Terrot’s first derailleur design, the 1905 Terrot Modèle H was a cleaned up version of Edmund Hodkinson’s Gradient. This was a three speed system, with chain lifters, in which the chain stayed in line and the cogs moved sideways. Back pedaling lifted the chain off the current in-line sprocket, you then shifted the sprockets so that your chosen gear was in-line and forward pedaling dropped the chain back onto the newly aligned sprocket.
Terrot’s second derailleur design, covered in this patent, was for the Terrot Numéro 1. This very simple model owed more to the Whippet New Protean than to Edmund Hodkinson’s Gradient. It used a conventional (in modern terms) two speed sprocket that did not move from side to side and had the larger cog closest to the spokes and the smaller cog closest to the frame. It had a metal ‘hook’, through which the chain ran, which shoved the chain sideways, moving it onto the other sprocket.
In the patent drawing the chain is shown as tensioned by a cunning three pulley system. In production Terrot used a two pulley system that was very modern in style.
Finally the larger cog is described as having special shifting areas, with one or more teeth missing and the adjacent teeth slightly bevelled.