TERRESTRIAL MAGNETISM. 109." 



intersection of the magnetic meridians), render it very 

 probable that the present position of the south magnetic 

 pole is in the interior of the great Antarctic land called 

 South Victoria, west of the Albert Mountains, of which the 

 active volcano Mount Erebus, rising to the height of more 

 than 12000 feet, forms a part. 



The situation, and the alterations in the form of the 

 magnetic equator, or line on which the dip is 0, have been 

 already spoken of by me in the " Description of Nature" in 

 Yol. i. (S. 190192 and 431 ; Engl. p. 172174, and 

 411). The earliest determination of the African node 

 (the intersection of the geographical and rnagnetical 

 equators) was by Sabine, at the commencement of his 

 Pendulum Expedition in 1822 ( 126 ) : at a later period, 1840, 

 the same savant, by combining the observations of Duperrey, 

 Allen, Dunlop, and Sulivan, formed a map of the magnetic 

 equator ( 127 ), from the west coast of Africa, (4 N. lat., 

 9 32' E. long.) through the Atlantic Ocean and Brazil 

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

 point where I had found north dip change to south, on the 

 Cordilleras, not far from the Pacific. The African node, 

 or point of intersection of the two equators, was, in 1837, in 

 3 02' E. long. ; in 1825 it had been in 6'57' E. long. The 

 secular movement of the node, in receding to the westward 

 from the lofty basaltic island of St. Thomas, had there-: 

 fore been at the annual rate of rather less than half a degree, 

 thus causing the line of no dip to impinge on the African 

 coast at a progressively more northern point ; whilst at the 

 same time it descended more to the south on the Brazilian 

 coast. The convex summit of the magnetic equator con- 

 tinues to be directed towards the south, its maximum 



