académie+des+sciences

the Academy of Science

académie [akademi]

   a. ( = société savante) learned society

• l'Académie (française) the Académie française

   b. ( = école) academy

   c. ( = circonscription) regional education authority

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For educational administration purposes, France is divided into areas known as académies, each administered by a « recteur d'académie ». Allocation of teaching posts is centralized, so that newly qualified teachers often begin their careers in académies other than the one in which they originally lived.

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Founded by Cardinal Richelieu in 1634, this prestigious learned society has forty elected life members, commonly known as « les Immortels ». They meet in a building on the quai Conti in Paris. The building's ornate dome has given rise to the expression « être reçu sous la coupole », meaning to be admitted as a member of the Académie française. The Académie arbitrates on correct usage.

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1) ( école) school

2) École, Université ≈ local education authority GB, school district US

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1) (= société) learned society

2) (= école) [art, danse] academy

3) ART (= nu) nude

4) ÉDUCATION (= circonscription) regional education authority

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académie nf

1 ( école) (de billard, danse) school; ( de police) academy; académie de peinture or de dessin art academy;

2 Admin ≈ local education authority GB, school district US;

3 Art ( figure) nude;

4 ( groupe de personnes) society.

[akademi] nom féminin

1. [société savante] learned society, academy

2. [école] academy

3. [salle]

4. ART nude

5. (familier) [corps] body, figure

6. ADMINISTRATION & ÉDUCATION ≃ local education authority (UK), ≃ school district (US)

Originally a group of men of letters who were encouraged by Cardinal Richelieu in 1635 to become an official body. L'académie française consists of forty distinguished writers known as les Quarante or les Immortels. Its chief task is to produce a definitive dictionary and to be the ultimate authority in matters concerning the French language.

SUBJECT AREA: Metallurgy

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After graduating in chemistry from the Ecole Polytechnique in 1887, Charpy continued to work there on the physical chemistry of solutions for his doctorate. He joined the Laboratoire d'Artillerie de la Marine in 1892 and began to study the structure and mechanical properties of various steels in relation to their previous heat treatment. His first memoir, on the mechanical properties of steels quenched from various temperatures, was published in 1892 on the advice of Henri Le Chatelier. He joined the Compagnie de Chatillon Commentry Fourchamboult et Decazeville at their steelworks in Imphy in 1898, shortly after the discovery of Invar by G.E. Guillaume. Most of the alloys required for this investigation had been prepared at Imphy, and their laboratories were therefore well equipped with sensitive and refined dilatometric facilities. Charpy and his colleague L.Grenet utilized this technique in many of their earlier investigations, which were largely concerned with the transformation points of steel. He began to study the magnetic characteristics of silicon steels in 1902, shortly after their use as transformer laminations had first been proposed by Hadfield and his colleagues in 1900. Charpy was the first to show that the magnetic hysteresis of these alloys decreased rapidly as their grain size increased.

The first details of Charpy's pendulum impact testing machine were published in 1901, about two years before Izod read his paper to the British Association. As with Izod's machine, the energy of fracture was measured by the retardation of the pendulum. Charpy's test pieces, however, unlike those of Izod, were in the form of centrally notched beams, freely supported at each end against rigid anvils. This arrangement, it was believed, transmitted less energy to the frame of the machine and allowed the energy of fracture to be more accurately measured. In practice, however, the blow of the pendulum in the Charpy test caused visible distortion in the specimen as a whole. Both tests were still widely used in the 1990s.

In 1920 Charpy left Imphy to become Director-General of the Compagnie des Aciéries de la Marine et Homecourt. After his election to the Académie des Sciences in 1918, he came to be associated with Floris Osmond and Henri Le Chatelier as one of the founders of the "French School of Physical Metallurgy". Around the turn of the century he had contributed much to the development of the metallurgical microscope and had helped to introduce the Chatelier thermocouple into the laboratory and to industry. He also popularized the use of platinum-wound resistance furnaces for laboratory purposes. After 1920 his industrial responsibilities increased greatly, although he continued to devote much of his time to teaching at the Ecole Supérieure des Mines in Paris, and at the Ecole Polytechnique. His first book, Leçons de Chimie (1892, Paris), was written at the beginning of his career, in association with H.Gautier. His last, Notions élémentaires de sidérurgie (1946, Paris), with P.Pingault as co-author, was published posthumously.

