470 THE PHYSICAL GEOGRAPHY OF THE SEA. 



880. The observations that we possess do not prove that the 

 The warmest waters warmest Water of intertropical seas is not at the 

 ihe?? at^iTbeiow the surface I thcj go no farther than to show that it 

 ''"^■*'^'^^- is sometimes not at the surface, and to suggest 

 that, in all probability, it is generally below,' especially in "blue 

 water." Eeason suggests it also. Supposing that, as a rule, the 

 liottest water is below the surface, we may, in order to stimulate 

 research, encourage investigation, and insure true progress, pro- 

 pound a theory in explanation of the phenomenon, looking to fu- 

 ture observations to show how far it may hold good. 



881. The flow of heat from the sun is held to be uniform, and 

 ThG annual supply of ^hc quantity of it that is annually impressed upon 

 tGiar heat uniform. ^-^Q earth is considcred as a constant. The sun 

 spots may make this "constant" a variable, but the amount annual- 

 ly received by the earth is so nearly uniform that our best instru- 

 ments have not been able to show us any variation in its uniform- 

 it3^ Some maintain that climates are undergoing a gradual change 

 as to temperature. However this may be as to certain localities, 

 Baron Fourier, after a long and laborious calculation, claims to 

 have shown that if the earth had been once heated, and, after 

 having been brought to any given temperature, 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, in 

 one second of time, a 12-inch globe of like materials if placed 

 under like conditions. It may be assumed that, for the whole 

 earth, there has not been, since the invention of the thermome- 

 ter, any appreciable change in the temperature of the crust of 

 our planet. 



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

 Quantity of heat dai- bccu Said (§ 271), to mclt a quantity of ice suffi- 

 j. impiesse upon q[qt^i iq incasc it iu a film 1-J- inch thick. What 



becomes of this heat after it is so impressed ? how is it dispensed 

 by the land? how by the sea? Let us inquire. 



883. The solar ray penetrates the solid parts of the earth's crust 

 only to the depth of a few inches, but, striking its fluid parts with 



repeated tests of the temperature of the water during the four hours we were run- 

 ning through it— the warm belt. 



"Ninety degrees is the highest temperature that I have ever known the water of 

 tl;e ocean to attain." 



