8 J. LeConte on Binocular Vision. 
houses above and nearer, and the larger farther away in the 
distance. 
On combining in a similar manner one of those skeleton 
of pees iution. In the first ara in most stereoscopic siokiies 
identical points. are farther apart than the eyes, and therefore, 
cannot be combined beyond the pictures without = aid of 
lenses or prisms. In the second place, even if the pictures are 
not farther apart than the eyes, and may therefore ie thus com- 
bined, the dissociation of the focal from the axial adjustment, 
as already explained in my first paper* is difficult and imperfect, 
aid the combined picture therefore is not clear. 
T wish now to apply the method proposed in my last article, 
in the representation of stereoscopic phenomena. The usua 
method, which I have used in figs. 1, 2, 3, and 4, because it is 
familiar, represents pertectly the position of objects seen single 
and therefore their relative distance or the depth of space, 
when the eyes are directed upon them consecutively ; but can- 
not represent the position of double vmages in the stereoscope any 
more than it can in natural vision. Fig. 7, gives the mode of 
representing by the usual method. A R, A Lis the position of 
the optic axes when objects aa in the foregrounds are com- 
bined at A and bd’+ the position of the double images of bé, 
seen at the same distance as A; BR,BL the direction of the 
optic axes when objects bb in the backgrounds are combined 
and seen at B and aa’, the apparent position of aa at the same 
distance as B. Fig. 8 gives the same when pictures are com- 
bined by squinting. 
Now it is evident that this mode of representation is not 
true, for we do not refer bb’ to the same distance as A, when 
we look at A, nor aa’ to the same distance as B when we look at 
B. The whole stereoscopic effect would be lost if we did. On 
the other hand my method of representation gives the true 
chow positions of the double images as we now proceed to 
show. 
When we gaze through a stereoscope the two pictures seem 
to slide aaeed over each other until they unite to form a single 
* This Jour., IL, xlvii, pp. 73 and 76. 
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