MAGNETIC INTENSITY. 93 



magnetic force not much less (1.803). For the weaker 

 northern or Siberian focus, 70 lat., 120 E. long., it was 

 found by Erman to be 1.74 in the relative scale, and by 

 Hansteen, 1.76, that is to say, about 13.3 in the absolute 

 scale. The Antarctic expedition of Sir James Ross has 

 shown us that the difference of the two foci in the southern 

 hemisphere is probably less than in the northern, but that- 

 each of the two southern foci exceeds both the northern in 

 intensity. The intensity in the stronger southern focus, 

 64 lat., 137 30' E. long., is at least 2.06 in the relative or 

 arbitrary scale, 1 while in the absolute scale it is 15.60; in 

 the weaker southern focus, 60 lat., 129 40' W. long., we find 

 also, according to Sir James Ross, that it is 1.96 in the arbi- 

 trary scale and 14.90 in the absolute scale. The greater or 

 lesser distance of the two foci from one another in the same 

 hemisphere has been recognised as an important element of 

 their individual intensity, and of the entire distribution of 

 the magnetic force. " Even although the foci of the southern 

 hemisphere exhibit a strikingly greater intensity (namely 

 15.60 and 14.90 in the absolute scale), than the foci of the 

 northern hemisphere (which are respectively 14.21 and 

 13.30), the total magnetic force of the one hemisphere cannot 

 be esteemed as greater than that of the other." 



" The result is, however, totally different when we sepa- 

 rate the terrestrial sphere into an eastern and western part, 

 in accordance with the meridians of 100 and 280 E. long, 

 reckoning from west to east in such a manner that the 

 eastern or more continental sphere shall enclose South 

 America, the Atlantic Ocean, Europe, Africa, and Asia, 

 almost as far as Baikal, whilst the western, which is the 

 more oceanic and insular, includes almost the whole of North 



1 I follow the value given in Sabine's Contributions, No. vii, p. 252 a 

 namely 15.60. We find from the Magnetic Journal of the Erebua 

 (Phil. Transact, for 1843, pt. ii, pp. 169172), that several individual 

 observations, taken on the ice on the 8th of February, 1841, in 77 47' 

 S. lat. and 172 42' W. long, yielded 2.124. The varlue of the intensity 

 15.60 in the absolute scale would lead us to assume provisionally that 

 the intensity at Hobarton was 13.51 (Magn. and Meteorol. Obscrv. made 

 at Hobarton, vol. i, p. 75). This value has, however, lately been slightly 

 augmented (to 13.56) (vol. ii, xlvi). In the Admiralty Manual, p. 17, 

 I find the southern focus of greatest intensity changed' to 15.8. 



