82 



ox THE PHYSIOLOGICAL CAUSES OF 



fork, by touching it for a moment with a finger, and the 

 second will continue the tone. The second will then 

 bring the first into vibration, and so on. 



But if a very small piece of wax be attached to the 

 ends of one of the forks, whereby its pitch will be 

 rendered scarcely perceptibly lower than the other, the 

 sympathetic vibration of the second fork ceases, because 

 the times of oscillation are no longer the same in each. 

 The blows which the waves of air excited by the first 

 inflict upon the sounding board of the second fork, are 

 indeed for a time in the same direction as the motions of 



Fio. 7. 



the second fork, and consequently increase the latter, 

 but after a very short time they cease to be so, and 

 consequently destroy the slight motion which they had 

 previously excited. 



Lighter and more mobile elastic bodies, as for example 

 strings, can be set in motion by a much smaller number 

 of aerial impulses. Hence they can be set in sympathetic 

 motion much more easily than tuning forks, and by 

 means of a musical tone which is far less accurately in 

 unison with themselves. 



