We have seen that when the sun's altitude is at an angle of 45° the shadows on the horizontal plane are the same length as the height of the objects that cast them. Here (Fig. 270), the sun still being at 45° altitude, although behind the picture, and consequently throwing the shadow of B forwards, that shadow must be the same length as the height of cube B, which will be seen is the case, for the shadow C is a square in perspective.
Fig. 270.
To find the angle of altitude and the angle of the sun to the picture, we must first find the distance of the spectator from the foot of the luminary.
| Fig. 271. |
From point of sight S (Fig. 270) drop perpendicular to T, the station-point. From T draw TF at 45° to meet horizon at F. With radius FT make FO equal to it. Then O is the position of the spectator. From F raise vertical FL, and from O draw a line at 45° to meet FL at L, which is the luminary at an altitude of 45°, and at an angle of 45° to the picture.
Fig. 272 is similar to the foregoing, only the angles of altitude and of the sun to the picture are altered.