Rainbows as a sign of no more global floods--no wonder the Watchtower Society doesn't want people to be educated!
I remember a fifth grade science experiment. We would shine a beam of light through a prism, and look at the different colors of the rainbow. The scientific explanation is that each droplet acts as a prism, and the different colors are refracted to different degrees. Each color needs a certain angle. The sinbeam that reaches us comes from only one angle. So this is what produces the whole range of colors: light reaching us from different angles is from a different color. It also explains why the rainbow is an arc: that proper angle depends on where the sun is relative to the viewer. You can also notice a rainbow in a sprinkler or a waterfall where there is a lot of spray.
Now, what does this have to do with never having another Flood again? Nothing! Personally, I don't even believe in the first Flood, since the water could have never pushed down the rock (which is heavier and thus would have sank under the water). If the lighter water pushed down the continent to form a basin for the water to drain, then why didn't the heavier rock where there was mountains sink even more? All explaining why the Tower doesn't want you to do well in school--so you will believe their Hebrew myths instead of science.