Chapter XIX: Pole Steam-Engine (2)

"The engine has forked faster the last week than she did before. I think that the great quantity of water that was laying round the mine at the surface is nearly drawn down, and that as we get down to a closer ground the drainage will not be so much. If we have dry weather the water will, at the next shallow level, fall off two strokes per minute before the next lift is in fork. If it continues the same we can continue to sink 20 fathoms per month, exclusive of the time it will take to fix the lifts. As we get down the house of water will lessen considerably. The expense of the engine is about 100l. per month. The sumpmen and others attending on the forking the water, about 100_l._ per month more. They have all the materials on the mine for the pit-work, therefore a very trifling sum will bring the water down to the 60-fathom level, when the mine will pay her own expense.

"I will thank you for an account of the meeting.

"Your obedient servant,
"R. TREVITHICK."

Mr. Phillip was the financial managing shareholder--more particularly with the Londoners--at that resuscitation of Herland Mine; and though the new engine was comparatively cheap, both in its first cost and in its consumption of coal, and satisfactorily reduced the water in the mine, payment for it was withheld because the currents of self-interest were against Trevithick. Mr. Joseph Price was the manager of a steam-engine manufactory at Neath Abbey, in South Wales, and had been in the habit of supplying castings for Cornish mines. Arthur Woolf was then striving to bring into use his patent double-cylinder engine, and patent high-pressure steam-boiler, which Trevithick looked on as copies from Hornblower and himself. This, added to Woolf's sarcastic manner of speech, roused Trevithick's anger.

Putting aside the words of the disputants, the fact is stated that the pole-engine, with a reduced steam pressure, worked a pump 14-1/2 inches in diameter, 10-feet stroke, fourteen strokes per minute; while the largest and best engine by Watt in Cornwall, placed on the same mine, with a 72-inch steam-cylinder, gave motion to a pump of 14 inches in diameter, 7-feet stroke, at twelve strokes a minute; being in round numbers just one-half the amount of the work performed by Trevithick's comparatively small engine, which had not a single feature of the Watt engine in it.

[Rough draft.]

"CAPTAIN JOE ODGERS, "PENZANCE, _March 7, 1816_.

"Sir,--I have your favour of the 27th February, and requested Mr. Page to send to you a sketch of the agreement. On seeing him yesterday, I found that he had neglected to send it to you. He will leave the country for London in a few days, and intends to call on you at Dolley's as soon as he arrives. I do not know that the agreement matters much for a few days up or down. The terms are well understood between us, which is that the adventurers and I equally share the advantages that may arise from this new engine over Boulton and Watt's. When you have fully arranged with your adventurers about the engine, please to write me, and I will immediately proceed to order the engine; and in the interim the agreement will be drawn up by Mr. Page, and executed either here or in London, just as may suit.

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

"P.S.--Herland engine goes on better and better. Your adventurers will get a satisfactory account by applying in town to Mr. Wm. Phillip, No. 2, George Yard, Lombard Street. He is the principal of the London adventurers."

Trevithick believed that mine adventurers would agree to pay him one-half the saving caused by his engines, as compared with the cost of fuel in the Watt engine. The duty performed by the latter was understood and agreed to generally; persons were chosen by the adventurers to experiment and report on the duty of Trevithick's pole-engine, that the amount of payment might be ascertained in proportion to the saving effected.

"MR. GIDDY, "PENZANCE, _April 2, 1816_.

"Sir,--I have long wished to write to you about the Herland engine, but first wished to see the engine loaded with a second lift, and a trial made of the duty. Yesterday was fixed on, before ordering another engine for the eastern shaft.

"The persons attended. The arbitrators gave the duty as forty-eight millions, and said they had no doubt the engine would perform above sixty millions before getting to the bottom of the mine.

"They were much within the duty, but I did not contend with them, as they said it was quite duty enough.

"The engine worked 9-1/4 strokes per minute, with 2 bushels of coal per hour for the whole time, 10-feet stroke. There were two pump-lifts of 14-1/2-inch bucket, making 43 fathoms, and 26 fathoms of 6-inch for house-water.

"The steam was from 100 to 120 lbs. to the inch. The valve open while the plunger-pole ascended 20 inches, then went the remainder of the 10-feet stroke expansive.

"It went exceedingly smooth and regular. Some time since, by way of trying the power of the engine, we disengaged the balance-bob. The engine worked twenty strokes per minute, with 17 tons of rods, &c., and drew 14-1/2-inch bucket 23-1/2 fathoms, and a 6-inch bucket 26 fathoms, 10-feet stroke, twenty strokes per minute.

