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.

    95/280 (page 69)
    of the arch, which, by trigonometry, comes out 150 English miles. The parallactic angle being so small, an error of | or 2° in the altitudes, is of great consequence.—Mr. Crostuwaite thinks the error in his observations could not exceed 14°, as the light was steady at the place where the altitude was taken.—Admitting the errors amounted to 2° at each place, which exceeds the bounds of probability, and that they were contrary ; we shall then find the height 83 miles in the one case, and 750 in the other, which may, I think, be safely considered as boundaries, betwixt which the true height was; and hence it may be inferred, that the arch would be visible to all Great Britain and Ireland ; that it is much to be wished, some persons in more distant places may have made similar observations upon the phenomenon, by which its height may be determined with more precision——In the mean time we shall consider it as 150 English miles. March 5.—The aurora at Kendal was seen at 8 P. M.; it was a bright still light awhile, but soon clouded.—The needle was not attended to. March 6.—At Kendal, a few fine streamers at 9 P. M. altitude 15°, and extent along the horizon 70°; exactly bisected by the magnetic meridian. It soon dwindled into a faint light. At 9h 35m brightest on the northern side.—The needle was 25° at 9h 4m,—24° 58’ at 9h 14m,—24° 50’ at 9h 35m, —24° 55’ at 10h 30m,—24° 52’ at 8 the next morning. March 13.—At Kendal the needle was, at 8h 830m 24° 30’,—at 10h 30m 25°’ 4’,—and 8 next morning 25° 4’.—There was a brightness northward at 10 P. M. but pretty much clouded ; this circumstance, with that of the needle, rendered it probable an aurora was in the atmosphere ;—it was confirmed by the follow- ing account. At Keswick, the same evening, at 8h 18ma horizontal arch, extent from NW. by W. to NNE. with faint streamers; the arch 20°, and streamers 25° altitude; the vertical streamers bore NNW. At 10, an arch from WSW. to ENE. its greatest alti- tude 30°: no streamers. March 30.—At Kendal, at 8 P. M. there appeared some faint concentric arches of an aurora; it was not further noticed till 8h 35m.