27. At the time the above paper was read before the Society, the four-wheeled engine had but few supporters, arising, no doubt, from the erroneous supposition, that the safety of the engine was in proportion to the number of wheels used.

28. It has, however, been steadily gaining ground in public estimation, and from the alterations going on in the construction of the six-wheeled engine, the advocates of them are evidently less confident in their superiority; and it is most gratifying to us that the advantages to be gained by the use of inside framing, which we then pointed out, are now tacitly admitted y our opponents of the greatest practical experience, who are gradually abandoning the outside frame.

"Messrs. Bury and Co. acknowledge that the four-wheeled engine had but few supporters in March 1840, but they say that since that time, it has been steadly gaining ground; they should have said, losing ground. The public, including nearly all the engineers of the day, many of whom are clear-sighted men on other subjects, are unable to see the merits of four-wheeled engines. The way in which Messrs. Bury and Co. here speak of inside framing, would lead persons unacquainted with the subject to believe that the outside framing is falling into disuse, but this is by no means the case."

29. As the inside frame becomes more and more general, the third pair of wheels will disappear, as not only useless, but really tending very materially to proaues those accidents which they are supposed to guard against.

30. Indisputable proof has been furnished, that an engine with inside framing cannot come down by the breakage of an axle; an engine, therefore, is equally safe on that plan of construction whether on four, six, or eight wheels.

"Since the circular was published, three instances at least have occurred, of four-wheeled engines having come down after the breaking of the front axle, by which accidents, taken collectively, it is believed more than one hundred lives have been sacrificed."

31. The advantages of four-wheeled engines, on our plan of construction, we maintain to be the following: 1st. The engine on four wheels is less costly than the one on six wheels; therefore to have the same number of engines, or the same power, on a line of railway, much less outlay of capital is required.

"The four-wheeled engine ought to be less costlythan the six-wheeled engine, but hitherto, I believe, that has not been the case. An additional number of inferior engines, of equal nominal power, will be required to compensate for the smaller power of each arising from that inferiority, as may be seen on the London and Birmingham and Grand Junction railways. The London and Birmingham Railway Company employ two engines to draw such trains as are drawn at full as high a speed by one engine on the Grand Junction railway, although, on the latter line, the engines are what are now called small."

32. 2d. It allows the engine to be got into less space, consequently it is more compact, firmer, less likely to derangement, and much lighter.

"The four-wheeled engine is, on the contrary, generally six inches, and often nine inches longer than the six-wheeled engine."

33. 3d. Though the engine is lighter, the adhesion is more perfect, from the weight on the driving wheels remaining nearly uniform, however unequal or out of level the rails may be; but in the engine with six wheels the adhesion is often imperfect (arising from the impossibility of mathematical precision in maintaining rails on the level,) although there may be fully as much weight on the driving wheels generally; that is, the fore and hind wheels sometimes carry the greatest part of the engine. When the driving wheels get into an uneven part of the road, and the constant action of the power of the engine is not resisted by the adhesion at these points, the driving wheels revolve without properly advancing the train, as every observant traveller knows; and all weight carried beyond what is necessary for adhesion on the rails, is an unprofitable lead, There is much less of this in the four-wheeled than the six-wheeled engine, seeing that there is only one pair of wheels used for adhesion both in the four and six-wheeled engine, when used for passenger traffic; but, as the four-wheeled engine is lighter than the six-wheeled engine, there is less power required to take it up the inclines, and therefore more available power left applicable to the traction of the train.

"The assumed superiority of four-wheeled engines would be more readily believed by railway proprietors, if Messrs. Bury and Co. would convince them that a greater amount of traffic can be done with the same number of four-wheeled engines and weight of fuel than can be done with six-wheeled engines."

34. 4th. The engine is safer, as it adapts itself better to the rails, not being so likely to run off the line at curves or crossings.

" 'At curves or crossings,' but what at the straight parts? The greater liability of four wheeled engines to run off the line in straight parts, is a fact incontrovertibly established by the experience of the Eastern Counties, the London and Brighton, and the Paris and Versailles railways."

35 5th. It is more economical in the working, requiring less fuel, there being also a less amount of depreciation, as there are fewer parts in motion, consequently, less friction, or wear and tear, and fewer parts to maintain; and even those are more easily got at, therefore much less expense is incurred in those repairs which are common to both plar.s.

"Every point in this paragraph is just the reverse of the truth.'

36. 6th. The buildings, turn-tables, lathes, drills, smithies, and other costly conveniences necessary for the maintenance and repair of the engines, are not required on so large and extensive scale, as the engine on four wheels is less in size than the one on six wheels.

"The whole of this is at variance with facts, except so much as refers to the size of the turn-tables."