a rapid rotation of the wheel. I have tried the experiment with
instantaneous photographs of the galloping horse, and I get three
results: first, no combination of successive phases occupying
one-tenth of a second gives anything resembling the "flying gallop" of
the racing plates (the Mycenaean and Stubbsian pose), or any other
conventional pose; second, no combination of successive instantaneous
photographs limited to ten second gives any pose which satisfies the
judgment and suggests a movement like the gallop; third, the
combination which comes nearest to satisfying the judgment as being a
natural appearance, but does not quite succeed in doing so, is one
formed by the fusion of figs. 2 and 3 of Pl. I. This gives all four
legs off the ground, drawn up or flexed beneath the horse's body, as
in Morot's picture of the sabre-charge at Resonville.

The fact is that we have to take into consideration two other factors
in the process, which we call "seeing," besides the duration of the
retinal impression or excitation. These are, first, attention, and
second, judgment. We are apt to think that "seeing" is a simple,
straightforward sort of thing, whereas it is really a strangely
complex and delusive process. "I did not see it, therefore it was not
there," or "You must have seen it; it was right in front of you," are
common assertions, and the belief that such assertions are justified
leads to miscarriage of justice in courts of law. Yet everyone knows
that he may stare out of the window of a railway carriage and have a
long panorama pass before his eyes, or may walk along a crowded street
and look his acquaintances in the face, and in neither case will he
have "seen" or recognized anything, or be able to give an account of
the scene that was pictured on the back of his eye. Attention, the
direction of the mind to the sensation, is necessary; and it appears
that it is very difficult (to some more than to others) to hold the
attention alert, and to give it to the _unexpected_. In fact, to a
very large extent we can only "see" (using the word to signify the
ultimate mental condition) that which we are prepared to see or that
which we expect to see. In the absence of such expectation, a very
strongly illuminated or well-marked, outstanding object is far more
readily "seen" than less marked objects. Accordingly, the outstretched
legs of the galloping horse, now in front and now behind, are "seen,"
whilst the rest of the phases a