XVIII. On certain dimensional properties of matter in the gaseous state. - Part I. Experimental researches on thermal transpiration of gases through porous plates and on the laws of transpiration and impulsion, including an experimental proof that gas is not a continuous plenum. - Part II. On an extension of the dynamical theory of gas, which includes the stresses, tangential and normal, caused by a varying condition of gas, and affords an explanation of the phenomena of transpiration and impulsion

The motion of gases through minute channels, such as capillary tubes, porous plugs, and apertures in thin plates, has been the subject of much attention during the last fifty years. The experimental study of these motions, principally by Graham, resulted in the discovery of several important properties of gases. And it is largely, if not mainly, as affording an explanation of these properties that the molecular theory has obtained such general credence. It does not appear, however, that either the experimental investigations of these motions or the theoretical explanations of the properties revealed have hitherto been in any sense complete.