Apparently this is the largest Tiffany art glass dome in the world. I don't know if there are larger non-Tiffany domes or something, but that's what the sign says. It's pretty impressive, and the entire room is gorgeous, although badly lit. In case you can't tell, this chandelier hangs down from the center of the dome.
The inscription around the bottom of the dome says: "Books are the legacies that a great genius leaves to mankind which are delivered down from generation to generation as presents to the posterity of those who are yet unborn."