MAGNETIC VARIATION. 14/5 



northward ; indeed it is so strongly curved at its north- 

 eastern extremity that the line of no variation forms an 

 ellipse, surrounding those lines which rapidly increase in 

 variation from without inwards. The most westerly and 

 the most easterly portions of this Asiatic curve of no varia- 

 tion, incline like the Atlantic line from south to north, and 

 in the space between the Caspian Sea and Lapland even from 

 SS.E. to NN.W. The third system, that of the Pacific, 

 which has been least investigated, is the smallest of all, and 

 lying entirely to the south of the geographical equator forms 

 almost a closed oval of concentric lines, whose variation is 

 opposite to that which we observe in the north-eastern part 

 of the Asiatic system, and decreases from without inwards. 

 If we base our opinion upon the magnetic declination ob- 

 served on the coast, we find that the African continent 88 only 

 presents lines which exhibit a western variation of from 6 

 to 29 ; for according to Purchas, the Atlantic line of no 

 variation left the southern point of Africa (the Cape of Good 

 Hope) in the year 1605, inclining further from east to west. 

 The possibility, that we may discover in some part of Central 

 Africa an oval group of concentric lines of variation, decreas- 

 ing to 0, and which is similar to that of the Pacific, can 

 neither be asserted or denied on any sure grounds. 



The Atlantic portion of the American curve of no varia- 

 tion was accurately determined in both hemispheres for the 

 year 1840, by the admirable investigations of General Sabine 

 who employed 1480 observations, and duly took into account 

 the secular changes. It passes in the meridian of 70 S. lat., 

 and about 19 W. long./ 9 in a NN.W. direction, to about 



w In the interior of Africa, the isogonic line of 22 15' W. is espe- 

 cially deserving of careful cosmical investigation, as being the interme- 

 diate line between very different systems, and as proceeding (accord- 

 ing to the theoretical views of Gauss), from the Eastern Indian Ocean, 

 straight across Africa on to Newfoundland. The very comprehensive 

 plan of the African expedition, conducted by Eichardson, Earth, and 

 Ovenveg, under the orders of the British Government, may probably 

 lead to the solution of such magnetic problems. 



sa Sir James Ross intersected the curve of no variation in 61* 30' S. 

 lat. and 27 10' W, long. ( Voyage to the Southern Seas, vol. ii, p. 357). 

 Captain Crozier found the variation in March, 1843, 1 38' in 70 43' S. 

 lat. and 21 28' \V. long., and he was therefore very near the line of no 

 variation. See Sabine, On the Magn. Declination in the Atlantic Ocecv* 

 for 1840, in the Phil. Transact, for 1849, pt. ii, p. 233, 



VOL, V. t 



