356 WATT. 



communicating motion to other apparatus. Next, he 

 applied steam directly as the agent, to raise the piston ; 

 and making a vacuum by the condensation of the 

 steam, he thus caused the atmosphere to press down 

 the piston. Guericke, the inventor of the air-pump, 

 had half a century earlier used the vacuum, made 

 by his machine in the same manner, as a mechanical 

 power, by the help of a piston and rod ;* and he 

 invented the valve, without which the vacuum could 

 not be produced. The application of the same 

 principle and of the same contrivance to steam was 

 Papin's ; and its importance, and his merit, are not 

 diminished by considering the source from which he 

 borrowed it.f Indeed the action of the air in the 

 sucking-pump is another form of the same experiment. 

 It must be added that to Papin also we owe the im- 

 portant invention of the safety-valve, although he did 

 not apply it to the steam engine. He introduced it as 

 a part of his digester, but suggesting that it was appli- 

 cable to the steam engine. 



It is, however, certain that the most rude and cum- 

 brous part of the former invention was continued by 

 Papin. The fire was applied to the water, and when it 

 had filled the cylinder with steam, the condensation 

 was only effected by withdrawing or extinguishing the 

 fire. Savery about the year 1 698 made considerable 



* See the distinct figure in his plate xiv., p. 109, of ' Experi- 

 menta nova Magdeburgica de Vacuo Spatio.' Amstelodami, 1672. 



\ Acta Eruditorum, 1688. The paper has an excellent and 

 clear figure. Nothing can be more groundless than Mr. Stuart's 

 statement that Baptista Porta had anticipated Papin in this impor- 

 tant step. The passage refers only to the rise of water in a vacuum. 

 See ' I tre Libri dei Spiritali,' 1606. 



