Disturbance of the Needle during an Aurora. 123 



rence of the aurora, and the striking irregularities, which follow, in 

 the broken line, represent those of the phases of the aurora ; the 

 second minimum, at, or before, twelve o'clock, corresponding to the 

 time of the occurrence of the diverging beams. 



Recurring to the table, to trace the changes of variation in the 

 needle within doors, we find it after nine P. M. sluggishly following 

 the changes of the needle out of doors, the north pole moving three 

 minutes of a degree to the westward between six and nine, P. M., 

 while the same pole of the needle without doors moved over 27.5 

 minutes : suddenly obeying the force which had already moved the 

 needle without doors, the variation diminishes 5.5' of a degree in five 

 minutes; between nine and ten, P. M. the diminution amounting 

 to 12.5', while that of the needle without, was but 2.5'. At this 

 point the needle within is stationary until after a decided impression 

 has been made upon the other needle, of which the variation began 

 again to increase. This increase is observable from forty minutes 

 past ten until half past eleven, between which observation and that at 

 twelve, the variation of the needle within doors has disminished 1.5', 

 and that without doors 16'. It should be observed that while this 

 needle regained at twelve o'clock the place which it had at half past 

 eleven, the one out of doors passed the corresponding point to the. 

 eastward, and was further to the east than at fifty minutes past ten. 

 The correspondence in the motion of the two needles, in any of the 

 intervals between two consecutive observations, although a general 

 one as to direction, is by no means the same in relative amount. 



It cannot fail to strike any one who attentively examines the fore- 

 going table, or the line traced to represent the results, that the great 

 changes in variation, the motions of the north pole of the needle to 

 the east or to the west, take place rapidly at the beginning of changes 

 in the phenomenon, and that the needle moves but slightly during 

 the continuance of the same class, and degree of brilliancy, of appear- 

 ances. The beautiful connexion which seems thus to be shadowed 

 out between the effects of electricity in motion, as recently developed 

 by the researches of Faraday, and these observed effects, is too ob- 

 vious not to strike the mind even of one more intent upon recording 

 facts than of hazarding speculations. 



The results of observations upon the dip recorded in the sixth col- 

 umn of the foregoing table, are not altogether regular. Between 

 ten, P. M. of the 10th, and one, A. M., of the Uth, there is a de- 

 crease to a minimum, which is sufficiently regular, a subsequent in- 



