28 WATT. 



The account of Lord Worcester is far from being 

 clear and distinct, and nothing appears to have resulted 

 from his suggestions. In 1690, Papin, an eminent 

 and able French engineer and author of the diges- 

 ter which goes under his name, living in London, 

 published a work in which he showed that he had made 

 two most important steps in the use of steam. Caus 

 and Worcester had applied the force directly to the 

 body which it was intended to move ; and it was 

 evident that, while that was a condition of its use, 

 very limited bounds must confine the operation. But 

 Papin, observing the use of the piston in a common 

 sucking-pump, applied this to the steam machine, 

 making it work in the cylinder, and be the medium of 

 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, 

 lie thus caused the atmosphere to press down the pis- 

 ton. 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 important invention of the safety-valve, al- 

 though he did not apply it to the steam engine. He 

 introduced it as a part of his digester, but suggesting 

 that it was applicable to the steam engine. 



* See the distinct figure in his plate xiv., p. 109, of Experimenta 

 nova Magdeburgica de Vacuo Spatio.' Amstelodami, 1672. 



f 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 important step. The passage refers 

 only to the rise of water in a vacuum. See ' I tre Libri dei Spiritali, ' 1606. 



