Physics and Mathematics to Geology. 



Table II. 



Values of E/10 6 . 



245 





Iron and Steel. 



Copper. 



Slate. 



Zinc. 



Stone. 



Lead. 



Highest value . 

 Lowest value... 



2953 

 984 



1254 

 1052 



1120 



910 



955 



873 



about 

 350 



199 

 51 



This table will give a general idea of the limits within 

 which E may reasonably be expected to lie, though some of 

 the data refer to material which is hardly likely to have been 

 isotropic. It shows that if the influence of the gravitational 

 forces on the eccentricity were negligible — which, however, 

 is not the case — the earth, though perfectly solid and elastic, 

 might reasonably be expected to display not a smaller but a 

 considerably greater eccentricity than it actually does. 



The question next arises whether the strains and stresses 

 produced by the rotation are such as are consistent with the 

 principles on which the application of the mathematical theory 

 rests. In the actual case of the earth this question is of im- 

 portance only in exceptional circumstances, owing to the pre- 

 ponderating influence of the gravitational forces, still it 

 possesses sufficient interest to claim separate consideration. 

 The following table gives . a sufficiently close approximation 

 to the numerical results obtained for the rotating body treated 

 above, when for E are substituted the values which answer to 

 the production by rotation alone of an eccentricity equal to 

 that of the earth. 



Table III.* 



n= 







•25 



•5 



Maximum stress-differ- 1 

 ence in tons weight per I 

 square inch j 



Greatest strain 



32f 

 •0040 



26 



S2i 

 •0029 



23 



32 

 •0018 



16 



Longitudinal stress in ^ 

 tons per square inch | 

 which would produce a )■ 

 strain equal to the great- | 

 est strain J 



* See (e) Tables III., VII., and IX. 



