Carpentry for Boys / In a Simple Language, Including Chapters on Drawing, Laying Out Work, Designing and Architecture With 250 Original Illustrations

by James Slough Zerbe

Fig. 132.

Shadows From a Solid Body.—We can understand this better by examining Fig. 129, which shows a vertical board, and a beam of light (A) passing downwardly beyond the upper margin of the board. Under these conditions the upper margin of the board appears darker to the vision, by contrast, than the lower part. It should also be understood that, in general, the nearer the object the lighter it is, so that as the upper edge of the board is farthest from the eye the heavy shading there will at least give the appearance of distance to that edge.

But suppose that instead of having the surface of the board flat, it should be concaved, as in Fig. 130, it is obvious that the hollow, or the concaved, portion of the board must intensify the shadows or the darkness at the upper edge. This explains why the heavy shading in Fig. 126 is at that upper margin.

Flat Effects.—If the board is flat it may be shaded, as shown in Fig. 131, in which the lines are all of the same thickness, and are spaced farther and farther apart at regularly increasing intervals.

Fig. 133.	Fig. 134.

The Direction of Light.—Now, in drawing, we must observe another thing. Not only does the light always come from above, but it comes also from the left side. I show in Fig. 132 two squares, one within the other. All the lines are of the same thickness. Can you determine by means of such a drawing what the inner square represents? Is it a block, or raised surface, or is it a depression?

Raised Surfaces.—Fig. 133 shows it in the form of a block, simply by thickening the lower and the right-hand lines.

Depressed Surfaces.—If, by chance, you should make the upper and the left-hand lines heavy, as in Fig. 134, it would, undoubtedly, appear depressed, and would need no further explanation.

Full Shading,—But, in order to furnish an additional example of the effect of shading, suppose we shade the surface of the large square, as shown in Fig. 135, and you will at once see that not only is the effect emphasized, but it all the more clearly expresses what you want to show. In like manner, in Fig. 136, we shade only the space within the inner square, and it is only too obvious how shadows give us surface conformation.