Protogenes had painted the mother of Aristotle. I know not how much the philosopher paid for the picture, but instead of the full payment, or perhaps over and above it, he gave the painter a piece of advice which was of more value than the money. Not, as I believe, in the way of flattery, but because he knew that art needed to make itself universally intelligible, he advised him to paint the exploits of Alexander. The whole world was ringing with the fame of them, and he could foresee that their memory would remain to all posterity. But Protogenes was not wise enough to follow this counsel. “Impetus animi,” says Pliny, “et quædam artis libido,”[84] a certain presumption in art, and a craving after something new and strange, led him to the choice of other subjects. He preferred the story of Ialysus,[85] of Cydippe, and others of like kind, whose meaning we can now scarce even conjecture. XII. Homer treats of two different classes of beings and actions,—the visible and the invisible. This distinction cannot be made on canvas, where every thing is visible, and visible in precisely the same way. When Count Caylus, therefore, makes pictures of invisible actions follow immediately upon pictures of visible ones; and in scenes of mixed actions, participated in by beings of both kinds, does not, and perhaps cannot, indicate how those figures which only we who look at the picture are supposed to see, shall be so represented that the characters in the picture shall not see them, or at least shall not look as if they could not help seeing them, he makes the whole series, as well as many separate pictures, in the highest degree confused, unintelligible, and self-contradictory. With the book before us this difficulty might finally be overcome. The great objection would be that, with the loss of all distinction to the eye between the visible and the invisible beings, all the characteristic traits must likewise disappear, which serve to elevate the higher order of beings above the lower. When, for instance, the gods who take different sides in the Trojan war come at last to actual blows, the contest goes on in the poem unseen.[86] This invisibility leaves the imagination free play to enlarge the scene at will, and picture the gods and their movements on a scale far grander than the measure of common humanity. But painting must accept a visible theatre, whose various fixed parts become a scale of measurement for the persons acting upon it. This scale is always before the eye, and the disproportionate size of any superhuman figures makes beings that were grand in the poem monstrous on canvas. Minerva, on whom Mars had made the first attack, steps backward and with mighty hand lifts from the ground an enormous stone, black and rough, which, in old times, had required the strength of many men to be rolled into its place and set up as a landmark.[87]