( 132 ) 
| dy, 
(dy,—dy,) — — (dx,—dz,) 
dix, 
d*y, 1 
or UT = 
du,’ ‘ (t,—2,) 
d 
dy, ae a dir, 
d*y, dix, 
or : ; db — 
dx, (z,—,) 
Oy ae dy, 
When we write it in this form we see that - == © for: that 
ar = 
1 
phasis for which dv, and dy, are zero, so for that phasis which 
coexists with the critical point of contact. If we write: 
dy, dy, 
ap ie” de AE, 
9 
de," de, (#,—«,) 
‚dy, aoe 
then the value of >, assumes for the plaitpoint, where «, = «, 
av 
1 
dy, dy, Bian 
and 7 =e = a shape which is indefinite. As, however, the points 
aL av 
3 1 
1 and 2 are situated on opposite sides of the plaitpoint, and the 
point 2 must always lie on the tangent of 1, and the curve contain- 
ing the points 1, the nodal envelope will present a point of inflection 
in the plaitpoint, i.e. in the point where it ends. The further con- 
tinuation to the locus of the critical points of contact belongs to the 
conjugated curve, and this must reverse its course either abruptly or 
fluently, where it meets the locus mentioned. 
Let us now pass to the discussion of the course of the nodal 
envelope in the case that a maximum pressure exists on one of the 
sides of the triangle. We shall suppose it to occur on the X-axis, 
so that the succession of the pressures is given by: 
Pr Pi S Pi SPs 
If for a certain value of 7, a maximum pressure occurs on the 
X-axis, then zr, = 0, and y, =0; from which follows that for 
the point representing the phasis with maximum pressure we have: 
en 0: 
The locus, represented by u, = 0, (see our previous communication 
p. 9) cuts therefore one of the sides of the triangle adjacent to the 
right angle, namely that one which joins the angles representing the 
first and the second component. Inside this triangle therefore also a 
continuous series of points occurs for which this condition is satisfied. 
The shape of this locus cannot be determined without the knowledge 
of the equation of state. [t might be derived from the equation on 
