in different Latitudes. \ I 



the dip remains nearly constant on the parallels situated at 

 equal distances on both sides this equator : so that, by following 

 this law, the maximum of dip takes place in two opposite point? 

 of the earth, of which the one situated towards the north will 

 be found in about 25 degrees of west longitude, and (90^ — 12'' 

 or) 76" of north latitude ; whilst the other, diametrically op- 

 posite to it, will have 205° of west longitude, and 78" of south 

 latitude. 



Here, therefore, are the poles of the magnetic equator ; and 

 such indeed are approximately the positions that Philosophers 

 have before assigned to them *. But if we confine our- 

 selves to the consideratiorl of that half of the earth where the 

 laws of the dip appear to be the most simple, we may proceed 

 far bctond these general indications. For we can represent 

 these dips within a trifle in numbers, by supposing a very small 

 magnet at the centre of the earth; or, which is more accurate, 

 two magnetic centres, infinitely near each other, whose actions 

 are exerted on all points of the surface of the globe, according 

 to the common laws of magnetic forces; that is to say, in the 

 inverse ratio of the squares of the distances. This result is con- 

 firmed by the observations given in a Memoir published by 

 M. Humboldt and myself on the alterations of terrestrial mag- 

 netism in different latitudes. If we call e the dip of the mag- 

 netic needle, towards the north, in a place whose magnetic lati- 

 tude is A', we have 



,. , sin 2x' 



tang {i + X)-- 



cos2>.'— ^' 



* Mr. Ralph Walker placed the south maainetic pole in latitiKJe 65", and 

 longitude 130° east; and the north pole in latitude 71 » and longitude 80" 

 west, from observations which lie says he made " in July last," and his 

 book was pubh^iied in 1794. 



Mr. Leonard Eulcr, in an elegant dissertation on this subject, published 

 in the Memoirs of the Academy of Sciences of Berlin, placed the north 

 pole in 76° of north latitude and 96" west from TcnerifT, and the south 

 pole in 38* south, and 158° west from Teneriff. These are for the year 

 1757. 



Mr. Churchman supposed, in 1800, the north pole to lie in latitude 58* 

 north, and longitude 134 • west from Greenwich, near Cape Fairweatlier ; 

 and the south pole in latitude 58' south and longitude 165'' east from 

 Greenwich. He also imagined that the north pole has moved to the east- 

 ward on a parallel of latitude about 65" since the beginning of 1600, and 

 concludes that it makes a revolution in 1096 years The south pule has 

 moved less, and completes its revolution in 2*289 years. 



Krafft plaeed the north pole in latitude 70° north and longitude 23* 

 west from London, and the south pole in latitude 50* south and longitude 

 92° east. 



VVilcke placed the north pole in latitude 75" north, and in the longitude of 

 California, and the south pole in latitude 70' south in the Pacific Ocean. 



This 



