HARMONY IN MUSIC. 83 



Now, then, if several tones are sounded in the neigh- 

 bourhood of a pianoforte, no string can be set in sym- 

 pathetic vibration unless it is in unison with one of those 

 tones. For example, depress the forte pedal (thus raising 

 the dampers), and put paper riders on all the strings. 

 They will of course leap off when their strings are put in 

 vibration. Then let several voices or instruments sound 

 tones in the neighbourhood. All those riders, and only 

 those, will leap off which are placed upon strings that 

 correspond to tones of the same pitch as those sounded. 

 You perceive that a pianoforte is also capable of analysing 

 the wave confusion of the air into its elementary con- 

 stituents. 



The process which actually goes on in our ear is 

 probably very like that just described. Deep in the 

 petrous bone out of which the internal ear is hollowed, 

 lies a peculiar organ, the cochlea or snail shell — a cavity 

 filled with water, and so called from its resembLance to 

 the shell of a common garden snail. This spiral passage 

 is divided throughout its length into three sections, 

 upper, middle, and lower, by two membranes stretched 

 in the middle of its height. The Marchese Corti dis- 

 covered some very remarkable formations in the middle 

 section. They consist of innumerable plates, micro- 

 scopically small, and arranged orderly side by side, like 

 the keys of a piano. They are connected at one end with 

 the fibres of the auditory nerve, and at the other with 

 the stretched membrane. 



Fig. 8 shows this extraordinarily complicated arrange- 

 ment for a small part of the partition of the cochlea. The 

 arches which leave the membrane at d and are re-inserted 

 at e, reaching their greatest height between m and o, 

 are probably the parts which are suited for vibration. 

 They are spun round with innumerable fibrils, among 

 which some nerve fibres can be recognised, coming to 

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