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Fig. 12 14 FIRST PRINCIPLES OF perpendicular to it. At a given distance to the right of VP, and perpendicular to HP, a staff S, surmounted by a small rectangular plate of any opaque material, and pierced with a sight-hole is fixed ; the height of this sight-hole from HP being supposed to equal that of an observer's eye from the ground. The sheet of glass VP being transparent, it is evident that the spectator, on looking through the sight-hole, will see the whole of the piece of fencing, and can judge of its appearance from the position occupied by his eye. If he wish for a record of this appearance he can obtain it by drawing on the glass what he sees through the sight-hole. The view he would get would be a perspective of the original object OO, or the fence. But its contour or outline on the glass, although similar, would be much smaller than its original. How much smaller, would entirely depend upon the distance between the eye at sight- hole, the sheet of glass VP, and the fencing OO. It is evident that the nearer VP is to OO, the eye remaining in the same position, the larger would be its image or picture upon VP, and the converse of this would obtain were the conditions reversed. It will be seen from the diagram that the perspective view of the original object is obtained by finding where the luminous or visual rays represented by broken lines proceeding from its principal points, are intercepted on VP in their passage to the eye, and then joining such points by right lines as in the original. Now, as these visual rays, or " projectors," are the means by which the view of the object is projected or thrown on VP, such a view is called a " projection," and in