402 
TRANSMISSION OF SONOROUS VIBRATIONS. 
them to the air, producing in it a series of undulations or 
waves, by which the sound is conveyed to a great distance. 
These undulations spread more widely* as they become more 
distant from the sounding body, just like the ripples produced 
on the surface of the water when we throw a stone into it; 
and in proportion as they spread, they become less powerful. 
This is the reason why Sound becomes less intense as the 
sounding body is more distant. Although air is the usual 
conducting medium for the sonorous undulations, liquids or 
solids may answer the same purpose. Thus if a person hold 
his head under water, whilst two stones are struck together, 
also under water, even at a considerable distance, he will hear 
the sound produced by the blow with extreme distinctness, 
and even with painful force. Or if the ear be laid against 
one end of a long piece of timber, whilst a scratch with a pin 
be made on the other, or a watch be laid upon it, even the 
faint sounds thus produced will be heard very distinctly. 
That a medium of some kind is necessary to convey the 
sonorous vibrations, is proved by the fact, that if a bell be 
made to ring in the receiver of an air-pump from which the air 
has been exhausted, no sound is heard, though Jts ringing 
becomes audible as soon as the air is allowed to re-enter. 
511. It. is a fact of much importance, in regard to the 
action of the organ of Hearing, that sonorous vibrations which 
have been excited and are being transmitted in a medium of 
one kind, are not imparted with the same readiness to others. 
The following conclusions have been drawn from experi¬ 
mental inquiries on this subject. I. Vibrations excited in 
solid bodies may be transmitted to water without much loss 
of their intensity, although not with the same readiness that 
they would be communicated to another solid, n. On the 
other hand, vibrations excited in water lose something of 
their intensity in being propagated to solids; but they are 
returned, as it were, by these solids to the liquid, so that the 
sound is more loudly heard in the neighbourhood of those 
bodies, than it would otherwise have been. hi. The sonorous 
vibrations of solid bodies are much more weakened by trans¬ 
mission to air; and those of air make but little.impression 
on solids, iv. Lastly, sonorous vibrations in water are trans¬ 
mitted but feebly to air; and those which are taking place in 
air are with difficulty communicated to water; but the com- 
