oxygen of the air and will burn. The heat evolved in this com.
bustion will dissolve the wax or tallow, which ascending through
the meshes of the wick is converted into vapour, and being thus
raised to the necessary temperature, enters into combustion ;
and so the process is continued so long as a supply of tallow or
wax is conveyed to the wick.
1589. Light of flame only superficial. It is evident the
light of the flame is only superficial, that part alone being in
combustion which is in contact with the air. The flame of a
candle or lamp is therefore, so far as regards light, hollow. It
is a column of gas with a luminous surface. As the gas within
the surface rises, it gets into contact with the air and becomes
luminous, and this continues until the column is brought to a
point. Thus the flame of a candle or lamp gradually tapers
until all the combustible vapour proceeding from the oil, wax,
or tallow receives its due complement of oxygen from the air,
and passes off. It speedily loses that high temperature which
renders it luminous, and the flame terminates.
1590. Illuminating power of combustibles. The light
afforded by lamps or candles formed of different substances has
different illuminating powers, according to the constituents of
these substances and the heat developed in their combustion.
The light, however, is not proportional to the heat. Hy-
drogen gas, which developes in its combustion a very intense
heat, produces but a feeble light.
1591. Constituents of combustibles used for illumination.
The chief constituents of the combustibles which are used for
the purposes of illumination are carbon and hydrogen, and the
whiteness of the flame is determined in a great degree by the
proportion of carbon.
The combination in this case produces carbonic acid and
water, the carbon combining with the oxygen to produce the
former, and the hydrogen to produce the latter.
1592. Spongy platinum rendered incandescent by hydrogen.
If a jet of hydrogen gas be directed upon a small mass of
spongy platinum, the metal will become incandescent, and will
continue so as long as the gas acts upon it, without, however,
suffering any permanent change.
An apparatus for producing an instantaneous light has been
contrived on this principle. By turning a stop-cock commu-
nicating with a small bottle in which the gas is generated in the
usual way, the jet of gas is thrown upon a small cup contain-
ing the spongy metal, which immediately becoming incan-
descent, is capable of lighting a match.
Some other metals, palladium, iridium, and rhodium, are
susceptible of the same effect.
This effect has not been yet explained in a clear or satis-
factory manner. See Turner's Chemistry, by Liebig and
Gregory, 8th edit. p. 542.
1593. Quantity of heat developed by combustibles. The
determination of the quantity of heat evolved by different com-
bustibles, is a question not only of great scientific interest, but
of considerable importance in the arts and manufactures. The
mutual relation between the quantities of the combustible, the
oxygen, and the heat developed, if accurately ascertained, could
not fail to throw light, not only on the theory of combustion,
but on the physics of heat in general. In the arts and manu-
factures, the due selection of combustible matter depends in a
great degree upon the quantity of heat developed by a given
weight in the process of combustion.
Nevertheless, there is no part of experimental physics in
which less real progress has been made, and in which the
process of investigation is attended with greater difficulties.
Experiments were made on certain combustibles by Lavoisier
and Laplace, by burning them in their calorimeter, and observing
the quantity of ice dissolved by the heat which they evolved.
Drs. Dalton and Crawford, Count Rumford and Despretz, as
well as Sir H. Davy, made various experiments with a like
object. It was not, however, until the subject was taken up by
Dulong that any considerable progress in discovery was made.
Unhappily, that eminent experimental inquirer died before his
researches were completed. Much valuable information has
been collected from his unfinished memoranda. The inquiry
has since been resumed by MM. Favre and Silbermann, and
has been prosecuted with much zeal and success. The estimates
which they have obtained of the quantities of heat developed in
the combustion of various substances, are found to be in general
accordance with those which appear to have been obtained by
Dulong, in the cases wftere they have operated on the same
combustible. Thus, in the case of hydrogen, the most important
of the substances under inquiry, Dulong found the heat de-
veloped to be expressed by 34601, while MM. Favre and
Silbermann estimated it at 34462, with relation to the same
1594. Table of the quantities of heat evolved in the combus-
tion of various bodies. In the following table is given the heat
developed in the combustions of the substances named in the
first column ; the thermal unit being the heat necessary to raise
a weight of water equal to that of the combustible one degree
of the scale of Fahrenheit's thermometer.
Quantity of Heat
Names of Substances.