"This was about 45,000 lbs. weight, with the speed of 200 feet per minute, which makes the duty performed more than the power of three 72-inch cylinders, single, of Boulton and Watt, say of 8-feet stroke, 10 lbs. to the inch, nine strokes per minute, which is more than these engines will perform. I have all the orders for every engine now required in the country, which is not to be wondered at, for one-tenth part of the expense in the erection will do, and the duty is not less than three times as much as other engines. This will be proved before we get to the bottom.

"The engine now works at about two-fifths of the load which she will have when at the bottom. When the next lift is in fork I will write to you again.

"I am, Sir, your humble servant,
"RICHARD TREVITHICK."

Independent examiners reported that the Herland pole-engine did forty-eight millions of duty, under various pressures of steam, up to 120 lbs. to the inch, working five-sixths of the stroke expansively, with a speed of twenty strokes a minute, or double the speed of the Watt engine; and the importance of those facts deserves the scrutiny and close study of youthful engineers. A small cheap engine, of 33-inch cylinder, similar in general construction to the Wheal Prosper pole-engine, but still more simple from the absence of air-pump and condenser, did as much work as three of Watt's largest engines with cylinders of 72 inches in diameter. This great stride in the useful value of the steam-engine was forced on the public by Trevithick's single-handed energy, when every man was against him, even Henry Harvey, his brother-in-law and friend, his former partner, Andrew Vivian, and his once carpenter and assistant, Arthur Woolf. As a closing attempt to finally crush him, he was made personally responsible for the payment of an engine erected for the benefit of others. This was the great trial test of the power and economy of the purely high-pressure expansive steam-engine as compared with the Watt low-pressure vacuum engine applied to large pumps.

"SIR, "HAYLE FOUNDRY, _18th April, 1816_.

"I was at Herland to-day. Captain Grose received a letter while I was there, signed by Captain William Davey and Joseph Vivian, requesting him to appoint others to attend the trial of the engine, as it would not be convenient for them to do it.

"Captain Samuel Grose, jun., brought down the drawing for your engine. He said he had taken off the working gear only. If you would wish it, we will make the working-gear and all the wrought-iron work on the drawing for the two engines ordered, and will take on a man or two immediately for that purpose. You will let me know about this before you set off, and also if any alteration is to be made in the beam for Wheal Treasure engine, since you have altered the size of the pole. We had cast the case, but I suppose it will suit some place else.

"Your obedient servant,
"HENRY HARVEY.

"MR. RICHARD TREVITHICK."

"About 1815 or 1816 I was employed by Captain Trevithick to erect various pole-engines, one of them at Saltram Stream. It had worked at Tavistock; it was a horizontal high-pressure pole puffer. Captain Samuel Grose was then erecting for Captain Trevithick a 24-inch high-pressure pole-engine at Beeralstone, on the Tamar, to drain a lead mine. I assisted Captain Grose. The stroke was about 8 feet. It worked with cross-head and side rods. There were two wrought-iron boilers about 3 feet 6 inches in diameter and 40 feet long. The fire and flues were outside. The steam pressure, 60 lbs. to the inch. I also erected a similar engine with a 20-inch pole at Wheal Treasure, now called Fowey Consols Mine; and one at Logassack, near Padstow. Those two had brass poles. It was found that the poles cut and wore in their passage through the stuffing box, the middle wearing more than the ends, causing steam to escape. A similar pole of Captain Trevithick's erecting was then working at Wheal Regent, near St. Austell.

"In 1818 I saw working at Wheal Chance Mine, near Scorrier, an old 60-inch cylinder Boulton and Watt engine. A pole of Trevithick's was fixed between the cylinder and the centre of the main beam. High-pressure steam was first worked under the pole and then expanded in the cylinder."[35]

[Footnote 35: Recollections of Captain H. A. Artha, Penzance, 1870.]

The late Mr. William Burral, for many years manager of the boiler-making department at Messrs. Harvey and Co., at Hayle, said:--

"About the year 1815 or 1816 I helped to erect at Treskerby Mine an engine for Captain Trevithick. Mr. Sims was the engineer of the mine. The engine had the usual cylinder, and close to it one of Captain Trevithick's poles was fixed. The boilers were Captain Trevithick's high-pressure. The steam was first turned on under the pole. When she had finished her up-stroke the steam passed from under the pole on to the top of the piston in the cylinder. There was a vacuum under the piston. The steam-cylinder was 58 inches in diameter, about 9 or 10 feet stroke. The pole was 36 inches in diameter, and a less stroke than the piston, because it was fixed inside the cylinder, nearer to the centre of the beam. There was a pole-engine then working at Wheal Lushington, also at Poldice, and at Wheal Damsel."