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SUBJECT AREA: Horology

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Le Roy was born into a distinguished horological family: his father, Julien, was Clockmaker to the King. Pierre became Master in 1737 and continued to work with his father, taking over the business when his father died in 1759. However, he seems to have left the commercial side of the business to others so that he could concentrate on developing the marine chronometer. Unlike John Harrison, he believed that the solution lay in detaching the escapement from the balance, and in 1748 he submitted a proposal for the first detached escapement to the Académie des Sciences in Paris. He also differed from Harrison in his method of temperature compensation, which acted directly on the balance by altering its radius of gyration. This was achieved either by mounting thermometers on the balance or by using bimetallic strips which effectively reduced the diameter of the balance as the temperature rose (with refinements, this later became the standard method of temperature compensation in watches and chronometers). Le Roy had already discovered that for every spiral balance spring there was a particular length at which it would be isochronous, and this method of temperature compensation did not destroy that isochronism by altering the length, as other methods did. These innovations were incorporated in a chronometer with an improved detached escapement which he presented to Louis XV in 1766 and described in a memoir to the Académie des Sciences. This instrument contained the three essential elements of all subsequent chronometers: an isochronous balance spring, a detached escapement and a balance with temperature compensation. Its performance was similar to that of Harrison's fourth timepiece, and Le Roy was awarded prizes by the Académie des Sciences for the chronometer and for his memoir. However, his work was never fully appreciated in France, where he was over-shadowed by his rival Ferdinand Berthoud. When Berthoud was awarded the coveted title of Horloger de la Marine, Le Roy became disillusioned and shortly afterwards gave up chronometry and retired to the country.

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SUBJECT AREA: Medical technology, Photography, film and optics

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At the age of 19 Marey went to Paris to study medicine, becoming particularly interested in the problems of the circulation of the blood. In an early communication to the Académie des Sciences he described a much improved device for recording the pulse, the sphygmograph, in which the beats were recorded on a smoked plate. Most of his subsequent work was concerned with methods of recording movement: to study the movement of the horse, he used pneumatic sensors on each hoof to record traces on a smoked drum; this device became known as the Marey recording tambour. His attempts to study the wing movements of a bird in flight in the same way met with limited success since the recording system interfered with free movement. Reading in 1878 of Muybridge's work in America using sequence photography to study animal movement, Marey considered the use of photography himself. In 1882 he developed an idea first used by the astronomer Janssen: a camera in which a series of exposures could be made on a circular photographic plate. Marey's "photographic gun" was rifle shaped and could expose twelve pictures in approximately one second on a circular plate. With this device he was able to study wing movements of birds in free flight. The camera was limited in that it could record only a small number of images, and in the summer of 1882 he developed a new camera, when the French government gave him a grant to set up a physiological research station on land provided by the Parisian authorities near the Porte d'Auteuil. The new design used a fixed plate, on which a series of images were recorded through a rotating shutter. Looking rather like the results provided by a modern stroboscope flash device, the images were partially superimposed if the subject was slow moving, or separated if it was fast. His human subjects were dressed all in white and moved against a black background. An alternative was to dress the subject in black, with highly reflective strips and points along limbs and at joints, to produce a graphic record of the relationships of the parts of the body during action. A one-second-sweep timing clock was included in the scene to enable the precise interval between exposures to be assessed. The fixed-plate cameras were used with considerable success, but the number of individual records on each plate was still limited. With the appearance of Eastman's Kodak roll-film camera in France in September 1888, Marey designed a new camera to use the long rolls of paper film. He described the new apparatus to the Académie des Sciences on 8 October 1888, and three weeks later showed a band of images taken with it at the rate of 20 per second. This camera and its subsequent improvements were the first true cinematographic cameras. The arrival of Eastman's celluloid film late in 1889 made Marey's camera even more practical, and for over a decade the Physiological Research Station made hundreds of sequence studies of animals and humans in motion, at rates of up to 100 pictures per second. Marey pioneered the scientific study of movement using film cameras, introducing techniques of time-lapse, frame-by-frame and slow-motion analysis, macro-and micro-cinematography, superimposed timing clocks, studies of airflow using smoke streams, and other methods still in use in the 1990s. Appointed Professor of Natural History at the Collège de France in 1870, he headed the Institut Marey founded in 1898 to continue these studies. After Marey's death in 1904, the research continued under the direction of his associate Lucien Bull, who developed many new techniques, notably ultra-high-speed cinematography.

