Extreme temperature chronometer

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Extreme temperature chronometer
Manufacturer	Thomas Mercer
Production years	20th century
Production location	England

This chronometer, by Thomas Mercer of St. Albans, is fitted with a balance-spring made of ‘elinvar’, an alloy nickel and steel, together with chromium and other elements, introduced about 1920 by Dr C. E. Guillaume.

[edit] How it works

The stiffness of an elinvar spring remains very nearly constant over a wide range of temperatures, and hence the rate of a chronometer employing it is only very slightly affected by temperature changes. The balance wheel of the chronometer exhibited is a solid one, and the small residual temperature effect can be compensated by a short pair of bi-metallic blades. In 1926 the British Engineering Standards Committee arranged a series of tests of chronometers suitable for use in aircraft. The tests, which were carried out at the National Physical Laboratory, extended over an unusually wide range of temperature from -200C to +500C. The change of rate of this chronometer was found to be small and remarkably consistent over the whole range of temperature, and the report of the test stated that ‘if it were found practicable, by further fine adjustment of the bi-metallic affixes, to compensate for the small temperature coefficient, It would appear possible to make the daily rate come within extremely fine limits, ±1 or 2 seconds, at all temperatures’.

[edit] Memories

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[edit] In the Science Museum's Records

Inv. No: 1931-716