SCIENCE. 



529 



nitely, the entire heat would be exhausted, and the 

 energy previously expended in separating the water into 

 steam would be wholly given up in external effect ; but 

 this exhaustion would not be complete until the absolute 

 zero of temperature was reached (viz., 461 below the 

 zero of Fahrenheit). I do not mean to say that an 

 ideally perfect engine necessarily involves unlimited 

 expansion, seeing that if instead of discharging the 

 steam at the end of a given expansion, we made the 

 engine itself do work in compressing it, we might, 

 under the conditions of Carnot's reversible cycle so 

 justly celebrated as the foundation of the theory of the 

 steam-engine, recommence the action with all the unutil- 

 ized heat in an available form. But an engine upon this 

 principle could only give an amount of useful effect cor- 

 responding to the difference between the whole work 

 done by the engine, and that very large portion of it ex- 

 pended in the operation of compression, and this differ- 

 ence viewed in relation to the necessary size of the en- 

 gine, would be quite insignificant, and would in fact be 

 wholly swallowed up in friction. Carnot did not intend 

 to suggest a real engine, and his hypothesis therefore 

 takes no cognizance of losses incident to the application 

 of an actual fire to an actual boiler. His ideal engine is 

 also supposed to be frictionless, and impervious to heat 

 except at the point where heat has to be transmitted to 

 the water, and there the condition of perfect conduction 

 is assumed. In short an engine which would even ap- 

 proximately conform to the conditions of Carnot's cycle 

 is an impossibility, and a perfect steam-engine is alike a 

 phantom whether it be sought for in the cyclical process 

 of Carnot, or under the condition of indefinite expansion. 

 Practically we have to deal with a machine which, like 

 all other machines, is subject to friction, and in expan- 

 ding the steam we quickly arrive at a point at which the 

 reduced pressure on the piston is so little in excess of the 

 friction of the machine as to render the steam not worth 

 retaining, and at this point we reject it. In figurative 

 language we take the cream off the bowl and throw away 

 the milk. We do save a little by heating the feed water, 

 but this gain is very small in comparison with the whole 

 loss. What happens in the condenser is, that all the re- 

 maining energy which has taken the form of internal 

 work is reconverted into heat, but it is heat of so low a 

 grade that we cannot apply it to the vaporization of water. 

 But although the heat is too low to vaporize water it is not 

 too low to vaporize ether. If instead of condensing by 

 the external application of water we did so by the similar 

 application of ether, as proposed and practised by 

 M. du Trembley twenty-five years ago, the ether would 

 be vaporized, and we should be able to start afresh with 

 high tension vapor, which in its turn would be ex- 

 panded until the frictional limit was again reached. At 

 that point the ether would have to be condensed by the 

 outward application of cold water and pumped back, in 

 the liquid state, to act over again in a similar manner. 

 This method of working was extensively tried in France 

 when introduced by M. du Trembley, and the results 

 were sufficiently encouraging to justify a resumption of 

 the trials at the present time, when they could be made 

 under much more favorable conditions. There was no 

 question as to the economy effected, but in the discus- 

 sions which took place on the subject it was contended 

 that equally good results might be attained by improved 

 applications of the steam, without resorting to an addi- 

 tional medium. The compound engine of the piesent 

 day does in fact equal the efficiency of Du Trembley 's 

 combined steam and ether-engine, but there is no reason 

 why the ether apparatus should not confer the same ad- 

 vantage on the modern engine that attended its applica- 

 tion to the older form. The objections to its use are 

 purely of a practical nature, and might very possibly 

 yield to persevering efforts at removal. 



I need scarcely notice the advantage to be derived from 

 increasing the initial pressure of the steam so as to 



widen the range of expansion by raising the upper limit 

 of temperature instead of reducing the lower one. It 

 must be remembered, however, that an increase of tem- 

 perature is attended with the serious drawback of in- 

 creasing the quantity of heat carried off by the gases 

 from the fire, and also the loss by radiation, so that we 

 have not so much to gain by increase of pressure as is 

 commonly imagined. 



But even supposing the steam-engine to be improved 

 to the utmost extent that practical considerations give us 

 reasons to hope for, we should still have to adjudge it a 

 wasteful though a valuable servant. Nor does there ap- 

 pear to be any prospect of substituting with advantage 

 any other form of thermodynamic engine, and thus we 

 are led to inquire whether any other kind of energy is 

 likely to serve us better than heat, for motive power. 



Most people, especially those who are least com- 

 petent to judge, look to electricity as the coming panacea 

 for all mechanical deficiency, and certainly the astonish- 

 ing progress of electricity as applied to telegraphy, and 

 to those marvellous instruments of recent invention 

 which the British Post Office claims to include in its 

 monopoly of the electric telegraph, as well as the won- 

 derful advance which electricity has made as an illumin- 

 ating agent, does tend to impress us with faith in its 

 future greatness in the realm of motive power as well. 



The difference between heat and electricity in their 

 modes of mechanical action is very wide. Heat acts by 

 expansion of volume which we know to be a necessarily 

 wasteful principle, while electricity operates by attraction 

 and repulsion, and thus produces motion in a manner 

 which is subject to no greater loss of effect than attends 

 the motive action of gravity as exemplified in the ponder- 

 able application of tailing water in hydraulic machines. 

 If then we could produce electricity with the same facility 

 and enconomy as heat, the gain would be enormous, but 

 this, as yet at least, we cannot do. At present by far 

 the cheapest method of generating electricity is by the 

 dynamic process. Instead of beginning with electricity 

 to produce power, we begin with power to produce elec- 

 tricity. As a secondary motor an electric engine may, 

 and assuredly will, play an important part in future ap- 

 plications of power, but our present inquiry relates to a 

 primary, and not a secondary, employment of electricity. 

 Thus we are brought to the question, from what source, 

 other than mechanical action, can we hope to obtain a 

 supply of electricity sufficiently cheap and abundant to 

 enable it to take the place of heat as a motive energy ? It 

 is commonly said that we know so little of the nature ot 

 electricity that it is impossible to set bounds to the means 

 of obtaining it ; but ignorance is at least as liable to mis- 

 lead in the direction of exaggerated expectation as in that 

 of incredulity. It may be freely admitted that the nature 

 of electricity is much less understood than that of heat, 

 but we know that the two are very nearly allied. The 

 doctrine that heat consists of internal motion of molecules 

 may be accepted with almost absolute certainty of its truth. 

 The old idea of heat being a separate entity is no longer 

 held except by those who prefer the fallacious evidence 

 of their senses to the demonstrations of science. 

 So also the old idea of electricity having a 

 separate existence from tangible matter must be 

 discarded, and we are justified in concluding that it is 

 merely a strained or tensional condition of the molecules of 

 matter. Although electricity is more prone to pass into 

 heat than heat into electricity, yet we know that they are 

 mutually convertible. In short I need scarcely remind 

 you, that according to that magnificent generalization of 

 modern times, so pregnant with great consequences, and 

 for which we are indebted to many illustrious investiga- 

 tors, we now know that heat, electricity, and mechanical 

 action, are all equivalent and transposable forms of en- 

 ergy, of which motion is the essence. 



To take a cursory view of our available sources of en- 

 ergy, we have, firstly, the direct heating powers of the 



