I picked this up at a surplus sale when I was in college, in the late 70’s. It’s most likely some microwave device, but what?
I should have put a ruler for scale, but it’s around 3” x 1.5” x 1.5”, silver plated (hence the tarnish). Clearly gas or vacuum filled (hence the nipple).
I don’t have any experience with waveguides, but this sure looks like something that goes in one…
I wonder if it may have been filled with a gas that reacts to some outside effect. The window letting you see the reaction. Any electrical contacts on it? Are the windows glass?
No, there are no contacts - two sides have the windows, and the other two are solid metal. The top and bottom are solid metal.
Yes, the windows are glass.
If it had some electrical hookups I thought it might have illuminated under power. Some old time gas charged light device.
Are the coils connected? What are they wrapped around? Looks more like heating elements than magnetic.
Are there coils on the other windowed side?
Brian
The spring type things seem to be continuous along the sides, but end at the bottom left corner at a flat spot. No type of connection point where the spring starts? How is that end of the spring attached?
Does it seem that the two sides of the thing are electrically insulated from each other?
I think the springs are just there for mounting - maybe they make a “friction” fit in whatever this thing goes into. There are no terminals anywhere on the device.
The lines on the glass are odd. Maybe they are meant to add a rough breaking point? X amount of pressure will break them, either from without or within. But I don’t see what sort of warning that might provide, without more connections to the device.
Just throwing out thoughts to maybe trigger other ideas from folks.
Does it react to any religious artifacts? 
If the two sides are electrically insulated from each other, the springs may be the contacts. Covering a large area and providing a pressure contact. Imagine the thing clamped between two plates with rectangular cutouts to accept the spring contacts tightly.
The whole thing is one metal box. The outside surface is completely conductive, other than the windows.
The groove around the edge was milled with a round bit. The interior edge with a flat bit. Does the rod on one side pull out?
Are the coils making contact the length of the object like heat sinks?
Is the glass beneath the metal or is it inside the machined surface?
Can you insert a probe into the port and see if there is space between the glass?
The port is hermetically (flame) sealed.
The glass appears to be fused to the inside surface of the box. I don’t have the device in front of me (I packed it), but it’s either a hermetic or epoxy seal.
A filter for particular wavelengths?
It has windows on both sides and a gas within. That can filter certain wavelengths depending on the gas. It it was in a particularly high intensity application the springs may have contacted a larger heat sink to transfer energy.
It screams high power microwave application. But what is another matter.
Silver plate, continuous contact around the edge, all very RF. Is there another set of spring contacts on the other side? A few more pics of it from various angles might help.
I am suspicious the windows may be fused silica. They have that look.
Some kind of high-power terminator, possibly? Squeeze the box into an open waveguide, the insides experience ohmic heating, the plate thing gets orange-hot, and the radiation leaves the window.
Though I am a little confused about the placement; it seems the nipple would get in the way if you tried to shove this in a rectangular waveguide. Maybe it could fit the other way around…
They remind me of the protective cage of a bulkhead lamp.
I wonder if the glass in this object was repurposed from something like that.
r/whatisthisthing might be worth a shot.
Come on, now, community; you pretty much know everything. After reading this, I must know. Don’t let me down!
Sorta looks like a TR cell. (A TR cell protects the sensitive, front-end circuitry in a RADAR receiver from power-overload. This will occur when the transmitter transmits a pulse. The gas inside the TR cell will ionize when it “sees” the high field strength, and thus the energy will be reflected instead of being sent to the receiver.) Just a guess.