2Nothing requires the architect’s care more than the due proportions of buildings. When the proportions are adjusted, and the dimensions found by calculation, then it is the part of a skilful man to consider the nature of the place, the purpose of the building, and the beauty of it; and either by diminutions or additions to find expedients, by means of which the appearance may not be injured by the additions to, or diminutions of, the established proportions that may be necessary.
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.
3But whether the sight arises from the impression which images make on the eye, or by an effusion of visual rays from the eye, as naturalists contend, it is certain that, in some way or other, the eye is often deceived.
4Since, then, some images are falsely conveyed, and others appear different from what they really are, I think it beyond doubt, that, according to nature and the circumstances of the place, diminutions or additions should be made, so that no defect may be apparent. To do this, however, is the result of genius, not the result of learning.
5The proportion of the symmetries is, therefore, to be first settled, so that thereon the necessary changes may be made with certainty. Then the length and breadth of the plan of the work is to be set out, and the parts thereof; after which, the proportions are adjusted as propriety requires, so that the pleasing arrangement may not be disturbed. The method of effecting this I am now about to describe, and shall begin with the court (cavædium).