I've seen pages from old catalogs offering fixtures with both gas mantles and electric sockets from the turn of the century. In small towns it wasn't at all unusual for the "electric-light plant" to shut down after 10 p.m. or so well into the 'teens.

Gas fixtures can burn pointing up or down... they blow gas inside a mantle so it makes no difference how they are oriented.

I have gas lights in my hunting cabin and they point down.

Good point about the lamps hanging down. They must be light bulbs. In San Francisco as a college student back in the sixties, I lived in an old Victorian flat that still had live gas jet sconces on the walls. We would light them just for fun as night illumination. No lamps - just the gas coming straight out of the fixture. Thank God we didn't burn the place down.

I suspect the chandelier was converted from gas to electric. I remember seeing gas piping, outlets and converted fixtures in my grandparents' house. It would have been a whole lot cheaper to add the electric fixtures than buy new.

The lighting fixture looks like it may be combined gas + electric. The lower lights look like they accept screw-in bulbs while valves appear to control the upper lights.

If it is all-gas, how did the lower lights burn upside down ?

Well, this photo may have been taken in the 1920s, but this room doesn't "roar". No cocktails served here. Flappers need not apply. The scene looks high Victorian, and from the size of that pipe coming down from the ceiling, the room is still lit by gas.