The "glass coffee maker" mentioned by a couple of people in its time was called a "vacuum pot." The lower pot was the "serving pot." You filled it with (preferably cold) water. The upper "globe" had a straight stem that extended down to within about a quarter inch of the bottom of the lower pot, and a glass rod sat in the stem.

Generally there was a fairly massive rubber(ish) gasket surrounding the stem that "sealed" the upper affair to the lower one.

The style existed before "modern materials," and some very old ones might have had a "ground glass" fitting between the stem of the upper bowl and the glass rod. Few of these survive.

After about 1940 or so, both of the bowls were made of "pyrex," which is reasonably heat resistant. The glass rod was usually a "soft glass" that could be molded to fit where it seated in the stem of the upper pot, so no "ground glass joint" was required, although in "transition era" pots they may have simulated the ground glass seal area, for appearance sake.

The rod kept the coffee grounds, placed in the upper bowl, from falling down into the lower pot.

The pot worked well on gas stoves, but occasionally an electric burner would crack one, so people with electric stoves (rare then) used a "heat diffuser" under the pot - which often was just the lid cut out of the top of a can of coffee, although you could buy a "heat spreader" for about a dime at the local five-and-dime.

When you heated the water in the bottom pot, the build up of pressure forced the water up into the top globe. If you heated too fast, occasionally the glass rod would "lift" and drop a few grounds back down into the bottom. Not recommended.

When all of the water was pushed up into the top, steam would come up through the stem. When the upper globe "bubbled" you turned off the burner and let the whole thing sit.

As the bottom pot cooled, the liquid (now coffee) was "sucked" back into the lower pot - hence the "vacuum pot" name. The "fit" between the upper globe stem and the glass rod was the only "filter" required.

The theory of this method was that when the water reached precisely the local boiling point it was pushed through the stem and up into the grounds in the upper globe, so that it was virtually impossible to "overheat" the coffee while it was brewing in the upper globe.

This was the standard coffee brewer in restaurants and in many homes in the central US from mid 1940s through the late 1950s, and makes a very consistent brew. If you have such a pot with a usable gasket, no cracks, and the glass rod isn't seriously chiped or cracked, there is no real reason not to use it if you like, although if it has "sentimental value" perhaps just for "special occasions."

Later on in the era when this style of brewing was commonly used, some restaurants went to an aluminum pot based on the same theory of operation, but there was something "unsatisfying" about not being able to see the color of the brew, so often the glass bottoms came back and only the aluminum "top can" was used - out of sight of the drinkers.

For research purposes, the popular brand name here was the "Cory" (or was it Corey?) coffee maker.

John