part twenty-five copper tubes of 3 inches diameter extended, which

were open to the fire-box at one end and to the chimney at the other. The fire-box, or furnace, 2 feet wide and 3 feet high, was attached immediately behind the boiler, and was also surrounded with water."

Stephenson knew of Trevithick's patent of 1802,[185] in which a three-tubed boiler is shown; and it was after that time that Oliver Evans and Fulton tried their experiments, and also the numerous engines with single or return double tube, at work in the principal towns of England prior to 1804,[186] and near his residence in childhood and in manhood.[187]

[Footnote 185: See vol. i., p. 128.]

[Footnote 186: See Trevithick's letter, Sept. 23rd, 1804, vol. ii., p. 2.]

[Footnote 187: Mr. Armstrong's note, vol. i., p. 184.]

George Stephenson's Killingworth boiler, "to which he added the steam-blast with such effect," was a copy of Trevithick's boiler and blast, working since 1804 in Newcastle-on-Tyne, and was precisely the boiler described by Stephenson; "in other cases the same result was obtained by returning the same tube through the boiler." This is an admission from Stephenson that Trevithick's patent boiler was the best in use up to about 1828.

A further proof of the indirect public gain from the use of Trevithick's return-tube boiler over a period of thirty years is their having supplied high-pressure expansive steam in the first experiments made with such steam by the Admiralty, at whose request Mr. Rennie and others examined the duty of the Cornish high-pressure expansive engine, and Captain King, R.N., in charge of the Admiralty Department at Falmouth in 1830, gave an order to Harvey and Co. to construct high-pressure steam-boilers for the Government vessel 'Echo'; in 1831 the machinery was put on board the 'Echo' in the Government Dockyard at Plymouth, and included three of Trevithick's return-tube boilers, made of wrought iron, each 5 feet 6 inches in diameter and 24 feet long, with internal return fire-tube 2 feet 2 inches in diameter. The fire-place end of the boiler was 6 feet 9 inches deep by 5 feet 6 inches wide, to give room for the fire-place and ash-pit. The steam pressure was 20 lbs. on the inch above the atmosphere, worked by double-beat valves, 6 inches in diameter, with expansive gear.

This new machinery was fixed under the superintendence of the writer, after which the Government engineers took charge of the vessel, and the writer who had, as the mechanic in charge, worked like a slave, though receiving but 1_s._ 6_d._ a day and expenses, was not invited to take any part in the experimental trials, nor ever heard of the result except in the ordinary rumours of Admiralty bungling on board the 'Echo.'

Those boilers were similar to the Trevithick boiler that had served the locomotive in Newcastle and elsewhere from 1801 to 1828, the first steamboat experiments in England, in Scotland, and in America, and the numerous high-pressure engines then at work.

The enlarging the fire-place end of boilers or fire-tubes has led to many forms. Trevithick's model of 1796[188] had an oval tube giving a greater spread of fire-*bars; the same is seen in the 1808 steamboat;[189] the Dolcoath boilers of 1811[190] show the oval and also the bottle-neck fire-tube; the Welsh locomotive of 1804[191] had the fire-tube contracted at its bend or return portion; the Tredegar puddling-mill fire-tube of 1801[192] tapered gradually from the fire-bridge to the chimney end; in the London locomotive of 1808[193] the fire-tube took the bottle-neck shape close to the fire-bridge. The accompanying sketch shows the bottle-neck contraction, only on the top and sides of the fire-tube was to give breadth to the fire-bars _d_, and thickness to the fire at bridge _c_, after which the flue portion of the fire-tube was contracted: this boiler was for many years a favourite in Cornwall. The bottle-neck contraction of the 'Echo' boiler was similar to the above, except that the enlargement of the fire-place was downwards instead of upwards, and the fire-tube, instead of going through the end of the boiler, returned to near the enlarged fire-place, when it passed out through the side of the boiler to the chimney, just as in the Tredegar puddling-mill boiler; all those variations were with the object of increasing the fire-grate, and at the same time keeping down the gross size and weight of boiler and its water.

[Footnote 188: See vol. i., p. 104.]

[Footnote 189: See vol. i., p. 335.]

[Footnote 190: See vol. ii., p. 169.]

[Footnote 191: See vol. i., p. 181.]

[Footnote 192: See vol. i., p. 223.]

[Footnote 193: See vol. i., p. 207.]

In 1805, Lord Melville failed to keep his appointment with Trevithick, on his proposal to construct a high-pressure steamboat.[194] Rennie, a pupil and friend of Watt, and familiar with Trevithick's high-pressure steam-dredgers on the Thames, was employed by Lord Melville and the Admiralty on the Plymouth Breakwater, where in 1813 Trevithick proposed the use of his high-pressure steam locomotive and boring engine.[195] In 1820 Rennie wrote to Watt, that the Admiralty had at last decided upon having a steamer; at that time fifteen years had passed since Trevithick's offer to propel the Admiralty by steam-puffers, and ten years more were to pass before they could make up their minds to venture on high-pressure steam from his boilers. The Steam Users' Association are equally hesitating, judging from words just spoken by an engineer, the son of an engineer:--

[Footnote 194: See Trevithick's letter, 10th Jan., 1805, vol. i., p. 324.]

[Footnote 195: Ibid., vol. ii., p. 24.]

