146 COSMOS. 



declination of one denomination, that is to say, east or west 

 declination, is enlarging and contracting in very different di- 

 rections in contiguous parts of the earth. The lines of no 

 variation in Western Asia and in the Atlantic are advancing 

 from east to west, the former line having crossed Tobolsk in 

 1716 ; while in 1761, in Chappe's time, it crossed Jekather- 

 inenburg and subsequently Kasan ; and in 1829 it was found 

 to have passed between Osablikowo and Doskino, not far 

 from Nishnei-Novgorod, and consequently had advanced 24 

 45' westward in the course of 113 years. Is the line of tho 

 Azores, which Christopher Columbus determined on the 13th 

 of September, 1492, the same which, according to the ob- 

 servations of Davis and Keeling, in 1607, passed through tho 

 Cape of Good Hope 1 ?* and is it identical with the one which 

 we designate as the Western Atlantic, and which passes from 

 the mouth of the River Amazon to the sea-coast of North 

 Carolina ? If it be, we are led to ask, What has become of 

 thejine of no variation which passed in 1600 through Kon- 

 igsberg, in 1620 (?) through Copenhagen, from 1657 to 1662 

 through London, and which did not, according to Picard, 

 reach Paris, notwithstanding its more eastern longitude, un- 

 til 1666, passing through Lisbon somewhat before 1668 ?f 

 Those points of the earth at which no secular progression 

 has been observed for long periods of time are especially 

 worthy of our notice. Sir John Herschel has already drawn 

 attention to a corresponding long period of cessation in Ja- 

 maica, $ while Euler and Barlow|| refer to a similar condi- 

 tion in Southern Australia. 



Polar Liglit. 



We have now treated fully of the three elements of terres- 

 trial magnetism in the three principal types of its manifesta- 

 tion namely, Intensity, Inclination, and Declination in ref- 



* Sabine, Magn. and Meteor. Obscrv. at the Cape of Good Hope, vol. 

 i., p. Ix. 



t In judging of the approximate epochs of the crossing of the line of 

 no variation, and in endeavoring to decide upon the claim of no prior- 

 ity in this respect, we must bear in mind how readily an error of 1 

 may have been made with the instruments and methods then in use. 



t Cosmos, vol. i., p. 181. 



Euler, in the Mem. de TAcad. de Berlin, 1757, p. 176. 



|| Barlow, in the Phil. Transact, for 1833, pt. ii., p. 671. Great un- 

 certainty prevails regarding the older magnetic observations of St. Pe- 

 tersburg during the first half of the 18th century. The variation seems 

 to have been always 3 15' or 3 30' from 1726 to 1772 ! Ilansteen, 

 Magneti:inus dcr Erde, s. 7, p. 143. 



