123 



of three years, I have been enabled to procure 

 the oscillation of the same needles, or needles 

 compared with each other, at Lima, under the 

 magnetic equator, at Mexico, at Naples, and at 

 Berlin, which afforded me the means of deter- 

 mining the relation that exists between the mag- 

 netic charges of the Globe in different climates. 

 From these extensive operations, an account of 

 which will be separately published, it follows, 

 that, supposing the intensity of the forces under 

 the equator ml, this intensity is, at Naples, 

 1-2745 ; at Paris, 1*3482 ; and at Berlin, 

 1-3703. 



We see already, that from the thirty-eighth to 

 the thirteenth degree of terrestrial latitude, in 

 the part of the northern Atlantic Ocean to which 

 the preceding table refers, the number of the 

 oscillations diminishes from 242 to 234, while the 

 dip varies from 75*76° to 50*67° of the centesi- 

 mal division. I endeavoured to make these ob- 

 servations in calm weather, and when the vessel 

 oscillated in a plane perpendicular to the plane 

 of the limb of the compass. The oscillations of 

 the needle are scarcely disturbed by those of the 

 vessel, the latter having, in a uniform wind, all 



may consider the points of the Globe that differ little in mag- 

 netic longitude as belonging to one system of forces. The 

 longitudes are computed from the point of intersection be- 

 tween the terrestrial and magnetic equators. 



2 E 