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See also: Demenÿ, Georges

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SUBJECT AREA: Canals, Civil engineering

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Aubert was educated at the Lycée Louis-leGrand in Paris, and entered the Ecole Polytechnique in 1913. His studies were interrupted by the First World War, when he served as an artillery officer, being wounded twice and awarded the Croix de Guerre in 1916. He returned to the Ecole Polytechnique in 1919, and from 1920 to 1922 he attended the Ecole Nationale des Ponts et Chaussées; he graduated as Bachelor of Law from the University of Paris.

In 1922 he began his long career, devoted principally to river and canal works. He was engineer in charge of the navigation works in Paris until 1932; he was then appointed Professor in the Chair of Internal Navigation at the Ecole des Ponts et Chaussées, a post he held until his retirement in 1961. From 1933 to 1945 he was general manager and later chairman of the Compagnie Nationale du Rhône; from 1945 to 1953, chairman of the electricity board of the Société Nationale des Chemins de Fer français; and from 1949 to 1967, chairman of the Rhine Navigation Company. Following his retirement, he was chairman of the Société des Constructions des Batignolles, and from 1966 consulting engineer and honorary chairman of SPIE Batignolles; he was also chairman of several other companies.

In 1919 he published La Probabilité dans les tires de guerre, for which he was awarded the Pierson-Perrim prize by the Académie des Sciences in 1922. During his career he wrote numerous articles and papers on technical and economic subjects, his last, entitled "Philosophic de la pente d'eau", appearing in the journal Travaux in 1984 when he was ninety years old.

Aubert's principal works included the construction of the Pont Edouard-Herriort on the Rhône at Lyon; the design and construction of the Génissiat and Lonzères-Mondragon dams on the Rhône; and the conception and design of the Denouval dam on the Seine near Andresy, completed in 1980. He was awarded the Caméré prize in 1934 by the Académie des Sciences for a new type of movable dam. Overseas governments and the United Nations consulted him on river navigation inter alia in Brazil, on the Mahanadi river in India, on the Konkomé river in Guinea, on the Vistula river in Poland, on the Paraguay river in South America and others.

In 1961 he published his revolutionary ideas on the pente d'eau, or "water slope", which was designed to eliminate delays and loss of water in transferring barges from one level to another, without the use of locks. This design consisted of a sloping flume or channel through which a wedge of water, in which the barge was floating, was pushed by a powered unit. A prototype at Mon tech on the Canal Latéral at La Garonne, bypassing five locks, was opened in 1973. A second was opened in 1984 on the Canal du Midi at Fonserannes, near Béziers.

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SUBJECT AREA: Horology, Metallurgy

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Guillaume came from a family of clock-and watchmakers. He was educated at the Gymnasium in Neuchâtel and at Zurich Polytechnic, from which he received his doctorate in 1883 for a thesis on electrolytic capacitors. In the same year he joined the International Bureau of Weights and Measures at Sèvres in France, where he was to spend the rest of his working life. He retired as Director in 1936. At the bureau he was involved in distributing the national standards of the metre to countries subscribing to the General Conference on Weights and Measures that had been held in 1889. This made him aware of the crucial effect of thermal expansion on the lengths of the standards and he was prompted to look for alternative materials that would be less costly than the platinum alloys which had been used. While studying nickel steels he made the surprising discovery that the thermal expansion of certain alloy compositions was less than that of the constituent metals. This led to the development of a steel containing about 36 per cent nickel that had a very low thermal coefficient of expansion. This alloy was subsequently named "invar", an abbreviation of invariable. It was well known that changes in temperature affected the timekeeping of clocks by altering the length of the pendulum, and various attempts had been made to overcome this defect, most notably the mercury-compensated pendulum of Graham and the gridiron pendulum of Harrison. However, an invar pendulum offered a simpler and more effective method of temperature compensation and was used almost exclusively for pendulum clocks of the highest precision.

Changes in temperature can also affect the timekeeping of watches and chronometers, but this is due mainly to changes in the elasticity or stiffness of the balance spring rather than to changes in the size of the balance itself. To compensate for this effect Guillaume developed another more complex nickel alloy, "elinvar" (elasticity invariable), whose elasticity remained almost constant with changes in temperature. This had two practical consequences: the construction of watches could be simplified (by using monometallic balances) and more accurate chronometers could be made.

