EXPERIMENTS ON HEAT AND COLD. \C)J 



ciently accounts for the fmall difference obferved in the refults 

 upon warm vapoury air and cold dry air. Hence vapour, 

 far from producing the change of temperature in queftion> 

 tends to diminifh the effect. 



If any doubt remained with me refpecting the real change 

 of temperature that takes place in the operations related above, 

 it was completely removed by the refults of the two following 

 experiments. 



EXPERIMENT 10. 



Inclofed a fmall graduated glafs tube of -^ of an inch inter- A fmall mano- 

 rial diameter, and JO inches long, with a (hoft column of "^ . wa8 in " 

 mercury in it, in the large receiver ; the tube was fealed at 

 one end and open at the other, fo that a portion of given Ca- 

 pacity was confined by the mercurial column, which Was neat 

 the open end of the tube, and fubject to rife or fall by any 

 variation of elafticity of the air on either fide, being a proper 

 manometer : then doubled the denfity of the air in the re- the denfity of 

 ceiver, and opening the flop-cock, the mercurial column foon ^^"^"y"/. 

 ran up to its former ftation, but inffantly turning the cock then reftored by 

 again, the mercurial column returned or fell down gradually a momentary 

 for 5 or lOfeconds, to the amount of nearly -^ of the whole f rom without, 

 aerial column, and then became ftationary. Again opening Tne manometer 

 the cock, a quantity of air ruffied out, and the mercury if t h e air in the 

 refumed its original ffation. Thefe effects were always the receiver had 

 fame, on a repetition of the experiment. foSd Sa^Ind 



become more 



EXPERIMENT 11. eiaftk. 



Let the mercurial column of the manometer down by a Exp. n. The 



wire to £ of the length of the tube from the fealed end ; then ^ a f ™™ et b " t a - s 



exhaufted f of the air from the receiver, which was feen by rarefied air: 



the mercury riling to the top of the tube ; and upon opening 



the cock the mercury fell to its former ffation, but then fud- 



denly turning the cock, the mercury gradually rofe for the The air let in 



fpace of 5 or 10 feconds to more than T V of its original height fl ?°. wed fl S ns of 



giving out heat* 

 >ove the ftationary point, and remained there till, the cock ' - 



ras opened : after which it refumed its proper ffation. 



The phenomena in the two laft experiments can be ex- Fuller /-xplana- 



plained only on the following principle : — The air in the re- . tion ; The air 

 i-i . - , . ^ ... in the manome- 



ceiver and in the manometer is iubjecl; to a like degree of ter recovers the 



rarefaction and condenfation in thofe experiments, or nearly common temp<;- 



/ ratuxe foonejr 

 lo. 



