Chap, iv.] HEARING. 1001 



than to the auditory epithelium. And the condition of the 

 tympanal apparatus as affected by disease will determine the 

 relative appreciation of low or high tones ; in certain states of 

 the tympanum the ear becomes unusually sensitive to high notes ; 

 an instance of this is seen in the paralysis of the stapedius 

 muscle due to injury or disease of the seventh nerve. 



§ 622. We dwelt, in speaking of vision, on our power of 

 appreciating differences of brightness or luminosity ; we have 

 a similar power of appreciating differences in loudness ; and 

 that relation between differences in the intensity of the stimulus 

 and differences in the intensity of the sensation, which we spoke 

 of as Weber's law (§ 550), holds good for hearing as well as 

 for vision. 



The power of distinguishing difference of pitch, the power 

 of recognizing 1 the difference between two notes of different 

 pitch, and the appreciation of the qualities of various musical 

 sounds which is built up on this, may in a general way be com- 

 pared to acuteness of colour vision. It is, however, very differ- 

 ent from that in many respects, and varies much more widely 

 than does that. As is well known the difference in this power 

 between different individuals, according as they have or have 

 not a ' musical ear,' is very great. Some persons, even though 

 fairly sensitive to differences of loudness, are unable to distin- 

 guish two notes differing considerably in wave-length. On the 

 other hand a well-trained ear can distinguish the difference of a 

 single or even of a half vibration a second, and that through a 

 long range of notes. As might be expected the power of ap- 

 preciating difference of pitch is not the same for all audible 

 notes. The range of an ordinary appreciation of tones lies 

 between 40 and 4000 vibrations a second, i.e. between the 

 lowest bass C (Cj 33 vibrations) and the highest treble C (C 5 

 4224 vibrations) of the piano ; tones above and below these, 

 even though audible, are distinguished from each other with 

 great difficulty. The power of recognizing, and being able to 

 name, a note when heard, is an extension of and based upon 

 this power of recognizing differences of pitch, though not by 

 itself exactly the same thing. 



§ 623. We said, in speaking of vision (§ 551), that, prob- 

 ably, several undulations falling in succession upon the retina 

 were necessary for the development of a visual sensation. In 

 like manner, in order that a distinct sensation of a musical 

 sound may be developed, several, or at least more than one 

 wave of sound must fall on the ear. The various observers 

 are not agreed as to the lower limit of the number of vibra- 

 tions necessary in order that the affection of consciousness 

 may take the form of a definite musical sound: some place 

 it at five, others higher, while it has been asserted that two 

 vibrations are sufficient. When the vibrations are thus lim- 



