Robert Esnault-Pelterie.
Image: US Library of Congress.

On this date in 1931, French experimenters Robert Esnault-Pelterie and Jean-Claude Barre begin their experiments with liquid propellant rocket engines. Despite Esnault-Pelterie losing the fingers of his left hand in a laboratory explosion three weeks later, he and Barre continue their efforts. A short essay about Pelterie and his work is available here.