A NEW THEOEY OF HEAB1NG. 337 



and then down the Reissnerian to the position of the 

 first wave, is the distance which has been travelled by 

 the first wave since it was in the position now occupied 

 by the second ; i.e. it is the distance travelled by the first 

 wave in the interval of time between the first and the 

 second. This distance thus depends entirely upon the 

 time-interval between the two waves. As the time- 

 interval between the two determines the pitch of the 

 tone-sensation produced by them (as shown by Kohl- 

 rausch's experiment referred to above) it is correct to say 

 that if a note be sounded consisting of two vibrations only 

 (in the absolute sense) then the point in the organ of 

 Corti where the two cochlear waves pass each other will 

 depend wholly upon the pitch of the note. In other 

 words, there is in the organ of Corti for each pitch a 

 definite point where this passing will occur. We shall 

 later see that though there is only one such point when 

 only two vibrations are produced, there may be a larger 

 number when more than two are produced. 



(2) The effect on the Organ of Corti and associated 

 structures produced by the simultaneous action of these 

 two waves may be most easily grasped by the mind by 

 consideration of a transverse section of the middle canal 

 at this level. First both upper and lower membranes are 

 motionless and the fluids are at rest. Then the two are 

 simultaneously drawn or forced apart, and coming to rest 

 for a moment then move suddenly towards each other 

 driving the fluid out of this region in both directions. 

 A more accurate idea may be obtained from consideration 

 of a longitudinal section through the mid-line of the two 

 membranes in this region. 



Figures 3, 4 and 5 represent three phases of the passing 

 of two such waves. They will be more easily understood 

 if compared with figures 1 and 2. The large arrows above 



