TROPICAL, EQUINOCTIAL, FIXED, AND BICORPOREAL SIGNS
Among the twelve signs, some are termed tropical, others equinoctial,
others fixed, and others bicorporeal.
The tropical signs are two: viz. the first thirty degrees after the
summer solstice, which compose the sign of Cancer; and the first thirty
degrees after the winter solstice, composing the sign of Capricorn.
These are called _tropical_, because the Sun, after he has arrived at
their first points, seems to _turn_, and to change his course towards a
contrary latitude;[43] causing summer by the _turn_ he makes in Cancer,
and winter by that which he makes in Capricorn.
There are also two equinoctial signs: Aries, the first after the vernal
equinox; and Libra, the first after the autumnal equinox: they are so
called, because the Sun, when in the first point of either, makes the
day and night equal.
Of the remaining eight signs, four are fixed, and four bicorporeal.
Those signs, which severally follow immediately after the two tropical
and the two equinoctial signs, are termed fixed, because, during the
Sun’s presence in them, the cold, heat, moisture or dryness, of the
season, which commenced on his arrival in the preceding tropical or
equinoctial sign, is then more firmly established: not, however,
that the temperament of the season has in itself actually increased
in vigour, but, having continued for some time in operation, it then
renders all things more strongly affected by its influence.
The bicorporeal signs severally follow the fixed signs; and, being thus
intermediately placed between the fixed and the tropical signs, they
participate in the constitutional properties of both, from their first
to their last degrees.
[43] In other words, the Sun then begins to diminish his declination,
which, at the first points of the said signs, is at its greatest amount.