e. Since cycles of the sun date from 9 years
before the Christian era, it is necessary to add the digit 9 to the
digits of the current year and then divide the result by 28. The
quotient is the number of cycles which has passed, and the remainder
will be the year of the cycle answering to the current year. The third
opening on the riband is labeled "Num. Aur." (golden number). Meton, an
astronomer of Athens, discovered in 432 B.C. that after a period of 19
years the new and the full moons returned on the same days of the month
as they had before, and this is called the cycle of the moon. The Greeks
were so impressed with this calculation that they had it inscribed in
letters of gold upon stone, hence the golden number. The First Council
of Nicaea in A.D. 325 determined that Meton's cycle was to be used to
regulate the movable feasts of the Church.

Immediately above the chapter rings is an opening through which the orb
of the sun is visible.

THE CHAPTER-RING ASSEMBLY

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