The relation between the thermal and electrical conductivities of me has for a long time engaged the attention of physicists. As far back as 1 Wiedemann and Franz propounded the law to the effect that the ratio of two conductivities was the same for all metals. In 1872 Lorenz, both on retical and experimental grounds, sought to establish that the above-mentio ratio was proportional to the absolute temperature. On the development the electron theory Drude, H. A. Lorentz, J. J. Thomson and others ha on the basis of various assumptions, arrived at the same conclusion as Lon Up to 1900, however, the experimental values were too uncertain to allow definite confirmation of the theory. In that year Jaeger and Diesselho published the result of their investigation, which gave directly the ratio of conductivities for a number of metals and alloys over the range 18° to 100° Lees has since, by an independent method, confirmed the values of Jaeger Diesselhorst for a number of metals at 18° C. and has carried the investigat own to —170° C. Meissner has experimented with some pure metals down —250° C. and Onnes and Holst even lower. The result of these investigations has been to show that between —100° C. + 100° C. the value of the function K/ λ T (K and λ being the thermal and ectrical conductivities and T the absolute temperature), is sensibly the samer the pure metals, with perhaps a slight tendency to fall with decreasing temrature. Below —100° C., however, the function shows an increasingly rapid with temperature and a considerable divergence between individual metals, ove a temperature of + 100° C. very few determinations of thermal conictivity have been made, and the object of the present series of experiments is been to measure, in this region, the thermal and electrical conductivities a number of metals of the highest purity obtainable commercially.