What is Six's thermometer?
[[File:Max Min Thermometer.JPG|250px|right|thumb|A maximum–minimum thermometer. The scales are Fahrenheit on the inside of the U and Celsius on the outside. The current temperature is 23 degrees Celsius, the maximum recorded is 25, and the minimum is 15; both read from the base of the small markers in each arm of the U tube. The bulbs are hidden by a plastic housing.]] '''Six's Maximum and Minimum thermometer''' is a [[thermometer]] that can show the maximum and minimum temperatures of a time period. British scientist [[James Six]] invented it in 1780.<ref>{{cite magazine | url=https://books.google.com/books?id=XCRCAQAAMAAJ | title=Symons's Monthly Meteorological Magazine | year=1869 |volume= 4| page=7 }}</ref> The same basic design is still in use. ==Design== It is made of a U-shaped glass tube with two separate temperature scales. There is a scale on each arm of the U. One is for recording the maximum temperature and the other for the minimum temperature. The arms of the U-shaped tube end in sealed glass bulbs. The bulb at the top of the minimum reading scale arm is full of [[alcohol]], the other tube contains a vacuum (or [[Low pressure area|low pressure]] alcohol vapour). ==How it works== In the bend of the U is a bit of [[Mercury (element)|mercury]], a [[metal]] that is liquid at [[room temperature]]. This is pushed around by the thermal expansion and contraction of the alcohol in the first bulb as it responds to the outside temperature. The vacuum in the other bulb allows free movement of the alcohol and mercury. It is the metal indices that measures the temperature; the mercury shows the temperature reading on both scales. This is unlike a normal mercury thermometer, in which the expansion and contraction of mercury itself indicate temperature. The maximum and minimum readings are recorded by two small steel markers which are sprung into the capillary tube so that they can slide, but only if a [[force]] is applied to them, either by being pushed by the mercury or under the influence of an external magn