It's a glass dome that goes over the filling chamber and top of the Volcano.. It collects the vapor so you can draw it through a whip (or a whip into a GonG device such as a bubbler or bong).

Yeah, I think the best way to describe it is a "G-on-G Vapor Hooka." These are going to turn out to be huge.. acessories are going to be made by some of the biggests glass artists.. Can't wait to get my custom stuff.