Page images

have also been informed, that in the town of Richmond, in Surrey, and at Infhip near Preston, in Lancafhire, it is ufual to bore for water through a lower ftratum of earth to a certain depth; and that when it is found at both thofe places, it rifes fo high as to overflow the furface of the well: all thefe facts contribute to establish the theory


[ocr errors][merged small]

[From the fame Publication.]

above mentioned. And there is reafon to conclude, that if fimilar experiments were made, artificial fprings, rifing above ground, might in many places be thus produced at fmall expence, both for the common purposes of life, and for the great improvement of lands by oc. calionally watering them."


"II. That light is an heterogeneous body, and that the fame attractive power operates with different degrees of force on its different parts.

II. That the light which efcapes from combuftibles when decompofed by heat, or by any other means, was, previoufly to its efcape, a component part of thofe fubftances.

"It is an obvious conclufion from these data, that when the attractive force, by which the several rays of light are attached to a body, is weakened, fome of those rays will efcape fooner than others. Those which are united with the leaft degree of power will efcape fir, and thofe which adhere to it most trongly will (if I may be allowed

the expreffion) be the last to quit may here recourfe to a familiar fact, which is analogous to this, and will illuarate it. If a mixture, confifting of equal parts of water, of fpirits of wine, and of other more fixed bodies, be placed over a fire; the first influence of that heat, to which all the ingredients are alike expofed, will carry off the fpirits of wine only. The next will carry off the fpirits of wine blended with particles of water. A till greater degree of heat will blend with the vapour which efcapes a part of the more fixed bodies, till at length what evaporates will be a mixture of all the ingredients which were at first expofed to the fire. In like manner, when the furface of a combustible is in a state of decompofition, thofe parts which are the leaft fixed, or which are united to it with the leaft force, will be feparated first. Amongst these the indigo rays of light will make the earliest appearance. By increafing the heat we fhall mix the violet with the indigo. By increasing it fill more we fhall add the blue and K 3 the

[ocr errors]

for about a minute, I found it be
gan to lose weight, on which I
immediately took it out, and placed
it at a distance from the beam. I
alfo immediately plunged a ther-
mometer in the freezing mixture,
and found the temperature 10 de-
grees; and on putting the ball of
the thermometer in the hollow at
the bottom of the glafs veffel, it
fhewed 12 degrees. I left the whole
for half an hour, and found the
thermometer, applied to the hol-
low of the glafs, at 32°. Every
thing now being at the fame tem-
perature, I weighed the glafs con-
taining the ice, after wiping it care-
fully, and found it had loft and
five divifions; fo that it weighed

all but one divifion, more than
when the water was fluid.

in fhewing the lofs of weight In ice on being heated.

"The beam I made ufe of was fo adjusted as that, with a weight between four and five ounces in each scale, part of a grain I made a difference of one divifion on the index. It was placed in a room, the heat of which was 37 degrees of Fahrenheit's thermometer, between one and two in the afternoon, and left till the whole apparatus and the brafs weights acquired the fame temperature.

"A glass globe, of three inches diameter nearly, with an indentation at the bottom, and a tube at the top, weighing about 451 grains, had about 1700 grains of New river water poured into it, and was, hermetically fealed, fo that the whole, when perfectly clean, weighed 2150 of a grain exactly; the heat being brought to 32 degrees, by placing it in a cooling mixture of falt and ice till it just began to freeze, and fhaking the whole together.

"After it was weighed it was again put into the freezing mixture, and let ftand for about 20 minutes; it was then taken out of the mixture: part of the water was found to be frozen; and it was carefully wiped, firft with a dry linen cloth, and afterwards with dry washed leather; and on putting it into the fcale it was found to have gained about the part of a grain. This was repeated five times: at each time more of the water was frozen, and more weight gained. In the mean time the heat of the room and apparatus had funk to the freezing point.

"When the whole was frozen, it was carefully wiped and weighed, and found to have gained of a grain and four divifions of the index. Upon ftanding in the fcale

"I now melted the ice, excepting a very finall quantity, and left the glafs veffel expofed to the air in the temperature of 32 degrees for a quarter of an hour: the little bit of ice continued nearly the fame. I now weighed it, after carefully wiping the glass, and found it heavier than the water was at first, one divifion of the beam. Laftly, I took out the weights, and found the beam exactly ba lanced as before the experiment.

