l82 COSMOS. 



part d" Russia, has now a western declination, while at tha 

 close of the seventeenth centnry the needle first pointed diia 

 north, in London in 1657, and in Paris in 1669, there beinf? 

 thus a difference of twelve years, notwithstanding the sn7all 

 distance between these two places. In Eastern Russia, tc 

 the east of the mouth of the Volga, of Saratow, Nischni-Now- 

 gorod, and Archangel, the easterly declination of Asia is ad- 

 vancing toward us. Two admirable observers, Hansteen and 

 Adolphus Erman, have made us acquainted with the remark- 

 able double curvature of the lines of declination in the vast 

 region of Northern Asia ; these being concave toward the 

 pole between Obdorsk, on the Oby, and Turuchansk, and con- 

 vex between the Lake of Baikal and the Gulf of Ochotsk. In 

 this portion of the earth, in northern Asia, between the mount- 

 ains of Werchojansk, Jakutsk, and the northern Korea, the 

 isogonic lines form a remarkable closed system. This oval 

 configuration^^ recurs regularly, and over a great extent of the 

 South Sea, almost as far as the meridian of Pitcairn and the 

 group of the Marquesas Islands, between 20^ north and 45^^ 



From Gilbert's Pkysiologia Nova de Magnete, we see plainly (and the 

 fact is very remarkable) that in IGOO the declination was still null in 

 the region of the Azores, just as it had been in the time of Columbus 

 (lib. 4, cap. 1). I believe that in my Examen Critique (t. iii., p. 51) 

 I have proved from documents that the celebrated line of demarkatiou 

 by which Pope Alexander VI. divided the Western hemisphere between 

 Portugal and Spain was not drawn through the most western point of 

 the Azores, because Columbus wished to convert a physical into a po- 

 litical division. He attached great importance to the zone (raya) " in 

 which the compass shows no variation, where air and ocean, the latter 

 covered with pastures of sea-weed, exhibit a peculiar constitution, 

 where cooling winds begin to blow, and where [as erroneous observa- 

 tions of the polar star led him to imagine] the form (sphericity) of the 

 Karth is no longer the same." 



* To determine v>rhether the two oval systems of isogonic lines, so 

 singularly included each within itself, will continue to advance for cen- 

 turies in "the same inclosed form, or will unfold and expand themselves, 

 is a question of the highest interest in the problem of the physical 

 causes of terrestrial magnetism. In the Eastern Asiatic nodes the dec- 

 lination increases from without inward, while in the node or oval sys- 

 tem of the South Sea the opposite holds good ; in fact, at the present 

 time, in the whole South Sea to the east of the meridian of Kamt- 

 Bchatka, there is no line where the declination is null, or, indeed, in 

 nhich it is less than 2^ (Erman. in Pogg., Anna!., bd. xxxi., $ 129). 

 Yet Cornelius Schouten, on Easter Sunday, 1616, appears to have fouiiil 

 th3 declination null somewhere to the southeast of Nukahiva, in 15" 

 south lat. and 132° west long., and consequently in the middle of the 

 present closed isogonal system. (Hansteen, Magnet, der Erde, 1819, § 

 28.) It must not be forgotten, in the midst of all these considerations, 

 that we can only follow the direction of the magnetic lines in tb jir 

 progress as they are projected upon the surface of the Earth. 