"Sir William Fairbairn said he had come to the conclusion, after many years' experience, that it was in their power to economize the present expenditure of fuel by a system which might not be altogether in accordance with the views of the members of the association or the public at large, and that was to increase the pressure of steam. He would have great pleasure in stating a few facts which might some day tend to bring about a change, if not a new era, in the use of steam. From the result of a series of experimental researches in which he had been engaged for several years on the density, force, and temperature of steam, he had become convinced that in case we were ever to attain a large economy of fuel in the use of steam, it must be at greatly-increased pressure, and at a rate of expansion greatly enlarged from what it was at present. Already steam users had effected a saving of one-half the coal consumed by raising the pressure from 7 lbs. and 10 lbs.--the pressure at which engines were worked forty years ago--to 50 lbs., or in some cases as high as 70 lbs. on the square inch."[196]

[Footnote 196: 'The Engineer,' March 15th, 1872: remarks by the Chairman at a meeting of the Manchester Steam Users' Association.]

Dear me! would have been Trevithick's exclamation had he read this; did I devote my whole life to the making known the advantages of high-pressure steam, and did I, seventy years ago,[197] really work expansive steam of 145 lbs. on the inch in the presence of many of the leading engineers of the day! Of course this short extract of a speech made by a member of a practical society, may not be taken as conveying fully the speaker's views, but it illustrates the immense difficulty Trevithick encountered in making his numerous plans acceptable to the public.

[Footnote 197: See Trevithick's letter, August 20th, 1802, vol. i., p. 154.]

Another modern statement bearing on inventions originating with Trevithick, but wearing new garbs with new names, shows the same tendency to ignore old friends, or, to say the least of it, to pass them by:--

"The trial of No. 36 steam-pinnace was made at Portsmouth yesterday. Her peculiarity consists in the arrangement of her propelling machinery, in the adaptation of the outside surface condenser, and a vertical boiler, both patented by Mr. Alexander Crichton. The condenser is simply a copper pipe passing out from the boat on one quarter at the garboard strake, and along the side of the keel, returning along the keel on the opposite side, and re-entering the boat on that quarter. The boiler is designed for boats fitted with condensing engines, and which, therefore, are without the acceleration of draught given by the exhausted steam being discharged into the funnel. It is of the vertical kind, and stands on a shallow square tank, which forms the hot well. The tubes are horizontal over the fire, the water circulating through them. The condensed steam is pumped into the well at a temperature of 100°, and being there subjected to the heat radiating from the furnace, is pumped back into the boilers at nearly boiling point. It is estimated that, under these conditions, the pinnace would run for nearly 48 hours without having to 'blow off' or carry a supply of fresh water, the waste water being made good by sea water."[198]

[Footnote 198: 'The Times,' November 24th, 1871.]

The peculiarity of this steam-pinnace of 1871, on which a patent was granted, is stated to be a metal surface condenser exposed to the cold water at the bottom of the boat, returning the condensed steam at about boiling temperature to the boiler, and a vertical boiler with horizontal tubes through which the water circulates, both of which in principle, if not in detail, are seen in the surface condenser of Trevithick's iron-bottom ship of 1809, and his vertical boiler of 1816,[199] and further illustrated in the inventions spoken of in this and the following chapter; and yet on so all-important a subject, dealt with in various ways by Trevithick from 1804 to 1832, his plans are reproduced as discoveries in 1871.

[Footnote 199: See vol. i., pp. 336, 364, 370.]

About 1828, Mr. Rennie, Mr. Henwood, and others, reported on the advantages of high-pressure expansive steam in Wheal Towan engine,[200] on the north cliffs of Cornwall, near Wheal Seal-hole Mine on St. Agnes Head, where in 1797 Trevithick had worked his first high-pressure steam-puffer engine in competition with the Watt low-pressure steam-vacuum engine. Captain Andrew Vivian was then his companion, and the Cow and Calf, two rocks of unequal size, a mile from the land, were from that time called Captain Dick and Captain Andrew, or the Man and his Man, and there they still remain in the Atlantic waves, fit emblems of their namesakes and their still living inventions. The stir made by those expansive trials led to the experiment in the 'Echo,' of which Mr. Henwood[201] thus speaks:--

[Footnote 200: See Mr. Henwood's report, vol. ii., p. 185.]

[Footnote 201: Residing at Penzance, 1871.]

"Captain William King, R.N., Superintendent of the Packet Station at Falmouth, attempted to impress on Viscount Melville, then First Lord of the Admiralty, the advantage of using high-pressure steam expansively in the Royal Navy, to whom Lord Melville replied that he had been taught by his friend, the late Mr. Rennie, that the danger attending such a course was very great, and that it would be difficult, if not impossible, to persuade him to the contrary."

Twenty-five years of precept and example caused the Admiralty to follow suit, and to request Mr. Ward, a Cornish engineer, to construct boilers and expansive valves for the Government steamboat 'Echo.' The writer was entrusted with fixing the machinery in the vessel at the Plymouth Dockyard, and before starting with it from Harvey and Co.'s foundry, waited on Captain King, R.N., at Falmouth, for his instructions, in happy ignorance of the fear of the Lords of the Admiralty to tread on Cornish high-pressure. After eying the applicant as captains in Her Majesty's service are apt to do when dealing with boys in the civil service, he vouchsafed to say, "Mind, young man, what you are about, for if there is a blow up, by ---- you'll swing at the yard-arm."