106 COSMOS. 



cussion to which his magnetic observations gave rise. 33 This 

 point lies south of Gaubade, between Angolola and Angobar, 

 the capital of the kingdom of Schoa, in 10 7' N". lat., and in 

 41 13' E. long. The course of the magnetic equator in the 

 interior of Africa, from Angobar to the Gulf of Biafra, is as 

 thoroughly unexplored as that in the interior of South 

 America, east of the chain of the Andes, and south of the 

 geographical equator. Both these continental districts are 

 nearly of equal extent, measured from east to west, each 

 extending over a space of about 80 of longitude, so that we 

 are still entirely ignorant of the magnetic condition of nearly 

 one quarter of the earth's circumference. My own observa- 

 tions of inclination and intensity for the whole of the in- 

 terior of South America, from Cumana to the Rio Negro, as 

 well as from Cartagena de Indias to Quito, refer only to the 

 tropical zone north of the geographical equator, while those 

 which I made in the southern hemisphere, from Quito as far 

 as Lima, were limited to the district lying near the western 

 coast. 



The translation of the African node towards the west from 

 1825 to 1837, which we have already indicated, has been con- 

 firmed on the eastern coasts of Africa by a comparison of the 

 inclination-observations made by Pant on, in the year 1776, 

 with those of Rochet d'Hericourt. The latter observer 

 found the magnetic equator much nearer the Straits of Bab-el- 

 Mandeb, namely, 1 south of the island of Socotora, in 8 40' 

 "N". lat. There was, therefore, an alteration of 1 27' lat. for 

 49 years, whilst the corresponding alteration in the longitude 

 was determined by Arago and Duperrey to have been 10 

 from east to west. The direction of the secular variation of 

 the nodes of the magnetic equator on the eastern coasts of 

 Africa, towards the Indian Ocean, was precisely similar to 

 that on the western coast. The quantity of the motion 

 must, however, be ascertained from much more accurate 

 results than we at present possess. 



The periodicity of the alterations of the magnetic inclina- 

 tion, whose existence had been noticed at a much earlier 

 period, has only been established with certainty and 

 thorough completeness within the last twelve years, since 

 the erection of British magnetic stations in both hemispheres. 

 33 Duperrey, in the Comptes rendus, t. xxii, 1846, pp. 804 806. 



