ay 
So: 
Aer + Ber A+B (A + B)q?’r  (B—A) gr? 
= ={(B-A eae 
r r n 2 713 
If we apply to the two members of this equation the operation 
v°, we find 
En P {Peete A Avot ad 
GES 
— qr qr 
deer + Be 
Ts 
In the same way equation (11) may also be deduced. 
On the other hand, if 22 4 4? +2? —=r?, it is possible to show 
that the solutions of the differential equations 7? y= + 9’ p‚, give 
exactly those functions that possess the property found by Prof. van 
OT 
4 
DER WAALS for the potential function — f 3 
r 
‚ We have, viz: 
dp dp dr dp dp (a ¥ dp dr 
dx De dr de dx? dr? dx dr de? 
and because 72 = 2? + y? 42: 
dr r da 1 od 
de da? 7 rs 
therefore 
dp dp x? dp fs = 
da? dr2 r? dr \r rö 
a Pp. 
If we deduce the expressions for ee = in the same way, 
we find by additien: 
dy 2 dp 0 
dr Bo Oty ea 
The differential equations 7? p= + g° may therefore be written 
in the following way: 
ap 2 dp 
— —= + ANS Fk ah 
dr? » dr Ja 5 (13) 
Tar 
