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ference of the weight of the air fallacy will be totally removed. I over the scale could ever amount to fall, therefore, reit at present the the 3 ad of a grain. I have, how. state of this part of the fubject; ever, contrived an apparatus which and leave it only proved, that was is executing, in which this cause of ter gains weight on being frozen."


poffefses the POWER of generating COLD. By GEORGE BELL, M. D.

From the Memoirs of the Literary and Philosophical Society at




Curious and important dif- carefaftion of the air with which

covery was announced to they were furrounded. the world in the fixty-fifth vo “ The quantity of heat which lume of the Philosophical Trans- different fubftauces contain, is, is actions. We are there informed, general, in proportion to their denthat Dr. Fordyce and other gentle-tity; and, in this proportion, they men, several different times, went communicate more or less of it to into a room, the air of which was others. A cubical foot of water heated to a degree far above that of contains a much greater quantity of the human blood; and though they heat, than a cubical foot of air, of semained there, sometimes for the the same temperature: and, if a {pace of half an hour, yet the heat third substance be added, its tempeof their bodies was not increased by rature will be considerably changed more than 3 or 4 degrees. From by the hot water, while by the hoc hence they concluded, that the live air it will hardly be changed in any ing body poffefses a peculiar power perceptible degree. Many facts of generating cold by fome occult may be adduced, which serve to il operation. The experiments seem luftrate, and, at the fame time, are to have been made with sufficient explained by this cause. Thus, the accuracy; but the conclusion drawn steam of boiling water will fcald a from them is liable to strong objec- person's hand, which can support tion. For, in forming it, several the heat of air, of the same tempecircumstances have been overlook. rature. And thus perhaps the weaed, which, in my opinion, afford an ther, when hazy and loaded with easy explanation of all the phenovapour, seems to our feeling, het. mena, on principles already known, ter than when pure and rare ; al. without referring them to a new law though by the thermometer it is of the animal body, which pro- found to be equally warm in both bably does not exift. These cir- instances, cumíançes I fhall endeavour to " This also was the true reason, point out,

why, in making those experiments, “ I. The first eause which pre Dr Fordyce always found that he vented their bodies from receiving could bear a greater degree of heat a greater increase of heat was, The in dry, than in moift air. But de BODIES. (167) thing shews more clearly the flow- to the surface, af a temperature infeness with which heat is imparted to rior to that of the surrounding air. a denser substance, from one that is By this means the small quantity highly rarefied, than a circumitance of heat which penetrated the skin mentioned in the paper in question : would be immediately carried off, " that even the small quantity of and transferred throughout the bomercury, contained in a thermome. dy: and it would have required the ter which the gentlemen carried space of many hours, before the with them into the room, did not whole mass could have received any arrive at the degree to which the considerable increase of heat. air was heated, during the whole 66 It has been adduced, in proof time they remained there." of the existence of the power of the

“ II. Another cause which, in living body to generate cold, that the given lituation, would diminish frogs, lizards, and other animals of the effect of the heated air, is, The the same fort, pofless it; for if evaporation made from the surface of touched, they feel cold. This the body.

proves only, that their heat is less “ That evaporation produces a than that of the hand, with which considerable absorption of heat, is they are felt; and perhaps less than well known: and, in making the that of the air, when the trial is experiments, there is reafon to be made. lieve, that it took place in a confi- " But it is extremely probable, derable degree. Dr. Fordyce, anxi. that no animal whatever can live in ous perhaps to establish his general health, for any considerable time, law, seems unwilling to allow its in an atmosphere of a temperature influence. But when it is consider- superior in heat to that of its own ed, that by the operation of the blood. Thus we find, that the ani. heat, the force of the circulation mals in question hide themselves in was increased, the pores of the skin the day-time among thick grass, relaxed, and the pressure of the in- where there is a great evaporation; ternal air diminished; when we are and in places into which the rays of told, that a turgescence of the veins, the sun cannot penetrate. Worms, and an univerfal redness of the fur- in hot weather, during the day, lie face of the body, took place; we deep in the ground; but in the are compelled to refuse credit to the night-time, when it is cool, rise to assertion, even of Dr. Fordyce, that the surface to refresh themselves in there was no evaporation. The eva. the dew. When frogs, worms, and poration must have been great, and such other animals, are exposed to would diminish the effect of the ex- air warmer than their blood, its internal heat by surrounding the sur- fluence is counteracted by the same face with a cool atmosphere, from causes which counteract its influe its temperature fit for the absorption ence on the human body, the evaof heat, and from its rarity, unfit poration from the surface of their for the ready transmission of it into bodies, and the coldness of their the body.

