THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



61 



this expwimeBt exhibit, if not strictly so, sufficiently correct data for all we 

 require in a practical point of view. ^ 



1 am aware that this ng-gregate result is composed of the effect of the 

 engines, the effect of the road, and the resistance of the carriages ; and that 

 each of these effects are hable to modification, to the extent to which each of 

 them influence the general result, and to which they are susceptible of fur- 

 ther improvement. We shall afterwards see to what extent each of these 

 operate in producing the general result, and we shall also see that this result 

 is completely and satisfactorily made out by subsequent experiments, on each 

 of these sections separately ; still, in practice, it is the ag:gregate result to 

 which we must look, and by which we must be guided in our inquiries into the 

 entire system. It is of tiie utmost importance to inquire into the causes, 

 that we may know how far the general result is capable of improvement, and to 

 what extent; but in practice, conclusions drawn from experiments on a working 

 scale and character, must carry with them considerable weight as a standard. 



I must here revert to the often repeated expressions of opinion, that in 

 laying down any st.andard of power in engines, and especially any standard 

 with reference to the power of locomotive engines, it should be a varying 

 one, dependant upon their presumed increased powers; and, that looking 

 back to the rapid strides of improvement made in the engines, we may natu- 

 rally look forward to further improvements, and that, therefore, our calcula- 

 tions should rather be founded upon what may probably be the powers of 

 these engines in future, than upon the powers they exhibit at the present 

 time. The force of this is irresistible, but we must not, where the result in- 

 volves the expenditure of an immense amount of capital, yield to prospective 

 theoretical improvements, unless they carry with them stronir, and almost 

 certain grounds of practical realisation. The great impulse of improve- 

 ment giveu to these engines has has been their powers of evaporation, in pro- 

 ducing a sufficiently rapid evolution of steam with an engine of a tangible 

 weight. The system of small tubes has effected more than could at one time 

 be reasonably expected, and we now not only accomplished an immense 

 rapidity of production of steam ; but we have likewise effected this witliout 

 any waste of fuel, and this is a most important element in the consideration. 

 By an inspection of the tables it will be seen, that the average weight 

 of coke required to convert a cubic foot of water into steam, is not 

 greater than what is required by the best constructed stationary engines, 

 and less than Mr. Watts' standard, viz. 81bs. Of coal to each cubic foot of 

 water. When we consider the ingenuity exercised for so long a period upon 

 this part of the economy of stationary engines, with so little effect, and this, 

 with engines infinitely more favourably circumstanced than the locomotive 

 engine, it becomes extremely qiic&tionable to what extent we ought to cany 

 speculations founded upon a presumed increase of evaporating power of 

 these engines. But'allowing to the most sanguine every possible extent of 

 imaginative improvement, and supposing that we could effect an equally 

 economical and as great a rapidity of production of steam, with the North 

 Star, as with enciues of the weight of the Venus, Neptune, and Apollo, 

 which are only of half the power, and which, it may be presumed, would be 

 the limits of speculation by the most fertile mind, what do we gain, we have 

 a saving of two tons weight. Or, if we were to go even further, and take 

 the lightest engine working on the ordinary railroads, and suppose their 

 powers of evaporation to be doubled, we gain no more than five or six tons 

 upon a railway of the width of the Great Western, and this would give us 

 20 tons at 41 miles an hour, instead of 1.5 tons, and so in proportion at other 

 velocities. The only reasonable speculation of future improvements, is in the 

 expectation that increased evaporating powers may be given to such engines 

 as the North Star; and that retaining the same weight of the present most 

 powerful engines, we may so incre.ise their evaporating powers as to produce 

 an increase of effect. Here, however, we have practical data to guide us even 

 in this respect in these tables : the comparative evaporating powers of the 

 jEoIus and the North Star, are 16.5 : 115, and the Venus 1G5 : 106. These 

 tables show, that with such an increase of powers of evaporation, no more 

 than about three miles an hour is gained by the North Star over the .'Eolus 

 both engines being of the same weight. It results, therefore, from these 

 experiments, that it wouU, practically considered, be imprudent to indulge n . 

 speculations which are only necessary in case of considerable improvements 

 being- eflected in the locomotive engine, and by which a much higher rate of 

 speed can be realized than these engines are at present capable of effecting : — 

 we shall afterwards see that there is a limit to the velocity of railway trains, 

 by an element over which we have no control, and that it would be impolitic 

 in a practical or commercial point of view, to attempt more than a certain 

 rate of speed. 



