sin 
From this ratio the course of the curve vp can be deducted, 
which is the locus of all poles of secant planes that cut the angle 
between the planes WV: / in a way so as to produce the apparent 
angle h= = For e= one finds ¢= 5 a mi x produces 
io. O 00E @ Oro = 5 — a; whilst for 9 = 27, « becomes again an 
B [A Bla 
he > n | 
| | | | 
4 
N 
5 al NN = 
ap) is \ yee zj 
5 \< a x 
s RW E 
a 
5B ae E El 
IE ESS S 
& laa en N Ela eN 
en SSN 
7. i S&S 
