Grace's Guide To British Industrial History

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Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 147,919 pages of information and 233,587 images on early companies, their products and the people who designed and built them.

Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 147,919 pages of information and 233,587 images on early companies, their products and the people who designed and built them.

Life of Richard Trevithick by F. Trevithick: Volume 2: Chapter 20

From Graces Guide

CHAPTER XX. THE WATT AND THE TREVITHICK ENGINES AT DOLCOATH.

Having up to 1816 traced the progress of the steam-engine in Cornwall through a century, during the latter half of which Trevithick, sen., and his son were among its most prominent improvers, the latter having devoted a quarter of a century to the work, the effect of which is shown in the skeleton outlines of a few classes of engines, one important feature still remains for examination before a correct judgment can be formed of the events of this period and their prime movers.

The use of an increasing pressure of steam gave increased force and value to the improved steam-engine, but the power of constructing engines and boilers to render the increased pressure manageable was the result of a lifetime of labour.

Savery, whose engine was scarcely more than a steam-boiler, failed to control its force, and is said to have blown the roof from over his head. The mechanism of Newcomen's engine was well arranged, but suitable only for the working of pumps, and its power was limited to the weight of the atmosphere, from which it was called the atmospheric engine.

In 1756, an atmospheric engine with a cylinder of 70 inches in diameter worked at the Herland Mine, "the only objection to which was the cost of the coal, to lessen which several methods had been suggested for increasing the elasticity of the steam, and reducing the size of the boiler". [1]

In 1775 Richard Trevithick, sen., removed the flat top of a Newcomen boiler, and substituted a semi-circular top, enabling it to contain stronger steam, and at the same time he improved the mechanical part of the engine by finding a better resting-place for the steam-cylinder than the top of the large boiler. Pryce gives a drawing of this engine as the best at that time in Cornwal1. [2]

It is known as a fact that every engine of magnitude consumes £3,000 worth of coal every year.

The fire-place has been diminished and enlarged again. The flame has been carried round from the bottom of the boiler in a spiral direction, and conveyed through the body of the water in a tube (one, two, or three) before its arrival at the chimney.

Some have used a double boiler, so that fire might act on every possible point of contact, and some have built a moonstone boiler, heated by three tubes of flame passing through it.

A judicious engineer does not attempt to load his engine with a column of water heavier than 7 lbs. on each square inch of the piston. [3]


While Pryce's book was being printed, Watt in 1777 wrote of the Cornish steam-engines:—

I have seen five of Bonze's engines, but was far from seeing the wonders promised. They were 60, 63, and 70 inch cylinders at Dolcoath and Wheal Chance. They are said to use each about 130 bushels of coals in the twenty-four hours, and to make about six or seven strokes per minute, the stroke being under 6 feet each. They are burdened to 6, 6.5, and 7 lbs. per inch. [4]


The 63-inch was an open-top cylinder atmospheric engine at Dolcoath Mine under the management of Trevithick, sen.: and shortly after, in 1777 or 1778, Watt's first engine was erected in Cornwall. [5]

In 1783 Trevithick, sen., gave Watt an order for a patent engine for Dolcoath, in size similar to the old Newcomen atmospheric, having a cylinder 63 inches in diameter, that a working trial might be made between the rival engines. The Watt engine having a cylinder-cover, with the patent air-pump and condenser, was known in the county as the Dolcoath great 63-inch double-acting engine. Three steam-engines were then at work in that mine: Trevithick senior's Carloose (then called Bullan Garden) atmospheric 45-inch cylinder, the atmospheric 63-inch cylinder, and Watt's 63-inch cylinder double-acting vacuum engine all of which continued in operation side by side for five years until 1788, when for a time Dolcoath ceased to be an active mine. Trevithick jun., was then a boy of seventeen years.

After ten years of idleness and rust, as if mourning the death of Trevithick, sen., in 1798 Richard Trevithick, jun., as engineer, and Andrew Vivian as manager, induced shareholders to resuscitate the old mine. Fire was again given to the voracious jaws of the boilers, and the three engines recommenced their labours and their rivalries.

A year or two before this Trevithick had made models of high-pressure steam-engines. Davies Gilbert, in 1796, met him among other engineers, giving evidence in the Watt lawsuits when he mentioned his ideas of an engine to be worked solely by the force of steam. Watt had claimed such an engine in his patent twenty-seven years before, but had failed to carry it into practice. Hornblower had tried something like it in his double-cylinder expansion engine, but he did not use high-pressure steam, and consequently also failed.

The idea, therefore, of expansive steam was not new, but the useful mastery of it was. Savery had tried expansive steam before Watt patented it; the latter went to law with Hornblower for an infringement of the idea, when neither of them had in truth constructed an expansive steam-engine. The low pressure of the steam from the boilers used by Hornblower and Watt did not admit of profitable expansion in the cylinder; at its full boiler pressure it constituted but a comparatively small portion of the power of the engine: to reduce that power by expansion was as apt to be a loss as a gain. The steam-engine was still dependent for its power mainly on steam as an agent for causing the required vacuum, until 1796, when Trevithick disclosed his method of constructing small cylindrical boilers and engines suitable for giving power from the strong pressure of the steam, irrespective of vacuum.

Lean, who favoured Watt rather than Trevithick, thus records the advent of Watt's expansive engine:-

In 1779 to 1788 Mr. Watt. introduced the improvement of working steam expansively, and he calculated that engines which would previously do nineteen to twenty millions would thus perform twenty-six millions but I do not find any record of this duty being performed in practice. In 1785 Boulton and Watt had engines in Cornwall working expansively, as at Wheal Gons and Wheal Chance in Camborne; but in these the steam was not raised higher than before, and the piston made a considerable part of the stroke therefore before the steam-valve was closed.

In 1798, on account of a suit respecting their patent, which was carrying on by Boulton and Watt, an account of the duty of all the engines in Cornwall was taken by Davies Gilbert, Esq., and the late Captain Jenkin, of Treworgie, and they found the average to be about seventeen millions. [6]


One of these so-called expansive Watt engines, erected at Wheal Chance, was converted into a real expansive engine by Trevithick, as described in the foregoing chapter, by his high-pressure steam-boilers and the addition of his pole-engine. The conversion of the other, a 63-inch low-pressure vacuum engine at Wheal Gons, will be traced in this chapter.

Mr. Taylor, who for many years interest in Cornish mining, says:-

In 1798 an engine at Herland was found to be the best in the county, and was doing twenty-seven millions, but being so much above all others, some error was apprehended. This engine was probably the best then ever erected, and attracted therefore the particular attention of Messrs. Boulton and Watt, who, on a visit to Cornwall, came to see it, 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. [7]


This best engine from the hands of Watt and Murdoch in the Herland Mine in 1798 may be taken as a Watt stand-point, when its usual duty was twenty millions; and Trevithick and Bull erected a competing engine, probably with an increased steam pressure, for Trevithick's portable high-pressure engines were at that time coming into notice, [8] but no trace remains of the result of this contest of the Watt and the Bull engine, though it was one of the causes of the lawsuits.

In 1799 Henry Clark worked as a rivet boy in Dolcoath, and carried rivets to construct Captain Trevithick's new boiler, said to be the first of the kind ever made. It looked like a great globe about 20 feet in diameter, the bottom hollowed up like the bottom of a bottle; under this the fire was placed: a copper tube attached to this bottom went around the inside of the boiler, and then passed out through the side of the boiler, the outside brick flues then carrying the heat around the outside of the boiler and into the chimney.

Captain Trevithick's first plunger-pole lifts in Dolcoath were put in at this time and worked by this engine. Glanville, the mine carpenter, was head man over the engines when Captain Trevithick was away. [9]


Charles Swaine worked as a rivet boy in making Captain Trevithick's cylindrical wrought-iron boilers for the Dolcoath engine. Several of Captain Trevithick's high-pressure boilers were working in the mines before that, but not made exactly like the Dolcoath engine boilers. When I was a boy about the year 1804, several years before I worked on the Dolcoath engine boilers, I carried father's dinner to the Dolcoath smiths' shop, where he worked, and used to stop and watch the wood beam going up and down of Captain Dick's first high-pressure steam-whim. She was not a puffer, but a puffer-whim worked near by, called the Valley puffer. At that time most of Captain Dick's high-pressure boilers were smallish, cast iron outside, and wrought-iron tube. [10]


In 1799, shortly after the reopening of Dolcoath Mine, Trevithick, jun., selected his father's secondhand atmospheric engine of 1775, [11] to further improve it by a new boiler of uniformly globular figure, with concave circular bottom, under which fire was placed; it was of wrought iron, 24 feet in diameter, surrounded by external brick flues; a large copper tube, starting from the boiler bottom, immediately over the fire, served as an internal flue, carrying the fire by a sweep around the interior in the water space, and then out through the side of the boiler into the external brick flue. It may be said that there was nothing new in a circular form of boiler, or in an internal tube but it will be admitted that this repaired engine, in this its third stride in the march of advancement, made publicly known those principles which in a few years more than doubled the power, the economy, and the applicability of the steam-engine. His patent drawing of 1802 shows this form of boiler applied to a small portable engine, in which, for the sake of simplicity of structure and cheapness, cast iron was used instead of wrought iron, and the internal tube omitted. [12]

The full detail estimate, from which the following items are extracted, of the cost of alteration was written by Trevithick, jun., in the book and on the page adjoining that containing the account of the former alteration and re-erection of the same engine by Trevithick, sen., in 1775.


The term "single" refers to its open-top cylinder as originally erected by Newcomen, when it was called the Carloose engine, and so it remained after its re-erection in 1775, under the name Dolcoath new engine, alias Bullan Garden but after the last re-erection in 1799 it had a cylinder-cover, and was called the Shammal 45-inch engine "working 20 lbs. to the inch" meant the force on each inch of the piston, including vacuum on the one side of 14 lbs. and steam on the other side of 6 lbs, to the inch.

Watt, on his first visit to Cornwall, in 1777, spoke disparagingly of the Newcomen atmospheric engines "burdened to 6 or 7 lbs. net to the inch." Fifty years later Stuart described Watt's engine as "using steam of a somewhat higher temperature than 212 degrees, so as to produce a pressure between 17 and 18 lbs. on each square inch of the piston yet in practice, from imperfect vacuum and friction, it cannot raise more water per inch than would weigh about 8.5 lbs.", [13] or an increase of net force — when compared with the Newcomen atmospheric — of only a pound or two on the inch in the lapse of years embracing the active lifetime of Watt. The cause of this slight increase of power is so simple that it has been passed by unnoticed by very many. The steam pressure in the Newcomen atmospheric was continued unaltered in the Watt vacuum engine. Trevithick constructed the first boiler and engine capable of safely and economically using the power of high-pressure steam. Nelson was obliged to come to close quarters, that his shot, propelled by weak cannon and low-pressure powder, might penetrate wooden ships. We now manufacture and control high-pressure powder, so that 12 inches of iron armour-plates cannot resist its force but this knowledge has taken nearly as long in growing to perfection as did the mastery of high-pressure steam, and its use in the much more complicated steam-engine.

Watt's engine, as described a quarter of a century after the expiration of his patent and the advent of the high-pressure steam-engine, still derived its gross force from 14 lbs. of vacuum and 2 or 3 lbs. of steam, resulting in a net force of 8.5 lbs. Trevithick's engine of 1799, which heralded the last hours of the Watt patent authority, and may be taken as the first distinct evidence of comparatively high-pressure steam in large Cornish pumping engines, derived its power from 14 lbs. of vacuum and 6 lbs. of steam, being together but 2 or 3 lbs. on the inch more than the Watt engine, but its net force of 12 lbs, to the inch was half again as much as the net force of the Watt engine, the increase being wholly from the steam pressure, which was never practised by Watt, and which in its almost unlimited force gives the greatly increased power to modern steam-engines.

Trevithick's estimate for a new engine of the same size as the old was £2,000, but as the old one could be improved for £1,300, the latter course was adopted, the wooden main beam with its segment head was retained, a cover was added to the cylinder, and a new piston-rod and piston; a pole air-pump was used in lieu of the more usual Watt air-pump bucket; a feed- pole forced water into the boiler, — an indirect proof of increased steam pressure. The new globular boiler with internal tube weighed 8 tons; the engineer's charge for carrying out the work was £66.

The use of strong steam as the prime mover of the steam-engine increased more rapidly beyond than within the limits of Cornwall, for in 1802 was erected at Coalbrookdale a high-pressure steam-puffer engine, to which Trevithick attached a pump which forced water through a column of upright pipes, that the power of the engine might be accurately measured. It worked with steam of from 50 to 145 lbs. on the inch, and wholly discarded the vacuum which had been Watt's mainstay.

The boiler is 4 feet diameter, the cylinder 7 inches diameter, 3-feet stroke. The water-piston is 10 inches in diameter, drawing and forcing 35 feet perpendicular, equal beam. I first set it off with about 50 lbs. on the inch pressure against the steam-valve, for the inspection of the engineers about this neighbourhood. The steam continued to rise the whole of the time it worked it went from 50 to 145 lbs. to the inch.

The engineers at this place all said that it was impossible for so small a cylinder to lift water to the top of the pumps, and degraded the principle, though at the same time they spoke highly in favour of the simple and well-contrived engine.

After they had seen the water at the pump-head, they said that it was possible, but that the boiler would not maintain its steam at that pressure for five minutes but after a short time they went off, with a solid countenance and a silent tongue. [14]


This high-pressure steam pumping engine in 1802 may be taken as the first pumping engine of the puffer class using such strong steam.

In the spring of the following year [15] a somewhat similar engine was erected in London.

The cylinder is 11 inches in diameter, with a 3.5-feet stroke. It requires the steam at a pressure of 40 to 45 lbs. to the inch to do its work well, working about twenty-six or twenty-seven strokes per minute. It is much admired by everyone that has seen it, and saves a considerable quantity of coal when compared with a Boulton and Watt. Mr. Williams, Mr. Robert Fox, Mr. Gould, and Captain William Davey were here, and much liked the engine; they gave me an order for one for Cornwall as a specimen.


This particular engine was for driving machinery in a cannon manufactory. A high-pressure pumping engine was at work at Greenwich, and some were at work in Cornwall.

PENYDARRAN, near CARDIFF,
October 1st, 1803.

