86 J. LeConte— Phenomena of Binocular Vision. 
zontal image much less than that of the vertical image. 
embodies his results, therefore, in a diagram like the above, 
except that the curves of the vertical and the horizontal lines 
are exactly equal each to each in every part of the diagram, 
while in mine the vertical curves are much greater. 
The following diagram plainly shows that the apparent tor- 
sion of the vertical and horizontal images are in opposite direc- 
1. tions. If the inclination 
aan _ or torsion of the images 
show a corresponding tor- 
sion of the eye, the evidence 
of the two images is con- 
tradictory. . There must, 
therefore, be a fallacy some- 
where. They both cannot 
be right; for when one 
indicates torsion of the eye 
to the right, the other indi- 
‘ates torsion to the left, 
and vice versa. The verti- 
eal and horizontal curves 
in the diagram are not 
everywhere at right angles 
to each other, as the ey ought 
to be, if they were both true representatives of ocular torsion. 
This is best shown by using an image in the form of a rect- 
angular cro 
Baperiment 8.—If such an image, made by gazing on a cross 
slit in the window, be used in the experiments already described, 
hen on turning the eyes obliquely upward and to the right, 
the cross by oe turning of the two parts in opposite directions 
is distorted, thus -/, so that the angles are not all right angles, 
but 70° and 110°, On: turning the eyes upward and to the left, 
the — sighs thus ~_, downward and to the right, thus evi 
to the vs --. The same mode of crossing is observed 
in the vo of the diagram, and in the crosses in the corners. 
It is perfectly evident that this distortion is produced by 
projection of the image on a plane inclined to the line of sight. 
Helmholtz also attributes this distortion to projection, but he 
gives no experimental wear nt = eliminating this source of 
fallacy. If he had done so he have escaped what I con- 
ceive to be the error into wiked has inadvertently fallen. 
The method which I use to eliminate this source of fal- 
lacy is the obvious one of projecting the Bh dd on a plane in 
every case perpendicular to the line of sig 
* With one eye “line of sight” is the proper term—but with two eyes “media 
line of see bs ee except in cael near objects the difference is so small that I 
shall neglect 
7 
