SECOND ENNEAD, BOOK EIGHT. Of Sight; or of Why Distant Objects Seem Small. 49 (OF PERSPECTIVE.) VARIOUS THEORIES OF PERSPECTIVE.

1. What is the cause that when distant visible objects seem smaller, and that, though separated by a great space, they seem to be close to each other, while if close, we see them in their true size, and their true distance? The cause of objects seeming smaller at a distance might be that light needs to be focussed near the eye, and to be accommodated to the size of the pupils50; that the greater the distance of the matter of the visible object, the more does its form seem to separate from it during its transit to the eyes; and that, as there is a form of quantity as well as of quality, it is the reason (or, form) of the latter which alone reaches the eye. On the other hand, (Epicurus) thinks that we feel magnitude only by the passage and the successive introduction of its parts, one by one; and that, consequently, magnitude must be brought within our reach, and near us, for us to determine its quantity.

QUALITY IS MORE ESSENTIAL THAN QUANTITY.

(Do objects at a distance seem smaller) because we perceive magnitude only by accident, and because color is perceived first? In this case, when an object is near, we perceive its colored magnitude; when at a distance, we perceive first its color, not well enough distinguishing its parts to gather exact knowledge of its quantity, because its colors are less lively. Why should we be surprised at magnitudes being similar to sounds, which grow weaker as their form decreases in distinctness? As to sounds, indeed, it is the form that is sought by the sense of hearing, and here intensity is noticed only as an accident. But if hearing perceive magnitude only by accident, to what faculty shall we attribute the primitive perception of intensity in sound, just as primitive perception of magnitude in the visible object is referable to the sense of touch? Hearing perceives apparent magnitude by determining not the quantity but the intensity of sounds; this very intensity of sounds, however, is perceived only by accident (because it is its proper object). Likewise, taste does not by accident feel the intensity of a sweet savor. Speaking strictly, the magnitude of a sound is its extent. Now the intensity of a sound indicates its extent only by accident, and therefore in an inexact manner. Indeed a thing's intensity is identical with the thing itself. The multitude of a thing's parts is known only by the extent of space occupied by the object.

DIFFERENCES OF COLOR AID IN THE PERCEPTION OF MAGNITUDE.

It may be objected that a color cannot be less large, and that it can only be less vivid. However, there is a common characteristic in something smaller and less vivid; namely, that it is less than what it is its being to be. As to color, diminution implies weakness; as to size, smallness. Magnitude connected with color diminishes proportionally with it. This is evident in the perception of a varied object, as, for instance, in the perception of mountains covered with houses, forests, and many other objects; here the distinctness of detail affords a standard by which to judge of the whole. But when the view of the details does not impress itself on the eye, the latter no longer grasps the extent of the whole through measurement of the extent offered to its contemplation by the details. Even in the case where the objects are near and varied, if we include them all in one glance without distinguishing all their parts, the more parts our glance loses, the smaller do the objects seem. On the contrary, if we distinguish all their details, the more exactly do we measure them, and learn their real size. Magnitudes of uniform color deceive the eye because the latter can no longer measure their extent by its parts; and because, even if the eye attempt to do so, it loses itself, not knowing where to stop, for lack of difference between the parts.

DISAPPEARANCE OF THE FORM IMPLIES THAT OF THE SIZE.

The distant object seems to us close because our inability to distinguish the parts of the intervening space does not permit us to determine exactly its magnitude. When sight can no longer traverse the length of an interval by determining its quality, in respect to its form, neither can it any longer determine its quantity in respect to magnitude.

REFUTATION OF ARISTOTLE'S "VISUAL ANGLE" THEORY.

2. Some51 hold that distant objects seem to us lesser only because they are seen under a smaller visual angle. Elsewhere52 we have shown that this is wrong; and here we shall limit ourselves to the following considerations. The assertion that a distant object seems less because it is perceived under a smaller visual angle supposes that the rest of the eye still sees something outside of this object, whether this be some other object, or something external, such as the air. But if we suppose that the eye sees nothing outside of this object, whether this object, as would a great mountain, occupy the whole extent of the glance, and permit nothing beyond it to be seen; or whether it even extend beyond the sweep of the glance on both sides, then this object should not, as it actually does, seem smaller than it really is, even though it fill the whole extension of the glance. The truth of this observation can be verified by a mere glance at the sky. Not in a single glance can the whole hemisphere be perceived, for the glance could not be extended widely enough to embrace so vast an expanse. Even if we grant the possibility of this, and that the whole glance embraces the whole hemisphere; still the real magnitude of the heaven is greater than its apparent magnitude. How then by the diminution of the visual angle could we explain the smallness of the apparent magnitude of the sky, on the hypothesis that it is the diminution of the visual angle which makes distant objects appear smaller?

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