4 * . ne ee * =~ ike vil 
pas eee, oe Hy 
W. B. Rogers on Binocular Vision. en 
Sey 
i, 
BY 
= 
a 
_ ponding in position and length to that presented to the right ot 
and let the two lines of ‘this left hand figure intersect seer -. 
_ at their centres. Looking now at these two drew bas 
_ Stereoscope the two strong lines each seen by a d iffer®nt aes will 
2 coincide and the resultant perspective life will a ante to occupy 
_ the same place as before ; but the faint line which now falls on 
_ aline of the left dea which corresponds with the line of the 
_ right retina on which one of the coinciding strong lines, viz., the 
vertical one, falls, anne in a different place.” The author adds, 
“This experiment affords another proof that there is no neces- - 
sary > sh gabaeaaa pe te between the corresponding points . 
of the two retinas,” 
In this tei! a: visual action and the consequent per- 
ception are analogous to those above described, and the explana- 
tion of the result is in all respects the same. As however too 
general a conclusion, has I think been drawn from it by the in- 
_ genious author, and as it has been the subject of an entirely dif- 
_ ferent interpretation by Sir D. Brewster, I propose to consider it 
more in 
Using a drawing of the proportions 
represented in fig. 38, and placing it on 
the upper stage of the stereoscope so that 
a may be opposite the left and 6 oppo- 
site the right eye, it is easy by a quick 
change of convergence to combine @ 
with c. ‘The perspective resultant thus 
formed is seen intersecting the plane of 
the diagram and the line bin the point O. 
If we carefully graduate the convergence 
so as to mark the different stages of the 
phenomenon we may bring a to touch the upper end of ¢ then to 
cross it successively nearer the middle, then to coincide with b 
then to cross on the other side of the centre, and lastly to touch 
the lower end of c. When this is done slowly the line a is seen 
in the various positions represented in fig. 39, always parallel to 8. 
ae 
Phil. Trans., 1838, Part 2, or Phil. Mag., April, 1852. 
Szconp ‘a Vol. XX, No. 60.—Nov., 1855. 42 
e 
b 
J 
