346 TEANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



That one wave may intensify the disturbance in the 

 relative positions of tectorial membrane and sensory hairs 

 produced by another wave, the two must coincide with 

 each other in phase in some part of the wave. Of course 

 if they be of unequal length they cannot coincide in all 

 parts. It would take us too far to consider the question 

 as to whether two series of sound-waves of simply-related 

 periods do tend to arrange themselves in a definite way 

 with relation to each other or not, and if so what that 

 relative position is. Fortunately we need not consider it, 

 for a study of the effects of combination of the waves due 

 to two tones in harmony with each other by simple 

 graphic methods shows that, however, they be combined 

 the combination will lead either to prolongation of the 

 period of advance of the two membranes towards each 

 other at the level of passing of the waves of either series 

 or to acceleration of the advance. Either of these effects 

 will lead alike to the augmentation of the relative move- 

 ment of tectoria and sense-hairs, at that point. Sounding 

 of two tones in perfect harmony with each other will 

 thus produce a slightly greater effect at each of the two 

 passing-points in the cochlea than the sounding of either 

 of the two alone. 



An effect differing from this, so far as the sensation is 

 concerned, may be produced at one or more other points. 

 Let the two notes be c' and g' {i.e., the middle c of the 

 pianoforte and its fifth) and let the musical interval 

 between them be a true fifth, i.e., let the ratio of the 

 numbers of their vibrations be as 2 : 3. 



Then the points of the organ of Corti stimulated in the 

 way described will be the points called (in accordance 

 with the simple nomenclature I have suggested) c' and 



g' or c' and -=-. The series of waves c' pass in corres- 



