363 
discussion, show us what molecules coming from above yield the 
other points of the boundary of the segment. Of course this can 
only take place completely, so long as 4= OP is smaller than 
r+. 
25 
For all the other points of the segment we can account either by 
moving A and B aside till the moving molecule can pass between 
them, or perhaps by its being bronght about in a former volume, 
which was larger than the present one, or more probably by the 
fact that the limiting value of rv is only a mean value of «. 
Let us draw some adjoining squares normal to the movement of 
the molecule P, as belonging to the successive molecules A, 5, ete. 
9 
we have in the centre the molecule e.g. A, and at distances 7 + 
the four sides of the square. As soon as — =r we have the critical 
- 
l 
Q density. But if — <rv we have the 
case we are treating now. (See fig. 2). 
> If now AQ is greater than 27, we have 
ae the case under discussion, that a is 
enlarged for righthand, and lefthand 
al action, and likewise for action directed 
D upwards and downwards, and round 
the point Q and round the three other 
vertices there is a certain space through 
which moving molecules can move 
without double contact. But as soon 
as AQ is greater than 2r, the opportunity for the movement 
is either entirely gone or only possible by exception. For the value 
q 
Fig. 2. 
AQ=2r we have the case that OP of fig. 1 is equal to 7+ ~ 
l 
pS Dae Erge A eee et 
or that 2[ 7 + 5 OT Be pe or 7r(V2 in Orb 
l 
(2—1)r. To this value of aes yY2—1 — 0,414..., the circum- 
ar 
stances are probably owing which cause the rigidity, for so far as 
it is independent of the particular form of the molecules. If in fig. 2 
we draw the two diagonals, in each of the four angular points a 
molecule might be placed, but the movement would be impossible, 
