MAGNETIC INCLINATION. i03 



mining the intersection of the magnetic meridian, render it 

 very probable that the south magnetic pole is situated in 

 the interior of the great antarctic region of South Victoria 

 Land, west of the Prince Albert mountains, which approach 

 the south pole, and are connected with the active volcano of 

 Erebus, which is 12,400 feet in height. 



The position and change of form of the magnetic equator, 

 that is to say, the line on which the dip is null, were very 

 fully considered in the Picture of Nature, Cosmos, vol i., 

 p. 176. The earliest determination of the African node 

 (the intersection of the geographical and magnetic equators) 

 was made by Sabine 36 at the beginning of his pendulum 

 expedition in 1822. Subsequently, in 1840, the same learned 

 observer noted down the results obtained by Duperrey, 

 Allen, Dunlop, and Sulivan, and constructed a chart of the 

 magnetic equator 27 from the west coast of Africa at Biafra, 

 (4 N. lat. 9 30' E. long.) through the Atlantic Ocean and 

 Brazil (16 S. lat., between Porto Seguro and Rio Grande,) to 

 the point where, upon the Cordilleras, in the neighbourhood 

 of the Pacific, I saw the northern inclination assume a 

 southern direction. The African node, as the point of inter- 

 section of both equators, was situated, in 1837, in 3 E. long., 

 while, in 1825, it had been in 657 / E. long. The secular motion 

 of the node, turning from the basaltic island of St. Thomas, 

 which rises to an elevation of more than 7000 feet, was there- 

 fore somewhat less than half a degree westward in the course 

 of a year ; after which the line of no inclination turned 

 towards the north on the African coast, whilst on the Bra- 

 zilian coast it is inclined southward. The convexity of the 

 magnetic equatorial curve is persistently turned towards 

 the south pole, while in the Atlantic Ocean it passes at a 

 distance of about 16 from the geographical equator. For 

 the interior of South America, the terra incognita of Mat to 



had so long cherished the ambitious hope," says this navigator, '"'to 

 plant the flag of my country on both the magnetic poles of our globe; 

 but the obstacles which presented themselves being of so insurniount 

 able a character was some degree of consolation as it left us no grounds 

 for self-reproach" (p. 247). 



26 Sabine, Pendul. Exper. 1825. p. 476. 



27 Sabine, in the Phil. Transact, for 1840, pt. i, pp. 136, 139, 146. I 

 follow for the progression of the African node the map which is 

 appended to this treatise. 



