Yes, it's a mercury arc rectifier. When I was a kid I recall seeing one in the Scince Museum in London, and it was working at the time. Emitted a blue-green glow when it was working. The cathode was a pool of mercury at the bottom, the anodes were (I think) carbon rods in the tubes around the sides.
In Crusty Mansions we are almost solid state now, just a few electromechanical activators remain, I wonder just how many electromechanical items we still use, but do not notice any longer in the average home?
I have come across Mercury Arc Rectifiers in my time, as these were the main way for rectifying huge amounts of AC traction power for Londons Underground trains. Sadly I never had a qualification to work with traction power, so I only came in contact with them when it became a problem to be solved by the LTE Research Laboratory.
Brilliant things in all ways, to long with the metal doors of the cabinets open and you got a brilliant sun tan, and what an unearthly glow to walk towards.
The DC power control resistors slung under the trains were something else and I regularly used the cast iron elements for dropping power from the DC main to run some of my more arcane experiments at the Laboratory.
@Crusty... "I only came in contact with them...." Which is still a lot more than most of us. Nice comment about the suntan.
I've watched a couple of the video links given...but none has satisfied my curiosity - what is a typical forward voltage drop for there devices?
" I wonder just how many electromechanical items we still use..." A surprisingly large number, I would say. My washing machine (+/- 10 yrs old) still has a few relays. Most household circuit breakers are still EM devices. And the average printer, of course, is full of them.