Apparently these are millennia old in concept. The fancy thing about the new version is the steel cylinder inside, I guess. And also that it got news coverage, which reintroduced the idea recently enough for it to hit my brain.
Apparently these are millennia old in concept. The fancy thing about the new version is the steel cylinder inside, I guess. And also that it got news coverage, which reintroduced the idea recently enough for it to hit my brain.