Absolute or Thermodynamic Scale—Constant Volume Gas Thermometer—Fixed Points for Calibration—National Physical Laboratory Scale—Temperatures above the Present Limit of the Gas Thermometer. III. THERMO-ELECTRIC PYROMETERS 20 General Principles—Metals used for Thermal Junctions— Changes in Thermal Junctions when constantly used—Electromotive Force developed by Typical Junctions—Practical Forms of Thermocouples— Liquid Element Thermocouples—Indicators for Thermo-electric Pyrometers—Special Features of Indicators—Standardizingof Indicators to read Temperatures directly—Standardization by Fixed Points— Standardization by Measurement of E.M.F.—Cold-Junction Compensators—Constant Temperature Cold Junctions— Special-Range Indicators—PotentiometerIndicators— Recorders for Thermo-electric Pyrometers—The Thread Recorder—The Siemens Recorder—Foster’s Recorder— Paul’s Recorder—The Leeds-Northrup Recorder— Control of Furnace Temperatures—Contact-Pen Recorders— Installations of Thermo-electric Pyrometers—Management of Thermo-electric Pyrometers—Laboratory Uses of Temperatures Thermo-electric Pyrometers—Measurement of Lower by the Thermo-electric Method—Measurement of Surface of Surface Temperatures—Measurement of Low Temperatures— Temperature of Steam, Exhaust Gases—Measurement of Differences of Temperature—Advantages of the Thermo-electric Method of Measuring Temperatures. IV. RESISTANCE PYROMETERS 101 General Principles—Measurement of Resistance by the Differential Galvanometer—Measurement of Resistance by the Wheatstone Bridge—Relation between Resistance of Platinum and Temperature—Changes in Resistance of Platinum when constantly Heated—Terms used in Resistance Pyrometry—Practical Forms of Resistance Pyrometers—Indicators—Siemens’ Indicator—Whipple’s Indicator—The Harris Indicator— The Leeds-Northrup Indicator—Siemens’ Differential Indicator—Recorders for Resistance Pyrometers—The Leeds-Northrup Recorder—Paul’s Recorder—Installation of Resistance Pyrometers—Management of Resistance Pyrometers—Special Uses of Resistance Pyrometers. V. RADIATION PYROMETERS 134