THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



71 



trial; sonif such filiorl pxpoi-ionee and such trials were at least necessary to 

 bring the system even on a par with others long previously in operation ; hut 

 this opportunity «e have not yet had. 



From the results obtained up to the present time, therefore, little could be 

 hoped for beyond very clear and decided indications of all defects, while the 

 advantages were still to be acquired ; and if, under such circumstances, the 

 performance had been nearly equal to that obtained on other lines, with the 

 benefit of long experience, I should liave been satisfied M'e should have had 

 a right to expect great improvements; we should have started from the point 

 at which others had arrived ; and when we had attained the same relative per- 

 fection in all parts which they had, with all the advantage of their previous 

 experience, and which we might calculate upon doing in a much shorter time, 

 we should be as much in advance of our present state as they are now of the 

 state in which they were some years ago. 



But I a]n prepared to shew that we are now in that position ; that the per- 

 formance of our engines is not merely as great, but greater, than that which 

 has yet been attained on other lines ; that those changes and improvements to 

 which I have alluded an; just commenced ; and that, even since l\Ir. Wood 

 made his experiments, the advance has been so great, that if he were now to 

 repeat them he must arrive at totally dilferent conclusions. 



Tables III. and IX. of his report give the performance of engines with 

 ditierent loads on the London and Birmingham, and on the Great Western 

 Railway. From them it would appear, that ou the Birmingham Railway the 

 same engines which took f>0 and 64 tons at 24 and 2vH miles j-.er hour, were 

 only capable of taking 34A and 33 tons at 32^ and 33 miles per hour, with 

 nearly double the consumption of coke per ton ; while on the Great Western 

 Railway the same engine — the North Star, was capable of carrying 82 tons at 

 3.3 miles per hour ; only 33 tons at 37 miles per hour, and Hi tons at 41 miles, 

 and to obtain which last additional velocity of four miles per hour the con- 

 sumption of coke per ton was more than doubled. 



Such an enormous diminution of effect by a comparatively small increase of 

 speed, if unavoidable, or necessarily consequent on the increased resistance of 

 the train, would undoubtedly justify the conclusion arrived at by Mr. Wood, 

 that to attempt to exceed 35 miles per hour is not advisable ; and conse- 

 quently, that so far as the system of the Great Western Railway was adapted 

 for high velocities it was unsuccessful. But these conclusions are founded 

 upon the statements above referred to. Experiments have since been made 

 giving very different results, and I can prove, that if an engine be properly 

 con.structed for high .speeds in the manner which I liave always proposed, that 

 there is no such " immense sacrifice of power incidental to an extreme high 

 rate of speed, or the accomplishment of a rate of thirty-eight or forty miles 

 per hour above that of tlnrty-two or thirty-live miles," (page 03 ;) and that 

 tile same engine, which was then only capable of taking sixteen tons at an 

 average velocity of thirty-eight and a maximum of forty one miles and a half 

 per hour, is now capable of taking forty tons ut an average velocity of forty 

 miles per hour; and further, that the consumption of coke per ton, so far 

 from being extravagant, is not so great as that of the engines on the TiOndon 

 and Birmingham Railway, when only travelling at a mean rate of thirty miles 

 per hour. 



The experiments have been made with the same engine and the same class 

 carriages as those used in Mr. Wood's experiments, and in every other re- 

 spect conducted in the same manner, and without any attempt to diminish 

 the resistance of the air, which may be done to a great extent, and which 

 as I shall hereafter have occasion to state, was always my intention, and has 

 been prepared for in the construction of engines and carriages. 



The comparison between the performance of this engine in September 

 last and at the present time will therefore stand tlms : — 



Cousmuption 

 Load. Average of Coke 



Tons, .-(peed, per ton per mile. 



September, 15.9 38i 2.70 



December, 40 40 " .90 



From which it appears that in less than three months (the change has really 

 been effected but lately) the performance of the engine is nearly trebled, 

 while the consumption is reduced to a moderate quantity, or by two-thirds 

 of that of the former experiments. 



The explanation of this change is easily given. The great diminution 

 in the useful effect of the engine in the former experiments did not arise 

 solely from the increased resistance of the train — which might have been 

 more difficult to overcome — but principally from the diminished power of 

 the engine at that speed. This might appear, at first sight, to be the same 

 thing, but such is by no means the case. The increased resistance of the 

 load to be moved might arise from causes which could not l)e controlled. 

 The diminished power of the engine might be a mechanical defect, capable 

 of being remedied, and investigation has proved the truth of this most satis- 

 factorily. The engines at that time were so regulated by the proportion of 

 some of their parts, that their power was crippled when the speed was in- 

 creased. The great quantity of steam which is required, could not, in fact, 

 escape, and if allowed to escape more freely, there was a deficiency of draft 

 in the furnace. This was a difficulty incidental to the high speeds, and 

 also to the increaseil diameter of the driving wheels, but it is a difficulty 

 which is capable of being overcome, and, in a great measure, has been over- 

 come. There is, however, no doubt, still room for improvement ; but if, in 

 so short a time, we have made this great advance, it is fair to presume that 

 we may make still further improvements. 



