( 247 ) 
Physics. — Prof. J. D. van DER WAALS offers on behalf of 
Dr. G. BAKKER of Schiedam a paper on: “The potential 
Aer Bear A st ‘ 
ear + .Be sin (qr + «) RR 
r r 
function p(r)= and p (r)= 
potential function of VAN DER WAALS”. 
In a previous paper I have pointed out that these potential func- 
tions lend to a spherical homogeneous shell or to a massive sphere, 
the density of which is a function of the distance from the 
centre, the property to attract an external point as if the mass were 
concentrated in the centre, if we leave a factor, depending on the 
radius, out of account. The differential equations, which are satisfied 
by these functions, are resp.: 
> 2 . . . . . . . 1 
and 
dp 2 d P 
pect ee On ate te NO) 
dr~ r dr 
If we substitute 2? +4? +2? for r°, these equations may also 
be written: 
i 0 an ea de kene aen (EG) 
and 
Up= tn dent teer 62) 
The resemblance of these differential equations with the well- 
known equation V29=0 for the potential of Newron, made it 
probable that these potential functions would have more in com- 
mon. The analogy was even closer than I expected. I found e. g. 
that the action between two systems of agens, spread over arbitrary 
spaces and surfaces, may be substituted by a system of tensions in 
the medium in a similar way as MAXWELL did for electric agens. 
In the first place we state the following theorems: 
I. If w represents the potential in a point 2, y, 4 of an agens 
which fills several spaces continuously, and is spread over several 
| Ae-t-+ Ber 
surfaces, the potential function being AU Ia ioe ERN we find 
for the potential, with the exception of some points and surfaces 
the differential equation: 
Viy=qw—A4n(A+Byo...-.- « (9) 
in which g represents the density in that point. 
