Earth's A^is of liotation. 99 



of the land beino^ at intervals above and beneath the waters, and to 

 chancres of teniperature over the same area. These effects he attri- 

 butes to a change in the earth's axis of rotation, arising from astro- 

 nomical causes,' and describes the results which would follow from 

 such conditions. As to the possibility of a change in the earth's 

 axis of rotation, we had a paper from Sir John Lubbock, in which 

 he first adverts to the revolution of a solid body on its principal 

 axis, and its continuing to do so for ever, unless such solid body be 

 acted upon by some extraneous force. He further observes that on 

 this supposition no change of climate would obtain on any given lati- 

 tude on the earth's surface, except from a change in internal tempe- 

 rature or the heat of the sun. 



He then notices that a change of climate alone is not sufficient to 

 account for geological changes, such as water covering a part of the 

 earth's surface at one time and not at another : and remarks that 

 the moon's attraction and the causes which produce the precession of 

 the equinoxes do not modify these conclusions. 



Sir John Lubbock then states, that " it is unlikely that when the 

 earth was first set spinning, the axis of rotation should exactly coin- 

 cide with the axis of figure, unless indeed it were all perfectly fluid." 

 He subsequently takes a period not so remote, when the earth, from 

 the diiferent fusibility of its component parts, might have been 

 partly solid in irregular masses and partly fluid, and afterwards a 

 still more advanced state, in which land and water irregularly occurred 

 on its surface, suited to the existence of animal life, always suppos- 

 ing the axis of rotation not to coincide with the axis of figure. If 

 any resistance exists, " the pole of the axis of rotation would describe 

 a spiral round the axis of figure, until finally it would become, as at 

 present, identical with it." Supposing a displacement of the axis, 

 the movement of the water from one equator to another and the con- 

 sequent changes of climate are pointed out. Glancing at friction 

 on the surface of the earth rendering the invariability of geographi- 

 cal latitude, otherwise existing, not a necessary consequence, — at our 

 ignorance of the earth's structure beneath its crust, — and of the his- 

 tory of the changes effected during the process of cooling, — Sir John 

 considers that " the utmost that can be accomplished by mathematics 

 is to explain under what hypothesis a change of the position of the 

 axis of rotation is possible or not." Adverting to the dictum of 

 Laplace, that the changes on the earth's surface and in the relative 

 positions of land and water cannot be accounted for by a change in 

 the position of the axis of rotation, he observes that in this state- 

 ment Laplace did not take into consideration either (1.), the disloca- 

 tion of the strata by cooling, or (2.), the friction of the surface. 

 Finally, our colleague, after admitting that if at any remote period 

 the earth had been a homogeneous spheroid of any pure metal in a 

 state of fusion, it would in cooling always revolve about the principal 

 axis of rotation, that of figure, considers that there is sufllicient evi- 



