104 COSMOS. 



rosso between the large rivers of Xingu, Madera, andUcayle, 

 we have no observations of the dip until we reach the chain 

 of the Andes, where, 68 geographical miles east of the shores 

 of the Pacific, between Montan, Micuipampa, and Caxamarca, 

 I determined astronomically the position of the magnetic 

 equator, which rises towards the north-west (7 2' S. lat., and 

 78 46' W. long.) . 



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 . 29 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 meri- 



- 3 I here give, in accordance with my usual practice, the elements of 

 this not wholly unimportant determination : Micuipampa, a Peruvian 

 mountain town at the foot of Cerro de Guelgayoc. celebrated for its 

 rich silver mines, 6 44' 25" S. lat., 78 33' 3" W. long., elevation above 

 the Pacific 11,872 feet, magnetic inclination 0.42 north (according to the 

 centesimal division of the circle) ; Caxamarca, a town situated on a 

 plateau at an elevation of 9362 feet, 7 8' 38" S. lat., 5h 23' 42" long., 

 inclination 0.15 south; Montan, a farm-house (or hacienda), surrounded 

 by Llama flocks, situated in the midst of mountains, 6 33' 9" S. 

 lat., 5h 26' 51" W. long., elevation 8571 feet, inclination 0.70 north; 

 Tomependa, on the mouth of the Chinchipe, on the river Amazon, in 

 the province of Jaen de Bracamoros, 5 31' 28" S. lat., 78 37' 30" W. 

 long., elevation 1324 feet, inclination 3.55 north; Truxillo, a Peru- 

 vian town on the Pacific, 8 5' 40" S. lat., 79 3' 37" W. long., inclina- 

 tion 2.15 south. Humboldt, Recueil d'Observ. Astron. (Mvellement 

 Barometrique et Geode"sique) vol. i, p. 316, No. 242, 244 254. For 

 the basis of astronomical determinations, obtained by altitudes of the 

 stars and by the chronometer, see the same work, vol. ii, pp. 379 391. 

 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 secular alteration, with the conjecture of Le 

 Monnier, which was based upon theoretical calculation. He says, " th 

 magnetic equator must be in 7 40' north of Lima, or at most in 6 30 

 S. lat., in 1776"(Zoi's du Magnetisme comparees aux Observations, pt. ii, 

 p. 59). _ 



9 Saigey, Mem sur VEquateur Magnetique d'apres les Observ. 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 thia 

 equator from 1 to 0.867. 



