6 The counterpoise P.

Having raised the piston to the top of the cylinder, the steam-pipe is opened by the handle a.

This causes steam to rush from the boiler, into the cylinder: the air is driven out through the snifting-valve X : and the water, produced by the steam which was condensed in heat- ing the cylinder, flows out through the eduction pipe Z.

When the assistant perceives that pure steam escapes from the snift- ing-valve, he closes the eduction and steam-pipes, and opens the injection cock ]N" : the water which rushes into the cylinder, condenses the steam : and, a vacuum is formed under the piston.

The atmosphere then pressing upon the piston, causes it immediately to descend ; and, the pump rod R being lifted, water is raised from the mine.