Alcohol thermometer to give a background for reading the scale. The range of usefulness of the thermometer is set by the boiling point of the liquid used. In the case of the ethanol-filled thermometer, the upper limit for measurement is 78 °C (172.4 °F), which makes it useful for measuring daytime, nighttime and body temperatures, although not for anything much hotter than these. Ethanol-filled thermometers are used in preference to mercury for meteorological measurements of minimum temperatures and can be used down to −70 °C (-94 °F). The physical limitation of the ability of a thermometer to measure low temperature is the
Reversing thermometer Reversing thermometer Unlike most conventional mercury thermometers, a reversing thermometer is able to record a given temperature to be viewed at a later time. If the thermometer is flipped upside down, the current temperature will be shown until it is turned upright again. This was the primary device used by oceanographers to determine water temperatures below the surface of the ocean from around 1900 to 1970. It consists of a conventional bulb connected to a capillary in which a constriction is placed so that upon reversal the mercury column breaks off in a reproducible manner. The mercury runs down into