82 G. PLARR ON THE SOLUTION OF THE EQUATION Vpgp=0. 
If now we would look at the surface from a point in the axis v, we would 
see—lIst, the jirst sheet spread out under the eye with its conics centred in the 
point e,v, and extending as far as the obliquely seen circles of radius e,, in 
the above two planes R, BR’. 
2d, Between these circles and the singular curve E=E,, e=e,,, or 
upper edge of the belt, we would see the second sheet in continuation of the 
first. 
3d, The third sheet will be shut out of view in this position of the eye, 
because the tangent plane along the curve forming the sharp edge of the belt 
is dipping downward and inward. 
When h, < 0 the surface will present exactly the same general features, 
only the roles of the axis 4, v, will be interverted. 
Without entering into details about the special cases, when 
hy Sh oP dl = | 
we will only remark that in these cases the surface [ = 0 becomes a surface 
of revolution round the axis », or \, respectively. 
When hi, = 0 the surface looses the intermediate sheet, the one which we 
called the 2d sheet. 
But in all cases the sharp edge corresponding to P=0, Q=0 is the 
feature most characteristic in the surface 
T=0. 
THE SECOND PART. 
As we announced in our introduction, we will establish the directions and 
tensors of the expressions of p and p’ satisfying to the conditions respec- 
tively of 
Voge = 0,.. Vpgp —-0. 
Both of these conditions lead us to establish the scalar equation /g = 0, 
Jo=a9—mg + mg—m; 
where m, ,, m,, are scalars whose expressions we need not repeat, and 
which are the same when they are calculated either with the help of ¢ or with 
that of ¢’. 