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See also: Le Roy, Pierre

SUBJECT AREA: Horology

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Huygens was born into a cultured and privileged class. His father, Constantijn, was a poet and statesman who had wide interests. Constantijn exerted a strong influence on his son, who was educated at home until he reached the age of 16. Christiaan studied law and mathematics at Ley den University from 1645 to 1647, and continued his studies at the Collegium Arausiacum in Breda until 1649. He then lived at The Hague, where he had the means to devote his time entirely to study. In 1666 he became a Member of the Académie des Sciences in Paris and settled there until his return to The Hague in 1681. He also had a close relationship with the Royal Society and visited London on three occasions, meeting Newton on his last visit in 1689. Huygens had a wide range of interests and made significant contributions in mathematics, astronomy, optics and mechanics. He also made technical advances in optical instruments and horology.

Despite the efforts of Burgi there had been no significant improvement in the performance of ordinary clocks and watches from their inception to Huygens's time, as they were controlled by foliots or balances which had no natural period of oscillation. The pendulum appeared to offer a means of improvement as it had a natural period of oscillation that was almost independent of amplitude. Galileo Galilei had already pioneered the use of a freely suspended pendulum for timing events, but it was by no means obvious how it could be kept swinging and used to control a clock. Towards the end of his life Galileo described such a. mechanism to his son Vincenzio, who constructed a model after his father's death, although it was not completed when he himself died in 1642. This model appears to have been copied in Italy, but it had little influence on horology, partly because of the circumstances in which it was produced and possibly also because it differed radically from clocks of that period. The crucial event occurred on Christmas Day 1656 when Huygens, quite independently, succeeded in adapting an existing spring-driven table clock so that it was not only controlled by a pendulum but also kept it swinging. In the following year he was granted a privilege or patent for this clock, and several were made by the clockmaker Salomon Coster of The Hague. The use of the pendulum produced a dramatic improvement in timekeeping, reducing the daily error from minutes to seconds, but Huygens was aware that the pendulum was not truly isochronous. This error was magnified by the use of the existing verge escapement, which made the pendulum swing through a large arc. He overcame this defect very elegantly by fitting cheeks at the pendulum suspension point, progressively reducing the effective length of the pendulum as the amplitude increased. Initially the cheeks were shaped empirically, but he was later able to show that they should have a cycloidal shape. The cheeks were not adopted universally because they introduced other defects, and the problem was eventually solved more prosaically by way of new escapements which reduced the swing of the pendulum. Huygens's clocks had another innovatory feature: maintaining power, which kept the clock going while it was being wound.

Pendulums could not be used for portable timepieces, which continued to use balances despite their deficiencies. Robert Hooke was probably the first to apply a spring to the balance, but his efforts were not successful. From his work on the pendulum Huygens was well aware of the conditions necessary for isochronism in a vibrating system, and in January 1675, with a flash of inspiration, he realized that this could be achieved by controlling the oscillations of the balance with a spiral spring, an arrangement that is still used in mechanical watches. The first model was made for Huygens in Paris by the clockmaker Isaac Thuret, who attempted to appropriate the invention and patent it himself. Huygens had for many years been trying unsuccessfully to adapt the pendulum clock for use at sea (in order to determine longitude), and he hoped that a balance-spring timekeeper might be better suited for this purpose. However, he was disillusioned as its timekeeping proved to be much more susceptible to changes in temperature than that of the pendulum clock.

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SUBJECT AREA: Medical technology

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After studies at colleges in Limoges and later in Paris, Arsonval became a doctor of medicine in 1877. In 1882 the Collège de France established a laboratory of biophysics with Arsonval as Director, and he was Professor from 1894.

His most outstanding scientific contributions were in the field of biological applications of electricity. His interest in muscle currents led to a series of inventions to assist in research, including the moving-coil galvanometer. In 1881 he made a significant improvement to the galvanometer by reversing the magnetic elements. It had been usual to suspend a compass needle in the centre of a large, stationary coil, but Arsonval's invention was to suspend a small, light coil between the poles of a powerful fixed magnet. This simple arrangement was independent of the earth's magnetic field and insensitive to vibration. A great increase in sensitivity was achieved by attaching a mirror to the coil in order to reflect a spot of light. For bacterial-research purposes he designed the first constant-temperature incubator controlled by electricity. His experiments on the effects of high-frequency, low-voltage alternating currents on animals led to the first high-frequency heat-therapy unit being established in 1892, and later to methods of physiotherapy becoming a professional discipline.

