( 654 ) 
RE 8 a, RT 8 A, (6%) 
v = — 3 v == 5 5 aca koe are ) 
2 TREO a yale 
which is again a good test of the exactness of our formula, 
deduced above. 
These two critical points are at the same time plaitpoints of the 
Ov 
(transversal) plait, for it can easily be shown, that (5 ) and also 
x 
oT : 
(5) will be there = 0. 
Ou p 
Before deducing the equation of the plaitpoint-curve, I shall first 
point out, that the second member of (6) is always positive, as 
consisting of the sum of two essential positive terms, so that the 
Tv, v-surface possesses nowhere points beneath the v, z-plane, which 
of course cannot occur, because 7’ cannot be negative. Further, 
that from (67) and (6%) results, that as to the limiting-curve (6%), 
there will be found 7’—O for «=O and x=1, and as to the 
limiting-curves (6), 7’ assumes again the value 0, as well for v — d, 
(resp. b,), as for v =o. 
Since the values of 42/7, and #/,, can be very different, according 
to different substances, the surface (6) will also present very different 
forms. Generally a greater value of 6 corresponds with a greater 
value of 7, and in that case the surface has the form, as is indicated 
in the figure. It is manifest already at superficial consideration, that 
this form will be pretty complicated. 
6. We will now determine from (6) the locus of the plaitpoints. 
. 