MR. GIDDY

, Sir,— In consequence of the engine bursting at Greenwich, I have been on the spot to inspect its effects. I found it had burst in every direction. The bottom stood whole on its seating; it parted at the level of the chimney. The boiler was cast iron, about 1 inch thick, but some parts were nearly 1.5 inch; it was a round boiler, 6 feet diameter; the cylinder was 8 inches diameter, working double; the bucket was 18 inches diameter, 21 feet column, working single, from which you can judge the pressure required to work this engine. The pressure, it appears, when the engine burst, must have been very great, for there was one piece of the boiler, about 1 inch thick and about 5 cwt., thrown upwards of 125 yards; and from the hole it cut in the ground on its fall, it must have been nearly perpendicular and from a very great height, for the hole it cut was from 12 to 18 inches deep. Some of the bricks were thrown 200 yards, and not two bricks were left fast to each other, either in the stack or round the boiler. It appears the boy that had care of the engine was gone to catch eels in the foundation of the building, and had left the care of it to one of the labourers; this man, seeing the engine working much faster than usual, stopped it, without taking off a spanner which fastened down the steam-lever, and a short time after being idle it burst, killed three on the spot and another died soon after of his injuries. The boy returned that instant, and was then going to take off the trig from the valve. He was hurt, but is now recovering; he had left the engine about an hour. I would be much obliged to you if you would calculate the pressure required to burst this boiler at 1 inch thick, supposing it to be a sound casting, and what pressure it would require to throw the materials the distance I have before stated, for Boulton and Watt have sent a letter to a gentleman of this place, who is about to erect some of those engines, saying that they knew the effects of strong steam long since, and should have erected them, but knew the risk was too great to be left to careless enginemen, and that it was an invention of Mr. Watt, and the patent was not worth anything. This letter has much encouraged the gentlemen of this neighbourhood respecting its utility; and as to the risk of bursting, they say it can be made quite secure. I believe that Messrs. Boulton and Watt are about to do me every injury in their power, for they have done their utmost to report the explosion, both in the newspapers and in private letters, very different to what it really was; they also state that driving a carriage was their invention; that their agent, Murdoch, had made one in Cornwall and shown it to Captain Andrew Vivian, from which I have been enabled to do what I have done. I would thank you for any information that you might have collected from Boulton and Watt, or from any of their agents, respecting their even working with strong steam, and if Mr. Watt has ever stated in any of his publications the effects of it, because if he condemns it in any of his writings, it will clearly show from that, that he did not know the use of it. Mr. Homfray, of this place, has taken me by the hand, and will carry both the engines and the patent to the test. There are several of Boulton and Watt's engines being taken down here, and the new engines being erected in their place. Above 700 horse-powers have been ordered at £12-12s. for each horse-power for the patent right, and the persons that ordered them make them themselves, without any expense to me whatever. If I can be left quiet a short time I shall do well, for the engines will far exceed those of Boulton and Watt. The engine at Greenwich did fourteen millions with a bushel of coals; it was only an 8-inch cylinder, and worked without an expansive cock, and under too light a load to do good duty; also on a bad construction, for the fly-wheel was loaded on one side, so as to divide the power of the double engine, and connected to the pump-rods on a very bad plan. I remember that Boulton and Watt's 20-inch cylinders when on trial did not exceed ten millions; I believe you have the figures in your keeping. Let us have the 60-horse power at work that is now building, and then I will show what is to be done. It will be loaded at 30 lbs. to the inch on each side the piston, it has an 8-feet stroke with an expansive cock, and the blowing cylinder directly over the steam-cylinder, as free from friction as possible. There was no engine stopped on account of this accident; but I shall never let the fire come in contact again with the cast iron. The boiler at Greenwich was heated red hot and burnt all the joints the Sunday before the explosion.

I have received a letter from a person in Staffordshire who has a cylinder-boiler at work with the fire in it, and he says the engine performs above all expectation; he requests me to give him leave to build a great many more. I shall put two steam-valves and a steam-gauge in future, so that the quicksilver shall blow out in case the valve should stick, and all the steam be discharged through the gauge. A small hole will discharge a great quantity of steam at that pressure. There will be a railroad-engine at work here in a fortnight; it will go on rails not exceeding an elevation of one-fiftieth part of a perpendicular and of considerable length. The cylinder is 8.5 inches in diameter, to go about two and a half miles an hour; it is to have the same velocity of the piston-rod. It will weigh, water end all complete, within 5 tons.

I have desired Captain A. Vivian to wait on you to give you every information respecting Murdoch carriage, whether the large one at Mr. Budge's foundry was to be a condensing engine or not.

Is it possible that this engine might be burst by gas?

I am, Sir,
Your very obedient servant,

RICHARD TREVITHICK.


This high-pressure puffer pumping engine at Greenwich, in 1803, worked a pump of 18 inches in diameter. The engine boy having fixed the safety-valve while he fished for eels, caused an explosion of the boiler. This was the first mishap from the use of high-pressure steam. The boiler was globular, 6 feet in diameter, and from an inch to an inch and half in thickness, made of cast iron; the cylinder, of 8 inches in diameter, was partly let into and fixed on the boiler. Its general design is seen in the patent drawing of 1802, Fig. 1.1 [16] Trevithick determined in future to use two safety-valves, and also a safety steam-gauge. At that time one of his high-pressure puffer-engines, with a cylindrical boiler and internal tube, was working in Staffordshire.

The Greenwich high-pressure puffer-engine did fourteen millions of duty with a bushel of coals, 84 lbs. A 60-horse-power engine was being built in Wales, with an 8-feet stroke, to work expansively with 30 lbs. of steam on the inch in the boiler. For a more thorough test with the low-pressure vacuum engines, in competition, the Government intended to use the new engines, and some of Watt's engines having been removed to make room for them, Boulton and Watt wrote to a gentleman who was about to order an engine from Trevithick,

We knew the effects of strong steam long since, and should have erected them, but knew the risk was too great. Moreover, it was an invention of Mr. Watt's, and the patent (Trevithick's) was not worth anything.


This admission clearly shows not only that Watt did not make high-pressure steam-engines, but that he did his best to prevent others from making them.

PENYDARRAN, CARDIFF,
January 5th, 1804.

MR. GIDDY,

Sir,— I received yours a few days since, and should have answered it sooner, but I was at Swansea for the last four weeks, and wished to return here to give you as full an account of our proceedings as possible.

We have had an 8-inch cylinder at work here by way of trial; it worked exceedingly well a hammer of the same size as now being worked here by an atmospheric engine 28 inches diameter, 5-feet stroke, which does not master its work with greater ease than the 8-inch cylinder. The 8-inch is now removed to Swansea, and is winding coals; the baskets hold 6 cwt. of coal; it lifts 80 yards in a minute and a quarter, and burns 6 cwt. of coal in twenty-four hours. There were twelve horses on this pit before, lifting 80 tons of coal in the course of the twenty-four hours. You may fairly state that the 8-inch cylinder does between thirty and forty horses' work in twenty-four hours, with 6 cwt. of coal.

One of Boulton and Watt's 18-inch double engine, about half a mile from it, lifting baskets of the same size, and with the same velocity, burns above three times the quantity of coal.

The 8-inch engine requires the steam to be about 46 or 48 lbs. to the inch to do its work well. The standers-by would not believe that such a small engine could lift a basket of coal, but are now much pleased with it, and have given orders for several more. There will be another at work here for the same purpose in about six weeks, a 15-inch cylinder, 6-feet stroke, which is a great power for a winding engine.

Mr. Watt says, in a letter to Mr. Homfray, that he could not make any of his experiments in strong steam answer the purpose. It is my belief that he never made any experiments of any consequence in strong steam.

A great number are building at different foundries. Mr. Sharratt, a founder at Manchester, who has four in building, said that he would not pay the patent right; on giving him notice of a trial he agreed to pay the patent right.

I have received a letter from London, saying that an engineer called Dixon has two engines on the same plan working; and says that he shall not pay anything to the patentee; that the words in Mr. Watt's specification are enough to indemnify him from my threats. We have had three counsels' opinions on the subject, and they all agree that the patent is good. Counsels Marratt and Gibbs principally treated on the construction of the engine, more than on the principle but Erskine was principally on the principle of the engine, and said very little of its construction. They all say the words in Mr. Watt's specification will have no weight whatever against us.

I shall leave this place to-morrow for London to make inquiry into those engines, and to get the business into court if they will contend. I shall be at No. 2, Southampton Street, Strand, and expect to be in town about five or six days, and if you will be so good as to return here, from Oxford, with me, I will call on you in my journey down. It is but 50 miles from Bristol, and not so much as 100 miles from Oxford, and the coach passes very near this place.

There is a great deal of machinery and milling here, which would engage your attention for a few days, and very pleasant gentlemen about the neighbourhood.

If I had not been called to Swansea to put up the winding engine, the road-engine would have been at work long since, but in my absence very little was done to it. The work is all ready, and a part of it put together. If I could tarry four or five days longer I could set it to work before going to London. They promise me that it shall be completed before my return. I think there is no doubt of its being finished, as I have Frank Bennetts here from Cornwall about it, and a plenty of hands to assist him.

I have a thousand things to relate to you, too much for paper to contain, therefore must request you to be so good as to go down from Oxford with me, and I will promise, on warrant, that the road-engine shall be finished before my return. When it is set to work I shall return to Cornwall.

I remain, Sir,
Your humble servant,

RICHARD TREVITHICK.


In 1804 an 8-inch cylinder high-pressure puffer-engine, with steam of 48 lbs. to the inch, worked a large hammer as well as a 28-inch cylinder atmospheric engine, and more economically than a Watt low-pressure steam vacuum engine with an 18-inch cylinder, which was five times as large as the little high-pressure. In consequence of this superiority those who came to witness the trial ordered several more of Trevithick's engines, one of which with a 15-inch cylinder and 6-feet stroke was to be at work in a few weeks.

Watt wrote to Mr. Homfray "that he could not make any of his experiments in strong steam answer the purpose", and Trevithick declared Watt never could have tried any experiments with high steam.

Dixon refused to pay patent right because the words of Mr. Watt's specification, "in cases where cold water cannot be had in plenty, the engines may be wrought by the force of steam only, by discharging the steam into the open air, after it has done its office, enough to indemnify him." Eminent counsel were of opinion that "the words in Watt's specification will have no weight whatever".

Marratt and Gibbs were inclined to rest on the difference in the construction of the two kinds of engines, while Erskine boldly said that the principle was different, and he cared little for the kind of construction.

The admission by Watt that he could do nothing with high steam after an experience of thirty years from the date of his patent, shows how difficult the work was to those who had to find the way; yet Trevithick had several at work within a few months of his first mental sight of a steam-engine without condensing water, fitful glimpses of which passed and repassed while he sat unobserved in the crowded law court in 1796 hearing the remarks of engineers and counsel.

The public until now called me a scheming fellow, but their tone is much altered. An engine is ordered for the West India Docks, to travel itself from ship to ship, to unload and to take up the goods to the upper floors of the storehouses.

Boulton and Watt have strained every nerve to get a Bill in the House to stop these engines, saying the lives of the public are endangered, by them, and I have no doubt they would have carried their point, if Mr. Homfray had not gone to London to prevent it in consequence of which an engineer from Woolwich was ordered down, and one from the Admiralty Office, to inspect and make trial of the strength of the materials. [17]


After a week or two another letter states,- [18] .

We are preparing to get the materials ready for the experiments by the London engineers, who are to be here on Sunday next. We have fixed up 28 feet of 18-inch pumps for the engine to lift water.

These engineeis particularly requested that they might have a given weight lifted, so as to be able to calculate the real duty done by a bushel of coal.

As they intend to make trial of the duty performed by tho coal consumed, they will state it as against the duty performed by Boulton's great engines, which did upward iof twenty-five millions, when their 20-inch cylinder's, after being put in the best order posesible, did not exceed ten millions. As you were consulted on all those trials of Boulton's engines, your presence would have great weight with those gents, otherwise I shall not have fair play. Let me meet them on fair grounds and I will soon convince them, of the superiority of the 'Pressure-of-steam engine.'


Watt left no stone unturned to prevent the use of high-pressure steam-engines, and fortune favoured him, for after four or five days Trevithick again wrote:

I am sorry to inform you that the experiments that were to be exhibited before the London gents are put off, on account of an accident which happened to Mr. Homfray. I find much disappointed on account of the accident, for I was desirous to make the engine go through its different work, that its effect might be published as early as possible. [19]


While constructing those numerous high-pressure engines for rolling mills, winding engines, and pumping engines, the Welsh and Newcastle locomotives were being made and worked, yet he found time to teach the people of Stourbridge.

STOURBRIDGE,
July 5th, 1804.

MR. GIDDY,
Sir,- I should have answered your letter some time since, but waited to set two other engines to work first. The great engine at Penydarran goes on exceedingly well. The engine will roll 150 tons of iron a week with 18 tons of coal. The two engines of Boulton's at Dowlais burn 40 tons to roll 160 tons; they are a 24-inch and a 27-inch double. The engine at Penydarran is 18.5 inches, 6-feet stroke, works about eighteen strokes per minute: it requires the steam about 45 lbs. to the inch above the atmosphere. I worked it expansive first, when working the hammer, which was a more regular load than rolling; then with steam high enough to work twelve strokes per minute with the cock open all the stroke; then I shut it off at half the stroke, which reduced the number of strokes to ten and a half per minute, the steam and load the same in both; but I did not continue to work it expansively, because the work in rolling is very uneven, and the careless workmen would stop the engine when working expansive.

When the cylinder was full of steam the rollers could not stop it; and as coal is not an object here, Mr. Homfray wished the engine might be worked to its full power. The saving of coal would be very great by working expansively.

The trials we have made for several weeks past against Boulton's engines have been by working with the cylinder full of steam. The cock springs out of its seat when water gets into the cylinder, and prevents any mischief from the velocity of the fly-wheel.

The tram-engine has carried two loads of 10 tons of iron to the shipping place since you left this. Mr. Hill says he will not pay the bet, because there were some of the tram-plates in the tunnel removed so as to get the road into the middle of the arch.

The first objection he started was that one man should go with the engine, without any assistance, which I performed myself without help; and now his objection is that the road is not in the same place as when the bet was made.

I expect Mr. Homfray will be forced to take steps that will force him to pay. As soon as I return from here there will be another trial, and some person will be called to testify its effects, and then I expect there will be a lawsuit immediately. The travelling engine is now working a hammer.

At Worcester last week we put a 10-horse engine to work in a glover's manufactory. The flue from the engine is carried through the drying room and dries his leather. The steam from the engine goes to take the essence out of the bark, and also to extract the colour out of the wood for dyeing the leather. Then it boils the dye, and the steam that is left is carried into his hot-house. It works exceedingly well. This week I put another to wind coals at this place, a 10-horse power, which works very well. All the tradesmen are set against it; they say that there is no carpenter or mason work about it, and very little smith work, and that it will destroy their business. The engineer on the spot is also against it very much. I do not expect that it will be kept long at work after I leave it, unless the proprietor takes care to prevent those people from doing an injury to it. Mr. Homfray was here yesterday, but is now returned to Penydarran. I shall go from here to Coalbrookdale.

There is an engine there almost ready for the West India Docks. It will be ready to send off to London in about four weeks. It will be a very complete engine. The pumps for forcing the water will be fixed on the back of the boiler. It will force 500 gallons of water 100 feet high in a minute; above ten times the quantity that engines worked by men can do. Mr. Homfray and myself shall be in town as soon as the castings are sent off. I hope you will be there at the time. If you wish to see the engines already at work in London, call on Mr. David Watson, steam-engine maker, Blackfriars Road. He lives up about 500 or 600 yards above the bridge on the left-hand side; you will see his name over his door. If you have time to inspect those engines you will find by comparing them against Boulton's, doing the same work, that there is a great saving of coal above other engines. . . . I shall go to Liverpool and Manchester from here, and again to Coalbrookdale.

There are three engines at the Dale begun, to work with condensers, for places where coal is scarce. I think it is better to make them ourselves, for if we do not, some others will, for there must be a saving of coal by condensing. But with small engines, or where coal is plentiful, the engine would be best without it. They say at the Dale about putting two cylinders, but I think one cylinder partly filled with steam would do equally as well as two cylinders,

That engine at Worcester shuts off the steam at the first third of the stroke, and works very uniformly. I cannot tell what coal it burns yet, but I believe it is a very small quantity. I shall know in a short time what advantage will be gained by working expansive. I expect it will be very considerable. There are a great many engines making and ordered. Boulton and Watt and several others are doing everything to destroy their credit, but it is impossible to destroy it now that it is so well known. I have not taken any of the ground at Bristol to remove. I called on them and told them it was possible to break the ground without men, and they wish me to take a piece to clear out, but would not set but a small piece at a time; therefore it would be disclosing the business to no purpose. They were very desirous to know the plan, but I would not satisfy them, neither will I unless they pay me for it in some way or other. If you direct for me at the Dale it will find me. I am happy to find that you have a seat in the House. I wish every seat was filled with such.

