52 DISCUSSIONS IN CLIMATOLOGY. 



off enormous ; but this alone would not account for 

 the non-disappearance of the snow and ice ; for, not- 

 withstanding this, the heat received is certainly more 

 than sufficient to melt all the snow which falls, great 

 as that amount may be. The real cause is that the 

 heat received is not sufficiently intense to raise the 

 temperature to the melting-point. More heat is actu- 

 ally received by the snow than is required to melt 

 it ; but it is dissipated and lost before it can manage 

 to raise the temperature of the snow to the melting- 

 point ; consequently the snow is not melted. Here 

 snow falls in the very middle of summer ; but snow 

 would not fall unless the temperature were near the 

 freezing-point. 



Foregoing principles applied to the case of the Glacial 

 Epoch. — Let us now apply the foregoing principles to 

 the case of the glacial epoch. As winter then occurred 

 in aphelion during a high state of eccentricity, that 

 season would be much longer and colder than at pre- 

 sent. Snow in temperate regions would then fall in 

 place of rain; and although the snowfall during the 

 winter might not be great, yet, as the temperature 

 would be far below the freezing-point, what fell would 

 not melt. As heat, which produces evaporation, is just 

 as essential to the accumulation of snow and ice as is 

 cold, which produces condensation, after the sun had 

 passed the vernal equinox and summer was approach- 

 ing, the consequent rise of temperature would be 

 accompanied by an increase in the snowfall. A melting 

 of the snow would also begin ; but it would be a very 

 considerable time before the amount melted would 

 equal the daily amount of snow falling. Rain, alter- 

 nating with snow-showers, would probably result; and, 

 for some time before midsummer, snow would cease 

 and give place entirely to rain. Melting would then 



