19th Century technology sometimes involves large-scale bearings. I am curious about the "chariot"-style bearings used in lighthouse optics, and the similar bearings used to support rotating telescope domes.
See the illustration of the interior of an observatory dome here: https://www.dunsink.dias.ie/grubbtelescope/ The rotating dome sits on a circle of wheels.
The chariot-style lighthouse lens bearing is shown in this video: https://www.youtube.com/watch?v=6yCZlbND32o
The rotating structure that supports the wheels, in both cases, is a bit like the cage in a ball bearing. But I'm not sure whether there's any mechanical advantage to having it rotate freely. Why not fix the wheels to the object that is being supported? Is this something to do with rolling resistance, or is there some other advantage to mounting the wheels on a separate structure that rotates independently?