The Sidéromètre was designed in the late 1930's by Commandant Bastien to provide a means of rapid position "fixing" for aerial navigation. Special tables were required, called "Aeronautical Ephemerids" and these were produced to be used with the instrument.An almost identical instrument from the same series, was described and illustrated by Anthony Randall in The Time Museum Catalogue of Chronometers, Rockford, Illinois 1992,pp. 110-111, figs 66 a-d.According to Anthony Randall, a Sidéromètre does not indicate sidereal time as such, although it is adjusted to run at sidereal, rather than mean time, and then converts this into degrees, minutes and seconds of rotation of the earth. The centre seconds hand, therefore, rotates not in sixty seconds of sidereal time but in the time taken by the earth to rotate through 1°, in relation to the stars. As the earth rotates through 1° in four minutes of time, the seconds hand rotates once every four miutes. The angular rotation of the earth is recorded by the numbered discs appearing in the dial apertures: degrees are shown on the right-hand side, tens of degrees in the centre, and hundreds of degrees on the left.There is an electrical input on the side of the box to connect to the power supply of the aeroplane-presumably about 24 volts. This provides the electrical energy for the bulbs and for a small thermostatically controlled heating element inside the box. Since the temperature inside an aeroplane of the period could drop to a very low value at high altitude, precautions were necessary to prevent rapid cooling of the inside of the box, with consequent risk of condensation in the mechanism and even te possibility of freezing of the oil. Although accurately compensated, the watch would otherwise also have been subject to a transient response due to rapid and extreme temperature change, and this had to be prevented.L. Leroy & Cie. The oldest watch manufacture in France, still active today, was founded by Charles Le Roy in 1764 in Paris at Quai des Orfèvres, I'Ile de la Cité. In 1788 the workshop was transferred to the Palais Royal which had been recently opened to the public by the Duc d'Orléans.It was in this building that the company Le Roy was housed for more than a century. It was also thanks to Le Roy that for first time in Paris, it was possible to find a choice of watches and pendulums that were entirely produced in his workshop (at that time, the majority of watches sold in France were imported from Switzerland). This novelty attracted a strong clientele, both French and foreign. Graced with the support of the King, the Queen and the Court, Charles Le Roy was often invited to thLouvre. He was noted for the perfection of his watches and his beautiful clocks that decorated the walls of the palaces and the mansions of princes throughout Europe. During an inventory of the royal palace, at least 27 clocks with his signature were found.During the French revolution, Charles Le Roy faced difficult times. His name invited many problems, and almost cost him his life. During La Terreur (period of the French Revolution from September 5, 1793, to July 27, 1794), he was obliged to turn his signature into the anagram: EYLOR which can still be found today on the clock dials and on the plates of watches produced during that era (even the Palais Royal was debaptised and the royal emblems (fleur de lys) that decorated the public building ad clocks, were destroyed.In 1827, satisfied with the work of his son, who he helped educate, Charles Le Roy made his son a partner hence changing the name to: Le Roy & Fils, Horlogers du Roi. It is from this point forward that the venerable and precious archives of the society can be found.In 1889, the company was taken over by Louis Leroy and for social reasons, the company name was changed to Ancienne Maison Le Roy & Fils, Horlogers du Roy, L. Leroy & Cie., successeurs. Louis Leroy, the son of the celebrated maker of chronometers, Horloger de la Marine, Théodore Leroy, took into account the thoughts of Charles Le Roy his predecessor which were contained in his report of 1840. The report was addressed to La Société d'Encouragement and stated that "....it is easy to sell many watces, but it is even more difficult to sell only the good ones". From this, Louis Leroy understood that the only way to assure the quality of watches that he sold, was to produce them by himself. Therefore, Leroy carefully studied the Swiss production and the French production of watches, and was struck by the many resources available in Besançon to produce high quality watches. He decided to open a manufacture in Besançon, merging different workshops and to begin his own production, consequentlybandoning all his Swiss suppliers. Now, surrounded by excellent workers and assisted by a skillful timer foreman that oversaw all of the talent, it was not long before success was to arrive. As early as Le Roy began to participate at the timing contests, organised for chronometers at the Observatory of Besançon, the results progressively improved. In 1890 the best watch was awarded 171 marks, whereas in 1894, for his first contest, Leroy was awarded 197 marks, receiving a gold medal and the prizfor the 5 best chronometers. In 1895, he received 3 gold medals and the prize for the 5 best chronometers. In 1898, he received again 3 gold medals and the prize for the best 5 chronometers. And, finally in 1899, he received 3 gold medals and the prize for the best chronometers.At the end of the century, the business centre of Paris moved from the Palais Royal to the Opera district. Therefore, L. Leroy & Cie. moved to 7, Boulevard de la Madeleine. The new premises were inaugurated shortly before the opening of the Exposition Universelle in 1900.In 1914, Louis Leroy took his brother Léon as a partnerbut without changing the Company name. His brother had already worked with him for several years, and together they continued to develop the production of chronometers, astronomical regulators, complicated watches, carriage clocks and mantel regulators.Appointed as Horloger de la Marine de l'Etat, the company Leroy was also the main supplier of chronometers for the Merchant Navy. The celebrated passenger-liner Normandie was also equipped with their chronometers. Watchmakers to the French Air Force and civil aviation, they were also suppliers of chronometer for sports clubs, and in charge of the official timing for the main competitions, first with a precision of 1/10 second, later with a precision of 1/100 second. Watchmakers of French and forign observatories, L. Leroy & Cie. were also specialists in the production of Constant Pressure Observatory accurate regulators, able to keep time with the highest precision (in four years, at the Observatory of Neuchâtel, in Switzerland, the rate of the Constant Pressure clock, did not even vary as much as a tenth of a second)In the early time of the speaking clocks, thanks to the Constant Pressure regulators, electrical impulse signals were transmitted from the Observatory of Paris, to the Bureau International de l'Heure, to provide precise time and to service the radio broadcast time signals, sent from the Eifel Tower.At the most important industrial and universal exhibitions, Leroy exhibited highly important and unique pieces such as in 1900, the celebrated Leroy No. 01, with 26 complications, now in Musée du Temps et de l'Histoire of Besançon. He was awarded by turns, gold medals and grand prizes, and appointed a member of the Jury out of competition, bringing to France fame and recognition for the high quality of its watch and clock production.Today, under the honorary presidence of Philippe Leroy, the son of Léon Leroy, L. Leroy & Cie, by law a French company with workshops in Switzerland, follow the same goals, producing prestigious mechanical complicated watches and precision clocks, highly praised by all the collectors.Literature:For a complete chronology and synopsis see: l'Art de l'Horlogerie en France du XVIe au XXe Siècle, Antiquorum Theme Auction, Geneva, Sunday November 14, 1993, pp. 210-212 and 218.