So called because, until 1987, the counterweight of the rotary mechanism ended its rotation here.
This mechanism drove an openwork screen which allowed the light in the lantern to move rhythmically. The adoption, in 1987, of a 2000 watt halogen bulb in place of the 6000 watt tungsten filament used since 1948, has enabled a programmer driven by a microchip to move the light rhythmically, and the turning screen was removed.
In 2006 this bulb was replaced by a 250 watt metallic halide bulb mounted on a transformer. A new rotating screen has been installed, run by an electric motor.
The floor is in black and white marble and has been replaced recently.