Chapter XIX: Pole Steam-Engine (1)

When in the autumn of 1810 Trevithick returned to Cornwall, the experience of ten busy years had established the practicability and usefulness of the high-pressure engine. The principles of the invention were now to be applied on engines of the largest size.

In 1811, the late Captain S. Grose, a young pupil of Trevithick's, was employed to erect at Wheal Prosper Mine, in Gwythian, the first high-pressure steam pole condensing engine. It was placed immediately over the shaft and pump-rods, requiring no engine-beam. The air-pump, feed-pump, and plug-rod were worked from the balance-bob. The pole was 16 inches in diameter, with a stroke of 8 feet. The boilers were two wrought-iron tubes, 3 feet in diameter and 40 feet long. The fire was external. Shortly after Captain H. A. Artha erected several of those pole-engines for Trevithick. The drawing shows the simplicity of parts of this highly expansive steam-engine, beginning the up-stroke with steam of 100 lbs. to the inch above the atmospheric pressure, expanding it during the stroke down to a pressure of 10 lbs., and then condensing to form a vacuum for the down-stroke. It cost 750 guineas.

The drawings of this expansive pole condensing engine are from the dimensions given by Captain Grose who erected it, and by Captain Artha who knew it well.

_a_, cast-iron pole, 16 inches diameter, 8-feet stroke; _b_, pole-case, a small bit larger in internal diameter than the pole; _c_, cross-head, fixed on top of pole; _d_, guides for cross-head; _e_, side rods connecting the two cross-heads[**typo beads corrected]; _f_, bottom cross-head; _g_, pump-rod; _h_, balance-beam, with box for weights; _i_, connecting rods from balance-beam to bottom cross-head; _k_, guides for air-pump cross-head; _l_, cross-head and side rods for working air-pump; _m_, air-pump, condenser, and water-cistern; _n_, feed-pump worked from air-pump cross-head; _o_, plug-rod worked from balance-beam; _p_, exhaust-valve; _q_, steam-valve; _r_, exhaust-pipe; _s_, steam-pipe; _t_, bracket for carrying working gear; _u_, expansive steam-horn and tappets; _v_, handles for working valves.]

Detail of Boilers:--_a_, two wrought-iron boilers, 3 feet in diameter, 40 feet long, using steam of 100 lbs. on the square inch above the atmosphere; _b_, cast-iron manhole door and safety-valve; _c_, ash-pit; _d_, fire-place; _e_, flues, the fire going first the whole length under the bottom of the boiler, then back again over the top, and into the chimney; _f_, brickwork; _g_, ashes or other convenient non-*conductor of heat; the fire-place ends of the boilers were 15 inches lower than the opposite ends, increasing the safety, with less liability to prime, and greater surface for superheating.]

"When a boy I was placed as an apprentice or learner with Captain Trevithick, before he left Cornwall for London. On his return to Cornwall, about 1810, he employed me to erect his first high-pressure expansive pole pumping engine at a mine in Gwythian.

"The pole was 16 inches in diameter; the stroke was very long, but I do not exactly recollect the length. It had a condenser and air-pump. There were two boilers made of wrought iron, 8 feet in diameter and 40 feet long. The fire was placed under them at one end, and flues went round them. A feed-pump forced water into the boilers; each had a safety-valve with a lever and weight. The steam in the boiler was 100 lbs. to the square inch. The pole was raised by the admission of the strong steam under its bottom. The steam-valve was closed at an early part of the stroke, and the steam allowed to expand; at the end of the stroke it was reduced to 20 lbs. or less, when the exhaust-valve allowed the steam to pass to the condenser, and the pole made its down-stroke in vacuum. A balance-bob regulated the movement of the engine.

"Trevithick's character in those days was, that he always began some new thing before he had finished the old."[23]

[Footnote 23: Captain Samuel Grose's recollections. 1858. Gwinear.]

Captain Artha, one of his assistants, said:--

"I erected several of Captain Trevithick's pole-engines. My brother Richard worked the one at Wheal Prosper when first erected. The pole made an 8-feet stroke. The case was fixed over the engine-shaft on two beams of timber from wall to wall. A cross-head was bolted to the top of the pole, and from it two side rods descended to a cross-piece under the pole-case, from which the pump-rod went into the shaft. A connecting rod worked a balance-beam, which worked the air-pump, feed-pump, and plug-rod for moving the valves. The steam, of a very high pressure, worked expansively."[24]

[Footnote 24: Captain H. A. Artha's recollections. Penzance, 1869.]

The first admission of the high-pressure steam under the pole was equal to a force of 8 or 9 tons, causing it and its attached pump-rods to take a rapid upward spring. Having travelled 1 or 2 feet of its stroke of 8 feet, the further supply of steam from the boiler was cut off, and its expansion, together with the momentum of the mass of pump-rods, completed the upward stroke. The pressure of the steam in the pole-case at the finish of the up-stroke would be reduced to say 10 or 20 lbs. to the inch, according to the amount of work on the engine. The steam then passed to the condenser and air-pump, and the engine made its down-stroke by the vacuum under the pole, and by the weight of the descending pole and pump-rods.

Each boiler was a wrought-iron tube 3 feet in diameter and 40 feet long, the fire-place under one end, with brick flues carrying the heated air under the whole length of the bottom of the boiler, and back again over the top or steam portion for superheating.

[Rough draft.]

"CAMBORNE, _28th February, 1813_.

