V. On a Method of Determining the Thermal Conductivity of Metals, with 
Applications to Copper, Silver, Gold, and Platinum. 
By James H. Gray, M.A., B.Sc, late 1851 Exhibition” Scholar, Glasgow University, 
Communicated by Lord Ketvin, P.RS. 
Received May 24,—Read June 14, 1894; Re-cast, with Additions, January 31, 1895. 
OF the different methods hitherto employed for the determination of thermal conduc- 
tivity of metals, only those which were elaborated by Forses and by Anasrrim have 
been successful in giving absolute results with fair approach to accuracy. The two 
methods, in the hands of these and subsequent experimenters, have given closely 
concordant results, both for copper and for iron. They, however, possess the dis- 
advantages of being exceedingly elaborate, requiring, as they do, very extensive 
preparations and comparatively large masses of the metals which are to be tested. _ 
For this reason, only the less costly metals can be tested, as it would be impracticably 
expensive to obtain a bar of gold or platinum, for example, a metre or more in length, 
and perhaps 2 square centims. section. 
The method used in the present investigation (for which a grant of £50 was obtained 
from the Government Research Fund) is free from these objections. It was suggested 
by Lord Kevin as far-back as thirty years ago, about the same time that the late 
Principal Forses began his experimental inquiry as to whether thermal conductivity 
varied with temperature. The chief advantages of this method are that (1) it is 
much simpler than the others ; (2) a test of the conductivity of any metal can be 
made in two or three hours; and (3) (perhaps most important of all) only a few 
grammes of the metal are necessary. Thus, even the rarest and most expensive 
metals can be tested, at very moderate cost. 
The method is essentially the experimental realization of the theoretical conditions 
implied in the fundamental formula 
— Y 
Oe eA en? 
where the symbols have their usual meaning. The metals to be tested are made in 
the form of wires of circular section. One end is kept at a constant temperature v, 
and the flow of heat Q, in a given time ¢, is measured. The length and section 
being known, all the data are obtained for the determination of the absolute value of 
30.5.95 
