Swiss gold watch with constant force escapement Circa 1850

Gold half hunting cased pocket watch by Hess & Metford
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A very fine, extremely rare Swiss 18 Carat gold half hunting cased pocket watch with constant force escapement, circa 1850. Frosted gilt movement, bar calibre, 10 jewels, constant force escapement with two stacked escape wheels using a tensioning spring to provide the constant force, large curved lever arm with counterpoise and recessed into the plate for security, cut bimetallic compensation balance, blued steel Breguet balance spring, index regulator. Hinged gold cuvette. White enamel dial with Roman numerals, outer minute track, subsidiary seconds and original blued steel spade hands. Case engine-turned à grains d’orge, polished borders, the front with a scallop edged, polished chapter ring with black Roman numerals, inner minute track and a reeded band. Dial and cuvette signed.
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Diameter: 50 mm
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Signed: Hess & Metford Succ.rs de Heil & Hess à Genève
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A constant force escapement incorporates a remontoire device to ensure constant force between the escape wheel and the balance. The escapement of the present watch works in the following way: The upper escape wheel comes to rest on the pallet fork which is at the same level. When the balance returns the anchor recoils which results in putting pressure on the internal tensioning spring. At the moment that the pallet exits, this spring is released and transmits power to the lower escape wheel. This wheel then gives the impulse to the anchor. The small spring, therefore, gives an impulse force that is constant during the entire operation of the escapement. The constant force escapement works very well, though the timekeeping results are not as good as those for a precision pocket chronometer.
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Hess & Metford. Were active in Geneva between 1840 and 1860 and succeeded the firm of Heil & Hess. The company’s reputation was principally for the sale of complicated, high-quality pocket watches destined for North America.