English silver technically highly interesting chronometer Circa 1864

Pocket watch with detent chronometer escapement
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A technically highly interesting sidereal time chronometer made by Reid & Sons in Newcastle, England, circa 1864. The open faced solid case of this watch is crafted from silver carries London Hallmarks 1864 and has an engine turned back with an empty cartouche. The numbered white enamel dial has Roman hour numerals, a subsidiary seconds dial at six o’clock with Arabic numerals and blued steel hands. The numbered extremely rare chronometer movement “sidereal time chronometer” features a detent chronometer escapement, a chronometer balance with gold screws, a helical hairspring, a diamond end stone and key winding.
Dial and movement with matching numbers and signed.
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Diameter: 52 mm
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Weight: 138 g
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Signed:
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Sidereal time chronometers
Only very few pocket chronometers were so called ‘sidereal time chronometers’. Sidereal time is also a true time, but in contrast to solar time, it depends only on the rotation of the Earth. In every astronomical observatory there is a pendulum clock or sidereal time chronometer regulated to sidereal time, so that sidereal time can always be read there. Regulating pendulum clocks or chronometers in sidereal time is the responsibility of chronometer makers or specialists, as electronic measuring instruments cannot be used for this purpose. A sidereal day is the length of one rotation of the Earth, measured from one culmination of a star to the next. It is essentially the same length on all days of the year.
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Reid
Reid & Sons, a silversmiths firm founded in Newcastle upon Tyne in 1788, did create and sell pocket watches. They were known for their silver and gold pocket watches, including those with English lever movements and fusee chains. The company, which is still in operation as part of the Goldsmiths Group, also made other notable items like the FA Cup and the Rugby League Trophy.