"I will engage to erect a puffer steam-engine, everything complete at the surface, on the Cost-all-lost Mine, capable of lifting an 8-inch bucket, 4-1/2-feet stroke, twenty-four strokes per minute, 30 fathoms deep, or 280 gallons of water per minute from that same depth, being a duty equal thereto, for 550 guineas. But if a condensing engine, 600 guineas. If of the same size as Wheal Prosper, 750 guineas.

"RICHARD TREVITHICK."

The engines, erected in 1811 or 1812, combined the novelty of the steam pole-engine, with the use of high-pressure steam of 100 lbs. on the square inch, and the comparatively untried principle of steam expansion, carried to what in the present day is thought an extreme and unmanageable limit.

The Wheal Prosper engine fixed near the sea-shore at Gwythian is referred to in Trevithick's note to Mr. Rastrick,[25] as "that new engine you saw near the sea-side, with me, is now lifting forty millions, 1 foot high, with 1 bushel of coal" (84 lbs.), "which is very nearly double the duty that is done by any other engine in the county."

[Footnote 25: See Trevithick's letter, January 26th, 1813, chap, xviii.]

This was probably the first application of high-pressure steam to give motion to pump-rods. The engine, as compared with the neighbouring Watt low-pressure steam vacuum pumping engines, was small, but the principles of high steam, expansive working, and vacuum, were combined successfully to an extent scarcely ventured on by modern engineers.

Trevithick's high-pressure condensing whim-engines had been for some years at work in Cornwall, but mine adventurers had not dared to risk the application of high-pressure steam to the large pumping engines, fearing its great power would prove unmanageable, and its rapid movement cause breakage of the pump-rods and valves.

Two distinct inventions or improvements, each of which was actually followed up in different mines, show themselves in this engine: one being the form of boiler to give with economy and safety high-pressure expansive steam for large engines; the other, the application of a pole in lieu of a piston, as a more simple engine for working with strong expansive steam, and more easily constructed by inexperienced mechanics, who had none of the slide lathes or planing machines so much used by engine builders of the present day.

"About 1814 Captain Trevithick erected a large high-pressure steam-puffer pumping engine at the Herland Mine. The pole was about 30 inches in diameter, and 10 or 12 feet stroke. There was a cross-head on the top of the pole, and side rods to a cross-head under the pole-case. The side rods worked in guides. The pole-case was fixed to strong beams immediately over the pump-shaft. The steam was turned on and off by a four-way cock. The pressure was 150 lbs. to the inch above the atmosphere. The boilers were of wrought iron, cylindrical, about 5 feet 6 inches in diameter and 40 feet long, with an internal tube 3 ft. in diameter. The fire-place was in the tube. The return draught passed through external brick flues.[26]

[Footnote 26: Recollections of the late Captain Charles Thomas, manager of Dolcoath Mine.]

"When a young man, living on a farm at Gurlyn, I was sent to Gwinear to bring home six or seven bullocks. Herland Mine was not much out of my way, so I drove the bullocks across Herland Common toward the engine-house. Just as the bullocks came near the engine-house the engine was put to work. The steam roared like thunder through an underground pipe about 50 feet long, and then went off like a gun every stroke of the engine. The bullocks galloped off--some one way and some another. I went into the engine-house. The engine was a great pole about 3 feet in diameter and 12 feet long. A cast-iron cross-head was bolted to the top of the pole. It had side rods and guides. A piece of iron sticking out from the cross-head carried the plug-rod for working the gear-handles. The top of the pole worked in a stuffing box. A large balance-beam was attached to the pump-rods, near the bottom cross-head.

"There were two or three of Captain Trevithick's boilers with a tube through them, the fire in the tube. They seemed to be placed in a pit in the ground. The brick flues and top of the bricks were covered with ashes just level with the ground. A great cloud of steam came from the covering of ashes.

"I should think the pressure was more than 100 lbs. to the inch. People used to say that she forked the mine better than two of Boulton and Watt's 80-inch cylinder engines. We could hear the puffer blowing at Gurlyn, five or six miles from the Herland Mine.

"In 1813 I carried rivets to make Captain Trevithick's boilers in the Mellinear Mine; they were 5 feet in diameter and 30 or 40 feet long, with an internal fire-tube. It took four or five months to build them. In the present day (1869) a fortnight would build them. The largest boiler-plates obtainable were 3 feet by 1 foot. We had to hammer them into the proper curve. The rivet-holes were not opposite one another. A light hammer was held against the rivet-head in riveting, in place of the present heavy one, so the rivet used to slip about, and the plates were never hammered home so as to make a tight joint."[27]

[Footnote 27: Recollections of Mr. James Banfield, Penzance, 1871.]

Lest the reader should doubt the comparative power of the Watt low-pressure vacuum and Trevithick's high-pressure steam-engines, a short but sufficiently close calculation shows that taking Stuart's[28] estimate of the effective power of the Watt engine at 8-1/2 lbs. on each square inch of the piston, and Trevithick's engine at anything approaching to 150 lbs. on each square inch, it becomes evident that the latter would be ten or twenty times more powerful than the former. A few figures will put the question in more practical form.

[Footnote 28: See Stuart's 'History of the Steam-Engine.']

The Wheal Prosper 16-inch pole high-pressure expansive steam vacuum engine commenced its up-stroke with steam of 100 lbs. on the inch, acting on the 122 square inches of the pole, which steam at the finish of the stroke was reduced by expansion to 10 lbs., giving, say, an average steam pressure of 55 lbs. The down-stroke was caused by a vacuum under the pole of 14 lbs. on the inch, reduced by, say, one-third loss in working the air-pump to 9 lbs., giving from the compound stroke a force of 64 lbs. on each square inch, which, multiplied by the area of the pole, gives a net force of 7808 lbs.

