The piston rods, by means of their crosshead, and the connecting rods actuate on the levers of the driving axis (axis that links two wheels, one on each side), transmitting to it a rotatory movement with the consequent rotation of the wheels on the rails. In the first locomotives there was only a driving axis; the need to drag increasingly heavier convoys required the transmission of rotatory movement to additional axes, to increase adherence on the rails, a factor that, as aforementioned, was of great concern for the first railway engineers. Later it was introduced an auxiliary system - which remains in use in modern locomotives - to improve adherence in difficult situations: it consists of dropping sand towards the rails in the very point where they make contact with the wheels. For this effect, steam locomotives carry sand in one or more domes attached to the upper part of the boiler.

The characteristics of the wheel arrangement can be indicated with three digits: the first one indicating the number of leading axes (the increase in speed required the addition of a fore "leading bogie" fitted with small wheels, which were able of a certain steering to facilitate the march of the locomotive when entering curves and switching tracks), the second one indicating the number of driving axes and the third one indicating the number of trailing axes (the rear "trailing bogie" uses similar wheels as the leading bogie, but it serves the purpose of supporting the weight of the cab and the firebox). In Anglo-Saxon countries the number of wheels is used instead of the number of axes. The letter "T" at the end of the numeration indicates that the locomotive has the tender incorporated into it and not as a separate vehicle.

Driving wheels and different wheel arrangements used in steam locomotives. Increasing the diameter of the driving wheels is the easiest way to achieve a greater speed. Note how driving wheels have an added weight to increase inertia, facilitating so the movement of the running gear.

Binding systems for rails: old system (to the left) and new system (to the right).

To the locomotive is attached a vehicle called tender for transporting fuel and water. Actually, the tender, along with the machine, is what constitutes the locomotive. Another important part is the driving cab. To the left, where the machinist is, are all the controls that affect the marching of the locomotive: the speed shift, the steam regulator, the command for the compressed-air brakes, the water level in the boiler and diverse manometers. The largest one indicates the pressure in the boiler and smaller ones indicate the pressure in the compressed-air deposits. Of great help for the stoker and required in the most powerful machines is the mechanical device - known as stocker - which transports the coal from the tender to the firebox, typically by means of a duct which has an auger - rotating screw - along it.

Interior of the driving cab of a steam locomotive Beyer-Garratt, type GMAM, in service in the South African railways. In the center it can be seen the hatch in which the coal is fed, by means of a mechanical loader, and to the right the feeding device.

Now that we have an idea of how these machines work, it would be interesting to note that the locomotives built by Robert Stephenson could march at an average speed of 50 kilometers per hour, and already in 1839 the trains of the South Western achieved a speed of 80 kilometers per hour while towing convoys weighing 50 tonnes. To increase the speed without altering the cylinders and running gear the engineers resorted to build locomotives with very tall driving wheels. In fact, in June 1846 the Great Western introduced a locomotive with wheels having 2.44 meters in diameter. This powerful machine effectuated the route between London and Swindon at an average speed of 95 kilometers per hour towing a load of 100 tonnes.

This same line, circa 1850, was theater of another episode of the race for speed: a powerful machine of the type "Iron Duke" traveled the 124 kilometers of the route in one hour and 12 minutes, at an average speed of 102 kilometers per hour. These speeds could be possible also due to the width of the track (the distance between the internal faces of the rails), which was larger than normal to allow the utilization of these locomotives, whose dimensions prevented them to run on tracks with normal width.

## The first manufacturers of railway equipment

The first industry that built a steam locomotive in England were the workshops led by Robert Stephenson, in Newcastle. From there departed the locomotives that inaugurated railroads all around the world, in France, Austria, Egypt, Australia or Canada. A direct competitor of Stephenson was Edward Bury & Company, who had in Liverpool a factory specialized in building locomotives with two driving wheels. Another very important manufacturer was Sharp Robert's & Company, which after being refounded several times took the name North British Locomotive Company. In 1940 existed in England more than 30 manufacturers.

In America, the production was localized initially in the Eastern States. In Philadelphia it was founded the first establishment of Matthias W. Baldwille, from which emerged that type of locomotive known as the "American type". This factory produced in a sole year (1836-37) 80 locomotives, a production truly remarkable in those times, in which the railway industry took its first steps. In the continental Europe, it was France the first country in producing locomotives, and it would be convenient now to remember Marc Seguin with the factory Chemins de Fer de Saint-Étienne.

American locomotive "Norris" built in 1846. Maximum speed: 55 kilometers/hour.

In Belgium, in 1839, from the factory of John Cockerill, a British manufacturer living there, emerged the locomotive called "Belgium", acquired by the state railways. In Germany, the first manufacturers were the workshops Borsing, followed by the factories in Munich, among others. In Italy the first machines of national construction departed from the workshops Ansaldo di Sampierdarena, in 1854. Regarding the cars, those reserved for first-class passengers in the starters of the railway travels reminded in its construction the conventional stagecoaches, while those reserved for third-class passengers, fully uncovered, left people exposed to the outdoor. Very soon these cars suffered notable transformations, and while in 1854 the locomotives still were of "free design", the cars had already acquired their classic aspect, with two or three wheel axes and box-shaped wooden structure.