64 On the Variety of Voices. 
agrees nearly with that of the body first put in mo- 
tion. For instance, let two equal strings be stretch- 
ed on a frame, with degrees of tension that are near- 
ly equal but not perfectly so; then, if either of them 
be made to vibrate, the other will accompany it in 
so distinct a manner, that their joint tone is easily 
known from the sound of either of them taken 
singly. This plain experiment reconciles the theory 
to common observation, as it points out the method 
followed by nature in compounding ordinary- tones 
from elementary sounds; for not only all musical in- 
struments, but also the vocal organs of men and 
animals are complex machines, consisting of one par- 
ticular part intended for the production of sound, 
which is connected with many others necessary to 
render the whole perfect. Now, it is evident that 
such of these secondary members as are nearly in 
unison with the principal, must participate of all its 
motions, forming in conjunction with it a number of 
simple sounds, all of them contained in a narrow in- 
terval,* which is terminated by one of the number 
* A circumstance that must be known to the most super- 
ficial observer may be brought forward to corroborate what 
is here advanced. We frequently find ourselves at a loss 
to identify a voice at a distance, which is in other respects 
familiar. The reason of this difficulty appears to be, that 
the feebler sounds that enter into its composition are per= 
ceived by a person standing near the speaker, but being lost 
to the distant ear, the tone becomes simpler, and the hear= 
er’s judgment is perplexed, 
