Finally, time to get back to covering some old (by now) Mythbusters episodes. I’ll start with the bonus episode aired a few weeks ago, “Ping-Pong Rescue” — an oldie but a goodie in which the Mythbusters try to raise a boat with ping-pong balls and lift a child off the ground with balloons.

This episode was all about buoyancy, the physical description of how stuff floats. Buoyancy goes all the way back to one of the scientific world’s earliest experts, Archimedes. According to legend, he had been tasked with figuring out whether a crown, given as a gift to the king of Athens, was composed of pure gold or of other, less valuable materials with merely a gold coating. The straightforward way would have been to melt the crown down in order to make an accurate measurement of its volume and thus determine its density, but the king, for some reason, didn’t want his crown damaged and so melting it was out of the question.

The bright idea that Archimedes eventually came up with was — we think — based on a principle that now bears his name (Archimedes’ Principle): that the buoyant force on an object immersed in water …