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that part of the sphere influenced by reflected light, which it could not have possessed if the shade tint had been extended to its circumference. Very little shade should be suffered to reach the outlines even of rough circular bodies, lest the coloring look harsh, and present a coarse appearance quite at variance with its natural aspect. Shadows also become lighter as they recede from the bodies which cast them, owing to the increasing amount of reflection which falls on them from surrounding objects.

Shadows appear to increase in depth as their distance from the spectator diminishes. In nature this increase is only appreciable at considerable distances. Even on extensive buildings, inequalities in the depth of the shadows are hardly perceptible; much less, then, can any natural gradation present itself in the shadows on a machine, which, supposing it to be of the largest construction, is confined to a comparatively small space. It is most important, however, for the effective representation of machinery, that the variation in the distance of each part of a machine from the spectator should at once strike the eye; and an exaggeration in expressing the varying depths of the shadows is one means of effecting that object. The shadows on the nearest and most prominent parts of a machine should be made as dark as color can render them, the colorist being thus enabled to exhibit a marked difference in the shadows on the other parts of the machine as they recede from the eye. The same direction is applicable in reference to shades. The shade on a cylinder, for instance, situated near the spectator, ought to be darker than on one more remote; in fact, the gradation of depth for the shades follows that which depicts the shadows. As a general rule, the color on a machine, no matter what it may be intended to represent, should become lighter as the parts on which it is placed recede from the eye.

Plates VII. and VIII. present some very good examples of finished shading.

Plate VII. represents, both in elevation and plan, different solids varıously penetrated and intersected. The rules for the projection of these solids have been given under the head of Geometrical Projection, and illustrated in plates IV., V., VI., and VII. They are selected with a view of exhibiting those cases which are of most frequent occurrence, and at the same time elucidating the general principles of shading.

Plate VIII. presents examples of shading and shadow.

Fig. 1 represents a hexagonal prism surmounted by a fillet. The most noticeable part of this figure is the shadow of the prism in the plan view. It presents a good example of the graduated expression which should be

given to all shadows cast upon plain surfaces. Its two extremities are remarkably different in their tone. As the shadow nears the prism, it increases rapidly in depth; on the contrary, as it approaches the other end, it assumes a comparatively light appearance. This difference is doubtlessly a great exaggeration upon what it would naturally display. Any modification of it, however, in the representation would destroy the best effect of the shadow.

The direction which the shades and shadows take in all the plans of the figures in this plate, is from the left hand lower corner. This is rigorously correct, supposing the objects to remain stationary, whilst the spectator views them in both a vertical and horizontal position. Nevertheless, to many, this upward direction given to the shadows has an awkward appearance, and, perhaps, in the plan of an entire machine, the shadows may look better if their direction coincide with that which is given to them in the elevation. If, however, the shadows be correctly projected, their direction is an arbitrary matter, and may be left to the taste of the draughtsman.

Figs. 2, 3, and 6 exemplify the complex appearance of shade and shadow presented on concave surfaces. It is worthy of particular notice, that the shadow on a concave surface is darkest towards its outline, and becomes lighter as it nears the edge of the object. Reflection from that part of the surface on which the light falls most powerfully causes this gradual diminution in the depth of the shadow, the greatest amount of reflection being opposite the greatest amount of light.

It may be as well to remark here, that no brilliant or extreme light should be left on concave surfaces, as such lights would tend to render it doubtful at first sight whether the objects represented were concave or convex. After the body-color-which shall be treated in a subsequent section-has been put on, a faint wash should be passed very lightly over the whole concavity. This will not only modify and subdue the light, but tend to soften any asperities in the tinting, which are more unsightly on a concave surface than on any other.

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The lightest part of a sphere (fig. 4) is confined to a mere point, around which the shade commences and gradually increases as it recedes. point is not indicated on the figure referred to, because the shade tint on a sphere ought not to be spread over a greater portion of its surface than is shown there. The very delicate and hardly perceptible progression of the shade in the immediate vicinity of the light point should be effected by means of the body-color of the sphere. If, for instance, the material of which the sphere is composed be brass, the body-color itself should be

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