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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    described (page 158). They consist of beams, nearly perpendicular to the horizon, (or rather parallel to the dipping-needle, at the place where they are incumbent,) and rainbow-like arches cross- ing the magnetic meridian at right angles ; the arches seem to precede the beams in point of time, and, soon after the beams are formed, the arches usually disappear, so that the relative situations of an arch, and row of beams originating from it, are not easily determined ; it may be presumed the beams either rise from the arches or fall from them : I am inclined to think the former is the case. Now the arches are generally steady for consider- able intervals of time ; but they are observed mostly to move along the meridian, either southward or northward, before they vanish ; this motion seems to be rather by starts than slowly progressive. If, therefore, two or more observers, situate on the same magnetic meridian, should be so fortunate as to take the altitudes of the highest point of any arch at the same moment of time, the height of the arch above the earth might readily be found by well known rules. The beams, in general, are quite too fugitive to be observed for this purpose. From the observations, page 68, the altitude of such arch was taken at Kendal and Keswick, and the result of calculation brings out the height one hundred and fifty miles. The base of twenty-two miles is, however, too short to place much reliance upon. A much finer appearance was observed, on the 29th of March, 1826, at various places in