Lot No. 539 (93rd Auction)
Thomas Mercer, Maker to the Admiralty, London, Movement No. 1986, 178 x 189 x 180 mm, circa 1872

A remarkable, rare ship's chronometer with 56h power reserve indicator and Hartnup's compensated balance - together with a copy of a letter written by Tony Mercer, in which he tells the story of this chronometer
Case: palisander, brass gimbals and bowl. Dial: silvered, signed, numbered. Movm.: brass movement, spring detent escapement according to Thomas Earnshaw, chronometer compensation balance according to Hartnup.

Tony Mercer , grandson of the famous Thomas Mercer, writes to the previous owner in 2004:
Your chronometer 1986 was made in 1872. You have a very good two-tier box which was made by my great uncle Thompson in Hull, a port on the east coast of England. The wood was Rosewood.
J. & T.T. Taylor of Kemble Street Prescot Lancashire were chronometer movement makers, they didn't finish their chronometers but sold the movements only. My grandfather and later my father Frank bought them (only the movement) not the escapement from them, that is why you think that it is a prototype. (...)

This marine chronometer with its unusual balance is a fine example for the efforts of English chronometer makers to control the middle temperature error, which lead to a number of different approaches like those by Kullberg, Poole, Airy and Mercer. Hartnupā€˜s balances were also used by other renowned makers such as Winnerl and Frodsham. A satisfactory solution was eventually found with new substances that were based on experiments conducted by Edouard Guillaume in Switzerland; he received a Nobel prize for his research in 1920.

John Hartnup (Fellow of the Royal Astronomical Society), the first Director of the Liverpool Observatory (1844-85) devised his own com pensation balance, which had a unique laminated rim. He worked with William Shepherd, the Liverpool chronometer maker, who made the first one. Instead of a single crossbar of the Earnshaw balance, there were three, all laminated and connected together in the form of a Z. The brass side of the laminate was uppermost on the central bar and underneath on the other two, which were attached to the central one by means of screws. The two outer bars carried a pair of laminated rims, having, as in the ordinary balance, the brass outside and the steel inside. But instead of being placed vertically, these were bevelled so that at the m iddle temperature, they were inclined at an angle of 45 degrees. These rims carried die balance weights and timing screws. Hartnup was also responsible for the time gun which was fired at midday to give signals to shipping lying in the Mersey. This was maintained by the Dock Board, under die charge of Professor Hartnup, who was interested in all types of timepieces, especially astronom ical clocks. He worked in conjunction with R. F. Bond of Boston, USA, and they experimented on the effects of placing a cup filled with small lead shot on top of a pendulum.
From: Tony Mercer, Chronometers. History, Maintenance and Repair, p. 160
Estimate  9,500 - 13,000 €

Price Realised  12,200 €
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