The expedient to which painters have recourse to indicate that a certain character is supposed to be invisible, is a thin cloud veiling the side of the figure that is turned towards the other actors on the scene. This cloud seems at first to be borrowed from Homer himself. For, when in the confusion of battle one of the chief heroes becomes exposed to a danger from which nothing short of divine aid can save him, the poet makes his guardian deity veil him in a thick cloud or in darkness, and so lead him from the field. Paris is thus delivered by Venus,[90] Idæus by Neptune,[91] Hector by Apollo.[92] Caylus never omits strongly to recommend to the artist this mist or cloud, whenever he is to paint pictures of such occurrences. But who does not perceive that this veiling in mist and darkness is only the poet’s way of saying that the hero became invisible? It always seems strange to me, therefore, to find this poetical expression embodied in a picture, and an actual cloud introduced, behind which, as behind a screen, the hero stands hidden from his enemy. This was not the poet’s meaning. The artist in this exceeds the limits of painting. His cloud is a hieroglyphic, a purely symbolic sign, which does not make the rescued hero invisible, but simply says to the observers,—“You are to suppose this man to be invisible.” It is no better than the rolls of paper with sentences upon them, which issue from the mouth of personages in the old Gothic pictures. Homer, to be sure, makes Achilles give three thrusts with his lance at the thick cloud[93] while Apollo is carrying off Hector,—τρὶς δ’ ἠέρα τύψε βαθεῖαν. But that, in the language of poetry, only means that Achilles was so enraged that he thrust three times with his lance before perceiving that his enemy was no longer before him. Achilles saw no actual cloud. The whole secret of this invisibility lay not in the cloud, but in the god’s swift withdrawal of the imperilled hero. In order to indicate that the withdrawal took place so instantaneously that no human eye could follow the retreating form, the poet begins by throwing over his hero a cloud; not because the by-standers saw the cloud in the place of the vanished shape, but because to our mind things in a cloud are invisible. The opposite device is sometimes used, and, instead of the object being made invisible, the subject is smitten with blindness. Thus Neptune blinds the eyes of Achilles when he rescues Æneas from his murderous hands by transporting him from the thick of the contest to the rear.[94] In reality, the eyes of Achilles were no more blinded in the one case than in the other the rescued heroes were veiled in a cloud. Both are mere expressions employed by the poet to impress more vividly on our minds the extreme rapidity of the removal; the disappearance, as we should call it.