When Joanny Panel decided that he wanted to offer an after-market derailleur to compete with Albert Raimond’s Le Cyclo, he adopted this design by Jean-Marie Dalibert, and marketed it as L’Izoard (named for the famous Alpine col).
Jean-Marie Dalibert had lost his left leg in the First World War but carried on cycling regardless, famously climbing the Grand Bois, a fearsome hill near Saint-Etienne, with the aid of his derailleur gears. He worked as a draughtsman at the Manufacture National d’Armes de Saint-Etienne alongside Claudius Boullier.
The L’Izoard derailleur is the earliest bell-crank design that I am aware of, making for a rather advanced top-normal derailleur with touring capacity. The patent drawings show a 13 to 24 teeth 3 speed freewheel, although I believe that the L’Izoard was offered as part of either a two speed or a three speed kit.
This is the first of Jean-Marie Dalibert’s two derailleur patents (the other is French patent # 642,104). This one describes the shift mechanism and shows Dalibert’s original mounting bracket and spring placement.