CHAP, v.] THE STEAM-ENGINE. S91 



A complete and detailed account of all such endeavours, and of the 

 rough mechanical means by which it has been attempted to utilise 

 the various forces of nature such as that of compressed and rarefied 

 air and of steam has an interest of its own jn regard to the history 

 of the progress of the application of human knowledge. But all 

 this would only be seriously instructive at the time when physics, 

 escaping from the period of subtle and unsuggestive explanations, was 

 entering upon that of experiment under the impulse of Galileo, Boyle, 

 and Huygeiis. The steam-engine could only have been invented, 

 or have received those improvements which make it a really practical 

 motive power, in an age that had seen the di covery of the properties 

 of air, the barometer and thermometer. Papin and Watt are the 

 offspring of Torricelli and Galileo. The steam-engine is the child of 

 two simple and fertile inventions; that of the barometer, which 

 proves and measures the atmospheric pressure, and compares it 

 with the elastic force of gases and vapours ; and that of the thermo- 

 meter, which measures the degrees of heat. The means of producing a 

 vacuum, whether in the barometric tube, or in a receiver from which 

 the air is exhausted by a pump the valuable invention of Otto von 

 Guericke had also been discovered when Denis Papin, of whom 

 France may well be proud, laid the foundations of the greatest 

 industrial revolution the world has ever seen. 



But that we may follow accurately the train of ideas which passed 

 in the minds of those great men whose names are associated with the 

 invention of the steam-engine, it is indispensable to enter into some 

 preliminary details. 



II. PAPIN. FIRST ATTEMPTS. 



As early as 1680 Huygens had proposed to utilize the expansive 

 force of gunpowder in the following manner. In a cylinder provided 

 with a movable piston he caused a certain quantity of powder to be 

 exploded, and the violent expansion of the gas drove the air contained 

 in the cylinder out of two openings so arranged that they closed 

 again immediately. A vacuum was thus made, or at least a partial 

 one (on the cooling and consequent loss of pressure of the gas con- 

 tained in the cylinder), so that the atmospheric pressure acted on the 



