ae. earns 
LD OP gi hv eas 
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; 
W. B. Rogers on Binéeuler Brinn. cre eae 
and oe instrument just described gives us its analysts, they 
“ both lead to the same conclusion as ‘regards the elementary im- 
Be ssions which are ae d in the _ perception of such a line 
It is important to rouile that in both these cases when the 
component perspective lines are nearly coincident, the perception 
to whic ey give rise in the ordinary rapid mode of vision is 
_ that of a single resultant or a physical line, in a perspective po- 
ay If we imagine such a line to be observed for the first’ 
e, there can be no doubt that it would appear confused and 
Eoabie until by looking at it with one eye only, or by turning it - 
into a position transverse to the direction of view, and by apply- 
ing the sense of touch from end to end, we rectify the impression 
made by the two nearly coincident intersecting images first perceiv- 
ed. By repetitions of this process, experience permanently connécts 
the idea of a single perspective line with tw nearly but not quite 
coincident intersecting images, of which che pili of pena 
_ continually changes its distance from the eyes. In a word, this 
double image, peculiar in its form and variations, becomes the op- 
~ tical sign of a perspective line, and whenever impressed upon the 
eyes, iy must by the law of association excite in us the idea of a sin- 
gle line in a perspective position 
Thus in the case of bi nocular vision the perception of a per- 
spective line as single is me Ari suggested by the two non-co- . 
incident pictures, provided their relation to one another is such as 
has usually accompanied our vision of such a single line. But 
when the two intersecting images make a considerable angle they 
depart from these conditions, and hence although as before ex- 
plained, each appears in more or less of a perspective position, 
28 nearly endwise, we see two greatly divergent images produc- 
ing a confused impression which, unless helped by information 
drawn from other sources, would leave us in doubt as to the true 
form of the object before us. 'The same uncertainty attends our 
judgment i in regard to the perspective resultant in the stereoscope 
when its two lines intersect at a considerable angle. 
17. Of the extent to which the successive combination must be 
Ee 
m what precedes it would appear that the perception of per- 
spectivebces in a binocular resultant or in a physical line requires 
order to create a definite perception of perspectiveness is a ques- 
tion of much beers rs difficult 
y: 
According to the v of Sir David Brewster no part of the 
_ object is seen single Bit distinctly but that to which the optic 
