what is this fixture?

I found this in the attic of a house built in 1908. The black wires on the left went outside through the soffit. Most of the house still had active knob & tube wiring. My voltage sniffer indicated that this fixture was ‘hot’.

Looks like an old communications system protector for the phone line.

Lightning arrester(telephone)

Yes, thank you. I went on Google with your idea and an image came up exactly like the one I found.

Yeah some kind of solenoid.

It’s not a solenoid.

Ooops that was a blurb.
Too much multitasking today.

surge arrester is designed to limit surge voltage by discharging the surge current to ground.

This is what is under that round thingy.

i.e. spark gap

Round Thingy

I didn’t want to get too technical for you Bob :wink: