306 Royal Society. 



the horizon to the central ring or pole. The beams appeared to be 

 at nearly equal distances from each other, the entire colunm of them 

 stretching over a space equal to about one-fifth part of the visible 

 horizon, in the form of a fan. The whole figure rapidly changed 

 from a pure white light into a glow of brilliant colours of every tint, 

 variegating the undulating waves as they rolled on their way to the 

 pole of the aurora. In the course of three minutes these gave place 

 to the white flashing radiations. 



During the time of the aurora there were a great number of small 

 meteors, the direction of whose motion was from east to west, and 

 which appeared to be considerably below the sphere of the aurora. 



A box containing a delicately balanced needle, was exposed upon 

 the ground during the display of the aurora, but. did not appear to 

 be affected in the slightest degree till about one o'clock, when it was 

 observed to be considerably deflected. At the time when the needle 

 was disturbed, there was a dense column of radiating light in the 

 north-west and south-east. The reflexion from the north-west was 

 so clear, that when made to fall upon the polarizing plate of 

 M. Biot's polarizing apparatus, and a film of mica was placed upon 

 the stage of the instrument, the various colours produced by the 

 mica were beautifully clear and distinctly seen in the analysing glass. 



The author considers that the phenomenon of the colours which 

 were noticed, was probably caused by exhalations or vapour floating 

 in the atmosphere, betwixt the light of the aurora and the observer, 

 causing a refraction of the rays transmitted to the eye, analogous to 

 that which produces the phenomenon of halos. The continued 

 undulations of the auroral light, and also the passing of the rays 

 through thick and thin portions of the vapour, may, he considers, 

 have produced the great variety of colours. During the time of 

 the exhibition of this phenomenon, a thin fog or vapour was observed 

 on both sides of the auroral fan. The author is of opinion that the 

 cause which produced the variety of tints, is different from that 

 which occasioned the red-coloured auroral clouds. At the time of 

 the latter phenomenon the moon's position was nearly due east, and 

 a cloud moved from the west towards the east, which in its course 

 passed between the moon and the observer; as soon as the cloud 

 obscured the light of the moon, the red colour to the north-west 

 disappeared, but became visible when an opening in the cloud allowed 

 the rays to pass through, and again vanished when another portion of 

 the cloud cut off the light; and when the cloud had finally passed 

 over, the red colour in the different parts of the sky resumed the 

 same tint that it possessed before the moonlight was obscured by 

 the cloud. The author states that it would thus appear, that when 

 the light of the moon was incident at a certain angle upon the white 

 light, or some kind of vapour that surrounded it, a red colour was 

 produced ; and hence that the moon is in some way or other con- 

 nected with the phenomenon. He remarks, that the red colour 

 was first observed in the east, and the moon being in that quarter 

 of the heavens, the rays proceeding from it would first come in 

 contact with that part of the aurora towards the east. When the 



