CHAS. R. DARLING. WOOLWICH, 1920. Preface to the First Edition The present treatise has been founded on a course of Cantor Lectures on “Industrial Pyrometry,” delivered by the author before the Royal Society of Arts in the autumn of 1910. The practice of pyrometry in recent years has progressed at a greater rate than the literature bearing upon it; and the author is not aware of the existence of any other book written in English which treats the subject from the standpoint of the actual daily use of the instruments. In the succeeding pages the exact measurement of temperature, as an end in itself, is made subordinate to the practical utility of pyrometers in controlling various operations; and consequently descriptions of appliances of interest only theoretically have either been omitted, or at the most briefly described. Nevertheless, the fundamental principles are in all cases fully explained, as an understanding of these is essential to the intelligent use of the appliances dealt with in the book. When necessary, numerical examples are given to illustrate the applications of the principles; and the reader who finds any difficulty in following the various explanations—which of necessity involve an understanding of many portions of the subject of heat—is referred to the author’s treatise on “Heat for Engineers,” issued by the publishers of the present volume. With regard to temperature scales, the author has in the main employed Centigrade degrees, but has recognised that the Fahrenheit degree is still largely used, and has therefore frequently expressed temperatures in terms of both scales. The number of those who find it an advantage in their calling to measure and control high temperatures is constantly increasing; and the manufacture of pyrometric appliances now gives employment to considerable numbers. The author trusts that the present treatise will prove of service to all thus concerned, and also to those who pursue the fascinating study of high temperature measurement from the purely scientific standpoint. In conclusion, the author expresses his thanks to the various firms, mentioned in the text, who have loaned blocks for the purpose of illustration, and who have furnished him with much valuable information. CHAS. R. DARLING. WOOLWICH, 1920. PYROMETRY CHAPTER I INTRODUCTION