Certificate No. 2336, delivered on March 27, 1892, to Mr. Boore from London. Certificate No. 2869, delivered on May 15, 1939 to Lord Granard, 73 rue de Varenne, for Mr. Macdonald, Berkely Square, London WI.Breguet invented the tourbillon regulator in 1795, but the patent was granted on Messidor 7, year 9 of the Republican calendar (June 26, 1801). The purpose of the invention was to eliminate positional errors by rotating the balance once each minute. By this means, the various errors for all the vertical positions, would produce a constant average rate. In order to achieve this, it is necessary to mount the whole escapement on a rotating platform and utilise the vibrations of the balance and sprig, to control the speed of the rotation. However, Breguet realised that a tourbillon rotating so rapidly would be subject to inertia problems. Each time the escapement is released to transmit impulse to the balance, the carriage must accelerate from rest, to enable the escape wheel to turn. Clearly, impulsing energy will be lost in overcoming the inertia of the carriage, so a stronger mainspring will be needed, resulting in greater wear and tear of the train and pivots. At the end of impulse, thescapement locks and the momentum of the carriage must be absorbed, involving the locking components in additional strain and wear.There is no practical need for a tourbillon to rotate so fast as once per minute. Breguet therefore, introduced slower moving tourbillons, usually with periods of rotation of four or six minutes. These have the advantage that they can be made thinner, because the drive can be applied to teeth on the edge of the carriage, instead of to a central pinion underneath. The carriage, while still remarkably light and elegant, does not have to be made of steel, a necessity if it were to be reduced to a mre skeleton yet still retain sufficient strength for movement. It can therefore, be made partially of brass with significant advantage of lesser susceptibility to rust and and magnetism.In addition to its slower tourbillon, this watch also have a Peto cross detent escapement with all the components made of steel, made in the form as it was improved by Breguet, with a gold pin at the detent horn, for the passing spring to work against. The movement is so slight, that oil should not be required. The cross detent escapement is better suited for a tourbillon, than the Earnshaw type of spring detent escapement, because the detent acts in tension and so, is better able to withstand te strain of locking the escapement and bringing the carriage to rest. The effect of using 21.600 vibrations per hour would be an improvement in rate, for the balance would be less affected by movement of the watch in wear. The position of the fusee and barrel have been reversed to gain the advantage of reduce the pressure on the fusee. The watch was also made with an offset centre arbor to make the most economical use of the available space within the confines of a circular movement. At last thcarriage has been made as thin as possible to save height, by making the upper cross member from the solid. The result of all these features is a singularly elegant and accurate watch, brilliantly designed and beautifully executed.All our thanks to Anthony Randall for his generous permission to allow the reproduction of large parts of the description of this watch and of the comments he wrote about it, in collaboration with Jean-Claude Sabrier, for The Time Museum Catalogue of Chronometers (Rockford, Illinois, 1991). The wonderful drawing by David Penney, of the escapement and the tourbillon carriage, are also drawn from this catalogue entry.Previously in the collection of the Time Museum, Rockford, Illinois (U.S.A.), this watch was described and illustrated by Anthony Randall, with material contribution of Jean-Claude Sabrier, for The Time Museum Catalogue of Chronometers (Rockford, Illinois, 1991).