increasing the surface presented by the flue tubes. He also further endeavoured to meet the difficulty by doubling the flue, the last engine which he constructed for the Stockton and Darlington Railway, previous to the building of the "Rocket," being constructed with a double tube, which thus presented a considerably greater surface to the fire. The "Lancashire Witch," built by him for the Bolton and Leigh Railway, and employed in the completion of the Liverpool and Manchester Railway embankments, was also constructed with a double tube, each of which contained a fire and passed longitudinally through the boiler. But this arrangement necessarily led to a considerable increase in the weight of these engines, which amounted to about twelve tons each; and as six tons was the limit allowed for engines admitted to the Liverpool competition, it was clear that the time was come when the Killingworth engine must undergo a further important modification.

For many years previous to this period, 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. As early as 1803, Mr. Woolf patented a tubular boiler, which was extensively employed at the Cornish mines, and was found greatly to facilitate the production of steam, by the extension of the heating surface. This boiler consisted of eight tubes placed horizontally in the centre of the longitudinal furnace; and they were so arranged that the whole current of the flame passed over them before it escaped into the chimney. Mr. Woolf stated the object of the arrangement to be, that "the tubes composing the boiler should be so combined and arranged, and the furnace so constructed, as to make the fire, the flame, and the heated air to act around, over, and among the tubes, embracing the largest possible quantity of their surface." In this arrange

ment the steam and water were within the tubes.

Various

modifications of this boiler were afterwards adopted. The ingenious Trevithick, in his patent of 1815, seems also to have entertained the idea of employing a boiler constructed of "small perpendicular tubes," with the object of increasing the heating surface. These tubes were to be closed at the bottom, opening into the common reservoir, from whence they were to receive their water, and into which the steam of all the tubes was to be united. It does not, however, appear that any locomotive was ever constructed according to this patent. Mr. W. H. James, a son of the first surveyor of the Liverpool and Manchester Railway, patented a new form of boiler in 1825, the object of which was to increase the heating surface by means of a series of annular tubes placed side by side, and bolted together, so as to form by their union a long cylindrical boiler, in the centre of which, at one end, the fireplace was situated. A model of this tubular boiler was shown by Mr. James to both Mr. Losh and Mr. Stephenson about 1827. Losh expressed the opinion that, if such a boiler could be put to Stephenson's engine, there would be no limits to its power; and Mr. James spoke of a speed of from twenty to thirty miles an hour, at which Mr. Stephenson shook his head, remembering, as no doubt he did, his severe cross-examination and denunciation by counsel before the House of Commons, for venturing to say that twelve miles an hour might be achieved by the locomotive on railways; and he said that was a rate of speed they did not now dare to talk about. Mr. Goldsworthy Gurney, the persevering inventor of steam-carriages for travelling on common roads, also applied the tubular principle extensively in his boiler, the steam being generated within the tubes. Messrs. Summers and Ogle invented a boiler for their turnpike-road steam-carriage, consisting of a series of tubes placed vertically over the furnace, through which the heated air passed before reaching the chimney. The application of the

same principle to the railway locomotive, it has been stated by a French author*, was first effected by M. Seguin, the engineer of the Lyons and St. Etienne Railway. He claimed to have patented a boiler, in 1828, in which he placed a series of horizontal tubes immersed in the water, through which the hot air passed in streamlets, thus greatly increasing the heating surface, and consequently the evaporative power. Two locomotives had been constructed at Mr. Stephenson's works in Newcastle for the St. Etienne Railway, which were sent to France in 1829. M. Seguin found that, by applying his invention to these engines in conjunction with the steam blast, he was at once enabled greatly to increase their power and speed. The same idea of a tubular boiler had occurred to Mr. Henry Booth, the secretary of the Liverpool and Manchester Railway, who strongly urged its adoption by Mr. Stephenson in the construction of the "Rocket" engine.

On the subject of this important combination we cannot do better than here quote the words of Mr. Robert Stephenson himself, in a statement with which he has favoured us:

"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

* Lobet, Des Chemins de Fer de France, 1845.

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.

"At this stage of the locomotive engine, we have in the multitubular boiler the only important principle of construction introduced, in addition to those which my father had brought to bear at a very early age (between 1815 and 1821) on the Killingworth Colliery Railway. In the 'Rocket' engine, the power of generating steam was prodigiously increased by the adoption of the multitubular system. Its efficiency was further augmented by narrowing the orifice by which the waste steam escaped into the chimney; for by this means the velocity of the air in the chimney—or, in other words, the draught of the fire-was increased to an extent that far surpassed the expectations even of those who had been the authors of the combination.

"From the date of running the Rocket' on the Liverpool and Manchester Railway, the locomotive engine has received many minor improvements in detail, and especially in accuracy of workmanship; but in no essential particular does the existing locomotive differ from that which obtained the prize at the celebrated competition at Rainhill.

"In this instance, as in every other important step in

U

science or art, various claimants have arisen for the merit of having suggested the multitubular boiler as a means of obtaining the necessary heating surface. Whatever may be the value of their respective claims, the public, useful, and extensive application of the invention must certainly date from the experiments made at Rainhill. M. Seguin, for whom engines had been made by my father some few years previously, states that he patented a similar multitubular boiler in France, several years before. A still prior claim is made by Mr. Stevens, of New York, who was all but a rival to Mr. Fulton in the introduction of steam-boats on the American rivers. It is stated that as early as 1807 he used the multitubular boiler. These claimants may all be entitled to great and independent merit; but certain it is that the perfect establishment of the success of the multitubular boiler is more immediately due to the suggestion of Mr. Henry Booth, and to my father's practical knowledge in carrying it out."

Mr. Booth's account of the same important invention, with which he has favoured the writer, is as follows:

"I was in almost constant communication with Mr. Stephenson, and I am not aware that he had any intention of competing for the prize till I communicated to him my scheme of a multitubular boiler. This new plan of boiler comprised the introduction of numerous small tubes, two or three inches in diameter, and less than an eighth of an inch thick, through which to carry the fire, instead of a single tube or flue, eighteen inches diameter, and about half an inch thick; by which plan we not only obtain a very much larger heating surface, but the heating surface is much more effective, as there intervenes between the fire and the water only a thin sheet of copper or brass, not an eighth of an inch thick, instead of a plate of iron of four times the substance, as well as an inferior conductor of heat.