1837.] 



Report on Terrestrial Magnetism, 



227 



observes, by the great discoveries of Oersted, Arago, Ampere, Seebeck, 

 and Faraday ; MM. Hansteen, Due, and Adolphe Erman have explor- 

 ed, in the whole of the immense extent of Northern Asia, the course 

 of the isoclinal, isogonal, and isodynamic curves j and M. Adolphe 

 Erman has had the advantage during a long voyage from Kamtschatka 

 round Cape Horn to Europe, of observing the three manifestations of 

 terrestrial magnetism on the surface of the earth, with the same instru- 

 ments, and by the same methods which he had employed from Berlin 

 to the mouth of the Obi, and thence to the Sea of Okhotsh. 



M. de Humboldt remarks that our epoch, marked by great discoveries 

 in optics, electricity, and magnetism, is characterized by the possibility 

 of connecting phenomena by the generalization of empirical laws, and 

 by the mutual assistance rendered by sciences which had long remained 

 isolated. Now, he observes, simple observations of horary variation or 

 of magnetic intensity made at places far distant from each other, reveal 

 to us what passes at great depths in the interior of our planet or in 

 the upper regions of our atmosphere : those luminous emanations, 

 those polar explosions which accompany the " magnetic storm" appear 

 to succeed the changes which the mean or ordinary tension of terres- 

 trial magnetism undergoes. 



M. de Humboldt considers that it deeply interests the advancement 

 of mathematical and physical sciences that, under the auspices of His 

 Royal Highness the President, the Royal Society should exert its 

 influence in extending the line of simultaneous observations, and in 

 establishing permanent magnetic stations in the tropical regions on 

 both sides of the magnetic equator, in high southern latitudes, and in 

 Canada. He proposes this last station because the observations of 

 horary variation in the vast extent of the United States are yet ex- 

 tremely rare. Those at Salem, calculated by Mr. Bowdich, and com- 

 pared by Arago with the observations of Cassini, Gilpin, and Beaufoy, 

 may, he remarks, guide the observers in Canada, in examining whe- 

 ther there, contrary to what takes place in Western Europe, the (diur- 

 nal ?) variation does not decrease in the interval between the vernal 

 equinox and the summer solstice. 



In a memoir published five years ago, M. de Humboldt states that 

 he has indicated as stations extremely favourable for the advancement 

 of our knowledge, New Holland, Ceylon, the Mauritius, the Cape of 

 Good Hope, the island of St. Helena, some point on the eastern coast 

 of South America, and Quebec. In order, he observes, to advance 

 rapidly the theory of the phenomena of terrestrial magnetism, or at 

 least to establish with more precision empirical laws, we ought to 

 extend, and at the same time to vary, the lines of corresponding ob- 

 servations ; to distinguish, in the observations, of the horary variations, 

 what is due to the influence of the seasons, to a clear or a cloudy atmo- 



