Gradient index optics demonstration.
https://www.youtube.com/watch?v=rnNjV3fh-4M
Previously:
https://www.homemadetools.net/forum/...271#post196135
https://www.homemadetools.net/forum/...458#post200680
https://www.homemadetools.net/forum/...906#post171516
https://www.homemadetools.net/forum/...584#post193345
https://www.homemadetools.net/forum/...814#post202245