I remain, Sir,
Your very humble servant,

RICHARD TREVITHICK.


Trevithick fully understood the value of the expansive principle in 1804: when working with steam of 45 lbs. to the inch, the engine went at a speed of twelve strokes a minute. On cutting off the steam at half-stroke, the speed and consequent work done fell to ten and a half strokes a minute in other words, the work performed by the engine fell off only one-eighth part, while the quantity of steam and consequently of coal was reduced by one-half. The principle was established, but the application was practically incomplete from the want of heavier fly-wheels, to give out their momentum during the latter half of the stroke, when the expanding steam was lessening its force.

"The saving of coal would be very great by working expansively, but as coal is not an object here," Mr. Homfray was careless about the expansion. Thirty-three years after this indirect check to steam-engine economy, the writer, then living in the Sirhowey Iron Works, and within stone's-throw of Mr. Homfray's Works, recommended the removal of the Boulton and Watt's waggon boilers, to make room for Trevithick's boilers, on the plea of saving one-half the fuel, and at the same time increasing the power of the engine, and thereby the pressure of the blast in the iron furnaces. The proprietor was careless about the saving of coal, and was doubtful that an increased blast would increase the quantity of iron smelted. The promise that the wages of one-half of the number of boiler firemen would be saved, was understood. Trevithick's high-pressure boilers replaced the Watt low-pressure, resulting in a largely increased quantity of iron from the greater power and pressure of blast in the furnaces, and at one-half the expenditure of coal in the boilers: ten men had been employed as firemen of the Watt boilers during twenty-four hours; with Trevithick's boilers, five men did the work.

The high-pressure puffer-engine, with an 18-inch cylinder, working with 45 lbs. of steam, rolled as much iron as the two larger low-pressure vacuum engines of Watt, of 24 and 27 inch cylinders, which together were more than three times the size of the high-pressure engine and cost three times as much.

At Stourbridge, as elsewhere, everyone was against the new plan. The engineer in charge did not like it, and the carpenters, smiths, and masons saw the end of their occupation as engine erectors, if there was no longer a necessity for foundations, well-work, &c., for condensing water, and many other things, necessary to complete a Watt engine; while the high-pressure puffer was no sooner unloaded than it was ready to work.

A great charm in Trevithick's character was his freedom and largeness of view in questions of competition. He was then making three engines at Coalbrookdale, to be worked with high-pressure steam, combined with the Watt air-pump and condenser and though smarting from the contest with his great rival, yet wrote, "I think it is better to make them ourselves, for if we do not, some others will, for there must be a saving of coal by condensing. But with small engines, or where coal is plentiful, the engine would be best without it."

Those words accurately describe the practice of the present day, though written sixty-six years ago, and were followed by others equally true in principle, though varied in form to suit special requirement. "They say at the Dale about putting two cylinders, but I think one cylinder partly filled with steam would do equally as well as two cylinders."

These sagacious views required the untiring labour of the following twelve years to perfect and make practical, when applied to the largest engines of the time; which we shall now trace in the construction of a strong and economical boiler, supplying high-pressure steam to the cylinder during only a comparatively small portion of the stroke, completing it by expansion, so that at its finish the steam had become of low pressure when passed to the condenser. The moving parts and expansive gear were so simplified as to be applicable to the then existing low-pressure steam vacuum engines without the complication of the double cylinders of Hornblower and Woolf.

PENYDARRAN PLACE,
December 26th, 1804.

DEAR SIR,
I have been favoured with your letter, and in answer, respecting Mr. Mitchell, I am at a loss to know from your letter what kind of iron he may likely want. If you will direct him to write to me, and explain himself, I will immediately reply to him and do what I can to assist and serve him. I believe there are vessels going over frequently from Cardiff to Cornwall with coals, that he might have part in cargo and the remainder in coals. I am happy to give you the most satisfactory account of our 'Trevithick's engine' going on well. It has now been at work many months, and is by far the best engine we have. We have for weeks weighed the coal, and knowing time work it does, can speak with with confidence. Its 18 inches diameter steam cylinder consumes as near as can be 3 tons of coal, in twenty-four hours, or 18 tons per week; and in this time it rolls with ease 130 tons long weight of iron from the puddling furnaces, at the some heat, into bars of 3 inches by about half an inch thick. Now, one on Messrs. Boulton and Watt's plan, of '24 inches' steam-cylinder, at our neighbouring works at Dowlais, employed in doing exactly the same kind of work, consumes full as much coal, and rolls only 90 tons in the week. These being facts, open for any person daily to see, must convince any dispassionate man of the superiority of 'Trevithick's engines,' and that the saving of fuel is nearly one-third, besides the other advantages of saving water and grease, which is no little. The packing of the piston now gives us little or no trouble, it goes from a fortnight to a month, opening the top now and then to screw it down, as it gets slack, which should be attended to. We use no grease or oil in packing the piston or working the engine, having found blacklead mixed with water, and poured 'a little now and then' through a hole on the top into the steam-cylinder, suits the packing of the piston much better, and is cheaper than anything else. About ls. worth of black-lead will last our engine a week. We are now so thoroughly convinced of the superiority of these engines that I have just begun another of larger size. The boiler is to be 24 or 26 feet long, 7 feet diameter, fire-tube at wide end 4 feet 4 inches, and at narrow end, where it takes the chimney, 21 inches, steam-cylinder 23 inches diameter. This boiler, on account of the length of its tube withinside, will, I have no doubt, get steam in proportion, and work the engine with much less coals than our present one. Trevithick is at Coalbrookdale, Manchester, &c., very busy, a great number of engines being in hand in that part of the world and I think by perseverance the prejudice is wearing away very fast, and in spite of all Messrs. Boulton and Watt's opposition, they must and will take the lead of theirs. Any person now wanting engines, must be next kin to an idiot to erect one of Boulton's in preference to Trevithick's. I find there is a small one making near you by Mr. Vivian. I hope they have corresponded with Trevithick about the proportions of it; if they have not, I shall be particularly obliged to you to desire them to do so, for by his experience of what he has done they may be benefited, for it would be a shocking thing to have a bad engine put up for the first time in his native county.

Mrs. Homfray unites with me in best compliments, and wishing you many happy returns of the season. I remain, dear Sir,

Your most obedient servant,

SAMUEL HOMFRAY.

To MR. DAVIES GIDDY.


The evidence in this contest between the Watt low-pressure steam vacuum engine and the Trevithick high-pressure steam-puffer engine is in favour of the new principle; for the steam-engine with an 18-inch cylinder did fifty per cent. more work than the vacuum engine with a 24-inch cylinder with an equal quantity of coal, though the latter was seventy-five per cent. larger than the former; and a still greater economy was expected from the larger boiler to be built, 26 feet long, 7 feet in diameter, with internal fire-tube 4 feet 4 inches diameter at the fire end, tapering to 21 inches at the chimney end. Thus in 1804 the cylindrical boiler in Wales had nearly reached its present form, and Homfray thought that none but idiots would prefer the Watt engine forgetting that Trevithick's near friends and neighbours were carrying on a similar contest at Dolcoath

PENYDARRAN PLACE,
January 2nd, 1805.

MR. DAVIES GIDDY,
Dear Sir,— I have duly received your favour enclosing a letter for Mr. Trevithick, and which I, according to your desire, forwarded to him at Manchester, where he now is; and a letter directed to him, to the care of Mr. Whitehead, Soho Foundry, Manchester, will find him, as he will stay a little time there, being very busy. I had lately the pleasure of writing to you, and gave you the account of our engine working, and the satisfaction it gives; I have nothing more to add on the subject, but that it is now at work, going on as usual, and I should be happy for you to have a sight of it.

We are beginning another of a larger size, and I have no doubt but by making the cylindrical boiler larger, so as to take a longer tube withinside it, by which means the fire will spend itself before it leaves the tube to go up the chimney, that we shall work to much better advantage in point of fuel than we do at this present one, as this boiler is so short that a great deal of the flame of the fire goes up the chimney. We are now better acquainted with the different proportions than we at first were, for which reason I am anxious that one now making by Mr. Vivian should be made according to the directions of Mr. Trevithick.

I beg leave to offer you the compliments of the season, and many happy returns, and

Remain, respectfully, dear Sir,
Your most obedient servant,

SAMUEL HOMFRAY.


Trevithick, always busy, was just now doing the work of a host, for everybody had to be taught bow to make high-pressure steam-engines and the Newcastle locomotive, the Thames steam-dredging, and other special applications of steam-power required his presence, especially the fight with Watt at Dolcoath Mine, where Andrew Vivian, as mine manager, was erecting a high-pressure steam-puffer whim-engine to compete with a Watt low-pressure steam vacuum whim-engine.

The adventurers grumbled because Captain Trevithick was so often away from the mine. Glanville, the mine carpenter, the head man over the engines, made a trial between Trevithick's high-pressure puffer whim and Watt's low-pressure condenser. When Captain Trevithick heard of it, he wrote down from London that he would bet Glanville £50 that his high-pressure puffer should beat Watt's low-pressure condenser. Then he came down from London and found that the piston of his engine was half an inch smaller in diameter than the cylinder. When a new piston was put in, she beat Boulton and Watt all to nothing. Persons were chosen to make a three or four weeks' trial, and when it was over, a little pit was found with coal buried in it, that Glanville meant to use in the Watt engine. [20]


Pooly, Smith, and others, say that Trevithick's Dolcoath puffer had the outer case of the boiler of cast iron, the fire-tube of wrought iron, the cylinder horizontal, and fixed in the boiler. Captain Joseph Vivian saw Trevithick's whim in Stray Park Mine about 1800 or 1801, and a similar one was erected in Dolcoath, and after a year or two a Boulton and Watt low-pressure whim was put up to beat it. The trial was in favour of the Watt engine, but everybody said the agents were told beforehand which way the report ought to go; so the engine that 'puffed the steam up the chimney was beaten'. Trevithick, who was busily engaged in Manchester at that time, the early part of 1805, when informed of what was going on in Cornwall, wrote:—

I fear that engine at Dolcoath will be a bad one. I never knew anything about its being built until you wrote to me about Penberthy Crofts engine, when you mentioned it. I then requested Captain A. Vivian to inform me the particulars about it, and I find that it will not be a good job. I wish it never was begun. [21]


CAMBORNE,
February 18th, 1806.

MR. GIDDY,
Sir, On my return from town I altered the pressure of the steam-engine at the bottom of the hill, Dolcoath. Before I returned there was a trial between mine and one of Boulton's; both engines in the same mine and drawing ores from the same depth. The result was, Boulton's beat the pressure-engine as 120 to 55. Since it was altered there have been three other trials the result was 147 to 35 in favour of the pressure of the steam-engine. They are now on trial for another month, and at the next account they intend to order a new boiler for the great engine, and work with high-pressure steam and condenser, provided this engine continues to do the same duty as was done in the former trials. This engine is now drawing from a perpendicular shaft, and Boulton and Watt's from an underlay shaft; but to convince Captain Jos. Vivian, we put it to draw out of the worst shaft in the mine, and then we beat more three to one; we lifted in forty-seven hours, 233 tons of stuff 100 fathoms with 47 bushels of coal. The engine was on trial sixty-six hours, but nineteen hours were hindered by the shaft and ropes, &C., which made the consumption of coals about 3/4ths of a bushel per hour. The fire-tube is 2 feet 3 inches diameter, and the fire-bars were only 14 inches long. The fire-place was but 2 feet 3 inches wide by 14 inches long, and the fire about 4 or 5 inches thick it raised steam in plenty; it was as bright as a star. The engine is now doing the work of two steam-whims; the other steam-whim in the Valley is turned idle, and both shafts will not more than half supply it. 233 tons are equal to nearly 2,000 kibbals, which were drawn in forty-seven hours.

Mr. Harris has a 12-inch cylinder making at Hayle, for Crenver, and Mr. Daniel has a 14-inch for Perran-sand, and a great number are waiting for the trial of this month, before altering their boilers to thereat engines.

The steam-whim that is now turned idle at the Valley was 13.5-inch cylinder, 4-feet stroke; it turned the whim one revolution to one stroke, and lifted the kibbal the same height at a stroke as my engine did, and I think took the same number of gallons of steam to lift a kibbal as mine did. Their steam was not above 4 lbs. to the inch; mine was near 40 lbs. to the inch; yet I raised my steam of near 40 lbs. with a third of the coals by which they got theirs of 4 lbs. to the inch. This is what I cannot account for, unless it is by getting the fire very small and extremely hot. Another advantage I have is, that there is no smoke that goes off from my fire to clog the fire sides of the boiler, while the common boilers get soot half an inch thick, and the mud falls on the bottom of the boiler, where the fire ought to act; but in these new boilers boilers the mud falls to the bottom, where there is no fire, and both the inside and outside of the tube are clean and exposed both to fire and water. This fireplace of 14 inches was 5 feet long when I came down, and then the coal did not do above one-seventh of the duty that it now does.

I would be very much obliged to you for your opinion on what I have stated, and what advantage you think the great engine is likely to get from working with steam about 25 lbs. to the inch, and shut of early in the stroke, so as to have the steam about 4 lbs. to the inch when the piston is at the bottom. I think this, with the advantage of the fire-place, will make a great saving.

The present fire-place is 22 feet from fire-door to fire-door, 9 feet wide, and 7 feet thick in fire. There is not one-tenth of the coals that are in the fire-place on fire at the same time; it will hold 30 tons of coals at one time, and I think that a great deal of coal is destroyed by a partial heat before it takes fire. A boiler on the new plan will not cost more than two-thirds of the old way, and will last double the time, and can be cleaned in three hours. It requires twenty-four hours in the old way, and we need to clean the boilers only one-fourth the number of times.

Though these trials have shown so fairly that it is a great advantage, my old acquaintances are still striving with all their might to destroy the use of it but facts will soon silence them.

I am about to enter into a contract. with the Trinity Board for lifting up the ballast out of the bottom of the Thames for all the shipping. The first quantity stated was 300,000 tons per year, but now they state 500,000 tons per year. I am to do nothing but wind up the chain for 6d. per ton, which is now done by men. They never lift it above 25 feet high. A man will now get up 10 tons for 7s. My engine at Dolcoath has lifted above 100 tons that height with 1 bushel of coals. I have two engines already finished for this purpose, and shall be in town in about fifteen days to set them at work. They propose to engage with me for twenty-one years. The outlines of the contract they have sent me down, which I think is on very. fair terms. I would thank you for your answer before I leave this county.

I am, Sir,
Your very humble servant,

RD. TREVITHICK.


In the trial at Dolcoath during his absence the high-pressure steam-puffer whim was beaten by Watt's low-pressure steam vacuum whim-engine as 55 to 120 but having corrected some oversight in the puffer-engine, it then beat Watt as 147 to 35. The trial was to be continued for a month; and provided the superiority of his whim-engine could be maintained, the adventurers would allow him to apply his high-pressure boilers to their large Boulton and Watt pumping engine. The trial with the whim-engines was for the greatest number of kibbals of mineral raised to the surface by the least consumption of coal. A dispute arose on the difference of the shafts, the one causing more friction to the moving kibbal than the other, when Trevithick agreed to take the worst shaft in the mine. On a trial during sixty-six hours Watt's engine was beaten by more than four times; and as Trevithick's engine did the work that before required two engines, one of the low-pressure steam Watt engines was removed that the engine working with 40 lbs. on the inch might perform the whole work.

