The making of this watch required remarkable precision and care. The heart of the watch ? the escapement - is a horological marvel. Breguet installed his own, very distinctive, "échappement naturel". This very special escapement is based on the principle of the chronometer escapement but with impulses in both directions. It requires two escape wheels and a special detent which locks and unlocks them. Far from a simple escapement, it was used by Breguet only for his best timekeepers. Less than 30 of them are known. One of the reasons Breguet devised the escapement "naturel" was that vegetable oils are far from stable, and the rates of watches varied depending on the viscosity of their oil. Breguet is known to have said: "give me perfect oil, I will give you a perfect watch". Unfortunately, no one having given it to him, Breguet decided to go without it. Escapements had been invented that did not need oil: detent escapements. They have a unidirectional impulse, are not very stable when worn, and are indeed apt to stop when worn. For scientific watches, Bre-guet did not object to using them, for they were not moved when observations were carried out. However, for everyday use and for his best pieces Breguet wanted to devise a bidirectional impulse watch that needed no oil. That was the origin of the escapement "naturel". He devoted special attention to this one. The detent, one of the most delicate elements, has the locking jewel mounted on special springloaded lever to assure that if the watch falls or receives a strong blow, the detent will not be damaged by the jewel?s going in the wrong direction. Breguet jeweled the entire escapement and the entire train, at a time when jeweling was very expensive and not yet well developed on the continent. In fact Breguet, from one of his trips to England, brought master watch jeweler, Mr. Hooker. He employed what at the time was a very fast train, 21,600 beats per hour to minimize the effects of the impulses transmitted to the balance by the wearer?s movements. This required either a very large mainspring or a slowing down of the rotation of the carriage. He opted for the latter. He also used a free-sprung escapement, a feature which he employed very rarely. Free-springing increases the isochronism of the watch but does not allow the owner to regulate it. Breguet used it only in his most precision timekeepers. In addition, he employed as a motive power the reverse fusee arrangement, which he used very rarely. It was first employed by Mudge in order to decrease wear on the center wheel bushing. However, the special attention afforded this watch is under-standable, the watch being the quintessence of Breguet precision horology. The Breguet invention of the tourbillon defeated the inherited problem of positional error. Regardless of how well the balance is poised statically, when installed in a watch it shows posi-tional errors due to the sagging of the balance spring, errors caused by centrifugal force, uneven expan-sion of the balance, and lack of uniformity of the balance lamina. The tourbillon does not eliminate these problems, but it averages them out. A tour-billon watch runs no better than a simple one, however the period of its carriage remains constant regardless of the vertical position. Consequently, although the rate of a tour-billon watch can vary within the period of its carriage, it can be regulated to be exact 360 times within a day (in the case of the four-minute tour-billon). So if a simple watch makes, say, three seconds positional error, one fitted with a tourbillon will make 0.008 seconds per day. The concept was ingenious and far from obvious. It eventually (100 years later) revolutionized precision timekeeping; tourbillon watches were often chosen for the most prestigious Astronomical Observatory Trials. This is the third watch ever sold with tourbillon car-riage. At the time only Bre-guet made tourbillons. He sold the first in 1805, the second in 1807; this one is the third. The whereabouts of the first one are unknown, and the se-cond was stolen from the L.A. Mayer Memorial Institute for Islamic Art. Thus, at present, this watch is the earliest tourbil-lon known to be in existence. It is in remarkably good condition with what appears to be its original crystal, probably made of rock crystal. After the death of Don Antonio, the watch ended up in the hands of a gentleman of Islamic ori-gin, who in 1841, had the watch overhauled by Bre-guet, (through his jewelers, Berthoud frères) and reques-ted that a new enamel dial made with Islamic numerals. The watch is described and illus-trated in "The Art of Breguet" by George Daniels, fig. 163, and "Le Tourbillon" by Reinhard Meis, p. 98. Don Antonio Pasquale de Borbon (1755-1817) Infant of Spain and son of King Charles III, he was born in 1755. He married his niece Marie-Amélie, the daughter of Charles IV, who died in 1798, and lived for a long time in relative obscurity. However, in 1808, when King Ferdinand VII was summoned to Bayonne by Napoleon, he organized a government in Madrid, and entrusted its direction to Don Antonio, his uncle. Murat, who had 25,000 troops watching Madrid, claimed to recognize only the former king, Charles IV. Although Don Antonio remained in communication with his nephew throughout the month, he was hampered by the lack of resolution of Ferdinand VII?s counselors and the members of the junta governement. On May 4, 1808, Don Antonio was forced to leave Madrid; the 11th he left Bayonne for Valençay, where he remained in captivity along with his nephew. Upon recovering his throne, Ferdinand made him Great Admiral of Castille. We are indebted to Emmanuel Breguet, curator of the Breguet Museum and Archives, for his invaluable help.