1866.] Position of the Axis of the Earih^s Crust. 



47 



The evidence of the extreme refrigeration of this portion of the earth at 

 the Glacial Period is constantly receiving fresh corroboration, and various 

 theories have been proposed which account for this accession of cold in a 

 more or less satisfactory manner. 



Variations in the distribution of land and v^ater, changes in the direction 

 of the Gulf-stream, the greater or less eccentricity of the earth's orbit, 

 the passage of the Solar System through a cold region in space, fluctuations 

 in the amount of heat radiated by the sun, alternations of heat and cold 

 in the northern and southern hemispheres, as consequent upon the precession 

 of the equinoxes, and even changes in the position of the centre of gravity 

 of the earth and consequent displacements of the polar axis, have all been 

 adduced as causes calculated to produce the effects observed ; and the 

 reasoning founded on each of these data is no doubt familiar to all. 



The possibility of any material change in the axis of rotation of the 

 earth has been so distinctly denied by Laplace* and all succeeding astro- 

 nomers, that any theory involving such a change, however tempting as 

 affording a solution of certain difficulties, has been rejected by nearly all 

 geologists as untenable. 



Sir Henry Jamesf, however, writing to the 'Atheneeum' newspaper in 

 18G0, stated that he had long since arrived at the conclusion that there 

 was no possible explanation of some of the geological phenomena testifying 

 to the climate at certain spots having greatly varied at different periods, 

 without the supposition of constant changes in the position of the axis of 

 the earth's rotation. He then, assuming as an admitted fact that the 

 earth is at present a fluid mass with a hardened crust, showed that slaty 

 cleavage, dislocations, and undulations in the various strata are results 

 which might be expected from the crust of the earth having to assume a 

 new external form, if caused to revolve on a new axis, and advanced the 

 theory that the elevation of mountain-chains of larger extent than at 

 present known produced these changes in the position of the poles. 



The subject was discussed in further letters from Sir Henry James, the 

 Astronomer Royal, Professors Beete Jukes and Hennessy, and others, but 

 throughout the discussion the principal question at issue seems to have 

 been whether any elevation of a mountain-mass could sensibly affect the 

 position of the axis of rotation of the globe as a whole, and the general 

 verdict was in the negative. 



At an earlier period (1848) the late Sir John Lubbock, in a short but 

 conclusive paper in the ' Quarterly Journal of the Geological Society',! 

 pointed out what would have been the efl^ect had the axis of rotation of the 

 earth not originally corresponded with the axis of figure, and also mentioned 

 some considerations which appear to have been absent from Laplace's 

 calculations. 



* Mec. Cel., vol. v. p. 14. 

 t Vol. V. p. 5. 



t 7\t,]ienaimTi, Aug. 25, ISGO, &c. 



