562. - The Art of Drawing consists in representing solids Upon a plane surface, so that a curious and nice adjustment of lines is made to present the same appearance to the eye as does the human figure, a tree, or a house. It is by the effects of light, in its reflection, shade, and shadow, that the presence of an object is made known to us; so upon paper it is necessary, in order that the delineation may appear real, to represent fully all the shades and shadows that would be seen upon the object itself. In this section I propose to illustrate, by a few plain examples, the simple elementary principles upon which shading, in architectural subjects, is based. The necessary knowledge of drawing, preliminary to this subject, is treated of in Section XV., from Arts. 487 to 498.