noun.
An instrument by which the temperatures (see temperature and thermometry) of bodies are ascertained, founded on the common property belonging to all bodies, with very few exceptions, of expanding with heat, the rate or quantity of expansion being supposed to be proportional to the degree of heat applied, and hence indicating that degree.
noun.
Hence, figuratively, anything which (roughly) indicates temperature.
noun.
A thermometer whose action is based on the variation of electrical resistance produced by changes of temperature in a metallic conductor. The difference in the resistance between a current passing through a conductor of known and one of unknown temperature gives the difference of temperature between the two. Also called differential-resistance thermometer. The most delicate form in which the principle is applied is the bolometer.
noun.
The Rutherford maximum has a light movable steel index at the top of the mercurial column. The tube is placed horizontal, and as the temperature rises the mercury pushes the index before it. When the temperature falls, the index is left in situ to mark the position of the maximum.
noun.
In Phillips's maximum, a small bubble of air makes a break in the upper part of the mercurial column. When the temperature begins to fall, the detached portion of the column is left behind to register the highest temperature.
noun.
The Negretti maximum has the bore of the tube partly closed by a constriction just above the bulb. In rising temperatures mercury is forced from the bulb past the constriction, but when the temperature falls the mercury cannot readily return to the bulb, and the top of the mercurial column indicates the maximum temperature. In order to reset the thermometer to the current air-temperature, the mercury is forced back into the bulb by whirling the instrument on a swing-pin. This form of maximum is used at the stations of the United states Weather Bureau.