THE SENSES. 193 



sensible to the brain the various musical notes and tones, one of them 

 answering to one tone, and one to another; while perhaps the other parts 

 of the organ of hearing discriminate between the intensities of different 

 sounds, rather than their qualities. 



"In the cochlea we have to do with a series of apparatus adapted for 

 performing sympathetic vibrations with wonderful exactness. We have 

 here before us a musical instrument which is designed, not to create 

 musical sounds, but to render them perceptible, and which is similar 

 in construction to artificial musical instruments, but which far surpasses 

 them in the delicacy as well as the simplicity of its execution. For, while 

 in a piano every string must have a separate hammer by means of which 

 it is sounded, the ear possesses a single hammer of an ingenious form in its 

 ear-bones, which can make every string of the organ of Corti sound sepa- 

 rately." (Bernstein.) 



About 3000 rods of Corti are present in the human ear; this would 

 give about 400 to each of the seven octaves which are within the compass 

 of the ear. Thus about 32 would go to each semi-tone. Weber asserts 

 that accomplished musicians can appreciate differences in pitch as small 

 as -g^h of a tone. Thus on the theory above advanced, the delicacy of 

 discrimination would, in this case, appear to have reached its limits. 



Sensibility of the Auditory Nerve. Any elastic body, e.g., air, a 

 membrane, or a string performing a certain number of regular vibrations 

 in the second, gives rise to what is termed a musical sound or tone. We 

 must, however, distinguish between a musical sound and a mere noise; 

 the latter being due to irregular vibrations. 



Qualities of Musical Sound. Musical sounds are distinguished 

 from each other by three qualities. 1. Strength or intensity, which is 

 due to the amplitude or length of the vibrations. 2. Pitch, which de- 

 pends upon the number of vibrations in a second. 3. Quality, Color, or 

 Timbre. It is by this property that we distinguish the same note sounded 

 on two instruments, e.g., a piano and a flute. It has been proved by 

 Helmholtz to depend on the number of secondary notes, termed har- 

 monics, which are present with the predominating or fundamental tone. 



It would appear that two impulses, which are equivalent to four single 

 or half vibrations, are sufficient to produce a definite note, audible as 

 such through the auditory nerve. The note produced by the shocks of 

 the teeth of a revolving wheel, at regular intervals upon a solid body, is 

 still heard when the teeth of the wheel are removed in succession, until 

 two only are left; the second produced by the impulse of these two teeth 

 has still the same definite value in the scale of music. 



The maximum and minimum of the intervals of successive impulses 



still appreciable through the auditory nerve as determinate sounds, have 



been determined by M. Savart. If their intensity is sufficiently great, 



sounds are still audible which result from the succession of 48,000 half 



VOL. II. 13. 



