General Description. 151

p. Waste-pipe, to conduct the superfluous waterfrom the top of the cylinder to the hot-well.

q. Injection and steam-cocks, alternately open-ed and shut by the plug-frame r, so that whenthe steam-pipe c is open to the cylinder, the con*nection with the injection cistern is closed, andvice versa.

s. The feeding-pipe, to supply the boiler withwater, furnished with a cock at t.

v. The snifting-valve, by which, at every ascentof the piston, the air extricated from the condens-ing water is driven out by the pressure of thesteam.

u. u. Two gauge-cocks, connected with pipespassing into the boiler, the one longer than theother, to ascertain the depth of water. Should oneof these furnish steam and the other water, thelatter may be considered at the required height.But if on the contrary both give steam, or bothwater, it is too high or too low.

w. Forcing-pump, worked by the main beam,for the supply of the injection-cistern, with whichit communicates by means of the pipe x x.

When the atmospheric engine is set to work,the boiler must be filled rather more than half fullof water, and the steam having attained a pressureof about one pound on each square inch of theboiler, the pump-rods will preponderate, and thepiston be drawn to the top of the cylinder. In afew moments the elastic vapour will be seen to