The Universe of Discourse

Why no disco balls

A couple of months ago I asked why the disco ball had to wait until the 20th century:

The 17th century could produce mirrors by gluing metal foil to the back of a piece of glass, so I wonder why they didn't. They wouldn't have been able to spotlight it, but they certainly could have hung it under an orbiculum. Was there a technological limitation, or did nobody happen to think of it?

I think the lighting issue is the show-stopper. To make good use of a disco ball you really do need a dark room and a spotlight. You can get reflections by hanging the ball under an orbiculum, but then the room will be lit by the orbiculum, and the reflections will be pale and washed out, at best.

Long ago I attended a series of lectures by Atsushi Akera on the hidden prerequisites for technological adoption. For example, you can't have practical skyscrapers without also inventing elevators, and you can't have practical automobiles without also inventing windshield wipers. (And windshields. And tires. And … )

This is an amusing example of the same sort. You can't have practical disco balls without also inventing spotlights.

But now I kinda wonder about the possibility of wowing theatre-goers in 1850 with a disco ball, lit by a sort of large hooded lantern containing a limelight and a (lighthouse-style) Fresnel lens.

[ Addendum: Apparently, nobody but me has ever used the word “orbiculum”. I don't know how I started using it, but it seemsthat the correct word for what I meant is oculus. ]

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