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PROFESSOR 0. REYNOLDS ON CERTAIN DIMENSIONAL 
the immediate object for which it was undertaken. The most important of these 
viz. : that gas is not a continuous plenum, has already been noticed in Art. 5, Part I. 
The dimensioned properties of gas. 
127. The experimental results, considered by themselves, bring to light the depen¬ 
dence of a class of phenomena on the relation between the density of the gas and the 
dimensions of objects, owing to the presence of which the phenomena occur. As long 
as the density of the gas is inversely proportional to the coarseness of the plate, the 
transpiration results correspond ; and in the same way, although not so fully investi¬ 
gated, corresponding phenomena of impulsion are obtained as long as the density of the 
gas is inversely proportional to the linear size of the objects exposed to its action. In 
fact, the same correspondence appears with all the phenomena investigated. 
We may examine this result in various ways, but, in whichever way we look at it, 
it can have but one meaning. If in a gas we had to do with a continuous plenum 
such that any portion must possess the same properties, we should only find the same 
properties, however small might be the quantity of gas operated upon. Hence, in the 
fact that we find properties of a gas depending on the size of the space in which it is 
enclose d, and of the quantity of the gas enclosed in this space, we have proof that gas 
is not continuous—or, in other words, that gas possesses a dimensional structure. 
In virtue of their depending on this dimensional structure, and having afforded us 
proof thereof, I propose to call the general properties of gas on which the phenomena 
of transpiration and impulsion depend, the Dimensional Properties of Gases. 
This name is also indicative of the nature of these properties as deduced from the 
molecular theory; for by this it appears that these properties depend on the mean 
range—a linear quantity which, cceteris paribus, depends on the distance between the 
molecules. 
In forming a conception of a molecular constitution of gas, there is no difficulty in 
realizing that such dimensional properties exist ; there is, perhaps, greater difficulty 
in conceiving molecules so minute and so numerous that, in the resulting pheno¬ 
mena, all evidence of the individual action is lost. But the real difficulty is to 
conceive such a range of observational power as shall embrace, on the one hand, a 
sufficient number of molecules for their individualities to be entirely lost, while, on the 
other hand, it can be so far localized as regards time and space that, if not the action 
of individuals, the actions of certain groups or classes of individuals becomes distin¬ 
guishable from the action of the entire mass. Yet this is what we have in the 
phenomena of transpiration and impulsion. 
Although the results of the dimensional properties of gases are so minute that it 
has required our utmost powers to detect them, it does not follow that the actions 
which they reveal are of philosophical importance only. The actions only become 
considerable within extremely small spaces, but then the work of construction in the 
