The mental process of attention results in a certain duration or memory of the mental condition which is a distinct thing from the primary retinal impression, and leads to the ignoring or mental obliteration of an instantaneous interval separating two phases of the position of moving legs which have strongly "arrested the attention." Hence, it seems that the most forward pose of the galloping horse's front legs and the most backward pose of its hind legs--though far from simultaneous, even in the slow changing retinal impressions--may be mentally combined by "the arrest of attention," and that the artist really ought to present his picture of the galloping horse with those two poses combined (although as a matter of scientific truth they do not occur simultaneously) in order that he may produce by his painted piece of canvas, as nearly as he can, the mental result which we call "seeing" a horse gallop. This combination of the front half of one figure with the hinder half of another so as to give in each case the extreme phase of extension of the legs I have made in Pl. I, fig. 12. But there is, further, in all "seeing" before even a mental result of _attention_ to the retinal picture is, as it were, "passed," admitted and registered as "a thing seen," the further operation of rapid criticism or _judgment_, brief though it be. We are always unconsciously forming lightning-like judgments by the use of our eyes, rejecting the improbable, and (as we consider) preposterous, and accepting and therefore "seeing" what our judgment approves even when it is not there! We accept as "a thing seen" a wheel buzzing round with something like fifty spokes--but we cannot accept a horse with eight or sixteen legs! The four-leggedness of a horse is too dominant a prejudice for us to accept a horse with several indistinct blurred legs as representing what we see when the horse gallops. The mind revolts at such a presentation, though it is true, and the whole scheme and composition of the artist is perverted or fails to gain attention and to exercise its charm--by the unwelcome presence in his picture of the revolting truth. It is the consideration of facts of this kind which enables us to understand the origin and importance of what are called "conventions" in pictorial or glyptic art. The artist is, in fact, operating by means of his painted canvas or moulded clay upon a queer, prejudiced, ill-seeing, dull, living creature--his brother-man. In order to give if possible to that brother, by means of a painted sheet, some or all of the delights, emotions, suggestions, perceptions of beauty, and so on, which he himself has experienced in contemplating a real scene, the artist has to present that scene, not as it really is, nor even as he thinks it really is, but in such a way that his canvas shall appeal to his brother's attention and judgment with the same emotional and intellectual result as the scene itself produced in him.