172 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Jl'ne. 



little affected by changes in the velocity of the wheel, from bcinfr 

 held stationary, to any velocity it may acquire by the ])rcssure of 

 the water on the vanes ; — or by any change in the circular motion 

 of the water onterinjr the wlieel (at its verge), either with or con- 

 trary to tlie circular motion of the wheel. 



In corroboration of this position, we have the experiments at 

 Troy, in whicli the discharfre (at the maximum) was a trifle less 

 than 50 per cent., owing probably to tlie unfavourable form of the 

 vanes ; — and the fourth set of my model improvements (the notes of 

 which you have), wliere the water passed, inwardly, througli a 

 structure, which, when the wheel was removed, was exactly similar 

 to such a wheel, — the quantity discharged in this instance, being 

 just 50 per cent, of the theoretic discharge. 



Among the many "interesting objects" at the American Institute 

 Fair, of the present season, there was a centre-discbarge reaction 

 wheel, in a very neatly constructed model, tlie wheel, about four 

 inches in diameter, being made of brass and neatly finished. To 

 the under side of a disk, attached to a vertical sluift, were attached 

 jilane vanes extending from the verge to a circle about one-half of 

 an inch from tlie verge. To these vanes was attached the annular 

 rim, in the usual way. The angle of the vanes directed the water 

 somewhat without the direction tangent to the inner diameter of 

 the annular rim, .ind after passing into the wheel, it fell through 

 the opening of the rim, and bottom of flume some inches, into 

 a basin beneath. The flume was a glass cylinder about seven inches 

 diameter ; and the supply, a constant stream of " Croton" through 

 a lead pipe, — falling in from the top of the cylinder. 



Suspecting from my former experiments that the discharge of 

 such a wheel must he uniform under all velocities, I took the op- 

 portunity of experimenting on this, by applying friction to the 

 shaft (about half an inch in diameter) with my fingers. / could 

 nuike no .sensible, variation in the height of surftiee by any change of 

 mlociti/, from being held, to running it beyond its natural free velocity 

 (by rolling the shaft between the thumb and fingers J, nvr by turning 

 the wheel backward. 



The accompanying cut represents a section of the vanes. 



TREATISES ON THE STEAM-ENGINE. 



The want of a satisfactory treatise on the steam-engine has 

 long been felt. The existing treatises, notwithstanding their 

 general merits, do not supply the whole of the information which 

 the engineer recjuires; and the looseness of scientific views, and the 

 neglect of systematic arrangement, observable in most of them 

 render mucb'of the knowledge imparted either dubious or inacces- 



We have been frequently called upon to give advice in the choice 

 of a work on this important subject. In answer to correspondents 

 who liad made an application of this kind, we replied some time 

 ago (vol. IX., page 392), that a complete treatise appeared to us 

 to be one of the desiderata of engineering literature. Several sub- 

 sequent letters strongly confirmed the opinion then expressed, that 

 the existing treatises on the theory, construction, and routine 

 management of the masterpiece of mechanical invention are not 

 what they ought to be — accurate, complete, and systkmatic. 



It is no disparagement of the efforts of those who have already 

 written on the subject, to assert that we now know more of it than 

 they did. This branch of knowledge is necessarily progressive. The 

 operations of the Bteam-engine have been extended in diversity 



and magnitude, and have attained a universality which to its great 

 inventor himself would have appeared incredible. The new de- 

 mands of the manufacturer, engineer, navigator, and mechanician, 

 stimulate and suggest new aiijdications of the most powerful 

 and most obetfient of the agents of human industry : upon ma- 

 chinery so complicated, the fertility of modern invention and the 

 boldness of modern enterprise are incessantly and successfully 

 exerted : while the minute details of the apparatus are constantly 

 receiving fresh improvements, as practical skill becomes more and 

 more developed and refined. 



Yet the apparatus itself is in the main unchanged. The steam- 

 engine of Watt is the steam-engine of 1848: the great inventor 

 bequeathed it to us almost perfect in aU its principal parts, and 

 the small amount we have been able to add to his legacy is a 

 striking and accumulative testimony to its original value. 



