the Displacement of Shore-lines. 415 



not even capable of obliterating the inequalities of the surface, 

 still less the internal tension produced bj the lengthening of 

 the sidereal daj. And as the day has become considerably 

 longei', the sea ought to be collected towards the poles and 

 the land uuder the equator, in case ih.e solid earth had not 

 changed its form. 



Others think that the earth may actually change its form. 

 The first who expressed this opinion, so far as I can find, is 

 Herbert Spencer. In the Philosophical Magazine (1847, vol. 

 XXX. p. 194) he published a small memoir, entitled " The Form 

 of the Earth no proof of original Fluidity," in which he main- 

 tains that even the solid earth may change its form, according 

 as the centrifugal force changes. AYhen a body increases in 

 size, the power of resistance to external forces increases only 

 as the square of the dimensions, while the wasting and de- 

 structive forces (weighty centrifugal force) increase in the 

 same proportion as the mass of the body, and therefore as the 

 cube of the dimensions. As the size increases we therefore 

 come to a point at which even the most solid body must yield 

 to the forces. We must therefore assume, says Spencer, that 

 the earth, by reason of its size, must yield and change its 

 form, in case the centrifugal force, for example, changes ; for 

 the most solid matter known to us, exposed to the same 

 forces which act upon the earth, would overstep the bounds of 

 solidity before attaining a thousand-millionth part of the 

 earth^s size. Tliis argument, in Prof. Schij^^tz^s opinion, is not 

 tenable. At any rate, I believe that Spencer is the first who 

 expressed the opinion that even a solid earth can change its 

 form. In the above-cited discourse of 18G9, Peirce says that 

 the lengthening of the sidereal day may be supposed to have 

 altered the form of the solid earth. And Principal Dawson, 

 in his 'Story of the Earth and Man' (ed. 9, 1887, p. 291), 

 says that this alteration of form by reason of the lengthening 

 of the sidereal day must have taken place at longer or 

 shorter intervals. So long as the crust of the earth did not 

 yield, the sea will have flowed towards the poles ; but when 

 the tension becomes so great that the solid crust bursts, the 

 equatorial regions wuU sink in and the sea will flow again 

 towards the equator*. 



* Similar opinions are expressed by Dr. E. Reyer ("Die Bewegung ini 

 ■ Festen/' iu Jahrb. K. K. Geol. Reichs. Wien, vol. xxx. 1880, pp. o4o et 

 seqq.). W. B. Taylor, in a memoir " On the Crumpling of the Earth's 

 Crust" (Amer. Joiuti. Sci. ser. 3, vol. xxx. 1885, pp. 249 et scqq.), ex- 

 presses himself against the theory of the earth's coutraction, and thinks 

 that the lengthening of the sidereal day is the cause of the changes in the 

 cru.st. A. ^Viuchell, in a memoir on the " Sources of Trend and Crustal 

 Surplasage" (Amer. Journ. I. c. p. 417), endeavours to show that the 



