CROLUS ''CLIMATE AND TIME.'' 817 



third influence had better not be insisted upon, however, as it is coun- 

 teracted by — 1. The immense amount of latent heat liberated in the 

 condensation of the vapor ; and, 2. The interception by these fogs of 

 the heat radiated from the earth. A substitute may be offered for it, 

 viz., by rendering the atmosphere diathermous, and therefore inca- 

 pable of absorbing the solar rays or of intercepting the radiation and 

 reflection from the earth. In consequence of the operation of these 

 agencies, the air in snow-covered regions seldom rises above the freez- 

 ing-point, and the solar heat is conveyed away into space and utterly 

 lost to the earth ; for, if a portion of it is absorbed by the snow and 

 ice during the hours of sunshine, it is not rendered sensible, owing 

 to the high latent and specific heat of these for'jas of water, and is 

 radiated away, unchecked by any "protecting blanket of vapor" 

 (which Professor Tyndall shows to be so efficacious in protecting 

 the earth from radiation, but which can not exist above snow-covered 

 regions), during the succeeding hours of darkness. 



This waste of solar energy, in turn, still further curtails the already 

 short summer, and permits the same causes to operate with increased 

 efiiciency during the succeeding season. Moreover, the reaction of 

 each effect upon its cause is such as to strengthen the cause, and the 

 interaction of all the agencies is such as to increase the efiiciency of 

 each. Each winter would thus add to the snow which had remained 

 unmelted during the intervening summer, until the accumulation of 

 snow was checked by the absence of vapor for condensation and pre- 

 cipitation ; for, as pointed out by Tyndall, the presence of large quan- 

 tities of vapor is the first essential for the formation of extensive gla- 

 ciers. 



It has been objected to the theory, that this picture has been over- 

 drawn — that no such slight cause could so seriously disturb the equi- 

 librium of the seasons ; it has even been shown mathematically that 

 the heat of a few days in summer would melt the total accumulation 

 of the previous winter. The answer to these objections is, that in such 

 calculation the operation of the agencies just described was disre- 

 garded, and hence that its results are unreliable ; that, though the 

 solar intensity is greater over polar regions in summer than in the 

 tropics, as shown by Meech, it is not sufficient to melt the annual ac- 

 cumulation of ice, else this ice never could have accumulated to so 

 vast an extent as to annually send forth thousands of colossal bergs to 

 be melted in temperate seas ; that not only in the Alps, but even in 

 the almost tropical Himalayas, where the sun shines with undiminished 

 intensity throughout the year, the direct effect of the solar energy is so 

 far below the accumulation of congealed vapor that the ice is only pre- 

 vented from piling up indefinitely by that property which enables it to 

 flow down to lower levels where the conditions described do not exist ; 

 that even in the northern portions of our own country the slight annual 

 film of snow retards the coming of summer by weeks if not months ; 

 VOL. XVI. — 52 



