RECORD OF AURORAL PHENOMENA. 45 



December IT, 1820. Temp. —30°. 



"At lh. 30m. a. m. (18th), a number of detached irregular masses of light were so arranged as to 

 form an arch 30° high, having a direction from N. W. to S. E. Weather clear, strong wind." — 

 Ibid., p. 608. 



December 18, 1820. Temp. —37°. 



"At 1 lh. 30m. p. m , the sky, which had previously been clear, was covered by a thin stratum of 

 clouds belonging to that modification of cirrus which forms the mackerel sky of sailors, con- 

 joined with small portions of what are termed by the same people ruares'-tails. Between the 

 bars of the former and the long fringes of the latter, streaks of deep-blue sky appeared. 

 These clouds were not dense enough to hide the larger stars completely, and from their first 

 appearance until they spread entirely over the sky, not more than a quarter of an hour elapsed. 

 On attentively regarding the sky for some time, the more rounded parts of the mackerel sky were 

 observed to send shoots across the blue spaces to unite with similar processes of the neighboring 

 masses. At the moment of junction, a yellowish light, with a slight tinge of red, was emitted 

 most brightly from the centres of the two clouds, but extending, though more faintly, to their 

 margins. A longer space of time had not elapsed than was required to note down these appear- 

 ances, when an arch of light was observed to cross the zenith, its extremities bearing east and 

 west, and terminating about 50° from the horizon. It was from 3° to 4° broad, and had a pale 

 gold-yellow color. When it ceased to emit light, its site was seen to be occupied by a range 

 of small fleecy clouds, similar to those already described, but more closely aggregated. The 

 moon now bore nearly south, and shone brightly, strongly illuminating the arch-formed range 

 of clouds just mentioned ; but their rarity was such that they showed no dark sides. Winds 

 very variable from S. W. to W. 

 About a quarter of an hour after the last observation, a round mass of cloud in the S. E. was 

 observed to assume, suddenly, an appearance of greater density, at the same time emitting from 

 its centre a yellowish light. Immediately after which, it shot forth towards the S. E. several 

 bright parallel horizontal streaks of light, which, crossing the near face of a neighboring mass 

 of clouds, became slightly curved from the south. They were about 8° or 10° above the 

 horizon, and were prolonged after passing before the clouds, through a portion of clear sky. A 

 few degrees beneath them, there were two or three dark layers of cirro-stratus. 

 The clouds, in their general arrangement at this period, had that appearance of convergency in 

 opposite points of the horizon which has been frequently noticed in a sky covered with cirri. 

 In the present instance, these points were at right angles to the magnetic north and south. In 

 the zenith, the mackerel sky prevailed ; but in the S. E. and N. W. (true), the clouds were more 

 dense, and presented various depending fringes towards the points of the horizon already men- 

 tioned. The magnitudes of the masses, too, in different parts of the sky, diminished so regu- 

 larly, as they receded from the zenith, as to convey an idea that their long sides were seen in 

 the N. E. and S. W. quarters of the sky, but their ends only in N. W. and S. E. quarters. 

 At midnight, several of the cirriform clouds, which were in the neighborhood of the moon's place, 

 reflected her light strongly, and hence appeared to have a pretty dense structure ; but when they 

 passed before the face of that luminary, they became nearly invisible, producing only a slight 

 halo or bur, but not sensibly diminishing the light. 

 At 20m. after midnight, the northern quarter of the sky became perfectly clear to the height of 35°, 

 the rest of the heavens being overspread by small fleecy clouds, separated by narrow intervals. 

 The edge of cloud bordering on the clear sky was well defined, ran east and west, and was 

 made up of the ends of small and rather broad parallel bars, having a direction from north to 

 south; a very common modification of cirrus. The moon was at this time wading through a 

 collection of small clouds, and was surrounded, at the distance of 10°, by a faint though distinct 

 halo. In the S. W., in a clear part of the sky, there existed a small spot of yellowish-white 

 light, which, for a few seconds, gradually increased in brightness, and then sent forth suddenly a 

 luminous beam, which, crossing a portion of the deep-blue sky, passed over the well-marked 

 edge of cloud above described, continued its course in front of the clouds, brightly illuminating 

 their faces, and terminated to the southward of the zenith, near the moon's place in the heavens. 



