Six's thermometer is a thermometer

Thermometer

Developed during the 16th and 17th centuries, a thermometer is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor Developed during the 16th and 17th centuries, a thermometer (from the...

 which can measure the maximum and minimum temperature

MMTS (meteorology)

A Maximum Minimum Temperature System or MMTS is a temperature recording system that keeps track of the maximum and minimum temperatures that have occurred over some given time period....

s reached over a period of time, usually during a day. It is commonly used wherever a simple way is needed to measure the extremes of temperature at a location, for instance in meteorology

Meteorology

Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

 and horticulture

Horticulture

Horticulture is the industry and science of plant cultivation including the process of preparing soil for the planting of seeds, tubers, or cuttings. Horticulturists work and conduct research in the disciplines of plant propagation and cultivation, crop production, plant breeding and genetic...

.

It is also commonly known as a maximum minimum thermometer, of which it is the earliest practical design and the most common type used.

It is an example of a registering thermometer, that is a thermometer that keeps a record of where the temperature has been in the past.

It gives three readings: the current temperature, the highest temperature reached since it was last reset, and the lowest temperature reached since it was last reset.

It was invented by Englishman James Six

James Six

James Six was a British scientist born in Canterbury. He is noted for his invention, in 1780, of Six's thermometer, commonly known as the Maximum minimum thermometer...

 in 1782, and named after him.