OSCILLATION. 



505 



so does a stone tied to a string, both of which objects are 

 shown in the illustration. 



In various departments of Art, Oscillation is absolutely 

 invaluable. We will take, for instance, the best known of these 

 examples, namely, the Pendulum, by which the movements of 

 clocks are regulated. Without some mode of regulation, the 

 works would run down rapidly, and the clock rendered inca- 

 pable of measuring time. But, in the Pendulum, we possess 

 a means of making a clock go at any desirable rate, and be 

 faster and slower at pleasure ; a long Pendulum working slowly, 

 anc 1 . a short one rapidly. 



How the Pendulum affects the working of a clock may be 

 seen by reference to the right-hand figure of the illustration. 





OSCILLATING WEIGHT. 



METRONOME. 



PENDULU3I. 



The movements of the clock are connected with the Pendulum 

 by means of an ingenious piece of mechanism called an 

 " escapement, " because it only allows the wheel shown in the 

 illustration to move one cog at each swing of the Pendulum. 



Now, as in the latitude of London a pendulum which is a 

 trifle more than thirty-nine inches in length swings once in a 

 second, it is evident that, by lengthening or shortening the Pen- 

 dulum, we have the rate of the clock entirely under command. 



For example, if a Pendulum be required to swing once in 



