320 Mr G. A. Rowell on the 



1806 the declination did not vary in the slightest degree, 

 although in London, during those years, it amounted to full 

 24°. This fact is important, as it shews that the American 

 pole, during those years, has not shifted its position, and 

 that the cause of the variation must be connected with the 

 old continent. 



In accordance with the theory of magnetism, I have ex- 

 plained, the change of declination may be fairly accounted 

 for, either by the cold of the Asiatic pole decreasing in in- 

 tensity, or by an elevation of temperature in Europe driving 

 the centre or pole of cold farther towards the east; and there 

 can be no doubt that both these circumstances followed the 

 geological changes I have alluded to. 



It may be difficult to prove that a change of declination, 

 which has been going on up to the present century, can be 

 owing to geological phenomena, which occurred so long pre- 

 vious, but I hope to shew that there are fair grounds for 

 such an opinion. 



Assuming that during the glacial period the condition of 

 Europe was similar to that of America at the present time, 

 we may conclude that ice extended from the shores of Nor- 

 way, Scotland, Iceland, &c, in a similar way to what it now 

 does from Greenland, Cumberland Island, and Labrador. 

 (The extent of ice from these shores is given in Johnston's 

 Atlas, and is shewn in the Map). The Arctic Sea must, 

 therefore, at that time, have been blocked up with ice much 

 more than at present, consequently the Asiatic pole of cold 

 could not then have been in its present position, but was proba- 

 bly situate about Nova Zembla ; and if so, it must since that 

 time have receded more than 40° of longitude towards the east. 



This change of position will account for the change of 

 declination in Western Europe, as the Asiatic pole is now 

 chiefly affected by the evaporation from the Indian Ocean, 

 and quite removed from the influence of evaporation from 

 the warmer parts of the Atlantic. It is impossible to prove 

 how long was required to produce these results, after the 

 geological changes to which I have alluded ; to arrive at 

 a fair conclusion on the subject, it may be well to suppose 

 similar changes to take place in America at this time : the 



