This very fine document is often regarded as the first real derailleur patent. It shows Jean Loubeyre‘s La Polyceler - a rod operated, fork type, 2 speed derailleur.
A notable feature is the double chain tensioner, with the usual tensioner on the bottom chain run, but also a second tensioner on the top chain run. I would speculate that this was because freewheels were relatively unknown in 1895 and La Polyceler used a twin fixed cog. It therefore required a tensioner that could cope with braking using the rear wheel.