat. 161

A was to the density of that at the surface of the reser-
voir B as the square of 24 to the square of 6, or as
i 6 to i.

I imagined that if the quantity of heat which a given
quantity of light is capable of exciting depended any
way on its density, as the densities were so different
in this experiment, I could not fail to discover the
fact by the difference of time which it would require
to raise the two thermometers the same number of
degrees.

Having continued the experiment more than an hour,
on a very fine day, when the sun was near the meridian
and shone extremely bright, I did not find that one of
the reservoirs was heated perceptibly quicker than the
other.

Experiment No. 2. — I placed the reservoir of heat
A still nearer the focus of the lens, in a situation where
the solar spectrum was only 4! lines in diameter, and
where blackened paper caught fire in two or three sec-
onds ; and I removed the reservoir B still farther from
the focus, advancing it forward till the diameter of the
spectrum was 2 inches 3 lines.

The densities of the light at the surfaces of the reser-
voirs in this experiment were as 32 to i.

The temperature of the reservoirs as well as that of
the atmosphere, at the beginning of the experiment, was
54° F., = 9f R.

The reservoir A, after having been exposed to the
action of very intense light near the focus of the lens
for 24 minutes 40 seconds, was raised to the tempera-
ture of 80° F., = 2 if R.

The reservoir B, which was much farther from the
fjcus of its lens, was raised to the same temperature,

VOL. II. II

162

Experimental Investigations

80° F., a little more quickly, or in 23 minutes 40 sec-
onds.

To raise the temperature of the reservoir A to 100°
F., = 3of° R., it was necessary to continue the experi-
ment for i hour 15 minutes 10 seconds, reckoning
from the commencement of it ; but the reservoir B
reached the same temperature in i hour 12 minutes 10
seconds.

The progress of this experiment from the beginning
to the end is exhibited in the following table.

Time taken.

Increases of

Temperature.

By A.

By B.

m. s.

m. s.

From 54° to 80° F.

24 40

23 40

80 85

7 45

7 30

85 90

9 55

9 o

90 95

13 30

13 o

95 100

19 20

19 o

From 54° to 100°

75 10

72 10

This experiment was begun at 7 minutes 30 seconds
after n, and finished at 22 minutes 40 seconds after 12,
the sky being perfectly clear during the time.

On comparing all the results of this experiment, we
see that the reservoir A, which was placed very near
the focus, was more slowly heated than the reservoir B,
which was at a considerable distance from it. The dif-
ferences of time, however, taken to heat them an equal
number of degrees were very trifling, and I think may
be easily explained without supposing the condensation
of light to increase its faculty of exciting heat.

In both the preceding experiments the solar rays
striking on the reservoirs of heat were convergent, and
they were even equally so on both sides. To deter-
mine whether •parallel rays have the same power of ex-

concerning Heat. 163

citing heat as convergent rays, I made the following
experiment.

Experiment No. 3. — Having removed the lens from
before the reservoir B, I suffered the direct rays of the
sun to fall on the blackened face of the reservoir, through
the circular hole, 3^ inches in diameter, in the round
brass plate which had been constantly placed before that
lens in the preceding experiments.

The reservoir A was placed behind its lens as in the
former experiments, and at the place where the solar
spectrum had 6 lines diameter.

Having exposed this apparatus to the sun, I found
that the reservoir B, on which the direct rays fell, was
heated sensibly quicker than the reservoir A, which was
exposed to the action of the concentrated rays near the
focus of the lens.

The temperature of the apparatus and of the atmos-
phere at the beginning of the experiment being 53° F.,
= 9!° R, the reservoir A required 23 minutes 30
seconds to raise it to the temperature of 80° F., = 2i|°
R. ; but the reservoir B, which was exposed to the
direct rays of the sun, acquired the same temperature
in 1 8 minutes 30 seconds.

To reach the temperature of 100° F., = 30^° R., took
the reservoir A i hour and 3 minutes, but the reser-
voir B 47 minutes 15 seconds only.

The following table will show the progress of this
experiment from the beginning to the end.

164

Experimental Investigah

Increases of

Time taken.

Temperature.

By A. By B.

From 53° to 65° F.

m. s.

8 26

7 o

65 70

4 10

3 15

70 75

5 10

3 45

75 8°

5 40

4 30

So 85

7 o

4 45

85 90

7 3°

5 45

90 95

10 30

8 o

95 100

13 10

10 15

100 105

20 0

14 45

From 53° to 105°

Si 36 ' 62 30

As a considerable part of the light that fell on the
lens before the reservoir A was lost in passing through
it, it is evident that the quantity received by this reser-
voir was less than that received by the reservoir B,
which was exposed to the direct rays of the sun ; and
we have seen that the latter was heated more rapidly
than the former.

As we know not exactly how much light was lost in
passing through the lens, we cannot determine from the
results of this experiment whether convergent rays be
more or less efficacious in exciting heat than parallel
rays ; but the difference in the times of heating was not
greater, as it appears to me, than we might have ex-
pected to find it, supposing it to be occasioned solely
by the difference between the quantities of light acting
on the reservoirs.

The result of the following experiment will establish
this point beyond doubt.

Experiment No. 4. — Having replaced the lens belong-
ing to the reservoir B, I adjusted this reservoir to such
a distance between the lens and its focus that the solar
spectrum was one inch in diameter; and I placed the
reservoir A at the same distance beyond its focus.

concerning Heat.

165

As the quantities of light directed toward both were
equal, and as the diameters of the spectra, and conse-
quently the densities of the light that formed them were
also equal, there could be no difference between the re-
sults of the experiments with the two reservoirs, except
what was occasioned by the difference in the direction of
the rays that formed the spectra. On one hand these
rays were convergent^ and on the other divergent ; and I
had inferred that if parallel rays were in reality less effica-
cious in exciting heat than convergent rays, as some
philosophers have supposed, divergent rays must be still
less efficacious than parallel rays, and consequently much
less than convergent rays.

Having made the experiment with all possible care,
I found no sensible difference between the quantities of
heat excited in a given time by divergent and convergent
rays.

The following are the particulars of the progress and
results of this experiment.

Increases of
Heat.

Time taken.

By A,
with divergent Rays.

By B,
with convergent Rays.

From 60° to 65° F.
65 70
70 75
75 80

4 5°

4 55
5 27
6 13

4 50
5 °

5 25
6 is

From 60° to 80°

21 25

21 30

From the results of all the experiments of which I
have just given an account to the Class, we may con-
clude that the quantity of heat excited or communi-
cated by the solar rays is always, and under all circum-
stances, as the quantity of light that disappears.

[This paper is, in part, printed from Nicholson's Journal, XII.
(1805), pp. 65 -75 and 154-171; and in part translated from the
Memoires de 1'Institut, etc., VI. (1805), pp. 88- 133.]

REFLECTIONS ON HEAT.

THE most excellent gift which man has received
from the Author of his being is the power which
he possesses of freeing himself from the prejudices aris-
ing from the deceptive testimony of his senses, and of
penetrating into the mysteries of Nature.

The animals see as we do, without doubt, that the
sun, moon, and stars rise and set ; man in a state of
nature, when his attention is aroused, discovers irregu-
larities in these movements ; the man of genius, how-
ever, does not allow himself to be deceived by appear-
ances, but causes to come forth from this confusion that
vast and wonderful system of laws which govern the
mechanism of the Universe.

The first step in science is to observe facts attentively,
and in their proper connection ; the second is to learn
to doubt. The sublime in science consists in employ-
ing it to extend the power and increase the innocent
enjoyments of the human race.

There is no branch of the physical sciences which is
so intimately connected with all the every-day occupa-
tions of man as that of Heat, and consequently there is
no one of them which interests him so closely.

Fire is the most universal and active agent with
which we are acquainted, and it is to the power which
he has been able to acquire over this wonderful princi-
ple that man owes the supernatural strength which has

Reflections on Heat. 167

made him superior to all animals, and master of land
and sea.

It is not at all surprising that an agent at once so
powerful and so manageable, so beneficent and so ter-
rible, should have become an object of admiration and
even of adoration among the nations of the earth ; but
it is more than surprising that a subject, the investiga-
tion of which is of such interest, should have been for
so long a time neglected.

This indifference to an object at once so curious and
so interesting can only be attributed to that lack of at-
tention with which men always regard those things that
they are accustomed to have before them at all times.

A proof that our knowledge on the subject of heat is
still extremely limited and imperfect lies in the differ-
ence of opinion which exists among the learned on the
nature of heat and its mode of action. Some regard it
as a substance, others as a vibratory motion of the particles
of matter of which a body is composed.

Those who have adopted the hypothesis of a peculiar
calorific substance which they call caloric suppose that
the heating of a body is always the result of an accumu-
lation of this substance in the body ; on the other hand,
those who regard heat as a vibratory motion which is
conceived to exist always with greater or less rapidity
among the particles of all bodies, consider heat as an
acceleration of this motion.

On the hypothesis of vibratory motion, a body which
has become cold is thought to have lost nothing except
motion ; on the other hypothesis it is supposed to have
lost some material substance, that is, caloric.

The eminent French philosophers, who proposed,
twenty-five years ago, the modern hypothesis of caloric,

1 68 Reflections on Heat.

far from considering the existence of this substance as
proved, always speak of it with that modest reserve
which characterizes men of superior excellence. They
propose the word in order to avoid circumlocutions
and to render the language of science more concise,
rather than to introduce a new opinion.

One of these philosophers, whom science and man-
kind still mourn, thus expresses himself in his ad-
mirable Traite Rlcmentaire de Chimie : "In the labours
which M. de Morveau, M. Berthollet, M. de Fourcroy,
and myself have performed in common on the reform
of the language of chemistry, we have felt that we ought
to banish from it those circumlocutions which render
the form of expression longer and more cumbersome,
less exact, and less clear, and which not seldom even do
not allow of ideas sufficiently well defined. We have,
therefore, designated the cause of heat, the eminently
elastic fluid which produces it, by the name caloric. In-
dependently of the fact that this expression answers our
purpose in the system which we have adopted, it has
besides another advantage, that of being able to adapt
itself to all sorts of opinions, since, strictly speaking,
we are not even obliged to suppose that caloric is a
material substance."

If the point in question, the existence or non-exist-
ence of caloric, were less important we might be content
with leaving it undecided ; but the use of heat is so
general, and the art of exciting and directing it is so
intimately connected with the perfecting of all the me-
chanical arts and with a great number of domestic ap-
plications, that we cannot take too much trouble in
becoming acquainted with it.

Without entering into the details of the various ex-

Reflections on Heat. 169

periments which have been performed in order to de-
termine the nature of heat, I will limit myself in this
memoir to some of the principal results of these re-
searches.

A very remarkable phenomenon, and one which must
have been noticed as soon as men had any acquaintance
with fire, is the radiation from solid bodies as soon as
they become very warm.

When a solid body — a bar of iron, for example — is
at about the temperature of the surrounding air, we
do not see or perceive anything which indicates that it
possesses a radiating surface ; but if we heat it strongly
in the glowing fire of a forge, the body changes color,
becomes at first red, then white, is visible in the dark,
lights up surrounding objects, and warms in a sensible
degree all objects which are struck by the rays which
it emits in all directions.

If we allow it to cool slowly in the undisturbed air
of a dark room, we see that it changes color again ; from
white it becomes red, then a darker red; the light which
it gives forth gradually diminishes ; the intensity of its
calorific rays becomes less at the same time, and soon
it ceases to shed light round about it.

It continues, however, to emit from its surface calo-
rific rays for some time after it has ceased to be lumi-
nous, as may be perceived by holding the hand near it.

The calorific rays which very warm bodies send off
from their surfaces pass through the transparent air
without heating it, nor do they heat sensibly those
bodies at whose surfaces they are reflected.

These very important facts, which ought not to be
forgotten, have been established by the results of a
large number of experiments.

170 Reflections on Heat.

We have thus taken one sure step in the investigation
of heat. We see that very warm bodies emit from
their surfaces rays which, passing (like rays of light)
through the air excite, at a distance, heat at the surfaces
of the surrounding objects on which they fall without
being reflected.

The existence of the calorific rays, which we are now
discussing, being actually proved, and their manner of
acting being evidently as I have described it, it is im-
portant to ascertain whether the knowledge of these facts
be not sufficient to form a theory of heat which will ex-
plain all these phenomena.

A theory which should have the advantage of ex-
plaining the communication of heat by a single method,
at once simple and easily understood, would be prefera-
ble, it seems to me, to one which, in order to explain
various phenomena, would be obliged to admit two
different modes of the communication of heat.

In order to form a clear and exact idea of the rays in
question and of the effects which they are capable of
producing, we must go back to their mechanical cause,
and consider them with regard both to their existence
and to their operation.

There are two ways of looking at the radiation from
an object ; the first, by conceiving the rays as emana-
tions of an actual substance thrown off from the surface
of the body ; the second, by considering these rays as
undulations which, starting from every point of the sur-
face of the radiating object, are propagated in all direc-
tions in straight lines in an elastic fluid which surrounds
it on every side.

The system of Newton supposes that the rays of light
are real emanations.

Reflections on Heat. 171

Sound, with which we are better acquainted than we
are with light, affords us an example of radiation or
undulation in an elastic fluid which most certainly is
not an emanation.

We have sufficiently clear ideas of the mechanical
operations by means of which the undulations of the
air which constitute sound are excited and propagated ;
but We have no conception of any possible mechanical
operation by means of which a material substance could
be sent forth continually and in all directions from the
surface of a body.

In physics, in order that an hypothesis may be ad-
mitted, it must be founded on the supposition of a con-
ceivable mechanical operation.

In order that the theory of heat which is founded on
the vibratory hypothesis may be admitted, it is neces-
sary to show that the vibrations in question can exist,
and that they can cause the rays or undulations which
objects emit from their surfaces, and by means of which
we suppose that bodies of different temperatures influ-
ence each other even at a distance, bringing about
reciprocal and simultaneous changes of temperature, so
that little by little they arrive at a common and inter-
mediate temperature.

If the particles which compose a body do not touch
each other (an opinion which is generally received, and
which appears very probable), as there is no doubt that
these particles are continually drawn one towards an-
other by the recognized force of universal gravitation,
it is impossible to conceive how, in an assemblage of
particles which form a tangible solid body, these parti-
cles can preserve their relative situations without being
in motion.

172 Reflections on Heat.

From this course of reasoning we might conclude
that the particles which compose a body are of necessity
in motion ; and if we admit the existence of an emi-
nently elastic fluid, — an ether which fills all space
throughout the universe, with the exception of that
occupied by the scattered particles of ponderable bodies,
— it is easy to conceive that the movements of the
particles which make up material objects must cause
undulations in this fluid ; and, on the other hand, the
undulations of this fluid must affect to a sensible de-
gree and modify the motions of the particles of these
bodies.

It might perhaps seem that these motions among the
particles of solid bodies would be incompatible with the
preservation of the forms of those bodies ; but by re-
flecting attentively on this subject it will be found that
such motions as are here supposed can well exist with-
out diminishing at all the stability of the external form
of the bodies.

It would follow necessarily, from the state of things
supposed by the hypothesis in question, first, that the
sum of the active forces in the universe must always
remain constant, in spite of all actions and reactions
taking place among the various bodies ; secondly, that
the particles of all ponderable bodies must of necessity
have the property of producing radiations.

Now, if we admit the existence of the ether, it is pos-
sible to explain the radiations of bodies in still an-
other manner ; it is by supposing that the particles
are kept apart from each other, not in consequence of
the action of the centrifugal force of those particles, but
by atmospheres composed of ether or of some other
fluid unknown to us, which is extremely elastic, and

Reflections on Heat. 173

that it is by the very rapid vibrations which take place
in these atmospheres that those undulations in the sur-
rounding ether are excited by means of which the tem-
perature of objects is altered.

The adoption of this latter hypothesis will reconcile,
to a certain extent, the theory of vibrations with that
of a calorific substance; but still the heating of a body
cannot be regarded, in any respect, as the result of the
accumulation of this substance, but as the acceleration
of its motion.

In order to establish on a firm foundation the theory
of heat which is based upon the vibratory hypothesis,
it is necessary not only to show that the vibrations in
question are possible, but also to prove that the undu-
lations which they should cause do really exist.

In the ordinary condition of things, the objects which
surround us do not afford any indication of radiation,
nor do they produce any effect capable of manifesting
itself to any one of our senses in such a way as to lead
us to suspect that they possess radiating surfaces. But
the philosopher who aims at penetrating into the mys-
teries of Nature must be continually on his guard that
he may not be deceived either by the testimony or by
the silence of his senses.

In the first place it is evident that our various organs
were formed with reference to the daily wants of life ;
and that, if they were too sensitive, the pleasure which
they afford us would be turned into actual pain.

If our ears had been constructed so as to be sensibly
affected by all the vibrations which take place in the
air, we should, without doubt, be stunned by the
intolerable noise, even in the deepest retirement ; and
if our eyes took cognizance of all the rays that strike

174 Reflections on Heat.

them, we should be dazzled by an insupportable flood
of light, even in the darkest night.

It is well known that, if the vibrations of a sonorous
body be less frequent than 30 in a second, or more
frequent than 3000 in a second, the undulations of
the air caused by these vibrations do not perceptibly
affect our organs of hearing ; and it is very probable
that the range of our organs of sight is still more
limited.

When we have found strong reasons for suspecting
the existence of agents which fail to manifest themselves
to our senses, we ought to employ all our skill in devis-
ing means for compelling them to discover themselves
and to unveil the mysteries of their invisible operations.

By means of an instrument which I have called a
thermoscope, and which is extraordinarily sensitive, I have
found not only that all bodies at all temperatures emit
rays, but also that the rays emanating from cold bodies
are as effectual in cooling warm bodies as the rays from
the latter are effectual in warming cold bodies.

The principal part of the instrument of which I have
made use in these delicate experiments consists of a
long glass tube bent at both ends, and having at each
extremity a very thin glass bulb an inch and a half in
diameter. The middle portion of this tube, which is
straight, is placed in a horizontal position, while the two
end portions, whose extremities are the two bulbs, are
turned upwards in such a way as to form right angles
with the horizontal portion of the tube. The hori-
zontal portion is from 15 to 16 inches in length, and
each of the two end portions, which are vertical, is
from 6 to 7 inches long. The internal diameter of
the tube should be about half a line.

Reflections on Heat. 175

By means of a little glass reservoir, an inch in length
and a line in internal diameter, inserted in the tube at
one of the elbows, there is introduced into the interior
of the instrument a small quantity of coloured spirit
of wine (exactly enough to fill the reservoir without
interfering with the free passage of the air from one
bulb to the other) ; this being done, the extremity of
the reservoir is sealed hermetically, and all communica-
tion between the air enclosed in the instrument and the
air of the outside atmosphere is forever interrupted.

The instrument is adjusted and prepared for use as
follows : —

The bulb which is farthest from the reservoir having
been warmed slightly with the hand, the instrument is
suddenly turned over, so as to bring the reservoir
uppermost, and in this way a small quantity of the
spirit of wine passes from the reservoir into the hori-
zontal part of the tube ; restoring immediately the in-
strument to its natural position, the observer withdraws
himself from it, and waits for the small quantity of
spirit of wine which has passed into the horizontal part
of the tube to become stationary ; this will be as soon
as the two bulbs have acquired the same temperature.

The little bubble of spirit of wine, wh'ch serves as
the index of the instrument, and which may be about
three quarters of an inch long, should become station-
ary nearly in the middle of the horizontal portion of the
tube ; if it is too near either of the elbows it must be
returned to the reservoir, and the operation performed
anew.

When this delicate operation is finished, the instru-
ment is ready for use. The method of employing it is
as follows : —

I ;5 Reflections on Heat.

One of the two bulbs is protected from the influence
(calorific or frigorific) of the warm or cold bodies pre-
sented to the other bulb by means of light screens cov-
ered with gilt paper; when the air in this latter bulb is
warmed or cooled by a body warmer or colder than the
thermoscope to which it is thus presented, the elasticity
of the air is affected by this change of temperature, and
the little bubble or column of spirit of wine which is in
the horizontal portion of the tube is compelled to move
and to take a new position.

The direction of the motion of this bubble indicates
the nature of the change which has taken place in the
temperature of the air which is enclosed in the bulb to
which the body is presented, and the distance traversed
by the bubble is the measure of the increase or diminu-
tion of the elasticity, and, as a consequence, of the tem-
perature of that air.

If the bubble recedes from the bulb to which the
object experimented upon is presented, it is evident
that the air enclosed in the bulb has been heated by the
influence of this body ; but when the bubble of spirit
of wine advances towards this bulb, we have a proof
that the air in the bulb has been cooled.

The rapidity with which the bulb moves is propor-
tional to the intensity of the action of the object pre-
sented to the instrument.

In order to compare the intensity of the calorific or
frigorific actions of two different objects, they are pre-
sented at the same time to the two bulbs of the instru-
ment, and their respective distances from the bulbs so
regulated that the bubble of spirit of wine remains at
rest in its proper position.

In this case it is evident that the action of the two

Reflections on Heat. 177

objects, each on the bulb to which it is presented, is of
precisely the same amount; hence we can calculate the
relative intensity of the radiation of each one of the
two objects from the extent of the surface presented
to the bulb, and from the square of its distance from
the bulb.

If we desire to compare the calorific action of a warm
body with the frigorific action of a cold body, we begin
by protecting one of the bulbs of the instrument by the
screens, and then present to the other bulb the two
objects, — regulating their respective distances in such a
manner that their actions exerted at the same time pro-
duce equal effects, that is, so that one warms the bulb
as much as the other cools it.

The equality in the amount of action is denoted by
the remaining at rest of the bubble of spirit of wine
which serves as the index of the instrument, and when
this equality is established, the relative intensity of the
radiation from the objects in question is calculated from
the amount of surface which they respectively present to
the bulb, and from the squares of their distances from it.

The sensibility of this instrument is so great that,
when it is at a temperature of 15° or 16° of Reaumur's
scale, if the hand be presented to one of the bulbs at a
distance of three feet, the heat radiating from the hand
is sufficient to cause the bubble of spirit of wine to move
forward several lines; and. the cooling influence of a
blackened metallic disk four inches in diameter, at the
temperature of melting ice, is such that, when presented
to the bulb at a distance of 18 inches, it causes the bub-
ble to advance in the opposite direction with a rapidity
which is very perceptible to the eye.

By means of this instrument I have discovered,

178 Reflections on Heat.

first, that all bodies at all temperatures (cold bodies as
well as warm ones) emit continually from their surfaces
rays, or rather, as I believe, undulations^ similar to the
undulations which sonorous bodies send out into the
air in all directions, and that these rays or undulations
influence and change, little by little, the temperature of
all bodies upon which they fall without being reflected,
in case the bodies upon which they fall are either warmer
or colder than the body from the surface of which the
rays or undulations proceed ; secondly, that the inten-
sity of the rays from different bodies at the same tem-
perature is very different, and that it is less in bodies
which reflect the rays of light than in those which ab-
sorb them, less in the metals than in their oxides, less
in opaque and polished bodies than in those which are
imperfectly transparent and unpolished, (a surface of
brass, for instance, emits four times as large a quantity
of rays at a given temperature when it is covered with
a coating of oxide, and five times as large a quantity
when it is blackened by the flame of a candle, as when
the surface of the metal is clean and well polished) ;
thirdly, that the rays which bodies of the same tem-
perature send out to each other have no tendency to
bring about any change of temperature in these bodies ;
fourthly, that the rays which any body whatever, at a
given temperature, sends continually from its surface in
all directions, are calorific or frigorific with regard to
other bodies on which they fall, according as these latter
are less warm or warmer than the body from which the
rays come; so that the same rays are calorific as re-
gards all bodies less warm than the one from which
they proceed, and frigorific as regards all those which
are warmer than this body.

Reflections on Heat. 179

From these facts we might conclude a priori, that
those bodies which, when warm, give off many calorific
rays would, when colder than the surrounding objects,
give off to them many frigorific rays. This is exactly
what my experiments have made evident to me.

In experiments made with bodies of the same size,
and of the same material, the intervals of temperature
being equal, the frigorific influences of cold bodies have
always appeared as real and effective as the calorific in-
fluences of warm bodies.

To one of the bulbs of a thermoscope, the tempera-
ture of which was 20° of Reaumur's thermometer, were
presented at the same time and at equal distances two
disks of metal of the same diameter. The temperature
of one of these disks was o° (that of melting ice), that
of the other was 40°. The index of the instrument by
remaining at rest showed that the bulb was cooled by
the rays from the cold body as much as it was heated
by the rays from the warm body.

If the surface of one of the disks, it matters not of
which, is blackened, the intensity of the radiation from
this blackened disk is increased to such an extent that
the other can no longer counterbalance it; but if the
second one is blackened also, the equality of action is
immediately re-established.

If the emanations from warm and cold bodies are
really undulations in an extremely rare and elastic fluid
which has been called ether, the communication of heat
and cold ought to be similar to the communication of
sound ; and all the mechanical contrivances which have
been invented to increase the intensity of sound ought
to be just as applicable for increasing the effects pro-
duced by these emanations from warm and cold bodies ;

180 Reflections on Heat.

and, indeed, I found that a speaking-tube (a conical
brass tube, well polished on the inside) placed between
one of the bulbs of the thermoscope and a hollow ball
of thin copper 3 inches in diameter, which, being filled
with pounded ice, was presented to it at a distance of
12 inches, increased more than three times the effect of
the cold body.

To use a rather strong metaphor, but one which ex-
presses perfectly the idea which I have conceived of the
mechanical operation in question, I will say that the
cold ball spoke at the larger opening of the speaking-
tube while the bulb of the thermoscope listened at the
smaller opening.

If it is true that the particles which make up all
material bodies are agitated continually by very rapid
vibratory motions, and that, in consequence of these
motions, all bodies at all temperatures send continually
from every point of their surfaces rays or undulations
similar to the undulations caused in the air by the
vibration of sonorous bodies; and if bodies of different
temperatures act one upon another at a distance, by
means of these rays or undulations, working simultane-
ously an interchange in temperature and gradually
bringing about a mean intermediate temperature, — we
ought then to regard the cooling of a warm body as the
result of the actual and positive operation of the sur-
rounding bodies less warm than itself; and since the
rays coming from warm bodies, and, as a consequence,
from cold bodies, are reflected in great measure by the
polished surfaces of opaque bodies, and since the rays
which are reflected produce little or no effect on the
bodies at whose surfaces they are reflected, we might
conclude a priori that opaque polished bodies ought to

Reflections on Heat. 181

cool or become warm more slowly than bodies imper-
fectly transparent and unpolished.

I will now detail the results of a series of experiments
made with a design of throwing light on this point, so
important in the science of heat.

I had made two cylindrical vessels, four inches in
diameter and four inches high, of thin sheet brass, well
polished on the outside. Having blackened one of
them over the flame of a candle, I filled them both with
boiling water, and left them at the same time to cool in
the air of a large quiet room. The one which was black-
ened cooled almost twice as fast as the one whose metal-
lic surface remained bright and clean. When the two
vessels had become of the same temperature as that of
the room in which they were situated, they were re-
moved into a room warmed by a stove, and I found
that the blackened vessel was heated twice as quickly as
the other.

The blackened vessel was cleaned and covered with a
single covering of fine linen, fitting closely to the
body of the instrument. Repeating the experiments
with the two vessels, that which was exposed naked to
the cold air took up 45 minutes in cooling through an
interval of 10 degrees on Fahrenheit's scale, that is, from
the 5oth to the 4Oth degree above the temperature of
the room ; the other vessel, covered with a coat of fine
linen, took up only 29 minutes in cooling through the
same interval.

When the two vessels had become of the same tem-
perature, they were removed into a warm room, and I
found that the vessel which was clothed with linen
acquired heat faster than the one whose surface was
naked.

1 82 Reflections on Heat.

If the results of these experiments do not furnish a
conclusive proof of the radiation from all bodies, and
that it is by means of these radiations from surrounding
objects that the temperature of a given body is changed,
they certainly lend to this conjecture a great degree of
probability.

Several other similar experiments were undertaken in
order to throw light on this point, and results were in-
variably obtained which tended to confirm the hypothe-
sis in question.

Of all known bodies the metals are the most opaque,
and it appears that they are so to an equal degree ; it
appears also that a naked metallic surface, or one that is
free from all dirt, is always polished in spite of those
irregularities of form by which the brilliancy of its metal-
lic lustre is broken up and apparently diminished. If
these conjectures are well founded, we may conclude that
all metals are equally competent to reflect from their
surfaces the rays that impinge upon them ; and if ob-
jects are heated and cooled by rays from surrounding
objects, we might conclude not only that of all known
bodies the metals ought to acquire heat or become cold
the least rapidly, but also that they ought to acquire
heat or become cold with the same degree of difficulty
or rapidity.

To put these suppositions to the test of experiment,
I procured several cylindrical vessels, of the same form
and dimensions but of different metals, and I found
that they did indeed all cool or acquire heat in the
same time. There were vessels of brass, tin, lead, and
others covered with thin coatings of gold and silver;
each vessel was four inches in diameter and four inches
high, and when filled with boiling water and exposed, in

Reflections on Heat. 183

winter, to the air of a large quiet room, they all
passed, in cooling, through the given interval of 10 de-
grees in from 45 to 46 minutes.

This equality in the degree of readiness with which
all the metals become cool or acquire heat is certainly
very remarkable ; and it seems to me very difficult of
explanation except by adopting the hypothesis that heat
is communicated by means of radiations.

As it might be supposed that a film of air, attached
by a certain force of attraction to the surfaces of the
metallic vessels, could have caused this apparent equal-
ity in their rate of cooling, I made the following ex-
periments to elucidate this point.

One of the two brass vessels was covered, first with
one, next with two, then with four, and finally with
eight coatings of spirit varnish, and the experiment with
the two vessels was repeated with each of these coatings.
While the vessel, the surface of which was bare, cooled
invariably through the given interval of 10 degrees in
45 minutes, the other vessel, which was varnished,
cooled more or less rapidly according to the thickness
of the coating of varnish with which its surface was cov-
ered, but always in a sensible degree more rapidly than
the one whose surface was naked : —

Minutes.

With one coating of varnish it cooled in . . 34i

With two coatings, in 29

With four coatings, in 24^

And with eight coatings, in . . . . . 27

As the film of air which is supposed to have been
attached to the surface of the vessel when this metal-
lic surface was not covered with varnish ought to have
been as completely driven off by one coating of varnish

184 Reflections on Heat.

as by two or by a greater number, it seems very difficult
to reconcile the results of these experiments with the
supposition that a film of air attached to the surfaces of
all the vessels, made as they were of different metals,
was the cause of their cooling all equally slowly.

When I repeated the experiment with a vessel of glass,
and with one of tinned iron of the same form and di-
mensions, I found that the glass vessel cooled much
more rapidly in the air than the one made of tinned
iron, although its walls were six times as thick as those
of the latter. In water the vessel of tinned iron cooled
most rapidly.

The results of all these experiments, and of a great
number of others which it would take too long to de-
tail here, convinced me that the ease with which a body
is heated or cooled depends very much on the nature
of the surface of that body, — these operations going on
more slowly and with more difficulty as the surface of
the body is more capable of reflecting the rays which
fall upon it; I was therefore impatient to submit the
theory of heat which I had adopted to the most search-
ing of tests, by employing it to explain some of the
grand and interesting phenomena of nature.

Close to us there occurs a most interesting phenome-
non, and one which, assuredly, is calculated to excite
our curiosity.

The people who inhabit hot countries are black,
while those who dwell in cold climates are white.

What advantages do the negroes derive from their
colour which makes them better fitted than the whites
for supporting without inconvenience the excessive heats
of their scorching climate ?

In all climates a large amount of heat is necessarily

Reflections on Heat. 185

excited in the lungs by the act of breathing; and when
man is placed in a situation where the air and all objects
about him are almost as warm as his blood, the sur-
face of his body ought to be of such a character as to
be readily cooled ; else the rays, very slightly cooling in
their action, which reach him from the surrounding ob-
jects, would not suffice to free him from the heat gener-
ated continually in his lungs, and he would soon find
himself oppressed and overcome by the accumulation of
this heat.

In a cold country, where the cooling of the surface
of a body by the cold objects which surround it is more
than sufficient to counterbalance the heat continually
produced by respiration, the body can be protected from
this excessive cooling action by clothing ; but we know
of no sort of clothing fitted to promote sufficiently the
cooling of the human body in a very hot climate.

What has Nature done to supply this want ? She
has given to the inhabitants of hot countries a black,
skin ; this colour gives to the negro such facility for
becoming cool that he feels perfectly comfortable in a
situation where a white man would be overcome by
the heat. But, in return, the negro shivers with cold
in a climate which the white man finds perfectly agree-
able.

Every one knows that a black surface reflects fewer
rays of light than a white surface ; and the results of
all the experiments performed by myself and by others
seem to show that those surfaces which are of such a
character as to reflect light also reflect the calorific or
frigorific rays which all bodies send continually from
their surfaces ; and if the temperature of a body is
changed in consequence of the action of surrounding

1 86 Reflections on Heat.

bodies through these radiations, it is seen clearly why
the negro suffers less from the heat of the tropics, and
more from the cold of the polar regions, than the man
with a white skin.

But when the negro is exposed to the action of calo-
rific rays — to those of the sun, for instance — must he
not be heated more than a white man ? It would be so,
without doubt, if Nature had not foreseen the danger
and provided means for warding off the evil.

When the negro is exposed to the rays of the sun, an
oily matter appears immediately at the surface of his
skin, and causes it to shine ; the calorific rays which
fall upon it are reflected to a great extent, and he finds
himself but little heated.

The sun sets, or the negro enters his hut ; the oil
which covers the surface of his body retires under his
skin, and he retains all the advantages which his colour
affords in aiding him to become cool.

If a coating of oil on the skin serves to protect the
body from the too violent action of calorific rays, it
ought to serve also, without doubt, to protect it from
the too violent action of frigorific rays in very cold
countries, especially in winter, when the sun never rises.
And, indeed, do not the Laplanders besmear themselves
with oil ?

But in the case of a question of so great interest, I
wished to omit nothing which might throw light upon it.

The following experiment seemed to me to establish
beyond doubt the principal facts.

Having covered two of my cylindrical vessels with
an animal substance, namely, with gold-beater's skin, I
painted one of them black with Indian ink, leaving the
other of its natural white color. Having filled both of

Reflections on Heat. 187

the vessels with hot water, I left them, at the same time,
to cool in the air of a large quiet room.

The vessel covered with a black skin represented a
negro ; the one covered with a white skin represented
a white man.

The negro cooled considerably more rapidly than the
white man, requiring 23^ minutes to cool through the
usual interval of 10 degrees, while the white man re-
quired 28 minutes to cool through the same interval.

This interesting experiment was made at Munich, the
26th of March, 1803. The results of these experi-
ments need no illustration ; and I leave to physiolo-
gists and physicians to determine what advantages may
be derived from them in taking measures for the pres-
ervation of the health of white men who are called
upon to dwell in hot countries.

[This paper is translated from the Moniteur Universe!, 9 Messidor,
An 12 (June 26, 1804).]

HISTORICAL REVIEW

VARIOUS EXPERIMENTS OF THE AUTHOR ON THE
SUBJECT OF HEAT.

A WRITER who directs the attention of the pub-
lic to a work upon a subject as important as it is
difficult of investigation must assuredly be allowed at
the very outset to state modestly the reasons which
entitle him to a hearing. It is also equally true that
a natural philosopher can with justice lay claim to the
confidence and approbation of the learned only so far
as his claims are based upon his own labours, upon
toilsome and accurate observations, as well as upon
experiments planned and executed with all possible
care.

To engage in experiments on heat was always one
of my most agreeable employments. This subject had
already begun to excite my attention when, in my
seventeenth year, I read Boerhave's admirable Treatise
on Fire. Subsequently, indeed, I was often prevented
by other matters from devoting my attention to it, but
whenever I could snatch a moment I returned to it
anew, and always with increased interest. Even now
this object of my speculations is so present to my mind,
however busy I may be with other affairs, that every-
thing taking place before my eyes, having the slightest
bearing upon it, immediately excites my curiosity and
attracts my attention.

Historical Review of Experiments on Heat. 189

This habit of many years' standing, by force of which
I seize with the greatest eagerness, and endeavour to
investigate, each and every phenomenon related even
in the slightest manner to heat and its operations which
comes to my knowledge, has suggested to me almost all
the experiments that I have performed with reference to
this subject.

In the year 1778 I was engaged in investigating the
force of gunpowder and the velocity of bullets dis-
charged from fire-arms. For this purpose I discharged
many times a musket-barrel which was loaded in vari-
ous ways, and which rested on two iron rods, perfectly
free (that is, without any stock), in a horizontal posi-
tion, about four feet from the ground.* This gave me
occasion to make a very striking observation.

Since these experiments were intended principally
to determine, from the recoil of the barrel, the veloci-
ties with which the bullets were discharged, it was
first necessary to ascertain how much the weight of
the powder which caused the discharge of the bullets
had to do with this recoil. In order to solve this
problem, I made several successive experiments, —
some with a charge of powder without any bullet,
and some with two, three, or even four bullets, one
upon another.

According to my usual practice, I seized the piece
with my left hand immediately after each discharge, in
order to hold it firmly until I had wiped it out with
some tow fastened to the rammer. I was therefore
not a little astonished to notice, on this occasion, that

* A detailed description of these investigations may be found in the seventy-first
volume of the Philosophical Transactions, and in the first volume of my Philosophical
Papers, which was published at London, in the year 1802, by Cadell and Davics. Sec
also Vol. I. p. I. '

igo Historical Review of Experiments

the barrel was always hotter when the charge had con-
sisted of powder alone than when loaded with one or
more "bullets.

I had, up to this time, no suspicion but that the
piece, on being discharged, became warm as an immedi-
ate consequence of the heat caused by the burning of
the gunpowder ; now, however, I was convinced by
the result of the above-mentioned experiment, that this
supposition was entirely without foundation.

For if we should hold that the gun in question was
actually heated by the inflammation of the powder,
since the flame would issue from the piece much more
rapidly when the charge consisted of powder alone than
when the same charge had to force out one or more
bullets, it would follow that a much higher degree of
temperature would be reached in the latter case than in
the former. But since the above-mentioned experiment
shows the contrary, it follows that the heating of the
piece in question is not due to the combustion of the
powder, but to the vibrations caused by the concussion
within the barrel, and to the operation, as rapid as it
is brief, of the elastic fluid generated by this com-
bustion.

No one is ignorant of the fact that a heavy blow is
much more effective in producing heat in a solid body
than a lighter one ; and if the hypothesis be well
founded that heat is nothing more than a continu-
ous, more or less rapid, vibratory motion among the
particles of solid bodies, this phenomenon is easily
explained.

Nothing is more certain than that the shock taking
place within the barrel, in the case of the above-men-
tioned experiment, by the combustion of the powder,

on the Subject of Heat. 191

was more vibrating or heavier when the charge was
fired without a bullet than when the elastic fluid gener-
ated by the combustion was obliged, in order to get
room for action, to push slowly before it one or more
balls, which were anything but light. On careful con-
sideration it seems to me that this circumstance is more
than sufficient to explain in a satisfactory manner the
results of the experiments in question, although I am
perfectly free to confess that I never could reconcile
myself to the hypothesis which has been developed
with regard to caloric.

The above-mentioned occurrence made so deep an im-
pression upon me, that I could hardly wait long enough
to procure the necessary instruments before undertak-
ing a number of successive experiments upon heat, in
order to arrive at some conclusion with regard to its
character, as well as to the manner of its operation.

I proposed, first of all, to undertake various experi-
ments on what has since been called the specific heat of
bodies. For this purpose, I procured from Mr. Fra-
ser, New Bond Street, London (now physical and
mathematical instrument maker to the King of Eng-
land), a considerable number of solid balls of precisely
the same diameter, namely, one inch. Some of these
balls were of gold, some of silver ; in short, they all were
of one metal or another, or of some solid substance
easily turned in a lathe. Each of these balls was sus-
pended by a thin silken cord, and I proposed to heat
the balls in certain liquids up to a given temperature,
and then to plunge them into a known quantity of water
which had been cooled in the same proportion. I drew
this inference, — that the degree of temperature which
the balls communicated to the known amount of water,

1 92 Historical Review of Experiments

as shown by the thermometer, would be more than suf-
ficient to calculate therefrom the proportional amount
of heat necessary to bring to the same temperature the
balls and an equal quantity of water.

I had already begun upon these experiments, but
before I could finish them the war made it necessary for
me to go to America. These researches were therefore
interrupted for several years ; and when, after the peace
of 1783, I returned to England, I learned that Wilkin,
in Sweden, had already carried out exactly what I had
proposed to myself. Since I had not the slightest
occasion to doubt the accuracy of the experiments
performed by this philosopher, I laid aside, as useless,
the apparatus which I had designed for my own in-
vestigations.

In the following year I left England and went to
Bavaria, where I was received into the service of the
late Elector. I brought with me several instruments
belonging to the above-mentioned apparatus, which are
still to be seen in the museum of the military school in
Munich.

For more than twenty years I have never in any of
my writings mentioned either my project and the prepa-
rations made for carrying out experiments on this point,
or the experiments I really made and which agree with
those of Wilkin, simply because I hate, and always
have hated, the character of a man who appropriates
the discoveries of another. I speak of them now rather
to convince the public that I have long thought about
this subject, than from any motive which might perhaps
have its origin in personal vanity.

My relations at the court at Munich, and that, too,
with a prince who was much interested in the promo-

on the Subject of Heat 193

tion of knowledge, afforded me during a period of four
years abundance of leisure to pursue, almost without
interruption, my physical investigations, and I em-
ployed this leisure in making a considerable number of
experiments on heat.

In the years 1785 and 1786 I was occupied in re-
searches as to the manner in which heat passes through
various substances an4 communicates itself still farther.
A detailed description of these experiments is to be
found in the two papers which I inserted in the Philo-
sophical Transactions of the Royal Society of London.
The first is in the seventy-sixth, the other in the eighty-
third, volume of this work. For the latter I received
the gold medal which this Society is accustomed to con-
fer annually.*

In the summer of 1785 I discovered that heat could
be transmitted through, or excited in, a Torricellian
vacuum.

Since this discovery has contributed not a little
towards strengthening me in the opinion which I have
since adopted with regard to the real character of heat,
I do not consider it at all superfluous to give here, with
all its details, an account of the experiment by which
this fact was established beyond doubt. This experi-
ment was conducted as follows.

After a skilful workman in Mannheim, Artaria by
name, had succeeded in fixing firmly the globular bulb
of a mercurial thermometer, half an inch in diameter, in
the centre of another glass bulb an inch and a half in
diameter, the space between the outer surface of the
thermometer bulb and the inner surface of the outside
ball, or the globe, was filled with mercury by means of a

* These papers were printed in 1797, in my eighth Essay. Sec Vol. I. p. 401.
VOL. II. 13

194 Historical Review of Experiments

barometer tube which was soldered to a small hollow
tube or point projecting outwards from the globe. This
projection extended downwards when the thermometer
fastened to the globe was in its natural upright posi-
tion.

As soon as the vacant space inside of the globe and
around the thermometer bulb, as well as the barometer
tube (thirty-six inches in length), was filled with mercury,
the end of the tube was dipped into a vessel of mer-
cury ; the tube was then inverted and brought into a
perpendicular position, so that the globe in which the
thermometer was fastened was at the top.

Since the instrument was converted in this way into
a true barometer, the mercury in the globe and in
the upper part of the barometer tube fell until the
upper surface of the mercury in the tube was twenty-
eight inches above the surface of the mercury in the
vessel, where it remained at rest, being kept at this
height by the pressure of the outside air. A lighted
wax-candle was now held at the upper part of the
tube where it entered the globe, and where the diame-
ter of the tube had previously been contracted, and
the flame was directed, by means of a blow-pipe, against
that part of the tube which it was desired to melt
together.

As the glass was softened by the heat, the pressure
of the outside air immediately forced the walls of the
tube together ; the whole operation was successful.

The barometer tube was then detached, and the bulb
of the thermometer was now surrounded on all sides by
a vacuum, as may be seen from the figure on the oppo-
site page.* The thermometer was filled with mercury,

* See also Vol. I., Plate to p. 404, Fig. i.

on the Subject of Heat.

'95

and provided with a scale, and I could then scarcely
master my impatience and wait for the. time when I
should satisfy myself whether heat would be able to
pass through this vacuum.

I now put the apparatus into a vessel filled with
water at 18° Reaumur, and left it there until I was sure
(from the scale of the instrument) that the bulb filled
with mercury, which was in the centre of the vacuum,
had reached this temperature of 18 degrees. I then
took the instrument out of this vessel, and held it for
some minutes in another full of hot water, which was
kept constantly boiling by a lamp placed under it.

Since the mercury in the tube of the thermometer
began to rise, although slowly, there remained no longer
any doubt that the heat of the boiling water really passed
through the vacuum into the bulb of the thermometer.

196 Historical Review of Experiments

The mercury in the thermometer rose in the follow-
ing manner : After the instrument had remained in the
boiling water i min. 30 sec. the mercury had risen from
1 8° to 27°. After the lapse of 4 minutes, it had risen
to 44T9o°:> and at the end of 5 minutes to 48 J°.

In order to estimate more accurately the relative
rapidity with which heat passed through a vacuum and
through air, I broke off the end of the small pointed
tube which projected from the under side of the globe
so that the air could freely enter the globe ; I then
melted the tube together a second time, by means of a
candle ; cooled my apparatus in water, and plunged it,
as soon as it had acquired the temperature of this water,
that is 1 8°, again into boiling water. The mercury rose
much more rapidly than in the preceding experiment.

The manner in which the temperature gradually in-
creased in both experiments is shown in the following
table.

When the spherical reservoir of the mercurial ther-
mometer, which was fastened in the centre of a glass
globe an inch and a half in diameter, was plunged into
boiling water, the times of ascent were as follows : —

In a Torricellian vacuum. Surrounded by air.

(Exp. No. i.) (Exp. No. 2.)

Time Heat Time Heat

elapsed. acquired. elapsed. acquired.

Upon being plunged into ~> fi0 Q0

boiling water }

m. s. o m. s. o

After remaining in it I 30 27 o 45 27

4 o 44-fr 2 10 44^

5 6 48J- 50 6oT%

From the results of these experiments it is evident
that the heat increases nearly twice as fast when the bulb
is surrounded by air as when it is in a vacuum.

I afterwards performed other experiments of the same

on the Subject of Heat. 197

kind without discovering the least difference from those
mentioned above. It would take too much time and
space to describe them all here. They are to be found,
however, in my memoir in the Philosophical Transac-
tions and in my eighth Essay.

I had subsequently several instruments of the same
sort made, in order to repeat and vary my experiments.
Sometimes I observed the time which they took in cool-
ing, sometimes that necessary for the heat to penetrate
them. Sometimes I performed the experiment in the
open air, sometimes in water. All these experiments
gave the same result, namely, that the thermometer
• bulb in a vacuum became warm or cold as the case
might be, the only difference being that it always took
nearly twice as long to effect this change of temperature
as was required when the bulb was surrounded by air.

The passage of heat through a vacuum was a fact of
such importance in the investigation of the nature of
heat, that I wished to confirm it by experiments which
would not allow a shadow of doubt.

That part of the thermometer tube which was in-
serted in the glass globe was in contact with this globe.
Hence the thought might suggest itself that a part of
the heat received or given out by the thermometer bulb,
which was surrounded by the vacuum, was. communi-
cated by means of the tube of the thermometer, since
a portion of this tube was surrounded by air or water in
which the heating or cooling was effected. In order to
be fully satisfied as far as this circumstance was con-
cerned, it occurred to me to repeat the experiment with
a thermometer suspended by a very fine silken thread
in the middle of a glass body of such size that the
thermometer with its tube was entirely contained in it.

1 98 Historical Review of Experiments

This glass body was then voided of air by means of
mercury.

The results of the experiments performed with these
instruments differed little or not at all from those made
with the apparatus previously described, therefore the
fact of the transmission of heat through the Torricellian
vacuum was established beyond any doubt.

These results are sufficiently known to the learned
world ; now the question arises as to how these results
can be reconciled with the theory which at the present
day has been adopted in regard to caloric. I must con-
fess freely, that, however much I might desire it, I never
could reconcile myself to it, because I cannot by any
means imagine how heat can be communicated in two
ways entirely different from each other.

Philosophers have made little or no mention of the
results of these investigations : I do not assume to ex-
plain their silence; if I myself mentioned them as little
as they, it is easy to imagine the cause of my silence.
It will at least be admitted that I have pointed out
plainly enough the doubts which the results of my ex-
periments could give rise to.

I afterwards undertook many other experiments to
determine accurately the various degrees of rapidity
with which heat passes into mercury when surrounded
by common or atmospheric air, by air saturated with
moisture, by carbonic acid gas, and by air brought to
various degrees of density.

In the year 1787 I made a series of experiments
which are described in the Philosophical Transactions
for 1792; my principal object was to investigate the
conducting power with regard to heat possessed by vari-
ous substances, especially by those which we are accus-

on the Subject of Heat. 1 99

tomed to use for clothing. The instrument which I
used in these experiments, and which I called a passage-
thermometery differs but slightly from that described
above. I fixed the bulb of a mercurial thermometer
half an inch in diameter within a glass globe an inch
and a half in diameter, with a long cylindrical neck ;
I then filled the space between the outer surface of the
thermometer bulb and the inner surface of the glass
globe with a certain quantity of the substance whose
conducting power was to be determined, and allowed
the instrument to cool in a mixture of pounded ice and
water. As soon as the thermometer showed me that
its bulb (which was in the middle of the glass globe)
had acquired and retained constantly the temperature
of the cooling mixture (that is, o° of Reaumur's scale),
I took the apparatus out of this cold mixture, plunged
it into boiling water, observed the times required for
the heat to pass into the bulb of the thermometer
through the surrounding substance, and inserted them
in a table, noting every ten degrees as accurately as
possible.

Since the water into which I plunged my appara-
tus was kept constantly boiling, it is evident that the
outside of the instrument, that is, the outer surface of
the globe, was always of the same temperature ; hence
the more or less rapid heating of the thermometer
bulb within the globe indicated the resistance which
the covering of the bulb offered to the passage of
the heat from the inner surface of the globe to the bulb
of the thermometer.

In this way I made several experiments; but as I
was inconvenienced by the steam rising from the boil-
ing water, and so experienced difficulty in noting the

2OO Historical Review of Experiments

rising and falling of the mercury, I changed my method
of operation, and no longer observed the time neces-
sary for the instrument to grow warm, but that neces-
sary for it to grow cold. .

When, therefore, my apparatus, plunged in boiling
water, had acquired such a temperature that the mercury
had reached 77° of Reaumur's scale, I took it out of
the boiling water and held it in the air, over the large
vessel filled with pounded ice and water, ready to plunge
it into this cooling mixture the very moment that the
mercury had fallen to 75°.

As soon as the mercury had reached this division of
the scale, I plunged my apparatus immediately into the
cooling mixture, and holding at the same time at my
ear a watch which beat half-seconds (which I carefully
counted), I waited for the moment when the mercury
had fallen to 70°. I then noted and recorded the time
elapsed, and in the same way observed the time when
the mercury had fallen to 60°, and thus proceeded,
noting every ten degrees, until the apparatus had cooled
to the temperature of 10°.

Sometimes the apparatus cooled to such an extent
that the mercury in the thermometer stood at o° ; this,
however, took up much time, and was attended with no
particular advantage, as the determination of the times
taken up in cooling from 70° to 10° was quite sufficient
for calculating the conducting power of every sort of
covering ; on this account I generally ended the experi-
ment when the mercury had just passed the 10° mark
on the scale.

During the time of cooling the apparatus in ice and
water, I moved it about in the mixture very slowly
and constantly from one place to another ; moreover, I

on the Subject of Heat.

201

always mixed the water with such a quantity of ice
that the temperature of this mixture remained con-
stant. •

Since in such experiments the thermometer bulb in
the middle of the glass globe was entirely surrounded
as well by the air contained in the globe as by the sub-
stances of which the covering consisted, I made a few
experiments to determine the time necessary for the
bulb of the thermometer to become cold again when the
globe contained nothing but air. I thus learned that
when the apparatus previously warmed in boiling water
was plunged into the mixture of cold water and pounded
ice, it required 576 seconds to cool from 70° to 10°
Reaumur.

The following table contains the results of several
experiments undertaken with a view to determine the
relative warmth of various substances such as are com-
monly used for clothing.

I only remark, in addition, that I always determined
the amount of the substance by weight (16 grains stand-
ard weight), and endeavoured to distribute it as equally
as possible in the globe, and in such a manner that the
bulb of the thermometer was surrounded by it.

Gradual Loss of
Heat.

Substances used for Covering.

Air.

Time

elapsed

38'
46

59
80

122
231

Raw

Silk.

Sheep's-
wool.

Cotton-
wool.

Fine
Lint.

Time
elapsed
80"

93
"5
15°
218
376

Beaver's
Fur.

Hare's
Fur.

Eider-
down.

From 70° to 60°
60 50

50 40
40 3°

30 20

20 10

Time
elapsed

94"

HO
133

185

273
489

Time
elapsed

79''
95
118
162
238
426

elapsed.
83"

95
117

152

221
378

Time
elapsed.
99"
116

153
1 8S
265
478

Time
elapsed.

97"
117
144

193

270

494

Time
elapsed.

98"
116
146
192

268
485

From 70° to 10°

576

1284

Jii8

1046

1032 1296

'3'5

' .V-5

202 Historical Review of Experiments

In order to determine what influence the density of
a covering or clothing of a given thickness exerted on
the warmth of this covering or on its power to confine
heat, I made three consecutive experiments with differ-
ent quantities of one and the same substance, namely,
with eider-down. For the first experiment I took 16
grains of this substance, for the second 32 grains, and
for the third 64 grains. In all cases I used the same
apparatus, so that the thickness of the covering always
remained the same.

The results of these three experiments are contained
in the following table.

The covering of
qua

Eider-down consisted of the following
itities of the substance.

Loss of Heat.

16 grains.

32 grains.

64 grains.

Time elapsed

Time elapsed.

Time elapsed.

From 70° to 60°

97"

Ill"

112"

60 50

117

128

130

50 40

MS

157

I65

40 30

192

207

224

30 20

267

304

326

20 • IO

486

565

658

From 70° to 10°

i304

1472

1615

Having convinced myself by these experiments that
the density of any covering or clothing exercises a very
considerable influence on its power to confine heat,
its thickness remaining the same, I now sought to dis-
cover what effect the internal structure or constitution
of the covering has on this power, its mean density and
its thickness remaining the same.

By the expression internal structure I mean the state
of division, whether fine or coarse, of the substance of
which the covering consists, in the space which it occu-
pies. This substance may be very fine and of delicate

on the Subject of Heat. 203

texture, and may be equally distributed through the
whole space occupied by it, — as raw silk, for example;
or it may be coarser and have larger interstices, — as,
for example, a covering consisting of bits of stout
sewing-thread, or one consisting of ravellings of cloth.

If heat really passed through the substances of which
the covering is made, and if the efficiency of such a
covering in restraining the same depended solely on the
greater or less difficulty which the heat meets in passing
through the solid parts of the covering, in that case
the warmth of a covering would be, c<eteris paribus, the
same as that of the raw materials employed in its con-
struction. It is evident, however, from the foregoing
experiments, as well as from those to be detailed here-
after, that heat is not propagated in any such manner.

In one of my previous experiments I had endeav-
oured to determine the warmth of 16 grains of raw
silk, which I had distributed equally in a certain space
about the bulb of a thermometer. I now repeated this
experiment twice, but with this difference : the first
time I surrounded the bulb of the thermometer with
1 6 grains of a sort of lint made from a piece of
white taffety ; the second time with 16 grains of white
sewing-silk, cut into small pieces, two inches long. The
results of these experiments are recorded in the fol-
lowing table. My apparatus was warmed in boiling
water, and then cooled in a mixture of water and
pounded ice.

204

Historical Review of Experiments

Substances of which the Covering consisted.

Loss of Heat.

Raw Silk,

Ravellings of Taf-

Silk Threads,

16 grains.

fety, 16 grains.

16 grains.

Time elapsed.

Ti me elapsed.

Time elapsed.

From 70° to 60°

94"

90"

67"

60 50

no

106

79

50 40

133

128

99

40 30

185

172

135

30 20

273

246

195

20 10

489

427

342

From 70° to 10°

1284

1169

917

Having convinced myself by these experiments that
the fineness of the particles or fibres of the substance
used as a covering contributes very much to the warmth
of the same, I made the following experiments to
determine what effect the condensing of the covering
would have, the quantity of matter of which it was com-
posed remaining the same, but the thickness being
decreased.

As I had already, by means of the foregoing experi-
ments, determined the warmth of coverings of raw
silk, wool, cotton, and linen when taking 16 grains
of each substance, and making thereof, about the bulb
of a thermometer, a globular covering half an inch
thick, I now took 16 grains of moderately coarse
threads of each of these four substances, and with them
I made four new experiments.

Instead of filling with these threads the entire space
between the bulb of the thermometer and the inner
surface of the globe, in the middle of which was the
bulb, I wound it around the bulb of the thermom-
eter, so that the latter looked exactly like a little
ball.

I now introduced, as before, the thermometer bulb

on the Subject of Heat.

205

thus enveloped, into the middle of a glass globe an inch
and a half in diameter ; to this globe was attached a neck
ten inches long, and of such a width as to allow of the
insertion of the bulb of the thermometer wrapped up
as described above, together wich the attached scale.

The results of these four experiments may be seen
in the following table; and that they may the more
easily be compared with those made with the same
quantity of the substances, but differently disposed, I
have placed side by side the results of the comparative
experiments.

The Bulb of the Thermometer was covered with 16 grains

oi one of the following substances.

Loss of Heat.

Silk.

Wool

Cotton.

Linen.

Raw.

threads.

Raw.

threads.

Raw.

In

threads.

Raw.

threads.

From 70° to 60°

94"

46"

79"

46"

83"

45"

80"

46"

60 50

no

62

95

63

95

60

93

62

50 40

133

»5

118

89

117

83

"5

83

40 30

185

121

162

126

152

"5

150

H7

30 20

273

I9I

238

20O

221

179

218

180

20 IO

489

399

426

4IO

378

370

376

385

From 70° to 10°

1284

904

mS

934

1046

852

1032

873

It would carry me too far if I brought forward
in detail all the experimental results obtained in my
researches undertaken to investigate the manner in
which heat propagates itself through the various cov-
erings. In my printed memoirs I have said all upon
this subject that can with reason be said. For the
present I have indicated clearly, not only the course
upon which I entered at the very beginning of my re-
searches, but also the object I had in view. Philos-
ophers may decide whether this course was the right

206 Historical Review of Experiments

one, and whether I pursued it with zeal and persever-
ance.

The few remarks and observations which follow were
occasioned by my researches made at that time.*

All the different substances which I had yet made use
of for covering the bulb of the thermometer (which
was contained within a glass globe an inch and a half
in diameter) had in a greater or less degree confined
the heat and prevented it from passing into or out
of the bulb of the thermometer as rapidly as it would
otherwise have done. Here then arose the important,
and as yet unanswered question, how and by what
mechanical operation had the coverings in question pro-
duced these effects ?

This much is certain, that the slowness of the cooling
of the bulb of the thermometer cannot by any possibil-
ity be a result of the non-conducting powers of those
substances of which the coverings consisted, consid-
ered simply as having hindered the passage of the heat,
for if, instead of regarding them merely as bad conduc-
tors of heat, we were to suppose them to have been
totally impervious to heat, still their volumes — that
is, the sum of all their solid parts or fibres — would
be so inconsiderable in proportion to the space they
occupied, that they would either have produced no
effect on the air filling their interstices, or this air would
have been sufficient of and for itself to have conducted
all the heat communicated in less time than was actually
taken up in the experiments. Here is the proof of this
statement.

The diameter of the glass globe being 1.6 inches, its
contents amounted to 2.14466 cubic inches. The di-

* See my eighth Essay, Vol. I. p. 455.

on the Subject of Heat. 207

ameter of the thermometer bulb was 0.55 of an inch,
and its contents 0.08711 of a cubic inch. Taking now
from the contents of the globe (2.14466 cubic inches)
the contents of the thermometer bulb (0.0871 1 of a cubic
inch), there remain 2.05755 cubic inches as the measure
of the space occupied by the substances by which the
bulb of the thermometer was surrounded.

Although the above-mentioned substances occupied
this space, they were very far from filling it, as will be
observed without my calling attention to the fact ; on
the contrary, this space contained a large quantity of
air, which occupied and filled the small interstices of
the substances in question.

For example, in one of the experiments the bulb was
covered with 16 grains of raw silk. As I had already
learned from experiment that the specific gravity of the
silk was to that of water as 1734 to 1000, it follows that
the volume of 16 grains of silk was equal to the volume
of 9.4422 grains of water. Further, as I cubic inch of
water weighs 253.185 grains, it follows incontrovertibly
that the space occupied by 9.4422 grains of water can be
reckoned at the highest at 0.037294 of a cubic inch, and
this amount of water (9.4422 grains) corresponds in
volume to 1 6 grains of silk.

We know, however, that the space which this small
quantity of silk (0.037294 of a cubic inch) occupies is
2.05755 cubic inches; hence it appears that, since
0.037294 is to 2.05755 as i is to 54, the silk which I
used in the experiment in question could not fill more
than -5^ of the space in which it was confined.

The longer we meditate upon these investigations,
the more we are struck by the importance of the
results that follow from them. I have never been

208 Historical Review of Experiments

able to explain them without rejecting altogether that
hypothesis according to which it is supposed that the
heat which may be in the air is communicated directly
from one particle of this fluid to another.

My researches on the propagation of heat in liquids
are sufficiently well known.* From them it has prob-
ably been seen how and in what manner I was com-
pelled by the results of my numerous experiments to
adopt the opinion with regard to this subject which I
have developed in my various writings.

I have examined with the greatest care the objections
which have been offered to the deductions which I have
drawn from my experiments, and I can assert with
truth — and to say this is a duty I owe to myself —
that neither in these objections nor in the result of any
new experiment, as far as my knowledge extends, has
the least thing occurred which could serve as a reason
for altering my opinion in regard to this subject. In
a paper which I sent last year to the Royal Society
at London,-]- I think that I have proved that water is
really a non-conductor of heat, as I suspected six years
ago.

I have now only a few words to say in addition,
about the various experiments which I made at different
times, to enable me (if it were in any way possible) to
answer decisively that important and much contested
question as to the materiality of heat, about which
philosophers have striven for so long a time.

Those who regard heat as a substance must, of
necessity, assume that it possesses weight. If now the

* A detailed description of my investigations in regard to this interesting subject is
contained in my seventh Essay, which appeared in London in the year 1797, in two
parts, together 188 octavo pages. See also Vol. I. p. 239.

f See p. 274.

on the Subject of Heat. 209

heating of a body is caused by the accumulation of this
substance in the body, it follows naturally that the
body must be heavier when it is warm than when it is
cold. Some natural philosophers have sought to deter-
mine this point ; I feel confident, however, that no one
has made more decisive experiments in this direction
than myself.*

I was provided with excellent instruments, and spared
neither trouble nor expense to arrive, by means of my
experiments, at a certain and convincing result. The
results obtained are, in few words, as follows.

I had a ball of very fine gold made, and weighed it
when perfectly cold, and again after heating it to such a
temperature that it was on the point of melting. Fur-
ther, I weighed a considerable amount of water, which I
had sealed hermetically in a flask, first in its liquid
state, then at the temperature of melting ice, then as
actual ice, and then again at its original temperature.
All these experiments convinced me that the weight
of a body is not changed in the least by heat.

Now although, as a consequence of the results of
these experiments, I was only still more strengthened in
those doubts which a number of other natural phenom-
ena had raised in my mind with regard to the existence
of caloric, still I saw at the same time only too well
that the essential point of the controversy was far from
being decided thereby. The defenders of caloric would
still object (as they have actually done) that this sub-
stance is far too subtile to be weighed upon our ordi-
nary balances.

* A paper in which are described in detail all my experiments upon this sub-
ject may be found in the Philosophical Transactions for 1799. See also page 1 ot this
volume.

VOL. II. 14

2io Historical Review of Experiments

After I had long meditated upon a way of putting
this interesting problem entirely out of doubt by a
perfectly conclusive experiment, I thought finally that
I had discovered it, and I think so still.

I argued that if the existence of caloric was a fact, it
must be absolutely impossible for a body or for several
individual bodies, which together made one whole, to
communicate this substance continuously to various
other bodies by which they were surrounded, without
this substance gradually being entirely exhausted.

A sponge filled with water, and hung by a thread in
the middle of a room filled with dry air, communicates
its moisture to the air, it is true, but soon the water
evaporates and the sponge can no longer give out moist-
ure. On the contrary, a bell sounds without inter-
ruption when it is struck, and gives out its sound as
often as we please without the slightest perceptible loss.
Moisture is a substance ; sound is not.

It is well known that two hard bodies, if rubbed to-
gether, produce much heat. Can they continue to pro-
duce it without finally becoming exhausted ? Let the
result of experiment decide this question.

It would be too tedious to describe here in detail
all the experiments which I undertook with a view
of answering in a decisive manner this important and
disputed question. They may be found in my memoir
On the Source of Heat excited by Friction. I have
had it printed in the Philosophical Transactions for
the year 1798 ; still these experiments bear too close a
relation to my later researches on heat for me to omit
attempting at least to give the reader a clear idea of the
experiments and of their results.

The apparatus which I used in these investigations

on the Subject of Heat. 211

is too complicated to be represented in this place ; *
still it will not be difficult for the reader, with the
help of the accompanying figure (see Plate V.), to
form a conception of the principal experiments and
their results.

Let A be the vertical section of a brass rod which is
an inch in diameter and is fastened in an upright posi-
tion on a stout block, B ; it is provided at its upper
end with a massive hemisphere of the same metal, three
and a half inches in diameter. C is a similar rod, like-
wise vertical, to the lower end of which is fastened a
similar hemisphere. Both hemispheres must fit each
other in such a way that both the rods stand in a per-
fectly straight vertical line.

D is the vertical section of a globular metallic vessel
twelve inches in diameter, which is provided with a
cylindrical neck three inches long and three and three-
quarters inches in diameter. The rod A goes through
a hole in the bottom of the vessel, is soldered into the
vessel, and serves as a support to keep it in its proper
position.

The centre of the ball, made up of the two hemi-
spheres which lie the one upon the other, is in the
centre of the globular vessel, so that, if the vessel is filled
with water, the water covers the ball as well as a part
of each of the brass rods.

If now the hemispheres be pressed strongly together,
and at the same time the rod C be turned, by some
means or other, about its axis, a very considerable
quantity of heat is generated by means of the friction
which takes place between the flat surfaces of the two
hemispheres.

* See Vol. I., Plate to p. 493.

2 1 2 Historical Review of Experiments

The quantity of the heat excited in this manner is
exactly proportional to the force with which the two
surfaces are pressed together, and to the rapidity of the
friction. When this force was equal to the pressure of
ten thousand pounds, and when the rod was turned
with such rapidity about its axis that it revolved thirty-
two times a minute, the quantity of heat generated by
the continual rubbing of the two surfaces together was
extraordinarily great. It was equal to the quantity given
off by the flame of nine wax-candles of moderate size
all burning together.

The quantity of heat generated in this manner dur-
ing a given time is manifestly the same, whether the
globular vessel D is filled with water, and the surfaces
of the two hemispheres rub on each other in this liquid,
or whether there is no water in the vessel, and the ap-
paratus by which the friction is produced is simply sur-
rounded by air.

