[ 28o ] 



171 ; which being alfo let up in 

 the large tube, I begin to make 

 forcibly this tube in the water- 

 trough exactly 30 feconds (begin- 

 ning the motion precifely at the 

 moment the two airs come into 

 contact), and place it directly after- 

 wards in the brafs tube, and let it 

 itand thus in the middle of the 

 trough for the fpace of one minute, 

 pouring continually water upon it, 

 to bring the temperature of the 

 glafs tube to that of the water; for, 

 holding it in the hand while ihak- 

 ing, it receives fome degree of heat 

 from the hand, and of courfe the co- 

 lumn of air within is rarified. I then. 

 Hide the- glafs tube up or down 

 within the brafs tube, which is filled 

 with water, till the two columns of 

 water come ,0 a level with each 

 other, and with the p of the brafs 



meafure, 



