The Pendulum and its Laws of Oscillation. 



Read before the Buffalo Society of Natural Sciences, Feb. 12th, 



By Austin M. Edwards. 



HISTORICAL. 



History furnishes us with the information that Galileo, in 

 1542, while in the Cathedral at Pisa, observed the oscillations 

 of a lamp which had been accidentally set in motion. He was 

 struck with the apparent measured regularity of its vibrations 

 and tested this observation by comparing these oscillations with 

 his own pulse. Galileo there invented the simple pendulum as 

 a means of measuring short intervals of time. But for many 

 years the pendulum was used without the clock movement, and 

 astronomers counted the oscillations performed in a given time 

 to measure the periods of celestial phenomena. 



THEORY. 



In describing the pendulum, I will first begin with a theo- 

 retically perfect pendulum, which would consist of a heavy 

 molecule suspended at the extremity of a perfectly flexible cord, 

 and oscillating in a vacuum. This ideal pendulum, of course, 

 could not exist, but to demonstrate the simple pendulum, we 

 will use a small metal ball suspended by a silk thread ; if this 

 freely suspended ball is drawn from the vertical and allowed to 

 oscillate, these oscillations will gradually diminish in extent, on 

 account of the earth's attraction, producing what are called long 

 and short arcs. The function of the clock movement proper, 

 besides registering the time and number of oscillations on the 

 dial, is to furnish to the pendulum the small amount of impulse 

 that is necessary to carry the same in its excursion from the 

 vertical line upwards, so it will return each time to the original 

 point of starting, and thus overcome the influence of gravity, 

 and add enough force in its descent towards the vertical to 

 maintain a uniform arc of oscillation to the required number of 

 degrees. The oscillations of the pendulum were thought and 



