On the Variety of Voices. 61 
the cause of that indefinite variety observable in the 
voices of men and the tones of sonorous bodies. 
The sounds which are constantly striking our ears, 
and with which we are alone acquainted, being prov- 
ed to be’ compounded of simple or elementary 
sounds, it may be safely concluded, that the vast 
variety of tones which prevails in the world, is solely 
occasioned by an union of simple sounds differing 
among themselves in acuteness, which, according to 
what has been shewn before, is the only distinguish- 
ing character they can possess, excepting loudness. 
It is evident from the preceding consideration, that 
every natural or ordinary tone consists of what is 
called in harmonics, an interval of sound; which is de- 
fined,* by writers on the science, to be a quantity ofa 
certain kind, terminated by a graver and an acuter 
sound, For, if tones be supposed to consist invari- 
ably of perfect simple unisons, the effect of any one 
aggregate on the ear would vary from that of any 
other in loudness and acuteness only, which being 
the characteristic of elementary sounds, it is clear 
that men are indebted to some other combination of 
these elements for their idea of the diversity in ques- 
tion. On the other hand, it is equally manifest that 
these intervals are not great; for, on the supposition 
of their being considerable, we should find no more 
difficulty in perceiving the terminating sounds pro. 
* Smith’s Harmonics, sect 1, art. 9. 
