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METHODS OF MEASURING TEMPERATURE. KZEH 1KIKFITHS, l Sr. H RMI ItLY M-LLOU Ol 1111 lNl lll ir Ol WALKS, MUMflU. 18SIST4KT IN TH PIIY Us i1 IT I HI N TlONAl. PHVSKHI, I. UtOlt 4 1 n Y ITII . i. v i TRoi rcnox iiAi. K. H. SIIIFFITIIS, F. R. S. SECOND EDITION, REVISED. lUitb LONDON CHARLES GRIFFIN COMPANY, LIMITKI 42 DRURY LANE, W. C. 2. 1925. Itj AM Reserved. Prtntetl m, reaf Rit Ml Jr Batn, fauntnl, PREFACE TO SECOND EDITION. THE firat edition of this book waa exhausted very quickly and for four years it has been unprocurable, aa the author was too occupied to make the necessary revision. For this second edition, in addition to the correction of certain errata, the changes are mainly in connection with the treatment of Optical Pyrometry. The patience of the publishers in resect to delay on the Authors part is gratefully acknowledged. K. J. 1925. PREFACE. TUB present volume is written for those concerned with the measurement of tom M ratlin, whether in scientific investigations or in the control of industrial o eic, Hona. Attention ha lwen devoted chiefly to the cxjxrimental basin of the. methods in general use, the calibration of the instruments, and the, pre cautions which must be observed in practice. While the volume is complete in itself, it is assumed that the reader is conversant with the fundamental principles of physics, and the aim has been to extend the general treatment given in standard text-books, mich as those of Poynting and Tho aon. It was not deemed desirable to devote much spare, to descriptions of the constructional details of p - meters, since the information is readily accessible, in the catalogues of tl nanufae. turcrs. A connected account, m givi u of the classicalresearches with tho gaa thermometer, which luue established, in a c. onc-retc form, the absolute scale of tem Hrature over the ran 2W to 1,550 C. And it is well to re member that although the el-, ical and radiation methods enable relative measurements to be made ii a high degree of precision, they are dejiendent on the gas thermometer vork for their evaluation in t Tinft of the funda mental scale of teni Mruiur. In subsequent chapters the various tyjHs of pyrometers are dealt with individually, the t . ory underlying the method and the. calibration of the instrument. An attempt as be, en made to net out clearly the errors to which pyro metric observations are liable, when the conditions of UH do not comply with those jwstulated by the theory upon which the design is bawd par ticularly in the case of instruments of tlm radiation ty e, . The illustrations have been prepared by Mr. Kdgar A. IrilfitliH, and the writer wishes to acknowledge his indebtedness to his brother for his contributions to the work. The deacriptiona of the apparatus in use at the National Physical Laboratory have been inserted with the kind permission of the Director, Sir Richard Glazebrook. K. G TKDDIHOTON, MIDDLESEX, December, 1917. v INTHOnUCTTON. THE need of a monograph on the measurement of temperature must, 1 think, have been evident to every physicist, and it was a great pleasure to me to know that the difficult tank of supplying this need was to he dis charged by one so capable at Dr. Kzer iriffiths. A erusal of Dr. Urifhthss ook has made m realise how rapid our progress has been in recent times in this essential and hitherto somewhat neglected branch of physical measurement. Accurate measurement oftemperature, is the basis of nearly all accurate measurements in physics, and it is sad to reflect on the amount of valuable work which has had to be scrap ed owing to lack of attention to this iitijtortant mat tor. That unreliable instrument the mercury thermometer has in the past been used with little knowledge, of its imperfections. Y can best-judge of the advances that have been made by recalling th conditions under which an observer had to work some thirty years ago. About 1888 I had the privilege of being called into consultation by Messrs...