74 THE BOTTOM OF THE SEA. 



there the polypi erect their most gigantic ramparts 

 of stone. 



If we were to sink a well on the shore to the depth 

 of 12,000 feet, the temperature at its bottom would 

 be about 300° Fahr. Yet we have just seen that the 

 temperature at the bottom of the sea is nearly con- 

 stant at 32°. This fact is sufficient to prove that the 

 water of the ocean exercises an immense influence on 

 the distribution of temperature over the surface of 

 the earth. 



The Ocean is in turn affected by heat, even to its 

 lowest abysses. Inequalities of temperature and of 

 saltness give birth to currents both on its surface 

 and in its depths. The former, however, are more 

 generally due to the action of the constant winds. 

 By-and-by we shall have to consider the action 

 exercised by curi'ents upon their bed. 



8. Cause of Waves — Their Height — Tliickness of the Mass of Water 

 in motion — Grouud-SNvells — ' Raz de Mare'e" — Waves of Trans- 

 lation — Measure of a Wave of TransL.tion, and of its Speed, in 

 the Pacific Ocean — Tides — Resume. 



When winds have not the constancy of the Trades, 

 they force the surface of the sea into heaps, and 

 plough it in furrows more or less deep : in a word, 

 they cause waves. This movement of the water does 

 not extend to any considerable depth. 



