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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    horizon to the western, will be one thousand eight hundred miles.— (See page 166.) Hence, if an arch is seen from the west of Ireland to descend to the west horizon, and from New York to descend to the east horizon, the parties will see } of their dis- tance covered by the arch. When it is considered that the Icelanders usually see the aurora to the north, and we in Britain on the same magnetic meridian, but 15° further from the pole, see the same aurora to the north, it 1s an unanswerable argument for its great elevation. If the summits of the beams of the aurora be three hundred miles above the earth in Iceland, they will be visible at Paris, (page 166;) and in Iceland, if the aurora extends 5° beyond the zenith to the south, it may still be characterized there as an au- rora borealis or xorthern lights, as the probability will be that more than three fourths of the illumin- ation will be derived from the northern half of the hemisphere. With regard to the exciting cause of the aurora, I believe it will be found in change of temperature. The phenomenon occurs most frequently in those months when the transitions of temperature are most rapid. In the following Table, the numbers of aurore seen in each month of the year are ar- ranged according to the sources from which they are derived. The first (1) is the list from page 178, or those observed at Kendal during five years ; the second (2) is from the list just before given; the