264 DISCOVERY OH. 



in Watt's time, yet the advance he made was a most 

 remarkable engineering achievement. 



The principles Watt followed in effecting his improve- 

 ments of the steam-engine were that the cylinder should 

 be kept as hot as the steam that enters it, that steam 

 should be condensed in a vessel distinct from the cylinder, 

 and that the steam itself should move the piston, instead 

 of the pressure of the atmosphere doing it, as was the 

 case with Newcomen's engine. 



Watt's earliest commercial engine (1769) represented 

 the realisation of these principles. The cylinder was 

 clothed with non-conducting materials, and fitted with 

 a steam-jacket in order to keep it hot ; condensation 

 of the steam was effected in a separate condenser, and 

 the piston was pushed down the cylinder by admitting 

 steam above it, the force of the steam thus taking the 

 place of the pressure of the atmosphere in the Newcomen 

 engine. A further improvement was made in 1782, 

 when Watt introduced for the first time the principle 

 of making the steam act alternately on the top and 

 bottom of the piston. The Watt engine, with its many 

 ingenious details of construction, was the prime mover 

 in most general use for eighty years, until the middle 

 of the nineteenth century, when the compound engine 

 and other highly developed forms began to be intro- 

 duced. 



Watt transformed a rude and imperfect steam-engine 

 into an efficient and powerful working instrument, and 

 by so doing accomplished the greatest work performed 

 by any engineer of modern times. He combined the 

 qualities of the practical mechanic with those of the 

 patient investigator, and the perfection to which he 

 brought the steam-engine was due even more to scientific 

 experiment than to mechanical skill. " Nature can 



