246 PHYSIOLOGY CHAP. 



has been lost. These functional affections cannot be produced 

 artificially by partial destruction of the basilar membrane of the 

 cochlea, as would be the case according to Helmholtz' theory. 

 They can readily be explained if we assume with Ewald that the 

 vibratory power of the tectorial membrane is hindered in some 

 way as occurs experimentally, when his elastic membrane is 

 imperfect. 



The abnormal phenomenon of the so-called " acoustic lacunae " 

 or " islands " was considered to be direct evidence for the resonance 

 theory. But Ewald proves that it can be still more easily 

 explained by his theory. He actually found that some of his 

 artificial elastic membranes, of which certain portions were 

 defective, showed lacunae in the series of stationary waves that 

 arise when a tone is produced near them. 



In conclusion, therefore, it may be said that although the 

 theory of sound-images is still imperfect, it appears to meet all 

 the principal objections made to the resonance theory. 



XII. Having thus studied the mechanism by which the 

 physical phenomenon of sonorous vibrations is transformed into 

 the physiological excitation of the nerves and centres of hearing, 

 we must briefly consider the aesthetic or emotional side of acoustic 

 perceptions, on which the art of music is founded. 



Music excites our emotions not only by melody, that is, the 

 rhythmical succession of pleasing tones of varying duration, but 

 also by harmony, that is, the simultaneous emission of a number 

 of tones, chords, and intervals. 



Melody is not governed by definite rules ; it is a purely 

 intuitive art, belonging to the region of imagination. Innate in 

 man, it has gradually been evolved and perfected in historical 

 times, in a varying degree in different races and individuals, and 

 is only to a minimal extent founded on onomatopoeia or the 

 imitation of tones and sounds in nature. Harmony, on the 

 contrary, is the foundation of the art of music : while it is 

 the result of artistic experience, it is subject to the laws of 

 acoustics which are its scientific foundation. The ta^k of the 

 physiologist is to determine the relations between the physical 

 laws of sonorous vibrations and the aesthetic or emotional 

 characteristics of auditory perceptions. 



Starting from the note selected as the standard of the inter- 

 national pitch, a = 435 double vibrations, 870 single vibrations 

 (Vol. III. p. 148), and counting up all the tones above and below 

 this note that can be perceived by a musically trained ear, we 

 obtain an extensive series of gradually rising or falling notes, 

 each of which can be distinguished from the next higher or lower 

 note. The next highest note to the standard is represented by 

 435 '4 d.v., and the next lowest by 434*6. The entire octave, i.e. 

 the interval c 1 - c 2 , is divisible into more than 1200 tones which 



