MAGNETIC INTENSITY. 93 



the northern hemisphere (which are respectively 14*21 and 

 13 •30), the total magnetic force of the one hemisphere can 

 not be esteemed as greater than that of the other." • 



"The result is, however, totally different when we sepa- 

 rate the terrestrial sphere into an eastern and western part, 

 in accordance with the meridians of 100° and 280° E. long., 

 reckoning from west to east in such a manner that the east- 

 ern or more continental sphere shall inclose South America, 

 the Atlantic Ocean, Europe, Africa, and Asia, almost as far 

 as Baikal ; while the western, which is the more oceanic and 

 insular, includes almost the whole of North America, the 

 broad expanse of the Pacific, New Holland, and a portion 

 of Eastern Asia." These meridians lie the one about 4° 

 west of Singapore, the other 13° west of Cape Horn, in the 

 meridian of Guayaquil. All four foci of the maximum of 

 the magnetic force, and even the two magnetic poles, fall 

 within the western hemisphere.* 



Adolph Erman's important observation of least intensity 

 in the Atlantic Ocean, east of the Brazilian province of Es- 

 piritu Santo (20° S. lat., 35° 0.2^ W. long.), has been already 

 mentioned in our Delineation of Kature.f He found in the 

 relative scale 0*7062 (in the absoli||| scale 5-35). This re-, 

 gion of weakest intensity was also twice crossed by Sir James 

 Ross, in his Antarctic expedition, J between 19° and 21° S. 

 lat., as well as by Lieutenant Sulivan and Dunlop in their 

 voyage to the Falkland Islands.§ In his isodynamic chart 

 of the entire Atlantic Ocean, Sabine has drawn the curve of 

 least intensity, which Ross calls the equator of less intensity, 

 from coast to coast. It intersects the West African shore 

 of Benguela, near the Portuguese colony of Mossamedes (15° 

 S. lat.) ; its summits are situated in the middle of the ocean, 

 in 18° W. long., and it rises again on the Brazilian coast as 

 high as 20° S. lat. Whether there may not be another zone 



* See the interesting Map of the World, divided into hemispheres by 

 a plane coinciding with the meridians o/'lOO anof 280 east of Greenwich, 

 exhibiting the unequal distribution of the magnetic intensity in the two 

 hemispheres, plate v., in the Proceedings of the Brit. Assoc, at Liver- 

 pool, 1837, p. 72-74. Erman found that the intensity of the terres- 

 trial force was almost constantly below 0-76, and consequently very 

 small in the southern zone between latitudes 24° 25' and 13° 18', and 

 between the western longitudes of 34° 50' and 32° 44', 



t Cosmos, vol. i., p. 187. 



t Voyage in the Southern Seas, vol, i., p. 22, 27 ; vide supra, p. 96, 



§ See the Journal of Sulivan and Dunlop, in the Phil. Transact. 

 for 1840, pt. i., p. 143, They found as the minimum only 0-800. 



