THE ACTINOMETRY OF THE SEA. 453 



that climates are imdergoing a gradual change as to temperature. 

 However tliis may be as to certain locahties, Baron Fomier, after 

 a long and laborious calculation, claims to have sIioami that if the 

 earth had been once heated, and after having been brought to any 

 given temperatiu-e, if it had then been plunged into a colder medium, it 

 would not in the space of 1,280,000 years be reduced in temperature 

 more than would a 12-inch globe of like materials in one second of 

 time if placed under like conditions. It may be assumed that for 

 the whole earth, there has not been since the invention of the ther- 

 mometer any appreciable change in the temperature of the crust of 

 our planet. 



. 884. The earth receives from the sun heat enough daily, it has 

 Sr^inT rested ^ becu Said (§ 271), to melt a quantity of ice sufficient 

 upon the earth. to iucasc it iu a film 1;^- incli tliick. What becomes 

 of this heat after it is so impressed, how is it dispersed by the land ? 

 how by the sea ? Let us inquire. 



885. The solar ray penetrates the sohd parts of the earth's crust 

 How far below the sur- onlv to the dcptli of a fow inchcs, but strikinsr its 



TilCG Q06S tllO llP'lt or ». X ^ O 



tiie sun penetrate ? fluid parts witli its light and heat, it penetrates the 

 sea to depths more or less profound, according to the transparency 

 of the waters. Let us, in imagination, divide these depths, whatever 

 they may be, into any niunber of stratifications or layers of equal 

 tliickness. The dnect heat of the sun is supposed to be extinguished 

 in the lowest layer ; the bottom layer, then, mil receive and absorb 

 the minimum amount of heat, the top the maximum ; consequently, 

 each layer, as w^e go from the top to the bottom, will receive less 

 and less of the smi's heat. 



886. Now, which will retain most heat and reach the highest 

 The stratum of temperatm'e ? Not the top layer, or that to which 

 warmest water. niost licat is imparted, because by evaporation heat is 

 carried off from the surface of the sea almost as fast as by the sun 

 it is impressed upon the surface of the sea ; not the bottom layer, 

 because that receives a minimum, which, though it cannot escape 

 by evaporation, may nevertheless fail to make any marked change in 

 temperature — fail, not by reason of no evaporation, but by the ever- 

 changing movements which, considering the length of time requh-ed 

 to heat the lower stratimi by such slow and gradual accumulation of 

 heat, would alter its place and vary its condition, and indeed re- 

 moving it beyond the reach of the observer. 



887. The layer, therefore, which accumulates most heat and 

 Its position. becomes waiTaest, should be neither at the bottom 



