2760. Then again one might find a monument painted on the far right hand side of a painting, an Obelisk of example, and the shadow it casts runs out from the monument to the right. In the same painting on the other side of the picture there might be a dog relieving himself on a rock and both the dog and the rock cast their shadows to the left, in the opposite direction as the obelisk.
Now, the reason the shadow on the right of the picture goes off to the
right and the reason the shadow on the left goes off to the left has a
simple explanation that almost every painter knows, but it is not what
you would expect.
Shadows are hard to paint because they have a tendency to look like a
misshapen old rugs spread out at the foot of some object. Since this is
often a problem, painters are in the habit of making their shadows as
short and as small as possible, and what better way that to have the
shadow exit right out of the picture by way of the nearby frame.
2763. In this way the shadow, so difficult to paint, leaves the stage of the painting, like a bad actor with a small part, slipping away from the stage by way of the nearest wing.