G. PLARR ON THE SOLUTION OF THE EQUATION Vpop=0 : Te 
fe=). = (h.—hs), with a tangent plane perpendicular to d. 
For E=0 the spherical conic is the intersection of the cone 
0= Th, Sr 
and the sphere 
Te=¢,—= ley + 77” r_271(Q’ |, 
As h; <0, the angle which the generating line ¢« forms with v is smaller 
when € is in the plane vA, than when ¢ is the plane yp, these angles being 
given by 



Aad ol. —h —h, a 
EI Nex E: h, M2 
owing to hohe 0 > hs. 
Also for = 0 (58) = = S08 =e,: (3). . 
Therefore ¢ is increasing when E passes through zero. 

For E=E, = -p 
the spherical conic on the first sheet is the intersection of the cone 
0 = LhiSre 
with the sphere 
= Te = oe = D(A, — hy) (hs — hy) (ho — hg) 
mega) FERRO (+h +he) 

The normal becomes 

Uy = (= + ot) €’, 
geet SNe (1 apaeas 
2Sh,h, 
ee =) DASA; (fy — hs) (tg —In) « 
The generating line ¢’, of the cone 2/,S'he’= 0, in the plane dy is given by 
0 =hSre + hSve, and as h,<0, 
this decomposes itself into : 
VOL, XXVIII. PART I. , 

