THE SENSE OF HEARING. 169 



with which alone the sensation of sound — the highest possible — consists; this 

 npper limit of the scale of sounds is not accurately ascertained, because with 

 different organs of hearing it is now higher, now lower. It is held, however, 

 that a sensation of sound no longer arises when the number of vibrations ex- 

 ceeds 64,000 in a second. This fact is well suited to show that sound exists 

 not without, originates not in, the vibrating sti'ing, but in our own sensation ; 

 eise were it difficult to see why, with a certain lowest and highest number of 

 vibrations, the laws of movement remaining wholly unchanged, this movement 

 should lose the property of sound. Very conceivable is it, on the other hand, 

 that the auditory nerve ceases to react when the vibrations which strike it fol- 

 low one another too slowly or too rapidly. An exact physiological explanation 

 of this restriction of the irritability of the auditory nerve to certain limits it is 

 not ill our power to give ; but it is interesting to observe that there is yet an- 

 other nerve of sense which affords a complete analogy to this state of relations — 

 the nerve, namely, of vision. As the nerve of hearing is excited by the waves 

 of sound, propagated to it from solid and fluid matter, so is the optic nerve ex- 

 cited by the v/aves of the luminous ether, which are subject to the same general 

 laws of undulatory movement. As waves of sound of different frequency produce 

 an impression of different qualities of the sensation of sound or a different pitch 

 of tone, so waves of light of different frequency give rise to perceptions of differ- 

 ent color, but, as in the case of the auditory nerve, only within certain limits of 

 rapidity. If more than 697,000,000,000 or less than 439,000,000.000 of vibra- 

 tions of the luminous ether follow one another in a second, the optic nerve is 

 insensible of any impression, even when the vibrations undoubtedly reach it. 

 Between the limits above assigned for the sense of hearing lies an endless series 

 of differently qualified sensations, every possible number of vibrations between 

 16,000 and 64,000 producing a modification of quality — a sound of definite 

 pitch. Yet we mean not thereby to say that our faculty of discrimination 

 among these different qualities is itself unlimited, or, in other words, that we 

 are conscious of a difference of quality in the sensation when two undulations 

 of different rapidity strike the ear near or after one another, how small soever 

 the difference may be. On the contrary, it is a fact easily substantiated 

 that most men have originally but " a poor ear," but that, through use, a tolera- 

 bly high degree of delicacy of hearing is attainable ; thus, while many scarcely 

 recognize two sounds as of different pitch, one of which is produced by 800, the 

 other by 810 vibrations in a second, there are musicians who seize the differ- 

 ence with accuracy, and distinguish the higher from the deeper tone when the 

 number of vibrations is 1,200 in the one, 1,201 in the other. The auditory 

 uerve, or, more properly, the organ of sensation on which it operates, is in this 

 respect subject to the same conditions with the rest of the organs of sense, being 

 susceptible, through judicious and attentive use, of improvement in its perform- 

 ance, and specially in its faculty of discriminating between sensations of differ- 

 ent quality. 



A highly interesting question, but one which unfortunately has set at naught 

 every attempt at explanation, arises out of the fact that we can perceive simul- 

 taneously a great niimber of sounds together, and distinguish the pitch, tone, 

 and strength of each of them. The harmonious association of different sounds may 

 often seem to the uninitiated a chaos, from which he is unable to distinguish the 

 individual members, while to the musically cultivated it is no difficult matter to 

 disentangle from the fullest instrumental or vocal orchestra each sound signal- 

 ized by a special pitch or tone, to follow the melody through all its inflections, 

 and clearly perceive all the transitions ; but even the laity know from experi- 

 ence that it is possible to single out an individual voice from the buzz of a com- 

 pany all speaking together. The art consists only in fixing the attention in- 

 flexibly on the tone or modulation which we desire to separate from the rest, 

 and in this respect also use refines and strengthens the discriminative fliculty of 



