MAGNETIC OBSERVATIONS. 75 



1850, pt i, pp. 201 219) ; Coincidence of the epochs of the 

 greatest vicinity of the sun with the greatest intensity of 

 the force in both hemispheres, and of the increase of inclina- 

 tion, p. 216 ; (10) On the amount of magnetic intensity in 

 the most northern parts of the New Continent and upon the 

 point of greatest magnetic force found by Captain Lefroy in 

 52 19' Lat. (Phil. Transactor 1846, pt, iii, pp. 237336) ; 

 (11) The periodic alterations of the three elements of terrestrial 

 magnetism, variation, inclination, and intensity at Toronto 

 and -Ffobarton, and on the connection of the decennial period 

 of magnetic alterations with the decennial period of the 

 frequency of solar spots, discovered by ScJiwabe at Dessau 

 (Phil. Transact, for 1852, pt. i, pp. 121124). The observa- 

 tions of variation for 1846 and 1851 are to be considered as 

 a continuation of those indicated in Ko. 1. as belonging to 

 the years 18401845. 



1839. Representation of magnetic isoclinal and isodynamic 

 lines from observations of Humphrey Lloyd, John Phillips, 

 Robert Were Fox, James Ross, and Edward Sabine. As 

 early as 1833 it was determined at the meeting of the 

 British Association in Cambridge, that the magnetic inclina- 

 tion and intensity should be determined at several parts of 

 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, pp. 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 12 years, at the Imperial Observatory at Prague, in 

 reference to the variation of all the elements of tur- 



