Modern electron theories indicate that the electrical and thermal conductivities of good conductors should stand in very close agreement with each other. One of the first theoretical developments was that of Drude. While perhaps, it will not be necessary to rewrite his formula here, we can at least state that he determined on purely theoretical grounds that the ratio of the thermal to the electrical conductivities for good conductors should he a function only of the absolute temperature. This theoretical formula has had excellent verification in the work of Jaeger and Disselhorst, who worked with most of the common metals. It occurred to the writer that an interesting experiment could be performed with an isolated crystal of selenium in order to determine whether or not the action of light lowers its resistance to heat conduction in the same or any other measure that it does in the case of the electrical resistance
