94 COSMOS. 



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 maxi- 

 mum of the magnetic force, and even the two magnetic poles 

 fall within the western hemisphere. 3 



Adolph Erman's important observation of least intensity 

 in the Atlantic Ocean, east of the Brazilian province of 

 Espiritu Santo (20 S. lat., 35 02' W. long.), has been 

 already mentioned in our Delineation of Nature. 4 He found 

 in the relative scale 0.7062 (in the absolute scale 5.35). 

 This region of weakest intensity was also twice crossed by 

 Sir James Ross in his Antarctic expedition 6 between 1 9 and 

 21 S. lat., as well as by Lieutenant Sulivan and Dunlop 

 in their voyage to the Falkland Islands. 6 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 C S. lat. Whether there may not be 

 another zone of tolerably low intensity (0'97), lying north of 

 the equator (10 to 12 lat.), and about 20 east of the Phi- 

 lippines is a question that must be left for future investiga- 

 tions to elucidate. 



I do not think that the ratio which I formerly gave of 

 the weakest to the strongest terrestrial force requires 

 much modification in consequence of later investigations. 

 This ratio falls between 1 : 2^ and 1 : 3, being sorne- 



3 See the interesting Map of the World, divided into hemispheres by a 

 plane coinciding with the meridians of 100 and 280 E. of Greenwich, 

 exhibiting the unequal distribution of the magnetic intensity in the two 

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

 1837, pp. 72 74. Erman found that the intensity of the terrestrial 

 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'. 



4 Cosmos, vol. i, p. 181. 



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



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

 1840, pt. i, p. 143. They found as the minimum only 0.800. 



