Observatoire

The Observatory was as important to the Academy as the Bibliothèque du roi. With its underground caverns, astronomical and meteorological apparatus, and collections of data from scientific expeditions, the Observatory resembled the House of Solomon. Yet it had serious disadvantages. Situated in the countryside at the southern edge of Paris, walled, and monitored by liveried veterans, it was physically remote from other Parisian intellectual centers. Designed by Perrault — who lacked architectural models or astronomical experience and had effected the expulsion of the one academician qualified to advise him — it was unsuitable for Cassini's work and had to be adapted. Originally intended to house all the activities and members of the Academy, it became the preserve of astronomers and mathematicians. Otherwise, only Huygens and Mariotte used it regularly, and even some astronomers preferred to work elsewhere.^[35]

Despite its shortcomings, the Observatory became the second major hub of the Academy. Academicians lived and worked in its cold and drafty quarters: Cassini's children were born there, and nearby Saint Jacques du Haut Pas became the parish church of the mathematicians and astronomers.^[36] Work on the Observatory began in 1667, and so great was the need for these facilities that academicians began working there in 1668. In 1671 the impatient Cassini moved in, although the Observatory was scarcely ready for habitation or regular observations. Thuret began maintaining its clocks in 1672, and in 1673 Jean Patigny was preparing astronomical engravings there.^[37] By 1687, when the building was completed and the Marly tower in place, the Observatory had cost more than 720,000 livres (table 2). Altogether its construction and maintenance accounted for 34 percent of the Academy's budget during the seventeenth century (table 17).^[38]

The building and its grounds were more than an astronomical observatory. Like their mythical forebears in Solomon's House, academicians

exploited the site for quite varied investigations. Underground tunnels, grottoes, pools, and pits — the remnants of disused quarries — were fortified with walls of cut stone and a statue of the Virgin and then used for experiments and meteorological observations. Behind the building stretched a terrace on which academicians mounted telescope masts, including the Marly tower. The aqueduct of Arcueil, which ran beside the walls, supplied subjects for study. From the staircase, Mariotte and La Hire experimented in 1683 with falling bodies, reproducing their tests at a nearby well. Nearly every day Cassini observed the direction of the wind from nearby windmills and recorded temperature, barometric pressure, and the state of the sky. With Mariotte he compared air pressure in the underground tunnels and on top of the building. From 1683 La Hire examined the declination of the magnetic needle at the Observatory. Sédileau and Cusset studied rainfall with apparatus made by Villette and Hubin that had been installed on the platform-roof of the Observatory (table 3b).^[39] The walls and floors of the building recorded data: Cassini made one room a giant sundial and transformed the floor of another into an immense universal map.^[40]

Architectural showpiece and symbol of royal patronage, the Observatory attracted many visitors despite its isolation. Germain Brice praised it in his guide book, Blondel included it among Parisian architectural monuments, and Martin Lister and John Locke mentioned it in their journals. A remarkable central staircase connecting the Observatory with its subterranean galleries was admired by such visitors as the duchess of Luxembourg and the prince and princess of Bournonville. The salle des machines on the second floor displayed models of machines and military engines, maps, and instruments, many formerly kept in the cramped quarters at the Library. Visitors also inspected the Academy's maps of the moon or of the night sky over Paris and studied mathematics and mechanics, parting with an appreciation of the Academy's observations and practical functions.^[41]

The apparatus at the Observatory represented a considerable investment by the crown. Research equipment for the astronomers included pendulum clocks made by Thuret, telescopes supplied by Le Bas, lenses purchased from Borelly, Hartsoeker, and Divini and Campani, a quadrant bought from Picard's estate, an azimuthal circle made by Migon, and various mathematical instruments by Lagny, Le Guern, Gosselin, and Sevin.^[42] There were also instruments that recorded knowledge. These included a "talking ephemerides," designed by Roemer and made by Thuret, that demonstrated the motions of the planets according to the Copernican system; a machine that demonstrated the causes of eclipses;

globes made by Migon and others under Roemer's supervision; and an expensive silver planisphere designed by Cassini and made by Butterfield.^[43] The royal treasury spent more than 85,000 livres to purchase and maintain these instruments for the Academy (table 3).

Of course, academicians also had their own apparatus, but royal patronage reduced the importance of individual owners and established the Academy as proprietor of essential equipment, including expensive items that few individuals could afford. The crown purchased instruments of particularly high quality, kept apparatus in good working order, and equipped expeditions. Above all, it provided permanent sites where academicians lived and worked. While other scientific societies lacked adequate equipment and emphasized demonstration and debate, the Academy, with its superior facilities and instruments, functioned as a research institution. The Observatory was central to this development.

Of the Academy's headquarters only the Observatory was originally designed to represent and serve the institution. Intended to unite the Academy in a permanent and sole residence, the Observatory in fact divided it. It separated the astronomers and mathematicians who lived there from the natural philosophers who lived at the Jardin royal or the Library. Nevertheless, the Observatory strengthened the Academy's ties to the public by attracting visitors and students. Like the Bibliothèque du roi and the Jardin royal, therefore, the Observatory functioned as research center, repository of equipment and records, tourist attraction, educational site, and home to academicians.