Diagonally from the sides of the center of the three larger indices, six
other indices revolve: three on the left from one center, and three on
the right from another. The uppermost of the three which are on the
right of the observer [and which are] decorated with a small disk of the
sun, runs its cycle once during a mean solar-astronomical year. The
second measures the distance of the sun from its apogee. The third
revolves 12 times, with each lunar revolution from one node to the same
[repeated] node. Under the point of the uppermost index, first lie the
months of the year which are inscribed, and the days of each month, but
having only 28 days assigned to February; then the signs of the zodiac,
and their several degrees. The circle corresponding to the middle index,
extending through the first semicircle from apogee to the lower perigee
and returning through the second semicircle to the upper locations of
apogee, shows the true equation or eccentricity of the sun, joined with
the little equation of the moon in syzygy. [These equations are]
measured by geometric-astronomic proportion for each distance of the
sun from its apogee or perigee in degrees, and in sufficiently small
parts of degrees, with the title added above in their proper places,
whether an addition is to be made to the mean location of the sun or a
subtraction from the same, so that the true longitude of the sun may be
calculated. Three circles are assigned to the lowest index, of which 30
degrees of distance of the moon from its nodes comprise the larger. The
middle circle is based on the hypothesis of the mean invariable
diameters (that is, of the sun, the moon, and the terrestrial shadow),
and is divided into hours and quarters of duration. The last circle is
divided by the trigonometric laws into the inches of magnitude of lunar
eclipses. Lying between these circles, there is another eccentric circle
(black with a spot) exhibiting the shadow of the earth, in which the
little moon sinks itself, carried by the lowest index. In any ecliptic
full moons, the patent number of inches of immersion somehow affects the
minds of the cultured, but also the scheme of maximum obscuration
affects the eyes of the illiterate themselves.