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light fall upon an object, and in order to make the shading of drawings consistent and systematic, the rays of light must always be considered as coming from a given direction, and after determining upon the direction in which they are to come, it should not be changed.

On this work, light may be assumed to come from the upper left hand corner of the drawing board, parallel with the surface of the board, and at an angle of 45 degrees with the horizontal and vertical lines of the drawing.

These rays of light are represented by the arrowheads of Nos. 1 and 2 in Figs. 58 and 59.

Any surface which these 45-degree lines strike is a light surface, and one which they do not strike is a dark surface. The line of intersection of two light surfaces is a light line, and not shaded, but the line of intersection of a light and a dark surface, or of two dark surfaces should be shaded.

Lines in the drawing which are drawn at 45 degrees and parallel with the rays of light are

never shaded. Referring again to No. 1, of Fig. 58, it will be seen that light strikes the lines A B and A C, which are therefore light lines, but because the object itself presents an obstacle to the further passage of light, the lines B D and C D are dark, and therefore shaded. In the same way we account for the light and heavy lines in No. 2. In No. 2 it will be observed that the arrowhead passing through the corner G would strike the line H K at Y. It will be asked why H K is not shaded above Y, as the lines of light do not strike it. According to what we have said on the subject, this should follow, but it will be seen that a line partly heavy and partly light would not look well, and, therefore, for the sake of preserving the system, a line of this kind and in such location is made light.

Another contradiction arises of a simi. lar nature, in connection with Nos. 3 and 4.

It would rightly be argued that owing to the wall or shell surrounding the hole, no light would strike the lines representing the rectangular hole, and therefore all four of those lines should be dark.

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1 of Fig. 59, the same difficulties or apparent contradictions arise that we have already mentioned. In such a case as this, in order to preserve the uniformity of the system, each branch must be considered entirely by itself, and then there will be no trouble.

In this figure, the lines A O, BO, CO, and DO, also the four lines, EO, FO, GO and H O are drawn at 45 degrees. The first four are drawn parallel to the direction of the rays of light, and are therefore not shaded, but in the case of the latter four, although drawn at 45 degrees, they are not parallel to the rays of light, and should therefore be treated as any other lines would.

In the case of the shading of circles, the reasoning is no different from that followed in the shading of straight lines. Those rays that strike the circle on a tangent determine the points at which the shading should begin. In shading a circle, draw in the light circle first, then with the same radius take a new center at an angle of 45 degrees from the first center, the distance between the two centers determining the width of the shade line at its widest point.

In No. 2, the second center is taken above, and in No. 3 below the first center. In putting in the second circle, use the same size of line as in the first, and fill in the space between them. In Fig. 60 we give exercises in shading, which will serve to show how the principles which we have discussed above, are applied on the shading of plumbing drawings.

In putting in the shade lines, they are usually drawn heavy at the outset, but it may possibly bə easier for beginners to ink their drawings in the usual way, and then go over the lines to be shaded afterward, making them several times heavier than the light lines. If those who do not take up the inking care to do so they may shade their pencil drawings by using on the heavy lines a very soft pencil.

In inking shaded drawings it is customary to put in the light horizontal lines first, then the heavy lines, and so with the vertical lines. This method will save the trouble of changing the adjustment on the pen so frequently, and will result in more even work.

FIG.60.

method followed in Nos. 3 and 4. Comparing Nos. 1 and 3, it will be seen that lines shaded in the one are light in the other, also in the case of Nos. 3 and 4. In No.

Fig. 61.

It will be found that very often a drawing will look better if the finer work, such as the supply pipes, etc., are not shaded, only the fixtures and larger connections being thus treated.

In Fig. 61 we give the elevation of the

plumbing system for a cottage house, the work being shaded. This is the first complete elevation that we have given as an elevation, but we believe that those who have followed foregoing instructions will have no dificulty in making this drawing.

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CHAPTER XII
HE method of shading which we

gave in the preceding chapter is
easy to handle, and it certain-

ly is of value in making the drawing very clear and distinct. There is also another method of shading, which, however, is much more difficult of execution.

This style of shading we show in Figs. 62, 63 and 64, and in order to be able to use it to good effect, considerable expe rience and practice is necessary. It is used more for ornamental purposes than for practical purposes, but still, no book on drawing would be complete without some attention to it. It is seldom or never that a drawing of any extent would be shaded throughout in this manner, but our readers will find, if they do much in the way of drawing, that its use will often be a valuable aid in showing up apparatus of different kinds, portions of plain drawings that are desired to be brought out with great clearness, etc.

In the use of this shading, there are exact rules that are laid down as to the point which should be shaded heaviest, as well as lightest. It will be sufficient, however, for our purposes to make this instruction very brief and to the point.

The results seen in Nos. 1 and 2, of Fig. 62, are obtained by giving the greatest shade effect to the right hand side of the figure, the lightest point being about midway, and the left hand side being shaded somewhat, though not so heavily as the right hand side. These two figures represent solid cylindrical figures. No. 3, a hollow cylindrical figure is shaded in exactly an opposite manner, that is, with the heaviest shading at the left, medium shade effect at the right, but with the lightest point still near the center. No. 4, a horizontal solid cylinder, is shaded

No 2.

No 3.

FIG. 63.

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