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.

    267/280 (page 241)
    minous beams arising from them or amongst them, nearly perpendicular to the surface of the earth, or rather parallel to the dipping needle at the subja- cent places. These concentric arches extend to 20°, sometimes 30°, but very rarely to 40° from the magnetic poles: thus, the aurora is seldom seen to the south, in Iceland, which is about 25° from the magnetic north pole; still more rarely in the Orkney and Shetland islands, which are 35° from the pole ; and very rarely over the middle of Great Britain and Ireland, which is nearly 40° from the pole: thus, in the list recently given of one hun- dred and eighty-four aurore, only five or six arches were seen to pass the zenith, in this country. Au- rore are more numerous in the State of New York than in Britain, because that State is only 30° from the magnetic pole. This fact shows the latitude, or distance from the equator, is not the regulating principle of the aurora, as no aurora has ever been seen, that I am aware of, in Europe, on the parallel of New York. In the years 1828 and 1830, there were one hundred and two appearances of the au- rora in the State of New York ; in this country we have only registered forty-two. As auroral arches are seen in Great Britain, Ire- land and America at the same time, (page 221, Sept. 29,) it may be presumed the arch extends sometimes uninterruptedly from Europe to America. If the arch be one hundred and fifty miles high, its visible extent, at any one place, from the eastern ea