It is also worthy of notice, that the plates of the tram or rolley-ways em ployed in coal mines, are usually fastened down by a single nail passing through a hole nearly at each end of the plate, and entering into a sleeper of wood. These nails, from the vibration of the parts in connexion, caused by the loaded waggons rolling over them, are apt to work loose very soon, and cause a breakage of the plates or rails; to obviate which, Messrs. Losh and Stephenson have intro duced the improvements described, and which appear well calculated to effect the object designed.
With respect to the advantages of the wheels described, it cannot be doubted that the introduction of malleable iron arms into cast metal rime has tended much to remedy the destructive results attending the previous use of common cast metal wheels; and that an economy of material and an increase of strength must have attended the change. The rims of wheels thus constructed, may also be case-hardened, without risk of breaking, either in cooling, or afterwards ; which is not the case when wheels are cast in one piece. It is also unques tionable, that great economy of expense and durability of structure were obtained by the introduction of malleable iron tires over cast-iron wheels ; because, when the former wear out, the wheels may be re-perfected at a very trifling expense ; and the elasticity of the malleable iron has a tendency to moderate and render innocuous the concussions received upon the cast metal.
In what relates to the locomotive engines employed upon railways, Messrs. Leah and Stevenson's invention consists " in sustaining the weight, or a part of the weight, of the engine upon pistons movable within cylinders, into which the steam or the water of the boiler is allowed to enter, in order to press upon such pistons ; and which pistons are, by the intervention of levers and connecting rods, made to bear upon the axles of the wheels of the carriage upon which the engine rests." In the sketch on the next page, Fig. 27 represents a cross section of the locomotive engine on the edge-railway : a a are the steam cylinders, contain ing the floating pistons b b, connected with the wrought iroh rods c c, the ends of which rest upon the brasses of the axles of the wheels d d. These pistons press equally on all the axles, and cause each of the wheels to press with an equal stress upon the rails, and to act upon them with an equal degree of friction, although the rails should not all be in the same plane ; for the bearing brasses have the liberty of moving in a perpendicular direction in a groove or elide, and, carrying the axles and wheels along with them, free the wheels to accommodate themselves to the inequalities of the railway. The objects of these floating pis tone are, to prevent the engine from receiving shocks, and preserve a steadiness of motion; inventors considering, that by acting on an elastic fluid, they produce the desired effect "with much more accuracy than could be obtained by employing the finest springs of steel to support the engine." A longitudinal section of this locomotive engine is given at page 401, in the description of Dodd and Stephenson's improvements, which it equally illustrates.
Mr. Elijah Galloway, in his His tory of the Steam Engsne, states that " these locomotive engines have been long in use at Killingsworth Colliery, near Newcastle, and at Hetton Colliery, on the Wear ; so that their advantages and defects have been sufficiently submitted to the test of experiment ; and it appears that, notwithstanding the great exertions on the part of the inventor, Mr. Stephenson, to bring
them into use on the different rail roads now either constructing or in agitation, it has been the opinion of several able engineers, that they do not possess those advantages which the inventor had anticipated; indeed, there cannot be a better proof of the doubt entertained regarding their utility, than the fact, that it has been determined that no locomotive engines shall be used in the projected railroad be tween Newcastle and Carlisle ; since, had their advantages been very apparent, the persons living immediately on the spot in which they are used, namely, Newcastle, would have been acquainted there with. The principal objections appear to be, the difficulty of sur mounting even the slightest ascent; for it has been found that a rise of only one-eighth of an inch in a yard, or 18 feet in a mile, retards the speed of one of these engines in a very great degree ; so much so, indeed, that it has been consi dered necessary, in some parts where they are used, to aid their ascent with their load by fixed engines, which drag them forward by means of ropes coiling round a drum. The steam cylinders below the boiler were found very defective, for, in the ascending stroke of the working piston, they were forced inwards by the con necting-rod pulling at the wheel in turning it round, and in the descending stroke the same pistons were forced as much outwards : this motion or play rendered it necessary to increase the length of the working cylinder as much as there was play in the lower ones, to avoid the danger of break ing or seriously injuring the top and bottom of the former by the striking of the piston when it is forced too much up or down. As our meaning may not be fully comprehended without elucidation, let us imagine the cylinder of a common beam-engine to be set upon springs which have a play of one foot ; the weight of the cylinder, when at rest, depresses the spring six inches ; but if the engine be put in motion, then, as the piston ascends and gives motion to the machinery, the springs below the cylinder, being, as it were, the abutments upon which the steam acts, are forced downwards against their seat with precisely the force that the piston exerts in overcoming the resistance of the machinery. In like manner, when the piston descends, as much weight or pressure will be taken oft' these springs by the same means : the cylinder would, therefore, vibrate or dance upon the bearing springs; and as the motion which it thus obtains is the reverse of the motion then given to the piston, the length of the cylinder should be greater to allow for the extreme vibration to which it is liable. A quantity of steam would, therefore, be lost in filling up this extra length of the cylinder at each stroke. This would also happen if the cylinder were ilrec4 as usual, and the carriages of the crank and fly-wheel supported upon springs ; and this arrange ment would then be exactly the same, in principle and effect, as the parts of the locomotive engine to which we now allude." In justice to Messrs. Loth and Stephenson, however, we are bound to acknowledge our admiration of' the several improvements introduced by them in the carriage wheels and rails, which form. so material a part of their specification.