THE POSITION OF THE BARTERS AXIS. 121 



being about equal to that brought down by the rivers in 

 solution, allowing for a greater rainfall and melting of a 

 considerable amount of ice, we should scarcely be able to 

 get by the first cause more than 18-27 miles in a million 

 years ; and the second might give 40-60 miles within very 

 recent geological periods. 



We thus see that, should these causes not have received 

 full allowance from Mr. G. H. Darwin, the amount of change 

 of i°-3° is nearly all that could be allowed for any geolo- 

 gically recent change, unless any agency could be found 

 which might work in a cumulative manner so as to increase 

 the effect. 



Although we must suppose that the change would take 

 place very gradually, the effects to be appreciated must be 

 considered as if they were brought about suddenly. Sup- 

 pose that the angle of the axis is changed one degree, 

 the earth as a yielding body must take the new figure 

 of rotation. Taking that hemisphere in which the bulge 

 is removed towards the south, we have an undue amount 

 of material in the south ; and this must cause phenomena 

 which would be equivalent to an elevation in the north, 

 displacing, if it should be an oceanic area, an amount of 

 water to be placed in another region. The direction may 

 be reversed in consequence of the unequal length of the 

 minor axes. There is a difference in the equatorial dia- 

 meters ; the shortest diameter is that drawn from somewhere 

 about the north of South America to the antipodes north 

 of Australia, the difference being from one to two miles. 



Further, the differences of the land-diameters are much 

 greater, so that the equatorial diameter of the portion of 

 greatest specific gravity (covered by the ocean of less) is 

 in some parts 5-6 miles less than the diameter of the 

 figure. The maximum effect which would be theoretically 

 possible for each degree of change, allowing for the dif- 