My fire-tube is 2 feet 3 inches in diameter, and the fire-bars only 14 inches long, and the fire only about 4 or 5 inches thick it raised steam in plenty, and was as bright as a star.


These words certainly imply the use of the blast-pipe, making the fire as bright as a star, and enabling the small boiler to give the required supply of steam. Several high-pressure puffer-engines had been ordered, and many persons were waiting the conclusion of the month's public trial to enable them to judge between the Watt and the Trevithick engine.

CAMBORNE,
March 4th, 1806.

MR. GIDDY,
Sir,— The day after I wrote to you the first letter, I received yours, and this day I have yours of the 1st instant.

I am very much obliged to you for the figures you have sent me. I am convinced that the pressure of steam will not hold good as theory points it out, because on expanding it will get colder, and of course lose a part of its expansive force after the steam-valve shuts. I think there can be no risk in making this trial on Dolcoath great engine, as they intend to have a new boiler immediately, so as to prevent stopping to cleanse; and a boiler on this new plan can be made for one-third less expense than on the old plan, when you count the large boiler-house and ashes-pit, and brickwork round the boiler. It is not intended to alter any part of the engine or condenser, but only work with high steam from this new boiler; and if this boiler only performs as good duty as the old one, it will be a saving of near £300 to them on the erection, The vast matter this great engine has in motion will answer in part the use of a fly-wheel: the whole of the matter in motion is near about 200 tons, at a velocity of about 160 feet a minute. This I know will not be sufficient; but it will be about equal to a fly-wheel of 20 feet diameter, 25 tons weight, twenty rounds per minute, if weight and velocity answer the same purpose.

Monday, the 18th February, being Dolcoath account-day, both engines have been on trial, and are to be continued until the next account, 17th instant. The engines are kept on the usual way, as at other times. Neither of the engines have done so much duty as on the first trials, as they have not been so strictly attended to. The average of the trial at this time stands 26 cwt. for a bushel of coals to Boulton and Watt's engine; mine, 83 cwt. for a bushel of coals.

If I do not remain in Cornwall to attend next Dolcoath account, I shall be in town about the 15th instant, otherwise about the 20th instant. I shall call on you immediately on my arrival. In this time I should be glad to hear from you again. The Trinity business will answer exceedingly well; I have two engines ready for that purpose to put to work on my arrival in town.

I am, Sir,
Your very humble servant,

RD. TREVITHICK.

P.S.— I would try the evaporation of water by both boilers, but Boulton and Watt's engine is so pressed with work, and being on the best part of the mine, they will not stop it a moment. A boiler of 8 feet diameter and 30 feet long will have as much fire-sides in the tube as there is now in Dolcoath great boiler. The fire-tube in this boiler would be 5 feet diameter, and a fire-place 6 feet long in it would be 30 feet of fire-bars. In the whim-engines I find that a fire-place 14 inches long and the tube 2 feet 3 inches diameter would, being forced, burn 1 bushel per hour. At this rate the great tube would burn near 12 bushels per hour, which is above the quantity that the great engine boiler can consume, now at work. Small tubes would have an advantage over large ones. Two boilers would not cost much more than one large one and be much stronger.


Carn Brae Castle (W. J. Welch)

The battle-ground of the fight between low and high pressure from 1806 to 1812 had also served for the personal encounter of Trevithick, sen., and Watt a quarter of a century before, when the Dolcoath great pumping engine was erected to compete with the two earlier atmospherics; all three were still at work, overlooked by Cam Brea hill and castle, once the resort of Druid priests, whose sacrificial rites are still traced, by the hollows and channels for the blood of victims on the granite rocks.

CAMBORNE,
March 21st, 1806.

Mr. GIDDY,
Sir, The trial between the two engines ended last Monday, which was Dolcoath day. Boulton and Watt's engine, per average of trial, 1 ton 20 cwt. 2 qrs., with 1 bushel of coals; the other, 5 tons 11 cwt. 3 qrs., with 1 ditto, the same depth of shaft. The adventurers ordered the new castings that were made for another of Boulton and Watt's engines to be thrown aside, and another new engine of mine to be built immediately. The great boiler for the old engine is not yet ordered.

I have received orders for nine engines within these four weeks, all for Cornwall. Two 12-inch cylinders, two 16-inch ditto, three 9-inch ditto, one 8-inch ditto, one 7-inch ditto. I expect one will be put to work next week at Wheal Abraham, for lifting water.

This day I shall leave Cornwall for London. Shall stop two days in the neighbourhood of Tavistock, and take orders for three engines. As soon as I arrive in town I will call at your lodgings. I expect that the patent will be brought into court about the end of May. A person in Wales owes us about £600 patent premium, and he says that the patent is not good. More particulars you shall have on my arrival.

The railroad is going forward. I have the drawings in hand for the inclined plane.

I am, Sir,
Your very humble servant,

RD. TREVITHICK.


The fact that expansion of steam caused reduction of heat was so evident to Trevithick that he ventured to doubt his friend's theory. The trials between the whim-engines having continued a fortnight, showed that the high-pressure steam-puffer had lifted 83 cwt., while the low-pressure steam vacuum only lifted 26 cwt. with the consumption of a bushel of coal. A suitable high-pressure boiler for the Watt low-pressure steam 63-inch pumping engine should be 30 feet long, 8 feet in diameter, with an internal fire-tube 5 feet in diameter; proportions approved of in the present day. The recommendation in 1806 to use small tubes may claim to be the first practical decision on the advantage of tubular boilers and at the same time we read of the first hesitating step on the part of the public to use high-pressure steam in a Watt low-pressure engine, which was still deferred for further consideration, even with the limited pressure of 25 lbs. to an inch; so the large Watt pumping engines were doomed for another four or five years to struggle through their work with low-pressure steam, though at that time Cook's Kitchen high-pressure expansive condensing whim-engine had been for years at work close by.

The shareholders professed to have fear of explosion; but party-feeling and ignorance were the real causes of opposition, for working men had no dread of the new engines, while influential men leaned toward Watt's old-fashioned plans.

This fear of Trevithick's expansive plans and high steam is the more surprising, because at that time a new boiler was required for the Watt 63-inch cylinder pumping engine and Trevithick's cylindrical tubular boiler could be made for one-third less cost than the Watt waggon boiler, thus saving £300, and in addition he promised to apply the higher pressure of steam to the Watt engine without any change in its parts or expenditure of money, and make it set in motion at the commencement of the stroke the 200 tons of pump-rods, the momentum of which would, with the expansion of the steam, when shutting it off soon after the first start in the movement of each stroke, carry it through to the end; and he practically compares this advantage from hoarded momentum in the pumping engine with his experience of the fly-wheel of the rolling-mill expansive engine in Wales.

The whim-engine with a fire-tube 2 feet 3 inches in diameter used 84 lbs. of coal per hour and at that rate one cylindrical boiler 30 feet long, 8 feet in diameter, with internal fire-tube 5 feet in diameter, would supply steam for Watt's 63-inch cylinder; but in place of it he preferred two smaller boilers, because small tubes have an advantage over large ones, and are much stronger. The whim trials — high-pressure puffer against low-pressure vacuum — went on for another fortnight, when high pressure, having done twice as much work as low pressure, with an equal consumption of coal, the adventurers threw aside the work that had been made for another Watt engine, ordering one in its stead from Trevithick but they could not just then make up their minds to place the Watt 63-inch pumping engine in his hands.

CAMBORNE,
May 30th, 1806.

DEAR SIR,
I am very happy to find you have so far continued your agreement with the Trinity gents, and think the bargain is a good one. Must still beg leave to remind you not to proceed to show what your engine will do till the agreement is fully drawn up and regularly signed.

Dolcoath agents, since they are informed of the accident at the iron-works in Wales, of the engine blowing to pieces, have requested me to have your opinion whether the old cylinder is strong enough for the boiler of the intended new engine, or whether you would recommend them to have a new one. Your answer to this as soon as possible, as Mr. Williams and some others are likely to make some objections.

Mr. Sims, the engineer, has published in the Truro paper, that one of Boulton and Watt's engines at Wheal Jewell has drawn more than a ton of ore over and above that drawn by the Dolcoath engine from the same depth by a bushel of coal. On inquiry I found they had only tried for twenty-two hours. They said they left off with as good a fire as they began with. This I argued was not a fair trial. They say they are now on a trial for a month.

The little engine at Wheal Abraham does its duty extremely well. The particulars as to consumption of coal cannot be fairly ascertained, as she has never been covered, is fed with cold water, and has not water to draw to keep her constantly at work.

I wish I could give a better account of the mines than is in my power to give, or of the standard price for ore, though the latter is rather looking up than otherwise. Our friend, North Binner Downs, is better than paying cost, but very little. At present the levels are all poor; the lode in the west shaft has underlayed faster than the shaft, and we have not seen it for several fathoms. The ground lately in the shaft has been cleaner killas, and if any alteration, better ground. It is now 9 fathoms under the 55-fathom level, and we are driving to cut the lode. The ground in the cross-cut is harder than when you were on the spot. The water is sinking in old Binner; it is about 7 fathoms under the adit in the western part, and deeper in the eastern part; we do not account for this. Wheal St. Aubyn combined poor. Wheal Abraham looks promising, and Creuver about paying cost. Dolcoath is better than when you left us, or when I was in London. The last sale was only about 800 tons. The next sale on Thursday is upwards of 1,100 tons, and we expect a little better standard.

I wish you could discover who that old gent is that wanted a large slice in Dolcoath, that I might get at him through some unknown channel, for I want money sadly.

Cook's Kitchen continues poor, Tin Croft ditto; Wheal Fanny not rich. We had a pretty little fight last account there with T. Kevill and W. Reynolds, Esquires: black eyes and bloody noses the worst effects. T. Kevill's face was much disfigured, and be might have found a new road out of his coat.

At a meeting of Condurrow adventurers yesterday, twenty-four of them agreed to have one of our engines, cylinder 12 inches in diameter and 6-feet stroke, provided the Foxes do not object to it. When the order is given I shall write to Mr. Hazeldine, provided I do not hear from you that it is better to send the order to any other place.

If you have occasion to write Mr. Hazeldine, I wish you would press him to hasten the engines for Wheal Goshen, &c.

I am served with a Vice-warden's petition by Mr. Harris for not working the Weith mine in a more effectual manner, and he prays the Vice-warden to make the sett void. The trial will come on some time the beginning of July, and by that time I suppose we shall have two fire-engines working thereon.

Had Mr. Harvey done as he was desired we should have had one working there at this time, but he has but now begun to do anything to it. We have the cylinder and ends home from Polgooth, and my cousin Simon Vivian is making the tubes. We have the other cylinder from Wheal Treasury, and I have ordered Horton to cast a cock for it the same as that at Dolcoath. We have cut the south lode at the adit level about 50 or 60 fathoms east of the engine, and have driven about 20 fathoms on it. It turns out about half a ton per fathom at £20 a ton. The ground at 40s. per fathom; this all in a hole, and is better going down. The back is sett to four men at 3s. 11d. their time is out this week, and I suppose they must have 5s. next. This may turn out a few thousands, and I think too promising a thing to give up to Mr. Harris.

I am happy to inform you that all our friends are in good health, and beg my most respectful compliments to Mrs. Rogers and adopted son; and am,

Dear Sir,
Yours very sincerely,

ANDW. VIVIAN

The promised news respecting the engine business I am very anxious to have, as it will I hope make me proud, as proud I shall be when I am able to pay everyone their demands, and have sufficient to carry on a little business to maintain my finally and self without the assistance of others. May you succeed in your undertaking and also be independent, is the sincere wish of your friend. John Finnis and others are anxious to know when they will be wanted. A. V.


The explosion at Greenwich in 1803 was made much of, though the fault was clearly not in the boiler. Three much years afterwards, in 1806, a steam-cylinder burst in Wales, therefore Mr. Williams, a large shareholder in Dolcoath, objected to the use of high-pressure expansive steam in their large Watt pumping engine, and desired their engineer, Mr. Sims, to make a competitive trial after his own fashion. At Condurrow Mine one of Trevithick's engines was to be ordered if the Foxes and Williamses did not object; and so it was that Trevithick's high-pressure steam-boiler was not ordered, and the Watt vacuum engine was for a longer time to receive no increase of power.

Some of Captain Dick's early boilers had flattish or oval fire-tubes. In 1820 I repaired an old one in Wheal Clowance Mine in Gwinear. The flat top had come down a little; we put in a line of bolts, fastening the top of the tube to the outer casing.

About 1818 I saw in Carsize Mine in Gwinear a pumping engine that Captain Dick had put up. The boiler was a cylinder of cast iron, with a wrought-iron tube going through its length in which the fire was placed. The steam-cylinder was vertical, fixed in the boiler. She had an air-pump and worked with a four-way cock. The steam was about 100 lbs. to the inch. [22]


About 1820 I removed one of Captain Trevithick's early high-pressure whim-engines from Creuver and Wheal Abraham, and put it as a pumping engine in Wheal Kitty, where it continued at work for about fifteen years. The boiler was of cast iron, in two lengths bolted together, about 6 feet in diameter and 10 feet long. At one end a piece was bolted, into which the cylinder was fixed, so that it had the steam and water around it. There was an internal wrought-iron tube that turned back again to the fire-door end, where the wrought-iron chimney was fixed; the fire-grate end of the tube was about 2 feet 6 inches in diameter, and tapered down to about 1 foot 6 inches at the chimney end. It was a puffer, working 60 lbs. of steam to the inch; it worked very well. There were several others in the county at that time something like it. It was made at the Neath Abbey Works in Wales. [23]


These boilers were of the kind first tried in Cornwall about 1800. The oval tube in the Kensington model of 1798 continued in use in Cornwall for many years. The cast-iron outer casing was soon abandoned, though one of them in Wales remained in work fifty years, using steam of 60 lbs. to 100 lbs. to the inch.

HAYLE FOUNDRY,
August 26th, 1810.

MY DEAR JANE,
I saw Captain Andrew Vivian on Wednesday, who told me that he had been offered £150 a year to inspect all the engines in the county, and report what duty they were doing, in order to stimulate the engineers. He declined accepting it, having too much to do already; and he thought it would be worth Trevithick's notice, as it would not take him more than a day or two in a month.

I remain, my dear Jane,
Yours sincerely,

H. HARVEY.

I wrote this letter on Sunday, with an intention of sending it then, but thought it best to wait until this day, in hopes of hearing the determination of Government in your favour; but your letter has arrived without the desired information. All that I can now say is, to desire that Trevithick will make up his mind to return to Cornwall immediately. H. H.


The application to the Government for remuneration for benefits conferred on the public was unsuccessful. The office of registrar of Cornish engines was unsuitable; fortuately for mining interests, illness obliged Trevithick to revisit his native county, for by the increased power and economy of his engines Dolcoath Mine, so frequently mentioned, and so important in olden time, now returns £70,000 worth of tin yearly.

Trevithick's first act on returning to Cornwall in 1810 was the erection of the high-pressure boilers and pole vacuum engine at Wheal Prosper; at the same time renewing his proposals to Dolcoath to use his improved boilers, which had been broken off in 1806, and to apply high-pressure steam to their low-pressure Watt engine, with the same safety and profit as in Wheal Prosper; the evidence was undeniable, so his plans were agreed to, and in the early part of 1811 the high-pressure boilers, called the Trevithick or Cornish boilers, were constructed in the Dolcoath Mine under his directions.

