Definitions of thermometer

  1. An instrument for measuring changes of temperature; as, the Fahrenheit thermometer, in which the freezing point of water is 32 degrees and the boiling 212 degrees; and the Centigrade thermometer, in which the corresponding points are 0 ( zero) and 100.
  2. An instrument by which the temperatures of bodies are ascertained; founded on the property which heat possesses of expanding all bodies, the rate or quantity of expansion being supposed proportional to the degree of heat applied, and hence indicating that degree. The thermometer consists of a slender glass tube, with a small bore, containing in general mercury or alcohol, which expanding or contracting by variations in the temperature of the atmosphere, or on the instrument being brought into contact with any other body, or immersed in a liquid or gas which is to be examined, the state of the atmosphere, the body, liquid, or gas, with regard to heat, is indicated by a scale either applied to the tube or engraved on its exterior surface. The ordinary thermometer consists of a small tube, terminating in a ball containing mercury, the air having been expelled and the tube hermetically sealed. There are two points on the scale, corresponding to fixed and determinate temperatures, one, namely, to the temperature of freezing water, and the other to that of boiling water. In the thermometer commonly used in this country, that of Fahrenheit, the former point is marked 32° and the latter 212°; hence the zero of the scale, or that part marked 0°, is 32° below the freezing- point, and the interval or space between the freezing- and boiling points consists of 180°. The zero point is supposed to have been fixed by Fahrenheit at the point of greatest cold that he had observed, probably by means of a freezing- mixture such as snow and salt. On the Continent, particularly in France, and nowadays in all scientific investigations, the Centigrade thermometer is used. The space between the freezing and boiling points of water is divided into 100 equal parts or degrees, the zero being at freezing and the boiling- point at 100°. Reaumur's thermometer, which is in use in Germany, has the space between the freezing and boiling points divided into 80 equal parts, the zero being at freezing. For extreme degrees of cold, thermometers filled with spirit of wine must be employed, as no degree of cold known is capable of freezing that liquid, whereas mercury freezes at about 39° below zero on the Fahrenheit scale. On the other hand, spirit of wine is not adapted to high temperatures, as it is soon converted into vapor, whereas mercury does not boil till its temperature is raised to 660° F. Mercury is most commonly used for thermometers employed for indicating all ordinary temperatures. For recording extremely high temperatures the pyrometer is used; and for indicating very slight variations the thermo- electric battery is employed.
  3. An instrument for measuring degrees of temperature.
  4. Thermometric, thermometrical.
  5. An instrument for measuring variations of temperature founded on the readiness and uniformity with which certain substances, especially mercury, expand or contract under an accession or diminution of heat.
  6. An instr. for measuring the degree of heat or temperature of bodies by the regular expansion of mercury, or of some other substance.
  7. Thermometric.