above the horizon at L·, on the right of the picture and behind the spectator (Fig. 276). If we transport the length L·f· to the opposite side and draw the vertical downwards from the horizon, as at FL, we can then suppose point L to be exactly opposite the sun, and if we make that the vanishing point for the sun's rays we shall find that we obtain precisely the same result. As in Fig. 277, if we wish to find the length of C, which we may suppose to be the shadow of P, we can either draw a line from A through O to B, or from B through O to A, for the result is the same. And as we cannot make use of a point that is behind us and out of the picture, we have to resort to this very ingenious device.
Fig. 276.
In Fig. 276 we draw lines L1, L2, L3 from the luminary to the top of the object to meet those drawn from the foot F, namely F1, F2, F3, in the same way as in the figures we have already drawn.
Fig. 278 gives further illustration of this problem.
Fig. 278.