The source of the heat which is generated by this
apparatus is inexhaustible. As long as the rod C is
turned about its axis, so long will heat be produced by
the apparatus, and always to the same amount.

If the globe-shaped vessel D is filled with water, this
water becomes hotter and hotter, and finally begins to
boil. I have myself in this way boiled a considerable
quantity of water.

If this experiment is performed in winter when the
temperature of the air is but little above the freezing-
point, and if the vessel D is filled with a mixture of
water and pounded ice, the quantity of heat caused
in a given time by the rubbing together of the two sur-
faces can be expressed very exactly by the amount of
ice melted by this heat.

on the Subject of Heat. 213

Since the apparatus affords heat continuously, and
always to the same amount, we can melt in this way as
much ice as we please.

But whence comes this heat ? This is the contested
point, to determine which was the real aim of the ex-
periment.

It is certain that it comes neither from the decom-
position cf the water nor from the decomposition of the
air Various experiments on this point, which I have
described at length in my memoir in the Philosophical
Transactions, are more than sufficient to establish this
fact beyond doubt.

Just as little does it come from a change in the ca-
pacity for heat brought about by friction in the metal
of which the hemispheres are composed. This is shown,
first, by the continuance and uniformity of the pro-
duction of the heat ; and, secondly, by an experiment
bearing directly on this point, by which I am con-
vinced that not the slightest change had taken place in
the capacity of the metal for heat.

Just as little does it come from the rods which
are attached to the hemispheres, for these rods were
always warm, the hemispheres communicating heat to
them.

Much less could this heat come from the air or the
water immediately surrounding the hemispheres, for the
apparatus communicated heat to both these fluids with-
out cessation.

Whence, then, came this heat? and what is heat
actually?

I must confess that it has always been impossible for
me to explain the results of such experiments except by
taking refuge in the very old doctrine which rests on

214 Historical Review of Experiments

the supposition that heat is nothing but a vibratory
motion taking place among the particles of bodies.

A bell, on being struck, immediately gives forth a
sound, and the oscillations of the air produced by these
vibrations forthwith cause a quivering motion in those
bodies with which they come in contact. On the other
hand, a sponge filled with water cannot give ofF its
moisture to the bodies in its vicinity for any length of
time without itself losing moisture.

A very illustrious philosopher, for whom I have al-
ways entertained the greatest respect, and whom, more-
over, I have the good fortune to count among my most
intimate friends, M. Bertholet, has, in his admirable
Essai de Statique Chimique, attempted to explain the re-
sults of this investigation, and to reconcile them with
that theory of heat which is founded upon the hypothe-
sis of caloric.

If a man as learned, as honest, as worthy, and as re-
nowned as is M. Bertholet, spares no pains in opposing
the errors of a natural philosopher or chemist, one can-
not and dare not keep silence unless, he wishes to ac-
knowledge himself vanquished. If, however, one can
produce proofs — a fortunate thing for all those who
find themselves driven to similar self-vindication — that
the objections of M. Bertholet have no foundation, he
has done very much towards establishing beyond doubt
the opinions and facts in question.

I will now endeavour to answer the objections which
M. Bertholet has offered to my explanation of the
above-mentioned experiments ; and, that the reader
may be in a position to give to these objections their
just value, I will insert them here in the writer's own
words.

on the Subject of Heat. 2 1 5

"Count Rumford has made a curious experiment
with regard to the heat which may be excited by fric-
tion. He causes a blunt borer to revolve very rapidly
(this borer revolved about its axis only thirty-two times a
minute} in a brass cylinder weighing thirteen pounds,
English weight (the cylinder weighed one hundred and
thirteen pounds and somewhat more\ and says that he
observed that this borer in the course of two (one ana
a half) hours, and under a pressure equal to 100
cwt., reduced to powder 4145 grains (8J ounces Troy)
of brass, and that an amount of heat was generated
during this operation sufficient to bring to boil 26.38
pounds of water, previously cooled to the freezing-
point. He asserts that he did not discover the slight-
est difference between the specific heat of the metallic
dust and that of the brass which had not experienced
the friction. Hence he supposes that the heat was
excited by the pressure alone, and was not at all due to
caloric, as is the opinion of most chemists.

" I will for the present satisfy myself with simply
inquiring whether it necessarily follows from this ex-
periment that we must renounce entirely the received
theory of caloric, according to which it is regarded as
a substance which enters into combination with bodies,
or whether this result cannot be explained in a satis-
factory manner by applying to the case in question
those laws of nature in accordance with which the opera-
tions of heat are manifested under other conditions.

"If the evolution of heat be regarded as a conse-
quence of the decrease of volume caused by the pressure,
then not only the metallic powder but also all the rest
of the brass cylinder must have contributed, though not
in an equal manner, to this evolution, by the powerful

2 1 6 Historical Review of Experiments

expansive effort of that portion which experienced the
greatest pressure, and consequently acquired the greatest
temperature, without being able to assume the dimen-
sions proper to this same temperature on account of
the less heated and less expanded parts ; consequently
there must have arisen, necessarily, a certain condensa-
tion of the metal in respect of its natural dimensions,
which condensation gradually decreased from the point
where the pressure was greatest to the surface. We may
suppose that this operation took place in a similar man-
ner in all parts of the cylinder.

"As a consequence of this decrease of volume, an
amount of caloric was given out equal to that which
would have caused a similar increase of volume, on the
supposition, that is, that the specific heat of the metal
does not change through this range of the scale of the
thermometer, and that the expansions are equal ; and
this, considering the range of temperatures and the
consequent expansions, is probably not far from the
truth. The entire amount of heat disengaged would
have, raised the cylinder to about 1 80° of Reaumur's
scale; and if the expansion of brass by heat is equal
to that of iron, which has been found to be y^o"o f°r
each degree of the thermometer, the 180 degrees would
have caused an expansion of y-^f -5- in each direction, and
the decrease of volume must have brought about the
same degree of heat if we suppose that the pressure
stood in equal relation to this expansion.

" Now there is a change, and sometimes a very consid-
erable one, wrought in the specific gravity of a metal,
by percussion, by the action of a fly-wheel, or by the
compression of a wire-drawing machine. It appears,
for example, that the specific gravity of platina and of

on the Subject of Heat. 2 1 7

iron, on being forged, is thus increased by a twentieth
part.

" Hence it appears that the experiment of Count
Rumford is far from explaining satisfactorily a property
which is well known, and called in question by no
one.

" It is easy, it is true, to arrange side by side in
an imposing manner the phenomena of heat ; if, how-
ever, you were to say to one who has little or no
knowledge of chemical speculations, * Count Rumford's
cylinder has, in the course of two hours, by means of
a violent friction, afforded all the heat required to dis-
solve in water, without changing its temperature, 15
kilogrammes of ice, or as much as 2 hectogrammes (6|
ounces) of oxygen would require [sic] in its combina-
tion with phosphorus,' I do not know at which of
these phenomena he would be most astonished.

" The slight changes which can take place in the
amount of combined caloric have so inconsiderable an
influence on the capacity for work of the caloric within
the narrow limits of the thermometric scale, that it
cannot be computed. Moreover, we have not, as
yet, adequate data for determining the nature of the
changes in this respect which take place in a solid body
in consequence of the particular condition of condensa-
tion into which it has been brought by means of a cer-
tain mechanical force, and by degrees of heat differing
greatly from each other.

" Besides, Rumford, in the experiment to determine
the specific heat of the filings of bell-metal thus ob-
tained, heated them to the temperature of boiling
water. But this extremely elastic metal would very
naturally as soon as left to itself, and especially dur-

2 1 8 Historical Review of Experiments

ing the operation just mentioned, resume that state of
expansion and that capacity for heat which is proper
to it at a given temperature, so that the effect of the
pressure to which it has been subjected partly disap-
pears again, just as a piece of metal which has been
hammered resumes its natural properties on being an-
nealed."

In reply to these remarks, I will call to mind what
follows.

ist. The discovery which I made, that no consid-
erable change had taken place in the specific heat of
the metallic dust produced by the friction, led me in
no way to the supposition that the heat excited in the
experiment could not come from the caloric set free.
I only found that the source of this heat was inex-
haustible. To explain this phenomenon, which has
never yet been explained, is the point now in ques-
tion, and I do not see how it can be explained except
by giving up altogether the hypothesis adopted in re-
gard to caloric.

id. If we actually suppose (and it is far from having
been proved) that the simple pressing together of a
metal is sufficient to expel the caloric contained in it,
still the explanation of such a natural phenomenon
would be advanced little or none; for since the action
of the force which causes the pressure is continuous, the
condensation of the metal brought about by this force
would in a short time reach its maximum ; and if
really in this operation ever so much caloric had been
disengaged from the metal, still it would very soon
disperse. The rubbing surfaces, on the contrary, con-
tinue to give forth heat, and that always to the same
amount.

on the Subject of Heat. 2 1 9

3d. In regard to the objection made to the experi-
ment which was undertaken with a view of determin-
ing whether a change had taken place in the capacity
of the metallic dust for heat, this can very readily be
answered, and in such a way that nothing, it seems to
me, can be said against it. If the temperature of boil-
ing water were really sufficient to give to these small,
forcibly condensed particles of metal the quantity of
heat necessary to bring them back to their original con-
dition as far as their capacity for heat is concerned, then,
as the water by which the apparatus was surrounded
finally began to boil, they must, without doubt, have
taken the necessary amount of heat from this water. If,
now, these particles of metal received finally from the
water the caloric which in the beginning they imparted
to it, the question arises, whence came the caloric which
served to heat, not only the water, but also the metal
and the objects immediately surrounding it ?

I am far from desiring to deceive any one by an im-
posing arrangement of facts ; but the facts in my ex-
periments were so very striking that it was altogether
impossible for me to help instituting comparisons and
making calculations with regard to them which would
make them clear, especially to those not yet sufficiently
acquainted with such investigations.

I will now close my remarks with an entirely new
computation. I will show whether it is probable
that the metal could supply all the heat which was pro-
duced by friction in the experiment in question. If
we are to make this supposition, we must, in the first
place, allow that all the heat came directly from the
particles of metal which were separated from the solid
mass of metal by the friction ; for, since the mass re-

220 Historical Review of Experiments

mained in the same condition throughout the entire
experiment, it is evident that it could contribute in no
measure to the effect produced.

We will now inquire how much heat would have been
developed if the experiment had been carried on without
cessation, until the whole mass of metal had been re-
duced to powder by the friction.

After the experiment had lasted an hour and a half,
there were 4145 grains (Troy) of the metallic dust, and
during that time an amount of heat was produced by
the friction sufficient to raise 26.58 pounds of ice-cold
water to the boiling-point.

Since the mass of metal weighed 113.13 pounds, or
791,910 grains, all this metal would have been reduced to
powder if the experiment had lasted uninterruptedly, day
and night, for 477^ hours, or for 19 days 21^ hours,
and during this time an amount of heat would have
been produced sufficient to have raised 5078 pounds
of water to the boiling-point.

Since the metal used in this experiment showed a
capacity for heat which was to that of water as o.n to
i, it is evident that this amount of heat would have
been sufficient to raise a mass of the same metal 46,165
pounds in weight through 180 degrees of Fahrenheit's
scale, or from the temperature of melting ice to that of
boiling water.

This amount of heat would be sufficient to melt a
mass of metal sixteen times heavier than that which I
used in the experiment.*

* Brass melts at a temperature of 3807° Fahrenheit; copper at 4587°; bell-
metal melts more easily than copper ; if, however, we suppose that it requires the
same heat for fusion, we find by a very simple calculation, that the amount of heat
necessary to raise the temperature of 46,165 pounds bell-metal through 180 degrees
would 'be sufficient to raise the temperature of i8n£ pounds through 4587

on the Subject of Heat. 221

Is it at all conceivable that such an enormous quan-
tity of caloric could really be present in this body ? But
even this supposition would be by no means sufficient
for the explanation of the fact in question, as I have
shown by a decisive experiment that the capacity of the
metal for heat has not sensibly altered.

Whence, then, came the caloric which the apparatus
furnished in such abundance ?

I leave this question to be answered by those persons
who believe in the actual existence of caloric.

In my opinion, I have made it sufficiently evident
that it was impossible for it to come from the metallic
bodies which were rubbed together, and I am absolutely
unable to imagine how it can have come from any other
object in the neighbourhood of the apparatus, for all
these objects received their heat constantly from the
apparatus itself.

I will now proceed to give an account of my further
investigations on the subject of Heat.

In the summer of the year 1800, I visited Scotland,
and on this occasion spent some months in Edinburgh.

It is well known that the University at that place
stands in high repute on account of the eminent scholars
occupying chairs there for more than fifty years in un-
interrupted succession.

One day I found myself in the company of Professor
Hope (the successor of the celebrated Black), Professors
Playfair and Stewart, and several other persons. We
repeated the experiment which Pictet undertook with
a view to determine the condensation and contraction

degrees, or to bring this number of pounds to the melting-point. From this calculation
it appears that a quantity of bell-metal, the temperature of which is at the melting-
point of ice, on being reduced by friction to the state of powder, gives out sixteen
times as much heat as would be necessary to melt it.

222 Historical Review of Experiments

of air by the cooling influence of cold bodies. It now
happened that for the first time my opinion on the
subject of heat was publicly announced.

Two metallic mirrors fifteen inches in diameter, with
a focal distance of fifteen inches, were placed opposite
each other, sixteen feet apart. When a cold body (for
example, a glass bulb filled with water and pounded
ice) as was the case on this occasion, was placed in the
focus of one of the mirrors, and a very sensitive air-
thermometer was placed in the focus of the other mir-
ror, the latter thermometer began immediately to fall.
If, instead of being placed directly in the focus, the
thermometer was removed a short distance from it to
one side, the cooling power which in the former case the
cold body had exerted upon it was no longer perceptible.

The matter was, however, not allowed to rest with
merely repeating the experiment of Pictet just as he
describes it, but I was allowed, in addition, to make
various changes, that I might lay aside every doubt, and
elucidate in the most convincing manner the fact in
question.

I expressed my opinion on the results of these ex-
periments in the following words : —

<c It is not possible that caloric has an actual exist-
ence. The communication of heat and the communi-
cation of sound seem to be completely analogous. The
cold body in one focus compels the warm body (the
thermometer) in the other focus to change its note?

It is owing to a peculiar circumstance, the further
discussion of which would be neither appropriate nor
useful in this place, that I here introduce word for word
the expression which I used on this occasion.

A considerable time before, I had already projected

on the Subject of Heat. 223

a series of experiments on the subject of radiant heat,
and in my sixth Essay, which treats Of the Manage-
ment of Fire and the Economy of Fuel, published at
London in I797> I had openly announced my purpose
of taking the work in hand as soon as possible.

The experiments I have just mentioned as being
performed in my presence by Professor Hope deter-
mined me not to put off this intention of mine a
moment longer.

As soon as I returned to London, I began imme-
diately to make all preparations for my researches. I
therefore communicated my intentions to Sir Joseph
Banks, at that time President of the Royal Society,
also to Mr. Cavendish, because both these gentlemen
(as well as myself) were managers of the Royal In-
stitution. As I wished to carry out my experiments
in the most decisive manner, and consequently with
the apparatus as perfect as possible, — which to all
appearance would require a considerable outlay, — I
was, at my request, authorized by the managers of
the Royal Institution to procure the new instruments
needed at the expense of the Institution, with the con-
dition, however, that these instruments should remain
at the Institution as its property, and be kept in its
cabinet.

As the principal object in this investigation was to
establish beyond doubt the cooling emanations from
cold bodies, I desired to accumulate the emanations and
concentrate them as much as possible, in order that
their action might be so much the more sensible.

Pictet took for his experiment, as is well known, two
metallic reflectors, and placed a cold body in the focus
of one of them, and a thermometer in the focus of

224 Historical Review of Experiments

the other. That the cooling influence which the cold
object exerted on the thermometer might be doubled,
I proposed in my experiment to have two cold bodies
and one reflector, and, in order to increase so much the
more the cooling effect on the thermometer, I intended
to place it in the upper part of an open cylindrical
vessel, the two cold bodies, however, being placed some-
what lower.

In Pictet's experiments both reflectors were in a hori-
zontal line, and the thermometer on which the cooling
influences were exerted was continually heated by the
vertical current from the air above, which was caused
necessarily by the cooling of the stratum of air immedi-
ately surrounding the thermometer; as a consequence,
the frigorific influence of the cold body was lessened by
the calorific influence of this current to such an ex-
tent that an equilibrium resulted. Still I expected that
in my case I should, in all probability, be able to carry
the cooling of the thermometer still farther, as I hoped
by the arrangement of my apparatus to prevent this
current, and at the same time to double the cooling
effect.

After long delay on the part of the workmen, the
necessary mirrors, four in number, were finally com-
pleted. They are now in the physical cabinet of the
Royal Institution at London, and are used in the an-
nual lectures on physics. If I am not mistaken, there
are several other instruments kept in the same place,
which I had expected to use in the projected experi-
ments on the radiation of bodies ; but most of the in-
struments designed for this investigation (made by Mr.
Fraser, New Bond Street) were made at my own ex-
pense and are still in my possession.

on the Subject of Heat. 225

It is only necessary to see this apparatus, which I
had made in the summer of 1801, to be immediately
convinced that I pursued my researches on the subject
of heat zealously and connectedly.

In the beginning of the year 1802 I was recalled to
Bavaria. I was, therefore, obliged to leave London in
the early part of the month of May, after I had actually
begun on a very few only of the experiments which
I had planned with so much pains. But as I was
firmly resolved to devote myself to them again, as soon
as I could obtain any leisure, however little, I took
back to Germany with me the greater part of this ap-
paratus which I had procured during my stay in Eng-
land.

During my journey, I remained three months at
Paris, so that I did not reach Munich before the end
of August. In the early part of the month of October,
however, I began my experiments.

As I had not been able to bring with me from Lon-
don the four large reflectors belonging to the Royal
Institution, and as I could not procure similar ones
in Bavaria, I was obliged to change the plan of my
investigations, and to try whether it might not be pos-
sible to discover the radiation from bodies in some
other way, and to make the effects of these radiations
manifest without the aid of the concentration brought
about by means of the metallic reflectors.

In the first experiments which I undertook, I had
this object in view, to determine whether the invisible
heating rays which a warm body (a heated stove, for
example) gives out are not of the same character as
those coming from the sun. For this purpose I pro-
cured three cylindrical boxes of very thin, soft wood,

VOL. ii. 15

226 Historical Review of Experiments

precisely alike, four and a half inches in diameter, three
inches high, and open above. In each of these boxes,
an inch and a quarter from the bottom, I put a cir-
cular metallic disk, a quarter of a line in thickness, and
of the same diameter as the inside of the box. This
disk, which formed a sort of optical screen in the in-
side of the box, was fastened in its place by a number
of very short wooden pegs, which went through the side
of the box.

In the middle of the bottom of the box was a circular
aperture, three quarters of an inch in diameter, closed
by a cork stopper.

In this stopper was a hole of three lines' diameter,
into which fitted a small mercurial thermometer pro-
vided with an oval reservoir. The divisions of the
scale were engraved upon the tube itself.* By means
of this stopper the thermometer was introduced into
the inside of the box in such a way that its bulb was
situated in the axis of the box, and in the middle of
the space between the bottom and the metallic disk.
This space, which was designed to serve as a reser-
voir of heat, was filled with a certain quantity of flat
silver threads, which had been picked out of old silver
lace.

In one box the metallic disk or reflector was brass;
in the second, tinned iron ; and in the third, ordinary
sheet-iron.

* I had four such thermometers made for me in England, and they did me good
service throughout the whole course of my experiments on the subject of heat. Their
tubes were made of very hard glass, three lines in diameter, and were polished down
on one side so as to present a flat surface, on which the divisions of the scale were
etched with fluoric acid. The tubes are six or seven inches long, and the bulbs for the
mercury are pear-shaped, and consequently not so liable to get broken as cylindrical
ones. In the pointed or lower part of the pear, the glass can be quite thick without
any disadvantage.

on the Subject of Heat.

227

The accompanying figure represents the vertical sec-
tion of one of these boxes in a horizontal position.
The stopper is also shown by diagonal lines, and a part
of the thermometer in its proper place.

In order to diminish the loss of heat which might
take place through the bottom and the sides of the box,
each one was covered inside and outside with well-sized
paper, then coated three times with copal varnish, and,
in addition to this, they were covered during the experi-
ment with an envelope of fur.

When one of the boxes was placed for a certain
length of time in the sun, so that its rays fell vertically
upon the metallic disk, there was a certain amount of
heat excited in the same ; and, as this heat was evenly
distributed within the box by means of the metallic
threads, it was possible to observe very exactly the vari-
ous degrees of heat by means of the thermometer ; if
all three boxes were placed at the same time in the sun,
it was possible to determine with certainty the relative
amounts of heat excited at the surface of the three differ-
ent metals used in the experiment.

228 Historical Review of Experiments

I was not at all surprised to find that the rays of the
sun excited more heat in a given time on the black and
unpolished iron disk than on the other two disks, which
were bright and polished ; I was, however, all the more
astonished by an entirely unexpected circumstance which
I noticed by chance during the cooling of the instru-
ments which had just been heated by the sun, a cir-
cumstance which arrested my attention.

After I had placed the three boxes close together, and
had exposed them to the influence of the sun's rays
until each had reached its maximum temperature, 1
took them away from the window at which they had
been standing at the time, and put them, bottom up-
wards, on a cold table in a corner of the room.

As I happened, about a quarter of an hour later, to
go past the table, I cast a single glance at the ther-
mometers, which now, in a vertical position, projected
from the reversed boxes. To my no slight astonish-
ment, I saw that the box which before contained the
most heat (the one which had the iron disk) was now
the coldest of all.

This phenomenon surprised me so much the more,
as I was convinced that this rapid cooling could not be
due to the fact that this box did not have sufficient
room to take up just as much heat as the others. For,
as I very well knew how much in these experiments
depended upon the boxes being precisely alike as regards
their contents, I had taken the greatest pains by similar
distribution of the silver threads to arrange them alike
before I began my experiments.

I cannot allow myself here to give in detail all the
conjectures and. projected experiments of which this dis-
covery was the cause. I will, therefore, say nothing

on the Subject of Heat. 229

further except that it made a firm and lasting impression
on my mind, and afterwards exerted much influence on
the manner in which I carried on my inquiries.

Meanwhile I did not allow this occurrence to hinder
me in the least from carrying out to the end the experi-
ments for which I had devised my apparatus. I had,
therefore, a cylindrical iron stove put into the middle
of a large room, and having surrounded it with fire-
screens, I caused all the windows in the room to be
opened. When the stove was sufficiently heated, I
found that no sensible change had taken place in the
mean temperature of the room. I now removed the
screens which surrounded the stove, and placed all three
of the boxes at the same time in the same position, that
is, twenty-four inches from the stove.

The box containing the iron disk, which previously
had contained the most heat after standing in the rays
of the sun, was also now the warmest after being sub-
jected to the influence of the rays which proceeded,
although invisibly, from the stove.

In order to become more closely acquainted with
these rays, I had several new instruments constructed ;
among others, four large air thermometers, and three
other thermometers of the same size filled with spirit
of wine. The bulbs of these thermometers were an
inch and three quarters in diameter, and contained either
various substances mixed with air or else simply spirit
of wine. The bulb of the first thermometer was filled
with air alone; in the second was a mixture of air and
eider-down ; in the third a mixture of air and very
thin flat silver threads ; the fourth contained air, eider-
down, and, at the same time, flat silver threads.

In the bulb of the first of the thermometers filled

230 Historical Review of Experiments

with spirit of wine, there was nothing besides this
fluid, in the second there was a mixture of spirit of
wine and eider-down, and in the bulb of the third ther-
mometer there was a mixture of spirit of wine and flat-
tened silver threads.

If, then, I exposed these thermometers in turn, now
to the influence of the rays of the sun, and again to the
influence of rays coming from bodies warmed by the
fire, I could, from the rapid or gradual heating of the
different thermometers, arrive at a sufficiently just con-
clusion with regard to the identity of the radiations or
to the difference between them.

It would be too tedious if I were to describe these
experiments here in detail. From some of them I
obtained many, in certain respects, very remarkable
results,* which allowed me to draw such conclusions as
pointed out clearly enough the way in which I must
proceed towards the chief object of my researches.

I afterwards procured other thermometers of very
large size. Their bulbs are round, and are made of
copper ; they are four inches in diameter. Their tubes,
which are glass, are thirty inches long, and are filled
with linseed oil. I use them in experiments designed
to determine the relative rapidity with which a warm
body (the thermometer itself) cools in different liquids
having the same temperature. This instrument is the

* I noticed, among other things, that the thermometer whose bulb contained a
mixture of spirit of wine and flat silver threads was much more sensitive in general,
and especially to very slight changes of temperature, than another thermometer of the
same size, the bulb of which contained only spirit of wine. It would, perhaps, be of
advantage to procure similar thermometers to use, if not ordinarily, at least on certain
occasions. I am firmly convinced that a thermometer whose bulb is filled with
mercury and platina cut into threads will be much more sensitive, that is, will indicate
the temperature much more quickly, than a thermometer of the same size filled, as is
usual, with mercury alone.

on the Subject of Heat. 231

only one that I could ever devise for such experiments
without fearing important objections on account of the
apparatus employed.

I possess, also, various other thermometers, intended
simply to receive and collect within themselves the calo-
rific or frigorific rays which fall upon their surfaces.
The reservoir of each consists of two cones of very thin
sheet brass, which lie one within the other, and are
fastened to each other, on the under side, in such a way
that there is an empty space, not quite a line in width,
between the inner surface of the outer cone and the
outer surface of the inner cone. The inner cone is four
inches in diameter, four inches high, and ends in a
point above. The diameter of the oufer cone is four
and a quarter inches, and it ends above in a cylindrical
tube three quarters of an inch in diameter and four
inches long. In this cylinder is fixed a glass ther-
mometer tube, and if the space between the two cones
be filled with linseed oil or coloured spirit of wine, this
instrument answers the same purpose as an ordinary
thermometer. The scale of this thermometer is fastened
firmly to this glass tube.

The outer wall of the instrument is shielded and
protected from the calorific or frigorific influences of
the surrounding air by means of a cylindrical box of
dry wood, thickly coated with varnish, and filled with
eider-down ; into this the body of the instrument fits.
This cover is four and a half inches high, and is, on the
inside, of the same diameter as the lower part of the
outer cone ; and the tube of the instrument, with its
attached scale, goes through a hole made in the bottom
of the box.

If, now, the outer blackened surface of the inner

232 Historical Review of Experiments

cone be held in the neighbourhood of and towards an
object which is giving off calorific (or frigorific) rays,
the heat (or cold) caused by these rays is communicated
to the fluid contained in the space between the two
cones, and this change of temperature brings about a
corresponding change in the level of the liquid in the
upper part of the tube ; by this means the amount of
heat (or cold) communicated can be estimated and
measured.

An instrument of this description, which I procured
in the year 1801, during my stay in England, is at
present in the physical cabinet of the Royal Institu-
tion at London. Two similar ones, fitted up in Bava-
ria, are still kept in my cabinet at Munich. I have
described this instrument thus minutely, simply because
I am convinced that it is of very great service in ex-
periments on the calorific and frigorific radiations from
various bodies, and because it has been my earnest de-
sire to induce natural philosophers to devote their atten-
tion to this subject, so worthy of investigation.

It only remains for me to say a few words in regard
to the experiments which I have described very fully
in the memoir read before the Royal Society on the
^d of February, 1804, which has been translated into
French by Professor Pictet.*

I performed these experiments in Munich, in 1803,
during the months of January, February, and March.
According as the results seemed of importance, I imme-
diately acquainted my friends in England and France
with -them. Among others, I communicated to Sir
Joseph Banks, then President of the Royal Society of
London, the very striking results of an experiment

* See page 23.

on the Subject of Heat. 233

which I made, on the nth of March, with two metal-
lic vessels, both of which — one being naked, and the
other having a covering of linen — I allowed to cool,
exposed to the air, after having first filled them with
warm water. In addition to this, I wrote him that
I had made several experiments with various vessels
blackened and covered with repeated coatings of varnish,
and I announced the results obtained. I also informed
him of the discovery which I made, with the help of my
tkermoscope, that different bodies of the same tempera-
ture give out very different quantities of calorific rays,
and that frigorific rays have just as real an existence as
the calorific rays from warm bodies.

Since Sir Joseph showed my letters to various per-
sons, and since I did not keep my experiments or their
results a secret from him or from any one else, my dis-
covery was publicly mentioned in London even as early
as the spring of the past year. As an incontrovertible
proof of this fact, I can bring forward a letter from a
friend of mine (to whom I had not mentioned my new
discovery in any way), in which he congratulates me
on the success of my researches, and informed me at
the same time that he had learned what he knew with
regard to my discoveries from Mr. Davy, a Professor
in the Royal Institution, who had spoken publicly of
them in his lectures on chemistry.

The memoir in which I gave an account of my in-
vestigations was finished early in May (1803); m the
early part of June I left Munich for a journey into
Switzerland. As I intended to proceed from Geneva to
Paris, I took with me my memoir and some of my
newly invented instruments, and among others the ther-
moscope.

234 Historical Review of Experiments

On reaching Geneva, in August, I read my memoir
in the presence of Professor Pictet, De Saussure, and
various other persons, and at the same time repeated
some of my experiments with the thermosc'ope.

As soon as I reached Paris, in the latter part of Oc-
tober, I had my memoir copied (by Mr. Cadel, of Glas-
gow, who was then in Paris), and sent it, in the middle
of December, to London by the younger Mr. Living-
ston, who was kind enough to deliver it in person to
Sir Joseph Banks on the 2jd of December. As the
Christmas recess of the Royal Society begins just after
this time, my memoir could not be read in a public
meeting of the Society until the 3d of February.

The 6th of June there were sent to me from Lon-
don (through the elder Mr. Livingston, Minister Pleni-
potentiary of the United States of North America at
Paris) two copies of my memoir, published by order
of the Royal Society. At the same time I received a
letter from Mr. Davy, Professor of Chemistry at the
Royal Institution, in which he informed me that Mr.
Leslie had, a short time previously, published a me-
moir on heat, and that in it he had described various
experiments which bore a resemblance to some which I
had performed.

The id of June I received at Paris, from M. Ber-
tholet, Mr. Leslie's book, which was sent to me by
Sir Joseph Banks. M. Bertholet had at the same time
received from England a copy of the work, which was
sent to him by one of his friends there.

As I had, only a short time before, occupied the
attention of the National Institute with an account
of my recent researches and discoveries,* the appear-

* Between the igth of March and the yth of May, 1804, I presented to the Na-

on the Subject of HeaL 235

ance of a book coming from England, and containing
a description of a number of experiments and discov-
eries in many respects not dissimilar to my own, could
not fail to create a certain feeling of surprise among the
philosophers of Paris, as I could plainly enough per-
ceive. I find myself, therefore, compelled, although
against my will, to explain as far as possible an occur-
rence which it is highly important for me should appear
in its true light.

I am far from intending to assert that Mr. Leslie had
any knowledge of those experiments of mine which
bore a resemblance to those which he announced pub-
licly in print. It is, however, equally certain that I
did not know, and could not have known, the least
thing about his. It will not be difficult for me to prove
this.

It might, perhaps, be just as easy for Mr. Leslie to
bring forward proofs that he knew absolutely nothing
about my experiments. This would be all the more
readily believed as he (in the course of certain remarks
made in a note with regard to the observations which
I offered in explanation of the propagation of heat in
liquids) speaks of me as of a man already dead* at the
time when he made these remarks.

It is certain that we are perfect strangers to each
other, that we do not know each other even by sight,
and that we never had any sort of correspondence with
each other.

As regards the priority of the public announcement of
our discoveries, this point can be easily made clear by

tional Institute five different memoirs on(this subject. They will probably be printed
in the " Memoires de 1'Institut."

* See the thirty-ninth note at the end of his work, beginning with the following
words : ^ A late ingenious experimenter."

236 Historical Review of Experiments

the statement of certain facts which do not admit of
doubt.

It is true that I cannot determine with any great ac-
curacy the time when Mr. Leslie's book, first saw the
light ; it cannot, however, possibly have been published
before the middle of May of this year, for the dedica-
tion is dated at Largo, in Fifeshire (Scotland), the 2oth
of May, 1804. This would be, consequently, nearly a
year after the time when the most remarkable results
of my investigations were known in London ; it would
be nine months from the time when, in Geneva, I read
the memoir containing the circumstantial and detailed
account of these investigations in the presence of a
number of celebrated philosophers ; it would be five
months later than the time at which this memoir was
placed in the hands of the President of the Royal So-
ciety of London ; and it would be more than a quarter
of a year from the time at which it was read publicly
before this Society.

Still the •priority in question, considered in and by
itself, is of such slight importance that I should not
have mentioned it at all, were it not that the facts which
go to establish it tend at the same time to strengthen a
far more important assertion, namely, that I am actually
the discoverer of what I announced as discoveries.

If Mr. Leslie and myself, the one in Scotland, the
other in Bavaria, each for himself and at about the
same time, did actually make the same discoveries, this
is a condition of things which has already happened
more than once before our time ; and then, as far as the
interpretation of these phenomena is concerned, we dif-
fer from each other in our mode of explanation to such
an extent that there can no question arise between us

on the Subject of Heat. 237

in regard to the ownership of our opinions. Nothing
is more certain than that, in this respect, we have not
borrowed one from the other in the slightest degree.

Besides, I have every reason for believing that even
if I had not described so particularly the facts which I
have brought forward, still all those who will take the
trouble to consider impartially the numerous experi-
ments on the subject of heat which I have made dur-
ing more than twenty years, will be convinced that I
must have been led to the investigations and discoveries
in question by the entirely natural connection of ideas
caused by my opinions on the subject, without needing
to borrow, in the slightest degree, from any person
whomsoever.

To close this historical review of my various re-
searches on the subject of heat, I will give a very brief
account of my labours in this connection, from my
arrival in Paris, until the close of the month of October
of the last year (1803).

As I had brought with me two thermoscopes, I had
them adjusted, by Dumontier, with all possible care; I
also sent to Munich for several other instruments which
I had used, the year before, in my experiments on
heat.

I also procured several new instruments, in order to
make new experiments ; among others, an apparatus
which I intended to use to determine the progress of
heat in a massive bar of metal, in glass, and in other
solid substances. All these instruments I showed to
several members of the National Institute, namely, to
MM. Laplace, Delambre, Prony, and Biot.

To these philosophers, and at the same time to M.
Bertholet as well, I proposed to perform the now well-

238 Historical Review of Experiments

known experiment of the cold body and the speaking-
tube (and this was before the instrument necessary for
the purpose had been invented), and thus to terminate
our (in all respects very friendly) controversy on the
reality of caloric.

This experiment was afterwards performed in the
physical cabinet of the National Institute in the pres-
ence of Laplace, Bertholet, and Charles. The result
was precisely as I had predicted.

On the 28th Ventose of the year 12 (the I9th of
March, 1804) I presented to the Mathematical and
Physical Class of the National Institute my first me-
moir, in which I described my thermoscope and a few
of the discoveries that I had made with the help of
this instrument.

On the fth Germinal (26th of March, 1804) I pre-
sented to the same Class a second memoir, in which I
sought to develop my ideas on the nature of heat, as
well as on the manner in which it is excited and com-
municated. At the same time I gave the results of cer-
tain experiments which I had made on the cooling of
warm bodies in the air. .

On the i gth Germinal (pth of April, 1804) I pre-
sented to the Class a third memoir, which treated of an
experiment, which I had recently made in Paris, on the
nature of heat ; by this experiment the influence of the
rays emanating from cooling bodies was rendered mani-
fest in a manner entirely new.

On the loth Floreal (joth of April, 1804) my fourth
memoir was presented to the Class. In this memoir I
described an experiment which I performed with two
flasks of equal size. One was made of glass, the other
of tinned iron. Both were filled with boiling water,

on tJie Subject of Heat. 239

and exposed at the same time to the air, in which they
were allowed to cool. The water contained in the glass
flask cooled twice as fast as that in the one made of
tinned iron, although the walls of the latter were much
thinner than those of the glass flask. This memoir
ends with some considerations on the comparison which
has been instituted between a warm body and a sponge
filled with water, and on the influence of radiation dur-
ing the warming and cooling of bodies.

On the iyth Floreal (yth of May, 1804) I laid before
the Class my fifth memoir, in which I gave an account of
an entirely new series of experiments, which I had made
in Paris, on the manner in which heat is propagated in
a massive bar of metal, six inches long ana an inch and
a half in diameter. This bar was heated at one end
by boiling water, and cooled at the other end some-
times with a mixture of pounded ice and water, and
sometimes simply with water of the temperature of the
air.

M. Biot, member of the Institute, made, at about the
same time with myself, several successive experiments
on the propagation of heat in metallic bars and other
solid bodies. He, however, used for this purpose bars
of a different length from mine, and higher tempera-
tures. Otherwise we obtained the same results from
our experiments.

He hit upon the fortunate idea of employing similar
experiments for measuring very high degrees of tem-
perature ; such, for example, as is necessary in the
preparation of porcelain, or for melting metals not
readily fusible.

As I was invited to prepare a condensed description
of my recent experiments on heat, to be read at the

240 Historical Review of Experiments on Heat.

public sitting of the National Institute on the 6th
Messidor (June 26, 1804), I presented the memoir
which follows.* As it has already been printed (in
the Moniteur of the pth Messidor, or the 29th of June,
1804), I may be allowed to introduce it into this col-
lection. The case is otherwise with the five other me-
moirs which I presented to the first class of the Insti-
tute; for as they will be embodied in the Me'moires
of the Class it would not be proper for me to publish
them earlier.

To complete this historical review, I must, in addi-
tion, say a word or two on my attempts to perfect the
application of heat to the arts and to all sorts of domes-
tic purposes. Among the fifteen Essays which I have
published in three octavo volumes are no less than
eight which treat of the use of heat. They are as fol-
lows : —

Essay IV. Of Chimney Fireplaces ; VI. On the
Management of Fire and Economy of Fuel ; X. Of
Kitchen Fireplaces; XII. Of the Salubrity of Warm
Rooms in Winter; XI II. Of the Salubrity of Warm
Baths, and the Mode of their Preparation ; XIV. Of
the Management of Fire in Closed Fireplaces ; XV.
Of the Use of Steam as a Vehicle for transporting
Heat.

* See page 166.

[This paper is translated from the German, as it appears in Vol. IV.
of Rumford's Kleine Schriften.]

EXPERIMENTS AND OBSERVATIONS

COOLING OF LIQUIDS IN VESSELS OF PORCELAIN,
GILDED AND NOT GILDED.

NOTHING affords more entertainment than to
compare the processes of the common arts of
life and the ordinary habits of the people in their
household operations with the principles of the physi-
cal and mathematical sciences. This comparison often
presents very curious points of resemblance, and leads
sometimes to very important improvements.

In all countries where the daily use of tea has become
common among the rich, teapots of silver are preferred
to those of porcelain or earthenware, and the reason
given for this preference is that the beverage when pre-
pared in the former is of a better quality than when pre-
pared in the latter. I was, for a long time, of the
opinion that this idea was owing simply to prejudice,
and without foundation ; but, having discovered some
years since that metallic vessels, when clean and bright
on the outside, possess the property of causing warm
liquids which are put into them to retain their heat for
a very long time, I began to see that the preference in
question might be the legitimate result of long experi-
ence, as is almost always the case with those preferences
which in the end are universally adopted.

VOL. II. l6

242 On the Cooling of Liquids in Vessels

In order to throw light on this subject, which had sev-
eral points of interest for me, I made the following-
experiment. I procured (from M. Nast, a celebrated
porcelain manufacturer, of Paris) two vessels of porce-
lain, of the same shape and of the same dimensions,
the one white, the other completely covered on the out-
side with gilding ; into these vessels I put equal quan-
tities (250 grammes, or a quarter of a litre) of warm
water, and then allowed them to cool gradually in a
large room free from currents of air, having placed them
three feet apart on a table in the middle of the room.

Each of the vessels was closed with a cork stopper,
and by means of a mercurial thermometer with a cylin-
drical bulb, fixed in the axis of the vessel in such a way
that while the thermometer was inserted in the cork the
scale remained on the outside of the vessel, I noted
very conveniently the progress of the cooling without
touching the vessel, and without even approaching it
sufficiently near for the heat of my body to interfere
sensibly with the operation of cooling.

The result of this experiment was as I had expected.
The gilded vessel cooled much more slowly than the
plain one. Starting at the same time with both vessels
at the same temperature, if it took half an hour for the
plain vessel to cool down through a certain number of
degrees, three quarters of an hour were necessary for the
gilded one to cool down to the same point.

This comparative experiment was repeated several
times, and invariably with the same result; the gilded
vessel always cooled more slowly than the plain one in
about the proportion of 3 to 2.

The advantage that can be gained from this remarka-
ble property, possessed by metallic surfaces, of resisting

of Porcelain, Gilded and not Gilded. 243

the cooling (or heating) action of surrounding bodies,
is too evident to need much explanation. Since, in
household economy, use is often made of porcelain ves-
sels for holding warm liquids, which it is desired to
keep warm for a long time, — as, for example, tea,
coffee, etc., — in all such cases it would be of advantage
to use vessels gilded on the outside ; or, if gilding be
found too expensive, it is possible to use, and with
equal advantage as regards retaining the heat, vessels
which are silvered or covered with a layer, no matter
how thin, of any other metal not liable to be readily
oxidized in the air.

As to gilding the vessels on the inside, it would be
to no purpose, for it would add nothing to the effect in
question, as I have learned from the results of several
experiments. This, however, applies only to simple
vessels ; for in case a double vessel were employed in
order to retain more effectually the heat of any sub-
stance, the outside vessel must be gilded on the inside
as well as on the outside ; in no case is it necessary for
the inner vessel to be gilded on the inside.

If it is a question of preserving the low temperature
of liquids or other cold substances, such as ice-creams,
etc., in this case, also, vessels having externally a polished
metallic surface should be used ; for a surface of this
description throws off by reflection a large portion of
the calorific rays which reach it from surrounding
objects, and consequently the vessel grows warm very
slowly.

Everybody knows how much time it takes to bring
water to boiling in a silver coffee-pot which is clean and
bright on the outside, especially before an open fire, or
on glowing coals which burn without smoke. It is,

244 ®n MIC Cooling of Liquids in Vessels

however, very easy to hasten materially the heating of
the liquid in this case ; all that is necessary is to begin
by blackening the outside of the coffee-pot over the
flame of a candle or of a lamp, or to destroy or conceal
in some other way the metallic lustre.

All the facts which I have just detailed are easily
explained, and, to my mind, satisfactorily, by the theory
of heat developed in the various memoirs on this sub-
ject which I have had the' honour of presenting to this
Assembly at different times.

If heat is nothing but a vibratory motion of the par-
ticles of a body, — a motion which always exists in all
bodies, but which has greater or less rapidity or inten-
sity according to the temperature of those bodies, — and
if a body which is warmer than those which surround it
is cooled on being exposed to their influence, not because
it has transferred to them something material, to which
the name of caloric has been given, but because of the
effect of the action upon it of those bodies by means of
their frigorific rays, that is to say, by the undulations
caused in the surrounding mass of the fluid ether, — un-
der these circumstances it is evident that the nature of
the exterior surface of the warm body, which renders
it more or less capable of reflecting the rays or undula-
tions which reach it from surrounding objects colder
than itself, ought to influence to a considerable extent
the rapidity of the cooling process.

Now, we know that, of all the substances with which
we are acquainted, the metals are the most impervious
to light, and, at the same time, and perhaps as a neces-
sary consequence, have for it the greatest reflecting
power; moreover, the results of a large number of
experiments have shown that they also possess in an

of Porcelain, Gilded and not Gilded. 245

eminent degree the power of reflecting the invisible rays
or undulations which all objects in nature send off con-
tinually and in all directions from their surfaces in con-
sequence of that peculiar motion of their particles which
constitutes their temperature.

Hence it appears that vessels having a metallic sur-
face on the outside must be well adapted for preserving
the temperature of the substances which they contain,
whether that temperature be high or low, warm or cold.

I am far from maintaining that the sort of material
of which the vessel is made, and the thickness of its
walls, are matters entirely indifferent, provided that the
outer surface be covered with a thin metallic layer which
is clean and bright. I am aware that neither heat nor cold
can be communicated or propagated through the walls
of a vessel, or of any other solid body, instantaneously,
and that this communication takes place more quickly
in some substances than in others, more quickly
through a thin wall than through a thick wall of the
same material ; and it is evident that this difference
must necessarily exert an influence on the rapidity of
the change of temperature of the vessel and of the
liquid it contains, whatever be the nature of the exter-
nal surface of the vessel.

For example, as porcelain is a worse conductor of
heat than gold or silver, a vessel of given form and
dimensions, made of porcelain and well gilded on the
outside, if filled with warm water, would cool rather
more slowly in the air, or even in a Torricellian vacuum,
than another vessel of the same dimensions made of
gold or silver, and filled with water of the same tem-
perature ; but if the vessels were exposed at the same
time to a strong and very cold current of air, or were

246 On the Cooling of Liquids in Vessels

plunged into cold water, the difference in the rate of
cooling would be much greater.

Hence we may conclude that teapots and coffee-pots
made of porcelain or earthenware and well gilded on
the outside would be not only as good, but even better
for common use than teapots and coffee-pots made of
silver.

If equal quantities of warm water are placed in two
porcelain vessels of the same form and dimensions, and
with walls of the same thickness, the one gilded on the
outside, the other plain, and these vessels are allowed
at the same time to cool in still air, the gilded vessel is
found to cool more slowly than the plain one in the
proportion of 3 to 2, as has already been remarked; but
if, instead of allowing the vessels to cool in air which is
undisturbed, they are exposed to the action of a strong
and cold current of air, the difference in the rapidity of
cooling will be much less, as 6 to 5, for example; and
if the current of air is very strong, and at the same
time very cold, this difference will be still smaller.

If, instead of exposing the vessels in the air, they are
plunged into cold water, the difference in the rapidity
with which they cool will be reduced to almost nothing.

In the cases last mentioned we can say that the ex-
terior surfaces of both vessels, although of different
natures, yet, on being exposed to so great a degree of
cold, are cooled to such an extent as to be in a condition
to transmit the heat coming from the interior of the
vessel as fast as it can reach them after making its way
through the thickness of the walls, which offer all the
while a certain amount of resistance to its passage.

To use another form of expression which I regard as
more exact, and consequently more suitable, especially

of Porcelain, Gilded and not Gilded. 247

before this illustrious Assembly, it might be said that in
the case in question the exterior surfaces (the one of
white porcelain, the other of gold) of the two vessels
being intimately exposed to the violent action of a rapid
succession of the very cold particles of the surrounding
fluid, became, both of them, cooled to such an extent
that they were reduced to about the same temperature
in spite of the continual heating action of the walls of
the vessels in contact with them on the opposite side ;
and that, as a consequence, since these surfaces exercised
on the walls of the vessels which they covered cooling
actions which were sensibly equal, the two vessels were
of necessity cooled with the same rapidity.

I will conclude this memoir with some observations
which may serve to throw light on a point in the theory
of heat which is of very great importance.

The great rapidity with which heat is communicated
from one body to another, when two bodies of different
temperatures are in contact, compared with the slowness
of communication which takes place when the bodies
are separated, however little, one from the other, has
had a considerable tendency to give authority to the opin-
ion quite generally adopted by chemists, that there are
two modes by which heat can be transmitted from one
body to another ; that is, at a distance, by radiant
caloric^ and, on contact, by an actual transfusion of the
same substance. If, however, attention be paid to a
fact which no one up to this time has called into ques-
tion, the phenomenon under consideration can, as it
seems to me, be explained in a perfectly clear and satis-
factory manner, without having recourse to such an
extraordinary supposition as that there are two different
modes by which heat is communicated.

248 On the Cooling of Liqiiids in Vessels

It is generally recognized (I might say that it is
proved) that the intensity of the action of calorific or
frigorific rays is inversely proportional to the squares of
the distances from the body from which they proceed ;
now, if this relation is constant, since the effect produced
by these rays in a given time must necessarily be in pro-
portion to the intensity of their action, it is evident
that at the point of contact (if, indeed, there can be an
actual contact between two bodies) the rapidity of the
calorific action between two particles of different tem-
peratures, and which are in contact, must be infinite.

But the time necessary to establish an equality of
temperature throughout the entire masses of two bodies
in contact, which are of sensible size and of different
temperatures, will depend not only on the size of the
bodies and on the extent of the surfaces by which they
are in contact, but also, and above all, on the greater or
less rapidity with which is propagated among the parti-
cles of the bodies that peculiar motion of those particles
which constitutes their temperature.

I will observe here, in passing, that if in the commu-
nication of heat between two bodies in contact, it were
only a question of the transfer from one to the other of
the excess of a fluid as rare and as elastic as caloric is
supposed to be, one would expect, it seems to me, an
action as instantaneous as the discharge of a Leyden jar.

It cannot be said, in objection, that the warm body
does not offer avenues enough for the escape of the
caloric, for it is proved that the pores of all bodies,
even of the most solid, are so considerable in compari-
son with the space occupied by the particles of those
bodies, that a fluid as rare as caloric is supposed to be
would be able to move about therein with great free-

of Porcelain, Gilded and not Gilded. 249

dom. Besides, it often happens that a very large surface
of the warm body is in contact with the cold body ; but,
even in this case, there is nothing in the action taking
place in the communication of the heat which resembles
in any way the sudden explosion which takes place on
the restoration of the equilibrium among the particles
of an elastic fluid ; on the contrary, the slow and meas-
ured progress of this communication, as well as all the
other phenomena that it presents, denote rather a grad-
ual operation, like that which takes place when the mo-
tion of a body is accelerated or retarded.

The following experiment may serve to explain and
confirm this important truth. If a ball of iron, three
or four inches in diameter, fastened to a long handle of
the same metal, be heated strongly in a forge until it is
of a whitish-red heat, and then taken from the fire and
plunged suddenly into cold water, the communication
of the heat to the water will be so far from being instan-
taneous that a considerable time will pass before the ball
ceases to be red and luminous at its surface ; and even
after the surface of the ball has cooled so far as no
longer to give off" visible light, the interior will still be
incandescent. It is easy to establish this last fact; for
if at this point the ball be taken from the water and
held in the air for a few moments, the surface of the
ball will again become red and luminous.

I confess frankly that I have never been able to rec-
oncile these phenomena with that hypothesis which sup-
poses that the increase of temperature of a body is due
to the accumulation within it of a very rare and ex-
tremely mobile substance, especially when I have con-
sidered the great ease with which such a fluid ought to
pass through the pores of all known bodies.

250 On the Cooling of Liquids in Vessels of Porcelain.

But whatever be the explanation given to the phe-
nomena which present themselves in the heating and
cooling of bodies, it is certain that every new fact relat-
ing to these actions which is discovered must tend to-
wards perfecting the science of heat as well as the arts
which depend upon it.

I flatter myself that this Assembly will find the re-
sults of the experiments which I have detailed suffi-
ciently curious and interesting to deserve its attention.

AN ACCOUNT

CURIOUS PHENOMENON OBSERVED ON THE
GLACIERS OF CHAMOUNY ;

TOGETHER WITH

SOME OCCASIONAL OBSERVATIONS CONCERNING THE PROPA-
GATION OF HEAT IN FLUIDS.

IN an excursion which I made the last summer, in the
month of August, to the glaciers of Chamouny, in
company with Professor Pictet of Geneva, I had an
opportunity of observing, on what is called the Sea of
Ice (Mer de Glace), a phenomenon very common, as I
was told, in those high and cold regions, but which was
perfectly new to me, and engaged all my attention. At
the surface of a solid mass of ice, of vast thickness and
extent, we discovered a pit perfectly cylindrical, about
seven inches in diameter and more than four feet deep,
quite full of water. On examining it on the inside with
a pole, I found that its sides were polished, and that its
bottom was hemispherical and well defined.

This pit was not quite perpendicular to the plane of
the horizon, but inclined a little towards the south as it
descended ; and in consequence of this inclination, its
mouth, or opening at the surface of the ice, was not
circular, but elliptical.

From, our guides I learned that these cylindrical holes
are frequently found on the level parts of the ice ; that
they are formed during the summer, increasing gradu-

252 Account of a curious Phenomenon

ally in depth, as long as the hot weather continues ; but
that they are frozen up and disappear on the return of
winter.

I would ask those who maintain that water is a
conductor of heat, how these pits are formed. On a
supposition that there is no direct communication of
heat between neighbouring particles of that fluid which
happen to be at different degrees of temperature, the
phenomenon may easily be explained ; but it appears to
me to be inexplicable on any other supposition.

The quiescent mass of water by which the pit remains
constantly filled must necessarily be at the temperature
of freezing, for it is surrounded on every side by ice ;
but the pit goes on to increase in depth during the
whole summer. From whence comes the heat that
melts the ice continually at the bottom of the pit ? and
how does it happen that this heat acts on the bottom of
the pit only, and not on its sides ?

These curious phenomena may, I think, be explained
in the following manner. The warm winds which in
summer blow over the surface of this column of ice-cold
water must undoubtedly communicate some small degree
of heat to those particles of the fluid with which this
warm air comes into immediate contact; and the par-
ticles of the water at the surface so heated, being rendered
specifically heavier than they were before by this small
increase of temperature, sink slowly to the bottom of
the pit, where they come into contact with the ice, and
communicate to it the heat by which the depth of the
pit is continually increased.

This operation is exactly similar to that which took
place in one of my experiments (see my Essay on the
Propagation of Heat in Fluids, Experiment 17), the

observed on the Glaciers of Chamouny. 253

results of which no person to my knowledge has yet
explained.

There is another very curious natural phenomenon
which I could wish to see explained in a satisfactory man-
ner by those who still refuse their assent to the opinions
I have been led to adopt, respecting the manner in which
heat is propagated in fluids. The water at the bottoms
of all deep lakes is constantly at the same temperature
(that of 41° Fahrenheit), summer and winter, with-
out any sensible variation. This fact alone appears to
me to be quite sufficient to prove that, if there be any
immediate communication of heat between neighbouring
particles or molecules of water, de proche en proche ^ or
from one of them to the other, that communication must
be so extremely slow that we may with safety consider
it as having no existence ; and it is with this limitation
that I beg to be understood when I speak of fluids as
being non-conductors of heat.

In treating of the propagation of heat in fluids, I
have hitherto confined myself to the investigation of
the simple matter of fact, without venturing to offer
any conjectures relative to the causes of the phenomena
observed. But the results of recent experiments on the
calorific and frigorific radiations of hot and of cold bodies
(an account of which I shall have the honour of laying
before the Royal Society in a short time) have given
me some new light respecting the nature of heat and the
mode of its communication; and I have hopes of being
able to show why all changes of temperature in trans-
parent liquids must necessarily take place at their sur-
faces.

I have seen, with real pleasure, that several ingenious
gentlemen in London and in Edinburgh have under-

254 Account of a curious Phenomenon

taken the investigation of the phenomena of the propa-
gation of heat in fluids, and that they have made a
number of new and ingenious experiments, with a view
to the further elucidation of that most interesting sub-
ject. If I have hitherto abstained from taking public
notice of their observations on the opinion I have
advanced on that subject in my different publications,
it was not from any want of respect for those gentle-
men that I remained silent, but because I still found it
to be quite impossible to explain the results of my own
experiments on any other principles than those which,
on the most mature and dispassionate deliberation I had
been induced to adopt ; and because my own experi-
ments appeared to me to be quite as conclusive (to say
no more of them) as those which were opposed to them ;
and, lastly, because I considered the principal point in
dispute, relative to the passage of heat in fluids, as being
so clearly established by the circumstances attending sev-
eral great operations of nature, that this evidence did not
appear to me to be in danger of being invalidated by
conclusions drawn from partial and imperfect experi-
ments, and particularly from such as are allowed on all
hands to be extremely delicate.

In all our attempts to cause heat to descend in liquids,
the heat unavoidably communicated to the sides of the
containing vessel must occasion great uncertainty with
respect to the results of the experiment ; and when that
vessel is constructed of ice, the flowing down of the
water resulting from the thawing of that ice will cause
motions in the liquid, and consequently inaccuracies of
still greater moment, as I have found from my own
experience ; and when thermometers immersed in a
liquid at a small distance below its surface acquire

observed on the Glaciers of Chamouny. 255

heat in consequence of a hot body being applied to the
surface of the liquid, that event is no decisive proof that
the heat acquired by the thermometer is communicated
by the fluid, from above, downwards, from molecule to
molecule, de proche en proche ; so far from being so, it is
not even a proof that it is from the fluid that the ther-
mometer receives the heat which it acquires ; for it is
possible, for aught we know to the contrary, that it may
be occasioned by the radiation of the hot body placed at
the surface of the fluid.

In the experiments of which I have given an account
in my Essay on the Propagation of Heat in Fluids,
great masses, many pounds in weight, of boiling-hot
water, were made to repose for a long time (three hours)
on a cake of ice, without melting but a very small por-
tion of it; and on repeating the experiment with an
equal quantity of very cold water (namely, at the tem-
perature of 41° Fahrenheit), nearly twice as much
ice was melted in the same time. In these experiments
the causes of uncertainty above mentioned did not exist,
and the results of them were certainly most striking.

The conclusions which naturally flow from those
results have always appeared to me to be so perfectly
evident and indisputable as to stand in no need either
of elucidation or of further proof.

If water be a conductor of heat, how did it happen
that the heat in the boiling water did not, in three hours,
find its way downwards to the cake of ice on which it
reposed, and from which it was separated only by a
stratum of cold water half an inch in thickness?

I wish that gentlemen who refuse their assent to the
opinions I have advanced respecting the causes of this
curious phenomenon would give a better explanation

256 Account of a curious Phenomenon

of it than that which I have ventured to offer. I could
likewise wish that they would inform us how it happens
that the water at the bottoms of all deep lakes remains
constantly at the same temperature ; and above all, how
the cylindrical pits above described are formed in the
immense masses of solid and compact ice which compose
the glaciers of Chamouny.

A remark, which surprised me not a little, has been
made by a gentleman of Edinburgh (Dr. Thomson),
on the experiments I contrived to render visible the
currents into which liquids are thrown on a sudden
application of heat or of cold. He conceives that the
motions observed in my experiments, among the small
pieces of amber which were suspended in a weak solution
of potash in water, were no proof of currents existing in
that liquid ; as they might, in his opinion, have been
occasioned by a change of specific gravity in the amber,
or by air attached to it. I am sorry that so mean an
opinion of my accuracy as an observer should have been
entertained, as to imagine that I could have been so
easily deceived. For nothing, surely, is easier than to
distinguish the motion of a solid suspended in a liquid
of the same specific gravity, which is carried along by a
current in the liquid, from that of a body which descends,
or ascends, in the liquid in consequence of its relative
weight or levity. In the one case the motion is uni-
form ; in the other, it is accelerated. In a current the
body may be carried forward in all directions, and
even in curved lines ; but when it falls in a quiescent
fluid by the action of gravity, or rises in consequence of
its being specifically lighter than the fluid, it must neces-
sarily move in a vertical direction.

The fact is, that I very often observed, in the course

observed on the Glaciers of Chamouny. 257

of my numerous experiments, the motions of small par-
ticles of matter of different kinds in water, which Dr.
Thomson describes ; but so far from inferring /row them
the existence of currents in that fluid, their cause was so
perfectly evident that I did not even think it necessary
to make any mention of them.

I cannot conclude this paper without requesting that
the Royal Society would excuse the liberty I have taken
in troubling them with these remarks. Very desirous
of avoiding every species of altercation, I have hitherto
cautiously abstained from engaging in literary disputes ;
and I shall most certainly endeavour to avoid them in
future.

I am responsible to the public for the accuracy of
the accounts which I have published of my experiments;
but it cannot reasonably be expected that I should
answer all the objections that may be made to the con-
clusions which I have drawn from them. It will, how-
ever, at all times, afford me real satisfaction to see my
opinions examined and my mistakes corrected ; for my
first and most earnest wish is, to contribute to the
advancement of useful knowledge.

[This paper is printed from the Philosophical Transactions of the
Royal Society, XCIV. (1804), pp. 23 - 29.]

VOL. II.

AN ACCOUNT

SOME NEW EXPERIMENTS ON THE TEMPERATURE
OF WATER AT ITS MAXIMUM DENSITY.

IN my seventh Essay on the Propagation of Heat
in Fluids, and in a paper published in the Philo-
sophical Transactions for the year 1804, in which I have
given an account of a curious phenomenon frequently ob-
served on the glaciers of Chamouny, I have ascribed the
melting of the ice below the surface of the ice-cold water
to currents of water slightly warmer, and consequently
slightly heavier, which descend from the surface to the
bottom of the ice-cold water; but the principal fact on
which this supposition is founded having been called
in question by various persons, I have endeavoured to
establish it by new and decisive experiments.

If it is true that the temperature of water at its maxi-
mum density is considerably higher than the freezing-
point of that liquid (as was announced many years ago
by M. de Luc), and that the communication of heat in
liquids is brought about by a movement of circulation
caused by a change of density in the particles of the
fluid resulting from a change of temperature, the ex-
planation that I have given of the phenomenon of the
melting of ice covered with a layer of ice-cold water by
heat applied to the surface of the water, would seem

The Temperature of Water, etc. 259

natural and admissible ; but if the density of water is
greater at the temperature of melting ice than at any
other more elevated temperature, as some philosophers
assert, it is evident that the vertical descending currents
of warm water which I have described cannot exist, and
my explanation must be rejected.

This inquiry interested me all the more, because the
fact in question had served as the foundation of the
theory which I gave in my seventh Essay on the pe-
riodical winds of the polar regions, and as the basis of
my conjectures on the existence of currents of cold water
in the depths of the sea coming from the polar regions
to the equator, and on the cause of the great difference
which is found in the temperature of different countries
situated in the same latitude and at the same height
above the level of the sea.

After meditating on the means which I should employ
to establish this important fact beyond doubt, I thought
of the experiment which I am about to describe, and
which is all the more interesting, since it not only
demonstrates the existence in a mass of water which is
warmed or cooled, of the currents assumed by my
theory, but proves at the same time that the temper-
ature at which the density of water is at a maximum is
actually some degrees above that of melting ice.

Having provided a cylindrical vessel (A, Plate VI.),
open above, made of thin sheet brass, 5^ inches in
diameter and 4 inches deep, supported on three strong
legs \\ inches high, I placed in it a thin brass cup
(B) 2 inches in diameter at its bottom (which is a
little convex downwards), 2^ inches wide at its brim,
and IT\ inches deep; this cup stands on three spread-
ing legs made of strong brass wire, and of such form

260 The Temperature of Water

and length that when the cup is introduced into the
cylindrical vessel, it remains firmly fixed in the axis of
it, and in such a situation that the bottom of the cup
is elevated just i^ inches above the bottom of the
cylindrical vessel.

In the middle of this cup there stands a vertical tube
of thin sheet brass J of an inch in diameter and T67 of an
inch in length, open above, which serves as a support
for another smaller cup (C), which is made of cork, the
brim of which is on the same horizontal level with the
brim of the larger brass cup in which it is placed.

This cork cup, which is spherical, being something
less than half of an hollow sphere, is I inch in diameter
at its brim, measured within, T% of an inch deep, and \
of an inch in thickness. It is firmly attached to the ver-
tical tube on which it stands, by means of a cylindrical
foot J of an inch in diameter and \ of an inch high,
which enters with friction into the opening of the vertical
tube.

On one side of this cork cup there is a small opening,
which receives and in which is confined the lower ex-
tremity of the tube of a small mercurial thermometer
(D). The bulb of this thermometer, which is spheri-
cal, is T3¥ of an inch in diameter, and it is so fixed in
the middle of the cup, that its centre is \ of an inch
above the bottom of the cup ; consequently it does
not touch the cup anywhere, nor does any part of it
project above the level of its brim.

The tube of this thermometer, which is 6 inches in
length, has an elbow near its lower end at the distance
of i inch from its bulb, which elbow forms an angle
of about no degrees, and the thermometer is so fixed
in the cork cup, that the short branch of its tube, namely,

at its Maximum Density. 261

that to the end of which the bulb is attached, lies in an
horizontal position, while the longer branch (to which a
scale made of ivory and graduated according to Fahren-
heit is affixed) projects obliquely upwards and outwards
in such a manner that the freezing-point of the scale lies
just above the level of the top of the cylindrical vessel
in which the cups are placed.

The cork cup, which was turned in the lathe, is neatly
formed, and in order to close the pores of the cork, it
was covered within and without with a thin coating of
melted wax, which was polished after the wax was cold.

The thermometer was fixed to the cork cup by means
of wax, and in doing this care was taken to preserve the
regular form of the cup, both within and without.

The vertical brass tube which supports this cup in
the axis of the brass cup is pierced with several small
holes, in order to allow the water employed in the ex-
periments to pass freely into and through it.

Having attached about 6 ounces of lead to each of
the legs of the brass cup, in order to render it the more
steady in its place, it was now introduced with its con-
tents into the cylindrical vessel, and the vessel was placed
in an earthen basin (E), and surrounded on all sides with
pounded ice. This basin was 1 1 inches in diameter at
its brim, 7 inches in diameter at the bottom, and 5 inches
deep, and was placed on a firm table in a quiet room.

Several cakes of ice were then placed under the bottom
of the brass cup, and the cup was surrounded on all
sides by a circular row of other long pieces of ice fixed
in a vertical position between the outer walls of the cup
and the walls of the cylindrical vessel. These pieces
were about 4 inches long, and extended from the bottom
of the vessel to within a very short distance of the top.

262 The Temperature of Water

All these pieces of ice having been fixed firmly in their
places by means of some little wooden wedges, ice-cold
water was poured into the cylindrical vessel until the
surface of this liquid was an inch above the upper edge
of the cork cup.

In this state of things it is evident that the two cups
were filled with and surrounded on all sides by water at
the temperature of melting ice, and that this temperature
was maintained constant by the pieces of ice with which
the water was in contact.

After having left the apparatus in this situation for
about an hour, in order to satisfy myself that the tem-
perature of the cold water was constant and uniform
throughout its entire mass, I made the following experi-
ment.

Experiment No. i. — A solid ball of tin (F) having
been provided, 2 inches in diameter, with a cylindrical
projection on the lower side of it, i inch in diameter
and J of an inch long ending in a conical point which
projected (downwards) |- of an inch farther, and having
on the other side a strong iron wire 6 inches long, which
served as a handle, — this ball, after having been im-
mersed for half an hour in a considerable quantity of
water at the temperature of 42° F., was withdrawn from
the water, wiped dry with a handkerchief of the same
temperature, placed without loss of time above the
cylindrical vessel, and fixed in such a position that the
entire conical point of the tin ball (| of an inch in length)
was submerged in the cold water contained in the vessel.

To fix and keep the metallic ball in its place, I used a
strong slip of tin (GH), 6 inches long and 2j- inches
wide, with a circular hole in the middle of it i inch
in diameter. This slip of tin being laid horizontally on

at its Maximum Density. 263

the top or brim of the cylindrical vessel in such a manner
that the centre of the circular hole coincided with the
axis of the cylindrical vessel, when the short cylindrical
projection belonging to the ball was introduced into that
hole, the ball was firmly supported in its proper place.

The ball was placed in such a position that the end of
the conical projection was immediately over the cork cup,
at the distance of \\ inches above the level of its brim
and consequently J of an inch above the upper part of
the bulb of the small thermometer which lay in this cup.

The quantity of cold water in the cylindrical vessel
had been so regulated beforehand that when the conical
point was entirely submerged, the surface of the water
was on a level with the base of this inverted cone, so
that the whole of the cylindrical part of the projection
was out of the water.