Hydrogen, at 15
Carbon, from C to CO 2
from sugar, from C to CO 2 -
Graphite, natural. No. 1.
from high mines, No. 1. -
natural, No. 2.
Graphite, from high mines, No. 2. -
Diamond, heated - - - - -
Oxide, from carbon, at CO 2 -
Gas, marsh - - -
C 2 H 4
C 4 H 4
Paramylene - - -
C 10 H'o
Amylene - - - -
C 22 H "*2
Celine - - - - -
Metamyline - - -
C 40 H 4 o
Ether, sulphuric -
HO 2 +C2o H 20
Spirit of wood
HO2+C 4 H 4
ethalic - - -
Acetone - - - -
C6 H+O 2
C32 H 3 2 Q2
Formiate of methylene - - - - -
C 4 H 4 0<
C H6 0"
Formiate of alcohol
C6 H O 4
Ether, acetic - - -
C8 H 8 O 4
Butyrate of methylene - - - - -
CM H'o O 4
Ether, butyric - - -
C'2 H 12 O 4
Acetate of alcohol, valeric - - - -
C20 H2 O 1
O 4 -^-C 2 H 2
acetic - - -
butyric - - -
4 +C'o H'o
O^-fC 38 H 38
phunic - - -
C' 2 H6 08
Terebene- - - -
Essence of turpentine - - - - -
citron - - - - -
Sulphur, native melted - - - - -
at instant of crystallization -
of carbon -
Carbon burnt with peroxide of azote at 10 -
Decomposition of peroxide of azote - - -
water oxygenated, 1 oxygen
Decomposition of oxide of silver absorbs
Iceland spar for CO2 and C to O, absorbs
Aragonite combined gives - - - -
,, separated absorbs - - - -
separated after combination absorbs
1595. Temperature of organized bodies not in equilibrium
with surrounding medium. Organized bodies in general
present a striking exception to the law of equalization of tem-
perature, since, with some rare exceptions, these bodies are
never at the temperature of the medium which surrounds them.
The human body, as is well known, has a permanent and
invariable temperature much more elevated than that of the
atmosphere. The animals of the polar regions are much
warmer than the ice upon which they rest, and those which
inhabit tropical climates colder in general than the air they
respire. The temperature of the bodies of birds is not that of
the atmosphere, nor of fishes that of the sea.
There is therefore, in organized bodies, some proper source
of heat, or rather some provision by which heat and cold can be
produced at need ; for the ponderable matter which composes
the bodies of these creatures must, like all ponderable matter,
be subject to the general law of equilibrium of temperature.
It is therefore necessary to ascertain what is the temperature
of organized creatures ; what are the quantities of heat which
they evolve in a given time to maintain this temperature ; and
what is the physical apparatus by which that heat is elaborated.
1596- Temperature of the blood in the human species. The
temperature of the blood in the human species is found to be
the same throughout the whole extent of the body, and is that
which is indicated by a thermometer, whose bulb is placed
under the tongue and held there until the mercurial column
becomes stationary. This temperature is 98'6, subject to
extremely small variations, depending on health, age, and
1597. Researches of Davy to determine the temperature of
the blood. Dr. John Davy, Inspector of Army Hospitals,
availed himself of the opportunities presented by his professional
appointment, and of a voyage made by him to the East, to make
an extensive and valuable series of observations on the tem-
perature of the blood in man, in different climates, at different
ages, and among different races, as well as upon the inferior
animals. These observations were made between 1816 and
The first series of observations were made during a voyage
from England to Ceylon, and, therefore, under exposure to
very various climates and temperatures. The temperature of
the blood was observed by means of a sensitive thermometer
applied under the tongue near its root, with every precaution
necessary to ensure accuracy. The principal results obtained
are collected and arranged in the following tables:
1598. Showing the Temperatures of the Blood of 13 Indi-
viduals in different Climates.
Showing the Temperatures of the Blood of 6 Individuals in
Showing the Temperatures of the Blood in the same Individual
at different Hours of the Day.
1 P. M.
Shoioing the Limits between which the Temperature of the Blood
in different Races was observed to vary in India. Air, 75
96-5 to 995
101 * 101-75
African Negroes -
98 to 98-5
Showing the Temperature of the Blood observed in different
Species of Animals.
Place of Observation.
