Rainbow Generator
Rainbows can appear in the sky when there are water droplets in the air and sunlight shines from behind them at a low angle, a rare moment when the sun is out but it is also raining and that you happen to be standing in the right place to see it.
But they also can be generated artificially, by holding a prism at the right angle on a sunny day or when sunlight strikes the spray from a hose or a fountain in just the right way. It should be possible to do that predictably and automatically.
I can imagine a cellphone app that communicates with an intelligent fountain or hose. The app determines if and when the brightness of the sun at a particular place and the sun’s height in the sky make rainbow creation feasible. Then you turn on the water spray and the app prompts you to move closer or father, left or right, to the best position for viewing the rainbow.
Public venues often point spotlights at spray from fountains. A rainbow generator could produce a similar effect, but as if by magic — without spotlights, just with water droplets and the sun.
