mechanical Condenfation and Rareficlion of Air. 6t 



fively: lft, with the bulb in the centre of the receiver; 

 2d, with the bulb retting on the wet leather of the plate y 

 and, 3d, with the bulb reding againft the fide of the receiver, 

 iftcafe; reduced by cxhauftion - 2°-45 



ad cafe - - - - 2-15 



3d cafe - - I .1 



3 ft cafe; raifed by reftoring the air - 4 .05 

 %d cafe - - - - 2 .25 



3d cafe - . - - - 2 .8 



Exp. IV. Inclofed a wine glafs with about a cubic inch 

 of water in it, containing the bulb of a thermometer, in a 

 receiver ; and, exhaufting the air, the thermometer funk half 

 a degree fuddenly, and then continued ft ationary ; upon re- 

 ftoring the air, it fuddenly rofe half a degree. 



All thefe experiments confirmed my conjecture of a much 

 greater degree of heat and cold being produced in thefe cafes 

 than the thermometer points out, but that its continuance is 

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

 of the mercury. The following experiments were made to 

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

 nerated in thofe operations. 



Exp. V. The fame receiver and fmall thermometer as 

 above being ufed, I found the exhauftion was effected by 

 working the pump one minute. The thermometer funk 

 nearly %° in the firft half minute, and the remainder, a few 

 tenths of a degree, in the latter half minute. The operation 

 being (topped, and things remaining in the fame ftate, it 

 required fome minutes of time before the thermometer re- 

 covered one degree of the heat loft. Upon opening the cock, 

 the receiver filled with air in five feconds, and the greateft: 

 velocity of the rifing mercury was about the end of that time. 

 ' The rifing continued for 30 or 40 feconds from its com- 

 mencement, but 3~4ths of the effecl were produced in the 

 firft ten feconds. The greateft velocity of the rifing mercury 

 is i° in 3[- feconds. After the thermometer had attained its 

 utmoft height, it began to fall again at the rate of ~ th of a 

 degree in a minute. 



Exp. VI. Took the fame thermometer and heated it to 

 50 above the temperature of the air; then let it be cooled 

 by the medium of air, and it began to fall at the rate of x° 

 in 3^ feconds. 



The two laft experiments feem to prove that when air is 

 let in to the receiver in the ordinary way, an increafe of 

 temperature of 50° is produced in the medium -within the re- 

 ceiver for ^[Ji'cQuc/t. This high temperature is reduced in a 



few 



