THE CONQUEST OF NATURE 



performed work only during one stroke of the piston. 

 A description of the mechanism at this stage of its 

 development may best be given in the words of the in- 

 ventor himself, as contained in his specifications in the 

 application for patent on his improvements in 1769. 



"My method of lessening the consumption of steam, 

 and consequently fuel, in fire-engines, consists of the 

 following principles: 



" First, That vessel in which the powers of steam 

 are to be employed to work the engine, which is called the 

 cylinder in common fire-engines, and which I call the 

 steam vessel, must, during the whole time the engine is 

 at work, be kept as hot as the steam that enters it; 

 first by enclosing it in a case of wood, or any other 

 materials that transmit heat slowly; secondly, by 

 surrounding it with steam or other heated bodies; and, 

 thirdly, by suffering neither water nor any other sub- 

 stance colder than the steam to enter or touch it during 

 that time. 



" Secondly, In engines that are to be worked wholly 

 or partially by condensation of steam, the steam is to be 

 condensed in vessels distinct from the steam vessels or 

 cylinders, although occasionally communicating with 

 them; these vessels I call condensers; and, whilst the 

 engines are working, these condensers ought at least 

 to be kept as cold as the air in the neighborhood 

 of the engines, by application of water or other cold 

 bodies. 



"Thirdly, Whatever air or other elastic vapor is not 

 condensed by the cold of the condenser, and may impede 

 the working of the engine, is to be drawn out of the 



[98] 