Old John Bryant, who worked the Dolcoath large engines both before and after the introduction of higher pressure steam, including the Carloose or Bullan Garden 45-inch cylinder engine, Wheal Gons 63-inch cylinder single engine, and the Watt 63-inch cylinder double, with the bee-but boiler, such as Trevithick, sen., used in 1775, [24] followed by the Watt waggon boiler, and afterwards by the globular boiler of Trevithick, jun., in 1799, [25] and still later also with the cylindrical boiler of 1811, gave the following statement, when seventy-four years old, to the writer:-

In the old bee-but and the waggon boiler the steam pressure in the boiler was not much; we did not trouble about it so long as the engines kept going: when the steam was too high it blew off through the feed-cistern. When Captain Trevithick tried his high steam in Dolcoath we hoisted up the feed-cistern as high as we could; when the steam got up, it blew the water out of the cistern. Captain Dick holloed out, "Why don't you trig down the clack?"

The cylindrical boilers when they were first put in leaked very much; we could hardly keep up the fire sometimes. I reckon the steam was 30 or 40 lbs. to the inch. Captain Dick's boilers made him lots of enemies. I heard say in one mine where he was trying his boilers against Boulton and Watt's waggon, a lot of gunpowder was put into the heap of coal. [26]


The waggon or hearse Watt boiler was attached to his 63-inch cylinder double, and the old man recollected having raised the water cistern, when Trevithick's globe boiler gave an increased pressure in 1799, ten or twelve years before the cylindrical boilers were made in Dolcoath.

Some time after Captain Dick's globe boiler and steam-whims had been at work in Dolcoath, a letter came down from London, saying that he would save the mine £100 a month if they would put in one of his new plan boilers.

They were put in hand in the mine, and I worked about them; they were wrought-iron cylindrical boilers, about 20 feet long, and 5 or 6 feet in diameter the fire-tube was about 3 feet in diameter; the fire returned around the outside in brick clues. Three boilers were put in side by side.

When Captain Dick first tried them, he said to the men, Now mind, the fire-bars must never have more than six inches of coal on them; give a shovel or two to one boiler, and then to another. When Captain Dick's back was turned, the men said they wasn't going to do anything of the sort, there would never be no rest for them. They used to say that the boilers saved more than £170 the first month. [27]


Clark, when a boy, in 1799, helped to construct Trevithick's globular boiler in Dolcoath, and recollected the events of the few following years, during the contests with the whim-engines about 1806, and the introduction of the large cylindrical wrought-iron boilers for the pumping engines in 1811, and the struggle preceding the downfall of the Watt low-pressure steam vacuum engine, to make room for the high-pressure expansive steam-engine, with or without vacuum.

About 1812 Captain Trevithick threw out the Boulton and Watt waggon boilers at Dolcoath and put in his own, known as Trevithick's boiler. They were about 30 feet long, 6 feet in diameter, with a tube about 3 feet 6 inches in diameter going through its length. There was a space of about 6 inches between the bottom of the tube and the outer casing. Many persons opposed the new plans. The Boulton and Watt low-pressure engine did not work well with the high steam, and the water rose in the mine workings. Captain Trevithick, seeing that he was being swamped, received permission from the mine managers to dismiss the old engine hands and employ his own staff. Captain Jacob Thomas was the man chosen to put things right. He never left the mine until the engine worked better than ever before, and forked the water to the bottom of the mine. Before that time the average duty in the county by the Boulton and Watt engines was seventeen or eighteen millions, and in two or three years, with Trevithick's boilers and improvements in the engines, the duty rose to forty millions. About 1826 he (Captain Vivian) was manager of Wheal Towan; their engines were considered the best in the county, doing eighty-seven millions; they had Trevithick's boilers, working with high-pressure steam and expansive gear; few if any of Boulton and Watt's boilers could then be found in the county. Sir John Rennie and other scientific men, who doubted the reports of the duty, came and made their own trials with the engines, and were satisfied that the duty was correctly reported.

About that time a Mr. Neville requested him to report on the engines at his colliery at Llanelthy; one was an atmospheric of Newcomen's, doing six millions; and four or five of Boulton and Watt's patent engines averaged fourteen millions. [28]


When at last the cylindrical high-pressure boiler was admitted, and men had been taught to fire them, many persons still liked the old plans, and among them the easy-going low-pressure enginemen. The consequence was that the Watt engines under their management refused the early doses of Trevithick's high steam, not easily digesting it, and their obstinacy nearly swamped Trevithick and his plans.

When a little boy, about 1812, I frequently carried my father's dinner from Penponds to Dolcoath Mine. One day, not finding him in the engine-house, I sought him in the account- house, but not knowing him in a miner's working dress, refused to give him his dinner. William West then worked with him. I heard there was difficulty in making the new boilers and the old engine work well; engineers from other mines looked on from a distance, not liking the risk of explosion. People seemed to be against the new plans; some labourers worked with them.


This narration — sixty years after the events — from Mr. Richard Trevithick, the eldest son of the engineer, shows that William West helped in applying high-pressure steam to the Watt low-pressure engine, and that but few sympathized with the innovators on old customs; but among them was Captain Jacob Thomas, who successfully fed the old engine with strong steam. At that time the Watt engines in Cornwall had been doing seventeen or eighteen millions; Trevithick's new boilers increased their duty to forty millions.

William Pooly [29] was working in Dolcoath before Captain Trevithick's new boilers were put in, and helped to put them in.

The Shammal 45-inch engine was an open-top cylinder, with a chain to the segment-head wooden beam. So was the 63-inch cylinder Stray Park engine, then called Wheal Gons [30] in Dolcoath sett, and the Boulton and Watt 63-inch cylinder double-acting.

There used to be great talking about different boilers; a boiler of Captain Trevithick's worked with higher steam than the others. Just before Captain Dick came back to the mine a Boulton and Watt hearse boiler had been repaired with a new bottom it was never used. I and William Causan took a job to cut up the boiler at ls. 6d. the hundredweight; it weighed 17 tons. Jeffrie and Gribble were the mine engineers; Glanville used to be considered Captain Dick's man in the mine. You could stand upright on the fire-bars in the middle hollow of the hearse boiler, and so you could in the outside brick flues; the middle hollow was like a horse-shoe. When Captain Dick put in his cylindrical boilers he altered the 63-inch single; there was hardly anything of her left but the main wall, with the wood bob and a chain to the piston-rod, and also to the pump-rods. There was an air-pump, and I think a second-hand cylinder was brought, but it was a 63-inch the old Shammal engine had been altered, too.

The new boiler put in was about 8 feet in diameter and from 30 to 40 feet long, two round tubes went through it the fire-place in one end of one tube and in the other end of the other tube; after going through the tubes the draught went into the brick flues under the bottom and sides. When the new engine was put in, Gribble said, "Why, these little things will never get steam enough;" everybody said so.

In the Boulton and Watt engines we didn't trouble about feed-pumps and gauge-cocks.

A wire came through a stuffing box in the top of the boiler; a biggish stone in the boiler was fastened to one end of the wire, the other end was fastened to a weighted lever near the water cistern, just above the boiler; when the water got low the stone opened the valve in the water cistern. That was when they were putting in Captain Dick's new cylindrical boilers to the old 63-inch engine. She did so much more work, with less coal, that in a year or so they agreed to throw out Boulton and Watt's engine, and to put in a stronger one that could stand Captain Dick's high steam. Jeffrie and Gribble were the mine engineers that put her up. The 76-inch cylinder came from Wales. The big beam was cast at Perran Foundry in 1815; you can see the name and date upon it now. The boiler and the gear-work were made in the mine. The exhaust-valve is exactly as when it was put in, worked by a rack-and-tooth segment. The equilibrium valve is unchanged, except that the rack is taken out and a link put in.

The steam-valve was taken out soon after she went to work, and the present double-beat valve was put in it is the first of the kind I ever saw. Some were made before that time with a small valve on the top of the big one, that opened first, to ease the pressure.

John West [31] fitted up the valve-gear in the mine with the expansive tappets, the same as when she stopped a month or two ago, and the same as the present new one has.

Captain Dick's cutting off his strong steam at an early part of the stroke, used to make the steam-valve strike very hard; so the new plan valve, with a double beat, was put in; that must have been about 1816 or 1817 and the valve and expansive horn for working were just exactly like what they have put into the present new engine in 1869. She was the engine that showed them how to fork the water, and burn only half the coal.

I worked in this mine the old atmospheric engines, and then Boulton and Watt; and then Trevithick's boilers in Boulton and Watt; and then Trevithick's boilers and engine and now I come every day to the new engine, though I can't do much. They give me 35s. a month; and my name is William Pooly, Dolcoath, 1869.


Three years ago (in 1869), when the writer entered the old engine-house in which Watt's 63-inch cylinder double had been erected in 1780, adjoining the old walls that then enclosed that early Newcomen 45-inch cylinder Carloose engine, re-erected by Trevithick, sen., in 1775 in Bullan Garden portion of Dolcoath, an old man sat near a small window in a recess in the thick will of the engine-house, within reach of the gear-handles of the Jeffrie and Gribble 76-inch cylinder engine that Trevithick, jun., had erected in 1816 on the foundations of the removed Watt engine; he held in one band a portion of slate from the roof, and in the other an old pocket-knife, one-half of the blade of which had been broken off, leaving a jagged fracture, with which he made the figures of some calculation on the rude slate; on his nose rested the brass frame of a pair of very ancient spectacles, with born glasses. He answered the writer's question by, "Yes, I am William Pooly; I worked this engine, and the other engines before it — the great double and the little Shammal working out of the same shaft; and I am seventy-four years of age. The 63 single worked upon a shaft up there she was called Wheal Gons." That old man, still living, had worked in Dolcoath Mine one of the first steam-engines of Newcomen the 45-inch, modified by Trevithick, sen.; then the 63-inch double of Watt; and, finally, the high-pressure engines of Trevithick, jun.; he saw the open-top cylinders, atmospheric of Newcomen, in the Shammal 45-inch and Wheal Gons 63-inch, with their wooden beams with segment-headed ends, moving in rivalry with the Watt 63-inch double, with cylinder-cover and parallel motion; he saw the two former engines, as altered by Trevithick, jun., using the higher steam from the globular boiler on which Henry Clark worked in 1799, when "there used to be great talking about different boilers, and a boiler of Captain Trevithick's worked with higher steam than the others; and the waggon boiler of Watt, that had just been repaired, was discarded and cut up;" thus described by Trevithick, "the fire-place is 22 feet from fire-door to fire-door, 9 feet wide, and 7 feet thick in fire," [32] which he proposed to replace in 1806 by a cylindrical boiler to give steam of 25 lbs. on the inch.

Pooly also saw the finishing stroke in 1811, when the boilers still known as the Trevithick or Cornish boilers, gave steam to the three engines after a twelve years' fight between low and high pressure, commencing with Trevithick's globular boiler and internal tube, in Dolcoath, in the year 1799, from which time it gained step by step, though in comparatively small engines, up to 1811, when the cylindrical boilers took the place of the condemned hearse and globular boilers, and gave really strong and expansive steam to the three Dolcoath pumping engines that from time immemorial had been rivals, causing all three of them to lift an increased quantity of water, and at the same time to save one-half in the cost of coal; this continued for four or five years, when in 1816 the 63-inch double and the 45-inch, being the youngest and the oldest of the three, were removed, that a new 76-inch cylinder, better adapted to Trevithick's expansive steam might more cheaply perform their joint work. Prior to this change the three engines were known by the names Shammal 45-inch, formerly Bullan Garden, [33] but before that as Carloose, of the period and form of the Pool engine; [34] Stray Park 63 single, formerly Wheal Gons, [35] dated from 1770 to 1777; and the 63-inch double of Watt in 1780.

DOLCOATH MINE,
March 29th, 1858.

SIR,
I have obtained the following information respecting the building of the first cylindrical boilers, as ordered by your late father for Dolcoath; and some information of the results as to the coals consumed, compared with the consumption by the boilers previously in use here.

George Row, now about seventy-two years old, and working at Camborne Vean Mine, says he assisted to build the two first cylindrical boilers with internal tubes used in Cornwall. They were built in Dolcoath Mine in the year 1811 they were 18 feet long, 5 feet diameter, having an oval tube 3 feet 4 inches in the largest diameter at the fire end the other or chimney end of the tube was somewhat smaller. They were found too small for the work to be done, and another boiler was built immediately, 22 feet long, 6 feet 2 inches diameter, and he believed a 4-feet tube.

John Bryant, now seventy-four years old, works a steam-engine at West Wheal Francis. He worked at Dolcoath the 63-inch cylinder double-acting engine, upon Boulton and Watt's plan. When he first worked her she had the old bee-but boiler, 24 feet in diameter. They were taken out for the Boulton and Watt waggon boiler, 22 feet long and 8 feet wide, with two fire-doors opposite one another.

Then the Boulton and Watt waggon was taken out for Captain Trevithick's boilers, which he worked for several years. Two boilers were put in, each 18 feet long, 5 feet diameter, with an internal oval tube, he thinks, 3 feet by 2 feet 6 inches. Shortly after, another boiler of similar form was added, 22 feet long, 6 feet diameter, 4-feet tube.

He cannot say what the saving of coal was, but remembers that the duty performed by the engine with the waggon boiler was thirteen to fourteen millions. Mr. William West came to the mine as an engineer, and by paying great attention increased the duty of the Boulton and Watt engine and boiler to about fifteen millions. He does not recollect the duty the engine performed with the cylindrical boilers.

Mr. Thomas Lean, of Praze, the present reporter of mine engines in the western part of Cornwall, in answer to a note I sent to him, says he has no account of any report of Dolcoath engines for the year 1812, but during the month of April in that year the engines did 21.5 millions. During the whole of 1813 that engine was reported to average a duty of twenty-one millions. The whole of the above are at per bushel of 93 lbs., and the whole of the accounts furnished by Mr. Lean are for Trevithick's cylindrical boilers.

From the Dolcoath Mine books I find the following Paid for coals for the whole mine during the year 1811, £1,150-15s-10d., or per month, £931-14s-7d. During the first three months of 1812 the coal averaged £1,000 per month. In May of this year, 1812, Captain Trevithick is entered on the books as paid £40 on account of boilers; and in August of the same year, for erecting three boilers, £105. I think the three boilers were at work in April, 1812, the month Mr. Lean gives as the first reported. From April, 1812, to December, during nine months, the cost of coals was £5,512-6s, averaging £612-9s-6d per month. During the next year, 1813, the cost for coal was £7,019-17s-5d, or an average per month of £590-16s-5d. I cannot find the price paid per ton for the coal in these years, but the average price during 1808 and 1815 was much alike, making it probable that the price per ton during 1811, 1812, and 1813, was nearly the same; and that the saving of the above £300 per month in Dolcoath was wholly on account of the saving effected by Trevithick's cylindrical boilers.

The testimony of John Bryant, that the duty with the waggon boiler was say fourteen millions, and that of Mr. Lean, giving twenty-one millions with the new Trevithick boiler, bear much the same proportion as the charges for coals in the respective periods above given.

In the year 1816 a new 76-inch single engine was erected in the place of the old Boulton and Watt 63-inch double engine with Trevithick's cylindrical boilers. The average duty performed during the year 1817 was 43.75 millions. This same engine is still at work, and her regular duty is from thirty-six to thirty-eight millions.

I am, Sir,
Your most obedient servant,

CHARLES THOMAS.

FRANCIS TREVITHICK, Esq.


