The Leith Walk of Edinburgh is another exams e of the aisler causeway, forming almost the only thoroughfare to the port of the Scottish metropolis. It is regulated by a special trust, and its toll is generally rented at 50001. per annum. The causeway of Leith Walk is nearly 2 miles in length ; its breadth between the curb-stones, which line off a spacious footpath on each side, may be taken at the average breadth of 57 feet. The stones with which it is paved are of a cubical form, of the largest dimensions of aisler causeway, and are laid upon a bed of sharp sea-sand, free of earthy particles. It is now (1836) above twenty years since Leith Walk was converted from a very bad common road into a spacious causeway ; and although its surface exhibits many inequalities, • yet it has continued during that comparatively long period, and may continue as long without requiring any considerable repair. Now if we compare this with the continual repair to which all metal roads, with a traffic similar to that of Leith Walk, are incident, we presume that the metal would require to be renewed at least every third year. The expense therefore, would have been much greater for the maintenance of the metal road than for causeway. ' Mr. Alexander Gordon, in his work on Elemental Locornotion, has selected some passages from the reports of the Holyhead Road Parliamentary Com mission, which are deserving attention. It appears, from these reports, that on a smooth, well-made London pavement, the tractive power necessary to move a given weight otra level, is only The stones should be accurately fitted to each other, and bedded on a good foundation of broken atones, put on in layers of 4 inches at a time until they be 12 inches thick, and then the well-dressea pavement of rectangular stones placed on it. Collision and surface resistance together being only of the weight to be moved, even where the surface is composed of numerous stones, the advantages of good pavement seem to us obvious, that it cannot but excite astonishment that they should be so much neglected. Mr. (in his evidence before the House of Lords in 1833) proved that the verybest pavement would cost only 13s. per square yard, and would cost nothing in repair for the first three years, and he gave in the following statement :— The old stone might last twenty years longer; but, at all events, would be worth eight shillings per yard, after ten years' wear. Most of the'London pavement appears to be laid down at an expense of seven shillings or ten shillings per yard. " If," says Mr. Macneill, in his evidence, " you take twenty miles of road near London, and also take the repairs of the roads for twenty years into account, I should say that paving would be the cheapest kind of road" A road of a similar description to the Commercial Road has been proposed by Mr. Macneill for the " London, Liverpool, and Holyhead Steam Coach and Road Company." On this steam carriages, and all other description of coaches, will be allowed to travel. If a portion of the road from London to Birmingham were laid off on one side, made in a solid manner with pitching and well-broken granite, it would fall very little short of a railroad, and the expense would not be very considerable. A double row of granite blocks or trams might be laid on one side of the road for the wheels of the carriages, and a stone pavement between the rows of granite blocks.
The adoption of this plan would enable steam carriages to travel with great velocity, would present no obstacles to other vehicles, would require no other sites than the present turnpike roads, and would prevent the immense outlay, and certain mischievous consequences that must inevitably result from railway speculations.
Mr. Henry Matthews, of Walworth, proposed aplan of stone railways, upon an extensive scale; the stones were to be four feet ling, ten inches deep, eleven inches in breadth at the top, and fourteen inches at the base ; at certain points the stones were to be connected by a kind of mortised joint. This plan pos sessed considerable merit, but the expense, estimated at IL 5s. per lineal yard, for each set of tracks, was an objection : it would, we think, also be found, that unless the cubic contents of these stones bore a greater proportion to their length, they would not withstand the necessary pressure of carriages.
Mr. Stephenson, the engineer, in the Edinburgh Encyclopedia, describes a mode of constructing a smooth and durable city road, which is both economical and ingenious.—" A street or highway, supposed to measure about thirty feet in breadth, is laid out in five compartments, independently of foot-paths. Two of these are laid with the aisler causeway tracks, five feet apart, the horse-paths of ruble causeway, or broken stones, in the usual way. A B C D (Fig. 1) points out a compartment of the road, laid partly with broken stones, in which E E and F F are the aisler causeway tracks, A B being a paved open drain, on the side of the road. I N ahows the limits of • road, also laid with tracks of aisler causeway, as marked at L L and M M ; but here the compartments between and on each side are paved with ruble, or inferior causeway stones. Fey. 2 is a section of the plan described under lig. 1, and shows the particular form of the aisler causeway tracks; a is a paved drain, b one of the sides, made with broken stones, c c two of the aisler causeway tracks, and d the horse path between them.
In the year 1825, Mr. Thomas Parkins obtained a patent for au improved mode of paving. The patentee proposed to lay on common roads continuous lines of granite blocks, on which the wheels of carriages are to run ; the upper 'surfaces are to be level with the road, the wider surface fiat, and the stones are fitted together by "bird's-mouth joints." Each stone is thus supported by the stones on each side of it, and prevented from partial depression. Whatever merit may be due to Mr. Parkins for the methods he has suggested, so many and so various are the improvements in pavements since the date of his patent, that it is unnecessary to describe more minutely the several raodes by which he proposes to connect the blocks of stones together.
In the same year, a patent was granted to Mr. John Lindsay, of the Island of Herm, near Guernsey, for certain improvements in paving; it is described in Vol. Xt. No. 64 of the London Journal. Fig. 3 is a cross section of the street ; D D is a properly-prepared foundation; 3 and c e are blocks of smooth granite, placed longitudinally, and parallel to each other, for the carriage wheels ; d d are also stone blocks, with trenches in their upper surfaces, to serve as drains for surface moisture or rain. The intermediate spaces s e e s are filled up by common paving stones, with their broadest surfaces downwards, the interstices to be filled with granite chips or cement. The central line of granite Mocks b is to be sufficiently broad to allow two carriages to ss ; and the side blocks c c are only required to be wide enough for one wheel to run on. Upon the curbs, carriages with heavy loads will pass with ease, and comparatively little labour to the horses. Mr. Lindsay's plan of preparing the foundation for the reception of the blocks, it is unnecessary to detail ; and we believe the method of fastening the blocks by cramps, or bars of iron, has been long known, and, in many cases, acted upon. Though we conceive his invention to possess but little novelty, the patentee deserves credit for attanpiing to improve our street pavement; so valuable, as we have before observed, is a smooth and solid roadway, that every suggestion for its attainment is entitled to respect. • The patents which have been granted for real or fancied improvements in this department are so numerous, that it is impossible to particularise them. The benefits of paving, as superior to all other methods of construction, is, we think, proved beyond doubt; and of that description of road-making, the tram way of granite blocks appears, in our humble opinion, to of all that can be desired. The writer of this article has frequent occasion to pass through the narrow street called Winchcomb-street, near the Haymarket. This is paved with blocks of granite, in a similar manner to the Commercial Road : though the acclivity is rather steep, the ease with which vehicles are impelled is proof sufficient, if proof were wanting, of how small a traction power is required on such a road. Under the bead Pavia° will be found some further information on the subject.