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SUBJECT AREA: Aerospace

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In 1783, following the early experiments with small hot-air balloons by the Montgolfier brothers, there was a growing interest in the prospect of a balloon flight with people on board. The Paris Académie des Sciences encouraged one of their physicists, Charles, to carry out experiments and produce a balloon. Charles enlisted the assistance of two brothers, Anne-Jean and Marie-Noël Robert, who were practical craftsmen with experience of coating silk fabric with rubber to make it impermeable to gases. Charles decided to use the recently discovered lighter-than-air gas, hydrogen, for his experiments rather than hot air. After making several unmanned balloons, he had a manned balloon ready for testing on 1 December 1783. Despite the fact that a Montgolfier balloon had already flown with two passengers, there was enormous public interest in the flight: one estimate suggested that 400,000 people turned out to watch. Charles and Marie-Noël Robert ascended from the gardens of the Tuileries and landed after two hours, having covered 45 km (28 miles). Technically the "Charlière" was far superior to the "Montgolfière" and was therefore used by most subsequent balloonists until the introduction of the modern hot-air balloon by the American Paul E. Yost in the 1960s. Following Meusnier's proposals for a dirigible (steerable) balloon, put forward during 1783–5, Charles and the Robert brothers built an elongated balloon incorporating Meusnier's ballonnet principle. It had a rudder but the method of propulsion, by opening and closing parasols used as paddles, was totally ineffective.

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SUBJECT AREA: Mechanical, pneumatic and hydraulic engineering

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Poncelet studied mathematics at the Ecole Polytechnique in Paris from 1807 to 1810. He joined the Army, gaining admission to the Corps of Engineers. He worked on the fortifications on the Isle of Walcheren in Holland, and in 1812 he found himself on the Russian front, engulfed in the disastrous defeat of the French at Krasnoi. Poncelet was left for dead on the field, but he was found by the Russians and taken to Saratov, where he was imprisoned for two years. He had ample opportunity there to ponder mathematical problems, a mental process from which stemmed his pioneering advances in projective geometry.

After his release he returned to this native city of Metz, where he undertook routine military engineering and teaching tasks. These left him time to pursue his mathematical studies in projective geometry. This bore fruit in a series of publications, most notably the first volume of his Traité des propriétés projectives des figures (1822, Paris), the first book to be devoted to the new discipline of projective geometry. With his election to the Académie des Sciences in 1834, Poncelet moved to Paris and devoted much of his time to developing courses in applied mechanics in the Faculty of Science, resulting in a number of books, especially the Introduction à la mécanique industrielle, physique ou expérimentale (1841, Paris: Metz). In 1848 he had attained the rank of general and was made Commandant of the Ecole Polytechnique, a post he held for two years. After his retirement in 1850 he was deeply involved in the industrial machines and tools division at both the Great Exhibition in London in 1851 and the similar exhibition in Paris in 1855.

Most of Poncelet's work in applied mechanics and technology was conceived during the period 1825–40. His technological innovations were centred on hydraulic engineering, and in 1826 he invented an inward-flow turbine. At the same time he directed his attention to the vertical undershot water-wheel, with wooden blades set radially and substituted curved metal blades: he used tight-fitting masonry and floors in the wheel pits so that all the water would be swept into the spaces between the blades. In addition, he ensured that the water flowing from the blades fell clear of the wheel and did not run in tail water. This greatly improved the efficiency of the water-wheel.

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SUBJECT AREA: Mechanical, pneumatic and hydraulic engineering

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Phillips was educated in Paris, at the Ecole Polytechnic and the Ecole des Mines. In 1849 he was awarded a doctorate in mathematical sciences by the University of Paris. He had a varied career in industry, academic and government institutions, rising to be Inspector- General of Mines in 1882.

It was well known that the balance of a watch or chronometer fitted with a simple spiral or helical spring was not isochronous, i.e. the period of the oscillation was not entirely independent of the amplitude. Watch-and chronometer-makers, notably Breguet and Arnold, had devised empirical solutions to the problem by altering the curvature of the end of the balance spring. In 1858 Phillips was encouraged to tackle the problem mathematically, and two years later he published a complete solution for the helical balance spring and a partial solution for the more complex spiral spring. Eleven years later he was able to achieve a complete solution for the spiral spring by altering the curvature of both ends of the spring. Phillips published a series of typical curves that the watch-or chronometer-maker could use to shape the ends of the balance spring.

