ivided further into 30 parts, which
are the 12 signs of the zodiac and the individual degrees of the signs
of distance of the sun and the moon from the head of the dragon.

In the second circle is read the latitude of the moon, measured by
degrees, etc., on a trigonometric scale, by signs and degrees of
distance of the moon from its nodes, that is, from the head or tail of
the dragon. When the second index is descending from the head of the
dragon to the tail, the latitude will be to the north of the solar path;
that is, the ecliptic. On the other hand, it will be south of the
ecliptic when the same index is returning upward from the tail to the
head of the dragon as advised by the title inscribed on the third
circle.

Finally, on the fourth and last circle are seen more prime minutes of
the circle for reducing the orbit of the moon to the ecliptic. That the
true longitude of the moon may be obtained more accurately, these must
be subtracted from the longitude of the moon already calculated in the
first and third quadrant of the circle of the second index. On the other
hand, they are to be added to the same in the second and fourth
quadrant, as is noted in their respective places, according to the
theory of right ascensions.

Here, then, [you have] as finally completed, delineation of the great
index which was partially described before in this book.

From two points of that index which perpendicularly correspond to the
center of these circles, a pair of compasses, by an unvaried aperture up
to the circumference of the first larger circle, has marked off four
segments of a circle. The two larger segments, equal among themselves,
in one aperture refer to the sun, and the two smaller in the other,
likewise equal, refer to the moon. The one pointer is for determining
the solar eclipses; the other, for lunar. Both segments of each
division, like little wings of the index, stretch to the extent of the
degree of distance of the moon from its nodes, and to which that
determined latitude corresponds. On one side, that latitude precisely
equals the radii of the earth, the sun, and the moon, as the termini of
solar eclipses; and, on the other side, precisely equals the radii of
the earth's shadow and of the moon, as the confines of lunar eclipses.
The apexes of the last index, diametrically limited [opposite], indicate
the age of the moon, and its mean distance from the sun; one pointer,
upon which the sun sits, measuring the