Steam Engines.
Humphrey Potter was a boy whose duty obliged him to open and shut the valves of a Newcomen steam-engine as it slowly went its rounds. He was a human sort of boy, who liked play better than his irksome task, so he found a way to rid himself of the drudgery of constantly moving his valve-handles to and fro. He tied a rod to the walking beam in such wise that it opened the valve at the proper moment, and, at another point in its circuit, when necessary, closed it. Then and only then did the steam-engine become self-acting. In the best modern types of engine this automaticity goes far indeed. Not only does the mechanism pump water as required into both the boiler and the condenser, it shuts off steam instantly when the engine moves too swiftly, and, when the engine speed is sluggish the port betwixt boiler and cylinders is opened to the full. And further: automatic stokers bear coal into the furnace at a rate which varies with the demand, should the steam pressure fall through an undue call for power, then an extra quantity of coal is borne upon the grate-bars. When oil is the fuel automatic stoking is, of course, at its best, there being neither cinders nor ashes to be removed—a duty, by the way, which in large central stations requires extensive machinery, all automatic.