1937 Claud Butler "Tour D'Angleterre"
This bike is what you might have seen if you attended the 1937 Tour de France. Incidentally this is the first year that Derailleurs were allowed in competition. The derailleur on this machine is called an Osgear and is an unrefined fork that moves the chain back and forth on the sprocket. The arm and jockey wheel mounted below the bottom bracket acts as a chain tensioner and is adjusted by a lever near the shifter. This was cutting edge bike technology at the time.