110 TERRESTRIAL MAGNETISM. 



distance from the geographical equator in the Atlantic 

 Ocean being 16. In the interior of South America, in the 

 Terra incognita of Matto Grosso, between the great rivers 

 Xingu, Madera, and Ucayale, there is an entire absence of 

 observations until the chain of the Andes is reached, where, 

 68 miles east of the Pacific, between Montan, Micuipampa, 

 and Caxamarca, I determined astronomically the place of 

 the magnetic equator, (7 V S. lat., 78 46' W. long.), 

 which is there in course of ascending to the north- west ( lii8 ) 

 The most complete investigation which we possess 

 towards a knowledge of the whole course of the magnetic 

 equator, is that made by my friend Duperrey, for the years 

 1823 1825. In the course of his voyage of circumnavi- 

 gation, he crossed the magnetic equator six times, and has 

 been enabled to lay it down from his own observations for 

 220 degrees of longitude. ( 129 ) The two nodes are situated, 

 according to Duperrey's map of the magnetic equator, one in 

 about 6 E. long, in the Atlantic Ocean, the other in 177^ 

 E.long., in the Pacific, between the meridians of the Viti and 

 Gilbert Islands. After quitting the west coast of the South 

 American continent, probably between Punta de la Aguja and 

 Payta, the magnetic equator continues, in its prolongation 

 westward, to approach the geographical equator, until, in the 

 meridian of the Mendafia group of islands, the two equators 

 are only two degrees apart. ( 13 ) Ten degrees further to the 

 west, in the meridian of the western part of the Paumotu 

 Islands, or Low Archipelago, in 154 E. long., Captain 

 Wilkes, in 1840, found a similar distance of fully two 

 degrees of latitude between the geographic and magnetic 

 equators. ( 1S1 ) The intersection or node in the Pacific is 

 not 180 from the node in the Atlantic, being situated, not 



