84 



CAPTAIN SABINE ON THE DIFFERENCE IN THE VIBRATIONS 



by Gumming was furnished by himself. The observations are detailed in the 

 Table A. at the close of the paper :— the following abstract exhibits the,rie»iits : 



^,, , , ,. f f.r.fl fl'.'.'t"'. :. 



London ; March 1828 ; Experiments with Pendulum 12. 



Therm. Vibrations at 62*. 



. 63.22 85963.85 



. 63.45 85963.61 



. 62.82 85963.52 



. 63,176 85963.60 



29.975 



62.32 

 62.42 

 61.13 

 61.32 



62.5 



85963.56 

 85963.55 

 85963.55 

 85963.55 



85963.60 



The height of the barometer corrected to the standard and reduced to 32° 

 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 ^^th 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 -j- 9.97 ; making 85973.57 vibrations at 62°»u UJ^tim <ji ! 



