WAVES 157 



of the deep ocean floor with the air which they must have. 

 Without it the water at great depths would have its air 

 exhausted and all life would be destroyed. 



At the surface of the ocean the temperature of the water 

 varies in a general way with the latitude; it is over 80 

 at the tropics and about the freezing point at the poles. 

 Near the poles and near the equator there is very little 

 variation in the temperature of the surface water during 

 the year, but in the intermediate latitudes the annual 

 variation is considerable. Below the surface the effect 

 of solar heat rapidly diminishes and at a depth of 300 ft. 

 it is probable that the annual variation in temperature is 

 nowhere more than 2 F. Below 600 ft. there is probably 

 no annual change in temperature. 



Waves. Experiment 73. Take a long, flexible rubber band 

 or tube and having fastened one end, stretch it somewhat. Now 

 strike down on it near one end with a small stick. A wavelike 

 motion will be seen to travel from end to end of the band. It is 

 evident that the particles of rubber do not enter into the lateral 

 movement, but that they simply move up and down, whereas the 

 wave movement proceeds along the band. A piece of paper folded 

 and placed lightly upon the band will move up and down but not 

 along the band. Thus, wave motion does not necessitate lateral 

 movement of the particles taking part in the wave. 



When the wind blows over water, it throws the surface 

 into motion and produces waves. The highest part of the 

 wave is called the crest and the lowest part the trough. 

 Trough and crest move along rapidly over the surface of 

 the water. The particles of the water themselves, how- 

 ever, move somewhat like those in the rubber band. That 

 the water itself does not move with the wave can be seen 

 when a floating bottle is observed. It moves up and down 



