LUTH - Observatoire de Paris

La tour de l'ancien régime : the earth bound epoch.

Mene Stephane — 2019-12-17T15:13:57Z

Ambitions dangereuses : Henri de Guise et sa cousine Mary, executés pour voler trop haut.

The Observatory campus occupies the upper part of an extensive park where once stood a splendid Renaissance Chateau (whose Communes entrance survives today) that was already used for royal festivities under François I, while the surrounding forest was used for hunting - including falconry, in which the ladies were active participants.

Chateau Vieux de Meudon, vallée du Chalais derrière, Communes à droite.

Henri IV, l'unificateur

During the troubled century following the reformation, it belonged (like much else) to the overweening Guise family, ancestors via Mary d'Ecosse of Britain's Stuart dynasty, and protectors of the author of Gargantua, Meudon curate Rabelais, an admirer, like Mary, of the literary Queen Marguerite from whom she learnt (too late) that « Hawking causes us to forget a thousand foolish thoughts ».

After the abrupt termination of their emulation of Icarus - by the execution, at royal command, of Mary in England, and of her cousins Henri and Louis de Guise in France - Marguerite's grandson, Henri de Navarre, used Meudon as a temporary power base during the installation of the Bourbon dynasty in 1589, which united France and Navarre on the basis of a religious compromise, shortly before England and Scotland were similarly united on the basis of the authorised Bible translation by Mary's son King James.
Proud of its Italianate Grotte - a source of inspiration for Mary's mentor Ronsard - the Chateau was already a historic monument when King James (reputedly « the wisest fool in Christendom ») chose the philosopher Herbert of Montgomery (author of Cherbury's Lutebook) as his ambassador to the Paris

Grand Dauphin, Louis

court of Louis XIII. However it was not until the time of Louis XIV that the Meudon site again became particularly important, because of its strategic position midway between Paris and the new headquarters of Royal Government at Versailles. In the late XVIIth century the parc was landscaped on an extravagant scale by two royal ministers - the munificent Servian and the ruthless Louvois - with finishing touches master minded by the architect Le Nôtre, before being taken over by the heir to the throne, the Grand Dauphin.

La Grotte des Guises, et ce qui l'a remplacé : le Chateau Neuf suivi de la Grande Coupole.

In 1706 (at his father's instigation) the Dauphin sacrificed the antique Grotte (despite its poetic sanctification by Ronsard) in order to use its location to supplement the existing Chateau Vieux by the addition of a gargantuan royal appartment block known as the Chateau Neuf. Major construction work on the plateau came to an end under the Dauphin's descendant, Louis XV, who (under the influence of his effective minister of culture, Madame de Pompadour) preferred the cosier downhill Chateau de Bellevue (now a scientific campus of the CNRS) and who used the upper Meudon parc mainly for hunting. By that time, the use of the fusil de chasse had made shooting a popular, though not necessarily more effective, alternative to the traditional falconry that had been so fashionable at the time of Marguerite and Mary. (Hawking is still needed to stop Meudon pigeons from overflying Villacoublay.) After neglecting it during his earlier years, Louis XVI brought the Meudon palace back into royal use as a home for his eldest son, Louis-Joseph, in the hope that the alarming state of health of the little Dauphin would benefit from the feature that would later attract the astronomers, namely cleaner air than in downtown Paris or even Versailles.
It had been at Meudon that the first Bourbon monarch had been informed of his ascension as Henri IV, but this time - just 200 years later - the augury was reversed : the ill starred Dauphin died at the age of 7 in 1789, only a few weeks before the hunting party at which - again at Meudon - the disconsolate Louis XVI was informed of the fall of the Bastille that signalled the doom of his entire dynasty. His catastrophic fate was interpreted in some quarters as historical retribution for the decisive role King Louis (and particularly his royal navy) had played in the downfall of the Ancien Regime in North America. The high point of his reign had been the formal recognition of the independence of the United States at the treaty of Paris in 1783, an occasion on which it was auspicious that (like lute player Herbert at the court of Louis XIII) the American representative, Benjamin Franklin, should have been what was then known as a savant, meaning a member of the scientific community that was destined to take over (from royal courtiers) the guiding role in the development of Meudon.

