ACTION OF TJfE TIDES 3 1 



Before leaving the zone of the coast where the sea is work- 

 ino- the ch'ff backward into kind, we must not fail to consider 

 the action of the tides on such a shore. \W; have already 

 noted some incidental effects of these singular movements 

 of the ocean waters ; we must now^ look upon their larger 

 manifestations, and consider how they affect the processes of 

 the shore. As is w^ell known to the reader, the tidal move- 

 ment is due to the attraction of the sun and moon ujjon the 

 mass of the earth ; in fact, every star in space pulls upon 

 the earth ; but the moon, because of its nearness, and the sun. 

 because of its magnitude, and as compared to the fixed stars 

 its relative propinquity to our sphere, pull with enough (energy 

 to raise the sea above its prevailing level. The attractions of 

 these bodies tend to divert the wdiole mass of the earth, and if 

 it were completely fluid in its depths, as geologists once sup- 

 posed, the sea and the land would alike rise in a low tidal 

 wave, and we should perhaps notice no movement of the 

 oceans. Because of certain features in this drawing action 

 of sun and moon, there are two tides corresponding to each of 

 the attracting bodies. If the earth were uniformly covered 

 by a very deep ocean, one of these tides would be approxi- 

 mately under the sun or satellite, and the other on the 

 opposite side of the earth. Owing, however, to the irregular 

 form of the lands, these tidal weaves have to chase around the 

 earth, rushing up the narrow spaces between the lands, and so 

 fall behind their due jilace. Moreover, because the solar and 

 lunar tides are sometimes in the same place and sometimes 

 far apart from each other, these two waves now and then con- 

 join their volume and again oppose each other. The result 

 is that the tides, though they have a certain regularity, are, 

 as regards their rise and fall, rather irregular phenomena. 



