308 On the Variations of the Terrestrial Magnetism. 



be susceptible, and consequently we confine ourselvet; to a 

 mere indication of" it. 



The phenomenon of the inclination has in maritime ob- 

 servatioas a particular and very remarkable advantage, 

 namely, tliar of not being subject to those areat progressive 

 variations which affect the dcdination. Without repeating 

 what we hnve already said above on the supposed constancy 

 ol' this phaeuomenon, it may be remarked that our formula 

 even affords a new proof that it may comprehend in the 

 same law the observations made thirty-six years ago in 

 Lapland, those which Lacaille brought back in 1731 from 

 the Cape of Good Hope, and those which M. Humboldt 

 has laiciy made in America. 



In short, when we tried to represent the inclinations in 

 different latitudes by the supposition of a magnet infinitely 

 small, very near the centre of the earth and perpendicular 

 to the magnetic equator, we did not pretend to consider 

 that hypothesis as any thing real, but only as a mathema- 

 tical abstraction useful to connect the results, and proper to 

 ascertain in future whether any changes exist. In regard 

 to the declina'.ion and intensity, \^'e freely confess that w^e 

 are entirely unacquainted with their laws or their causes; 

 and if anv philosopher is so fortunate as to bring them to 

 one principle, which explains at the same time the varia- 

 tions of the iiK-iination, it will no doubt be one of the 

 greatest discov ries ever made. But this research, exceed- 

 ingly difficuit, requires perhaps before it be attempted more 

 observations, and in p.T.rticular more precise observationa 

 than have hitherto been collected. For this reason we 

 thought we might pre ent to the class the preceding re- 

 searches, imperfec? as they are, begging it to receive them 

 with indulgence. Shtjuld we be so happy as to find that 

 our results appear ot anv utility, we propose to unite all the 

 exact observaiions which have b-^en made on this subject, 

 in order to give the utmost degree of precision to the law 

 we have discovered. 



Jj^RTHERN 



