MAGNETIC VARIATION. 125 



middle latitudes at about 9 or 10 A.M., whilst the maximum 

 did not appear to occur before 9 or 10 P.M. 66 Farther to the 

 north, at Hammerfest, in Finmark, 70 40' lat., Sabine found 

 that the motion of the needle was tolerably regular, as in the 

 south of Norway and Germany, 67 the western minimum being 

 at 9 A.M. and the western maximum at Ih. 30m. P.M.; he 

 found it, however, different at Spitzbergen, in 79 50' lat., 

 where the above-named turning hours fell at 6 and at 

 7h. 30m. A.M. In reference to the Arctic polar archipelago, 

 we possess an admirable series of observations, made during 

 Captain Parry's third voyage, in 1825, by Lieutenants Foster 

 and James Ross, at Port Bowen, on the eastern coast of 

 Prince Regent's Inlet, 73 14' N. lat., which were extended 

 over a period of 5 months. Although the needle passed 

 twice in the course of 24 hours through that meridian, 

 which was regarded as the mean magnetic meridian of the 

 place, and although no Aurora borealis was visible for fully 

 2 months (during the whole of April and May), the periods 

 of the principal elongations varied from 4 to 6 hours, and 

 from January to May, the means of the maxima and minima 

 of the western variation differed by only Ih.! The quantity 

 of the decimation rose in individual days from 1 30' to 

 6 or 7, whilst at the turning periods it hardly reaches as 

 many minutes. 88 Not only within the Arctic circle, but 

 also in the equatorial regions, as, for instance, at Bombay, 

 18 56' lat., a great complication is observable in the horary 

 periods of magnetic variation. These periods may be 

 grouped into two principal classes, which present great dif- 

 ferences between April and October on the one hand, and 

 between October and December on the other, and these are 

 again divided into two sub- periods, which are very far from 

 being accurately determined. 69 



56 Voy. en Islande et en Greenland, execute en 1835 et 1836, sur la 

 Corv. la Recherche; Physique (1838), pp. 214225, 358367. 



5 ? Sabine, Account of the Pendulum Experiments, 1825, p. 500. 



53 See Barlow's "Report of the Observations at Port Bowen," in the 

 Edlnb. New Philos. Journal, vol. ii, 1827, p. 347. 



59 Professor Orlebar, of Oxford, former superintendent of the Mag- 

 netic Observatory of the Island of Colaba, erected at the expense 

 of the East India Company, has endeavoured to elucidate the com- 

 plicated laws of the changes of declination in the sub-periods (Ob- 

 servations made at the Mayn. and Meteor. Observatory at Bombay in 



