On Fluorescence Absorption

Abstract

IT is desirable to direct attention to Prof. R. W. Wood's most important paper in the Philosophical Magazine for December, 1908, on a method of showing fluorescent absorption directly if it exists; but it seems certain that he has, at the end, drawn a conclusion from his experiments the very opposite, as I venture to think, to that to which they really lead. He compares the light apparently transmitted by a fluorescent body when fluorescence is, and is not, taking place, and finds that there is no difference in the resultant effect. This, I think, is as it should be; but the inference he draws is that there is no difference in the absorption. For my part I must admit that it only confirms my results published in the Philosophical Transactions, vol. cxci., A, 1898, that there is such an absorption; for if there were none such the light apparently transmitted would be less when the body is not fluorescing, owing to the fact that the fluorescent light would increase the apparent transmission, and a flickering should ensue; but Wood's experiment demonstrates that this is not so. The inference I should draw, then, is that during fluorescence there is an increased absorption of the light transmitted.