I knew that the particles of ice-cold water which were
tjius brought into contact with the conical point could
not fail to acquire some small degree of heat from that
relatively warm metal, and I concluded that if the par-
ticles of water so warmed should in fact become heavier
than they were before, in consequence of this small
increase of temperature, they must necessarily descend in
the surrounding lighter ice-cold liquid, and as the heated
metallic point was placed directly over the cork cup,
and fixed immovably in that situation, I foresaw that
the descending current of warm water must necessarily
fall into that cup and at length fill it, and that the pres-
ence of this warm water in the cup would be announced
by the rising of the thermometer.

The result of this very interesting experiment was
just what I expected: the conical metallic point had not
been in contact with the ice-cold water more than 20

264 The Temperature of Water

seconds when the mercury in the thermometer began to
rise, and in 3 minutes it had risen three degrees and
a half, namely, from 32° to 35^°; when 5 minutes had
elapsed it had risen to 36°.

Another small thermometer placed just below the
surface of the ice-cold water, and only T2Q- of an inch from
the upper part of the conical point and on one side of
it, did not appear to be sensibly affected by the vicinity
of that warm body.

A third thermometer, the bulb of which was placed
in the brass cup just on the outside of the cork cup and
on a level with its brim, showed that the water which
immediately surrounded the cork cup remained con-
stantly at the temperature of freezing during the whole
time that the experiment lasted.

As I well knew from the results of the experiments
on the propagation of heat in a solid bar of metal,* that
no one of the particles of cold water in contact with the
surface of the conical projection, in the experiment which
I have just described, could acquire by this momentary
contact a temperature as high as that of the warm metal,
I was by no means surprised to find that the thermom-
eter belonging to the cork cup rose no higher than 36°.

In order to see if it could not be made to rise not
only higher, but also more rapidly, by employing the
metallic ball heated to such a temperature as it might be
supposed would be sufficient to heat those particles of
ice-cold water which should come into contact with its
conical point, to the temperature at which the density
of water is supposed to be a maximum, I made the
following experiment.

* An account of these experiments has been given in a memoir presented to the
Mathematical and Physical Class of the National Institute of France, on the yth of
May, 1804. See also p. 144.

at its Maximum Density. 265

Experiment No. 2. — Having removed the ball, I gently
brushed away the warm water which in the last experi-
ment had been lodged in the cavity of the cork cup, and
which still remained there, as was evident from the indi-
cation of the thermometer belonging to the cup ; I then
placed several small cakes of ice in the cylindrical vessel,
which ice, floating on the surface of the water in the ves-
sel, prevented the water from receiving heat from the
surrounding air, which at that time was at the temper-
ature of 70° F. As the cork cup had been a little heated
by the warm water in the foregoing experiment, time
was now given it to cool.

As soon as the cup and the whole mass of the water
in the cylindrical vessel appeared to have acquired the
temperature of freezing, I carefully removed the cakes
of ice which floated on the surface of the water, and in-
troduced once more the projecting conical point belong-
ing to the metallic ball into the ice-cold water in the
vessel, placing it exactly in the same place which it had
occupied in the foregoing experiment ; but this ball,
instead of being at the temperature of 42° F., as before,
was now at the temperature of 60° F.

The results of this experiment were very striking,
and, if I am not much mistaken, afford a direct, unex-
ceptionable, and demonstrative proof, not only that the
maximum of the density of water is in fact at a temper-
ature which is several degrees above the point of freezing,
but also that warm currents do actually set downwards
in ice-cold water, whenever a certain small degree of
heat is applied to the particles of that fluid which are at
its surface, as I have already announced in my Essay on
the Propagation of Heat in Fluids.

The conical metallic point had been in its place no

266 The Temperature of Water

more than 10 seconds when I distinctly saw that the
mercury in the thermometer belonging to the cork cup
was in motion, and, when 50 seconds had elapsed, it had
risen four degrees, viz. from 32° to 36°.

When 2 minutes and 30 seconds had elapsed, reckon-
ing from the moment when the metallic point was intro-
duced into the cold water, the thermometer had risen
to 39°, and at the end of 6 minutes to 39^-°, when it began
to fall ; but very slowly, however, for at the end of 8
minutes and 30 seconds it was at 39!°.

A small mercurial thermometer, the bulb of which
was placed on one side of the cork cup at the distance
of about y2Q- of an inch from it, showed no signs of being
in the least affected by the vertical current of warm water
which descended from the conical point into the cup in
this experiment.

This experiment was repeated four times the same
day (the I3th of June, 1805), and always with nearly
the same results. The mean results of these four ex-
periments were as follows : —

Time elapsed, reckoned
from the beginning of
the experiment.

m. s.
O O

Temperature <
water in the
cup, as show
the thermom
Degrees.

At

o

10

began to rise 32+

At

0

23

had risen to . . . . -33

0

28 '

" " " 34

0

35

" " " 35

0

48

" " " 36

I

3

" " " 37

I

35

« « « 38

2

32

" " " 39

3

41

•««««« 391

4

48

" " " 392

6

5

" " " 391

at its Maximum Density. 267

As I had found by some of my experiments made in
the year 1797 (of which an account is given in my
seventh Essay, Part I.) that water at the temperature of
about 42° F., and .consequently what we should call very
cold, melted considerably more ice, when standing on it,
than an equal quantity of boiling-hot water in the same
situation, I was very curious to see whether the ther-
mometer, the bulb of which lay in the cork cup, would
not also be less heated by the ball when it should be
applied very hot to the surface of the water, than when
its temperature was much lower.

Seeing that this research ought to throw great light on
the mysterious operations of the distribution of heat
in liquids, I hastened to make the following experiment.

Experiment No. 3. — The cylindrical vessel with its
contents having been once more reduced to the uniform
temperature of freezing water, the metallic ball was heated
in boiling water, and being as expeditiously as possible
taken out of that hot liquid, its projecting conical point
was suddenly submerged in the ice-cold water, as in the
former experiments.

The result of this experiment was very interesting.
It was not till 50 seconds had elapsed that the ther-
mometer began to show any signs of rising, and at the
end of i minute and 7 seconds it had risen only 2
degrees.

In the foregoing experiment, when the metallic ball
was so much colder, the thermometer began to rise in
10 seconds, and at the end of I minute and 3 seconds it
had risen 5 degrees.

This difference is very remarkable, and if it does not
prove the existence and great efficacy of currents in con-
veying heat in fluids, I must confess that I do not see

268 The Temperature of Water

how the existence of any invisible mechanical operation,
the progress of which does not immediately fall under
the cognizance of our senses, can ever be demonstrated.
As the experiment made with the ball heated in boil-
ing water appeared to me to be very interesting, I
repeated it twice, and its results were always nearly the
same. The mean results of these three experiments
were as follows : —

Time elapsed, reckoned Temperature of the
from the beginning of water in the cork
the experiment. cup, as shown by
the thermometer.

m.

s.

Degrees.

O

O

At

O

5°

the thermometer began to rise . . 32+

At

I

2

had risen to 33

I

7

" " " 34

I

18

2

2

" " " 36

3

2

" " 36i

4

17

" " " 37

6

12

" " " 38

7

'7

" " " 38^

0

0

" « " 784-

14 o ****•*. . . . . . 38^

By comparing the mean results of these experiments
with the mean results of those in which the ball was at
the temperature of 60° or less, we. may see how much
more rapid the communication of heat in the cold water
from above downwards was when the metallic ball was
relatively cold than when it was much warmer ; but we
must not consider of too much importance the deter-
mination of the relative rapidity thus made, because it
is more than probable that it was not till after the
conical metallic point had been considerably cooled by

at its Maximum Density. 269

contact with the cold water that the vertical descending
currents could exist by which the thermometer was at
length heated. At the beginning of the experiment
made with the tin ball warmed in boiling water, the
particles of water which were in immediate contact with
the conical point while it was still very warm, were
heated to a temperature higher than that at which the
density of water is at a maximum, and the density of
these particles being diminished by this high degree of
heat, the vertical currents in the cold water were at the
beginning ascending currents, as I satisfied myself by
means of a small thermometer placed by the side of the
conical point at a distance of T2¥ of an inch from its base,
and immediately below the surface of the cold water :
this thermometer began to rise very rapidly as soon as
the warm metallic point was plunged into the cold
water.

Another small thermometer, the bulb of which was
situated at about the same distance from the axis of the
conical projection, but -J- of an inch below the surface of
the cold water, preserved throughout the entire experi-
ment the appearance of perfect rest.

The results of this last experiment are all the more
interesting because they afford a demonstrative proof that
it was neither by a direct communication of heat in the
water, which was at rest, from molecule to molecule, de
proche enproche, nor by calorific radiations passing through
the water, that heat was communicated from the metallic
point to the bulb of the thermometer, but actually by a
descending current of warm water ; for it is perfectly
evident that if this heat had been communicated either
by a direct transfer in the water from molecule to mole-
cule or by calorific radiations passing from the surface

2 70 The Temperature of Water

of the metal through the water, which remained at rest,
this communication would naturally have been the most
rapid when the metallic point was the warmest. What
did take place was exactly contrary to this, as we have
just seen. Moreover, the small thermometer, which
was placed close to the metallic body on one side, and
which in this experiment was in no degree affected by
the heat of this body, would not have failed to acquire
as much heat at least as that placed in the cork cup, which
was situated below the metallic body and at a greater
distance from it.

The considerable amount of time which elapsed in the
experiments performed with the tin ball heated in boil-
ing water before the thermometer in the cork cup began
to be so sensibly affected, and the rapidity with which it
was then warmed through several degrees as soon as it
began to rise, indicate a fact which it is important to
notice. In order to throw light upon this fact, we
must consider carefully the operation of the heating of
cold water by the warm metallic surface with which it
was in contact, and examine it in its progress and in
all its details.

Let us begin by supposing that the conical point of
the ball, at the temperature of boiling water, has just
been submerged vertically up to the level of its base in
a mass of undisturbed water at the temperature of melt-
ing ice. As the particles of water, which in this case
are in contact with the warm metallic surface, cannot
pass, all of a sudden, from the temperature of melting
ice to that of boiling water without passing through all
the intermediate degrees, and since these particles at the
temperature of melting ice cannot become warmer with-
out becoming more dense, it is evident that they must

at its Maximum Density. 271

have a tendency to descend, and consequently to leave
the surface of the metal, as soon as they begin to acquire
heat ; but experiment showed that, instead of descend-
ing, they were actually pushed upwards : this proves
that they were heated so rapidly that, before they had
time to leave the surface of the metal and to escape
from its calorific influence, they had acquired a temper-
ature so elevated that their density, after having passed
rapidly the point of its maximum, became even less than
it was at the temperature of melting ice. But after
some moments, the metallic body having cooled some-
what, and the communication of heat to the particles of
water taking place more slowly, these particles, having
become more dense on account of a slight increase
of temperature, had time to escape before becoming
warmer, and at that time the descending current sud-
denly began.

This fact interests me the more, as it may serve in
some sort to explain a phenomenon which I observed in
an experiment made eight years ago, an account of
which I gave in my Essay on the Propagation of Heat
in Fluids.*

The phenomenon to which I have alluded was this :
Having poured some mercury into a small cylindrical
glass vessel 2 inches in diameter and 3-|- inches deep,
until this fluid filled the vessel to the height of an inch,

1 poured on to the mercury twice as much water (that is,

2 inches), and, plunging the vessel up to the level of the
upper surface of the mercury into a freezing mixture of
pounded ice and sea-salt, the temperature of the air
being 60° F., I allowed the whole to cool quietly, in
order to see in what part of the water the ice would first

* See Vol. I. p. 357.

272 The Temperature of Water

appear. It was at the bottom of the water, where this
liquid was in contact with the mercury, that the ice
formed.

The layer of water which rested immediately on the
surface of the mercury having been cooled to about the
temperature of 41° F., where the density of water is at
its maximum, the particles of this water, which were
then in immediate contact with the mercury, losing still
more of their heat, became of necessity less dense, and
had consequently a tendency to leave the bottom of the
water and to ascend upwards ; but the rapidity with
which they were cooled by the mercury was so great
that they were frozen before they could escape from the
cooling influence of this cold body.

After all that I have said about the warm and cold
currents which take place in a liquid which is warmed
or cooled, it might perhaps be thought that I regard
these currents as composed of single particles of the
liquid, which, having been in immediate contact with
the body which gives or which receives the heat, are
all of the same temperature. I am all the farther from
holding this opinion, since I know from the results
of several experiments made expressly for elucidating
this point, (and which I shall have the honor of present-
ing to the Class on another occasion,) that a liquid
current cannot pass through another liquid mass which
is at rest, and which is of the same kind and of about
the same specific gravity, without producing a per-
ceptible mixture of the two liquids ; much less, therefore,
can a small current of warm water pass without mixing
through a mass of cold water ; and the farther it advances
the more it will be mixed, and the more, in consequence,
will its temperature be found to be lowered.

at its Maximum Density. 273

For example, in the experiments of which I have just
given an account, the cork cup, which received the
current of warm water descending from the metallic
point of the tin ball, was only \ of an inch below the
extremity of this point ; if this distance had been greater,
the thermometer in the cup would certainly have risen
to a less height : for this reason these experiments ought
not to be regarded as suitable for determining with great
exactness the temperature at which the density of water
is at a maximum, but rather as proving that this tem-
perature is really several degrees of the thermometric
scale above that of melting ice; and this is all that I am
particularly interested in showing at the present time.

Judging from the constant temperature which is found
at all seasons at the bottom of deep lakes and from the
results of several direct experiments, we may conclude
that water is at its maximum density when it is at the
temperature of about 41° of Fahrenheit's scale, which
corresponds to 4° on that of Reaumur, and to 5° of the
Centigrade scale.

[This paper is translated from the Memoires de 1'Institut, etc., VII.
(1806), pp. 78-97. The greater part of the translation is taken from
Nicholson's Journal, XI. (1805), pp. 225-235.]

18

INQUIRIES

CONCERNING

THE MODE OF THE PROPAGATION OF HEAT IN
LIQUIDS.

THE motions in fluids which result from a change
in their temperature give rise to so great a number
of phenomena, that philosophers cannot bestow too
much pains in investigating that interesting branch of
knowledge.

When heat is propagated in solid bodies, it passes
from particle to particle, de proche en proche , and appar-
ently with the same celerity in every direction ; but it
is certain that heat is not transmitted in the same manner
in fluids.

When a solid body is heated and plunged in a cold
liquid, the particles of the liquid in contact with the
body, being rarefied by the heat that they receive from
it, and being rendered specifically lighter than the sur-
rounding particles, are forced to give place to these last
and to rise to the surface of the liquid ; and the cold par-
ticles that replace them at the surface of the hot body,
being in their turn heated, rarefied, and forced up, — all
the particles thus heated by a successive contact with
the hot body form a continued ascending current,
which carries the whole of the heat immediately towards
the surface of the liquid, so that the strata of the liquid
situated at a small distance under the hot body are not
sensibly heated by it.

Inquiries concerning the Mode, etc. 275

When a solid body is plunged in a liquid which is
hotter than the body, the particles of the liquid in con-
tact with the body, being condensed by the cooling they
undergo, descend, in consequence of the increase of
their specific gravity, and fall to the bottom of the
liquid ; and the strata situated above the level of the
cold body are not cooled by it immediately.

It is true that the viscosity of liquids, even of those
which possess the highest known degree of fluidity, is
still much too great to allow one of their particles indi-
vidually being moved out of its place by any change of
specific gravity occasioned by heat or cold ; yet this does
not prevent currents from being formed, in the manner
above described, by small masses of the liquid composed
of a great number of such particles.

The existence of currents in the ordinary cases of the
heating and cooling of liquids cannot any longer be called
in question ; but philosophers are not yet agreed with
respect to the extent of the effects produced by those
currents.

In treating of abstruse subjects, it is indispensably
necessary to fix with precision the exact meaning of the
words we employ. The distinction established between
conductors and non-conductors of heat is too vague not to
stand in need of explanation. An example will show
the ambiguity of these expressions.

If two equal cubes of any solid matter, — copper, for
instance, — of two inches in diameter, the one at the tem-
perature of 60°, the other at 100°, be placed one above
the other,- the cold cube will be heated by the hot one,
and this last will be cooled.

If the cold cube be placed upon a table and its upper
surface covered by a large plate of metal, — of silver, for

276 Inquiries concerning the Mode of the

instance, — a quarter of an inch thick, and if the hot cube
be placed upon this plate immediately above the cold
cube, the heat will descend through the metallic plate with
a certain degree of facility, and will heat the cold cube.

If a dry board of the same thickness with the metallic
plate be substituted in its place, the heat will descend
through the wood, but with much less celerity than
through the plate of silver.

But if a stratum of water or of any other liquid be sub-
stituted in place of the metallic plate or of the board,
the result will be very different. If, for instance, the cold
cube being placed in a large tub resting on the middle
of its bottom, the hot cube be suspended over it by
cords, or in any other manner so that the lower surface
of the hot cube be immediately above the upper surface
of the cold cube, at the distance of a quarter of an inch,
and the tub be then filled with water at the same tem-
perature as that of the cold cube, the heat will not
descend from the hot cube to the cold one through the
stratum of water of a quarter of an inch in thickness that
separates them.

We may with propriety call silver a good conductor of
heat, and dry wood a bad conductor ; but what shall we
say of water ? I have called it a non-conductor for want
of a more suitable term, but I always felt that that word
expresses but imperfectly the quality that was meant to
be designated.

In the experiment of the two cubes plunged in water,
if the hot cube be placed below and the cold cube above
it, the heat will not only be communicated from the hot
to the cold cube, but it will pass even more rapidly than
when the two cubes are separated by a plate of silver.
But in this case it is evident that the heat is transported

Propagation of Heat in Liquids. 277

by the ascending currents which are formed in the liquid
in consequence of the heat which it receives from the
hot body.

The existence of these currents in certain cases has
been known a long time, but philosophers have not been
sufficiently attentive to the many curious phenomena
that depend upon them. It has not even been suspected
with what extreme slowness heat passes in fluids, from
particle to particle, de proche en proche, in cases where
the effects of such communication become sensible.

For some time after I had engaged in this interesting
inquiry, I conceived that this kind of communication
was absolutely impossible in all cases ; but a more atten-
tive examination of the phenomena has convinced me
that this conclusion was too hasty. As early as the be-
ginning of 1800, in a note published in the third edition
of my Seventh Essay, I announced a conjecture that the
non-conducting power of fluids might perhaps depend
solely on the extreme mobility of their particles ; and it
is certain, if this conjecture is well founded, liquids must
necessarily become conductors of heat (though very im-
perfect ones) in all cases where this mobility of their
particles is destroyed, as well as in these rare but yet
possible cases, where a change of temperature can take
place in a liquid without giving its particles any ten-
dency to move, or to be moved out of their places.

The unequivocal results of a great many experiments
have shown, that in ordinary cases, and perhaps in all
cases where heat is propagated in considerable masses of
fluids, its distribution is accomplished precisely in the
manner that the new theory supposes, that is to say, by
currents. And it is certain that the knowledge of that
fact has enabled us to explain in a satisfactory manner

278 Inquiries concerning the Mode of the

several interesting phenomena of nature, which before
were enveloped in much obscurity.

When a hot solid body is plunged in a cold liquid,
there can be no doubt concerning the existence of the
vertical ascending currents which are formed in the
liquid, and which convey to the surface the heat which
its particles have received ; but with respect to the strata
of liquid situated under the hot body, are they or are they
not heated by this body by means of a direct communication of
heat from above downwards^ from f article to particle,, these
particles remaining in their places? This is a question on
which philosophers are not yet agreed. As it is a ques-
tion of great importance, I have long meditated on the
means of deciding it ; and after several unsuccessful
attempts, I have at last succeeded in making an experi-
ment which I think is decisive.

As the apparatus which I used for this experiment,
and which I have the honour of laying before the assem-
bly, is somewhat complicated ; and as it is indispensably
necessary to be intimately acquainted with it, in order to
form a judgment concerning the degree of confidence
which the results of the experiment may deserve, — it is
necessary to give a detailed description of this machinery.
The annexed figure gives a distinct representation of its
principal parts. It is drawn on a scale of a quarter of
an inch to the inch, English measure.

A B (Plate VII.) is a board, of oak, seen in profile;
it is ii inches thick, 18 inches long, and n inches
in breadth. It serves to support two square upright
pillars, C C, i8J inches in height and i| inches square.
They are firmly fixed in the board at the distance of 1 1
inches asunder, and serve to support the two cross-
pieces, D E, F G, at different heights.

Propagation of Heat in Liquids. 279

These cross-pieces are each pierced with two square
holes, at the distance of 1 1 inches one from the other,
into which the upright pillars C C enter, and the cross-
pieces are supported at any height that is required, by
means of a screw of compression. These screws are
represented in the figure.

The cross-piece F G, which is represented in pro-
file, is 17 inches in length, and i| inches thick, and 3
inches in breadth. It is pierced in the middle by a
cylindrical hole of 2 inches in diameter.

The cross-piece D E is 17 inches in length by ij
inches in thickness. It is 3 inches wide at each end and
6 inches in the middle, where it is pierced by a circular
hole 5 inches in diameter.

The cross-piece D E serves to support the annular
vessel H I, of which a vertical section passing through
its axis is seen in the figure. This vessel, formed of
thin brass plates, is 5 inches in diameter without, 3
inches in diameter within, and 27^ inches in depth.
This vessel is filled with water during the experiments
to the height of 2 J inches ; and its form is such, that, if
the water that it contains were frozen into a solid mass
of ice, this piece of ice would have the form of a tube
or perforated cylinder of i inch in thickness and 2|-
inches high by 5 inches in diameter without. Its cylin-
drical cavity would be precisely 3 inches in diameter.

K L is a vertical and central section of a cylindrical
vessel of tin of 10 inches in diameter by 4^- inches in
depth. It is filled with water to the height of 4 inches,
as it is seen in the figure.

The cross-piece D E is placed at such a height that
the bottom of the annular vessel H I is plunged a
quarter of an inch under the surface of the water con-
tained in the great cylindrical vessel K L.

280 Inquiries concerning the Mode of the

In the axis of this last vessel is placed a small hemi-
spherical cup of wood 2 inches in diameter without and
|- of an inch thick. It is kept in its place by a short
vertical tube of tin, soldered to the bottom of the cylin-
drical vessel K L, into which the stalk of the cup fits
tightly.

The middle of the cavity of this cup is occupied by
the bulb of a small mercurial thermometer of great sen-
sibility. Its tube, which has an ivory scale, is laid down
horizontally, and fixed in one side of the cup, through
which the tube passes, in such a manner that the lowest
part of the bulb is elevated ^ of an inch above the
bottom of the cup. The diameter of the bulb being
T37 of an inch, and the hemispherical cup having % inch of
radius within, it is evident that the upper part of the
bulb is j1^- of an inch below the level of the brim of the
cup that contains it. To avoid charging the figure with
too many details, the scale of the thermometer is not
drawn, but the tube is distinctly represented.

The horizontal cross-piece F G serves to support a
very essential part of the apparatus, which remains to be
described.

This cross-piece supports, in the first place, a vertical
tube of wood, M, 6T% inches in length and 2 inches in
diameter without. Its interior diameter is i^ inch.
This tube is supported by a projecting collar (repre-
sented in the figure), 2-| inches in diameter, which rests
on the cross-piece F G. It is a vertical and central sec-
tion of this tube that is represented in the figure, and it
is dotted in order to distinguish it from the surrounding
parts of the apparatus.

The lower part of this tube is plunged T67 of an inch
under the surface of the water in the large cylindrical

Propagation of Heat in L iquids. 2 8 1

vessel K L ; and it is placed precisely above the wooden
cup in the prolongation of its axis, the lower extremity
of the tube being at the distance of ^ of an inch above
the horizontal level of the brim of the cup.

On the top of the tube of wood is placed a cylindrical
vessel N O, of sheet brass, 3 inches in diameter, 2}
inches high, which has a lateral spout, P Q, placed a
little above the level of its bottom.

From the middle of the bottom of this vessel, there
descends a cylindrical tube of brass, 6 inches in length
and i inch in diameter, which ends below in a hollow
conical point, as represented in the figure.

R S is a vertical and central section of a funnel of
brass, which ends below in a cylindrical tube of T3g- of an
inch in diameter and 6T6-g- inches long. This funnel is
kept in its place in the axis of the cylindrical vessel
N O by the exact fitting of its upper edge upon that
of the vessel into which it is adjusted.

The lower end of the tube of this funnel is surrounded
by a projecting edge or flange in the form of a hollow
inverted cone. The diameter of this conical projecting
brim above, at its base, is ^ of an inch, and it is sol-
dered below to the end of the tube.

When hot water is poured into the funnel, this liquid,
descending by the tube of the funnel, strikes against
the inner surface of the hollow inverted cone which ter-
minates the vertical tube that belongs to the vessel
N O, and then, rising up through this last tube into that
vessel, it runs off by its spout. It was with a view to
force this water to come into more intimate contact with
the hollow cone that the projecting edge, in form of an
inverted cone, was added to the lower end of the tube of
the funnel.

282 Inquiries concerning the Mode of the

The object chiefly in view in the arrangement of this
apparatus was to give to the conical point which termi-
nates the vertical tube of the vessel N O, an elevated
temperature, which should remain constant during some
time, for the purpose of observing if the heat, which
must necessarily be communicated by this metallic point
to the small quantity of water with which it is in con-
tact, and which is confined in the lower part of the
wooden tube M, would descend, or not, to the ther-
mometer which was placed in the wooden cup.

There was still one source of error and uncertainty
against which it was necessary to guard. The heat
communicated through the sides of the wooden tube to
the water contained in the great cylindrical vessel K L
might be transported to the sides of that vessel, and,
being then communicated from above downwards
through these sides, might heat successively the lower
strata of the liquid, and at last that stratum in which the
thermometer was.

It was to prevent this that the annular vessel H I was
used, and it performed its office in the following man-
ner: The particles of water contained in the great vessel
K L, which, being in contact with the exterior surface of
the wooden tube, were heated by that tube, could not fail
to rise to the surface, and there they 'necessarily came
into contact with the interior sides of the annular vessel,
to which they communicated the excess of heat they had
received from the wooden tube.

This heat, passing readily through the thin metallic
sides of that vessel, was given off as fast as it was re-
ceived to the particles of cold water contained in the
vessel which were in contact with its sides, and these
particles, rising to the surface of the water con-

Propagation of Heat in Liquids. 283

tained in the annular vessel in consequence of their
acquired heat and levity, the progress of the heat from
the wooden tube to the sides of the large vessel K L,
was interrupted, and all the heat that passed through the
sides of the wooden tube was by these means turned aside
in such a manner that it could no longer disturb the
progress of the experiment, nor affect the certainty of its
results.

Before I proceed to give an account of the result of
this inquiry, I shall take the liberty to recall the atten-
tion of the Assembly to the most important circum-
stances of the experiment.

On pouring boiling water in a small uninterrupted
stream into the funnel, the hollow conical point which
terminates the vertical tube belonging to the vessel N O
was heated, and kept at a constant temperature little
under that of boiling water.

This point was surrounded by a small quantity of
water contained in the cavity of the lower part of the
wooden tube, and as this water could not change its
place nor be displaced by the surrounding cold water,
being enclosed and protected by the sides of the wooden
tube, it would necessarily become very hot in a short
time.

But this small quantity of hot water lay immedi-
ately upon a stratum of cold water, which separated it
from the bulb of the thermometer, placed directly under
it at the distance of only half an inch.

If heat could pass in the water from above downwards,
it would no doubt pass from the lower stratum of hot
water contained in the open end of the wooden tube to
the bulb of the thermometer, which lay immediately
below it and at so small a distance.

284 Inquiries concerning the Mode of the

Three experiments were made with this apparatus,
and always with exactly the same results. In the first,
a stream of boiling water was poured into the funnel
during 10 minutes ; in the second, during 12 minutes;
and in the third, during 15 minutes.

The thermometer, whose bulb was in the wooden cup,
remained at perfect rest from the beginning of the experi-
ment to the end of it without showing the slightest sign
of being in any way affected by the hot water which was
so near it.

These experiments were made at Munich in the month
of July, 1805 ; the temperature of the air and of the
water contained in the vessel K L being 70° Fahrenheit.

A small thermometer placed in the water contained in
the annular vessel H I, in such a manner that its bulb
was scarcely submerged, marked that this water had
received a little heat in each of the three experiments.

Another similar thermometer placed in the water con-
tained in the large vessel K L, immediately under its
surface and near one side of the vessel, showed that this
water had not acquired any sensible increase of temper-
ature during the experiments.

From the results of these experiments we are au-
thorized to conclude, that heat does not descend in
water to a sensible distance, in cases where the particles
of the liquid which receive heat are exposed to be dis-
placed and forced upwards by the surrounding colder
and denser particles, that is to say, in all the cases (and
they are the most common) where heat is applied to the
strata of the liquid situated under its surface.

But the results of the experiments in question do not
prove that heat cannot in any case descend in water; and
still less can it be inferred from them, that all direct com-

Propagation of Heat in Liquids. 285

munication of heat in this liquid, from particle to par-
ticle, de proche en proche, is impossible. They do not
even prove that heat did not descend, to a small distance^
below the level of the end of the wooden tube in these
experiments ; for it is certain that that event could take
place without the thermometer, which was situated a
little lower, being in any way affected by that heat.

The particles of water situated at a very small distance
below the level of the lower end of the wooden tube,
being heated by the stratum of hot water which rested
immediately on them, might have been displaced by the
surrounding colder and denser particles, and forced to
rise to the surface ; and these last being in their turn
heated, forced upwards and replaced by other cold par-
ticles, it is evident that the heat could not make its
way downwards so far as to arrive at the thermometer
through a stratum of liquid, which, though apparently
at rest, was nevertheless in part composed of particles
which were continually changing.

I have long suspected that the apparent impossibility
of a direct communication of heat between neighbouring
particles of fluids depends solely on the great mobility
of those particles (see note, p. 202, Vol. II. of my
Essays, jd edition, London, 1800); and if this sus-
picion be well founded, it is certain that when this
mobility ceases, the effect which depends on it must
cease likewise.

When I speak of the mobility of the particles of a
liquid amongst each other, I am very far, as I have
already observed, from supposing that individually they
can enjoy a free motion. I was formerly of that opinion,
but a more attentive investigation of the phenomena has
convinced me that I was mistaken. But although one

286 Inquiries concerning the Mode of the

individual particle of a liquid can never be put in mo-
tion in consequence of a change of its specific gravity
occasioned by a change of temperature, yet what cannot
happen to a single particle may easily and must neces-
sarily happen to small masses of the liquid consisting
of a great number of these particles united, as is abun-
dantly proved by the currents which are so easily excited
by the contact of a hot or cold body plunged in a
liquid.

The force by which the particles of liquids adhere to-
gether is very great, and it is more than probable that it
is the cause of many very interesting phenomena, and
amongst others of the suspension of the heavy bodies
which much lighter liquids so frequently hold in solu-
tion.

From the result of an experiment which I made some
years ago in order to determine the measure of the vis-
cosity or the want of perfect fluidity in water at the tem-
perature of 64° F., I found reason to conclude that a
solid body, having a surface equal to 368 square inches,
which should weigh only one grain Troy more than an
equal volume of water, would remain suspended in that
liquid ; and from this datum it is easy to find by calcu-
lation what ought to be the diameter of a small solid
spherule of the heaviest matter, — of gold, for instance,
— in order to its remaining suspended in water in con-
sequence of the viscosity of that liquid.

Having made this calculation in order to satisfy my
curiosity, I found that a solid spherule of pure gold, of
the diameter of ^"oWir (or exactly ^-g-grT^) °f an incn>
ought to remain suspended in water in consequence of
the adhesion of the particles of that liquid to each other.
But I shall return to this subject on a future occasion.

Propagation of Heat in Liquids. 287

[THE preceding paper is printed from Nicholson's Journal, XIV.
(1806), pp. 355- 363. The paper, in a somewhat modified form, ap-
pears in the Bibliotheque Britannique (Science et Arts), XXXII. ( 1 806),
pp. 123-141, to which periodical it was contributed by Count Rum-
ford in manuscript, which was translated by the French editor. In
this version the beginning of the paper is much abridged ; but in the
latter part Rumford elaborated his speculations in regard to the effects
produced by viscosity on the propagation of heat in liquids more at
length than in Nicholson's Journal. In order to give fully his views
on the subject, this portion of the French paper is here appended.

" If there is no direct communication of heat between contiguous par-
ticles of water at different temperatures, then the apparent mean tem-
perature, which results so quickly when cold water is poured into a
mass of warm water, must be produced by currents caused by differ-
ences in the specific gravity of the masses of the liquid at different tem-
peratures. And if it is asked why the hot and cold particles, thus mixed
together, do not separate again, on account of the difference in their
specific gravity, we must seek for the reason in the imperfect fluidity of
the water. This cause may keep the particles of water suspended, out
of their natural position, just as it keeps in suspension, as well in other
liquids as in water, particles of foreign substances, which, although
specifically heavier or specifically lighter than the medium, are so small
that the amount by which they are heavier or lighter than the surround-
ing liquid is not sufficient to overcome its viscosity.

" This want of perfect fluidity, a condition common to all liquids" in
different degrees, gives rise to a great number of very interesting phe-
nomena, and it is a subject worthy of the close attention of philosophers.

" From the result of an experiment which I made a long time ago in
order to determine the measure of the viscosity of pure water at the
temperature of 64° F., that is the force necessary to separate contigu-
ous particles of that liquid, I found reason to conclude that a solid body,
having a surface equal to 368 square inches, which should weigh only
one grain Troy more than an equal volume of water, would remain sus-
pended in that liquid ; and from this datum it is easy to find, by calcu-
lation, what ought to be the diameter of a small solid spherule of the
heaviest matter, — of gold, for instance, — in order to its remaining
suspended in water in consequence of the viscosity of that liquid : and

288 Inquiries concerning the Mode of the

it is also easy to prove, from the inflection which light experiences in
passing over the surface of an opaque solid body, that a considerable
quantity of opaque solid matter could be held suspended in water
without sensibly diminishing its transparency, and without changing its
colour; that is to say, without giving any indication of its presence.*

"I have long suspected that the suspension of solid substances which
are held in solution by liquids is due solely to the imperfect fluidity of
the solvents, and the results of a great number of experiments which I
have made to elucidate this important subject have always confirmed
this opinion. Since, then, bodies specifically heavier than water can
nevertheless remain suspended in that liquid, there can be no difficulty
in admitting that isolated particles of cold water can equally remain
motionless in the warm water with which they find themselves acci-
dentally mixed. But although this may be true of the individual par-
ticles, the same principle cannot apply to masses of sensible size made
up of a great number of these particles. These masses must yield to
the natural effect of the differences in their specific gravity, and form
currents which will be ascending or descending according as the masses
in question are warmer or colder than the surrounding liquid ; and
these currents must contribute very largely to the intimate mixture of
the particles at different temperatures, and must soon bring about a cer-
tain uniform temperature throughout the entire mass of the liquid.

" I said this uniformity of temperature may be only apparent ; because,
if water is really a perfect non-conductor of heat, the particles of cold
water, at least those which have not been warmed by contact with the
walls of the vessel in which they are contained, ought to remain cold
in spite of their more or less intimate mixture with the warm particles;
but, notwithstanding this fact, the mean temperature of the liquid, as
shown by the thermometer, will be precisely the same as if there had
been an actual communication of heat among the particles.

" Long after I had had reason to persuade myself that all the heat ac-
quired by liquids, when they are warmed, is communicated by the ves-
sel containing them to the individual particles, which are successively

* In order to satisfy my curiosity, I found, by calculation, the diameter which a
small solid spherule of gold ought to have in order to its remaining suspended in
water in consequence of the viscosity of that liquid. I found this diameter to be
— ^ — , or, in round numbers, — — of an inch ; that is to say, about two hundred
times smaller than the diameter of a single fibre of raw silk, as spun by the worm, —
an object which is so fine as scarcely to be visible.

Propagation of Heal in Liquids. 289

brought into contact with its sides by the currents formed in the mass
of the liquid, — a long time, I say, after I had adopted this opinion, I
continued to doubt whether single particles of warm water, when com-
pletely surrounded by particles of cold water, and remaining undis-
turbed in the midst of them, might not be able to communicate to
these neighbouring particles that excess of heat which the shortness of
the time of contact when the particles are in motion does not allow
them to impart to each other. Indeed, if the property of water by
which it is an apparent non-conductor of heat depends solely upon
the extreme mobility of its particles, it is evident that the communica-
tion of heat, under the circumstances just supposed, must necessarily
take place ; and it must be remembered that in this case the fluidity of
the liquid, as far as the particles in question are concerned, is as truly
destroyed as if the entire mass were converted into ice.

"The inquiry as to the non-conducting power of fluids — an inquiry to
which my experiments and observations have given rise — is, no doubt,
of great interest to science ; and, whatever may be the final result of
its investigation, I shall regard myself fortunate in having drawn the
attention of a great number of enlightened philosophers towards an
object which was long neglected, and which was so worthy of being
studied."]

»9

EXPERIMENTS AND OBSERVATIONS

ADHESION OF THE PARTICLES OF WATER TO
EACH OTHER.

WE often see small bodies of a specific gravity
much exceeding that of water float upon the
surface of that fluid. Such, for example, are very small
grains of sand, fine filings of the metals, and even small
sewing-needles.

So extraordinary a phenomenon has not failed to
excite the attention of philosophers. It formed a sub-
ject of discussion at the last sitting of the Class, and as
this remarkable fact is intimately connected with a sub-
ject of research upon which I have been long employed,
I shall here give an account of some experiments I have
made to elucidate the same, which have afforded results
of considerable interest.

Suspecting that the presence of air adhering to these
small floating bodies, which is generally considered as
the cause of their supension, is not indispensably neces-
sary for the success of the experiment, I made the fol-
lowing experiments.

Experiment No. i. — Having half filled with water a
wine-glass one inch and a half in diameter at its edge,
I poured on the surface of the water a stratum of sul-
phuric ether, one inch and a half in thickness ; and
when the whole was perfectly still, I took a very small

On the Adhesion of the Particles of Water, etc. 291

sewing-needle with a pair of pincers, which I introduced
below the ether, where, holding it horizontally at a small
distance from the surface of the water, I let it fall. The
needle descended to the water, and there floated on its
surface.

Experiment No. 2. — Having melted some tin, I poured
it into a spherical wooden box, and, shaking it strongly,
the metal in cooling was reduced to powder, which was
then sifted.

On examining this powder with a magnifier, it ap-
peared composed of small spherules of different sizes ;
but these spherules were too small to be distinguished
by the naked eye.

I took up on the point of a spatula a very small
quantity of this metallic powder, and poured it gently
from the height of a quarter of an inch on to the surface
of the ether which rested upon the water in the glass.

The powder descended wholly through the ether, and
when it arrived at the surface of the water, it remained
floating.

Experiment No. 3. — Having poured a large drop of
mercury into a china plate, I broke it into a great num-
ber of small spherules.

In order to take up and convey these small spherules
one by one, I made a small tool or shovel out of a piece
of brass wire, five inches long, and about one twentieth
of an inch in diameter, bent to a right angle at one
of its extremities. This bent part was about a quar-
ter of an inch long, and was hammered flat, sharpened,
and made a little concave.

By means of this tool I took up a small spherule of
mercury, about one sixtieth of an inch in diameter, which
I carefully conveyed into the stratum of ether to the

29 2 On the Adhesion of the Particles

distance of about one twentieth of an inch from the sur-
face of the water beneath ; and there, by a little inclina-
tion of the instrument, I caused the spherule of mercury
to roll gently on to the surface of the water.

The spherule descended to that surface, and there re-
mained floating.

When the eye was placed lower than the surface of
the water, and the spherule was observed by looking up-
wards through the glass, it appeared suspended in a kind
of bag, a little below the level of the surface.

Having placed a second spherule of mercury on the
surface of the water, it immediately moved towards the
former, and, approaching it with an accelerated motion,
fell down into the same cavity, which then became lon-
ger ; but the two spherules did not unite.

Having placed a third spherule on the surface of the
water, it joined the two others; but the weight of these
three spherules together being too great to be supported
by the kind of pellicle which is formed at the surface of
the water, the bag was broken, and the spherules de-
scended through the water to the bottom of the vessel.

When the experiment was made with a spherule of
mercury a little larger, namely, about the fortieth or fif-
tieth of an inch, it never failed to break the pellicle of
the water, and to descend through that liquid to the
bottom of the glass. But when the viscidity of the
water was increased by dissolving a small quantity of
gum-arabic in it, still larger spherules of mercury were
supported at the surface of the liquid.

A spherule of mercury of a proper size to be sup-
ported by water at its surface, if placed gently there,
would not fail to make its way through the pellicle of
the water, if let fall from too great an height.

of Water to each other. 293

All the preceding experiments were repeated with
a stratum of essential oil of turpentine, and afterwards
with one of oil of olives, placed on the water contained
in the glass instead of the ether, and the results were
in all respects similar. I thought, however, that the
spherules of mercury which were suspended upon the
water were rather larger when the surface of the water
was covered with oil than with ether; and in the ex-
periments made with the powder of tin poured on the
oil, the finest parts of the powder in very small quan-
tity floated on the surface of the oil.

Experiment No. 4. — Having found means to place a
stratum of alcohol on the water contained in the glass,
so that the two liquids appeared as distinct from each
other as when the upper stratum was oil, I poured
from a very small height a small quantity of the very
fine powder of tin upon the alcohol.

This powder totally descended through the alcohol
and the water, without giving the smallest indication of
its having been subjected to any resistance at the sur-
face of the latter fluid.

Though this last surface appeared .very distinctly to
the eye, yet, judging from the manner in which the
metallic powder descended to the bottom of the glass,
I am disposed to think that it had no existence ; and, in
fact, it is probable that it was destroyed by the chemical
action of the alcohol in contact with the water.

In order to examine more accurately the kind of film
which is formed at the surface of the water, I made the
following experiment.

Experiment No. 5. — In a cylindrical glass with a solid
foot, the diameter of which was fourteen lines, or about
an inch and a half English, and ten inches in height, I

294 OH t?ie Adhesion of the Particles

poured very limpid water to the height of nine inches,
and on the water I placed a stratum of ether, three lines
or twelfths of an inch in thickness. I then placed on
the surface of the water a number of small solid bodies,
which remained suspended, such as a small spherule of
mercury, some pieces of extremely fine silver wire, two
or three lines in length, and a little of the powder of
tin. When the whole was perfectly tranquil, I took
the glass in both hands, and carefully raising it, I turned
it three or four times round its axis with considerable
rapidity, keeping it in a vertical position. All the small
bodies suspended at the surface of the water turned
round along with the glass and stopped when it was
stopped ; but the liquid water below the surface did
not at first begin to turn along with the glass, and its
motion of rotation did not cease all at once upon stop-
ping that of the vessel. In fact, all the appearances
showed that there was a real pellicle at the surface of the
water, and that this pellicle was strongly attached to the
sides of the glass so as to move along with it.

Upon examining with a good magnifier, through the
stratum of ether, the small bodies which were supported
at the surface of the water, the existence of this pellicle
could no longer be doubted ; more particularly when it
was touched with the point of a needle. For in this
case all the small bodies were observed to tremble at the
same time.

Having left this small apparatus at repose in a quiet
chamber until the stratum of ether was entirely evap-
orated, I examined it again with a magnifier. The sur-
face of the water was precisely in the same state ; the
small solid bodies were still there, in the same situation,
and at the same distances from each other.

of Water to each other. 295

When this experiment was made with a cylindrical
glass of much larger diameter, the effects of the adhesion
of the pellicle of the water to the sides of the vessel
were much less sensible with regard to those parts of
the same which were situated near the axis. It was dif-
ficult to prevent the small bodies which floated on the
surface of the water from uniting, and when united they
often formed masses too heavy to continue to be sup-
ported; and, having broken the pellicle of the water,
they fell to the bottom of the vessel.

If the particles of water adhere strongly to each other,
it appears to me to be a necessary consequence that a
kind of pellicle will be formed at the upper surface of
the liquid, and even at all its surfaces, whatever may be
in other respects the mobility of these particles, or rather
of the small liquid masses composed of a great number
of them, when they are remote from the surface and
possess their fluidity without impediment.

When a small solid body, placed on the surface of
water, becomes wetted, it immediately descends beneath
the pellicle, which no longer opposes its resistance.
At this period the viscidity of the water begins to mani-
fest itself in a very different manner, but with infinitely
less effect than when it acts at the confines of the
liquid. But it is not yet time to inquire into this part
of our subject.

With a view to render sensible the resistance which
the pellicle of the inferior surface of a stratum of water
opposes to a solid body which passes through that
stratum by falling freely downwards, I made the follow-
ing experiment.

Experiment No. 6. — Having filled a small wine-glass
to about half its height with very pure mercury, I

296 On the Adhesion of the Particles

poured a stratum of water of three lines in thickness
upon the mercury, and upon that a stratum of ether of
two lines.

When the whole was at rest, I took with the small
tool before described a spherule of mercury of about one
third of a line in diameter, and let it fall through the
stratum of ether.

This spherule, being too heavy to be supported by the
pellicle at the superior surface of the water, broke it, and
descended through that fluid ; but upon its arrival at
the inferior surface it was stopped, and remained there,
preserving its spherical form.

I moved this spherule with the extremity of a feather,
and even compressed it; but it always preserved its
form without mixing with the mass of mercury on which
it appeared to rest.

It was no doubt the pellicle of the inferior surface of
the stratum of water which prevented this contact, and
as this pellicle was supported by the mercury on which
it rested, I was not at all surprised to find that it could
support, without being broken, a spherule of mercury
much larger than the pellicle of the superior surface
could support.

In order to satisfy myself that the viscidity of the
water was the cause of the suspension of this mercurial
globule at the bottom of that fluid, I repeated the ex-
periment and varied it by substituting water containing
a certain quantity of gum-arabic, in solution, in the
place of pure water ; and I found, in fact, that much
larger spherules were supported when the viscidity of
the water was thus augmented.

To prove this fact in another manner, I again varied
the experiment, by placing a stratum of ether im-

of Water to each other. 297

mediately upon the mercury. The particles of this
liquid appear to have very little adhesion to each other;
for which reason I imagined that the kind of film that
would be formed at its surface must have very little
force. The results of my experiment fully confirmed
this conjecture.

The very smallest spherules of mercury which I let
fall through this liquid seldom failed to mix immediately
with the mass of mercury on arriving at its surface,
where they entirely disappeared ; and I have never suc-
ceeded in causing either a spherule of mercury, or the
smallest metallic particle, or any other body of greater
specific gravity than ether, to swim upon its surface.

The results of the experiment were not perceptibly
different when alcohol was substituted in the place of
ether.

It is known that ether evaporates very rapidly. Is
not this another proof that the particles of this liquid
adhere to each other with much less force than those of
water ? But the following experiment proves this fact
in a decisive manner.

Experiment No. 7. — Having half filled a small cylin-
drical glass with mercury, I placed on the mercury a
stratum of ether four lines in thickness, and blew upon
the ether with a pair of common bellows.

In less than one minute the ether. had disappeared.

The same experiment being made with water, no sen-
sible quantity of this fluid had disappeared in one min-
ute.

The objects which are before our eyes from the earli-
est periods of our lives seldom employ our meditation,
and not often our attention. We see, without sur-
prise, immense masses of dust raised by the winds and

298 On the Adhesion of the Particles

carried to great distances ; and at the same time we
know that every particle of this powder is really a stone,
almost three times as heavy as water, and of a size so
considerable that its form may be perfectly seen by
means of a good microscope.

And we see also, without surprise, that water, which is
much lighter than dust, and is composed of particles in-
comparably smaller, is not carried off by the wind in
the same manner.

In order to convince ourselves that the particles of
water do strongly adhere to each other, and that they re-
quire to do so in order to prevent the greatest confusion
in the universe, we need only figure to ourselves the in-
evitable consequences that would result from the want
of such an adhesion.

The particles of water would be raised and carried off
by the winds with infinitely more facility than the finest
and lightest dust. Every strong breeze setting in from
the ocean would bring with it a great inundation.
Navigation would be impossible, and the banks of all
the seas, lakes, and large rivers would be uninhabitable.

The adhesion of the particles of water to each other is
the cause of the preservation of that liquid in masses.
It covers the surface with a very strong pellicle, which
defends and prevents it from being dispersed by the
winds. Without this adhesion, water would be more
volatile than ether, and more fugitive than dust.

But the adhesion is also the cause of other phenom-
ena, which are of the greatest importance in the phe-
nomena of nature.

The viscidity which results from the mutual adhesion
of the particles of water renders this fluid proper to
hold all kinds of bodies in solution, as well the most

of Water to each other. 299

heavy as the lightest, provided always that they be re-
duced to very minute particles.

I have found, by a calculation founded on facts which
appear to me to be decisive, that a solid spherule of
pure gold, of the diameter of s¥-oV<5T °f an mcn>
would be suspended in water by the effect of its viscid-
ity, even though this small body should be completely
wetted and submerged in a tranquil mass of the fluid.

This viscidity, or want of perfect fluidity, which
causes it to hold every kind of substance in solution,
renders it eminently proper to become the vehicle of
nourishment to plants and animals; and we accordingly
see that it is exclusively employed in this office.

If the adhesion of the particles of water to each other
were to cease, and the fluidity of this body were to
become perfect, every living being would perish by
inanition.

May I be permitted to remark the simplicity of the
means employed by Nature in all her operations !

May I be permitted to express my profound admira-
tion and adoration of the Author of so many wonders !

[This paper is printed from Nicholson's Journal, XV. (1806),
pp. 52-56, 157-159' I73-I75-]

CONTINUATION

OF

EXPERIMENTS AND OBSERVATIONS

ON THE

ADHESION OF THE PARTICLES OF LIQUIDS TO
EACH OTHER.

BEFORE proceeding with the account of my ex-
periments, I shall take the liberty of going back
to a distant period, and of describing to the Class an
occurrence which first fixed my attention on this subject
and led me to engage in these researches.

Being occupied in the year 1786 with a series of
experiments on the oxygen gas which is disengaged from
water when this liquid mixed with various solid sub-
stances is exposed to the action of the sun's rays, among
the substances employed in my investigation was a
quantity of raw silk, wound from the cocoon on pur-
pose for this experiment, in a single thread, just as it is
produced by the silkworm.

It being necessary for completing my calculations that
I should determine with precision the amount of the
surface of this thread, which was almost two leagues in
length, and which weighed in the air only about 20
grains Troy, and having no means of measuring di-
rectly the exact diameter of the thread, I undertook to
calculate it from the known length of the thread and
the specific gravity of the substance.

It was in weighing this substance in water to ascertain
its specific gravity, that I encountered difficulties which

On the Adhesion of the Particles of Liquids, etc. 301

for a long time seemed to me insurmountable, but by
the exercise of patience and due precaution, I succeeded,
after somewhat long and difficult labour, in accomplish-
ing my object.

Those who are in the habit of making delicate experi-
ments with the hydrostatic balance will conjecture imme-
diately, before I have time to say it, that it was the air
which remained obstinately attached to the surface of
the silk when I weighed it in water, which rendered this
operation so difficult.

I do not wish to abuse the patience of the Class by
giving it a detailed account of all the means I was obliged
to try before finding an efficient remedy for this incon-
venience ; it will suffice to say, that the silk was weighed
finally in water, and with precision, and I will here add
in passing, that the specific gravity of this substance was
found to be to that of water as 1734 is to 1000. The
following phenomenon, however, which I noticed while
weighing the silk in water, struck me forcibly.

The silk being in the form of a skein about 6 inches
long, and tied loosely in order to allow the water readily
to enter among all the threads, it was hung from one of
the arms of an excellent hydrostatic balance in a large
mass of distilled water which had previously been freed
from air by long boiling.

The weight of the silk in this situation having been
determined, it was then placed, by means of silver pincers,
and without taking it from the water, into a small glass
vessel of oval form, about 2 inches in diameter and 3
inches long, and weighed again.

The weight of the silk when weighed in the small
glass vessel was sensibly greater than when it was weighed
out of the vessel in the same large amount of water, and

302 On the Adhesion of the Particles

on repeating the experiment several times, the result
was always the same.

The following appeared to me to be a satisfactory ex-
planation of this phenomenon.

As silk is one of those substances which can be wet
by water, it is evident that the particles of the liquid
which were in immediate contact with the surface of the
thread must have remained attached to it. These parti-
cles, having become thus fixed and immovable, were in
contact with other particles which still enjoyed their free-
dom of motion, and these particles again were in contact
with others farther from the silk, and so on. Now, as
the fluidity of various liquids is evidently very different,
it is more than probable that no liquid possesses perfect
fluidity; consequently water does not: and if any force
whatever is needed to separate its particles and make
them move on each other, it is evident that, in this case,
if a solid body specifically heavier than water were
plunged into a quiet mass of this liquid, there should be
an apparent loss of weight on account of the viscosity
of the liquid, and this loss of weight would be in pro-
portion to the extent of the surface of the body.

If, for example, the body is suspended by a thread,
the thread will not support all the excess of the weight
of the body over the weight of a mass of the liquid
equal to the volume of the solid body; fora part of this
excess would be supported by the adhesion which exists
among those particles of the liquid which are in contact
with the particles attached to the surface of the body.

This appeared to me too evident to need demonstra-
tion or even further explanation.

In one of the experiments in question, the silk being
suspended freely in the water, it was in contact with this

of Liquids to each other. 303

liquid by a very great surface (about 550 square inches),
and its loss of weight on account of the viscosity of the
liquid was very sensible ; but when it was weighed in a
small vessel which had been previously counterpoised
very exactly in the water, the arm of the balance sup-
ported all the excess of the weight of the silk over that
of an equal bulk of water without any diminution.

The results of these experiments have furnished data
for calculating, with sufficient exactness, the degree of
force with which particles of water adhere to each other,
when it is a question of causing them to move one
upon the other at a temperature of about 60° F., and I
found it to be such that a solid body specifically heavier
than water, having a surface equal to 368 square inches
(English), when submerged in water, ought to lose in
weight, on account of the viscosity of the water, an
amount equal to I grain Troy.

The discovery of this fact has put me in position, not
only to prove that all bodies in nature, the heaviest as
well as the lightest, can be suspended and supported
in still water, on account of its viscosity, provided they
are reduced to a sufficiently small size, but also to deter-
mine by calculation that a solid spherule of gold about
STTiF^nnr °f an ^ncn 'm diameter would remain sus-
pended in this manner, as I have already announced to
the Class in the memoir read at the session held on the
1 6th of June, the past year (1806).*

Having announced facts as remarkable as these, I re-
frained from entering into more minute details. I did
not even think it necessary to observe that, even if I
should have deceived myself somewhat in my estimation
of the force of cohesion of the particles of water, still, if

* This calculation will be found in a note at the end of this paper (page 315).

304 On the Adhesion of the Particles

it be only granted (and this cannot be called into ques-
tion) that the fluidity of this liquid is not absolutely
perfect, but that a certain amount of force is necessary,
no matter how small it may be, to separate the particles
from each other, this alone will be sufficient to establish
all that I have asserted with regard to the necessary con-
sequences of the adhesion of the particles of liquids to
each other.

It would only be a question in each case of supposing
that a solid body immersed in any liquid be reduced to
a sufficiently small size, and it could be proved that it
must necessarily remain suspended there. But it is
easy to see that the greater the force of cohesion be-
tween the particles of a liquid, the more capable this
liquid becomes of holding in suspension foreign bodies
of all sorts.

Water appeared to me to possess this quality to a re-
markable degree ; and it is certain that if there had been
need of a vehicle for the nourishment of plants and ani-
mals, one capable of holding in suspension and of trans-
porting from one place to another all sorts of substances,
very different in weight and size, without affecting them
chemically, it would never have been possible to find one
more fitted for this purpose than water.

Is it not probable that this is one of the principal de-
signs of the existence of this liquid in the economy of
Nature ?

Being accustomed to see traces of great wisdom and
of admirable simplicity in all those dispositions of
Nature which I have been able to comprehend, I have
been perhaps too much inclined, in my ordinary medita-
tions, to admit this conclusion. I must, however, con-
fess that the facts which have seemed to me to render it
probable have made a deep impression upon me.

of Liquids to each other. 305

Having found that the adhesion of the particles of
water to each other is so considerable, I was not slow to
perceive that this adhesion ought to manifest itself in a
very peculiar and sensible manner at the surface of the
liquid ; and it was then that I saw clearly that it might
be possible to explain in a satisfactory manner several
phenomena which have always been regarded as difficult
of explanation ; as, for example, the suspension of heavy
bodies of small size which appear to float on the surface
of the water ; the concave form taken on by the surface
of water when confined in a small vessel ; the change of
this form into convex when, the vessel having been filled
to the brim, more liquid is added; the suspension of
liquids in capillary tubes, etc.

I wrote, in the winter of 1800, a memoir on this sub-
ject, which I afterwards showed to several persons,
among others to Professor Pictet, of Geneva, when he
was in London in 1801 ; also to Sir Charles Blagden.
The reason for not publishing it at that time was that I
needed the assistance of profound analysis in order to
finish it.

When I arrived at Paris in the spring of 1802, I took
advantage of this occasion to consult the greatest geom-
eters of the century on the embarrassing question which
stood in my way. Four persons now present in this
Assembly can remember the circumstance. I desired to
know the form which the vertical middle section of a
drop of water, or other liquid substance, would take if
placed on a plane horizontal surface, supposing that the
liquid was restrained solely by the resistance of a pellicle
exerting a given force on its surface.

The problem appeared very simple, but its solution
is extremely difficult. I did not know at that time

306 On the Adhesion of the Particles

that Segner had attempted to solve it. I had no knowl-
edge of the memoir which he published on this subject
more than forty years ago in the first volume of the
memoirs of the Royal Society of Gottingen.

If I recall these facts, it is simply to prove that I have
not taken the liberty of occupying the attention of the
Class with a subject as difficult as a research on the
adhesion of the particles of liquids, and the various phe-
nomena dependent upon it, without previous medita-
tion ; and to prove that the opinions which I have ven-
tured to bring before it were adopted a long time since,
and have been often examined before being announced.

I have most certainly nothing more at heart than to
preserve the esteem and deserve the confidence of every
member of this illustrious Assembly. The favour which
they have shown me in giving me the right to sit among
them, which I regard in the light of a very distinguished
honour, as well as my respect for their talents, makes
me hold it as a sacred duty never to abuse their atten-
tion with trifles, or crude ideas, or opinions formed in
haste and ill-digested.

If I ventured to speak of the pellicle of the water, it is
because I really believed in its existence ; and I believe
in it still, and more firmly than ever.

Allow me to recall to the Class the phenomena which
have seemed to me to indicate its existence.

When I have seen little steel needles float on the sur-
face of this liquid without sinking into it, and even
without being wet ; when I have seen little globules of
mercury roll about on the surface of the water, then, com-
ing to rest, and sinking to a certain depth in the liquid
without, however, being -wet by it, remain as though
suspended in a small pocket ; when I have seen diminu-

of Liquids to each other. 307

tive spider-like insects, with long legs, run about over
the water without their feet sinking into the liquid, or
even being wet by it ; .when I have seen several minute
bodies at a distance from each other, resting upon the
surface of the water contained in a small vessel, tremble
every time that the surface of the water was touched
with the point of a needle, — I have been unable to
doubt the existence of a resisting surface, a sort of pel-
licle on the surface of the liquid.

There is another phenomenon which seems to me to
furnish a demonstrative proof of the existence of this re-
sisting surface. When water is heated in any vessel,
as soon as the liquid begins to become warm a consider-
able quantity of air is disengaged in the form of spheri-
cal bubbles, larger or smaller, which, passing through the
liquid from below upwards, escape into the air. Now
it very often happens that these little bubbles, after
having traversed the liquid with great rapidity, are
stopped all of a sudden when they have nearly reached
the surface.

What is it that stops these bubbles if not a resisting
pellicle at the surface of the liquid ?

I endeavoured, but in vain, to explain these facts, by
calling to my aid the atmospheric air. I saw clearly,
as I observed the little globule of mercury situated in
its little pocket, which sank sensibly lower than the
level surface of the water, and which was scarcely large
enough to hold the globule, — I saw, I say, that the film
of air, which we might suppose still attached to the sur-
face of the globule (if such a film really existed), could
not be thick enough to buoy up this heavy body and
make it float, hydrostatically, on the surface of the water.
But when to the testimony of these experiments and to

308 On the Adhesion of the Particles

that of several others of the same sort, which can readily
be performed, is added the evidence furnished by the
certain knowledge which we have of a strong adhesion
which exists among the particles of water, and of the
effect which this adhesion must necessarily produce at
the surface of the liquid, it seems to me impossible to
call into doubt the existence of a resisting layer extremely
thin at the surface of the water.

In announcing the. existence of a sort of pellicle at
the surface of liquids, I was far from thinking that it
was a new idea. I am aware that several philosophers,
and among others one of our celebrated colleagues, M.
Monge, had suspected it before I did, but I think that I
was the first to devise and perform decisive experiments
which have established the fact beyond doubt ; and it is
certain that the observations that I have published on
the effect which the adhesion of the particles of liquids
to each other must have in the economy of Nature, have
been borrowed from no one.

If the existence of a resisting film at the surfaces of
liquids has just been confirmed by the results of the
learned analytical researches of one of our celebrated col-
leagues, I ought, without doubt, to regard this event
as a proof very flattering to me, that my conjectures on
this subject were not ill founded.

I know that there are some persons who imagine
that the results of the calculations of the illustrious
author of the Mecanique Celeste on the rising of liquids
in capillary tubes are opposed to the opinions which
I have published on the adhesion of the particles of
liquids to each other ; but, as far as I have been able to
understand the data on which these calculations are
founded, it seems evident to me that the attraction with

of Liquids to each other. 309

which M. La Place supposes the particles of the liq-
uid to be endowed, does not differ essentially from
the force which I have designated by the name adhesion ;
and with regard to the pellicle, of which I have often
spoken, since the calculation of this learned geometrician
and philosopher is founded on the supposition that the
mutual attractions of the particles of the liquid situated
a certain distance below the surface of the liquid do not
contribute in any way to the rising of the liquid in a
capillary tube, nor to any other similar effects which he
has considered, it seems to me that the calculations of
M. La Place simply relate to the force of cohesion of
the layer of particles at the surface, or, in other words,
to the pellicle in question.

I must, however, confess that I am not sufficiently
well versed in the higher geometry to understand fully
the calculations of M. La Place on this subject ; and
I shall take good care not to pass judgment on them.
One must have, without doubt, a very profound acquaint-
ance with analytical methods to feel the force of his
demonstrations ; but I have such a high opinion of the
talents of this man, learned and worthy of esteem both
as a geometrician and as a natural-philosopher, that I
am always inclined to receive his opinions in matters of
science (as well as on every other subject) with the
greatest deference.

The researches to which I have sought to call the
attention of philosophers would be, no doubt, of less
importance if it was merely a question of the explana-
tion of a few facts, isolated and of little utility in their
applications ; but the adhesion of the particles of liquids
to each other is probably the cause of a great variety of
phenomena which affect us intimately ; and for this rea-

310 On the Adhesion of the Particles

son the subject must be regarded as very interesting.
It seems to me that it is to this adhesion, and to the
changes of its intensity, arising from different circum-
stances, that we must look for the proximate cause of
the growth of plants and of animals.

I have already observed that the strong force of adhe-
sion existing among the particles of water renders this
liquid peculiarly fitted to serve as the vehicle for con-
veying nourishment to all living beings; and I think
that I can show that this force of adhesion can be very
much decreased, that this actually happens very often,
and that one of the necessary consequences of such a
diminution would be the deposition or precipitation of
foreign matters which this liquid holds in suspension
on account of its viscosity.

If water ascends as sap in the capillary tubes of trees
as far as the leaves, it is possible that it there undergoes
some change, or that it there receives some addition,
which diminishes its viscosity, and disposes it in this way
to deposit matters which it holds in suspension and
which contribute to the growth of the plant.

If, during the digestion of food which takes place in the
stomach, water, aided perhaps by the gastric juice, seizes
at first upon nutritive particles of every sort which are
there found and holds them in suspension, is it not
possible that this liquid thus loaded, being mixed subse-
quently with a portion of bile, at its entrance into the
intestinal canal, is by this means rendered less viscous
and consequently better fitted to pass easily through the
lacteal veins, and more disposed to yield up the nutri-
tive particles as it enters into circulation ?

In case this conjecture be well founded, we ought,
undoubtedly, to find that a mixture of bile with water

of Liquids to each other. 31 1

would diminish, to a sensible extent, the viscosity of
this latter liquid ; and I actually found by experiments
which I shall have the honour of laying before the Class
at some future time in detail, that mixing i part of bile
with 1000 parts of water diminishes the adhesion of
the particles of water to each other nearly one third,
that is to say, in the ratio of 23 to 16 ; and that if i part
only of bile be mixed with 30,000 parts of water, the
diminution is still very apparent. In a mixture of i
part of bile with 300 parts of water, the adhesion in
question is reduced almost one half.

Milk is a liquid which seems to be already elaborated
and fitted to serve as nourishment for animals ; now I
have found, by decisive experiments, that the adhesion
among the particles of this animal fluid is less than that
among the particles of water in the proportion of 13
to 19!.

The adhesion of the particles of urine to each other
varies considerably. I have found it from 13 i to 16,
that of water being 19!.

Many persons have endeavoured to discover the nature
of diseases by the examination of the urine; no one,
however, as far as I know, has ever proposed to measure
the force of adhesion of its particles to each other, a
thing as easy to determine as it is useful to ascertain.

How interesting it would be to know the force of
adhesion of the particles of the gastric juice, of the pan-
creatic juice, of the lymph, and of the blood, both in
health and in the various diseases ! Of how great im-
portance would a knowledge of these facts be to the
physiologist and to the physician !

How useful it would be for those who study vegeta-
ble physiology to know the adhesive force of the parti-

312 On the Adhesion of the Particles

cles of the sap when rising and when descending, and
that too in the various seasons !

How much light would be thrown on all chemical
operations taking place in the wet way, if we could esti-
mate exactly the force of adhesion existing among the
particles of the various liquid agents which there come
into play !

How many wonderful reactions there are which seem
to depend on such a simple thing as the imperfect flu-
idity of liquids !

It seems to me that the facts which I have just an-
nounced are of such a character as to excite all our curi-
osity, and I hasten to make them public in order to
induce all those who cultivate the sciences to assist me
in these interesting researches.

I feel deeply that all that a single individual can effect
by his own labours during the course of his short life,
in extending the vast domain of science, is unfortunately
a very small matter. It is only by the simultaneous
efforts of a large number of men with good heads and
skilled hands that we can hope to see a sensible advance
of this great enterprise, of which men will never see the
completion ; and for this reason those who with true
love for science take more delight in seeing its progress
than in obtaining the pleasures of gratified vanity, ought
rather to seek to associate with themselves a great num-
ber of zealous and skilful co-labourers than to endeav-
our to do everything themselves.

Happily for the progress of this new branch of re-
search, the apparatus to be employed is portable, and of
great simplicity, and the experiments are as easy to per-
form as their results are decisive and satisfactory. In
general, the only thing needed will be an inverted si-

of Liquids to each other. 313

phon, with one of its capillary arms provided with a
scale for measuring the height of the liquid in this arm
above the level of the top of the column in the large
arm ; for it is now well established, by the results of
conclusive experiments, that the heights to which vari-
ous liquids rise in the same capillary tube are in pro-
portion to the degrees of force with which the particles
of the several liquids adhere to each other.

