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William Renda, Paris, France. 1952. Movement net, 15"h x 7.5"w x 4.25"d, w/ dome  17"h x 9.5" diameter. One minute period  flying tourbillon with pinwheel escapement driven by a sector gear from a 2.5" diameter one second balance wheel. Count wheel strike powered from separate spring barrel. Gilded movement and frame.

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The tourbillon, (French for 'whirlwind') is recognized as one of the more difficult complications to make. It was invented by Abraham-Louis Breguet in 1795 to compensate for positional errors in watches. This is accomplished by mounting the escapement in a rotating frame, so that the effect of gravity cancels out when the escapement is rotated 180. By encasing the entire escapement within a rotating frame (the tourbillon), the frame, as it rotates,  constantly varies the position of the balance wheel in relation to its environment. The effects of gravity were particularly problematic when pocket watches were carried in the same pocketed position for most of the day. In a tourbillon, the entire escapement assembly rotates, including balance wheel, escapement wheel, and pallet fork.

Of course, this is entirely superfluous in a stationary table top clock. This fact coupled with the difficulty of fabrication, results in few such examples having been made in the larger versions necessary for a table top skeleton clock.

William Renda is unknown as a clockmaker. In fact he signed the movement as 'William Renda, Ingenieur, a Paris'. Apparently he considered himself an engineer or perhaps a machinist rather than a clockmaker. It is possible that this is a unique piece. The quality of the work is first rate as exemplified by the gilded finish of the frame as well as the fine bluing of the screws, clicks and their springs which are beautiful. A star pattern was used for several of the wheels. Three points for the balance, five for the count and six for the great wheel - an artistic balance of symmetry to the size of the wheel. All spoked wheels are attached to their collets by screws. The dial is made from two pieces of silvered plates that sandwich the blue enamel number plaques with a separate engine-turned bezel. Since the tourbillon is vertically mounted, the pinwheel escapement needed to be exactly counter-balanced on the tourbillon cage. In addition the pinwheel escape pallets had to have their own poising weight.

Following are several video clips of the tourbillon escapement, the last showing the clock striking: 12, 3, 4, 5.

 

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