The Herland 33-inch pole high-pressure expansive steam puffer-engine commenced its up-stroke with steam of 150 lbs. on the inch, acting on the 855 square inches of the pole, which steam at the finish of the stroke--we will suppose--was reduced by expansion to 75 lbs., giving an average steam pressure of, say, 112. As this puffer-engine used no vacuum, the down-stroke gave no increase of power; its compound stroke was therefore a force of 112 lbs. on each square inch, which, multiplied by the area of the pole, gives a net force of 95,760 lbs.

To compare the Trevithick high-pressure steam pumping engine, with the Watt low-pressure steam pumping engine, take one of the largest of the latter, made about that time, say, with an 80-inch cylinder, which commenced its down-stroke with steam of, say, 3 lbs. on the inch, acting on the 5000 square inches of the piston, which steam at the finish of the stroke--the writer is describing the usage at that time, for Watt himself advocated a less steam pressure--was reduced by expansion to, say, 1 lb., giving an average steam pressure of, say, 2 lbs. on the top of the piston, whose under side was in vacuum equal to 14 lbs. on the inch, reduced by, say, one-third loss in working the air-pump to 9 lbs., which power, from vacuum added to the 2 lbs. from steam, gives a net force of 11 lbs. on each square inch of the piston. As the Watt pumping engine moved in equilibrium during its up-stroke, it thereby gained no increase of power; its compound stroke was therefore a force of 11 lbs. on each square inch, which, multiplied by the area of the piston, gives a net force of 55,000 lbs.

The practical comparison therefore stands,--Trevithick's 16-inch pole high-pressure steam, and vacuum, on each inch 64 lbs., net force 7808 lbs.; Trevithick's 33-inch pole high-pressure steam, without vacuum, on each inch 112 lbs., net force 95,760 lbs.; Watt's 80-inch piston, low-pressure steam, and vacuum, on each inch 11 lbs., net force 55,000 lbs. As the first cost was mainly dependent on the size, the Trevithick engine was commercially much more valuable than the Watt engine.

"I saw Captain Trevithick's puffer working at the Herland Mine. The steam used to blow off like blue fire--it was so strong. The lever on the safety-valve was about 3 feet long, with a great weight on it, more than a hundredweight. The engine did not answer very well, for the packing in the pole stuffing box used to burn out, and a cloud of steam escaped. The greatest difficulty was in the leaking of the boilers. You could hardly go near them. Before that time we always put rope-yarn between the lap of the boiler-plates to make the seams tight. Captain Dick's high-pressure steam burnt it all out. He said, 'Now you shall never make another boiler for me with rope-yarn.' Everybody said it was impossible to make a tight boiler without it. We put barrowfuls of horse-dung and bran in Captain Dick's boilers to stop the leaks."[29]

[Footnote 29: Henry Clark of Redruth, in 1869, aged eighty-three years.]

This difficulty of making a tight and safe boiler, that puzzled Watt, was moonshine to Trevithick. When the strained boiler and flinching rivets allowed the boiler-house to become full of dense steam, Trevithick told them to cover it up with ashes, they would not see it quite so much then, and it would keep the heat in the boiler. Bran or horse-dung inside was a good thing as a stop-gap, though it added not to the strength of the boiler. Trevithick was himself in a cloud of steam in the engine-house; yet, with such surroundings, he turned on and off his gunpowder steam, from his cannon of a pole-case, of 40 tons force, sending his bolt-shot pole, 33 inches in diameter, its destined course of ten feet, and back again, as though it were a shuttlecock, several times in a minute.

Having by one or two years of experience proved the value of his new pole-engine, he applied for a patent on the 13th June, 1815,[30] of which the following is the portion referring particularly to the pole-engine:--

[Footnote 30: See full copy of patent, chap. xvi.]

"Instead of a piston working in the main cylinder of the steam-engine, I do use a plunger-pole similar to those employed in pumps for lifting water, and I do make the said plunger-pole nearly of the same diameter as the working cylinder, having only space enough between the pole and the cylinder to prevent friction, or, in case the steam is admitted near the stuffing box, I leave sufficient room for the steam to pass to the bottom of the cylinder, and I do make at the upper end of the cylinder for the plunger-pole to pass through a stuffing box of much greater depth than usual, into which stuffing box I do introduce enough of the usual packing to fill it one-third high. Upon this packing I place a ring of metal, occupying about another third part of the depth of the stuffing box, this ring having a circular groove at the inside, and a hole or holes through it communicating with the outside, and with a hole through the side of the stuffing box; or, instead of one ring containing a groove, I sometimes place two thinner rings, kept asunder by a number of pillars to about the distance of one-third of the depth of the stuffing box, and I pack the remaining space above the ring or rings, and secure the whole down in the usual manner. The intention of this arrangement is to produce the effect of two stuffing boxes, allowing a space between the two stuffings for water to pass freely in from the boiler or forcing pump through a pipe and through the hole in the side of the stuffing box, so as to surround the plunger-pole and form the ring of water for the purpose of preventing the escape of steam by keeping up an equilibrium between the water above the lower stuffing and the steam in the cylinder. By this part of my said invention I obviate the necessity of that tight packing which is requisite when steam of a high pressure is used, and consequently I avoid a greater proportion of the usual friction, because a very moderate degree of tightness in the packing is quite sufficient to prevent the passage of any injurious quantity of so dense a fluid as water. And I do further declare that I use the plunger-pole, working in a cylinder and through a double stuffing, either with or without a condenser, according to the nature of the work which the steam-engine is to perform."

