14 Mac Leod, The Place of Science in History. 



engine had taken a really practicable form, it was em- 

 ployed to pump water from mines, and to raise water for 

 the use of towns. 



Savery's machine was perfected by J. T. DESAGULIERS, 

 who applied to it the safety-valve, invented by Papin, 

 and who substituted condensation by a jet of cold water 

 in the interior of the receiver for the exterior condensation 

 employed by Savery. 



In 1690 DENIS PAPIN conceived the idea of utilising 

 steam pressure to raise a piston sliding in a cylinder, the 

 piston afterwards to redescend under the combined in- 

 fluence of the atmospheric pressure and the vacuum pro- 

 duced by the condensation of the steam. Unfortunately 

 his invention was inpracticable because he employed 

 the cylinder at the same time as a boiler. Among Papin's 

 inventions one might mention a boiler with internal 

 heating. This was the first conception of a system later 

 universally adopted. 



In 1705 THOMAS Newcomen and his assistant JOHN 

 Cawley gave a practicable form to the cylinder and 

 piston. They fixed the piston to one end of a lever, the 

 other end being provided with a counterpoise. When 

 the piston had reached the bottom of its stroke the 

 admission under the piston of steam provided by a boiler 

 allowed the piston to ascend under the influence of the 

 counterpoise. Then the tap through which the steam 

 had entered, was shut, and a jet of cold water introduced 

 into the cylinder (Savery's method) condensed the steam 

 and produced a vacuum : the piston descended under the 

 influence of atmospheric pressure and worked a pump. 

 A fresh jet of steam expelled the water by means of an 

 escape valve, and permitted a fresh stroke of the piston. 



1 About 1680 DENIS Papin applied the safety-valve which he had in- 

 vented to his digester. 



