As a preteen, Robert Brown took a scary dive for pearls in his grandfather's lake.
“You would be shocked to learn how fast you can make it to the bottom of a lake with a cinder block tied to your leg. I know this rate, by my own empirical investigation, to be thirty feet per second, give or take. If you’re in the mind to disconfirm this experimentally determined value, I will tell you how to repeat this experiment for yourself. First, convince yourself there are freshwater pearls in the mussels that live in your grandfather’s lake…”