Pumping.
In incandescent lamps a periodical recurring change in intensity due to
bad running of the dynamos, or in arc lamps to bad feeding of the
carbons.
Fig. 277. SPRENGEL AIR PUMP.
Pump, Sprengel.
A form of mercurial air pump. A simple form is shown in the cut. Mercury
is caused to flow from the funnel A, through c d to a vessel B. A side
connection x leads to the vessel R to be exhausted. As the mercury
passes x it breaks into short columns, and carries air down between
them, in this way exhausting the vessel R. In practice it is more
complicated. It is said to give a better vacuum than the Sprengel pump,
but to be slower in action.