The first practical use of steam power was applied to the pumping of water from the deep mines of Cornwall. Newcomen’s engine, which antedated Watt’s by several decades, was known as an atmospheric engine. It consisted of a cylinder fitted with a piston, but the top of the cylinder was open. The piston was connected to one end of a lever or walking beam, the other end of which was connected by a chain with the plunger of a pump situated at the bottom of the mine shaft. Little power was required to lift the piston because it was counterbalanced by the chain and plunger attached to the opposite end of the walking beam. The real work was done in pushing the piston down and thereby raising the pump plunger. Steam under low pressure was let into the cylinder under the piston to raise it and then a jet of water was sprayed into the steam-filled cylinder. This condensed the steam, producing vacuum and the atmospheric pressure acting on the upper surface of the piston forced the piston down, raising the pump plunger. The engine ran very slowly, making only about 15 strokes per minute. Later it was improved, producing about 30 strokes per minute. WATT’S STEAM ENGINE Watt was the first man to build an engine in which the real work was done by the pressure of steam as in modern steam engines. As long as the steam engine was used for pumping water the reciprocating piston could be connected directly to the pump plunger and it was unnecessary to exert power on both sides of the piston, but in 1782 Watt obtained a patent on a double-acting engine. Steam was admitted first on one side of the piston and then on the other. The walking beam was connected by means of a connecting rod to a crank on a shaft that carried a flywheel, and the seesaw motion of the beam was converted into rotary motion of the wheel. This opened up new industrial opportunities for the steam engine. The steam was exhausted from the cylinder into a condenser, i.e., a chamber, in which a spray of water converted the steam into water, producing a vacuum, thereby relieving the piston of back pressure and virtually adding that much more power to the steam operating on the opposite side of the piston. A pump driven by the engine drew the water and the air liberated from the condensed steam out of the condenser. Watt invented an ingenious governor to control the flow of steam to the engine and insure a uniform motion. (See Figure 47.) This governor consisted of a pair of levers hinged to a revolving shaft and each provided with a ball weight at its free end. The shaft was revolved by the engine and if the engine tended to run too fast the balls were thrown out by centrifugal action. In so doing they operated a throttle valve cutting down the steam supply. When the engine slowed down the balls would drop, admitting more steam. In this way the speed of the engine was kept within close limits. The ball governor in improved form is still widely used in stationary engines.