272 Mr. Christie on the Aurora Borealis. 



manner in which the needle was adjusted, and how the cha- 

 racter of the forces acting upon it may be inferred from the 

 changes observed in its direction. 



I suspended a light needle, six inches in length, by a fine 

 brass wire ^i^th of an inch in diameter, and twenty-three 

 inches long, within a compass-box, having a ring graduated 

 to thirds of a degree. In the direction of the axis of the 

 needle, and at equal distances from its centre, were placed 

 two twelve-inch-bar magnets, the south-pole of each being 

 towards the south. These were made gradually to approach 

 the needle until their repulsive force on its poles was some- 

 what greater than the terrestrial directive force. When this 

 was the case, there were three positions of the needle in which 

 the forces acting upon it were in equilibrio, viz., when its south 

 pole or marked end pointed south when it pointed some- 

 where between north and west and likewise when it pointed 

 somewhere between north and east. At the time when the 

 observations which I am about to give were made these posi- 

 tions were nearly south, N. 37 W., N. 37 E., and the observa- 

 tions were made on the deviations of the needle when it 

 pointed between north and west. 



Being engaged on the 19th of April in preparing for a 

 journey, I should not have observed the needle on that even- 

 ing, nor have been aware of the occurrence of the aurora, had 

 not Mr. Faraday called to inform me of it. A few minutes 

 before ten o'clock, when I first saw it, there was a steady 

 stream of yellowish light in the west, 12 or 14 in breadth 

 near the horizon, and clearly perceptible to the height of 40, 

 although the moon was quite free from cloud : to the north 

 there were streamers shooting upwards, and masses of white 

 light sometimes forming irregular arches. Shortly afterwards 

 there arose from the horizon a very strong stream of light, 

 nearly in the magnetic meridian, 3 or 4 in breadth, very 

 distinct to the height of 50, and gradually lost towards the 

 zenith. This stream continued steady for about four minutes, 

 when it gradually disappeared. Immediately after this I ob- 

 served the needle, adjusted as I have described. 



At 10 h. P. M., I found the needle vibrating between 

 N. 43 40' W. and N. 42 40 7 W. The vibrations, continuing 



