842 



SCIENCE 



[N. S. Vol. XXVII. No. 700 



position, Helmholtz was met by an apparent 

 anachronism. The musical scale, identical 

 with the modern musical scale in all essen- 

 tials, antedated by its use in single part 

 melody the invention of chordal composi- 

 tion, or, as Helmholtz expressed it, pre- 

 ceded all experience of musical harmony. 

 In seeking an explanation of this early in- 

 vention of the musical scale Helmholtz 

 abandoned his most notable contribution, 

 and relegated his explanation of harmony 

 and discord to the minor service of ex- 

 plaining a fortunate, though, of course, an 

 important use of an already invented sys- 

 tem of musical notes. The explanation of 

 the original invention of the musical scale 

 and its use in single-part music through 

 the classical and the early Christian eras, 

 he sought for in purely esthetic considera- 

 tions—in exactly those devices from which 

 he had just succeeded in rescuing the ex- 

 planation of harmony and discord. 



The human ear consists of three parts — 

 in the nomenclature of anatomy— of the 

 outer, middle and inner ear. The outer 

 and inner ears are connected by a series 

 of three small bones traversing the middle 

 ear and transmitting the vibrations of 

 sound. The inner ear is a peculiarly 

 shaped cavity in one of the hard bones of 

 the skull. That part of the cavity with 

 which we are here concerned is a long 

 spiral passage called from its resemblance 

 to the interior of a snail shell, the cochlea. 

 The cavity has two windows which are 

 closed 'by membranes. It is to the upper- 

 most of these membranes that the train of 

 three small bones reaching from the drum 

 of the outer ear is attached at its inner 

 end. It is to this upper membrane, there- 

 fore, that the vibration is communicated, 

 and through it the vibration reaches the 

 fluid which fills the inner cavity. As the 

 membrane covering the upper window 

 vibrates, the membrane covering the lower 

 window yielding also vibrates, and the mo- 



tion of the fluid is in the nature of a slight 

 displacement from one to the other win- 

 dow, to and fro. From between these 

 windows a diaphragm, dividing the passage- 

 way, extends almost the whole length of 

 the cochlea. This diaphragm is composed 

 in part of a great num^ber of very fine 

 fibers stretched side by side, transverse to 

 the cochlea, and called after their dis- 

 coverer, fibers of Corti. On this dia- 

 phragm terminate the component fibers of 

 the auditory nerve. When the liquid 

 vibrates the fibers vibrate in unison, the 

 nerve terminals are stimulated, and thus 

 the sensation of sound is produced. These 

 fibers of Corti are of different lengths and 

 presumably are stretched with different 

 tensions. They therefore have different 

 natural rates of vibration and a sym- 

 pathetic resonance for different notes. 

 The whole has been called a harp of several 

 thousand strings. 



Were these fibers of Corti very free in 

 their vibration, each would respond to and 

 would respond strongly only to that par- 

 ticular note with whose frequency it is in 

 unison. Because of the fact that they are 

 in a liquid, and possibly also because of 

 the manner of their terminal connections, 

 they are considerably damped. Because 

 of this their response is both less in amount 

 and less selective in character. In fact, 

 under these conditions not one, but many 

 fibers vibrate in response to a single pure 

 note. A considerable length or area of 

 the diaphragm is excited. So long as the 

 exciting sound remains pure in quality, 

 constant in pitch and constant in intensity, 

 the area of the diaphragm affected and the 

 amplitude of its vibration remain un- 

 changed. If, however, two notes are 

 sounded of nearly the same pitch, the areas 

 of the diaphragm affected by the two notes 

 overlap. In the overlapping region the 

 vibration is violent when the two notes are 

 in the same phase, weak when they are- 



