STIMULI APPROPRIATE FOR THE ORGAN OF HEARING 491 



C. TIMBRE 



If the same tone be struck successively on different instruments, as the 

 violin, piano, clarinet, flute, etc., even a musically untrained ear can readily 

 distinguish the instruments. This property of a musical tone which differs 

 with the instrument producing it is described as the timbre or quality. It is 

 this property also by which we distinguish human voices. 



Inasmuch as the cause of timbre cannot lie in the frequency nor the 

 amplitude of the vibrations, it must be referred to dissimilarities in their 

 form. To a certain extent also it is due to the way in which the tone is 

 struck. 



How is this difference in form of the vibration to be explained? When 

 a piano string is set in vibration the pitch of the tone produced depends upon 

 two things: the length of the part vibrating, and the tension of the string. 

 The tension remaining the same, the longer the vibrating part the deeper the 

 pitch. If the operator touch the middle of a string lightly with his finger 

 and then cause it to vibrate, each half will vibrate independently and so 

 twice as many vibrations per second are made as by the whole string. The 

 tone produced is therefore the octave of the tone given by the whole string. 

 In the same way a string can be caused to vibrate in thirds and fourths, etc., 

 and the number of vibrations of the corresponding tone will then be three, 

 four, etc., times as high as that of the whole string. 



Now whenever the string vibrates as a whole, it divides itself spontane- 

 ously into two, three, four, five, etc., vibrating parts. Hence, it gives in 

 addition to its fundamental tone other tones whose vibration frequencies are 

 two, three, etc., times as great as the fundamental, all of them fused into 

 the peculiar sound of that particular string. The tones produced by the 

 partial vibrations of the string are called the overtones or partial tones, and 

 when the vibration frequency of the overtones is a multiple of that of the 

 fundamental, they are called harmonious overtones. The .harmonious over- 

 tones for c are given in the following example: 



+* jo. ^ 



What has been said of the piano string is true for musical instruments 

 in general, inclusive of the human voice. But there are sounds which are 

 fairly free of overtones and so consist of a simple tone only as, e. g., the 

 proper sound of a tuning fork. Such tones are unusually soft, and free from 

 sharpness or roughness. Comparing the timbre of a simple tone with that 

 of a compound tone, including its lower harmonious overtones, the latter is 

 found to be fuller sounding, more metallic and brighter than the simple tone. 



Since by far the greater number of tones are compound it is evident that 

 any variation in the number or intensity of the overtones will produce some 

 difference in the character of the tone; hence we may point to differences 



