PROGRESS IN MAGNETISM. 63 



men! of a law regulating the manifestation of force which is 

 a proximate, although not the ultimate, end of all investiga- 

 tions, has been satisfactorily effected in many individual 

 phases of the phenomenon. All that has been discovered by 

 means of physical experiments concerning the relations 

 which terrestrial magnetism bears to excited electricity, to 

 radiating heat and to light, and ail that we may assume in 

 reference to the only lately generalised phenomena of dia- 

 magnetism, and to that specific property of atmospheric 

 oxygen polarity opens at all events the cheering prospect, 

 that we are drawing nearer to the actual nature of the 

 magnetic force. 



In order to justify the praise which we have generally ex- 

 pressed in reference to the magnetic labours of the first half 

 of our century, I will here, in accordance with the nature 

 and form of the present work, briefly enumerate the principal 

 sources of our information, arranging them in some cases 

 chronologically, and in others in groups. w 



1803 1806. Krusenstern's voyage round the world (1812); 

 the magnetic and astronomical portion was by Horner (Bd. iii, 

 s. 317). 



1804. Investigation of the law of the increase in the in- 

 tensity of terrestrial magnetic force from the magnetic 

 equator northward and southward, based upon observations 

 made from 1799 to 1804. (Humboldt, Voyage aux Regions 

 Equinoxiales du Nouveau Continent, t. iii, pp. 615 623 ; 

 Lametherie, Journal de Pliysique, t. Ixix, 1804, p. 433 ; the 

 first sketch of a chart showing the intensities of the force, 

 Cosmos, vol. i, p. 179). Later observations have shown that 

 the minimum of the intensity does not correspond to the 

 magnetic equator, and that the increase of the intensity 

 in both hemispheres does not extend to the magnetic pole. 



1805 1806. Gay-Lussac and Humboldt, Observations of 

 Intensity in the south of France, Italy, Switzerland, and 

 Germany. Memoir "es de la Societe d'Arcueil, t. i. pp. 1 22. 



pp. 



839, 



Compare the observations of Quetelet, 1830 and 1839, with a 



68 The dates with which the following table begins (as, for instance, 

 from 1803 1806) indicate the epoch of the observation, while the 

 figures which are marked in brackets, and appended to the titles of the 

 works, indicate the date of their publication, which was frequently 

 much later. 



