292 Mr. O.Fisher — Changes of Latitude on the Earth's Surface. 



tions short of a change in latitude are to account for the flora of a 

 warm climate within the arctic circle. We therefore appeal to him, 

 and to others similarly qualified, to look at this subject from both 

 sides. 



Dr. John Evans, in a paper which he read before the Eoyal 

 Society in 1866/ suggested a cause why, in his opinion, a moun- 

 tainous region, newly upheaved above the general surface of the 

 earth, would have a tendency to travel towards the equator, mov- 

 ing the rest of the crust along with it. " My hypothesis," he said 

 ten years later, in his Presidential Address of 1876, " was founded 

 on the assumption of the globe consisting of a comparatively thin 

 crust with an internal fluid nucleus, over which the crust could 

 slide when from any geological cause its equilibrium was dis- 

 turbed." * But the hypothesis under which he then appealed to 

 physicists for a solution of the question, if not intended by him 

 to be different from the above, has, at any rate, been so taken by 

 Mr. Twisden,^ and Mr. G. Darwin,* and, following them, by Mr. Hill ; 

 for all these gentlemen have supposed the globe solid from the 

 surface to the centre. I do not think that any geologist can easily 

 entertain this opinion ; and when, in handling the subject, one omits 

 all reference to any other possible supposition as to the state of the 

 earth's interior, it seems to me that he is not rendering that help to 

 his less accomplished brethren which he might render. 



The causes, which lead physicists to regard the problem from their 

 point of view, may partly be, first, that the great problem of Pre- 

 cession and Nutation has always been so treated. They are, there- 

 fore, already some way on their road towards the elucidation of any 

 other question of this class. Secondly, the perhaps gi'eatest living 

 physicist in this kingdom has pronounced in the strongest language 

 against the doctrine of a fluid interior. He appears, in consequence 

 of a conversation with Professor Newcomb, to have given up the 

 original argument against it from precession and nutation. " Inter- 

 esting in a dynamical point of "sdew as Hopkins' jDroblem is, it cannot 

 afibrd a decisive argument against the earth's interior liquidity."^ 

 But there remain the tides. " The solid crust would yield so freely to 

 the deforming influence of the sun and moon, that it would simply 

 carry the waters of the ocean up and down with it, and there would 

 be no sensible tidal rise and fall of water relatively to land." ^ I 

 have inquired '^ whether, taking their lagging into consideration, it is 

 certain that the crests of the tidal waves in the ocean and in the 

 crust would occur simultaneously at the same place : because, unless 

 they did so, we might still have a tide relatively to land. Eecently, 

 at the Cambridge Philosophical Society, when Mr. Hill gave some 

 illustrations corroborative of Mr. G. Darwin's results, Mr. Darwin 

 told the meeting, in reply to some remarks of mine, that he had 



1 Proc. Eoy. Soe. No. 82, 1866. 



2 Quart. Journ. Geol. Soc, vol. xxxii. Presidential Address, p. 108. 

 2 Quart. Journ. Geol. Soc, vol. ixxiv. p. 35. 



* Trans. Royal Soc. vol. 167, part i. 



s Sir W. Thomson's Sectional Addi-ess, Nature, vol. xiv. 1876, p. 429, 2nd column. 



6 Ibid. "' Quart. Journ. Geol. Soc, 1875, p. 470. 



