The recent improvement in the process of manufacture of pure aluminium, and the consequent lowering in its price, has placed it within the reach of those who desire to make any experiments requiring large quantities of this substance. It seemed desirable that an investigation of the thermal conductivity of aluminium and its alloys should be made, but before obtaining the necessary bars a smaller bar was obtained from experiments on which a preliminary notion was got of the thermal conductivity; this being necessary in order to determine the most convenient dimensions for the long bars used in Forbes's method of conducting these experiments.