13. Of the Significance of Atmospheric Signs.

Observations of the signs that are to be seen around the sun, moon, and planets would also be useful for a foreknowledge of the particular events signified.
We must, then, observe the sun at rising to determine the weather by day and at setting for the weather at night, and its aspects to the moon for weather conditions of longer extent, on the assumption that each aspect, in general, foretells the condition up to the next. For when the sun rises or sets clear, unobscured, steady, and unclouded, it signifies fair weather; but if its disk is variegated or reddish or sends out ruddy rays, either directly outward or turned back upon itself, or if it has the so-called parheliac clouds on one side, or yellowish formations of clouds, and as it were emits long rays, it indicates heavy winds and such as come from the angles to which the aforesaid signs point. If at rising or setting it is dark or livid, being accompanied by clouds, or if it has halos about it on one side, or the parheliac clouds on both sides, and gives forth either livid or dusky rays, it signifies storms and rain.
We must observe the moon in its course three days before or three days after new moon, full moon, and the quarters. For when it appears thin and clear and has nothing around it, it signifies clear weather. If it is thin and red, and the whole disk of the unlighted portion is visible and somewhat disturbed, it indicates winds, in that direction in which it is particularly inclined. If it is observed to be dark, or pale, and thick, it signifies storms and rains.
We must also observe the halos around the moon. For if there is one, and this is clear, and gradually fading, it signifies fair weather; if there are two or three, storms; if they are yellowish, and broken, as it were, storms accompanied by heavy winds; if they are thick and misty, snowstorms; pale, or dusky, and broken, storms with both winds and snow; and the more of them there are the more severe the storms. And the halos that gather about the stars, both the planets and the brilliant fixed stars, signify what is appropriate to their colours and to the natures of the luminaries which they surround.
As for the fixed stars, which are close together in some number, we must observe their colours and magnitudes. For if they appear brighter and larger than usual, in whatever part of the sky they may be, they indicate the winds that blow from their own region. As for the clusters in the proper sense, however, such as Praesepe and the like, whenever in a clear sky their clusters appear to be dim, and, as it were, invisible, or thickened, they signify a downpour of water, but if they are clear and constantly twinkle, heavy winds. Whenever, of the stars called the Asses on each side of Praesepe, the One to the north becomes invisible, it means that the north wind will blow, and the One to the south, the south wind.
Of occasional phenomena in the upper atmosphere, comets generally foretell droughts or winds, and the larger the number of parts that are found in their heads and the greater their size, the more severe the winds.
Rushing and shooting stars, if they come from one angle, denote the wind from that direction, but if from opposite angles, a confusion of winds, and if from all four angles, storms of all kinds, including thunder, lightning, and the like. Similarly clouds resembling flocks of wool are sometimes significant of storms. And the rainbows that appear from time to time signify storms after clear weather and clear weather after storms. To sum up the whole matter, the visible phenomena, which appear with peculiar colours of their own in the atmosphere in general, indicate results similar to those brought about by their own proper occurrences, in the manner already explained in the foregoing.
Let us, then, consider that thus far, in outline, there has been given an account of the investigation of general questions, both in their more universal aspects and in particular detail. In the following we shall supply in due order the procedure for the prediction which follows the genethlialogical form.

Ptolemy's Tetrabiblos

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