‹‹‹ Vitr. 6.2.1 | Table of Contents | Vitr. 6.2.3 ›››
2For an object under the eye will appear very different from the same object placed above it; in an inclosed space, very different from the same in an open space. In all these matters it requires great judgment to adopt the proper means, since the eye does not always form to itself the true image of an object, and the mind is often deceived by the false impression. Thus in painted scenery, though the surface is a perfect plane, the columns seem to advance forward, the projections of the mutuli are represented, and figures seem to stand out. The oars of ships, also, though the parts immersed in the water are really straight, have the appearance of being broken; those parts only appearing straight which are above the level of the water. This arises from the part immersed in the water reflecting its image in an undulating state up to the surface of the water, through a transparent medium, which, being there agitated, gives the oar a broken appearance.
2The look of a building when seen close at hand is one thing, on a height it is another, not the same in an enclosed place, still different in the open, and in all these cases it takes much judgment to decide what is to be done. The fact is that the eye does not always give a true impression, but very often leads the mind to form a false judgment. In painted scenery, for example, columns may appear to jut out, mutules to project, and statues to be standing in the foreground, although the picture is of course perfectly flat. Similarly with ships, the oars when under the water are straight, though to the eye they appear to be broken. To the point where they touch the surface of the sea they look straight, as indeed they are, but when dipped under the water they emit from their bodies undulating images which come swimming up through the naturally transparent medium to the surface of the water, and, being there thrown into commotion, make the oars look broken.