For 141 years, physicists like Richard Feynman have puzzled over a question of fluid flow: how would a sprinkler rotate if it were underwater, sucking in the stuff instead of spewing it? Now, a team ...

The image illustrates the experimental set-up: (a) Cut-away schematic of the floating sprinkler, (b) Flow control apparatus operating in suction mode, and (c) Flow imaging with a laser sheet ...