XVI. On the permanent temperature of conductors through which an electric current is passing, and on surface conductivity, or emissivity

Abstract

The experiments of which an account is given in the following paper were commenced several months ago in connexion with a theoretical investigation by Sir William Thomson, “On the Effect of Clothing,” showing the dependence of the effect on the relation between the dimensions of the covered body, and the dimensions and physical properties of the covering. A primary object of the experiments was the determination, for practical purposes, of the temperature of electric light conductors. The preliminary experiments have led to results which seem to be of considerable importance, and they point to the necessity for a fresh determination of the “emissivity” or “surface-conductivity” of bodies of various dimensions, and under various circumstances as to surroundings and as to air pressure. With respect to the determination of the permanent temperatures of wires carrying electric currents, very little seems to have been done experimentally. In fact, the only important experiments on the subject seem to be those of Mr. Preece, on the currents required to fuse and to raise to a dull red heat platinum wires of different diameters. These were communicated to the Royal Society in a paper read April 3, 1884. I may here remark that the results given by Mr. Preece differ in a very definite way from those which I have obtained; but it is to be noticed that the temperatures of Mr. Preece’s determinations were much higher than those at which I have, up to the present, experimented.