784 
PROFESSOR 0. REYNOLDS ON CERTAIN DIMENSIONAL 
?=(>=■ 
(17) 
l 3 +d 2 +?C=7=“ 3 .(18) 
\/7T 
€v+€v =lr i(>+ y i£ = £€+££=- .( 19 ) 
7T 
Also if r is the absolute temperature of the gas, p the intensity of pressure, M the 
mass of a molecule, and p the density of the gas, we have for uniform gas 
M 
o 
= /ca 
2 
( 20 ) 
( 21 ) 
t—- 1 
p « 3 M 
( 22 ) 
in which k 3 varies with the nature of the gas, and is otherwise constant. 
73. The adoption of equations (15) to (22) restricts the application of the results 
that may be arrived at to gases of uniform molecular texture such as air and hydrogen. 
For these equations do not apply to a varying mixture of gases. In order to render 
them applicable to such a mixture it would be necessary to consider throughout the 
investigation the presence of at least two systems of molecules. This would add 
greatly to the complication, whereas none of the experimental results which it is 
my immediate object to explain involve a varying mixture. 
It will be seen, however, that at least one important result which has not hitherto 
been explained could be fully explained in this way. This is the transpiration of a 
varying mixture of two gases through a porous plate. The possibility of such an 
explanation will be seen from the results obtained for a simple gas. 
74. Table XX. contains all the value of cr(Q) carried across the axial planes by the 
several groups of molecules in a uniform gas for all the quantities Q which are 
important in this investigation. 
