74 ON TEE PHYSIOLOGICAL CAUSES OF 



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

 which leave the membrane at d and are reinserted at e, reach- 

 ing 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 them through the holes near c. The 

 transverse fibres g, h, i, k, and the cells o, also appear to belong 

 to the nervous system. There are about three thousand arches 

 similar to d e, lying orderly beside each other, like the keys of 

 a piano in the whole length of the partition of the cochlea. 



In the so-called vestibulum, also, where the nerves expand 

 upon little membranous bags swimming in water, elastic appen- 

 dages, similar to stiff hairs, have been lately discovered at the 

 ends of the nerves. The anatomical arrangement of these 

 appendages leaves scarcely any room, to doubt that they are set 

 into sympathetic vibration by the waves of sound which are 

 conducted through the ear. Now if we venture to conjecture 

 it is at present only a conjecture, but after careful considera- 

 tion I am led to think it very probable that every such 

 appendage is tuned to a certain tone like the strings of a piano, 

 then the recent experiment with a piano shows you that when 

 (and only when) that tone is sounded the corresponding hair- 

 like appendage may vibrate, and the corresponding nerve-fibre 

 experience a sensation, so that the presence of each single such 

 tone in the midst of a whole confusion of tones must be in- 

 dicated by the corresponding sensation. 



Experience then shows us that the ear really possesses the 

 power of analysing waves of air into their elementary forms. 



By compound motions of the air, we have hitherto meant 

 such as have been caused by the simultaneous vibration of 

 several elastic bodies. Now, since the forms of the waves of 

 sound of different musical instniments are different, there is 

 room to suppose that the kind of vibration excited in the pas- 

 sages of the ear by one such tone will be exactly the same as 

 the kind of vibration which in another case is there excited by 

 two or more instruments sounded together. If the ear analyses 

 the motion into its elements in the latter case, it cannot well 



