SENSITIVE FLAMES, ETC. 193 



and firm foundation on which Kirchhoff's law now securely 

 rests. 



But supposing the vibration be not a simple but a 

 compound one, that is to say, the coalescence of many 

 and varied vibrations will such a complex or intricate 

 wave-form be able to set a body in motion ? It Can do so 

 by virtue of the fact that, however complex the wave-form 

 may be, it can be resolved into a series of simple pendular 

 vibrations. If a body can respond to one of the constituents 

 of the compound tones, a feeble resonance or sympathetic 

 vibration will be produced. Thus, if we take a bundle of 

 tuning-forks of different pitch, and sound them together, they 

 will generate by the coalescence of their sounds a compound 

 tone, which, falling upon a certain silent fork, will set that 

 fork into motion if the particular period of vibration of the 

 silent fork be found among the constituents of the com- 

 pound tone. That you have already seen in one form. It 

 would have been very evident to you if, instead of striking 

 one tuning-fork, I had struck twenty or thirty with notes 

 of different pitch. Only one of those forks would have been 

 concerned in setting the silent fork in motion namely, 

 that one which vibrated in exactly the same period as the 

 silent fork. Helmholtz has rendered it extremely probable 

 that this is the manner in which we are enabled to dis- 

 tinguish the mixed multitude of sounds in an orchestra. 

 A structure in our ears called Corti's arches, is attached to an 

 elastic membrane called the inembrana basilaris, the par- 

 ticular tension of which appears to tune these Corti's arches 

 so that they are capable of responding to notes of different 

 pitch. 



We have shown the effect of synchronism on the recep- 

 tion of sympathetic vibration, so that if we have a Corti's 

 arch capable of responding to a certain tone it will be 

 thrown into violent vibration by a corresponding note. 

 The neighbouring arches will be thrown into less vigorous 

 motion, and thus we may imagine these structures tuned, 

 as it were, to notes of different pitch, as, indeed, Helmholtz 

 has shown to be extremely probable. The investigations 

 of Mayer have shown that insects seem to possess an 

 analogous mode of hearing by the reception of vibrations 

 through filaments attached to their bodies. 



Now, so far we have seen the acceptance of vibration by 



VOL. II. O 



