Hoyal Society. 69 



7. The expression obtained for the variation of gravity shows that, 

 if the angular velocity of rotation of the earth remained unchanged, 

 the waters on its surface would tend to accumulate towards the 

 equator, for the increase of gravity, in going from the equator to the 

 poles, would be less according as the shell's thickness increased. 



March 22. —"An Account of the Aurora Borealis of the 17th of 

 November ISiS." By the Rev. Charles F. Watkins. Communicated 

 by the Marquis of Northampton, V.P.R.S. 



The author states that : " About half-past 7 p.m. the sky assumed 

 the appearance which it usually does immediately preceding the ac- 

 tion of what are called the Northern Lights. In the northern half 

 it was quite clear for about forty-five degrees from the meridian, of 

 a pale blue, and covered with a faint light, such as generally ushers 

 in the moon at her rising. Towards the east and west this light 

 gradually diminished, and south of those cardinal points the dimness 

 as gradually thickened. 



" Soon after eight the coruscations began by the usual lambent 

 strokes of a shining filmy matter, like the sudden shooting forth and 

 instantaneous retroceding of a serpent's tongue. They commenced 

 in the north-east, and shot upwards in an angle of about 70 degrees 

 of inclination towards the south, and to about 60 degrees in length, 

 more or less, leaving the sky clear to the north, and in a manner 

 gradually chasing the clouds, upon whose receding bounds they 

 glanced further to the south. 



" In a short time the same kind of electrical action commenced 

 in the north-west quarter of the heavens, and continued simultane- 

 ously with that from the north-east, both increasing in rapidity, in- 

 tensity and depth of colour ; till at length an entire hemispherical 

 arch of crimson and purple, but with uneven edges, spanned the 

 heavens from east to west, and remained suspended there for seve- 

 ral minutes. By degrees this arch broke up into separate masses of 

 highly and parti-coloured clouds, resembling those which are seen 

 floating about after the setting of an ardent sun. Meanwhile the 

 lighter coruscations continued, — now glancing upwards on the north- 

 ern edges of the clouds, which were still slowly receding to the south, 

 and now shooting up beneath them as they steadily retreated. At 

 the same time others of a redder hue played now alternately, and 

 now in union with them. 



" About a quarter past nine an extraordinary phenomenon oc- 

 curred, such as I never before witnessed ; the zenith assumed the 

 appearance of a crimson coronary apex to distinct but connected 

 bands of various shades of crimson, green and purple, in which the 

 crimson prevailed, flowing down from thence like a canopy, encir- 

 cling the upper portion of the heavens, which to me presented the 

 inside view of a ribbed and vaulted cupola. By degrees this beau- 

 tiful creation dissolved, and the body of clouds, against which the 

 electrical forces seemed to have been in hostile pursuit, fled away to 

 the south ; the elementary action ceased : a silent calm returned, 

 and nothing but the tranquil light, still shining in the north, re- 

 mained to indicate the recent scene. The wind had blown with a 



