WAVE-ACTION IN NATURE. 7 



Toepler caught the air-waves on the instant, and got a glimpse of their 

 circular, and even their shaded aspect. 



We have said that "the difference between noise and music is, that 

 in noise the waves strike the ear irregularly, while in music they are 

 regular, and so rapid as to blend together. Any sound which becomes 

 continuous by rapid periodic strokes is said to be musical. " If a watch, 

 for example, could be caused to tick with sufficient rapidity say one 

 hundred times a second the ticks would lose their individuality, and 

 blend to a musical tone. And, if the strokes of a pigeon's wings could 

 be accomplished at the same rate, the progress of the bird through 

 the air would be accompanied by music. In the humming-bird, the 

 necessary rapidity is attained ; and, when we pass on from birds to 

 insects, where the vibrations are more rapid, we have a musical note 

 as the oi'dinary accompaniment of the insect's flight." 



Sounds vary in pitch, and the pitch depends upon the rate of vibra- 

 tion. The greater the number of vibrations in a second, the shorter 

 and quicker are the waves, and the higher the tone. It has been de- 

 termined, in various ways, exactly how many vibrations there are in 



Fig. 6. 



a a 



Constitution of Ate-Waves 



each musical note. Savart employed a toothed wheel, which could be 

 set in motion at any desired rate of speed, and which had attached a 

 small recording apparatus that gave the number of revolutions in a 

 second. Fig. 7 represents the mechanism, and the mode of using it. 

 While the wheel is in revolution, a thin visiting-card, or a piece of 

 pasteboard, is held against its toothed edge. The card is bent a little 

 by each tooth, as it goes by, and springs back to its first position as 

 soon as it is released. When the wheel is turned slowly, there is heard 

 only a succession of taps, distinctly separable one from another; but, as 

 the rapidity of the rotations increases, the number of strokes increases 

 also, and they soon unite to form a musical sound, while, exactly as 

 the motion is accelerated, the sound rises in pitch. In this way it is 

 possible to count the number of vibrations in producing every note in 

 the musical scale. 



