ON MODELLING, PERSPECTIVE, EKGUAVING, AND PRINTING. 115 



proper outlines. Sometimes, for the delineation of large objects requiring 

 close inspection, it has been found useful to employ two similar frames, the 

 one a little smaller than the other, and placed at a certain distance from it, so 

 that every part of the object, when seen through the corresponding divisions 

 of both frames, appears in the same manner as if the eye were situated at a 

 very remote point. It was in this manner that the elegant anatomical figures 

 of Albinus were executed. (Plate VII. Fig. 99.) 



But if it be required to lay down, in the plane of a picture, the projection 

 of an object, of which the actual dimensions and situation are given, we may 

 obtain the requisite measures from the properties of similar triangles, and the 

 consideration of the rectilinear motion of light. We may consider our picture 

 as a reduced copy of a projection formed on an imaginary plane, which, a.» 

 well as the picture, is generally supposed to be in a vertical situation, and 

 which stands on the horizontal plane, at the point where the objects to be 

 represented begin. In order to find the position of the image of a given 

 right line, we must determine the point in which a line parallel to it, passing 

 through the place of the eye, cuts the plane of the picture; this is called the 

 vanishing point of the given line, and of all other lines parallel to it, since 

 the image of any such line, continued without limit, will be a right line di- 

 rected to this point, but never passing it. When the lines to be represented 

 are parallel to the picture, the distance of their vanishing point becomes in- 

 finite, and their images are also parallel to the lines and to each other. The 

 centre of the picture, or that point v/hich is nearest to the eye, is the vanish^ 

 ing point of all lines perpendicular to the picture; through this point it is 

 usual to draw a horizontal and a vertical line: we may then lay off downwards 

 on the vertical line the distance of the eye from the picture, in order to find 

 the point of distance, which serves to determine the position of any oblique 

 lines on a horizontal plane: for if we draw a ground plan of any object, cou- 

 siderijig the picture as a horizontal surface, we may find the vanishing point 

 of each of it s lines, by drawing a line parallel to it through the point 

 of distance, until it meets the horizontal vanishing line. (Plate VII. 

 rig. 100, 101.) , 



In order to find the position of the image of a given point of a line, wc 

 must divide the whole image in such a manner, that its parts may be to each 



