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 in the treasury of the emperors of the Tang dynasty. Probably the most ancient zodiacal representation in existence is a fragment of a Chaldacan planisphere in the British Museum, once inscribed with the names of the twelve months and their governing signs. Two only now remain.

A zodiac on the “astrological altar of Gabies” in the Louvre illustrates the apportionment of the signs among the inmates of the Roman Pantheon; and they occur as a classical reminiscence in the mosaic pavements of San Miniato and the baptistery at Florence, the cathedral of Lyons, and the crypt of San Savino at Piacenza. Zodiacal symbolism became conspicuous in medieval art. Nearly 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. 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 Vézelay. The cathedrals of Amiens, Sens and Rheims are decorated in the same way. In Italy the signs and works survive fragmentarily 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 Iffley in Oxfordshire offer good specimens. In the zodiac of Merton College, Oxford, Libra is represented by a judge in his robes and Pisces by the dolphin of Fitzjames, warden of the college, 1482–1507. The great rose-windows of the Early Gothic period were frequently painted with zodiacal emblems; and some frescoes 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. The “zodiac of labours” was replaced in French castles and hotels by a “zodiac of pleasures,” in which hunting, hawking, fishing and dancing were substituted for hoeing, planting, reaping and ploughing.

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.

The hieroglyphs representing the signs of the zodiac in astronomical works are found in manuscripts of about the 10th century, but in carvings not until the 15th or 16th. 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.

See also the article, and the separate articles on the constellations. The whole subject of the history of the zodiac is very obscure. See generally Franz Boll, Sphaera (Leipzig, 1903); also the bibliographies to and.

ZODIACAL LIGHT, a faint illumination of the sky, surrounding the sun and elongated in the direction of the ecliptic on each side of the sun. It is lenticular in form, brightest near the sun, and shades off by imperceptible gradations, generally becoming invisible at a distance of 90° from the sun. Until a recent time it was never observed except in or near the zodiac; hence its designation. Its breadth varies with the time and place of observation, depending upon the position of the ecliptic with respect to the horizon. In the tropics, where the ecliptic is nearly perpendicular to the horizon, it may be seen after the end of twilight on every clear evening, and before

twilight on every clear morning, unless blotted out by moonlight. It then presents a nearly vertical wedge-shaped form, the base of which extends 15° or 20° on each side of the point at which the ecliptic intersects the horizon. The point of the wedge is quite indefinite, the extremely diffuse light gradually fading into invisibility at a height which may range from 50° to 70° or even more, according to the keenness of the observer’s vision. The boundary everywhere is ill defined so that no exact statement of the extent of the light can be made. The brightness is at its maximum along its central line, called the axis of the light. Along this axis the brightness continually increases as the sun is approached. Owing to the softness of the outline, it is not possible to fix the position of the axis with precision; but, so far as observations have been made, it is found that it lies near the ecliptic, though deviating from it by a quite sensible amount.

Having this position, the conditions of visibility will be best when the ecliptic, and therefore the axis of the light, are nearly perpendicular to the horizon, and, as the angle between the ecliptic and horizon becomes acute, will deteriorate, slowly at first, more and more rapidly afterwards, owing to the increasing effect of atmospheric absorption. This effect is enhanced by the light being brighter as we approach the sun. More and more of the brighter regions of the light will then be near the horizon the more acute the angle. The result is that the light can be only indistinctly seen when the angle with the horizon is less than 45°, unless in a region where the atmosphere is unusually clear. From this statement of the conditions it will be seen that the tropical zone is the most favourable for observation, and that the most favourable hour of the day at which the light can be seen must always be the earliest after sunset and the last before sunrise. Practically, this is when twilight is first ended in the evening, and about to begin in the morning. At these hours the angle of the ecliptic with the horizon varies with the season. At the close of evening twilight the angle is greatest about three weeks before the vernal equinox. The months of February and March are therefore best for the evening observations in the northern hemisphere, but the light can generally be seen from January until April. Similar favourable conditions prevail in the morning from September to November.

It is clear that the light proceeds from a region surrounding the sun, and lenticular in form, the axis of the lens being nearly perpendicular to the ecliptic, while the circumference extends at least to the orbit of the earth. If it did not extend so far as this it could not be seen as frequently as it is at a distance of 90° from the sun. The accompanying figure shows the form of the outline, as it would appear to an observer on an outer planet were the light of the sun cut off. The hypothesis which best explains all the phenomena is that the light is that of the sun reflected from an extremely tenuous cloud of particles having the form and extent described, and becoming more and more tenuous as the earth’s orbit is approached until, immediately outside the orbit, it fades into complete invisibility. The fact that the light widens out toward the sun leads to the inference that it entirely surrounds the sun. It is therefore of interest to test this inference by observations at midnight in such a latitude that the distance of the sun below the horizon is no more than necessary to preclude the possibility of twilight. Such an opportunity is offered when the sun is near the summer solstice, in latitudes not differing much from 50° north. A transparent atmosphere and clear horizon are necessary, conditions which can best be secured on a mountain top. The visibility of a light corresponding to the inference was shown by Simon Newcomb, by observations at the top of the Brienzer Rothorn, in 1905. Previously to this, E. E. Barnard had observed the same phenomenon at Chicago. The only source of doubt as to the validity of the conclusion that this is really the zodiacal light arises from the possibility that, after the close of the ordinarily recognized twilight, there may be a faint illumination arising from the reflection of light by the very rare upper atmosphere, shown by the phenomena of meteors to extend some hundred miles or more above the earth’s surface. The problem of