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THURSDAY, JUNE 21, IJ 



THE STEAM-ENGINE. 

 The Steam- Engine. By G. C. V. Holmes. (London : 

 Longmans, 1887.) 



r*HIS treatise is intended as an elementary text-book 

 *- for technical students. In many respects it fulfils its 

 purpose, at least better than any book of moderate size 

 with which we are acquainted. It is clearly written ; its 

 arrangement, if not the best possible, is orderly ; it is so 

 far practical that problems arising in the actual design 

 and use of steam-engines are not ignored, but attacked 

 in a sufficiently elementary way ; and the rationale of 

 processes involved in the use of steam is explained 

 adequately and correctly on the whole. The woodcuts 

 represent fairly good examples of construction, with the 

 exception of one or two, like those of the injector and 

 exhaust-ejector, which are antiquated, and one or two 

 others so bad that they are obviously mere imaginary 

 sketches. Nevertheless the book fails of being what a 

 really good elementary text-book of the steam-engine 

 might easily be — what, indeed, anyone of Mr. Holmes's 

 competence would make it, if some experience in teaching 

 had shown him the needs and difficulties of engineering 

 students. It is a little to be feared that Mr. Holmes's 

 book is marred by an attempt in part to adapt it to the 

 requirements of some existing examinations on the steam- 

 engine, which are more scrappy and less scientific than 

 the worst of existing text-books. If only a really 

 adequate practical and elementary text-book were 

 written, it would control the examinations instead of 

 needing to be adapted to them. 



The treatise includes the mechanics, the thermo- 

 dynamics, and rules for the design of steam-engines. 

 The portions included under the last head are by far the 

 weakest portions of the book. The scattered discussions 

 of the strength of some portions of engines and boilers 

 are too vague and general to be of practical value. The 

 rules for the strength of fly-wheels at p. 246, and that for 

 area of steam passages at p. 204, are examples of the 

 kind of useless rules which stop short of encountering 

 any one of the actual difficulties of ordinary designing. 

 It is just these portions of the book which seem designed 

 to meet the exigencies of a student cramming for an 

 examination, and the book would be improved by their 

 omission. An elementary treatise on the steam-engine 

 might well leave questions of design on one side, and 

 confine itself to a descriptive account of engines and 

 boilers, with theory enough to explain the actions involved. 

 But then it is neither necessary nor useful in such a 

 treatise to introduce elementary physics and mechanics. 

 A technical student may be assumed to know elementary 

 science. " I have not assumed," says the author, " the 

 slightest acquaintance on the part of the reader with the 

 sciences of heat and motion, and have consequently de- 

 voted many pages to the explanation of such parts of 

 these sciences as are necessary for the proper under- 

 standing of the working of engines." Hence we find 

 a chapter on the nature of heat, including a discussion of 

 the melting of ice, and the graduation of thermometers. 

 There are definitions of mass, weight, force, and velocity, 

 and arithmetical examples of the laws of motion. Surely 

 Vol. xxxviii.— No. 973. 



all this would only be justifiable in an age when elementary 

 books were scarce and dear. An ordinary student finds 

 it a tiresome obstruction, when the way to the subject of 

 the book is barred by such repetition. On the other hand, 

 a brief but clear and critical account of the methods by 

 which Regnault determined the fundamental constants 

 for steam would have been very useful. It would have 

 shown both the meaning of the terms used, and the 

 probable trustworthiness of the determinations. In place 

 of this, we find only verbal definitions and formulae. 



The thermodynamical portion of the book is probably 

 its best and clearest part, and that in which it is most in 

 advance of any quite elementary book of a similar kind. 

 It must be understood that in criticizing this portion we 

 do not ignore the fact that the author has done a service 

 to elementary technical students. 



On p. 67 a diagram is copied from Maxwell, and called 

 a diagram of isothermals of dry saturated steam. It has 

 escaped the author that for dry saturated steam there is 

 no isothermal. At a point in the curve, say at 212 , the 

 steam is saturated : on one side of this it is a mixture of 

 steam and water, or conventionally wet steam ; on the 

 other side it is superheated steam. The saturation curve 

 so useful in steam-engine calculations is nowhere 

 mentioned. Further, in any modern treatment of the 

 steam-engine it ought to be recognized that the engineer 

 is always or almost always dealing not with dry saturated 

 steam but with wet steam. The algebraical expressions 

 for the total heat, &c, of wet steam should be introduced 

 along with those for dry steam. Curiously, nowhere in 

 this book can we find an expression for the latent heat 

 of steam, though no quantity is so often required. The 

 total heat is given, and so the latent heat can be inferred> 

 but surely the ordinary approximate expression for latent 

 heat is also useful. 



In Chapter III. the theory of perfect engines is given. 

 Following the precedent of treatises of wider scope, the 

 author begins with the laws of expansion of permanent 

 gases. Next the theorem about a reversible engine is 

 given, but in a form in which it is restricted to the case of 

 an air-engine. The efficiency of the reversible engine so 

 obtained is afterwards spoken of as the efficiency of 

 perfect heat-engines in general. But the independence 

 of the result on the nature of the fluid employed is no- 

 where indicated. The diagram for a perfect steam-engine 

 is given on p. 113. But no elementary student will 

 perceive why the efficiency of this is the same as that 

 of the air-engine, at least without explanation. The only 

 idea ordinary students get from the theorem about the 

 Carnot engine is that the efficiency of any engine 

 is proportional to the range of temperature in the 

 cylinder. In the case of the actual steam-engine this is 

 so wrong as to be nearly the reverse of the truth, and 

 the misconception is hardly anywhere adequately guarded 

 against. It is very doubtful whether the Carnot engine 

 ought to be introduced into the elementary theory of the 

 steam-engine. An ordinary indicator-diagram can be 

 taken, and the relation of the heat expended to the heat 

 utilized determined. From the feed measurement and 

 indicator-diagram the steam liquefied at the end of 

 admission and at exhaust can be ascertained. The heat 

 expenditure corresponding to work of admission, ex- 

 pansion, and expulsion can be calculated. From the 



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