416 



THE STEAM-ENGINE. 



maintaining it being considerably less than that of an improved steam-engine. 

 The low pressure of the steam used in working it, rendered it perfectly safe. 

 While Savery's engine, to work with effect, required that the steam confined 

 in the vessels should have a bursting pressure amounting to about thirty pounds 

 per square inch, the pressure of steam in the boiler and cylinder of the at- 

 mospheric engine required only a pressure about one pound per square inch. 

 The high pressure also of the steam used in Savery's engine, was necessarily 

 accompanied, as we shall presently explain, by a greatly increased temperature". 

 The effect of this was, to weaken and gradually destroy the vessels, especially 

 those which, like the steam-vessels V and V (fig. 3), were alternately heated 

 and cooled. 



Besides these defects, the power of Savery's engines was also very restricted, 

 both as to the quantity of water raised and as to the height to which it was 

 elevated. On the other hand, the atmospheric engine was limited in its power 

 only by the dimensions of its piston. Another considerable advantage which 

 the atmospheric engine possessed over that of Savery, was the facility with 

 which it was capable of driving machinery by means of the working-beam. 

 The merit, however, of Newcomen's engine, regarded as an invention, and 

 apart from merely practical considerations, must be ascribed principally to its 

 mechanism and combinations. We find in it no new principle, and scarcely 

 even a novel application of a principle. The agency of the atmospheric pres- 

 sure acting against a vacuum, or partial vacuum, had been long known : the 

 method of producing a vacuum by the condensation of steam had been suggested 

 by Papin, and carried into practical effect by Savery. The mechanical power 

 obtained from the direct pressure of the elastic force of steam, used in the 

 atmospheric engine to balance the atmosphere during the ascent of the piston, 

 was suggested by De Caus and Lord Worcester. The boiler, gauge-pipes, and 

 the regulator, were all borrowed from the engine of Savery. The idea of using 

 the atmospheric pressure against a vacuum or partial vacuum, to work a piston 

 in a cylinder, had been suggested by Otto Guericke, an ingenious German 

 philosopher, who invented the air-pump ; and this, combined with the produc- 

 tion of a vacuum by the condensation of steam, was subsequently suggested by 

 Papin. The use of a working-beam could not have been unknown. Never- 

 theless, the judicious combination of these scattered principles must be ac- 

 knowledged to deserve considerable credit. In fact, the mechanism contrived 

 by Newcomen rendered a machine which was before altogether inefficient, 

 highly efficient : and, as observed by Tredgold, such a result, considered in a 

 practical sense, should be more highly valued than the fortuitous discovery of 

 a physical principle. 



