If the eye or observer E is lowered, the shortening of BC and AD will be even more noticeable. These two sides will become shorter and shorter. Indeed, if the eye E descends to point H, for example, the ray that transfers angle B₁ to the eye H will further approach the one that starts from angle C₁, and then the eye H will see the side BC no larger than C₁F, with point F hiding point B from view, and so on.

We see that, in perspective planes, the closer the plane is to the level of the eye, the more it is seen in foreshortening. The more lines CD and BA, for example, (fig. 2) parallel to each other and to eye H, seem to come closer to each other. On the contrary, the more the plane is below the eye level, the less foreshortening there will be, and it will appear more as it would if seen geometrically; more CD, BA will seem to distance themselves from each other.

This can be easily verified by the following experiment:

One places before oneself, horizontally, the square cardboard sheet that has already been used in the previous experiment. At the two furthest angles from the eye, at the angles B, and A, for example (fig. 2), one attaches, with a pin or otherwise, two threads, whose two ends are joined near the eye. At the other two angles C, D, two rods are fixed perpendicularly, which will be represented by the lines C₁ and D_mn. It will then be seen that the two threads, representing visual rays, will come to intersect these two rods more or less high, depending on whether the eye is higher or lower. The distance between the base of these rods and the meeting point of each of these threads, represented for the observer as the length of the sides CB and DA as they see it, will finally be how they must represent it when they wish to draw from life. The experiment is very easy indeed, and yet it is already a step forward in fact for Perspective.

Conversely, if a plane is positioned higher than the eye, one will not see above it, for the rays reporting the objects to the eye will always traverse a straight line. Eye A (fig. 3) will therefore not see above the plane B_CDF, since the ray that starts from eye A, after meeting angle C, passes above angle D. Therefore, one cannot see angle D; the same applies to angles B₁E; it results that eye A, not seeing above this plane, will see below it. Indeed, the ray B_A transfers angle B to eye A (fig. 4); the ray A transfers angle C; the rays D, A, E_f transfer angles D, E always to eye A. Since eye A sees the four angles B, C, D, E, it will see the plane below.

If this plane (still horizontal) was exactly at the height of the eye, one would see instead of a plane, just a horizontal line. In fact, the line C_B, which is horizontal for eye A, would fully hide line ED, again for eye A (fig. 4).

One could still use the threads and repeat the previously indicated experiment to accurately understand what we have just described.

Do not think that any line posed perpendicularly or vertically, like line A_B for eye B (fig. 5), undergoes no foreshortening. But any receding line, such as line AC that appears to move away for eye D, undergoes foreshortening: line AC will not appear longer than A_E to eye or observer D. The same applies to planes.

RECAPITULATION.

We have defined Drawing, and we have announced that one must practice drawing from life from the very first lesson, if one wants to be able to draw everything one sees, which is the only seriously useful aim one can propose when one has decided to learn Drawing.

After providing some indispensable preliminary notions, we have presented some General Principles of Drawing from Life. We have established:

1^° That the basis of drawing lies in distinguishing what one truly sees from what one thinks one sees, and that Drawing primarily involves the education of the eye; one must absolutely draw only what one sees.