Geoscience Reference
In-Depth Information
by anyone. The visiting scientists brought their own equipment to the Observatory
for their experiments and took it away when the experiments were finished.
In contrast to an observatory today where its equipment is bought, built, and main-
tained as a common facility for all visiting scientists, the Observatory held minimum
equipment for common use. This situation was similar to that of John Flamsteed,
the first Astronomer Royal at the Royal Observatory in Greenwich, and during
his tenure there from 1675 to 1719, he bought his telescopes and clocks out of his
own salary. When he died, the state claimed ownership of his instruments as crown
property. In response, his widow sent a servant to steal the telescopes and clocks
away during the night, and sold them to provide financial support in her widow-
hood. One long-case clock for astronomical use had a pendulum 2 meters long
but this was altered to the conventional size for a domestic clock to make it more
saleable. Only recently was this clock restored to its place in the Octagon Room at
Greenwich.
It was not until 1771 under the rule of Louis XV that the post of Director materialized,
notably through César-François Cassini de Thury (1714-1784), known as Cassini III,
the second son of Cassini II, and grandson of Cassini I. The final astronomical member
of the Cassini family was Jean-Dominique Cassini (1748-1845), son of Cassini III,
named in honor of his grandfather and known as Cassini IV, also formally a Director
of the Paris Observatory and ennobled as the Comte de Thury. Formalities aside, the
Observatory was essentially under the successive authority of Cassinis I, II, III and IV
and they were, whether explicitly called that or not, the Observatory's first four
Directors. Collectively these four men are known as the Cassini dynasty.
Places
Château de Thury
The town of Thury-sous-Clermont (Oise) is directly associated with the Cassini dynasty.
Cassini I took the title of Lord of Thury and Fillerval and the Château de Fillerval was the
country residence of Cassini II to Cassini IV. Cassini III, who was born in the old castle,
took the name Cassini de Thury after the town. He demolished the old castle of his birth
but died before he could complete the present one, largely built by Cassini IV. Cassini IV
was officially ennobled as the Comte de Thury and retired here from his life of science,
lucky enough to keep his head after he was deposed from the Paris Observatory's director-
ship in 1793 by the revolutionary government. At the Château de Thury, he wrote memoirs,
poetry, and was active in local politics. He died here in 1845, and his tomb is in the church's
cemetery. The castle was damaged by fire and also by the Second World War but has been
restored and is presently a business school.
In his time in Paris, Cassini I mapped the Moon and made observations of
Jupiter's satellites to use as natural clocks. He observed the eclipses of the satellites
and progressively drew up more accurate tables for predicting them. He also dis-
covered that Saturn's rings were separated in two by what is now known as
Cassini's Division. The European Space Agency's spacecraft, CASSINI, which
arrived at Saturn in 2004 to explore the planetary system, is called such after him.
He made other discoveries of physical astronomy (i.e. the nature of celestial
objects), but this work of brilliant individual studies was regarded with mixed feel-
ings by some Academy astronomers, who thought that the Observatory should
concentrate on more fundamental, large scale works, or “big science” projects like
the survey to establish the Paris Meridian.
