SWIRLS OF THE SEA 



27 



tides is popularly supposed to be a surface 

 movement, but it is not the less of far-reaching 

 eiTect. Possibly the tide was what Mahomet 

 called "the swelling sea," for apparently the 

 sea does swell and advance with the incoming 

 water. For six hours it floods in upon every 

 harbor, bay, and creek, creeps up the beaches, 

 rises along the dunes, and climbs the walls of 

 the cliffs; then for six hours, just as quietly it 

 ebbs and slips away from beach and inlet, 

 leaving its trail of algce and sea life behind it 

 on the shore. The fisher-boy, as he rocks in 

 his boat, watches it rise twice each day, sees 

 it linger for a time, sees it disappear, and 

 dreamily wonders from what depth it came and 

 to what abyss it returns. And why, he asks, 

 does it come in each day an hour later? 



The cause of the tides seems to have been 

 correctly divined by Newton. His generaliza- 

 tion of the law of gravitation apparently ac- 

 counts for the disturbance; and the moon and 

 the sun with their attractive powers are ac- 

 counted the disturbers. The moon, by reason 

 of its nearness, has an influence upon the earth 

 of more than double that of the sun. The 

 solid surface of the ground apparently does not 

 rise to its attraction, but the waters of the sea 

 do. The direct pull upon the waters which are 



The swell- 

 ing sea. 



The tides. 



Cause of 

 the tides. 