The experiments for determining the diminution pro-
duced in this force by a given increase of temperature
demand more complicated apparatus and special care.
The apparatus which I have used in this research is
before the Class. Since, in the present state of the physi-
cal sciences, we can hardly flatter ourselves that we are able
to take a single step in advance, except with the aid of
instruments devised with care and executed with the
utmost precision, I always regard it as a duty to afford
the Class an opportunity of judging, by its own obser-
vation, of the excellence of those used by me in such
new experiments as I have the honour of describing to
the Class.

I will show, presently, the way in which this appara-
tus is used, and I will give to the Class, at a subsequent
sitting, the account of the results of the experiments in
which it has been employed.

I will conclude this memoir with some observations
on a very important point, which should, perhaps, be
still further elucidated.

I have shown how I have proceeded in measuring
that sort of adhesion of the particles of water to each
other which produces the viscosity of this liquid, that
is, the force which must be exerted in order to cause
those particles to move on each other ; but we must

314 On the Adhesion of the Particles

by no means suppose that the same force will suffice to
separate these same particles from each other, when two
of them, which are in contact, are drawn in opposite
directions along the line passing through their centres.

The very considerable weight of a drop of water
which remains suspended from a solid body shows
evidently that this latter force is incomparably greater
than I have found the former to be. Now, when a solid
body rests on the surface of a liquid, it cannot pene-
trate into it without breaking the layer of particles
which are at this surface, and which may be considered
as forming a sort of pellicle ; in order to break this
pellicle, it is evidently necessary to separate the parti-
cles which compose it, by compelling them to withdraw
from each other directly or nearly in lines passing
through their centres, and it is for this reason that small
solid bodies specifically heavier than water remain on
the surface of this liquid without penetrating into it.

Likewise, when water issuing from the upper extrem-
ity of the shortened capillary tube of an inverted siphon
forms a small hemispherical mass, resting on the end of
the tube and attached to its walls, the convex surface of
this small mass of liquid is formed by a layer of parti-
cles which resist, with all the force of their attraction
for each other, every effort tending to separate them ;
and it is the resistance of this single layer of particles,
or of several layers resting immediately one upon an-
other, and together forming a sort of very thin pellicle,
which sustains the entire weight of the column of water
in the other arm of the siphon, which is situated above
the level of the surface of this small mass of liquid.

I have recently established this fact by means of an
experiment, which I regard as decisive.

of Liquids to each other. 315

Having found a way of placing in the middle of this
small hemispherical mass of water little isolated solid
bodies which displaced a great part of the liquid with-
out being wet by that which remained, this arrange-
ment produced no change, either in the exterior form
or in the dimensions of the little hemisphere, or in the
force displayed in resisting the pressure of the more
elevated column of water in the other arm of the
siphon.

NOTE.

(See page 303.) The following calculation, which is neither long
nor difficult to follow, may be of service in understanding what has
just been advanced.

A cubic inch of water, English measure, weighs 253.175 grains
Troy ; consequently a spherical mass of this liquid 10.8233 mcnes in
diameter, and which would have a surface of 368 square inches, would
weigh 168,060 grains. And since the specific gravity of gold is to
that of water as 192,581 is to 10,000, a sphere of gold of the same
diameter would weigh 3,236,525 grains in vacuo.

Now, a similar sphere weighed in water would lose of its weight
in vacuo an amount equal to the weight of a mass of water of a volume
equal to that of the sphere. It would weigh, therefore, 3,236,525

168,060=: 3,068,465 grains, a deduction being made for the slight

amount of its weight which it would lose on account of the viscos-
ity of the liquid.

Since the surface of the globe is equal to 368 square inches, we see,
from the result of the experiment of which we have just given an
account, that this decrease of weight must be exactly one grain.
Consequently the sphere suspended in water will weigh on the beam
of the balance only 3,068,464 grains, and it will lose -;J— of its
weight on account of the viscosity of the liquid.

Let us suppose, now, that the diameter of this sphere were 10 times
as small, or 1.08233 inches, and let us see according to what law the
effect produced on the viscosity of the liquid will be increased by this
diminution of volume.

The volumes and consequently the weights of spheres of different
diameters being as the cubes of those diameters, while their surfaces

3 1 6 On the Adhesion of the Particles

are as the squares of the same lines, it is evident that the weight of the
small sphere mentioned above must be 1000 times less than the weight
of the large sphere (the cube of 10 being 1000 and its square 100),
consequently the smaller sphere ought to weigh in water only 3068.465
grains (deduction being made for the effect of the viscosity of the
liquid), and its surface would be 3.68 square inches.

Since the diminution of weight which was due to the viscosity of
the liquid was only I grain when the surface of the sphere was 368
square inches, it is evident that this diminution ought to be loo times
smaller, or — of a grain, in the case of the smaller globe which has
100 times less surface ; now ^ of a grain in the case of a body which
weighs only 3068.465 grains is — ^-. of the real weight of the body
in water, and by this amount the weight will be diminished on account
of the viscosity of the liquid. This quantity is precisely 100 times
more considerable, relatively to the weight of the body in water, than
we have found it to be in the case of a body 10 times as large.

Hence we may conclude (and this can also easily be shown by a rigor-
ous demonstration) that when a solid sphere heavier than water is sub-
merged in this liquid, the decrease of weight due to the viscosity of
the liquid is inversely proportional to the diameter of the sphere.

For example, if, when the diameter of the sphere was 10.3233
inches, the decrease of its weight in water due to the viscosity of
that liquid is to its weight in the same liquid in the ratio of i to
3068465 ; —

The diminution of weight due to
the viscosity of the liquid will be to
When the diameter is reduced to the weight of the body in water

1.08233 of an inch

0.108233

0.0108233

0.00108233

0.000108233

0.0000108233

0.00000108233

306846.5
30684.65
3068.465
306.8465
30.68465
3.068465
0.3068465

And in this last case it is evident that the minute body must of
necessity remain suspended in the liquid.

I know very well that these long numerical calculations must seem
superfluous to geometers accustomed to algebraic calculation ; but many
persons who are unacquainted with algebra desire to have brought
within their reach satisfactory proofs of the truth of a conclusion
which is given out to them as certain, especially when it is to serve as

of Liquids to each other. 317

the foundation of a theory which is applied to very interesting
phenomena.

As soon as it is shown that the diminution of weight which a
sphere plunged into water experiences as a result of the viscosity of this
liquid is inversely proportional to the diameter of the sphere, and
when we know the amount of this diminution in a particular case, it
is easy to determine, by a very simple calculation, what will be the
diminution taking place in another case.

For example, we can determine what will be the diameter of the
largest sphere of gold which will remain suspended in water on account
of the viscosity of this liquid. Proceeding in this manner, I found
this diameter equal to — — . of an inch.

83.505

[This paper is translated from the French as it appears in the Biblio-
theque Britannique (Science et Arts), XXXIV. (1807), pp. 301 -313,
and XXXV. pp. 3- 16.]

OF THE SLOW PROGRESS

SPONTANEOUS MIXTURE OF LIQUIDS

DISPOSED TO UNITE CHEMICALLY WITH EACH
OTHER.

IN order to obtain the most exact knowledge of the
nature of the forces which act in the chemical com-
bination of various bodies, one must study the phe-
nomena of these operations, not only in their results,
but more especially in their progress.

When we mix together two liquids which we wish
to have unite, we take care to shake them violently, in
order to facilitate their union ; it might, however, be
very interesting to know what would happen, if, instead
of mixing them, they were simply brought into contact
by placing one upon the other in the same vessel, tak-
ing care to cause the lighter to rest upon the heavier.

Will the mixture take place under such circumstan-
ces ? and with what degree of rapidity ? These are
questions interesting alike to the chemist and to the
natural-philosopher.

The result would depend, without doubt, on several
circumstances which we might be able to anticipate, and
the effects of which we might perhaps estimate a priori.
But since the results of experiments, when they are
well made, are incomparably more satisfactory than con-
clusions drawn from any course of reasoning, especially
in the case of the mysterious operations of Nature, I

Of the Progress of the Mixture of Liquids, etc. 3 1 9

propose to speak before this illustrious Assembly sim-
ply of experiments that I have performed.

Having procured a cylindrical vessel of clear white
glass i inch 8 lines in diameter, and 8 inches high,
provided with a scale divided from the bottom upwards
into inches and lines, I put it on a firm table in the
middle of a cellar, where the temperature, which
seemed to be tolerably constant, was 64 degrees of Fah-
renheit's scale.

I then poured into this vessel, with due precautions,
a layer of a saturated aqueous solution of muriate
of soda, 3 inches in thickness, and on to this a layer
of the same thickness of distilled water. This opera-
tion was performed in such a way that the two liquids
lay one upon the other without being mixed, and when
everything was at rest I let a large drop of the essential
oil of cloves fall into the vessel. This oil being spe-
cifically heavier than water, and lighter than the solution
of muriate of soda on which the water rested, the drop
descended through the layer of water ; when, however,
it reached the neighbourhood of the surface of the saline
solution it remained there, forming a little spherical
ball, which maintained its position at rest, as though it
were suspended, near the axis of the vessel.

I then poured, with proper precautions, a layer of
olive oil four lines in thickness on to the surface of the
water, to prevent the contact -of the air with the liquid,
and having observed, by means of the scale attached to
the vessel, and noted down in a register, the height at
which the little ball was suspended, I withdrew, and,
locking the door, I left the apparatus to itself for
twenty-four hours.

In a preliminary experiment, made to determine in

320 Of the Progress of the spontaneous Mixture

what proportions the saturated solution should be mixed
with distilled water, that the mixture might have the
same specific gravity as the oil of cloves, I found that
a mixture composed of i measure of the solution and
9 measures of distilled water had a slightly higher spe-
cific gravity than the oil ; but with 10 measures of dis-
tilled water the oil sank in the mixture.

As the little ball of oil, designed to serve me as an
index, was suspended a very little above the upper sur-
face of the layer of the saturated solution, this showed
me that the precautions which I had taken were suffi-
cient to prevent the mixing of the distilled water and
the saline solution when I put one upon the other, and
I knew that this mixture could not take place subse-
quently without causing at the same time my little
sentinel, which was there to warn me of this event, to
ascend.

There was, however, a single source of error which
I was obliged to guard against. I had observed, in
other experiments of this kind, that the air which was
disseminated through or dissolved in water containing
in solution a small quantity of muriate of soda left
the liquid, and attached itself to the little ball of oil of
cloves which I had introduced into it, and, having
formed on top of it a little bubble scarcely visible,
caused it to ascend in the liquid, even when the density
of the liquid had not changed at all.

To prevent this accident, I boiled for some time
both the saturated solution and the distilled water em-
ployed in the experiment, in order to free them from
air, and, for the same reason, I subsequently covered
the water with a layer of olive oil to prevent the contact
of this water with the atmospheric air.

of Liquids disposed to unite with exch other. 32 i

After the little apparatus mentioned above had been
left to itself for twenty-four hours, I entered the cellar,
taking a light in order to note the progress of the ex-
periment, and I found that the little ball had risen 3 lines.

The next day, at the same hour, I observed the
ball again, and I found that it had risen about 3 lines
more ; and thus it continued to ascend about 3 lines a
day for six days, when I put an end to the experiment.

I afterwards made nearly similar experiments with
saturated aqueous solutions of nitrate of potash, car-
bonate of potash, and carbonate of soda. In each of
these experiments the surface of the saturated solution
was covered with a layer of distilled water 3 inches in
thickness, but the surface of this layer of water was
not covered by a layer of olive oil ; it was exposed to
the air, and this circumstance was, without doubt, the
reason that the daily results of a single experiment were
not always the same two days in succession.

The little ball of oil of cloves, which served as an
index to mark the progress of the mixture of the satu-
rated solution with the distilled water resting upon it,
ascended usually 2 or 3 lines in twenty-four hours, but
sometimes I found that it had left its position and had
risen to the very surface of the water.

In such cases it was, without doubt, borne upwards
by the air which it had attracted from the liquid ; for
when I allowed a fresh drop of the same oil to fall into
the water, I found that it never failed to descend im-
mediately in the liquid, and to take up its position 2 or
3 lines above the level at which, the day before, I had
found the ball which had now left its place.

In the experiments made with solutions of carbonate
of soda and carbonate of potash, the balls of oil

322 Of the Progress of the spontaneous Mixture

changed in appearance by the end of two or three
days ; from being transparent, they became semi-opaque
and of a whitish color ; they changed at the same time
with regard to their specific gravity as well, and became
a little lighter. These changes were evidently due to
the beginning of saponification.

This accidental circumstance made it necessary for
me to renew each day the drop of oil which served as
the index, allowing the others to pursue their way to
the surface of the liquid without paying any further
attention to them.

By using as indices little glass balloons of proper
size and thickness, instead of the drops of oil, the
inconveniences arising from the saponification of the
oil might be avoided.

But without spending more time on the details of
these experiments, I hasten to return to their results.
They showed that the mixture went on continually, but
very slowly, between the various aqueous solutions
employed and the distilled water resting upon them.

There is nothing in this result to excite the surprise
of any one, especially of chemists, unless it is the ex-
treme slowness of the progress of the mixture in ques-
tion. The fact, however, gives occasion for an inquiry
of the greatest importance, which is far from being easy
to solve.

Does this mixture depend upon a peculiar force of
attraction different from the attraction of universal
gravitation, a force which has been designated by the
name of chemical affinity ? Or is it simply a result of
motions in the liquids in contact, caused by changes
in their temperatures ? Or is it, perhaps, the result of
a peculiar and continual motion common to all liquids,

of Liquids disposed to unite with each other. 323

caused by the instability of the equilibrium existing
among their molecules ?

I am very far from assuming to be able to solve this
great problem, but it has often been the subject of my
thoughts, and I have made at different times a consid-
erable number of experiments with a view of throwing
light into the profound darkness with which the subject
is shrouded on every side.

At a subsequent sitting of the Class, I shall have the
honour of giving an account of the continuation of my
researches on this interesting subject.

[This paper is translated from the Memoires de 1'Institut, etc., VIII.,
ii., pp. 100-115.]

OF THE USE OF STEAM

VEHICLE FOR TRANSPORTING HEAT.

MANY attempts have been made, at different
periods, to heat liquids by means of steam in-
troduced into them ; but most of these have failed ;
and, indeed, until it was known that fluids are non-con-
ductors of heat, and, consequently, that heat cannot
be made to descend in them (which is a recent discov-
ery), these attempts could hardly succeed; for, in
order to their being successful, it is absolutely necessary
that the tube which conveys the hot steam should open
into the lowest part of the vessel which contains the
liquid to be heated, or nearly on a level with its bottom;
but as long as the erroneous opinion obtained, that heat
could pass in fluids in all directions y there did not appear
to be any reason for placing the opening of the steam-
tube at the bottom of the vessel, while many were at hand
which pointed out other places as being more convenient
for it.

But to succeed in heating liquids by steam, it is ne-
cessary, not only that the steam should enter the liquid
at the bottom of the vessel which contains it, but also
that it should enter it coming from above.

The steam-tube should be in a vertical position, and
the steam should descend through it previous to its
entering the vessel, and mixing with the liquid which it

Of the Use of Steam. 325

is to heat; otherwise this liquid will be in danger of
being forced back by this opening into the steam-boiler :
for, as the hot steam is suddenly condensed on coming
into contact with the cold liquid, a vacuum is necessarily
formed in the end of the tube; into which vacuum the
liquid in the vessel, pressed by the whole weight of
the incumbent atmosphere, will rush with great force
and with a loud noise ; but if this tube be placed in a
vertical position, and if it be made to rise to the height
of six or seven feet above the level of the surface of the
liquid which is to be heated, the portion of the liquid
which is thus forced into the lower end of the tube will
not have time to rise to that height before it will be met
by steam, and obliged to return back into the vessel.

There will be no difficulty in arranging the apparatus
in such a manner as effectually to prevent the liquid to
be heated from being forced backwards into the steam-
boiler ; and when this is done, and some other neces-
sary precautions to prevent accidents are taken, steam
may be employed, with great advantage, for heating
liquids, and for keeping them hot in a variety of cases
in which fire, applied immediately to the bottoms of the
containing vessels, is now used.

In dyeing, for instance, in bleaching, and in brewing,
and in the processes of many other arts and manufac-
tures, the adoption of this method of applying heat
would be attended not only with a great saving of
labour and of fuel, but also of a considerable saving
of expense in the purchase and repairs of boilers, and
of other expensive machinery : for, when steam is used
instead of fire, for heating their contents, boilers may
be made extremely thin and light; and as they may
easily be supported and strengthened by hoops and

326 Of the Use of Steam

braces of iron, and other cheap materials, they will cost
but little, and seldom stand in need of repairs.

To these advantages we may add others of still greater
importance. Boilers intended to be heated in this man-
ner may, without the smallest difficulty, be placed in any
part of a room, at any distance from the fire, and in
situations in which they may be approached freely on
every side. They may, moreover, easily be so surrounded
with wood, or with other cheap substances which form
warm covering, as most completely to confine the heat
within them and prevent its escape. The tubes by
which the steam is brought from the principal boiler
(which tubes may conveniently be suspended just below
the ceiling of the room) may, in like manner, be cov-
ered so as almost entirely to prevent all loss of heat by
the surfaces of them, and this to whatever distances
they may be made to extend.

In suspending these steam-tubes, care must, however,
be taken to lay them in a situation not perfectly horizon-
tal^ under the ceiling, but to incline them at a small
angle, making them rise gradually from their junction
with the top of a large vertical steam-tube, which con-
nects them with the steam-boiler, quite to their farthest
extremities ; for, when these tubes are so placed, it is
evident that all the water formed in them, in conse-
quence of the condensation of the steam in its passage
through them, will run backwards, and fall into the
boiler, instead of accumulating in them and obstructing
the passage of the steam (which it would not fail to do
were there any considerable bends or wavings, upwards
and downwards, in these tubes), or of running forward
and descending with the steam into the vessels contain-
ing the liquids to be heated, — which would happen if

as a Vehicle for transporting Heat. 327

these tubes inclined downwards^ instead of inclining up-
wards, as they recede from the boiler.

In order that clear and distinct ideas may be formed
of the various parts of this apparatus, even without
figures, I shall distinguish each part of it by a specific
name. The vessel in which water is boiled in order to
generate steam — and which, in its construction, may be
made to resemble the boiler of a steam-engine — I shall
call the steam-boiler; the vertical tube which, rising
up from the top of the boiler, conveys the steam into
the tubes (nearly horizontal) which are suspended from
the ceiling of the room, I shall call the steam-reservoir.
To the horizontal tubes I shall give the name of conduc-
tors of steam; and to the (smaller) tubes which, de-
scending perpendicularly from these horizontal conductors,
convey the steam to the liquids which are to be heated,
I shall exclusively appropriate the appellation of steam-
tubes.

The vessels in which the liquids that are to be heated
are put, I shall call the containing vessels. These vessels
may be made of any form ; and, in many cases, they
may, without any inconvenience, be constructed of wood,
or of other cheap materials, instead of being made of
costly metals, by which means a very heavy expense may
be avoided ; or they may be merely pits sunk in the
ground, and lined with stone or with bricks.

Each steam-tube must descend perpendicularly from the
horizontal conductor with which it is connected, to the
level of the bottom of the containing vessel to which it
belongs; and, moreover, must be furnished with a good
cock, perfectly steam-tight, which may best be placed
at the height of about six feet above the level 'of the
floor of the room.

328 Of the Use of Steam

This steam-tube may either descend within the vessel to
which it belongs, or on the outside of it, as shall be found
most convenient. If it comes down on the outside of
the vessel, it must enter it at its bottom by a short
horizontal bend ; and its junction with the bottom of
the vessel must be well secured, to prevent leakage. If
it comes down into the vessel on the inside of it, it
must descend to the bottom of it, or at least to within
a very few inches of the bottom of it ; otherwise the li-
quid in the vessel will not be uniformly or equally heated.

When the steam-tube is brought down on the inside
of the containing vessel, it may either come down per-
pendicularly and without touching the sides of it, or it
may come down on one side of the vessel and in con-
tact with it.

When several steam-tubes belonging to different con-
taining-vessels are connected with one and the same
horizontal steam-conductor, the upper end of each of
these tubes, instead of being simply attached by solder
or by rivets to the under side of the conductor, must
enter at least one inch within the cavity of it ; otherwise
the water resulting from a condensation of a part of the
steam in the conductor by the cold air which surrounds
it, instead of finding its way back into the steam-boiler,
will descend through the steam-tubes, and mix with the
liquids in the vessels below ; but when the open ends
of these tubes project upwards within the steam-conductor y
though it be but to a small height above the level of its
under side, it is evident that this accident cannot happen.

It is not necessary to observe here, that, in order that
the ends of the steam-tubes may project within the hori-
zontal conductor, the diameters of the former must be
considerably less than the diameter of the latter.

as a Vehicle for transporting Heat. 329

To prevent the loss of heat arising from the cooling
of the different tubes through which the steam must
pass in coming from the boiler, all those tubes should
be well defended from the cold air of the atmosphere,
by means of warm covering ; but this may easily be
done, and at a very trifling expense. The horizontal
conductors may be enclosed within square wooden tubes,
and surrounded on every side by charcoal dust, fine
sawdust, or even by wool ; and the steam-tubes, as
well as the reservoir of steam, may be surrounded, first
by three or four coatings of strong paper, firmly attached
to them by paste or glue, and covered with a coating
of varnish, and then by a covering of thick coarse
cloth. It will likewise be advisable to cover the hori-
zontal conductors with several coatings of paper ; for, if
the paper be put on to them while it is wet with the
paste or glue, and if care be taken to put it on in long
slips or bands, wound regularly round the tube in a
spiral line from one end of it to the other, this cover-
ing will be useful, not only by confining more effectually
the heat, but also by adding very much to the strength
of the tube, and rendering it unnecessary to employ
thick and strong sheets of metal in the construction
of it.

However extraordinary and incredible it may appear,
I can assert it as a fact, which I have proved by repeated
experiments, that if a hollow tube, constructed of sheet
copper jV of an inch in thickness, be covered by a coat-
ing only twice as thick, or ^ of an inch in thickness,
formed of layers of strong paper, firmly attached to it
by good glue, the strength of the tube will be more than
doubled by this covering.

I found by experiments, the most unexceptionable

330 Of the Use of Steam

and decisive, — of which I intend at some future period
to give to the public a full and detailed account, — that
the strength of paper is such, when several sheets of it
are firmly attached together with glue, that a solid cylin-
der of this substance, the transverse section of which
should amount to only one superficial inch, would sus-
tain a weight of 30,000 pounds avoirdupois, or above
13 tons, suspended to it, without being pulled asunder
or broken.

The strength of hemp is still much greater, when it is
pulled equally in the direction of the length of its fibres.
I found, from the results of my experiments with this sub-
stance, that a cylinder of the size above mentioned, com-
posed of the straight fibres of hemp glued together, would
sustain 92,000 pounds without being pulled asunder.

A cylinder of equal dimensions, composed of the
strongest iron I could ever meet with, would not sus-
tain more than 66,000 pounds weight; and the iron
must be very good not to be pulled asunder with a
weight equal to 55,000 pounds avoirdupois.

I shall not, in this place, enlarge on the many advan-
tages that may be derived from a knowledge of these
curious facts. I have mentioned them now, in order
that they may be known to the public ; and that ingen-
ious men, who have leisure for these researches, may be
induced to turn their attention to a subject, not only
very interesting on many accounts, but which promises
to lead to most important improvements in mechanics.

I cannot return from this digression without just
mentioning one or two results of my experimental
investigations relative to the force of cohesion, or
strength of bodies, which certainly are well calculated
to excite the curiosity of men of science.

as a Vehicle for transporting Heat. 331

The strength of bodies of different sizes, similar in form
and composed of the same substance^ — or the forces by
which they resist being pulled asunder by weight sus-
pended to them, and acting in the direction of their
lengths, — is not in the simple ratio of the areas of their
transverse sections, or of their fractures^ but in a higher
ratio ; and this ratio is different in different sub-
stances.

The form of a body has a considerable influence on
its strength, even when it is -pulled in the direction of its
length.

All bodies, even the most brittle, appear to be torn
asunder^ or their particles separated, or fibres broken,
one after the other ; and hence it is evident that that form
must be most favourable to the strength of any given
body, pulled in the direction of its length, which enables
the greatest number of its particles, or longitudinal
fibres, to be separated to the greatest possible distance
short of that at which the force of cohesion is over-
come, before any of them have been forced beyond that
limit.

It is more than probable that the apparent strength
of different substances depends much more on the
number of their particles that come into action before
any of them are forced beyond the limits of the attrac-
tion of cohesion, than on any specific difference in the
intensity of that force in those substances.

But to return to the subject more immediately under
consideration. As it is essential that the steam em-
ployed in heating liquids, in the manner before described,
should enter the containing vessel at or very near its
bottom, it is evident that this steam must be sufficiently
strong or elastic to overcome not only the pressure

332 Of the Use of Steam

of the atmosphere, but also the additional pressure of
the superincumbent liquid in the vessel ; the steam-
boiler must therefore be made strong enough to con-
fine the steam, when its elasticity is so much increased,
by means of additional heat, as to enable it to overcome
that resistance. This increase of the elastic force of the
steam need not, however, in any case, exceed a pressure
of five or six pounds upon a square inch of the boiler,
or one third part , or one half, of an atmosphere.

It is not necessary for me to observe here, that in
this and also in all other cases where steam is used as a
vehicle for conveying heat from one place to another, it
is indispensably necessary to provide safety-halves of
two kinds, — the one for letting a part of the steam
escape, when, on the fire being suddenly increased, the
steam becomes so strong as to expose the boiler to the
danger of being burst by it; * the other for admitting
air into the boiler, when, in consequence of the diminu-
tion of the heat, the steam in the boiler is condensed,
and a vacuum is formed in it ; and when, without this
valve, there would be danger, either of the sides of the
boiler being crushed, and forced inwards by the pressure
of the atmosphere from without, or of the liquid in
the containing ves'sels being forced upwards into the
horizontal steam-conductors, and from thence into the
steam-boiler. The last-mentioned accident, however,
cannot happen, unless the cocks in some of the steam-
tubes are left open. The two valves effectually pre-
vent all accidents.

* The steam which escapes out of the boiler through the safety-valve may very
easily be made to pass into the reservoir of water which feeds the boiler, and be con-
densed there; which will warm that water, and by that means save a quantity of heat
which otherwise would escape into the atmosphere and be lost.

as a Vehicle for transporting Heat. 333

The reader will, no doubt, be more disposed to pay
attention to what has here been advanced on this inter-
esting subject, when he is informed that the proposed
scheme has already been executed on a very large scale,
and with complete success ; and that the above details
are little more than exact descriptions of what actually
exists.

A great mercantile and manufacturing house at Leeds,
that of Messrs. Gott and Company, had the courage, not-
withstanding the mortifying prediction of all their
neighbours, and the ridicule with which the scheme was
attempted to be treated, to erect a dyeing-house^ on a very
large scale indeed, on the principles here described and
recommended.

On my visit to Leeds in the summer of the year
1800, I waited on Mr. Gott, who was then mayor of
the town, and who received me with great politeness,
and showed me the cloth-halls and other curiosities of
the place ; but nothing he showed me interested me
half so much as his own truly noble manufactory of
superfine woollen cloths.

I had seen few manufactories so extensive, and none
so complete in all its parts. It was burnt to the ground
the year before, and had just been rebuilt on a larger
scale, and with great improvements in almost every
one of its details.

The reader may easily conceive that I felt no small
degree of satisfaction, on going into the dyeing-house,
to find it fitted up on principles which I had some share
in bringing into repute, and which Mr. Gott told me
he had adopted in consequence of the information he
had acquired in the perusal of my Seventh Essay.

He assured me that the experiment had answered,

334 Of the Use of Steam

even far beyond his most sanguine expectations ; and,
as a strong proof of the utility of the plan, he informed
me that his next-door neighbour, who is a dyer by pro-
fession, and who at first was strongly prejudiced against
these innovations, had adopted them, and is now con-
vinced that they are real improvements.

Mr. Gott assured me that he had no doubt but they
would be adopted by every dyer in Great Britain in the
course of a very few years.

The dyeing-house of Messrs. Gott and Company,
which is situated on the ground floor of the principal
building of the manufactory, is very spacious, and con-
tains a great number of coppers, of different sizes ; and as
these vessels, some of which are very large, are distributed
about promiscuously, and apparently without any order
in their arrangement, in two spacious rooms, — each
copper appearing to be insulated, and to have no con-
nection whatever with the others, — all of them to-
gether form a very singular appearance.

The rooms are paved with flat stones, and the brims
of all the coppers, great and small, are placed at
the same height (about three feet) above the pavement.
Some of these coppers contain upwards of 1800 gallons ;
and they are all heated by steam from one steam-boiler^
which is situated in a corner of one of the rooms,
almost out of sight.

The horizontal tubes, which serve to conduct the
steam from the boiler to the coppers, are suspended
just below the ceiling of the rooms : they are made,
some of lead and some of cast-iron, and are from
four to five inches in diameter ; but when I saw them,
they were naked, or without any covering to confine
the heat. On my observing to Mr. Gott that coverings

as a Vehicle for transporting Heat. 335

for them would be useful, he told me that it was
intended that they should be covered, and that coverings
would be provided for them.

The vertical steam-tubes^ by which the steam passes
down from the horizontal steam-conductors into the cop-
pers, are all constructed of lead ; and are from -| of an
inch to 2j inches in diameter, being made larger or
smaller according to the sizes of the coppers to which
they belong. These steam-tubes all pass down on the
outsides of their coppers, and enter them horizontally at
the level of their bottoms. Each copper is furnished
with a brass cock, for letting off its contents; and it is
rilled with water from a cistern at a distance, which is
brought to it by a leaden pipe. The coppers are all
surrounded by thin circular brick walls, which serve not
only to support the coppers, but also to confine the
heat.

The rapidity with which these coppers are heated by
means of steam is truly astonishing. Mr. Gott assured
me that one of the largest of them, containing upwards
of 1800 gallons, when filled with cold water from the cis-
tern, requires no more than half an hour to heat it till
it actually boils ! By the greatest fire that could be
made under such a copper, it would hardly be possible
to make it boil in less than an hour.

It is easy to perceive that the saving of time which
will result from the adoption of this new mode of ap-
plying heat will be very great ; and it is likewise
evident that it may be increased almost without limita-
tion, merely by augmenting the diameter of the steam-
tube. Care must, however, be taken, that the boiler be
sufficiently large to furnish the quantities of steam
required. The saving of fuel will also be very consid-

336 Of the Use of Steam

erable. Mr. Gott informed me that, from the best
calculation he had been able to make, it would amount
to near two thirds of the quantity formerly expended,
when each copper was heated by a separate fire.

But these savings are far from being the only advan-
tages that will be derived from the introduction of these
improvements in the management of heat. There is
one, of great importance indeed, not yet mentioned,
which alone would be sufficient to recommend the very
general adoption of them. As the heat communicated
by steam can never exceed the mean temperature
of boiling water by more than a very few degrees, the
substances exposed to it can never be injured by it.

In many arts and manufactures this circumstance will
be productive of great advantages, but in none will its
utility be more apparent than in cookery, and especially
in public kitchens, where great quantities of food are
prepared in large boilers ; for, when the heat is con-
veyed in this manner, all the labour now employed in
stirring about the contents of those boilers, to prevent
the victuals from being spoiled by burning to the bot-
toms of them, will be unnecessary, and the loss of heat
occasioned by this stirring prevented ; and, instead of
expensive coppers or metallic boilers, which are some-
times unwholesome, and always difficult to be kept clean,
and often stand in need of repairs, common wooden
tubs may, with great advantage, be used as culinary
vessels ; and their contents may be heated by portable
fireplaces, by means of steam-boilers attached to them.

As these portable fireplaces and their steam-boilers
may, without the smallest inconvenience, be made of
such weight, form, and dimensions, as to be easily
transported from one place to another by two men,

as a Vehicle for transporting Heat. 337

and be carried through a doorway of the common width,
with this machinery, and the steam-tubes belonging to
it, and a few wooden tubs, a complete public kitchen,
for supplying the poor and others with soups and
also with puddings, vegetables, meat, and all other
kinds of food prepared by boiling^ might be established
in half an hour in any room in which there is a chim-
ney (by which the smoke from the portable fireplace
can be carried off); and when the room should be no
longer wanted as a kitchen, it might, in a few minutes,
be cleared of all this culinary apparatus, and made ready
to be used for any other purpose.

This method of conveying heat is peculiarly well
adapted for heating baths. It is likewise highly probable
that it would be found useful in the bleaching business
and in washing linen. It would also be very useful in
all cases where it is required to keep any liquid at about
the boiling-point for a long time without making it boil ;
for the quantity of heat admitted may be very nicely
regulated by means of the brass cock belonging to the
steam-tube. Mr. Gott showed me a boiler in which
shreds of skins were digesting in order to make glue, which
was heated in this manner ; and in which the heat was
so regulated that, although the liquid never actually
boiled, it always appeared to be upon the very point
of beginning to boil.

This temperature had been found to be best calculated
for making good glue. Had any other lower tempera-
ture been found to answer better, it might have been
kept up with the same ease, and with equal precision,
by regulating properly the quantity of steam admitted.

I need not say how much this country is obliged to
Mr. Gott and his worthy colleagues. To the spirited

338 Of the Use of Steam

exertions of such men, who abound in no other coun-
try, we owe one of the proudest distinctions of our
national character, that of being an enlightened and an
enterprising people.

In fitting up the great kitchen at the house of the
Royal Institution, I availed myself of that opportunity
to show, in a variety of different ways, how steam may
be usefully employed in heating liquids.

On one side of the room, opposite to the fireplace,
and where there is no appearance of any chimney, I
fitted up a steam-boiler, of cast-iron, which, to confine
the heat, is so completely covered up by the brickwork
in which it is set, that no part of it is seen. This boiler
is supplied with water from a reservoir at a distance
(which is not seen), and by means of a cock, which is
regulated by an hollow floating ball of thin copper, the
water in the boiler always stands at the same height or
level.

The steam from this boiler rises up perpendicularly
in a tin tube, which is concealed in a square wooden
tube, by the side of the wall of the room, and enters
an horizontal tin tube (concealed in the same manner)
which lies against the wall and just under the ceiling.

From this horizontal steam- conduct 'or three tubes de-
scend perpendicularly (concealed in three square wooden
tubes), and enter three different kitchen boilers (on a
level with their bottoms), which are set in brickwork
against the same side of the room where the steam-
boiler is situated.

As each of these boilers has its separate fireplace,
properly furnished with a good double door and regis-
ter ash-pit door, and also with a canal, furnished with
a damper, for carrying off the smoke, either of these

as a Vehicle for transporting Heat. 339

three boilers may be used for cooking, either with a fire
made under it, or with steam brought into it from the
neighbouring steam-boiler.

The object I had principally in view in this arrange-
ment was to show, in the most striking and convincing
manner, that all the different processes of cookery
which are performed by boiling, such as boiling meat
and vegetables in boiling water, making soups, stew-
ing, etc., may in all cases be performed quite as well,
and in many much better, by heating the liquid which
is to be boiled, and keeping it boiling, by admitting hot
steam into it, than by making a fire under it.

By using one of these boilers alternately in these two
ways, on different days, in preparing the same kind of
food, I concluded that all doubts on this subject would
be most effectually removed.

To exhibit in a manner still more striking the appli-
cation of steam to the boiling of liquids for culinary
purposes, the following arrangement has been made and
completed. A horizontal steam-conductor (concealed
in a square wooden tube), communicating at right angles
with the steam-conductor before described, passes, just
below the ceiling, from the middle of one side of the
room to the middle of the ceiling, and ends in a ves-
sel in the form of a flat drum, about 10 inches in diame-
ter and 5 inches high, which is attached to the ceiling
perpendicularly over the centre of a large table which
is placed in the middle of the room.

On the outside of this drum, or short hollow cylinder
(which is made of tin and covered with wood, to con-
fine the heat), there are, at equal distances, four project-
ing horizontal tubes, each about i inch in diameter
and 2 inches long, which communicate with the inside

340 Of the Use of Steam

of the drum. These tubes all point to the same centre,
namely, to the centre of the drum.

To each of these short horizontal tubes there is fixed
one end of a steam-tube composed of three pieces, fixed
to each other, and movable, by means of joints, which
are all steam-tight. •

The end of this compound flexible steam-tube is
united to the end of the short tube which projects from
the side of the drum, by means of a steam-joint, in
such a manner that the steam-tube attached to the
drum, and communicating with it, may either be folded
up in joints or lengths just under the ceiling, or it
may be made to hang down from the end of the short
tube to which it is attached. The lower joint, or
rather division, of this flexible steam-tube, which reaches
nearly to the top of the table, is furnished with a brass
cock, by which it is occasionally closed, or, rather, by
which it is always kept closed when it is not in actual
use.

I might perhaps spare myself the trouble of describ-
ing the manner in which this culinary steam-apparatus
is used, as the imagination of the reader will most prob-
ably have run before me. I shall, however, just men-
tion a very striking and pleasing manner of making the
experiment, in which the action of this machinery will
be exhibited to great advantage.

If the cold water which is to be heated and made
to boil by the steam is put into a large glass bowl or
jar, on plunging the lower end of one of the flexible
steam-tubes into the water, and then opening the steam-
cock, the agitation into which the water in the glass
vessel will be thrown will be visible through the glass ;
and the passage of the steam, in its elastic form, upwards

as a Vehicle for transporting Heat. 341

through the Water into the air, after the water has become
boiling hot and not before, will be an instructive, as well
as an amusing experiment.

Those of the flexible steam-tubes which are not in
actual use are kept so folded up (in order to their being
out of the way) that their two upper divisions, lying
by the side of each other in a horizontal position, are
just under the ceiling of the room ; while their lower
divisions hang vertically downwards, pointing towards
the table.

In order that the kitchen may not be filled with steam
when any of the boilers on the side of the room are
used, their covers are all furnished with steam-tubes,
which, communicating by a particular contrivance with
a horizontal steam-tube which lies immediately over
these boilers just under the ceiling, and which, by pass-
ing through the wall of the building, opens into the
external air, all the waste steam from these boilers is
carried out of the kitchen.

Before I conclude this Essay, I shall add a few obser-
vations concerning an application of steam which has
not yet, to my knowledge, been made, but which there
is much reason to think would turn out to be of very
great importance indeed in many cases. This is the em-
ploying of it for communicating degrees of heat above
that of boiling water.

I was led to meditate on this subject by an account I
received, not long ago, of some very surprising effects
which were produced in bleaching, by using the steam
of a very strong solution of potash for boiling the linen,
instead of water ; as I was confident that no part of the
alkali could possibly be evaporated in this process, I
could not account in any other way for the effects pro-

342 Of the Use of Steam

duced, but by supposing them to have been owing to
the high temperature of the steam which rose from this
strong lixivium ; and as steam, at a high temperature,
might easily be procured and applied to the linen with-
out the use of the alkali, I thought it would be worth
while to try the experiment with hot steam produced
from pure water. I mentioned this idea to Mr. Duffin,
Secretary of the Linen Board in Ireland, who is himself
concerned, in an extensive way, in the bleaching business,
who has promised to make some experiments on this
subject, which I took the liberty to point out and to
recommend to him as being likely to lead to interesting
results.

Meditating on the various uses to which hot or
(which is the same thing) strong steam might be applied,
it occurred to me that it would probably be found to be
extremely useful in alum works, for concentrating the
liquor from which alum is crystallized. There are, as
is well known, many difficulties attending the evapora-
tion and concentration of that liquid ; and it is never
done without occasioning a very considerable expense,
as well for fuel, of which large quantities are consumed,
as also on account of the frequent repairs of the pans,
which are found to be necessary.

Most, if not all these difficulties might, I think, be
avoided by introducing strong steam into this liquor,
instead of concentrating it over a fire. This concen-
tration might certainly be effected as well, and probably
better and more expeditiously, by using hot steam, than
by the immediate use of the heat of a fire, and the
expense occasioned by the wear and tear of the apparatus
would, no doubt, be much less in the former case than
in the latter ; and if it should be found (which is not

as a Vehicle for transporting Heat. 343

unlikely) that some certain temperature is more advan-
tageous in this process than any other, that temperature^
when once discovered, may be preserved, with very little
variation, when steam is used (by placing a valve, loaded
with a proper weight, in the steam-tube, and obliging the
steam to lift that valve, in order to pass through the tube);
but there is no possibility of regulating, with any pre-
cision, the degrees of heat employed when liquids are
evaporated in boilers over a fire.

I would just point out one more application of steam,
which, if I am not much mistaken, will turn out to be
very advantageous indeed in many respects ; — it may be
employed in heating the fermented liquor from which
ardent spirits are distilled.

A proposal for introducing watery vapour into a
liquor from which pure ardent spirits are to be distilled,
or forced away by heat, will, no doubt, be thought very
extraordinary by those who have never meditated on
the subject ; but when they shall have considered it with
attention, they will find reason to conclude that this
method of distilling bids fair to be very useful. The
saving of expense for coppers and other costly utensils
and machinery would be very considerable, and the
danger of the flavour of the spirits being injured by the
burning of the liquor to the sides of the copper would
be entirely removed.

Steam has already been introduced, in several great
manufactories in this country, into drying-houses, and em-
ployed with the best effects for heating and drying linen,
cotton, and woollen goods, after they have been washed ;
it has also been used in the drying-rooms of several paper-
manufactories. When it is used for any of these pur-
poses, it should be introduced into tubes of large diam-

344 Of tfie Use of Steam, etc.

eter, or into several smaller tubes, constructed of very
thin sheet copper (or into any other metallic tubes, hav-
ing a large surface, that would be cheaper) ; and these
tubes should be placed nearly in a horizontal position
in the lower part of the drying-room and under the goods
that are to be dried; and (in order to economize the
heat as much as possible) the water resulting from the
condensation of the steam in the steam-tubes should
be conducted by small tubes, well covered with warm
covering, into the reservoir which feeds the steam-
boiler.

[This paper is printed from the English edition of Rumford's Es-
says, Vol. III. pp. 475-498.]

OBSERVATIONS

RELATIVE TO

THE MEANS OF INCREASING THE QUANTITIES OF
HEAT OBTAINED IN THE COMBUSTION OF FUEL.

IT is a fact which has been long known, that clays,
and several other incombustible substances, when
mixed with sea coal in certain proportions, cause the
coal to give out more heat in its combustion than it can
be made to produce when it is burned pure or unmixed ;
but the cause of this increase of heat does not appear
to have been yet investigated with that attention which
so extraordinary and important a circumstance seems to
demand.

Daily experience teaches us that all bodies — those
which are incombustible, as well as those which are
combustible and actually burning — throw off in all
directions heat, or rather calorific (heat-making) rays,
which generate heat wherever they are stopped or ab-
sorbed; but common observation was hardly sufficient
to show any perceptible difference between the quanti-
ties of calorific rays thrown off by different bodies, when
heated to the same temperature or exposed in the
same fire, although the quantities so thrown off might
be, and probably are, very different.

It has lately been ascertained, that, when the sides and
back of an open chimney fireplace in which coals are
burned are composed of firebricks, and heated red-hot,

346 Means of increasing the Quantities of Heat

they throw off into the room incomparably more heat
than all the coals that could possibly be put into the
grate, even supposing them to burn with the greatest
possible degree of brightness. Hence it appears that a
red-hot burning coal does not send off near so many
calorific rays as a piece of red-hot brick or stone of the
same form and dimensions ; and this interesting dis-
covery will enable us to make very important improve-
ments in the construction of our fireplaces, and also in
the management of our fires.

The fuel, instead of being employed to heat the room
directly or by the direct rays from the fire, should be so
disposed or placed as to heat the back and sides of the
grate, which must always be constructed of firebrick
or firestone, and never of iron or of any other metal.
Few coals, therefore, when properly placed, make a
much better fire than a larger quantity, and shallow
grates, when they are constructed of proper materials,
throw more heat into a room, and with a much less
consumption of fuel, than deep grates ; for a large mass
of coals in the grate arrests the rays which proceed from
the back and sides of the grate, and prevents their com-
ing into the room ; or, as fires are generally managed,
it prevents the back and sides of the grate from ever
being sufficiently heated to assist much in heating the
room, even though they be constructed of good materi-
als and large quantities of coals be consumed in them.

It is possible, however, by a simple contrivance, to
make a good and an economical fire in almost any grate,
though it would always be advisable to construct fire-
places on good principles, or to improve them by
judicious alterations, rather than to depend on the use
of additional inventions for correcting their defects.

obtained in the Combustion of Fuel. 347

To make a good fire in a bad grate, the bottom of
the grate must be first covered with a single layer of
balls, made of good firebricks or artificial firestone, well
burned, each ball being perfectly globular, and about
2-J or 2-| inches in diameter. On this layer of balls
the fire is to be kindled, and, in filling the grate, more
balls are to be added with the coals that are laid on ;
care must, however, be taken in this operation to mix
the coals and the balls well together, otherwise, if a
number of the balls should get together in a heap, they
will cool, not being kept red-hot by the combustion of
the surrounding fuel, and the fire will appear dull in
that part; but if no more than a due proportion of the
balls are used, and if they are properly mixed with the
coals, they will all, except it be those perhaps at the
bottom of the grate, become red-hot, and the fire will
not only be very beautiful, but it will send off a vast
quantity of radiant heat into the room, and will con-
tinue to give out heat for a great length of time. It is
the opinion of several persons who have for a consid-
erable time practised this method of making their fires,
that more than one third of the fuel usually consumed
may be saved by this simple contrivance. It is very
probable that, with careful and judicious management,
the saving would amount to one half, or fifty per cent.

As these balls, made in moulds and burnt in a kiln,
would cost very little, and as a set of them would last
a long time, — probably several years, — the saving of
expense in heating rooms by chimney fires with bad
grates, in this way, is obvious ; but still, it should be
remembered that a saving quite as great may be made
by altering the grate, and making it a good fireplace.

In using these balls, care must be taken to prevent

348 Means of increasing the Quantiti.s of Heat

their accumulating at the bottom of the grate. As the
coals go on to consume, the balls mixed with them will
naturally settle down towards the bottom of the grate,
and the tongs must be used occasionally to lift them up ;
and as the fire grows low, it will be proper to remove
a part of them, and not to replace them in the grate
till more coals are introduced. A little experience will
show how a fire made in this manner can be managed
to the greatest advantage and with the least trouble.

Balls made of pieces of any kind of well-burned hard
brick, though not equally durable with firebrick, will
answer very well, provided they be made perfectly
round ; but if they are not quite globular, their flat sides
will get together, and by obstructing the free passage of
the air amongst them and amongst the coals will pre-
vent the fire from burning clear and bright.

The best composition for making these balls, when
they are formed in moulds and afterwards dried and
burned in a kiln, is pounded crucibles mixed up with
moistened Sturbridge clay ; but good balls may be made
with any very hard burned common bricks, reduced to a
coarse powder, and mixed with Sturbridge clay, or even
with common clay. The balls should always be made
so large as not to pass through between the front bars
of a grate.

These balls have one advantage, which is peculiar to
them, and which might perhaps recommend the use of
them to the curious, even in fireplaces constructed on
the best principles : they cause the cinders to be con-
sumed almost entirely ; and even the very ashes may
be burned, or made to disappear, if care be taken to
throw them repeatedly upon the fire when it burns with
an intense heat. It is not difficult to account for this

obtained in the Combustion of Fuel. 349

effect in a satisfactory manner, and in accounting for it
we shall explain a circumstance on which it is probable
that the great increase of the heat of an open fire where
these balls are used may in some measure depend.
The small particles of coal and of cinder which in a
common fire fall through the bottom of the grate and
escape combustion, when these balls are used can hardly
fail to fall and lodge on some of them ; and as they
are intensely hot, these small bodies which alight upon
them in their fall are soon heated red-hot, and disposed
to take fire and burn ; and as fresh air from below the
grate is continually making its way upwards amongst
the balls, every circumstance is highly favourable to the
rapid and complete combustion of these small inflam-
mable bodies. But if these small pieces of coal and
cinder should, in their fall, happen to alight upon the
metallic bars which form the bottom of the grate, as
these bars are conductors of heat, and, on account of
that circumstance, as well as of their situation, — below
the fire, — never can be made very hot, any small
particle of fuel that happens to come into contact with
them not only cannot take fire, but would cease to burn,
should it arrive in a state of actual combustion.

These facts are very important, and well deserving of
the attention of those who may derive advantage from
the improvement of fireplaces and the economy of fuel.

There are some circumstances w.hich strongly indicate
that an admixture of incombustible bodies with fuel,
and especially with coal, causes an increase of the heat,
even when the fuel is burned in a closed fireplace. No
fireplace can well be contrived more completely closed
than those of the iron stoves in common use in the
Netherlands ; but in these stoves, which are heated

350 Means of increasing the Quantities of Heat

by coal fires, a large proportion of wet clay is always
coarsely mixed with the coals before they are introduced
into the fireplace. If this practice had not been found
to be useful, it would certainly never have obtained gen-
erally, nor would it have been continued, as it has
been, for more than two hundred years.

The combination of different substances, combus-
tible and incombustible, to form, artificially, various
kinds of cheap and pleasant fuel, particularly adapted
for the different processes in which the fuel is employed,
is a subject well worthy of the attention of enterprising
and ingenious men. , How much excellent fuel, for
instance, might be made with proper additions and
proper management, of the mountains of refuse coal-
dust that lie useless at the mouths of coal-pits ; and
how much would it contribute to cleanliness and ele-
gance if the use of improved coke, or of hard and light
fire-balls, could be generally introduced in our houses
and kitchens, instead of crude, black, powdery, dirty
sea coal ! Of the great economy that would result from
such a change there cannot be the smallest doubt.

It is a melancholy truth, but at the same time a most
indisputable fact, that, while the industry and ingenuity
of millions are employed, with unceasing activity, in
inventing, improving, and varying those superfluities
which wealth and luxury introduce into society, no
attention whatever is paid to the improvement of those
common necessaries of life on which the subsistence
of all, and the comforts and enjoyments of the great
majority of mankind, absolutely depend.

Much will be done for the benefit of society, if means
can be devised to call the attention of the active and
benevolent to this long-neglected, but most interesting
subject.

obtained in the Combustion of Fuel. 351

The Royal Institution seems to be well calculated to
facilitate and expedite the accomplishment of this im-
portant object. Indeed, it is more than probable that
this, precisely, is the object which was principally had
in view in the foundation and arrangement of that
establishment.

[This paper is printed from the Journals of the Royal Institution of
Great Britain, I. (1802), pp. 28-33.]

DESCRIPTION OF A NEW BOILER,

CONSTRUCTED

WITH A VIEW TO THE SAVING OF FUEL.

IT is well known that much is gained in the saving of
fuel, when an extensive surface is given to that part
of the boiler against which the flame strikes; but this ad-
vantage is often counterbalanced by great inconveniences.
For a boiler of the form usually employed, having the
bottom very much extended in proportion to its ca-
pacity, must necessarily present a great surface to the at-
mosphere, and the loss of heat, occasioned by the cold
air coming in contact with this surface, may be more
than sufficient to compensate the advantage derived from
the extended surface of the bottom. And where the
boiler is employed for producing steam, as it is indis-
pensably necessary that it should be of a thickness suf-
ficient to resist the expansive force of the steam, it is
evident that, if the diameter be augmented (with a view
to increase the surface of the bottom), a considerable ex-
pense is incurred on account of the additional strength
that must be given to the sides.

Having been engaged in the year 1796 in a set of ex-
periments in which I employed the steam of boiling
water as a vehicle of heat, I had a boiler made for this
purpose, on a new construction, which answered well,
and even beyond my expectations ; and as this boiler
might be used with advantage in many cases, even where

Description of a new Boiler, etc. 353

it is only required to heat liquids in an open boiler,
this, and another motive, which it would be useless to
mention in this place, have lately induced me to con-
struct one here (at Paris) and to present it to the In-
stitute.

The object chiefly had in view in the construction of
this boiler was to give it such a form, that the surface
exposed to the fire should be great in comparison with
its diameter and capacity ; and this without having a
great surface exposed to the cold air of the atmosphere.

The body of the boiler is in the shape of a drum. It
is a vertical cylinder of copper 12 inches in diameter and
12 inches high, closed at top and at bottom by circular
plates.

In the centre of the upper plate there is a cylindrical
neck 6 inches in diameter and 3 inches high, shut at
top by a plate of copper 3 inches in diameter and 3
lines in thickness, fastened down by screws.

This last plate is pierced by three holes, each about
5 lines in diameter. The first, which is in the centre
of the plate, receives a vertical tube, which conveys
water to the boiler from a reservoir, which is placed
above. This tube, which descends in the inside of the
boiler to within an inch above the circular plate which
forms its bottom, has a cock near its lower end. This
cock is alternately opened and shut, by means of a float-
er which swims on the surface of the water contained in
the body of the boiler.

The second of the holes in the plate that closes the
neck of the boiler receives the lower end of another
vertical tube, which serves to convey the steam from
the boiler to the place where it is to be used.

The third hole is occupied by a safety-valve.

VOL. ii. 23

354 Description of a new Boiler, constructed

This description shows that there is nothing new in
the construction or arrangement of the upper part of
this boiler. In its lower part there is a contrivance for
increasing its surface, which has been found very useful.

The flat circular bottom of the body of the boiler,
which, as I said before, is 12 inches in diameter, being
pierced by seven holes, each 3 inches in diameter, seven
cylindrical tubes of thin sheet-copper, 3 inches in diam-
eter and 9 inches long, closed below by circular plates,
are fixed in these holes, and firmly riveted, and then
soldered to the flat bottom of the boiler.

On opening the communication between the boiler
and its reservoir, the water first fills the seven tubes,
and then rises to the cylindrical body of the boiler ; but
it can never rise above 6 inches in the body of the
boiler, for when it has got to that height, the floater is
lifted to the height necessary for shutting the cock that
admits the water.

When the height of the water in the boiler is dimin-
ished a few lines by the evaporation, the floater descends
a little, the cock is again opened, and the water flows in
again from the reservoir.

As the seven tubes that descend from the flat bottom
of the body of this boiler into the fireplace are sur-
rounded on all sides by the flame, the liquid contained
in the boiler is heated, and made to boil in a short time,
and with the consumption of a relatively small quan-
tity of fuel ; and when the vertical sides of the body
of the boiler and its upper part are suitably enveloped,
in order to prevent the loss of heat by these surfaces,
this apparatus may be employed with much advantage
in all cases where it is required to boil water for procur-
ing steam.

with a View to the Saving of Fuel. 355

And as in the case where the boiler is constructed on
a great scale, the seven tubes that descend from the bot-
tom of the boiler into the fire may be made of cast-iron,
whilst the body of the boiler is composed of sheet-iron
or sheet-copper, it is certain that a boiler of this kind,
sufficiently large for a steam-engine, a dyeing-house, or
a spirit-distillery, would cost much less than a boiler of
the usual form, of equal surface and power.

But in all cases where it is required to produce a great
quantity of steam, it will be always preferable to em-
ploy several boilers of a middling size, placed beside
each other, and heated each by a separate fire, instead
of using one large boiler heated by one fire.

I have shown in my Sixth Essay, on the management
of fire and the economy of fuel, that beyond a certain
limit there is no advantage derived from augmenting
the capacity of a boiler.

It will be perceived that the boiler which I have the
honour of presenting to this Society is of a form fit for
being placed in a portative furnace, and it was actually
intended for that purpose.

Its furnace, which is made of bricks, with a circular
iron grate of 6 inches in diameter, is built in the inside
of a cylinder of sheet-iron, 17 inches in diameter and 3
feet high, and can be easily transported from place to
place by two men.

This cylinder of sheet-iron, which is divided into
two parts, in order to facilitate the construction of the
masonry, weighs only forty-six pounds. The masonry
weighs about a hundred and fifty pounds, and the boiler
twenty-two pounds.

In order to form an estimate of the advantage which
the particular form of this boiler gives it in accelerating

356 Description of a new Boiler, constrticted

its heating, we may compare the extent of surface that
it presents to the action of the fire with that of the flat
bottom of a common boiler.

The diameter of the bottom of a cylindrical boiler
being 12 inches, the surface is 113.88 square inches;
but the surface of the sides of the seven tubes that de-
scend from the flat bottom of our boiler (which is like-
wise 12 inches in diameter) is 593.76 square inches.
Therefore the new boiler has a surface exposed to the
direct action of the fire, more than five times greater
than that of a boiler of equal diameter and of the ordi-
nary form ; how much this difference must affect the
celerity of heating is easy to conceive.

In the manner in which boilers are usually set, their
vertical sides are but little struck by the flame, and on
that account I have not taken the effect of the sides into
consideration in my estimate ; but even taking them
into account, the new boiler will always have a surface
exposed to the fire at least twice as great as that of a
common cylindrical boiler of the same diameter, as can
easily be shown.

The new boiler being 12 inches in diameter and 12
inches high, and each of its seven tubes being 3 inches
in diameter and 9 inches high, its surface is 1160.44
square inches, without reckoning the circular plate that
closes its top, nor its neck.

The surface of the bottom and sides of a cylindrical
boiler of 12 inches in diameter and 12 inches high will
be 566.68 square inches.

As the quantity of heat that enters a boiler in a given
time is in proportion to the extent of surface that the
boiler presents to the fire, it is evident that, other
circumstances being the same, a .boiler with tubes de-

with a View to the Saving of Fuel. 357

scending from its bottom will be heated at least twice
as soon as a cylindrical boiler of the same diameter with
a flat bottom.

In order that a cylindrical boiler with flat bottom,
surrounded by flame on all sides, might have the same
extent of surface exposed to the fire as a boiler with
tubes, it would be necessary to give it a diameter greater
than that of the boiler with tubes in the proportion of
the square root of 1 160.44 t° the square root of 566.68,
that is, of 17.171 to 12.

Therefore, in order that a cylindrical boiler with a
flat bottom might have the same extent of surface ex-
posed to the fire as our boiler with tubes of 12 inches
in diameter, it would be necessary to give it a diameter
of 17.171 inches.

But if the diameter of a boiler intended for pro-
ducing steam be increased, it is necessary, at the same
time, to increase its thickness, in order to increase its
strength.

The necessary increase of thickness, and the expense
that it will occasion, can be easily calculated.

The effort that an elastic fluid exerts against the sides
of the containing vessel is in proportion to the surface
of a longitudinal and central section of the vessel, and
consequently in proportion to the square of its diameter,
the form remaining the same. Hence we may conclude,
that a steam-boiler of a cylindrical form with a flat bot-
tom, which has the same extent of surface exposed to
the fire as a boiler of 12 inches in diameter with tubes,
should be at least twice as thick as this last, in order
to have an equal degree of strength for resisting the
expansive power of the steam.

The boiler which I have the honour of presenting to

358 Description of a new Boiler, etc.

the Society is particularly intended to serve as a steam-
boiler, but it may undoubtedly be applied to other pur-
poses. Having shown it to M. Auzilly, son of a con-
siderable soap-manufacturer of Marseilles, he thought
that it might be employed with advantage in the making
of soap ; and from what he told me of the process, and
of the boilers employed in that art, I am persuaded
that the experiment would succeed perfectly.

But, after all, it remains to be determined whether it
would not be still more advantageous to employ steam
as a vehicle of heat in the making of soap, instead of
lighting the fire under the bottom of the vessel in which
the soap is made.

The result of an experiment which we are to make,
M. Auzilly and myself, will probably throw some light
upon this question.

[This paper is printed from Nicholson's Journal, XVII. (1807),
pp. 5-10.]

EXPERIMENT

USE OF THE HEAT OF STEAM, IN PLACE OF THAT
OF AN OPEN FIRE, IN THE MAKING OF SOAP.

I HAD the honour of announcing to this Assembly,
at the last meeting but one, that M. Auzilly a'nd
myself were to make an experiment on the use of steam
in the making of soap. This experiment we have
made, and with perfect success.

I have the honour to lay before the Society a piece
of soap of about ten cubic inches, made in my labora-
tory by this new process, which required only six hours
of boiling, whereas sixty hours and more are necessary
in the ordinary method of making soap.

From all the appearances that we observed in the
course of this experiment, and from its results, we
think ourselves authorized to conclude that this new
method of making soap cannot fail to be advantageous in
every respect, and that it will soon be generally adopted.

We propose to repeat the experiment on a larger
scale, as soon as we shall be able to procure the neces-
sary utensils, and we beg the Society to appoint com-
missioners to be present during its execution.

As I intend to communicate to the Institute, upon a
future occasion, all the details of our experiment, with
an account of the apparatus we employed in it, I shall

360 On the Use of the Heat of Steam,

for the present make only one observation on the prob-
able cause of the acceleration of the formation of soap,
which we observed. I believe that this acceleration is
due in great measure, if not entirely, to a motion of a
peculiar kind in the mixture of oil and lye, occasioned
by the sudden condensation of the steam introduced
into the liquor. It is a sharp stroke, like that of a
hammer, which made the whole apparatus tremble.

These strokes, which succeeded rapidly in certain cir-
cumstances, and which were violent enough to be heard
at a considerable distance, must necessarily have forced
the particles of oil and alkali to approach each other,
and consequently to unite.

As the violence of these strokes diminished greatly as
soon as the liquid had acquired nearly the temperature
of the steam, I propose to supply this defect by a par-
ticular arrangement of the apparatus in the experiment
we are going to make. I shall divide the vessel into
two parts, by a horizontal diaphragm of thin sheet cop-
per, and, causing a slow current of cold water to pass
through the lower division or compartment of the ves-
sel, I shall introduce steam into it, through a particular
tube destined for that purpose, as soon as the mixture
of oil and alkali which occupies the upper division of
the vessel is become too hot for condensing the steam.

The steam which enters the water (always kept cold)
that fills the lower compartment of the vessel will be
condensed suddenly, and the sharp strokes which result
will be communicated through the thin diaphragm to
the hot liquid contained in the upper division of the
vessel, and will, I expect, accelerate the union of the
oil with the alkali. I shall then shut almost entirely
the cock which admits steam into the upper division of

in place of an open Fire, in making Soap. 361

the vessel, in order to prevent a useless consumption
of steam and heat.

I shall not fail to give an account of the results of
this new experiment to this Assembly ; and I shall re-
joice if by any researches I shall be so happy as to con-
tribute to the improvement of an art which is undoubt-
edly of great importance to society.

[This paper is printed from Nicholson's Journal, XVII. (1807),
pp. 10- 12.]

ACCOUNT

NEW EXPERIMENTS ON WOOD AND CHARCOAL.

HAVING had occasion to dry several kinds of
wood, to ascertain how much water was con-
tained in them, I procured a piece of each kind six
inches long and half an inch thick, and planed off some
pretty thin shavings, which I kept to dry for eight days
in a room, the temperature of which was constantly
about 60° F. The wood had been previously drying
two or three years in a joiner's workshop.

Of each kind of shavings I took 10 grammes (154.5
grains), which I placed on a china plate in a kind of
stove made of sheet-iron, and heated them moderately
by a small fire under the stove for twelve hours, after
which they were suffered to cool gradually during
twelve hours more. The stove, being surrounded with
brickwork, was still hot twelve hours after the fire had
been extinguished.

On taking out the china plates in succession and
weighing the shavings anew, their weight was found to
be diminished about one tenth, some a little more,
others a little less. When the shavings were put into
the stove, their weight was 10 grammes ; when taken
out, it was about 9. Their colour was not perceptibly
altered, and they had no appearance of having been ex-
posed to a strong heat.

Account of some new Experiments, etc. 363

Desirous of knowing how far the drying of wood
might be carried, I replaced them all in the stove, which
I heated as before, neither more nor less, for twelve
hours, and afterward left to cool slowly for twelve
hours.

On taking out the shavings the next day, they had all
changed colour more or less ; from a yellowish-white
they had become light brown, dark brown, more or less
yellow, and some of a fine purple.

Their weight, which was at first 10 grammes, was now
found to be

Oak . . . .7.16 Cherry . . . 8.60

Elm . . . 8.18 Linden . . 7.86

Beech ... 8.59 - (after having

Maple . . . 8.41 been in the open air

Ash .... 8.40 twenty-four hours) . 8.06

Birch . . . 7.40 Male fir . . . 8.46

Service . . . 8.46 Female fir . . . 8.66

Wishing to know whether the wood might not be
reduced to charcoal by continuing the moderate heat of
the stove a long time, I took half the linden shavings,
which weighed 4.03 grarnmes, placed them in a china
saucer supported by a cylindrical earthen vessel 3 inches
in diameter and 4 inches high, put this on an earthen
plate, and covered it by a glass jar 6 inches in diameter
and 8 inches high. On the earthen plate was a layer of
ashes about an inch deep, serving to close the mouth of
the jar slightly.

This little apparatus being placed in the stove, it was
heated a third time for twelve hours, and then left
twelve hours without fire, to cool gradually.

On taking out the apparatus, I found that the wood

364 Account of some new Experiments

was become perfectly black, and that the glass jar was
yellowish, and its transparency diminished.

On weighing the shavings, which retained their origi-
nal figure completely, I was surprised to find that they
weighed only 2.21 grammes. As they were the remains
of 5 grammes of wood, and as, from the experiments
of Messrs. Gay-Lussac and Thenard, I had expected to
find in this wood at least fifty per cent of charcoal, I did
not think it possible to reduce the weight of the shav-
ings to less" than 2.5 grammes, particularly with the
moderate heat I employed.

To clear up my doubts, I replaced the apparatus
in the stove, and heated it again as before for twelve
hours, and afterwards left it in the stove twelve hours
to cool.

On taking out the apparatus, I found that the shav-
ings weighed only 1.5 grammes. The jar was less trans-
parent, and of a blackish-yellow colour throughout, but
particularly in its upper part, above the level of the
brim of the saucer in which the shavings were. These
shavings were still of a perfect black.

Having heated the apparatus again for twelve hours,
and then left it to cool, I was surprised, on taking it out
of the stove the next day, to find that the jar had again
become clear and transparent. Not the least trace of
the yellow coating with which its inner surface had been
covered now remained.

On examining the wood, I found that this also had
changed its colour. It had assumed a bluish hue,
pretty deep, but very different from the decided black it
had before. Its weight was 1.02 grammes.

I put it twice more into the stove, and each time its
weight was diminished, so that the 5 grammes of wood

on Wood and Charcoal. 365

were reduced at last to 0.27 of a gramme, or about a
twentieth of the original weight.

I am persuaded that I should have diminished it still
more, if I had continued the experiment longer ; but it
has been tried long enough to establish this remarkable
fact, that charcoal can be dissipated by a heat much less than
has been considered necessary to burn it.

It may be supposed that I was very desirous of
knowing whether the same thing would occur to charcoal
already formed by the usual process. Accordingly I
took a piece of charcoal from my kitchen, heated it to a
strong red heat, and, while it was still red, put it into a
marble mortar, and powdered it. Having passed it
through a sieve, I took 4.03 grammes of the powder,
placed it in the saucer, heated it in the stove twelve
hours, and then left it twelve hours to cool. On taking
it out, it weighed but 3.81 grammes.

As this powdered charcoal was nothing but a collec-
tion of small bits of charcoal, which were in contact
with the air only by a very small surface compared with
that of the shavings, I made another experiment, the re-
sult of which was more striking and more satisfactory.

Having enclosed in a cloth a quantity of powdered
charcoal, that had been passed through a sieve, I beat it
strongly in a place where the air was still ; and when the
air appeared to be well loaded with the fine dust of the
charcoal, I placed on the ground a white china saucer,
quitted the place, and left the dust to settle.

The saucer was covered with it, so as to appear of a
very dark gray.

Before all the dust had settled, I wrote some letters
on the saucer with the point of my finger, and these let-
ters were afterward covered with a still finer dust.

