704 TERRESTRIAL MAGNETISM. 



On Feb. 11, another of the term days, there was great dis- 

 turbance of the magnetometer, but there seemed great doubt 

 whether the aurora had any connexion with it. This was eight 

 days after the sun had returned. 



[The results are recorded in divisions of the scale employed, and 

 the reading 318 corresponds to the mean declination : on days 

 when there were no remarkable disturbances, the change in the 

 deflection was from 10 to 15 divisions of the scale. 



On Jan. 5, at 9 p.m., the reading was 298, and increased to 326 

 at 9.30 p.m., after which the change was 20 divisions in 5 minutes, 

 and 16 more in the next 2 minutes to 362, then back to 315 in 

 the next 2 minutes, and to 298 in the next 2 minutes. 



Again, on Feb. 11, from 7.30 to 8, the changes in declination 

 are from 298*57 to 213-40. For some hours the disturbances 

 in both directions are very great. From lOh. to 13h. the change 

 is from 210 to 360. 



Each division of the scale is equivalent to 2' • 2, so that this 

 change of deflection amounts to 5° 30'. 



On March 21, again, there are great disturbances at 18h. and 

 19h., but not so sudden nor so great as on the 11th of February; 

 they are chiefly in the opposite direction.] 



" The observers were troubled with cloudy weather, which often 

 may have prevented them from seeing the aurora. Still it must 

 be considered that the declination needle was not generally greatly 

 disturbed by the aurora." 



Dr. Borgen remarks, with regard to the return of the sun being 

 accompanied by magnetic disturbance, that Dr. Kane's observa- 

 tions also show the greatest disturbance in the magnetic declina- 

 tion on Feb. 16, soon after the return of the sun. 



The maximum westerly declination occurs at 6 to 7 p.m., and 

 the minimum declination at 4 to 5 a.m., the needle being in its 

 mean position at 10 or 11 in the morning and in the evening 

 (Copenhagen time). The difference of time between Copenhagen 

 and Sabine Island is 2h. 6m. 



In November 1869, as the sun sinks towards the horizon, the 

 movement of tlie needle was observed to increase, whilst Dec. 21 

 shows very little disturbance of the needle ; the disturbance again 

 increases as the sun returns towards the horizon. The changes 

 which take place in the Polar regions are much greater than cor- 

 responding changes which are also observed in lower latitudes. 



" It would seem that with the appi-oach of the observer to the 

 magnetic pole the disturbances are increased." 



[As Dr. Borgen observes also : — " This is scarcely borne out, 

 " at any rate not to the same extent, by Dr. Kane's observa- 

 *' tions." Nor does it seem to be borne out by the observations 

 of English expeditions at Point Barrow, and at points nearer the 

 magnetic pole ; nor again by the results of the Austro -Hungarian 

 Expedition.] 



The Dip. 



The magnetic dip was determined on Aug. 6, 1869, by the 

 dipping needle, and on Aug. 7 by the induction magnetometer 

 with the astatic galvanometer. 



