Six's thermometer

Six's maximum and minimum thermometer is a registered thermometer that can record the maximum and minimum temperatures reached over a period of time, for example 24 hours. It is used to record the extremes of temperature at a location, for instance in meteorology and horticulture. It was invented by the British scientist James Six, in 1780; the same basic design remains in use.

It is also commonly known as a maximum–minimum, minimum–maximum, maxima–minima or minima–maxima thermometer, of which it is the earliest practical design.

The thermometer indicates the current temperature, and the highest and lowest temperatures since the last reset. It is the first thermometer to be able to recorded both minimum and maximum daily temperatures.

The Six's thermometer cannot measure temperatures below -38.8 °C due to the solidification of mercury at this temperature. Although this is not an issue in most inhabited placed, it can be one in particularly cold placed, where a thermometer using different liquids should be used to record these lower temperatures, such as a Rutherford-type minimum thermometer.