THE STEAM-ENGINE. 153 



of these condensers was put to work in the building below 

 us about two years ago, applied to a high-pressure engine 

 driving the machinery in the Exhibition. The ejector con- 

 denser is an extremely simple apparatus and one readily 

 applied to any existing engine, and there are in it no 

 working parts. I will not endeavour to describe the principle 

 of its action, because if time permits I propose to repeat 

 the explanation I have given elsewhere of the principle of 

 Giffard's injector, and this explanation is applicable to the 

 ejector condenser. 



About the earliest instance we have of the expansion 

 engine doing admirable duty, is the Cornish pumping-engine, 

 which is shown in diagrams 19 and 19 a. You are aware that 

 those engines are single-acting, that the steam comes in at the 

 top side of the piston, the vacuous condition being below; 

 after the piston has gone down a certain distance, the steam- 

 valve is closed by the action of the plugtree and the rest of 

 the journey is performed by expansion. When applied to a 

 mine the engine lifts the weight of the pump-rods, and on the 

 return journey, the equilibrium-valve being open, the weight 

 of those rods acting on the plunger-pump raises the water 

 up to the surface of the ground. In a mine, therefore, the 

 resistance to this engine is constant, because the depth of 

 the mine being constant the head of water against the 

 pump is constant. Those engines were admirable machines 

 in their day, and they developed an economy which prior 

 to that time had been thought to be impossible. Their per- 

 formance is commonly expressed, as you know, in millions 

 of duty, that is to say, in millions of pounds raised one 

 foot high by the combustion of 1 1 2 pounds of coal. Before 

 the year 1855, the record used to be in millions of pounds 

 raised one foot high by the combustion of a bushel of coal, 

 which was taken as 94 pounds. You are probably aware 

 that in 1811, Mr. Lean, a Cornish engineer, the inventor 

 of the plunger-pump, established Lean's Reporter. He 

 commenced, I think, with three engines in the counties of 

 Cornwall and Devon, and in his Eeporter he gave month 

 by month the performances of the respective engines. A 

 great deal of emulation was caused thereby, and there is no 

 doubt that the establishment of that "Eeporter" was a 

 great incentive to engineers to improve the quality of their 

 engines. The conversion of millions of pounds duty into 



