Is this off the back of a video of a 1970s Open University style presenter showing the properties of isochromus curves - i loved watching it and realised that these are national treasures of programs - and also was quite stunned by the assumption one would have a round empty tobacco tin lying around to do the experiment with - times do chnage :-)
I suspect it is... It turned up in my YouTube suggestions yesterday. Here's a link: https://youtu.be/eBc827pwKf0
Seriously though, I would be weirdly fascinated to see what else you guys subscribe to and if there are any correlations to my subscriptions. I find this channelling people into little boxes fascinating, and those curves are also very cool.