Some time ago, following the publication of a paper by one of my former students, Mr. C. H. Skinner, I attempted to check his results by direct experiment. The paper referred to dealt with the optical constants of isolated selenium crystals. Of these constants, the reflecting power is the only one that offers itself to an easy experimental test. It must be said that the results obtained by Skinner were obtained by indirect means, and since the equations used in reducing his results to optical constants were somewhat complicated, and rested on foundations none too sure, it was important for our own satisfaction at least, to make a direct test of their accuracy
