the fun. He had in November before feen it in its defcent; and now haftened to complete his obfer vations upon it, from the royal obfervatory of France. His defign in this part of his tour was to fettle a correfpondence between the royal aftronomers of Greenwich and Paris; and to improve himself under the great Caflini. He went thence to Italy, where he spent great part of 1681; but his affairs calling him home, he returned to England. In 1683, he published his Theory of the variation of the magnetical compass; in which he fupposes the globe to be a great magnet, with 4 magnetical poles, or points of attraction: but afterwards thinking that this theory was liable to great exceptions, he procured an application to be made to K. William, who appointed him commander of the Paramour Pink, with orders to feek by obfervations the difcovery of the rule of variations, and to lay down the longitudes and latitudes of his majefty's fettlements in America. He fet out on this attempt on the 24th Nov. 1698; but having croffed the line, his men grew fickly; and his lieutenant mutinying, he returned home in June 1699. Having got the lieutenant tried and cathiered, he failed a 2d time in Sept. following, with the fame ship, and another of lefs bulk, of which he had alfo the command. He now traverfed the vaft Atlantíc from one hemisphere to the other, as far as the ice would permit him: and having made obfervations at St Helena, Brazil, Cape Verd, Barbadoes, the Madeiras, the Canaries, the coaft of Barbary, and many other latitudes, arrived in Sept. 1700; and published a general chart, in 1701, fhowing at one view the variation of the compass in all those places. Capt. Halley had been at home little more than half a year, when he was fent by the king, to obferve the course of the tides, with the lon. and lat. of the principal head-lands in the British channel; which having executed with his ufual accuracy, he published a large map of the Channel. Soon after, the Emperor of Germany refolving to make a convenient harbour for shipping in the Adriatic, Capt. Halley was fent by queen Anne to view the two ports on the coaft of Dalmatia. He embarked on the 22d Nov. 1702; paffed over to Holland; and going through Germany to Vienna, he proceeded to Iftria; but the Dutch oppofing the defign, it was laid afide. The emperor made him a prefent of a rich diamond ring from his finger, and honoured him with a letter of recommendation, written with his own hand, to queen Aane. Soon after his return, he was fent again on the fame bufinefs; when paffing through Hanover, he supped with the electoral prince, after. wards king George I. and his fifter the queen of Pruffia. On his arrival at Vienna, he was the fame evening prefented to the emperor, who fent his chief engineer to attend him to Iftria, where they repaired and added new fortifications to thofe of Triefte. Mr Halley returned to England in 1703; was made profeffor of geometry in the univerfity of Oxford, and received the degree of LL.D. He was scarcely settled at Oxford, when he began to tranflate into Latin from the Arabic, Apollonius de fellione rationis ; and to restore Apollonius's books Defectione fpatii, from the account given of them by Pappius; and he published the whole work in 1706. Afterwards he had a thare

in preparing for the prefs Appollonius's Conics and ventured to fupply the whole 8th book, the original of which is also loft. He likewise added Serenus on the fection of the cylinder and cone, printed from the original Greek, with a Latin tranflation, and published the whole in folio. In 1713, he was made fecretary of the Royal Society; in 1720, king's aftronomer at the royal obfervatory at Greenwich; and, in 1729, a member of the Academy of Sciences at Paris. He died. at Greenwich in 1742. His principal works are, 1. Catalogus fellarum australium. 2. Tabule aftronomica. 3. An abridgment of the aftronomy of comets, &c. He also published several works of Sir Ifaac Newton, who had a particular friendship for him, and to whom he frequently communicated his difcoveries.

HALLIARDS, n. f. [corrupted from haul and yard.] the ropes or tackles ufually employed to hoift or lower any fail upon its respective maft or stay. See JEARS.

HALLIFAX, Samuel, a learned English bishop, born at Chesterfield, in 1730, and educated at Cambridge, where he was regius professor of civil law. In 1781, he was made Bp. of Gloucefter, and in 1789 Bp. of St Afaph. He published an Analyfis of civil law, and Sermons on the prophecies. He died in 1790, aged 60.

HALLING, a lake of Norway, 64 miles NNW. of Chriftiania.

