IV. On repulsion resulting from radiation.—Part VI

Abstract

387. Although the general character of the reactions which cause repulsion under the influence of radiation is now understood, much light may he thrown on the subject by an experimental examination of the direction and strength of the lines of pressure inside the case of a radiometer on which light is allowed to fall. Radiation will pass almost unimpeded through a very thin, colourless and transparent substance such as mica, but molecular pressure or stress is arrested by such a body (232). By introducing fixed or movable screens in various parts of the case of a radiometer, the direction of pressure can be determined at will, and its force can be modified in many ways, whilst all the other conditions of the experiment remain unchanged. In the present Part I propose to give the results of a long series of experiments on the action of thin mica screens in modifying the movements of the fly of a radiometer; I shall examine the action of the residual gas, the action of the sides of the glass case, and the applicability of the information so afforded to the construction of instruments of greatly increased sensitiveness for the purposes of research and illustration; and I shall also describe other experiments which have been tried from time to time during the last few years—experiments which at the time were isolated in their bearings, but which now fit into their places.