88 A. M. Mayer—Researches in Acoustics. 
The point of the membrane to which the fibers are attached 
is actuated by a motion which is the resultant of all of the 
elementary pendulum-vibrations existing in the composite 
sonorous wave, and the composite vibrations of this point are 
sent through each of the fibers to its respective fork. Thus, 
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 sound- 
ing pipe agitates the membrane and the connecting fibers.* 
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 approx!- 
mately reproduces the timbre of the reed-pipe. If we could by 
them with their relative intensities correctly preserved, we 
should have an echo of the sound of the reed after the latter had 
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 
illustrates the hypothesis of audition framed by Helmholtz to - 
account for this—among other facts,—that the ear can decom- 
pose a composite sound into its sonorous elements. Helmholtz 
* See section 4 of this paper for an account of the degree of precision of this 
method of sonorous analysis. ; 
* 
