336 PRACTICAL LESSONS IN SCIENCE. 



water and in narrow bodies of water these waves make strong to 

 and fro currents. 



Ocean currents are as common as the waves, but are not quite 

 as manifest or as easily understood. They are caused mainly by 

 the winds and by the tides. Unequal heating and evaporation 

 would seem to be efficient causes of currents, but a little in- 

 vestigation shows that the effect of one tends to neutralize the 

 effect of the other. The rotation of the earth and the form and 

 arrangement of the land masses help to determine the direction 

 of the currents. In general the currents have the same direction 

 as the winds. The equatorial currents flow westerly with the 

 easterly winds, and the Japan current and the Gulf stream flow 

 northeasterly with the southwest winds, etc. Beside the surface 

 currents there are strong under currents toward the equator. 

 Thus the heat of the sun, the attraction of the earth, causes 

 winds and streams of water, waves and currents in the ocean, 

 and the attraction of the sun and moon cause the tides, all 

 efficient agents active in geological phenomena. 



