hind rollers after an average wear of seven years, during which time 60,000 tons of metalling had been consolidated by one road-roller. The driving rollers are subjected to great wear, as may be imagined, aud the renewal of these forms one of the heaviest items of expenditure. Various means have been devised to remedy this by adopting steel for the tires, while renewable rims are recommended by many makers of rollers. These have all more or less failed to overcome the difficulty, as the renewable tires, although appearing to satisfy the requirements in practice, are unfortunately found to be wanting in many essential particulars. In all probability a new fire-box, tubes, and other minor parts will be required in the course of a few years; so that the actual cost of steam roadrolling may be somewhat more than the sum just stated. An inclusive sum (having regard to the probable future requirements of renewals and repairs) of £23 per annum for each roller should be sufficient to keep it in efficient working order. This is at the rate of 5 per cent. on the purchase price of a 15-ton roller. The only other direct and available information on the subject of a reliable nature, so far as the author is aware, is detailed in a paper by Mr. E. T. Hooley, County Surveyor of Notts,* on 'Steam Rolling,' which, besides alluding to the matter of repairs, describes in a lucid and exhaustive manner the history of steam road-rollers, and the work performed by them generally. Mr. Hooley states in effect that after five years' service it was found necessary to send the rollers, three in number, to the makers' works to be thoroughly overhauled and supplied with new sets of wheels. The total cost of these repairs and renewals amounted to £388, 18s., which is equal to an annual expenditure of 6 per cent.; when returned the rollers were practically as good as new. 310. Judging by the number of steam road-rollers at present in use an idea may be formed of the high appreciation of road-rolling in this country, when it is stated that the firm of Aveling & Porter alone have made and sold over 3000 steam road-rollers, the majority weighing from 10 to 15 tons. In London alone more than 100 rollers are in daily use on an area of 400,000,000 square yards of macadamized and flint roads, which represent over 2000 miles of road having an average width of 30 feet. 311. The cost of steam road-rollers and accessories are detailed in the subjoined table, which applies only to the usual type of machine used; special requirements to suit particular circumstances involve a larger cost A paper on 'Steam Rolling' read before the Incorporated Association of Municipal and County Engineers, and published in their Proceedings, vol. xxii. p. 284. TABLE XXXV. Description of Plant. Cost of Roller and 15-ton road-roller, single cylinder, £ 8. d. 460 0 0 15-ton road-roller, single cylinder, convertible, with roller wheels only, no traction wheels or fore-carriage, roller 600 0 0 Set of four traction wheels and fore-carriage, 75 0 0 12-ton road-roller, single cylinder, 400 0 0 12-ton road-roller, single cylinder, convertible, with roller 525 0 0 wheels only, no traction wheels or fore-carriage, Set of four traction wheels and fore-carriage, 65 0 0 10-ton road-roller, single cylinder, If made compound, extra, 15-ton roller, 375 0 0 75 0 0 12 55 0 0 Sleeping-van to accommodate four men, 60 0 75 0 65 0 312. Scarifiers or Machines for Breaking up Macadam Roads.-In repairing the surface of a road by the aid of a road-roller, the usual practice is to lay a sufficient thickness of metalling to bring the contour of the road into proper form, which often involves the application of considerable quantities of material. Laying macadam one stone thick on a hard road and then rolling it, is not to be recommended, both on economical grounds and because great damage often results from the metalling being crushed when so spread. If the surface of a road is loosened to a sufficient depth preparatory to re-forming and applying the macadam, one stone thick may suffice to meet the requirements of the case, which, without this being done, would require a coating of metal of unnecessary thickness being applied to ensure satisfactory results. 313. It seems strange that, even before steam rollers were introduced, a contrivance for scarifying roads on the agricultural harrow and plough principle was patented in 1817 by Clay, and designated "a harrow which is intended to scarify the uneven part of any road." It is stated that attempts have been made from time to time, not only in this country but also in France, to construct a machine having the same object as Clay's, and drawn by horses, but it is evident that little or no advance was made in the construction of a practical machine for this purpose until within comparatively recent years. 314. The propriety of scarifying macadam roads does not appear to be fully appreciated, owing probably to a want of experience in the matter, or possibly to its having been so rarely resorted to that the actual work performed by the machine has not been sufficiently known. In districts where macadam scarifiers have been introduced and practically applied, it is considered to be an indispensable adjunct in connection with steam rolling. This is a subject of considerable importance in connection with the maintenance of roads, and as such operations can be executed by machinery at a considerably less cost than by hand labour, a full description will be given of mechanical scarifiers and of the results obtainable by their use. 315. Qualifications which a macadam Scarifier should possess.