The thermometer with minimum and maximum is a Thermomètre making it possible to measure the maximum and minimal temperatures attack during a given time interval. He was invented by James Six in 1782. It is an instrument usually used for the domestic uses, but also in meteorology and horticulture.

Description

It is about a single thermometer, whose capillary stem is folded in form of " U" , and carries two graduations (with the result that one with the impression that there are two thermometers). The bulb contains alcohol, and the stem contains a mercury section.

Operation

When the weather is hot, alcohol dilates and pushes back the limits side empties, and when the weather is cold, the whole contracts and pushes back the limits side bulb.

One puts in the stem two small markers (out of plastic). They are pushed back by mercury (because the surface tension of mercury does not enable him to be easily penetrated), but alcohol (or the vacuum) do not involve them. When the limit of mercury moves on them, they are pushed, and when the limit forsakes them, they remain on the spot.

In this manner, they make it possible to locate the maximum (side empty) and minimum (with dimensions alcohol) of the undergone temperatures as long as one did not make a restoring.

Restoring

The mechanism of restoring is variable. The markers generally contain an iron needle: a sweeping of the tube by a magnet is then enough to bring back the indicator on the current mercury level.

Certain versions are intended to be employed with horizontal, the restoring being done by rectifying the thermometer, which makes fall down the markers by gravity.

Alternatively, the markers are magnetized, and attracted by a metal plate placed behind the thermometer, which plates them against the tube and prevents them from slipping. A button makes it possible to move back the plate, releasing the markers who fall down on the mercury surface by gravity.

External bonds

• the thermometer of Six - Florence, Museum of the history of sciences
• Physics Theory: Thermometers

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