70 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



recorded in the [ireceding section. The tliird section, from pages 6.0 to ti8, 

 is devoted to the investigation of the stability of the rails and eaiTiages. The 

 remainder of the I'oport is occupied with the eouclusioiis arrived at, founded 

 upon the preceding <diservations and results. 



As regards llio construction of the road, to which the third section princi- 

 pally relates, ]Mr. \\'ood ajipears to he of opinion, that for high speeds, con- 

 tinuous longitudinal bearings of timber form a good mad, and that the mode 

 adopl'd on the Great Western Railway of securing the rail to the timber is 

 good ; but tlint the system of piling is bad, and that the weight of rail and 

 scantling of limber hitherto adopted on the portion of the line completed, are 

 insuflRcient. All this is in perfect accordance with the plans proposed for the 

 futnre eonsti'uction of the road. A rail considerably stifler and longitudinal 

 timber of gi'cater scantling are prepared, and a plan has been recommended to 

 you and approved of, in which the use of the piles is abandoned. Though I 

 do not, therefore, difler from Mr. Wood in his results, I think it right to say 

 here, as regards the experiments themselves which are recorded, that those 

 upon the deflection of the rails of the Great Western Railway necessarily give 

 a much less favourable result than would have been obtained had an average 

 been taken of experiments over the whole line : these experiments have been 

 confined iilmost exclusively to a short space of about two miles in the clay 

 cuttings in the neighbourhood of I'addington, where we liave always met with 

 the greatest difficulties, and which is undoubtedly the worst part of the road. 

 I conclude that this was accidental, and that want of time alone has prevented 

 further experiments being made; nevertheless, the results must not be taken 

 as a correct average of the line. As regards those upon the comparative 

 smoothness of the carriages, I am botmd to say that I doubt the accuracy of 

 the instruments. I always maintained that they were not correct in principle, 

 and were quite capable of indicating greater movements in an easy carriage 

 or on a good road, than in a rough carriage or on a bad road, if the motion of 

 the former should happen to coincide with the natural motion of the instru- 

 ment ; or, if the former should be of a character to which the instrument, from its 

 construction, might be more susceptible. If the instrument were good as 

 E comparative measure, it would, of course, in each experiment, indicate the 

 rough and smooth portions of our line. Now certainly, according to the 

 Table 15, there are no indications which would enable us to point out cor- 

 rectly these diti'erent parts of our line, although they are distinctly perceptible 

 to the traveller, and well known to us. And, upon turning to the Table, and 

 the correspnnding portions of the line referred to, I find, from an exact know- 

 ledge of every part of it, that the numbers indicate rather the reverse of the 

 fact, giving the low*est amount between the second and seventh miles, which 

 is a bad part, and the highest between the seventh and fifteenth, where the 

 road is good. It is not, however, xipon this discordance in the results that I 

 found my objection to the instruments used. Tliey might have been correct, 

 whilst the instrument was taulty. But considering the principles upon which 

 they were constructed to be unsound, and as I do not hence attach much 

 importance to the results, t only now allude to them, to prevent my silence 

 being misunderstood. 



But, in the absence of an accurate instrument, the public are perhaps most 

 competent to determine whether, on the whole, they find the travelling on the 

 Great Western Railway as comfortable, and tlie motion as easy, even at pre- 

 sent, as upon other lines ; and this, notwithstanding the shorter time 

 our road has been opened, the greater speed of our engines, and that as 

 yet we work under all the disadvantages of new tools (carriages and road 

 inclusive), in which experience is absolutely necessary to adapt the vari- 

 ous parts to each other. Unless, indeed, instruments are contrived which 

 shall separate the different sources of motion, and measure them accurately, 

 they will hardly afl'ord as correct information as the mere sensations of a care- 

 ful observer. 



Upon the question of the assumed amount of resistance from the air, as de- 

 duced from experiments made upon that part of the Liverpool and Manchester 

 Railway called \A'histon inclined plane, if, practically, the high speed be attain- 

 able, as I w ill prove it to be without the extravagant'cousumption of fuel which 

 was supposed to be unavoidable, it is perhaps unnecessary to occupy your time 

 at present with an inquiry into the subject. But as it has been looked upon 

 as the discovery of a new cause brought into operation, from which we are to 

 apprehend new and hitherto unexpected results, I must say alow words upon 

 it. The resistance to a body moving through the air has long been known, 

 and although perhaps not with perfect accuracy, yet tables giving a near 

 approximation were made and published sixty or seventy years ago, by 

 Sraeaton, (Phil. Trans. .51st vol.,) as well as by other eminent men, and are 

 now to be found in most elementary works. 



-Any calculations founded upon these Tables shew that resistance of the 

 atmosphere is very considerable, and varies in some ratio approaching to that 

 of the squares of the velocities. I have long since, and frequently, made 

 such calculations, which I believe, if judiciously made, would give more cor- 

 rect results, though not nearly so large as the' experiments before us ; they 

 would at least be free from several very serious sotu'ces of error. 



That there must liave been some great sources of error is evident from the 

 striking discrepancies between the result of the experiment on the Whistou 

 plane and every day's experience upon it. The passenger train, in descending 

 this plane, with the steam shut off the engine, which then causes some con- 

 siderable resistance, fiequently acquires a vcrv high velocity, exceeding forty 

 miles rather than thirty miles per hour, and requiring the iise of the break. 

 This I have seen occur without any favouring wind, while in the experiments, 

 Jiotmthstanding the assistance of a breeze, the carnages did not acquire a 

 Telocity of more than 3^ miles per hour. Although this is so contradictory, 

 there is nothing really inconsistent with the full operation of resistance of the 

 atmosphere, but merely an evident indication of the circumstances being 

 quite dissimilar in the experiment from those which occur iu actual practice. 



