CHAPTER XL 



THE MECHANISM OF THE STEAM 

 ENGINE. 



In the theory of the generation of steam it will be 

 remembered that the heat of the burning fuel was but 

 the motion (vibrations) of its molecules; that if this 

 motion was transferred to the water in the boiler 

 (through contact with the sheet and flues) it absorbs 

 a portion of the heat, that is, its molecules commence 

 to vibrate rapidly until the boiling point is reached, 

 at which point it fails to increase in temperature 

 though the fire continues to burn. This was because 

 a portion of it, the heat, the energy, the work-doing 

 power of the molecules, was transferred into giving a 

 longer swing to the molecules of the water until they 

 lost their power of staying together (their cohesion), 

 and separated, forming an elastic, expanding gas 

 called steam. The engine is but an instrument for 

 transmitting the motion of expanding particles of 

 steam into a regular, constant movement which may 

 be made to do work, and the better the parts are 

 arranged and adjusted with this in view, the more 

 and better work it will do. 



THE CYLINDER. 



The usual method of obtaining work from heat is 

 to admit the steam from a boiler, where it has been 



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