to the 52d degree of S. latitude. The results were pub lished in a General Chart of the Variation of the Compass in 1701 ; and immediatelyafterwards he executed by royal com mand a careful survey of the tides and coasts of the British Channel, an elaborate map of which he produced in 1702. On his return from a journey to Dalmatia, for the purpose of selecting and fortifying the port of Trieste, he was nomi nated, November 1703, Savilian professor of geometry at Oxford, and received an honorary degree of doctor of laws. Between 1713 and 1721 he acted as secretary to the Royal Society, hiving previously during eight years (1685-93) filled the same office, and early in 1720 he succeeded Flamsteed as astronomer-royal. Although in his sixty- fourth year, he undertook to observe the moon through an entire revolution of her nodes (eighteen years), and actually carried out his purpose. He died in the full possession of his faculties, January 14, 1742, at the age of eighty-five. Halley s most notable scientific achievements were his detection of the "long inequality "of Jupiter and Saturn, and of the acceleration of the moon s mean motion ; his dis covery of the proper motions of the fixed stars ; his theory of variation, including the hypothesis of four magnetic poles, revived by Hansteen in 1819, and his suggestion of the magnetic origin of the aurora borealis ; his calculation of the orbit of the 1682 comet (the first ever attempted), coupled with a prediction of its return, strikingly verified in 1759 and 1835; and his indication (in 1716, Phil. Trans., No. 348) of a method still used for determining
the solar parallax by means of the transits of Venus.
His principal works are Catalogus Stellar um Australian, London, 1679, the substance of which was embodied in vol. iii. of Flamsteed s Ifistoria Ccelcstis, 1725 ; Synopsis Astronomicc Comcticee, Oxford, 1705 ; Astronomical Tables, London, 1752 ; also eighty-one mis cellaneous papers of considerable interest, scattered through the Philosophical Transactions. To these should be added his version from the Arabic (which language lie acquired for the purpose) of the treatise of Apollonius De sectione rationis, with a restoration of his two lost books De sectione spatii, both published at Oxford in 1706; also his fine edition of the Conies of Apollonius, with the treatise by Serenus De sectione cylindri et coni, Oxford, 1710, folio. His edition of the Spherics of Menelaus was published by his friend Dr Costard in 1758.
HALLOWEVEN or Hallowe’en, the vigil of Hallowmas or All Saints Day. For some account of the singular observances by which it used to be, and to some extent still is, distinguished in Scotland and elsewhere, reference may be made to such works as Brand s Popular Antiquities, Chambers s Book of Days, or better still to the well-known poem of Burns. Though sometimes neglected in modern practice, the most essential part of HalloAve en ritual seems to consist in the lighting by each household of a bonfire at nightfall. This points to the very ancient and widely- diffused practice of kindling sacred fires at certain seasons of the year. While the Germanic nations had their Oster- feuer and Johannisfeuer, the Celtic had their Bealtine or Beiltine (see Beltane) and Samhtheine, the former on the eve of May 1, and the latter on the eve of November 1. Probably the winter as well as the summer festival was from the beginning regarded as a season at which the fairies were both unusually active and unusually propi tious; but there is no evidence to show that the methods of divination at present usually resorted to, although of great antiquity, were originally regarded as limited in their efficacy to any one day. See Grimm s Deutsche Mythologie, ch. xx. (Elemente), and ch. xxxiv. (Aberglaube).
HALLUIN, a town of France, in the department of Nord and arrondissement of Lille, and 11 miles N.N.E. of Lille, is situated near the right bank of the Lys. It contains several religious and benevolent institutions, including a hospital. The manufactures comprise linen and cotton goods, bricks, and oil. The family of Halluin or Halowin is mentioned as early as 1266. Baron Walter II. was one of the forty hostages sent to England in 1360 in exchange for the French King John. George of Halluin or Halowin was a general in the service of Henry V., and an ambassador to England. He died in 1537, leaving several treatises in Latin. The family, to which the title of duke had been granted in 1581, became extinct about the middle of the 17th century. Population of the town (1876), 8584.
HALMSTAD, the chief town of the Swedish Ian Halland or Halmstad, is situated on the east shore of the Cattegat, about 76 miles S.S.E. of Gothenburg, and at the mouth of the river Nissa. The castle is the residence of the gover nor of the province. Mention of the church of Halmstad occurs as early as 1462, and the fortifications are men tioned first in 1225. The latter were demolished in 1736. The Dominican and Franciscan monasteries, formerly in the town, are now quite destroyed. The harbour, built in 1837-40, at a cost of about 5250, admits ships of 10 feet draught, by means of which some trade in deals, pitch, and tar is carried on. The salmon-fishery is important. An archaeological society holds its meetings in Halmstad, and the popular magazine SvensJca Family Journalen is pub lished there. There are both mineral and sea-water baths in the neighbourhood. The oldest town-privileges of Halmstad date from 1307, while the first recorded event in its military history is the battle of Nissa, between Harold Hardrada and Sven Ulfsson. During the revolt of the miner Engelbrekt, it twice fell into the hands of the rebels in 1434 and 1436. The town appears to have been frequently chosen as the meeting-place of the rulers and delegates of the three northern kingdoms ; and under the union of Calmar it was appointed to be the place for the election of a new Scandinavian monarch whenever necessary. The Ian of Halland formed part of the territory of Denmark in Sweden, and accordingly, in 1534, during his war with the Danes, Gustavus Vasa assaulted and took its chief town. In 1660, by the treaty of Copenhagen, the whole district was ceded to Sweden. In 1676 Charles XII. defeated near Halmstad a Danish army, which was attempting to retake the district, and since that time Halland has formed part of Sweden. The population of the town in 1875 was 7136.
HALO (Latin, halo ; Greek, aXws), a luminous circle of light surrounding one of the heavenly bodies. A better definition perhaps would be " a ring of coloured light formed by refraction, on the passage of light from one of the heavenly bodies through the aqueous vapour surrounding the earth." This would include coronae and rainbows, and similar phenomena.
Halos may be divided into the following classes:—
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A. Simple. 1. Encircling B. Compound, i.e., halo systems. .C. Coron?e. a. Rainbows. 2. Opposite ft. Fog-bows and mist halos. y. Mountain spectres.
but in the tropics small halos were observed by Humboldt round the planet Venus. The formation of encircling halos of the classes A and B is generally attributed to refraction and reflexion of the rays of light by the presence of minute snow crystals in the upper strata of the air, and they occur usually when cirrus or cirro-stratus clouds exist. This theory was originated by" Descartes, and was adopted by Marriotte (in 1686), and subsequently followed by Dr Young and Sir Isaac Newton. It is, however, probable that some halos and certainly all coronaa (class C) are formed by refraction of light from globules of water suspended in the atmosphere. Simple halos are either about 22 degrees or 47 degrees in diameter. The ice or snow crystals, being
hexagonal in form, sometimes produce a double refraction,