HALLINGDAL, a river of Norway, which runs into the bay of Chriftiania, near Holmeftrand, HALLNAS, a town of Sweden, in Upland. HALLOES, a town of Germany, in Holstein. * HALLOO. interj. [The original of this word is controverted: fome imagine it corrupted from a lui, to him! others from allons, let us go! and Skinner from baller, to draw.] A word of encouragement when dogs are let loose on their game.

Some popular chief, More noify than the reft, but cries halloo, And, in a trice, the bellowing herd came out. Dryden. (1.) * To HALLOO. v. a. [baler. French.] To encourage with fhouts

If, whilft a boy, Jack ran from school,
Fond of his hunting-horn and pole,
Though gout and age his speed detain,
Old John balloos his hounds again.
1. To chafe with fhouts -

3.

Prior.

(2.) To HALLOO. v. n. 1. To cry as after the dogs.

A cry more tunable

Was never balloo'd to, nor cheer'd with horn. Shakespeare.

2. To treat as in contempt.-Country folks hallooed and houted after me, as the arranteft coward that ever fhowed his fhoulders to his enemy. Sidn.

*To HALLOW. v. a. [halgian, halig, Sax. holy.] 1. To confecrate; to make holy.-When we fanctify or ballow churches, it is only to tefti

fy

fy that we make them places of publick refort; that we inveft God himfelf with them, and that we fever them from common ufes. Hooker.-It cannot be endured to hear a man profefs, that he putteth fire to his neighbour's house, but yet fo halloweth the fame with prayer, that he hopeth it fhall not burn. Hooker.

Is't Cade that I have flain, that monftrous traitor?

Sword, I will ballow thee for this thy deed, And hang thee o'er my tomb, when i am dead. Shakefp.

My prayers

Are not words duly hallow'd, nor my wishes More worth than vanities; yet prayers and wifhes Are all I can return. Shakefp. Henry VIII,

God from work Now refting, bleffed and hallow'd the feventh day,

As refting on that day from all his works,
But not in filence holy kept.

Milton.

Then banish'd faith fhall once again return, And veftal fires in ballow'd temples burn. Dry, No fatyr lurks within this hallow'd ground; But nymphs and heroines, kings and gods a bound. Granv. 2. To reverence as holy; ballowed be thy name. (1.) HALLSTATT, a town of Auftria, on the Halftatter, with a salt mine, 25 m. S. of Gemunde. (2.) HALLSTATT, a town of Franconia, at the conflux of the Maine and Rednitz, 3 miles N. of Bamberg.

HALLSTATTER, or HALLSTATTER SEE, a lake of Auftria, 6 miles S. of Gemunden.

1

* HALLUCINATION. n. f. {hallucinatio, Lat.] Errour; blunder; miftake; folly.-A wafting of flesh, without cause, is frequently termed a be witched difeafe; but queftionlefs a mere hallucination of the vulgar. Harvey,-This must have been the hallucination of the tranfcriber, who probably mistook the dash of the I for a T. Addison. HALLUIN, a town of France in the dept. of Oife; 10 miles SE. of Breteuil.

HALM. n. f. [bealm, Saxon.] Straw: pronounced HAWM: which fee.

HALMOTE, or HALIMOTE, n. f. is the fame with COURT BARON, the word implying a meeting of the tenants of the fame hall or manor. The name is ftill retained at Lufton, and other places in Herefordshire. See COURT, No I, § 4; and MOTE.

HALMSTADT. See HELMSTADT. HALNA, a town of Sweden, in W. Gothland, (1.) * HALO. n. f. A red circle round the fun or moon. If the hail be a little flatted, the light tranfmitted may grow so ftrong, at a little less diftance than that of 26 degrees, as to form a halo about the fun or moon; which balo, as often as the hailftones are duly figured, may be coloured. Newton.-1 faw by reflexion, in a veffel of ftagnating water, three balos, crowns or rings of colours about the fun, like three little rainbows, concentric to his body. Newton.

