S. Newcomb—OroWs Climate and Time. 267 



" The heated air rising off the hot burning ground of the 

 equator, after ascending a few miles, becomes exposed to the 

 intense cold of the upper regions of the atmosphere ; it then 

 very soon loses all its heat and returns from the equator much 

 colder than it went thither." * * * "During all this time 

 [while the upper current is traveling from the equator toward 

 the poles] the air is in a region below the freezing point ; and 

 it is perfectly obvious that by the time it begins to descend it 

 must have acquired the temperature of the region in which it 

 has been traveling." 



This passage is quoted as showing the weakness whicli eve- 

 rywhere marks Mr. Croll's reasoning on the subject of temper- 

 ature. With all the care and study he has devoted to the sub- 

 ject, we are entirely unable to reconcile his views with the 

 known laws of heat. The facts that the same amount of heat 

 is given off when water freezes or vapor condenses which is 

 necessary to melt the ice or to evaporate the water ; that the 

 amount of heat developed by the compression of air is equal 

 to that absorbed by its expansion ; that if, from any cause, 

 heat passes very slowly from a warm body A to a cool body 

 B, it will also pass slowly from B to A when B is the warmer ; 

 that a body cannot abstract heat from another without itself be- 

 coming warmed, belong to a class which he does not seem to 

 bear in mind. In the passage we have quoted, he speaks of 

 the hot air rising from the earth and becoming exposed to the 

 intense cold of the upper regions of the atmosphere. But, 

 what can this cold be but the coldness of the very air itself 

 which has been rising up? If the warm air rises up into the 

 cold air, and becomes cooled by contact with the latter, the lat- 

 ter must become warm by the very heat which the fbi-mer 

 loses, and if there is a continuous rising current, the whole re- 

 gion must take the natural temperature of the rising air. This 

 temperature is indeed much below that which maintains at 

 the surface, for the simple reason that air becomes cold by ex- 

 pansion according to a definite and well known law. 



Having thus got his rising current constantly cooled off by 

 contact with the cold air of the upper regions, it has to 

 pass on its journey toward the poles "in a region below the 

 freezing point." Here again the question arises whether Mr. 

 CroU conceives that the temperature of a region can be any- 

 thing materially different from the temperature of the air or 

 other substance which fills the region. Apparently he does, 

 ^or he speaks of the air "acquinng the temperature of the 

 region," but what the difference is, or can be, he does not ex- 

 plain. There is such a thing as temperature expressive of the 

 amount of radiant heat passing through a diathermanous region, 

 but the " upper regions " are exposed to the radiation of the sun 

 on the one side, and of the earth's lower atmosphere on the other, 



