Meteorological observations and essays / By John Dalton.

  • John Dalton
Date:
1834
Catalogue details

Licence: Public Domain Mark

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

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    Keswick and Whitehaven, another at Kendal, and another at Lancaster,—to which I would add, one over Carlisle, and another about one mile north of Warrington. I find it necessary now to assume some given height for the arches ; I cannot well allow them to be less than one thousand yards from the ground, because that is the height of Skiddaw; and Mr. CrostuwalIte, who reported to me a great number of observations on the aurora, never saw one be- twixt Keswick and that mountain, though they frequently rested on various parts of the mountain apparently, from its N. W. aspect. To follow up Mr. Farquuarson’s plan, we must next assume the length of the fringes or streamers to be, sup- pose another one thousand yards, making the sum- mit of each streamer two thousand yards above the ground: we must also assume the angle which the thickness of the rainbow-like arch subtends at the earth’s surface when in the zenith, say 5°. Then the absolute thickness of the ring will be found about eighty-seven yards ; if it is moved one mile from the zenith, or (which is the same thing) if we move one mile from the ring, its altitude will be no more than 30°; if two miles, then 16°; if three miles, 12°; if four miles, 8°, &c. ; at which great distance it would probably be invisible, only sub- tending about ¥ of a degree. The arch being in the zenith, the streamers over it would be invisible ; at one mile distance a row of streamers would be