nsidering a similar experience, gives his opinion
that not the absence of fusion for the moving eye, but its presence
for the resting eye, needs explanation. "More than a thousand
interruptions per second," he believes, "give a series of sharply
defined retinal processes." But as for the fusion of moving objects
seen when the eyes are at rest, Cattell says, "It is not necessary and
would probably be disadvantageous for us to see the separate phases."
Even where distinct vision would be 'disadvantageous' he half doubts
if fusion comes to the rescue, or if even the color-wheel ever
produces complete fusion. "I have never been able," he writes, "to
make gray in a color-wheel from red and green (with the necessary
correction of blue), but when it is as nearly gray as it can be got I
see both red and green with an appearance of translucence."

[1] Cattell, J. McK., PSYCHOLOGICAL REVIEW, 1900, VII., p. 325.

That the retina can hold apart more than one thousand stimulations per
second, that there is, in fact, no such thing as fusion, is a
supposition which is in such striking contrast to all previous
explanations of optical phenomena, that it should be accepted only if
no other theory can do justice to them. It is hoped that the following
pages will show that the facts do not demand such a theory.

Another simple observation is interesting in this connection. If at
any time, except when the eyes are quite fresh, one closes one's eyes
and attends to the after-images, some will be found which are so faint
as to be just barely distinguishable from the idioretinal light. If
the attention is then fixed on one such after-image, and the eyes are
moved, the image will suddenly disappear and slowly emerge again after
the eyes have come to rest. This disappearance during eye-movements
can be observed also on after-images of considerable intensity; these,
however, flash back instantly into view, so that the observation is
somewhat more difficult. Exner,[2] in speaking of this phenomenon,
adds that in general "subjective visual phenomena whose origin lies in
the retina, as for instance after-images, Purkinje's vessel-figure,
or the phenomena of circulation under discussion, are almost
exclusively to be seen when the eye is rigidly fixed on a certain
spot: as soon as a movement of the eye is made, the subjective
phenomena disappear."

[2] Exner, Sigmund, _Zeitschrift f. Psychologie u. Physiologie
der Sinnesorgane_, 1890, I.,