"Captain Artha recollects at Wheal Alfred Mine in 1812 the 66-inch cylinder pumping engine used a pole air-pump; one or two whim-engines on the same mine also used them. Wheal Concord pumping engine, in 1827 had a similar air-pump. Old Wheal Damsel, near Treloweth, used one as late as 1865. The condensing water and air passed through a branch with a valve on it near the top of the pole-case, just under the stuffing box There was a foot-valve at the bottom of the pole-case."[36]

[Footnote 36: Captain Artha became the resident engineer at the Real del Monte mines in Mexico; Captain Samuel Grose, one of the first Cornish mine engineers; and Mr. Burral, the engineer of a department at the engine-works of Messrs. Harvey and Co.]

The writer has had the pleasure of personal acquaintance with each of those three gentlemen, who as young engineers commenced their labours in the erection of Trevithick's engines.

No sooner had Trevithick perfected the pole condensing engine and then the pole puffer-engine, than he, in conjunction with Sims, who had just taken part in the erection of one of his high-pressure steam pole-engines for working the pumps at Beeralstone Mine, combined the pole with the ordinary Watt vacuum engines, supplying them with steam from his high-pressure boilers, in other words, converting them from their original form of low-pressure vacuum engines to high-pressure expansive compound steam-engines.

The old 60-inch cylinder Boulton and Watt engine, at Wheal Chance (one of Watt's favourite engines), was in 1818 transformed into a high-pressure engine, with Trevithick's pole placed between the centre of the main beam and the steam-cylinder. The high-pressure steam from Trevithick's new boilers was turned under the pole for the up-stroke, after which it was expanded in the old and much larger cylinder on the top of the piston causing the down-stroke; it then, by its passage through the equilibrium valve, allowed the piston in the large cylinder to make its up-stroke, by equalizing the pressure of steam on its top and bottom, while a fresh supply of strong steam from the boiler admitted under the pole gave power to the up-stroke; and finally, the comparatively low-pressure steam under the large piston passed to the condenser and air-pump to form a vacuum for the down-stroke, as in the Watt engine.

Sims, the engineer at Wheal Chance, one of the mines in the eastern or Watt district, was converted and became in 1815 or 1816 a partner with Trevithick, and erected, at Treskerby Mine, Trevithick's high-pressure pole of 36 inches in diameter, as an addition to the old Watt engine working with a cylinder 58 inches in diameter.

Watt, then, within a year or two of his death, was too old to any longer take part in the contest; his engine in the hands of others was converted and became a high-pressure expansive engine.

Trevithick, as a further proof that he could do without the Watt patent air-pump bucket, with its piston and valves, removed it from a Watt engine at Wheal Alfred Mine in 1812, replacing it by one of his poles, answering the same purpose, but different in construction. Many other mines used them; one remained at work in Old Wheal Damsel in 1860. They have also been used in steamboat air-pumps.

Having traced during a period of five or six years the rise and progress of the high-pressure expansive pole condensing-engines, the high-pressure expansive pole puffer-engine, and the combined pole and cylinder high-pressure engine, their value in a commercial sense may be further tested by the public acts of the time. Lean, an authority on such matters, and certainly not given to unduly praise Trevithick, spoke as follows on the duty of those particular engines at various periods; and not the least noteworthy is the fact, that Herland, Poldice, and Treskerby, that were prominent in the early use of the Watt engine, threw off their allegiance but shortly before the last days of the great engineer, and converted his low-pressure steam vacuum engines into Trevithick high-pressures.

"In 1798 Messrs. Boulton and Watt, who on a visit to Cornwall, came to see it--'the Herland engine'--and had many experiments tried to ascertain its duty; it was under the care of Mr. Murdoch, their agent in the county. Captain John Davey, the manager of the mine, used to state that it usually did twenty millions, and that Mr. Watt, at the time he inspected it, pronounced it perfect, and that further improvement could not be expected.

"In 1811 the average duty of the three engines (Boulton and Watt's) on Wheal Alfred Mine was about twenty millions. These engines were at that time reckoned the best in the county.

