A Limelight Operator on the Fly-Floor (An Illustration from 1874)

The limelight operator uses an open face limelight to floodlight the stage
below. Gas could escape from the bag if pressure was uneven, a hazard,
which could cause explosions. A weights is therefore used to maintain
even pressure.
The limelight operator’s assistant manipulates the weight to ensure a
steady gas flow. When needed he would exert his own weight by standing
on the board..