By this time our experiment, which started out so simply, has become perhaps a little puzzling to follow. But I don’t mind if it has; for I wish you to realise that, although this matter of direction and angles is simple in principle, it works out in a very complicated way. The more we realise this, the more we shall realise the wonderful effects of light upon color. As a beginning, let us imagine that the hub of the wheel is a center of heat, white-hot, and that the spokes are rays of light, not stationary like the woodwork but travelling outward at great speed. The shaft of light that runs straight down and strikes the ground at right angles to the surface, would make the spot where it touches very bright. The second shaft, however as it reaches the ground further off from the hub will illumine the spot with less light. Moreover, since it hits an acute angle and is travelling fast, some of it will glance off the spot. It will be reflected from the surface back and forth, somewhat as a ball is tossed backwards and forwards from the hands of a group of children.