The perspective drawings prepared by architects sometimes have the principal lines put in by the rules of geometrical perspective as taught in the art schools, but usually they are found by a special method shown in the accompanying diagram, where a very simple building is chosen to indicate the course pursued. The drawings being often on separate sheets, the plan is first fastened down on the table by drawing-pins. A suitable point of view is then selected, and a common pin stuck in to represent the spectator. A narrow strip of paper is now fixed by two drawing-pins, and a line ruled upon it in the position chosen for the transparent plane, or picture plane, which should touch the nearest angle of the building, and a straight-edge is used to mark lines across the picture plane from the pin to all the chief angles of the plan, as on line a b, writing the names against the chief ones so as to know one from the other. A line representing the ground line is then drawn below the position of spectator, as if the view were a section, vertical lines drawn from the corners of the building, and the heights of the angles set off above the ground line. Dotted lines are now drawn from the extremities of these to the pin, cutting the picture plane in the points marked.

Now, for the perspective, take a clean sheet of paper, and fasten it down on a drawing-board, pin the strip of paper a b horizontal near the bottom edge, and project vertical lines from the points which represent the angles of the building. Decide where the bottom of the nearest angle in the perspective shall be, and above it set off the heights where the dotted lines crossed the picture plane, measured from b, and from them draw horizontal lines to intersect vertical lines drawn from ab. Join the intersections, and the two visible sides of the house will be obtained. Produce these to intersect on each side, and the two vanishing points will be found. For the remainder draw vertical lines from any given points on ab, such as c d, set up the height of the parts on the front angle of the perspective, such as e f, place a straight-edge from these points to line with the vanishing point, and the intersection witli the vertical lines will give the required perspective. Geometrical perspective is useful as giving a scientific foundation and reason for the appearances of objects of all kinds when viewed naturally by the eye.

Ordinary drawings of buildings and details are merely conventional representations, and although they may be looked upon as flat models, and are most useful, they do not represent things as they are seen. Architects' perspective is an empirical or "rule of thumb" method suited to the circumstances, but not available as a basis for the general study of the subject.

Architects' Perspective Drawings.