Petit Dauphin, Louis-Joseph, 1784

It was not just for diplomatic activity that 1783 was an exceptionally memorable year in Paris. More immediately significant for the future of Meudon - from whose terrace it would have been telescopically observable - was the aerostatic realisation of the dream of Icarus, first using hot air, and shortly afterwards using the more effective hydrogen balloon technology invented by the physicist Jacques Charles. As a first hand witness of this epoch making breakthrough, Franklin lost no time in informing his correspondent Joseph Banks (discoverer of Australia with Captain Cook) who was then President of the Royal Society in London. Like the naively conservative King Louis (who feared air accidents) but for other reasons, Banks was reticent, recalling that it was British fundamental research - meaning the recent discovery of hydrogen by Henry Cavendish - that had made the French achievement possible, and suggesting that it was of less basic scientific interest than the the idea - put forward about the same time by Cambridge astrophysicist John Michel - of what is now called a black hole - something whose visual appearance would first be calculated at Meudon, though not until a couple of centuries later. Banks concluded his reply to Franklin with the prediction that, sooner or later, the art of flying would be developed for use in warfare. Within less that ten years, in the upshot of the revolution, it was destined to be at Meudon that this prophecy would first be fulfilled.

Louis XVI : portrait offert à Franklin, 1784, du roi qui voulait empêcher Charles de voler trop haut.

La tour du tournoyage : the age of uncontrolled flight

Mene Stephane — 2019-12-17T14:58:46Z

Though peacefully prosperous during most of the intervening years, the Meudon site was subject to damaging military occupation at both the beginning and the end of the constitutionally unsettled period from the foundation of the turbulent First Republic in the aftermath of the 1789 Revolution to the restoration of stability with the establishment of the Third Republic in 1871. The Chateau Vieux was « accidentally » destroyed in 1795, during first wave of occupation, by revolutionary army forces commanded by the recently promoted Colonel Laclos, previously known (and still remembered) for his

Pierre Choderlos de Laclos.

daring authorship, as a young officer under the Ancien Regime, of Liaisons dangereuses. A relatively uneventful period of routine repare and maintenance for use by the imperial or royal authorities in the long period from the reign of Napoleon I to that of Napoleon III, was followed by another military occupation at the period of the Paris Commune - this time by Bavarian units of Bismark's besieging army - of which the outcome was the destruction of the upper part (but not the foundations) of the Chateau Neuf.

It was in the pre-brumaire years (1792-1799) of the First Republic that Meudon's future vocation as a centre of what is now called aerospace research and developent was precociously manifested, when it was designated by the government as the site for the development of advanced

Entreprenant au siège de Maubeuge.

technology for military applications. It was not as a literary celebrity but as a leading expert in the technology of explosive projectiles (for use both on land and at sea) that Choderlos de Laclos was chosen to command the establishment that was set up for the purpose of producing such (evidently dangerous) munitions in the (thereby doomed) Chateau Vieux.

However what has retained the attention of later aerospace historians is not what happened in the Chateau Vieux, but the hardly less dangerous work

N.J.Conté, cyclopéen en Egypte

undertaken at the same time in the Chateau Neuf, under the

direction of Captains Nicolas Conté (a chemist) and Jean Coutelle (a physicist) both former students of D^r Charles, the inventor of the hydrogen balloon that had prompted the warning to Franklin that flying would be be used for war. The fulfilment of that prophecy was the task for which Conté and Coutelle were sent to Meudon. The outcome (in which the Chateau Neuf survived but Conté lost an eye) was the construction of the first batch of usefully operational balloons, namely Entreprenant, Céleste, Hercule, and finally (for Bonaparte's Egyptian expedition) Intrépide.

Piloted by aeronaut Coutelle himself, the Entreprenant successfully carried out several successful battlefield surveillance missions on the Northern front in 1794. Despite these positive results (but after a more disappointing performance in Egypt, where much of the equipment was destroyed by Nelson) Bonaparte's Consular government deemed that the Meudon air force was insufficiently cost effective, and it was therefore disbanded. This rather ignominious dismissal from military service, and the ensuing liberation from Coutelle's tether, made it possible at last for the Entreprenant to show what it could do. When its new owner, the free entrepreneur Etienne Robertson,

L-J. Gay-Lussac, aéronaute météorologiste

claimed to have reached the amazing hight of 7 Km in 1803, the government was goaded to bring the Enterprenant back into public service for scientific purposes. After reconditionning by Conté, the veteran aerostat was confided in 1804 to the physicists Jean-Baptiste Biot (specialist in magnetism) and Louis-Joseph Gay-Lussac. With Biot as ballast the ceiling was reached at the relatively modest hight of 4 Km, but finally - voyaging alone with minimal equipment - Gay-Lussac did indeed reach the 7 Km target altitude, this time under scientifically controled conditions. The Meudon balloon thus established a record that stood unchallenged for half a century.

