in different Latlhdes. 305 



prevent us from extending too far the consequences of the 

 laws which we observe*. 



From the preceding results, we may calculate the points 

 where the axis of the magnetic equator pierces the terres- 

 trial surface ; for their latitudes are equal to the comple- 

 ments of the obUquitv of thai equator, and then- meridian is 

 at 100' of longitude from its nodes. The north magnetic 

 pole is found also at 97-7975° (79^ l'4'O of north latituae, 

 and at 33-3719° (30° 2' 5") of longitude w'est from Pans, 

 which places it to the north of America. 1 he other mag- 

 netic pole, symmetric to the preceding, is situated in the 

 same latitude solath, and at 66-6281° (149° 67 55 ) of lon- 

 gitude east from Paris, which places it amidst the eternal 

 ice : indications entirely analogous to those of Wilke and 

 Lemonnier. ., . 



If we could reach these poles, the compass would be seen 

 vertical ; but if any confidence can be placed in the law 

 which we have discovered, this would be the only difference 

 which would be observed in regard to the inclination, and 

 we should be still as far distant as in Europe from the real 

 centres which produce it. This result might appear to be 

 of such a nature as to diminish the interest one might have 

 in visiting these horrid regions, had we not also the hope ot 

 discoverinc^ there new phiEuomena in regard to the inten- 

 sity of the magnetic force, and the influence of meteors. 



These consequences do not entirely accord with the 

 opinion pretty generally received, and which ascribes the 

 increase of the magnetic effects towards the north to the 

 ereat quantity of iron dispersed throughout these regions; 

 but it appears to us that this opinion is not agreeable to the 

 truth. The cordillera of the Andes contains an enormous 

 quantity of magnetic iron : the native iron of Chaco, that 

 problematic mass analogous to that of Pallas, and those ot 

 Xacateras in Mexico, is found even under tlie tropics f- 



• Since this memoir was read, we can advance something inore positive. 

 Observations made at the Cape of Good Hope, Cape Horn and New Hol- 

 land, by different navigators,' are very exactly represented by o"-" f^^mula 

 and it follows, that it extends also to the austral hemisphere. We hope 

 soon to have mtmerous and very exact observations on 'he..ncl.nat on of 

 the needle in that part of the earth. But we have thought it our duty to 

 add to our table such results as relate to it, and winch we have been able 

 to procure. We have inserted also two observations on the intensity, made 

 with Sreat care by M.Ro.sel, during the expedition oi dTntrecasteaux which 

 are verv important, as they prove that the terrestrial magnetic force in- 

 creases Lo in the auaral hemisphere in proportion as one removes from the 

 eouator Xote iil llit Auihon of the :\Jt'notr. *, • j • • r . .t,o» 



Twe may now add to the preceding considerations this decisrve fact tha 

 thJ intensity aho increa.es when one Approaches the south pole.-Aoa iy 

 thr Authort of Hit Memoir. 



Vol. 22. No. 88. S^/)M8Q5, U ^'^ 



