268 S. Newcomb—Oroirs Climate and Time. 



and there is no proof that these do not equa] the surface tem- 

 perature. Having thus cooled off his upper current still farther 

 bj its passage through this " cold region," and that without the 

 region becoming any warmer, he leaves it to find its way to the 

 earth's surface, entirely oblivious of the fact that an amount of 

 heat will be evolved by compression in the polar regions, or 

 whereever the current reaches the earth again, fully equal to 

 that which it lost when it rose from the equator. If he had 



when it rose from the earth in the tropics, and again when i 

 reached the earth in northern regions, and thus determined the 

 amount of heat given out during its passage, his course would 

 have been much more logical. 



We do not propose to enter into the question of fact, how 

 much of an upper current there really is passing from the tropics 

 to the poles. But, if it is as great as is commonly supposed, it 

 must be as powerful as ocean currents in tending to equalize 

 the temperature of the globe. The fact that it is cold during 

 its passage, instead of being a disadvantage, is a positive 

 advantage, because the heat which it carries being latent in form 

 is not liable to be dissipated by radiation. 



Another proposition which the author attempts to prove, by 

 reasoning which seems equally inconclusive, is, that the mean 

 temperature of the ocean is greater than that of the land over 

 the entire globe. We may examine his argument, for the 

 reason that the proposition is a fundamental one in his theories 

 of climate. The most natural and conclusive way of establish- 

 ing such a proposition, would be by actual observations of 

 temperature, but no attempt to do this is made. The author 

 rests his doctrine wholly on four a priori reasons, which we may 

 consider in their order. 



(1.) " The ground stores up heat only by the slow process of 

 conduction, whereas water, by the mobility of its particles, and 

 its transparency for heat rays, especially those from the sun, 

 becomes heated to a considerable depth rapidly. The quantity 

 of heat stored up in the ground is thus comparatively 

 small, while the quantity stored up in the ocean is great" 

 We can hardly stop to criticise these sentences, implying as they 

 do, that the rapidity with which solar heat is absorbed by a 

 body determines its temperature, and also depends on its dia- 

 thermancy, and that a body which is heated only by the slow 

 process of conduction must be permanently colder than one 

 into which the radiant heat of the sun can penetrate. 



(2.) "The air is probably heated more rapidly by contact 

 with the ground than with the ocean ; but on the other hand 

 it is heated far more rapidly by radiation from the ocean than 

 from the land. The aqueous vapor of the air is to a great ex- 



