397 



merits from the magnetic equator to the pole * ; 

 but the rapidity of this increase appears to vary 

 under different meridians. When two places 

 have the same dip, the force is greatest to the 

 west of the meridian which traverses the centre 

 of South America ; and diminishes on the same 

 parallel at the east toward Europe. In the 

 southern hemisphere it seems to attain it's mini- 

 mum on the eastern coast of Africa ; and then 

 augments anew, on the same magnetic parallel, 

 as far as toward New Holland. I found the 

 intensity of the force at Mexico almost as great 

 as at Paris, yet the difference of the dip is more 

 than thirty-one degrees centf\ My needle, which 

 oscillated beneath the magnetic equator (in 

 Peru) two hundred and eleven times, would not 

 have oscillated under the same equator, in the 

 meridian of the Philippine Islands, at the utmost 

 only two hundred and two or two hundred and 

 three times. This striking difference results 

 from the comparison of my observations of in- 

 tensity made at Santa Cruz in Teneriff with 

 those collected there by Mr. de RosselJ seven 

 years before. 



* From the point where the magnetic equator crosses 

 Peru as far as Paris, 1* : 1-3703. (Obs. Astr.,\o\. i, p. lxxv. 

 MSmoires d'Arcueil, vol. 1, p. 21.) 



+ Mexico (in lat. 19° 25' 45", long. 101° 25' 30"). Dip 

 46 85°. Intensity of force, 242. Paris (in lat. 43° 5(V 15", 

 long. 0°0). Dip in 1798, 77*62°. Intensity, 245. 



X My needle oscillated at Teneriff two hundred and thirty- 



