J. LeConte on Binocular Vision. 73 
for this purpose, had been destroyed and I found difficulty in 
again obtaining a suitable pattern. I therefore constructed a 
pattern by ruling black lines on a large sheet of paper so as to 
make perfectly equal squares 14 inches wide. With this sim- 
ple diagram my success in all the preceding experiments was 
really marvellous. The colored patterns before used form far 
more beautiful images, but for scientific purposes the ruled 
diagram is far preferable. With this diagram standing upright 
before me at the distance of sixteen inches, I got with great ease 
seven successive images on this side of the object and one beyond. 
the images on this side were defined, with great ease and 
perfect distinctness although the nearest, both by measurement 
ed and measured, was but 11 inches from the root of the 
nose, but I afterward found that there was no limit except the 
i ——— 
images were no longer perfect, not from any want of distinct- 
ness of the lines, but because the horizontal lines of the two 
es were no longer parallel but crossed one another as 
shown in the figure (fig. 4), and therefore could not be made 
to coalesce perfectly. The explanation of this will be given in 
its proper place, The still nearer images, as for instance those 
within 1} inches could not be retained ; the strain on the in- 
terior recti muscles of the eye was too great. 
the image beyond the object is much more difficult to ob- 
tain with clearness, ially if the object be near the eyes. 
At the distance of two feet from the object, I obtained the 
image very clearly and without much difficulty, but on ap- 
proaching to within ten or twelve inches it was only by patient 
trial for some time that it could be brought out with perfect 
inctness. When the object was twelve inches from the eyes 
‘the imag by calculation was found to be about thirty inches dis- 
tant, “By tuning the diagram eo that the diagonals were hor- 
zontal and similar points therefore more than two inches apart, 
the image was seen at the distance of about six feet. It] 
