THE STEAM-ENGINE. 



415 



the top of the cylinder by the weight of the rod D. This ascent of the piston 

 is also assisted by the circumstance of the steam being somewhat stronger than 

 the atmosphere. 



When the piston has reached the top, the regulating valve R is closed, and 

 the condensing valve H opened, and another descent produced, as before, and 

 so the process is continued. 



The manipulation necessary in working this engine was, therefore, the 

 alternate opening and closing of two valves ; the regulating and condensing 

 valves. When the piston reached the top of the cylinder, the former was to 

 be closed, and the latter opened ; and, on reaching the bottom, the former was 

 to be opened, and the latter closed. 



The duty of working the engine requiring no great amount of labor, or skill, 

 was usually intrusted to boys, called, cock boys. It happened that one of the 

 most important improvements which has ever been made in the working of 

 steam-engines was due to the ingenuity of one of these boys. It is said that 

 a lad, named Humphrey Potter, was employed to work the cocks of an at- 

 mospheric engine, and being tempted to escape from the monotonous drudgery 

 to which his duty confined him, his ingenuity was sharpened so as to prompt 

 him to devise some means by which he might indulge his disposition to play 

 without exposing himself to the consequences of suspending the performance 

 of the engine. On observing the alternate ascending and descending motion 

 of the beam above him, and considering it in reference to the labor of his own 

 hands, in alternately raising and lowering the levers which governed the cocks, 

 he perceived a relation which served as a clue to a simple contrivance, by 

 which the steam-engine, for the first time, became an automaton. When the 

 beam arrived at the top of its play, it was necessary to open the steam-valve 

 by raising a lever, and to close the injection valve by raising another. This 

 he saw could be accomplished by attaching strings of proper length to these 

 levers, and tying them to some part of the beam. These levers required to be 

 moved in the opposite direction when the beam attained the lowest point of its 

 play. This he saw could be accomplished by strings, either connected with 

 the outer arm of the beam, or conducted over rods or pulleys. In short, he 

 contrived means of so connecting the levers which governed the two cocks by 

 strings with the beam, that the beam opened and closed these cocks with 

 the most perfect regularity and certainty as it moved upward and downward. 



Besides rendering the machine independent of manual superintendence, this 

 process conferred upon it much greater regularity of performance than any 

 manual superintendence could insure. 



This contrivance of Potter was very soon improved by the substitution of a 

 bar, called a plug-frame, which was suspended from the arm of the beam, and 

 which carried upon it pins, by which the arms of the levers governing the cocks 

 were struck as the plug-frame ascended and descended, so as to be opened and 

 closed at the proper times. 



The engine thus improved required no other attendance except to feed the 

 boiler occasionally by the cock T, and to attend the furnace. 



However the merit of the discovery of the physical principles on which the 

 mechanical application of steam depends may be awarded, it must be admitted 

 that the engine contrived by Newcomen and his associates, considered as a 

 practical machine, was immeasurably superior to that which preceded it ; 

 superior, indeed, to such a degree, that while the one was incapable of any 

 permanently useful application, the other soon became a machine of extensive 

 utility in the drainage of mines ; and, even at the present time, the atmospheric 

 engine is not unfrequently used in preference to the modern steam-engine, in 

 districts where fuel is abundant and cheap ; the expense of constructing and 



