360 
extension. So long as the distance of the molecules is great enough 
to allow the passage, a does not change, or inappreciably little, and 
when the mean distance is small enough to prevent this passage, 
there is a reason to cause appreciable increase of a. To show this 
in a simple way, and render the calculations possible L shall con- 
sider the molecules, even the more complex ones, as spheres. The 
rapid revolution, in which the axes of the molecules will assume 
all possible directions in an exceedingly short time is the cause that 
they may be considered as bodies for which no direction can be 
given in which the dimension is greater or smaller than in other 
directions. 
Let us put the radius of such a sphere = 7, and the diameter 
— 2, the distance of the centres being represented by 27 + /, then 
the case for which /= 2r will have to be considered as transition case. 
If /=r, then the space available for a molecule for its movement 
is a space equal to 8-times the volume ofa molecule. And as 4-times 
this volume js represented by 5, the volume occupied by -the sub- 
stance is for this transition case, equal to 25,. Now it is remarkable 
that this case occurs, either entirely or all but entirely, at the critical 
volume. My earlier considerations have made me find vj, = 2,2, for 
the critical volume. But for bj I had found almost 6; = 0,96,, hence 
vk = 1,98b,. We shall not make an error of any importance if we 
change the value 1,98 into 2. And this may even possibly be quite 
accurate, but at the moment I ‘will not enter into this any further. 
If />2r, two molecules can never be touched at the same time 
— only when departures from the normal state occur, this simul- 
taneous contact can take place, but then this deviation would be 
replaced by an opposite one at other places. The assumption of 
complexes also implies departures from the normal state, and I will 
now try to demonstrate that the increase of « at greater densities 
already follows on the supposition that the distribution of state is 
perfectly normal. 
And | will account for it by this that according as the density 
increases, a greater number of molecules has simultaneous contact. 
The function of force for the attraction of the molecules is not 
known, and I have seen when drawing up the equation of state 
that it need not be known. For material points and for molecules 
“in comparatively large volume the resulting attraction may be 
a 
brought in the form [ have chosen, viz.: — A posteriori I found by 
Vv 
comparison of the capillary constant with the eonstant of the mole- 
cular pressure that the attraction seems to exist only at the impact 
