Chambers's encyclopaedia; a dictionary of universal knowledge for the people . er in which the phenomenon takes place. It isbriefly as follows: A dingy aspect of the sky in the direction ofthe north is generally the precursor of the aurora; and this gradu-ally becomes darker in color, and assumes the form of a circularsegment surrounded by a luminous arch, and resting at each endon the horizon. This dark segment, as it is called, has the appear-ance of a thick cloud, and is fiequently seen as such in the fadingtwilight before the development of the auroral light. Itsdensfty must, however, be v
Chambers's encyclopaedia; a dictionary of universal knowledge for the people . er in which the phenomenon takes place. It isbriefly as follows: A dingy aspect of the sky in the direction ofthe north is generally the precursor of the aurora; and this gradu-ally becomes darker in color, and assumes the form of a circularsegment surrounded by a luminous arch, and resting at each endon the horizon. This dark segment, as it is called, has the appear-ance of a thick cloud, and is fiequently seen as such in the fadingtwilight before the development of the auroral light. Itsdensfty must, however, be very small, as stars are sometimes seenshining brightly tliroughit. This dark segment is bounded by alumiiimis (Mc/iof a bluish-wliite color, which varies in breadthfrom 1 to 6 diameters of the moon, having the lower edge shaplydefined, and the upper edge only when the breadth of the arch issmall. This arch may be considered to be a part of a luminousring elevated at a considerable distance above the earths surface,and having its center corresponding with some point near the. Aurora Borealis. north pole. An observer several degrees south of this auroralring would see towards the nortli only a small arc of it, the largerpart being liid by the earth: to one situated not so far south, itwould appear as a larger and higher arch; to one placed below it,it would be seen as an arcli passing through the zenith; and toone situated within the ring and further north, it would be foundas an arch culminating in the south. On this supposition, nearlyall the various iiositioiis of the auroral arch ma} be accounted center of the ring corresponds probably witli the magneticnorth, which is at present situated in the island of Boothia it is that in Greenland, which is situated to the east of thisisland, tlie auroral arch lias been seen stretching from north tosouth with its highest point in the west. The luminous arch, once formed, remains visible for severalhours, and is in a
Size: 1732px × 1443px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidchamberssenc, bookyear1888
