64 C. Hamteen on the [Jan. 



America, while the whole of the Southern Atlantic, be- 

 tween South America and New Holland, is completely 

 destitute of any magnetic notice. According to De Rossel, 

 the intensity of Van Dieman's Land is 1*6. Tracing the 

 50° of latitude from South America to New Holland, we 

 observe that the intensity about the meredian 290° east, 

 must be somewhat above 1 *5, and that it decreases to 0*9 

 about 30° east from Ferro. 



Under Van Dieman's Land, 170° east from Ferro, it ap- 

 pears to be 1*7. Thus, it may be inferred that in the 

 southern hemisphere there are two maxima of intensity 

 on these two points, where the declination and inclination 

 of the needle have indicated the existence of two magnetic 

 poles. 



In the neighbourhood of the equator at Rio Janeiro, 

 Bahia, the Island of Ascension, and St. Thomas, the inten- 

 sity is = 0*9. Through these points, if a curve be dr^wn, 

 indicating this intensity, it will cut the equator at 30° east 

 from Ferro, and traverse Africa and the Indian Ocean near 

 the equator, and thence will pass through Java and Sura- 

 baya, where according to De Rossel it is 0*917. This 

 line by reflection is curved to the south as far as 50°S.L., 

 and gradually reaches Bahia. If we follow a meridian 

 from North to South, we observe that the intensity gradu- 

 ally decreases, and again increases on the south of the 

 equator ; but they differ much in different meridians. The 

 intensity in the meridian 300° at New York is 1-8, (40° N. L.) 

 and 1-0 in 7° S. L. in Peru. In the meridian 40° the greatest 

 intensity is 1*55, while in 20° or 30° S. L. the intensity is 

 scarcely above 0*8, which appears the smaller minimum, 

 using the term comparatively. Hence, the smallest inten- 

 sity # 8 in Africa, is to the greatest intensity 1*9 in North 

 America, as 1 to 19 or 1 to 2*4. 



Another remark is that the intensity upon the whole, is 

 greater in the northern than in the southern hemisphere. 

 Thus we find the intensity at New York in 40° North to be 

 1*8, while in the same southern latitude in New Holland 

 the magnetic force is only 1*57. The same fact holds with 

 regard to the Siberian pole ; for on the borders of China 

 south of the Baikal sea in 50° N. L. intensity is 1*6, but 

 in the same southern latitude only 1*3. 



