Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/846

796 Z O D Z O D Zodiacal as a classical reminiscence in the mosaic pavements of San Miniato symbols and the baptistery at Florence, the cathedral of Lyons, and the in archi- crypt of San Savino at Piacenza. 1 Zodiacal symbolism became tecture. conspicuous in mediseval art. ISTearly all the French cathedrals of the 12th and 13th centuries exhibit on their portals a species of rural calendar, in which each month and sign has its corresponding labour. The zodiac of Notre Dame of Paris, opening with Aquarius, is a noted instance. 2 A similar series, in which sculptured figures of Christ and the Apostles are associated with the signs, is to be seen in perfect preservation on the chief doorway of the abbey church at Vezelay. The cathedrals of Amiens, Sens, and Rheims are decorated in the same way. In Italy the signs and works sur vive fraginentarily in the baptistery at Parma, completely on the porch of the cathedral of Cremona and on the west doorway of St Mark s at Venice. They are less common in England ; but St Margaret s, York, and the church of Iniey in Oxfordshire offer good specimens. In the zodiac of Merton College, Oxford, Libra is re presented by a judge in his robes and Pisces by the dolphin of Fitzjames, warden of the college, 14S2-1507. 3 The great rose-win dows of the Early Gothic period were frequently painted with zodiacal emblems ; and some frescos in the cathedral of Cologne contain the signs, each with an attendant angel, just as they were depicted on the vault of the church at Mount Athos. Giotto s zodiac at Padua was remarkable (in its undisturbed condition) for the arrangement of the signs so as to be struck in turns, during the corresponding months, by the sun s rays. 4 The " zodiac of labours " was replaced in French castles and hotels by a " zodiac of plea sures," in which hunting, hawking, fishing, and dancing were sub stituted for hoeing, planting, reaping, and ploughing. 5 It is curious to find the same sequence of symbols employed for the same decorative purposes in India as in Europe. A perfect set of signs was copied in 1764 from a pagoda at Verdapettah near Cape Comorin, and one equally complete existed at the same period on the ceiling of a temple near Mindurah. ti Zodiacal The hieroglyphs representing the signs of the zodiac in astrono- hiero- mical works are of late introduction. They are found in manu- glyphs. scripts of about th.e 10th century, but in carvings not until the 15th or 16th. 7 Their origin is unknown ; but some, if not all of them, have antique associations. The hieroglyph of Leo, for instance, occurs among the symbols of the Mithraic worship. 8 (A. M. C.) ZODIACAL LIGHT. The zodiacal light is usually de scribed as a cone or lenticularly-shapecl glow of nebulous light, seen after sunset or before sunrise, extending up wards from the position of the sun nearly in the direction of the ecliptic or of the sun s equator. This description, though fairly correct for the higher latitudes, does not represent accurately what is seen in the tropics, where the light is often a very conspicuous object. There, if an observer on a clear, moonless night watches the western sky from soon after sunset till the last trace of twilight has disappeared, he will notice that the twilight seems to linger longer near where the sun sank below the horizon, and that gradually a nebulous whitish band of light, broad towards the horizon and narrowing first rapidly and then more slowly upwards, begins to stand out clearly from the vanishing twilight, which spreads along a much wider and nearly horizontally-topped arc of the horizon. This is the zodiacal light. When seen on a perfectly clear night, it will be noticed that it fades imperceptibly on both borders and towards the vertex, and that its light is distinctly brighter towards the base than at greater altitudes. Its width and brightness, and the height of the vertex, differ very much from time to time, partly on account of actual variations, but much more from differences in the trans parency of the atmosphere. In England it is seldom observed except in the months of March, April, and May shortly after sunset, or about October before sunrise. This is due to no change in the light itself, but simply to the 1 Fowler, Archceoloyia, vol. xliv. p. 172. 2 Viollet-le-Duc, Diet, de I Arch, francaise, vol. ix. p. 551 ; Le Gentil, Mfrm. de I Acad., Paris, 1785, p. 20. 3 Fowler, Archsnolor/ia, vol. xliv. p. 150. 4 Ibid., p. 175. 5 Viollet-le-Duc, Diet, de I Arch., vol. ix. p. 551. 6 John Call, Phil. Trans., vol. Ixii. p. 353. Cornp. Houzeau, Biblio graphic Astronomique, vol. i. pt. i. p. 136, where a useful sketch of the general results of zodiacal research will be found. 