"In 1816 Sims erected an engine at Wheal Chance, to which he applied the pole adopted by Trevithick in his high-pressure engine. This engine attained to forty-five millions; and in 1817 it did 46·9 millions.

"In 1814 Treskerby engine is reported as doing 17·48 millions.--Wm. Sims, engineer.

"In 1820 Treskerby engine, to which Trevithick's high-pressure pole had been adapted, had reached 40·3 millions."[37]

[Footnote 37: Lean's 'Historical Account of the Steam-Engine in Cornwall,' pp. 11, 32, 36.]

The Herland engine of Watt in 1798 did twenty millions; in 1816 Trevithick's high-pressure pole puffer in the same mine did forty-eight millions. In 1820 his high-pressure pole-engine was combined with a Watt low-pressure engine, thereby more than doubling its economical duty.

In 1813 Trevithick wrote:--

"That new engine you saw near the sea-side with me (Wheal Prosper high-pressure pole condensing engine) is now lifting forty millions one foot high, with a bushel of coal, which is nearly double the duty that is done by any other engine in the county. A few days since I altered a 60-inch cylinder engine at Wheal Alfred to the same plan, and I think she will do equally as much duty. I have a notice to attend a mine meeting, to erect a new engine equal in power to a 63-inch cylinder single."[38]

[Footnote 38: See Trevithick's letter, January, 1813, vol. ii., p. 55.]

In the four or five years from his return to Cornwall in 1810, to his leaving for South America in 1816, he doubled the duty and the power of the steam-engine. Watt once said he had received an oblique look from Trevithick, sen. The time was now come for Trevithick, jun., to return the compliment; his improved engines having made their way into the eastern mine district, which Watt once looked upon as his own.

Trevithick was short of money and on the point of leaving England for South America, when Mr. Sims, in the employ of Messrs. Williams and Co., favourable to low pressure, was sent to negotiate for the purchase of a share in Trevithick's patent of 1815 for the high-pressure steam expansive pole-engine.

"18th October, 1816.--Agreement between Trevithick and Mr. William Sims, prepared by myself and Mr. Day, solicitor for Mr. Sims, or for Mr. Michael Williams, under whom Sims acted, recites, that in consideration of 200_l._ paid by Sims, he was to have a moiety of the patent for Cornwall and Devon, and that I should have power to act and make contracts whilst Trevithick was out of England.

"The day after contract signed, Trevithick sailed in the 'Asp,' Captain Kenny, for South America. I was on board when the ship sailed.

"I see among my papers, in May, 1819, in reference to the patent, is the following note:--'Mr. Michael Williams said it was verbally agreed that Captain Trevithick should have one-quarter part of the savings above twenty-six millions.' This, I believe, was the average duty of the engines at that time.

"I had several assurances relative to Trevithick's claims, and much correspondence, but no allowance was made from any mines but Treskerby and Wheal Chance; though Trevithick's patent and boilers were used throughout the county without acknowledgment; and the duty of the engines had soon increased from twenty-six millions to about seventy millions.

"In 1819 I attended at the account-houses of Treskerby and Wheal Chance, of which the late Mr. John Williams, of Scorrier, was the manager, in consequence of some of the adventurers objecting to continue the allowances on the savings to Captain Trevithick, when Mr. Williams warmly observed, that whatever other mines might do, he would insist, as long as he was manager for Treskerby and Wheal Chance, the agreement made should be carried into effect.

"I remain, my dear Thomas,
"Your very affectionate father,
"RD. EDMONDS."[39]

[Footnote 39: Portion of a letter written at Penzance, 8th February, 1853.]

The agreement with Mr. Sims, or rather with Mr. Michael Williams, late M.P. for Cornwall, who exercised large authority in Cornish mines, was that he should have for 200_l._ one-half of the patent for the high-pressure pole-engine, as applied to Cornwall and Devon.

Trevithick had desisted from securing a patent for the large high-pressure steam-boilers and expansive working, on a verbal understanding that he should receive one quarter of the saving from the reduced consumption of coal by those two particular inventions, twenty-six millions of pounds of water raised one foot high by a bushel of coal of 84 lbs., being the duty of the best Watt engines, to be taken as a starting-point for the payment. Treskerby and Wheal Chance paid for the pole-engine, but the Trevithick boilers suitable for high steam, and the simple methods of working it expansively, had been made so generally public, that people professed to think they had a right to them, when but a few years before they had thrown the inventor off his guard by saying "everybody knows that the Cornish boiler is your plan, and as it cannot be denied, a patent will be of no service."

