Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/419

and then the large and small halos are seen at the same time, and, reflexion taking place from the surfaces of the crystals, additional halos or parts of halos are formed as in figs. 1 and 2. At the points of intersection of the halos, images of the sun or moon sometimes appear ; when seen with the former, they are called parhelia or mock-suns, and when with the latter, paraselene or mock- moons. They are some times accompanied with flaming tails, and are usually of prismatic colours, as also are the halos and coronas. The latter are seen when fleecy clouds or mist intervene between the spectator and the sun or moon, to which they are in immediate proximity, thereby distinguished from the halos, which are formed at a distance from those luminaries. The predominating colour in coronse is red or orange.

Fig. 1.—Solar halos and parhelia seen at Brighton, June 5, 1875, by F. E. Sawyer, from 4 to 5.45 p.m. The halo a was a large one, having the zenith for its centre and going entirely round the heavens. It was a white band, and passed through the sun and the mock suns. The parhelia were of prismatic colours and had flaming tails.

Fig. 2—Halo system observed at Aberdeen, January 23, 1870, at 2 p.m. (see Symon's Monthly Meteorological Magazine, 1870, pp. 1 and 32, and frontispiece).

Fig. 3—A mountain spectre as seen by F. E. Sawyer on the Rigi, shortly after sunrise, August 18, 1877.

The second principal division of halos includes those which are seen opposite to the sun and moon. The first class of these comprises rainbows (a), which are occasioned by refraction of the light from the sun or rnoon, produced by falling rain, causing a bow with the prismatic colours in concentric bands and arranged as they appear in the solar spectrum. When the rain is abundant an inner bow is formed, the colours in which are in inverted order. Rainbows when seen from mountain tops and the topmasts of ships are completely circular. Fog-bows and mist halos (B) are somewhat similar. The former are frequently white in colour, and are seen in the English Channel, and also off the banks of Newfound land, being called by sailors " fog-eaters," from their in dicating a dispersion of the fog or mist. They appear to be formed in a horizontal or very oblique plane. Mist halos are seen in the vapour of fountains or waterfalls, and resemble rainbows. Mountain spectres (y) are caused by reflexion, and often appear accompanied by chromatic halos (see fig. 3). They generally occur on mountains when the sky between the observer and the sun is clear and there is a mist or cloud on the side of the mountain opposite to the sun, on which the summit of the mountain and the buildings and persons standing near are reflected. The most notable of mountain spectres is that of the Brocken, in the Harz mountains. Howitt says of this:—

"If the fog is very dry, you see not only yourself but your neigh bour ; if very damp, only yourself, surrounded by a rainbow-coloured glory, which becomes more lustroxis and beautiful the damper and thicker the fog is, and the nearer it approaches."

FIG. 4. A system of lunar halos and paraselenes figured in Buchan s Meteorology, p. 193.

Many of the ancient descriptions of miraculous appearances in the heavens may be attributed to the phenomena before mentioned. Among the chief of these is the appearance of a cross which the emperor Constantine alleged he saw in the heavens about noon when marching against Maxentius (about 313 a.d.), and which was the cause of his conversion to Christianity (Eusebius, Vitcu Constant., i. 27). Some writers have doubted the occurrence; but it is quite possible Constantine saw part of a system of solar halos, and two of these at right angles would form a cross (see fig. 4). The Brighton Herald of April 10, 1852, records a similar phenomenon on April 1st of that year at Brighton:—

"Sun setting, evening very fine with slight haze westward, when a ray of brilliant light shot upwards about 20 degrees above the horizon, directly perpendicular from the sun, and soon after its appearance it was crossed by a horizontal band of light of a paler colour, but about the some breadth. It formed a perfect cross, and lasted half an hour."

Halos and rainbows are considered valuable prognostica tions of future weather. Fragments of rainbows seen on detached clouds are called ivind-dogs, and are said to be a sign of wind. When the diameter of a corona contracts it shows the water particles are uniting into larger ones which may fall in rain, whereas if the corona extends, the particles are growing smaller, indicating increasing dryness. The open side of a halo is in some places considered to foretell the quarter from which bad weather may be expected.

See M. A. Bravais, " Memoire sur les Halos et les Phenomenes optiques qui les accompagnent" (Journal dc I jZcole Royale Pah/tech nique, 31 cahier, tome 18, Paris, 1847); Buchan, Introductory Text- Book of Meteorology, 1871; Proc. Met. Soc., 1875, vol. ii., new ser., pp, 438 to 444.

(f. e. s.)

HALS, Frans, was born at Antwerp according to most

authorities in 1584, and died at Haarlem in 16GG. As a portrait painter second only to Rembrandt, he displayed extraordinary talent and quickness in the exercise of his art coupled with improvidence in the use of the means which that art secured to him. At a time when the Dutch nation fought for independence and won it, Hals appears in the ranks of

its military guilds. He was also a member of the chamber