geared wheels driven by the engine and the driving wheels, a friction clutch intervenes to enable the engine to be started and worked for a few strokes without any load, and also to give the power of proceeding easier round bends. There are two different speeds upon the gearing, either of which may be used to suit the load to be overcome. It cannot be said that any of the forms of traction engine yet introduced are unexceptionable. But upon the whole it appears to be the best plan to construct the boiler with upright tubes, to form the driving wheels of wrought-iron drums, which would be unable to lift the mud or dust, and to apply self-acting clutches to the driving wheels, so that in bends of the road, one clutch would alone act, the other being for the moment rendered inert by overrunning the axle. The toothed wheels should in all cases be made of wrought iron or of malleable cast iron, and it appears advisable to have two coupled driving wheels on each side, to gain the necessary adhesion without cutting into the road. Springs and equilibrium levers should be employed, and to enable the springs to act, the toothed wheel which drives the road wheel should be of bevel gear with a bevel pinion working into it, and fixed on an upright shaft in which there is a sliding triangular socket. Two cylinders may be used, working independently but capable of being worked in concert, by the aid of a friction clutch on the crank shaft, and these cylinders will adjust their own speed to answer the requirements demanded by

the bends of the road. The steam should be worked very expansively to save water and also to save fuel, and should be condensed by some simple surface apparatus that would also heat the air proceeding to the fires.

Steam Rollers.-It has long been an objection to the use of macadamised roads that a considerable time elapses before they are consolidated by the traffic passing over them, and that during this painful period the traction is very heavy, and both horses and vehicles suffer injury. In France great steam rollers have been for some time in use, for consolidating these roads, and the system has subsequently been introduced into this country; and Mr. Clark of Calcutta, Messrs. Aveling and Porter of Rochester, and others, have contrived and constructed such rollers with varying success. The most perfect form of road roller yet introduced, however, is that contrived by Mr. David Thomson, of Messrs. Morland and Son's, London, and which is shown in fig. 112. There are two cylinders working downward to a cross shaft, which carries two pitched chain pinions, that give motion through the medium of the chains to the roller, which constitutes one great driving wheel extending from side to side of the carriage. The steering is accomplished by the aid of the leading wheels, each of which is carried in a forked vertical axis capable of being swivelled by a worm wheel at its upper end. The whole machinery is carried by a wrought-iron framing 19 ft. 8 in. long, 8 ft. wide,

and 6 ft. deep, and standing 8 ft. above the roadway. The total weight of the machine is 25 tons, of which 21 tons are carried by the roller and the rest by the leading wheels. The roller is 6 ft. long, and 7 ft. diameter, and is constructed of wroughtiron plates, riveted together, the plate being in. thick, with internal stiffening stays; and wearing

plates are applied to its exterior, which may be renewed when worn out. The cylinders are each of 11 in. diameter, and 18 in. stroke, and five revolutions of the engines produce one of the roller. The boiler is vertical, 4 ft. 2 in. diameter, and 10 ft. 3 in. high, with 64 Field tubes, 2 external diameter. The engine is fitted with the link motion to render