36 | 
of the molecules against each other (ef. Continuität p. L110). If we 
accept this as perfectly correct, it follows from this that when the 
- distance of the molecules is so great that double contact never takes 
place, the value of @ remains the same, but that increase of « will 
be found when this double contact takes place. If this is not entirely 
true, the following calculation will only be an approximation. The 
idea that the collisions of the molecules are in close connection with 
the attraction, which is expressed at the cited place, will therefore 
be used here to calculate this increase of a. 
Let us draw three circles of equal size representing spherical 
molecules, with a radius —v7. The two first circles have their centres 
at the same level, and are at a distance from each other = 2r + 
+/(/< 2r). The third circle represents the molecule moving from 
above downward. If we suppose for a moment that this third molecule 
moves just halfway the molecules A and B, and that the distance of these 
molecules is 2 X = /< 2r, it will touch the two molecules exactly 
at the same time. Then there is formed a triangle, the vertex of 
which is the centre of the third molecule. The height PO is 
eee ae tee rear) See 
je — a or — ie de BTR 
f 2 2r 2r | 
l 
which is only equal to zero, when se r, and the two molecules 
A and B are at a distance from each other equal to 27, large 
l 
enough to allow free passage to the moving molecule. If ; AP Ry 
then double contact takes place in points lying halfway on AP and LP. 
If a line is erected normal to AB and passing through these 
points, this line may be considered as. the projection on the plane 
ABP of the boundary of the surface of the molecules of points, in 
which the ordinary value of a is exerted, and of such points in 
which an increased value is exerted. Both on A and on P this 
boundary is a circle, which cuts off a spherical segment. Let us 
call the thickness of that segment , then: 
or 
