CHAP, vii.] VARIOUS TYPES OF STEAM-ENGINES. 443 



VI. WATT AND THE STEAM-ENGINE. 



We have just seen that Newcomen's engines were simply pumps, 

 of great value doubtless, for draining the water from mines, but not 

 true prime movers capable of furnishing a regular and constant 

 motion adapted to the requirements of every kind of manufacture. 

 The reason of this is simple. The atmospheric pressure which pro- 

 duces the downward motion of the piston is the true motive force in 

 these engines, which have no effective power during the upward 

 motion : this was enougli for working the pumps to which they 

 were applied, but it was a serious drawback for a prime mover, which 

 should have no intermittence of action. 



The atmospheric engines were thus single-acting engines. Watt 

 transformed them into double-acting machines. The cylinder, open 

 at the top, was replaced by a cylinder closed at its two ends, and 

 divided by the piston into two distinct chambers into which the steam 

 alternately penetrates, and is then allowed to escape into the condenser. 



Thus was created the true steam-engine in which the elastic fluid 

 is the true motive power and sole cause of the motion. The oscilla- 

 tions of the piston then communicate oscillations of equal force, and 

 of equal amplitude to the beam. In one word, with double action 

 the steam-engine became a universal prime mover, applicable to all 

 kinds of industry. 



Besides this, by rendering the steam-engine capable of universal 

 employment, Watt opened the door by this very means for all the 

 subsequent improvements. He himself devoted all his powers and all 

 his intelligence to this at first arduous task. By the invention of the 

 governor he reduced still further the irregularities of the motion. 

 " The efficacy of the governor is such," says Arago in his biographical 

 notice of Watt, " that there might be seen some years ago in Man- 

 chester, in the cotton-spinning factory of a talented . mechanician, 

 Mr. Lee, a clock set in motion by the steam-engine of the establish- 

 ment, and which went about as well as an ordinary spring clock beside 

 it. Watt's governor, and a pretty free use of fly-wheels, are the true 

 secret of the astonishing perfection of the industrial productions of our 

 day ; it is these that now enable the steam-engine to work entirely 

 free from stoppages, and by these it is possible to embroider muslins 



