A century's PROGRKSS OF THE STKAM KNGINK. r,«)9 



costsof its production. In rl.oosin^an .noin.. typ.' for anv appli<-ation 

 seek that which retiuM.s in useful power the larovst an./.unt ..f v ah.e 

 tor each unit expended in its procurement. 



Progress in the improvement of the steam e,.oine is measured l.y 

 the gain m ^"duty" secured Uy impi-ovement in its c(,nstruction and 

 operation. This gain is exhihit.'d in Hg. o, in wliich are presented 

 the curves of mean efficiency of the steam engine of the best types 

 from the time of Smeaton and the Newcomen engine to the end of 

 the nineteenth century. 



A duty curve measures the gain in amount of useful uoric performed 

 by the unit of fuel consumed; the curve of heat and steam and fuel 

 consumption exhif)its the quantity consumed per horsepower and per 

 hour. It may be also noted that the internal wastes of the engine, at 

 first constituting 95 pei- cent of all the heat and steam and fuel siip- 

 plied, have become extinguished to such an extent that SU j)er cent or 

 more of the steam has become available foi- use in the engine cylinder. 



A.D.l(o0 17G0 1780 . 1800 1820 1840 1800 1880 1900 £ 



FIG. 5.— PROGRESS OF STEAM ENGINE EFFICIENCY, I750-I9OO 



The curve of heat, steam, nnd fuel consuniplion i>. pcriiaps. the 

 most familiar measure of the growth of the engine elHcimcy during 

 the century just elapsing. The scale is one of thousands of British 

 thermal units per indicated horse^wwer per hour and of pounds of 

 steam for similar units, it being assumed that each p(»un<l >l()iv> I.ikki 

 heat units between feed water and steam temi)eratures. It is also a 

 scale of tenths of a pound per horsepower per hour, avsnming tin- 

 most efficient of steam boilers— with an evaporation of K" pounds of 

 steam per pound of fuel— to l)e employed. It will l)e seen that the 

 gain has recently approximated 20.()(M>.(K)() foot-pounds per |(Mip..unds 

 of fuel on the duty scale, 1 pound of steam and one-tenth pound of 

 fuel, per decade, on the scale of heat expenditure, and that the decrease 

 in magnitude of internal wastes has been, and is at present. ab<.ut 1 

 per cent per decade. These rates of gain may be taken as those ol 



