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| King Louis XIV
in dispute with the Pope and with Bologna summoned Cassini to Paris |
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Cassini left
for Paris on 25 February 1669. When he
arrived, he was given a prestigious apartment in the Gallery of the Louvre,
under restoration at the time.
Two days after his arrival, Cassini was received
by King Louis XIV,
who informed him the reasons of his invitation:
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his assistance was greatly requested for the reorganization
of the "great Astronomical Observatory"
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he also invited him to join the newly
established "Académie Royale des Sciences",
conceived to "foster and develop the scientific
progress"
Cassini, a positive man, with a flair for anything
that was progress, a follower of Galileo’s methods, with great resolution
took up the commitments he was assigned to. Immediately he set to reorganizing
the "Obsevatoire".
His intent was to create a "system"
of observers, through over Europe, all of them connected each other. An
organization that «would
be of great help to Astronomy and Geography»
[Vincenzo
Viviani].
He conceived the "Obsevatoire"
as an "unicum into a whole".
He wanted the "Observatoire" to operate as if it was a sole, gigantic and
sophisticated instrument.
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| King
Louis XIV and his Minister Colbert cherished a re-making of the topography
of France |
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«The King
showed a particular interest for the great terrestrial map that Cassini’s
apprentices outlined on the floor of the northern Tower of the "Observatoire"»
[Anna Cassini
1998].
This was the beginning
of the great work that Cassini devoted to the "Carte de Cassini" throughout
many years. He was not able to finish this commitment. His successors completed
it.
This work was of great
importance, both politically and economically, for the Nation (France).
Cassini’s cartographic survey was essentially
astronomical, based on the determination
of longitude, through the observation of
the eclipses of Jupiter’s satellites.
This was possible due to the studies Cassini had
carried out on the Medicean stars and on the relevant ephemerides, which
he published.
Cassini himself
said: "… how
valid is this method to improve the knowledge of Geography and to amend
the charts of the Navy".
Several expeditions
were conducted in different places and periods under
Cassini’s supervision, making evident his top
class "managerial "
capacities … He even designed "rugged"
instrumentation, purposely studied for military use, able to stand both
mechanical and climatic stress conditions and specifically designed to
bear frequent moving about.
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| A
successful mission to Cayenne allowed to compute the parallax of Mars ...
therefore, its distance from the Earth ...
through Kepler’s third law the A.U. became
known. |
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Expeditions were also conducted throughout the
Colonies, such as the one, extremely successful of Jean Richer to Cayenne,
in French Guiana, that allowed, cartography apart, to compute
the exact position of Mars with respect to some stars nearby.
Simultaneously, Cassini was able to carry out his observations in Paris
… the parallax of Mars was finally measured. That parallax that Tycho had
so assiduously looked for, unfortunately using a method that was unfit.
Parallax is 15.8", a distance Paris-Cayenne
that, seen from Mars, is equal to 5803 km and a distance Earth-Mars equal
to 75,751,226 km … (a
data similar to the one of Cassini).
The distance Earth-Sun
= 1 AU by definition. The distance Mars-Sun
= 1.524 AU as per the 3rd law of
Kepler ...
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75,751,226 km = 0.524 AU
therefore 1 AU = 75,751,226 / 0.524
= 144,563,409 km. The
error is 3.6% only !!!!
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| Geodetic and
topographic surveys; furthermore the
extent of the Meridian ... |
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Cassini is a true
expert of geodetic and topographic surveys,
an experience and a knowledge indispensable to trace the "great
map of France"
… a work of sacrifice and often difficult, that Cassini, was able to face
heartily and courageously due to his good health.
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«With the help of his son Jacques
and of his grand-son Maraldi,
Cassini travelled
through Southern France,
to compute the extent of the arc of meridian
between Paris-Perpignan (county town of the
Eastern Pyrenees), while he committed his assistant De LaHire, astronomer
of the "Observatoire",
to proceed from Paris toward the Northern side of France» [Anna
Cassini 1998].
The tables of the eclipses of the Medicean stars,
with further improvements, were published again in 1693.
The topographic
survey of France was an outstanding
contribution and the realisation of Colbert’s
projects, supported by the "Accadémie".
This undertaking was important, because for the
first time, a great work, strictly scientific, was completed. It was named
the "Carte de Cassini": the whole of France
was faithfully represented in 182 sheets.
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This was the birth of modern cartography,
based on the observation of the celestial vault.
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| An
example of map from the "Carte de Cassini",
one of his great masterpieces !!! ... |
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click for full
image ... |
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