358 WAIT. 



f 



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 me- 

 chanism 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 

 subsequently made some other mechanical improve- 

 ments. With these exceptions the steam engine con- 

 tinued exactly in the same state from the time of New- 

 comen 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 atmo- 

 sphere 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 



