The New Student's Reference Work/Thermostat, Electrical

Ther′mostat, Elec′trical, is an instrument for giving an alarm when the temperature rises to a point where the instrument completes the circuit, or when it falls to a point to produce a similar result. They are used in stoves, hothouses, dwellings and wherever uniform temperature is of vital importance. They are also used as maximum thermometers or fire-alarms. Various devices are employed, the simplest being the ordinary mercurial thermometer, the upper end of the tube not being hermetically sealed, but closed by an airtight cork of rubber, through which passes a metallic rod that can be raised or lowered in the tube. Whenever the expanding mercury reaches the tip of the rod, an electric current is closed and the alarm sounded. This alarm-current may be arranged so as to set off an electromagnet which will open or close a register or regulate the draft in the furnace. See Thermograph.