Seatpost that allows the effective ST angle to be adjusted while riding:



The bike it's on was custom built in '72 by Singer for Jerry Collier, who assembled it with lots of esoteric parts he'd collected over decades, so no telling when the post was made. '50s maybe? I hung out with Jerry a lot in the '70s (and drooled on this bike) but if I ever asked about the seatpost, I don't remember what he said.

I wouldn't be surprised if Daniel Rebour drew it BITD. Check Heiko Strömer's Rebour archive maybe?

Bike now belongs to Jerry's old friend Nelson Miller. See it here (Flickr) and then waste hours looking through all Nelson's other albums, it's a treasure trove.