252 Variations nf tJie Terrestrial Magnetism 



have none in the neighbourhood of the equator : but wc 

 will not venture to compare these two classes of observa- 

 tions, which iTiav belong to dilFerent bv^tenis of forces, as 

 will bemcntioned hereafter. 



, Howes'er, the only comparison of results, collected in 

 Am-rica by M. Mumboldt, appears to us to establish with 

 *c^Maintv the increase of the magnetic force from the equa- 

 tor to the poles ; and, without wishing to connect them 

 t(X> cU^selv with the esi^eriments made in Euro[)e, we must 

 rc.maik. thai, tiie latter accord so far also with the preceding" 

 a<> to indicaie the phaeiionienon. 



. If we have thus divided the observations into zones pa- 

 i;6Uei to the equator, it is in order tiiat we may more easily 

 si'rovv the truth of the fact which results from them, and 

 ia parllcular to render the demonstration independent of 

 tho&e small anomalies which are inevitably mixed with 

 these results. 



Though these anomalies arc very trifling, thcv are, how- 

 ever, so sepsible, and so frequently occur, that thev cannot 

 bo ascribed entirely to errors in the observations. It ap- 

 pears more natural to ascribe them to the intluence of local 

 circumstances, and the particular attractions exercised by 

 collections of ferrugineous matters, chains -of mountains, 

 or by the large masses of the continents. 



One of us, indeed, having this summer carried to the 

 Alps the raa^jnetic needle employed in one of his late aerial 

 cxcursicms, he found that its tendency to return to the 

 magnetic meridian was constantly stronger in these moun- 

 tains than it was at Paris before his departure, and than it 

 lias been found since his return. This needle, which n)ade 

 at Paris &3"9° in 10 minutes of time, has varied in the fol- 

 lowing manner in the different places to which it was car- 

 ried : 



Niimher of oscillations ia 

 Plr.ces cf oliscrva'ion. ten minutes of time. 



Paris before his departure - &3-9 



Turin » _ _ h7'2 



On Mount Gcnevre - 89'2 



Grenoble ^ - _ 87-4 



Lyons _ _ . 87.3 



Geneva _ _ _ 86"3 



Dijon T - , - 84*5 



Paris, on his return - 83' 9 



These experiments were made with tlie greatest care, con- 

 jointly with excellent obscr-.'crs, and always emploving the 

 same watch verified by small pendulums, and taking the 



