Instruments for determining high temperatures, such as those of furnaces and the fusingpoints of metals. They are of various classes, including the “contact” or “immersion” type, being so called because one part of the pyrometer is immersed in the heated material; and the “distance” type, in which no such part is immersed. The mercury thermometer is a simple form of the firstnamed class, and can be applied in respect of temperatures up to 500 degrees C. The thermoelectric pyrometer consists of two dissimilar metals in wi re form, at the tip of which is a rod enclosed in a protecting tube, and this receives the heat and is termed the “hot junction,” while the other ends of the two wires are outside the source of heat. The temperature registered on an indicator is the difference between that of the two junctions. Many combinations of metals are available. Nickelchromium alloys are stated to give the highest electromotive force in commercial use, ant: are useful for temperatures up to about 1,360 degrees C.

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Definition of  PYROMETERS