Report on Terrestrial Magnetism. 319 



England, from the times of Gilbert, Graham, and Halley to 

 the present, observes M. de Humboldt, has afforded a copious 

 collection of materials, adapted to the discovery of the physical 

 laws which govern the changes of the variation, whether at the 

 same place, according to the hours of the day and the seasons 

 of the year, or atdifferentdistances from the magnetic equator, and 

 from the lines of no variation. After adverting to the continued 

 observations of Gilpin and of Beaufov, omitting, however, to men- 

 tion the important ones by Canton, he observes that the arctic 

 expeditions have furnished a rich harvest of observations to 

 Captains Sabine, Franklin, Parry, Foster, Beechey, and James 

 Ross, and Lieutenant Hood ;* and that thus physical geography 

 is indebted to the attempts which have been made to discover 

 the north-west passage, and also to the explorations of the icy 

 coast of Asia, by Wrangel Lutke, and Anjou, for a considerable 

 accession of knowledge on terrestrial magnetism and meteoro- 

 logy. Excited, he observes, by the great discoveries of Oersted, 

 Arago, Ampere, Seebeck, and Faraday ; MM. Hansteen, Due, 

 and Adolphe Erman have explored, in the whole of the immense 

 extent of Northern Asia, the course of the isoclinal, isogonal, 

 and isodynamic curves ; 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 terres- 

 trial magnetism on the surface of the earth, with the same in- 

 struments, and by the same methods which he had employed from 

 Berlin to the mouth of the Obi, and thence to the Sea of 

 Okhotsb. 



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 generaliza- 

 tion of empirical laws, and by the mutual assistance rendered 

 by sciences which had long remained isolated. Now, he ob- 

 serves, 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 ema- 

 nations, those polar explosions which accompany the " magnetic 



* To this long list we may now add the name of Captain Bach ; nor ought 

 the name of Mr Fisher to be omitted. 



