720 COSMOS. 



observed at the magnetic stations which, since 1828, have begun 

 to cover a considerable portion of the earth's surface, both in. 

 northern and southern latitudes;*' but four times in every cen- 

 tury an expedition of three ships should be sent out, to examine 

 as nearly as possible at the same time the state of the mag- 

 netism of the earth, so far as it can be investigated in those 

 parts which are covered by the ocean. The magnetic 

 equator, or the curve at which the inclination is null, must 

 not merely be inferred from the geographical position of its 

 nodes (the intersections with the geographical equator) ; but 

 the course of the ship should be made continually to vary 

 according to the observations of inclination, so as never to 

 leave the tract of the magnetic equator for the time being. 

 Land expeditions should be combined with these voyages, in 

 order, where masses of land cannot be entirely traversed, to 

 determine at what points of the coast-line the magnetic 

 (*urves (especially those having no variation) enter. Special 

 attention might also perhaps be deservedly directed to the 

 movement and gradual changes in the oval configuration, and 

 almost concentric curves of variation of the two isolated 

 closed systems in Eastern Asia, and in the South Pacific in 

 the meridian of the Marquesas Group.f Since the memo- 

 rable Antarctic expedition of Sir James Clarke Ross, (1839 

 1843,) fitted out with admirable instruments, has thrown so 

 much light over the polar regions of the southern hemisphere, 

 and has determined empirically the position of the magnetic 

 south pole ; and since my honoured friend, the great mathe- 

 matician, Frederick Gauss, has succeeded in establishing the 

 first general theory of terrestrial magnetism, we need not 

 renounce the hope that the many requirements of science and 

 navigation will lead to the realisation of the plan I have 

 already proposed. May the year 1850 be marked as the first 

 normal epoch in which the materials for a magnetic chart 

 shall be collected ; and may permanent scientific institutions 

 (Academies) impose upon themselves the practice of reminding 

 every twenty-five or thirty years governments, favourable to 

 the advance of navigation, of the importance of an under- 

 taking whose great cosmical importance depends on its long 

 continued repetition. 



* Cosmos, pp. 184 186. 

 t Op. tit., p. 175. 