7 R. Brown, Archseoloijia, vol. xlvii. p. 341 ; Sayce, in Nature, vol. xxv. p. 525. 8 See Lajard, Culte de Mithra, pi. xxvii. fig. 5, &c. circumstance that at other seasons the ecliptic makes so small an angle with the horizon that a light lying in or near it does not rise sufficiently high above the mists of the horizon to be seen after the twilight has vanished. In lower latitudes, where the angle made with the horizon is greater, while the duration of twilight is shorter, it can be easily seen at all seasons when there is a clear sky and no moon, except when Venus is an evening star, in which case the great brightness of that planet often almost, completely obliterates the comparatively faint zodiacal light, at least in its neighbourhood. The zodiacal light has frequently been described as having a reddish yellow tint ; but this seems to be erroneous, for, when seen under favourable conditions, it is distinctly white and very similar to that of the Milky Way. Any colour that may have been observed is doubtless due to atmospheric causes. Among the Moslems, to whom it is important on ritual grounds to determine accurately the moment of daybreak, at which during Ramadan the daily fast begins, the morning zodiacal light appears to have been observed from an early period, and is known as the " false dawn " or the "wolf s tail" (liedhouse, in Journ. R. A. 8., July 1878). But in Christian Europe it seems to have been first observed by Kepler, who described its appearance with considerable accuracy and came to the conclusion that it was the atmosphere of the sun. Descartes wrote about it in 1630 and Childrey in 1659; but the attention of astronomers was first prominently called to it by Dominic Cassini, who first saw it on 18th March 1683. It is to him that it owes the name which it now bears. He explained it by supposing the existence of a flat, luminous ring encircling the sun, nearly in the plane of his equator, and accounted for its disappearance on the same principle as that which accounts for the vanishing of Saturn s ring. Mairan (1731), like Kepler, ascribed the light to the sun s atmosphere ; and this explanation was generally accepted, till Laplace showed that it was untenable, since no real solar atmosphere could extend to anything like the distance from the sun which is reached by the zodiacal light. He further showed that, even if the solar atmosphere did extend far enough, it would not have the lenticular appearance ascribed by observers to the zodiacal light, since the polar axis would be at least two -thirds of the equatorial axis. Since then many observers have made a study of the subject, amongst whom may be mentioned Jones, Piazzi Smyth, Jacob, Brorsen, Schmidt, Backhouse, Liais, and Wright. Extent. The way in which the light fades off gradually towards the boundaries makes it extremely difficult to determine accurately the true position of the light or its extent. Various observations show that at times the base, at an elongation of about 20, may have a width of from 25 to 30, while at an elongation of 60 the breadth is frequently as much as 20, but usually much less. The distance of the vertex from the sun frequently exceeds 90, and Mr Liais and others have recorded cases when the light has been traced completely round from the western to the eastern horizon. This is very uncommon ; but it is not at all rare to find the light stretching nearly to the meridian three hours after sunset, and several ob servers have recorded the existence of a bright patch of light almost opposite to the position of the sun. This is known as the Gcgcn- schcin, and though it has been seen comparatively seldom its exist ence must be accepted as proved ; for its position has been deter mined by actual measurement by several astronomers, and their results agree with quite as great closeness as can be expected in the determination of the position of such an object. A lengthened series of observations was made on the zodiacal light by the Rev. G. Jones, chaplain of the United States steam frigate " Mississippi," in the China and Japan Seas in 1855. He charted the apparent posi tion of the cone of light on a large number of nights and mornings, and came to the somewhat startling conclusion that his observations could be explained only by supposing the existence of a nebulous ring round the earth within the orbit of the moon. He recorded that twice near 23 28 N! lat. , with the sun at the opposite solstice, he had seen "the extraordinary spectacle of the zodiacal light,

simultaneously at both the east and west horizons from 11 to 1