W. B. Rogers on Binocular Vision. 175 
oblique as is most likely to happen, the curve rvs will of course 
become an arc of a circle whasses the cutting plane takes the 
position of the sub-contrary sectio 
Fourth. When the circular are is convex towards the right 
line meena the two are combined in front of the plane of the dia- 
r component arc and right 
a. line, and rvs is their bi- 
tween the plane of AB 
CD and the eyes, it is 
evident that the plane 
must be an are ‘a 
a ellipse. Asin the preceding case the * of the ellipse will 
a jak vee the distance between AB and CD, _ it will become 
cular in the position of the sub-contrary sectio 
hese et effects of the eso ae union ee a right line 
are & circular are may be thus summed up. 
When the are is conver to the right line and the union is 
effected beyond the plane of the diagram, or when thavang 4 seg, ; ae : 
the binocular resultant may be either an ellipse, a paravo 
an hyper bola, but in “ve case it will tura its th e: 
a fowarils the observ 
e 
aes beyond the plane of the diagram, 
the line a 
B. Binocular resultant of two circular a 
In this as in the preceding combinations rae optical centres are 
be regarded as immoveable during the experiment. Each eye 
*ave to the line and they are combined im front _- thedingtam, — oe 
