1 AU parallel horizontal lines see in perspective tend to meet at a point on the horizon which we call the vanishing point. The only time this does not happen is when you stand at a point equidistant from both ends of any form having parallel lines. But since human eyes are not Hke those of a chicken, which can see out of both sides of its head, the minute you move your eyes to follow any lines that are parallel then you must be guided by the laws of linear perspective.
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2 Nature has given us the ability to see objects in three dimensions; consequently, we have to use at least two vanishing points in order to achieve the sense of the third dimension. (It is possible to have recourse to any number of vanishing points, as only objects in parallel rows have common vanishing points. But again, for our purposes this is a needlessly involved study.)
3 The laws of perspective dictate that all things of equal size will increase or diminish in the appearance of their measurements in proportion to their nearness or distance from the viewer. Thus, the nearest corner of any parallel structure (such as a house) must be longer from bottom to top than either of the farther corners. But since the sides of the canvas (or paper) on wliich we work remain parallel, hence per-spectivehj stationary, the movement of receding lines toward their vanishing points will induce a sense of interior space in pictures.
4 The vanishing points for horizontal lines always occur on the horizon, and the horizon is invariably at eye level, regardless of one's position. Those things which require you to look up in order to see them are above eye level, hence, rising above the horizon. The reverse is true of things which require your looking down upon them. When you have thoroughly learned to distinguish between these two you will have graduated from that class of beginners which draws things that are above eye level as though they were looking down upon them, or the other way around.
5 While it is possible in some cases to do so, it is usually best not to have both vanishing points occur within the drawing proper so as to avoid the compression of space in the composition that can result in perspectival distortion. Therefore, whenever you have occasion to use linear perspective make sure to keep one vanishing point on the drawing proper, with the other somewhere outside the margin.
6 The panoramic scene is ordinarily too vast and complicated for any practical use of linear perspective in its composition. It may, however, be visualized in terms of the huge checkerboard that I have outlined. Any successful painting of a panoramic scene must depend on the total unity of its conception with regard to color, form, and rhythm. Here it is well to remember the maxim: "Anything that doesn't help your picture, hurts your picture." Consequently, you should be careful to include only that which will make for a well integrated composition.
7 It is not necessary to employ linear perspective in all your composition. But wherever you are faced with the problem of getting things in your painting or drawing to lie flat or stand upright; or whether it is a question of things seen either above or below eye level, you can work these things out in separate practice drawings. For the rest, do not (as in the case of the talented young art student) confuse freedom of expression with the abandonment of knowledge. For knowledge is something to keep in your back pocket for every emergency. And you may be sure that there will be many an occasion when you will be grateful to have this knowledge.