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SUBJECT AREA: Mining and extraction technology, Steam and internal combustion engines

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A don of the Ecole Polytechnique and the Ecole Supérieure des Mines in Paris, Rateau joined the French Corps des Mines in 1887. Between 1888 and 1898 he taught applied mechanics and electro technics at the Ecole des Mines in St-Etienne. Trying to apply the results of his research to practise, he became into contact with commercial firms, before he was appointed Professor of Industrial Electricity at the Ecole Supérieure des Mines in Paris in 1902. He held this position until 1910, although he founded the Société Anonyme Rateau in Paris in 1903 which by the time of his death had subsidiaries in most of the industrial centres of Europe. By the middle of the nineteenth century, when the increasing problems of ventilation in coal mines had become evident and in many countries had led to several unsatisfactory mechanical constructions, Rateau concentrated on this problem soon after he began working in St-Etienne. The result of his research was the design of a centrifugal fan in 1887 with which he established the principles of mechanical ventilation on a general basis that led to future developments and helped, together with the ventilator invented by Capell in England, to pave the way for the use of electricity in mine ventilation.

Rateau continued the study of fluid mechanics and the applications of rotating engines, and after he had published widely on this subject he began to construct many steam turbines, centrifugal compressors and centrifugal pumps. The multicellular Rateau turbine of 1901 became the prototype for many others constructors. During the First World War, when he was very active in the French armaments industry, he developed the invention of the automatic supercharger for aircraft engines and later diesel engines.

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SUBJECT AREA: Metallurgy

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Soon after graduating from the Ecole des Mines at St-Etienne in 1910, Chevenard joined the Société de Commentry Fourchambault et Decazeville at their steelworks at Imphy, where he remained for the whole of his career. Imphy had for some years specialized in the production of nickel steels. From this venture emerged the first austenitic nickel-chromium steel, containing 6 per cent chromium and 22–4 per cent nickel and produced commercially in 1895. Most of the alloys required by Guillaume in his search for the low-expansion alloy Invar were made at Imphy. At the Imphy Research Laboratory, established in 1911, Chevenard conducted research into the development of specialized nickel-based alloys. His first success followed from an observation that some of the ferro-nickels were free from the low-temperature brittleness exhibited by conventional steels. To satisfy the technical requirements of Georges Claude, the French cryogenic pioneer, Chevenard was then able in 1912 to develop an alloy containing 55–60 per cent nickel, 1–3 per cent manganese and 0.2–0.4 per cent carbon. This was ductile down to −190°C, at which temperature carbon steel was very brittle.

By 1916 Elinvar, a nickel-iron-chromium alloy with an elastic modulus that did not vary appreciably with changes in ambient temperature, had been identified. This found extensive use in horology and instrument manufacture, and even for the production of high-quality tuning forks. Another very popular alloy was Platinite, which had the same coefficient of thermal expansion as platinum and soda glass. It was used in considerable quantities by incandescent-lamp manufacturers for lead-in wires. Other materials developed by Chevenard at this stage to satisfy the requirements of the electrical industry included resistance alloys, base-metal thermocouple combinations, magnetically soft high-permeability alloys, and nickel-aluminium permanent magnet steels of very high coercivity which greatly improved the power and reliability of car magnetos. Thermostatic bimetals of all varieties soon became an important branch of manufacture at Imphy.

During the remainder of his career at Imphy, Chevenard brilliantly elaborated the work on nickel-chromium-tungsten alloys to make stronger pressure vessels for the Haber and other chemical processes. Another famous alloy that he developed, ATV, contained 35 per cent nickel and 11 per cent chromium and was free from the problem of stress-induced cracking in steam that had hitherto inhibited the development of high-power steam turbines. Between 1912 and 1917, Chevenard recognized the harmful effects of traces of carbon on this type of alloy, and in the immediate postwar years he found efficient methods of scavenging the residual carbon by controlled additions of reactive metals. This led to the development of a range of stabilized austenitic stainless steels which were free from the problems of intercrystalline corrosion and weld decay that then caused so much difficulty to the manufacturers of chemical plant.

