334 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OF 



it is not sufficient that the diurnal, regular, or disturbed 

 march of the needle should be observed at the magnetic 

 stations, which, since 1828, have begun to cover a consi- 

 derable portion of the earth's surface, both in northern and 

 southern latitudes ; ( 513 ) it would also be requisite to send 

 four times in each century an expedition of three ships, 

 which should have to examine, as nearly as possible at the 

 same time, the state of magnetism over all the accessible 

 parts of the globe which are covered by the ocean. The, 

 magnetic equator, or the line where the inclination is 0, 

 must not merely be inferred from the geographical positions 

 of its nodes (or intersections with the. geographical equa- 

 tor), but the course of the ship should be made to vary 

 continually, in accordance with the observations of inclina- 

 tion, so as never to quit the line forming the magnetic 

 equator at that time. Land expeditions should be com- 

 bined with the undertaking, in order, where masses of 

 land cannot be entirely traversed, to determine exactly at 

 what points of the coast the magnetic lines (and espe- 

 cially the lines of no variation) enter. The two isolated 

 "closed systems" or ovals, in eastern Asia, and m the 

 Pacific in the meridian of the Marquesas, ( 514 ) may, in 

 their movements and gradual changes of form, be deserv- 

 ing of particular attention. Since the memorable antarctic 

 expedition of Sir James Clark Boss (18391843), pro- 

 vided with excellent instruments, has thrown a great light 

 over the high latitudes of the southern hemisphere, and 

 determined empirically the place of the magnetic south 

 pole, and since my honoured friend Friedrich Gauss lias 

 succeeded in establishing the first general theory of ter- 

 restrial magnetism, we need not abandon the hope that 