If, therefore, great speed is attainable— if there are no natural causes, no 

 insurmountable obstacles— the position taken by Mr. Wood (and in taking 

 which he was perfectly justified, by the evidence before him) becomes totally 

 changed. The hypothesis is ao longer correct oa which the opiniou was 



formed and expressed in page 1)8, in the following words: — " If such a con 

 elusion" — viz. , the practical limit of 35 miles per hour — "is warranted by these 

 investigafions and experiments, then it results that it is not necessary for the 

 attainment of such a rate of speed that the gauge should be seven feet." But 

 all the advantages pointed out in the two following paragraphs of the Report 

 as resulting from an increased width of gauge over the four feet eight inch, 

 apply in a still greater degree than under the circumstances which existed at 

 the time. Some doubts are expressed as to the advantage of so great an in- 

 crease of gauge as seven feet; but these doubts, again, appear to arise entirely 

 from the circumstance, tliat the results of the experiments then made upon the 

 performance of the engines were unfavourable. The reverse appears now 

 to he the case; the work performed with a given consumption of coke i.s 

 much greater than in any of the experiments made upon other lines, the de- 

 tails of which are given in the Report. 



On the subject of the seven-feet gauge, I can add very little to what I have 

 said before. It was adopted expressly to enable ns to effect that arrange- 

 ment which is recommended at page 08. 



'*We see that there isadiminution of friction, by the increase of the diameter 

 of the wheels, but it is doubtful to what extent this is modified by elevating the 

 bodies of the carriages ; a broad gauge, by allowing the bodies of the carriages 

 to be placed within the wheels, and thus to reduce the height of the carriages, 

 and consequently diminish the area of the frontage, is an advantage, consider- 

 ing the great amount of resistance arising from the atmosphere." 



To effect this, with the most convenient form of body, similar to that ordi- 

 narily adopted on railways, does require, as I have frequently stated in pre- 

 vious reports, a width of at least feet 10 inches. 



The advantage of stability is probably directly in proportion to the increased 

 width ; and upon this point I will quote the words of Mr. Wood, page 68 : — 



" The remaining proposition is, that a wider gauge affords increased stability 

 to the carriages, and, consequently, increased steadiness of motion. The dia- 

 i^rams given will show how tar this has been effected on the present portion of 

 the Great Western Railway, and certainly these docucnents would prove that 

 this has not yet been accomplished. Considering, however, the causes of the 

 different motions of railway carriages, there can be no doubt that an increased 

 width of gauge must tend to produce that effect. In the present instance this has 

 been counteracted by the construction andpresenteondition ofthe road and carri 

 ages ; and therefore, it appears to me^ the only conclusion we can come to is, 

 that in similarly constructed railways the wider gauge will afford greater sta- 

 bility and steadiness of motion to the carriages." 



As regards the expense of forming the railway of increased width, BIr. 

 Wood has made a mistake, which I believe he will correct in the Appendix. 

 The estimate of the increased cost is £39,000 only, instead of £151,840. 

 Upon all these points I have so frequently explained my views to you, that I 

 shall take the hberty to quote a passage from my report of the 1.5th of August, 

 which contains in a small compass the grounds upon which I adhere to my 

 opinions in favour of the width of gauge I have selected :^ 



" It has been asserted that four feet eight inches, the width adopted on the 

 Liverpool and ^lanchester railway, is exactly the proper widtli for all railways, 

 and that to adopt any other dimension is to deviate from a positive rule which 

 experience has proved correct ; but such an asseition can be maintained by no 

 reasoning. Admitting, for the sake of argument, that, under the particular 

 circumstances in which it has been tried, four feet eight inches has been proved 

 the best possible dimension, the question would still remain — What are the 

 best dimensions under the circumstances? 



".Mthough a breadth of four feet eight inches has been found to create a cer- 

 tain resistance on curves of a certain radius, a greater breadth would produce 

 only the same resistance on curves of greater radius. 



" If carriages, and engines, and more particularly, if wheels and axles of a 

 certain weight, have not been found inconvenient upon one railway, greater 

 v^'cights may be employed, and the same results obtained, on a railway with 

 better gradients. 



" To adopt a gauge of the same number of inches on tlie Great Western 

 Railway as on the Grand Junction Railway, would, in fact, amount practically 

 to the use of a different gauge in similar railways. The gauge which is well 

 adapted to the one is not well adapted to the other, unless, indeed, some mys- 

 terious cause exists, which has never yet been explained, for the empirical law 

 which would fix the gauge under all circumstances. 



" Fortunately, this no longer requires to be argued, as too maiiy authorities 

 may now be quoted in support of a very considerable deviation from this pre- 

 scribed width, and in every case the change has been an increase. 



" I take it for granted that, in determining the dimensions in each case, due 

 regard has been had to the curves and gradients of the line, which ought to 

 form a most essential, if not the principal, condition. In the report of the com- 

 missioners upon Irish railways, the arguments are identically the same with 

 those which 1 used w hen first addressing you on the subject in my report of 

 October, 1835. 



" The mechanical advantage to be gained by increasing the diameter of the 

 carriage wheels is pointed out ; the necessity, to attain this, of increasing the 

 width of way ; the dimensions of the bridges, tunnels, and other principal works, 

 not beiu" materially affected by this, but, on the other hand, the circumstances 

 which limit this increase being the curves ou the line, and the increased pro- 

 portional resistance on inclinations (and on this account it is stated to be almost 

 solely applicable to very level lines), and lastly, the increased expense, which 

 could be justified only by a great traffic. 



'* The whole is clearly argued in a general point of view, and then applied to 

 the particular case, and the result of this application is the recommendation of 

 of the adoption of 6 feet 2 inches on the Irish railways. Thus an increase in 

 the breadth of way to attain one particular object — viz., the capability of in- 

 creasing the diameter of the carriage-wheels, without raising the bodies ofthe 

 carriages, is admitted to be the most desirable, but is limited by certain cir- 

 cumstances, — namely, the gradients and curves of the line, and the extent of 

 traffic. 



