September 12, 1S84.] 



SCIENCE 



237 



plainly visible facts, and of what ultimately seem 

 obvious principles, observe the rise and progress of 

 our hardly yet completed theory of that greatest of 

 human inventions, the steam-engine. 



Studying the history of the development of this 

 theory, it cannot fail to become strikingly evident 

 that, throughout, experimental knowledge and practi- 

 cal construction have been constantly in advance of 

 the theory; and that the science of the conversion of 

 heat-energy into mechanical power has, in all stages 

 of this progress, come in simply to confirm general 

 conclusions, previously reached by deduction from 

 experience and observation, to give the reasons for 

 well-ascertained facts and phenomena, and often 

 — not always promptly or exactly — to define the 

 line of improvement, and the limitations of such 

 advance. 



The theory itself began by the correlation of the 

 facts determined by the experiments of Kumford and 

 Davy at the beginning of the century, those an- 

 nounced by Joule and Thomson many years later, 

 and the laws developed by Clausius, Kankine, and 

 Thomson, at the middle of the century. But Watt 

 had discovered, a hundred years ago, the facts which 

 have since been found to set limits to the efficiency of 

 the engine. Smeaton, in many respects the greatest 

 mechanical engineer of his time, made practically 

 useful application of the knowledge so acquired, and 

 endeavored to secure immunity from these wastes by 

 thoroughly philosophical methods. Clarke, a gener- 

 ation ago, showed how the losses first detected by 

 Watt set; a definite limit, under the conditions of 

 familiar practice, to the gain to be secured by the ex- 

 pansion of steam; and Cotterill, within a few years, 

 has shown, by beautiful methods of treatment, their 

 magnitude, and how these wastes take place. Hirn 

 and Leloutre, in France, have similarly thrown light 

 upon the phenomena of ' cylinder condensation,' and 

 De Freminville has suggested the method of remedy. 

 Yet it is only now that we are beginning to see that 

 the philosophy of heat-engines is not simply a thermo- 

 dynamic theory, and that it involves problems in 

 physics, and a study of the methods of conduction and 

 transfer of heat, without doing work from point to 

 point in the engine. We are only now learning how 

 to apply the knowledge gained by Isherwood twenty 

 years ago, and by Hirn and by Clarke still earlier, in 

 solving the problem of maximum efficiency of the 

 steam-engine. We have only now discovered that 

 the ' curve of efficiency,' as Prof. Thurston has called 

 it, is not the curve of mean pressure for ' adiabatic ' 

 expansion, as Rankine called it; for 'isentropic' ex- 

 pansion, as Clausius would call it; but that it is a 

 curve of very different form and location, and that 

 it is variable with every physical condition affecting 

 the working of the expanding fluid in the engine. 

 We have only now learned that every heat-engine has 

 a certain ' ratio of expansion for maximum efficien- 

 cy,' which marks the limit to gain in economy by ex- 

 pansion ; which limit is fixed for each engine by the 

 nature of the expansion, and the method and extent 

 of wastes of heat. All the facts of this case were ap- 

 parently as obvious, as easily detected and weighed in 



their influence upon the theory of heat-engines, years 

 ago as to-day. Even the latest phase of the current 

 discussion of efficiencies of heat-engines, that relat- 

 ing to their commercial efficiency, would seem to have 

 been as ready for development a generation ago, when 

 first noted by Rankine, as to-day; yet what is now 

 known as a simple and easily formulated theory has 

 been several decades in growing into shape, notwith- 

 standing that all the needed facts were known, or 

 readily determinable, at the very beginning 'of the 

 period marked by its evolution. It is only within a 

 year or two that it has become possible to say that 

 the theory of the steam-engine, as a case in applied 

 mechanics, has become so complete that the engineer 

 can safely rest upon it in the preparation of his de- 

 signs, and in his calculations of power, economy, and 

 commercial efficiency. 



Professor Thurston then referred to the knowledge 

 now being collected as to the strength, elasticity, and 

 enduring capacity of the materials used in construc- 

 tion. But the slow progress of scientific development 

 in matters relating to common practice in the useful 

 arts is hardly less remarkable than the difficulty with 

 which scientific principles, even when well estab- 

 lished and well known among scientific and educated 

 men, sink down into the minds of the masses. Per- 

 haps no principle in the whole range of physical 

 science is better established and more generally 

 recognized than that which asserts the maximum 

 efficiency of fluid in heat-engines to be a function 

 simply of the temperatures of reception and rejec- 

 tion of heat, and to be absolutely independent of the 

 nature of the working-fluid. 



This was shown by Carnot sixty years ago, and 

 has been considered one of the fundamental princi- 

 ples of thermo-dynamics from that time to this. 

 Nevertheless, so rarely is it comprehended by me- 

 chanics, and so difficult is it for the average mind 

 to accept this truth, that the most magnificent 

 fallacies of the time are based upon assumptions 

 in direct contradiction of it. The various new 

 ' motors ' recently brought before the public with 

 the claim of more than possible perfection have 

 taken hundreds of thousands of dollars, within 

 the past two or three years, from the pockets of 

 credulous and greedy victims. It is not sufficient 

 to declare the principle: the comparison of steam 

 with ether, and of air or gas with carbon-disulphide 

 or chloroform, must be made directly, and the results 

 presented in exact figures, before the unfortunate 

 investor, whose rapaciousness is too often such as to 

 cause him to give ear to the swindler rather than 

 to the well-informed and disinterested professional 

 to whom he would ordinarily at once go for advice, 

 can be induced to withdraw from the dangerous but 

 seductive scheme. It is true that the principle does 

 not as exactly apply to a comparison of efficiencies of 

 machine, and that the vender of new motors usually 

 seizes upon this point as his vantage-ground ; but a 

 careful comparison of the several fluids, both as to 

 efficiency of fluid and efficiency of machine, through- 

 out the whole range of temperatures and pressures 

 found practicable in application, such as has recently 