Rat - -
Felix pardus -
101 to 104
103 to 104
104 to 105
103 to 104
Lat. N. 8 23' at sea.
Jungle "fowl -
103-5 to 105-5
Place of Observation.
Common hen -
Lat. S. 34 1' at sea.
106 to 107
Duck - ...
Teal - ...
Snipe - ...
Testudo midas ...
Lat. N. 2 7'.
T. geometrica -
Rana ventricosa ...
Common frog ...
Lat. S. 8 23'.
Lat. S. 1 14'.
Trout - - - - -
Lat. N. 6 57'.
76 to 76|
Gryllus hoematopus ?
Apis ichneumonia? -
Scorpio afer -
1599. Deductions from these observations. The conclusions
deduced from these observations and experiments are, that the
temperature of man, although nearly constant, is not exactly so ;
that it is slightly augmented with the increased temperature of
the climate to which the individual is exposed ; that the tem-
perature of the inhabitants of a warm climate is higher than
those of a mild ; and that the temperature of the different races
of mankind is, cceteris paribus, nearly the same. This is the
more remarkable, inasmuch as among those whose tem-
peratures thus agree, there is scarcely any condition in common
* This was the temperature of the heart, which lies near the surface. In
the deeply-seated muscles the temperature was 99.
except the air they breathe. Some, such as the Vaida, live
almost exclusively on animal food ; others, as the priests of
Boodho, exclusively on vegetables ; and others, as Europeans and
Africans, on both.
1600. Birds have the highest, and amphibia the lowest tem-
perature. Of all animals birds have the highest temperature ;
mammalia come next; then amphibia, fishes, and certain
insects. Mollusca, Crustacea, and worms stand lowest in the
scale of temperature.
1601. Experiments of Breschet and Becquerel. Experi-
ments were made by MM. Breschet and Becquerel to ascertain
the variation of the temperature of the human body in a state
of health and sickness. They employed for this purpose com-
pound thermoscopic needles, composed of two different metals,
which, being exposed to a change of temperature, indicated with
great sensitiveness the sensible heat by which they were affected,
by means of a galvanometer on a principle similar to the
electroscopic apparatus used by M. Melloni, already described,
(1564). The needles were adapted for use by the method of
1602. Comparative temperature of blood in health and sick-
ness. It was found that in a state of fever, the general tempe-
rature of the body sometimes rose from 1 0% 8 to 3'6.
It was also ascertained in several cases of local chronic and
accidental inflammation, that the temperature of the inflamed
part was a little higher than the general temperature of the
body, the excess however never amounting to more than from
l-8 to 3-6.
1603. Other experiments by Breschet and Becquerel. It
resulted from these researches that, in the dog, the arterial
blood exceeds in temperature the veinous by about l - 8. It
was also found that the temperature of the bodies of the
inhabitants of the valley of the Rhone and those of the Great
St. Bernard, both men and inferior animals, were the same.
1604. Experiments to ascertain the rate of development of
animal heat. A series of experiments was made by Lavoisier
and Laplace to determine, by means of their calorimeter already
described, the quantity of heat developed in a given time by
various animals ; but more recently much more extensive re-
searches in this department were made by Dulong, which have
produced important results. In these experiments the animal
ANIMAL HEAT. 143
under examination was shut up in a copper cage sufficiently
capacious to be left at ease, and being submerged in a glass
vessel of water, the air necessary for respiration was supplied
and measured by a gasometer, while the products of respiration
were carried away through the water, to which they imparted
their heat, and were afterwards collected and analyzed. Each
experiment was continued for two hours. After the proper
corrections had been applied, the heat developed by the animal
was calculated by the heat imparted to the water.
Dulong determined these thermal quantities with great pre-
cision for numerous animals of different species, young and
adult, carnivorous and frugivorous. The animals during the
experiment being subject neither to inconvenience nor fatigue,
it might be assumed the heat they lost was equal to that which
they reproduced. On analyzing the products of respiration it
was found that they were changed as air is which has under-
gone combustion. The oxygen of the atmospheric air which
was introduced into the cage was in fact combined with carbon
and formed carbonic acid. So far, therefore, as concerned this
point, a real combustion may be considered as having taken
place in the lungs. Thus much was inferred in general as to
the source of animal heat from the discoveries of Lavoisier.
