MAGNETIC INTENSITY. 91 



in both hemispheres we find the maxima of the terrestrial 

 force coinciding with a comparatively small dip. 98 



However admirable and abundant are the observations of 

 intensity which we owe to the expeditions of Sir James Ross, 

 Moore, and Clerk, in the Antarctic polar seas, there is still 

 much doubt in reference to the position of the stronger and 

 weaker focus in the southern hemisphere. The first of these 

 navigators has frequently crossed the isodynamic curves 

 of greatest intensity, and from a careful consideration of 

 his observations, Sabine has been led to refer one of the 

 foci to 64 S. lat. and 137 30' E. long. Ross himself, in the 

 account of his great voyage, 97 conjectures that the focus lies 

 in the neighbourhood of the Terre d'Adelie, discovered by 

 D'Urville, and therefore in about 67 S. lat. and 140 B. long. 

 He thought that he had approached the other focus in 60 S. 

 lat. and 125 W. long.; but he was disposed to place it some- 

 what further south, not far from the magnetic pole, and 

 therefore in a more easterly meridian. 98 



Having thus established the position of the four maxima 

 of intensity, we have next to consider the relation of the 

 forces. These data can be obtained from a much earlier 



96 Sabine, in the Seventh Report of the Brit. Assoc. p. 77. 



9 ' Sir James Ross, Voyage in the Southern and Antarctic Regions, vol. i, 

 p. 322. This great navigator, in sailing between Kerguelen's Land and 

 Van Diemen's Land, twice crossed the curve of greatest intensity, first 

 in 46 44' S. lat. 128 28' E. long, where the intensity increased to 

 2.034, and again diminished, further east, near Hobarton, to 1.824 

 (Voy. vol. i, pp. 103 104) ; then again, a year later, from January the 

 1st to April the 3rd, 1841, during which time, it would appear from 

 the k>g of the Erebus that they had gone from 77 47' S. lat. 175 41' E. 

 long, to 51 16' S. lat. 136 50' E. long., where the intensities were 

 found to be uninterruptedly more than 2.00, and even as much as 

 2.07 (Phil. Transact, for 1843, pt. ii, pp. 211215). Sabine's result for 

 the one focus of the southern hemisphere (64 S.lat. 137 30' E. long.) 

 which I have already given in the text, was deduced from observations 

 made by Sir James Ross between the 19th and 27th of March, 1841 

 (while crossing the southern isodynamic ellipse of 2.00, about midway 

 between the extremities of its principal axis), between the southern 

 latitudes 58 and 64 26', and the eastern longitudes of 128 40' and 

 148 20' (Contrib. to Terr. Magn. in the Phil. Transact, for 1846, pt. iii, 

 p. 252). 



98 Ross, Voyage, vol. ii, p. 224. In accordance with the instructions 

 drawn up for the expedition, the two sonthern foci of the maximum of 

 intensity were conjectured to be in 47 S. lat. 140 E. long, and in CO 

 S. lat. 235 E long. (vol. i, p. xxxvi). 



