62 C. Hans teen on the Jan.] 



latitude, but that under one and the same latitude in one 

 meridian it must be greater than in another. 



In 1799 Humboldt found that the oscillations of the needle 

 became constantly slower towards the South as far as about 

 7° S. L. in Peru, where the needle remained horizontal. 

 The direction of the magnetic force was also horizontal. 

 Southward from this point it begins to increase. 



The smallest intensity being taken as unity, then the 

 greatest force was in Mexico 1*32, and Paris 1 35. 



Captains Ross and Sabine increased our data with regard 

 to the magnetic force, but from the observations of Parry 

 and Franklin, Hansteen conceives that no accurate in- 

 ferences can be deduced, as the needles changed their mag- 

 netic state. The results of these observations as well as 

 those of Oersted and Erikson in Germany, France and 

 England ; of Keilhau, Bock, and Abel in Germany, Tyrrol 

 and Switzerland ; of Keilhau in Spitzbergen ; of Hansteen 

 in Norway, Sweden, Denmark and Finland ; (Pogg. xivj 

 and of Sabine in Africa, have afforded materials for a mag- 

 netic chart upon which the intensities of the different paral- 

 lels may be compared by what Hansteen terms isodynamic 

 lines. From these it appears that the intensity in America 

 in the same latitudes is much greater than in Europe, and 

 that the isodynamic lines running parallel with the equator in 

 America and in the Atlantic Ocean, pass towards the North- 

 east, but again in Europe resume their parallelism with the 

 equator. The line which represents, in the northern 

 hemisphere, the intensity 1*5, a little to the north of 

 Havannah, winds to the north-east by Iceland, and then 

 east between Spitzbergen and the North Cape. This line 

 of intensity again passes southward, and incloses the other 

 magnetic north pole in Siberia. The definition of this line 

 is in conformity with the observations made by Hansteen. 



Some time before Hansteen's tour in Siberia, Captain 

 King who was sent by the British Government to examine 

 the coast between Rio de Janeiro and Valparaiso, supplied 

 with Hansteen's apparatus for determining the intensity, 

 communicated many of his observations, through the 

 Admiralty, to Hansteen. Hansteen procured a very in- 

 teresting suite of data from Captain Liitke, determined 

 between the years 1826 and 1829, from Behring's Straits 



