TE11RESTRIAL MAGNETISM. 97 



and horizontal needles having become more and more 

 general), that the magnetic force and the inclination undergo 

 very dissimilar modifications, that the minimum of force 

 is in many places considerably distant from the line of no 

 dip ; and even, that in the northern part of Canada and 

 the Hudson Bay territories, in the meridian of about 92 or 

 93 W. long., the intensity of the magnetic force, instead 

 of increasing, decreases from about the lat. of 52 to the 

 magnetic pole in lat. 70. At the Canadian focus of 

 greatest magnetic force in the northern hemisphere, deter- 

 mined from Lefroy's observations, the inclination of the 

 needle, in 1845, was only 73 7', and in both hemispheres 

 the maxima of magnetic force are found associated with 

 inclinations much less than 90.( 96 ) 



Excellent and abundant as are the observations of mag- 

 netic force which we owe to the expeditions of Sir James 

 Ross, and Captains Moore and Clerk, in the Antarctic Seas, 

 yet there still remains much doubt respecting the positions 

 of the stronger and the weaker focus in the southern hemi- 

 sphere. James Eoss crossed the isodynamic curves of 

 highest value in several places, and after a careful discussion 

 of his observations Sabine places the one focus about the 

 lat. of 64 S.,.long. 137 30' E. Eoss himself, in the 

 narrative of his great voyage, ( 97 ) supposes the one focus to 

 be in the vicinity of the Terre Adelie discovered by .D'Ur- 

 ville, or in about lat. 67 S., long. 140 E. He thought 

 he was approaching the other focus in 60 S. lat., and 125 

 "W. long. ; but was afterwards inclined to place it consider- 

 ably farther to the south, nearer the magnetic pole, and 

 therefore in a more easterly meridian. ( 98 ) 



VOL. IV. H 



