It is the most refrangible of the seven primary colors of the solar spectrum.
Whetstone.
What’s refrangible?
Bluegrass.
I know!
Whetstone.
Scythe.
Let me illustrate. You discover by a violet light a beautiful fish in the water, and you wish to catch it. Now, you must throw your hook, dart, or net, not directly at it, but a considerable space this side, according to the depth.
Whetstone.