70 TERRESTRIAL MAGNETISM. 



Coast of Siberia and on the Icy Sea. (Important phseno- 

 mena of the Aurora Borealis : Th. ii. S. 259.) 



1820. Scoresby, Account of the Arctic Eegions : 

 (experiments on the magnetic force : Yol. ii. p. 537 

 554.) 



1821. Seebeck's discovery of thermo-magnetism and 

 thermo-electricity. The contact of two metals (first tried 

 with bismuth and copper), or differences of temperature at 

 the two points of contact of a metallic ring, are recognised 

 as sources of excitement of magneto-electric currents. 



18211823. Weddell's voyage in the Southern Polar 

 Sea, to latitude 74 15' S. 



1822 1823. Sabine's two important expeditions for the 

 exact determination of the magnetic inclination and variations 

 of the magnetic force, and of the length of the pendulum 

 in different latitudes (west coast of Africa to the Equator, 

 Brazil, Havanna, Greenland to latitude 74 23', Norway 

 and Spitzbergen to latitude 79 50'). This comprehensive 

 work was published in 1824 : (Account of Experiments to 

 determine the Figure of the Earth, p. 460509.) 



1824. Erikson's magnetic observations on the shores of 

 the Baltic.' 



1825. Arago discovered rotation-magnetism. This 

 unexpected discovery was a consequence of his noticing, 

 when at Greenwich, that the time required by a dipping 

 needle, when set in vibration, to come to rest, was influenced 

 by neighbouring non-magnetic substances. In Arago's rota- 

 tion experiments the vibrations of a needle were found to be 

 affected by water, ice, glass, charcoal, and mercury. ( 70 ) 



1825 1827. Boussingault's magnetic observations in 

 different parts of South America (Marmato, Quito). 



