MODIFICATION OF THEORY EXAMINED. 123 



melting, not an accumulation of the ice. The same 

 process is undoing on the southern hemisphere what 

 it is doing on the northern. Similarly, of course, 

 when the northern winter solstice begins to move 

 towards the perihelion, the mutual reactions of these 

 physical causes will be reversed and will go on with 

 increasing intensity till the perihelion is reached, 

 melting the very ice which they had previously 

 produced. 



We have already seen that the greater the extent of 

 the eccentricity the greater is the effect resulting from 

 the actions of the physical causes, whether this effect 

 be the production of ice on the cold hemisphere, or its 

 removal from the warm. It is evident that the same 

 thing must necessarily hold true in regard to the 

 mutual reactions of the physical causes. Conse- 

 quently, if the mutual actions and reactions of the 

 physical causes, brought into operation during a high 

 state of eccentricity, led at the Glacial Epoch to the 

 great accumulation of ice when the winters were in 

 aphelion, they must have led to an equally great 

 melting and dispersal of that ice when precession 

 brought the winters round to perihelion. These 

 causes would be as efficient in the removal of the 

 ice as they were in its production. In so far as the 

 physical and astronomical causes were concerned, the 

 greater the amount of ice formed during the cold 

 periods the greater would be the amount melted 

 during the warm interglacial periods. 



This conclusion follows so obviously from the fore- 

 going principles that it seems almost superfluous to 

 dwell further on the subject, the more so as it will be 

 seen in the next chapter that the correctness of the 

 conclusion is established by the facts of geology and 

 palaeontology. 