blood. Such accidental exposure “ III. But another very power- happens more frequently to them, ful cause of the body's having pre- than to the human species; and, served its temperature in the given from the inferiority of their fize, tituation, remains to be noticed ; they would be sooner heated which is, The fucceffive afflux of blood through, and leis able to resist the

L 4


.noxious effects of the hot air, were 96 to 100 degrees, which happened not their

power of resisting it made in the experiments, rather to the up in another respect. In luch litu- acceleration of the biood, than to ations, the evaporation from the the intlux of heat froin the external surface of their bodies is greater ; air. While the cause of animal for the skin is more lax, and is als heat remains unknown, it would be · Ways covered with moisture. It is, presumption to affert, that thele are perhaps, for this purpose also, that the only means by which the body it is rough and uneven ; which, by is enabled to rehst

' the efficis of erextending the surface, causes a ternal heat. There may be others; greater evaporation,

and it is not unreasonable to fup" These may be said to be the pose, that as external cold, perhaps means through wbich the human by its tonic influence, increases the body is preserved, in nearly the power of the body to generate heat, fame temperature, when it happens io external heat may diminish that to be placed, for a time, in an at. power, and thus leflen the quantity mosphere of a superior degree of of heat generated within, while the heat. They seem to me so adequate evaporation, produced by the fame to this effect, that I would even cause, guards it againit receiving venture to impute the increase of any acceffion from without." the temperature of the body, from


Easox, M. D.


| From the fame Publication. ] HERE are few pheno- performed without air; but Mr.

mena in nature, which Watt, contrary to the theory sup. have puzzled philosophers more, ported by Lord Kaimes and Dr. Hathan the ascent of vapour ; and the milton, has proved, that when was different theories laid down by doc- ter in vacuo was boiled with a de fors Halley and Defaguliers, have gree of heat very little greater than been rejected, while another, not that of the human body, the steam less liable to obječtions, has been came over, and was condented in almost universally received. the refrigeratory. But he relares,

* This theory, which į shall that the evaporation was not quiche presently mention, was at first in- er than in the open air. vented by a French gentleman, “ 2. Were the doctrine of foluMonsieur le Roi, and afterwards re- tion true, the air would be hearier, vived by Lord Kaimes, and doctor the more water it contained; and, Hugh Hamilton. It is this—that as clouds contain a great portion of the air diffolves water, as water water, they ought to float on the does saline substances : the solution surface of the earth, and not in the being perfect, the air will become higher regions, as we daily obtransparent.

serve, " Objections. 1. Were this the- 3. We never couid expect any ory true, evaporation could not be rain, unless the air were fuperiatu


rated with water; and it would only mosphere is electrified, but much vield to us, what it could not retain stronger in frosty, chan in warm in folution.

weather, and by no means less in " 4. It is universally allowed, the night than in the day : it is likce that heat contributes very inuch to- wise itronger in elevated than in wards converting waterinto vapour, low places. From these facts we which is again condensed by cold. may be enabled to account, why In what mamer will the doctrine of evaporation is carried on during folution account for the spontaneous very cold weather. All the heat evaporation of water, and its being contained in water, abore what is Tufpended in air, in the coldest wea. fufficient to keep it in a fluid state, ther, cven when the thermometer is will convert it into vapour; which, below the freezing point. Though in a north or north-east wind, when I cannot allow of ruch a solution as the electric matter greatly abounds, above mentioned, I can, however, will be carried off with much.rapireadily admit of a strong attraction dity; and, by the power of electri. betwixt air and water : for no air is city, will be rendered still lighter, found without water, and no water the higher it ascends; each particle without air.

