84 
CAPTAIN SABINE ON THE DIFFERENCE IN THE VIBRATIONS 
by Cumming was furnished by himself. The observations are detailed in the 
Table A. at the close of the paper : — the following abstract exhibits the results : 
London; March 1828; Experiments with Pendulum 12. 
Barom. 
Therm. 
Vibrations at 62°. 
March 17- 
30.132 . 
.... 63.22 
85963.85 
17- 
30.129 . 
.... 63.45 
85963.61 
18. 
30.125 . 
.... 62.82 
..... 85963.52 
18. 
30.040 . 
.... 63.175 
85963.60 
19. 
29.480 . 
.... 62.32 
85963.56 
19. 
29.485 . 
.... 62.42 
85963.55 
20. 
29.375 . 
.... 61.15 
85963.55 
20. 
29.270 . 
.... 61.32 
85963.55 
29.975 . 
.... 62.5 
85963.60 
The height of the barometer corrected to the standard and reduced to 32 c 
is 29.952. 
The mean result is 85963.60 vibrations in a mean solar day, the pendulum 
being at 62°, the air at 62°.5, the barometer 29.952 inches, and the mercury 32°. 
To reduce this result to the number of vibrations which would have been 
made had the pendulum vibrated in a vacuum, I have introduced for the 
first time a reduction obtained by direct experiment ; namely, by vibrating the 
pendulum alternately in the air and in a rarefied medium very nearly ap- 
proaching to a vacuum. The particulars of this experiment I hope shortly 
to communicate to the Royal Society ; and may state in the mean time as its 
result, that the barometer being at 30 inches, the mercury at 32°, and the air 
at 45°, a pendulum, similar in form and materials to the one used on the present 
occasion, made 10.36 vibrations per diem less than when vibrating in a vacuum. 
To adapt this reduction to the variations which the meteorological instru- 
ments undergo in different experiments, it will be remembered, that the specific 
gravity of air varies directly as the height of the barometer, and inversely as 
its expansion of T1 joth part of its bulk for each degree of Fahrenheit. 
The reduction in the present case, for barometer 29.952 inches, and ther- 
mometer 62°.5, is + 9.9/ ; making 85973.57 vibrations at 62°. 
