1 44 COSMOS. 



According to the facts which we already generally know 

 concerning the position of lines of no variation, it would 

 appear that instead of the four meridian systems which were 

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

 to pole, 87 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 

 cannot, in accordance with the present state of our know- 

 ledge, 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 manner, 

 exhibiting one curvature directed southward and another 



tion, which I would here advocate, would, if it led to periodically- 

 repeated determinations, and consequently to expeditions prosecuted 

 simultaneously by land and sea, in accordance with some preconcerted 

 plan, give the double advantage of, in the first place, yielding a direct 

 practical application and affording us a correct knowledge of the annual 

 progressive movement of these lines ; and secondly, of supplying many 

 new data for the further development of the theory enounced by Gauss 

 (Gauss, 25). It would, moreover, greatly facilitate the accurate deter- 

 mination of the progression of the two lines of no inclination and no vari- 

 tion, if landmarks could be established at those points, where the lines 

 enter or leave continents at stated intervals, as, for instance, in the 



years 1850, 1875, 1900 In expeditions of this kind, which 



would be similar to those undertaken by Halley, many isoclinal and 

 isogonic systems would necessarily be intersected before the lines of no 

 declination and no inclination could be reached, and by this means the 

 horizontal and total intensities might be measured along the coasts, so 

 that several objects would thus be simultaneously attained. The views 

 which I have here expressed are, I am happy to find, supported by a 

 very great authority in nautical questions, viz. Sir James Ross. (See his 

 Voyage in the Southern and Antarctic Regions, vol. i, p. 105.) 



87 Acosta, Historia de las Jndias, 1590, lib. i, cap. 17. I have already 

 considered the question whether the opinion of Dutch navigators re- 

 garding the existence of four lines of no variation may not, through the 

 differences between Bond and Beckborrow, have had some influence on 

 Halley 'a theory of four magnetic poles (Cosmos, vol. ii, p 658) 



