I am not entirely sure what is going on in this patent - but Boizot seems to be proposing a system in which a derailleur with a pulley cage holding two pulleys moves a chain laterally across a multiple freewheel - much as in a modern derailleur.

However there also seems to be some kind of pawl mechanism (items E, F & H on the drawings) that may be designed to temporarily reduce the chain tension at the instant of shifting. The exact operation of this device remains a mystery to me.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Société Charles Boizot et Cie
• Country: France
• Date: French application June 1910
• Derailleur brands: Boizot
• Derailleurs: Boizot 2 speed, Boizot Tri-direct?