EXPERIMENTS ON HEAT AND COLD, J(J3 



fo fhort as not to effect a material change in the temperature greater than 

 of the mercury. The following experiments were made to J^J^^* 

 afcertain what may be the real degree of heat and cold gene- 

 rated in thofe operations. 



EXPERIMENT 5. 



The fame receiver and fmall thermometer as above being Exp. 5. The 



ufed, I found the exhauftion was effeaed by working the <- ime of fub u fi - 



J ° dence much left 



pump one mivute. The thermometer funk nearly 2° in the than of fubfe- 



iirft half minute, and the remainder, a few tenths of a degree, q uent r,fe in ** 

 in the latter half minute. The operation being flopped, and ' 



things remaining in the fame ftate, it required fome minutes 

 of time before the thermometer recovered one degree of the 

 heat loll. Upon opening the cock, the receiver filled with 

 air in five feconds, and the greateft velocity of the riling mer- 

 cury was about the end of that time. The riling continued and the time of 

 for 30 or 40 feconds from its commencement, but | of the Judiion of the 

 cffeft were produced in the firft 10 feconds. The greateft external air 

 velocity of the rifing mercury is 1 ° in 3| feconds. After the ^^fobfe-^ 

 thermometer had attained its utmoft height, it began to fall quent fall. 

 again at the rate of T ~ of a degree in a minute. 



EXPERIMENT 6. 



Took the fame thermometer and heated it to 50° above the Exp. 6. By 



temperature of the air, then let it be cooled by the medium of neatin S th ^ ran4 



air, and it began to fall at the rate of 1° in 3f feconds. letting it cool in 



The two laft experiments feem to prove that when air is let the air » lt was 

 . . ., ! . ., ,. r . r. r , found that an 



in to the receiver in the ordinary way, an mcreafe of tempera- e i eV ation of 50* 



ture of 50° is produced in the medium within the receiver for 3- was required to 

 feconds. This high temperature is reduced in a few feconds by JJJeflSfcwu* 

 1'ie receiver and furrounding bodies, to their own temperature, the former ex- 

 periment. 



EXPERIMENT 7. Suc \ thcre ?£fe 



was the real rife.. 

 On condenfed Air, 



Took a large fpherical glafs receiver, the capacity of which E xp . 7. Ther- 

 was fomething more than twice that of the former (above one mometer in con- 



ii x . 7 r , , . , ,*. r denfed air role 



•gallon), and iuipended a thermometer in the centre ot it, ot a f uc idenly when 



larger bulb than that before ufed ; the receiver had a brafs cap the air wai let 



and ftop-cock adapted to it: then doubled the denfity of the 10 ' 



air within it by a condenfer. The thermometer rofe 2 9 or 



more. Let out the air fuddenly and the thermometer imtne- 



M 2 diatelv 



