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SHADES AND SHADOWS In order to prepare sketches and make them attractive, a brief treatment of Shades and Shadows will be taken up, the main general rules and principles being explained, which may he applied to ordinary architectural drawing.

By the use of shades and shadows, very im portant effects are produced. The general pro portions of the cornice, for example, are empha sized by using shadows. The relative amount of window area to wall area is clearly shown by the use of shadows.

The light is always assumed as coming over the left shoulder of the person looking at the drawing, and at an angle as explained later. This assumption is always made, being merely a conventional or customary way of considering the light. The idea intended is to produce the same effect on a drawing that the sun in this one position would produce on the building. While the sun would actually produce a shadow on one side of the building at one time, and on another side at another time, in architectural drawing this variation is not shown. No matter what elevation or side of the building is being considered, the light is always from the same direction.

Thus we see that in Figs. 24 and 25 the sun really would make one side always in shadow, but we do not so consider it. In Fig. 24 we see the side A is in sunlight, and the side B is in shade. Looking now at Fig. 25, we see side B in sunlight, and C, which was the rear end, now in shade. This is the conventional method of considering the rays of light for architectural drawings. No matter what elevations or draw ings are considered, or how many of the same building on the same sheet, the direction of the rays of light is fixed.

Perhaps it will make the understanding of this subject clearer if we define the terms shade and shadow. That portion of a building or drawing is said to be in "shade" which is turned away from the assumed rays of light; or, it receives no rays of light, in contrast to the sides which are in light or upon which the light falls.

If a body is placed between the light and a plane upon which the rays might fall, such a body will prevent a portion of the rays from striking the plane, thereby causing a shadow upon the plane.

All rays of light are assumed as parallel and considered as straight lines.

The rays of light are assumed as coming over the left shoulder, or sloping downward and backward. This is the diagonal of a cube. The projections of this diagonal in the vertical plane and in a horizontal plane are at 45 degrees, while the true angle of the diagonal with the plane is slightly less than 35 degrees 16 minutes. If we assume the side of the cube as 1, then the true length of this diagonal is nearly one and three quarters. In Fig. 26, we see the cube and the diagonal drawn as a heavy line with an arrow head indicating the direction of the light. Fig. 27 shows the elevation and plan of the same cube.

The shadow of a point is where the ray of light surrounding the point intersects the plane upon which the shadow falls. In Fig. 28, we see the light surrounding the point, and inter secting the plane, giving the shadow of the point upon the plane. The shadow is located as far down and as far to the right of the point in space as the point is from the surface or plane upon which its shadow falls. Fig. 29 shows the plan of the point, its distance from the plane, and the plane.

The shadow of a straight line in space is the intersection of the light surrounding this line with the plane of shadow. By casting the shad ows of the extremities of the line and connecting these points of shadows, we have the shadow of the line. All points of the line in space will cast shadows upon the plane as far down and as far to the right as the point is from the plane.

If the line is parallel to the plane, the shadow will be equal in length and parallel to the line itself. See Fig. 30 for an elevation, and Fig. 31 for the plan of the line and plane.

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