Meteorological observations and essays / By John Dalton.

  • Dalton, John, 1766-1844.
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Meteorological observations and essays / By John Dalton. Source: Wellcome Collection.

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    reality, as well as in appearance, at the same dis- tance from the spectator as the cloud is. The author next presents us with an aurora, seen on the 22nd of November, 1825, under such a com- bination of circumstances as, he thinks, seems de- cisive of this question. Besides the small detached clouds, this evening, there was ‘“‘ another of a quite different character extended along the whole west- ern part of the sky, to about 25° or 30° above the horizon. It was one dense sheet or stratum com- paratively with the other clouds, very dark below, waved or furrowed from north to south, and cut off, at its east side, in an apparently straight edge, tending nearly north and south. It was coming on very slowly towards the east, and had, before next morning, prevailed over the other clouds, covering the heavens, and accompanied with a fresh westerly breeze, after a frosty night, which the 22nd of November was. The large sheet of cloud was much more elevated than the small de- tached ones, as was fully proved by some of the latter being projected in perspective on its dark under surface, and there appearing as white masses fully enlightened by the moon.’’* There were two auroral arches that evening, with streamers rising from them and slowly pro- * This great black cloud which the author describes, was nothing more than the one which is usually seen (or rather imagined) under the low brilliant aurore, and through which, stars of the first magnitude may be seen. It is a mere contrast of light and shade, and the cloud vanishes when the aurora does. Ere er