34 i 



then see how far it was .supported by observation. Of course, if 

 these two were at variance, something must be wrong with one 

 or tlie other; but the fact, whatever it might be, remained the 

 s.,i The theory upon which he had been working was that 



of sympathetic ivrations, which certainly appeared capable of 

 application to most of the phenomena of sound, heat, light, and 

 electricity, and might reasonably be held also to apply to some 

 of the obscure problems of psychology. The vibrations which we 

 appreciate as sound, being from their comparative slowness easier 

 to understand and to demonstrate than those of light, were taken 

 by the lecturer as an illustration of the theory referred to. It 

 was to be remembered that the pitch of a sound depended upon 

 the length of the wave, and that its loudness increased with the 

 height — e.g. the note middle C was the result of 256 double 

 vibrations per second, and no matter how this number of vibra- 

 tions was produced, whether by a siren, a tuning-fork, a string, 

 by the tapping of a card upon the cogs of a revolving wheel, 

 or by any other method, the note C would be heard. If a string 

 tuned to give out this number of vibrations had a tuning-fork of 

 the same pitch sounded near it, the string would at once respond, 

 and, being set in vibration, would as a matter of course give out 

 a similar sound. This was what was meant by sympathetic 

 vibration. In accordance with this theory it was understood that 

 the rods of Corti in the cochlea of the human ear were each 

 responsive to their special sounds, and it was further assumed 

 that the more delicate rods of the retina were similarly responsive 

 to the more subtle vibrations of light, the vibrations so excited 

 being conveyed by the auditory and optic nerves respectively to 

 tli^ sensorium, and there interpreted as sound and light. In the 

 case <>f light it was shown that interpretation played a large part, 

 ami that many well-known illusions were neither optical nor 

 ocular, but purely mental — the impression of increased diameter 

 ol ill*- sun and moon when near the horizon, which was common 

 to many people, being cited as a familiar instance. Illustrations 

 were also given to show that the range of sound and of colour 

 appreciable by the human ear and eye was limited; but there 

 was every probability that there were vibrations beyond the 

 eon pass of our physical capacity to appreciate, and it might 

 fairly be assumed that it was quite possible that the more delicate 

 organisation of insects would be capable of appreciating sounds 