Chevenard soon concluded that only the nickel-chromium system could provide a satisfactory basis for the subsequent development of high-temperature alloys. The first published reference to the strengthening of such materials by additions of aluminium and/or titanium occurs in his UK patent of 1929. This strengthening approach was adopted in the later wartime development in Britain of the Nimonic series of alloys, all of which depended for their high-temperature strength upon the precipitated compound Ni3Al.

In 1936 he was studying the effect of what is now known as "thermal fatigue", which contributes to the eventual failure of both gas and steam turbines. He then published details of equipment for assessing the susceptibility of nickel-chromium alloys to this type of breakdown by a process of repeated quenching. Around this time he began to make systematic use of the thermo-gravimetrie balance for high-temperature oxidation studies.

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SUBJECT AREA: Aerospace

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Just a few days after the first balloon flight by the relatively primitive Montgolfier hot-air balloon, a design for a sophisticated steerable or "dirigible" balloon was proposed by a young French army officer. On 3 December 1783, Lieutenant (later General) Jean Baptiste Marie Meusnier of the Corps of Engineers presented to the Académie des Sciences a paper entitled Mémoire sur l'équilibre des machines aérostatiques. This outlined Meusnier's ideas and so impressed the learned members of the Academy that they commissioned him to make a more complete study. This was published in 1784 and contained sixteen water-colour drawings of the proposed airship, which are preserved by the Musée de l'Air in Paris.

Meusnier's "machine aérostatique" was ellipsoidal in shape, in contrast to those of his unsuccessful contemporaries who tried to make spherical balloons steerable, often using oars for propulsion. Meusnier's proposed airship was 79.2 m (260 ft) long with the crew in a slim boat slung below the envelope (in case of a landing on water); it was steered by a large sail-like rudder at the rear end. Between the envelope and the boat were three propellers, which were to be manually driven as there was no suitable engine available; this was the first design for a propeller-driven aircraft. The most important innovation was a ballonnet, a balloon within the main envelope that was pressurized with air supplied by bellows in the boat. Varying the amount of air in the ballonnet would compensate for changes in the volume of hydrogen gas in the main envelope when the airship changed altitude. The ballonnet would also help to maintain the external shape of the main envelope.

General Meusnier was killed in action in 1793 and it was almost one hundred years from the date of his publication that his idea of ballonnets was put into practice, by Dupuy de Lome in 1872, and later by Renard and Krebs.

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SUBJECT AREA: Photography, film and optics

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The son of a tax collector, Ducos du Hauron began researches into colour photography soon after the publication of Clerk Maxwell's experiment in 1861. In a communication sent in 1862 for presentation at the Académie des Sciences, but which was never read, he outlined a number of methods for photography of colours. Subsequently, in his book Les Couleurs en photographie, published in 1869, he outlined most of the principles of additive and subtractive colour photography that were later actually used. He covered additive processes, developed from Clerk Maxwell's demonstrations, and subtractive processes which could yield prints. At the time, the photographic materials available prevented the processes from being employed effectively. The design of his Chromoscope, in which transparent reflectors could be used to superimpose three additive images, was sound, however, and formed the basis of a number of later devices. He also proposed an additive system based on the use of a screen of fine red, yellow and blue lines, through which the photograph was taken and viewed. The lines blended additively when seen from a certain distance. Many years later, in 1907, Ducos du Hauron was to use this principle in an early commercial screen-plate process, Omnicolore. With his brother Alcide, he published a further work in 1878, Photographie des Couleurs, which described some more-practical subtractive processes. A few prints made at this time still survive and they are remarkably good for the period. In a French patent of 1895 he described yet another method for colour photography. His "polyfolium chromodialytique" involved a multiple-layer package of separate red-, green-and blue-sensitive materials and filters, which with a single exposure would analyse the scene in terms of the three primary colours. The individual layers would be separated for subsequent processing and printing. In a refined form, this is the principle behind modern colour films. In 1891 he patented and demonstrated the anaglyph method of stereoscopy, using superimposed red and green left and right eye images viewed through green and red filters. Ducos du Hauron's remarkable achievement was to propose theories of virtually all the basic methods of colour photography at a time when photographic materials were not adequate for the purpose of proving them correct. For his work on colour photography he was awarded the Progress Medal of the Royal Photographic Society in 1900, but despite his major contributions to colour photography he remained in poverty for much of his later life.