Though Trevithick has been spoken of as a visionary, intractable schemer, observation shows that he adhered with tenacity to original ideas, proved to be good. The plunger-pole pump, the water-pressure engine, the Camborne locomotive, the pole steam-engine, were all built on the same groundwork originally started with, of greatest simplicity of form, and absence of many pieces; and it may be observed that he never applied for a patent until the value of the idea had been proved by experiment.

In practice the difficulty of keeping the pole-packing in order was one of the objections to the plan; for it either leaked, or, if packed tight, caused much friction and wearing away of the middle of the pole faster than the ends, from the greater speed at the middle of the stroke. The steam-ring was therefore of importance in the engine, in those days of inaccurate workmanship; like the water cup on the gland of the plunger-pump packing, it prevented external air from injuring the vacuum.

"MR. GIDDY, "CAMBORNE, _July 8th, 1815_.

"Sir,--About a fortnight since I received letters from Lima, and also letters to the friends of the men who sailed with the engines. They arrived on the 29th January, after a very good passage, and without one hour's sickness. Both their and my agreements were immediately ratified, and they are in high spirits. The ship finished discharging on the 11th February, which was the day those letters sailed from Lima with $12,000 for me, which has all arrived safe.

"I shall make another fit-out for them immediately. I expect that all the engines will be at work before the end of October; half of them must be at work before this time. The next day, after their letters sailed for Europe, they intended to go back to the mines. Woolf's engine is stopped at Herland, and I have orders to proceed. A great part of the work is finished for them, and will be at work within two months from the time I began. I only engage that the engine shall be equal to a B. and Watt's 72-inch single, but it will be equal to a double 72-inch cylinder. It is a cast-iron plunger-pole, over the shaft, of 33 inches diameter, 10-feet stroke. The boiler is two tubes, 45 feet long each, 3 feet diameter, 1/2 an inch thick, of wrought iron, side by side, nearly horizontal, only 15 inches higher at the steam end of the tubes, to allow the free passage of steam to the steam-pipe. There are two 4-inch valves, one the steam-valve, the other the discharging valve. I have made the plunger-case and steam-vessel of wrought iron 3/4 of an inch thick. The steam-vessel is 48 inches in diameter. The plunger stands on beams over the shaft, with the top of it at the level of the surface, with a short T-piece above the plunger-pole, and a side rod on each side, that comes up between the two plunger-beams in the shaft; this does away with the use of an engine-beam, and the plungers do away with the use of a balance-beam.

"The fire is under the two tubes, and goes under them for 45 feet, and then returns again over them, and then up the chimney. Those tubes need no boiler-house, because they are arched over with brick, which keeps them from the weather, and scarcely any engine-house is needed, only just to cover the engineman.

"Suppose a 72-inch cylinder (having 4000 inches), at 10 lbs. to the inch, an 8-feet stroke, working nine strokes per minute (which is more strokes of that length than she will make when loaded to 10 lbs. to the inch).

Inches.
4000 in a 72-inch cylinder, single.
10 lbs. to the inch.
-------
40000
8 feet stroke.
-------
320000
9 strokes per minute.
-------
2880000 lbs. lifted one foot high per minute.
-------

"Suppose a 33-inch plunger-pole, 10-feet stroke, ten strokes per minute (which is not so fast by three or four strokes per minute as this engine will go, because she will have no heavy beam to return, neither will she have to wait for condensing, like B. and Watt's, which, when loaded, hangs very long on the injection).

855 square inches in a 33-inch plunger-pole.
10 strokes per minute.
-------
8550
10 feet stroke.
-------
85500
34 lbs. to the inch, real duty.
-------
342000
256500
-------
2907000 lbs. lifted one foot high per minute.
-------

"I should judge that less than 50 lbs. to the inch above the atmosphere would be quite enough to do the work of a 72-inch cylinder single, which is but a trifle for those wrought-iron tubes to stand. This engine, everything new, house included, ready for work, will not exceed 700_l._ Two months are sufficient for erecting it. The engine of Woolf's, at Wheal Vor, which is but two-thirds the power of a 72-inch cylinder, single power, cost 8000_l._, and was two years erecting. I would be much obliged to you for your opinion on this business.

"I remain, Sir,
"Your very humble servant,
"Richard Trevithick.

"I am sorry to say that the mines in general are very poor."

He shows that with steam of 34 lbs. to the inch, his Herland pole puffer steam-engine of 33 inches in diameter would be equal in power to the Watt low-pressure steam vacuum engine, with a 72-inch cylinder. Herland, like Dolcoath and Wheal Treasury, was the chosen battle-ground of rival engineers; fifty years after Newcomen had there erected his famously large 70-inch cylinder engine, Watt surpassed it in size by a cylinder 2 inches more in diameter, and, after personally superintending its erection in 1798, declared that "it could not be improved on." Mr. Davey, the mine manager, considered that it did twenty millions of duty, though Mr. Watt had made it twenty-seven millions with a bushel of coal.[31] This difference is probably explained by the then Cornish bushel weighing 84 lbs., while Watt generally calculated a bushel at 112 lbs.

[Footnote 31: Lean's 'Historical Statement of the Steam-Engine,' p. 7.]

