12. Of the Investigation of Weather in Detail.

Now that these facts have been stated in introduction, the method of dealing with the significations in detail involves the following procedure. For One method is that which is more generally conceived, with relation to the quarters, which will demand, as we have said, that we observe the new moons or full moons which most nearly precede the solstitial and equinoctial signs, and that, as the degree of the new moon or of the full moon may fall in each latitude investigated, we dispose the angles as in a nativity. It will then be necessary to determine the rulers of the place of the new moon or full moon and of the angle that follows it, after the fashion explained by us in the preceding sections dealing with eclipses, and thus to judge of the general situation from the special nature of the quarters, and determine the question of degree of intensification and relaxation from the nature of the ruling planets, their qualities, and the kinds of weather which they produce.
The second mode of procedure is based on the month. In this it will be necessary for us to examine in the same way the new moons or full moons that take place, in the several signs, observing only this, that, if a new moon occurs nearest to the solstitial or equinoctial sign just past, we should use the new moons which take place as far as the next quadrant, and in the case of a full moon the full moons. It will be needful similarly that we observe the angles and the rulers of both the places, and especially the nearest appearances of the planets, and their applications and recessions, the peculiar properties of the planets and of their places, and the winds which are aroused both by the planets themselves and by the parts of the signe in which they chance to be; still further, to what wind the latitude of the moon is inclined through the obliquity of the ecliptic. From all these facts, by means of the principle of prevalence, we may predict the general conditions of weather and the winds of the months.
The third step is to observe the even more minutely detailed indications of relaxation and intensification. This observation is based upon the configurations of the sun and the moon successively, not merely the new moons and full moons, but also the half moons, in which case the change signified generally has its beginning three days before, and sometimes three days after, the moon's progress matches that of the sun. It is based also upon their aspects to the planets, when they are at each of the positions of this kind, or likewise others, such as trine and sextile. For it is in accordance with the nature of these that the special quality of the change is apprehended, in harmony with the natural affinities of the attending planets and of the signs of the zodiac for the ambient and the winds.
The day by day intensifications of these particular qualities are brought about chiefly when the more brilliant and powerful of the fixed stars make appearances, matutine or vespertine, at rising or setting, with respect to the sun. For ordinarily they modulate the particular conditions to accord with their own natures, and none the less too when the luminaries are passing over One of the angles.
For the hour by hour intensifications and relaxations of the weather vary in response to such positions of the stars as these, in the same way that the ebb and flow of the tide respond to the phases of the moon, and the changes in the air-currents are brought about especially at such appearances of the luminaries at the angles, in the direction of those winds towards which the latitude of the moon is found to be inclining. In every case, however, One should draw his conclusions on the principle that the universal and primary underlying cause takes precedence and that the cause of particular events is secondary to it, and that the force is most ensured and strengthened when the stars which are the lords of the universal natures are configurated with the particular causes.

Ptolemy's Tetrabiblos

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