366 Account of some new Experiments

I imagined it possible that the part covered by a very
fine dust might be found whitened, while that covered
with a stratum of coarser charcoal powder would be
found perhaps still black.

The result of the experiment showed that this pre-
caution was not necessary. All the charcoal powder
disappeared completely in the stove, and the saucer
came out perfectly white.

Another saucer, which had been blackened a little by
rubbing it with lampblack, and placed in the stove by
the side of that blackened with charcoal dust, came out
of the stove as black as it went in. As soon as I saw
that the linden shavings converted into charcoal might
be dissipated by the moderate heat of the stove, I sus-
pected that they had been consumed slowly by a silent
and invisible combustion, and that the product of this
combustion could be nothing but carbonic acid gas.

To clear up this point I made the following experi-
ment.

Having procured a stock of very dry birch shavings
in ribands about a twentieth of a line thick, near half
an inch broad, and six inches long, I dried them for
eight days in a room heated by a stove, where the tem-
perature was about 60° F., the shavings being laid on a
table at a distance from the stove. Of these shavings
thus dried, I took 10 grammes, which I placed on a
china plate, and heated in the stove, in the manner
already described, for twenty-four hours. When taken
out of the stove, they weighed but 7.7 grammes, and
had acquired a deep brown colour inclining to purple.
They were still wood, however ; for, though deeply
browned, they burned with a very fine flame.

Of these brown shavings I made three parcels, each

on Wood and Charcoal. 367

weighing 2.3 grammes. The first was placed in the
stove on a white china plate, supported by a tile, but
not covered. The second was put into it in a similar
manner, except that it was covered with a glass jar, 6
inches in diameter and 6 inches high.

The third parcel was put into a glass vessel, 6 inches
high, but only an inch and a quarter in diameter. This
narrow vessel was put into a glass jar 3 inches in diameter
and 7 inches high, which, being slightly closed with its
glass cover, was also placed in the stove on a tile.

As the door of the stove (which is double, the better
to confine the heat) does not shut so close as to prevent
the free passage of air, and as the china plates on
which two of the parcels were placed were flat, every
circumstance was favourable for the free transmission of
the carbonic acid gas arising from the decomposition of
these two parcels by slow combustion, and there was
nothing to prevent the progress of this operation. But
the third parcel being enclosed in a narrow vessel, as
this gas is much heavier than atmospheric air, the first
portion of this gas arising from a commencement of
combustion of the wood could not fail to descend in
the vessel toward its bottom, gradually expel the air,
and at length fill the vessel completely ; and as this sort
of inundation by carbonic acid gas could not fail to
stop the combustion, I expected to find that this parcel
of shavings would be preserved, at least in part, even
though both the others should be entirely consumed.

The stove having been heated in the usual manner, I
found the next day that the results of the experiment
had been such as I anticipated. The two parcels of
shavings placed on the china plates had disappeared en-
tirely, nothing at all remaining except a very small

368 Account of some new Experiments

quantity of ashes, of a white colour inclining a little to
yellow.

The yellow ashes in the plate that was not covered
with a glass jar were deranged and dispersed by the
wind occasioned by opening the door of the stove too
suddenly ; but those in the other plate, being protected
by the glass, were found all together. As they still re-
tained their original figure of shavings, though reduced
to a very small bulk, this appeared to me a demonstra-
tive proof that the shavings, whence they arose, had not
been burned by a common fire. For this reason, and
also on account of their extraordinary colour, approach-
ing very near that of the wood in its natural state, I
preserved them, to show them to the Class. They
weighed only 0.04 of a gramme ; and as the shavings,
of which they were the remains, weighed 2.987 grammes
on coming out of the hands of the joiner, these ashes
make only one and one third per cent of the weight
of the wood.

The third parcel of shavings, which had been placed
in a narrow glass vessel, had not disappeared, but the
wood was converted into perfect charcoal. I have the
honour to present it to the Class, in the same vessel in
which it was charred.

As the three parcels of shavings were of the same
wood, and equal in weight ; as they were exposed to-
gether to the same degree of heat, and for the same
time ; and as the two portions that were placed so as to
facilitate the escape of the carbonic acid gas arising from
their decomposition, disappeared entirely, while the
third, which was so circumstanced that the escape of this
gas was impossible, did not disappear ; — it seems to me
that there can be no doubt of the cause of the phenom-

on Wood and Charcoal. 369

ena that presented themselves ; and it is certainly a
curious fact, that charcoal, which has hitherto been con-
sidered as one of the most fixed substances known, can
unite itself to oxygen, and form with it carbonic acid
gas, at a temperature much below that at which it burns
visibly.

[This paper is printed from Nicholson's Journal, XXXII. (1812),
pp. 100— 105.]

RESEARCHES

HEAT DEVELOPED IN COMBUSTION AND IN THE
CONDENSATION OF VAPOURS.

SECTION I. — Description of a new Calorimeter.

\ TTEMPTS have been long ago made to measure
JT\. the heat that is developed in the combustion of
inflammable substances ; but the results of the experi-
ments have been so contradictory, and the methods
employed so little calculated to inspire confidence, that
the undertaking is justly considered as very little ad-
vanced.

I had attempted it at three different times within
these twenty years, but without success. After having
made a great number of experiments with the most
scrupulous care, with apparatus on which I had long
reflected, and afterward caused to be executed by skilful
workmen, I had found nothing, however, that appeared
to me sufficiently decisive to deserve to be made public.
A large apparatus in copper more than twelve feet long,
which I had made at Munich fifteen years ago, and
another, scarcely less expensive, made at Paris four years
ago, which I have still in my laboratory, attest the de-
sire I have long entertained of finding the means of
elucidating a question^ that has always appeared to me
of great importance, both with regard to the sciences
and to the arts.

On the Heat developed in Combustion, etc. 371

At length, however, I have the satisfaction of an-
nouncing to the Class, that, after all my fruitless
attempts, I have discovered a very simple method of
measuring the heat manifested in combustion, and this
even with such precision as leaves nothing to be desired.

That the Class may be the better able to judge of my
method of operating, and the reliance that may be
placed on the results of my experiments, I place my
apparatus before it.

The principal part of this apparatus is a kind of
prismatic receiver, eight inches long, four inches and a
half broad, and four inches three quarters high,* formed
of very thin sheets of copper. This receiver, which well
deserves the name, already celebrated, of calorimeter ', is
furnished with a long neck, near one of its extremities,
three quarters of an inch in diameter, and three inches
high, intended to receive and support a mercurial ther-
mometer of a particular shape. The receiver has also
another neck, an inch in diameter and the same in
height, situate in the centre of its upper part, and closed
by a cork.

Within this receiver, two lines above its flat bottom,
is a particular kind of worm, receiving all the products
of the combustion of the inflammable substances burned
in the experiments, and transmitting the heat manifested
in this combustion to a considerable body of water,
which is in the receiver.

This worm, which is made of thin copper, occupies
and covers the whole bottom of the receiver, yet with-
out touching either its bottom or its sides. It is a flat
tube, an inch and a half broad at one end and an inch at
the other, and half an inch thick throughout. It is

* French measure.

372 On the Heat developed in Combustion

bent horizontally, so as to pass three times from one
end of the receiver to the other, and is supported in its
place, two lines above the bottom of the receiver, by
several little feet.

The aperture that forms the mouth of the worm is
a circular hole in its bottom, near its broadest end.
Into this hole is soldered a perpendicular tube, an inch
in length and an inch in diameter, reaching within the
worm to the height of a quarter of an inch above its
bottom.

This tube passes through a circular hole in the bot-
tom of the receiver, to which also it is soldered. Its
lower aperture is seven lines below the bottom of the
receiver ; and through this the products of the combus-
tion enter into the worm.

The other extremity of the worm passes horizontally
through the perpendicular end of the receiver, opposite
to that near which the products of the combustion enter
the worm.

The worm, before it passes through the end of the
receiver, is fashioned into the shape of a round pipe,
half an inch in diameter ; and an inch in length of this
pipe is seen without the receiver. This piece is made
to fit tight into another similar tube, belonging to the
worm of another receiver, which I call the secondary
receiver ; the purpose of which is to receive the heat
that might still be found in the products of combustion,
after they have passed through the worm of the prin-
cipal receiver.

To support these two receivers in the air, so as not
to touch the table that supports them, each of them is
fixed in a frame of dry linden wood, made of rods an
inch square. Round the bottom of each receiver is a

and in the Condensation of Vapours. 373

copper rim, three lines deep, which is fastened by a row
of very small nails to the wooden frame. The body of
the receiver itself enters about a line into the frame, to
which it is very accurately fitted.

The flat form of the worm is essential to the perfec-
tion of the apparatus, as is evident when its purpose is
considered.

All the products of the combustion being elastic
fluids, and consequently substances incapable of com-
municating their heat but by proceeding particle after
particle to deposit it on the surface of the cold and
fixed body intended to receive it, it was indispensable so
to construct the apparatus that the hot fluids should of
necessity be spread beneath and against a large flat sur-
face, placed horizontally, and always cold.

Before I employed horizontal worms made of flat
tubes, I had more than once tried those of the common
form ; but they never answered my purpose otherwise
than so imperfectly that I could never make any account
of the experiments in which they were employed.
There is no doubt but the shape I have adopted for the
worm of my calorimeter would be very advantageous
for every kind of apparatus for distillation.

One thing very important in the construction of my
apparatus is the shape of the thermometer which I
employ to measure the temperature of the water in the
receiver. This thermometer — which I made myself, and
which, after having undergone every kind of trial, has
always appeared good — is a mercurial thermometer,
divided according to Fahrenheit's scale. It is one of
four, all similar, that I employed at Munich, in the
winter of 1802, in my experiments on the refrigeration
of liquids enclosed in vessels.

374 On Mie Heat developed in Combustion

The reservoir of this thermometer is cylindrical,
about two lines in diameter only, and four inches high ;
and as the water in my calorimeter is four inches deep,
this thermometer always indicates the mean temperature
of the fluid, whatever may be the temperature of its
different strata.

In my various inquiries concerning heat, I have had
frequent opportunities of seeing the importance of this
precaution ; and I cannot conceive how any one can
expect to avoid great mistakes in measuring the temper-
ature of liquids heated or cooled, if we do not attend
to this. For my own part, I confess I pay little regard
to the experiments of which I am told, when I know
they are so negligently made ; and assuredly I shall
never waste my time in attempting to build theories on
their results.

In using the apparatus I have described, several pre-
cautions are necessary. In the first place, it is obvious
that when the object is to ascertain the quantity of heat
developed in the combustion of any inflammable sub-
stance, it is indispensably necessary so to arrange mat-
ters that the combustion shall be complete. I have thought
that it might be so considered, whenever the substance
burned leaves no residuum, and burns with a clear
flame, without smoke or smell.

The least smell, particularly that peculiar to the in-
flammable substance burned, is a certain indication that
the combustion is imperfect.

I had long sought, before I was able to find, to my
satisfaction, a mode of burning very volatile liquids,
such as alcohol and ether ; but I have at length discov-
ered it, as will soon appear. I have frequently suc-
ceeded in burning highly rectified sulphuric ether, with-

and in the Condensation of Vapours. 375

out the least smell of ether being diffused through the
room ; and it was in these instances alone that I con-
sidered the experiments as accurate.

As to wood, I have found a very simple method of
burning it completely, without the least appearance of
smoke or smell. I got a joiner to plane me shavings
about half an inch wide, a tenth of a line thick, and six
inches long; and holding these in the hand or with
pliers, elevated at an angle of 45° or thereabout, and
with the edges perpendicular, they burned like a match,
with a very clear flame.

The slip of wood that burns being very thin, and placed
between two flat flames which press on it closely, it is
exposed to the action of so strong a heat that it burns
perfectly and entirely.

If the shavings employed be too thick, a portion of
the charcoal of the wood remains, particularly if it be
oak, or any other wood of slow and difficult combus-
tion ; and in this case the experiments are defective.
But if the shavings be sufficiently thin> and well dried,
I have found that any kind of wood may be burned
completely.

In burning candles, wax tapers, or fat oils in lamps,
the only precautions necessary are so to arrange the
wick as to yield no smoke ; to place the flame properly
in the aperture of the worm ; and to surround the
apparatus on all sides by screens, to prevent the flame
from being deranged by the wind.

In these experiments there is one source of error,
too obvious to escape the most superficial observer, and
to which it was important to attend. While the calo-
rimeter is warmed by the heat developed in the combus-
tion of the inflammable substance which is burning at

376 On the Heat developed in Combustion

the aperture of the worm, it is continually cooled by
the ambient air that surrounds it on all sides. It would
be possible, no doubt, by calculations founded on a
knowledge of the law of refrigeration of the receiver,
which might be found by separate experiments, to ascer-
tain the quantity of the effect produced by the refrigera-
tion in question ; and this even with a certain degree of
precision : but it would have been impossible by this
method, or by any other known, to calculate the effects
of another cause of error, less obvious perhaps, but
certainly more weighty, than that of the refrigeration
of the external surface of the receiver.

The nitrogen which is mixed with the oxygen of the
atmospheric air is necessarily carried into the worm
with the proper products of the combustion ; and with-
out a precaution, which it occurred to me to employ to
prevent the effects of this cause of error by making
a compensation for them, all the experiments would
have been of no value.

Fortunately the method I employed to obviate the
effects of this cause of error was sufficient to prevent at
the same time those that might have arisen from the
cooling of the outer surface of the receiver.

As the receiver is cooled, whether by the atmospheric
air in contact with its external surface or by the nitro-
gen and other gases traversing the worm with the
products of combustion, only so far as the worm is
hotter than the surrounding air, while, on the contrary,
it is heated by these elastic fluids whenever it is at a
lower temperature than they are, — by arranging matters
so that the temperature of the water in the receiver shall
be a certain number of degrees, 5° for instance, below
the temperature of the air at the beginning of the ex-

and in the Condensation of Vapours. 377

periment, and putting an end to the experiment as soon
as the water in the receiver has acquired a temperature
precisely the same number of degrees higher than the
air, the receiver will be heated by the air during half
the time of continuance of the experiment, and cooled
by it during the other half; so that the calorific and fri-
gorific effects of the air on the apparatus will counter-
balance each other, and produce no perceptible effect on
the results of the experiments ; consequently they will
require no correction.

When we are making experiments to elucidate natural
phenomena, it is always more satisfactory to avoid
errors, or to compensate them, than to trust to calcu-
lation for appreciating their effects.

As the law of the variation of the specific heat of water
at different temperatures is not known, and as we have
but an imperfect knowledge of the true measure of the
intervals of temperature marked by the divisions of our
thermometers, to prevent the effects that our uncertainty
on these points would have on the subject of inquiry, I
took care to make my experiments in a room where the
temperature varied very little, and to confine them to a
few degrees of elevation of the temperature of the water
in the receiver.

It is true, I made some experiments in a room where
the air was much colder, and in which I employed ice
instead of water to fill the receiver ; but these experi-
ments were for a particular purpose, and are not classed
with the others. Besides, they never afforded such
uniform and satisfactory results as those made under
other circumstances.

It has been fully proved, not only by the results of
my experiments, but by the experiments of others also,

37 8 On the Heat developed in Combustion

that the vapour of water in contact with ice frequently
freezes, while this same ice is melting by the heat, or
that its thaw appears fully established.

To give an idea of the reliance that may be placed on
the results of the experiments made with the new appa-
ratus I have just described, I will introduce here the
particulars of an experiment made purposely to discover
its degree of perfection.

Having filled two receivers, properly connected with
each other, with water at the temperature of the air of
the room, 55° F., I burned a wax taper under the mouth
of the principal receiver, so that all the products of the
combustion passed through the worm of the secondary
receiver, after having traversed that of the principal.
Each of the receivers contained 2371 grammes [36621.5
grains] of water.

The following are the results of the experiment : —

TIME OF THE OBSERVATION.

Hour, Mia. Sea

9 37 55°

49 42 65

56 15 70

10 2 52 75

9 32 80

16 34 85

23 54 90

27

31 40 95

39 35 100

47 4° I05

From the results of this experiment it appears that
the water in the secondary receiver did not begin to be
heated perceptibly till that in the principal receiver had
been heated 15° or 20°; and, as I had intended from
the beginning never to continue an experiment longer
than was necessary to raise the temperature of the

and in the Condensation of Vapours. 379

water in the principal receiver 10° or 12° F., it may be
supposed that, as soon as I found by this experiment
how little heat remained in the products of combustion
after they had passed through the worm of the principal
receiver, I relinquished my original design of operating
with the two receivers joined together. As it was evi-
dent, from the above results, that the second receiver
could never be sensibly affected, or indicate anything
except the confidence I might place in the indications
of the first, I resolved to dispense with the trouble of
using it.

It may be seen by the description I have given of
this apparatus, that it may be used very conveniently
for ascertaining the specific heat of gases, as well as
that made apparent in the condensation of vapours, and
generally in all researches where the quantity of heat
communicated by an elastic fluid in cooling is to be
measured. And as it would be extremely easy, by very
simple means, to separate completely the products of
the vapours condensed in the worm from the* gases
that pass through it without being condensed, I cannot
avoid hoping that this apparatus will become useful as
an instrument to be employed in chemical analyses.
This, however, would only be an extension of the
method already employed with so much success by
M. de Saussure, and by Messrs. Gay Lussac and
Thenard.

As soon as my apparatus was finished, I was eager
to see what quantity of heat I should find in the com-
bustion of wax and in that of olive oil, that I might
afterward compare the results of my experiments with
those of M. Lavoisier's ; and, as I have the most
implicit reliance on everything published by that excel-

380 On the Heat developed in Combustion

lent man, I sincerely wished to find in this comparison
a proof of the accuracy of my method, and at the same
time a confirmation of the estimates of M. Lavoisier.

SECTION II. — Experiments made with white Wax.

The air of the room being at the temperature of 6 1° F.,
2781 grammes of water, of the temperature of 56° F.,
were put into the receiver of the calorimeter (including
the quantity of this liquor that represents the specific
heat of the instrument), and, a lighted wax taper having
been properly placed at the entrance of the worm, the calo-
rimeter was heated for 13 minutes and 26 seconds, when,
the thermometer announcing that the water had acquired
the temperature of 66° F., the taper was extinguished.

As I took care to weigh the taper before it was lighted,
I found, by weighing it at the end of the experiment,
that 1.63 grammes of wax had been burned.

To express the results of this experiment so as to ren-
der them obvious, and at the same time easy to be com-
pared with the results of other similar experiments, we
will see how much water of the temperature of melting
ice would have been made to boil, at the mean pressure
of the atmosphere, by the heat made apparent in the
combustion of the 1.63 grammes of wax burned.

The distance on Fahrenheit's scale between the tem-
perature of melting ice and boiling water being 180°, if
the burning of 1.63 grammes of wax were requisite to
raise the temperature of the water in the calorimeter 10°,
the burning of 29.34 grammes would have been necessary
to raise it 180°; and, if 29.34 grammes of wax could
furnish by combustion sufficient heat to raise the tem-
perature of 2781 grammes 180°, a gramme of this

and in the Condensation of Vapours. 38 1

inflammable substance must furnish enough to heat
94.785 grammes of water to the same point.

Consequently, one pound of white wax, or wax taper,
should furnish, in burning, sufficient heat to raise 94.785
pounds of water from the temperature of melting ice to
the boiling point.

To find how many pounds of ice this quantity of heat
would melt, we have only to add to the number of pounds
of water at the temperature of melting ice it would cause
to boil the third part of this number, and the sum would
express the weight of the ice in pounds.

This, then, for white wax is : —

94-78$
+ 31-595

= 1 26.380 IBs. of ice melted for I Ib. of the wax burned.

Before I compare the result of this experiment with
that of an experiment made with the same substance by
M. Lavoisier, I will give an account of two other ex-
periments I made with wax, as the reader will undoubt-
edly be struck with the uniformity of their results. This
is so remarkable that I should scarcely venture to pub-
lish them had I not proofs that all my experiments were
actually made and minuted down before I began my cal-
culation of their results, and were I not assured that
any person who will follow my method, using the same
apparatus, will find the same results on repeating my
experiments.

As the mode of operating in making these experiments
must now be well known, I may suppress the particulars
in what follows without inconvenience, and give only the
results of the experiments.

I will begin with three experiments made with white

382 On the Heal developed in Combustion

wax; and to render them more easy to compare, I will
give them together in a tabular form.

Results of three Experiments on the Burning of white Wax, showing the
Quantity of Water that would be heated 1 80°, or of Ice that would
he melted, by one pound Weight of it.

1

Temp, of the water

Results.

u Quantity
•5 of wax
^ butned.

£

employed
ing.

Quantity
of water
heated.

of its
tempera-
ture.

at the be-
ginning of
the exp.

at the
end of the
exp.

Tempera-
ture of
the air.

Pounds
of water
heated

1 80°

Pounds
of ice

melted.

Grms.
1 1.63
2 2.36

m. s.
13 24
I9 30

Grms.
2781

Degrees.

io°F.
Hi

Degrees.
51

Degrees.
65* '

Degrees.

61° F.

58

Ibs.
94.785
94.926

Ibs.
126.38
126.608

3 2.17

18 15

<3i

5»i

6

58

94-337J125.783

If we take the mean term between the results of these
experiments, we shall find that the quantity of heat de-
veloped in the combustion of wax is such that one pound
of this substance is sufficient to raise 94.682 pounds of
water from the temperature of melting ice to the boiling
point, and consequently that it should melt 126.242
pounds of ice.

According to the experiments of M. Lavoisier, the
heat developed in the combustion of one pound of white
wax was sufficient to melt 133.166 pounds of ice.

The difference between the results of our experiments
with this substance is not very great ; and if those of
M. Lavoisier were made at a time when the temperature
of the air was only a few degrees higher than that of
melting ice (which I have no means of ascertaining), the
quantity of nitrogen that must have entered into the
calorimeter, with the oxygen employed to support the
combustion, would have been so great as to account suf-
ficiently for the difference. But the very great difference

and in the Condensation of Vapours. 383

between the results of our experiments made with olive
oil proves that one or other of our processes must have
been defective.

The mean result of several experiments made with
olive oil gave me for the measure of the quantity of heat
developed in the combustion of one pound of this sub-
stance 90.439 pounds of water heated 180° F., or 120
pounds of ice melted, neglecting the fraction.

In the experiments of M. Lavoisier, more than 148
pounds of ice were melted by the heat that appeared to
result from the combustion of one pound of this oil.

It is true that this result was considered by that emi-
nent philosopher himself as too great to be capable of
explanation ; and he added, with that modesty which
rendered him so engaging and so respectable: "We
shall probably find ourselves under the necessity of
making corrections, perhaps pretty considerable ones,
in most of the results I have given ; but I did not
think this a sufficient reason to delay affording their
assistance to those who might intend to pursue the
same object."

As it appears very probable that all the fat oils, when
perfectly pure, are composed of the same principles, I
was curious to see whether rape oil, purified by sulphuric
acid, would not afford more heat in its combustion than
olive oil, when burned in its natural state. The result
of three experiments showed me that rape oil, thus puri-
fied, does, in fact, yield more heat than olive oil. The
difference is, indeed, pretty considerable, and more than
I could have suspected.

The combustion of I Ib. of purified

rape oil gave . . . 93.073 Ibs. of water heated 1 80°.
I Ib. of olive oil gave . . 90.439 " " " "

384 On the Heat developed in Combustion

Chemists may tell us whether the quantity of incom-
bustible matter separated from rape oil in purifying it
be sufficient, or not, to account for this difference.

On comparing the results of the experiments made
with white wax and those with the purified oil, it
appears that equal weights of these substances afford
nearly equal quantities of heat in their combustion; and
as, in fact, this ought to be the case, from the quantities
of combustible matter they contain, the result tends to
strengthen our confidence in this method of measuring
the heat developed in combustion.

The combustion of

I Ib. of white wax gave . 94.682 Ibs. of water heated 1 80°.
I Ib. of purified oil . . 93.073 " " " "

As the object I had chiefly in view in this series of
experiments was to ascertain the quantities of heat
developed in the combustion of pure hydrogen and
carbon, in order to render this method useful in some
chemical analyses, I examined particularly those in-
flammable substances that had been analyzed with most
care.

Several attempts have been made to ascertain these in-
teresting questions by direct experiments, in burning
pure hydrogen, or pure hydrogen and carbon ; but the
results of these researches have varied so much that they
cannot be relied on.

According to Crawford, the heat developed in the
combustion of one pound of hydrogen gas is sufficient
to raise the temperature of 410 pounds of water 180° F.
But the estimation of M. Lavoisier is much lower.
According to him, this heat would raise only 221.69
pounds of water the same number of degrees.

and in the Condensation of Vapours. 385

On the other hand, M. Lavoisier estimates the quan-
tity of heat developed in the combustion of charcoal
much higher than Dr. Crawford. I have many reasons
to believe that they both estimate it too high ; and, if
this opinion be confirmed, we must estimate the heat de-
veloped in the combustion of hydrogen a little higher
even than Crawford has done, to be able to account for
that manifested in my experiments.

From several experiments, which I made five years ago,
it appeared to me that one pound of charcoal, dried as
much as possible before it was weighed by heating it red-
hot in a crucible, was not capable of raising more than
from 52 to 54 pounds of water from the temperature
of melting ice to a boiling heat.

According to Crawford, this heat should suffice to boil
57. 606 pounds, and according to Lavoisier,y2. 375 pounds.

We shall see how these estimates agree with the results
of my experiments.

As the experiments made with wax yielded very uni-
form results, and as the analysis of this substance has
been made with great care, I shall examine how the
quantities of hydrogen and carbon in this substance
agree with the quantity of heat that it afforded me in
combustion.

According to the analysis of Messrs. Gay-Lussac and
Thenard, a pound of this substance contains

Carbon . . . . . , . . . 0.8179 Ib.
Free hydrogen 0.1191

If we adopt the calculations of Dr. Crawford, both for
the heat furnished by the hydrogen and that furnished by
the carbon, we shall have for the heat that should be
furnished by the combustion

VOL. II. 25

386 On the Heat developed in Combustion

Pounds of water raised
from 32° to 212°.

Of 0.1191 lb. of hydrogen, after tne ratio of 410
Ibs. of water raised from 32° to 212° by burning
I lb. of hydrogen 48.831 Ibs.

Of 0.8179 lb. of carbon, after the ratio of 57.606
Ibs. of water raised from 32° to 212° by burning
I lb. of carbon ...... 47.116 "

Total of the heat that ought to be furnished by the
quantity of combustible matter (hydrogen and car-
bon) in i lb. of white wax .... 95-947 "

Quantity of heat furnished by I lb. of white wax,
during its combustion, according to my experi-
ments 94.682 '

If we adopt the calculations of M. Lavoisier for the
heat furnished by carbon and hydrogen in their combus-
tion, we shall have for the heat that ought to be furnished
by the burning

Of 0.8179 lb. of carbon, after the ratio of 72.375 Ibs.

of water heated 1 80° by I lb. . . . 59. 195 Ibs.
Of 0.1191 lb. of hydrogen, after the ratio of 221.69

Ibs. of water heated 180° by i lb. . . 26.403 "

Total of the heat that ought to be furnished by the

combustible matter in i lb. of white wax . 85.598 "

From the results of these calculations it appears that
the estimations of Dr. Crawford agree much better with
the experiments than those of M. Lavoisier.

Let us see how the results of the experiments made
with fat oils agree with the estimations of these gentle-
men.

According to the analysis of Messrs. Gay-Lussac and
Thenard, a pound of olive oil contains

Carbon 0.7721 lb.

Free hydrogen ....... 0.1208

and in the Condensation of Vapours. 387

According to the calculations of M. Lavoisier, we have,

For 0.7721 Ib. of carbon . 55.881 Ibs. of water heated 180°.
" 0.1208 Ib. of hydrogen . 26.780 " " " "

Total ... . 82.661 " "

According to the calculations of Dr. Crawford, it is,

For 0.7721 Ib. of carbon . 44-478 Ibs. of water heated 180°.
" 0.1208 Ib. of hydrogen . 49-528 " " " "

Total .... 94.006 " " " "

According to the experiments, I pound of purified rape
oil furnished heat sufficient to raise 93.073 pounds of
water 180°; and i pound of olive oil enough to heat
90.439 pounds.

From all these comparisons it follows that the estima-
tions of Dr. Crawford agree much better than those of
M. Lavoisier with the results of my experiments.

SECTION III. — Experiments made with Spirit of Wine,
Alcohol, and Sulphuric Ether.

As the component parts of these inflammable liquids
may be considered as well ascertained by the results of
the excellent investigation of M. de Saussure, I under-
took to examine them for the second time, in order to
discover what quantities of heat are developed in their
combustion. I had begun this undertaking five years
ago ; but, after having made a considerable number of
experiments, I desisted from it on account of the great
difficulties that occurred. As soon, however, as I had
found means of rendering my apparatus more perfect, I
formed the project of recommencing it.

Before I enter into the particulars of my experiments,
I must say a few words respecting the difficulties that

388 On the Heat developed in Combustion

occurred to me, even after I had my new apparatus, and
of the means I employed to surmount them. I even
found myself exposed to dangers, which it is necessary
for me to mention as a caution to those who may under-
take the same inquiry.

When I made the experiments with highly rectified
alcohol, and more particularly with ether, I found it very
difficult to prevent a portion of these volatile liquids
from escaping in the state of vapour from the bulk of
them remaining in the lamp. I procured a small lamp,
resembling in shape a small round snuff-box, with a noz-
zle rising from the centre of the circular plate, which
closed it atop ; and on this plate was fixed a small pan,
to hold cold water, for keeping the nozzle cool and pre-
venting the heat from being communicated to the body
of the lamp. But this precaution was not sufficient,
when I burned ether, as I found to my cost; for, though
the pan was twice the diameter of the lamp, and filled
with very cold water, the water was so heated in a few
minutes that an explosion took place from vapour of
ether kindling in the air with a flame that rose to the
ceiling. Indeed it was near setting the house on fire.

Warned by this accident, I procured a new lamp, much
smaller than the former, being only an inch in diameter
and three quarters of an inch deep ; and its nozzle, which
was only two lines in diameter, was three quarters of an
inch high. To keep this small lamp cool while burning,
it was placed in a small pan, and kept constantly im-
mersed in a mixture of water and pounded ice to within
a quarter of an inch of the extremity of the nozzle.
These precautions were sufficient to prevent any explo-
sion, though not the evaporation either of the ether or of
the alcohol. This fact I learned from observing that, as

and in the Condensation of Vapours. 389

often as I made two consecutive experiments without
filling the lamp afresh, the alcohol constantly appeared
weaker in the second experiment than in the first.

The cause of this phenomenon was not difficult to dis-
cover. The most volatile and consequently the most
combustible parts of this liquid, being diffused in vapour
in the interior of the lamp, found means of escaping
through the nozzle with the part of the liquid that trav-
.ersed the match, leaving the alcohol that remained in the
lamp perceptibly weakened.

To remedy this imperfection, I constructed a third
lamp, which I now submit to the inspection of the Class.
It is made of copper, and has the shape of a small cylin-
dricaf vase, an inch and a half in diameter, and three
inches high, swelling out a little atop, and closed hermet-
ically by a copper stopple, which, being ground with
emery, fits tight into the neck of the vase. Through
the centre of this stopple passes a small perpendicular
hole, which can be shut completely or left a little open,
as may be required, by means of a small screw carrying
a copper collar.

A small tube, about an eighth of an inch in diameter
and two inches and a half long, proceeds horizontally
from the side of the vase very near the bottom. At the
distance of an inch and four lines from the vase this tube
is bent at a right angle, rising upwards perpendicularly
to form the nozzle of the lamp.

This little tube is everywhere very thin, except at its
upper extremity, where it is made thicker, to admit of
being shaped so as to fit tight into a very small cylindri-
cal extinguisher, five lines high by three and a half in
diameter, intended to close the nozzle hermetically with-
out touching or deranging the wick, the moment the

390 On the Heat developed in Combustion

lamp ceases to burn, and to keep it constantly closed
when the lamp is not lighted.

Without this precaution, in experiments made with
ether, so large a quantity of this volatile liquid would
evaporate through the nozzle of the lamp while weigh-
ing, that it would be impossible to ascertain the quantity
burned.

The nozzle of the lamp is steadied by two pieces of
wire, proceeding from it horizontally, and soldered to the
body of the lamp.

To keep this lamp constantly cold, as well as the
liquid it contains, it is placed in a small pan, and covered
completely, except the extremity of its nozzle and that
of its neck, with a mixture of pounded ice and water.

When the lamp is weighed, it is taken out of the pan,
and well wiped with a dry cloth before it is put into the
scale.

When the lamp is kindled, the operator must not for-
get, after it has burned two or three minutes, to open
the screw that closes its stopple a little, though but
'very little, otherwise it might go out.

As the little horizontal tube, by which the liquid that
is burned passes from the reservoir of the lamp to its
nozzle, is always filled with liquid, so 'that it can have
no communication with the vapour diffused in the upper
part of the reservoir, this vapour cannot escape by the
nozzle of the lamp, as it did before I thought of this
method of preventing it.

If I have been very minute in my description of this
lamp, it is because I thought it necessary to spare those
who might be disposed to repeat my experiments, or make
similar ones, all the difficulties I had to surmount before
I found the means of having under command the com-
bustion of very volatile inflammable liquids.

and in the Condensation of Vapours. 39 1

As the apparatus I have employed has now been de-
scribed, it will be easy to follow the steps of my experi-
ments, and to appreciate their results. I will endeavour
to describe them clearly, but also as briefly as possible.

Having procured a stock of spirit of wine of the shops,
and of alcohol of different degrees of purity, I ascertained
with the greatest care their specific gravities at the tem-
perature of 60° F., taking that of water at the same tem-
perature as 1000000. I chose this temperature that I
might afterward the more easily ascertain the quantities
of water that each ought to contain, according to the
tables constructed from the experiments of M. Lowitz.

The following table will show the specific gravity of
each, and the quantity of pure alcohol of Lowitz and of
water contained in it.

Liquid.

Specifi^ravity

Composition.

Pure alcohol
of Lowitz.

Water.

Alcohol of 42°
Alcohol of the shops
Spirit of wine of" 33°

817624
847140
853240

0.9179

0.8057
0.7788

0.0821
0.1943
0.2212

The following are the results of the experiments made
to ascertain the quantities of heat which these liquids fur-
nished in burning.

In three experiments made with the spirit of wine the
quantities of heat manifested were, —

In the ist, 53.260 Ibs. of water raised from the temperature of
" zd, 51.727 " melting ice to that of ebullition.

" 3^ 52-855 "
The mean result is . ... • . . 52.614 Ibs.

As a pound of this liquid contained but 0.7788 of the
alcohol considered by Lowitz as pure, the other part

392 On the Heat developed in Combustion

(= o. 22 1 2) being only water, which does not burn, to find
how much water would be raised from the temperature
of melting ice to that of ebullition by a pound of the pure
alcohol of Lowitz, we have only to divide the quantity,
that is, the measure, of the mean heat developed in the
experiments with the spirit of wine by the fraction that
expresses the quantity of alcohol in a pound of this
liquid.

Thus, we have |^ = 67.558 pounds, the measure of
the heat developed in the combustion of one pound of
pure alcohol of Lowitz, according to the mean result
of the experiments made with spirit of wine.

In two experiments made with the alcohol of the shops,
the mean result was 54.218 pounds; and, as this con-
tained 0.8057 pound of pure alcohol, we have for the
measure of the heat developed in the combustion of
i pound of pure alcohol ^^ = 67.293 pounds of water
heated 180° F.

Of three experiments made with the alcohol at 42°, the
mean result was 61.952 pounds of water heated 180° F.
by the heat developed in the combustion of one pound
of this liquid.

Hence, I pound of pure alcohol should furnish heat
enough in burning to raise 67.57 pounds of water 180°
F.; for £Hf = 67.101.

Taking the mean between the results of these eight
experiments with three alcoholic liquors, we shall have
for the measure of the heat developed in the combustion
of one pound of pure alcohol of Lowitz 67.317 pounds
of water raised from the temperature of melting ice to
that of ebullition.

It will be extremely interesting, no doubt, to know
whether this quantity of heat agree with the quantities

and in the Condensation of Vapours. 393

of combustible matter (carbon and hydrogen) in alcohol.
We will see.

According to the analysis of M. de Saussure, i pound
of the alcohol of Lowitz contains

Carbon 0.4282 Ib.

Free hydrogen . . . . . . . 0.1018

Water 0.4700

Now, according to the calculations of Dr. Crawford,
we shall have for the measure of the heat developed in
the combustion of

0.4282 Ib. of carbon . 24.667 Ibs. of water heated 180° F.
0.1018 Ib. of hydrogen . 41.738 " " " "

Total .... 66.405 " " " "

The experiments gave us . 67.317 " " " "

It is rare in a research of such delicacy to find the re-
sults of experiment agree so perfectly with those of cal-
culation.

SECTION IV. — Heat developed in the Combustion of Sul-
phuric Ether.

I have already mentioned the difficulties which I
overcame before being able to regulate the combus-
tion of this substance in such a way as to render the
results of my experiments regular and satisfactory ; but
I met with still further difficulties in the course of this
delicate inquiry.

As alcohol is necessarily employed in making sulphuric
ether, and as these two liquids may be united in any
proportions, it is extremely difficult, if not impossible,

394

the Heat developed hi Combustion

to separate them entirely ; and as both are colourless and
limpid, either when mixed or separate, we can scarcely
judge of the degree of purity of the ether, except by its
specific gravity, and even in this way but very imperfectly.

The most highly rectified sulphuric ether which I could
procure, and which I employed in my experiments, was
prepared in M. Vauquelin's laboratory. Its specific
gravity is 728.34 at the temperature of 16° Reaumur.
As that which was employed by M. de Saussure in his
analysis was only of the specific gravity of 717 at the
same temperature, by regarding the ether which I em-
ployed as being a mixture of the same degree of purity
with that of M. de Saussure, and the pure alcohol of
Lowitz having a specific gravity of 792, we shall find,
upon making a calculation, that the ether which I em-
ployed was a mixture of 85 parts of ether of the spe-
cific gravity of 717, and 15 parts of pure alcohol of Lo-
witz of the specific gravity of 792.

On burning this mixture under my calorimeter, after
having brought my apparatus to the highest degree of
perfection, I obtained the following results : —

Duration of the ex-
periment.

Ether burned.

Quantity of water
heated.

Temper
water

ature of
n the
meter

il

1

wf

•5

1

H

Result.

I

Quantity of water !
heated 180° of i
Fahrenheit with '
the heat devel-
oped in the com- !
bustion of one ,
pound of the [
combustible.

At the com-
mencement.

^|6

m. s.
II
II 15

9

20

22

Grms.
I.96
2.01
2.

3-29

3.06

Grms.
2781

Degrees.
54i

58|

lei

Degrees.

69!
731

Degrees.

ioi-°F.

I0t

17

16

Degrees

60° F.
60
60
61

79.996
80.710
80.146
79.884
80.784

Mean result of the five experiments 80.304

and in the Condensation of Vapours. 395

Continuing to make use of the estimates of Crawford,
for the quantities of heat developed in the combustion of
hydrogen and carbon, we shall see if these estimates are
sufficient to account for the heat manifested in these five
experiments.

As the ether employed was a mixture of 15 parts of
pure alcohol of Lowitz, and 85 parts of ether of the
specific gravity of 717 at the temperature of 16° Reau-
mur, and consequently similar to the ether analyzed by
M. de Saussure, we shall begin by determining the quan-
tity of heat which ought to be developed in the combus-
tion of these fifteen parts of alcohol.

As M. de Saussure has shown that in one pound of
Lowitz's alcohol (of the specific gravity of 792) there
are 0.4282 pound of carbon and 0.1068 pound of free
hydrogen, we ought to find in 0.15 pound of this same
liquid 0.06423 pound of carbon, and 0.01527 of free
hydrogen.

According to the estimate of Crawford, 0.06423 pound
of carbon ought to furnish a sufficiency of heat in its
combustion to raise the temperature of 3.7002 pounds
of water 180° F. ; and 0.01527 pound of hydrogen
ought to furnish enough to raise 6.2607 pounds of
water the same number of degrees ; and these two quan-
tities of water, making together 9.9609 pounds, afford
a measure of the quantity of heat which must be devel-
oped in the combustion of the 15 parts of alcohol,
which are found mixed with 85 parts of ether, in order
to form the combustible liquid employed under the
name of sulphuric ether in my experiments.

Now, as one pound of this mixed liquid has furnished
in its combustion enough of heat to raise 80.304
pounds of water 180° F., if we deduct from this mass

396 On the Heat developed in Combustion

the quantity of water which the 15 per cent of alcohol
must heat (= 9.909), that which remains (= 70.3431
pounds of water) will be the measure of the quantity of
heat developed in the combustion of 85 per cent of
ether of the gravity of 717, which exists in this com-
bustible liquid.

According to the analysis of sulphuric ether made by
M. d.e Saussure, we ought to find in one pound of this
liquid (of the specific gravity of 717)

Carbon 0.590 Ib.

Free and combustible hydrogen . . . . 0.194
Oxygen and hydrogen in the proportions necessary to

form water . . . , .0.216

Consequently, we ought to find in 0.85 pound of the
same kind of ether the following quantities of combus-
tible substances, viz. : —

Carbon . . " . . ... . 0.5015 Ib.

Free and combustible hydrogen . . . 0.1651

We shall now see if these quantities of combustible
substances are sufficient to account for the heat which is
manifested in our experiments.

The 0.5015 pound of carbon ought to furnish suf-
ficient heat to raise 28.89 pounds of water 180° F. ;
and the 0.1651 pound of hydrogen sufficient to heat
67.64 pounds the same number of degrees.

These two masses of water form together 96.53
pounds ; but we shall see that the quantity of heat fur-
nished by the 85 parts of ether in the experiments can-
not be greater than that which is necessary to heat
70.3431 pounds of water 180° F.

As the experiments have been made with the greatest

and in the Condensation of Vapours. 397

care, and frequently repeated, and always with very uni-
form results ; and as the estimates which we have adopted,
with respect to the quantities of heat which are developed
in the combustion of hydrogen and in that of carbon,
have been confirmed so as to leave little doubt upon this
subject, — upon investigating the cause of the great differ-
ence between the quantity of heat actually developed in
the combustion of the 85 parts of sulphuric ether burned
in the experiments which we have examined, and the
quantity given by calculation, we are compelled, in my
opinion, to admit that there is an error in the analysis
of this liquid, and that it does not contain so much free
and inflammable combustible matter as M. de Saussure
ascribes to it.

As it seems to me to be much more probable that an
error has been committed in determining the quantity of
free hydrogen in this substance than in determining the
quantity of carbon, I shall suppose with M.de Saussure
that there is really in one pound of sulphuric ether (of the
specific gravity of 717) 0.59 of carbon ; but instead of
estimating the quantity of free hydrogen in this liquid
according to the results of M. de Saussure, I shall adopt
the estimate of Mr. Cruickshanks.

This excellent chemist concluded, from his experi-
ments, that in the vapour of sulphuric ether the carbon
is to the hydrogen as 5 to i.

In the 0.85 pound of sulphuric ether (specific gravity
717) which were mixed with the 0.15 pound of alcohol,
in order to form one pound of the mixed liquid employed
in my experiments, there were 0.5015 pound of carbon ;
and dividing this number by 5, we shall see that this
carbon ought to be united with 0.1003 pound of free
hydrogen, instead of being united with 0.1651 pound, as
we shall suppose according to M. de Saussure.

398 On the Heat developed in Combustion

Let us now see if, by adopting the analysis of Mr.
Cruickshanks with respect to the hydrogen, instead of
that of M. de Saussure, the calculation will agree better
with the experiment.

We have seen that the quantity of water heated
1 80° Fahrenheit, which represents the quantity of
heat which must be developed in the combustion
of the 0.15 Ib. of alcohol, was . . . 9.9609 Ibs.

And that the quantity answering to 0.5015 Ib. of

carbon, which exists in the 0.85 of ether, was . 28.89

We shall for the present add that which answers
to the combustion of 0.1003 Ib. of free combus-
tible hydrogen, which, according to Mr. Cruick-
shanks, ought to be found united to this quantity
of carbon in order to form the ether . . 41.123

These three quantities of water together are the
measure of the heat which must be developed in
the combustion of one pound of sulphuric ether of
the kind employed in my experiments . . 79-9739

The mean result of five experiments was . . 80.304.

This coincidence between the calculation and the ex-
periment is, doubtless, too remarkable to be owing to
chance ; but I am ready to prove that it occurred without
being foreseen or expected.

From all these results we may conclude, that one pound
of sulphuric ether, of the specific gravity 717 at the
temperature of 16° Reaumur, or of the same species
with that employed by M. de Saussure, should have
furnished in combustion enough of heat to raise 82.369
pounds of water 180° F., viz. : —

That furnished by 0.59 Ib. of carbon . . . 33.989 Ibs.
And that furnished by 0.118 Ib. of hydrogen . 48.380

82.369

and in the Condensation of Vapours. 399

If the proportion of free hydrogen in the ether ana-
lyzed by M. de Saussure was really such as he has deter-
mined it to be, one pound of this liquid ought to furnish
a sufficiency of heat in its combustion to raise 113.566
pounds of water 180° F., viz. : —

That furnished by 0.59 Ib. of carbon . . . 33.989 Ibs.
And that which was furnished by 0.194091 of hy-
drogen 79-577

113.566

But I can the less persuade myself that this liquid can
furnish in its combustion so much heat, because one
pound of white wax furnished no more than what was
sufficient to heat 94.682 pounds of water the same num-
ber of degrees.

According to the analysis of M. de Saussure, 100 parts
of sulphuric ether, of the specific gravity of 717, at 16°
Reaumur, are composed of

Carbon 59 parts

Hydrogen 22

Oxygen 19

Supposing that the 19 parts of oxygen are combined
with 3.6 parts hydrogen, so as to form with them 21.6
parts water, 100 parts of this kind of ether ought to be
composed of

Carbon ......... 59

Free and combustible hydrogen .... 19.4

Consequently, inflammable substances . . . 78.4

Water . 21.6

400 On the Heat developed in Combustion

From the result of my experiments, 100 parts of this
kind of ether ought to be composed of

Carbon ......... 59

Free or combustible hydrogen .... n.8

Consequently, combustible substances . . . 70.8
Water . 29.2

100

Or, reducing the water to its elements, —

Carbon ......... 59

Hydrogen, free or combustible . . . . 11.8

Ditto, non-combustible .... 3.5

15.3

Oxygen . . . • . . . . 25.7

100

According to M. de Saussure's analysis, as well as from
the results of my experiments, 100 parts of pure alcohol
of Lowitz, qf the specific gravity of 792, at the temper-
ature of 1 6° Reaumur, are composed of

Carbon » » -. . . . . 42.82

Free or combustible hydrogen . .. .. . . 10.18

Consequently, combustible substances . . . 53
Water . 47

100

Or, reducing the water to its elements, 100 parts of
this alcohol are composed of

Carbon . . 42.82

Hydrogen, combined and non-combustible . 5.64

Hydrogen, combustible . ... . . 10.18

15.82

Oxygen . . . .'-•'. . . 41.36

and in the Condensation of Vapours. 40 1

By supposing that water exists completely formed both
in alcohol and ether, the constituent parts of these two
liquids would be, according to the results of our inquiries,

Alcohol. Ether.

Carbon 42.82 59

Combustible hydrogen .... 10.18 11.8

Water ....... 47 29.2

The elements of water exist most assuredly both in al-
cohol and ether ; but there is good reason to believe that
water does not exist in its natural state of condensation
in these two substances, neither when they are in a state
of liquidity, nor when, being sufficiently heated, they are
transformed into elastic fluids.

When we mix water with alcohol, there is a consider-
able change both in temperature and volume, which in-
dicates a new arrangement of elements, or a chemical
action ; and what proves in a still more certain manner
that this action has taken place, the liquid which results
from this mixture may be distilled, i. e. vaporized by
heat, and afterwards condensed, without being decom-
posed : but it is, above all, in the little heat which is de-
veloped in the condensation of the vapour of alcohol and
ether that we discover certain proofs that the oxygen and
hydrogen which exist as elements in these liquids do not
exist in the state of water. I shall recur to this subject
again.

SECTION V. — On the Quantity of Heat developed in
the Combustion of Naphtha.

The naphtha which I made use of in my experiments
was supplied by M. Vauquelin : it had been purified by

VOL. II. 26

402 On the Heat developed in Combiistion

distillation, and its specific gravity at the temperature of
56° F. was 827.31.

The following are the details and results of two ex-
periments made with this liquid on the 29th of January,
1812.

The capacity of the calorimeter for heat was equal to
that of 2781 grammes of water.

Duration
of the
experiment.

Quantity of
naphtha
burned.

Elevation of
the tempera-
ture of the
calorimeter in
degrees of
Fahrenheit.

Result.

Pounds of water heat-
ed 180° with i Ib. of
this substance.

ist Experiment
2d Experiment

32
36

Grammes.

4-45'

2.77

Degrees.

i6°F.

I2f

Ibs.
73.881

72.77!

Mean result 73.3 76

The naphtha was burned in the same small lamp
which I had employed in my experiments made with
alcohol and sulphuric ether; but as I had not been able
to succeed in burning the naphtha without smoke, I
cannot rely implicitly upon the results of these experi-
ments. Perhaps with pure oxygen gas we might succeed
in burning it entirely.

I have met with the same difficulty in burning oil of
turpentine and colophon ; and for this reason I thought
it would be useless to detail my experiments with these
two substances.

SECTION VI. — On the Quantity of Heat developed in the
Combustion of Tallow.

Having procured tallow candles of a good quality,
those which are called six in the pound \ I burned one un-
der the calorimeter, taking care to keep it well snuffed,
in order to avoid smoke.

and in the Condensation of Vapours. 403

The following are the details and results of two ex-
periments made on the same day (i6th of November,
1811) with one of these candles.

The capacity of the calorimeter for heat was equal to
that of 2371 grammes of water.

Time while the
candle was
burning under
the calorim-
eter.

Quantity of
tallow burned.

Elevation of
the tempera-
ture ofthe
water in the
calorimeter.

Result.

Quantity of water
heated 180° with the
heat developed in the
combustion of i Ib. of
tallow.

1st Experiment
zd Experiment

m. s.

16 2
16 50

Grammes.

1.6

i-7

lo^F.

io*

Ibs.
84.385
82.991

Mean result . . .
We have seen that with white wax the result was .
With purified rape oil .....
And with olive oil

. 83.688
94-682

• 93-°73
90.439

SECTION VII. — Quantity of Heat developed in the Com-
bustion of Charcoal.

If we could burn under the calorimeter some pieces
of wood made into charcoal with the same facility that we
burn thin pieces of dry wood, the investigation in ques-
tion would not be attended with difficulty ; but the
charcoal cannot be burned in this manner. We can
light a piece of charcoal very well, and if it be very thin
it continues to burn until it is entirely consumed ; but
the combustion is so slow, and furnishes so little heat,
that it would require several hours to heat the calorim-
eter sufficiently to give an appreciable result ; and for
this single reason the result could not but be extremely
uncertain.

I have long endeavoured, but without success, to find

404 On the Heat developed in Combustion

a method, by steeping thin chips of wood in some in-
flammable liquid, to burn the charcoal more rapidly.

Some chips of wood of a known weight, perfectly
dried and strongly heated, were plunged into white wax,
melted and very hot, and the chips, when taken out and
cooled, were again weighed.

Their augmentation in weight gave me the quantity
of wax which they had imbibed ; and as I knew accu-
rately how much heat this quantity of wax should have
given in its combustion, if the chips thus prepared had
been burned properly under the calorimeter, I should
certainly have discovered how much heat the charcoal
would have furnished ; but the experiment did not suc-
ceed.

The wax was entirely burned, and the chip of wood
became very red ; but it was not burned, at least not en-
tirely, nor in such a way as to give me the least hope of
being able to derive any advantage from my experi-
ment ; and I did not succeed any better by steeping my
chips of charcoal in melted tallow, in oil, alcohol, sul-
phuric ether, naphtha, essential oil of turpentine, in a
solution of gum-arabic, and in that of sugar. I have
also tried colophon, but without more success.

I have made several experiments in order to deter-
mine directly the quantity of heat which is developed
in the combustion of considerable masses of charcoal
(80 grammes) burned in a small stove, under a calorime-
ter of a large size, which I procured at Paris four years
ago, and which I have still in my laboratory ; but the
results of these experiments have been too variable to
satisfy myself.

After all the care which I took, I found that the ex-
periments of Crawford were better than mine ; and as

and in the Condensation of Vapours. 405

they furnished more heat than I could find, I have not
hesitated to adopt their results instead of relying upon
my own.

SECTION VIII. — Quantities of Heat developed in the Com-
bustion of Wood.

In a memoir which I had the honour to present to the
Class on the 9th of September, 1812, I gave an account
of a considerable number of experiments (upwards of
fifty) which I made in order to determine the quantities
of heat which are developed in the combustion of dif-
ferent kinds of wood.

From the results of these experiments, it appears
that, at equal weights, the light and soft woods give
out a little more heat than the compact and heavy
woods ; but as the difference is very small, we may
rather ascribe it to a greater degree of humidity in the
latter.

It is certain that the compact retain humidity with
more tenacity than the light woods, and a small dif-
ference in the dryness of a wood ought to produce a
sensible effect on its apparent weight, and consequently
upon the result of the calculations which we employ in
order to determine the heat which it furnishes.

In physical and chemical researches, it is always satis-
factory to be able to compare the results of new experi-
ments with those of more ancient date, particularly
when the latter have been made by persons remarkable
for their accuracy.

M. Lavoisier has shown that equal quantities of heat
are produced in the combustion of 1089 parts in weight
of oak, and 600 parts of charcoal ; consequently equal

406 On the Heat developed in Combustion

quantities of heat ought to be furnished in the com-
bustion of one pound of oak and 0.55 of a pound of
charcoal.

According to the experiments of Dr. Crawford, one
pound of charcoal furnishes in its combustion enough
of heat to raise the temperature of 57.608 pounds of
water 180° of F.

Consequently the temperature of 31.684 pounds of
water would be raised the same number of degrees by
the heat furnished in the combustion of 0.55 pound of
charcoal.

According to the result of the experiments of M.
Lavoisier, this same quantity of heat ought to be fur-
nished in the combustion of one pound of oak.

Having made four consecutive experiments with
very good dry oak wood, and in very thin slips, burned
so as to give out neither smoke nor smell, and which
left but an inappreciable quantity of ashes and no char-
coal, I obtained the following results : —

Number of
experiments.

Quantity of wood
burned.

Elevation of the
temperature of
the calorimeter.

Result.

Pounds of water heated 180°
with one pound of combustible.

2

3
4

Grammes.
5.10

5-13
5.12

4-95

Degrees.

ioj° F.
10*

I Of
10

Ibs.
31.051
31-623

3I-94I
31.212

Mean r<
Result
expei

according to Lavoisier and Crawford's } ^
iments ... j '

It is rare to find experiments made by different per-
sons at distant periods, and with very different appara-
tus, which agree better together.

But experiments which are well made can never fail

and in the Condensation of Vapours. 407

in agreeing in their results, whatever be the difference
of the methods employed : it is, nevertheless, necessary
to remark, that the coincidence in question could not
be so perfect as it appears, for everything depends upon
the equality of the humidity which may exist in the
wood and charcoal employed, — a circumstance which it
is impossible to establish.

SECTION IX. — On the greatest Intensity of Heat which
it is possible to produce by the Combustion of inflammable
Substances.

It is well known that the heat of a small fire seems to
be less intense than that of a large fire, even when the
same species of combustible is employed ; but I do not
know that it has been attempted to determine the limits
of the intensity of a fire, or the greatest degree of
heat which it is possible to produce by means of com-
bustion.

In order to elucidate this subject, it is necessary to
consider attentively what passes in the chemical opera-
tion which we call combustion.

In all known cases where two elementary substances
unite together so as to form a new substance, there, is a
change of temperature, so that the new substance at
the moment of its formation has a temperature differing
strongly from that of the surrounding bodies. Conse-
quently, the surrounding bodies are always either heated
or cooled more or less by the new body which has been
formed.

But in order that this effect may be sensible to our
organs, or capable of acting in a sensible manner upon
our apparatus, it is necessary that the quantity of the

408 On the Heat developed in Combustion

new substance formed should be considerable ; for it is
certain that the most intense heat, if it be developed in
a very small particle of matter, may exist without pro-
ducing any sensible effect which could give us any indi-
cations of its existence.

It is not less true that the chemical union of two
atoms, two different elementary substances, ought al-
ways, under every circumstance, to be accompanied with
one and the same change of temperature ; for this union
takes effect in a place so distant, relative to all the
other bodies (if, in every case, all the interstices are not
filled with particles of an ethereal fluid), that, we can-
not conceive how the change of temperature in question
may be either augmented or diminished by the effect
of the action of these surrounding bodies.

It is extremely probable, from what we have been
able to remark in a great number of phenomena, that
the approximation of the elementary particles of bodies
is always accompanied by an elevation of their tempera-
ture; and as there cannot be new substances formed ex-
cept in consequence of an approximation and the chem-
ical union of elementary particles, we may conclude
that there cannot be new chemical compositions without
a development of heat.

We may form an idea of what passes in combustion,
by considering the phenomena which take place when
water freezes.

At a certain temperature, which is invariable, the
molecules of the liquid are disposed to approximate in
order to form a solid body, ice ; and the first particle
of ice which is formed is accompanied by a develop-
ment of a certain quantity of heat, which quantity is
invariable.

and in the Condensation of Vapours. 409

It is also very probable that it is at a temperature
which is invariable that the oxygen and hydrogen are
disposed to approximate and unite in order to form an
atom of vapour, and that the intensity of the heat devel-
oped at the moment of this union is also invariable, and
that it is always manifested in all its intensity in the
atom of vapour which is formed.

But as the atom of vapour is extremely small, and sur-
rounded by bodies relatively very cold, its heat is soon
dissipated.

There is, however, a method, which appears certain,
that we .may employ in order to determine the tempera-
ture of an atom of vapour at the moment of its forma-
tion, and by this means we may know what is the high-
est temperature which it is possible to procure by means
of combustion.

We have seen that, according to the results of the
researches of Dr. Crawford, it seems that when i
pound of hydrogen is burned, enough of heat is de-
veloped on this occasion to elevate the temperature
of 410 pounds of water 180° F. (= 100 degrees cen-
tigrade).

Now as i pound of hydrogen perfectly dry is united
by burning to 7.3333 pounds of oxygen, and forms
with it 8.3333 pounds of steam, it is evident that
the quantity of heat which exists in 8.3333 pounds of
steam at the instant when this steam is formed, is
equal to that which is necessary to raise the temperature
of 410 pounds of water 180° F., or to elevate the tem-
perature of 73,800 pounds of water, one degree of the
scale of Fahrenheit.

From this calculation we may conclude that the quan-
tity of heat which exists in i pound of steam, at the

4io On the Heat developed in Combiistion

instant when it is formed, is sufficient- to raise the tem-
perature of i pound of water 10,063 degrees.

If the capacity of the steam for heat was equal to that
of liquid water, it is very certain that the temperature
of the. vapour at the instant of its formation would be
that of 10,063° F.

In order to form an idea of this degree of intensity,
we may compare it to an intensity of heat which is
known.

A piece of iron heated until it becomes red even in
daylight has then the temperature of 1000° F. ; con-
sequently the temperature of the steam at the instant
of its formation would be ten times higher than that of
red-hot iron : but as, according to Crawford, the capa-
city of the steam for heat is greater than that of water
in the proportion of 1.55 to i, the temperature in ques-
tion will be less than that of 10,063° i° tne same pro-
portion. It will therefore be equal to 8750° F.

Here, therefore, is the limit of the intensity of the
heat in the midst of the greatest fire, in which pure
hydrogen would be employed as a combustible, and in
which the fire would be fed by pure oxygen. This is an
intensity which we may approach more or less, but which
we can never attain.

As Wedgwood's pyrometer indicates much higher
temperatures, it seems demonstrated by the result of
this calculation that the scale of this pyrometer is faulty.
These doubts have been stated by other chemists.

But in order to decide definitively upon this inter-
esting question, it would be indispensably necessary to
know accurately the capacity of steam for heat at different
temperatures; a thing unknown, and which is difficult to
determine.

and in the Condensation of Vapours. 4 1 1

Upon examining the subject attentively, we shall
find, however, reasons for thinking that the capacity of
steam for heat ought necessarily to be diminished with
the increase of its temperature. The following calcula-
tions may serve to elucidate this subject.

In order to determine the highest degree of tempera-
ture which can exist in the midst of the greatest fire
when pure hydrogen is the only combustible employed
and when the fire is fed by atmospheric air, it is necessary
to remark that, as oxygen and nitrogen are intimately
mixed in the atmosphere, the heat which results from
the combustion of hydrogen ought to be immediately
divided between the vapour which results from the
union of the hydrogen with the oxygen, and the nitro-
gen which is found necessarily mixed with this vapour.

In order to simplify our inquiry, we shall commence
by supposing that all the oxygen which exists in the
atmospheric air is employed.

In this case, as it requires 7.3333 pounds of oxy-
gen to be united to i pound of hydrogen in order to
compose 8.3333 pounds of steam, and as the atmos-
pheric air is composed of 21 pounds of oxygen gas
mixed with 79 pounds of nitrogen, the 7.3333 pounds
of oxygen which are united to i pound of hydrogen in
order to form 8.3333 pounds of steam, ought to be
found mixed with 27.587 pounds of nitrogen ; conse-
quently the heat developed in the combustion of i
pound of hydrogen ought to be also divided between
8.3333 pounds of steam and 27.587 pounds of nitro-
gen ; and this partition ought to take place in the
direct ratio of the weights of these two fluids, and
of their capacity for heat.

The capacity of the steam being to that of nitrogen

4 1 2 On the Heat developed in Combustion

as 1.55 to 0.7036 (according to Crawford), all the heat
in question will be divided so that the steam shall
retain the part of it represented by the number 9.5832
(=8.3333 X I-SS) ' an<^ the nitrogen will receive the
other part of it, = 19.41 (being the product of 27.587
multiplied by 0.7036).

Now, as the two numbers 9.5832 and 19.41 are bo.th
in the proportion of i to 2.0254, it is evident that the
temperature will be the same which we should have if
all the heat in question was equally divided between
the steam which would result from the combustion
of 3.0254 pounds of hydrogen, i. e. between 25.2113
pounds of steam.

And as we have seen that the heat manifested in the
combustion of i pound of hydrogen, which is in the
8.3333 pounds of steam which are the products of this
combustion, is sufficient for raising the temperature of
this steam to that of 8750° F., it is evident that if this
same quantity of heat is divided among 25.2113 pounds
of steam, the temperature of this steam could not be
higher than 2891° F.

This is, therefore, the highest temperature which we
ought to find in the midst of a strong fire fed by the
atmospheric air in which the combustible burned is
pure hydrogen.

As this temperature is much lower than that which
we can excite by combustion, even without employing
pure hydrogen or pure oxygen, the result of this calcu-
lation furnishes a demonstrative proof that the capacity
for heat of steam, or rather that of nitrogen, is diminished
when its temperature is increased. In all probability,
the capacities of both, and generally of all elastic fluids,
are diminished when their temperature is increased.

and in the Condensation of Vapours. 413

We shall now see what is the highest temperature
which it would be possible to attain by burning char-
coal, and by blowing the fire with pure oxygen gas.

According to Crawford, I pound of charcoal gives
heat sufficient in its combustion to raise the temperature
of 57.608 pounds of water 180° F., or to raise the tem-
perature of 9369.44 pounds of water i degree.

Now, as i pound of charcoal is united to 2.5714
pounds of oxygen in burning, and forms with it 3.5714
pounds of carbonic acid, the heat which is found in
3.5714 pounds of carbonic acid at the instant of its forma-
tion would be sufficient to raise the temperature of
9369.44 pounds of water i degree; consequently the
heat which is in i pound of this acid at the moment
of its formation would be sufficient to raise the tempera-
ture of 3643.6 pounds of water i degree.

Here we have the quantity of heat which exists in the
carbonic acid at the instant of its formation. In order
to know what is the intensity which it would indicate
if we could measure it at this moment by means of a
thermometer, it would be necessary to know precisely
the specific heat of the carbonic acid. If, with Crawford,
we take it at 1.0459 (tnat of water being taken = i),
we shall have 3811° F. for the measure of the intensity
of the heat which exists in the carbonic acid at the
moment of its formation, and consequently for the
intensity of the greatest fire made with charcoal (without
mixture of hydrogen), even in the case where the fire is
fed by -pure oxygen.

It remains to determine the temperature which we
might hope to obtain by burning charcoal with atmos-
pheric air.

As we have found that the temperature of the 3.5714

414 On the Heat developed in Combustion

pounds of carbonic acid, which are the product of the
combustion of i pound of charcoal, is that of 3811° F.
at the moment of its formation, we have only to ascertain
how much the temperature of this acid ought to be
diminished by the mixture of the nitrogen which must
'necessarily be there when the oxygen employed in the
combustion of the charcoal is furnished by the atmos-
pheric air.

As, in the atmospheric air, every pound of oxygen
is mixed with 3.7619 pounds of nitrogen, the 2.5714
pounds of oxygen employed in the combustion of I
pound of charcoal ought to be mixed with 9.6735
pounds of nitrogen ; consequently all the heat devel-
oped in the combustion of i pound of charcoal will
be found divided between 3.5714 pounds of carbonic
acid and 9.6735 pounds of nitrogen.

And as the specific heat of the carbonic acid is to that
of nitrogen as 1.0459 to °'7°3^j tms neat w^ be divided
between these two substances in the proportion of
(3.5714 X 1.0459 =) 3-7354 to (96735 X 0.7036=)
6.8062, which is in the proportion of i to 6.8221 or of
3.5714 to 6.5075; and thence we may conclude that
the temperature of the mixture of 3.5714 pounds of car-
bonic acid and of 9.6735 of nitrogen would be the same
as if we had mixed with the 3.5714 pounds of carbonic
acid 6.5075 pounds more of this same acid, making to-
gether 10.0789 pounds of carbonic acid.

Now, as the heat developed in the combustion of i
pound of charcoal was sufficient to raise the temperature
of the 3.5714 pounds of carbonic acid coming from this
combustion to that of 3811° F., this same quantity of
heat ought to be sufficient to raise the temperature of
10.0789 pounds of carbonic acid to the temperature
of 1350° F.

and in the Condensation of Vapours. 4 1 5

This is, according to the results of this calculation,
the highest temperature which we ought to expect to
find amid the strongest charcoal fire fed by atmospheric
air.

But we are very certain that the intensity of the heat
of the strongest charcoal fire is far superior to the above
calculation ; consequently we are authorized to conclude
that the capacity for heat of the carbonic acid, and that
of nitrogen gas, are much diminished when these elastic
fluids are exposed to a 'very high temperature.

If, in endeavouring to discover the limit of intensity
of a charcoal fire, I have supposed the fire to be 'very
large^ it is not because I suppose that the heat developed
in combustion is more intense at the primitive source in a
large than in a small fire ; but as a small fire is always
surrounded by bodies relatively very cold, such as the
bars of the grate, etc., the products of the combustion
(which are always at the instant of their formation at the
same temperature) are so rapidly cooled when the fire is
small, that the temperature which we may find in such a
fire is necessarily lower than that which we find in the
midst of a larger fire, where a greater quantity of the
same kind of combustible is employed.

