MAGNETIC OBSERVATIONS. 75 



the empire, and in the summer of 1834 this suggestion was 

 fully carried out by Professor Lloyd and General Sabine, 

 and the operations of 1835 and 1836 were then extended to 

 Wales and Scotland (Report of the Meeting of the Brit. Assoc. 

 held at Newcastle, 1838, p. 49-196), with an isoclinal and 

 isodynamic chart of the British islands, the intensity at 

 London being taken as =1. 



1838-1843. The great exploring voyage of Sir James 

 Ross to the South Pole, which is alike remarkable for the 

 additions which it afforded to our knowledge by proving the 

 existence of hitherto doubtful polar regions, as well as for 

 the new light which it has diffused over the magnetic con- 

 dition of large portions of the earth's surface. It embraces 

 all the three elements of terrestrial magnetism numerically 

 determined for almost two thirds of the area of all the high 

 latitudes of the southern hemisphere. 



1839-1851. Kreil's observations, which were continued 

 for twelve years, at the Imperial Observatory at Prague, in 

 reference to the variation of all the elements of terrestrial 

 magnetism, and of the conjectured soli-lunar influence. 



1840. Horary magnetic observations with one of Gam- 

 bey's declination compasses during a ten years' residence in. 

 Chili, by Claudio Gay (see his Historia fisica y politico, de 

 Chile, 1847). 



1840-1851. Lamont, Director of the Observatory at Mu- 

 nich. The results of his magnetic observations, compared 

 with those of Gottingen, which date back as far as 1835. 

 Investigation of the important law of a decennial period* in 



* Arago has left behind him a treasury of magnetical observations 

 (upward of 52,600 in number) carried on from 1818 to 1835, which 

 have been carefully edited by M. Fedor Thoman, and published in the 

 (Euvres Completes de Francois Arago (t. iv., p. 498). In these observ- 

 ations, for the series of years from 1821 to 1830, General Sabine has 

 discovered the most complete confirmation of the decennial period of 

 magnetic declination, and its correspondence with the same period, in 

 the alternate frequency and rarity of the solar spots (Meteorological Es- 

 says, London, 1855, p. 350). So early as the year 1850, when Schwabe 

 published at Dessau his notices of the periodical return of the solar 

 spots (Cosmos, vol. iv., p. 83), two years before Sabine first showed 

 the decennial period of magnetic declination to be dependent on the 

 solar spots (in March, 1852, Phil. Tr. for 1852, pt. i., p. 116-121 ; Cos- 

 mos, vol. v., p. 76, note}, the latter had already discovered the import- 

 ant result that the sun operates on the earth's magnetism by the mag- 

 netic power proper to its mass. lie had discovered (Phil. Tr. for 1850, 

 pt. i., p. 216; Cosmos, vol. v., p. 136) that the magnetic intensity is 

 greatest, and that the needle approaches nearest to the vertical direc- 

 tion, when the earth is nearest to the sun. The knowledge of such a 



