I found the mechanism again. Not in the book this time, in a back room with the light off, bolted to the floor like it had always been there. A spool and a motor and voltage stickers nobody reads. The man who let me in said it pulls a curtain. He said it twice, which is once more than a true thing needs saying.

I took the picture with the flash because the switch did nothing. I tried the switch on the way out and it worked fine. Go back to the folio if you think I am reaching. I put them side by side for an hour. The teeth are the same teeth.