"For many years previous to this period (1829), ingenious mechanics had been engaged in attempting to solve the problem of the best and most economical boiler for the production of high-pressure steam. Various improvements had been suggested and made in the Trevithick boiler, as it was called, from the supposition that Mr. Trevithick was its inventor. But Mr. Oliver Evans, of Pennsylvania, many years before employed the same kind of boiler, and as he did not claim the invention, the probability is that it was in use before his time. The boiler in question was provided with an internal flue, through which the heated air and flames passed, after traversing the length of the under side of the boiler, before entering the chimney. "This was the form of boiler adopted by Mr. Stephenson in his Killingworth engine, to which he added the steam-blast with such effect. We cannot do better than here quote the words of Mr. Robert Stephenson on the construction of the 'Rocket' engine:--'After the opening of the Stockton and Darlington, and before that of the Liverpool and Manchester Railway, my father directed his attention to various methods of increasing the evaporative power of the boiler of the locomotive engine. Amongst other attempts, he introduced tubes (as had before been done in other engines)--small tubes containing water, by which the heating surface was materially increased. Two engines with such tubes were constructed for the St. Etienne Railway, in France, which was in progress of construction in the year 1828; but the expedient was not successful; the tubes became furred with deposit, and burned out. "'Other engines, with boilers of a variety of construction, were made, all having in view the increase of the heating surface, as it then became obvious to my father that the speed of the engine could not be increased without increasing the evaporative power of the boiler. Increase of surface was in some cases obtained by inserting two tubes, each containing a separate fire, into the boiler; in other cases the same result was obtained by returning the same tube through the boiler; but it was not until he was engaged in making some experiments, during the progress of the Liverpool and Manchester Railway, in conjunction with Mr. Henry Booth, the well-known secretary of the company, that any decided movement in this direction was effected, and that the present multitubular boiler assumed a practicable shape. It was in conjunction with Mr. Booth that my father constructed the 'Rocket' engine.