94 THE ADDRESSES, LECTURES, ETC., OF 



accomplish all our purposes of smelting, cooking, and heating, 

 without the use of any combustible matter ; but such conversion 

 would be attended with so much difficulty and expenditure that 

 one cannot conceive human prosperity under such laborious and 

 artificial conditions. 

 We come now to the question 



How SHOULD FUEL BE USED ? 



I propose to illustrate this by three examples which are typica 

 of the three great branches of consumption. 



0. The production of steam power. 



5. The domestic hearth. 



c. The metallurgical furnace. 



Steam Engine Consumption. I have represented on a 

 diagram two steam cylinders of the same internal dimensions, the 

 one being what is called a high pressure steam cylinder, provided 

 with the ordinary slide valve for the admission of steam and its 

 subsequent discharge into the atmosphere, and the other so 

 arranged as to use the steam expansively (being provided with the 

 Corliss variable expansion gear) and working in connection with 

 a condenser. I have also shown two diagrams of the steam 

 pressures at each part of the stroke, assuming in both cases the 

 same initial steam pressure of 60 Ibs. per square inch above the 

 atmospheric pressure, and the same load upon the engine. They 

 show that in the latter case the same amount of work is accom- 

 plished by filling the cylinder roughly speaking up to one-third 

 part of the length as in the other by filling it entirely. Here we 

 have then an easy and feasible plan of saving two-thirds of the 

 fuel used in working an ordinary high-pressure engine, and yet 

 probably the greater number of the engines now actually at work 

 are of the wasteful type. Nor are the indications of theory in 

 this case (or in any other when properly interpreted) disproved by 

 practice ; on the contrary, an ordinary non-expansive non-con- 

 densing engine requires commonly a consumption of from 10 to 

 12 Ibs. per horse-power per hour, whereas a good expansive and 

 condensing engine accomplishes the same amount of work with 

 2 Ibs. of coal per hour, the reason for the still greater economy 

 being, that the cylinder of the good engine is properly protected 



