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



("25 inch) it was nearly the same as lie found for graphite plates, or 

 for apertures in thin plates. 



Having established this law of corresponding results at correspond- 

 ing densities, it became apparent that the results obtained with plates 

 of different coarseness, and with the same plates, but with different 

 densities of gas, followed a definite law. This law, which admits of 

 symbolical expression, shows that there exists a definite relation 

 between the results obtained, the lateral dimensions of the passages, 

 and the density of the gas. 



This law is important in reconciling results which have hitherto 

 appeared to be discordant and as tending to complete the experimental 

 investigation, but it has another and a more general importance. 



It may not appear at first sight, but on consideration it will be seen 

 that this law amounts to nothing less than an absolute experimental 

 demonstration that gas possesses a heterogeneous structure — that it is 

 not a continuous plenum of which each part into which it may be 

 divided has the same properties as the whole. 



It would appear that Graham must have had this proof, so to speak, 

 under his eyes, and it is strange that both he and other observers have 

 overlooked it. It seems possible, however, that they were not alive to 

 the importance of such a demonstration. It is now so generally 

 assumed that gas is molecular, that the weakness of the evidence on 

 which the assumption is based and the importance of further proof 

 are points which are apt to escape notice. 



The Importance of an Experimental Demonstration that Gas Possesses 

 Molecular Structure. 



5. The idea of molecular gas does not appear to have originated 

 from the recognition of properties in gas which were inconsistent with 

 the idea of a continuous plenum, but from a wish to reconcile the 

 properties of gas with the properties of other substances, or, more 

 strictly, with some general property of matter. And the general 

 conviction which may be said to prevail at the present time is owing 

 to the simplicity of the assumptions on which the molecular hypothesis 

 is based, and the completeness with which many of the properties of 

 gas have been shown to result from this hypothesis. But it will be 

 readily seen that however simple may be the assumptions of the 

 kinetic theory, and however completely the properties of gases may 

 be shown to follow from these assumptions, this is no disproof of the 

 possibility that gas may be a continuous substance, each elementary 

 portion of which is endowed with all the properties of the whole, and 

 unless this is disproved there may exist doubts as to the necessity for 

 the kinetic theory. % 



Any direct proof, therefore, that gas is not ultimately continuous 

 altogether alters the position of the molecular hypothesis. 



