vSO THE PENDULUM. 



THE PENDULUM. 



By the Pendulum is meant a heavy body sus- 

 pended by a cord or wire, and made to vibrate or 

 oscillate. It is a very important instrument, from 

 its enabling us to measure very small portions of 

 time, and to regulate the going of clocks. 



The vibration of bodies when suspended must 

 have been long observed; but it was Galileo who 

 first noticed the properties which render it so useful, 

 which is a striking proof of the way in which men 

 of genius reflect upon incidents which to others 

 afford no interest. It is said, that while observing 

 the oscillations of a lamp which was hung from the 

 ceiling, he noticed, that although they diminished 

 gradually, yet whether great or small, they were 

 performed in equal times. Struck with this re- 

 markable circumstance, he repeated many experi- 

 ments with weights hung from cords, and thus 

 developed all those facts which finally rendered 

 the pendulum so valuable. Galileo, as well as the 

 other astronomers of that period, employed the 

 pendulum for measuring time in astronomical ob- 

 servations, but it was reserved for Huygens to 

 apply it to the regulation of clocks. 



We shall here consider the pendulum merely as 

 consisting of a weight and a string. 



P C (Plate 5. fig. 9.) is a pendulum, consisting of 

 a body P, attached to a thread P C which is fastened 

 to the point C and is moveable round it. If the 

 body P was let free, and not retained by the thread, 

 it would fall in the vertical line P L; but being re- 

 tained by the thread P C, it is forced to describe 

 the arch P A, which is the segment of a circle, of 

 which P C is the radius. 



