218 



CAPTAIN SABINE ON THE REDUCTION TO A VACUUM 



The air was then admitted, and in the afternoon (July 14) the following 

 observations made. 



The vibrations in air in this experiment were as follows : 



July 13. Previous to the vibration in a rare-") „j.„^„ „„ „ or. .r>^ • i, 



fied medium j ^^^''^'^^ ' ^^'■«"^- 29-404 inches. 



*^"mretdmed?um * ^^ *^^;^^'^*^^'^ ^" ^} 85950.84; Barom. 29.459 



Mean 



85950.85 ; Barom. 29.431 



The vibrations in a rarefied medium reduced") „.„.-_,. ^ , -, • u 



to the same temperature as those in air j 8^959^; Gaug e I.7I i nches. 



Whence there appears, as the result of this experiment, a difference of 9.065 

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

 27.721 inches : the temperature of the air of full pressure being 69°.7, and that . 

 of the rarefied air 69°.09. This result is equivalent to the reduction to a va- 

 cuum for the vibration in 30 inches of air of that temperature, of 9.81 vibrations 

 per diem. The " correction for buoyancy" is 5.92 vibrations. 



The cement and paint had been effectual in preventing the leakage ; from half 

 past ten on the evening of the 13th to half past eight on the following morning, 

 as shown in the table, and subsequently until 1 P.M. on the same day, when 

 the pendulum was still vibrating, but in an arc too small to admit of the obser- 

 vation of coincidences, the gauge at 1 .8 underwent no perceptible change. The 

 introduction of the oak boards had also contributed considerably to the firm- 

 ness of the suspension plate : the excess of vibration on an immoveable support 

 being reduced from 18 vibrations a day in the former experiment to 5 J in the 

 present ; whilst the accordance of the results on the two occasions furnish- 

 ing the reduction to a vacuum, gave reason to conclude, that the comparative 



