140 COSMOS. 



According to the facts which we already generally know 

 concerning the position of lines of no variation, it would ap- 

 pear that, instead of the four meridian systems which were 

 believed at the end of the 16th century to extend from pole 

 to pole,* there are probably three very differently formed 

 systems of this kind, if by this name we designate those 

 groups in which the line of variation does not stand in any 

 direct connection with any other line of the same kind, or 

 can not, in accordance with the present state of our knowl- 

 edge, be regarded as the continuation of any other line. Of 

 these three systems, which we will separately describe, the 

 middle, or Atlantic, is limited to a single line of no varia- 

 tion, inclining from SS.E. to NN.W., between the parallels 

 of 65° south and 67° north latitude. The second system, 

 which lies fully 150° farther east, occupying the whole of 

 Asia and Australia, is the most extended and most compli- 

 cated of all, if we merely take into account the points at 

 which the line of no variation intersects the geographical 

 equator. This system rises and falls in a remarkable man- 

 ner, exhibiting one curvature directed southward and anoth- 

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

 eastern extremity that the line of no variation forms an el- 

 lipse, surrounding those lines which rapidly increase in vari- 

 ation from without inward. The most westerly and the 

 most easterly portions of this Asiatic curve of no variation 

 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 northeastern part 

 of the Asiatic system, and decreases from without inward. 

 If we base our opinion upon the magnetic declination ob- 

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



* Acosta, llistoria de las Indicts, 1590, lib. i., cap. 17. I have al- 

 ready considered the question whether the opinion of Dutch naviga- 

 tors regarding the existence of four lines of no variation may not, 

 through the differences between Bond and Beckborrow, have had some 

 influence on Halley's theorv of four magnetic poles {[Cosmos, vol. ii., 

 p. 280). 



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

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

 mediate line between very different systems, and as proceeding (ac- 

 cording to the theoretical views of Gauss) from the Eastern Indian 