When a large charcoal fire is well lighted up in a close
stove, constructed with bricks or fire-stones, all the inte-
rior surfaces become excessively hot, and the heat accu-
mulates and becomes very intense throughout the whole
'interior of the stove, so that iron and even stones are
melted in it, and flow like liquids ; but when the fire-
place is small, it is with difficulty that it can be heated
so much as to make the sides red-hot ; and if the fire-
place be very small, a charcoal fire cannot be kept up at
all, even with continual blowing. We may truly say

41 6 On the Heat developed in Combustion

that such a fire dies of cold, an expression which with as
much force as justice describes the event as it really
happens.

But if it be the cold communicated by the surround-
ing bodies which hinders a very small charcoal fire from
burning, could we not make it burn by guarding it in a
proper manner against the cold ?

This is an experiment which I tried six years ago with
the greatest success, and which ended in my causing to
be made small portable cooking-stoves now in general
use in Paris, and elsewhere for aught I know.

By surrounding the body of the stove with two strata
of enclosed air, the cooling of the fireplace and the char-
coal it contains is hindered ; and in this way the char-
coal burns perfectly well, and the fire is so well kept up
that it obeys a small register, which regulates the quan-
tity of air admitted into the body of the stove.

Some judgment may be formed of the advantages
which ought to result from the use of these small porta-
ble furnaces in cooking, etc., arising from the saving of
time and combustibles, when we are informed that the
combustion may be regulated without any difficulty, so
as to consume the charge of charcoal in 20 minutes with
a brisk heat, or so as to keep up a moderate fire for
three hours.

With these portable cooking-stoves it is indispensably
necessary to use kettles or saucepans of a particular
construction. They ought to be suspended by their
rims, in large circles of wrought-iron or copper, the bet-
ter to keep in the heat. The circle of a saucepan ought
to be half an inch more in breadth than the saucepan is
in depth.

But to return to the main branch cf my subject. If

and in the Condensation of Vapours. 417

the present state of our knowledge does not admit of
our establishing with a rigorous precision the highest
temperature which it is possible to excite by means of
the combustion of inflammable bodies, the calculation
which I have submitted to the Class may nevertheless
serve to guide our conjectures on this interesting sub-
ject. They will at all events show what is wanting to
enable us duly to appreciate the subject.

SECTION X. — On the Quantity of Heat developed in the
Condensation of the Vapour of Water.

Having filled the calorimeter and placed it on its
stand, a current of vapour was introduced into the
worm through a cork placed in the lower aperture of
the worm. This cork having been perforated with a
hole two lines in diameter, in the direction of its axis,
a small cork (two lines in diameter and two in height)
was fitted into it, and four other holes about a line in
diameter, pierced horizontally through the sides of the
large cork at two lines below its upper extremity, and
communicating with the hole two lines in diameter in
the axis of this cork, afforded a passage to the vapour,
to admit of its entering by four small channels horizon-
tally into the worm.

As the apertures of these small channels were higher
than the level of the flat bottom of the worm, the water
which resulted from the condensation of this vapour
did not prevent the vapour from continuing to flow
through these passages.

This vapour came from a long-necked matrass contain-
ing distilled water, which was put on a portable stove
placed in a chimney at some distance from the calorime-

VOL. ii. 27

4 1 8 On the Heat developed in Combustion

ter ; and in order to stop all direct communication of
heat between the stove and the calorimeter, the former
was masked by plates, and the tube which conducted
the vapour to the calorimeter was well covered with
flannel.

The cold water which filled the calorimeter was of a
lower temperature than that of the chamber by 6° F.,
and when the thermometer of the calorimeter announced
an augmentation of temperature by 12° F., an end was
put to the experiment.

The water produced by the condensation of the va-
pour in the worm was carefully weighed; and from its
quantity, as well as from the heat communicated to the
calorimeter, the heat developed by the vapour in its con-
densation was determined.

As a small part of the heat communicated to the
calorimeter proceeded from the cooling of the water
condensed in the worm, after the vapour had been
changed into water, an account was kept of this heat.
It was supposed that the water at the moment of con-
densation was at the temperature of 212° F., being that
of boiling water ; and it was determined, by calculation,
what part of the heat communicated to the calorimeter
must have been owing to this boiling water.

In making this calculation, no account was taken of
the difference in the capacity of water for heat which
depends on its temperature ; this is but imperfectly
known, and besides, the correction which would have
been the result could not but have been very small.

The following are the details and results of two ex-
periments made on the 2ist of January, 1812.

and in the Condensation of Vapours. 419

Dumber
of exp.

Temper-
ature of
the
room.

State of the calorimeter (equal in capacity
for heat to 2,781 grammes of water).

Quantity of
vapour con-
densed into
water in the
worm.

Result.

Quantity of wa-
ter which maybe
heated 1° F. with
the heat devel-

Temperature
at the begin-
ning of the

Temperature
at the end of
the experi-

Elevation of
its tempera-

experiment.

ment.

ture.

densation of i lb.

' of vapour.

Degr's.

Degrees.

Degrees.

Degrees.

Grammes.

Ibs.

I

61

55

67\

in

29.61

1029.3

2

62}

57}

67i

•°i

24.4

1052.3

Mean result 1040.8

By expressing the mean result of these two experi-
ments in the way employed by Mr. Watt and others, I
shall say that 1040 degrees of heat (Fahrenheit) are
liberated in the condensation of steam, and that con-
sequently this very quantity of heat is employed and
rendered latent when the water, already at the tempera-
ture of boiling water, is changed into steam.

The duration of each of these two experiments was
from ten to eleven minutes, and I had boiled the water
some time in the matrass (to drive out the air which it
contained) before I directed the steam from it into the
worm of the calorimeter.

As the results of these experiments have been very
uniform, and as they agree very well with the later ex-
periments made by Mr. Watt with a view to determine
the same question, I have not thought it necessary to
repeat them.

I have, besides, been very much occupied with the fol-
lowing branch of my inquiries.

SECTION XI. — Of the Quantity of Heat developed in the
Condensation of the Vapour of Alcohol.

As chemists are not agreed as to the state of the ele-
ments of the water which exist in alcohol, I thought
that, by determining with precision the quantity of heat

420 On the Heat developed in Combustion

which is developed, we should be better able to form
conjectures as to the state of the water, if it be at all
times found in this inflammable liquid.

The results of the experiments which I made with
alcohol are less regular than those of the experiments
made with water, as might have been expected ; but they
have nevertheless been sufficiently uniform to establish
a fact which will be regarded, without doubt, as very
curious and important.

As the vapour which is extracted from spirit of wine
when boiled, varies a little with the intensity of the fire
used in boiling it, I took care to note the time which
was taken in every experiment, in order to be able to
judge, by comparing the quantity of vapour condensed
with the time employed to form it, of the intensity of
the heat employed to boil the liquid.

In the following table we shall see the details and
results of five experiments made on the same day
(January 21, 1812) with alcohol of different degrees of
strength. The capacity of the calorimeter was always
equal to that of 2781 grammes of water, and the ther-
mometer employed was that of Fahrenheit.

3

9

r

State of the calor

meter.

ij

Result.

1

1

I

9

|

B

V

1

if

l?^c

1

11

I

1

Z

a

i

-SJ

HKi

1

1!
P

u

IS.

li

1!

1

1

v £

Us'

f ^ll i

Jz;

CO

H '

H

s

&

§

Min.

Uram.

I

85342

7

61°

541°

68i°

1 44°

69.86

499.54

2

85342

5

61

56

66^

IOJ

52.21

476.83

3

84714

8

6oJ,

55*

^5i

10

48.82

500.03

4

81763

4i

61

56

66-^

IO2

56.6l

479.92

5

85342

6*

64

57

7»i

Hi

7I-31

499.65

and in the Condensation of Vapours. 42 1

On determining, by calculation, the quantity of water
which may be heated one. degree^ by the heat developed
in the combustion of one pound of this vapour, I took
care to keep an account of the difference between the
capacity of water for heat and that of alcohol, when I
determined how much heat should have been communi-
cated to the calorimeter by the alcohol, and produced
by the condensation of the steam, by being cooled in the
worm.

In order to prove the state of the elements of the
water which exist in the steam of alcohol, it must be
shown how much water these elements ought to form.

We shall select the experiment which was made with
alcohol of the specific gravity of 81,763, and which con-
tained the least water. The quantity of steam con-
densed in this experiment was 56.61 grammes.

In 100 parts of this alcohol there were

91.79 parts of pure alcohol of Lowitz, and
8.21 parts of water.

Consequently there were in the 56.61 grammes of
alcohol condensed in the calorimeter,

51.962 grammes of alcohol of Lowitz, and
4.648 grammes of water.

Now, as M. de Saussure has shown that there are 47
parts of water in 100 parts of alcohol of Lowitz, there
must have been 24.422 grammes of water in the 51.962
grammes of alcohol of Lowitz, which were condensed in
the calorimeter.

If to this quantity of water ( = 24.422 grammes) we
add the 4.648 grammes which were found mixed with
51.962 grammes of alcohol of Lowitz, in order to com-
pose the 56.61 grammes of alcohol employed in the

422 On the Heat developed in Combustion

experiment, we shall have 29.07 grammes of water which
ought to have existed ready formed either in the common
state of water or in some other state, in the 56.61 grammes
of alcohol condensed in the calorimeter.

But the condensation of 29.07 grammes of steam into
liquid water ought to have of themselves furnished more
heat than we had, in the experiment in question, in the
condensation of these 29.07 grammes of elements of
water with 27.57 grammes of carbon and hydrogen,
which concur with these elements in forming the steam
of the alcohol which was condensed.

If we apply a similar calculation to the results of the
experiments made with alcohol which contained more
water, the result of the inquiry will be still more strik-
ing.

In the experiment No. 5 the alcohol employed was
of the specific gravity of 85,342 ; consequently 100 parts
of this alcohol were composed of

77.88 parts of alcohol of Lowitz, and
22.12 water.

And in the experiment 71.31 grammes of vapour of
alcohol were condensed.

There were, therefore, in these 71.31 grammes of con-
densed alcohol,

55.688 grammes of alcohol of Lowitz, and
15.622 grammes of water.

In the 55.688 grammes of alcohol of Lowitz there
were 26.102 grammes of water, according to the analysis
of M. de Saussure ; and this last quantity of water
( = 26.012 grammes), added to the quantity found above,
viz. 15.622 grammes, makes 41.727 grammes of water
which ought to have existed, either as steam or other-

and in the Condensation of Vapours. 423

wise, in the 7 1.31 grammes of alcoholic vapour condensed
in the calorimeter, in the experiment in question.

In order to simplify our calculation, and to render
our comparisons more striking, we shall show how much
pure water, in vapour, ought to have been sufficient to
furnish, in its condensation, the same quantity of heat
which was furnished by the condensation of 71.31
grammes of alcoholic vapour, in the experiment in
question.

In this experiment the temperature of the calorimeter
was raised to 14}° of Fahrenheit.

In the second experiment, made with the steam of
pure water, the temperature of the same calorimeter was
raised io|° of Fahrenheit, with the heat developed in
the condensation of 24.4 grammes of this vapour.

Consequently the temperature' of the calorimeter must
have been elevated to 14^° of Fahrenheit, with the heat
which must have been developed in the condensation
of 33-695 grammes of steam from pure water.

Now, as the hydrogen and the oxygen forming the ele-
ments of 41.727 grammes of water, which are found to
form constituent parts of the 71.31 grammes of vapour
of alcohol condensed in the experiment in question, only
furnished in their condensation the same quantity of
heat as 33-695 grammes of steam of pure water should
have furnished, it is clearly proved, in my opinion, that
these elements are not so united as to form water, so
long as they concur in the formation of alcohol.

I have discovered that the vapour of sulphuric ether
furnishes about one half less of heat in its condensation
than that of alcohol, and consequently one fourth only
of what is furnished by the steam of water of equal
weight ; but, having been interrupted by an accident in

424 On the Heat developed in Combustion, etc.

the course of my experiments with ether, I am desirous
of finishing them before I publish the results.

[The first three sections of this paper are printed from Nicholson's
Journal, Vol. XXXII. (1813), pp. 105-125; the remainder from
Tilloch's Philosophical Magazine, Vol. XLI. (1813), pp. 439 — 444,
and Vol. XLII. pp. 296-307, and Vol. XLIII. (1814), pp. 64-69.
On pages 392, 410, and 412 there are several numerical errors and in-
consistencies ; but, as the original French memoirs are not accessible, no
attempt has been made to reconcile them.]

ON THE CAPACITY FOR HEAT

CALORIFIC POWER OF VARIOUS LIQUIDS.

THIS subject is of rather an obscure nature, and it
has been so little examined, that it will be useful
to begin by elucidating it as well as I can.

Let us suppose two cylindrical vessels, with very thick
sides, made of lead or any other metal, and perfectly
equal in size, each being capable of containing a pint.

These two vessels being at the freezing-point, we
shall pour into the one a pound of water at the tem-
perature of 96° F. (= 28J° R.), being that of the
blood, and into the other a pound of olive oil at
the same temperature.

Each of these liquids will heat the cold vessel in
which it is placed, the vessel in its turn will cool the
liquid, and both the liquid and the vessel will latterly
be of the same temperature.

If water and oil of olives had the same calorific power,
a pound of water at the temperature of 96° would heat its
cold vessel precisely as much and not more than a pound
of oil would heat its vessel, the two vessels being of
the same weight and at the same temperature at the
commencement of the experiment.

But experience shows that water heats its vessel much
more than oil does ; consequently the calorific power of
water is greater than the calorific power of oil of olives,

426 On the Capacity for Heat, or

when the quantities of these two liquids are estimated by
their weight ; and, if we designate the calorific power
of water by i, the calorific power of oil of olives will
be expressed by a fraction under i.

The power with which any given body, solid or
liquid, being at a given temperature, resists the calorif-
ic or frigorific action of bodies warmer or colder than
itself, is in proportion to its calorific power; and the
greater is this power, the longer it resists these actions
of surrounding bodies.

If, under equal surfaces, a pound of water and a
pound of oil of olives, both at the same temperature
(96° F.), are placed at the same time in a place where
the temperature is lower (that of freezing, for instance),
the oil of olives will be cooled much more rapidly than
the water.

If it be in a warm place that the two liquids are
exposed, the oil of olives will still have its temperature
most rapidly changed ; it will be more heated than the
water.

In two cylindrical glass vessels, of equal size and very
thin, place equal quantities of water, and at the same tem-
perature (96° F.).

A piece of lead weighing a pound, and a piece of cop-
per of the same weight, having been cooled in a mixture
of pounded ice and water, remove them from this cold
mixture and plunge each of them suddenly into one of
the vessels of water.

The two masses of water will be cooled, but that
which contains the copper most, for the calorific power
of copper is greater than the calorific power of lead.

We may also say that the frigorific power of copper is
greater than the frigorific power of lead, and, in the case

Calorific Power of various Liquids. 427

in question, the expression, perhaps, will be most suit-
able.

It is always the same power; it is that by means of
which any body resists the action of surrounding bodies,
and which tends to change its temperature either by in-
crease or diminution.

Much obscurity has been introduced into the science
by vague ideas being attached to the words hot and cold;
but it will not suit my purpose to enlarge upon this
subject at present. I have already delivered my opinion
in a former paper.

The little heat which I discovered in the condensation
of alcohol having induced me to think that the specific
heat of this liquid had not been accurately determined,
and wishing to know it precisely, in order to enable me
to finish the calculations which were necessary for eluci-
dating the results of some of my experiments, I con-
structed a small and very simple apparatus, by the help
of which I could easily, and as I presume accurately,
determine it.

This apparatus consists of a small bottle of a particu-
lar form, constructed of thin leaves of red copper, in-
tended to contain the liquid which is to be the subject of
the experiment ; and a small cylindrical vase, also con-
structed of thin pieces of red copper, in which I place
water at a certain temperature. Into this water I plunge
the bottle of copper containing the liquid which is the
subject of the experiment; this liquid being of a differ-
ent temperature from that of the water in the outer vase.

As the capacity of the vase for heat, as well as that
of the bottle, is known, I determine, by a very simple
calculation, the capacity for heat of the liquid contained
in the bottle. This calculation, which is well known, is

428 On the Capacity for Heat, or

founded in the changes which take place in the temper-
ature of liquids, in the vase and in the bottle, by taking
a uniform temperature, when the bottle is immersed in
the water contained in the vessel.

In order that this equality of temperature may be
speedily brought about, the form of the bottle is such
that it has a very great surface relative to its small
capacity, and in order to manage it without touching it,
its neck, which is small, is closed by a long cork, which
serves as a handle.

In order to diminish as much as possible the effect
of the atmosphere and of surrounding bodies upon the
apparatus, while the experiment is going on, the quan-
tity of water in the vessel is regulated so as to keep the
bottle wholly submerged in the liquid, and even the
upper end of the neck covered, when the bottle is im-
mersed. The vessel which contains this water is placed
and suspended by a ring of cork in another vessel larger
and higher, and the interval between the two is filled
with eider-down.

The form of the bottle is such that its horizontal
section presents the figure of a rectangular cross. Some
idea may be conceived of its form and dimensionSj if
we suppose a square piece of stick, each facet of which
is four lines broad by four inches three lines in length,
upon the four faces of which we have fixed four sticks of
the same length (i. e. four inches three lines), but each
of them being four lines thick by eight broad.

The four sticks last described will exhibit the figure
of the bottle ; for the square piece of stick will be con-
cealed by them from our view.

The neck of the bottle is in the prolongation of its
axis ; it is four lines diameter by four high ; it ought to

Calorific Power of various Liquids. 429

be circular; the cork should be an inch long, and the
bottle weigh 76.07 grammes without its cork.

The cylindrical vase which contains the water is two
inches diameter, and four inches nine lines high, and it
weighs 74.65 grammes.

The exterior vessel, in which the latter is suspended
by the cork ring, is five inches three lines high, and
three inches diameter, so that the sides and bottom are
everywhere separated by an interval of six lines; this in-
terval is filled with eider-down, as already mentioned.

To prevent the water from touching the eider-down,
the cork ring is covered with a thin coating of mastic.

In order to ascertain the temperature of the bottle,
and of the liquid which it contains, without being
obliged to plunge a thermometer into the bottle, which
would in this case be inconvenient, I employed a very
simple method.

I placed a large bucket filled with water in a room
with a northern aspect. I allowed it to assume the
temperature of the room, taking care to shut the door
and windows day and night. I placed the small bottle
on a stand in this bucket, keeping the upper part of the
cork only out of the water. As the bottle is small and
has a large surface, it speedily acquires the temperature
of the bucket of water ; but, in order to be well con-
vinced that the bottle and the liquid which it contains
have acquired the temperature in question, I leave the
bottle a considerable time in the bucket, frequently half
an hour and sometimes more.

In giving a detailed account of an experiment made
with this apparatus, I shall have an opportunity of giv-
ing clear and precise ideas of the different parts of my
apparatus, and of the particular objects which they are
intended to attain.

430 On the Capacity for Heat, of

Having found by various preliminary experiments
made with water that the capacity for heat of the cylin-
drical vessel with that of the thermometer employed to
determine the temperature of the water which it con-
tained, was equal to that of 24.3 grammes of water, and
that the specific heat of the bottle of copper was equal
to that of 8.36 grammes of water, I made the following
experiment with purified linseed-oil.

I put into the cylindrical vessel 180 grammes of
water ; the temperature of the room was 59^° F. I
filled the copper bottle with the above oil, and corked it.
I cooled it in a bucket of water at the temperature
of 44j° F. The oil in the bottle weighed 82.55
grammes.

The bottle, having had time to acquire the tempera-
ture of 44!° F., was withdrawn from the bucket, and
placed in a cylindrical vessel of tinned iron, of about
four inches diameter and six high, filled to the height
of four inches and a half with water at the temperature
of 44i° F.

The bottle, being submerged in this vessel of cold
water, was carried into the room where I had placed the
small vessel of copper belonging to the apparatus; it
was then taken out of the cold water, and plunged into
the water contained in the small cylindrical vessel of
copper, which contained 180 grammes of water at the
temperature of 59^° F.

A thermometer having a cylindrical reservoir four
inches long, which was placed in this vessel beside the
copper bottle, soon fell, and in three or four minutes it
marked 56^-° of F., where it remained a long time sta-
tionary, and afterwards began to ascend slowly.

The capacities for heat of the warm bodies which

Calorific Power of various Liquids. 431

were cooled in this experiment were equal to that of
204.3 grammes of water ; viz., —

That of the water employed . . . . 180 grammes.
That of the vases and thermometer . . . 24.3

Total . . . 204.3
The capacity for heat of the bottle containing the oil was equal to

that of 8.36 grammes of water.

And to this we must add the cold water ad-
hering to the bottle, when it came out of the
cold water, and was plunged into the water
contained in the copper vessel. I found by a
particular experiment that this quantity of
water was ...... 1.04

Total .... 9.40

Now, as the temperature of the warm water in the
cylindrical vase of copper was that of 59!° before the
mixture, and 56^° after the communication of the heat
had been obtained, it is evident that this water was
cooled 2-f°. But if we multiply the number of grammes
of water which the specific heat of this water represents,
and that of the vessel (= 204.3 grammes), by the number
of degrees which it has been cooled (2|) we shall have
a product which will express the number of grammes
of water which would have been cooled i° F. by a
loss of heat equal to that which the vessel and its con-
tents supported in this experiment. It is 204.3 X 2.75
= 561.84 grammes.

We shall now see what part of this heat was com-
municated to the bottle and to the small portion of
cold water attached to it, and what part to the oil con-
tained in the bottle.

As the temperature of the bottle and its contents was
44 £° F. before the mixture, and 65^° afterwards, it is

43 2 On the Capacity for Heat, or

evident that the bottle had acquired \i\° of heat ; conse-
quently, if we multiply 9.4 (the number which expresses
the sum of the capacities for heat of the bottle, and of
the cold water adhering to it) by 12^ we shall have a
product which will express the number of grammes of
water which would have been heated one degree by the
heat communicated during the experiment to the bottle,
and to the small portion of water which adhered to it.

It is 94 X 12.25= 111-15 grammes.

If from the heat lost by the vessel and the warm
water, which we have found equal to that which is
necessary for raising the temperature of 561.84
grammes of water one degree of F., . . . 561.84 grammes
we take the quantities which the bottle and the
water adhering to the bottle have received . . 115.15

we shall have . . . '.-'.- . . 446.69 grammes

of water heated one degree, expressing the quantity of
heat employed for raising to 12-^° F. the temperature
of the 82.55 gimmes of linseed oil which were put
into the bottle.

On dividing this number (446.69) by ii\, we shall
see how many grammes of water would have been
heated one degree by the quantity of heat in question.

It is therefore _ ° — 36.464 grammes of water.

By the results of this calculation we find that the
same quantity of heat which is necessary to raise the
temperature of 36.464 grammes of water 12^ degrees
of Fahrenheit's thermometer is sufficient to raise the
temperature of 82.55 grammes of oil the same number
of degrees.

Consequently the capacity of water for heat is greater
than that of oil of linseed in the proportion of 82.55 to

Calorific Power of various Liquids. 433

36.464 ; and if we express the capacity of the water by
«»//>', as is usually done, the capacity of the above oil
ought to be expressed by the fraction 0.44172.

These details must no doubt appear superfluous to
those who are versed in the higher branches of knowl-
edge, and who are accustomed to express the most com-
plete relations by algebraical signs ; but it must be rec-
ollected that the subject of which I treat is familiar to
few, and that it is necessary to explain with rigorous
accuracy the principles upon which the method em-
ployed is founded, as well as the manner of using the
apparatus which I recommend.

On repeating twice the experiment made with pure linseed oil I
had as a result in one of these experiments a capacity for heat equal

to o 4441 1

and in the other equal to ...... 0.47193

If to these two results we add that of the first ex-
periment, equal to ...... 0.44172

we shall have as a mean result ... . 0.45192

The following are the results of some experiments
made with other liquids. Olive oil furnished : —

Specific heat of olive oil.

ist experiment 0.45944

2d experiment ....... 0.43422

3d experiment .... ... 0.42183

Mean result . . . 0.43849

Three experiments made with naphtha gave the fol-
lowing results : —

Specific heat of naphtha.

1st experiment ...... 0.43408

2d experiment ....... 0.39234

3d experiment 0.41905

Mean result . . . 0.41519
VOL. ii. 28

434 On the Capacity for Heat of various Liquids.

Three experiments made with spirits of turpentine
gave the following results : —

Specific heat of turpentine.

1st experiment 0.29322

zd experiment 0.37031

3d experiment 0.34216

Mean result . . . 0.33856

Two experiments with alcohol, of the specific gravity
of 817,624, gave the following results : —

Specific heat of alcohol.

1st experiment ....... 0.54924

ad experiment ••- § * . . . . 0.55063

Mean result . . . 0.54993

Two experiments with spirit of wine, of the specific
gravity of 85,324, gave the following results: —

Specific heat of spirit of wine.

1st experiment . . . . " . . . 0.57840

zd experiment . . . • '•'•• . 0.58317

Mean result . . 0.58078

Two experiments with sulphuric ether, of the specific
gravity of 72,880, gave as results : —

Specific heat of sulphuric ether.

1st experiment ....... 0.53711

2d experiment . ' . . ' 0.54768

Mean result ... * 0.54329

I was at first much surprised to find so great a ca-
pacity for heat in sulphuric ether, but my astonishment
was diminished when I recollected that this liquid can
unite with alcohol in all proportions without exhibiting
any symptoms of a chemical action ; for this reason,
therefore, we ought to expect to find the same capacity
for heat in both liquids.

[This paper is printed from Tilloch's Philosophical Magazine, XLIII. (1814), pp.
212-218.]

INQUIRIES

RELATIVE TO THE STRUCTURE OF WOOD,

The specific Gravity of its solid Parts, and the Quantity
of Liquids and elastic Fluids contained in it under
various Circumstances ; t/ie Quantity of Charcoal to
be obtained from it; and the Quantity of Heat pro-
duced by its Combustion*

SINCE the days of Grew and Malpighi, there have
been but few regular inquiries into the structure
of wood. The science of botany has, indeed, taken
an excursive range ; and the indefatigable zeal of mod-
ern naturalists, who have travelled over all the known
world, has made us acquainted with an astonishing
number of plants, unknown before in Europe, and
therefore called new, by which our gardens and apart-
ments are embellished with a profusion of gay flowers ;
but still the knowledge of the vegetable economy is
scarcely at all advanced. The circulation of the sap in
plants is still a subject of dispute, and the causes of its
ascension are very imperfectly known. The specific grav-
ity of the solid parts which form the wood of plants is
unascertained, and, by consequence, the proportions of
solids, of liquids, and of elastic fluids ; the component
parts of a plant, with the variations to which they are
subject in different seasons, are matters of which we are
still ignorant.

436 Inquiries relative to the Structure of Wood.

It is, indeed, known, that the wood of a tree remains
and preserves its primitive form after it has been con-
verted into charcoal ; but no one has explained this
extraordinary phenomenon, very little attention having
been paid to it.

An earthen vessel becomes hard and brittle in the
potter's furnace ; the vessel shrinks during the operation
of baking, but it undergoes no alteration of shape.
This phenomenon is easily accounted for; the water,
which distended the particles of the clay, kept them at
a distance from each other, and rendered the mass soft
and flexible, having been expelled by the power of the
heat, the several particles contract themselves together,
and form a hard brittle body, though the clay remains
the same before and after the operation.

Is it not possible that wood is converted into char-
coal by a similar process ? For either the charcoal is
already formed in the wood, or, the wood being decom-
posed, the charcoal is formed of its elements or a part
of them. But is it not evidently impossible that the
elements of a solid body should be so totally deranged
as to separate them entirely from each other without
destroying the form or figure of the body ?

In the sequel of this paper it will be shown that the
specific gravity of the solid parts of any kind of wood
is very nearly the same as that of the charcoal obtained
from it, — a circumstance that gives a great degree of
probability to the hypothesis that the two substances
are identically the same.

But I do not mean to amuse the Class with a detail of
my own conjectures ; it is to my experiments and their re-
sults that I now claim the honour of calling its attention.

I was by accident first induced to enter upon this

Inquiries relative to the Structure of Wood. 437

examination and inquiry into the structure of wood.
In the course of a long series of researches upon heat,
I wished to determine the quantities of that element
produced by the combustion of different kinds of wood;
but I had scarcely begun the inquiry when I found that,
in order to procure satisfactory results to my experi-
ments, it was indispensably necessary to obtain a better
knowledge of wood itself; and therefore I immediately
devoted myself to the study.

My first aim was to determine the specific gravity of
the solid parts which compose the fabric of the wood,
in order afterwards to determine the quantities of sap
or water contained in wood under various circumstances.

Having found that very thin shavings filled with sap,
or even with water, could be thoroughly dried in less
than an hour, without injury to the wood, in a stove
kept at a higher temperature than that of boiling water,
or at about 500° of Fahrenheit's scale (= 260° French),
I determined on using shavings of this description in
my experiments.

SECTION I. — Of the specific Gravity of the solid Parts
of Wood.

I began with the wood of the lime-tree, of which the
texture is very fine and regular. From a small board,
five inches long and half an inch thick, very dry, I took
a quantity of thin shavings with a very sharp plane.
These were exposed for eight days in the month ot
January upon a table in a large room not otherwise
occupied, in order that they might attract from the
atmosphere all that moisture which, as an hygrometric
body, they were capable of imbibing. The temperature
of the room was about 46° F.

438 Inquiries relative to the Structure of Wood.

Ten grammes (154.5 grains) of those shavings, laid
on a china plate, were placed in a large stove made of
sheet-iron, and there exposed to a regular heat of about
245° F. for two hours, in the course of which time they
were frequently taken out and weighed in order to observe
the progress of their desiccation. When they ceased to
lose weight, the operation was stopped ; when perfectly
dried, their weight was 8.121 grammes.

By previous trials with my apparatus, I had learned
that if the stove was too much heated the shavings
became discoloured, which is always indicated by the
emission of a particular odour, very readily to be per-
ceived ; but, by a careful regulation of the fire, this
accident may be avoided and the shavings be thoroughly
dried without injury, or even subjecting them to any
sensible alteration.

I concluded that they had not undergone any change,
because, upon again exposing them to the atmosphere,
they regained the same weight which they had, under
similar circumstances, prior to their being dried in the
stove.

Being thus possessed of the weight of my shavings,
as well under exposure to the air as in a dried state,
which latter I could not but look upon as being perfect,
it only remained to ascertain their weight in water when
all their vessels and pores were completely filled with
that liquid, to enable me to determine the specific grav-
ity of the solid parts of this wood, which was accom-
plished without difficulty by the following process : —

A cylindrical copper vessel, 10 inches in diameter and
as many deep, was filled with water from the Seine,
previously well filtered, and, being set upon a common
chafing-dish, was made to boil for some time, to expel

Inquiries relative to the Structure of Wood. 439

the air contained in the water. The shavings were then
thrown into the boiling water, and kept in that state for
an hour. The water was not long in filling the vessels
and pores of the shavings, from which it dislodged the
air contained in them ; so that the wood, specifically
heavier than the water, was precipitated to the bottom
of the ves.se!, and there remained.

When the vessel was removed from the chafing-dish,
the water was suffered to cool to the temperature of 60°
F., and then, plunging in both hands, I placed (under the
water) all the shavings in a cylindrical glass vase, whose
weight I had previously ascertained, which was sus-
pended in the water by a silken cord, fastened at its
other extremity to the arm of an accurate hydrostatic
balance.

On weighing the shavings in the glass case thus im-
mersed, I found their weight equal to 2.651 grammes.

As the shavings, while dry, weighed 8.121 grammes
in the air, and 2.651 grammes in the water, they must
have lost 5.47 grammes of their weight in the latter ;
consequently they must have displaced 5.47 grammes of
water; and the specific gravity of the solid parts of this
wood must be to that of the water at the temperature
of 60° F. as 8.1 21 to 5.47, or as 14,846 to 10,000.

It may perhaps excite some surprise that the solid
parts of so light a wood as that of the lime-tree should
be heavier, by nearly one half, than water, taken in
equal bulks. But this surprise will, without doubt, be
increased when I declare that the specific gravities of the
solid parts of all kinds of wood are so nearly alike as
almost to induce a belief that there is the same identity
in the ligneous substance of all sorts of wood as in the
osseous substance of all species of animals.

440 Inquiries relative to the Structure of Wood.

I procured, from a joiner's workshop, dried wood
of the eight following species ; viz., poplar, lime, birch,
fir, maple, beech, elm, and oak ; and had them cut into
small boards, 5 inches in length and 6 inches broad,
from each of which I planed off some thin shavings,
and exposed them to the air for eight days, in the
month of January, in a large room, where the tempera-
ture, which varied but little, was about 40° to 45° F.

When these shavings had acquired their ordinary de-
gree of dryness under existing circumstances, 10 grammes
of each sort were weighed off, and, being laid separately
in china plates, were thoroughly dried in the stove.

On being taken out of the stove, they were again
weighed, and then thrown into boiling water, to ex-
pel the air from their pores and to moisten them thor-
oughly. When they had boiled for an hour, they were
suffered to remain in the liquor till it was sufficiently
cool ; and after they had been weighed in the water,
the specific gravity of their solids was calculated in the
usual way.

The following table gives the details and results of
this inquiry : —

Species of
wood.

Weight.

Specific gravity
of the solid parts
of the wood.

Weight of
a cubic inch of
the solid parts
of the wood.

Exposed
to the air in
a room in

Thoroughly
dried in a
stove.

In the water
at 60° F.

Grammes.

Grammes.

Grammes.

Grammes.

Poplar

10

8.045

2.629

14854

29.45

Lime

10

8. 121

2.651

14846

29.40

Birch

10

8.062

2.632

14848

29.44

Fir

IO

8.247

2.60 1

14621

28.96

Maple

10

8.137

2.563

14599

28.93

Beech

10

8.144

2.832

15284

3°-3°

Elm

10

8.180

2-793

15186

30.1 1

Oak

10

8.336 | 2.905

15344

30.42

Water 10000 '9-83

Inquiries relative to 'the Structure of Wood. 441

The specific weight of the solid matter which com-
poses the fabric of these woods is so nearly alike in
them all, that the small variations to be observed in the
different experiments may perhaps be accounted for
otherwise than by supposing the ligneous substance to
be essentially different in the several species.

The charcoal obtained from the various kinds of
wood, if carefully prepared, has no sensible difference;
and all the seerwoods give nearly the same chemical
results when treated in the same manner. Hence, with-
out doubt, we have good reason to suspect that the
ligneous substance of all woods is identical. But with-
out stopping to discuss this question at present, I shall
endeavour to elucidate another, no less interesting, and
which yields results more satisfactory.

SECTION II. — Of the Quantities of Sap and Air discovered
in Trees and in Seerwoods.

Grew and Malpighi discovered in plants certain ves-
sels which they suspected to be destined for the recep-
tion of air; and many physiologists have supposed that
the air found shut up in the vessels of plants (if it
be really confined there) would necessarily cause a re-
action upon the neighbouring vessels, with an elastic
force as variable as the temperature to which this elastic
fluid is exposed, and might probably contribute to the
circulation of the sap.

It would, doubtless, be an interesting question to de-
termine precisely the quantity of air contained in plants
in different seasons and under various circumstances.
By examining the variations to which this quantity of
air is subjected, and combining them with other simul-

442 Inquiries relative to the Structure of Wood.

taneous phenomena, we might hope to make some dis-
covery which may assist us a little to elucidate the pro-
found obscurity that at present conceals this part of the
vegetable economy.

The specific gravity of the solid parts of a plant being
known, it becomes very easy to determine in every case
the quantity of air contained in its vessels and pores.

The following example will render this position per-
fectly clear.

An oak in complete health, in a growing state, was
cut down on the 6th of September, 1812. A cylindrical
piece, 6 inches long and rather more than an inch in
diameter, taken from the middle of the trunk of this
young tree, 3 feet above the earth, weighed, when full
of sap, 181.57 grammes.

Upon plunging this piece of wood into a cylindrical
vessel about I J inch in diameter and 6\ inches in height,
filled with water at the temperature of 62° F., it displaced
188.57 grammes of the water;* whence I conclude
with certainty, that this piece of oak, filled with sap,
possessed a bulk equal to 9.5093 cubic inches, that its

* In order to determine and keep an account of the quantity of water remaining on
the surface of this piece of wood at the instant of withdrawing it from the vessel, it
was weighed when taken out, whilst still quite wet. As its weight had been taken
previously to the operation, the augmentation it had acquired from the water was ascer-
tained to a nicety.

The vessel when empty weighed 188.22 grammes, and when filled with water at
the temperature of 60° F., 474.9 grammes ; so that it contained 286.68 grammes of
water. When the piece of wood was plunged into the water, a small glass plate,
about two inches in diameter and two lines in thickness, ground with emery to fit it
to the edges of the vessel, so as to close it hermetically, was laid upon its mouth, to
shut up the piece of wood with the water still remaining in the vessel, whilst its out-
side was wiped with a dry cloth.

When the exterior of the vessel had been thoroughly dried, the glass cover was
carefully removed, and the piece of wood withdrawn ; the vessel was then weighed
again with its remaining contents of water ; and from its weight the quantity of water
displaced by the wood was calculated.

Inquiries relative to the Structure of Wood. 443

specific gravity was 96,515, and, consequently, that a
cubic inch of it weighed 19.134 grammes.

When the piece of wood had been reduced to the
shape of a small board, about half an inch in thickness,
I took from it forty very thin shavings weighing 19.9
grammes, but when thoroughly dried in the stove, at
a temperature of 262° F., they weighed only 12.45
grammes.

From this experiment, it is evident that the wood in
question, being full of sap, was composed of 12.45
ligneous parts, and 7.45 parts of water, or of sap, whose
specific gravity is nearly the same as that of water.

Now, as one cubic inch of this wood weighed 19.134
grammes, it is very certain that it was composed of
11.971 grammes of ligneous parts, which were conse-
quently solids, and of 7.163 grammes of sap.

But we have already seen, from the results of the
experiments detailed in the former part of this memoir,*
that a cubic inch of the solid parts of the wood of the
oak weighs 30.42 grammes : —

Consequently the 11.971 grammes of solid parts
found in one cubic inch of this wood, when the
tree was alive, could have no greater bulk
than 0-39353 cubic inch.

As one cubic inch of water weighs 19.83
grammes, the 7.163 grammes of sap found in
the cubic inch of this wood must have occu-
pied a bulk equal to ..... 0.36122

Consequently a cubic inch of the wood in ques-
tion contained a quantity of air whose bulk
was equal to 0.24525

Making together .... l.ooooo

* See the table, page 440.

444 Inquiries relative to the Structure of Wood.

We conclude from these results, that a young oak, in
a growing state, at the beginning of September, when
the wood appears to be diffused with sap, contains, nev-
ertheless, about a fourth of its bulk of air, and that its
solid ligneous parts do not make quite -fa of its bulk.
But we shall presently see that the lighter woods contain
still less of ligneous parts, and more of air, than the oak.

A young Italian poplar, 3 inches in diameter, meas-
ured at 2 feet above the earth, was cut down on the
6th of September, while the tree appeared to be in a
growing state. The specific gravity of a piece taken
from the middle of the trunk was found to be 57,946;
consequently a cubic inch of this wood weighed 11.49
grammes.

From a piece of this wood, apparently full of sap,
forty thin shavings were taken, 6 inches in length' and
half an inch broad. The wood from which these shav-
ings were planed weighed 12.37 grammes; and the
shavings, when thoroughly dried in the stove, weighed
7.5 grammes.*

We hence conclude that a cubic inch of this wood, in
its original state, while the tree was still alive, contained
7.1531 grammes of ligneous parts which formed the
fabric of the wood, and 4.3369 grammes of sap, differ-
ing in its specific gravity little or nothing from common
water.

* As the heat excited by the plane in taking off these shavings was sufficient to
evaporate a very sensible quantity of sap belonging to the wood from which they were
cut, the shavings became perceptibly dry during the operation ; for I found that forty
thin shavings sometimes lost more than one gramme (about — of their weight)
in less than a minute. In order to obtain their true weight, whilst they still remained
part of the wood, I adopted the precaution of weighing the piece of wood both the
moment before and the moment after the operation of planing. The difference in
the weight of the wood, under these two circumstances, indicates the weight neces-
sary to be given to the shavings, and which is here always attributed to them.

Inquiries relative to the Structure of Wood. 445

As one cubic inch of the solid parts of this kind
of wood weighs 29.45 grammes,* the 7.1531
grammes of ligneous parts found in a cubic
inch of the trunk of the living tree, in Sep-
tember, could only have occupied the space of 0.24289 cubic inch.

And the 4.3369 grammes of sap, contained in it,

only 0.21880

Consequently, in one cubic inch of this wood

there was a bulk of air equal to . . . 0.53831

Total I. ooooo

The difference between the structure of the oak and
of the poplar becomes very conspicuous on making a
comparison, according to the subjoined method, between
the constituent parts of these two kinds of wood, both
in a growing state.

Thus, a cubic inch of wood is composed of: —

Ligneous parts. Sap. Air.

The oak . . . 0.39353 0.36122 0.24525
The poplar . . 0.24289 0.21880 0.53831

This striking difference in the proportions of the
ligneous substance, of sap, and of air, discovered in these
two species, sufficiently explain the difference observable
in their weight and hardness. This inquiry may prob-
ably lead to other discoveries of more general utility in
the study of the vegetable economy.

SECTION III. — Of the relative Quantities of Sap and Air
found in the same Tree, in Winter and in Summer ; and
in different Portions of the same Tree, at the same Time.

The following experiments were undertaken with a
view to discover the difference between the quantities of

* See the table, page 440.

446 Inquiries relative to the Structure of Wood.

sap and air found in the wood composing the trunk of
a large tree, in winter and in summer.

On the 2oth of January, 1812, I had a lime-tree felled
of about twenty-five or thirty years' growth, which had
stood among several others of the same age in my gar-
den at Auteuil. On taking a piece of wood from the
middle of the trunk, at about 3 feet above the ground,
it appeared to be filled and even drowned in sap. Its
specific gravity was 76,617 ; consequently, one cubic
inch of the wood weighed 15.788 grammes.

Having planed off 10 grammes of thin shavings from
this piece, and dried them thoroughly in the stove, I
found their weight reduced 4.72 grammes.

Thus in possession of the specific gravity of the solid
part of this wood, it was easy to determine, with the aid
of these data, the constituent parts of a cubic inch,
which were as follows : —

Ligneous parts .... 0.25353 cubic inch.

Sap 0.44549

Air . 0.30098

On the 8th of September, in the same year (1812), I
had a piece of wood (= 5.84 cubic inches) cut from the
trunk of another lime, of equal age with the former
(from 25 to 30 years), at the height of 3 feet above the
earth. This tree was in a growing state, and the piece
taken from it, after it had been trimmed by the joiner,
weighed 87.8 grammes, and displaced 115.8 grammes of
water, at the temperature of 62° F. ; consequently, its
specific gravity was 75,820. In the month of January
the specific gravity of this same species of wood had
been found to be 79,617.

Inquiries relative to the Structure of Wood. 447

From the piece of wood taken from the tree on the
8th of September, I had 14.19 grammes of thin shav-
ings planed off, which, after they had been thoroughly
dried in the stove, weighed only 7.35 grammes. Hence
we have, as the constituent parts of a cubic inch of this
wood : —

Ligneous parts 0.26489 cubic inch.

Sap 0.36546

Air 0.36965

1. 00000

From the results of these two experiments, we may
conclude that the body of the tree contains more sap in
the winter than in summer, and more air in summer
than in winter. But the following experiments demon-
strate the sap to be very disproportionately distributed
in the several parts of the same tree, at the same season.

On the 8th of September, I had a branch, about 3
inches in diameter, cut from the lime just spoken of,
and which issued from the trunk at the height of 10 feet
above the surface of the earth. From the lower end of
this branch I took a piece of wood, and subjected it
to the investigation requisite to ascertain its constituent
parts.

Its specific gravity was 70,201. The same day I found
the specific gravity of a piece of the trunk of the same
tree to be 75,820.

Surprising as this difference appeared, my astonish-
ment was still more excited, on finding that a piece of
wood of three years' growth, cut from the upper end of
the same branch, where it was but one inch in diameter,
had a specific gravity of 85,240.

There was, therefore, much more sap and less air in

448 Inquiries relative to the Structure of Wood.

the wood of the upper extremity of the branch than in
the lower, which was nearer to the body of the tree.

I afterwards examined the young shoots of the current
year, in the same tree, as well as in several other species
of wood, and uniformly found that the specific gravity
of the young wood, that is to say, of the current year,
is always considerably greater than that of the same
species of wood when grown older. Doubtlessly, be-
cause it contains more sap and less air than the old
wood.

In the management of experiments for determining
the specific gravity of wood of the current year, it is in-
dispensably necessary to take an account of the space
occupied by the pith, without which precaution we
shall be led to false conclusions.

I found the specific gravity of the oak of the current
year to be 116,530; that of the elm 110,540. Young
shoots of these trees, deprived of their bark and pith,
descend rapidly on being thrown into water ; whilst
species of the same tree, more advanced in age, swim
on the surface, even when the wood is green, and more
full of sap.

This fact is worthy the attention of persons occupied
in the study of vegetable physiology.

I was next curious to examine the root of the lime
from which I had already had one piece of wood from
the trunk, and two pieces from one. of its branches.
With this view, on the 8th of September, 1812, I caused
one of its roots, of about 2 inches diameter, to be
taken up, and cut from it a piece weighing 93.25
grammes, which displaced 115.8 grammes of water. Its
specific gravity was 80,527, and, consequently, greater
than that of the wood extracted from the trunk of the

Inquiries relative to the Structure of Wood. 449

same tree, but less than that cut from the upper end of
one of its branches. 20.48 grammes of thin shavings,
from this piece of the root of the lime, weighed only
10.85 grammes after being thoroughly dried in the
stove.

From these data, I determined the constituent parts
of a cubic inch of the root thus : —

Ligneous parts ..... 0.28775 cubic inch.

Sap 0.37358

Air 0.33867

The constituent parts of a cubic inch of the body of
the same tree were, as we have shown : —

Ligneous parts 0.26489 cubic inch.

Sap 0.36546

Air 0.36965

The constituent parts of a cubic inch of the wood of
the same tree, taken the same day from the lower ex-
tremity of a branch, were : —

Ligneous parts 0.25713 cubic inch.

Sap 0.27513

Air 0.46774

Lastly, the constituent parts of a cubic inch of the
wcod, taken near the upper extremity of the same branch,
wee : —

Ligneous parts 0.25388 cubic inch.

>ap . . . ..-.-.. 0.47599
Vir 0.27013

1 .00000
vo, a. 29

450 Inquiries relative to the Structure of Wood.

For the more easy comparison of the results of these
four experiments upon the wood of the lime-tree, made
on the same day, with different portions of the same tree,
I have collected them together in the following table.

A cubic inch of wood was
composed of

Ligneous
parts.

Sap.

Air.

The root ....
The trunk ....
The lower end of a branch
The upper end of " .
Wood taken from the trunk of a ~\
lime-tree of the same age, on >
the 20th of Jan. . . )

0.28775
0.26489
0.25713
0.25388

°-25353

0-37358
0.36546
0.27513
0.47599

0.44549

0.33867
0.36965
0.46774
0.27013

0.30098

Being desirous to ascertain whether a difference con-
siderable enough to be valued existed between the wood
of the heart, or core, and the sap-wood found between
the rind and the body of the same tree, I took, on the
nth of September, an elm fagot, 5 inches in diameter,
lopped from a large tree, which had been felled on the
2oth of the preceding April, and had two cylindrical
pieces, each 6 inches in length, cut out of it. The
thickest of these taken from the core weighed I9I.O5/
grammes, and displaced 194.45 grammes of water; thtf
other, consisting of the sap-wood, weighed 93.6'
grammes, and displaced 111.45 grammes of water.

The specific gravity of the core was, therefore, 98,251;
that of the sap-wood, 81,764. But as the fagot hd
lain exposed to all the summer rains, the wood was ar
from being dry. I was, however, much surprised at ds-
covering that the core of the wood was more char/ed
with sap or water than that of the same kind of w-od
when in a growing state, — a fact which induces a us-
picion that the sap in trees is not enclosed in vesels
or tubes apparently impervious to that liquid.

Inquiries relative to the Structure of Wood. 451

To obtain a better knowledge of the wood in ques-
tion, I planed off forty shavings, 6 inches in length and
half an inch in breadth, from a small board cut from the
core ; with an equal number of shavings, of similar di-
mensions, from another board cut from the sap-wood.

The forty shavings from the core, taken just as they
were planed off, weighed 16.37 grammes, and 10.53
grammes after they had been thoroughly dried in the
stove.

The forty shavings of sap-wood weighed 1 6.97 grammes
before they were dried, and 11.99 grammes afterwards.

Thus possessed of the specific gravity of the solid
parts of this kind of wood, it only remained to deter-
mine, from these data, the constituent parts of an inch
of the wood, which was readily performed, as fol-
lows : —

Ligneous parts. Sap. Air.

In the core of the elm . . 0.41622 0.35055 0.23323

In the sap-wood . . . 0.38934 0.23994 °-37°72

It appears, from the results of these experiments, that
the sap-wood of the elm contains rather more ligneous
parts in its timber than the core of the same tree ; and
that it contains much less sap and more air. But as
the tree had been felled nearly five months before it
became the subject of investigation, it is very possible
that the sap-wood had become much drier than the core
of the tree.

I had purposed to repeat these experiments upon
wood in a growing state and upon seerwood ; but the
interference of other occupations has prevented a con-
tinuance of the inquiry. It cannot, however, but lead
to results curious in themselves ; and I therefore recom-
mend it to the notice of all students in vegetable econ-

452 Inquiries relative to the Structure of Wood.

omy, as well as to those who love that noble science, and
feel a gratification in being able to remove the veil under
which the mysterious operations of nature are concealed.
The particular object which I had in view in explor-
ing the structure of wood has led me by a way by no
means likely to be fertile in interesting discoveries ; but
I have begun the work, and feel myself bound to com-
plete it, in preference to every other consideration.
These fascinating researches, I am aware, have already
carried me too far, and I must now resign them into
the hands of others, in order to fulfil my engagements.
This I do most cheerfully, and it will give me the great-
est pleasure to behold a field, too long neglected, once
more broken up.

SECTION IV. — Of the Quantities of Water contained in
Woods considered as dry, or Seerwoods.

Wood is a hygrometric substance, and, when exposed
to the atmospheric air, always imbibes a visible quantity
of water, varying, however, with the temperature and
humidity of the air.

If the moisture in the wood were confined in vessels
so constructed as to be totally impervious to water,
the fabric of the wood would be uniformly the same,
with the exception only of the variations caused in its
dimensions by change of temperature, in which case it
would be very easy to determine the quantity of water
contained in the wood, when the specific gravity of its
solid parts was known. But, as the bulk of all woods
is considerably diminished in drying, the experiment is
rendered rather prolix, though by no means difficult,
and its results are clear and satisfactory.

Inquiries relative to the Structure of Wood. 453

A few examples will suffice to point out the method
to be pursued.

The composition of the oak, in a growing state, at
the beginning of September, has been already given. In
order to ascertain the change which this wood under-
goes by the process of drying, I made the following
experiment.

From a fagot of oak, 5^ inches in diameter, which,
covered with its bark, had been exposed to dry in the
open air for eighteen months, I took a piece of rather
more than an inch square and 6 inches in length; it was
good firewood, and seemed very dry.

This piece, after being trimmed by the joiner, weighed
126.2 grammes, and displaced 157.05 grammes of water;
its specific gravity was consequently 80,357, and a cubic
inch weighed 15.939 grammes.

Forty-three shavings of this wood, 6 inches long
and half an inch broad, weighed 17.9 grammes ; but
when thoroughly dried in the stove, they were reduced
to 13.7 grammes. They were therefore, prior to being
put into the stove, composed of 13.7 grammes of solid
parts — that is to say, of dry or seerwood — and 4.2
grammes of water.

The results of this experiment indicate that 100 kilo-
grammes of this excellent firewood contained 76 kilo-
grammes of seerwood and 24 of water; which is,
probably, the ordinary state of the best firewood sold in
the timber-yards of Paris, and all other places.

Were the wood to be kept for several years in a dry
place, secured from the rain, it is possible that it might
become dry to such a degree as to contain only about 12
per cent of water, and 88 of seerwood. But it will
appear in the sequel that wood of any kind, exposed to

454 Inquiries /-dative to the Structure of Wood.

the atmosphere, could never become more dry, on
account of its hygrometric quality, which it constantly
preserves.

The following are the constituent parts of a cubic
inch of firewood employed in this experiment : —

Ligneous parts, or seerwood

Sap, or water

Air

0.40166 cubic inch.
. 0.18982
0.40852

Thus we are enabled clearly to demonstrate the differ-
ence between the oak in a growing state, and the same
kind of wood after it has been felled and dried in the
air, secured from the rain, for eighteen months : —

Jn a cubic inch of oak, in a grow- 1

Q-39353

! 0.36122

0.24525

In a cubic inch of the same kind ~\

1

of wood, after it had been >

0.40 1 66

i 0.18982

0.40852

felled and dried for 18 months )

|

Dry wood, i Water.

By comparing the relative quantities of seerwood
contained in a piece of timber while in a growing state,
and in the same timber after it has been dried, we may
ascertain how much its fabric has shrunk by desicca-
tion.

It appears from these experiments, that the oak sold
in the timber-yards of Paris for firewood contains
rather more than one half of the sap which it formerly
had in a growing state.

I have made several similar experiments upon other
species of wood ; but their results are better calculated
for exhibition in a table than for circumstantial detail.

Inquiries relative to the Structtire of Wood. 455

SECTION V. — Of the Quantities of Water attracted from the
Atmosphere by Woods of various Species ', after being per-
fectly dried.

It has been long known that charcoal imbibes the
humidity of the atmosphere with considerable eager-
ness ; but I have discovered that dry wood attracts it
with still greater avidity. The following are the details
and results of a series of experiments made last winter,
with a view to elucidate this subject.

Having procured thin shavings, about 5 inches long
and half an inch broad, of nine different species of the
woods of our climate, in order more certainly to re-
duce them to an equal degree of dryness, I began my
experiment by boiling them for two hours in water, that
they might be thoroughly impregnated with that ele-
ment.

I then dried them well in a stove, in which they were
kept during 24 hours, exposed to a temperature higher
than that of boiling water, at about 250° of Fahrenheit's
scale.

On taking them out of the stove, they were carefully
weighed, being still hot ; they were then suffered to re-
main in the open air for 24 hours, in a large room,
whose temperature was uniformly during the day and
night at about 45° to 46° F. This was on the ist of
February, 1812.

The weight of the shavings, on being removed from
the stove thoroughly dried, and after having been ex-
posed to the air of the large room, was as follows : —

456 Inquiries relative to the Structure of Wcod.

Wei

?ht.

Species of wood

On being
withdrawn from
the stove.

After exposure
for 24 hours, in

temperature of
V F.

Italian poplar ......
Lime-tree, seasoned, and fit for the joiner's use
" green wood ....
Beech
Birch

Grammes.
3-58
5.28

5-39

7.02

4- 4-1

Grammes.

445
6.40

6.47

8.62

c. 4.7

Fir
Elm
Oak
Maple

5.41
5.87
6.46

4.76

6.56
7.16

7-93
5.85

Hence it appears that 100 parts of the wood, after 24
hours' exposure in the large room, were composed of dry
wood and water in the following proportions : —

loo parts of

Poplar .
Lime-tree, seasoned

" green
Beech .
Birch
Fir .
Elm
Oak .
Maple .

Seerwood.
80.55
82.50

83-3I
8144
80.62
82.4

81.80
83.36
81-37

Water.

'9-55
17.50
16.69
18.56
19.38

7-53
17.20
16.64
18.63

I suffered all these woods to remain in the large
room during eight days, but their weight was very little
augmented ; and as often as the temperature of the air
of the room was raised above 46° F. they lost weight.
So that the above may be considered as their habitual
state of dryness during the winter, in our climate.

To ascertain the quantity of moisture habitually re-
tained by these woods in the summer, I made the fol-
lowing experiments.

Thin shavings of the species of woods below, half an
inch broad, were thoroughly dried in the stove, and then

Inquiries relative to the Structure of Wood. 457

exposed for 24 hours in a room with a northern aspect,
whose temperature was tolerably uniform at 62° F. The
following are the results : —

Weight.

At the

were found

Species of wood.

Wlian A~ .

accustomed
state of

When dry.

humidity in

the air at

Seerwood.

Water.

62° F.

Grammes.

Grammes.

Parts

Parts

Elm, the core

IO-53

11.55

9I.l85

8.815

" the sap-wood

11.99

I3-IS

91.197

8.803

Oak, seasoned and fit for

the joiner's use .

13.70

15.05

91.030

8.970

Oak felled 6th Sept. .

12.45

13.70

90.667

9-333

Lime, seasoned

7.27

7.80

93.205

6.795

" when growing .

6.75

7-30

92.466

7-534

" the root

9.96

10.80

92.222

7.778

Elm, seasoned .

9.25

10.80

9I-I33

8.867

Italian poplar

7.50

8.00

93-75°

6.250

With a view to ascertain the habitual state of the
dryness of woods in autumn, I carefully preserved these
same shavings till the 3d of November, in a northern
chamber, not inhabited ; at which period its tempera-
ture had stood for several days at 52° F., with little
variation. I then weighed the shavings, and from their
weight calculated the quantity of water contained in
them.

The following table, containing the results of all
these experiments, displays, in a familiar and satisfactory
manner, the customary state of the woods, in different
seasons, in our climate.

Species of wood.

ioo parts in weight of wood, cut into thin shavings and
exposed to the air, contained water

In summer,
at a temperature of
6/ F.

In autumn,
at a temperature of

S£F.

In winter,
at a temperature of
45°F.

Poplar . .
Lime .
Oak ...
Elm .

Parts.
6.25

7.78
8.97

8.86

Parts.

»•!$

11.74
12.46

I 1. 12

Parts.

'9-55

17.50
16.64
17.20

45 8 Inquiries relative to the Structure of Wood.

From a comparison of these results it appears that
these woods, when exposed to the air at a temperature
of 45° F., contain twice the quantity of water that they
do when the temperature of the air is at 60° F. But it
is necessary that the wood be cut into very thin shav-
ings, to enable it to become suddenly in equilibria with
the air, conformably to its quality of a hygrometric
body ; otherwise the state of the air may change, and
that very frequently, before its humidity or dryness can
have had sufficient opportunity to produce all its effect
upon the wood.

To discover what is termed the medium dryness of any
species of wood, in our climate, it is requisite that we
be acquainted with the quantity of water contained in
wood every day of the year, and even in every hour and
every minute, which is obviously impossible ; but there
is another method to be pursued in this inquiry, much
less laborious and which will lead to results as satisfac-
tory as the nature of the subject will admit.

As a very large piece of wood, a large beam for in-
stance, dries so very gradually in the air as not to attain
a state of perfect dryness in less than 50 or 60 years, it
is sufficient to examine the interior of such a beam, after
having been sheltered for 80 or 100 years from the rain,
to discover the state of such part of the wood as may
still be considered sound.

In pulling down old houses, we meet with beams
proper for the present inquiry.

An old castle in my neighbourhood being pulled
down, I had an opportunity of examining the interior
of a large oaken beam, which had, without doubt, been
there more than 150 years, and as it formed part of the
timbers of the edifice, had been secured from the rains.

Inquiries relative to the Structure of Wood. 459

A piece of this wood in a high state of preservation,
after it had been planed by the workman, was accurately
weighed, and then plunged into water, to ascertain its
specific gravity. It weighed 75.05 grammes, and dis-
placed no grammes of water, at the temperature of
61° F. ; its specific gravity, therefore, was 68,227, and a
cubic inch weighed 13.53 grammes.

Forty shavings of the wood weighed 11.4 grammes,
which were reduced to 10.2 grammes when they had
been thoroughly dried in the stove.

Hence we may conclude that a cubic inch of this old
wood was composed of

Ligneous parts ..... 0.39794 cubic inch.

Water 0.07186

Air 0.53020

We may also conclude from these results, that the
wood of the centre of a large oaken post, though kept
for ages out of the reach of the rain, can never contain,
in our climate, less than 10 per cent of its weight in
water; and that a cubic inch of such wood contains
more than half a cubic inch of air.

The yearly medium temperature at Paris is about 54]-°
F. ; now, as we have just seen that the habitual state of
dryness in woods at the temperature of 52° F. is such
as to give about n per cent of water for 100 parts of
wood, we must not be surprised at finding 10 per cent
of water in the interior of a large beam, after it had
been sheltered from the rain during 150 years. .

To ascertain whether the property of wood to attract
moisture from the atmosphere was augmented or dimin-
ished by the beginning of carbonization, I made the fol-
lowing experiments.

460 Inquiries relative to the Structure of Wood,

Fourteen grammes of ash-shavings, after being highly
dried on a marble slab over a chafing-dish, were exposed
to the air, in the month of February, in a large room
whose temperature was about 20° F., and in 15 hours
they had gained 1.65 grammes in weight.

Fourteen grammes of the same sort of shavings, hav-
ing been first scorched in the stove till they had assumed
a brown color, were at the same time dried over the
chafing-dish, and exposed with the others to the cold air
for the same length of time ; but they gained in weight
only i.oi grammes, while those which had not been
scorched, as already stated, had gained 1.65 grammes.

Fourteen grammes of the shavings of lime-wood, in
their natural state, and fourteen grammes of the same
kind of shavings, after they had been violently scorched
in the stove, were dried together over the chafing-dish,
and then exposed in the open air, at the temperature of
40° F. for 15 hours. The shavings in their natural
state gained 1.33 grammes in weight ; while those that
had been scorched gained 0.7 grammes.

A similar experiment, upon shavings of the cherry-
tree, some in their natural state, and others scorched,
was productive of the same result.

Whence we conclude that wood in its natural state
attracts the moisture of the air more copiously than it
does after having been subjected to the first degree of
carbonization.

From similar experiments upon wood and charcoal, I
find that dry wood attracts humidity more powerfully
than dry charcoal.

It would be worth ascertaining, whether wood is not
also more powerfully attractive of gas than charcoal ;
but as I have not time to enter upon this particular

Inquiries relative to the Structure of Wood. 46 1

inquiry, I can only recommend it to those whose inclina-
tions may lead that way. Leaving, therefore, this subject
untouched, I must, without any further circumerration,
pursue the original object I had in view in these disqui-
sitions upon wood, namely, to endeavour to become
acquainted with those inflammable substances which burn
on setting fire to a piece, of wood under a calorimeter.

SECTION VI. — Of the Quantities of Charcoal to be obtained
from different Kinds of Wood.

Having discovered that pieces of wood, more or less
thick, may be perfectly carbonized in glass vases with
thin tops, closely covered, and exposed for two or three
days to a moderate heat in a stove, I adopted this
method in all my experiments on the carbonization of
wood.

The glass vases which I make use of are what the
chemists call proofs, with feet : they are small cylindrical
vessels, about i^ inch in diameter and 6 inches in height;
the covers consist of glass plates about 2 inches in diam-
eter and from 2 to 3 lines in thickness, neatly ground
with very fine emery, well diluted with water, on a large
glass slab ; and, the edges of the vases being ground with
the same exactness, they become hermetically closed by
the covers, so as to preclude every access of the air, es-
pecially if the edges of the vases and the whole surface
of the covers be well rubbed with black-lead.

The elastic fluids, in escaping from the interior of the
vases, occasionally raise the cover for a moment, on one
side, even when surmounted by 'a considerable weight;
but as it is only raised a very little, and falls again im-
mediately, the vase is never open more than an instant

462 Inquiries relative to the Stritcture of Wood.

at a time, and then not so as to admit the obtrusion of
any extraneous matter.

When one of these vases is put into the stove, it is
placed upon a square tile, or half-brick, of burned earth,
and another of the same kind is also laid upon the cov.er
to keep it steady.

During the carbonization of the wood, the interior
of the vase is always clouded, assuming a very deep
blackish-yellow colour ; and during the operation a
strong smell of soot or of pyroligneous acid issues
from the stove ; which is even insupportable at the
commencement, if it be too nearly approached, as well
as on withdrawing the vases from the stove, if the covers
be removed without due precaution.

There is, therefore, a decomposition during the carbon-
ization of wood, and a formation of pyroligneous acid.
This fact has been long known ; but, in some of my
experiments, and particularly in those made upon fir, with
a very moderate fire, I obtained a product, which, upon a
very exact scrutiny, appeared to me to be bitumen.

This product had been condensed upon the glass
cover, whence it had afterwards run in large drops upon
the vertical surface of the side of the vase. It was hard
and brittle, of a dark yellow colour ; it was not affected
by boiling water, nor by boiling alcohol, but was grad-
ually dissolved by sulphuric ether.

It would be superfluous here to enter upon the de-
tails of all my experiments relative to the carbonization
of wood. As the process I have employed cannot now
but be well known, after what I have said in this memoir
and in the one that I had the honour to present to the
Class on the joth of December in last year, I shall here
only give the result of those experiments.

Inqiiiries relative to the Structure of Wood. 463

The six following, made with different species of
wood, were so uniformly alike in their results, that I
was much surprised.

One hundred parts (10 grammes) of the six follow-
ing kinds of wood, in thin shavings, and thoroughly
dried, were carbonized at one time in the stove, in glass
vases, well closed with flat glass covers. As the heat
was managed with great care, in order to determine
with precision, from the weight of the vases, the mo-
ment when the operation was finished, the experiment
occupied four days and as many nights. When the
vases with their contents ceased to lose weight, the pro-
cess was stopped, and the charcoal was weighed while
still hot.

The following were the results : —

100 parts in weight of

dry wood
gave in dry charcoal.

The medium term of the results of these six experi-
ments gives 43.33 parts of charcoal in 100 parts of dry
wood ; and as they were made with woods differing
considerably in their apparent weight, their hardness,
and other distinctive physical characters, we may con-
clude, from the great similarity of the results of these
experiments, that none of the circumstances from which
the woods derive their particular characters have any
material influence upon the quantities of charcoal they
are capable of yielding ; and hence we may deduce that
the ligneous substance or seerwood, if not the same in
all, is at least composed of identical substances.

Poplar
Lime

43-571

)arts.

Fir .
Maple
Elm
. Oak

44.18

42-23
43.27

43-00

«

464 Inquiries relative to the Structure of Wood.

There is still, however, a very interesting question re-
maining for discussion, namely, Is the seerwood char-
coal ?

To elucidate this question, I began by examining
whether charcoal had the same specific gravity as seer-
wood.

I, therefore, reduced some common oak-charcoal,
which appeared to be well manufactured, into pieces
about the size of small peas, and then boiled them in
a pretty good quantity of Seine water, previously well
filtered ; the pores of the charcoal were speedily so com-
pletely filled with this liquid, that, becoming heavier than
the water, in equal bulk, it precipitated itself to the bot-
tom of the vessel, and there remained.

On removing the vessel from the fire, the water was
suffered to cool to the temperature of 60° F. ; and then
the charcoal, while still submerged, was put into the
small glass vase of the hydrostatic balance, and weighed.
Its weight in the water, at the temperature of 60° F.,
was 2.44 grammes.

When the charcoal was taken out of the water, it was
put into a cylindrical glass vessel i^ inch in diameter,
and 6 inches in height, in which it was thoroughly dried
in the stove at a temperature of about 265° F.

After it had been six hours in the stove, it was taken
out and weighed while still hot, and found to be equal
to 6.7 grammes ; therefore its specific gravity was

I57,273-

We have before shown that the specific gravity of

the solid parts of oak, in the state of seerwood, is

/*-/•' I

This is certainly very similar to that of charcoal made
of the same kind of wood ; but we have not yet proved

Inquiries relative to the Structure of Wood. 465

seerwood to be charcoal ; on the contrary, we have just
seen that it requires 100 parts of seerwood to obtain
43-33 Parts °f dry charcoal.

