5^8 GENERAL REMARKS. 



stations in the second of these localities only^ between Africa and 

 New Zealand. At Hobart Town, Sydney, and King George Sound, 

 there appears to have been little or no change in the dip since 

 the commencement of the present century. 



The arrangement of the changes of dip in the southern hemis- 

 phere in four divisions, characterised by an alternate increase and 

 decrease of dip, is in correspondence with the double flexure of the 

 lines of dip ; and is a consequence of the western motion of the 

 two southern magnetic poles. 



Careful observations made at St. Petersburgh, have shewn that 

 the annual change of the dip in the northern hemisphere takes 

 place altogether between the months of May and December ; there 

 being in fact a small movement in an opposite direction between 

 December and May. This fact is of great interest in its bearing on 

 the study of the causes of the magnetic phenomena. We have as 

 yet no corresponding knowledge in regard to the southern hemis- 

 phere. The magnitude of the annual change which Captain Fitz- 

 Roy's observations show is now taking place at the Cape of Good 

 Hope, is deserving of attention in this respect. A large amount of 

 annual change is obviously highly favourable for a determination 

 of all the circumstances belonging to it ; and its existence at the 

 Cape, where there is already a fixed observatory, points to that 

 station as most eligible for this investigation. 



The observations at Ascension shew that the epoch is fast 

 approaching when the needle will pass from north to south dip at 

 that island : it is extremely desirable that the period at which this 

 change takes place should be determined with as much precision 

 as possible. 



III. Intensity. 



I have discussed in the Seventh Report of the British Association, 

 the very important inferences in regard to the general distribution 

 of magnetism in the southern hemisphere, afforded by Captains 

 King and Fitz-Roy's most valuable series of intensity observa- 

 tions ; but no inferences in regard to the changes which this phe- 

 nomenon may be supposed to undergo can be drawn, as has been 

 done in the cases of the variation and dip, because we possess no 

 observations of the intensity made at a sufficiently early period to 

 afford good materials for such a comparison. 



EDWARD SABINE. 



