I had one many years ago.
You've probably seen pictures of them. There is a glass decanter on the bottom and a separate glass globe that fits on top of the decanter with an air tight seal between. There is a glass tube that extends down from the galss globe into the decanter.
You put water in the decanter and coffee in the globe, connect the two pieces and put it on the burner. As the water heats, pressure builds in the bottom decanter and forces the hot water up into the top globe through the tube, where it mixes with the coffee. When all the water has moved from the bottom to the top, you turn off the burner. As the pot cools, pressure in the bottom container drops, drawing the coffee back in.
You separate the two pieces and serve the coffee.
I can't say that the coffee brewed in that contraption was any better or worse than what I brew now.
Here are some: