315 



ring under water, but produce a much graver sound than 

 in the air. 



1 That water also is a vehicle of sound, is proved by 

 the fact last mentioned, by the distinctness with which 

 the blows of workers around a diving-bell are heard 

 above, and by the fact that fishes hear very acutely.'* 



III. MOTION OF SOUND. 



1. Communication of sound through solids. 



Sound is communicated also through solids. The 

 vibrations move even with greater rapidity through a 

 solid substance ; the following are examples : 



';Children often suspend a pair of tongs or other metal- 

 lic substance by a string, the end of which is pressed 

 into the ear. The sound in this case, is heard much 

 more distinctly than usual, the vibrations being conveyed 

 by the solid fibres of the string. In the same manner 

 the scratch of a pin at one end of a log of wood is 

 directly heard by the ear applied at the other end', 

 although through the air it is not at all audible. Sava- 

 ges often discover the proximity of enemies, or of prey, 

 by applying an ear to the ground and hearing their tread. 

 The approach of horsemen at night is easily discovered 

 in the same way. The report of a cannon placed on 

 ice, is carried much farther by the ice than by the arr 

 around. In the military operation of mining, or cutting 

 away under ground, for the purpose of entering a citadel, 

 or blowing up fortifications, the approach of the enemy 

 is often discovered by the subterranean sound of the ' 

 pioneers' tools. The awful muttering of earthquakes is 

 merely the sound of subterranean explosions, conveyed 

 from amazing distances, by the solid earth. 



' The readiness with which solids receive and transmit 

 sounds, is further perceived in the fact, that a small 

 musical box while held in the hand, is scarcely audible, 

 but when pressed against a table or a door, will rival a 

 little harp. The vibration communicated from the box, 

 pervades the whole of the wood, and the extended surface 

 then acting on the air increases the effect. The con- 



* Arnott. 