1605. Total quantity of heat explained by chemical laics
without any especial vital cause. It remained, however, to
verify this discovery by showing that the exact quantity of heat
evolved in the animal system could be accounted for by the
chemical phenomena manifested in respiration ; and this Dulong
After having determined the quantity of heat lost by the
animal, he calculated the quantity of heat produced by respir-
ation. The air which was furnished to the animal was mea-
sured by the gasometer, and the changes which it suffered were
taken into account by analyzing the products of combustion
discharged through the water from the cage. These products
were as follows :
1. The vapour of water.
2. Carbonic acid.
The vapour of water analyzed gave a certain quantity of
oxygen and hydrogen, the carbonic acid a certain quantity of
carbon and oxygen, and the azote was sensibly equal to the
quantity of that gas contained in the atmospheric air supplied
to the animal. .It followed that the oxygen of the atmospheric
air which had been supplied combined in the lungs partly with
carbon and partly with hydrogen, producing by respiration
carbonic acid and the vapour of the water, being exactly the
products resulting from the combustion of a lamp or candle.
Now the quantity of heat produced by the combustion of given
quantities of carbon and hydrogen being taken and compared
with the quantity of animal heat developed, as given by the
heat imparted to the water, was found exactly to correspond ;
and thus it followed that the source of animal heat is the same
as the source of heat in the common process of combustion.
When these researches were first made, it appeared that the
quantity of heat actually developed in the animal system ex-
ceeded the quantity computed to result from the chemical change
which the air suffered in respiration, and it was consequently
inferred that the balance was due to a certain nervous energy
or original source of heat existing in the animal organization
independently of the common laws of physics. Dulong, how-
ever, had the sagacity to perceive that the phenomenon admitted
of a more satisfactory and simple explanation, and succeeded at
length in showing that the difference which had appeared
between the quantity of heat developed in respiration, and the
quantity due to the chemical changes which the air suffered in
this process, was accounted for by the fact that the quantity of
heat developed in the combustion of hydrogen and oxygen had
been under-estimated, and that when the correct coefficient
was applied, the quantity of heat due to chemical changes suf-
fered by the air in respiration was exactly equal to the quantity
of heat developed in the animal system.
THE SENSATION OF HEAT.
1606. Indications of the senses fallacious. The senses, though
appealed to by the whole world as the most unerring witnesses
of the physical qualities of bodies, are found, when submitted
THE SENSATION OF HEAT. 145
to the severe scrutiny of the understanding, not only not the
best sources of exact information as to the qualities or degrees
of the physical principles by which they are severally affected,
but the most fallible guides that can be selected, often in-
forming us of a quality which is absent, and of the absence of
one which is present.
Nor should this be any matter of surprise. Our Maker in
giving us organs of sense did not design to supply us with
philosophical instruments. The eye, the ear, and the touch,
though admirably adapted to serve our purposes, are not severally
a telescope, a monochord, and a thermometer. An eye which
would enable us to see the inhabitants of a planet, would ill
requite its owner for that ruder power which guides him through
the town he inhabits, and enables him to recognize the friends
who surround him. The comparison of the instruments which
are adapted for the uses of commerce and domestic economy
with those destined for scientific purposes supply an appropriate
illustration of these views. The delicate balance used by the
chemist in determining the analysis of the bodies upon which
he is engaged would, by reason of its very perfection and
sensibility, be utterly useless in the hands of the merchant or
the housewife. Each class of instruments has, however, its
peculiar use, and is adapted to give indications with that degree
of accuracy which is necessary, and required for the purposes
to which it is applied.
1607. Sense of touch a fallacious measure of heat. The
touch is the sense by which we acquire a perception of heat".
It is evident, nevertheless, that it cannot inform us of the quan-
tity of heat which a body contains, much less of the relative
quantities contained in any two bodies. In the first place, the
touch is not aifected by heat which exists in the latent state.
Ice-cold water and ice itself have the same degree of cold to
the touch, and yet it has been proved that the former contains
140 of heat more than the latter.
1608. Its indications contradictory. But it may be said
that even the thermometer does not in this case indicate the
presence of the excess of heat in the liquid. The sense of feel-
ing will however be found almost as fallacious as regards the
temperature of bodies ; for it is easy to show that the sense of
warmth depends as much upon the condition of the part of the
body which touches or is surrounded by the warm or cold