ee ete a Sa 
ait ss 
W. LeConte Stevens—Notes on Physiological Optics. 295 
tion, but the judgment is much vitiated as we depart from the 
conditions of normal vision. Even for a=7° 20’ my estimate 
of distance was too small, and as a a the curve shows 
strikingly how fallacious must be any conclusions drawn from 
Brewster's theory that there is a necessary connection between 
apparent eae and optic nitisg he or, as he expressed 
it, that we e distance,” instead of judging it as contended 
by rete 
the variation in apparent distance is not very great between 
the limits of —2° and +5°, within which the optic angle is in- 
cluded in most cases of binocular vision with lenticular stereo- 
scopes. This explains my remark in a former article that the 
rather by physical perspective. In these cases, it will be ob- 
served, the fie of view is quite limited, and the optic angle 
not very lar 
Sir David Bactueee! noticed the strong effects obtained with 
convergence of visual lines by combining the images of per- 
fectly similar patterns, recurring regularly and in great num- 
er, on large surfaces. en an extended field of view is 
occupied by such images, the effect of contraction in the rectus 
muscles seems to be more marked in comparison with that of 
the other elements of perspective, in estimating absolute dis- 
tance there being no contrast of background and foreground to 
interfere. This enhancement is noticeable also when the vis- 
