396 



on the Upper Oroonoko and the Rio Negro, 

 these observations are of great importance for 

 the theory of lines of equal intensity, or isody- 

 namic lines*. The number of oscillations is 

 the same at Javita and at Quito, and yet the 

 magnetic dip is 26*4° at the former of these 

 places ; and at the latter, 1 4 -85°. The force 

 under the magnetic equator (at Peru) being ex- 

 pressed by unity, we find the intensity of force at 

 Cumana = 1*1779; at Carichana = 1*1575; at 

 Javita 1-0675 ; at San Carlos = 1*0480. Such is 

 the decrement of the force from north to sout h in 

 eight degrees of latitude, between sixty-six de- 

 grees and a half and sixty-nine degrees of longi- 

 tude west of Paris, I mention expressly the 

 difference of the meridians ; for in submitting 

 my isodynamic observations to new researches, 

 a geometrician deeply versed in the study of 

 terrestrial magnetism, Mr. Hansteen, discovered, 

 that the intensity of the force varies in the same 

 magnetic parallel according to fixed laws, and 

 that the knowledge of these laws causes a great 

 part of the anomalies to disappear, which this 

 phenomenon seemed to offer. It is in general 

 certain, as I have concluded from the whole of 

 my observations, that the intensity of force aug- 



* See the great work of Mr. Hansteen, which has ap- 

 peared in Norway, under the title of Ueber der Magnetismus 

 der Erde, 1819, p. 14, and 6—77. 



f Journal de Physique, vol. lix, p. 287. 



