Meteorological observations and essays / By John Dalton.

  • John Dalton
Date:
1834
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Licence: Public Domain Mark

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

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    stitution of the aurora, namely, ‘that the aurora borealis has, in all cases, a determinate arrange- ment of figure, and follows an invariable order in its appearance and progress,” &c. So far I think I understand the author, and have nothing material to object to it; but I cannot comprehend the re- mainder of the description, and therefore cannot say whether Mr. F.’s ideas and mine are the same or not. But as I do not find one word in it as to the height of the phenomenon, or its distance from the surface of the earth, or to its being within, or be- yond the limits of the atmosphere, | may presume that the author can accommodate his hypothesis to any one height, to that of one thousand feet, one thousand yards, or one thousand miles above the earth, as circumstances may require. At page 113 of the Philosophical Transactions, we come to the consideration of height. Mr. F. had inferred, in the essay in 1823, from seeing a phosphorescent light apparently emerge from a cloud, that the light really arose from the cloud ; and the like on another occasion, in 1825. This last was so clear, that ‘‘it was impossible for a spectator to refer the aurora to a distance more remote than that of the mass of clouds; or to be- lieve that the former, and the light of the latter, were not parts of the same phenomenon.” This may be thought sound reasoning with some; but to me it is somewhat the same as inferring that the moon, emerging from behind a dense cloud, is ac- tually rising out of the body of the cloud, and is in