212 W. B. Rogers on Binocular Vision. 
ues in the plane of the paper, or more properly in a parallel plane 
behind — in which the diagram is actually placed. 
If now by suffering the eyes to range up and down along the 
sandenen I combine the corresponding points in somewhat quick 
succession, I observe the various phases above parts to fol- . 
ow one another rapidly and at the same time I see the compo- 
nent lines assuming in part or wholly, the appearance of inter- 
secting lines in relief. ‘This effect, however, recurs only tran- 
onic succession as to Soinis about the perspective e 
is is more readily done with fig. 21, whose Neos are inelined 
at an angle of 30°. On first viewing these lines placed on the 
upper stage, I sometimes see a resultant consisting of intersecting 
subside to the ie plane. It is easy by giving the eyes free 
range along the resultant to continue this perspective effect, and 
again by shespelilie them to a slow change of convergence, to pro- 
duce all the phases of intersection in the parallel plane without any 
appearance of relief. 
Fig. 22 
Bianeing along a part of the figure have been ‘carried through 
23. 
eS tasice # pa 10°, the appearance of 
the resultant is sometimes that of a single 
perspective line and sometimes that of two 
such lines intersecting but very close to one 
another. It is important to remark that the 
latter effect always presents itself when we 
endeavor to fix the co nvergency of the 
axes, and that when we succeed in main- 
taining this direction, even for a few moments, the perspective 
lines, as in the preceding cases, lose their relief and present them- 
selves in some phase of intersection in the parallel plane. 
