SOUND AND MUSIC 77 



fro till they come to rest. The particles ordinarily being 

 a little separated from each other as the motions advance, 

 are driven on each other, and a condensation takes place, 

 then, as they recoil, there is a separation and rarefaction, 

 and this process is repeated, while the vibrations go on. 

 The particles are made to vibrate, not in a direction 

 transverse to the advancing wave, but in a line with it. 

 The condensations correspond to the crests of the waves 

 of the sea, and the rarefactions to the troughs. As the 

 waves of water rise till they reach the greatest height 

 and then begin to fall, so the particles advance till 

 they reach the greatest condensation and then begin 

 to rarefy. 



All material particles convey waves. They are forwarded 

 not by air only, but by hydrogen and all gases, water and 

 all liquids, stones, and the firmest solids, iron, and every 

 metal. Divers in the sea hear the waves dashing against 

 the shore. Every wave as it strikes the sand creates 

 innumerable motions in the air, the solid ground, and in 

 the water. Sound runs easily through the sea. A bell 

 weighing 800 Ib. was let down about 20 feet into 

 the sea through a well hole in a specially constructed 

 vessel, the clapper of the bell remaining under the 

 control of those on board the ship. When the bell was 

 struck it was plainly heard in the hold of another ship 

 a mile away. When it was replaced by a man and a 

 speaking trumpet, listeners could hear at a distance of 

 three miles. The earth carries sound. An ear put to it 

 will hear the tramp of infantry, the march of cavalry. 

 Sound waves pass also through stone walls, and along 

 iron rods. 



Waves are periodic and musical or non-periodic and 

 unmusical. The motions of the pendulum of a clock are 

 periodic. The times of its swinging to and fro are 