Captain Charles Thomas, who was one of the most experienced of Cornish miners, for many years the manager of Dolcoath, and in youth the acquaintance of Trevithick, states that the new high-pressure boilers were made in the mine in 1811, and gave their first supplies of strong steam to the three large pumping engines in April, 1812, with such good effect that the increasing water which had threatened to drown the mine was speedily removed, and that with a saving of nearly one-half of the coal before consumed. Prior to their use Dolcoath Mine paid £1,000 monthly for coal but for the latter nine months of the year, in consequence of the new boilers, the cost was reduced to £612 a month. This saving in the pumping cost of one mine crowned with success the high-pressure steam engineer, who had been steadily gaining ground during his fight of twelve or fourteen years on the battle-ground chosen by Watt thirty-three years before.

The low price of tin and copper, which caused so many engines to cease working about the close of the last century, had changed for the better, and the present century opened with an increasing demand for steam power. Trevithick's high-pressure portable engines had worked satisfactorily for several years and as a means of making public the relative duty performed by Cornish pumping engines, and of solving conflicting statements on the rival systems of low and high pressure steam, it was determined that an intelligent person should examine and give printed monthly reports of the amount of duty done by the different engines, and in 1810 Captain Andrew Vivian was requested to take this work of engine reporter in hand; on his refusal it was offered to Trevithick. In August, 1811, Mr. Lean commenced such monthly reports, showing that the duty of twelve pumping engines at the end of that year averaged seventeen millions, exactly the duty done by the Boulton and Watt engines thirteen years before, as reported by Davies Gilbert and Captain Jenkin 1798, proving the small inherent vitality of the Watt engine.

In 1814 the Dolcoath pumping engines, with Trevithick's cylindrical boiler and high steam expansion, are thus reported:— "The Boulton and Watt, Dolcoath great double engine, 63-inch cylinder, did a duty of 21.5 millions; the Shammal 45-inch cylinder, single engine, did 26.75 millions; and the 63-inch single, Stray Park engine, 32 millions." Shammal engine, nearly 100 years old, beat the Watt engine of more than half a century later and so did Stray Park 63-inch, which Watt had laughed at when he first tried his hand as an engineer in Cornwall in 1777. [36]

The marked change in these three engines, while for two or three years under Trevithick's guidance, becoming more powerful and economical, raised the usual swarm of detractors, and in 1815 a special trial was made, which lasted for two days, to test the reported increased duty by the cylindrical boilers and expansive working.

The unbelievers were then convinced, and agreed to throw out the Boulton and Watt great double engine 63-inch cylinder, together with its neighbour, the worn-out old 45-inch, and put in their stead one engine with a cylinder of 76 inches in diameter, with expansive valve and gear, and parts strong enough and suitable to the high-pressure steam, on Trevithick's promise that it should do more than the combined work of the other two with one-half the coal.

In 1816 this new engine commenced work, and did forty millions of duty, increasing it during the next two or three years to forty-eight millions, being three times the duty performed by the Watt 63-inch double engine before it was supplied with steam from Trevithick's boilers, and twice as much as it performed when so supplied. Lean says, "This was the first instance of such duty having been performed by an engine of that simple construction." The other mines followed Trevithick's advice, but never paid him a penny. On this Lean again says, "The engines at work in the county in 1835 would have consumed £80,000 worth of coal over and above their actual consumption yearly, but for the improvements that had been made since 1814."

Trevithick's Dolcoath 76-inch Cylinder Pumping Engine, Errected in 1816, Ceased Working 1869. (See key below)
Cylinder, main beam, and Pump-rod of Dolcoath 76-inch Cylinder Engine
Boilers Erected in 1811 at Dolcoath, Used in the Boulton and Watt 63-inch Engine and then in the new 76-inch until 1869. (See key below)

Trevithick's engines were very durable, as well as cheap in first cost and in working expense. This famous Dolcoath 76-inch engine remained in constant work night and day for fifty-four years after which good service the steam-pipes, being thinned by rust, were held together by bands and bolts; the steam-case around the cylinder would no longer bear the pressure of steam; the interior of the cylinder from wear was one inch larger in diameter than when first put in, and had to be held together by strap-bolts. The original boilers were said to remain, only they had been repaired until not an original plate remained but there they were in the old stoke-hole in 1869, when, from the fear of some part of the engine breaking and causing accident, it was removed.

In 1867 the writer was a member of the Dolcoath Managing Committee, when it was determined that the old engine of 1816 should be replaced by a new one. The cylinder sides were reduced in thickness by half an inch; the steam-pipes and nozzles were thinned by rust and decay the valves and gear-work remained in good order. Captain Josiah Thomas, the present manager of, the mine, offered to sell this old engine at scrap price, that it might be stored in the Patent Museum at Kensington as a memento of the early high-pressure expansive steam pumping engine.

The steam-cylinder of 1816 was cast in South Wales; the beam still working in the new engine of 1869 was cast in the foundry of the Williams' at Perran. John West replaced the original flat expansive steam-valve with a double-beat valve; the gear was principally made by him on the mine, and remained in good working to the last. This double-beat valve is the first the writer has met with; it is of the same form as the modern double-beat valve; an earlier plan was to have a small valve on the top of the main valve. The steam in ordinary working was shut off when the piston had moved from an eighth to a quarter of its stroke.

The Gons, or Stray Park 63-inch cylinder, survived its companions, the 63 double, and 45 single, for some ten or fifteen years, having beaten both of them in duty. A memorandum in Trevithick's handwriting shows that he in 1798, when designing his large globular boiler with internal flue at, the reworking of Dolcoath, tested the relative duty of the Watt 63-inch double and the 63-inch single engine, then called Wheal Gons, the latter in its original form of open-top cylinder atmospheric; shortly after which it probably received a cover about the same time as the 45-inch, for both those engines were thoroughly repaired by Trevithick at the reworking of the mine, twelve or fourteen years prior to the use of the cylindrical boilers.

At the time that Boulton and Watt made their trial of Seal-hole engine against Hornblower's engine at Tin Croft, the engines were put in the best order, and good coals brought in for the purpose, to work for twenty-four hours. The trial was attended by the principal mining agents; the result was about ten millions by each engine.

At Dolcoath Mine an old atmospheric engine continued to work for several years by the side of one of Boulton and Watt's engines of the same size; the water lifted and coals consumed were carefully taken and made known to the public, showing that Boulton and Watt's engine performed, when compared with the old engine, as 16 to 1O. [37]


Hornblower was an active engineer in Cornwall before Watt; the patent of the latter claiming the sole right of working an engine by steam in the cylinder, [38] drove the former to use two cylinders, in one of which the expansion was carried out, as a means not described in Watt's patent; a lawsuit was the consequence. The two engines when tried by Trevithick [39] performed an equal duty of ten millions. In 1798 he tested the Dolcoath atmospheric 63-inch single against Watt's great 63-inch double action. "The atmospheric performed ten millions," precisely the duty of the patent Watt and the patent Hornblower contests of six years before; but the Watt Dolcoath engine, then considered the best he had made, did sixteen millions. These trials in 1792 and 1798 enable us to compare the Newcomers, the Hornblower, and the Watt engines shortly after which Trevithick tried higher steam in one or more of those same engines from his globular boiler. [40]

CAMBORNE,
March 10th, 1812.

SIR CH. HAWKINS,
Sir,— This day I shall attend the account at Wheal Prosper mine, in Gwythian, to contract with the adventurers for erecting a steam-engine on my improved plan, for drawing the water 50 fathoms under the adit. I called on Wheal Liberty adventurers at St. Agnes last week, and found that several of them had given up their shares rather than put in a new engine, and the remainder of them very sick.

I told them that I would fork the water with the present engine, and draw instead of 40 gallons each stroke, 47 fathoms deep (which she did), 85 gallons per stroke, 65 fathoms deep, by altering the engine on the same principle as I have done with the Dolcoath great engine, and several more that are now altering. The expense of altering the engine, and forking the water to bottom, and proving the mine, will not exceed £1,000.

All the adventurers are very anxious to again resume their shares and make the trial, on condition that I will undertake the completion of the job at a certain sum, but not otherwise.

I am certain, from what Dolcoath engine is doing, that I can far exceed the power above stated, and perform the duty with one-half the coal the engine consumed before, and would not hesitate a moment to engage the job on the terms they propose, but I have not money sufficient to carry it into execution, as I must lay out a large sum in erecting the engine on the Gwythian Mine, and unless I can be assisted with £500, shall not be able to undertake the job. If you think it worth your notice to encourage this undertaking by lending me the above sum for six months, I will pay you interest for it, and before drawing any part of it from you would get materials in the mine that should amount to above that sum, and also give you an order on the adventurers to repay you the whole sum before receiving any part myself.

As I have been a bankrupt, perhaps you may scruple on that account, but that business is finally settled, and I have my certificate; and indeed never was in debt to any person; not one shilling of debt was proved against me under the commission, nothing more than the private debts of my partner.

At Wendron we are working an engine lately erected on a copper lode, which has a very promising appearance, and near this spot you have land at Besperson, where there is also a very kindly copper lode, which deserves trial; if you are inclined to grant a sett, I think I can find adventurers to join me to try the mine.

I have lately read a letter from your hind, that the engine continues to mend; it far exceeds my expectation. I am now building a portable steam-whim, on the same plan, to go itself from shaft to shaft; the whole weight will be about 30 cwt., and the power equal to twenty-six horses in twenty-four hours.

The only difference in this engine and yours will be the fire in the boiler, and without mason-work, on account of making it portable. I shall pass the rope from the fly-wheel round the cage of the horse-whim.

If you should fall in with any West India planter that stands in want of an engine, he may see this one at work in a month, which will prove to him the advantage of a portable engine, to travel from one plantation to another. The price, completely finished and set to work, free of all expense, in London, £105.

I am, Sir,
Your very humble servant,

RD. TREVITHICK.

N.B.— Captain John Stephens informed me; a few days since, that the lead mine at Newlyn was rich.


In Wheal Prosper Mine the first high-pressure expansive steam-condensing pole-engine had been worked, just before the date of the foregoing letter, and that evidence of increased power and economy was immediately followed by the application of the same principles of high-pressure steam and very expansive working to the Watt low-pressure steam vacuum engines at Wheal Alfred, Dolcoath, and other mines, with such satisfactory results as to warrant his offering, on the battle-ground of his first attack on the Watt low-pressure steam vacuum principle at Seal-hole in St. Agnes, fourteen years before, [41] at his own pecuniary risk, to so apply those principles in the Wheal Liberty low-pressure steam-engine, which had failed to drain the mine, lifting only at the rate of 1,880 gallons of water one fathom high at each stroke; that it should lift an increased quantity of water, and that, too, from an increased depth, making the load equal to 5,525 gallons, and to perform such increase of work with one-half of the quantity of coal before used; in other words, he was willing to engage to make the old low-pressure steam-engine perform by its conversion into a high- pressure steam-engine threefold its original work, and also to increase its duty or economic value sixfold; resting his argument on the similar changes, then to be seen in operation at Wheal Alfred Mine, and especially in the Watt 63-inch double-acting engine at Dolcoath, whose history we have been tracing. Well might Sir Charles Hawkins hesitate to believe what the experience of sixty years has barely sufficed to make plain to us.

PENZANCE,
March 27th, 1813.

CAPTN. TREVITHICK,
Sir, — In consequence of the conversation that has passed between you and West Wheal Tin Croft adventurers, the said adventurers have resolved to put an engine on that mine, agreeable to the proposals offered by you; that is, the engine shall be capable of lifting a 5-inch bucket, 50 fathoms, 4-feet stroke, 15 strokes per minute, or a duty equal thereto; for which they will pay you 50 guineas one month after the engine shall be at work, and 50 guineas more at four months after that, and 50 guineas more at four months from that time, making the full payment of 150 guineas in nine months from the time the engine shall set at work, the adventurers paying all expense, except the engine materials, which shall be delivered on the mine. But in case the engine not performing the above duty, the adventurers to be at liberty to return the same engine, and you to pay back all the money that you had received for the said engine.

Signed by GABL. BLEAVETT,
in behalf of the Adventurers and Company.


Trevithick was willing to spend more than his last penny in establishing the superiority of his high-pressure steam expansive engines, but the selfishness of adventurers retarded their progress. The atmospheric, mentioned by Watt as working in Dolcoath in 1777, [42] did five or six millions of duty, yet in Trevithick's hands, about 1798 to 1800, when he erected his globular boiler with internal tube, one of them was tested with the 63-inch Watt low-pressure vacuum engine, when the latter did sixteen millions to ten millions by the atmospheric engine, being nearly double the duty it performed in its original form; and we shall still trace this same engine as Bonze or Gons until it increased to six times its first duty under the name of Stray Park 63-inch.

Trevithick having erected a high-pressure steam condensing whim-engine at Cook's Kitchen [43] and Dolcoath a high-pressure puffer whim-engine, pleaded hard in 1806 [44] to be allowed to supply the large pumping engines of Newcomen and Watt with higher pressure steam from his cylindrical boiler, which after years of consideration Dolcoath, in 1811 agreed to. 1813 he wrote -

That new engine you saw near the sea-side with me is now lifting forty millions, one foot high, with one bushel of coal, which is very nearly double the duty that is done by any other engine in the county. A few days since I altered a 64-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. [45]


The beneficial results of those acts are too large to be here entered into in detail. In round numbers, the early pumping engines of Newcomen did five millions; [46] Trevithick caused them to do ten millions of duty with a bushel of coal. Watt, during thirty years of improvements, caused the duty to reach sixteen or twenty millions in 1800. Trevithick, on the expiry of the Watt patent, then came into play, and before he had reigned half the time of Watt, again doubled the duty of the steam-engine, as he states in 1813 "his new engine was doing forty millions, being nearly double the duty of any other engine in the county." These statements by Trevithick agree very nearly with the generally-received accounts of the progressive duty of the large pumping steam-engine.

In 1798 Davies Gilbert, Esq., and the late Captain Jenkin of Treworgie, found the average of the Boulton and Watt engines in Cornwall to be about seventeen millions. In August, 1811, the eight engines reported averaged 15.7 millions. During the year 1814 Dolcoath great engine, with a cylinder of 63 inches in diameter, did twenty-one and a half millions nearly. Dolcoath Shammal engine, with a cylinder of 45 inches in diameter, did three-quarter millions. Dolcoath Stray Park twenty-six and engine, with a cylinder of 63 inches in diameter, did thirty-two millions.

In 1815 a trial was made, to prove the correctness of the monthly reports. Stray Park engine at Dolcoath was chosen for the purpose, because its reported duty was such as led some persons to entertain doubts of its accuracy. The trial was continued for ten days, to the full satisfaction of all concerned.

In 1816, Jeffrie and Gribble erected a new engine, 76-inch cylinder, single, at Dolcoath, which did forty millions. This was the first instance of such duty having been performed by an engine of that simple construction.

In 1819, Dolcoath engine performed the best during this year, and at one time reached forty-eight millions.

In 1820, Treskerby engine, to which Trevithick's high-pressure pole had been adapted, reached 40.3 millions.

In 1816, Sims also erected an engine at Wheal Chance, to he applied the pole adopted by Trevithick in his high-pressure engines. This engine attained to forty-five millions.

In 1828 public attention had now been attracted to the improvements which Captain Grose had introduced into his engine at Wheal Towan. The duty of this engine, in the month of April this year, equalled eighty-seven millions.

This again gave rise to suspicions of error in the returns. This engine was accordingly subjected to a trial (as Stray Park engine had been in 1815), which was superintended and conducted by many of the principal mine agents, engineers, and pitmen of other mines.

