THE growth of the science of matter at high temperatures in the last century has been largely determined by the perfection of methods of measuring high temperatures. Prior to that time manufactures at high temperatures were of necessity empirical and dependent on the unaided skill and judgment of craftsmen. It was impossible to measure furnace temperatures much more exactly than in the time of Shadrach, Meshach and Abednego. The progress can be realized by comparing the symposium on “Gas Temperature Measurement” (J. Inst. Fuel, March 1939) with the modest and pioneering classic of Le Chatelier “Les Mesures des Temperatures Elevees” published only so recently as 1900. This report, with its discussions, covers more than 100 quarto pages and forms an excellent summary of the art of pyrometry as it exists to-day—an art which makes use of almost every branch of physics. In the symposium all pyrometric matters were considered, but considerable attention was directed to the suction pyrometer for measuring temperatures of gases flowing through flues. Dr. G. Naeser described a recent introduction to pyrometric technique—a colour brightness pyrometer—which makes use of colour instead of the intensity of radiation. Advantages are claimed in connexion with the measurement of the temperature of melted metal.