having at its centre a compensating gear, and at each end suitable chain or sprocket wheels, whereon, and upon toothed rings upon the road wheels, ran two pitch or driving chains, the speed of the engine as compared with that of the road wheels being either as 6 to 1 or as 13 to 1, in accordance with the wheels in gear at the time. The higher degree of speed enabled the carriage to travel at the rate of from 10 to 12 miles an hour. Intermediate speeds were obtained by the regulation of the engine, and steam was provided for working the latter from a boiler of the Field type, 4 feet high by 2 feet in diameter, and having about 34 square feet of heating surface and 1.76 feet of grate surface, working at a pressure of 135 lbs. per square inch, and which boiler was fed by an injector from a water-tank fitted with a suitable strainer. A cast-iron receptacle was provided at the bottom of the chimney into which the exhaust steam was delivered, and from the centre of which it issued up the said chimney, and a blast valve was also used, and was, when the road surface was such as not to require a powerful blast, kept only slightly open. This valve acted as a variable blast, admitting of the back pressure in the cylinders being reduced when required.

The chain wheels were fitted with teeth which admitted of adjustments being made for wear, and radius rods connected to the chain pinion bearings and to the axle were provided for maintaining the proper distance between the said chain wheels.

One of the axles, viz., that carrying the two wheels, was bent to take in the boiler. The wheels were the ordinary type of wooden carriage wheels with the usual iron tyres, the drivers being 4 feet in diameter

and fitted with lever brakes, and the single steering wheel 2 feet 6 inches, and connected by means of suitable rods with a steering pillar surmounted by a hand wheel.

Blackburn's Steam Road Carriage.

Blackburn's steam dog-cart, for which a patent was granted in 1877, was fitted with a torpedo engine.

Steam was supplied by a boiler composed of coils of tubes, petroleum fuel being employed, and the fire blown up by a blast from a fan or blower worked by the engine. The exhaust steam was condensed in an air condenser, wherein it was delivered into a large number of tubes located round the circumference of a fan or blower in such a manner as to be constantly subjected to the cooling action of a powerful current of air.

Thompson's Road Steamer.

Thompson, of Aberdeen, designed a type of traction engine known as a road steamer, several of which were run for many years on a number of the trunk roads of Northern India, working regular services of trains for both goods and passengers.

The provision of narrow gauge railways, however, rendered this method of transporting goods and passengers unnecessary, and their use was consequently discontinued.

Thompson was the first to apply indiarubber tyres to the wheels of road locomotives.

CHAPTER III.

RECENT EXAMPLES OF STEAM ROAD CARRIAGES.

COMING now to steam-carriages of more recent date, we may take as fair examples of what has been done in this direction, those of Serpollet, Le Blant, De Dion & Bouton, Hartley, Thornycroft, Simonds, and Sautenard, the two latter of which are of the steam velocipede class.

The advantages of the steam-engine have been already alluded to, and will be easily understood when it is remembered that it affords a very large capacity of regulation of power, is capable of being readily fitted with reversing gear, is easily managed, and can be stopped or started on the instant, and without the slightest difficulty; and as water and fuel are practically everywhere obtainable, is therefore adapted for universal use. As against these obvious. advantages must be placed the objection that the working medium, ie., steam, has to be produced on the road, thereby necessitating the use of a heavy, cumbrous, and more or less bulky boiler or generator. It is in this generator indeed that the great obstacle to the satisfactory use of steam lies. The steamengine itself can be readily made extremely light, and

yet be thoroughly efficient, but the construction of a boiler or steam generator of the requisite power and of sufficient lightness is a problem the solution of which is beset with much difficulty. The flashing boiler, with its instantaneous generation, ceases to make steam on the stoppage of the engine and feed pump, is very safe, and possesses many other advantages for the purpose in question; but on the other hand, the reserve of thermal energy is very small, and is soon exhausted when drawn upon, thus making but little provision for emergencies. The tubes and their casing also are very heavy, and the said tubes, moreover, are rapidly destroyed by the great heat to which they are naturally exposed. On the other hand, again, the high pressure boiler, whether of the water-tube or other type, whilst affording great power, continues to make steam during a temporary stoppage, and consequently gives rise to blowing off and waste, a defect which, however, could be considerably modified by the provision of some arrangement for arresting the combustion or radiant heat upon the stoppage of the carriage.

Serpollet's Steam Road Carriage.

The first of the more recent types of steam road carriages, to be noticed in point of efficiency, is that fitted with the Serpollet generator and motor, the former of which has proved itself fairly adapted for the purpose in question, enabling as it does a pressure of from 15 to 20 atmospheres to be easily maintained by the simple injection into the series of tubes of which it is composed of a continuous stream of water,

the said pressure being capable of being temporarily raised still higher, upon any emergency arising, by simply increasing the amount of the said feed.

Messrs Serpollet have been for a considerable time past experimenting in steam-carriages, and have produced some very efficient machines, one of their latest types being illustrated in the longitudinal sectional diagramatical view (Fig. 5). In this view, M indicates the motor, which is located forward beneath

the floor of the carriage, where it is enclosed so as to completely protect it from dirt and injury; G is the boiler or generator, which is situated at the rear, and is supplied with feed-water from the feed-water tank E, placed, as shown in the illustration, beneath the main seat of the carriage; R is one of the rear or driving wheels, which is connected to the motor shaft through chain or sprocket wheels and pitch chain C, and toothed gearing, as described later; B is the foot lever for operating the brake mechanism; L is the