MAGNETIC OBSERVATIONS. 67 



dition 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. Secbeck's discovery of thermo-magnetisni and ther- 

 mo-electricity. The contact of two unequally warmed metals 

 (especially bismuth and copper), or differences of temperature 

 in the individual parts of a homogeneous metallic ring, were 

 recognized as sources of the production of magneto-electric 

 currents. 



1821-1823. Wcddell's Voyage into the Antarctic Ocean 

 as far as lat. 74° 15'. 



1822-1823. Sabine's two important expeditions for the 

 accurate determination of the magnetic intensity and the 

 length of the pendulum in different latitudes (from the east 

 coasts of Africa to the equator, Brazil, Havana, Greenland 

 as far as lat. 74° 23', Norway and Spitzbergen in lat. 79° 

 50'). The results of these very comprehensive operations 

 were first published in 1824, under the title of Account of 

 Experiments to determine the Figure of the Earth, p. 460-509. 



1824. Erikson's Magnetic Observations along the shores 

 of the Baltic. 



1825. Arago discovers Magnetism of Rotation. The first 

 suggestion that led to this unexpected discovery was afford- 

 ed by his observation on the side of the hill in Greenwich 

 Park of the decrease in the duration of the oscillations of an 

 inclination-needle by the action of neighboring non-magnetic 

 substances. In Arago' s rotation experiments the oscillations 

 of the needle were affected by water, ice, glass, charcoal, and 

 mercury.* 



1825-1827. Magnetic Observations by Boussingault in 

 different parts of South America (Marmato, Quito). 



1826-1827. Observations of Intensity by Keilhau at 20 

 stations (in Finmark, Spitzbergen, and Bear Island), by 

 Keilhau and Boeck, in Southern Germany and Italy (Schum., 

 Astr. Nachr., No. 146). 



1826-1829. Admiral Liitke's Voyage Round the World; 

 the magnetic part was most carefully prepared in 1834 by 

 Lenz (see Partie Nautique du Voyage, 1836). 



1826-1830. Captain Philip Parker King's Observations 

 in the southern portions of the eastern and western coasts 

 of South America (Brazil, Montevideo, the Straits of Ma- 

 gellan, Chili, and Valparaiso). 



* Cosmos, vol. i., p. 179. 



