The first gadget is by far the most important; it shows wave motion in two dimensions, at a 90 degree angle, the first is vertical and shows compression/expansi

The first gadget is by far the most important; it shows wave motion in two dimensions, at a 90 degree angle, the first is vertical and shows compression/expansion of the various wave constituent parts. The other is horizontal, and shows the apparency of wave motion. Observation: It should be possible to create spiral waves in space, using both principles...