Neither is seerwood simply a hydrure of dry wood,
as we shall see in the sequel.

It should seem that the fabric of a plant, which may
perhaps be nothing but pure charcoal, is always cov-
ered with a substance analogous to the flesh which con-
ceals the skeleton of an animal. This vegetable flesh
does not exist in considerable masses ; for, as the
plant is not under the necessity of moving from one place
to another in search of nourishment, it has no need
either of flexible joints in its skeleton, nor of muscles
capable of exerting a great force ; and it probably arises
from the circumstances of the skeleton and the flesh
being very intimately blended together, that they are not
discriminated and distinguished from each other.

I consider seerwood as the skeleton of the plant,
with the flesh, though quite dried, still adhering to it;
and as we have seen that there are 43.33 parts of char-
coal in 100 parts of seerwood, I should say that 100
parts of seerwood are composed of

Charcoal 43.33 parts.

Vegetable flesh, dried 56.67

Making together .... 100.00 parts.

The beautiful analyses of Messrs. Gay-Lussac and
Thenard have shown us that seerwood is composed of
carbon, hydrogen, and oxygen ; and that two different
species of wood analyzed by them (the beech and the
oak) were composed of these three elements in nearly
equal proportions. They also discovered that the oxy-
gen and hydrogen in these woods are in the requisite

VOL. II. 30

466 Inquiries relative to the Structure of Wood.

proportions for the formation of water ; wherefore they
concluded that carbon was the only combustible sub-
stance contained in wood.

It will appear in the sequel, how well the results of
these ingenious inquiries accord with those of my ex-
periments.

But first, I shall examine what quantity of charcoal it
is possible to obtain from different species of woods,
under various degrees of dryness, pursuing the method
already adopted in my experiments.

From the mode in which charcoal is ordinarily made,
a very considerable portion is lost and improvidently
burned during the operation.

As it appears to be clearly proved, by the results of
the six experiments above related, that the quantity
of charcoal to be obtained from any given quantity of
wood is invariably in proportion to the quantity of
dry ligneous substance contained in the wood, the in-
quiry into the quantities of charcoal to be produced
from different species of woods, at various degrees of
dryness, becomes limited to that of the quantities of
wood absolutely dry, contained in the woods in question.

It has been shown that 100 parts in weight of oak,
thoroughly dried, give 43 parts of charcoal.

We have likewise seen, that 100 parts of oak as dry
as it can be made in summer, at the temperature of 62°
F., contain only 91 parts of seerwood, and, conse-
quently, that 100 parts of such wood would furnish
only 39.13 parts of charcoal.

From the results of an experiment of which • I have
given an account in this memoir, it appears that 100
parts of oak, in the state wherein it is found when ex-
posed to the winter's air, at the temperature of 46° F.,

Inquiries relative to the Structure of Wood. 467

contain only 83.36 parts of seerwood ; consequently,
100 parts of such wood would yield no more than 35.84
parts of charcoal.

From the examination we have made of the oak in
that state in which it is deemed fit for burning, we
have found that 100 parts of this kind of wood contain
only 76 parts of absolutely dry wood ; whence we con-
clude that 100 parts of such wood would produce 32. 68
parts of charcoal.

It has been shown that 100 parts of an oak felled on
the 6th of September, while in a growing state, contained
only 62.56 parts of seerwood, and that, consequently,
100 parts of such wood would yield only 26.9 parts of
charcoal.

In making these calculations, no account has been
taken of the quantity of wood, or other combustible,
burned in order to heat the closed vessel in which the
wood was carbonized, pursuant to the process here
adopted. But it may be remarked that such quantity
will be increased or diminished according to the con-
struction of the furnace and the arrangement of the
other parts of the apparatus ; and it will always be too
considerable to be omitted in the list of expenses.

As M. Proust obtained only 19 or 20 parts of char-
coal in 100 of oak, it is probable that some waste
occurred in the process ; but as it is certain that in the
carbonization of wood some loss will happen, so in
the ordinary method of making charcoal there is always
a considerable reduction of the quantity that ought to
be produced, arising from the quantity of wood con-
sumed, either wholly or in part, to obtain heat sufficient
to char the portion of wood that is reduced to a coal.

Messrs. Gay-Lussac and Thenard found from 52 to

468 Inquiries relative to the Structure of Wood.

53 parts of carbon in 100 of seerwood, but 100 parts
of seerwood yielded me only 43 parts of charcoal; this
difference, however, it is easy to explain, as will be seen
in the sequel.

SECTION VII. — Of the Quantities of Heat developed in
the Combustion of different Species of Wood.

Many persons have already endeavoured to determine
the relative quantities of heat furnished by wood and
charcoal in their combustion ; but the results of their
inquiries have not been satisfactory. Their apparatus
has been too imperfect, not to leave vast incertitude in
the conclusions drawn from their investigations. In-
deed, the subject is so intricate in itself, that with the
best instruments the utmost care is requisite, lest, after
much labour, the inquirer should be forced to content
himself with approximations instead of accurate results
and valuations strictly determined.

All woods contain much moisture, even when ap-
parently very dry ; and as the persons alluded to have
neglected to determine the quantities of absolutely dry
wood burned by them, much uncertainty prevails in the
results of all their experiments.

Another source of uncertainty lies in the great quan-
tity of heat suffered to escape with the smoke and other
products of the combustion.

As the calorimeter used in my experiments has been
described in a memoir which I had the honour to pre-
sent to the Class on the 24th of February, 1812, it is
unnecessary here to resume that subject ; suffice it to
explain, in a few words, the various precautions I
adopted in burning wood under the calorimeter.

Inquiries relative to the Striicture of Wood. 469

I picked out the woods intended for the experiment
from a joiner's workshop, and they all appeared to be
quite dry ; I had them formed into small boards, 6
inches in length and |- an inch thick. From these
boards I had some shavings planed off, about ^ of a
line thick, J an inch broad, and 6 inches in length.

When these shavings were sufficiently dry, they were
burned, one by one, under the mouth of the calorimeter;
and I took care to hold them, by means of a small pair
of nippers, so as to make them burn with a brisk flame,
and without the least smoke or smell or calculable
residuum in ashes.

The following is the method I pursued in making
these experiments.

The calorimeter, filled with water at a temperature of
about 5° of Fahrenheit's thermometer lower than that of
the apartment in which the experiments were made, was
placed upon its stand at the height of about 18 inches
above the table on which the apparatus was laid.

The extremity of the calorimeter containing the open-
ing, which I call its mouth, projects about 4 inches be-
yond the edge of the stand, so as easily to admit the
point of the flame from the small piece of burning
wood; and the height of the stand is so adjusted that
the operator may rest both his elbows on the table,
while his hands sustain the fragment of wood to be
burned.

Near the calorimeter stands a small lamp, by which
the pieces of wood, or rather shavings, may, without
loss of time, be set on fire and burned in succession ;
and care is taken to have always in the hand a sufficient
quantity of the shavings, of a known weight.

The very small portions of the shavings which remain

470 Inquiries relative to the Structure of Wood.

between the nippers are carefully preserved, and weighed
at the close of the experiments, to determine precisely
how much of the wood has been consumed.

An assistant keeps his eye constantly on the ther-
mometer attached to the apparatus, and announces the
moment when the water in the calorimeter has attained
a temperature as much higher than that of the room as
it was below it at the beginning of the operation ; and
the flame from the piece of wood then burning is imme-
diately blown out.

The remains of the shaving are laid aside, to be after-
wards weighed with the other fragments.

The water in the calorimeter was then stirred, by
shaking it, taking care to hold the instrument by its
wooden frame, and the temperature of the water was
minutely observed and set down in a register.

An experiment of this kind usually occupies about
10 or 12 minutes, according to the nature of the wood
and the number of degrees to which the temperature of
the calorimeter is raised.

I made choice of the birch for my first experiments,
because the texture of its wood is very firm and even,
and burns with a very regular flame.

To give the details and their results in few words, I
have placed them together in the subjoined table.

The calorimeter, with the water it contained, was
equal in capacity, as to heat, to 2781 grammes of water.

Inquiries relative to the Structure of Wood. 471

Heal developed in the Combustion of Birch Wood.

| No. of exp.

Quantity of

wood consumed.

Heat communi-
cated to the
calorimeter.

Result.
With the heat developed in combustion
of i pound of combustible

Pounds ol water Pounds of water
heated 1° of at the temperature of
Fahrenheit's melting ice, thrown
thermometer. | into ebullition.

Grms.

Degr's.

Firewood, 2 years old

I

5.00

10$

I C87C -1

32.445

2

4.00

8i

( J / J j

32.841

Shavings dried in the air

3

4-55

10}

| 6261 \

34.805

" " "

4

4-54

10}

34.881

Shavings highly dried

over a chafing-dish .

5

3-97

10

} \

38.916

Shavings highly dried

over a chafing-dish .

6

2.58

6*

\ 7002 \

38.925

Shavings highly dried

over a chafing-dish .

7

4-97

I2i

J I

38.858

Shavings highly dried

and scorched in a stove

8

5.07

10}

3I-325

Shavings highly dried

and scorched in a stove

9

5.10

10}

.

31.052

Shavings scorched, but

not to so high a degree

10 4.89

lOj

5971

33.174

On comparing the results of these six experiments,
all made with the same kind of wood, in thin shavings,
it will appear that the drier the wood, the greater was the
quantity of heat produced from a given weight of shav-
ings. But I found, in taking account of the quantities
of moisture contained in the woods, the quantities of
heat were always sensibly proportional to those of the
dry wood burned, with the exception, however, of the
three latter experiments, which were made with wood
highly dried for 24 hours in a stove, and which gave
several indications, by no means equivocal, of the be-
ginning of a decomposition.

The shavings most scorched in the stove gave less

472 Inquiries relative to the Structure of Wood.

heat than those which had been less scorched ; the two
sorts being taken in equal weights.

In all these experiments more or less water dripped
from the worm, a certain proof that some hydrogen had
been burned ; this fact I was very desirous to verify, on
account of its great importance to science.

It is not, therefore, mere carbon which furnished all
the heat developed in the combustion of woods ; of this
important fact we shall shortly have an additional proof.

As the great quantity of nitrogen carried along with
the products of the combustion, and which, after having
passed through the worm, was lost in the atmosphere,
also, without doubt, took with it a little more moisture
than it had brought into the apparatus, a calculation of
the quantity of water formed in the combustion of wood,
grounded only on that found in the worm, would be erro-
neous, though there was always considerably more than
necessary to demonstrate that water had been formed.

Before we close this paper, we shall point out a mode
whereby the quantity of water thus formed may be
estimated, even to such a degree of precision as to leave
nothing more to be desired. But it is first necessary to
determine the quantity of heat developed in the com-
bustion of the carbon found in this wood, and which
was totally consumed.

Although our experiments on the carbonization of
wood, in close vessels, by a moderate fire, leave no
doubt as to the quantities of charcoal which the woods
therein employed were capable of producing, still the
knowledge of this fact is not alone sufficient to enable
us to determine the quantity of carbon contained in the
wood.

As 100 parts of wood are required for 43 of charcoal,

Inquiries relative to the Structure of Wood. 473

it is evident that the seerwood is at least partially de-
composed when the charcoal is produced in the process
of carbonization, that is to say, when the skeleton of
the wood is deprived of its flesh, and left naked ; and
it is well known that a great quantity of pyroligneous
acid is formed in the carbonization of wood, and this
acid contains carbon.

From the process employed by Messrs. Gay-Lussac
and Thenard, in their learned analysis, there can be no
doubt that they discovered and kept an account of all
the carbon found in the woods analyzed by them ; and
as there was no pyroligneous acid formed in my experi-
ments when the wood was totally consumed without
either smoke or smell, it is manifest that in this case all
the carbon contained in the wood was burned.

According to the analyses of Messrs. Gay-Lussac and
Thenard, 100 parts of oak, perfectly dry, contain 52.54
parts of carbon ; and 100 parts of beech contain 51.45.

Now, as it seems to me extremely probable that the
dry ligneous substance is palpably the same in all woods,
I shall take the medium term of the results of these
two analyses, and consider it as an indubitable fact, that
100 parts of perfectly dry wood contain 52 parts of
carbon.

Therefore, as 100 parts of seerwood furnished me
with only 43 of charcoal, we must conclude, if dry char-
coal be considered as carbon, that of the 52 parts of
carbon contained in 100 parts of seerwood, 9 are taken
up in the composition of the pyroligneous acid formed
in the carbonization of the wood, which 9 parts make
more than 17 per cent of all the carbon contained in
the wood.

Though charcoal should not be purely carbon, we

474 Inquiries relative to the Structure of Wood.

must, nevertheless, admit that there is still a much
greater proportion of carbon employed in the formation
of that acid, or of other substances which fly off into the
atmosphere during the process of the carbonization of
the wood.

In pursuing inquiries in natural philosophy, the first
object that demands attention is to keep an accurate
account of weights ; and so long as we proceed with the
balance in hand, there is little hazard of being misled.

And here, before I proceed further in the inquiry into
the sources of the heat developed during the combustion
of wood, I shall exhibit a general table of the details and
results of forty-three experiments made upon eleven dif-
ferent kinds of the woods of our climate. As I shall have
occasion to refer to some of these experiments for the
establishment of facts, it is requisite that they should
first be known.

All these experiments having been made and registered
long before I began the calculations ultimately adopted
for the elucidation of their results, I have not hesitated
to rely on them. And further, as they were made with
all possible care, and with instruments to me apparently
perfect, I can answer for their accuracy.

New experiments ever bear a certain value ; all the
knowledge which constitutes the imperishable riches of
mankind consists only of accurate statements of well-
conducted experiments. Happy they who have the
good fortune of contributing something to the general
stock !

Inquiries relative to the Stmcture of Wood. 475

Heat developed in the Combustion of various Species of Wood.

Species of
wood.

Quality.

Number of the experiment.

Quantity of wood burned.

Heat communicated to the
calorimeter whose capac-
ity was equal to 2781
grammes of water.
Quantity of water at the
thawing temperature,
boiled by the neat de-
veloped in the combus-
tion of one pound of
combustible.

Grms.

Degr's.

Pounds.

Lime

Joiner's dry wood, 4 years old

(II

( I2

4.52

4-55

34.609
34-805

Same kind highly dried over a
chafing-dish •

1*3
(14

4.06
3.80

IOJ

10

40^58

Same kind, rather less dried .

15

5-57

14

38.833

Beech

Joiner's dry wood, 4 or 5 years
old

(16

4-74

io|

33-817

(17

4.72

I0i

33-752

Same kind, highly dried over a
chafing-dish •

(18

(19

5.07
4-43

12

I Of

36.334
36.184

Elm

oiner's wood, rather moist .

20

6-34

1 'i

27.147

oiner's dry wood, 4 or 5 years
old

(21

5.28

I Of

30359

(22

5-45

I °f

30.051

Same kind, highly dried over

(24

4-70
5.28

I°i

II.1,

34-5 '5
33-651

Same kind, dried and scorched

in the stove .....

2C

A QO

8

3O.QOO

Oak

Common firewood, in moder-

T'w

j^-y

26

. 0.

8

2C.CQO

Same kind in thicker shavings ;

'

j j y

leaving a residuum of charcoal

27

6.40

10*

24.748

Same kind in thin shavings .

28

6.14

26.272

Same kind, thin shavings, well

dried in the air ....

29

7.22

13

29.210

[oiner's wood, very dry, in
thin shavings

(30
(31

5-3°

5-33

10}

29.880
19.796

Ash

Thick shavings, leaving 0.92
gramme of charcoal . . .
Joiner's common dry wood .

32
33

6.48
5.29

II

10.1

26.227
30.666

Same kind, shavings dried in

the sir • • • •

1.A

3.78

81

33.720

Same kind, highly dried over

Jl

J 1

4

a chafing-dish

35

5-23

12

35-449

476 Inquiries relative to the Structure of Wood.

Heat developed in the Combustion of Wood. (Continued.)

"c

1

1

|lt

!W^

'«

1

isss

Zllll

Species of
wood.

Quality.

U

•8

•a

|| H

ll|lsd

1

X

l|i|

.f.S-gl^J

fc

I

^"S - u
ffi

pill

Grms.

Degr's.

Pounds.

Maple

Seasoned wood, highly dried

over a chafing-dish

36

3.85

9

36.117

Service

Same kind

1 7

36. 1 30

Same kind, scorched in a stove

51

38

4-3°

9

32.337

Cherry

Joiner's dry wood ....

39

4-75

33-339

Same kind, highly dried over

a chafing-dish

4-O

4-16

IC^

36.QO4

Same kind, scorched in a stove

T

41

T J v

5.00

HJL

j w y T~

34-763

Fir

Joiner's common dry wood .

42

5-35

I0i

30.322

Shavings, well dried in the air

43

4.09

Q

34.000

Highly dried over a chafing-

dish

A A

3 72

37 37Q

Dried and scorched in a stove

TT

45

j*/ *

4.40

j / • j / y

33-358

Thick shavings, leaving much

charcoal

4.6

4r i

6i

28 6cK

Poplar

Joiner's common dry wood .

T"

47

•3 *

4-'3

9i

"^J

34.601

Same kind, highly dried over a

chafing-dish • •

4-8

3.QC

qi

77 T f\ T

Hornbeam

Joiner's dry wood . .

T"

(49

(5°

j y j

5.01

ya

I0l

31.800
31.609

Oak

Dried to {8l'JW°°rJ imper-

fectly burned, leaving a resid-

uum of charcoal, in the

combustion, of o. 8 1 gramme

51

6.i4

ioi

26.421

0.73 «

52

4-83

8"

25.591

0.94 "

53

6.71 u

25.917

These experiments might lead to a great number of
observations ; but I shall endeavour to reduce them to
the exposition of a few simple facts which they pre-
sent.

One fact, certainly very curious and of the first im-
portance to the knowledge of the vegetable economy,

Inquiries relative to the Structure of Wood. 477

appears to be well established ; namely, that the skele-
ton of trees is pure charcoal, and that it exists in a
perfect state in wood.

If this charcoal did not exist perfectly formed in
wood, it could not possibly preserve its form, while its
envelope of vegetable flesh is destroyed by the fire in
the process of carbonization.

As the vegetable flesh contains hydrogen as well as
carbon, it is more inflammable than charcoal, and is con-
sumed at a lower temperature; and, by proper manage-
ment of the fire, it may be totally destroyed without the
enclosed skeleton of charcoal being injured.

Some months ago I presented the Class with a small
sprig of charcoal produced from a piece of oak partially
burned under my calorimeter. It was nearly 'all the
charcoal contained in the piece. All the coal or flesh
of the wood burned with a brisk flame, and the skeleton
of the wood had got red, but the heat was not sufficient
to consume it.

The charcoal-maker seldom does more than burn the
flesh of the wood, and leaves the skeleton of charcoal
naked.

The dry vegetable flesh produces more heat in its
combustion than an equal weight of dry charcoal.

Shavings scorched in the stove by a great heat yield
less heat in their combustion than shavings of -the same
kind of wood, whose vegetable flesh has not been
touched. See experiments Nos. 5, 6, 7, 8, 9, 10, 25,

38, 41, 45-

In tables of experiments similar to those registered in
the preceding table, it is scarcely possible to have errors
on the greater side ; but they may easily enough happen
on the lesser. We may, therefore, place the more con-

478 Inquiries relative to the Structure of Wood.

fidence in those wherein the quantities of heat manifested
have been the greatest.

In the experiments Nos. 13 and 14, the wood of the
lime-tree, dried over a chafing-dish, was productive of
more heat than any other wood that I examined.

The result, it will be seen, was for i pound of this
wood burned in experiment,

No. 13 . . 39.605 pounds of water heated 180° F., and in

No. 14 . . 40.658 " " "

Medium . .40.1315

In order accurately to ascertain how much water this
wood contained, I dried thoroughly in the stove a parcel
of shavings which had been previously dried over the
chafing-dish, and found that it still retained 6.977 per
cent of water.

Therefore we may conclude that i pound of this
wood contains only 0.93023 pound of seerwood.

Now, if 0.93023 pound of seerwood will heat 40.-
1315 pounds of water 180° F., i pound of the same
wood ought to heat 43.141 pounds; and I therefore
take this quantity of water heated 180° F. as the stand-
ard of the heat developed in the combustion of i pound
of wood perfectly dried.

Many persons have endeavoured to account for the
heat manifested in the combustion of wood, by attrib-
uting it altogether to the charcoal contained in the wood
burned.

This hypothesis we have now to examine.

It has been seen, that 100 parts of the wood of the
lime-tree, perfectly dried, yielded 43.59 Parts °f char-
coal ; consequently i pound of this wood, thoroughly
dried, can contain only 0.4359 pound of charcoal.

Inquiries relative to the Striicture of Wood. 479

According to the results of Crawford's experiments,
which we have found to be very accurate, i pound of
charcoal furnishes in its combustion only the necessary
heat for raising 57.608 pounds of water 180° F. ; there-
fore the charcoal contained in i pound of dry lime-wood,
equal to 0.4359 pound, can furnish in its combustion no
more heat than is necessary to raise 25.111 pounds of
water 180°; but as the experiment has given 43.141
pounds, there must certainly have been some other sub-
stance burned beside the charcoal, and which could have
been none other than hydrogen.

Before we determine the quantity of hydrogen con-
sumed, it is essential to ascertain how much heat has
been furnished, not merely by the charcoal itself, but
by the charcoal and the carbon contained in the wood ;
for it is very certain that all the carbon was burned,
since no pyroligneous acid was formed.

According to the analyses of Messrs. Gay Lussac and
Thenard, i pound of dry wood contains 0.52 pound of
carbon.

If we adopt Crawford's estimate, we shall find that
the combustion of 0.52 pound of carbon ought to fur-
nish heat sufficient to raise 29.956 pounds of water
1 80° F.

Deducting this quantity of water from that given by
the experiment, namely, 43.141 pounds, we shall have
13.185 pounds as the measure of the heat produced by
the combustion of the hydrogen consumed in the experi-
ment.

From the results of this inquiry we may conclude, that
of the heat manifested in the combustion of wood,
rather more than two thirds are produced by the com-
bustion of the carbon, and a little less than one third by
the hydrogen consumed.

480 Inquiries relative to the Structure of Wood.

These data supply us with an easy method of deter-
mining the quota of free and combustible hydrogen con-
tained in seerwood.

According to Crawford's estimate, which we have fol-
lowed all along, i pound of hydrogen yields in its
combustion heat sufficient to raise 410 pounds of water
180° F. ; therefore, the 13.185 pounds heated 180° in
the experiment in question must have required 0.035158
pound of hydrogen, which is consequently the amount
of free and combustible hydrogen contained in i pound
of seerwood.

Assuming the medium term of the results of the two
analyses of dry wood, made by Messrs. Gay Lussac and
Thenard, i pound of seerwood would be composed of

Carbon ....... 0.52 pound.

Hydrogen and oxygen, in the necessary pro-
portions for forming water . . 0.48

i. oo

From the result of my experiments, i pound of seer-
wood is composed of two distinct substances ; namely, —

A skeleton of charcoal weighing . . . 0.43 pound.
Vegetable flesh 0.57

And these 0.57 pound of vegetable flesh are com-
posed of

Carbon, free and combustible . . . 0.090 pound.
Hydrogen, free and combustible . . °«°35
Hydrogen and oxygen, in the necessary pro-
portions for the formation of water . . 0.445

Inquiries relative to the Structure of Wood. 48 1

In making these estimates, I have availed myself of
the valuation of the total quantity of carbon contained
in seerwood, given in the analysis of Messrs. Gay
Lussac and Thenard ; and I have supposed the 43 per
cent of charcoal, which I found to be contained in seer-
wood, to be pure carbon.

Should it ultimately appear that charcoal is not pure
carbon, which is extremely probable, numerous altera-
tions in all these estimates must follow, though the ex-
periments made upon the woods will always retain their
value. And I cannot but hope that they will be fre-
quently repeated, with such variations as may conduce to
important discoveries.

It will be a satisfaction to me to know that I have
put into the hands of more skilful workmen than my-
self some instruments of which they may advanta-
geously avail themselves : and to have pointed out, as
well as a little smoothed, a new path, wherein they may
walk without danger of being lost.

SECTION VIII. — Of the Quantity of Heat lost in the Car-
bonization of Wood.

In making charcoal, a considerable quantity of heat
is dissipated and lost in the air; whence it is evident
that the same amount of heat cannot be obtained from
burning a given quantity of charcoal as would be fur-
nished by the combustion of the wood of which it is
formed.

We can now determine, with great precision, the loss
of heat which is inevitable in making charcoal, even
when all possible precautions have been taken; as well
as that which happens every day in the process employed
by the charcoal-maker.

482 Inquiries relative to the Structure of Wood.

As the combustion of i pound of charcoal, perfectly
dry, yields heat sufficient to boil 57.608 pounds of
water, at the thawing temperature ; and as I pound of
wood, thoroughly dry, furnishes 0.4333 pound of dry
charcoal, it follows, that the charcoal produced from i
pound of dry wood should furnish in its combustion
heat sufficient to boil 24.958 pounds of water, at the
thawing temperature.

But we have already seen that the combustion of
i pound of wood, thoroughly dry, should furnish suffi-
cient heat to boil 43.143 pounds of water at the freezing
temperature ; or, which is the same thing, to raise it
1 80° of Fahrenheit's thermometer.

These two numbers (43.143 and 24.958), which ex-
press the quantities of heat in question, being in the
proportion of 100 to 57.849, it is evident that the loss
of heat inevitable in the carbonization of wood is up-
wards of 42 per cent, or exactly 42.151 per cent of the
total quantity that the wood will furnish.

In order to determine the loss of heat which occurs
in the forests, by the ordinary process of the charcoal-
burner, it is requisite to ascertain the precise product
of charcoal from a given quantity of wood, though it is
probable that this product is very variable. M. Proust
estimates it at 20 per cent in weight at the highest.

Adopting, for a moment, this estimate, and suppos-
ing the carbonized wood in the same state of dryness as
what is usually sold for firewood ; as 100 pounds of such
wood contains only 0.76 pound of perfectly dry wood,
this quantity would furnish in its combustion only the
degree of heat necessary to raise 32.043 pounds of
water 180° F.

But the 0.20 pound of charcoal produced by the car-

Inquiries relative to the Structure of Wood. 483

bonization of I pound of this wood, according to the
usual process, can only furnish by combustion a suffi-
cient quantity of heat to raise 11.521 pounds of water
180° F. ; and as the numbers 32.043 and 11.521 are
nearly in the proportion of 100 to 36, it should seem
that the loss of heat in question is about 64 per cent.

One very important fact, which appears to be well
ascertained by the results of this inquiry, is, that all the
charcoal produced from the carbonization of 3 pounds
of any kind of wood scarcely gives more heat in its
combustion than would be furnished by i pound of the
same sort of wood burned, and in its natural state.

[This paper is printed from Nicholson's Journal, XXXIV. (1813),
PP- 3I9~325» and XXXV., pp. 95-117.]

CHIMNEY FIREPLACES,

PROPOSALS FOR IMPROVING THEM TO SAVE FUEL;
TO RENDER DWELLING-HOUSES MORE COMFORT-
ABLE AND SALUBRIOUS, AND EFFECTUALLY TO
PREVENT CHIMNEYS FROM SMOKING.

CHAPTER I.

Fireplaces for burning Coals, or Wood, in an open Chimney,
are capable of great Improvement. — Smoking Chimneys
may in all cases be completely cured. — The immoderate
Size of the Throats of Chimneys the principal Cause of all
their Imperfections. — Philosophical Investigation of the
Subject. — Remedies proposed for all the Defects that have
been discovered in Chimneys and their open Fireplaces. —
These Remedies applicable to Chimneys destined for burning
Wood, or Turf, as well as those constructed for burning
Coals.

THE plague of a smoking chimney is proverbial;
but there are many other very great defects in open
fireplaces, as they are now commonly constructed in
this country, and indeed throughout Europe, which,
being less obvious, are seldom attended to ; and there
are some of them very fatal in their consequences to
health ; and, I am persuaded, cost the lives of thou-
sands every year in this island.

Those cold and chilling draughts of air on one side
of the body while the other side is scorched by a chim-

Of Chimney Fireplaces. 485

ney fire, which every one who reads this must often
have felt, cannot but be highly detrimental to health,
and in weak and delicate constitutions must often pro-
duce the most fatal effects. I have not a doubt in my
own mind that thousands die in this country every year
of consumptions occasioned solely by this cause, — by a
cause which might be so easily removed ! — by a cause
whose removal would tend to promote comfort and con-
venience in so many ways !

Strongly impressed as my mind is with the impor-
tance of this subject, it is not possible for me to remain
silent. The subject is too nearly connected with many
of the most essential enjoyments of life not to be highly
interesting to all those who feel pleasure in promoting
or in contemplating the comfort and happiness of man-
kind. And without suffering myself to be deterred
either by the fear of being thought to give to the sub-
ject a degree of importance to which it is not entitled,
or by the apprehension of being tiresome to my readers
by the prolixity of my descriptions, I shall proceed
to investigate the subject in all its parts and details with
the utmost care and attention. And first with regard
to smoking chimneys.

There are various causes by which chimneys may be
prevented from carrying smoke, but there are none that
may not easily be discovered and completely removed.
This will doubtless be considered as a bold assertion ; but
I trust I shall be able to make it appear in a manner per-
fectly satisfactory to my readers that I have not ventured
to give this opinion but upon good and sufficient
grounds.

Those who will take the trouble to consider the na-
ture and properties of elastic fluids, of air, smoke, and

486 Of Chimney Fireplaces.

vapour, and to examine the laws of their motions, and
the necessary consequences of their being rarified by
heat, will perceive that it would be as much a miracle
if smoke should not rise in a chimney, all hindrances
to its ascent being removed, as that water should refuse
to run in a syphon, or to descend in a river.

The whole mystery, ' therefore, of curing smoking
chimneys, is comprised in this simple direction ; find
out and remove those local hindrances which forcibly prevent
the smoke from -following its natural tendency to go up the
chimney ; or rather, to speak more accurately, which pre-
vent its being forced up the chimney by the pressure
of the heavier air of the room.

Although the causes by which the ascent of smoke in
a chimney may be obstructed are various, yet that cause
which will most commonly, and I may say almost uni-
versally, be found to operate, is one which it is always
very easy to discover, and as easy to remove, — the bad
construction of the chimney in the neighbourhood of the
fireplace.

In the course of all my experience and practice in
curing smoking chimneys, — and I certainly have not
had less than five hundred under my hands, and among
them many which were thought to be quite incurable, —
I never have been obliged, except in one single instance,
to have recourse to any other method of cure than
merely reducing the fireplace, and the throat of the
chimney, or that part of it which lies immediately above
the fireplace, to a proper form and just dimensions.

That my principles for constructing fireplaces are
equally applicable to those which are designed for burn-
ing coal, as to those in which wood is burned, has lately
been abundantly proved by experiments made here in

Of Chimney Fireplaces. 487

London ; for of above a hundred and fifty fireplaces
which have been altered in this city under my direction,
within these last two months, there is not one which has
not answered perfectly well.* And by several experi-
ments which have been made with great care, and with
the assistance of thermometers, it has been demon-
strated, that the saving of fuel, arising from these im-
provements of fireplaces, amounts in all cases to more
than half) and in many cases to more than two thirds, of
the quantity formerly consumed. Now as the altera-
tions in fireplaces which are necessary may be made at a
very trifling expense, — as any kind of grate or stove may
be made use of, and as no iron work but merely a few
bricks and some mortar, or a few small pieces of fire-
stone, are required, — the improvement in question is
very important when considered merely with a view to
economy ; but it should be remembered, that not only
a great saving is made of fuel by the alterations pro-
posed, but that rooms are made much more comfortable,

* Eves and Sutton, bricklayers, Broad Sanctuary, Westminster, have alone altered
above ninety chimneys. The experiment was first made in London at Lord Palmers-
ton's house in Hanover Square; then two chimneys were altered in the house of Sir
John Sinclair, Baronet, President of the Board of Agriculture ; one in the room in
in which the Board meets, and the other in the Secretary's room; which last being
much frequented by persons from all parts of Great Britain, it was hoped that circum-
stance would tend much to expedite the introduction of these improvements in various
parts of the kingdom. Several chimneys were then altered in the house of Sir Joseph
Banks, Baronet, K. B., President of the Royal Society. Afterwards a number were
altered in Devonshire House ; in the house of Earl Besborough, in Cavendish Square,
and at his seat at Rockhampton ; at Holywell House, near St. Alban's, the seat of
the Countess Dowager Spencer; at Melbourne House; at Lady Templeton's, in Port-
land Place; at Mrs. Montagu's, in Portman Square; at Lord Sudley's, in Dover
Street; at the Marquis of Salisbury's seat, at Hatfield, and at his house in town; at
Lord Palmerston's seat in Broadlands, near Southampton, and at several gentlemen's
houses in that neighborhood ; and a great many others ; but it would be tiresome to
enumerate them all, and even these are mentioned merely for the satisfaction of
those who may wish to make inquiries respecting the success of the experiments.

488 Of Chimney Fireplaces.

and more salubrious ; that they may be more equally
warmed, and more easily kept at any required tempera-
ture ; that all draughts of cold air from the doors and
windows towards the fireplace, which are so fatal to
delicate constitutions, will be completely prevented ;
that in consequence of the air being equally warm all
over the room, or in all parts of it, it may be entirely
changed with the greatest facility, and the room com-
pletely ventilated when this air is become unfit for res-
piration, and this merely by throwing open for a mo-
ment a door opening into some passage from whence
fresh air may be had, and the upper part of a window ;
or by opening the upper part of one window and the
lower part of another. And as the operation of venti-
lating the room, even when it is done in the most com-
plete manner, will never require the door and window
to be open more than one minute, in this short time
the walls of the room will not be sensibly cooled, and
the fresh air which comes into the room will, in a very
few minutes, be so completely warmed by these walls,
that the temperature of the room, though the air in it
be perfectly changed, will be brought to be very nearly
the same as it was before the ventilation.

Those who are acquainted with the principles of
pneumatics, and know why the warm air in a room
rushes out at an opening made for it at the top of a
window when colder air from without is permitted to
enter by the door or by any other opening situated
lower than the first, will see that it would be quite im-
possible to ventilate a room in the complete and expedi-
tious manner here described, where the air in a room is
partially warmed, or hardly warmed at all, and where
the walls of the room, remote from the fire, are con-

Of Chimney Fireplaces. 489

stantly cold ; which must always be the case where, in
consequence of a strong current up the chimney, streams
of cold air are continually coming in through all the
crevices of the doors and windows, and flowing into the
fireplace.

But although rooms furnished with fireplaces con-
structed upon the principles here recommended, may be
easily and most effectually ventilated (and this is cer-
tainly a circumstance in favour of the proposed im-
provements), yet such total ventilations will very sel-
dom, if ever, be necessary. As long as any fire is kept
up in the room, there is so considerable a current of air
up the chimney, notwithstanding all the reduction that
can be made in the size of its throat, that the continual
change of air in the room which this current occasions
will, generally, be found to be quite sufficient for keep-
ing the air in the room sweet and wholesome ; and, in-
deed, in rooms in which there is no open fireplace, and
consequently no current of air from the room setting
up the chimney, — which is the case in Germany and all
the northern parts of Europe, where rooms are heated
by stoves, whose fireplaces, opening without, are not sup-
plied with the air necessary for the combustion of
the fuel from the room ; and although in most of the
rooms abroad, which are so heated, the windows and
doors are double, and both are closed in the most exact
manner possible, by slips of paper pasted over the crevi-
ces, or by slips of list or fur, yet when these rooms are
tolerably large, and when they are not very much crowded
by company, nor filled with a great many burning lamps
or candles, the air in them is seldom so much injured
as to become oppressive or unwholesome, and those
who inhabit them show by their ruddy countenances, as

490 Of Chimney Fireplaces.

well as by every other sign of perfect health, that they
suffer no inconvenience whatever from their closeness.
There is frequently, it is true, an oppressiveness in the
air of a room heated by a German stove, of which those
who are not so much accustomed to living in those
rooms seldom fail to complain, and indeed with much
reason ; but this oppressiveness does not arise from the
air of the room being injured by the respiration and
perspiration of those who inhabit it ; it arises from a
very different cause, — from a fault in the construction
of German stoves in general, but which may be easily
and most completely remedied, as I shall show more
fully in another place. In the mean time, I would just
observe here with regard to these stoves, that as they
are often made of iron, and as this metal is a very good
conductor of heat, some part of the stove in contact
with the air of the room becomes so hot as to calcine or
rather to roast the dust which lights upon it ; which never
can fail to produce a very disagreeable effect on the air
of the room. And even when the stove is constructed
of pantiles or pottery-ware, if any part of it in contact
with the air of the room is suffered to become very hot,
which seldom fails to be the case in German stoves con-
structed on the common principles, nearly the same
effects will be found to be produced on the air as when
the stove is made of iron, as I have very frequently had
occasion to observe.

Though a room be closed in the most perfect manner
possible, yet, as the quantity of air injured and rendered
unfit for further use by the respiration of two or three
persons in a few hours is very small compared to the
immense volume of air which a room of a moderate
size contains ; and as a large quantity of fresh air

Of Chimney Fireplaces. 491

always enters the room, and an equal quantity of the
warm air of the room is driven out of it every time the
door is opened, there is much less danger of the air of
a room becoming unwholesome for the want of ventila-
tion than has been generally imagined ; particularly in
cold weather, when all the different causes which con-
spire to change the air of warmed rooms act with in-
creased power and effect.

Those who have any doubts respecting the very great
change of air or ventilation which takes place each time
the door of a warm room is opened in cold weather,
need only set the door of such a room wide open for a
moment, and hold two lighted candles in the doorway,
one near the top of the door and the other near the bot-
tom of it : the violence with which the flame of that above
will be driven outwards, and that below inwards, by the
two strong currents of air which, passing in opposite
directions, rush in and out of the room at the same time,
will be convinced that the change of air which actually
takes place must be very considerable indeed ; and these
currents will be stronger, and consequently the change
of air greater, in proportion as the difference is greater
between the temperatures of the air within the room and
of that without. I have been more particular upon this
subject, — the ventilation of warmed rooms which are
constantly inhabited, — as I know that people in gen-
eral in this country have great apprehensions of the bad
consequences to health of living in rooms in which there
is not a continual influx of cold air from without. I
am as much an advocate for a free circulation of air as
anybody, and always sleep in a bed without curtains on
that account; but I am much inclined to think, that the
currents of cold air which never fail to be produced in

49 2 Of CJiimney Fireplaces.

rooms heated by fireplaces constructed upon the com-
mon principle, — those partial heats on one side of the
body, and cold blasts on the other, so often felt in
houses in this country, — are infinitely more detrimental
to health than the supposed closeness of the air in a
room warmed more equally, and by a smaller fire.

All these advantages, attending the introduction of
the improvements in fireplaces here recommended, are
certainly important, and I do not know that they are
counterbalanced by any one disadvantage whatsoever.
The only complaint that I have ever heard made against
them was that they made the rooms too warm ; but the
remedy to this evil is so perfectly simple and obvious,
that I should be almost afraid to mention it, lest it
might be considered as an insult to the understanding
of the person to whom such information should be
given ; for nothing surely can be conceived more per-
fectly ridiculous than the embarrassment of a person
on account of the too great heat of his room, when it
is in his power to diminish at pleasure the fire by which
it is warmed ; and yet, strange as it may appear, this
has sometimes happened !

Before I proceed to give directions for the construc-
tion of fireplaces, it will be proper to examine more
carefully the fireplaces now in common use; to point
out their faults ; and to establish the principles upon
which fireplaces ought to be constructed.

The great fault of all the open fireplaces, or chimneys,
for burning wood or coals in an open fire, now in com-
mon use, is, that they are much too large ; or, rather, it
is the throat of the chimney^ or the lower part of its open
canal, in the neighborhood of the mantle and immedi-
ately over the fire, which is too large. This opening

Of Chimney Fireplaces. 493

has hitherto been left larger than otherwise it probably
would have been made, in order to give a passage to the
chimney-sweeper; but I shall show hereafter how a
passage for the chimney-sweeper may be contrived with-
out leaving the throat of the chimney of such enor-
mous dimensions as to swallow up and devour all the
warm air of the room, instead of merely giving a pas-
sage to the smoke and heated vapour which rise from
the fire, for which last purpose alone it ought to be
destined.

Were it my intention to treat my subject in a formal
scientific manner, it would doubtless be proper, and
even necessary, to begin by explaining in the fullest
manner, and upon the principles founded on the laws
of nature, relative to the motions of elastic fluids, as
far as they have been discovered and demonstrated, the
causes of the ascent of smoke; and also to explain and
illustrate upon the same principles, and even to measure
or estimate by calculations, the precise effects of all
those mechanical aids which may be proposed for assist-
ing it in its ascent, or rather for removing those ob-
stacles which hinder its motion upwards ; but as it is
my wish rather to write a useful practical treatise than a
learned dissertation, — being more desirous to contribute
in diffusing useful knowledge by which the comforts
and enjoyments of mankind may be increased, than to
acquire the reputation of a philosopher among learned
men, — I shall endeavour to write in such a manner as to
be easily understood by those who are most likely to profit
by the information I have to communicate^ and consequently
most likely to assist in bringing into general use the
improvements I recommend. This being premised, I
shall proceed, without any further preface or introduc-

494 Q/ Chimney Fireplaces.

tion, to the investigation of the subject I have under-
taken to treat.

As the immoderate size of the throats of chimneys is
the great fault of their construction, it is this fault
which ought always to be first attended to in every
attempt which is made to improve them ; for however
perfect the construction of a fireplace may be in other
respects, if the opening left for the passage of the
smoke is larger than is necessary for that purpose, noth-
ing can prevent the warm air of the room from escaping
through it ; and whenever this happens, there is not
only an unnecessary loss of heat, but the warm air which
leaves the room to go up the chimney being replaced by
cold air from without, the draughts of cold air, so often
mentioned, cannot fail to be produced in the room,
to the great annoyance of those who inhabit it. But
although both these evils may be effectually remedied
by reducing the throat of the chimney to a proper size,
yet in doing this several precautions will be necessary.
And first of all, the throat of the chimney should be in
its proper place : that is to say, in that place in which it
ought to be, in order that the ascent of the smoke may
be most facilitated ; for every means which can be em-
ployed for facilitating the ascent of the smoke in the
chimney must naturally tend to prevent the chimney
from smoking; now as the smoke and hot vapour which
rise from a fire naturally tend upwards, the proper place
for the throat of the chimney is evidently perpendicu-
larly over the fire.

But there is another circumstance to be attended to
in determining the proper place for the throat of a
chimney, and that is to ascertain its distance from the
fire, or how far above the burning fuel it ought to be

Of Chimney Fireplaces. 495

placed. In determining this point, there are many
things to be considered, and several advantages and dis-
advantages to be weighed and balanced.

As the smoke and vapour which ascend from burning
fuel rise in consequence of their being rarefied by heat,
and made lighter than the air of the surrounding at-
mosphere ; and as the degree of their rarefaction, and
consequently their tendency to rise, is in proportion to
the intensity of their heat ; and further, as they are
hotter near the fire than at a greater distance from it, it is
clear that the nearer the throat of a chimney is to the
fire, the stronger will be what is commonly called its
draught^ and the less danger there will be of its smoking.
But on the other hand, when the draught of a chimney
is very strong, and particularly when this strong draught
is occasioned by the throat of the chimney being very
near the fire, it may so happen that the draught of air
into the fire may become so strong as to cause the fuel
to be consumed too rapidly. There are likewise several
other inconveniences which would attend the placing of
the throat of a chimney very near the burning fuel.

In introducing the improvements proposed, in chim-
neys already built, there can be no question in regard to
the height of the throat of the chimney,^for its place
will be determined by the height of the mantle. It can
hardly be made lower than the mantle; and it ought
always to be brought down as nearly upon the level with
the bottom of it as possible. If the chimney is apt to
smoke, it will sometimes be necessary either to lower
the mantle or to diminish the height of the opening of
the fireplace, by throwing over a flat arch, or putting in
a straight piece of stone from one side of it to the
other, or, which will be still more, simple and easy in

496 Of Chimney Fireplaces.

practice, building a wall of bricks, supported by a flat
bar of iron, immediately under the mantle.

Nothing is so effectual to prevent chimneys from
smoking as diminishing the opening of the fireplace in
the manner here described, and lowering and diminishing
the throat of the chimney; and I have always found,
except in the single instance already mentioned, that a
perfect cure may be effected by these means alone, even in
the most desperate cases. It is true, that when the con-
struction of the chimney is very bad indeed, or its situ-
ation very unfavourable to the ascent of the smoke, and
especially when both these disadvantages exist at the
same time, it may sometimes be necessary to diminish
the opening of the fireplace, and particularly to lower it,
and also to lower the throat of the chimney, more than
might be wished ; but still I think this can produce no
inconveniences to be compared with that greatest of all
plagues, a smoking chimney.

The position of the throat of a chimney being de-
termined, the next points to be ascertained are its size
and form, and the manner in which it ought to be con-
nected with the fireplace below, and with the open canal
of the chimney above.

But as the.se investigations are intimately connected
with those which relate to the form proper to be given to
the fireplace itself, we must consider them all together.

That these inquiries may be pursued with due method,
and that the conclusions drawn from them may be clear
and satisfactory, it will be necessary to consider, first,
what the objects are which ought principally to be had
in view in the construction of a fireplace; and secondly,
to see how these objects can best be attained.

Now the design of a chimney fire being simply to

Of Chimney Fireplaces. 497

warm a room, it is necessary, first of all, to contrive
matters so that the room shall be actually warmed ;
secondly, that it be warmed with the smallest expense
of fuel possible ; and, thirdly, that, in warming it, the
air of the room be preserved perfectly pure and fit for
respiration, and free from smoke and all disagreeable
smells.

In order to take measures with certainty for warming
a room by means of an open chimney fire, it will be
necessary to consider how, or in what manner, such a fire
communicates heat to a room. This question may per-
haps, at the first view of it, appear to be superfluous
and trifling, but a more careful examination of the
matter will show it to be highly deserving of the most
attentive investigation.

To determine in what manner a room is heated by an
open chimney fire, it will be necessary, first of all, to
find out under what form the heat generated in the com-
bustion of the fuel exists, and then to see how it is
communicated to those bodies which are heated by it.

In regard to the first of these subjects of inquiry, it
is quite certain that the heat which is generated in the
combustion of the fuel exists under two perfectly dis-
tinct and very different forms. One part of it is com-
bined with the smoke, vapour, and heated air, which rise
from the burning fuel, and goes off with them into the
upper regions of the atmosphere ; while the other part,
which appears to be uncombined, or, as some ingenious
philosophers have supposed, combined only with light,
is sent off from the fire in rays in all possible directions.

With respect to the second subject of inquiry,
namely, — how this heat, existing under these two differ-
ent forms, is communicated toother bodies ; it is highly

VOL. n. 32

49 8 Of Chimney Fireplaces.

probable that the combined heat can only be communi-
cated to other bodies by actual contact with the body with
which it is combined ; and with regard to the rays which
are sent off by burning fuel, it is certain that they com-
municate or generate heat only when and where they are
stopped or absorbed. In passing through air, which is
transparent, they certainly do not communicate any heat
to it; and it seems highly probable that they do not
communicate heat to solid bodies by which they are
reflected.

In these respects they seem to bear a great resem-
blance to the solar rays. But n order not to distract
the attention of my reader or carry him too far away
from the subject more immediately under consideration,
I must not enter too deeply into these inquiries respect-
ing the nature and properties of what has been called radi-
ant heat. It is certainly a most curious subject of philo-
sophical investigation, but more time would be required
to do it justice than we now have to spare. We must,
therefore, content ourselves with such a partial examina-
tion of it as will be sufficient for our present purpose.

A question which naturally presents itself here is,
What proportion does the radiant heat bear to the com-
bined heat ? Though that point has not yet been de-
termined with any considerable degree of precision, it
is, however, quite certain, that the quantity of heat
which goes off combined with the smoke, vapour, and
heated air, is much more considerable, perhaps three or
four times greater, at least, than that which is sent off
from the fire in rays. And yet, small as the quantity is
of this radiant heat, it is the only part of the heat gene-
rated in the combustion of fuel burned in an open fire-
place, which is ever employed, or which can ever be em-
ployed, in heating a room.

Of Chimney Fireplaces. 499

The whole of the combined heat escapes by the chim-
ney, and is totally lost ; and, indeed, no part of it could
ever be brought into a room from an open fireplace,
without bringing along with it the smoke with which it
is combined ; which, of course, would render it impos-
sible for the room to be inhabited.' There is, however,
one method by which combined heat, and even that
which arises from an open fireplace, may be made to
assist in warming a room ; and that is by making it pass
through something analogous to a German stove, placed
in the chimney above the fire. But of this contrivance
I shall take occasion to treat more fully hereafter; in
the mean time I shall continue to investigate the prop-
erties of open chimney fireplaces, constructed upon the
most simple principles, such as are now in common
use ; and shall endeavour to point out and explain all
those improvements of which they appear to me to be
capable. When fuel is burned in fireplaces upon this
simple construction, where the smoke escapes immedi-
ately by the open canal of the chimney, it is quite evi-
dent that all the combined heat must of necessity be
lost ; and as it is the radiant heat alone which can be
employed in heating a room, it becomes an object of
much importance to determine how the greatest quantity
of it may be generated in the combustion of the fuel,
and how the greatest proportion possible of that gene-
rated may be brought into the room.

Now, the quantity of radiant heat generated in the
combustion of a given quantity of any kind of fuel
depends very much upon the management of the fire,
or upon the manner in which the fuel is consumed.
When the fire burns bright, much radiant heat will be
sent off from it ; but when it is smothered up, very little

500 Of Chimney Fireplaces.

will be generated ; and indeed very little combined
heat, that can be employed to any useful purpose;
most of the heat produced will be immediately expended
in giving elasticity to a thick dense vapour or smoke
which will be seen rising from the fire ; and the combus-
tion being very incomplete, a great part of the inflam-
mable matter of the fuel being merely rarefied and
driven up the chimney without being inflamed, the fuel
will be wasted to little purpose. And hence it appears
of how much importance it is, whether it be considered
with a view to economy, or to cleanliness, comfort, and
elegance, to pay due attention to the management of a
chimney fire.

Nothing can be more perfectly void of common-
sense, and wasteful and slovenly at the same time, than
the manner in which chimney fires, and particularly
where coals are burned, are commonly managed by ser-
vants. They throw on a load of coals at once, through
which the flame is hours in making its way ; and fre-
quently it is not without much trouble that the fire is
prevented from going quite out. During this time, no
heat is communicated to the room ; and what is still
worse, the throat of the chimney, being occupied merely
by a heavy dense vapour not possessed of any consider-
able degree of heat, and consequently not having much
elasticity, the warm air of the room finds less difficulty
in forcing its way up the chimney and escaping, than
when the fire burns bright; and it happens not unfre-
quently, especially in chimneys and fireplaces ill con-
structed, that this current of warm air from the room,
which presses into the chimney, crossing upon the cur-
rent of heavy smoke which rises slowly from the fire,
obstructs it in its ascent, and beats it back into the

Of Chim ney Fireplaces. 50 1

room ; hence it is that chimneys so often smoke when
too large a quantity of fresh coals is put upon the fire.
So many coals should never be put on the fire at once,
as to prevent the free passage of the flame between. In
short, a fire should never be smothered ; and when
proper attention is paid to the quantity of coals put on,
there will be very little use for the poker ; and this cir-
cumstance will contribute very much to cleanliness and
to the preservation of furniture.

Those who have feeling enough to be made miserable
by anything careless, slovenly, and wasteful, which hap-
pens under their eyes, who know what comfort is, and
consequently are worthy of the enjoyments of a clean
hearth and cheerful fire, should really either take the
trouble themselves to manage their fires (which, indeed,
would rather be an amusement to them than a trouble),
or they should instruct their servants to manage them
better.

But to return to the subject more immediately under
consideration. As we have seen what is necessary to
the production or generation of radiant heat, it remains
to determine how the greatest proportion of that gene-
rated and sent off from the fire in all directions may be
made to enter the room, and assist in warming it. Now,
as the rays which are thrown off from burning fuel have
this property in common with light, that they generate
heat only when and where they are stopped or absorbed,
and also in being capable of being reflected without gene-
rating heat at the surfaces of various bodies, the knowl-
edge of these properties will enable us to take measures,
with the utmost certainty, for producing the effect re-
quired,— that is to say, for bringing as much radiant
heat as possible into the room.

502 Of Chimney Fireplaces.

This must be done, first, by causing as many as pos-
sible of the rays, as they are sent off from the fire in
straight lines, to come directly into the room ; which can
only be effected by bringing the fire as far forward as
possible, and leaving the opening of the fireplace as
wide and as high as can be done without inconvenience ;
and secondly, by making the sides and back of the fire-
place of such form, and constructing them of such
materials, as to cause the direct rays from the fire, which
strike against them, to be sent into the room by reflection
in the greatest abundance.

Now it will be found, upon examination, that the
best form for the vertical sides of a fireplace, or the
covings (as they are called), is that of an upright plane,
making an angle with the plane of the back of the fire-
place of about 135 degrees. According to the present
construction of chimneys, this angle is 90 degrees, or
forms a right angle ; but as in this case the two sides or
covings of the fireplace (A C, B D, Plate VIII., Fig. i)
are parallel to each other, it is evident that they are very
ill contrived for throwing into the room by reflection
the rays from the fire which fall on them.

To have a clear and perfect idea of the alterations I
propose in the forms 'of fireplaces, the reader need only
observe, that, whereas the backs of fireplaces, as they
are now commonly constructed, are as wide as the open-
ing of the fireplace in front, and the sides of it are of
course perpendicular to it and parallel to each other, — in
the fireplaces I recommend, the back (/' k, Plate IX.,
Fig. 3) is only about one third of the width of the open-
ing of the fireplace in front (a b\ and consequently that
the two sides or covings of the fireplace (a i and b k\
instead of being perpendicular to the back, are inclined

Of Chimney Fireplaces. 503

to it at an angle of about 135 degrees; and in conse-
quence of this position, instead of being parallel to each
other, each of them presents an oblique front towards
the opening of the chimney, by means of which the
rays which they reflect are thrown into the room. A
bare inspection of the annexed drawings (Plate VIII.,
Fig. i, and Plate IX., Fig. 3) will render this matter
perfectly clear and intelligible.

In regard to the materials which it will be most ad-
vantageous to employ in the construction of fireplaces,
so much light has, I flatter myself, already been thrown
on the subject we are investigating, and the principles
adopted have been established on such clear and obvious
facts, that no great difficulty will attend the determina-
tion of that point. As the object in view is to bring
radiant heat into the room, it is clear that that material
is best for the construction of a fireplace, which reflects
the most, o'r which absorbs the least of it ; for that heat
which is absorbed cannot be reflected. Now, as bodies
which absorb radiant heat are necessarily heated in con-
sequence of that absorption, to discover which of the
various materials that can be employed for constructing
fireplaces are best adapted for that purpose, we have
only to find out by an experiment, very easy to be
made, what bodies acquire least heat when exposed to
the direct rays of a clear fire ; for those which are least
heated evidently absorb the least, and consequently
reflect the most radiant heat. And hence it appears
that iron, and, in general, metals of all kinds, which are
well known to grow 'very hot when exposed to the rays
projected by burning fuel, are to be reckoned among the
'very worst materials that it is possible to employ in the
construction of fireplaces.

504 Of Chimney Fireplaces.

The best materials I have hitherto been able to dis-
cover are fire-stone, and common bricks and mortar.
Both these materials are, fortunately, very cheap; and
as to their comparative merits, I hardly know to which
of them the preference ought to be given.

When bricks are used, they should be covered with a
thin coating of plaster, which, when it is become per-
fectly dry, should be whitewashed. The fire-stone
should likewise be whitewashed, when that is used ;
and every part of the fireplace, which is not exposed to
being soiled and made black by the smoke, should be
kept as white and clean as possible. As white reflects
more heat, as well as more light, than any other colour,
it ought always to be preferred for the inside of a chim-
ney fireplace, and black, which reflects neither light nor
heat, should be most avoided.

I am well aware how much the opinion I have here
ventured to give, respecting the unfitness of iron and
other metals to be employed in the construction of open
fireplaces, differs from the opinion generally received
upon that subject ; and I even know that the very
reason, which, according to my ideas of the matter, ren-
ders them totally unfit for the purpose, is commonly as-
signed for making use of them ; namely, — that they soon
grow very hot. But I would beg leave to ask what ad-
vantage is derived from heating them ?

I have shown the disadvantage of it; namely, — that the
quantity of radiant heat thrown into the room is dimin-
ished ; and it is easy to show that almost the whole of
that absorbed by the metal is ultimately carried up the
chimney by the air, which, coming into contact with
this hot metal, is heated and rarefied by it, and, forcing
its way upwards, goes off with the smoke ; and as no

Of Chimney Fireplaces. 505

current of air ever sets from any part of the opening of
a fireplace into the room, it is impossible to conceive
how the heat existing in the metal composing any part
of the apparatus of the fireplace, and situated within its
cavity, can come, or be brought, into the room.

This difficulty may be in part removed, by supposing,
what indeed seems to be true in a certain degree, that
the heated metal sends off in rays the heat it acquires
from the fire, even when it is not heated red-hot ; but
still, as it never can be admitted that the heat absorbed
by the metal, and afterwards thrown off by it in rays, is
increased by this operation, nothing can be gained by it ;
and as much must necessarily be lost in consequence of
the great quantity of heat communicated by the hot
metal to the air in contact with it, which, as has already
been shown, always makes its way up the chimney, and
flies off into the atmosphere, the loss of heat attending
the use of it is too evident to require being further in-
sisted on.

There is, however, in chimney fireplaces destined for
burning coals, one essential part, the grate, which cannot
well be made of anything else but iron ; but there is no
necessity whatever for that immense quantity of iron
which surrounds grates as they are now commonly con-
structed and fitted up, and which not only renders them
very expensive, but injures very essentially the fireplace.
If it should be necessary to diminish the opening of
a large chimney in order to prevent its smoking, it
is much more simple, economical, and better in all
respects, to do this with marble, fire-stone, or even with
bricks and mortar, than to make use of iron, which, as
has already been shown, is the very worst material that
can possibly be employed for that purpose ; and as

5o5 Of Chimney Fireplaces.

to registers, they not only are quite unnecessary where
the throat of a chimney is properly constructed, and of
proper dimensions, but in that case would do much
harm. If they act at all, it must be by opposing their
flat surfaces to the current of rising smoke in a manner
which cannot fail to embarrass and impede its motion.
But wre have shown that the passage of the smoke
through the throat of a chimney ought to be facilitated
as much as possible, in order that it may be enabled to
pass by a small aperture.

Register stoves have often been found to be of use ;
but it is because, the great fault of all fireplaces con-
structed upon the common principles being the enor-
mous dimensions of the throat of the chimney, this
fault has been in some measure corrected by them ; but
I will venture to affirm that there never was a fireplace
so corrected that would not have been much more im-
proved, and with infinitely less expense, by the altera-
tions here recommended, and which will be more par-
ticularly explained in the next chapter.

CHAPTER II.

Practical Directions designed for the Use of Workmen, show-
ing how they are to proceed in making the Alterations
necessary to improve Chimney Fireplaces, and effectually to
cure smoking Chimneys.

ALL chimney fireplaces, without exception, whether
they are designed for burning wood or coals, and
even those which do not smoke, as well as those which
do, may be greatly improved by making the alterations

Of Chimney Fireplaces. 507

in them here recommended ; for it is by no means
merely to prevent chimneys from smoking that these im-
provements are recommended, but it is also to make
them better in all other respects as fireplaces ; and when
the alterations proposed are properly executed, which
may very easily be done with the assistance of the fol-
lowing plain and simple directions, the chimneys will
never fail to answer, I will venturet to say, even beyond
expectation. The room will be heated much more
equally and more pleasantly with less than half the fuel
used before ; the fire will be more cheerful and more agree-
able, and the general appearance of the fireplace more
neat and elegant ; and the chimney will never smoke.

The advantages which are derived from mechanical
inventions and contrivances are, I know, frequently
accompanied by disadvantages which it is not always
possible to avoid ; but in the case in question, I can say
with truth, that I know of no disadvantage whatever
that attends the fireplaces constructed upon the prin-
ciples here recommended. But to proceed in giving
directions for the construction of these fireplaces.

That what I have to offer on this subject may be the
more easily understood, it will be proper to begin by
explaining the precise meaning of all those technical
words and expressions which I may find it necessary or
convenient to use.

By the throat of a chimney, I mean the lower ex-
tremity of its canal, where it unites with the upper part
of its open fireplace. This throat is commonly found
about a foot above the level of the lower part of the
mantle, and it is sometimes contracted to a smaller size
than the rest of the canal of the chimney, and some-
times not.

508 Of Chimney Fireplaces.

Plate X., Fig. 5, shows the section of a chimney on
the common construction, in which d e is the throat.

Fig. 6 shows the section of the same chimney
altered and improved, in which di is the reduced throat.

The breast of a chimney is that part of it which is
immediately behind the mantle. It is the wall which
forms the entrance from below, into the throat of the
chimney in front, or towards the room. It is opposite
to the upper extremity of the back of the open fireplace,
and parallel to it ; in short, it may be said to be the back
part of the mantle itself. In the figures 5 and 6, it is
marked by the letter d. The width of the throat of the
chimney (d e, Fig. 5, and d iy Fig. 6) is taken from the
breast of the chimney to the back, and its length is taken
at right angles to its width, or in a line parallel to the
mantle (a, Figs. 5 and 6).

Before I proceed to give particular directions respect-
ing the exact forms and dimensions of the different
parts of a fireplace, it may be useful to make such
general and practical observations upon the subject as
can be clearly understood without the assistance of
drawings ; for the more complete the knowledge of
any subject is, which can be acquired without drawings,
the more easy will it be to understand the drawings when
it becomes necessary to have recourse to them.

The bringing forward of the fire into the room,
or rather bringing it nearer to the front of the opening
of the fireplace, and the diminishing of the throat of
the chimney, being two objects principally had in view
in the alterations in fireplaces here recommended, it is
evident that both these may be attained, merely by bring-
ing forward the back of the chimney. The only ques-
tion therefore is, how far it should be brought forward.

Of Chimney Fireplaces. 509

The answer is short, and easy to be understood, — bring
it forward as far as possible, without diminishing too
much the passage which must be left for the smoke.
Now as this passage, which, in its narrowest part, I
have called the throat of the chimney^ ought, for reasons
which are fully explained in the foregoing chapter, to be
immediately, or perpendicularly, over the fire, it is evi-
dent that the back of the chimney must always be built
perfectly upright. To determine therefore the place for
the new back, or how far precisely it ought to be
brought forward, nothing more is necessary than to as-
certain how wide the throat of the chimney ought to be
left, or what space must be left between the top of the
breast of the chimney, where the upright canal of the
chimney begins, and the new back of the fireplace carried
up perpendicularly to that height.

In the course of my numerous experiments upon
chimneys, I have taken much pains to determine the
width proper to be given to this passage, and I have
found, that, when the back of the fireplace is of a
proper width, the best width for the throat of a
chimney, when the chimney and the fireplace are at the
usual form and size, is four inches. Three inches might
sometimes answer, especially where the fireplace is very
small, and the chimney good, and well situated; but as
it is always of much importance to prevent those acci-
dental puffs of smoke which are sometimes thrown into
rooms by the carelessness of servants in putting on sud-
denly too many coals at once upon the fire, and as I
found these accidents sometimes happened when the
throats of chimneys were made very narrow, I found
that, upon the whole, all circumstances being well con-
sidered, and advantages and disadvantages compared

5 1 o Of Chimney Fireplaces.

and balanced, four inches is the best width that can be
given to the throat of a chimney ; and this, whether the
fireplace be destined to burn wood, coals, turf, or any
other fuel commonly used for heating rooms by an open
fire.

In fireplaces destined for heating very large halls, and
where very great fires are kept up, the throat of the
chimney, may, if it should be thought necessary, be
made four inches and an half, or five inches wide ; but I
have frequently made fireplaces for halls, which have
answered perfectly well, where the throats of the chimneys
have not been wider than four inches.

It may perhaps appear extraordinary, upon the first
view of the matter, that fireplaces of such different sizes
should all require the throat of the chimney to be of
the same width ; but when it is considered that the
capacity of the throat of a chimney does not depend on
its width alone, but on its width and length taken
together, and that in large fireplaces, the width of the
back, and consequently the length of the throat of the
chimney, is greater than in those which are smaller, this
difficulty vanishes.

And this leads us to consider another important point
respecting open fireplaces, and that is, the width which
it will, in each case, be proper to give to the back. In
fireplaces as they are now commonly constructed, the
back is of equal width with the opening of the fireplace
in front ; but this construction is faulty on two accounts.
First, in a fireplace so constructed, the sides of the
fireplace — or covings, as they are called — are parallel to
each other, and consequently ill contrived to throw out
into the room the heat they receive from the fire in the
form of rays ; and secondly, the large open corners,

Of Chimney Fireplaces. 5 1 1

which are formed by making the back as wide as the
opening of the fireplace in front, occasion eddies of wind
which frequently disturb the fire, and embarrass the
smoke in its ascent in such a manner as often to bring
it into the room. Both these defects may be entirely
remedied by diminishing the width of the back of the
fireplace. The width which, in most cases, it will be
best to give it is one third of the width of the opening
of the fireplace in front. But it is not absolutely neces-
sary to conform rigorously to this decision, nor will it
always be possible. It will frequently happen that the
back of a chimney must be made wider than, according
to the rule here given, it ought to be. This may be
either to accommodate the fireplace to a stove, which,
being already on hand, must, to avoid the expense of
purchasing a new one, be employed ; or for other
reasons ; and any small deviation from the general rule
will be attended with no considerable inconvenience. It
will always be best, however, to conform to it as far as
circumstances will allow.

Where a chimney is designed for warming a room of
a middling size, and where the thickness of the wall of
the chimney in front, measured from the front of the
mantle to the breast of the chimney, is nine inches, I
should set off four inches more for the width of the
throat of the chimney, which, supposing the back of the
chimney to be built upright, as it always ought to be,
will give thirteen inches for the depth of the fireplace,
measured upon the hearth from the opening of the fire-
place in front to the back. In this case, thirteen inches
would be a good size for the width of the back; and
three times thirteen inches, or thirty-nine inches, for the
width of the opening of the fireplace in front ; and the

512 Of Chimney Fireplaces.

angle made by the back of the fireplace and the sides
of it, or covings, would be just 135 degrees, which is
the best position they can have for throwing heat into
the room.

But I will suppose that in altering such a chimney it
is found necessary, in order to accommodate the fire-
place to a grate or stove already on hand, to make the
fireplace sixteen inches wide. In that case, I should
merely increase the width of the back to the dimensions
required, without altering the depth of the chimney or
increasing the width of the opening of the chimney in
front. The covings, it is true, would be somewhat
reduced in their width by this alteration ; and their
position with respect to the plane of the back of the
chimney would be a little changed; but these alterations
would produce no bad effects of any considerable conse-
quence, and would be much less likely to injure the fire-
place, than an attempt to bring the proportions of its
parts nearer to the standard, by increasing the depth of
the chimney, and the width of its opening in front ; or
than an attempt to preserve that particular obliquity of
the covings which is recommended as the best (135
degrees), by increasing the width of the opening of the
fireplace, without increasing its depth.

