This advert is the earliest mention, that I am aware of, of the Boizot 4 speed derailleur. I believe that, like the Boizot 5 speed system, the 4 speed system used a chainwheel that moved sideways to provide a straighter chainline.

The text appears to suggest that Boizot can offer a choice of 2, 3, 4, 5 or 6 speed gear systems set up with the développements you desire (in increments of 0.20 metres). That is is quite an offer.

(Source gallica.bnf.fr/ Bibliothèque nationale de France)

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• Publisher: T.C.F. Revue Mensuelle
• Country: France
• Date: March 1913
• Derailleur brands: Boizot
• Derailleurs: Boizot Bi-direct, Boizot Tri-direct, Boizot 4 speed, Boizot 5 speed