Photo's and info supplied by Alan Nadon:

Quote
This is a dimmer switch for four chandeliers in the dining room of my
favorite watering hole. I think it was installed at the end of prohibition or maybe before. It may have been used in a local research laboratory before it was pressed into service for lighting control. The
total load is about 2,000 watts maximum. I think it can handle the load.


[Linked Image]


[Linked Image]