891 
All these relations are graphically represented by Fig. fa and 
. Fig. 16, in which the values of wu are given in function of the time. 
High temperatures (uo large, p small). 
distances 5 
distances 
finite comp. large 
Repulsion 
es he a 
& small tz finite tb 
small very small 
Weak collisions. Strong collisions. 
(*‘/f not very great; u = 1/5 92; co = 6). (e/s very great, or T somewhat lower; 
Fig. 1e. up? = Uy"; Cy = 3). 
Fig. 14. 
In the so-called “weak” collisions the velocity of the colliding 
molecule will not diminish suddenly, but gradually. This is among 
others fulfilled when the attractive force is supposed to change into 
a repulsive one already before the molecules collide. It may then be 
further assumed that the repulsive force does not become infinite 
before the impact itself, so that in general — unless the velocity is 
infinitely great — the two molecules will never be in absolute contact. 
Hence there is always between o and a value s’ somewhat greater 
than s (the distance of the centres at contact) a certain space, in 
which the decrease of velocity in consequence of the repulsive forces 
can take place; and there always remains — even at 7’=0— some 
distance, however slight, between the molecules, because of course 
/ cannot become smaller than o. 
It is self-evident that this somewhat modified way of considering 
the matter is only of a formal nature. Theoretically there is nothing 
changed when s is displaced to 6, and s’ from a point within s to 
a point outside it; now, however, we need not think the molecule 
greatly compressed in the weak collisions, as we had to do with 
the former way of considering the matter. 
The two above figures also show clearly why in the case of 
Fig. 1a u,? approaches to '/, u,’, and in the case of Fig. 16 to w’,. 
For as e.g. in the first case the time, during which the repulsive 
forces act, is so much greater than that under the influence of the 
attractive forces, the  time-average will lie in the neighbourhood of 
58* 