Trevithick declining to believe Watt's prognostication, a public test of Watt's engines in the county was demanded; Mr. Davies Gilbert, with Mr. Jenkin, were requested to report on their duty, and gave it in 1798 as averaging seventeen millions.[32] During the same year the adventurers in Herland Mine engaged Trevithick and Bull, jun., to erect a 60-inch cylinder Bull engine to compete with Watt's 72-inch cylinder. The result of this fight is not traceable, nor what took place there during the succeeding fifteen years; when in 1814 Woolf erected in Cornwall his double-cylinder engine to compete with Watt's engine, and Trevithick attacked them both with his Herland high-pressure pole puffer in 1815, when he erected at his own risk and cost a 33-inch pole-engine, engaging that it should, both in power and economical duty, equal the Watt 72-inch engine. The boilers were similar in form to those used a year before in Wheal Prosper high-pressure steam vacuum pole-engine, being two wrought-iron tubes, each 45 feet long and 3 feet in diameter, made of plates half an inch thick. The fire was in external flues. The engine was fixed directly over the pump-rods in the shaft, using neither main beam nor air-pump.

[Footnote 32: Lean's 'Historical Statement of the Steam-Engine,' p. 7.]

Trevithick's rough hand-sketch shows the steam-ring in the stuffing box and the steam-vessel; the particular use of the latter he has not described: probably it was because Cornish pumping engines, not having the controlling crank to limit the movement of the piston, are obliged to trust to the very admirable, but little understood, steam-cushion, without which the ascending piston would inevitably strike and break the cylinder-cover, while in the pole puffer-engine this danger was during the descent of the pole, and therefore the discharge-steam valve was closed, while the steam in the pole-case was still of ten or more pounds to the inch, so that by the time the pole reached the finish of its down-stroke, it had compressed this steam-cushion, filling also the steam-vessel, with a pressure approaching to that in the boiler, and equal to the weight of the pole and pump-rods. A comparatively small supply of steam from the boiler into the steam-vessel brought it up to the boiler pressure, sending the pole and pump-rods upwards with a spring. The steam-valve then closed, allowing the momentum of the great weight of pump-rods, together with the expanding steam, to complete the up-stroke. The discharge-valve was then opened for a moment, allowing a blast of steam to escape, reducing the pressure say to one-half. The weight of the rods caused their downward movement, raising the load of water in the plunger-pole pumps, and at the same time compressing the steam from the pole-case into the steam-vessel, equal at the finish of the stroke to the support of the pole and pump-rods. This most simple steam-engine combined in the greatest degree the two elements of expansion and momentum.

The up-stroke began with a much higher pressure of steam than was necessary to raise the load; having given momentum to the rods, the supply of steam was cut off, and the stroke was completed by expansion. The down-stroke began with a comparatively low pressure of steam under the pole. The unsupported pump-rods fell downwards, setting in upward motion the column of water in the plunger-pole pumps. The discharge-valve was closed long before the completion of the down-stroke, and the momentum of the moving mass of rods and water compressed the steam driven from the pole-case into the steam-vessel up to a pressure equal to the support of the pole and pump-rods. The pole was, therefore, continually floating or rising and falling in steam of ever-varying pressure.

Trevithick' s figures show the working power of the 33-inch pole as much greater than Watt's 72-inch cylinder engine, even when the steam pressure in the former was much reduced, and that Woolf's double-cylinder engine, of less power, cost ten times as much as the pole-engine. This sum probably included the costly buildings required for the beam-engines, which Trevithick's plan dispensed with.

The reader may judge of the perfection of mechanism in this plain-looking engine from the fact that a pole, with 150 lbs. of steam to the inch in the boiler, was equal to 50 or 60 tons weight, thrown up and down its 10-feet stroke ten or fourteen times a minute, with a limit of movement perfectly under control, while modern engineers are building ships' turrets because of the difficulty of raising and depressing a 30-ton gun from the hold to above the water level.

[Rough draft.]

"SIR, "CAMBORNE, _September 12th, 1815_.

"I received a letter dated the 20th of August, from Mr. Davies, in which he did not mention the name of Herland castings. On the 24th of the same month I wrote to you, informing you of the same, and requesting to know what state of forwardness the castings were in. On the 30th of August I received another letter from Mr. Davies, not saying what state of forwardness the castings were in, nor when they would be finished, only that they would set their hands about them, and that I might expect a letter from you stating the particulars, which has not yet come to hand. I have waited so long that I am quite out of patience. You will know that it is now nearly double the time that the castings were to have been finished in, and you have not yet answered my letters as to the state of the castings nor when they will be finished. I must again request you to write to me on this subject, otherwise I must immediately remove the orders to some other founders that may be a little more attentive to their customers. I must be informed in the positive, whether the castings will be at Bristol by the next spring-tide, as a vessel is engaged for the purpose of taking them to Cornwall.

"Yours, &c.,
"R. T.

"MR. JOHN RASTRICK,
"_Chepstow, South Wales_."

Rastrick, whom he had known at the Thames Driftway, had become the managing engineer at the Bridgenorth Foundry.

[Rough draft.]

"MR. GEORGE COWIE, "CAMBORNE, _September 29th, 1815_.