"The acquifition of weight found on water's being converted into ice, may arife from an increase of the attraction of gravitation of the matter of the water; or from fome fubftance imbibed through the glafs, which is neceffary to render the water folid.

"Which of these pofitions is true may be determined by forming a pendulum of water, and another of ice, of the fame length, and in every other refpect fimilar, and making them fwing equal arcs. If they mark equal times, then certainly there is fome matter added

[ocr errors]


the burning body arrive at the per-
foration where the prifm catches
them, they muft pafs through a
medium which will abforb a great
part of the indigo and the violet.
On the other hand, owing to the
imperfection of the decompofition,
very few of the red rays are fepa-
rated from their bafis, and confe-
quently the yellow and the orange
rays are thofe alone which pafs
through the unburnt fmoke of the

in the center of which I made a
fmall perforation. As the light of
the burning body efcaped through
this perforation, I examined it with
a prifin, and obferved the follow-
ing appearances. When the fpi-
rits of wine were fet on fire, all
the rays appeared in the perfora-
tion; but the violet, the blue, and
the green, in the greatest abundance.
When the combustion of the fpirits
was checked, by throwing fome
fal ammoniac into the mixture, the
red rays difappeared; but when,
by the long continuance of the
flame, the fal ammoniac was ren-
dered fo hot as to increafe rather
than diminish the combuftion, the
red rays again appeared at the per-
foration. If the fcreen was ma-
naged fo that the different parts of
the flame might be examined fepa-
rately, I always obferved that the
colours varied according to the de-
gree of heat. At the bafe of the
flame, or where the heat was leaft,
the indigo, the violet, and a very
fmall tinge of the blue and green
appeared. As I approached the
vertex of the flame, the rays which
efcaped became more and more nu-
merous till I reached the top, when
all the rays appeared in the prifm.
It should be attended to, that when
the red rays first made their ap-
pearance, their quantity was fmall,
and gradually increafed as the eye
in its examination approached that
part where the heat was greateft.
Mr. Melvill, when he made fome
of the preceding experiments, ob-
ferved that the yellow rays fre-
quently efcaped in the greatest
abundance; but this fingularity
proceeded from fome circumstances
which efcaped his attention. In
confequence of mixing acids or
falts with the burning fpirits, a
very denfe fume of unignited par-
ticles arifes, and before the rays of

"I would now proceed with obferving, that, befides the increase or decrease of heat, there are other modes of retarding or accelerating the combuftion of bodies, by which alfo may be examined fome of the preceding illustrations.


1. A candle burns moft rapidly and brilliantly in dephlogiiticated air.

"2. The blue colour of a fulphureous flame in pure air is changed into a dazzling white.


". The flame of inflammable air, when mixed with nitrous air, is green. It is white ftrongly tinged with the indigo and violet when mixed with common air; but when mixed with dephlogisticated air, or furrounded by it, the brilliancy of its flame is most fingularly beautiful,

"If the preceding facts prove that light, as an heterogeneous body, is gradually decompofed during combuftion; if they prove likewife, that the indigo rays escape with the least heat, and the red with the greatest; I think we may rationally account for feveral fingulari. ties in the colours of different flames. If a piece of paper, impregnated with a folution of copper in the nitrous acid, be fet on fire, the bottom and fides of the flame are always tinged with green. Now this flame is evidently in that weak K4 state

[ocr errors]

ference of the weight of the air over the fcale could ever amount to the 32d of a grain. I have, how ever, contrived an apparatus which is executing, in which this caufe of

fallacy will be totally removed. I fhall, therefore, reit at prefent the state of this part of the fubject; and leave it only proved, that was ter gains weight on being frozen."

SOME REMARKS on the OPINION that the ANIMAL BODY poffeffes the POWER of generating COLD. By GEORGE BELL, M. D.

[From the MEMOIRS of the Literary and Philofophical Society at Manchester.]



