In 1904 Terrot bought the patents to Edmund Hodkinson’s Gradient derailleur design and marketed a developed version in 1905 as the Terrot ‘Modèle H’ (for ‘Hodgkinson’). This was a three speed system, with chain lifters, in which the chain stayed in line and the cogs moved sideways.
The operation of the gears seems to be basically similar to that of Edmund Hodgkinson’s original designs, with a chain lifting device operated by back-pedalling, and a block of cogs that could then be moved from side to side. Forward pedalling then cleared the chain lifter and dropped the chain onto the chosen cog. The main development introduced by Terrot in this patent appears to be that the cogs are shifted laterally using a toggle chain on the non-gear side, running through a hollow axle. Hodgkinson had used a variety of plates and levers on the gear side to shove the cogs sideways. This is all an eery precursor of the route taken by TriVelox 20 years later - who also started using a plate on the gear side to move their cogs sideways and then adopted a toggle chain system on the non-gear side running through a hollow axle.