36 REPORT— 1839. 



in the voyages of arctic discovery. In these voyages also, as is 

 well known, one locality, where the dip of the needle is 90°, 

 has been visited and determined by Captain James Clark Ross : 

 and it is the opinion of some philosophers that this may not be 

 the only point in the northern hemisphere where the direction 

 of the dipping needle is vertical, and the intensity of the hori- 

 zontal force consequently evanescent. 



But, when we turn to the antarctic regions, we find nothing 

 decisive or determinate. There are no continents admitting of 

 overland exploration, and the seas, which must be the scene of 

 inquiry, are visited by no commercial enterprise, and traversed 

 by no casual vessels belonging to the British or any other navy. 

 Nevertheless, it is vain to hope for a complete magnetic theory 

 till this desideratum be supplied. The unsymmetrical form of 

 the magnetic curves will baffle every attempt to reduce them 

 under general laws, and will remain, as at present, an object of 

 idle wonder, until these points, which may be looked upon as 

 the keys to the enigma they offer, shall have been ascertained. 

 It is on this ground that the Association have agreed, in their 

 4th Resolution herewith submitted, to recommend to Her Ma- 

 jesty's Government the appointment of an expedition expressly 

 destined to the investigation of the magnetic phaenomena of the 

 antarctic regions. 



The magnetic pole (or poles) of the southern hemisphere are, 

 in all probability, inaccessible, but this does not prevent their 

 situations being ascertained with tolerable precision by the con- 

 vergence of the magnetic meridians in their neighbourhood ; 

 taken in conjunction with observations of the dip ; by occasion- 

 ally landing and observing on the ice out of the reach of the 

 ship's attraction; and by exploring, as far as possible, all those 

 localities in which the needle may be observed to change its 

 direction with rapidity. 



On the other hand there is reason to believe, from Major 

 Sabine's report to the British Association in 1837, that the 

 points of greatest intensity are accessible, the one lying in 

 somewhere about 50° S., to the south of Van Diemen's Land ; 

 the other in about 60° S., about midway between the meridians of 

 Van Diemen's Land and Cape Horn : positions named, how- 

 ever, rather with a view to fix our ideas as to the means of re- 

 search, than from supposing it possible to speak with precision 

 at present. 



These points, it would, of course, be desirable that the vessels 

 of the expedition should endeavour to attain, or at least to ap- 

 proach sufficiently to settle their position and the amount of 

 the maxima of intensity. 



