OF THE VIBRATIONS OF AN INVARIABLE PENDULUM. 



227 



Whence there appears as the result of this experiment, a difference of 5.705 

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

 16.08 inches of mercuiy at 32°; the temperature of the air of full pressure 

 being 35°.67, and that of the rarefied medium 36°.63. 



li 



Exp. VII. — February 9th and 10th. Clock gaining 4"" 14^38. 



This experiment was undertaken for a distinct purpose ; that of ascertaining 

 the comparative retardation of a pendulum vibrating in an atmosphere of hy- 

 drogen gas, and in an atmosphere of common air. It had been suggested to 

 me by Mr. William Hasledyne Pepys, that a nearer practical approach to the 

 vibration in a vacuum, than the pump had hitherto effected, might be accom- 

 plished, by filling the apparatus with hydrogen gas, and pumping out to the 

 extent that the pump could carry the process of exhaustion ; when the small 

 portion of the gas remaining in the apparatus, being 13 times lighter than a 

 remainder of air which would effect the gauge to an equal amount, might be 

 expected to have an influence on the vibration diminished in the ratio of the 

 respective specific gravities of air and hydrogen. To ascertain, therefore, 

 whether the retardations of air and hydrogen gas were in that ratio was the 

 object of this experiment, which was accomplished by vibrating the pendulum, 

 1st, in the ordinaiy atmosphere; and 2nd, in an atmosphere of hydrogen gas, 

 of equal pressure, or as nearly so as circumstances would permit. 



First, in air. 



Observer. 



Thermometers 



1 



Stand- 

 ard 

 Barom. 



Times of 



Disapp. Rc-app, 



Coincidence. 



Arc registered 

 and true Arc. 



Mean 

 Interval. 



Correc- I Reduc- 

 tion for ) tion to 

 Arc. 36°. 



Corrected 



Vibratioiu 



at 36°. 



Captain_ 

 Sabine.' 



1 



2 



3 



22 



23 



24 



37.7 



38.1 



incll. 



37.8 

 38.'5 



30.200 



14 45 

 22 58 

 31 13 

 7 43 

 30.156 15 58 

 24 14 



14 58 



23 12 

 31 25 



8 16 

 16 32 



24 46 



h m s 

 21 23 05.17 



16 14.83 



Div. o 



0.85 = 1.02 



0.235 = 0.S 



M94.745 



+ 0.61 



+ 0.88 



30.193; Capill. + 0.019; Reduction to 32° — 0.019; =30.193. 



86305.57 



86305.57 



The air was then withdrawn until the gauge indicated 0.7 inch; and 

 hydrogen gas was introduced, passed through a cylinder containing muriate 

 of lime, till the mercury in the barometer tube rose to 30 inches. The gas was 



2 g2 



