Shiny Stockbridge Something

I have no idea what this thing is. It's just something a bit mad-looking that I found while mooching round a charity shop in Stockbridge.

Made of glass, and about 9 inches across, it had quite a cool purple base. As you can see, it also had strange nobbly bits on: they reminded me of the shape of really cheap childhood ice lollies. Does anyone know what it might be?