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, 14*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 south in 

 eight degrees of latitude, between sixty-six degrees 

 and a half and sixty-nine degrees of longitude 

 west of Paris. I mention expressly the difference 

 of the meridians ; for in submitting my isodyna- 

 mic observations^ to new researches, a geome- 

 trician deeply versed in the study of terrestrial 

 magnetism, Mr. Hansteen, discovered, that the 

 intensity of the force varies in the same mag- 

 netic parallel according to fixed laws, and that 

 the knowledge of these laws causes a great part 

 of the anomalies to disappear, which this phe- 

 nomenon seemed to offer. It is in general cer- 

 tain, 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 appeared 

 in Norway, under the title of Ueber der Magnetismus der 

 Erde, 1819, p. 14, and 66—77. 



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



