Variation of the Magnetic Needle. 319 



son's Bay, the current from the Baltic and the German Ocean 

 passing into the Atlantic, between Norway and the Shetland 

 Islands, taking the place of the cold stream from Hudson's 

 Strait. 



It is to these circumstances I attribute the depression of 

 temperature during the glacial period, and the subsequent 

 rise of temperature to the German Ocean becoming open to 

 the Atlantic, and the descent of icebergs from the Arctic 

 regions into the Baltic being prevented by the elevation of 

 land in the north of Europe. 



I will now endeavour to shew the probability that the 

 variation in the declination of the needle has been caused by 

 this change of temperature. 



All the earliest observations on the needle shew that 

 Europe was at that time within the influence of the European 

 or Asiatic pole, as the declination was eastward. Columbus 

 is said to have been the first European who observed a 

 western declination. When on his voyage of discovery to 

 America in 1592, he found the eastern declination become 

 less and less, — near the Azores he crossed the line of no 

 declination, and then found it become westward. Now, as 

 there are two magnetic poles in this hemisphere, there must 

 be a line of no declination where the influences of the two 

 poles are equal ; and it is obvious that it was this line of no 

 declination which Columbus crossed, as the declination on 

 each side diverged from it. In 1657 this line had passed 

 eastward, and there was no declination in London, — at this 

 time the declination was still eastward at Paris. In 1666, 

 i.e. nine years later, it was at Paris, and the declination in 

 London had become eastward, — since that time it has gone 

 farther and farther eastward, and is now about 43° east 

 longitude. Nearly all Europe has thus become under the 

 influence of the American pole, and the declination in Lon- 

 don has gradually changed from 11° 15' east in 1580, to 24° 

 30' west, in the early part of the present century, since 

 which time no change of importance has taken place. 



During the time these changes of declination occurred in 

 Europe, no change of importance was observed in America? 

 and there is positive proof, that in Jamaica, from 1660 to 



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