Invert a tall glass jar in a dish of water, and place a lighted taper
under it; as the taper consumes the air in the jar, the water, from
the pressure without, _rises up_ to supply the place of the oxygen
removed by the combustion. In the operation of cupping the operator
holds the flame of a lamp under a bell-shaped glass. The air within
this being rarefied and expanded, a considerable portion is given
off. In this state the glass is placed upon the flesh, and as the air
within it cools it contracts, and the glass adheres to the flesh by the
difference of the pressure of the internal and external air.