always imaged as curves, no matter
what the shape of the lens forming the image may be. (For a more
detailed statement see page 170, at close of note.) Since, however, our
investigation had to do only with those curves which were due to the
qualities peculiar to the lens, we had to replace the spherical by a
plane projection surface. In front of the eye thus modified a strong
light was placed at such a distance that the image of it, produced on
the improvised back of the eye by the cornea and the lens, was a sharply
defined point of light. Now, when the source of light was moved, the
point of light would also move on the glass plate. Sitting at some
distance behind the eye, we observed the movements of this point through
a telescope. Thus we became witnesses of what happens upon the horse's
retina when a moving object passes in front of his eye. Although we saw
the point of light move through relatively long distances both
horizontally and vertically, no sort of deflection in its pathway could
be noted. Berlin's exposition does not hold true for the eyes of the
horses, either living or dead, which were examined by us.

[Footnote Z: Since no opportunity was given us to examine Hans's
eyes we do not know what their condition is in this respect. Though
it would have been interesting to know, it would hardly make any
difference in the views presented. If Hans should prove to be either
far or near-sighted, then, if we are to make any supposition at all,
it would be that the defect could not be very great, since near
sightedness exceeding 2 or 3 diopters and far-sightedness exceeding
one diopter is seldom found in the case of the horse. According to
Mr. von Osten, Hans at one time manifested a tendency to shy easily.
Be this as it may, for little could be concluded from it, since in
many extremely shy horses, no kind of visual imperfection can be
discovered.]

But in the case of some of the horses in whom Berlin had seen the
phenomenon for which we sought in vain, he himself tells us, the
deflection was very slight. In that case, it would appear, no great
advantage would be gained along the lines indicated. But even assuming
the degree of deflection to be very great, his theory goes to pieces on
the very point it was supposed to explain. A concrete example will make
this clear. If Mr. von Osten, standing two feet away from the horse,
raised his head 1/5 millimeter (which figure