Complication · Display
Thermometer Indication
Partially verifiedA subsidiary display showing ambient temperature, most often driven by a bimetallic strip or spiral coiled inside the case and coupled to a hand, added as an auxiliary instrument function alongside a watch's or clock's timekeeping.
Definition
A subsidiary display showing ambient temperature, most often driven by a bimetallic strip or spiral coiled inside the case and coupled to a hand, added as an auxiliary instrument function alongside a watch's or clock's timekeeping.
Historical origin
Thermometer-equipped watches and, more commonly, combination clock-and-thermometer instruments (sometimes paired with a barometer or hygrometer as a household 'weather station' piece) were produced from at least the nineteenth century, drawing on the same bimetallic-strip principle used in standalone thermometers and in some compensation balances.
How it works
A coiled bimetallic strip, made of two metals with different rates of thermal expansion bonded together, is fixed at one end within the case and coils or uncoils as temperature changes, its free end linked to a pointer that sweeps across a printed temperature scale.
Because the bimetallic element sits inside a closed case worn against the body or kept indoors, the reading reflects the temperature of the case and its immediate surroundings rather than true open-air ambient temperature, a limitation noted in the literature on such instruments and worth bearing in mind when assessing the reading's practical accuracy.
No connection exists between the thermometer mechanism and the going train; the two share only a case and dial, and the thermometer element requires no winding or maintaining power of its own.
Pocket watch context
Occasionally fitted to combination pocket instruments (compendium watches incorporating a compass, thermometer or altimeter alongside timekeeping) as a novelty rather than a mainstream complication.
Wristwatch context
A rare novelty complication in wristwatches, generally offered as a curiosity rather than a precision instrument, given the inherent limitation that a case-mounted bimetallic strip mainly tracks the wearer's body heat and clothing insulation rather than open ambient air temperature.
Clock context
More commonly encountered in combination mantel-clock instruments than in a wristwatch or pocket watch context, where a thermometer (and often a barometer) dial is set alongside the clock dial in a single case, a popular nineteenth- and early twentieth-century domestic instrument format.
Identification
- A subsidiary dial or scale marked in temperature units (Celsius, Fahrenheit, or both) with no mechanical link visible to the going train
- A coiled bimetallic strip, rather than gearing, connecting the case interior to the indicating hand
- Readings should be assessed with caution as an indication of case-interior rather than true open-air temperature
Servicing notes
The bimetallic element itself rarely needs service, but its calibration can drift or be disturbed if bent during case or movement work; recalibration against a known reference thermometer, and careful handling during any case service, should be left to a watchmaker or clock restorer familiar with the specific instrument.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Diagram
Sources & references
- Britten, F. J., Old Clocks and Watches and Their Makers
- Extent of nineteenth-century thermometer-watch production not independently quantified from sources consulted.
Where sources disagree, the disagreement is stated rather than resolved silently.