CAPTIVE MOLECULES 



steam vessels or condensers by means of pumps, wrought 

 by the engines themselves, or otherwise. 



"Fourthly, I intend in many cases to employ the ex- 

 pansive force of steam to press on the pistons, or what- 

 ever may be used instead of them, in the same manner 

 in which the pressure of the atmosphere is now em- 

 ployed in common fire-engines. In cases where cold 

 water can not be had in plenty, the engines may be 

 wrought by this force of steam only, by discharging the 

 steam into the air after it has done its office. 



"Sixthly, I intend in some cases to apply a degree of 

 cold not capable of reducing the steam to water, but 

 of contracting it considerably, so that the engines shall 

 be worked by the alternate expansion and contraction 

 of the steam. 



"Lastly, Instead of using water to render the pistons 

 and other parts of the engine air- and steam-tight, I em- 

 ploy oils, wax, resinous bodies, fat of animals, quick- 

 silver and other metals in their fluid state." 



ROTARY MOTION 



It must be understood that Watt's engine was at 

 first used exclusively as an apparatus for pumping. 

 For some time there was no practical attempt to apply 

 the mechanism to any other purpose. That it might 

 be so applied, however, was soon manifest, in considera- 

 tion of the relative speed with which the piston now 

 acted. It was not until 1781, however, that Watt's 

 second patent was taken out, in which devices are de- 

 scribed calculated to convert the reciprocating motion 



[99] 



