ot
astigmatic. We cannot, however, immediately conclude from the fact that
an objective movement is imaged as being greater in extent on the
retina, that it will therefore be more readily perceived by much less
that it will appear greater to, the horse, than would be the case if the
lens were normally constructed. The visual percept is not immediately
dependent upon the retinal processes, for between the two are
interpolated complex, inaccessible nervous processes. Still, Berlin
believes that he is justified in drawing this conclusion from a number
of relevant considerations. Accepting it, he believes that it would be
possible for the horse to perceive movements, that for the human eye,
which is not subject to this form of astigmatism, would lie below the
threshold.

[Footnote Y: "Butzenscheiben" are the small circular panes of green
glass, used in leaded windows in early days. They are high in the
middle (hence the name: "Butze," a protuberance) with a number of
concentric circles around the central elevation.--Translator.]

This theory, the simplicity of which certainly must make a strong
appeal, has been adopted by a number of well-known investigators
(Schleich[40], Koenigshoefer[41]). If we also could accept it, then Hans's
phenomenal power of perceiving the movements of objects would be
explained. But doubts arise which restrain us. Even if we were to accept
Berlin's view in general, we should still come upon the following
difficulties. In the first place, it is questionable whether the
peculiar form of astigmatism mentioned is indeed as common as he
supposes.[Z] The references in the literature are exceedingly meager on
this point. In order to make a few tests at least, I undertook to
examine nine horses with the aid of Dr. R. Simon, oculist, to whom I am
greatly beholden for the assistance given in these and other tests to be
mentioned presently. In not one of the nine cases did we discover
anything like the curved deflection which is supposed to be the sign of
the form of astigmatism in question. But in order to test objectively
whether Berlin's assumption were justified, we examined in the
laboratory fresh specimens taken from two horses. The eyes were fastened
in a frame in what corresponded to their normal position. Their
posterior spherical wall (i. e., their respective retinal surface) was
replaced by a piece of ground glass. On a spherical surface linear
movements of a point of light are