Sy pet 48 
dy Az 
d*s i 
‘ye 
dx? > atz? (’y +F) 
d®z a’ary 
da dy A’2* 
A pales 6's 
dy? wo Gm+y 
Those surfaces, which have no centre, are represented by the 
equation 
ay? + a’? + 2c'x = 0. 
The principal axis being the axis of z, and the plane of xy being 
a tangent plane through the vertex of the surface. 
The differential coefficients of the first and second order are, in 
this case 
day A’x 
aa he ee 
dz ay 
Gace 
dz re 
dx 
dz 
ar 0. 
Pe. in Ik 
iain. 
Let these five coefficients be expressed by p, q, r, s, t, and let 
their values be substituted in the equation 
