ON TUB THEORY OF TUB STEAM-ENGINE. 577 



physical phenomena are therefore no less important in their influence 

 upon the behaviour of the engine, and upon its efficiency, and are no less 

 essential elements for consideration in the general theory of the engine, 

 than those taken into account in the purely thermodynamic theory. 



James Watt, as above stated, discovered this cause of the limitation of 

 the efficiency of the steam-engine. He not only discovered the fact of the 

 existence of this method of waste, but experimentally determined its 

 amount in the first engine ever placed in his hands. It was in 1763 that 

 he was called upon to repair the little model of the Newcomen engine, 

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

 new boiler, he set up the machine and began his experiments. He found, 

 to his surprise, that the little steam- cylinder demanded four times its own 

 volume at every stroke, thus wasting, as he says, three-fourths of the 

 steam supplied, and requiring four times as much ' injection water ' as 

 should suffice to condense a cylinder full of steam. It was in the course 

 of this investigation that he discovered the existence of so-called 'latent 

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

 of this immense waste. He proposed to himself the problem of keeping 

 the cylinder ' as hot as the steam that entered it;' he solved this problem 

 by the invention of the sepai'ate condenser and the steam-jacket, and thus 

 the discovery of the limitation of the thermodynamic theory here noted 

 was the source of Watt's fame and fortune. 



John Smeaton, a distinguished contemporary of Watt, and perhaps 

 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 large number 

 of Newcomen engines between 1765 and 1780, 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 five and six feet in diameter 

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

 not be 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 

 thoroughly 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 is 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 was 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 management, 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 themselves that this water is always due to ' priming ' at the 

 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 

 the moisture actually present iu the average steam-engine. He considers 



1884. F ° & pp 



