66 COSMOS. 



as early as 1813. This work has exercised an undoubted 

 influence on the encouragement and better direction of geo- 

 magnetic studies, and it was followed by the author's general 

 charts of the curves of equal inclination and intensity for a 

 considerable part of the earth's surface. 



1819. The observations of Admirals Roussin and G-ivry 

 on the Brazilian coasts between the mouths of the rivers 

 Maranon and La Plata. 



18191820. Oersted made the great discovery of the fact 

 that a conductor that is being traversed by a closed elec- 

 tric current, exerts a definite action upon the direction of 

 the magnetic needle according to their relative positions, 

 and as long as the current continues uninterrupted. The 

 earliest extension of this discovery (together with that of 

 the exhibition of metals from the alkalies and that of the 

 two kinds of polarization of light probably the most bril- 

 liant discovery of the centuiy ) 69 was due to Arago's observ- 

 ation, that a wire, through which an electrical current is 

 passing, even when made of copper or platinum, attracts 

 and holds fast iron filings like a magnet, and that needles 

 introduced into the interior of a galvanic helix become 

 alternately charged by the opposite magnetic poles in ac- 

 cordance with the reversed direction of the coils (Ann. de 

 Chim. et de Phys., t. xv, p. 93). The discovery of these 

 phenomena, which were exhibited under the most varied 

 modifications, was followed by Ampere's ingenious theore- 

 tical combinations regarding the alternating electro-magnetic 

 actions of the molecules of ponderable bodies. These com- 

 binations were confirmed by a series of new and highly 

 ingenious instruments, and led to a knowledge of the laws 

 of many hitherto apparently contradictory phenomena of 

 magnetism. 



1820 1824. Ferdinand von Wrangel's and Anjou's ex- 

 pedition to the north coasts of Siberia and to the Frozen 

 Ocean. (Important phenomena of polar light, see th. ii, 

 s. 259.) 



1820. Scoresby's Account of the Arctic Regions ; experi- 

 ments of magnetic intensity, vol. ii, p. 537 554. 



1821. Seebeck's discovery of thermo-magnetism and 



69 Malus's (1808) and Arago's (1811) ordinary and chromatic polari- 

 Kution of Light. See Cosmos, vol. ii, p. 715. 



