260 W. B. Taylor— Crumpling of the Earth's Crust. 



of tides therefore give a secure contradiction to that hypothe- 

 sis."* 



That a siliceous crust of 20 miles average thickness, and an 

 overlying aqueous ocean of three miles average depth, should 

 have (as required by the argument) so equal a coefficient of 

 mobility, that sea and land could thus " together rise and fall," 

 might well be pronounced incredible. Professor Thomson 

 himself proceeds to very seriously damage his "secure contra- 

 diction" of " the geological hypothesis," by adding immediately 

 after the passage just quoted : " We shall see indeed presently 

 that even a continuous solid globe of the same mass and diame- 

 ter as the earth would if homogeneous and of the same rigidity 

 as glass, or as steel, yield in its shape to the tidal influence, 

 three-fifths as much, or one-third as much, as a perfectly fluid 

 globe, "f 



When we have learned the elements of depth, inertia and 

 fluidity of the disturbed layers beneath the geologis crust, then 

 and not till then may the beginnings of a mathematical theory of 

 the telluric tides be attempted ; and some plausible measure of 

 their "lagging" be suggested. But in our profound and in- 

 superable ignorance of these interior conditions determining the 

 magnitude and direction of the tidal crests, it is idle for the 

 mathematician (with whatever array of formidable differential 

 equations) to gravely assure us that '■ no very considerable por- 

 tion of the interior of the earth can even distantly approach 

 the fluid state."$ 



It is in fact quite incontrovertible, that whether the geologic 

 crust have for its content a glowing lava, or Thomson's ideal 

 steel, it is equally subject to lunar and solar tides fully com- 

 parable to the more apparent ocean tides. This last surviving 

 argument for solidity, from the theory of the tides, should 

 therefore be dismissed as being no less futile than the aban- 

 doned argument, from the theory of precession. § 



* Nat. PMLos., 1867, vol. i, sect. 833, p. 690. Retained in the new edition. 



f Same work; sect. 833, pp. 690, 691, and sect. 834, pp. 691-694. 



\ Mr. George H. Darwin in a very abstract memoir: " On the bodily tides of 

 viscous and semi-elastic spheroids, and on the Ocean Tides upon a yielding 

 nucleus," read before the Royal Society of London, May 23, 1878, arrives at the 

 conclusion: "Unless the viscosity were very much larger than that of pitch, the 

 viscous sphere would comport itself sensibly like a perfect fluid, and the ocean 

 tides would be quite insignificant. It follows therefore that no very considerable 

 portion of the interior of the earth can even distantly approach the fluid state." — 

 Phil. Trans. Roy. Soc, vol. clxx, p. 28. 



§ Professor Thomson, who in 1862 had re-enforced and exaggerated the Hop- 

 kins argument, by maintaining that the earth's defect (by deformation) from the 

 theoretical amount of precession, is " much smaller for instance than it would be 

 if its effective rigidity were no more than the rigidity of steel," in consequence of 

 an oral discussion with our colleague Professor S. Newcomb, in 1876, with a 

 frankness worthy of all praise, made a full surrender of the position, in his 

 address before the mathematical and physical section of the British Association : 

 Report Brit. Assoc, Sept., 1876, vol. xlvi. part II, pp. 1-12), and has since con- 



