"Whatever the 'chances' may be, what are the facts! Not only have the greatest number of accidents happened with four-wheeled engines, but those accidents have been among the most disastrous that have occurred."
38. Whilst, therefore, those individuals who have advocated the use of the six-wheeled engines are constantly changing their ideas, at one time adopting a large fire-box with the outside frame, and the addition of a third pair of wheels behind the heavy box to carry it, then changing to the small fire-box, with the third pair of wheels placed before it, and, subsequently, by the tardy adoption of the inside frame; we have been steadily persevering with our original plan, of engines on four wheels, which is now brought to a state of perfection for power and economy far beyond anything we could have expected. In proof of this, we can confidently refer to the London and Birmingham, the Eastern Counties, the Midland Counties, the North Union, the Lancaster and Preston, and the Manchester, Bolton and Bury railways, which are worked exclusively with the form of engine we have adhered to; and also to the Edinburgh and Glasgow, Glasgow and Ayr, and Runcorn Gap and St. Helen's, and several other lines which have in part adopted it.
39. In justice to ourselves we have thought it right to lay these remarks before the public, at the same time that we are quite ready to construct engines upon six, or any other number of wheels, freeing ourselves from the responsibility of the consequence of any other plan than our own; and only requesting that such of our friends and the public as may entrust their orders to us will permit us at least, for the safety of travellers, and our own credit, to adhere to inside framing.
Burt, Curtis, and Kennedy.
"It appears from this, that the four-wheeled engine 'has been steadily gaining ground, until Messrs. Bury and Co. have discovered that it would be more profitable to make six-wheeled engines than - to close their works." February 2, 1843.
We were unwilling to interrupt the continuity of the foregoing controversy by any remarks of our own, as they would perhaps have caused some confusion as to their authorship; but we will now briefly observe, that some pars of the replies of the "Practical Engineer" are somewhat irrelevant to the subject, and of no public interest; which would have been avoided, had Messrs. Bury and Co. expressed themselves with more discrimination as to the origin of the particular arrangements of construction they alluded to. For our own parts, we never for a moment supposed that those gentlemen meant to lay a claim of invention to four-wheeled engines, or to inside framing; - because it must have been notorious to the most superficial observers, that those modes of construction were more extensively adopted than any other, in the early locomotive engines. But we regarded the observations in their circular, which gave rise to the animadversions of the "Practical Engineer," merely as a defence of those arrangements which long practical experience in manufacturing for the most successful line of railway in the kingdom (where they have been underiatingly used,) had led them to consider the best: and which circumstance, we may add, has earned for them a high reputation as practical engineers.
Explanation of Figs. 1 and 2. In this Engine the bearings are inside the wheels, and the weight of the engine and boiler is carried at A A. The tendency of the axle therefore is to bend downwards in the centre, whilst the pressure of the flange against the rails in going round curves has a contrary tendency. Thus, one strain counteracts the effects of the other; and, if the axle breaks, the wheels can spread out no farther below than the amount of allowance for play between the flange of the wheel and the rail. The wheels therefore being confined between the rails by the flange pressing against the inside of the rails, may proceed with safety to the next station.
Explanation of Figs. 3 and 4. The gravity or insistent weight of this Engine with outside frame, is carried at 6 B outside the wheels. The gravity of the entire engine and boiler in this case, tends to bend the axle upwards in the middle, and the pressure of the flange of the wheels against the rails in going round curves, acts in the same direction, and in addition to it. This continued bending of the axle destroys the fibre of the iron, and ultimately it breaks; and when it is broken, the tendency of the axle upwards, as before shown, forces the wheels between the rails, there being no outside flange to prevent it, as is shown in Fig. S.
Had we space to go into the subject at large, we could show by reference to authentic official documents that "A Practical Engineer" has committed himself on several points, but we have only room to admit a short letter, addressed to the Editor of the Mechanics' Magazine, signed J. G. S. (vol. xxxvii. page 246,) which completely disproves the assertions of the before mentioned gentleman on some very important points. The letter states, "Your correspondent, the ' Practical Engineer,' asserts, that the engines of Messrs. Bury and Co. on the London and Birmingham railway, consume more coke per mile per carriage, than those on the Liverpool and Manchester. He also says, that, on the Grand Junction railway, one engine is employed to draw a train of equal weight, and at an equal speed, to one which on the London and Birmingham requires two engines. Now, the annexed tables will show the opposite to be the case on the Grand Junction; and from Time-tables in Pambour's Treatise on the Locomotive Engine (pp. 312, 313) I find the average quantity of coke consumed on the Liverpool and Manchester to be about the same as on the Birmingham, though in no case does it average so low as 29lbs. per ton per mile, as in the annexed tables.
The 'Practical Engineer ' says also, that in his opinion, Messrs. Bury and Co's. inside frame is very defective in point of durability. Perhaps he will give his reasons for thinking so, and show the advantage of the heavy outside framing of wood.
"J. G. S."