120 TERRESTRIAL MAGNETISM. 



Humboldt. Sawelieff. 



1829. 1851. 



Kasan. . . . 68 26'-7 68 30'-8 



Saratoff . . . 64 40'-9 64 48'-7 



Sarepta . . . 62 15''9 62 39'-6 



Astrachan . . 59 58''3 60 27'-9 



Tor the Cape of Good Hope we possess a very long, and 

 if we do not go farther back than from Sir James Ross and 

 Du Petit Thouars in 1840, to "Vancouver in 1791, a very 

 satisfactory comparison of observations of inclination, com- 

 prising an interval of almost fifty years. ( 142 ) 



The question whether the height of the station has any 

 unequivocally discernible influence on the magnetic inclina- 

 tion and force, ( l43 ) was the subject of careful examination 

 by me in my journeys in the Andes, the Ural, and the 

 Altai Mountains. I have already remarked, in the section 

 on the Force, how few unfortunately are the localities which 

 are suited to throw any certain light upon this inquiry, as 

 the points compared ought to be so near to each other as 

 to avoid all suspicion that the magnetic differences may be 

 due, not to the difference of elevation, but to the inflections 

 of the isodynamic and isoclinal curves, or to diversity in 

 the character of the rocks. I will confine myself to the 

 four principal results of the inclination in respect to which 

 I thought at the time, and on the spot, that they indicate, 

 with greater certainty than the force observations, an 

 influence of elevation in diminishing the inclination of the 

 needle. 



On the Silla de Caracas, which rises almost perpendicu- 

 larly 8100 Trench feet above the sea-coast of La Guayra, 



