346 Mr. C. Ohree on some Applications of 



According to the ' Text-book,' the theory of a thin crust con- 

 taining liquid or viscous matter is exposed to " weighty and 

 indeed insuperable objections/' p. 18, and " is now abandoned 

 by most geologists,'"' p. 43. 



According to Dr. Croll* the "general opinion among 

 geologists " is that the earth " consists of a fluid interior sur- 

 rounded by a thick and rigid [really solid] crust." 



Professor Prestwich f believes that " the crust rests on a 

 yielding substratum, and that of no great thickness." In 

 fact he advocates the third of the above-mentioned theories, 

 and believes 30 miles to be probably in excess of the crust's 

 thickness. Most writers on the subject appear to have sub- 

 sidiary theories of their own. 



Whether the assurance that the question is beyond the reach 

 of experiment accounts for the multitude of theories and the 

 confidence with which they are proposed, is a question for 

 philosophers not mathematicians to consider, but it seems a 

 priori a possible explanation of such a declaration of faith as 

 that of Mr. W. B. Taylor % :— " The liquidity of our globe, and 

 the relative thinness of its encrusted envelope, — as attested by 

 all legitimate geological induction, — will be assumed without 

 misgiving or hesitancy ; and the supposed mathematical argu- 

 ments for its solidity ignored as essentially fallacious and 

 wholly inconclusive." 



Of course, if the geological evidence were conclusive, it 

 would be mere waste of time further to consider the matter, 

 but the evidence that satisfies Mr. Taylor does not seem to 

 carry conviction to all geologists even in America. Mr. Gr. F. 

 Becker §, for instance, who appears to have some practical 

 experience, says : — " For a considerable number of years I 

 have constantly had the theory of the earth's solidity in mind 

 while making field observations on upheaval and subsidence, 

 with the result that to my thinking, the phenomena are capable 

 of much more satisfactory explanation on a solid globe than 

 on an encrusted fluid one." 



It may thus be not wholly unprofitable to glance briefly at 

 some of the arguments which some of the advocates of the 

 several theories base on their ideas of the properties of solid 

 bodies. 



Mr. Taylor's object is to get an equatorial circumference 

 some 10 per cent, in excess of its present value, so as to 

 account for the lateral compression at the surface observed in 



* ' Climate and Time,' p. 395. 



t ' Geology,' vol. ii. p. 540. 



% American Journal of Science, vol. xxx. (1885), p. 250. 



§ American Journal of Science, vol. xxxix. (1890), pp. 351, 352. 



