472 THE PHYSICAL GEOGRAPHY OF THE SEA. 



diated thence again. They will reveal to us knowledge concern- 

 ing its actinometry in other aspects. We shall learn how absorp- 

 tion by, as well as radiation from, the under strata is afiected by 

 a rough sea, as when the waves are leaping and tossing their white 

 caps, and how by its glassy surface, as when the winds are hushed 

 and the sea smooth. 



887. Here we are reminded, also, to anticipate the discovery 

 Expected discoveries, of ucw bcautics and frcsh charms among the won- 

 ders of the sea. We have seen (§ S6Q) that while the heat of the 

 sun is impressed alike upon sea and land, nevertheless the solid 

 part of the earth's crust radiates much more freely than the fluid. 

 On the land the direct heat of the sun operates only upon a mere 

 shell a few inches in thickness; at sea it penetrates into the depths 

 below, and operates upon a layer of water many feet thick. The 

 solid land-crust has its temperature raised high by day and cooled 

 low down by night; but the most powerful sun, after beating down 

 all day with its fiercest intensity upon this liquid covering, has 

 not power to raise its temperature more than three or four de- 

 grees. This covering serves as a reservoir for the solar heat. In 

 the depths below it is concealed from the powers of intense radi- 

 ation, and held by the obedient ocean in readiness to be brought 

 to the surface from time to time, and as the winds and the clouds 

 call for it. Here it is rendered latent by the forces of evapora- 

 tion, and in this form, having fulfilled its office in the economy 

 of the ocean, it passes off into the air, there to enter, in mysterious 

 ways, upon the performance of its manifold tasks. ^ 



888. As evaporation goes on by day or night, the upper stra- 

 Actinic processes, tum is rendered heavier by reason of both the heat 



and the fresh water which are borne away by evaporation ; the up- 

 per water, having been thus rendered both Salter and cooler, has its 

 specific gravity increased so much the more. On the other hand, the 

 strata below, receiving more heat by day than they dispense again 

 by radiation day and night, grow actually warmer and specifically 

 lighter; and thus, by unseen hands and the "clapping of the 

 waves," the waters below are brought to the surface, and those on 

 the surface carried down to unknown depths ; and thus, also, we 

 discover new and strange processes which have been ordained for 

 the waters of the ocean in their sj^stem of vertical circulation. 



889. Thus we arrive at the conclusion that the ocean is the 



