III. Approximate determinations of the heating-powers of arcturus and a Lyræ

About twelve months ago I began to make observations upon the heating-power of the stars. My first arrangements were simply these: I made use of a delicate reflecting astatic galvanometer, and a thermo-electric pile of nine elements. The pile was screwed into the tube of a negative eyepiece of the Greenwich Great Equatoreal, from which the eye-lenses had been removed. I soon convinced myself that the heat, condensed by the object-glass of twelve and three-quarters inches upon my pile, was appreciable in the case of several of the brighter stars; but the endless changes in the zero-point of the galvanometer-needle, and the magnitude of these changes, compared with those arising from the heating-power of the stars, prevented me from making any attempts to estimate the absolute magnitude of the effects produced. Every change in the state of the sky, every formation or dissipation of cloud, completely drove the needle to the stops.