(2.) HALO, or CORONA, in optics, is a luminous circle furrounding the fun, moon, planets, or fixed ftars. Sometimes thefe circles are white, and fometimes coloured like the rainbow, Sometimes one only is vifible, and fometimes feveral

concentric halos appear at the fame time. Thofe which have been seen about Sirius and Jupiter were never more than 3°, 4°, or′5°, in diameter; thofe which furround the moon are, also, fometimes no more than 3° or 5°; but thefe, as well as thofe which furround the fun, are of very different magnitudes, viz. of 12° 0', 22° 35′, 30° o', 38° 0', 41° 2′, 45° 0′, 46° 24', 47° 0', and 90°, or even larger than this. Their diameters alo fometimes vary during the time of observation, and the breadths both of the coloured and white circles are very different, viz. of 2, 4, or 7 degrees. -Their colours are more diluted than those of the rainbow; and they are in a different order, according to their fize. (See 10.) Mr Huygens obferved red next the fun, and a pale blue outwards. Sometimes they are red on the infide and white on the outside. M. Weidler obferved one that was yellow on the infide and white on the outfide. In France, one was observed in 1683, the middle of which was white; after which followed a border of red, next to it was blue, then green, and the outermoft circle was a bright red. In 1728, one was feen of a pale red outwardly, then followed yellow and then green, terminated by a white. In Holland, M. Mufchenbroeck says, 50 may be seen in the day time, almost every year; but they are difficult to be obferved, except the eye be fo fituated, that not the body of the fun, but only the neighbouring parts of the heavens, can be feen. Mr Middleton fays, that this phenomenon is very frequent in North America; for that there is generally one or two about the fun every week, and as many about the moon every month. Halos round the fun are very frequent in Ruffia, M. Epinus fays, that from the 23d April, 1758, to the 20th Sept. he himself had obferved no lefs than 26, and that he has fometimes feen twice as many in the same space of time.

(3.) HALOS, APPEARANCES SIMILAR TO. Similar, in some respects, to the halo, was the remarkable appearance which M. Bouguer describes, as obferved on the top of Mount Pichinca, in the Cordilleras. When the fun was juft rifing behind them, fo as to appear white, each of them faw bis own fhadow projected upon it, and no other. The diftance was fuch, that all the parts of the fhadow were eafily diftinguishable, as the arms, the leg, and the head; but what furprised them moft was, that the head was adorned with a kind of glory, confifting of 3 or 4 fmall concentric crowns, of a very lively colour, each exhibiting all the va rieties of the primary rainbow, and having the circle of red on the outfide. The intervals between thefe circles continued equal, though the diameters of them all were conftantly changing. The last of them was very faint, and at a confiderable diftance was another great white circle, which furrounded the whole. As near as M. Bouguer could compute, the diameter of the first of thefe circles was about 53 degrees, that of the second 11, that of the third 17, and fo on; but the diameter of the white circle was about 76°. This phenomenon never appeared but in a cloud confifting of frozen particles, and never in drops of rain like the rainbow. When the fun was not in the horizon, only part of the white circle was visible, as M. Bouguer frequently obferved afterwards. Similar

to

ference of the circle; fo that, according to the known principles of geometry, the angle, under which the object appears in this cafe, must be just half of what it is in the other.

to this curious appearance was one feen by Dr M'Fait in Scotland; who obferved a rainbow round his fhadow in the mift, when he was upon an eminence above it. In this fituation the whole country round feemed buried under a vast deluge, and nothing but the tops of diftant hills appeared here and there above the flood. In those upper regions the air, he fays, is at that time very pure and agreeable. At another time he obferved a double range of colours round his fhadow. The colours of the outermost range were broad and very distinct, and every where about two feet diftant from the fhadow. Then there was a darkish interval, and after that another narrower range of colours, closely furrounding the fhadow, which was very much contracted. He thinks that these ranges of colours are caufed by the inflection of the rays of light, the fame that occafioned the ring of light which furrounds the fhadow of all bodies, obferved by M. Maraldi, and this author. Edin. Efays. Vol. i. p. 198.