From the beginning of the empire of Napoleon I to the end of that of Napoleon III, the Meudon campus reverted to its less exciting earlier role as a royal palace of secondary importance, while the development of flight proceeded elsewhere with only limited success : though useful for scientific exploration of the atmosphere, the aerostats were found to be more trouble

mid XIXth century view over the Seine towards Montmartre from terrace of Meudon's Chateau Neuf .

that they were worth for either military or commercial purposes. Their weakness was what might be desribed as the Flying Dutchman problem, with reference to the opera that was one of the most noteworthy creations of this otherwise relatively unremarkable period of Meudon history. This first major work by the subsequently controversial musician Richard Wagner was written in what is now the Avenue de l'Observatoire, where its composer was a temporarily bankrupt refugee from Saxony (so literally a fleeing Deutsch man) in 1841.

An allegorical expression of the plight of wind-drifting flyers in those pioneering days was provided in Act 1, by the plaintive song of the Flying Dutchman, whose words were « Unmoglich duncht mich, dass ich's nenne die Lander alle, die ich fand : das eine nur, nach dem ich brenne, ich find'es nicht mein, mein Heimatland ! » which roughly means I have found plenty of other places, but what I still seek is the way to get home ! The solution to the problem was prophetically proposed at the beginning of Act 2, where it was suggested that the way to bring the flyer home would be to use a spinning wheel to drive the wind : in the words of the accompanying audioclip « ... gutes Radchen, braus und suaus ! Ach ! gabst du Wind, er kam geshwind. Spinnt ! Spinnt ! ... »

Forty years later, when the musical wizard was nearing the end of his provocative life - but barely a mile from where these imaginative words were written - Meudon's Etang de Chalais was chosen for the first serious program of construction of the necessary spinning wheel machinery - whose essential element was of course a screw propellor.

Le tournage du retour : the aerospace age

Mene Stephane — 2019-12-17T14:49:35Z

Charles Renard aéronaute

It was not until the installation of the 3rd Republic that Meudon regained its role (this time permanently) as an aerospace center. In 1877

Arthur Krebs ingénieur

the upper plateau Campus, including the little that was left of the Chateau Neuf, was allocated to the astronomy community under the leadership of Jules Janssen, while the lower valley Campus bordering on the Etang de Chalais was allocated to a new generation of aeronauts under the leadership of Charles Renard, whose mission was to set up an establishment for the development of aircraft that would not merely drift downwind (unless tethered, like Entreprenant during military service) but that would be able to reach a chosen destination, and, in particular, to get home.

Jules Janssen, astronome

While Janssen was salvaging the little that was left of the Chateau Neuf (essentially just the part that had previously belonged to the Grotte)

Hangar Y du Chalais : le retour 1884

for use as the foundation for the construction - specially for planetary observations - of what was to be (and still is) the largest refracting telescope in Europe, Captain Renard was busy with the more rapid erection of the gargantuan shed known as Hangar Y, whose purpose was to house a new 50m long airship called La France.

The new airship was fitted out, for the first time, with effectively operational spinning wheel machinery of the appropriate kind, consisting of an electrically powered screw propellor developed by the military engineer Arthur Krebs.

La France de Renard et Krebs. Janssen's 1884 view from Meudon

The result would have been particularly appreciated by Janssen who (though crippled as far as ordinary walking was concerned) was an experienced balloonist in his own right. He may not yet have realised that he would have his own place in aeronautical history for his observation, during an eclipse of the sun in 1868, of the spectral lines of a hitherto unknown element, since called helium, that was later identified as the lightest of the inert gases, and that was therefore destined to replace Cavendish's inflamable hydrogen in modern airships. As shown in the accompanying photo, Janssen and the other astronomers had a grandstand view when their aeronautical colleagues triumphantly demonstrated the first practical solution of the Flying Dutchman problem in several memorable flights (at speeds up to 20 Km/h) in the sky above our Observatory in the autumn of 1884. After each flight - and this what was what had not been possible before - the airship was able to return safely under full control to its home base, the still remarkably well preserved Hangar Y, in the sheltered valley below.

