THERMOMETER

n. Thu6rm-o2m'est-u5r. From flep^dv, heat, and nerpov, a measure. Fr., thermometre. Ger., T. An instrument or apparatus for measuring degrees or variations of sensible heat. Its construction is based on the property po e ed by certain substances of expanding or contracting regularly as the temperature is increased or diminished. The ordinary t. consists of a bulb communicating with a tube of very small bore, the bulb and adjacent part of the tube containing mercury, while the distant part of the tube is empty. With a rise of temperature the mercury expands so as to fill more and more of the tube. The temperature is indicated by a scale attached to the tube. The scale is graduated by marking off equal intervals as degrees, the unvarying distance between the marks that indicate the freezing point and boiling point of water being divided into 180 of these degrees in the Fahrenheit t., 100 degrees in the centigrade t. or Celsius's t., and 80 in Reaumur's t. The freezing point of water is the zero in the centigrade t. and Reaumur's t., but Fahrenheit put his zero 32 below that point, and the boiling points of water in the three are thus 100, 80, and 212. The Fahrenheit scale (symbol, Fahr. or F.) is that in general use, especially for meteorological and clinical observations; but in some countries the centigrade (symbol C.), which is that now chiefly employed in scientific research, takes its place; they are connected by the formula F = f C. + 32. For very low temperatures alcohol is used instead of mercury, and very high temperatures are measured by the pyrometer, [a. 48.] Air t. Ger.. Lufft. A t. in which the temperature is measured by the expansion of air. [a, 48.] Breguet's t. A t. for measuring small differences of temperature by the expansion of a metallic spiral. [B.] Celsius's t. As commonly used, the centigrade t.. but Celsius made the boiling point of water and the freezing point 100. CLINICAL THERMOMETER. [o, 48.] Centigrade t. See under T. Cerebral t. An instrument for taking the temperature of the surface of the head. [D.] Cf. Cerebral THERMOMETRY. Clinical t. A t. for ascertaining the temperature of the body. It has a thin bulb and is usually self registering. Cf. Surface t. De Lisle's t. A t. formerly used in Ru ia, having the boiling point of water marked zero and the freezing point placed at 150. [a, 35.] Fahrenheit t. Ger., E, he; E2, ell; G, go; I, die; I2 in; N, in; N2, tank: [s. 616]