MAGNETIC OBSERVATIONS. 67 



thermo-electricity. The contact of two unequally warmed 

 metals (especially bismuth and copper) or differences of tem- 

 perature in the individual parts of a homogeneous metallic 

 ring, were recognised as sources of the production of mag- 

 neto-electric currents. 



1821 1823. Weddell'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, Havannah, Green- 

 land as far as lat. 74 32', 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, pp. 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 

 afforded by his observation on the side of the hill in Green- 

 wich Park of the decrease in the duration of the oscillations 

 of an inclination needle by the action of neighbouring non- 

 magnetic substances. In Arago's rotation experiments, the 

 oscillations of the needle were affected by water, ice, glass, 

 charcoal, and mercury. 70 



1825 1827. Magnetic Observations by Boussingault in 

 different parts of South America (Marmato, Quito). 



18261827. 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 Lutke's voyage round the world; 

 the magnetic part was most carefully prepared in 1834 by 

 Lenz (see Partie N antique 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, Monte Video, the Straits of 

 Magellan, Chili, and Valparaiso). 



18271839. Quetelet, Etat du Magnetisme Terrestre 



7 Cosmos, voL i, p. 172. 



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