**CLAUDIUS PTOLEMY:**

**TETRABIBLOS**

**OR THE QUADRIPARTITE MATHEMATICAL TREATISE**

**15. Of Signs which Behold each other and Signs of Equal Power.**

**Again they say that the parts which are equally removed from the same tropical sign, whichever it may be, are of equal power, because when the sun comes into either of them the days are equal to the days, the nights to the nights, and the lengths of their own hours are the same. These also are said to "behold" One another both for the reasons stated and because each of the pair rises from the same part of the horizon and sets in the same part.**