We shall therefore briefly describe here Mr. Birkinshaw's rollers, with reference to the following figure, which repre sents an elevation, or side view, pair of them. It will be observed, that the peripheries of each roller are indented with a series of grooves, like mouldings; each groove, except one in the upper roller, corresponding in form with another in the lower roller that is opposite to it; and that the figures represented by the hollow spaces left between the pair of rollers, are produced by the opposite surfaces being brought into contact. It will therefore be obvious, that when a red-hot bar of iron ie. applied to the grooves of such rollers, forced round by a powerful steam-engine with great velocity, the iron will be compressed into the same form throughout its length. The form of rail now most approved o4 which we shall have occasion hereafter to describe, is made by the same kind of machinery just noticed. It may be deserving of remark, in this place, that Mr. Birkinshaw sug gested at the end of his specification, that his bars (eighteen feet long) should be, welded together, end to end, continuously, so as to form an extensive line without any joint, and thus avoid the jolting and concussions consequent upon the carriage wheels striking against the ends of each length of the ordinary rails, where they are connected to the chairs. The introduction of this suggestion serves to show what great mistakes are made, sometimes by the cleverest men, for want of a little reflection ; and we Make no doubt that the patentee became soon sensible of what most of our readers are aware of, that a rail so con structed, without any provision for the expan sion and contraction which takes place in the metal from atmospheric changes of tempera ture, must inevitably soon be thrown into ruins by the twisting of the rail, and the con tinual motion of the chairs and sleepers. And our only motive for thus noticing so singular an oversight is, that the inexperienced and confiding reader of the specification may not fall into a similar error.
The long wcod-cut in the margin was de signed by Mr. Birkinshaw, to exhibit his im proved railway ; and the long train of loaded coal waggons drawn by a single horse, serves to show the kind of waggons, and the nature of the power in general we at the period of the patent, 1820. 4 Mr. Birkinshaw also pro posed the form of rail shown in the annexed figure, which, he says "maybe used to ad vantage in some situations," without, however, specifying them. We shall therefore take leave to remark, :in this place, that it is particularly suited to the top surface of Mr. Palmer's sus pension railway, an invention of great merit, which will presently appear in its chronological order.
The eminent success of Mr. Birkinshaw's new rails had the effect, as might be expected, of stimulating the proprietors of rival and neighbouring iron works, to try their skill in the same field of invention. Hence we find Mr. William Losh, of Newcastle-upon-Tyne, obtaining an exclusive privilege for his certain in the construction of iron rails for roads," on the 14th of September, 1821 ; which we find explained, in the enrolled parchment, to consist, "First, in using, placing, and fixing bars of malleable iron on the upper surface of a line of cast-iron rails or malleable iron rails, of what ever form such rails may be in the longitudinal direction of the rails when laid, so as to form an uninterrupted line the whole length of the bar, which may be as long as it shall be found convenient and economical to use, and of the same breadth as the upper surface. of the rails to which it is fixed, or a little broader or narrower. Secondly, in some cases I fix a band or strap of malleable iron to the under surface of rails made of cast-iron, in order that such band or strap may, by its power of give support to the cohesion of the parts of the cast-iron rails and admit of its being made lighter, and thus save expense, while it adds to security from breakage. Thirdly, I claim as an improvement, a rail formed by fixing two bars of malleable iron on their sides or edges, and fixing them in that position by bolts and studs, or by any other convenient method; and on their upper edges placing and fixing a flat bar of malleable iron, or one which is slightly curved or rounded at the edges, to diminish friction, so that the bar or plate, placed and fixed on the upper edges of the two malleable iron bars, shall form the surface upon which the wheels of the waggon or carriage are to revolve." The inventor next proceeds to give " a full and particular descrip
tion of all and every " of his modes and contrivances for connecting the arta of this compound rail; but as these are of too uninteresting a nature to ease the general reader, and quite unnecessary to the practical man, we ah omit them. It is not, however, to be wondered at, that Mr. Lash, who was a great iron-founder, should endeavour to protect his own metal by a species of conser vative reform, against the sweeping radical changes advocated by Mr. Birkin shaw ; but all the "bolts, chains, rivets, and straps" of the former have entirely failed in supporting the conservative fabric, and the iron rule of Birkinshaw which first manifested itself amongst the collieries of the north, has since been demonstrated at Liverpool and Manchester, is now about to extend itself to Birmingham and London, and will, doubtless, soon embrace every town in the empire.
We have already observed, in the foregoing part of this article, that in the earliest constructed railroads, which were chiefly confined to a descending trade, from the coal mines to the shores of the neighbouring rivers, very little atten tion waspaid to the formation of planes of uniform inclinations ; and the latter were so great as to render it difficult to draw up the empty-waggons on their return. Very abrupt acclivities were partially levelled, and deep chasms and ravines only filled in : consequently, the power which the horses had to exert on the same line of road fluctuated considerably. In some parts the animals were overworked, and in others they were an incumbrance; so that it often became necessary to unhook their traces, and let them follow the waggons, which descended simply by their own gravity. For a long period, the horse was the only power used upon railways. To this succeeded the application of the power of gravity, to cause a descending heavy body to raise a lighter up an opposite inclined plane, a process which had previously been employed upon canals, in drawing the empty boats out of the water on to a higher level, by means of the descent of the loaded boats down the declivity. But a little consider ation will show that this kind of power can only be resorted to in peculiar cir cumstances and situations. It is only where a preponderance of goods has to be conveyed in one direction, and where, upon any declivities occurring in the line of road, that preponderance is capable of overcoming the gravity of the returning carriages, that the action of gravity can be used to advantage. It is, therefore, of importance, to ascertain upon what declivities, with a given preponder ating load, this power ft available ; the object of all such inclined planes being to convey down a certain quantity of goods in a given time, and to do this with the least expenditure of power. In forming a railroad, therefore, with the view of using this species of traction, it is not only necessary that the descent of the plane be such as to give a preponderance to the loaded carriages over those which are empty, but such a preponderance as will cause them to descend, and drag up the empty carriages with the requisite velocity. For if we give to the plane a greater degree of inclination than requisite, we expose the ropes and carriages to an unnecessary strain, and consequently to additional wear and cost ; and if the inclination be not sufficient, the proper performance will not be accomplished. The laws which govern bodies descending inclined planes have been very ably Mr. Nicholas Wood, in his Practical us OR Railroads, accompanied with such illustrations as will render the subject a matter of easy cal culation to those of our readers who may be interested in the subject ; to which work we have, therefore, great pleasure in referring them. We shall, however, here avail ourselves of the description given by that eminent engi neer, of the manner of working self-acting inclined planes in the neighbourhood of New castle-upon-Tyne.