102 HABIT AND INTELLIOENCE. - [chaf. 



vibratiou are the same in all bodies whatever ; but vibrat- 

 ing strings exemplify those laws in their greatest sim- 

 plicity and in the most manageable form, for which reason 

 it is best, in treating of elementary acoustics, to speak 

 Olio string of strings only. If two strings have the same period of 

 another vibration, and one of these is set vibrating, the sonorous 

 vibrating, vibrations produced by it will set the other string vibrating 

 in unison : from the analogy of the case, and from the won- 

 derful way in which the auditory nerve-fibres in " Corti's 

 organ" are stretched like the strings of a violin across a 

 Action of bridge, we have every reason to believe that those nerves 

 the'uerTes ^^'^ ^^^^'^ Sympathetically vibrating strings. Every sound 

 of the ear. vvMch enters the cavity of the ear sets in vibration that 

 nerve which is strung to its own pitch, and its vibrations 

 produce in the auditory ganglia the sensation of sound. 



It ought to be stated that this theory is not offered as a 

 demonstrated truth, but only as' having a very high degree 

 of analogical probability. It is not easy to see any way 

 in which it could be experimentally verified. 

 Tone of I have next to speak of the tone of sounds, which is 



'^"""'^ ■ a more complex fact than their pitch. The physical theory 

 of tone may thus be stated in outline : — The tone of a 

 how sound is produced by the union of secondary sonorous 



produced, -^^^ygg^ qj, overtones, with the primary sonorous wave, or 

 fundamental. When the fundamental is not accompanied 

 by any overtones, its soimd is soft and dull, as that of 

 a timing-fork.^ But such sounds are very unusual : there 

 are overtones in nearly all sounds. Consequently, neaii}^ 

 all sounds are not simple but complex sounds. The over- 

 tones are of higher pitch than the fundamental. Tlie 

 pitch of the fundamental is what defines the pitch of the 

 complex sound. A fundamental may be accompanied by 

 many overtones. In a word, the tone of a sound is due 

 to the combination of secondary sonorous vibrations with 

 the fundamental. The secondary sonorous vibrations are 

 of course due to the production of secondary vibrations 

 in the musical string or other sonorous body. 



But now a question arises. How is any such thing pos- 



^ Tj'udall's Lectures ou Sound. 



