30 WATT. 



made no use at all of the direct force of steam ; it 

 worked entirely by means of the vacuum ; and hence it 

 is sometimes and justly termed the atmospheric engine, 

 as its moving force is the pressure of the atmosphere. 

 Desaguliers, who has given the best description of 

 Newcomen and Cawley's engine, about the year 1717 

 or 1718 made several of those engines, in which he 

 executed Papin's suggestion of using the safety-valve. 

 In the same year Beighton perfected the mechanism 

 whereby the engine itself shut and opened the valves, 

 by which the supply of steam to the cylinder and of 

 water to the boiler is regulated ; and Smeaton subse- 

 quently made some other mechanical improvements. 

 With these exceptions the steam engine continued 

 exactly in the same state from the time of Newcomen 

 to that of Watt, above half a century later. 



We have thus seen how very slowly this great 

 invention was brought to the state in which Mr. Watt 

 found it, and how considerable a number of persons con- 

 tributed each a small share to its progress. Let us enu- 

 merate these steps : they are at least six in number. S. 

 de Caus made steam act to raise water ; Worcester per- 

 formed this operation in a more regular and mechanical 

 manner; Papin used the condensation of steam, and 

 through that the atmospheric pressure, as well as the 

 direct expansive force, and he worked the engine by a 

 piston; Savery condensed by refrigeration instead of the 

 mere absence of fire, but did not use the atmosphere; 

 Newcomen used the jet for condensing and the atmos- 

 phere for pressure, but did not use the direct force of 

 steam ; Desaguliers introduced the safety-valve ; Beigh- 

 ton and Smeaton improved the mechanism ; D'Alesme 

 needs not be mentioned, as we are not informed what 

 plan he executed, but he certainly made no step himself. 

 If the direct force of steam, as well as atmospheric 

 pressure, had been both employed, with the jet of cold 

 water, the safety-valve, and the contrivance for regu- 

 lating the supply -valves, a far better engine than any 



