This is the earliest patent for a derailleur that I have found that is held by Albert Raimond, the ‘patron’ of Cyclo and one of the titanic figures of derailleur history.
I am not entirely clear what genuinely original ideas are added to Claudius Bouillier’s 1924 patent - but it’s now a 3 speed and has some nice touches like the flanged polygonal tension pulley. The operating mechanism has also been turned around - with the peg now mounted on the main axle and the spiral cut into the sleeve instead of vice-versa.
Browse associated derailleurs.
Cyclo Standard 1932