It's a reminder how 20-20 hindsight makes solutions obvious. Most modern
cyclists probably think today's gear systems must be the only reasonable
possibility.
But many other schemes were tried before most people settled on
parallelogram derailleurs, tension cable with spring return, and two
sprung jockey wheels for tensioning the chain.
BTW, I've read that the "myth and lore" of the day held that chain
tension must be manually controlled so as to completely minimize it,
because _any_ excess tension in the lower run of chain would slow a
cyclist dramatically.
These days, we don't give that idea a thought. These ideas come and go.
--
- Frank Krygowski