MAGNETIC INCLINATION. lUo 



The most complete series of observations which we pos- 

 sess in reference to the position of the magnetic equator was 

 made by my old friend Duperrey during the years 1823- 

 1825. He crossed the equator six times during his voyages 

 of circumnavigation, and he was enabled to determine this 

 line by his own observations over a space of 220°.* Accord- 

 ing to Duperrey's chart of the magnetic equator, the two 

 nodes are situated in long. 5° 50^ E. in the Atlantic Ocean, 

 and in long. 177° 20^ E. in the Pacific, between the merid- 

 ians of the Fejee and Gilbert islands. While the magnet- 

 ic equator leaves the western coasts of the South American 

 continent, probably between Punta de la Aguja and Payta, 

 it is constantly drawing nearer in the west to the geograph- 

 ical equator, so that it is only at a distance of 2° from it, 

 in the meridian of the group of the Mendana Islands.! 

 About 10^ farther west, in the meridian which passes 

 through the western part of the Paumotu Islands (Low 

 Archipelago), lying in 153° 50^ E. long.. Captain Wilkes 

 found that the distance from the geographical equator in 

 1840 was still fully 2°.J The intersection of the nodes in 

 the i^acific is not as much as 180° from that of the Atlantic 

 nodes; that is to say, it does not occur in 174° 10' W. long., 

 but in the meridian of the Fejee Islands, situated in about 

 177° 20^ E. long.'- If, therefore, we pass from the west coast 



79° 3' 37" W. long., inclination 2*'15 south. Humboldt, Recueil 

 d'Observ. Astron. (Nivellement Barometrique et Geodesique), vol. i., 

 p. 316, No. 242, 244-254. For the basis of astronomical determina- 

 tions, obtained by altitudes of the stars and by the chronometer, see 

 the same work, vol. ii., p. 379-891. The result of my observations 

 of inclination in 1802, in 7° 2' S. lat., and 78° 48' W. long., accords 

 pretty closely by a singular coincidence, and notwithstanding the sec- 

 ular alteration, with the conjecture of Le Monnier, which was based 

 upon theoretical calculation. He says, "the magnetic equator must 

 be in 7° 45' north of Lima, or at most in 6° 30' S. lat., in 177G" {Lois 

 du Magnetisme comparees aux Observations, pt. ii., p. 59). 



* Saigey, M^m. sur VEqiiatmr Magnctique d'apres les Ohserv. du 

 Capitaine Duperrey, in the Annales Maritimes et Coloniales, Dec, 1833, 

 t. iv., p. 5. Here it is observed that the magnetic equator is not a 

 curve of equal intensity, but that the intensity varies in different parts 

 of this equator from 1 to 0-8G7. 



t This position of the magnetic equator was confirmed by Erman 

 for the year 1830. On his return from Kamtschatka to Europe, he 

 found the inclination almost null at 1° 30' S. lat., 132° 37' W. long. ; 

 in 1° 52' S. lat., 135° 10' W. long.; in 1° 54' lat., in 133° 45' W. 

 long. ; in 2° 1' S. lat., 139° 8' W. long. (Erman, Magnet. Beob., 1841, 

 s. 636). 



X Wilkes, United States Exploring Expedition, vol. iv., p. 263. 