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abr nf Académie des Sciences

SUBJECT AREA: Photography, film and optics

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A man of considerable intellect, Cros occupied himself with studies of topics as diverse as Sanskrit and the synthesis of precious stones. He was in particular interested in the possibility of colour photography, and deposited an account of his theories in a sealed envelope with the Académie des Sciences on 2 December 1867, with instructions that it should be opened in 1876. Learning of a forthcoming presentation on colour photography by Ducos du Hauron at the Société Française de Photographie, he arranged for the contents of his communication to be published on 25 February 1869 in Les Mondes. At the Société's meeting on 7 May 1869, Cros's letter was read and samples of colour photography from Ducos du Hauron were shown. Both had arrived at similar conclusions: that colour photography was possible with the analysis of colours using negatives exposed through red, green and blue filters, as demonstrated by Clerk Maxwell in 1861. These records could be reproduced by combining positive images produced in blue-green, magenta and yellow pigments or dyes. Cros and Ducos du Hauron had discovered the principle of subtractive colour photography, which is used in the late twentieth century. In 1878 Cros designed the Chromometre, a device for measuring colours by mixing red, green and blue light, and described the device in a paper to the Société Française de Photographie on 10 January 1879. With suitable modification, the device could be used as a viewer for colour photographs, combining red, green and blue positives. In 1880 he patented the principle of imbibition printing, in which dye taken up by a gelatine relief image could be transferred to another support. This principle, which he called hydrotypie, readily made possible the production of three-colour subtractive photographic prints.

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SUBJECT AREA: Photography, film and optics, Recording, Telecommunications

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He received no formal education, but was brought up by his father, a distinguished teacher and philosopher. He dabbled in diverse subjects (modern and ancient languages, mathematics, drawing) in 1856–60 when he became an instructor at the institute of the Deaf-Mute at Paris. He became a prolific inventor and poet and took part in artistic life in Paris. In the 1867 Exposition Universelle in Paris, Cros contributed a facsimile telegraph; he deposited with the Académie des Sciences a sealed text on photography which was not opened until 1876. In the meantime he published a small text on a general solution of the problem of colour photography which appeared almost simultaneously with a similar publication by Louis Ducos du Hauron and which gave rise to bitter discussions over priority. He deposited a sealed paper on 18 April 1877 concerning his concept of apparatus for recording and reproduction of sound which he called the paléophone. When it was opened on 3 December 1877 it was not known that T.A. Edison was already active in this field: Cros is considered the conceptual founder of reproducible sound, whereas Edison was the first "to reduce to practice", which is one of the US criteria for patentability.

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SUBJECT AREA: Photography, film and optics

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The son of a minor official in a magistrate's court, Daguerre showed an early aptitude for drawing. He was first apprenticed to an architect, but in 1804 he moved to Paris to learn the art of stage design. He was particularly interested in perspective and lighting, and later showed great ingenuity in lighting stage sets. Fascinated by a popular form of entertainment of the period, the panorama, he went on to create a variant of it called the diorama. It is assumed that he used a camera obscura for perspective drawings and, by purchasing it from the optician Chevalier, he made contact with Joseph Nicéphore Niepce. In 1829 Niepce and Daguerre entered into a formal partnership to perfect Niepce's heliographic process, but the partnership was dissolved when Niepce died in 1833, when only limited progress had been made. Daguerre continued experimenting alone, however, using iodine and silver plates; by 1837 he had discovered that images formed in the camera obscura could be developed by mercury vapour and fixed with a hot salt solution. After unsuccessfully attempting to sell his process, Daguerre approached F.J.D. Arago, of the Académie des Sciences, who announced the discovery in 1839. Details of Daguerre's work were not published until August of that year when the process was presented free to the world, except England. With considerable business acumen, Daguerre had quietly patented the process through an agent, Miles Berry, in London a few days earlier. He also granted a monopoly to make and sell his camera to a Monsieur Giroux, a stationer by trade who happened to be a relation of Daguerre's wife. The daguerreotype process caused a sensation when announced. Daguerre was granted a pension by a grateful government and honours were showered upon him all over the world. It was a direct positive process on silvered copper plates and, in fact, proved to be a technological dead end. The future was to lie with negative-positive photography devised by Daguerre's British contemporary, W.H.F. Talbot, although Daguerre's was the first practicable photographic process to be announced. It captured the public's imagination and in an improved form was to dominate professional photographic practice for more than a decade.

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