in different Latiindss. - soS 



'produced \>y a magnet, lafi a itely small, placed in the centre 

 of the terrestrial surface; but by calculating from this for- 

 mula the inclination for the different latitudes, I have found 

 precisely the same numbers as M. Huinboldt observed cither 

 iu Europe or in America ; and it is not his observations only 

 that are represented in this manner; but those which have 

 beeti made in Russia, and at Kola in Lapland, durino" the 

 last transit of Venus, are also comprehended under the same 

 law. This is proved by the table annexed to this memoir, 

 in which I have calculated the observations of Mallet and 

 Pictet, with a part of those of M. Hun)boldt, which I took 

 at random, but, however, in svich a manner as to include all 

 the rest in the intervals. 



It is seen that the results of the formula deviate very little 

 from the observations ; but these difl'erences may be rendered 

 still smaller. By examining, indeed, the progress of the 

 errors, it is seen that the numbers given by calculation are a 

 httle too small in America for the low latitudes, and a little 

 too great for the high latitudes ; which shows that the whole 

 may be allowed, w ith some slight modifications, thither by 

 changing, however little, the node and inclination of the 

 magnetic equator, which two observations cannot determine 

 with the utmost exactness, or by displacing ever so little 

 our small magnet, leaving, however, its centre in the plane 

 of the magnetic equator, and placing it in such a manner 

 that it shall be a little nearer America than Europe. It is 

 by the observations themselves, when we shall have a greater 

 number, that we must be guided in these small correc- 

 tions. 



In a word, it must not be expected that we can represent 

 in a rigorous manner, by a mathematical law, all the in- 

 clinations observed J for the phiEnomcnon of the inclination, 

 thoush more regular than the other magnetic effects, is not 

 tree from some anomalies : this may be easily seen on con- 

 structing the curve given by the observations themselves. 

 Thus, for example, the inclination observed at Popavan is 

 0° 10' greater than at St. Carlos del Kio Negro, though 

 the magnetic latitude of the latter is 0-6832' (3- "') greater. 

 The case is the same with observations made at Javita and 

 Santa-Fe. (.)ther anomalies are discovered in the compara- 

 tive progress of the observations and forumla. This is the 

 case in regard to Carichana, St. Thonias de la Guyane, and 

 Carthagena. The increase of the inclination from the first 

 to the second of these points is by no mean^ in harmony 

 •A-ith the increase I'rom the second to the third ; and if we 



compare 