The quantity of coal consumed in 1835, compared with the quantity that would have been consumed by the same engines in the same time, had they remained unimproved from the year 1814, shows that the saving to the county amounts to 100,000 tons of coal, or £80,000 sterling per annum. [47]


Lean seems to have calculated on a bushel of coal as 94 lbs. In 1798, when Trevithick was about to give increased pressure of steam to the Cornish engines, his friend Davies Gilbert reported the average duty of the Watt engine in Cornwall to be seventeen millions.

In August, 1811, the reported duty averaged 15.7 millions. This was the month and year in which Trevithick, after twelve years of working evidences of the reasonableness of his promises of increased power and economy from using high-pressure steam, was allowed to erect his cylindrical boilers for the large pumping engines in Dolcoath Mine.

Has the reader realized that the 45-inch atmospheric Carloose engine, of nearly 100 years before, [48] had in 1775 [49] become the Bullan Garden engine of Trevithick, sen., which was improved and re-erected by Trevithick, jun., in 1799, [50] when the name was again changed, this time to Shammal, because it was linked to another engine, no other than the Watt 63-inch double engine? This Shammal 45-inch took steam from the globular boiler, using a pole air-pump [51] and a Watt condenser, though retaining the beam with the arched head and chain connection; and again in 1811 took still more highly expansive steam from the cylindrical boilers with a new beam and parallel motion, enabling it in 1814 to beat its rival, the Watt Dolcoath great double engine. [52] The old 63-inch Gons, under the name of Dolcoath Stray Park engine, with Trevithick's improvements, did sixty-seven per cent. more work than the Watt 63-inch with an equal quantity of coal. This startling fact was disbelieved by the advocates of low-pressure steam, and as the visible change in the Dolcoath engine from Newcomen to Watt, and from Watt to Trevithick, had been gradual and not very striking, and the public were careless of principles, the one most puffed was most thought of; but the money saved was tangible, and in 1815 a special trial was made, which lasted two days, to discover if it was really true that Trevithick's appliances could so increase the duty of the engine. The 63-inch cylinder, then called Stray Park engine, was selected; the result proved that the large saving reported from Trevithick's boilers and expansive working during the last three or four years, was an incontrovertible fact.

The high-pressure steam was also given to the defeated Watt 63-inch double engine; yet this newest of the three engines was the first to be condemned, and her place was taken in 1816 by an engine of 76 inches in diameter, which Trevithick promised should, with his high steam and new expansive gear, do the work of the Watt 63-inch and the old 45-inch put together which was more than fulfilled by its doing forty millions, and, as Lean says, "was the first instance of such duty having been performed by an engine of that simple construction."


In 1819 the new 76-inch engine which had been erected by the mine engineers, Jeffrie [53] and Gribble who had long been employed by Trevithick in Dolcoath, was the best in the county, doing forty-eight millions, nearly three times the duty as given by Mr. Gilbert for the Watt engine in 1798. In 1827 Trevithick's pupil, Captain Samuel Grose, erected his Wheal Towan engine, which performed a duty of eighty-seven millions, some of the working drawings of which were made by the writer. In 1835 the principle laid down by Trevithick had become so general in the county as to cause a saving to the Cornish mines, in coal alone, of £80,000 yearly. In addition to this, the increased power of the engine lessened the first cost by at least one-half.

The national importance of such weighty facts calls for further corroborative proof, for we can scarcely believe that two atmospheric low-pressure steam-engines, made before the time of Watt, could be altered so as to perform more work, and at a less cost than the Watt engine, by an ingenious supply of higher steam pressure from Trevithick's boilers, together with the Watt air-pump and condenser. The following words from Watt are descriptive of his practice, though contrary to his patent claim:-

At a very early period, while experimenting at Kinneil, he had formed the idea of working steam expansively, and altered his model from time to time with that object. Boulton had taken up and continued the experiments at Soho, believing the principle to be sound, and that great economy would attend its adoption.

The early engines were accordingly made so that the steam might be cut off before the piston had made its full stroke, and expand within the cylinder, the heat outside it being maintained by the expedient of the steam-case. But it was shortly found that this method of working was beyond the capacity of the average enginemen of that day, and it was consequently given up for a time.

"We used to send out," said Watt to Robert Hart, "a cylinder of double the size wanted, and cut off the steam at half-stroke."

This was a great saving of steam, so long as the valves remained as at first; but when our men left her to the charge of the person who was to keep her, he began to make, or try to make, improvements, often by giving more steam. The engine did more work while the steam lasted, but the boiler could not keep up the demand. Then complaints came of want of steam, and we had to send a man down to see what was wrong.

This was so expensive, that we resolved to give up the expansion of the steam until we could get men than could work it, as a few tons of coal per year was less expensive than having the work stopped. In some of the mines a few hours' stoppage was a serious matter, as it would cost the proprietor as much as £70 per hour. [54]


Pole expresses the same view, intimating that Watt only used team of 1 or 2 lbs. pressure to the inch.

In Watt's engine, as is well known, the pressure of steam in the boiler very little exceeded the pressure of the atmosphere. He recommended that when the engine was underloaded, this excess should be equal to about 1 inch of mercury; and when full loaded, ought not to exceed 2 inches; adding, "It is never advisable to work with a strong steam when it can be avoided, as it increases the leakages of the boiler and joints of the steam-case, and answers no good end." [55]

Mr. Watt's engines with such boilers (which will not retain steam of more than 3 1/6 lbs. per square inch above the atmosphere) cannot be made to exert a competent power to drain deep mines, unless the supply of steam to the cylinder is continued until the piston has run through more than half its course. [56]

In 1801-2 Captain Trevithick erected a high-pressure engine of small size at Marazion, which was worked by steam of at least 30 lbs. on the square inch above atmospheric pressure. In 1804, as Mr. Farey admits, [57] the same gentleman introduced his celebrated and valuable wrought-iron cylindrical boilers, [58] now universally used in this county.

To these, everyone at all acquainted with the Cornish improvements ascribes a great part of the saving we have obtained. This will further appear from an extract from a valuable work edited by John Taylor, Esq., F.R.S. [59]

The monthly consumption of coal in Dolcoath Mine was, in 1811, 6,912 bushels in 1812, 4,752 bushels. [60] The alteration in the boilers was the introduction of Captain Trevithick's cylindrical boilers in the Place of the common waggon boilers, which had until then been there in use.

Mr. Woolf, as Mr. Farey states, came to reside in Cornwall about the year 1813, and his first engines for pumping water from mines were set up by him in 1814.[61]


The foregoing was read at the Philosophical Society in 1831, to refute erroneous statements on the Watt and Trevithick engines. My friend Mr. Henwood had at that time made official experiments in conjunction with Mr. John Rennie on the detail, working, and duty of high-pressure steam Cornish engines, the Watt low-pressure steam principle having been wholly given up. Rees's 'Cyclopedia' [62] also bears the following similar testimony to date of the increased duty:—

Trevithick's high-pressure engine was erected in Wales in 1804 to ascertain its powers to raise water. The duty was seventeen millions and a half pounds raised one foot high for each bushel of coals.

The high-pressure steam-engines require a greater quantity of coals, in proportion to the force exerted, than the engine of Mr. Watt, and consequently are not worked with advantage in a situation where coals are dear.

From the reports of the engines now working in the mines of Cornwall, which, with the exception of a few of Woolf's engines, are all on Mr. Watt's principle, and most of them constructed by Messrs. Boulton and Watt, taking the average of nine engines — bad, good, and indifferent together — they were found in August, 1811, to raise only thirteen millions and a half. But when it was known by the engine keepers that their engines were under examination, they took so much pains to improve the effects, that by gradual increase the engines in 1815 lifted twenty-one millions and a half, taking the average of thirty-three engines. In 1816, Stray Park, a 63-inch cylinder, 7 feet 9 inches stroke, single-acting, being one of the three engines on the vast Dolcoath Mine; its performance in four different months was thirty-one, thirty-one and a quarter, twenty-eight, and twenty-eight and a half millions.


This statement reveals a source of error in estimating the relative values of the Watt and the Trevithick engine; that of the latter was the Welsh locomotive, compared in duty with the large Watt pumping engine, pointed out in Trevithick's letter [63] of that time, as an unfair comparison the small high-pressure puffer, in 1804, is admitted to have done seventeen and a half millions of duty with a bushel of coal of 84 lbs., while in Rees' calculation of the engines, he gives Watt 94 lbs, of coal to a bushel and having stated that the Waft pumping engines in Cornwall, in 1811, averaged but thirteen and a half millions of duty, draws the false conclusion that the high-pressure cannot compete with the low-pressure where coals are dear; yet he agrees with other writers that the great increase in the duty of the Cornish pumping engines commenced from 1811 (when Trevithick first gave them his high-pressure steam); and states that in 1816 the Stray Park 63-inch cylinder single-acting engine, [64] being one of three then working in Dolcoath did thirty-one millions.

The 'Encyclopedia Britannica ' on the question of duty states:- [65]

The duty of the best of Smeaton's engines was, in 1772, 9,450,000 foot pounds per cwt. of coal. On the expiration of Watt's patent, about the year 1800, the highest duty of his engines amounted to twenty millions, or more than double the former duty, which may represent the economical value of the improvement effected by Watt under his various patents.

The reported duty of Cornish pumping engines, by the consumption of 94 lbs. of coals, rose from an average of nineteen millions and a half, and a maximum of twenty-six millions in 1813, to an average of sixty millions and a maximum of ninety-six millions in 1843. It is necessary to bear in mind the distinction between the duty of a bushel of coal and 112 lbs.


Here, also, are the same general facts as to the duty of the Watt, engine, and the marked and rapid increase of duty dating from Trevithick's Dolcoath engines in 1811; but the confusion and even contradictions in the statements prove how little the subject was understood.

A rough draft, prepared by Mr. Edmonds on Trevithick's return from America, dated 1828, for an application to Parliament for remuneration to Trevithick, says, "That this kingdom is indebted to your petitioner for some of the most important improvements that have been made in the steam-engine."

"That the duty performed by Messrs. Boulton and Watt's improved steam-engines in 1798, as appears by a statement made by Davies Gilbert, Esq., and other gentlemen associated for that purpose, averaged only fourteen millions and a half (pounds of water lifted 1 foot high by 1 bushel of coal), although a chosen engine of theirs under the most favourable circumstances lifted twenty-seven millions, which was the greatest duty ever performed till your petitioner's improvements were adopted, since which the greatest duty ever performed has been sixty-seven millions, being much more than double the former duty. That, prior to the invention of your petitioner's boiler, the most striking defect observable in every steam-engine was in the form of the boiler, which in shape resembled a tilted waggon, the fire being applied under it, and the whole being surrounded with mason work. That such shaped boilers were incapable of supporting steam of a high pressure or temperature, and did not admit so much of the water to the action of the fire as your petitioner's boiler does, and were also in other respects attended with many disadvantages. That your petitioner's invention consists principally in introducing the fire into the midst of the boiler and in making the boiler of a cylindrical form, which is the form best adapted for sustaining the pressure of high steam."

"That the following very important advantages are derived from this your petitioner's invention. This boiler does not require half of the materials, nor does it occupy half the space required for any other boiler. No mason work is necessary to encircle the boiler."

"That, had it not been for this your petitioner's invention, those late vast improvements which have been made in the use of steam could not have taken place, inasmuch as none of the old boilers could have withstood a pressure of above 6 lbs. to the inch beyond the atmosphere, much less a pressure of 60 lbs. to the inch, and is capable of standing a pressure of above 150 lbs. to the inch."


Trevithick's retrospect views of 1828 are supported by the letter of the late Michael Williams, M.P., the most experienced of Cornish mine workers, but belonging to the eastern district that had been for many years the users of the Watt engines in Cornwall.

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 boilers, 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 overestimate the benefit conferred, either directly or indirectly, by the late Mr. Trevithick on the mines of this county. I have often expressed my opinion that he was at the same time the greatest and the worst-used man in the county. [66]


The late Sir John Rennie and other scientific persons were, about 1830, associated with Mr. Henwood [67] in examining the work performed by Cornish pumping engines: their reports are curtailed in the following comments on Wheal Towan engine, similar to Trevithick's Dolcoath engine of 1816, except perhaps that the last named was a little inferior in its detail movements, while much less care was taken to avoid unnecessary loss of heat. Mr. Henwood also gave indicator diagrams of the expansion of the steam, on one of which the writer has marked ten horizontal lines, indicating the position of the piston at each foot of its stroke, and ten longitudinal lines dividing the diameter of the cylinder into tenths. The steam pressure in the boiler was 4.68 lbs. on the square inch above the atmosphere, or 4.68 lbs. for each of the ten longitudinal line divisions. x to F the length of the cylinder for a 10-feet stroke of the piston. By the time the piston had moved through one-twentieth of its course, reaching c, the expansive working had commenced; and when one-tenth of the stroke had been run half of a division was cut off, showing by the curved indicator line the decrease in pressure of steam to 44.46 lbs. The comparatively small passage through the steam-valve not giving room for sufficient steam to follow up the increasing speed of the piston, led to its continued expansion in the cylinder, and by the time the piston had moved 2 feet, reaching D, the steam pressure was reduced by two divisions or 9.36 lbs., or a pressure of 37.44 lbs. on the piston at this point the steam-valve was closed, and the remaining four-fifths of the stroke was performed by expansion at the fifth horizontal line, or middle of the stroke, only three divisions of steam are left, giving a pressure of 14.04 lbs. to the inch; at the finish of the stroke there is only half a division, from E to F, or 2.34 lbs. of steam to the inch above the pressure of the atmosphere. On the return up-stroke of the piston, when it had reached within a foot of the finish of its course at C, the equilibrium valve closed, causing the enclosed steam of 2.34 lbs, to the inch to be compressed at the finish of the up-stroke shown by the curve G A to 9.36 lbs. on the inch, equal to its pressure about the middle of the down-stroke at N.

Trevithick's expansive engine therefore, commencing its work with steam of 46.8 lbs, on the inch above the atmosphere, only took a full supply from the boiler during one-tenth of its stroke, and none after one-fifth had been performed, while at the finish of the stroke it had about the same pressure, as Watt began with. The power of the Watt low-pressure steam vacuum pumping engine was increased by Trevithick from two to three fold, and its economical duty in about the same proportion; in other words, he increased the effective power of the steam-engine two or three fold without additional consumption of coal.

In the Wheal Towan engine the steam-cylinder was 80 inches in diameter, with a 10-feet stroke. The shaft was 900 feet in depth; the main pumps 16 inches in diameter; the pump-rods were of wood, about 14 inches square, and weighed more than the column of water in the pipes. The boilers were Trevithick's cylindrical with internal tube, wholly of wrought iron. The cylinder and steam-pipes were surrounded with sawdust about 20 inches in thickness, as a non-conductor of heat. The upper surfaces of the boilers were covered with a layer of ashes for the same purpose. The duty performed was 86.58 millions of pounds of water, raised one foot high by the consumption of a bushel of coal weighing 84 lbs. The immense power and economy of this engine are best understood by its average labour costing only one farthing in coal for lifting 1,000 tons one foot high.