—A macadam road-scarifier, to be of any practical advantage, must be of a light but strong construction, easily manipulated, and form part of, or be permanently attached to, the road-roller or traction-engine. It should be capable of being used both when the engine is moving forward and when it is moving backward, while the engine wheels should not be allowed to compress the portion of road just broken up when making a fresh cut' parallel with it. The teeth or tines should be spaced sufficiently close to ensure the crust of the road being completely loosened, and the mechanism regulating the depth of the cut should be so arranged that the teeth or tines can be instantly raised clear of the road when necessary. This is particularly desirable when working in towns in order that crossings, gratings, tobies, or other obstructions may be safely passed while the engine is in motion; the depth to which it is intended to penetrate the macadam will depend on circumstances, but for all practical purposes it need not exceed 5 inches. The working of the machine should be so arranged as to avoid the stones composing the crust of the road being violently strewn about, with the possible risk of incurring danger to pedestrians and vehicular traffic, or damage to house or shop windows when working in populous places. The best known scarifying machines made within the last few years in this country and employed in some instances with marked success, are given in the following list in chronological order. 316. Different Makers of Scarifiers.-Rutty's road-scarifier, 1884; Voysey & Hosack's apparatus for breaking up streets, etc., 1890; Jackson's road-scarifier, 1891; Wallis's machine for breaking, etc., the surface of roads, 1891; Henderson's macadam road-breaker, 1891; Messrs. J. Fowler & Co., road-scarifier, 1894; Morrison's (Aveling & Porter) road-scarifier, 1895; Rutty's road-scarifier, 1896; Burrel & Rutty's road-breaking machine, 1897; Fowler's scarifier, 1897; Marshall's scarifier, 1898; Bomford's scarifier, 1898; Hosack's scarifier, 1898. Of the various machines mentioned, the author will describe the main features of Rutty's original scarifier as improved in 1894, and give the amount and cost of work effected by its use. This machine has done excellent work for many years past, and still maintains its position as a capable and effective mechanical appliance under certain conditions. These conditions will be referred to later on. Morrison's machine, which is manufactured by Messrs. Aveling & Porter, and fixed to their road-rollers or traction-engines, will also be described, and details given as to its working capacity and cost. This machine is capable of performing heavy or continuous scarifying, and of working with equal facility and advantage backwards or forwards. As it is usually attached to the engine, but can be detached in a few minutes if necessary, it is available for work at a moment's notice; this is a convenient arrangement when the repairs on the roads are carried out on the patching system. The other machines mentioned in the preceding list, so far as any special features possessed by them are of interest, will be briefly noticed in their chronological order. 317. Rutty's Scarifier.-The general features of this machine are shown in fig. 111. It is made up of a heavy cast-iron box or trolley a, to either end of which a bracket b is fixed, carrying the boss c through which the quick-threaded screw d in the depth-regulating frame e works. This frame is rigidly held in position by deep recesses on each side, between which the boss slides, the lower ends being carried by small road wheels which travel in a line with the axis of the machine, while the means of regulating the depth is provided at the upper end of the frame e by a handle g. The rogulating-frame and bearing-wheel ƒ are placed in a raking position, as shown in the illustration, fig. 111. Lugs, h, are cast on the box-frame at the corners, to which are attached draw-links and pins, forming the means for attaching the drag-chains. The teeth or scarifying tools i, are placed in sockets j, and pass through the lower part of the cast-iron frame a. They are generally set at an angle of 60° with the road, and are held firmly in position by means of screws k. The road wheels for supporting the box-frame a are carried by an axle m, which can be adjusted transversely, so as to permit of the wheel being placed in the recess n, by which means the machine can be worked close up to the kerb-stones or edge of footpaths when necessary. This scarifying machine is capable of penetrating hard macadam to a depth varying from 1 inch to 5 inches. The work is commenced at the crown of the road, and gradually continued towards the side; when the other portion is commenced the engine hauling the scarifier is turned round or reversed if necessary. The width of the cut or extent of surface loosened each turn is about 18 inches. This machine being on the trailing principle, cannot be pushed backwards; the engine, therefore, has to be disconnected from the scarifier when the length of road operated on has been traversed. To avoid the necessity of turning the engine completely round, a draw-gear arrangement is fixed on the front of the engine, by which the scarifier is drawn when making the return cut. It will be obvious that even with this arrangement a considerable loss of time is involved when operating on a short length of road. The time occupied in changing the position of the engine will depend greatly on the aptitude of the driver, but generally it may be taken at 25 per cent. of the actual working time engaged on a piece of road of about three hundred yards in length. The latest arrangement in connection with working this scarifier is to harness it to an engine in front of the driving-wheel and alongside of the steeringwheels. It is held in position, as far as it possibly can be so under the circumstances, by means of chains attached to the side of the fork, the spindle for carrying the hind wheel scrapers, and a bar of iron fixed at rear of the tender. By this means the scarifier can be hauled in either direction without reversing or turning the engine. The great width occupied by this combination, is, however, rather a serious matter on narrow roads. This machine, which weighs 2 tons, performs its work very effectively, and there is little ridging of the macadam when the teeth are working at an average depth; the latest make of this machine has four tines, which are capable of loosening a width of 21 inches; the cost of this scarifier is £100 delivered. 318. Voysey & Hosack's Scarifier.-This machine consists of a double cast-iron frame, the inner or tool frame working within the external one. The front part of the external frame is attached to the tender of the engine by means of a pivot shaft, while at the rear or hind part it is carried by small road wheels. The road surface is scarified by means of an arrangement consisting of a |