In order to illustrate this subject more fully, we will
suppose one case more. We will suppose that in
the chimney which is to be altered, the width of the fire-
place in front is either wider or narrower than it ought
to be, in order that the different parts of the fireplace,
after it is altered, may be of the proper dimensions. In
this case, I should determine the depth of the fireplace,
and the width of the back of it, without any regard to the
width of the opening of the fireplace in front ; and when

Of Chimney Fireplaces. 5 1 3

this is done, if the opening of the fireplace should be only
two or three inches too wide, — that is to say, only two
or three inches wider than is necessary in order that the
covings may be brought into their proper position with
respect to the back, — I should not alter the width of this
opening, but should accommodate the covings to this
width, by increasing their breadth, and increasing the
angle they make with the back of the fireplace ; but if
the opening of the fireplace should be more than three
inches too wide, I should reduce it to the proper width
by slips of stone, or by bricks and mortar.

When the width of the opening of the fireplace in
front is very great compared with the depth of the fire-
place, and with the width of the back, the covings in
that case being very wide and consequently very
oblique, and the fireplace very shallow, any sudden
motion of the air in front of the fireplace (that motion,
for instance, which would be occasioned by the clothes
of a woman passing hastily before the fire, and very
near it) would be apt to cause eddies in the air, within
the opening of the fireplace, by which puffs of smoke might
easily be brought into the room.

Should the opening of the chimney be too narrow,
which however will seldom be found to be the case, it
will, in general, be advisable to let it remain as it is, and
to accommodate the covings, to it, rather than to attempt
to increase its width, which would be attended with a
good deal of trouble, and probably a considerable
expense.

From all that has been said, it is evident that the
points of the greatest importance, and which ought
most particularly to be attended to in altering fireplaces
upon the principles here recommended, are, the bringing

VOL. n. 33

514 Of Chimney Fireplaces.

forward the back to its proper place, and making it of a
proper width. But it is time that I should mention
another matter upon which it is probable that my reader
is already impatient to receive information. Provision
must be made for the passage of the chimney-sweeper
up the chimney. This may easily be done in the fol-
lowing manner. In building up the new back of the
fireplace, — when this wall (which need never be more
than the width of a single brick in thickness) is
brought up so high that there remains no more than
about ten or eleven inches between what is then the top
of it and the inside of the mantle, or lower extremity
of the breast of the chimney, — an opening, or door-
way, eleven or twelve inches wide, must be begun in the
middle of the back, and continued quite to the top of
it, which, according to the height to which it will com-
monly be necessary to carry up the back, will make the
opening about twelve or fourteen inches high ; which
will be quite sufficient to allow the chimney-sweeper to
pass. When the fireplace is finished, this doorway is to
be closed by a few bricks, by a tile, or a fit piece of
stone, placed in it, dry or without mortar, and confined
in its place by means of a rabbet made for that purpose
in the brick-work. As often as the chimney is swept,
the chimney-sweeper takes down this temporary wall,
which is very easily done, and when he has finished his
work he puts it again into its place. The annexed
drawing (Plate X., Fig. 6) will give a clear idea of this
contrivance ; and the experience I have had of it has
proved that it answers perfectly well the purpose for
which it is designed.

I observed above, that the new back, which it will
always be found necessary to build in order to bring the

Of Chimney Fireplaces. 5 1 5

fire sufficiently forward, in altering a chimney con-
structed on the common principles, need never be
thicker than the width of a common brick. I may say
the same of the thickness necessary to be given to the
new sides, or covings, of the chimney; or if the new
back and covings are constructed of stone, one inch and
three quarters, or two inches, in thickness, will be suffi-
cient. Care should be taken in building up these new
walls to unite the back to the covings in a solid manner.

Whether the new back and covings are constructed
of stone, or built of bricks, the space between them
and the old back and covings of the chimney ought to
be filled up, to give greater solidity to the structure.
This may be done with loose rubbish, or pieces of
broken bricks, or stones, provided the work be strength-
ened by a few layers or courses of bricks laid in mortar ;
but it will be indispensably necessary to finish the work,
where these new walls end, that is to say, at the top of
the throat of the chimney, where it ends abruptly in the
open canal of the chimney, by a horizontal course of
bricks well secured with mortar. This course of bricks
will be upon a level with the top of the doorway left for
the chimney-sweeper. ,

From these descriptions it is clear, that, where the
throat of the chimney has an end, that is to say, where
it enters into the lower part of the open canal of the
chimney, there the three walls which form the two cov-
ings and the back of the fireplace all end abruptly. It
is of much importance that they should end in this
manner ; for were they to be sloped outward and raised
in such a manner as to swell out the upper extremity of
the throat of the chimney in the form of a trumpet, and
increase it by degrees to the size of the canal of the

5 1 6 Of Chimney Fireplaces.

chimney, this manner of uniting the lower extremity of
the canal of the chimney with the throat would tend to
assist the winds which may attempt to blow down the
chimney, in forcing their way through the throat, and
throwing the smoke backward into the room ; but when
the throat of the chimney ends abruptly, and the ends
of the new walls form a flat horizontal surface, it will be
much more difficult for any wind from above to find
and force its way through the narrow passage of the
throat of the chimney.

As the two walls which form the new covings of the
chimney are not parallel to each olher, but inclined,
presenting an oblique surface towards the front of the
chimney, and as they are built perfectly upright and
quite flat, from the hearth to the top of the throat,
where they end, it is evident that a horizontal section
of the throat will not be an oblong square ; but its
deviation from that form is a matter of no consequence ;
and no attempts should ever be made, by twisting the
covings above, where they approach the breast of the
chimney, to bring it to that form. All twists, bends,
prominences, excavations, and other irregularities of
form, in the covings of a chimney, never fail to pro-
duce eddies in the current of air which is continually
passing into and through an open fireplace in which a
fire is burning; and all such eddies disturb either the
fire, or the ascending current of smoke, or both, and
not unfrequently cause the smoke to be thrown back
into the room. Hence it appears, that the covings of
chimneys should never be made circular, or in the form
of any other curve, but always quite flat.

For the same reason, that is to say, to prevent eddies,
the breast of the chimney, which forms that side of the

Of Chimney Fireplaces. 5 1 7

throat that is in front, or nearest to the room, should
he neatly cleaned off, and its surface made quite regular
and smooth.

This may easily be done by covering it with a coat
of plaster, which may be made thicker or thinner in
different parts as may be necessary in order to bring the
breast of the chimney to be of the proper form.

With regard to the form of the breast of a chimney,
this is a matter of very great importance, and which
ought always to be particularly attended to. The worst
form it can have is that of a vertical plane, or upright
flat ; and next to this, the worst form is an inclined
plane. Both these forms cause the current of warm air
from the room, which will, in spite of every precaution,
sometimes find its way into the chimney, to cross upon
the current of smoke, which rises from the fire, in a
manner most likely to embarrass it in its ascent, and
drive it back. The inclined plane which is formed by a
flat register placed in the throat of a chimney produces
the same effects ; and this is one reason, among many
others, which have induced me to disapprove of register
stoves.

• The current of air, which, passing under the mantle,
gets into the chimney, should be made gradually to bend
its course upwards, by which means it will unite quietly
with the ascending current of smoke, and will be less
likely to check it, or force it back into the room. Now
this may be effected with the greatest ease and certainty,
merely by rounding off the breast of the chimney or back
part of the mantle, instead of leaving it flat, or full of
holes and corners ; and this, of course, ought always to
be done.

I have hitherto given no precise directions in regard

5 1 8 Of Chimney Fireplaces.

to the height to which the new back and covings ought
to be carried. This will depend not only on the height
of the mantle, but also, and mpre especially, on the
height of the breast of the chimney, or of that part of
the chimney where the breast ends and the upright canal
begins. The back and covings must rise a few inches, 5
or 6 for instance, higher than this part, otherwise the
throat of the chimney will not be properly formed ; but I
know of no advantages that would be gained by carry-
ing them up still higher.

I mentioned above, that the space between the walls
which form the new back and covings, and the old back
and sides of the fireplace, should be filled up; but this
must not be understood to apply to the space between
the wall of dry bricks, or the tile which closes the passage
for the chimney-sweeper, and the old back of the chim-
ney ; for that space must be left void, otherwise, though
this tile (which at most will not be more than two
inches in thickness) were taken away, there would not
be room sufficient for him to pass.

In forming this doorway, the best method of proceed-
ing is to place the tile or flat piece of stone destined for
closing it in its proper place, and to build round it, or
rather by the sides of it, taking care not to bring any
mortar near it, in order that it may be easily removed
when the doorway is finished. With regard to the rab-
bet which should be made in the doorway to receive it
and fix it more firmly in its place, this may either be
formed at the same time when the doorway is built, or
it may be made after it is finished, by attaching to its
bottom and sides, with strong mortar, pieces of thin
roof tiles. Such as are about half an inch in thickness
will be best for this use ; if they are thicker, they will

Of Chimney Fireplaces. 5 1 9

diminish too much the opening of the doorway, and
will likewise be more liable to be torn away by the
chimney-sweeper in passing up and down the chimney.

It will hardly be necessary for me to add, that the
tile, or flat stone, or wall of dry bricks, which is used
for closing up this doorway, must be of sufficient height
to reach quite up to a level with the top of the walls
which form the new back and covings of the chimneys.

I ought, perhaps, to apologize for having been so
very particular in these descriptions and explanations ;
but it must be remembered that this chapter is written
principally for the information of those who, having
had few opportunities of employing their attention in
abstruse philosophical researches, are not sufficiently
practised in these intricate investigations to seize, with
facility, new ideas, and consequently, that I have fre-
quently been obliged to labour to make myself under-
stood.

I have only to express my wishes that my reader may
not be more fatigued with this labour than I have been ;
for we shall then most certainly be satisfied with each
other. But to return once more to the charge.

There is one important circumstance respecting chim-
ney fireplaces destined for burning coals, which still
remains to be further examined ; and that is the grate.

Although there are few grates that may not be used
in chimneys constructed or altered upon the principles
here recommended, yet they are not, by any means, all
equally well adapted for that purpose. Those whose
construction is the most simple, and which, of course,
are the cheapest, are beyond comparison the best, on all
accounts. Nothing being wanted in these chimneys but
merely a grate for containing the coals, and in which

520 Of Chimney Fireplaces.

they will burn with a clear fire, and all additional appa-
ratus being not only useless, but very pernicious, all
complicated and expensive grates should be laid aside,
and such as are more simple substituted in the room of
them. And in the choice of a grate, as in everything
else, beauty and elegance may easily be united with the
most perfect simplicity. Indeed, they are incompatible with
everything else.

In placing the grate, the thing principally to be
attended to is to make the back of it coincide with the
back of the fireplace ; but as many of the grates now in
common use will be found to be too large, when the
fireplaces are altered and improved, it will be necessary
to diminish their capacities by filling them up at the
back and sides with pieces of fire-stone. When this is
done, it is the front of the flat piece of fire-stone which
is made to form a new back to the grate, which must be
made to coincide with and mark part of the back
of the fireplace. But in diminishing the capacities of
grates with pieces of fire-stone, care must be taken not
to make them too narrow.

The proper width for grates destined for rooms of a
middling size will be from 6 to 8 inches, and their
length may be diminished more or less, according as the
room is heated with more or less difficulty, or as the
weather is more or less severe. But where the width of
a grate is not more than 5 inches, it will be very diffi-
cult to prevent the fire from going out.

It goes out for the same reason that a live coal from
the grate that falls upon the hearth soon ceases to be red-
hot ; it is cooled by the surrounding cold air of the at-
mosphere. The knowledge of the cause which produces
this effect is important, as it indicates the means which

Of Chimney Fireplaces. 521

may be used for preventing it. But of this subject I
shall treat more fully hereafter.

It frequently happens that the iron backs of grates
are not vertical, or upright, but inclined backwards.
When these grates are so much too wide as to render it
necessary to fill them up behind with fire-stone, the in-
clination of the back will be of little consequence ; for
by making the piece of stone with which the width of
the grate is to be diminished in the form of a wedge, or
thicker above than below, the front of this stone, which
in effect will become the back of the grate, may be
made perfectly vertical, and, the iron back of the grate
being hid in the solid work of the back of the fireplace,
will produce no effect whatever; but, if the grate be
already so narrow as not to admit of any diminution of
its width, in that case it will be best to take away the
iron back of the grate entirely, and, fixing the grate
firmly in the brickwork, cause the back of the fireplace
to serve as a back to the grate. This I have very fre-
quently done, and have always found it to answer per-
fectly well.

Where it is necessary that the fire in a grate should
be very small, it will be best, in reducing the grate with
fire-stone, to bring its cavity, destined for containing the
fuel, to the form of one half of a hollow hemisphere ;
the two semicircular openings being one above, to
receive the coals, and the other in front, or towards the
bars of the grate ; for when the coals are burned in such
a confined space, and surrounded on all sides, except in
the front and above, by fire-stone (a substance peculiarly
well adapted for confining heat), the heat of the fire will
be concentrated, and, the cold air of the atmosphere
being kept at a distance, a much smaller quantity of

522 Of Chimney Fireplaces.

coals will burn than could possibly be made to burn in
a grate where they would be more exposed to be cooled
by the surrounding air, or to have their heat carried off
by being in contact with iron, or with any other sub-
stance through which heat passes with greater facility
than through fire-stone.

Being persuaded that, if the improvements in chimney
fireplaces here recommended should be generally adopted
(which I cannot help flattering myself will be the case),
it will become necessary to reduce, very considerably,
the sizes of grates, I was desirous of showing how this
may, with the greatest safety and facility, be done.

Where grates, which are designed for rooms of a
middling size, are longer than 14 or 15 inches, it will
always be best, not merely to diminish their lengths, by
filling them up at their two ends with fire-stone, but,
forming the back of the chimney of a proper width,
without paying any regard to the length of the grate, to
carry the covings through the two ends of the grate in
such a manner as to conceal them, or at least to conceal
the back corners of them in the walls of the covings.

I cannot help flattering myself that the directions
here given in regard to the alterations which it may be
necessary to make in fireplaces, in order to introduce
the improvements proposed, will be found to be so
perfectly plain and intelligible that no one who reads
them will be at any loss respecting the manner in which
the work is to be performed ; but as order and arrange-
ment tend much to facilitate all mechanical operations,
I shall here give a few short directions respecting the
manner of laying out the work, which may be found use-
ful, and particularly to gentlemen who may undertake
to be their own architects, in ordering and directing the

Of Chimney Fireplaces. 523

alterations to be made for the improvement of their
fireplaces.

Directions for laying out the Work.

If there be a grate in the chimney which is to be
altered, it will always be best to take it away ; and when
this is done, the rubbish must be removed, and the
hearth swept perfectly clean. \

Suppose the annexed figure (Plate VIII., Fig. i) to
represent the ground plan of such a fireplace; A B
being the opening of it in front, A C and B D the two
sides or covings, and C D the back.

Figure 2 shows the elevation of this fireplace.

First, draw a straight line, with chalk or with a lead-
pencil, upon the hearth, from one jamb to the other,
even with the front of the jambs. The dotted line A
B (Plate IX., Fig. 3) may represent this line.

From the middle C of this line (A B) another line
c d is to be drawn perpendicular to it, across the hearth,
to the middle d of the back of the chimney.

A person must now stand upright in the chimney,
with his back to the back of the chimney, and hold a
plumb-line to the middle of the upper part of the breast
of the chimney (Plate X., Fig. 5, d\ or where the canal
of the chimney begins to rise perpendicularly ; taking
care to place the line above in such a manner that the
plumb may fall on the line c d^ drawn on the hearth from
the middle of the opening of the chimney in front to
the middle of the back, and an assistant must mark the
precise place e> on that line where the plumb falls.

This being done, and the person in the chimney hav-
ing quitted his station, 4 inches are to be set off on
the line c d, from e towards d; and the point /, where

524 Of Chimney Fireplaces.

these 4 inches end (which must be marked with chalk,
or with a pencil), will show how far the new back is to
be brought forward.

Through /"draw the lineg hy parallel to the line A B,
and this line g h will show the direction of the new
back, or the ground line upon which it is to be built.

The line cf will show the depth of the new fireplace ;
and if it should happen that f /is equal to about one
third of the line A B, and if the grate can be accom-
modated to the fireplace instead of its being necessary
to accommodate the fireplace to the grate, in that case
half the length of the line cfis to be set off from /on
the line g f h> on one side to k, and on the other to /,
and the line / k will show the ground line of the fore-
part of the back of the chimney.

In all cases where the width of the opening of the
fireplace in front (A B) happens to be not greater, or
not more than two or three inches greater, than three
times the width of the new back of the chimney (/' k\
this opening may be left, and lines drawn from / to
A and from k to B will show the width and position
of the front of the new covings ; but when the open-
ing of the fireplace in front is still wider, it must be
reduced, which is to be done in the following manner.

From c, the middle of the line A B, c a and c b
must be set off equal to the width of the back (/ k\
added to half its width (//), and lines drawn from / to
a and from k to b will show the ground plan of
the fronts of the new covings.

When this is done, nothing more will be necessary
than to build up the back and covings, and, if the fire-
place is designed for burning coals, to fix the grate in its
proper place, according to the directions already given.

Of Chimn y Fireplaces. 525

When the width of the fireplace is reduced, the edges
of the covings a A and b B are to make a finish with
the front of the jambs. And in general it will be best,
not only for the sake of the appearance of the chimney,
but for other reasons also, to lower the height of the
opening of the fireplace, whenever its width in front is
diminished.

Fig. 4 (Plate IX.) shows a front view of the chimney
after it has been altered according to the directions here
given. By comparing it with Fig. i (which shows a
front view of the same chimney before it was altered),
the manner in which the opening of the fireplace in
front is diminished may be seen. In Fig. 4, the under
part of the doorway by which the chimney-sweeper gets
up the chimney is represented by white dotted lines.
The doorway is represented closed.

I shall finish this chapter with some general observa-
tions relative to the subject under consideration ; with
directions how to proceed where such local circum-
stances exist as render modifications of the general plan
indispensably necessary.

Whether a chimney be designed for burning wood
upon the hearth, or wood or coals in a grate, the form
of the fireplace is, in my opinion, most perfect when
the width of the back is equal to the depth of the fireplace,
and the opening of the fireplace in front equal to three
times the width of the back, or, which is the same thing,
to three times the depth of the fireplace.

But if the chimney be designed for burning wood
upon the hearth, upon handirons, or dogs, as they are
called, it will sometimes.be necessary to accommodate
the width of the back to the length of the wood ; and
when this is the case, the covings must be accommodated

526 Of Chimney Fireplaces.

to the width of the back and the opening of the chim-
ney in front.

When the wall of the chimney in front, measured
from the upper part of the breast of the chimney to the
front of the mantle, is very thin, it may happen, and
especially in chimneys designed for burning wood upon
the hearth, or upon dogs, that the depth of the chim-
ney, determining according to the directions here given,
may be too small.

Thus, for example, supposing the wall of the chimney
in front, from the upper part of the breast of the chim-
ney to the front of the mantle, to be only 4 inches
(which is sometimes the case, particularly in rooms situ-
ated near the top of a house), in this case, if we take
4 inches for the width of the throat, this will give 8
inches only for the depth of the fireplace, which would
be too little, even were coals to be burned instead of
wood. In this case I should increase the depth of the
fireplace at the hearth to 12 or 13 inches, and should
build the back perpendicular to the height of the top of
the burning fuel (whether it be wood burned upon the
hearth, or coals in a grate), and then, sloping the back
by a gentle inclination forward, bring it to its proper
place, that is to say, •perpendicularly under the back part of
the throat of the chimney. This slope (which will bring
the back forward 4 or 5 inches, or just as much as the
depth of the fireplace is increased), though it ought not
to be too abrupt, yet it ought to be quite finished at the
height of 8 or 10 inches above the fire, otherwise it may
perhaps cause the chimney to smoke ; but when it is
very near the fire, the heat of the fire will enable the
current of rising smoke to overcome the obstacle which
this slope will oppose to its ascent, which it could not

Of Chimney Fireplaces. 527

do so easily were the slope situated at a greater distance
from the burning fuel.*

Figs. 7, 8, and 9 (Plate X.) show a plan, elevation,

* Having been obliged to carry backward the fireplace in the manner here
described, in order to accommodate it to a chimney whose walls in front were
remarkably thin, I was surprised to find, upon lighting the fire, that it appeared to
give out more heat into the room than any fireplace I had ever constructed. This
effect was quite unexpected ; but the cause of it was too obvious not to be immedi-
ately discovered. The flame rising from the fire broke against the part of the back
which sloped forward over the fire, and this part of the back being soon very much
heated, and in consequence of its being very hot, (and when the fire burned bright it
was frequently quite red-hot,) it threw off into the room a great deal of radiant heat.
It is not possible that this oblique surface (the slope of the back of the fireplace)
could have been heated red-hot merely by the radiant heat projected by the burning
fuel ; for other parts of the fireplace nearer the fire, and better situated for receiving
radiant heat, were never found to be so much heated j and hence it appears that the
combined heat in the current of smoke and hot vapour which rises from an open fire
may be, at least in fart, stopped in its passage up the chimney, changed into radiant
heat, and afterwards thrown into the room. This opens a new and very interesting
field for experiment, and bids fair to lead to important improvements in the construc-
tion of fireplaces. I have of late been much engaged in these investigations, and am
now actually employed daily in making a variety of experiments with grates and fire-
places, upon different constructions, in the room I inhabit in the Royal Hotel in Pall
Mall ; and Mr. Hopkins, of Greek Street, Soho, Ironmonger to his Majesty, and
Mrs. Hempel, at her Pottery at Chelsea, are both at work in their different lines of
business, under my direction, in the construction of fireplaces upon a principle entirely
new, and which, I flatter myself, will be found to be not only elegant and convenient,
but very economical. But as I mean soon to publish a particular account of these
fireplaces, with drawings and ample directions for constructing them, I shall not
enlarge further on the subject in this place.' It may, however, not be amiss just to
mention here, that these new invented fireplaces not being fixed to the walls of the
chimney, but merely set down upon the hearth, may be used in any open chimney ;
and that chimneys altered or constructed on the principles here recommended are par-
ticularly well adapted for receiving them.

The public in general, and more particularly those tradesmen and manufacturers
whom it may concern, are requested to observe, that, as the author does not intend to
take out himself, or to surfer others to take out, any patent for any invention of his
which may be of public utility, all persons are at full liberty to imitate them, and
vend them, for their own emolument, when and where and in any way they may
think proper; and those who may wish for any further information rejpccting any of
those inventions or improvements will receive (gratis) all the information they can
require by applying to the author, who will take pleasure in giving them every assist-
ance in his power.

528 Of Chimney Fireplaces.

and section of a fireplace constructed or altered upon
this principle. The wall of the chimney in front at a
(Fig. 9) being only 4 inches thick, 4 inches more added
to it for the width of the throat would have left the
depth of the fireplace measured upon the hearth b c only
8 inches, which would have been too little; a niche c
and e was therefore made in the new back of the fire-
place for receiving the grate, which niche was 6 inches
deep in the centre of it, below 13 inches wide (or equal
in width to the grate), and 23 inches high ; finishing
above with a semicircular arch, which, in its highest
part, rose 7 inches above the upper part of the grate.
The doorway for the chimney-sweeper, which begins
just above the top of the niche, may be seen distinctly
in both the Figs. 8 and 9. The space marked £ (Fig.
9) behind this doorway may either be filled with loose
bricks, or may be left void. The manner in which the
piece of stone (f, Fig. 9) which is put under the mantle
of the chimney to reduce the height of the opening of
the fireplace, is rounded off on the inside, in order to
give a fair run to the column of smoke in its ascent
through the throat of the chimney, is clearly expressed
in this figure.

The plan (Fig. 7) and elevation (Fig. 8) show how
much the width of the opening of the fireplace in front
is diminished, and how the covings in the new fireplace
are formed.

A perfect idea of the form and dimension of the fire-
place in its original state, as also after its alteration, may
be had by a careful inspection of these figures.

I have added the drawing (Fig. 10, Plate XI.) merely
to show how a fault, which I have found workmen in
general whom I have employed in altering fireplaces are

Of Ch im ney Fireplaces. 529

very apt to commit, is to be avoided. In chimneys like
that represented in this figure, where the jambs A and B
project far into the room, and where the front edge of
the marble slab <?, which forms the coving, does not
come so far forward as the front of the jambs, the work-
men in constructing the new covings are very apt to
place them, not in the line c A, which they ought to do,
but in the line c o, which is a great fault. The covings
of a chimney should never range behind the front of the
jambs, however those jambs may project into the room;
but it is not absolutely necessary that the covings should
make a finish with the internal front corners of the
jambs, or that they should be continued from the back
c quite to the front of the jambs at A. They may
finish in front at a and by and small corners, A, 0, a, may
be left for placing the shovels, tongs, etc.

Were the new coving to range with the front edge of
the old coving <?, the obliquity of the new coving would
commonly be too great ; or the angle d c o would exceed
135 degrees, which it never should do y or at least never by
more than a very few degrees.

No inconvenience of any importance will arise from
making the obliquity of the covings less than what is
here recommended; but many cannot fail to be pro-
duced by making it much greater ; and as I know from
experience that workmen are very apt to do this, I have
thought it necessary to warn them particularly against it.

Fig. 1 1 shows how the width and obliquity of the
covings of a chimney are to be accommodated to the
width of the back, and to the opening in front and
depth of the fireplace, where the width of the opening
of the fireplace is less than three times the width of the
new back.

VOL. ii. 34

53° Of Chimney Fireplaces.

As all those who may be employed in altering chim-
neys may not perhaps know how to set off an angle of any
certain number of degrees, or may not have at hand the
instruments necessary for doing it, I shall here show
how an instrument may be made which will be found to
be very useful in laying out the work for the brick-
layers.

Upon a board about 18 inches wide and 4 feet long,
or upon the floor or a table, draw three equal squares
(A, B, C, Fig. 12, Plate XIII.), of about 12 or 14
inches each side, placed in a straight line, and touching
each other. From the back corner c of the centre
square B draw a diagonal line across the square A, to its
outward front corner f, and the adjoining angle formed
by the lines d c and c/will be equal to 135 degrees, the
angle which the plane of the back of a chimney fire-
place ought to make with the plane of its covings. And
a bevel m n being made to this angle with thin slips of
hard wood, this little instrument will be found to be
very useful in marking out on the hearth, with chalk,
the plans of the walls which are to form the covings of
fireplaces.

As chimneys which are apt to smoke will require the
covings to be placed less obliquely in respect to the
back than others which have not that defect, it would be
convenient to be provided with several bevels, — three
or four, for instance, forming different angles. That
already described, which may be called No. i, will
measure the obliquity of the covings when the fireplace
can be made of the most perfect form ; another, No. 2,
may be made to a smaller angle, dee; and another, No.
3, for chimneys which are very apt to smoke, at the still
smaller angle d c i. Or a bevel may be so contrived, by

Of C/i im ney Fireplaces. 531

means of a joint, and an arch, properly graduated, as to
serve for all the different degrees of obliquity which it
may ever be necessary to give to the covings of fire-
places.

Another point of much importance, and particularly
• in chimneys which are apt to smoke, is to form the
throat of the chimney properly, by carrying up the
back and covings to a proper height.

This workmen are apt to neglect to do, probably on
account of the difficulty they find in working where the
opening of the canal of the chimney is so much re-
duced. But it is absolutely necessary that these walls
should be carried up 5 or 6 inches at least above the
upper part of the breast of the chimney, or to that
point where the wall which forms the front of the throat
begins to rise perpendicularly. If the workman has in-
telligence enough to avail himself of the opening which
is formed in the back of the fireplace to give a passage
to the chimney-sweeper, he will find little difficulty in
finishing his work in a proper manner.

In placing the plumb-line against the breast of the
chimney, in order to ascertain how far the new back is
to be brought forward, great care must be taken to
place it at the very top of the breast, where the canal
of the chimney begins to rise perpendicularly ; otherwise,
when the plumb-line is placed too low, or against the
slope of the breast, when the new back comes to be
raised to its proper height, the throat of the chimney
will be found to be too narrow.

Sometimes, and indeed very often, the top of the
breast of a chimney lies very high, or far above the fire
(see Figs. 13 and 14, Plate XIII., where d shows the
top of the breast of the chimney) ; when this is the case,

532 Of Chimney Fireplaces.

it must be brought lower, otherwise the chimney will be
very apt to smoke. So much has been said, in the first
chapter of this essay, of the advantages to be derived
from bringing the throat of a chimney near to the burn-
ing fuel, that I do not think it necessary to enlarge
on them in this place, taking it for granted that the
utility and necessity of that arrangement have already
been made sufficiently evident; but a few directions for
workmen, to show them how the breast (and conse-
quently the throat) of a chimney can most readily be
lowered, may not be superfluous.

Where the too great height of the breast of a chimney
is owing to the great height of the mantle (see Fig. 13),
or, which is the same thing, of the opening of the fire-
place in front, which will commonly be found to be the
case, the only remedy for the evil will be to bring down
the mantle lower; or, rather, to make the opening of
the fireplace in front lower, by throwing across the top
of this opening, from one jamb to the other, and im-
mediately under the mantle, a very flat arch, a wall of
bricks and mortar, supported on straight bars of iron,
or a piece of stone (/^, Fig. 13). When this is done,
the slope of the old throat of the chimney, or of the
back side of the mantle, is to be filled up with plaster,
so as to form one continued flat, vertical, or upright
plane surface with the lower part of the wall of the canal
of the chimney, and a new breast is to be formed lower
down, care being taken to round it off properly, and
make it finish at the lower surface of the new wall built
under the mantle; which wall forms, in fact, a new mantle.

The annexed drawing (Fig. 13), which represents the
section of a chimney in which the breast has been
lowered according to the method here described, will

Of Chimney Fireplaces. 533

show these various alterations in a clear and satisfactory
manner. In this figure, as well as in most of the others
in this essay, the old walls are distinguished from the
new ones by the manner in which they are shaded; the
old walls being shaded by diagonal lines, and the new
ones by vertical lines. The additions, which are formed
of plaster, are shaded by dots instead of lines.

Where the too great height of the breast of a chimney
is occasioned, not by the height of the mantle, but by
the too great width of the breast, in that case (which,
however, will seldom be found to occur), this defect
may be remedied by covering the lower part of the
breast with a thick coating of plaster, supported, if
necessary, by nails or studs driven into the wall which
forms the breast, and properly rounded off at the lower
part of the mantle. (See Fig. 14.)

CHAPTER III.

Of the Cause of the Ascent of Smoke. — Illustration of the
Subject by familiar Comparisons and Experiments. — Of
Chimneys which affect and cause each other to smoke. — Of
Chimneys which smoke from Want of Air. — Of the Eddies
of Wind which sometimes blow down Chimneys^ and cause
them to smoke.

T

HOUGH it was my wish to avoid all abstruse
_ philosophical investigations in this essay, yet I
feel that it is necessary to say a few words upon a sub-
ject generally considered as difficult to be explained,
which is too intimately connected with the matter under

534 Of Chimney Fireplaces.

consideration to be passed over in silence. A knowl-
edge of the cause of the ascent of smoke being indis-
pensably necessary to those who engage in the improve-
ment of fireplaces, or who are desirous of forming just
ideas relative to the operations of fire and the manage-
ment of heat, I shall devote a few pages to the investi-
gation of that curious and interesting subject. And as
many of those who may derive advantage from these in-
quiries are not much accustomed to philosophical dis-
quisitions, and would not readily comprehend either the
language or the diagrams commonly used by scientific
writers to explain the phenomena in question, I shall
take pains to express myself in the most familiar man-
ner, and to use such comparisons for illustration as may
easily be understood.

If small leaden bullets, or large goose-shot, be mixed
with peas, and the whole well shaken in a bushel, the
shot will separate from the peas, and will take its place
at the bottom of the bushel ; forcing, by its greater
weight, the peas, which are lighter, to move upwards, con-
trary to their natural tendency, and take their places above.

If water and linseed oil, which is lighter than water,
be mixed in a vessel by shaking them together, upon
suffering this mixture to remain quiet the water will
descend and occupy the bottom of the vessel, and the
oil, being forced out of its place by the greater pressure
downwards of the heavier liquid, will be obliged to rise
and swim on the surface of the water.

If a bottle containing linseed oil be plunged in water
with its mouth upwards, and open, the oil will ascend
out of the bottle, and, passing upwards through the mass
of water, in a continued stream, will spread itself over
its surface.

Of Chimney Fireplaces. 535

In like manner, when two fluids of any kind, of dif-
ferent densities, come into contact, or are mixed with
each other, that which is the lightest will be forced up-
wards by that which is the heaviest.

And as heat rarefies all bodies, fluids as well as solids,
air as well as water or mercury, it follows that two por-
tions of the same fluid, at different temperatures, being
brought into contact with each other, that portion which
is the hottest, being more rarified, or specifically lighter
than that which is colder, must be forced upwards by this
last. And this is what always happens in fact.

When hot water and cold water are mixed, the hottest
part of the mixture will be found to be at the surface
above ; and when cold air is admitted into a warmed
room, it will always be found to take its place at the
bottom of the room, the warmer air being in part ex-
pelled, and in part forced upwards to the top of the
room.

Both air and water being transparent and colourless
fluids, their internal motions are not easily discovered
by the sight ; and when these motions are very slow,
they make no impression whatever on any of our senses,
consequently they cannot be detected by us without the
aid of some mechanical contrivance. But where we
have reason to think that those motions exist, means
should be sought, and may often be found, for render-
ing them perceptible.

If a bottle containing hot water tinged with logwood,
or any other colouring drug, be immersed, with its
mouth open, and upwards, into a deep glass jar filled
with cold water, the ascent of the hot water from the
bottle through the mass of cold water will be perfectly
visible through the glass. Now, nothing can be more

536 Of Chimney Fireplaces.

evident than that both of these fluids are forced or
pushed,, and not drawn upwards. Smoke is frequently
said to be drawn up the chimney, and that a chimney
draws well or ill; but these are careless expressions,
and lead to very erroneous ideas respecting the cause of
the ascent of smoke, and consequently tend to prevent
the progress of improvements in the management of
fires. The experiment just mentioned with the coloured
water is very striking and beautiful, and it is well calcu-
lated to give a just idea of the cause of the ascent of
smoke. The cold water in the jar, which, in conse-
quence of its superior weight or density, forces the
heated and rarefied water in the bottle to give place to
it, and to move upwards out of its way, may represent
the cold air of the atmosphere, while the rising column
of coloured water will represent the column of smoke
which ascends from a fire.

If smoke required a chimney to draw it upwards,
how happens it that smoke rises from' a fire which is
made in the open air, where there is no chimney?

If a tube, open at both ends, and of such a length
that its upper end be below the surface of the cold water
in the jar, be held vertically over the mouth of the
bottle which contains the hot coloured water, the hot
water will rise up through it, just as smoke rises in a
chimney.

If the tube be previously heated before it is plunged
into the cold water, the ascent of the hot coloured water
will be facilitated and accelerated, in like manner as
smoke is known to rise with greater facility in a chimney
which is hot, than in one in which no fire has been made
for a long time. But in neither of these cases can it,
with any propriety, be said that the hot water is drawn

Of Ch im ney Fireplaces. 537

up the tube. The hotter the water in the bottle is, and
the colder that in the jar, the greater will be the velocity
with which the hot water will be forced up through the
tube ; and the same holds of the ascent of hot smoke in
a chimney. When the fire is intense, and the weather
very cold, the ascent of the smoke is very rapid ; and
under such circumstances chimneys seldom smoke.

As the cold water of the jar immediately surrounding
the bottle which contains the hot water will be heated
by the bottle, while the other parts of the water in the
jar will remain cold, this water so heated, becoming
specifically lighter than that which surrounds it, will be
forced upwards ; and if it finds its way into the tube will
rise up through it with the coloured hot water. The
warmed air of a room heated by an open chimney fire-
place has always a tendency to rise (if I may use that in-
accurate expression), and, finding its way into the chim-
ney, frequently goes off with the smoke.

What has been said will, I flatter myself, be sufficient
to explain and illustrate, in a clear and satisfactory man-
ner, the cause of the ascent of smoke; and just ideas
upon that subject are absolutely necessary in order to
judge, with certainty, of the merit of any scheme pro-
posed for the improvement of fireplaces, or to take
effectual measures, in all cases, for curing smoking
chimneys. For, though the perpetual changes and alter-
ations which are produced by accident, whim, and
caprice, do sometimes lead to useful discoveries, yet the
progress of improvement under such guidance must be
exceedingly slow, fluctuating, and uncertain.

As to the causes of the smoking of chimneys, they
are very numerous and various ; but as a general idea
of them .may be acquired from what has already been

538 Of Chimney Fireplaces.

said upon that subject in various parts of this essay,
and as they may, in all cases (a very few only excepted),
be completely remedied by making the alterations in
fireplaces here pointed out, I do not think it necessary
to enumerate them all in this place, or to enter into
those long details and investigations which would be
required to show the precise manner in which each of
them operates, either alone or in conjunction with others.

There is, however, one cause of smoking chimneys
which I think it is necessary to mention more particu-
larly. In modern-built houses, where the doors and
windows are generally made to close with such accuracy
that no crevice is left for the passage of the air from
without, the chimneys in rooms adjoining to each other,
or connected by close passages, are frequently found to
affect each other; and this is easy to be accounted for.
When there is a fire burning in one of the chimneys, as
the air necessary to supply the current up the chimney
where the fire burns cannot be had in sufficient quanti-
ties from without, through the very small crevices of
the doors and windows, the air in the room becomes
rarefied, not by heat, but by subtraction of that por-
tion of air which is employed in keeping up the fire, or
supporting the combustion of the fuel, and, in conse-
quence of this rarefaction, its elasticity is diminished,
and being at last overcome by the pressure of the ex-
ternal air of the atmosphere, this external air rushes in-
to the room by the only passage left for it, namely, by
the open chimney of the neighbouring room ; and the
flow of air into the fireplace, and up the chimney where
the fire is burning, being constant, this expense of air is
supplied by a continued current down the other chimney.

If an attempt be made to light fires in both. chimneys

Of Chimney Fireplaces. 539

at the same time, it will be found to be very difficult to
get the fires to burn, and the rooms will both be filled
with smoke.

One of the fires — that which is made in the chimney
where the construction of the fireplace is best adapted
to facilitate the ascent of the smoke ; or, if both fireplaces
are on the same construction, that which has the wind
most favourable, or in which the fire happens to be
soonest kindled — will overcome the other, and cause
its smoke to be beat back into the room by the cold air
which descends through the chimney. The most ob-
vious remedy in this case is to provide for the supply
of fresh air necessary for keeping up the fires by open-
ing a passage for the external air into the room by a
shorter road than down one of the chimneys ; and when
this is done, both chimneys will be found to be effectu-
ally cured.

But chimneys so circumstanced may very frequently
be prevented from smoking, even without opening any
new passage for the external air, merely by diminishing
the draught (as it is called) up the chimneys ; which
can best be done by altering both fireplaces upon the
principles recommended and fully explained in the fore-
going chapters of this essay.

Should the doors and windows of a room be closed
with so much nicety as to leave no crevices by which a
supply of air can enter sufficient for maintaining the fire,
after the current of air up the chimney has been diminished as
much as possible by diminishing the throat of the fireplace,
in that case there would be no other way of preventing
the chimney from smoking but by opening a passage for
the admission of fresh air from without; but this, I
believe, will very seldom be found to be the case.

540 Of Chimney Fireplaces.

A case more frequently to be met with is, where cur-
rents of air set down chimneys in consequence of a
diminution and rarefaction of the air in a room, occa-
sioned by the doors of the room opening into passages
or courts where the air is rarefied by the action of some
particular winds. In such cases the evil may be reme-
died, either by causing the doors in question to close
more accurately, or (which will be still more effectual)
by giving a supply of air to the passage or court which
wants it by some other way.

Where the top of a chimney is commanded by high
buildings, by cliffs, or by high grounds, it will fre-
quently happen, in windy weather, that the eddies
formed in the atmosphere by these obstacles will blow
down the chimney, and beat down the smoke into the
room. This, it is true, will be much less likely to happen
when the throat of the chimney is contracted and prop-
erly formed than when it is left quite open, and the fire-
place badly constructed ; but as it is •possible that a chim-
ney may be so much exposed to these eddies in very
high winds as to be made to smoke sometimes when the
wind blows with violence from a certain quarter, it is
necessary to show how the effects of those eddies may
be prevented.

Various mechanical contrivances have been imagined
for preventing the wind from blowing down chimneys,
and many of them have been found to be useful ; there
are, however, many of these inventions, which, though
they prevent the wind from blowing down the chimney,
are so ill-contrived on other accounts as to obstruct the
ascent of the smoke, and do more harm than good.

Of this description are all those chimney-pots with
flat horizontal plates or roofs placed upon supporters

Of Chimney Fireplaces. 541

just above the opening of the pot ; and most of the
caps which turn with the wind are not much better. One
of the most simple contrivances that can be made use
of, and which in most cases will be found to answer the
purpose intended as well or better than more com-
plicated machinery, is to cover the top of the chimney
with a hollow truncated pyramid or cone, the diameter
of which above, or opening for the passage of the
smoke, is about 10 or n inches. This pyramid, or
cone (for either will answer), should be of earthen-
ware or of cast-iron ; its perpendicular height may
be equal to the diameter of its opening above, and the
diameter of its opening below equal to three times its
height. It should be placed upon the top of the chim-
ney, and it may be contrived so as to make a handsome
finish to the brick-work. Where several flues come out
near each other, or in the same stack of chimneys, the
form of a pyramid will be better than that of a cone for
these covers.

The intention of this contrivance is, that the winds
and eddies which strike against the oblique surface of
these covers may be reflected upwards, instead of blow-
ing down the chimney. The invention is by no means
new, but it has not hitherto been often put in practice.
As often as I have seen it tried, it has been found to be
of use; I cannot say, however, that I was ever obliged
to have recourse to it, or to any similar contrivance ; and
if I forbear to enlarge upon the subject of these inven-
tions, it is because I am persuaded that when 'chimneys .
are properly constructed in the neighbourhood of the fire-
place, little more will be necessary to be done at the top
of the chimney than to leave it open.

I cannot conclude this essay without again recom-

542 Of Chimney Fireplaces.

mending, in the strongest manner, a careful attention to
the management of fires in open chimneys ; for not only
the quantity of heat produced in the combustion of
fuel depends much on the manner in which the fire is
managed, but even of the heat actually generated a
very small part only will be saved, or usefully em-
ployed, when the fire is made in a careless and slovenly
manner.

In lighting a coal fire, more wood should be employed
than is commonly used, and fewer coals ; and as soon
as the fire burns bright, and the coals are well lighted,
and not before, more coals should be added to increase
the fire to its proper size.*

The enormous waste of fuel in London may be esti-
mated by the vast dark cloud which continually hangs
over this great metropolis, and frequently overshadows

* Kindling-balls, composed of equal parts of coal, charcoal, and clay, the two
former reduced to a fine powder, well mixed and kneaded together with the clay
moistened with water, and then formed into balls of the size of hens' eggs, and
thoroughly dried, might be used with great advantage instead of wood for kindling
fires. These kindling-balls may be made so inflammable as to take fire in an instant,
and with the smallest spark, by dipping them in a strong solution of nitre and then
drying them again; and they would neither be expensive nor liable to be spoiled by
long keeping. Perhaps a quantity of pure charcoal, reduced to a very fine powder
and mixed with the solution of nitre in which they are dipped, would render them
still more inflammable.

I have often wondered that no attempts should have been made to improve the
fires which are made in the open chimneys of elegant apartments, by preparing the
fuel ; for nothing surely was ever more dirty, inelegant, and disgusting than a com-
mon coal fire.

Fire-balls, of the size of goose-eggs, composed of coal and charcoal in powder,
mixed up with a due proportion of wet clay, and well dried, would make a much
more cleanly, and in all respects a pleasanter, fire than can be made with crude coals ;
and I believe would not be more expensive fuel. In Flanders and in several parts of
Germany, and particularly in the Duchies of Juliers and Bergen, where coals are used
as fuel, the coals are always prepared before they are used, by pounding them to a
powder, and mixing them up with an equal weight of clay, and a sufficient quantity
of water to form the whole into a mass which is kneaded together and formed into
cakes 5 which cakes are afterwards well dried and kept in a dry place for use. And

Of Chimney Fireplaces. 543

the whole country, far and wide ; for this dense cloud is
certainly composed almost entirely of unconsumed coat,
which, having stolen wings from the innumerable fires
of this great city, has escaped by the chimneys, and con-
tinues to sail about in the air, till, having lost the heat
which gave it volatility, it falls in a dry shower of ex-
tremely fine black dust to the ground, obscuring the at-
mosphere in its descent, and frequently changing the
brightest day into more than Egyptian darkness.

I never view from a distance, as I come into town,
this black cloud which hangs over London, without
wishing to be able to compute the immense number of
caldrons of coals of which it is composed ; for, could
this be ascertained, I am persuaded so striking a fact
would awaken the curiosity and excite the astonishment
of all ranks of the inhabitants, and perhaps turn their

it has been found by long experience, that the expense attending this preparation is
amply repaid by the improvement of the fuel. The coals, thus mixed with clay, not
only burn longer, but give much more heat than when they are burned in their crude
state.

It will doubtless appear extraordinary to those who have not considered the subject
with some attention, that the quantity of heat produced in the combustion of any
given quantity of coals should be increased by mixing the coals with clay, which is
certainly an incombustible body ; but the phenomenon may, I think, be explained in
a satisfactory manner.

The heat generated in the combustion of any small particle of coal existing under
two distinct forms, namely, in that which is combined with the flame and smoke
which rise from the fire, and which, if means are not found to stop it, goes off im-
mediately by the chimney and is lost, and the radiant heat which is sent off from the
fire, in all directions, in right lines; I think it reasonable to conclude, that the parti-
cles of clay, which are surrounded on all sides by the flame, arrest a part at least of the
combined heat, and prevent its escape; and this combined heat so arrested, heating
the clay red-hot, is retained in it, and, being changed by this operation to radiant heat,
is afterwards emitted, and may be directed and employed to useful purposes.

In composing fire-balls, I think it probable that a certain proportion of chaff— of
straw cut very fine, or even of saw-dust — might be employed with great advantage. 1
wish those who have leisure would turn their thoughts to this subject, for I am per-
suaded that very important improvements would result from a thorough investigation
of it.

544 Of Chimney Fireplaces.

minds to an object of economy to which they have hith-
erto paid little attention.

Conclusion.

Though the saving of fuel which will result from the
improvements in the forms of chimney fireplaces^ here
recommended, will be very considerable, yet I hope to
be able to show in a future essay that still greater
savings may be made, and more important advantages
derived, from the introduction of improvements I shall
propose in kitchen fireplaces.

I hope, likewise, to be able to show in an essay on
cottage fireplaces, which I am now preparing for publica-
tion, that three quarters^ at least, of the fuel which cot-
tagers now consume in cooking their victuals and in
warming their dwellings, may with great ease, and with-
out any expensive apparatus, be saved.

[This paper is printed from the English edition of Rumford's
Essays, Vol. I, pp. 305-387.]

546 Of Chimney Fireplaces,

EXPLANATION OF THE FIGURES.

PLATE VIII.
FIG. i.

The plan of a fireplace on the common construction.
A B, the opening of the fireplace in front.
C D, the back of the fireplace.
A C and B D, the covings.

See page 523.

FIG. 2.

This figure shows the elevation, or front view, of a
fireplace on the common construction. See page 523.

PLATE VIII.

Fig-,1.

548 Of Chimney Fireplaces.

PLATE IX.
FIG. 3.

This figure shows how the fireplace represented by
the Fig. i is to be altered, in order to its being im-
proved.

A B is the opening in front, C D the back, and A C
and B D the covings of the fireplace in its original
state.

a b its opening in front, / k its back, and a i and b k
its covings after it has been altered ; e is a point upon
the hearth upon which a plumb suspended from the
middle of the upper part of the breast of the chimney
falls. The situation for the new back is ascertained by
taking the line ef equal to four inches. The new back
and covings are represented as being built of bricks, and
the space between these and the old back and covings as
being filled up with rubbish. See page 523.

FIG. 4.

This figure represents the elevation or front view of
the fireplace (Fig. 3) after it has been altered. The
lower part of the doorway left for the chimney-sweeper
is shown in this figure by white dotted lines. See page

525-

PLATE IX.

1 I I *

Feet.

55° Of Chimney Fireplaces.

PLATE X.
FIG. 5.

This figure shows the section of a chimney fireplace
and of a part of the canal of the chimney on the com-
mon construction.

a b is the opening in front ; b c the depth of the fire-
place at the hearth ; d the breast of the chimney.

d e^ the throat of the chimney, and d /, g e, a part of
the open canal of the chimney.

FIG. 6.

Shows a section of the same chimney after it has been
altered.

k I is the new back of the fireplace ; / / the tile or
stone which closes the doorway for the chimney-sweeper;
di the throat of the chimney, narrowed to four inches;
#, the mantle, and £, the new wall made under the man-
tle, to diminish the height of the opening of the fireplace
in front.

N. B. — These two figures are sections of the same
chimney which is represented in each of the four pre-
ceding figures.

PL ATI. X

Fijr.6.

552 Of Chimney Fireplaces.

PLATE XI.

FIG. 7.

This figure represents the ground plan of a chimney
fireplace in which the grate is placed in a niche, and in
which the original width A B of the fireplace is consid-
erably diminished.

a b is the opening of the fireplace in front after it has
been altered, and d is the back of the niche in which the
grate is placed. See page 527.

FIG. 8.

Shows a front view of the same fireplace after it has
been altered ; where may be seen the grate, and the
doorway for the chimney-sweeper. See page 527.

FIG. 9.

Shows a section of the same fireplace, c d e being a
section of the niche, g the doorway for the chimney-
sweeper, closed by a piece of firestone, and / the new
wall under the mantle, by which the height of the open-
ing of the fireplace in front is diminished. See page
527.

PLATE XI,

Scale y[.

f 1

554 Of Chimney Fireplaces.

PLATE XII.
FIG. 10.

This figure shows how the covings are to be placed
when the front of the covings (a and ^) do not come so
far forward as the front of the opening of the fireplace,
or the jambs (A and B). See page 528.

FIG. ii.

This figure shows how the width and obliquity of the
covings are to be accommodated to the width of the back
of a fireplace, in cases where it is necessary to make the
back very wide. See page 529.

PLATE XII.

Pig.10.

Fig.ll.

5 5 5 Of Chimney Fireplaces,

PLATE XIII.

FIG. 12.

This figure shows how an instrument called a bevel
(m »), useful in laying out the work, in altering chimney
fireplaces, may be constructed. See page 530.

FIG. 13.

This shows how, when the breast of a chimney (d) is
too high, it may be brought down by means of a wall
(h) placed under the mantle, and a coating of plaster,
which in this figure is represented by the part marked
by dots. See page 532.

FIG. 14.

This shows how the breast of a chimney may be
brought down merely by a coating of plaster. See page

533-

PLATE XIII.

Tig". 13.

SUPPLEMENTARY OBSERVATIONS

CONCERNING

CHIMNEY FIREPLACES.

OBSERVATIONS CONCERNING OPEN CHIMNEY FIRE-
PLACES.

An Account of various Faults that have been committed by
Workmen, in England, who have been employed in altering
Chimney Fireplaces, and fitting them up according to the
Method recommended by the Author, in his Fourth Essay.

— Consequences which have resulted from these Mistakes.

— Necessity of adhering strictly, and without Deviation, to
the Directions which have been given. — Those Particulars
are pointed out in which Workmen are most liable to fail.

I WAS much flattered on my return to England, in
September, 1798, after an absence of two years, to
find that the improvements in the construction of chim-
ney fireplaces, which I had recommended in my Fourth
Essay, published in London in the beginning of the
year 1796, were coming into use in various parts of the
country; and I have since taken a good deal of pains
to find out how they have answered, and what faults
and imperfections have been discovered in them. And
as the information I have obtained by these inquiries
has enabled me to make several remarks and observa-

560 Of Chimney Fireplaces.

tions relative to the construction and management of
these fireplaces, that may be of use to those who have in-
troduced them, or may be desirous of introducing them,
I feel it to be my duty to lay them before the public.

It has been objected to these fireplaces, that they
sometimes occasion dust and ashes to come into the
room when the fire is stirred. I have examined several
fireplaces said to have been fitted up on my principles,
that have certainly had that fault; but I have common-
ly, I might say invariably, found, that their imperfections
have arisen from faults in their construction. Either
the grate has been brought out too far into the room, or
the opening of the fireplace in front has been left too
wide or too high, or the workman has neglected to
lower and to round off the breast of the chimney, or,
what I have often found to be the case, several of these
faults have existed together, in the same fireplace.

When the throat of a chimney is situated very high
up above the mantle, and especially when the mantle
and breast of the chimney, or the wall that reposes on
the mantle, are very thin, workmen who are employed
to alter chimneys, setting about the work with their
minds strongly prepossessed with what they consider as
the leading principle 'in the construction of these fireplaces,
namely, that the throat of the chimney should not be
more than four inches wide, they are very apt to bring
the grate too far forward. In dropping their plumb-
line from the breast of the chimney, they do not reach
up high enough into the chimney, but take a part of the
breast, where it still goes on to slope backwards, for the
bottom of the perpendicular canal of the chimney.
They also very often commit another fault, not less
essential, and that has the same tendency, in neglecting

Of Chimney Fireplaces. 56 1

to bring down the throat of the chimney nearer to the fire,
when it happens to be situated too high.

This I have not only recommended in my Essay on
Chimney Fireplaces, but have given the most particular
directions how it is to be done (see page 531), and, to
mark the importance of the object still more strongly,
have accompanied those directions by an engraving.

It is indeed a very important point, that the throat
of the chimney should be near the fire, and it should
always be carefully attended to. It is likewise very im-
portant to " round off the breast of the chimney" though
this, I find, is very often entirely neglected, even by
workmen who have had much practice in the construc-
tion of the fireplaces I have recommended.

The breast of a chimney should always be rounded
off in the neatest manner possible, beginning from the
very front of the lower part of. the mantle, and ending
at the narrowest part of the throat of the chimney,
where the breast ends in the front part of the perpen-
dicular canal of the chimney. If the under surface of
the mantle is flat and wide, it will be impossible to
round off the breast properly ; and that circumstance
alone renders it indispensably necessary, in those cases,
to alter the mantle, or to run under it a thinner piece of
stone, or a thin wall of bricks, supported on an iron
bar, in order that the breast of the chimney may be
brought to be of the proper form, and the throat of the
chimney may be brought into its proper situation.

If the under side of the mantle be left broad and flat,
it is easy to perceive that the cloud of dust or light
ashes that rises from a coal fire nearly burned out when
it is violently stirred about with a poker, striking per-
pendicularly against this flat part of it, must unavoid-

voi.. ii. 36

562 Of Chimney Fireplaces.

ably be beat back into the room ; but when the breast
of the chimney is properly rounded off, the ascending
cloud of dust and smoke more easily finds its way into
the throat of the chimney, and is even directed and
assisted in some measure by the warm air of the room
that gets under the mantle, and is going the same way.

Another very common fault that I have observed in
chimney fireplaces, that have been altered on what have
been called my principles, and which has a direct ten-
dency to bring dust, and even smoke, into the room, is
the sloping of the covings too much, and leaving the
opening of the fireplace in front too wide. I have said,
in my Essay on Chimney Fireplaces, that where chimneys
are well constructed and well situated, and have never
been apt to smoke, in altering them the covings may be
placed at an angle of 135 degrees with the back; but I
have expressly said that they should never exceed that
angle, and have stated at large the bad consequences
that must follow from making the opening of a fireplace
very wide, when its depth is very shallow (see page
510). I have also expressly said (page 530), that,
for chimneys that are apt to smoke, the covings should
be placed less obliquely^ in respect to the back, than in
others that have not that fault. But most of the work-
men who have altered chimneys seem to have paid little
attention to these distinctions, and I have frequently
found, and sometimes in fireplaces that have been re-
markably shallow, that the covings have been placed at
an angle even more oblique than that above mentioned.

Another cause that sometimes has considerable effect
in bringing dust and smoke into rooms, from the fires
that are made in them, is the great nicety with which the
doors and windows are fitted in their frames, which pre-

Of Chimney Fireplaces. 563

vents a sufficient quantity of fresh air from coming into
the room to supply a brisk current up the chimney. It
is, however, evident, that all the alterations in fireplaces
on the common construction, that have been recom-
mended in order to improve them, must tend directly
and very powerfully to lessen this evil; but nothing will
so completely remedy it as lowering the mantle, and
diminishing the width of the fireplace.

How many fireplaces in close rooms have been cured
completely of throwing puffs of smoke and dust into
the room, merely by placing a register stove in them !
But there is surely nothing peculiar to a register-stove
that could enable it to perform such a cure, but merely
as it serves to diminish the width and height of the
opening of the fireplace ; and how much easier could
this be done with marble, or other stone, or with bricks
and mortar, plastered over and incrusted in front with
proper ornaments in stucco, or in artificial stone !

I am the more anxious that something of this sort
should be introduced, as the openings of chimney fire-
places are in general certainly too wide and too high,
and as I am convinced that there is no way of reducing
them to a proper size, that would be so cheap, or more
effectual, or that could be made more ornamental.

Those who are fond of the glitter of polished steel,
and have no objection to the expense of it, or to the
labour that is required to keep it bright, may surround
their fireplaces in front with a border of it, for there it
will do no harm, and may use grates and fenders of the
most exquisite workmanship; but if they wish to have
a pleasant, cheerful, and economical fire, the covings of
their fireplaces must be placed obliquely, and they must
not be constructed of metal ; and if the sides and back

564 Of Chimney Fir ep faces.

of the grate be constructed of fire-bricks instead of iron,
the fire will burn still brighter, and will send off consid-
erably more radiant heat into the room.

I have abundant reason to think, that if, in construct-
ing or altering chimney fireplaces, the rules laid down in
my essay on that subject are strictly adhered to, chim-
neys so fitted up will very seldom be found either to
smoke, or to throw out dust into the room ; and should
they be found to have either of these faults, there is a
remedy for the evil, as effectual as it is simple and ob-
vious : Bring down the mantle and the throat of the chim-
ney lower ; and if it should be found necessary, reduce the
width of the opening of the fireplace in front, and diminish
obliquity of the covings.

These alterations will certainly be effectual to prevent
either smoke or dust from coming into the room when
there is a fire burning in the grate ; but it sometimes hap-
pens, and indeed not unfrequently, that dust and soot
are drawn down a chimney in which there is no fire, to
the great annoyance of those who are in the room, and
to the great damage of the furniture. When this hap-
pens, it is commonly occasioned by a very strong
draught up another chimney, in which there is afire, in an
adjoining room ; and when that is the case, the most
simple remedy is to alter that other chimney, and, con-
structing its fireplace on good principles, to reduce its
throat to reasonable dimensions. But if the passage of
the air down a chimney in which there is no fire is occa-
sioned by strong eddies of wind, there is no remedy for
that evil but placing a chimney-pot, of a peculiar con-
struction, on the top of the chimney, which shall coun-
teract the effect of those eddies ; or by closing up the
throat of the chimney occasionally, by a door made for
that purpose of sheet-iron.

Of Chimney Fireplaces. 565

If the doorway that is left in the back of the fireplace
for giving a passage to the chimney-sweeper, instead of
being closed with a tile, or with a flat piece of stone, set
in a groove made to receive it, according to the direc-
tions given in my Fourth Essay, be closed with a flat
piece of cast-iron, or of plate-iron, fixed at its lower
end, to the lower end of the doorway, by a hinge, or
movable on two gudgeons, — this plate may easily be so
contrived as to serve occasionally as a register or door
for diminishing or closing the throat of the chimney.

As this plate, situated at tht back part of the chimney,
could not produce any of those bad effects that have
with reason been attributed to the registers of common
register-stoves (which are placed on the breast of the
chimney), it appears to me to be very probable, that it
would be found useful as a register for occasionally
altering the size of the throat of the chimney, and regu-
lating its draught, as well as for occasionally closing up
that passage entirely. It would certainly be worth while
to try the experiment*

Before I quit this subject, I must mention another
fault, which workmen employed in altering chimney fire-
places that are furnished with grates or stoves with
sloping backs are very apt to make. They leave the
back of the grate in its place, and instead of carrying up
the back of the fireplace perpendicularly from the bottom
of the grate, they first begin to carry it up perpendicu-
larly from the top of the iron plate that forms the back
of the grate ; and as this plate not only slopes back-
wards considerably, but rises several inches above the

* Since the introduction of the cottage and gridiron grates, this contrivance has
come into very general use, and experience has shown it to be extremely useful. I
would strongly recommend it to those who fit up chimney fireplaces on these princi-
ples, never to omit this register ; it costs a mere trifle, and is very useful on many

accounts.

566 Of Chimney Fireplaces.

level of the upper bar of the grate, this necessarily
throws the fire very far into the room. This tends to
bring both smoke and dust into the room, not only be-
cause it brings the fire too far forward, but also because
it occasions the air of the room, that slips in by the
sides of the covings, to get behind the current of smoke
that rises perpendicularly from the fire, which air fre-
quently crowds the smoke forward, and causes it to
strike against the mantle. This is a great fault, and I
am sorry to say that I have found it very common in
many parts of England, where attempts have been made
to introduce the fireplaces I have recommended. Where
grates with sloping backs are used in fitting up these fire-
places, these backs must either be taken quite away or
bricked up, and the new back part, or back wall of the
fireplace, must be made to serve as a back for the grate,
against which the burning fuel is laid.

As I am giving an account of the mistakes that have
been made by some of those who have been employed
in fitting up chimney fireplaces on the principles I have
publicly recommended, it will naturally be expected that
I should take some notice of those numerous improve-
ments that have been announced to the public, said to
have been made in stoves, grates, etc., to which adver-
tisers in the newspapers have thought proper to affix
my name. As I am" extremely anxious not to injure
any man, either in his reputation for ingenuity, or in
his trade, or in any other way, I shall not say one word
more on this subject than what I feel it to be my duty
to the public to declare, namely, that I am not the in-
ventor of any of those stoves or grates that have been
offered to the public for sale under my name.

Having mentioned the inconveniences that sometimes

Of Chimney Fireplaces. 567

arise from doors and windows being fitted to their
frames with so much nicety as not to give a sufficient
passage to air from without to get into the room to
supply the current up the chimney, which must always
exist when a fire is burning in the room, I embrace this
opportunity of mentioning a contrivance for remedying
this defect, which I am persuaded would not only be
found most effectual for that purpose, but would at the
same time contribute very essentially to rendering dwell-
ing-houses more salubrious and more comfortable, by
facilitating the means of warming them more equally
and ventilating them more easily and more effectually.

In building a house, an air-canal^ about twelve or
fifteen inches square, in the clear, and open at both
ends, may be constructed in or near the centre of each
stack of chimneys; and two branches from this air-
canal, both furnished with registers, may open into each
of the adjoining rooms, — one of these branches opening
into the fireplace, just under the grate, and the other
over the fireplace, and near the top of the room, or just
under the ceiling. Each of these branches should be
about four inches square, in the clear ; and to prevent
the uncouth appearance of the open mouth of that which
opens into the room over the fireplace, it may be masked
by a medallion, a picture, or any other piece of orna-
mental furniture proper for that use, placed before it at
the distance of one or two inches from the side or wall
of the room.

The bottom of this air-tube should reach to the
ground, where it should communicate freely with the
open air of the atmosphere; but it should not rise quite
so high as the chimneys (or canals for carrying off the
smoke) are carried up, but should end (by lateral open-

568 Of Chimney Fireplaces.

ings, communicating with the air of the atmosphere)
immediately above the roof of the house.

If this air-tube be situated in the middle of a build-
ing, it is evident that a horizontal canal or tube of
communication must be carried from its lower orifice to
some open place without the building, in order to estab-
lish a free circulation of fresh air, both upwards and
downwards, in the air-tube. I say both upwards and
downwards, for sometimes the current of air in the tube
will be found to set upwards, and sometimes down-
wards. Its direction will depend on the winds that hap-
pen to prevail, or rather on the eddies they occasion in
the air out of doors in the neighbourhood of the build-
ings ; and it is no small advantage" that will arise from
leaving both ends of the air-tube open, that the tube
will always be supplied with a sufficiency of air, what-
ever eddies the winds may occasion. It is easy to per-
ceive how powerfully this must operate to prevent
those puffs of smoke which, in high winds, are fre-
quently thrown into some rooms by the eddies, and the
partial rarefactions of the air that they occasion ; but
this is far from being the only or the most important
of the advantages that will be derived from this air-tube.
Those who consider what an immense quantity of air is
required to supply the current that sets up the chimney
of an open fireplace, where there is a fire burning, must
perceive what an enormous loss of heat there must be,
when all this expense of air is supplied by the warmed
air of the room, and that all this warmed air is necessa-
rily and constantly replaced by the cold air from with-
out, which finds its way into the room by the crevices
of the doors and windows. But all this waste of heat,
or any part of it, at pleasure, may be prevented by the

Of Chimney Fireplaces. 569

scheme proposed ; for if the air necessary to the combus-
tion of the fuel, and to the supplying of the current up
the chimney, be furnished by the air-tube, the warmed
air in the room will remain in its place ; and as this will
in a great measure prevent the cold currents from the
crevices of the door and windows, the heat in the room
will be the more equable, and consequently the more
wholesome and agreeable on that account.

But there are, I am told, persons in this country,
who are so fond of seeing what is called a great roaring
fire, that even with its attendant inconveniences, of
roasting and freezing opposite sides of the body at the
same time, they prefer it to the genial and equable
warmth which a smaller fire, properly managed, may be
made to produce, even in an open chimney fireplace.
To recommend the air-tubes to persons of that descrip-
tion, I would tell them, that, by closing up, by means
of its register, the lower branch of communication (that
which ends just under the grate) and setting that situ-
ated near the top of the room wide open, they may in-
dulge themselves with having a very large fire in the
room with little heat, and this with much less inconven-
ience from currents of cold air from the doors and win-
dows than they now experience.

It is easy to perceive that by a proper use of the two
registers, together with a judicious management of the
fire, the air in the room may either be made hotter or
colder, or may be kept at any given temperature, or the
room may be most effectually ventilated ; and that this
change of air may be effected either gradually or more
suddenly. And here it may perhaps be the proper place
to observe, that in all our reasonings and speculations
relative to the heating of rooms by means of open chim-

570 Of Chimney Fireplaces.

ney fires, we must never forget that it is the room that
heats the air •, and not the air that heats the room.

The rays that are sent off from the burning fuel gen-
erate heat only when and where they are stopped or
absorbed; consequently they generate no heat in the air
in the room in passing through it, because they pass
through if, and are not stopped by it, but, striking against
the walls of the room, or against any solid body in the
room, these rays are there stopped and absorbed, and it is
there that the heat found in the room is generated. The
air in the room is afterwards heated by coming into con-
tact with these solid bodies. Many capital mistakes have
arisen from inattention to this most important fact.

It is really astonishing how little attention is paid to
events which happen frequently, however interesting
they may be as objects of curious investigation, or
however they may be connected with the comforts and
enjoyments of life. Things near us, and which are
familiar to us, are seldom objects of our meditations.
How few persons are there who ever took the trouble to
bestow a thought on the subject in question, though it
is, in the highest degree, curious and interesting !

[This paper is printed from the English edition of Rumford's
Essays, Vol. III., pp. 387 — 400.]

END OF VOL. II.

Cambridge : Electrotyped and Printed by Welch, Bigelow, & Co.

UNIVERSITY OF CALIFORNIA AT LOS ANGELES

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