After the death of his father, Robert Stephenson continued, as he had already done for several years, to conduct the business of building locomotives, as well as of constructing railroads. The work of locomotive engine-building was done at Newcastle, and for many years those works were the principal engine-building establishment of the world. After their introduction on the Liverpool & Manchester road, the engines of the firm of Robert Stephenson & Co. were rapidly modified, until they assumed the form shown in Fig. 57, which remained standard until their gradual increase in weight compelled the builders to place a larger number of wheels beneath them, and make those other changes which finally resulted in the creation of distinct types for special kinds of work. In the engine of 1833, as shown above, the cylinders, _A_, are carried at the extreme forward end of the boiler, and the driving-wheels, _B_, are coupled directly to the connecting-rod of the engine and to each other. A buffer, _C_, extends in front, and the rear end of the boiler is formed into a rectangular fire-box, _D_, continuous with the shell, _E_, and the flame and gases pass to the connection and smoke-pipe, _F_, _G_, through a large number of small tubes, _a_. Steam is led to the cylinders by a steam-pipe, _H H_, to which it is admitted by the throttle-valve, _b_. A steam-dome, _I_, from which the steam is taken, assists by giving more steam-space far above the water-line, and thus furnishing dry steam. The exhaust steam issues with great velocity into the chimney from the pipe, _J_, giving great intensity of draught. The engine-driver stands on the platform, _K_, from which all the valves and handles are accessible. Feed-pumps, _L_, supply the boiler with water, which is drawn from the tender through the pipes, _e_, _f_.