Long Range Temperature and Pressure Variables in Physics1

Abstract

METHODS OF PYROMETRY. THE endeavour to provide suitable apparatus for high temperature measurement is one of long standing. The student of the subject is fairly overwhelmed with the variety of devices which have been proposed. There are few phenomena in physics which have not in some way or other been impressed into pyrometric service, often indeed by methods of exquisite physical torture. I cannot, of course, even advert to many of these this afternoon, as my purpose will have to be restricted to such devices as have usefully survived. Thus a whole group of “intrinsic thermoscopes,” as Lord Kelvin calls them—apparatus in which some property of the substance is singled out for measurement—will be overlooked. Pyrometry will some day receive substantial aid from the phenomena of solid thermal expansion, dear to the hearts of old Wedgwood, of Prof. Daniellsr of the citoyen Guyton-Morveau, and recently to Prof. Nichols, Dr. Joly and others; but even the “meldometer,” which has received Ramsay's encouragement, and recent heroic attempts to measure the expansion of platinum, have not yet entered the arena to stay.2 The same may be said of vapour pressure, ebullition and certain dissociations, of which the former is entirely too liberal in dispensing pressure, and the latter too negligent in readjusting it. Little has been done with heat conduction regarded as subservient to the measurement of high temperatures; little with colour and the spectrum, even though Draper and Langley in America, and many others elsewhere have paid tribute; little with polarisation. The wave-length of sound has told Cagniard Latour and our own A. M. Mayer much about high temperature, but it did not tell them enough.