Further improvements of the spinning wheel propulsion machinery - most notably by the introduction of the internal combustion engine - enabled the use of purely aerodynamical (rather than aerostatic) lift at the beginning of the XXth century, which entailed the requirement of a long landing strip. This

La soufflerie du Chalais, Meudon's gargantuan subsonic windtunnel

lead to the transfer of actual flighing activities to other bases (such as Villacoublay on the plateau nearby). Nevertheless Meudon's Chalais valley establishment continued to be developped as a technological research centre, with the focus of interest transferred from Hangar Y to the (by the standards of the time) gargantuan wind tunnel that was constructed after the overwhelming importance of air power had been definitively demonstrated during the First World War. The Meudon aviation research base has since become a unit of the Office National d'Etudes et de Recherches Aérospatiales, which now operates modern supersonic wind tunnels there.

While these developments were going on in the valley below, the Observatory on the plateau above evolved by stages towards its present

Grande lunette

configuration - first as a separate organisation, and since 1926 as part of a united Observatoire de Paris, with headquarters in the historic downtown campus established (opposite the Luxembourg Palace) by Louis XIV for the astronomer Jean Dominique Cassini. The most spectacular step (shortly after the construction of the Eiffel Tower in 1889) was the completion of the giant (83 cm aperture) refracting telescope known as the Grande Lunette in the prominent domed turret at the center of the partially reconstructed Chateau Neuf, whose silhouette was thereby restored to something more like what it had been at the time of the Grotte. Whereas the more commonly employed mirror technology is preferred for faint sources such as distant galaxies, a refracting telescope is advantageous for sources such as planets, for which the main problem is to achieve sufficiently high resolution.

Grande Coupole, Tour Solaire, and Laboratoire d'Astrophysique de Meudon, alternating with opposite view towards Paris, showing the murk that motivated the move to Meudon

As Janssen's main professional concern had been not with galaxies or planets but with the Sun, it was logical that Meudon should develop as the most important European centre for Solar astronomy, a field that has special technical problems of its own. It was for this purpose that the last important step in the achievement of the present layout of the Campus was completed in 1969, by the construction of the conspicuous mushroom shaped Tour Solaire, which is designed to bypass the air turbulence that develops near the ground on sunny days, while at the same time the development of theoretical, as well as observational, work was facilitated by the construction of the Laboratoire d'Astrophysique de Meudon under the guiding influence of Evry Schatzman, a pioneer of the theory of the (transparent but extremely hot) Solar corona.

The problem of getting past turbulent or simply absorbent layers of the atmosphere has always been a major problem of astronomers, and has lead to the construction of telescopes of various kinds in successively higher mountain sites, and to the continued use of balloon supported instrumentation, as in the record breaking aerostatic ascent from Meudon, for the purpose of observing Mars, by the astronomer Audouin Dollfus in 1959.

The most recent progress in getting past the astmosphere has of course, been by the use of satellites and other space probes. For this reason, the ground based observational equipment in a historic Observatory such as that of Cassini, and even that of Meudon, is no longer as important as it used to be.

Evry Schatzman, astrophysicien

Nevertheless (in partnership with other institutions such as the University of Paris VII) the Observatoire de Paris, and particularly its Meudon Campus, remains at the forefront of new developments, notably as a base for the development of space launched instrumentation for modern detectors, which are no longer restricted to visible light, but are susceptable to infra red, X-rays, and much more. Since the pionneering initiative of Schatzman, the Meudon Campus has also become a center for the development of theoretical astrophysics, particularly in the recently established LUTH, which is concerned not just with phenomena that are directly observable, but also with what goes on out of sight, as for example in the central regions of ordinary stars (such as the Sun) and of more exotic objects such as neutron stars and particularly in the black holes that are thought to account for spectacular but still mysterious phenomena such as quasars.