Physics and Mathematics to Geology, 347 



mountain-chains. Thus, following Professor Darwin *, he 

 supposes the earth to have once possessed a much greater 

 angular velocity than at present, and speaks of a " consistent 

 crust (of some few miles thickness)" as having formed " when 

 the rotation of our planet was at four times its present rate " 

 (I. c, p. 257) . The equatorial radius would then have been, he 

 says, some 4359 miles, and the polar some 3291. The change 

 of shape, as the rotation fell off, would account, he thinks, for 

 observed phenomena. He considers his conclusions opposed 

 by Sir W. Thomson's theory that the earth solidified through- 

 out and retains at least approximately its original eccentricity. 

 It is on this point that he refers to the data supplied by Mr. 

 Herbert Spencer's "juster physical insight;" and he adds, 

 apparently as his own contribution to the argument, — a The 

 supposition that a granite mountain or equatorial protuberance 

 400 miles high or iOO miles high could for a moment support 

 itself, would hardly be entertained by a practical engineer ;" 

 and in a footnote, " The limiting modulus of height of a 

 granite pyramid (equalling one side of its square base) is 

 somewhat less than eleven miles" (I. c. p. 258). I am quite 

 ready to agree with Mr. Taylor that if solidification occurred 

 under the conditions he supposes the eccentricity must have 

 altered enormously and that in a non- elastic way, and I 

 hardly suppose that Sir W. Thomson would oppose this view. 

 No one, however, so far as I know, has propounded the theory 

 of an elastic solid spheroidal earth of eccentricity '65 rotating 

 completely in six hours, so that the investigation of the strains 

 and stresses required by such a theory is unnecessary. I can 

 quite imagine that on any probable theory of density the 

 magnitude of the strains is hardly likely to be consistent with 

 the application of the mathematical theory of elasticity. The 

 force of Mr. Taylor's remarks as to the pyramid I, however, 

 fail to see. Such an isolated mass exists under totally differ- 

 ent conditions from any portion of a solid sphere or spheroid, 

 and one might as well argue as to the impossibility of a liquid 

 interior from the fact that an isolated liquid column 100 miles 

 high has not yet been observed on the earth's surface. If 

 Mr. Taylor were, however, to calculate the strains and stresses 

 in such a thin shell as he supposes, of material showing any- 

 thing resembling the structure of ordinary rock, with a rate 

 of rotation such as he mentions, I very much doubt whether 

 he would find it in an essentially better position than his 

 imaginary pyramid. 



After this criticism Mr. Taylor considers the question of the 

 probable degree of rigidity of our planet quite irrelevant, but 



* Phil. Trans. (1879), p. 532. 



