238 



THE SEAS 



which are the horizontal currents moving the water which 

 forms the progressing tidal wave. In the open oceans the 

 wave, as already mentioned, is only a foot or so high, so 

 that the tidal stream is imperceptible ; but near the coasts 

 where the tidal wave increases in height the tidal stream 

 may be considerable. 



v«*Lli?e 



SPRING TIDE5 



..v.l- 



-.fSUH^ 



LAST QUA are a 



NEAP TIDES 





■€>'■ 



Fig. 50. — Diagram illustrating the action of sun and moon in 

 causing spring and neap tides. 



Waves 



Waves are an integral part of the sea. It is rarely, if 

 ever, the case that the sea is so calm that there is not the 

 slightest ripple, or failing that a long low swell, the after- 



