Back in the 70's there was a phenomenon called the "Great Bicycle Boom". Scads of citizens were becoming more conscious about fitness. Running and cycling were becoming extremely popular. Getting bicycles out into the public's hands was done through all sorts of channels. Hardware stores, traditional bicycle shops, and even gas stations were selling bicycles back then. The major catalog stores of the time: Sears, J.C. Penney's, and Montgomery Ward's were also selling bicycles. This one here is a J.C.Penney's rig. A five speed urban bike. (And maybe you thought urban bikes were something new? No, they were very popular then as well.)
This particular bicycle is approximately from the earlier part of the 70's. Even for that time, this bike was using an antiquated type of rear derailleur that works pretty well, actually. It uses a "dual pull" cable set up where the ends of the cable both terminate at the rear derailleur. Look closely at the rear of the mech here and you can see two cables entering. Now look below the "w" embossed on the parallelogram. There you can see the clamp that secures both ends of the cable.
Here is the underside of the shifter. The entire grip rotates to initiate shifts, much like a motorcycle throttle. I didn't crack open the housing, but I assume the mechanism pulls cable in either direction by some means. The screw at the bottom adjusts the friction feel of the shifter.
The shifter worked flawlessly and the feel is much like a down tube friction shifter. Of course, being a city bike, having the entire grip rotate isn't a performance issue like it might be on a mountain bike.
Here is a look at the cable entry points on the crusty looking derailleur. Two adjuster barrels, and the left part of the cable makes a near 90 degree bend over to the right there where both ends of the cable terminate.
Because there are two cables running the show, there is no spring in the parallelogram of the rear mech. You don't have to rely on a spring to pull the cable back through some potentially contaminated housings. It actually is a pretty cool idea for an urban commuter rig that is reliable in all sorts of conditions.
Not to mention the five speed rear freewheel and beefy chain, which would take nigh unto forever to wear out.
By the way, this bike worked perfectly well. I'm sure its owner will enjoy the upright seated position, and the smooth ride.