The Borghesi Astronomical Clock in the Museum of History and Technology: Contributions from the Museum of History and Technology, Paper 35Bedini, Silvio A.
History
The Borghesi Astronomical Clock in the Museum of History and Technology: Contributions from the Museum of History and Technology, Paper 35
Bedini, Silvio A.
Astronomical clocks
Nevertheless, not far from the earth you should imagine
fabricated, as from most refined crystal, the heaven of the
moon everywhere equidistant from the center of the earth and
revolving separately on the same poles (prolonged even to this
place) on which the Primum Mobile and the heaven of the fixed
stars revolve. In the middle of this, that is, in some point
equally removed from the poles, you place the center of the
lunar epicycle, movable also by the common rotation of the
lunar heaven. I refrain from the other movements of the moon in
latitude, etc., as also those of the five planets, etc., which
the theory in no way excludes, lest by a variety of congested
motions explained too abundantly, either you might be confused
about the fundamental concept of the system or, while adorning
the theory and trying to embellish the least things more
widely, you might reject also the things which are capital.
Here you already have the whole machine, but still inert and to
be animated for the first time by motions accommodated to the
system. Nevertheless, before I assign motion to the individual
parts of the world, so that the thing might later appear more
clearly to you, I arrange all things thus: first, as if by
hand, I turn the Primum Mobile until the Boreal magnetic point
comes to the level or the area of the semicircle described in
the supreme immobile convexity; then I turn the heaven of the
fixed stars until, for example, the heel of Castor (a star of
the third magnitude), almost in the ecliptic and indeed in our
time not far distant from the solstitial colure, likewise falls
nearly at the level of the aforesaid semicircle. Later, I turn
the lunar heaven until I bring the center of the lunar epicycle
to the same level. Then, I turn the earth until some
predetermined city, for example, Trent, situated in the
northern zone with a latitude of about forty-six degrees, is
brought to the oft-mentioned level.
From things arranged in this way and from what has gone before,
it is evident (with the motions of the luminaries in epicycles
left out, however, lest you be distracted by the explanation)
that at Trent, just as in the whole northern hemisphere, it is
the summer solstice; and, conversely, in the southern
hemisphere, it is the winter solstice. The reason is because
the northern magnetic point together with the northern half of
the earthly axis is at its highest point towards the sun,
immovably residing in a line sent through the level of the
highest semicircle; and, conversely, the southern magnetic
point with the corresponding half of the axis is most removed
from the same. It further follows, that noonday and the new
moon coincide, and the heel of Castor almost reaches the
summit, etc.
Public-domain text, read in full here on John Shaqi.
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