I907-] 



AND CONTRACTION OF THE EARTH. 



205 



Some prominent geologists believe that the outflow of heat from 

 the nucleus would produce a deep-seated secular contraction such as 

 they imagine might have caused the subsidence of the ocean basins 

 (cf. Chamberlin and Salisbury's '' Geology," Vol. I., pp. 563 and 



567). 



If the initial distribution of temperature in any plane section of 

 the earth corresponds to the ellipse 



+ 



r 



— I 



the distribution after a sufficient interval t may be taken to be 



(9) 



a a [i — e ) 



In other words the form and dimensions of the ellipse will change 

 with the time. The two ellipses will intersect at four points, and 

 if they be revolved about the common minor axis, these points of 

 intersection generate circles of no change of temperature ; the points 

 are given by the condition 



Here x becomes identical with the radius of the circle about the 



Fig. I. Section of Ellipsoids. 



