In a separate chapter in his second volume, entitled "Descriptio
Authomatis Summa totius Operis Mechanici" (Description of the
Automaton--Summary of the Complete Mechanism), Father Borghesi provided
a description of the functions of the various indicators, prefixing it
with the short poem shown in figure 18. He then continues:
In the middle of the frontispiece, as at the center of the
universe, the terraqueous globe of the week revolves, with a
daily motion turning from right to left, bringing with it from
the round window the coming day and at the circumference the
circle of hours common to the sun, to the moon, to the fixed
stars, to the head and tail of the dragon, and to the raging
sea.
The second circle revolves the synodic-periodic measure of the
raging sea, the days of the median lunar-synodic age, the signs
and individual degrees of the signs of the distance of the moon
from the middle of the sun within the time of 29 terrestrial
revolutions, hours 12.44.3.13. This circle revolves likewise
from right to left around the center of the earth. In this
second circle, another little orb revolves, bringing with it
the epicycle of the moon, in which the little circle of the
moon (whose illuminated middle always faces towards the sun),
running from left to right through the signs of the anomaly;
within 13 revolutions of the earth, hours 18.39.16. It descends
from apogee to perigee and in just as many others it returns
from perigee to apogee, to be carried down thus to true, back
and front from the longitude and distance from the sun and from
the middle of the earth.
The third circle (on which I have tried to indicate
astronomically-geometrically in their places, the degrees of
lunar latitude both in the south and in the north, and some
fixed stars, those, namely, which can be separated by us from
the moon which goes between) from left to right turns around
the center of the earth, stretching out the head and tail of
the dragon, on the inside above the second circle for noting
and measuring the sun (but I should rather say the earth), and
the eclipses of the moon, within 346 revolutions of the earth,
hours 14.52.23.
The fourth circle, in which the heaven of the fixed stars,
reduced to the correct ascent of our times, the signs of the
zodiac and the individual degrees of the signs, the months of
the year and the single days of the month can be seen, likewise
makes its journey around the earth from left to right in 365
terrestrial revolutions, hours 5.48.56.; that is, within a
median astronomical year. Above this annual orb, the sun, in
its small epicycle, gliding through the 12 signs of the
anomaly, within the space of 182 terrestrial revolutions, hours
15.6.58., from left to right, falls from apogee to perigee;
and, within the same time, rises from perigee to apogee, and
brings with it, the index, namely its central radius, inhering
to the axis of the equatorial orb and cutting the four greatest
circles from the center.
When the sun has been moved around, Iris shows from six windows
the era, that is, the current year. Two winged youths take
their place next to Iris, carrying the Julian period: namely,
the Roman indiction, the cycle of the sun and the golden
number, on a leaf of paper held between them. The imperial
eagle stands out on top (as if added to the frontispiece)
carrying on its breast the dominating planet and in its talons
the ecclesiastical calends (that is, the dominical letter and
the epact).