of minute Forces on the Rate of the Seco?ids Pendulum. 345 



S°. When the heavy end was lowest, it equalled the clock 

 pendulum at an extent of 3°*5. 



The pendulum was next reduced in weight to 4 pounds 

 3 ounces. When the vibrations were adjusted so as to make 

 them alike, either when the light end or the heavy end was 

 lowest, they were found to be slightly slower than those of the 

 clock, even at the extent of vibration of o, 5. But in a degree 

 of exhaustion the same as above, with the heavy end lowest, 

 the pendulum equalled the clock at an extent of vibration of 

 3°. When the light end was lowest, it equalled the clock at 

 an extent of vibration of 2°. The knife-edges were not al- 

 tered in either of the experiments. 



It appeared from these experiments, that when the heavy 

 end of the pendulum was lowest, it vibrated faster by 4\5 se- 

 conds in 24 hours, when its weight was 9 pounds 10 ounces, 

 than when its weight was 4 pounds 3 ounces ; and when the 

 lighter end of the pendulum was lowest, there was a greater 

 difference between the times of its vibrations in the light and 

 heavy states. When the adjusting weight was shifted towards 

 the heavy end, a great effect was produced on the time of the 

 vibrations of the pendulum when the lighter end was lowest, 

 and but a small effect in the contrary case. When the pen- 

 dulum was nearly adjusted in both these cases, the difference 

 in the times of its vibrations when the heavy ends were lowest, 

 may be safely taken as the real difference between the times of 

 the vibrations in the light and the heavy states of the pendu- 

 lum. This difference is no doubt considerable, and is suffi- 

 cient to give some countenance to the supposition that a heavy 

 pendulum is more influenced by gravity than a light pendu- 

 lum. 



If, however, the approximation in the times of vibration 

 shown in the experiments, with the light pendulum vibrating 

 in air and in the state of exhaustion, be taken into considera- 

 tion, it will appear that if the pendulum had been properly 

 adjusted and made to vibrate in a perfect vacuum in both 

 cases, there would have been no difference in the times. 



In the next experiment, my object was principally to show 

 the effect of a current generated in the air by the motion of a 

 pendulum. The convertible pendulum was adjusted symme- 

 trically, by fixing brass weights at the one end, and the wooden 

 patterns of these weights at the other, so as to make it vibrate 

 with the clock pendulum when either end was lowest. When 

 the heavy end was lowest the long vibrations were slower and 

 the short vibrations quicker, as usual; but when the light end 

 widi the wooden patterns was lowest, there was no difference 



Third Series, Vol. 2. No. 11. May 1833. 2 Y 