Curious and important dif covery was announced to the world in the fixty-fifth vo lume of the Philofophical Tranf actions. We are there informed, that Dr. Fordyce and other gentlemen, feveral different times, went into a room, the air of which was heated to a degree far above that of the human blood; and though they remained there, fometimes for the fpace of half an hour, yet the heat of their bodies was not increased by more than 3 or 4 degrees. From hence they concluded, that the live ing body poffeffes a peculiar power of generating cold by fome occult operation. The experiments feem to have been made with fufficient accuracy; but the conclufion drawn from them is liable to strong objection. For, in forming it, feveral circumstances have been overlook ed, which, in my opinion, afford an eafy explanation of all the phenomena, on principles already known, without referring them to a new law of the animal body, which probably does not exist. Thefe circumftances I fhall endeavour to point out.

I. The firft eaufe which pree vented their bodies from receiving a greater increase of heat was, The

rarefaction of the air with which they were furrounded.

"The quantity of heat which different fubftauces contain, is, in general, in proportion to their denfity; and, in this proportion, they communicate more or less of it to others. A cubical foot of water contains a much greater quantity of heat, than a cubical foot of air, of the fame temperature: and, if a third fubftance be added, its tempe rature will be confiderably changed by the hot water, while by the hot air it will hardly be changed in any perceptible degree. Many facts may be adduced, which ferve to il luftrate, and, at the fame time, are explained by this caufe. Thus, the fteam of boiling water will feald a perfon's hand, which can fupport the heat of air, of the fame tempe rature. And thus perhaps the wea ther, when hazy and loaded with vapour, feems to our feeling, hotter than when pure and rare; al though by the thermometer it is found to be equally warm in both inftances,

"This also was the true reafon, why, in making thofe experiments, Dr. Fordyce always found that he could bear a greater degree of heat in dry, than in moist air. But no

[ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors]

thing fhews more clearly the flow-
nefs with which heat is imparted to
a denfer fubftance, from one that is
highly rarefied, than a circumstance
mentioned in the paper in question:
"that even the fmall quantity of
mercury, contained in a thermome-
ter which the gentlemen carried
with them into the room, did not
arrive at the degree to which the
air was heated, during the whole
time they remained there."

"II. Another caufe which, in the given fituation, would diminifh the effect of the heated air, is, The evaporation made from the furface of the body.

"That evaporation produces a confiderable abforption of heat, is well known: and, in making the experiments, there is reafon to be lieve, that it took place in a confiderable degree. Dr. Fordyce, anxious perhaps to establish his general law, feems unwilling to allow its influence. But when it is confidered, that by the operation of the heat, the force of the circulation was increafed, the pores of the fkin relaxed, and the preffure of the internal air diminished; when we are told, that a turgefcence of the veins, and an univerfal redness of the furface of the body, took place; we are compelled to refufe credit to the affertion, even of Dr. Fordyce, that there was no evaporation. The evaporation must have been great, and would diminish the effect of the external heat by furrounding the furface with a cool atmosphere, from its temperature fit for the abforption of heat, and from its rarity, unfit for the ready tranfmiffion of it into the body.

to the furface, of a temperature inferior to that of the furrounding air. By this means the fmall quantity of heat which penetrated the kin would be immediately carried off, and transferred throughout the body: and it would have required the fpace of many hours, before the whole mafs could have received any confiderable increase of heat.

"III. But another very power ful caufe of the body's having preferved its temperature in the given fituation, remains to be noticed; which is, The fucceffive afflux of blood

"It has been adduced, in proof of the existence of the power of the living body to generate cold, that frogs, lizards, and other animals of the fame fort, poffefs it; for if touched, they feel cold. This proves only, that their heat is lefs than that of the hand, with which they are felt; and perhaps lefs than that of the air, when the trial is made.

"But it is extremely probable, that no animal whatever can live in health, for any confiderable time, in an atmosphere of a temperature fuperior in heat to that of its own blood. Thus we find, that the animals in queftion hide themselves in the day-time among thick grafs, where there is a great evaporation; and in places into which the rays of the fun cannot penetrate. Worms, in hot weather, during the day, lie deep in the ground; but in the night-time, when it is cool, rife to the furface to refresh themselves in the dew. When frogs, worms, and fuch other animals, are expofed to air warmer than their blood, its influence is counteracted by the fame caufes which counteract its influ ence on the human body, the evaporation from the furface of their bodies, and the coldness of their blood. Such accidental expofure happens more frequently to them, than to the human fpecies; and, from the inferiority of their fize, they would be fooner heated through, and lefs able to refift the дохі


« PreviousContinue »