304 Prof. 0. Reynolds on certain Dimensional [Feb. 6, 



L f< 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 Experi- 

 mental 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 the Gas, and affords an explana- 

 tion of the Phenomena of Transpiration and Impulsion." 

 By OSBORKE Reynolds, F.R.S., Professor of Engineering at 

 Owens College. Received January ] 7, 1879. 



Abstract of Part I (Experimental). 



Section I (Introduction). 



1. 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 dis- 

 covery of 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 investi- 

 gations of these motions, or the theoretical explanations of the 

 properties revealed, have hitherto been in any sense complete. There 

 exists a whole class of veiy marked phenomena which have escaped 

 the notice of Graham and other observers, while several of the most 

 marked and important facts discovered by Graham have hitherto 

 remained unconnected by any theory. 



2. Amongst the best known of the phenomena is the difference in 

 the rates at which different gases transpire through minute channels, 

 and the consequent difference in the pressure which ensues when two 

 different gases, initially at the same pressure, are separated by a porous 

 plate. But it does not appear that hitherto an attempt has 

 been made to ascertain the existence of what may b considered a 

 closely analogous phenomenon — that a difference of temperature on 

 the two sides of the plate might cause gas, without any initial differ- 

 ence of pressure or any difference in chemical constitution, to pass 

 through the plate — nor am I aware that such a result from a difference 

 of temperature has been in any way surmised. 



I have now ascertained by experiments, which will be described 

 at length, that a difference of temperature may be a very potent 

 cause of transpiration through porous plates. So much so, that 



