afcrihed to Heat. 387 



icmperature of the medium in which they arc expofed ;— or the time taken up in that 

 operation ; and, confequently, was not abfolutely certain as to the equality of the tem- 

 peratures of the contents of the bottles at the time when tl>eir weiglits vrzit compared, 

 I determined now to repeat the experiments, with fuch variations as fliould put the 

 matter in queftion out of all doubt. 



I was the more anxious to affure myfelf of the real temperatures of the bottles and 

 of tlieir contents, as any difference in their temperatures might vitiate the experiment, 

 not only by caufing unequal currents in the air, but alfo, by caufing, at the fame time, 

 a greater or lefs quantity of moifture to remain attached to the glafs. 



To remedy thefe evils, and alfo to render the experiment more ffriking and fatisfac- 

 tory in other refpefts, I proceeded in the following manner. 



Having provided three bottles, A, B, and C, as nearly alike as poflible, and refem- 

 bling in all refpefts thofe already defcribed ; into the firft, A, I put 4214,28 grains of 

 •i\rater, and a fmall thermometer, made on purpofe for the experiment, and fufpended 

 in the bottle in fuch a manner that its bulb remained in the middle, of the mafs of water; 

 into the fecond bottle, B, I put a like weight of fpirit of wine, with a like thermome- 

 ter; and, into the bottle, C, I put an equal weight of mercury. 



Thefe bottles, being all hermetically fealed, were placed in a large room, in a corner 

 jfar removed from the doors and windows, and where the air appeared to be perfeftly 

 quiet; and, being fuflFered to remain in this fituation more than twenty-four hours, the 

 heat of the room (61°) being kept up all that time with as little variation as poflible, and 

 the contents of the bottles A and B appearing, by their inclofed thermometers, to be 

 exaftlyat the fame temperature, the bottles were all wiped with a very clean, dry cam- 

 bric handkerchief ; and, being afterwards fufFered to remain expofed to the free air of 

 the room a couple of hours longer, in order that any inequalities in the quantities of 

 heat,— tor of the moifture attached to their furfaces, — which might have been occafioned 

 by -the wiping, might be correfted by the operation of the atmofphere by which they 

 were funrounded, they were all weighed, and were brought into the moft exaft equili- 

 'brium with each other, by means of fmall pieces of very fine filver wire, attached to 

 necks of thofe of the bottles which were the lighteft. 



This being done, the bottles were all removed into a room in which the air was at 30°; 

 where they were fufFered to remam, perieftly at reft and undifturbed, forty-eight hours; 

 the bottles A and B being fufpended to the arms of the balance, and the bottle C fuf- 

 pended, at an equal height, to the arm of a fland conftrufted for that purpofe, and 

 placed as near the balance as pofTible, and a very fenfible thermometer fufpended by 

 the fide of it. 



Attheend of forty-eight hours, — during which time the apparatus was left in this fitu- 

 ation, — I entered the room, opening the door very gently, for fear of difturbing the ba- 

 lance ; 



