Moderator lamp
The moderator lamp is a type of 19th century oil lamp. It displaced the more complex Carcel lamp since its mechanism was simpler. The moderator lamp was invented by M. Franchot in 1837. [1]
A moderator lamp provides a pressurized supply of oil to the lamp wick by use of a spiral spring-loaded piston operating on a cylindrical oil reservoir. A regulating mechanism, the "moderator", compensates for the varying force of the spring as the piston descends. The moderator is a wire that runs through a tube in the center of the piston. When the spring is near the top of the reservoir, the wire runs through the full length of the tube. As the piston and tube lowers, and the spring force decreases, the wire is withdrawn from the tube and the flow of oil encounters less resistance. A steady stream of oil flows upward to the wick, with excess oil falling back into the reservoir above the piston. [2]
The piston, made of leather discs clamped between metal washers, was also fitted with a valve to allow the piston to be withdrawn and the reservoir to be filled with oil. A winding key was provided with a rack, so that the piston could be raised and tension placed on the spring. These lamps were fueled by vegetable oil such as colza oil or rapeseed oil. These oils would be too thick to travel up a lamp wick without some applied pressure.
Moderator lamps replaced the more complex clockwork-driven Carcel lamps and were widel used by the end of the 19th century.