Page:Popular Science Monthly Volume 12.djvu/144

132 catch rigged with a cord from the beam overhead—which performed the work for him.

The boy, thus making the operation of the valve-gear automatic, increased the speed of the engine to fifteen or sixteen strokes a minute, and gave it a regularity and certainty of action that could only be obtained by such an adjustment of its valves. This ingenious young mechanic afterward became a skillful work-man, and an excellent engineer, and went abroad on the Continent, where he erected several fine engines.

26. Potter's rude valve-gear was soon improved by Henry Beighton, and the new device was applied to an engine which that talented engineer erected at Newcastle-on-Tyne in 1718, in which engine he substituted substantial materials for Potter's unmechanical arrangement of cords, as seen in Fig. 12.

In this sketch, r is a plug-tree, plug-rod, or plug-frame, as it is variously called, suspended from the great beam with which it rises and falls, bringing the pins p and k, at the proper moment, in contact with the handles k k and n n of the valves, moving them in the proper direction and to the proper extent. A lever safety-valve is here used, at the suggestion (it is said) of Desaguliers.

The piston was packed with leather or with rope, and lubricated with tallow.

27. Further improvements were effected in the Newcomen engine by several engineers, and particularly by Smeaton, and it soon came into quite extensive use in all of the mining districts of Great Britain, and it also became generally known upon the Continent of Europe.

Its greater economy of fuel as compared with the Savery engine in its best form, its greater safety—a consequence of the low steam-pressure adopted—and its greater working capacity, gave it such manifest superiority that its adoption took place quite rapidly, and it continued in general use in some districts where fuel was cheap up to a very recent date. Some of these engines are even now in existence.

From about 1758 to the time of the introduction of the Watt engine, this was the machine in almost universal use for raising large quantities of water.