122 COSMOS. 



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,* the western min- 

 imum 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 Lieu- 

 tenants Foster and Jamgs Ross, at Port Bowen, on the east- 

 ern coast of Prince Regent's Inlet, 73 14' N. lat, which 

 were extended over a period of five months. Although the 

 needle passed twice in the course of twenty-four hours through 

 that meridian, which was regarded as the mean magnetic 

 meridian of the place, and although no Aurora Borealis was 

 visible for fully two months (during the whole of April and 

 May), the periods of the principal elongations varied from 

 four to six hours, and from January to May the means of 

 the maxima and minima of the western variation differed by 

 only one hour! The quantity of the declination rose in in- 

 dividual days from 1 30' to 6 or 7, while at the turn- 

 ing periods it hardly reaches as many minutes.f Not only 

 within the Arctic circle, but also in the equatorial regions 

 as, for instance, at Bombay, 18 56' lat. a great complica- 

 tion is observable in the horary periods of magnetic varia- 

 tion. These periods may be grouped into two principal 

 classes, which present great differences between April and 

 October on the one hand, and between October and Decem- 

 ber on the other, and these are again divided into two sub- 

 periods, which are very far from being accurately determ- 

 ined.:!: 



* Sabine, Account of the Pendulum Experiments, 1825, p. 500. 



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

 the Edinb. Neiu PJdlos. Journal, vol. ii., 1827, p. 347. 



I 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 endeavored to elucidate the complica- 

 ted laws of the changes of declination in the sub-periods (Observations 

 made at the Magn. and Meteor. Observatory at Bombay in 1845, Results, 

 p. 2-7). It is singular to find that the position of the needle during 

 the first period from April to October (western min. 7h. 30m. A.M., 

 max. Oh. 30m. P.M. ; min. 5h. 30m., max. 7 P.M.) coincides so close- 

 ly with that of Central Europe. The month of October is a transition 

 period, as the amount of diurnal variation scarcely amounts to two 

 minutes in November and December. Notwithstanding that this sta- 

 tion is situated 8 from the magnetic equator, there is no obvious reg- 



