On the Variety of Votces. 63 
cases which alone can be supposed adequate to the 
effect, have been separately examined, viz. a com- 
bination of perfect unisons, and of great and small 
intervals. The two first of these being rejected on 
sufficient reasons, the last is admitted of necessity to 
be the true cause of the subject under examination. 
The principles of the theory being now established, 
it is proper to say something, in the next place, on 
that part of the mechanism of sonorous bodies, by 
which the combination of elementary sounds is form- 
ed. It would be superfluous to treat this branch of 
the enquiry in a diffuse manner, a concise statement 
of the cause appearing sufficient to prove the coinci- 
dence of facts and the preceding conclusions. 
The mechanism in question which is capable of 
producing effects so diversified to sense, though so 
slightly discriminated in nature, depends on a prin- 
ciple that is easily understood. It is purely this: if a 
vibratory motion be imparted to any one of a sys- 
tem of elastic bodies that are connected together, the 
same is immediately communicated in a less degree 
‘to every body of the system, whose time of vibrating 
ascribes the whole effect to the force and celerity of the 
pulses of air striking the auditory organs, no regard being 
paid to the qualities in question; excepting that a greater 
degree of elasticity renders a body capable of sounding for. 
a longer time than one possessed of a less degree: hence a 
vessel of brass is more sonorous than one of wood both in 
in point of loudness and duration, 