"I received your favour of the 20th, and on the 23rd called on Mr. Wm. Sims, your engineer, who went with me to Beeralstone Mine the same day. We arranged on the spot what was necessary for the engine. I hope it will be at work in good time, before the winter's floods set in. Nothing can prevent it, unless the castings are detained by contrary winds. The boilers are nearly finished in Cornwall. The castings at Bridgenorth are in a forward state. I intend leaving this evening for Bridgenorth, to ship the castings, both for Herland and Beeralstone. It was the wish of the agents on the mine that these castings might be sent to Swansea, and taken from thence to the mine with a freight of coal. I shall, if possible, get the Herland castings in the same ship. The workmen making your boilers want an advance of cash to enable them to finish. They provide both iron and labour, for which they are to receive 42_l._ per ton for the boiler when finished; the weight will be about 8 tons. You may send this money to Mr. Sims or to me, or otherwise you may direct it to Mr. N. Holman, boiler-maker, Pool, near Truro. 100_l._ will satisfy them for the present. I hope to be in London this day week, and will call at your office.

"Yours, &c.,
"R. TREVITHICK."

The pole-engine was not only used in several mines shortly after its first introduction, but Mr. Sims, the leading engineer of the eastern mines, not generally favourable to Trevithick, advocated its application in the traditional Watt district.

Scarcely had he smoothed the way with one opponent than another sprung up in an unexpected quarter. His brother-in-law, Harvey, with his once friend, Andrew Vivian, then a partner with Harvey, opposed his plans at the Herland. They were annoyed at Trevithick's sending his orders for castings and machinery to Bridgenorth, and may have had doubts of the success of the new inventions. They had authority in the mine, probably as shareholders, a position generally acquired in Cornwall by those who supply necessary mine material, as well as by the smelters who buy the mineral from the mines. The Williamses and Foxes, controlling the eastern district of mines, were also shareholders and managers, supplying machinery and buying the mine produce.

[Rough draft.]

"SIR, "PENZANCE, _13th December, 1815_.

"Yesterday I was at Herland, where I was informed that Captain Andrew Vivian had been the day before, on his return from Mr. Harvey's, and discharged all the men on the mine, without giving them a moment's notice. Before the arrival of the castings the pitmen, sumpmen, carpenters, and smiths were very busy getting the pit-work ready; at which time H. Harvey and A. Vivian were exulting in reporting that the iron ore was not yet raised that was to make the Herland castings. The day that they heard of their arrival they discharged all the labourers, and ordered the agents not to admit another sixpence-worth of materials on the adventurers' account, or employ any person whatever.

"The agents sent a short time since to Perran Foundry[33] for the iron saddles and brasses belonging to the balance-bob, the property of the adventurers; but they refused to make them, with a great deal of ill-natured language about my engine.

[Footnote 33: Belonging to Williams and Co.]

"I am determined to fulfil my engagement with the adventurers, and yesterday ordered all the smiths, carpenters, pitmen, and sumpmen to prepare the adventurers' pit-work, and ordered the agents to get the balance-bob and every other thing that may be wanted at my expense, so as to fork the first lift, which I hope to have dry by Monday three weeks. The engine will be in the mine this week, and in one fortnight after I hope the engine will be at work, and in less than a week more the first twenty fathoms under the adit will be dry.

"In consequence of the Perran people refusing to send the saddles and brasses for the balance-bob, we will make shift in the best way we can without them. The brasses I have ordered on my own account at Mr. Scantlebury's. The coals for the smiths I have also ordered, and the same for the engine to fork the first lift. This is very uncivil treatment in return for inventing and bringing to the public, at my own risk and expense, what I believe the country could not exist without. I am determined to erect the engine at all events and upset this coalition before I leave Europe, if it detains me one year to accomplish it.

"I remain, Sir,
"Your very humble servant,
"RICHARD TREVITHICK.

"MR. PHILLIP,
"_George Yard, Lombard Street_.

"P.S.--I should be glad to hear from you what is going forward respecting an arrangement of the shares."

[Rough draft.]

"GENTLEMEN, "PENZANCE, _23rd December, 1815_.

"I have received the Herland castings, and am very seriously sorry to say, after we had fixed together the castings on the mine and made the joints, on attempting to put the plunger-pole into the case it would not go down; neither would either of the rings go to their places into the cylinder and on to the pole; therefore the whole engine must be again taken to pieces and sent to a turning and boring mill to be newly turned and bored. How to get this done I cannot tell, for the founders here will not do it because they had not the casting them. Already great expenses have been incurred by delays, and now to send them back to Bridgenorth at an immense loss of time and money will be a very serious business indeed. I think that either the cylinder is bored crooked or the plunger-pole turned crooked, or both, as it will sink farther down into the cylinder on turning it round on one side than it will on the other. The whole job is most shamefully fitted up, and was never tried together before sent off. Write to me by return of post and say what I am to do in this dilemma.

"Yours, &c.,
"RICHARD TREVITHICK.

"HAZELDINE, RASTRICK, AND CO.,
"_Bridgenorth_."

The new engine-work from Bridgenorth on arrival was found to be so inaccurately made that the pole would not go into the pole-case. Henry Phillips,[34] who saw the engine make its first start, says:--

[Footnote 34: Still working in Harvey's foundry at Hayle, 1869.]

"I was a boy working in the mine, and several of us peeped in at the door to see what was doing. Captain Dick was in a great way, the engine would not start; after a bit Captain Dick threw himself down upon the floor of the engine-house, and there he lay upon his back; then up he jumped, and snatched a sledge-hammer out of the hands of a man who was driving in a wedge, and lashed it home in a minute. There never was a man could use a sledge like Captain Dick; he was as strong as a bull. Then, he picked up a spanner and unscrewed something, and off she went. Captain Vivian was near me, looking in at the doorway; Captain Dick saw him, and shaking his fist, said: 'If you come in here I'll throw you down the shaft.' I suppose Captain Vivian had something to do with making the boilers, and Captain Dick was angry because they leaked clouds of steam. You could hardly see, or hear anybody speak in the engine-house, it was so full of steam and noise; we could hear the steam-puffer roaring at St. Erth, more than three miles off."

