768 iiEPORT — 1881. 



comprised under the three leading ideas of internal work, external work, and tem- 

 perature, and no phraseology should be used that conflicts with those ideas. 



The modern theory of heat has thrown new light upon the theory of the steam 

 eno-ine. We now know what is the mechanical value in foot-pounds of the beat 

 €Volved in the combustion of 1 lb. of coal. In practice we can determine how 

 much of that heat is transmitted to the water in the boiler, and we are taught how 

 to calculate the quantity which in the process of vaporization takes the form of 

 internal work. We can determine how much disappears in the engme in the shape 

 of external work, including friction, and the remainder, with the exception of the 

 trifling quantity saved in the feed water, we know to be lost. Taking a good con- 

 densing engine as an example, we may roughly say that, dividing the whole heat 

 energy into ten equal parts, two escape by the chimney, one is lost by radiation 

 and friction, six remain unused when the steam is discharged, and one only is 

 realised in useful work. It may be fully admitted that the greater part of the 

 aggreo-ate loss is inevitable, but are we to suppose that the resources of science, 

 ingenuity, and skill have been exhausted in the attamment of .so miserable a result ? 

 Nothincr but radical changes can be expected to produce any great mitigation of 

 the present monstrous waste, and without presuming to say what measures are 

 practicable and what are not, I will briefly point out the directions m which 

 amelioration is theoretically possible, and shaU afterwards advert to the question 

 whether we may hope to evade the difficulties of the steam engine by resorting 

 to electrical methods of obtaining power. . . a , 



To begin with the loss which takes place in the application of heat to the 

 boiler why is it that we have to throw away, at the very outset of our operations, 

 twice as much heat as we succeed in utilising in the engine ? The answer is that 

 in order to force a transmission of heat from the fire to the water m the boiler, a 

 certain excess of temperatm-e over that of the water must exist in the fui-nace and 

 flues and the whole of the heat below the required excess must pass away unused, 

 except the trifling portion of it which disappears in the production of draught. 

 Further, that since we cannot avoid admitting tlie nitrogen of the air along with 

 the oxyi-en, we have to heat a large volume of neutral gas which has no other 

 efiect than to rob the tire. Considering what eflbrts have b9en made to facilitate 

 the transmission of the heat by augmenting the evaporative siu'face, and using thm 

 tubes as flues, it is vain to expect any great result from further perseverance m that 

 direction and unless a method can be devised of burnuig the fuel inside instead of 

 outside the apparatus, so as to use the heated gases conjointly with the steam as a 

 workino- medium in the engine, a remedy appears to be hopeless. We already 

 .practise" internal combustion in the gas engine, and it is clear that with gaseous 

 ftiel at all events, we could associate such a mode of combustion with the vaporisa- 

 tion of water. We may even regard a gun as an engine with internally burnt 

 fuel and here I may remark that the action of heat in a gun is strictly analogous 

 ,to that of heat in a steam engine. In both cases the heat is evolved from chemical 

 combination, and the resulting pressures differ only in degree. The gun is the 

 equivalent of the cylinder, and the shot of the piston, and the diagrams represent- 

 ing the pressure exerted in the two cases bear a close resemblance to each other, 

 mile the powder is burning in the gun we have a nearly uniform pressure, just 

 as we have in the cylinder while the steam is entering, and in both cases the 

 uniform pressure is followed by a diminishing pressure, represented by the usual 

 curve of expansion. If in the steam engine we allowed the piston to be blown 

 out it would act as a projectUe, and if in the gun we opposed mechanical resist- 

 ance to the shot, we might utilize the effect in a quieter form of motive power 

 But it is a remarkable fact that such is the richness of coal as a store of mechanical 

 energy, that a pound of coal, even as used in the steam engine, produces a dynamic 

 effect about five times greater than a pound of gunpowder burnt in a gun. 1 can- 

 not, however, on this account encourage the idea that steam may be advantageously 

 substituted for gunpowder in the practice of gunnery. 



And now to turn from the fire which is the birth-place of the motive energy, 

 let us follow it in the steam, to the condenser, where most of it finds a premature 

 tomb From the point at which expansion commences in the cyhnder the tempera- 



