The engines are placed horizontally underneath the carriage body; the boiler is at the back, and a blast is employed to excite the combustion of the fuel, the supply of which is regulated by an engine man, who has a seat at the back for attending to it. The passengers are placed in the open carriage body, and their seats are formed upon the tops of the water tanks. There are two working cylinders 7 1/2 inches diameter, and 15 3/4 inches length of stroke. The steam-ways are 2 1/4 and 2 3/4 inches diameter.
The last experimentalist in the department of common road locomotion whose labours we shall notice, is Mr. F. Hills, of Deptford. Mr. Hills devoted much time and went to great expense in his endeavours to construct a compact and efficient boiler, and to bring the weight and dimensions of the machinery within moderate and practical limits; and at length so fully mastered the practical difficulties of his task, that a company was formed for building and running carriages constructed according to his plan, and an act of incorporation was applied for; but failing to obtain the clause for limiting the responsibility of the shareholders to the proportion of their shares, and the railway mania beginning to manifest itself at the same time, the company was dissolved, and Mr. Hills retired from the field. In the course of his experiments, Mr. Hills constructed several carriages with which he performed numerous journeys on the public roads; selecting those which, from the peculiar difficulties they presented, were most likely to point out every variety of provision that required to be made, or circumstances to be guarded against.
The Windsor, Brighton, Hastings, and similar roads were traversed by him with uniform success; and amongst other performances, we may state, that the journey to Hastings (64 miles) and back was performed in one day, each journey being accomplished in one half the time occupied by the coaches. One of the improvements comprehended in the last of Mr. Hills' patents, from its originality, extreme ingenuity, and the perfect manner in which it attains the object in view, calls for particular notice. One of the difficulties attending the construction of locomotive carriages, is the connexion of the driving wheels with the machinery, so as to obtain the full adhesion of the wheels, and at the same time to allow facility in turning sharp curves. Mr. James, as we have already noticed in one of his earliest attempts, fixed each of the driving wheels upon a short and separate axle, and applied two steam cylinders (at right angles to each other) to drive each wheel, but this added greatly to the complexity of the apparatus; another inventor employed only three wheels in his carriage, and applied the power to a single wheel, which ran in advance of and between the tracks of the other two.
The plan, however, most commonly resorted to, was to fix one wheel to the axle and to connect the other to the axle by a sliding clutch; but as it was impossible for the steersman to lock and unlock-the wheels at every sudden turn the carriage might be required to make, and great friction would have been created by the skidding of the wheels had both been fixed, the practice was to drive generally with only one wheel fixed, and to lock the other in ascending hills, where the whole amount of adhesion might be required. By Mr. Hills' arrangement, the objections to which all previous plans were liable are completely obviated; the adhesion of both wheels is constantly exerted to propel the carriage, and without the slightest attention on the part of the driver, the power exerted by the engines is exactly proportioned to the space each wheel passes through in describing the sharpest curves.
The engraving represents Mr. Hills' arrangement for connecting the driving wheels with the axle and the engines. a a are the driving wheels, which are fixed upon two tubes or boxes; b b through which the axle or driving shaft c passes, as shewn by the dotted lines, the tubes being loose upon the shaft; d d are two bevelled wheels which turn upon two pins e e, fixed upon the centre of the shaft, and which work into two similar wheelsff, fixed upon the tubes b b, the four wheels being all geared together; g g are the cranks fixed upon the ends of the shaft at right angles to each other, and to which the connecting rods are attached. Upon examining the figure it will be seen, that so long as the wheels continue to run in a straight line, the tubes b b do not revolve upon the axle, but turn round with it, and carry round the wheels as if they were fixed to the axle; but upon any deviation from a straight line, the wheels, at the same time that they advance with the axle, revolve more or less (according to the sharpness of the curve) upon the axle in contrary directions, the outer wheel having a forward, and the inner wheel having a backward movement; so that the actual advance of the outer wheel exceeds that of the inner wheel, as much as the length of the outside curve exceeds that of the inside curve, and thus no skidding takes place.