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any fixed point on the fcale : take, for example,the thirty degrees included between the fortiethand the tenth degree above the heat of tire room.Let this be a ftandard and reduce it to unity •,then fill the glafs with any other liquid, and thetime of its lofing the fame thirty degrees willexprefs in dire 3 proportion the fpecific caloric. 1Thefe refults only give the fpecific caloric ofequal bulks, to reduce them to equivalent ex-preffions of equal weights divide them by thefpecific gravities. Thus Mr. Leflie found thata very thin glats ball of 2-1 inches diameter filledwith water, cooled a certain number of degreesof temperature in 70 minutes, and when filledwith oil it cooled to the fame point in 32minutes. Therefore, reducing water to 1., thefpecific caloric of oil of equal bulk will be .4 6.This divided by .92, the fpecific gravity of oil,will give .5 for the fpecific caloric of equalweights. When folids are to be examined theymuit be broken into fragments, put into theglafs globe, and filled up with water, and thefpecific effect of the water mult be feparatelyeftimated and dedu&ed from that which belongsto the folid, by rules of which the reader willfind many examples in Crawford’s treatife. Inufing this apparatus with perfect accuracy, thefeparate effect of the glafs fhould alfo be ac-counted for, and care fhould be taken in thecooling to avoid currents of air, or any othercircumftance that might derange the uniformityof the procefs.

The capacity of gaffes and vapours differsrefpectively, according to the nature of the gas ;and alfo in each individual gas, it varies largelyaccording to its denfity, or the preflure to whichit is expofed. Every aeriform fubftance beinga highly elaftic fluid, is readily dilated or con-dented by diminifhing or adding to its preflure,and it is found that fudden dilatation producescold in the furrounding bodies, and fudden con-denfation gives out heat. Confequently thecapacity for caloric mull encreafe by expanfion,and a fimilar effect, but much lefs in degree,takes place by this procefs, as in the prodigiousexpanfion of water into fleam, or ether intoetherized vapour; that is, the abforption ofcaloric from all the adjacent parts,, in order tofupply the demand produced by the hiddenencreafe of capacity for caloric in the vapour.

It has long been obferved that if a ther-mometer be enclofed in a fmall receiver and themr brilkiy exhaufted, the mercury rapidly finksa few degrees, after which it flowly rifes to thecommon, temperature of the room. When the

1 Journ. Phyf. torn. 48- p-

air is again let into the receiver, the thermometeragain fuddenly rifes a few degrees above thecommon temperature, after which it flowlyfettles again to the fame point, fhewing theoppofite effect of condenfation in diminifhingthe capacity for caloric, and confequently ex-pelling a part of the heat of the air in a fenfibleform. An artificial condenfation of the commonair produces a fimilar effedt. This is performedfor experiment in a condenfer, which is a flrongair-tight pillon, by working which an additionalquantity of air may be thrown into any confinedveffel. A thermometer enclofed in it rifes feve-ral degrees during the condenfation. The fameextrication of heat from condenfed air is alfo{hewn in working the air-gun, which foon makesthe barrel very fenfibly hot to the hands; andthe blaft of condenfed air when difcharged onthe bulb of a thermometer finks it a few degrees,owing to the cold produced by the hidden ex-panfion. This finking occurrence takes placeon a vaft fcale at the fountain of Hiero, at themines of Chemnitz, in Hungary . A part of themachinery for working thefe mines is a perpen-dicular column of water 260 feet high, whichpreffes on a quantity of air enclofed in a tightrefervoir. The air is confequently condenfedto an enormous degree by this height of water,which is equal to 8 or 9 atmofpheres, and whena pipe communicating with this refervoir ofcondenfed air is fuddenly opened, it rufhes outwith extreme velocity, inflantly expands, and in-fo doing it abforbs fo much caloric as to pre-cipitate the moifture it contained, in a fhowerof very white compact fnow, or rather hail,which may readily be gathered on a hat held inthe blaft. The force of this is fo great that theworkman who holds the hat is obliged to leanhis back againft the wall to retain it in itspofition. p If the cock of the pipe is only partlyopened, the fnow is flill more compadl.

Another finking experiment, the direct reverfeof the foregoing (that is the fudden heating ofbodies contiguous to air in the a£t of conden-fation) is given in the Bulletin des Sciences. qIf the air be very rapidly compreffed in the ballof an air-gun, fo great a quantity of heat is dif-engaged from it at the firfl flroke as actually tofet fire to a morfel of' amadou (or fungus matchwith nitre) enclofed in the ball. If the body of-the pump be terminated with a moveable endformed by a piece of fleel fcrewed on, and fur-nifhed in its centre with a glafs lens, a ray ofvivid light will be perceived on the firfl flrokeof the pifton.

* Phil. Jour. vol. ix. p 3 oa *