A thermometer so designed that it registers the maximum temperature attained during an interval of time. The liquid-in-glass type of maximum thermometer has a bore that is constricted between the bulb and graduated portion of the stem. As the temperature rises, a portion of the mercury is forced past the constriction and into the graduated section. This mercury is retained when the temperature falls and serves to indicate the highest temperature reached. Bimetallic thermometers with a circular scale are also used as maximum thermometers. A free index mounted concentrically with and driven by the thermometer index is held by friction at the maximum temperature. Compare minimum thermometer; see Townsend support.