(4) HALOS, ARTIFICIAL. Halos may be produced by placing a lighted candle in the midft of team in cold weather. If glass windows be breathed upon, and the flame of a candle be placed fome feet from it, while the spectator is alfo at the distance of fome feet from another part of a window, the flame will be surrounded with a coloured halo. And if a candle be placed behind a glafs receiver, when air is admitted into the vacuum within it, at a certain degree of denfity, the vapour with which it is loaded will make a coloured halo round the flame. This was obferved by Otto Guericke. In Dec. 1756, M. Mufchenbroeck obferved, that when the glass windows of his room were covered with a thin plate of ice on the infide, the moon appearing through it was furrounded with a large and variously coloured halo; and, opening the window, he found that it arofe entirely from that thin plate of ice, for none was feen except through it. Dr Kotelnihow, having, like Dr Halley, made very accurate obfervations to determine the number of poffible rainbows, confiders the coloured halo which appears about a candle, as the fame thing with one of these bows which is formed near the body of the fun, but which is not visible on account of his exceffive fplendor. (5.) HALOS, DESCARTES AND GASSENDI'S HYPOTHESES OF. M. Defcartes obferves, that the halo never appears when it rains; from which he concludes that this phenomenon is occafioned by the refraction of light in the round particles of ice, which are then floating in the atmosphere; and though these particles are flat when they fall to the ground, he thought they must be protuberant in the middle before their descent; and according to this protuberancy he imagined that the diameter of the halo would vary.-In treating of meteors, Gaffendi fuppofed, that a halo is of the fame nature with the rainbow, the rays of light being in both cafes twice refracted and once reflected within each drop of rain or vapour, and that all the difference there is between them arifes from their different fituation with refpect to the obferver. For, whereas, when the fun is behind the fpectator, and consequently the rainbow before him, his eye is in the centre of the circle; when he views the halo, with his face towards the fun, his eye is in the circumVOL. XI. PART I.

(6.) HALOS, EXPERIMENTS AND THEORY OF DECHALES RESPECTING. M. Dechales endeavours to fhow that the generation of the halo is fimilar to that of the rainbow. If, fays he, a sphere of glafs or cryftal, AB, Plate CLXXIII. fig. 1. full of water, be placed in the beams of the fun fhining from C, there will not only be two circles of coloured light on the fide next the fun, and which conftitute the two rainbows; but there will also be another on the part oppofite to the fun, the rays belonging to which, meeting at E, afterwards diverge, and form the coloured circle G, as will be vifible, if the light that is transmitted through the globe be received on a piece of white paper. The colours alfo will appear to an eye placed in any part of the furface of the cone FEG. Measuring the angle FEH, he found it to be 23 degrees. They were only the extreme rays of this cone that were coloured like thofe of the rainbow. This experiment he thought fufficiently illuftrated the generation of the halo; fo that whenever the texture of the clouds is fuch, as not entirely to intercept the rays of the fun or moon, and yet have fome degree of density, there will always be an halo round them, the colours of the rainbow appearing in those drops which are 23o distant from the fun or moon. If the fun be at A, and the spectator in B, (fig..2.) the halo will be the circle DEF, DBE being 46° or twice 23. The reason why the colours of the halo are more dilute than thofe of the rainbow, he fays, is owing principally to their being formed not in large drops of rain, but in very small vapour; for if the drops of water were large, the cloud would be fo thick, that the rays of the fun could not be regularly tranfmitted through them; and, on the other hand, he obferved, that when the rainbow is formed by very thin vapours, the colours hardly appear. As for thofe circles of colours which are fometimes feen round candles, it was his opinion that they are owing to nothing but moisture on the eye of the observer; for that he could never produce this appearance by means of vapour only, if he wiped his eyes carefully; and he had obferved that fuch circles are visible to fome perfons and not to others, and to the fame perfons at one time and not another.

(7) HALOS, HUYGENS'S THEORY OF. The moft confiderable and generally received theory, refpecting halos is that of Mr Huygens. Sir Ifaac Newton mentions it with refpect, and Dr Smith in his Complete Syftem of Optics, does not hint at any other. The occafion of Mr Huygens publifhing his thoughts on this fubject was the appearance of a halo at Paris, on the 12th May 1667, of which he gave an account in a paper read at the Royal Academy in that city, which was afterwards tranflated and published in the English Philof. Trant. See Lowthorp's Abridgment, Vol. II. p. 189. This article contains the heads of a difcourfe, which he afterwards composed, but never quite finished, and which has been tranflated, with fome additions, by Dr Smith, from whom the following account is chiefly extracted. Mr Huy. gens was first led to think particularly upon this