70 J. LeConte on Binocular Vision. 
are made to coincide perfectly, and the eyes be then held stead- 
ily in this position for some time, the patterned surface will be 
distinctly seen in exquisite miniature, not at its proper distance 
but between the real object and the eye, at a distance depend- 
ing upon the interval between the centers of the contiguous 
similar figures of the pattern. If the pattern be very regular 
the illusion is complete—we 1 
actually seem to be looking 
at a real object. In this ex- q Yn 
periment the position of the 
eyes is such that, of two con- 
and the image is seen at the met 
crossing of the visual lines. 
‘hus if one eye be directed 
R 
RK 
; Z 7 é 
ce’ and a and dat d’, and so on ~ 
for all the figures of the pattern. The dotted line d’ a’ c’ will 
be the position of the image surface. The image thus obsiee 
may be a little indistinct at first, but it gradually grows per- — 
fectly clear. As soon as the image is distinctly seen and the — 
outlines of the figures well defined, . it may be retained without 
viewing this saaeuaies image surface precisel if it were a 
‘Teal ; Ge ti - eed 
_If now while viewing the image in the last experiment we 
repeat. upon it the same ne experiment, i.e., if by increasing the 
convergence of the optic axes we bring again the two contigu- — 
- eas in coincide , @ new cannes is s formed between the 
but to figures separated by an Paeaiag. one, Thus in the — 
figure (gs Sando WHE be ed and dand — 
au ay tile Salas ee hee ah 2 