Mr. John Williams[40] stated "that whatever other mines might do, he would insist, as long as he was manager for Treskerby and Wheal Chance, the agreement made should be carried into effect." The Williamses paid to Trevithick 300_l._ for the saving of coal by the pole patent engine, as an "acknowledgment of the benefits received by us in our mines;" but no payment was made for the greater invention of the high-pressure steam-boilers then in general use.

[Footnote 40: Mr. John Williams had the remarkable dream, many hours before the event, enabling him to describe the particulars of the assassination of Perceval in 1812.]

In 1814 the Watt Treskerby engine did seventeen and a half millions. Trevithick's boiler and pole were applied, and the duty was increased to more than forty millions. In 1816 the same changes were made in Wheal Chance, and the duty rose to more than forty-six millions. The consumption of coal was reduced to one-half, amounting in round numbers to a gain of 500_l._ a month in those two mines alone. /#

"TREVINCE, near TRURO,

"DEAR SIR, _5th January, 1853_.

"I am favoured with your letter of the 31st ult., enclosing also one from Mr. F. Trevithick, of the 24th idem, and have much pleasure in complying with your joint request to the best of my ability. I was well acquainted with the late Mr. Rd. Trevithick, having had frequent occasion to meet him on business and to consult him professionally; and I am gratified in having the present opportunity of bearing testimony to his distinguished abilities, and to the high estimation in which the first Cornish engineers of the day then regarded him. I need scarcely say that time has not lessened the desire in this county especially to do him justice. As a man of inventive mechanical genius, few, if any, have surpassed him, and Cornwall may well be proud of so illustrious a son.

"At this distance of time I can scarcely speak with sufficient exactness for your purpose of the numerous ingenious and valuable mechanical contrivances for which we are indebted to him, but in reference to his great improvements in the steam-engine I have a more particular recollection, and can confidently affirm that he was the first to introduce the high-pressure principle of working, thus establishing a way to the present high state of efficiency of the steam-engine, and forming a new era in the history of steam-power. To the use of high-pressure steam, in conjunction with the cylindrical boiler, also invented by Mr. Trevithick, I have no hesitation in saying that the greatly-increased duty of our Cornish pumping engines, since the time of Watt, is mainly owing; and when it is recollected that the working power now attained amounts to double or treble that of the old Boulton and Watt engine, it will be at once seen that it is impossible to over-estimate the benefit conferred, either directly or indirectly, by the late Mr. Trevithick, on the mines of this county. The cylindrical boiler above referred to effected a saving of at least one-third in the quantity of coal previously required; and in the year 1812 I remember our house at Scorrier paying Mr. Trevithick the sum of 300_l._ as an acknowledgment of the benefits received by us in our mines from this source alone. Mr. Trevithick's subsequent absence from the county, and perhaps a certain degree of laxity on his own part in the legal establishment and prosecution of his claims, deprived him of much of the pecuniary advantage to which his labours and inventions justly entitled him; and I have often expressed my opinion that he was at the same time the greatest and the worst-used man in the county.

"Amongst the minor improvements introduced by him, it occurs to me to notice that he was the first to apply an outer casing to the cylinder, and by this means prevent, still further than Watt had succeeded in doing, the loss of heat by radiation.

"As connected with one of the most interesting of my recollections of Mr. Trevithick, I must mention that I was present by invitation at the first trial of his locomotive engine, intended to run upon common roads, and of course equally applicable to train and railways. This was, I think, about the year 1803, and the locomotive then exhibited was the very first worked by steam-power ever constructed.

"The great merit of establishing the practicability of so important an application of steam, and the superiority of the high-pressure engine for this purpose, will perhaps more than any other circumstance serve to do honour through all times to the name of Trevithick. The experiment which was made on the public road close by Camborne was perfectly successful; and although many improvements in the details of such description of engines have been since effected, the leading principles of construction and arrangements are continued, I believe, with little alteration, in the magnificent railroad-engines of the present day. Of his stamping engine for breaking down the black rock in the Thames, his river-clearing or dredging machine, and his extensive draining operations in Holland, I can only speak in general terms, that they were eminently successful, and displayed, it was considered, the highest constructive and engineering skill. As a man of enlarged views and great inventive genius, abounding in practical ideas of the greatest utility, and communicating them freely to others, he could not fail of imparting a valuable impulse to the age in which he lived; and it would be scarcely doing him justice to limit his claims as a public benefactor to the inventions now clearly traceable to him, important and numerous as these are. From my own impressions I may say that no one could be in his presence without being struck with the originality and richness of his mind, and without deriving benefit from his suggestive conversation. His exploits and adventures in South America, in connection with the Earl of Dundonald, then Lord Cochrane, will form an interesting episode in his career; and altogether, I am of opinion that the Biography which you have undertaken will prove highly interesting and valuable, and I wish you every success in carrying it out.