Again; in the experiments themselves, a circumstance is mentioned which 

 destroys the apparent agreement between the result and the theory, and which 

 would prove that the resistance of the atmosphere is even much greater than 

 is stated, and in fact makes it so excessive, and so different from the result 

 obtained from the experiment on the Madeley inclined plane, which is also 

 given, as to destroy any dependence upon either of them. 



It is stated in p. 05, that " there was a pretty strong wind directly in favour of 

 the motion of the train, down the Whiston plane." Now, 10 miles an hour 

 is below the velocity of anything that can be called" a pretty strong wind," 

 — but assume 1 miles, so as to be on the safe side — deducting this from the 

 ;i2.1 miles, we have '22\ as the real velocity of the train passing through th« 

 air, or the velocity to which alone any atmospheric resistance could be due. 

 At this velocity, 2,31bs. per square foot would be the utmost effect that could 

 be produced by the air, and the 3201bs. ascribed to atmospheric resistance 

 would therefore require 143 square feet of surfeue : if the four carriages had 

 been placed by the side of each other instead of behind, this surface would 

 hardly have been obtained ; or, again, if the 3291bs. were due to the atmos- 

 pheric resistance of four carriages of the narrow gauge at 224- miles per hour, 

 at -10 miles the same four caniages would meet the resistance of l,0631bs., 

 which alone, without any allowance for friction, or for the increased width 

 of carriages, would be a greater resistance than the North Star engine is capa- 

 ble of overcoming. But the North Stor, as I shall hereafter shew, does take 

 a train of seven carriages, weighing 40 tons, and having seats for 188 passen- 

 gers, at 40 miles per hour, which according to the above data would require, 

 including friction, a tractive power of somewhere about l,5001bs., probably 

 nearly double that which the engine can possibly exert at that speed. But 

 these discrepaticies arc easily accounted for. 



The experiments were made with very light loads, ISf and 18 tons; and 

 consequently the assumed comparative resistance for the air, which would bo 

 nearly the same even had there been .50 tons, appears much larger. The 

 friction of .50 tons would have been 28.51bs., and the atmospheric resistance 

 being still 3291bs., the relative per centage of the total resistance would have 

 been 44 and o6, and to the 44 per cent, has to be added, all the friction of 

 the engine itself, which is also a constant quantity independent of any resist- 

 ance of the air ; taking this at 15, or one-third of that of the trains, the pro- 

 portion becomes 51 for friction, and 49 for some other resistance, instead of 

 22 and 78. 



But the sources of en'or to which I have alluded are much more serious, 

 and appear to me so incapable of measurement, and consequently of correc- 

 tion, as to render the experiments useless. 



The circumstances were not really, though apparently so, in any one point 

 similar to those of an ordinaj-y train in jnotion. In the first place, the car- 

 riages are sent with the square end to meet and receive the full resistance due 

 to their surface, which is totally diflerent from the case when the engine pre- 

 cedes them. In the next place, this resistance is acting entirely against the 

 front of the first carriage of the train, while the motive power, — viz. the gra- 

 vity, is behind, that is, acting upon each carriage, and pushing one upon 

 another. Everybody experienced in railways knows that in such a case the 

 carriages are thrown out of square, and a degree of resistance created which 

 would alone account for the whole. 



The ultimate conclusions, however, at which Mr. Wood aiTives on all the 

 principal points, vrill, upon perusal, be found to have been governed by the 

 results of the experiments upon the performance of the engines, and the as- 

 sumed resistance of the trains at liigh speed ; the exiJcriments upon the resist- 

 ance of the air being made to ascertain if this assumed increase of resistance 

 could be accounted for. 



The mechanical advantage of large wheels for the caniages is, of course, 

 admitted ; but high speeds being assumed to be practically or economically 

 unattainable, the reduction of friction is considered unimportant. I shall 

 now, therefore, consider tliis branch of the subject — the performance of tlie 

 engines. 



The locomotive engines niuniug upon the ordinary railways are the result 

 of nearly ten years' experience ; during which time the most talented manu- 

 facturers have been constantly engaged, not in inventing any new construc- 

 tion of engine, — for certainly, seven, if not eight years since, Messrs. 

 Stephenson constructed, what, in form and general arrangement, was exactly 

 similar to that now mad|0— but simply in adapting and proportioning the 

 different parts the one to Bie other, and by such trifling changes, if they can 

 be called so, important improvements have been effected, and greater speed 

 and economy attained. 



On the engines made for the Great Western Railway the same experi- 

 enced manufacturers ha\e been employed ; but as a higher speed was sought, 

 a lai-ger evaporating surface of boiler . J|kreciuired ; and many of those pro- 

 portions which had been long studied, ■Bp*) which perfection had to a great 

 extent been attained, were necessarilT&ltered : and yet these machines, 

 brought into operation without the possibility of any sufficient previous trials, 

 in which their defects could be discovered or improvements introduced, are 

 taken as the full measiu-e of what can be effected in the new system of which 

 they form a part. It is certainly cimtrary to all experience to suppose that 

 they should at once be well adapted to a new system; for not only would this 

 have required more fore.'^ight than the most eminent of those engaged i» their 

 constniction could possibly possess, but it involved a departure from many 

 rules in favour of which long and successful experience had, to a certain de- 

 gree, created a prejudice. 



The experience of at least some months of the actual working of these en- 

 gines, and that at a time when we should be sufficiently free from all the em- 

 barrassments of the first opening of the line to allow of such alterations being 

 tried as appeared likely to effect improvements, which involves the ability to 

 throw out of work any engine upon which it might be necessary to make the 



