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| image title | Maximum thermometer and minimum thermometer |
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| caption | Inside the Radcliffe Observatory's Stevenson screen are four thermometers. The maximum thermometer (horizontal upper) is a mercury-in-glass, with a narrow constriction close to the bulb that allows the mercury to expand horizontally into the capillary but breaks the thread when the mercury in the bulb contracts, leaving mercury in the capillary indicating the maximum temperature. The minimum thermometer (horizontal lower) uses a spirit (typically clear alcohol) as the temperature sensor. When the temperature falls the spirit contracts into the bulb dragging a small light pin inside the tube that is just dipping into the spirit in the capillary. As the temperature rises the spirit squeezes past the pin leaving the end closest to the bulb marking the minimum temperature. See also Six's Maximum and minimum thermometer, MI008. |
| code | MI007 |
| Section | Meteorological instruments |
| Subsection | Surface-based instruments |
| image credit | © The Open University |
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