Possibly unique English gold chronometer Circa 1882-1883

Chronometer with prepatent Bonniksen 52½ minute carrousel
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An extremely fine, exceptionally rare and possibly unique English 18 carat gold open faced keyless pocket chronometer with prepatent Bonniksen 52½ minute carrousel with spring detent escapement, the first watch of this series, Hallmarked London 1882-1883. Frosted gilt  1/2 plate movement, going barrel, 52½ minute carrousel carriage with foliate engraved cock, jeweled Earnshaw type spring footed detent escapement, freesprung cut bimetallic compensation balance, blued steel balance spring with terminal curve, diamond endstone. Gold hinged cuvette. White enamel dial with Roman numerals, outer minute track, subsidiary seconds  and original blued steel spade hands.  Large and heavy polished case by Frederick Thoms & Samuel Smith (master marks FT & SS). Dial and movement signed.
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Diameter: 57 mm
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Signed: English Revolving Escapement Chronometer by S. Smith & Son 9 Strand London
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This is almost certainly the first carrousel watch with a detent chronometer escapement. It is certainly the first watch of the famous ‘No. 239’ series that established the record for number of marks obtained at Kew Observatory for pocket chronometers. The absence of the Bonniksen patent number indicates the watch was made before the 1893 patent of the carrousel, it is therefore of great historical interest in the development of precision watchmaking. This watch could be termed experimental since the ‘No. 239’ watches did not achieve greatness until nearly 1900, whereas the present watch was certainlymade before 1893, the case bears Hallmarks for 1883. It is likely that the movement was experimented on by Smith’s in parallel with Bonniksen’s development of the carrousel and was cased in a stock case, making it a prototype piece. The carrousel watches immediately dominated the Kew lists of top performing chronometers as of 1894. Given the phenomenal results of ordinary carrousels, apparently Smith’s sought to develop a carrousel that achieved record marks. The present watch is the progenitor of the one that went on to achieve 88.1 marks, c.1900. Three No. 239 watches went to Kew: 239-2 (1901), 239-4 (1902 and 1903) and 239-6 (1907). The carrousel, or ‘Revolving Escapement Pocket Chronometer’, is thus described in Smith’s literature: “This watch obtained the ‘Record’ number of marks at Kew Observatory for a pocket chronometer, obtaining 88.1 out of a possible 100, the separate awards being 33.1 for variation of daily rate, 37.6 for changes of position, and 17.4 for temperature variation. It is hardly necessary to say that in every minute detail this watch is the perfection of watchwork. The cases are very finely made, weighing nearly 4 ozs of 18 ct gold, the dial is also of very special quality, the most careful attention having been paid to the working out of the divisions. We venture to think that this watch will remain at the top of the list of high class English watches… we pay a bonus to our workmen according to the number of marks obtained… this watch with the Record of 88.1 has been a considerable expense to us, and the price is £ 105”.