47 
1887 .] .Professor Tait on Kinetic Theory of Gases. 
The motion of the layer of P x s at x is (if approximately steady) 
given by the equation 
d / IVh \ _ 8 2 + M P i P 2 / _ \ 
A, *1 / 3 1 2 V .*1*1 Pj + Pj^ 1 2 '> 
where the right-hand side depends on the collisions between the 
two kinds of gas in the layer, s being the semi- sum of the diameters. 
Prom these we obtain 
3 Pi + P 2 
1 1 / f ~ \\ cZ 2 Gri 
-+^ 0 21 6 i+»i 2 S 1 )j-^ 1 . 
dt \16s 2 Jh 1 hfh l + A 2 ) p 
In the special case, when the masses and diameters are equal in 
d 2 G 
the two gases, the diffusion-coefficient (the multiplier of -^- 2 1 above) 
has the value 
+ 3 Cl )o-( 
=-4a-8. 
•677 Jh Jh 
It is therefore inversely as the density, and directly as the square 
root of the absolute temperature. And the case of two infinite 
vessels, connected by a tube of length l and section S, and contain- 
ing two gases whose particles have equal masses and diameters, the 
SpA. 
rate of flow of either is P8 in mass per unit of time. 
Other cases are treated ; and among these it is shown that with 
equal masses, and constant semi-sum of diameters, difference of 
diameters favours diffusion. The remainder of the paper is devoted 
to the interdiffusion of two gases whose particles have masses in the 
special ratio 16:1, the case of oxygen and hydrogen. The rate of 
diffusion (in a tube of unit section and of length l, connecting two 
infinite vessels filled with the gases (the semi-sum s of the diameters 
being constant) is given by the expression, 
A . P 
rrls 2 Jh '> 
where A depends, as follows, on the ratio of the diameters : — 
Ratio of Diameters. A. 
0 
1 
1 
3 
1 
1 
3 
1 
1 
0 
3*48 
3-31 
3-46 
3*79 
4*26 
