500 STUDIES IN ADVANCED PHYSIOLOGY. 



the pitch being higher the shorter the tongue. In the case 

 of stringed instruments the pitch depends upon the tight- 

 ness with which the string is stretched, as well as upon the 

 length of the string. In the tuning of a violin, for instance, 

 the pitch of the string is first determined by the tightness, 

 and after that, the pitch is varied by shortening the length 

 of the string in definite proportions by placing the finger 

 upon the same. 



3. The Quality of Sounds. If in the same room a 

 note should be sounded by each of a half dozen instruments 

 and the intensity and pitch of this note be made as nearly 

 the same as possible, the ear could nevertheless distinguish 

 without the least difficulty between the sounds produced by 

 the violin, the piano, the horn, the organ, or the human 

 voice. This property of a sound by means of which, even 

 when pitch and intensity are the same, we are able to make 

 these very definite distinctions is called the quality of a 

 sound. There are, therefore, as many different qualities 

 as there are kinds of sounds. Even in the case of human 

 beings nearly every voice has its own quality and we are 

 able to recognize an individual very readily by his voice. 

 The question now arises what the physical basis for the dis- 

 tinctions is. 



This is not so easily made clear without having at one's 

 disposal a more detailed knowledge of harmonics than can 

 be assumed in this discussion. A few hints or suggestions, 

 however, as to its explanation may be helpful. If we pic- 

 ture to ourselves sound waves in the form of water waves, 

 it is evident that the height of a wave represents the loud- 

 ness of the sound, and the length of the wave; that is, the 

 distance from the crest of one wave to the crest of the next 

 one, represents the pitch. Now, in this analogy the form 

 of the wave determines the quality of it. Every one who 

 has been at the lakeside or at the seashore, or, still better, 

 far out on the ocean, must have been struck with the variety 

 of the forms of waves from the gentle, undulating swell with 



