( 125 ) 
Ph Pi Pi 
or ©, ee O/B (l—a#,—y,) : 
an equation in which all exponents are positive as appears from the 
values of p,, p, and ps. 
For C=O this equation is satisfied by 7,—=0 and therefore the nodal 
envelope coincides with the Y-axis, For C=o either y, or 1—7,—y, 
is zero, and for this value of C the nodal envelope coincides with 
the X-axis and the hypothenuse. For the special case, for which 
P, = 2p, and p,=3p, the equation assumes the following shape: 
n= C Ni Gr 4): 
This is the equation of a conic section which touches the X-axis 
and the hypothenuse in the points in which they cut the Y-axis. 
Whatever the values of p,, p, and p, may be, the curve will touch 
the X-axis and the hypothenuse in the points mentioned, if only the 
condition p, <p, <p, be satisfied, and the same would hold true 
if on the other hand p, >> p, > p, be fulfilled. The nodal envelope 
for which C=O will of course be an exception to this rule. 
In the adjoined figure 18 the 
Ps general course of the nodal envelope 
is represented in the above de- 
scribed circumstances. Though the 
calculated formula only holds for 
ws, and w', == constant the shape 
of the curve will agree in main 
features with the one, drawn here, 
always if neither on the sides, 
nor anywhere in the middle of 
p the surface of saturation a maxi- 
FP. 1-X 2 
: mum pressure occurs. 
Fig. 13. Only the details are different. 
For the locus of the points where the tangent of the nodal envelope 
is parallel to the J’-axis for instance, we find in the case that 
ue, and w',, are constant a right line passing through the intersection of 
x, Yi . 
the X-axis and the hypothenuse. For sate for such points and 
1 
so dx, == 0. But then also z,—7x, = 0. 
As follows from the equations (p. 11). 
vn _ Ale)" YI 
pal 1+ 4, (ei —=1) Hf (=H) 
Proceedings Royal Acad. Amsterdam. Vol. V. 
