524 CALLOTECHNICS. 



form the perspective required. Hence, a simple mode of drawing 

 in perspective, consists in using a vertical frame, divided by cross 

 threads into small squares, with a sight vane placed behind it, to fix 

 the position of the eye while looking through it. The paper being 

 divided, by pencil lines, into corresponding squares, we have only to 

 draw in each of these, the objects which are seen in the correspond- 

 ing squares of the vertical frame ; which, from its use, is called a 

 perspectograph. 



In perspective, objects appear smaller when they are more distant; 

 and their appearance changes, as we change our point of view. When 

 a near object hides a more remote one, the part which is hidden, is 

 not represented; as the nearer object fills its place. In general, lines 

 which are truly vertical, are drawn vertical in the picture ; but hori- 

 zontal lines appear oblique, unless they are precisely on the level of 

 the eye, or else parallel to the plane of the picture. If they are 

 above the level of the eye, their farthest end appears the lowest: 

 otherwise the effect is reversed. Lines which are truly parallel, and 

 recede from the observer, are drawn converging, in perspective, to- 

 wards their vanishing point, at which, if they were infinitely pro- 

 longed in reality, they would all appear to meet upon the picture. A 

 line drawn through the eye, and parallel to them, will meet the per- 

 spective plane, or picture, in their vanishing point, which is thus 

 found. Objects seen obliquely, appear smaller than their real size; 

 and are then said to be foreshortened ; as when a carriage wheel, 

 seen obliquely, is represented by an ellipse ; or a square represented 

 by a trapezoid. Of the general principles of design, or composition, 

 we have no room here to speak. 



2. The art of Shading, called by the French clair-obscure, 

 and by the Italians, chiaro oscuro, consists in making the different 

 parts of the picture either light or dark, according to the actual 

 appearance of the objects represented ; that is, in expressing the 

 lights, shades, and shadows, which depend on the direction and in- 

 tensity of the light. The lights, technically so called, are the 

 brightest parts of a picture : the shades, are those parts of objects 

 which are turned from the light ; and the shadows, are those parts 

 from which the light is intercepted by some other object. The 

 middle tints, are intermediate between the lights and shades ; and 

 the reflected lights, are diminutions of the shade, produced by reflec- 

 tion from adjacent objects. The brilliant points, or parts, are those 

 which reflect their light directly to the eye ; being the very brightest 

 parts of the picture. The dead points, are those which receive no 

 light, either direct or reflected ; and hence are the darkest parts of 

 the picture ; by which all the other shading should be adjusted. 



The shading is easiest, and most distinct, when all the objects are 

 lighted from only one source ; as the sun, or an elevated window : 

 by which cross lights are avoided. In rounded bodies, the shades 

 vary gradually: but in angular bodies the transitions are often abrupt, 

 and extreme. Shadows generally terminate gradually ; and the faint, 

 indistinct edge, in which the transition takes place, is called the 

 penumbra. A bright object, seen in front of a dark one, that is, on 

 a dark ground, appears to stand out from the picture, and is then 