repelling each other, and prevent. “ Water, which is eight hundred in the cold from condensing the times heavier than air, by a very vapour, in its afcent through the small degree of heat may be con- cold regions of the atmosphere. verted into vapour, which vapour is The higher it rises, the more 1pace one thousand eight hundred times there is for expansion; and the more lighter than air, according to Mr. it is expanded, the clearer will the l'att. It confequently follows, that atmosphere appear, and, probably, vapour will rise up in the atmo- the higher the mercury will rise in sphere, to the height of its own the barometer. specific gravity ; but, long before " It likewise appears, that the it could reach to so high a region, it electric matter is more fenfible near would be condensed by cold, and the surface of the earth, in cold return to the earth in rain, were it northern countries, than in warm not for the latent heat it contains, fouthern places. M. Volta, with a and the electric matter in the air. very simple apparatus, on the up

" Whatever I mention concern- per gallery of St. Paul's, produced ing electricity is from faets, and not an electric fpark, which, he told from any theory written about it, me, in Italy, could not be done, which is above my comprehenfion. but on a very high mountain, or in But as the terms now in use, viz. a situation greatly elevated. This positive and negative, or plus and seems a wife provision in nature, minus, are generally, best under- that the electric matter Nould apItood, I shall express myself by pear near the surface of the earth them. The able Nollet has proved, in cold climates, to raise up and that water electrified, will evaporate fufpend the vapour in the air, which faster, than water which is not elec. otherways would be condensed by trified. Does is not follow, that the cold; whereas, in warm coun. the more electric matter is in the tries, the heat of the earth will be air, the quicker the evaporation of sufficient to raise vapours to a great water will be? And Mr. Cavallo height, which are afterwards car. has proved, that at all times the at. ried fill higher, by the electric mat


ter in the upper regions. This, the same, and generally, heavy rain perhaps, is the cause, why the air immediately, or soon after, follows : is so clear and transparent in warm this is well known to the inhabitants climates.

of, and travellers among, moun. “ By making some observations tains. on the falling of rain, we shall have 46 From this we can cafily ac. other proofs, that the electric mat. count, why thunder-showers are ofter is the great cause by which va- ten partial, falling near, or among pour is supported in the atmosphere. mountains, and the rain in such Here I must observe a fact, well quantities, as to occasion rivers to known to all present, that bodies be overflowed; whilst, at the di. electrified, by the same electric stance of a few miles, the ground power (no matter whether positive continues parched up with drought, or negative) repel each other; and, and the roads covered with duit. when electrified by the different “ It often happens, that one clap powers, that is, the one plus and of thunder is not sufficient to prothe other minus, attraet each other: duce rain from a cloud, nor even a on coming into contact, an equili. second : in short, the claps must be brium is restored, and neither of repeated, till an equilibrium is rethem will shew any signs of electri. ltored, and then the rain mult, of city.

confequence, fall. Sometimes we 6. From this it follows : if two may have violent thunder and lightclouds are ele&trified by the fame ning without rain, and the black power, they will repel each other, appearance of the leavens may be and the vapour be suspended in changed to a clear transparent íky, both; but, when one is pofitive and especially in warm weather. To the other negative, they will attract account for this, it must be rememeach other, and restore an equili. bered, as I lately faid, that one or brium. The electric power, by more claps of thunder are not alwhich the vapour was suspended, ways sufficient to produce rain from being now destroyed by the mutual the clouds : so, if an equilibrium action of the clouds on each other, be not restored, little or no rain will the particles of water will have an fall, and in a short time the electric opportunity of running together matter, passing from the earth to into each other, and, as they aug- the clouds, or the superabundant ment in fize, will gain a greater quantity in the air, will electrify degree of gravity, descending in those black clouds, by which means small rain, or a heavy thower, ac- the particles of vapour will be excording to circumstances.

panded, raised higher, and the air « A cloud, highly electrified, become clear. Clouds may be meltpaffing over a high building or ed away, even when we are looking mountain, may be attracted by, and at them, by another cause, that is, be deprived of its electricity, with by the heat of the fun. We know, put or with a violent explosion of that transparent bodies are not hearthunder. If the cloud is electrified ed hy the fun, but opaque ones are ; plus, the fire will descend from the the clouds being opaque bodies, are cloud to the mountain ; but, if it be warmed by the rays of the sun shin. electrified minus, the fire will as- ing on them, and any additional çend from the mountain to the quantity of heat will rarify the vacloud. In both cases, the efect is pour, and occation its expanding in


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