What is the Oblivion-symbol gauntlet in the Midden?

If, while facing the "palm" of the gauntlet, you look to your right, you'll see a table with a journal and a key on it. The journal will mention a summoning ritual, and four rings that were taken from the gauntlet, and which are now stored in the Arcaneum.

On the floor around the outer ring, there's a chest called the "Investigator's Chest;" the key from the table by the journal will open this chest, and you'll find the four rings. Go back down to the Midden and use trial-and-error to get the rings on the right fingers - each ring will only go on one finger, so this takes very little time. Be prepared for a bit of a fight, as using the gauntlet summons a rather beastly fellow. I'm not sure if you HAVE to fight him or not, but I did, and he wasn't too bad.