218 
CAPTAIN SABINE ON THE REDUCTION TO A VACUUM 
The air was then admitted, and in the afternoon (July 14) the following 
observations made. 
No. of 
Coincid. 
Therm. 
Barom. 
Times of 
Arc registered 
and true Arc. 
Mean 
Interval. 
Correc- 
tion for 
Arc. 
Reduc- 
tion to 
70°. 
Corrected 
Vibrations 
at 70°. 
Disapp. 
Re-app. 
Coincidence. 
1 
OO 
69.9 
69.4 
inch. 
29-50 
29-50 
m s 
45 29 
59 15 
m s 
45 38 
59 38 
h m s 
2 45 33.5 
4 59 26.5 
0 / o / 
1 18 = 1 08 
0 33 = 0 26 
s 
382.52 
+ 0.95 
s 
— 0.15 
85950.84 
69.65 
29-50 ; Index + 0.066 ; Reduction to 32° — 0.107 ; = 29.459. 
85950.84 
The vibrations in air in this experiment were as follows : 
July 13. Previous to the vibration in a rare- 
fied medium 
ire - 1 
85950.86 ; Barom. 29.404 inches. 
July 14. Subsequent to the vibration in a j 85950 84 Barom . 29 , 459 
rarefied medium J 
Mean 
85950.85 ; Barom. 29.431 
The vibrations in a rarefied medium reduced^ Q . , 
to the same temperature as those in air J ’ & '' 
Whence there appears, as the result of this experiment, a difference of 9.065 
vibrations per diem, corresponding to a difference of atmospheric pressure of 
27-7^1 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^ 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 
