Prof. A. M. Mayer's Researches in Acoustics. 273 



seut through each of the fibres to its respective fork. Thus 

 each fibre trausmits to its fork the same composite vibratory 

 motion, while each fork can only vibrate so as to give the 

 simple pendulum-vibration of a simple sound; for each fibre is 

 attached to its fork at a point which lies in the upper node of 

 the segments into which the fork divides when it gives its 

 higher harmonic. Now, if Fourier's theorem has " an existence 

 essentially real," any fork will select from the composite vibra- 

 tory motion which is transmitted to it that motion which it 

 has when it freely vibrates ; but if its proper vibration does not 

 exist as a component of the resultant motion of the membrane, 

 it will not be in the least affected. Now this is exactly what 

 happens in our experiment ; for when the pipe is in tune with 

 the harmonic series of forks, the latter sing out when the mem- 

 brane is vibrated \ but if the forks be even slightly thrown out 

 of tune with the membrane, either by loading them or by alter- 

 ing the length of the reed, they remain silent when the sounding- 

 pipe agitates the membrane and the connecting fibres*. Thus 

 have I shown that the dynamic application of Fourier's theorem 

 has " an existence essentially real/'' 



It is indeed very interesting and instructive thus to observe 

 in one experiment the analysis and synthesis of a composite 

 sound. On sounding the reed it sets in vibration all the forks 

 of the harmonic series of its fundamental note ; and after the 

 reed has ceased to sound, the forks continue to vibrate, and 

 their elementary simple sounds blend into a note which approxi- 

 mately reproduces the timbre of the reed-pipe. If we could by 

 any means obtain all of the elementary vibrations and have them 

 with their relative intensities correctly preserved, we should have 

 an echo of the sound of the reed after the latter had ceased to 

 vibrate ; but the impossibility of thus obtaining the highest com- 

 ponents of the reed, and the difficulty of reproducing the relative 

 intensities of the harmonics in the covibrating forks, allow us 

 but partially to accomplish this effect. 



2. An Experimental Illustration of Helmholtz's Hypothesis of 



Audition. 



The experiment which we have just described beautifully illus- 

 trates the hypothesis of audition framed by Helmholtz to account 

 for this, among other facts — that the ear can decompose a 

 composite sound into its sonorous elements. Helmholtz founds 

 his hypothesis on the supposition that the rods of Corti, in the 

 ductus cochlearis, are bodies which covibratc to simple sounds — 



* See section 5 of this paper for an account of the degree of precision 

 of this method of sonorous analysis. 



Phil. Mag. S. 4. Vol. 48. No. 318. Oct. 1874. T 



