120 DISCUSSIONS IN CLIMATOLOGY. 



observed that the greater the amount of the eccen- 

 tricity, the greater will be the effect resulting from 

 the combination of these physical agents, whether that 

 effect be the production of snow and ice on the cold 

 hemisphere, or the melting of them on the warm, — 

 whether it be their production when the winter sol- 

 stice of a hemisphere is in aphelion, or their melting 

 when that solstice is in perihelion. 



We have, however, to take into account not merely 

 the action of the physical agents, but their mutual 

 reactions on each other. The effect of this mutual 

 reaction is very striking. Not only do the physical 

 agents, in their actions, all lead to one result, viz., an 

 accumulation of snow and ice when the winters are in 

 aphelion, but their efficiency in bringing about this 

 result is actually strengthened by their mutual re- 

 actions. To illustrate this effect I may quote the 

 following from Chapter III. of this volume. 



' To begin with, we have a high state of eccentricity. 

 This leads to long and cold winters. The cold leads to 

 snow, and although heat is given out in the formation 

 of the snow, yet the final result is that the snow inten- 

 sifies the cold : it cools the air and leads to still more 

 snow. The cold and snow bring a third agent into 

 play — fogs, which act still in the same direction. The 

 fogs intercept the sun's rays ; this interception of the 

 rays diminishes the melting-power of the sun, and so 

 increases the accumulation. As the snow and ice 

 continue to accumulate, more and more of the rays are 

 cut off; and on the other hand, as the rays continue 

 to be cut off, the rate of accumulation increases, 

 because the quantity of snow and ice melted 

 becomes thus annually less and less. In addition, 

 the loss of the rays cut off by the fogs lowers the 

 temperature of the air and leads to more snow being 



