. Canadian foundryman (1918). red such as: 1. Expansion instruments, themercury-in-glass thermometer,and various other types in whichdifferential expansion of somekind, either liquid or solid, is themeans of measurement. 2.—The electric resistance thermo-meter, depending for its action upon thechange in resistance by a coil of wirewhen its temperature changes. 3.—The thermo-electric or thermo-couple pyrometer, depending for its ac-tion upon the electro-motive force or volt-age developed at the junction between two dissimilar metals or alloys when thatjunction is heated to a temperature dif-fer
. Canadian foundryman (1918). red such as: 1. Expansion instruments, themercury-in-glass thermometer,and various other types in whichdifferential expansion of somekind, either liquid or solid, is themeans of measurement. 2.—The electric resistance thermo-meter, depending for its action upon thechange in resistance by a coil of wirewhen its temperature changes. 3.—The thermo-electric or thermo-couple pyrometer, depending for its ac-tion upon the electro-motive force or volt-age developed at the junction between two dissimilar metals or alloys when thatjunction is heated to a temperature dif-ferent from the remainder of the electriccircuit. 4.—Melting-point pyrometers, in whichthe melting of some alloy or mixture ofsalts or clay indicates the passage abovea certain fixed temperature, these may betermed fixed point pyrometers. B. Distant pyrometers, in which nopart of the instrument is subjected to theactual temperature to be measured, butwhich operates entirely at a distancefrom the hot body under measurement,. FIG. l. comprising:— 5.—The optical pyrometer, in which themeasurement of temperature is made bymatching the brightness or color of thehot body against that of a standard in theinstrument and computing the tempera-ture by the adjustment which has to bemade in the instrument. 6.—The total radiation pyrometer, which measures the temperature of thehot body by means of the radiated energytherefrom, both luminous and non-luminous. Variation In Indications It must be remembered that a pyro-meter in which the sensitive portion issubjected to the temperature measuresactually the temperature of its sensitiveportion. It is clear that the temperatureof the hot junction may be differentfrom the material in the furnace, bath orother apparatus, due to the conditionsbriefly mentioned below. (a) Thermal conduction of thepyrometer sheath. It is usual, andgenerally necessary, to employ anouter sheath to protect the actualthermo-couple from the action ofthe furnace ga
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