My home inspector husband believes it could be an early heat detector that was wired to some sort of light that would go off if heat was detected. I have no idea if this is even remotely true. Haha.

Haha - thanks! That's the best guess we've had so far!

I love these "what is this gadget" threads! That would be my guess too -- fire alarm heat sensors. Check out item #223032035336 on the big auction website for a photo of a similar sensor.

Is there an alarm panel anywhere in the house? I suppose that even if there were at one time, it might have been removed, so that might not be indicative.

Check out this discussion which confirms the above theories.

https://www.google.com/amp/s/amp.reddit.com/r/whatisthisthing/comments/5fy6yz/my_girlfriends_sister_bought_a_house_built_in/?source=images

Darn it. I have to tell him he’s right.

Looks exactly like this one.

Believe it or not, Dictaphone made fire alarms as well as dictation machines. The one in the furnace room of my childhood home was brown bakelite, was connected to some ancient-looking batteries.