Having thus obtained, as far as the time permitted, the power and capa- 

 bilities of the engines upon the Great Western Road, the next step was by a 

 similar set of experiments to obtain the powers of the engines on railways 

 of the^ordinary width and construction. To accomplish this, application was 

 made to the directors of the London and Birmingham Kailway, who very 

 handsomely granted permission to make any experiments which might not 

 interfere with the traffic upon the road. When, liowever, it is considered 

 that these experiments can only be made in the interval between the trains 

 passing along the line ; that on the Great Western Railway, where, from the 

 line being short, much greater facilities are afforded for making the experi- 

 ments than upon a long line of road, the experiments occupied from the 13lh 

 of September to the 13th of October ; and when it is also considered that 

 these experiments involve considerable cxpen.se, and the almost exclusive 

 attention of the persons connected with the locomotive department, it is quite 

 unnecessary to state that it was extremely difficult to avail ourselves of the 

 permission granted by that company, without such interference with the 

 regular traffic of tUe road as would have been unjustifiable. 



The engines upon these railways, however, are not so varied in their con- 

 struction as those of the Great Western Railw.ay, and therefore a less num- 

 ber of experiments were necessary ; for, instead of having to determine the 

 power of each different kind of engine, it only required experiments to deter- 

 mine the power of almost one engine, the other being so nearly alike, the 

 performance of one correctly ascertained was, in fact, the standard of power 

 of the whole. 



I\Tr. Robert Stephenson, in the most handsome manner, placed at my dis- 

 posal some experiments made on that railway on the powers of their engines 

 during- the summer of this yrar, and, for the purpose of checking these by 

 my own personal observation, he arranged and accompanied me on an expe- 

 rimental trip from the Camden Town station to Boxmoor and back, and gave 

 me an opportunity of making otlier trips to corroborate the accuracy of his 

 experiments. 



Table III. will show the result of those experiments on the London and 

 Birmingham Uailv/ay. 



TABLE III. 



ACCOUNT OF THE PF.RFOUMANCES OF THE ENGINES ON THE LONDON AND 

 BIRMINGHAM RAILWAY. 



These experiments, the results of which are shown in the aheve fable, were 

 made, as will be seen by an inspection of the section, upon a part of the rail- 

 way, the gradients of which .-.re very variable; the inclination being in some 

 parts 16 feet in a mile, and are the mean result in both directions. 



Table IV. is a summary of these experiments arranged for comparison with 

 those on the'Great Western Railway. 



TABLE IV. 



TAHLE OF THE POWERS OF THE ENGINES OP THE LONDON AND BIRMINGHAM 



RAILWAY. 



Load in Tons 



of 

 Carriages and 



Passengers. 



Harvey Comlje engine, ^2 inch 

 cyiiuder, 5 feet wheels. 



No. 15. i\Ir. Bury's eh;?ine, 1 2 inch 

 cylinder, 5' feet wheels . 



Maximum speed Coke per ton per 

 in miles per hour. mile in lbs. 



32.65 

 34:45 



63.45 

 63.91 



64.36 



67.20 



32.88 



32. t 



25.33 



.89 



.59 



.504 



Maximum speed 

 in miles per hour. 



Coke per ton per 

 mile in lbs. 



32.41 

 32.04 

 23.81 



.58 



From this it will be seen that, on a railway of the ordinary widih, where the 

 gradients are variable, and where the resistance is more than doubled in some 

 parts, a mean velocity of 32 miles an hour may be maintained with loads 

 varying from 32 to 54 tons. These experiments were made for the express 

 purpose of comparison with those on the Great Western Railway, and with the 

 same loads ; and thev are, therefore, presented as expermients for such a 

 comparison. I have" done this in preference to producing as comparisons 

 other exper:mcnts made on the Grand Junction, and Liverpool and Manchester 

 Railways ; as if I had done so, these experiments not being made in the same 

 manner, many explaniitions would have been required ; it will, however, be 

 seen, on inspecting the results of the other experiments, that the general com- 

 parative result of the perform.ances of the engines on the London and Bir- 

 mingham R.ailways is corroborated by those other experiments. 



On comparing the results of these experiments with those made on the 

 Great Western Railway we find, that with the same load, or whh a load of ^ 

 tons, a greater rate of speed is accomplished by the Noith Star engine; but 

 that the perform.ances of the engines on the London and Birmingham Railnay 

 with that load, nearly approach those on the Great Western of a less pov/er 

 than the North Star, but of a greater power than the London and Birmingham 

 engines. With a load of DO tons, the North Star engine on the Great Western 

 Railway, acomplished a mean velocity of about two miles an hour greater; 

 the Jiioh\% engine the same rate; but the Venus, Neptune, and Apollo en- 

 gines, of the same power as those on tlie London and Birmingham RailwBy, 



