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 ..its 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. in. 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- 