By the end of January, 1816, the engine was ready for work, and after ten days of experience, he thus described the result:--

"MR. DAVIES GIDDY, M.P., "PENZANCE, _11th February, 1816_.

Sir,--I was unwilling to write you until I had made a little trial of the Herland engine. It has been at work about ten days, and works exceedingly well; everyone who has seen it is satisfied that it is the best engine ever erected. It goes more smoothly than any engine I ever saw, and is very easy and regular in its stroke. It's a 33-inch cylinder, 10-1/2-feet stroke. We have driven it eighteen strokes per minute. In the middle, or about two-thirds of the stroke, it moved about 8 feet per second, with a matter in motion of 24 tons; and that weight returned thirty-six times in a minute, with 2 bushels of coal per hour. This of itself, without the friction, or load of water, is far more duty than ever was done before by an engine. I found that it required about 80 lbs. to the inch to work the engine the first twelve hours, going one-third expansive, twelve strokes per minute, 10-1/2-feet stroke, with 24 bushels of coal. The load of water was about 30,000. This was occasioned by the extreme friction, the plunger-pole being turned, and the plunger-case bored, to fit so nicely from end to end, that it was with great difficulty we could at all force the plunger-pole down to the bottom of the plunger-case. This is now in a great degree removed, and since we went to work we have thrown into the balance-box 4 tons of balance, and it would carry 3 tons more at this time. We must have carried that load in friction against the engine, therefore, if you calculate this, you will find it did an immense duty, going twelve strokes per minute, 10-1/2-feet stroke, with 2 bushels of coal per hour. The engine is now working regularly twelve strokes per minute, with 60 lbs. of steam, 10-1/2-feet stroke, three-quarters of the stroke expansive, and ends with the steam rather under atmosphere strong, with considerably within 2 bushels of coal per hour. I would drive her faster, but as the lift is hanging in the capstan rope under water, they are not willing to risk it. I have raised the steam to 120 lbs. to the inch, the joints and everything perfectly tight. I took the packing out of the stuffing box and examined it, and found that the heat had not at all injured it; the packing is perfectly tight, not a particle of steam is lost.

"I have offered to deposit 1000_l._ to 500_l._ as a bet against Woolf's best engine, and give him twenty millions, but that party refuses to accept the challenge. I have no doubt but that by the time she is in fork she will do 100 millions, which is the general opinion here. The boilers are certainly the best ever invented, as well as the other parts. The draught is the best you ever saw; I have only one-quarter part of the fire-bars uncovered, yet from one-quarter part of the fire-place that I first made, I find plenty of steam. The greatest part of the waste steam is condensed in heating the water to fill the boiler; what escapes is a mere nothing. The engine will be loaded, when in fork, about 52 lbs. to the inch. Now suppose I raise the steam so high at the first part of the stroke as to go so expansive as to leave the steam, at the finish, only atmosphere strong, shall I, in that case, use any more coal than at present? The materials and joints will stand far more than that pressure; 500 lbs. to the inch would not injure them. When the engine gets on two lifts, I will write to you again, and in the meantime please to give me your thoughts on the engine. Every engine that was erecting is stopped, and the whole county thinks of no other engine.

"Your very obedient servant,
"RD. TREVITHICK."

The new pole puffer-engine worked so satisfactorily and its movements were so manageable that the length of the stroke was increased by the spare 6 inches, which had been allowed as a margin in case of its overrunning its intended stroke. It would bear being worked at eighteen strokes a minute, while the Watt 72-inch engine did not exceed nine strokes a minute; with steam in the boiler of 80 lbs. to the inch it performed its work when the steam supply was cut off at two-thirds of the stroke, completing it by expansion. It also worked well with steam of 120 lbs. to the inch; but the want of strength in the pump-rods and the requirements of the mine caused the regular working pressure of steam to be reduced to 60 lbs. on the inch, and to be cut off when the pole had moved through the first quarter of its stroke. The excellent draught causing the fire-bars to be reduced to one-quarter of their original surface, and the heating the feed-water by the waste steam in this powerful pumping engine, indicate the use of the blast-pipe as at that time worked in the Welsh puddling-mill engine. Watt's engine was for a moment forgotten, that he might challenge Woolf to a trial, giving him as a help twenty millions, or the understood duty of the Watt engine. This non-condensing pole-engine, with 20 tons of pump-rods, moved at a maximum speed of 8 feet a second, and was equal to its work with a steam pressure of 52 lbs. on the inch. Trevithick contemplated extending the expansive principle even further than he had done in the Wheal Prosper pole condensing engine, so that at the finish of the up-stroke the steam should only be about the pressure of the atmosphere, or say from 1 to 10 lbs. on the inch, having commenced it with steam of from 100 to 200 lbs. on the inch, and cutting off the supply from the boiler when the pole had gone but a very small part of its upward stroke, more or less as the mine requirements admitted of it. The principle of expansive working and momentum of moving parts was of necessity modified in its application to pump-work.

"DEAR TREVITHICK, "EASTBOURNE, _February 15th, 1816_.

"I have been called here by the decease of my wife's uncle, and consequently your letters of the 11th did not reach me till this day.

