HEARING. 417 



Water is the medium of sound to aquatic 

 animals, as the air is to terrestrial animals. 

 Sounds are, indeed, conveyed more quickly, and 

 to greater distances, in water than in air, on ac- 

 count of the greater elasticity of the constituent 

 particles of water, within the minute distance 

 required for their action in propagating sound. 

 Stones, struck together under water, are heard 

 at great distances by a person whose head is 

 under water. Franklin found by experiment 

 that sound, after travelhng above a mile through 

 water, loses but little of its intensity. According 

 to Chladni, the velocity of sound in water is 

 about 4900 feet in a second, or between four and 

 five times as great as it is in air. 



Solid bodies, especially such as are hard and 

 elastic, and of uniform substance, are also ex- 

 cellent conductors of sound. Of this we may 

 easily convince ourselves by applying the ear 

 to the end of a log of wood, or a long iron rod, 

 in which situation we shall hear very distinctly 

 the smallest scratch made with a pin at the 

 other end ; a sound, which, had it passed 

 through the air only, would not have been heard 

 at all. In like manner, a poker suspended by 

 two strings, the ends of which are applied to the 

 two ears, communicates to the organ, when struck, 

 vibrations which would never have been heard 

 under ordinary circumstances. It is said that 

 the hunters in North America, when desirous of 



VOL. II. E E 



