164 * J. LeConte on Binocular Vision. 
contemplated ; then the lines A N, Lv Rv, will represent the 
position of the median line and the two visual lines and R A, 
L A of the ee ‘Bie from the object A totheeyes. The visual 
result, if al e lines were visible, is ee by fig. 2. 
The object A fig. 1, is seen double at a and a’, fig. 2. If, 
instead of one ‘object at A, there be two similar siete @ g., 
stereoscopic pictures at v and v, fig. 1, then these will combine 
and be seen single at V somewhere along the combined visual 
lines E . 2. Of course there will be seen also, unless cut 
off by a septam, two other images, v and v’, to the extreme 
right and left, as already explained in my previou us paper. 
cannot even conceive how these phenomena can be represented 
by the usual metliod. 
VIL In binocular vision the law of corresponding points may 
be opposed to the ve of direction. In such cases the law of corres- 
aga points 
There are two fa known fundamental laws of vision, visi 
the law of visible direction and the law of corresponding points.* 
The one is the fundamental law of monocular, as the other is of 
binocular vision. The one gives the true position of all objects 
ra 
images. e former is cote regarded as the more funda- 
* The law of visible direction may be thus expressed: Every impression on the 
retina reaching it by a he line oe through the optic center, is referred back 
the same ray line true place in space. Thus for every radiant point in 
the object Bees oot ding focal point in the retinal image, and every 
focal point is referred back along its ray line 0 ies corresponding radiant, and the 
ote ge (object its proper position. Or it may be 
otherwise expressed th us: Space in front z us is, under all circumstances, an 
outward projection of retinal states With the eyes open, is the 
an outward projection of the passive state of the retina 
retinal concave with all its states is projected. outward and becomes the external 
spatial concave, and the two meeseajent point for point. Now the lines connect- 
ing the corresponding points internal and external intersect each other at the 
tic | ae ak i 
riefly expressed : Tmagine | 
ye-balls p together in such wise that they erengicue g coincide 
treughode then the coincident points of a two retinz are t are called 
corresponding points. Now the law of corresponding points declares gor images 
or impressions of any kind falling upon corresponding points of the two retin® 
are referred back to the same place in space and the arn seen single, while 
i e determina 
nding po ble. 
tion of the a as a geometric problem, is Pyacvaimnent of the surface oF 
line, the ray lines from every point of which would impress corresponding points 
of the re 
