W. B. Rogers on Binocular Vision. 219 
sultant of the uncovered portions and partly of the wire, the for- 
mer appearing as the continuation of the latter. 
We may I think conclude from these experiments that the 
coincidence of the wire with the resultant of the inclined lines, 
instead of proving this resultant to be impressed on the eyes asa 
single line, merely shows that in respect to relief both it and the 
Wire are viewed under the same visual conditions. 
It is to be remarked that for these experiments the lines of the 
diagram ought to be as slender as is consistent with great distinct- 
hess and the wire as thin as it can be made without a loss of ri- 
gidity. When the lines are broad or the wire thick there is an 
appearance of singleness near the point of intersection due to the 
overlapping of the two images which in the case of slightly in- 
clined lines may extend through much or all of their length. 
14. Tapering form of the perspective resultant. 
In repeating these experiments it will be observed that while 
the wire coinciding with the perspective resultant.ap 
changing thickness throughout its whole length, this resultant 
seems to increase slightly in diameter from the near to the remote 
end. ‘The cause of this difference although obvious, is not un- 
Worthy of remark. In the case of the wire the retinal picture in 
each eye is of course wider for the near than for the remote end, 
and would if uncorrected, convey the impression of an object ta- 
eyes. ‘Thus the diameter of the resultant disc or lines actually 
subtends the same angle in both eyes for every part of the length. 
and in this ease the enlargement towards the farther extremity is 
_ Very obvious. 
