ANTHELIA

(Yunanca köken — orijinale bakınız.) Luminous coloured rings, or glories, observed under certain conditions round the shadow of the spectator's own head. The conditions of the phenomenon are two; first, that the sun be near the horizon, and secondly, that the shadow be projected on a surface covered with dew drops, as a field of gra or stubble, or on a dense cloud or fog-bank, distant about 50 or GO yards. Generally the luminous appearance is very faint, and only one or two rings can be traced; but sometimes, in favourable circumstances, it is strikingly vivid, and two or three small ci>ncentric circles appear, surrounded by a much larger one, of whitish light, the head of the observer's shadow being at the common centre. Such brilliant Anthelia were observed by Bouguer and his companions on the clouds of the Andes (Figure de la Terre, p. 43.), and by Scores by on the fog-banks in the Arctic seas. Scores by gives the following dimensions of the rings as measured by him on one occasion: radius of the first or innermost ring 2°; of the second 40 45'; of the third 6° 30'; and of the outermost 3S0 50'. The cause of interior rings is thus explained l)y Fraunhofer. Light falling directly from the sun on the anterior side of an aqueous globule undergoes a refraction, and a portion of this refracted and consequently coloured light on falling on the interior surface of the opposite side of the globule is reflected back to the eye of the spectator. The large surrounding circle is supposed to be formed by a double reflection, as in the case of the ordinary rainbow. See Halo, in DicT. [s. 1365]