152 Magnetism of the Earth. 



of war, at present engaged in a scientific voyage. In a letter which 

 I have received from him, dated from New Archangel, (Norfolk 

 Sound,) in July, 1827, he has been so obliging as to communicate 

 to me the results of several observations, which he had found oppor- 

 tunities of making in the passage from Conception. I have not avail- 

 ed myself of them in the accompanying sketch of the isodynamic 

 curves, because I regard his communication as private, until he shall 

 have returned and made his own observations public. At the date of his 

 letter, he was on the point of sailing for Bhering's Strait and Kamt- 

 chatka, in which voyage, as well as in his subsequent operations, he 

 will doubtless have obtained results of great interest. 



If we now direct our attention to the southern hemisphere, we find 

 nearly the whole field of enquiry untrodden. Of published observa- 

 tions, there are only those made by M. de Rossel, in the voyage of 

 D'Entrecasteaux, at Java, Amboyna, and Van Diemen's Land. Of 

 observations made, but not yet published, there are, (1st.) those of 

 Captain de Freycinet, at several stations visited by the expedition 

 under his command : of these no public account has yet, I believe, 

 been given : (2d.) those which are at present in progress by Captain 

 King, whilst engaged in the survey of the southern parts of Soutli 

 America. The results obtained by him in the first year of his sur- 

 vey, have been received in England : they commence at Rio Ja- 

 neiro, and are continued at intervals down the eastern coast, as far 

 as Port Famine : he will probably have since extended them to Con- 

 ception, on the western side, the limit of his survey in that quarter. 

 The results transmitted will require some slight modifications on his 

 return to this country, to compensate for differences of temperature, 

 &;c. : but none that can interfere with their general effect, in eviden- 

 cing a progressively and rapidly increasing intensity, from the neigh- 

 borhood of Rio, where it corresponds with the curve marked No. 9, 

 in the sketch of the northern hemisphere, to the Straits of Magellan, 

 where it is intermediate between the intensities designated by No. 2 

 and 3. The observations of M. de Rossel, indicate in like manner, 

 that at the period of his voyage, (towards the close of the last cen- 

 tury,) the several intensities, from that represented by No. 9, to that 

 represented by No. 2, were all comprised between Java in tlie north 

 west, and Van Diemen's Land in the south east. Hence, as far as 

 the evidence hitherto extends, it would appear that there are two 

 points of maximum intensity, in the southern as well as in the north- 

 ern hemisphere : but the geographical position of those points, and 



