266 G. II Darwin — Stresses caused in the Earth by 



The mean level bisecting elevations and depressions as 2,480 

 meters (8,150 feet) below the sea-level, and the greatest eleva- 

 tion and depression from that mean level as 3,009 meters 

 (9,840 feet), it results that the average height of the land above 

 sea-level is 350 meters, and the average depression of dried sea- 

 bed is 3,150 meters. 



It thus appears that 3,000 meters would be a proper greatest 

 elevation and depression to assume for the harmonic analysis 

 of this paper, if the earth were homogeneous. But as the den- 

 sity of superficial rocks is only a half of the mean density of 

 the earth, I shall take 15o<> meters as the greatest elevation and 

 depression from the mean equilibrium spheroid of revolution. 



It is proper here to note that the height of the undulations of 

 elevation and depression in the zonal harmonic inequalities is 

 considerably ^renter toward the poles than it is about the 

 equator; it might, therefore, be maintained that by making 

 1500 meters the equatorial height we are taking too high an 

 estimate. But the state of stress caused in the sphere at any 

 point depends very much more on the height of the inequality 

 in the neighborhood of a superficial point immediately over the 

 point considered, than it does on the inequalities in remote 

 parts of the sphere. 



Now in all the inequalities, except the second harmonic, I 

 have considered the state of stress in the equatorial region, and 



If the latter average be p times as great ag the former 





h—350 meters, very nearly, 



t depth of the subi . : re] is 3009 I 



ets of this paper had h.vn cm-rected, Professor Stokes 



The geological dei extent render our ( 



ients flat-topped.— Added May 4, 1882.] 