"The account you give me of your new engine has been extremely gratifying. The duty performed by the engine in giving a velocity of 8 feet in a second, thirty-six different times in a minute, to 24 tons of matter, by the consumption of 2 bushels of coal in an hour, is indeed very great, amounting to about fifty-seven and three-quarter millions. So that when you obtain a proper burden, and the extraordinary friction arising from the too close fitting of the plunger-pole and case is reduced, there seems to be no doubt of your engine performing wonders.

"I am of opinion that the stronger steam is used, the more advantageous it will be found. To what degree it should be applied expansively must be determined by experience in different cases. It will depend on the rate at which the engine requires to be worked, and on the quantity of matter put into motion, so that as large a portion as possible of the inertia given in the beginning of the stroke may be taken out of it at the end.

"Some recent experiments made in France prove, as I am told, for I have not seen them, that very little heat is consumed in raising the temperature of steam. And if this is true, of course there must be a great saving of fuel by using steam of several atmospheres' strength, and working expansive through a large portion of the cylinder. I have really been impatient for a week past to receive some account of your machine, having learned nothing about it, except from a paragraph dated Hayle in the Truro paper of last Saturday week, and somehow or other the next paper has not reached me,

"I hope to be in London about Tuesday next, but at all events direct to me there, as my letters are regularly forwarded.

"Believe me, dear Sir,
"Yours ever most faithfully,
"DAVIES GIDDY."

[Rough draft,]

"MR. JOHN ADAMS, "BROMSGROVE, _8th March, 1816_.

"Sir,--I received your favour of the 12th February, but did not answer it in due course, because I was then erecting an engine on the new plan, which is now at work, and performs exceedingly well. It is equal in power to a 72-inch diameter cylinder, double power of B. and Watt's. The expense of erection, and the consumption of coals in this engine, are not one-third of a B. and Watt's to perform the same work. I am the same Trevithick that invented the high-pressure engine. I have sent out nine steam-engines to the gold and silver mines of Peru. I intend to sail for that place in about a month or six weeks, but shall appoint agents in England to erect these engines.

"No publication or description whatever has been in circulation, neither is it required, for I have a great many more orders than I can execute.

"I have not seen anything of Mr. Losh's patent engine, or Mr. Collins'.

"If you should go to London I advise you to call on Mr. Jas. Smith, Limekiln Lane, Greenwich, who is an agent for me, and will soon be able to show you an engine on this plan at work.

"I remain, &c.,
"R. TREVITHICK."

Unless the foregoing letters are based on error, the only conclusion to be drawn is that Watt, on the expiry of his patent right and of twenty-eight years of labour, having erected his masterpiece in Cornwall, was within a few years so beaten that Trevithick, in his challenge to Woolf, offered to throw in the Watt engine as a make-*weight, and with such odds to bet him two to one that his comparatively small and cheap high-pressure engine should beat the two big ones, both in power, in first cost, and in economical working. The Watt engine was one of his largest, with a 72-inch cylinder. Its power was equal to Trevithick's 33-inch pole-engine, when worked with steam of 34 lbs. to the inch; but the latter also worked with three times that pressure of steam, whereby its power was increased threefold. The first cost of these engines was probably in inverse proportion to their power. Trevithick's cost 700_l._, while three times that sum would not pay for the Watt engine. The reported duty of Watt's Herland engine was twenty-seven millions; and if the trial was with his ordinary bushel of 112 lbs. of coal, the duty would only be equal to twenty millions with 84 lbs. of coal, which constituted the Cornish bushel.

Trevithick's pole high-pressure steam-engine did fifty-seven millions; in other words, performed the same work as the Watt engine with less than half of the daily coal. This large economy led to orders for many engines, on his promise that they should cost much less than those of Watt of equal power, and should perform the work with one-third of the coal. Some believed him, though others were stony-hearted, and as obstinate as donkeys.

[Rough draft.]

"MR. PHILLIP, "PENZANCE, _8th March, 1816_.

"Sir,--I long since expected to have heard from you that my agreement with the Herland adventurers was executed. I have in every respect fulfilled my part of the engagement with the adventurers, and expect that they will do the same with me. The engine continues to work well. Every person that has seen it, except Joseph Price, A. Vivian, Woolf, and a few other such like beasts, agrees that it is by far the best engine ever erected. Its performance tells its effects, in spite of all false reports.

"Joseph Price and A. Vivian reported that the engine was good for nothing, that it would not do four millions, and that at the next Tuesday meeting they would turn it idle. On the evening before the meeting they met at Camborne for that purpose.

"Captain A. Vivian did not attend the meeting. I could not help at the meeting threatening to horsewhip J. Price for the falsehoods that he with the others had reported.

"I hear that he is to go to London to meet the London committee on Monday. I hope the committee will consider J. Price's report as from a disappointed man. It is reported that he has bought very largely in Woolf's patent, which now is not worth a farthing, besides losing the making my castings, which galls him very sorely.

"The water sinks regularly 20 fathoms per month, including every stoppage. On Monday next I expect they will be putting down the second lift. The water rises about 8 inches per hour when the engine is idle, and when at work will sink it again at the same rate, showing that the engine is equal to double the growing stream. When drawing from the pool the sinking is not much above 4 inches per hour, which shows that the water drains from a great distance from the country. The engine is going fourteen strokes per minute, 10-feet stroke, 14-1/2-inch box. When Herland worked last they drew a 14-inch box, 7-feet stroke, twelve strokes per minute in winter, and seven strokes per minute in summer. Therefore it appears that the winter water is about from seven to eight strokes per minute, and the summer water from four to five strokes per minute for this engine.