AURIF′EROUS. Syn. Au′′rifer, Aurif′erus, L.; Aurifère, Fr.; Goldhaltig, Ger. In, mineralogy, that yields or contains gold; as auriferous sand, a. quartz, &c.
AURIPIGMEN′TUM†. [L.] Literally, paint of gold; appr., native orpiment. See Arsenic.
AURO-CHLO′′RIDES (klōre′-īdz). Compounds of terchloride of gold with chlorides of other bases. They may be prepared by mixing the terchloride of gold with the chloride of the base, in atomic proportions, and setting aside the solution to crystallise.
Prop., &c. Most of the auro-chlorides crystallise in prisms, dissolve in both alcohol and water, have an orange or yellow colour, and are decomposed at a red heat.
AURO-CY′ANIDES (ĭdz). In chemistry, compounds of cyanide of gold with cyanides of other bases. They may be formed in a similar manner to the auro-chlorides. Auro-cyanide of potassium is much used in electro-gilding.
AURORA BOREALIS. This luminous phenomenon, which is occasionally seen in our own country on clear frosty nights, and much more frequently and vividly by the dwellers in more northern latitudes, has been supposed to have an electrical origin, and to be occasioned by the passage of electricity through the rarefied strata of the upper regions of the atmosphere from the poles towards the equator. But physicists look upon this explanation as unsatisfactory, and inadequate to account for the effects produced. The hypothesis, however, seems to derive some support from the following fact:—
If one of Gassiot’s vacuum tubes be brought near to a powerful electrical machine, both while the machine is in motion and for some
time after, flashes of light may be seen passing from the wire at one end of the tube to the other extremity, which flashes bear a great resemblance to the auroral rays. The great doubt, however, is whether the conditions necessary to the production of the aurora are similar to those prevailing during this experiment, a doubt not lessened by the difficulty of satisfactorily accounting for the rarefied state of the atmosphere which is assumed to exist.
The forms which the aurora assumes are very varied and of great beauty; there appears, however, to be some general similarity in its aspect at the same locality. Its appearance is briefly as follows:—A dingy aspect in the heavens in a northernly direction is usually the precursor of the aurora; and this gradually becomes darker in colour, and assumes the form of a circular segment surrounded by a luminous arch, and resting at each end on the horizon. This dark segment presents the appearance of a thick cloud, and is frequently seen as such in the fading twilight, before the auroral light manifests itself. The density of this segment must, however, be very inconsiderable, as stars may sometimes be seen shining brightly through it.
This dark segment is bounded by a luminous arch of a blueish-white colour, which varies in breadth from 1 to 6 diameters of the moon, having the lower edge sharply defined, and the upper edge only when the breadth of the arch is small. This arch may be considered to be a part of a luminous ring, elevated at a considerable distance above the earth’s surface and having its centre corresponding with some point near the north pole. The preceding description indicates the general features of the appearance of the aurora borealis; but several auroras have been described which presented striking peculiarities. Sometimes the phenomenon assumed the form of one or more curtains of light, depending from dingy clouds whose folds were agitated to and fro as if by the wind. Sometimes this curtain appeared to consist of separate ribbons of light, arranged side by side in groups of different lengths, and attaining their greatest brilliancy at the lower edges. In this country the aurora borealis seldom assumes the distinctness and brilliancy which characterise its appearance in northern latitudes, but the description thus given indicates the type to which such appearance of the meteor more or less approaches. During the winter that prevails in the northern hemispheres the inhabitants of the arctic zone are deprived for months together of the sun’s light, and their long dreary night is relieved by the light emanating from this beautiful meteor, which shines with great frequency and brilliancy in those regions.