310 Geological Phenomena explained 



is round this centre that the pole of the equator turns on a 

 radius of 23° 28', performing its revolution, according to 

 Delambre, in 25,920 years. 



It may be proper to notice here an objection of the French 

 astronomers, founded on an observation of the illustrious 

 De la Place. In his Exposition of the System of the World* , he 

 states : — "All the researches I have made on the displacing of 

 the poles of rotation on the surface of the earth prove to me 

 that it is insensible." 



It is difficult to account for such a conclusion, after the 

 admission that the poles of rotation revolve in th^ circum- 

 ference of a circle f of 2816 geographical miles in diameter. 

 Our globe seems to offer the only solution possible. M. de 

 la Place had found from observation, that, during the space 

 of 2000 years, the length of the day had but very slightly 

 varied ; and thence he probably conjectured the immobility of 

 the pole. 



If M. de la Place had had our globe before him, he would 

 have found that we, in western Europe, are situated near the 

 first meridian, on the colure of the winter solstice, which passes 

 through the poles of the ecliptic and the equator. 



The pole of the equator is now at nearly its greatest dis- 

 tance from us: it has moved through 30 degrees in 2160 

 years, which is about the commencement of the astronomical 

 observations on which any reliance can be placed. Its motion, 

 as it regards us, is therefore nearly due west ; and M. de la 

 Place appears to have been led into the error from the versed 

 sine of the arc being so small, that, for the last 2000 years, none 

 of the great phenomena arising from the change of position 

 of the pole could possibly afi'ect the portion of the globe 

 we inhabit. The great changes in the northern hemisphere 

 have, during this period, been confined to Russia and North 

 America, the history of which is confined to a few centuries. 



It would, therefore, seem that M. de la Place has mistaken 

 the versed sine of the arc of 30° for the real approach of the 

 ecliptic to the equator. 



The first point, therefore, is to determine the position of 

 the pole of the ecliptic. M. Guesney has supposed it to be 

 placed m the magnetic meridian passing through the island of 

 Ferro, at the distance of 23° 28' from the pole of the equator, 

 or in the polar circle at the back of Iceland; and geological 

 phenomena prove that he is very near the truth. 



From this point, then, and its antipodes, I have traced the 



* Exposition du Systeme du Monde, p. 277. f Ibid., p. 95. 