"Believe me, my dear Sir,
"Yours very faithfully,
"MICHAEL WILLIAMS.

"E. WATKIN, Esq.,
"_London and North-Western Railway_,
"_Euston Station, London_."

Arthur Woolf shortly after that time (1811) erected his double-cylinder engines in Cornwall. The late Captain Samuel Grose, when giving the writer his recollections of Trevithick, said:--

"When he returned from London to Cornwall, about 1810 or 1811, he employed me to look after the erection of the Wheal Prosper high-pressure engine. Oats, Captain Trevithick's head boiler-maker, was constructing the boilers; Woolf came into the yard, and examined them. 'What do'st thee want here?' asked Oats. 'D--n thee, I'll soon make boilers that shall turn thee out of a job!' was Woolf's reply. He was a roughish man. When his brother Henry mutinied at the Nore, Woolf, who was then working an engine in Meux's brewery, and had married the lady's maid, made interest with his employer to save Henry from being hanged at the yard-arm, and afterwards found employ for him in Cornwall. He was but a clumsy mechanic. Woolf used to blow him up by saying, 'D--n thee, I wish I'd left thee to be hanged.'"

The writer, who knew Oats, has heard him tell similar stories of the rival engineers.

In 1800, Woolf, who had been a mine carpenter, went to London with the first high-pressure steam-engine which Trevithick had sent beyond the limits of Cornwall[41]--probably to Meux's brewery,[42] for he was there in 1803, and in the receipt of 30_l._ a year from Trevithick as engine-fireman. From the date of Woolf's patent in 1804, his pay from Trevithick ceased, and with it their friendship. Trevithick used to say, "Woolf is a shabby fellow."

[Footnote 41: See Trevithick's account-book, vol. i., p. 90.]

[Footnote 42: Captain John Vivian's recollections, vol. i., p. 142.]

Patents sprang up like mushrooms after Trevithick had so liberally cast forth the seeds of the high-pressure engine, making the security, or even the form of a patent, a doubtful matter. The perfecting of expansive high-pressure engines was like the boiler, the result of years of trial. When matured in 1816 it saved Cornwall and the world one-half of the coal that before had been consumed in low-pressure steam-engines. Every engineer became, more or less, an expansive worker, and Trevithick's saving of hundreds of thousands of pounds annually to the general public, gave to him little or no reward.

At the period of those high-pressure pole-engine experiments, Trevithick had devoted twenty years of constant labour to the improvement and extended use of the steam-engine, causing it to assume every variety of form except that of the Watt patent engine, an approach to which was unusual, as evidenced in the high-pressure steam Kensington model of 1796, without beam, parallel motion, air-pump, or condenser, having no one portion either in principle or detail similar to the Watt engine, being portable and not requiring condensing water, with single and double cylinders, placed vertically or horizontally. Having during twelve busy years constructed over a hundred high-pressure steam-engines, scarcely any two of which were exactly alike, he departed if possible still further from the Watt type, and went back apparently, though not in reality, to the Newcomen engine, simplifying it by the omission of the great bob, and use of condensing water, as in the nautical labourer and steamboat engine of about 1810,[43] and the South American mine engines of 1816,[44] which had open-top cylinders, more like a Newcomen than a Watt, but if possible even more simple and primitive-looking than the former. Again, compare the thrashing engine of 1812[45] with the Newcomen of 1712:[46] the great and all-important difference being that one was a high-pressure steam-engine, the other a low-pressure atmospheric engine. Then came the varieties of high-pressure steam pole-engines, working very expansively either as puffers or condensers, retaining the same dissimilarity to the Watt engine: and lastly, the combination of the high-pressure pole with the Watt patent engine, thereby causing the old Watt engine to do more than double the work it had done when new from the hands of the maker, and also to perform this increase of work with a decrease in the consumption of coal.

[Footnote 43: See vol. i., p. 336.]

[Footnote 44: See chap. xxi.]

[Footnote 45: Vol. ii., p. 37.]

[Footnote 46: Vol. i., p. 5.]

The following chapter will trace the adaptation of high-pressure expansive steam, from cylindrical boilers, to the form of pumping engine still in general use.