This consideration greatly simplifies the labour of compiling a 

 perfect exposition of the combination of the mechanism. But 

 though the innovations of practice be here confined to details, in 

 other respects the changes have been fundamental. Experience 

 has effected great alterations in the purposes, the management, 

 and the dimensions of the engine itself; and the accessory parts, of 

 which the boiler and furnace are the principal, have received modi- 

 fications which have completely changed their character. 



The theory of the steam-engine is also fundamentally different to 

 that originally proposed : that Tredgold's views of the rationale 

 of its action have been totally falsified by subsequent experi- 

 ence may be unhesitatingly asserted. It is much to be regretted 

 that his authority, deservedly great as it in some respects is, has 

 given weight to opinions which of themselves cannot stand the test 

 either of theory or practice. It is still more to be regretted that 

 mistaken partiality to his works should have induced subsequent 

 writers to gloss over his errors, and defend tliat which is indefen- 

 sible. When the theory of the Count de Pambour appeared, its 

 obvious truths ought not to have been resisted by absurd prejudice 

 in favour of our countryman. De Pambour is right — Tredgold and 

 his followers wrong. This sounds like a very dogmatic assertion : 

 and we intend it to be so, for if the lucid demonstrations of De 

 Pambour fail to convince his opponents, they are either too per- 

 verse or too dull to be converted : we are driven as a last resource 

 to assertion, e^' euthedni, and to resist frivolous contradictions by 

 the weight of great names. The theory of De Pambour had no 

 sooner appeared, than all scientific writers renounced their pre- 

 vious views, and without reluctance signified their adhesion to his. 



Not indeed that all his conclusions are absolutely indisputable. 

 The chief problem to which he addressed himself was this: — Given 

 the dimensions of an engine, to ascertain the resistance it will 

 overcome at a given velocity, or the velocity at which it w ill over- 

 come a given resistance. Now, the main diflSculty of the question, 

 and that which De Pambour has only partially met, is to ascertain 

 the amount of resistance. It is an essential element, and any 

 uncertainty res])ecting it affects the whole subject. Without 

 particularising further, we may observe that he has erroneously 

 estimated the resistance to which locomotive engines are subject, 

 and has assumed a law of friction (Coulomb's) which is in this case 

 inapplicable. Another difficulty is in ascertaining the actual 

 efficiency of the boiler. Its apparent evaporation and its effective 

 evaporation are not tlie same — jiart of the w ater being drawn into 

 the cylinders in a liquid state. The amount of " priming" depends 

 on minute and varied circumstances, — the violence of ebullition, — 

 the foulness or purity of the water, — its level in the boiler, — and 

 the capacity of the steam-pipes. Certainly, no mathematical for- 

 mula, such as De Pambour has laid down independently of these 

 considerations, can be universally and exactly correct. 



The materials for an improved treatise are abundant ; and those 

 who enter on the task of comjiiliiig such a work, should ransack 

 every source of information. Notwithstanding our strictures on 

 Tredgold, we are disposed to think that his work ought to be the 

 basis of a new treatise. There are many reasons which conduce to 

 this conclusion. In the first place, on comparison, his plan and 

 arrangement seem the most perspicuous hitherto publislied. In 

 the second place, most engineers are familiar with it. This is a 

 great point : readers do not like to be constantly learning out of 

 new books, and engineers especially have seldom time to spare in 

 familiarising tliemselves with new systems. 



The plan which jMr. Eaton Hoogkinson has pursued in his edi- 

 tion of the " Treatise on Cast-iron," appears to be the best for 

 the case before us : he has left his author's text as he found it, 

 appending his own coiTections and additions. With respect to a 

 treatise on the steam-engine, the authorities to be searched and 

 cited are numerous and valuable. In pure theory, the views of 

 De Pambovr should be clearly stated, with the modification above 

 suggested. Some of Professor Moseidy's most useful practical 



