Tetrabiblos and Centiloquy

...but for those of them for which there is a manifest cause. And since things of this kind, which are noted in that place through these figures, can contribute to our utility in this science original: "sciaz", likely "scientiam" referring to the science of astrology, we have decided that it should be passed over in silence in this place.

¶ Chapter 14. On the affinities of the four signs and figures.

Primarily, the affinity of the parts of the circle of signs the Zodiac among themselves is that which is held in the figures: such as the parts between which there is the length of one diameter, and which are subtended by two right angles. These are 6 signs and 180 degrees This refers to the 'Opposition' aspect. And also the parts between which there is a trine length, which encompasses one right angle and a third of the same original: "trientem"; 120 degrees; and these are 4 signs and 120 degrees. Also the parts between which there is a tetragonal tetragonal: a square aspect length, which contains one right angle; and these are 3 signs and 90 degrees. Furthermore, the parts in which there is a hexagonal hexagonal: a sextile aspect length, which encompasses two-thirds original: "bisse" of one right angle; and these are two signs and 60 degrees. The reasons why they observed these lengths alone and no others, we shall learn from that which follows. For the reasons for observing the length of one diameter are manifest of themselves, because they are placed in opposition to it along a straight line.

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