ON TIIK THEOKY <)K TIIK BiTEAM-KNGIXi:. 



.-)77 



Itburth ill 

 quantity 

 1 this loss 

 IS steam- 

 tlie pvo- 

 1 cylinder, 

 breasf 9 as 

 [the time 

 cylinder 

 Hence 

 low piston 

 lam, a low 

 It These 



i)liysical jihononu'ua nro ihcrcfore no loss important in their infhionco 

 iiiMiii llie bohavioiir ol' the cnf^iiK', and upon its ellitiiency, and mo no less 

 t!ssL'iitial cU'inents lor consitieiation in tlio f^eniiial theory of tlio ciigiuo, 

 than those taken into account in the purely thorniodynaniic theory. 



.IiiMies Watt, as above stated, discovered this eauso of the limitation of 

 the fllieiency of the Hteaui-en<;iii('. lli; not only discovered tiie fact of tho 

 oxistenoo of tliis method of wuste, hut exi)erirnentally determined its 

 amount in the iirst engine ever pljieed in his hands. It was in 17(lo that 

 ho was called upon to repair the little model of tho Neweomen engine, 

 then and still in the cabinets of tho University of Glasgow. Making a 

 new hoiler, ho set up the machine and began his experiments. lie found, 

 to Iiis surprise, that the little steam-eylinder demanded four limes its own 

 volume at every stroke, thus wasting, as lie says, three-fourths of tho 

 steam supplied, and reipiiring four times as miicli ' injection wiiter' as 

 should sulhce to condense a cylinder full of steam. It was in tho course 

 of this investigation that lie discovered tho existence of so-called 'latent 

 heat.' All of Watt's iirst inventions were directed toward the reduction 

 of tliia inunen.so waste, lie ])roposed to himself the problem of keeping 

 the cylinder ' as hot as the steam that entered it;' ho solved this j)roblem 

 by the invention of the sejiarate crmdenser and the steani-jai^ket, and thus 

 tiie discovery of the limitation of the thermodynamic theory here noted 

 was the source of Watt's fume and fortune. 



John Smeaton, a distinguished contemporary of Watt, and jierliaps 

 the most distinguished engineer of his time, not only seems to have been 

 well aware of this defect of the steam-engine, but also was possibly even in 

 advance of Watt in attempting to remedy it. He built a largo number 

 of Neweomen engines between 17Go and 17S0, in some if not many of 

 which he attempted to check loss by this now familiar ' cylinder-con- 

 densation' in. engines, some of which were live and six feet in diameter 

 of cylinder by lining pistons and heads with wood. This practice may 

 not bo practicable with the temperatures now usual ; but no attempt has 

 been made, so far as is known to the writer, to follow Smeaton in his 

 tliorougldy philosophical plan of improvement. Cylinder- condensation 

 remains to-day, as in the time of Smeaton and Watt, the chief source of 

 waste in all well-designed and well-constructed heat-engines. 



It i,s a curious fact, and one of great interest as illustrating the gulf 

 formerly separating the philosopher studying the steam-engine and 

 working out its theory from the practitioner engaged in its construction 

 and operation in the earlier days of engineering, that, notwithstanding 

 the fact that this waste Avas familiar to all intelligent engineers, from 

 the time of the invention of the modern steam-engine, and was recorded 

 in all treatises on engine construction and nuinagement, the writers on 

 the theory of the machine have apparently never been aware that it gives 

 rise to the production, in the working cylinder, of a large amount of 

 water mingled with the steam. In fact, it has often been assumed by 

 engineers therasclves that this water is always due to ' priming' at tho 

 boiler. Even Rankine, writing in 1849-50, while correctly describing 

 the phenomenon of cylinder-condensation, made the mistake of attributing 

 the presence of the water in steam-cylinders to the fact of condensation 

 of dry steam doing work by expansion, apparently not having noted the 

 fact that this would only account for a very insignificant proportion of 

 tho moisture actually present in the average steam-engine. He con.siders 



1884. p p 



