One interesting feature of this simple, rod operated, mechanism is that, as the pulley cage is moved inwards a simple angled slot in its bracket also moves it forward - tracking the profile of the freewheel in a simple way. All very simple - but possibly effective.
As an aside, it’s impressive that the St-Étienne patent office was still open at 17:58 on the 1st of February 1935 - a Friday. It seems unlikely that Friday was late opening night, so perhaps those long, lazy, lunch hours necessitated later closing.
Browse associated derailleurs.
BGA Velectrik 1935?