A NEW THEORY OF HEARING. 331 



successive region of the membrane and adjoining fluids 

 throughout the whole length of the spiral. 



This disturbance I will call a wave, in spite of its 

 difference from any other known kind of wave in the 

 following respect, viz., the potential energy is that of fibres 

 stretched at right angles to the direction of transmission, 

 and the kinetic energy is that of moving fluids ; while in 

 other waves the kinetic and potential energy consist in 

 movement and stress of one and the same medium. The 

 inertia of the fibres in the basilar is here insignificant 

 while in the vibrating string of a fiddle or of a cord thrown 

 into waves, or of a solid, liquid or gas transmitting a 

 sound wave or of the water in an oceanic wave the inertia 

 is all-important. Expressed in another way the whole of 

 the kinetic energy of this wave is in the fluids ; the whole 

 of its potential energy is in the membrane. The kinetic 

 and the potential are equal, and the whole energy of the 

 wave remains constant throughout its transmission, save for 

 a portion, which must be very small, and which is converted 

 by internal friction into heat or other disturbances. 



Two important questions now arise which are intimately 

 connected with each other ; they are : — 



(a) What is the extent or amplitude of displacement 

 of each part of the membrane? and (b) what is the velocity 

 of transmission of the wave? Neither question admits 

 of a very definite answer but it is important to give a 

 partial answer to both. 



The spiral canals of the cochlea are not of uniform 

 width throughout, but are much narrower in the apical 

 than in the basal region. Suppose for a moment, what 

 is not true, that the basilar membrane is of uniform 

 width ; then the wave in passing from the wider to the 

 narrower part of the canal would gain in amplitude : for 

 at each successive level the volume of fluid to be moved 



