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Giovanni
de Dondi was a lecturer in logic, mathematics, astronomy and astrology
(at his time both of them were concerned with the study of the skies)
and built in the fourteenth century an astrarium for a long time celebrated
for its complexity and completeness.
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The
instrument gained for him, his contemporary astonishment due the
massive information available. Giovanni de Dondi was ahead of his
time using mechanical techniques that were in normal use later a
couple of centuries.
Perhaps this is the reason when repairs to the Astrarium were due
, nobody had been clever enough to handle it .
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moon dial
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Venus dial
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For
this reason - after alternate misfortunes -it was dismantled to use the
brass( which at that time was a very expensive metal). Fortunately Giovanni,
giving high proof of his scientific mind, handed down a very detailed
account of the construction of his astrarium
A.D. MDCCCCLXXXXVII SUMMO PONTEFICE
JOANNE PAULO II FELICITER REGNANTE DEO ADIUVANTE ET OPITULANTE
ASTRARIUM EXEGI AD EXEMPLAR PERACTI A DOMINE JOANNE DE DONDI INGENIO
ACUTISSIMO PRAEDITO AD MCCCLXIIII
CAROLUS CROCE
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His
"Tractatus Astrarii" is preserved in the Capitular of
Padua.
It
is written in medieval Latin and is completed with
sketches showing such an accuracy and clarity to be comparable to
those of modern engineering.
Units of measurement in XIVth century were limited to the needs
of the daily life , that is the length of a piece of cloth or the
distance between the Abbey and the Prince's Palace - and therefore
not suitable to give the measure of those small pieces fitted in
the astrarium.
Giovanni
solved this problem using reference units such as "the
thickness of the blade of a big knife", or "the
thickness of the blade of a small knife," or in the
case of holes, "like that of a goose feather",
or " hen feather" and so on.
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dial of dragon's
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The
astrarium built by Giovanni gives information on the position in
the sky of all planets known at his times.
In
Ptolemaic solar system, the earth is located at
the center of the solar system and the sun and five planets (Venus,
Mars, Saturn, Mercury and Jupiter) make their revolution around
it.
The basic idea behind the Astrarium is very simple and thus really
genius.
The
clock moves a wheel (making one turn in a day) that in turn moves
a wheel (making one turn in a year) which in turn at the same time
gives motion (through a lot of gears) to all the pointers which
gave the position of the stars in the sky. In this last motion is
to be found the great complexity of the instrument, for Giovanni
had to apply to very sophisticated mechanical virtuosity to enforce
all the parameters of each star position.
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inside view of
moon dial
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Writing
in his Tractatus the clock is of common type (communiis
horoligii) Giovanni tells us the know-how for building
clocks was well established at his time and we can deduce something
about the date first mechanical clocks appeared in the western world.
Giovanni
then summons anybody not being acquainted with horology to try to
build his astrarium : |
the wheel of the year
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Non sollicitor autem ut modum aptationis huiusmodi ac firmandi prescriptas
rotas axesque earum et frenum multum exquisita determinatione
describam ,quoniam facilia sunt aput illum qui habet ingenium tantum
quantum necessarium est ad concipienda plurima alia que scribentur
deinceps,propter quod si ad ista leviora non sufficis,aliorum difficilium
compositionem prosequi non presumas.
He
then challenges his reader's skill giving just the number of wheels
teeth to be used in the clock, giving no details about the construction
of it.... but also giving -to the point of being almost pedantic
-a lots of hints and tips for all the other parts shown in the Tractatus.
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