66 THE POPULAR SCIENCE MONTHLY. 



engine into two parts ; using one part as a steam-boiler, and the other 

 as a separate water-vessel. 



Savery duplicated those parts of the earlier engine which acted the 

 several parts of pump, steam-cylinder, and condenser, and added the 

 use of the jet of water to effect rapid condensation. 



Newcomen and Cawley next introduced the modern type of en- 

 gine, and separated the pump from the steam-engine proper : in their 

 engine, as in Savery's, we notice the use of surface-condensation first ; 

 and, subsequently, that of a jet of water thrown into the midst of the 

 steam to be condensed. 



Watt finally effected the crowning improvement of the single cylin- 

 der-engine, and completed this movement of differentiation by sepa- 

 rating the condenser from the steam-cylinder, thus perfecting the gen- 

 eral structure of the engine. 



Here this movement ceased, the several important processes of the 

 steam-engine now being conducted each in a separate vessel. The 

 boiler furnished the steam ; the cylinder derived from it mechanical 

 power; the vapor was finally condensed in a separate vessel; while the 

 power, which had been obtained from it in the steam-cylinder, was 

 transmitted through still other parts to the pumps, or wherever work 

 was to be done. 



Watt also took the initiative in another direction : He continually 

 increased the efficiency of the machine by improving the proportions of 

 its parts and the character of its workmanship ; and thus made it pos- 

 sible to render available many of those improvements in detail which 

 are only useful when the parts can be skillfully made. 



Watt and his contemporaries also commenced that movement toward 

 higher pressures of steam, used with greater expansion, which has been 

 the most striking feature noticed in the progress of the steam-engine 

 since his time. Newcomen used steam of barely more than atmospheric 

 pressure, and raised 105,000 pounds of water one foot high, with a 

 pound of coal consumed. Smeaton raised the steam-pressure to eight 

 pounds, and increased the duty to 120,000. Watt started with a duty 

 of double that of Newcomen, and raised it 320,000 foot-pounds per 

 pound of coal, with steam at ten pounds. To-day, Cornish engines of 

 the same general plan as those of Watt, but worked with forty to sixty 

 pounds of steam, and expanding three to six times, do a duty that Mill 

 probably average, with good ordinary engines, 600,000 foot-pounds per 

 pound of coal. 



The increase of steam-pressure and expansion which has been seen 

 since Watt's time has been accompanied by a very great improve- 

 ment in workmanship, a consequence of rapid increase in the perfection 

 and the wide range of adaptation of machine-tools, of higher skill and 

 intelligence in designing engines and boilers, increased piston-speed, 

 greater care in obtaining dry steam, and in keeping it dry until thrown 

 out of the cylinder either by superheating, or by steam-jacketing, or 



