214 



CAPTAIN SABINE ON THE REDUCTION TO A VACUUM 



The glasses were then removed, and the pendulum raised on the ys ; in 

 which operation it was observed that it had not quitted its place during the 

 experiments, in which it had been twice set in motion and twice stopped by 

 the wire which passes through the stuffing-box. The pendulum was then re- 

 moved, and the horizontality of the planes examined and found perfectly correct. 



The vibrations in air, before and after those in the rarefied medium, were as 

 follows : 



In the morning, before the vibration in \ ar^qo-r r,A . 

 the rarefied medium J ' • ■> 



Barom. 29.861 



In the evening, after the vibration ml orr>oT ^n n ™ orw o^r. 

 ii ix A A- f 85937.40 ; J3arom. 29.829 



the rarefied medium J 



Mean 



85937.47 ; Barom. 29.845 



The vibrations in the rarefied medium, re-") orqAA or Ca p-p 7 OS 

 duced to the same temp, as those in air . . J ' ° 



Whence there appears, as the result of this experiment, a difference of 7.38 

 vibrations per diem, corresponding to a difference of atmospheric pressure of 

 22.765 inches: the temperature of the air of full pressure being 72°.01 ; and 

 that of the rarefied air 72°.5. 



The indications of the thermometer in the rarefied medium have been in- 

 creased 0°.7, to compensate the effect produced on the thermometer by the 

 removal of the full pressure of the atmosphere. It has been noticed, that on 

 the pump being worked, the thermometer, which previously stood at 71°.4, fell 

 to 70°.7j which it indicated when the pressure was reduced to 7 inches. The 

 converse took place when the air was re-admitted. To ascertain whether this 

 effect was rightly ascribed to the removal of the pressure of the atmosphere on 

 the exterior of the ball and tube of the thermometer, the following experiment 



