CAPTIVE MOLECULES: THE STORY OF THE STEAM ENGINE 



WE come now to that all-important trans- 

 former of power, the steam engine. Every- 

 body knows that steam is a state of water 

 in which, under the influence of heat, the molecules have 

 broken away from the mutual attraction of cohesion, 

 and are flying about at inconceivable speed, rebounding 

 from one another after collision, in virtue of their elas- 

 ticity, exerting in the aggregate an enormous pressure in 

 every direction. It is this consideration of the intimate 

 character of steam that justifies the title of the present 

 chapter; a title that has further utility as drawing a 

 contrast between the manner of working with which we 

 are now to be concerned, and the various types of 

 workers that we have previously considered. 



In speaking of the animal machine and of work ac- 

 complished by the air and the water, we have been con- 

 cerned primarily with masses of matter, possessing and 

 transmitting energy. Of course molecules since they 

 make up the substance of all matter could not be 

 altogether ignored, but in the main we have had to do 

 with molar rather than with molecular motion. Now, 

 however, we are concerned with a mechanism in which 

 the molecular activities are directly concerned in per- 

 forming work. 



