the same distance from the first, as the first is from the eye, though they be of the same size, the second will appear half the size of the first; and, if the third be at the same distance behind the second, it will diminish two thirds; and so on, by degrees, they will, at equal distances, diminish in proportion; provided that the interval be not more than twenty cubits[1]; at which distance it will lose two fourths of its size: at forty it will diminish three fourths; and at sixty it will lose five sixths, and so on progressively. But you must be distant from your picture twice the size of it; for, if you be only once the size, it will make a great difference in the measure from the first to the second.
Chap. CXVI.—What Parts of Objects disappear first by Distance.
Those parts which are of less magnitude will first vanish from the sight[2]. This happens, because the shape of small objects, at an equal distance, comes to the eye under a more acute angle than the large ones, and the perception of them is less, in proportion as they are less in magnitude. It follows then, that if the large objects, by being removed to a great distance, and consequently coming to the eye by a small angle, are almost lost to the sight, the small objects will entirely disappear.
