The results obtained by different observers in their researches on the influence of temperature on the electric conducting power of metals do not agree at all together. The differences in their results may be partly owing to their not having tested pure metals, and partly to their not having taken into consideration the fact that, when a wire of a pure metal is heated for the first time to 100°C., an alteration in the conducting power of the wire is observed on its again being cooled; in fact, it is necessary to keep the wire for several days at 100° before its conducting power, on again being cooled, becomes constant. In the experiments we are about to detail we have taken great care to employ only pure metals, as well as a method and a disposition of the apparatus with which great accuracy could be obtained.