thermostat

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A device, as in a home heating system, a refrigerator, or an air conditioner, that automatically responds to temperature changes and activates switches controlling the equipment.

Century Dictionary and Cyclopedia

1. n. An automatic instrument or apparatus for regulating temperature. It is essentially a modification of the thermometer, so arranged that, in place of indicating thermal variations, it controls the source of heat or of ventilation, and thus indirectly regulates the temperature. One of the earliest forms of thermostat was that devised by Dr. Ure. It consisted of a bar composed of two metals, say steel and copper, having different degrees of expansion under the same temperature. This bar, when fixed in position, was made by simple mechanical means to open a furnace-door, move a damper, or open a window, by means of the bending of the bar under the influence of an increase in heat. Other forms of this thermostat have since been used to make or break an electric current, and thus move an armature that controls a damper, steam-valve, or other heat-regulating mechanism. Another form consists of a balanced thermometer that, under the movements of the mercury in a tube pivoted in the center in a horizontal position, would rise or fall, and thus control a damper or fire-door. Another form consists of a thermometer resembling a thermoelectric alarm (see thermo-electric), except that the closing of the circuit by the rise of the mercury in the tube operates a fire-door or damper in place of sounding an alarm. Where a thermostat is merely used to ring a bell, it is called a thermostatic alarm. A very simple and yet delicately responsive form is a slender bar of gutta-percha, fixed at one end, and attached at the other to a lever, which is caused to act by the expansion or contraction of the bar. Another form of thermostat consists of a bent tube partly filled with mercury. The heat expands the air in the larger end of the tube and displaces the mercury, and this in turn moves a piston controlling, by means of some mechanical device, a steam-valve or damper. Another form, used with steam-heating furnaces, consists of an elastic diaphragm in a cylinder, the pressure of the steam against the diaphragm serving to move a piston that controls the damper of the furnace. Such appliances are also called heat-regulators. More recently, the name has been given to fusible plugs used to control automatic sprinklers, a rise in the temperature causing the plug to melt and release the water. This, however, is only a trade use of the word.

Wiktionary

1. n. a device that automatically responds to changes in temperature by activating a heating or cooling system to maintain the temperature at a desired setting

GNU Webster's 1913

1. n. (Physics) A device which automatically regulates temperature, or provides a signal used by another device to regulate temperature. The temperature-sensitive signal may be electronic, as that produced by a thermocouple. The signal may also be caused mechanically, as by the unequal expansion of different metals, liquids, or gases by heat, which can then cause the opening or closing of the damper of a stove, or the like, as the heat becomes greater or less than is desired.

WordNet 3.0

1. n. a regulator for automatically regulating temperature by starting or stopping the supply of heat
2. v. control the temperature with a thermostat