2^0 Refrigeratim of the Earth, 



of continuous light, and paralysed by months of uninterrupted 

 darkness. The distribution of light, therefore, as well as of 

 heat, must formerly have been different from what it is at pre- 

 sent. 



To meet this further difficulty, recourse is had to physical as- 

 tronomy, which gives us the precession of the equinoxes, and a 

 shifting axis of rotation : but the periodical changes of astrono- 

 mers are insufficient to explain the phenomena to which I have 

 just drawn your attention. It has therefore been suggested that 

 a greater change may, in the course of ages, have been produced 

 on the axis of the earth^s rotation by some foreign cause, say the 

 collision of a comet. 



Such change is undoubtedly possible, but of possibilities there 

 is no end, and we must circumscribe our researches to render 

 them useful. Sir John Herschel gives us no encouragement, 

 therefore, to proceed with this speculation. Mr Conybeare also 

 dissuades us from it, but by an argument which to me at least 

 appears inconclusive. 



His argument, founded upon the lunar theory, is this, — that 

 the internal strata of the earth are ellipses parallel to its exter- 

 nal outhne, their centres being coincident, and their axes identi- 

 cal with that of the surface. The present axis of the earth must 

 therefore have been its axis from the beginning. It may have 

 been so, yet I should like to be told by what process the form 

 of the internal strata of< the earth had been so nicely determined. 

 Possibly, however, I may not understand the expression " in- 

 ternal strata'''' All I believe to be ascertained is, that of corre- 

 sponding sections of the interior the density is nearly the same, 

 and if so, my inference is, not that the earth has never changed 

 its axis of rotation, but that, if it has done so, the interior was 

 then sufficiently pliant to accommodate itself to the change. 



A much more formidable objection to the employment of such 

 a cause is, that, if once called in, we must take it with all its 

 consequences. The effects produced by it will not be what we 

 wish performed, but what its nature obliges it to perform. In 

 explaining the phenomena of Melville Island, it might render 

 inexplicable those of the rest of the world. If we choose to 

 change the axis upon which the earth revolves, let us at least fix 

 upon the best time for doing it ; now. What is that time ? Im- 