At or about that time an old intimate of Trevithick's, Captain Nicholas Vivian, managed the mine, and Mr. Neville, a shareholder, also a user of steam-engines in Wales, observing the economical working of Wheal Towan high-pressure steam expansive engine, doing eighty-seven millions, requested its manager to examine colliery engines, all of which were of the low-pressure kind; one of them was a Newcomen atmospheric, whose duty was six millions; four or five others were Watt low-pressure steam vacuum engines, doing fourteen millions; therefore the high-pressure steam-engine did six times as much work with a bucket of coal as the low-pressure steam vacuum, and fourteen times as much as the low-pressure steam atmospheric engine. Several competitive trials by the county engineers were published about that time, in one of which, after a personal examination of the engine, Mr. W. J. Henwood [68] and others reported a duty of 92.6 millions with a 91-1b. bushel of coal. [69]

Mr. Rennie had been a pupil, a fellow-worker with low-pressure Watt, and while his son, Sir John Rennie, was examining the high-pressure steam expansive engine erected by Trevithick's pupil, Captain Samuel Grose, under the management of Trevithick's friend, Captain Nicholas Vivian, the latter was engaged in reporting on certain low-pressure steam-engines in Wales, one of which was a Newcomen's atmospheric, probably the last of its race, whose principle of construction was a century old, working in company with the Watt low-pressure steam vacuum engine, then half a century old, the principles of both systems being on their last legs, and under the care of Trevithick's supporters.

During this jumble of engines, old and new, without a clear comprehension of their differences in principle, Trevithick, who had just returned from America, and lived within a few miles of Wheal Towan looked on unconsulted and unconcerned on questions which in his mind had been settled by him in Dolcoath fifteen or twenty years before. The writer, during the Wheal Towan controversy, was the daily companion of Trevithick, and made drawings of the engine at the works of Harvey and Co., of Hayle, where it was constructed about 1827.

Captain Samuel Grose's Wheal Towan engine was in general character similar to his teacher's Dolcoath 76-inch engine of 1816, working with about the same steam pressure and degree of expansion. The valves, gear, and nozzles were perhaps improved in detail but the groundwork was unchanged. The first high-pressure steam Cornish pumping engine made in France was designed and superintended by the writer at the works of Messrs. Perrier, Edwards, and Chaper, at Pompe-h-feu, in Chaillot, a suburb of Paris. The principle was the same as the Dolcoath engine, and the detail differed but little from it or the Wheal Towan, except that its exterior was a little more artistic than its prototypes in Cornwall, in keeping with French requirements. It was built in 1836, within a few yards of the low-pressure steam pumping engine erected by Perrier and others in 1779, which still continued pumping water from the Seine for the supply of Paris. Stuart says,-

An engine by Boulton and Watt was sent to France, and erected by M. Perrier at Chaillot, near Paris. The French engineer, Proney, with a detestable illiberality, attributes all the merit of the improvements in the Chaillot engine to his friend Perrier, the person who merely put together the pieces he had brought from Soho. [70]


The Perrier of 1779 was related to the Perrier of the Pompe-a-feu engine-building works of 1836, and his nephew took the Trevithick engine from Paris to a coal mine not far from Brussels, but not fully understanding the use of the balance-bob — the woodwork for which had not been completed in Paris, though all other parts bad been fully erected — did not find it easy to manage the engine. The writer viewed Perrier's move as an infringement of the agreement between him and Edwards, the partner of Perrier and Chaper, and therefore declined to take any further interest in the engine.

Mr. Edwards had before that been a partner with Woolf, in a small engineering works in Lambeth; and the writer had also before that been a pupil of Woolf's, in the works of Messrs. Harvey and Co., of Hayle.

Plate XIII. La Belle Machine

The drawing of La Belle Machine ' (Plate XIII.), of 1836, serves not only as a record of that time, but also in conjunction with the drawing of Dolcoath engine of 1816, enables an engineer to form a sufficiently correct idea of the Wheal Towan engine and boilers of 1827, which in effective duty is scarcely excelled by the best pumping engines of the present day.

The events connected with those Paris engines bring together the engineering works of Watt, Proney, Perrier, Trevithick, and Woolf, in the person of his once partner, Edwards. The writer, when constructing 'La Belle Machine,' had not the slightest knowledge of those links, and heard the name and repute of his engine by the following chance:-

In 1838 a passenger leaving the train of the Great Western Railway at Drayton Station, asked the writer's permission to walk on the line and examine its construction. During a short conversation he mentioned the having purchased at a sale in France the drawings of an engine known as 'La Belle Machine,' representing the Cornish high-pressure expansive steam pumping engine:— a, steam-cylinder, 48 inches in diameter, 8-feet stroke; b, steam-pipe from boiler; c, regulating steam-valve, double beat; d, regulating rod and handle for steam-valve; e, expansive steam-valve double beat; f, balanced lever and rod for opening expansive valve expansive clamp on plug-rod, with regulating rod and thumb-screws; h, cataract-rod for relieving expansive valve-catch; i, quadrant relieving the catch; j, plug-rod; k, equilibrium valve, double beat; l, clamp in plug-rod to close equilibrium valve by its action on the handle; m, balanced lever and rod to open equilibrium valve; n, quadrant and catch relieving equilibrium valve by the action of cataract-rod; o, regulating slide on cataract-rod; p, equilibrium stem-pipe conveying steam from the top to the bottom of the piston; q, exhaust-valve, double beat; r, clamp on plug-rod, closing the exhaust-valve by its descent on the handle; s, balance lever and rod, opening exhaust-valve; t, quadrant and catch, relieving equilibrium valve by the action of cataract-rod; u, regulating slide on cataract-rod; v, exhaust-pipe to condenser; w, Y-posts for carrying the gear. The steam in the boiler was from 40 lbs. to 50 lbs, on the square inch above the atmosphere.

Lean states that had the pumping engines at work in Cornwall in 1835 remained unimproved since 1814, at which time they had benefited by three years of continuous improvement, a yearly additional expenditure of £80,000 for coal would have been the consequence, and that the first step was Trevithick's expansive steam from the cylindrical tubular boiler, engines using such steam performing a duty three or four fold what Boulton and Watt had ever attained, or perhaps thought possible of attainment. [71] The birth of the idea of using expansive steam may in truth be traced back nearly one hundred years to the time of Newcomen's atmospheric engine, and the hope expressed in 1746 of a smaller boiler and more elastic steam [72] was partially realized in the engine and boiler of Trevithick, sen., in Bullan Garden in 1775, followed in 1780 by the competing engine erected by Watt in Dolcoath Mine, under Trevithick's management. Little further change was made until 1799, when the globular boiler and internal tube of Trevithick, jun., gave a second start to the use in large engines of more expansive steam and even this partial move was the result of years of thought and practical experiment for in 1792, when twenty-one years of age, he was the elected judge on a competitive trial between the Watt engine at Seal-hole, patented in 1782, and Hornblower's double-cylinder engine at Tin Croft. Each engine performed a duty of ten millions, both of them were called expansive, while in fact neither of them were so, for the pressure of the steam in the boiler did not admit of it. As Lean says, " As the steam used was raised but little above the pressure of the atmosphere, it was found that the power gained did not compensate for the inconvenience of a more complicated and more expensive machine." Or, as Watt said to Robert Hart,"We resolved to give up the expansion of the steam until we could get men that could work it," as he found it more costly than profitable. Again in 1798, Trevithick's own writing records his experiment in Dolcoath between the Bullan Garden 45-inch atmospheric engine and the Watt 63-inch great double-acting engine, when the latter did sixteen millions to ten millions by the atmospheric. At that very time he was constructing his high-pressure steam portable engines, and in the following year, after seven years of most active experience, prompted by the Watt lawsuit against Cornish engineers, he in 1799 gave the beaten 45-inch engine steam of a higher pressure from the stronger globular boiler. People following the ideas of Watt, were still afraid of Trevithick's plans, distinctly laid down in his letters of 1806, recommending a cylindrical boiler for the Dolcoath pumping engine, because similar boilers giving steam to his whim-engines have enabled them to beat the Watt whims. This continued until 1810, when the greatly increased power and economy of the high-pressure expansive steam pumping engine at Wheal Prosper caused the neighbouring Dolcoath in 1811 to give Trevithick's plans free scope. The long smouldering rivalry between low and high pressure, on the eve of the final discomfiture of the former, burst forth in loud words and evil prognostications, causing the mining interest of Cornwall to appoint an examiner who should publish monthly the duty performed by the various pumping engines, the first of which appeared in the autumn of 1811, when Trevithick was building his boilers in Dolcoath, and preparing the engines, as far as was possible, to submit to strong steam. By expansive valves and suitable gear, balance of power between the engine and the pump-work necessitating balance-bobs, strengthening the pit-work to bear the more powerful and sudden movement, and fifty other things, which we know must have presented themselves in such work, occupied the greater part of Trevithick's time from 1811 to 1814. That first report enumerates twelve pumping engines, probably all of them Watt engines, averaging a duty of seventeen millions.

We have before traced the rapid and immense increase in the power and in the duty of Cornish pumping engines from 1811, and it may be taken as comparatively true in the larger sense applying to the improvement of the steam-engine everywhere.

Dolcoath Mine, one hundred years ago, under the management of Trevithick, sen., followed by his son as the strong-steam engineer, and by his grandson as one of the committee of management in these modem times, has served during that long period to illustrate the progress of the steam-engine, and still in active service, was thus spoken of in 'The Times' of Dec. 18th, 1871: - This old and extraordinary mine is how raising about 100 tons of tin every month, worth from £8,000 to £9,000.

See Also

Foot Notes

  1. Borlase's 'Natural History of Cornwall.'
  2. See drawing, vol. i., p. 25.
  3. See Pryce's 'Mineralogia Cornubiensis,' published 1778. Appendix.
  4. Smiles' 'Lives of Boulton and Watt.'
  5. See vol. i., p. 30.
  6. Lean's 'Historical Statement of Steam-Engines in Cornwall,' p. 7.
  7. Records of Mining,' by John Taylor, FRS., &c., part i., p. 155; published 1829.
  8. See vol. i., p. 95.
  9. Henry Clark's recollections in 1869.
  10. Working in the Valley smiths' shop, in Dolcoath Mine, in 1869.
  11. See vol. i., p. 25.
  12. See vol. i., p. 128.
  13. Stuart's 'History of the Steam-Engine,' published 1824.
  14. See Trevithick's letter, August 22nd, 1802, vol. i., p. 153.
  15. See Trevithick's letter, May 2nd, 1803, vol. i., p. 158.
  16. See vol. i., p. 128.
  17. See Trevithick's 'letter, 22nd February, 1804, vol. i., p. 161.
  18. See Trevithick's letter, 4th March, 1604, vol. i., p. 166.
  19. See Trevithick's letter, 9th March, 1804, vol. i., p. 168.
  20. Recollections of Henry Clark, living at Redruth in 1869.
  21. See Trevithick's letter, January 10th, 1805, vol. i., p. 324.
  22. Banfield's recollections in 1869.
  23. Reflections of Captain G. Eustace, engineer, residing at Hayle, 1868.
  24. See vol. i, p. 25.
  25. See vol ii., p. 119.
  26. Old John Bryant's statement in 1858.
  27. Clark's recollections in 1869, when he was eighty-three years old, and resided at Redruth.
  28. Captain Nicholas Vivian was a schoolfellow and intimate friend of Trevithick's, he resided at Camborne in 1858, when he gave his recollections.
  29. William Pooly worked the Dolcoath 76-inch engine in 1869; his recollections were given in the old engine-house, on the spot Once occupied by Watt and his 63-inch great double engine.
  30. Smiles speaks of this as Bonze's.
  31. Three Wests, all skillful mechanical engineers, were employed at that time in Dolcoath, all of them known to the writer, who thinks the double-beat valve was the handiwork of John West, not related to Trevithick's partner
  32. See Trevithick's letter, February 18th 1806 vol ii. p. 143.
  33. See vol. i., p. 25.
  34. See vol i., p. 5.
  35. Query Bonze, spoken of by Smiles.
  36. See vol. i., p. 30; vol. ii., p. 115.
  37. Memorandum in Trevithick's writing.
  38. See vol. i., p. 46.
  39. See vol. i., p.57
  40. See vol. ii. p. 119.
  41. See vol. i., p. 90.
  42. See vol. i., pp. 30, 57; vol. ii., p. 115.
  43. See vol. i., p. 91.
  44. See vol. ii., p. 142.
  45. See Trevithick's letter, January 26th, 1813, vol. ii., p. 55.
  46. See vol. i., p. 41.
  47. Lean's 'Steam-Engine in Cornwall.'
  48. See vol. i., p. 21.
  49. See vol. i., p. 25.
  50. See vol. ii., p. 120.
  51. See vol. ii., p. 122.
  52. See Lean's report, vol. ii., p. 175.
  53. See vol. i., p. 106.
  54. Smiles 'Lives of Boulton and Watt,' p. 228.
  55. Appendix A to Tredgold, 'Pole on Cornish Engines,' p. 49.
  56. 'Phil. Mag. and Annals,' N.8., vol. viii., p. 309, by W. J. Henwood.
  57. Ibid., p. 313.
  58. Ibid., vol. i., p. 127.
  59. Records of Mining,' p. 163.
  60. Alteration in the boilers that year.
  61. 'Phil. Mag. and Annals,' vol. x., p. 97, 'Notes on Some Recent Improvements of the Steam-Engine in Cornwall', by W. Jory Henwood, F.G.S.
  62. See Rees 'On the Steam-Engine.' published 1819.
  63. See vol. i., p. 166.
  64. See Watt's statement, vol. ii., p. 115.
  65. See 'Steam-Engine,' published 1860.
  66. See letter of Michael Williams, chap. xix
  67. Henwood, 'Edinburgh Journal of Science,' 10.
  68. Address, Royal Institution of Cornwall, by W. J. Henwood, 1871.
  69. Trevithick calculated 84 lbs. to a bushel; Watt generally 112 lbs.; Lean: 94 lbs., but latterly 112 lbs.
  70. Stuart 'On the Steam-Engine', p. 141.
  71. See Lean's Historical Statement, p. 154; published 1839.
  72. See vol. i., p. 7.
  • TREVITHICK'S DOLCOATH 76-INCH CYLINDER PUMPING ENGINE, ERECTED IN 1816, CEASED WORKING 1869. (see drawing above)
    • a, steam-cylinder, 76 inches in diameter, 9-feet stroke;
    • b, steam jacket;
    • c, steam expansion-valve, 11 inches diameter, double beat; the up per beat 11 inches diameter, the under beat 9.5 inches, valve 8 inches long;
    • d, expansive cam on plug-rod;
    • e, plug-rod for moving the gear;
    • f, expansive horn;
    • g, equilibrium valve, 13 inches in diameter, single beat moved by a tooth-rack and segment;
    • h, exhaust-valve, 14.5 inches in diameter, single beat moved by a lever and link;
    • i, equilibrium-valve handle;
    • j, exhaust-valve handle;
    • k, Y-posts for carrying the gear arbors;
    • 1, main beam in two plates of cast iron;
    • m, parallel motion;
    • n, feed-pump rod;
    • o, air-pump bucket-rod, the pump, 2 feet 9 inches diameter;
    • p, the main pump rods.


  • CYLINDER, MAIN BEAM, AND PUMP-ROD OF DOLCOATH 76-INCH CYLINDER ENGINE. BOILERS ERECTED IN 1811 IN DOLCOATH, USED IN THE BOULTON AND WATT 63-INCH ENGINE, THEN IN THE NEW 76-INCH UNTIL 1869. (see drawing above)
    • a a, two wrought-iron cylindrical boilers, 5 feet in diameter, 18 feet long, with internal fire-tube, oval, 3 feet 4 inches by 3 feet;
    • b, a boiler, 6 feet 2 inches diameter, 22 feet long, cylindrical tube, 4 feet diameter in the tire-place, the remainder 3 feet;
    • c, brick bridge;
    • d, fire-bars;
    • e, brick external flues under toiler;
    • f, brick side-flues;
    • g, ashes, or other non-conductor; steam 30 to 50 lbs. on the inch above the atmosphere.