Amongst my great-grandfather’s papers is a typewritten manuscript with the following text. It is apparently a draft of a paper intended for publication based on lectures which he had previously given.

He died the following year and appears to have got no further with it, so I have no idea where, or in what form he intended to publish. It is clearly not complete, and the final version would certainly have included illustrations and his photographs. Some of his photos I have posted elsewhere on this site have come from a box labelled “lecture notes” and would be suitable for inclusion.

I present the text here in the form I have it, the only changes I have made are to include the pencilled alterations and corrections he made to the draft.

 

Notes on the History of the Steam Engine.

Thomas Newcomen, James Watt and the Steam Engines.

By Clarence Owen Becker M.I.Mech.E.  August 1946.


The knowledge of the force of steam as a source of power applied for useful purposes dates from about the year 1700, so that the Steam Engine as we know it today is comparatively a modern invention This is the more surprising when Hero of Alexandria in a recorded list of mechanical inventions described what is generally considered as the first steam engine. This consisted of a copper globe suspended between trunnions through one of which steam passed from a boiler below. The steam from the globe issued from two nozzles directed tangentially and by its reaction caused the globe to revolve. The date of this invention is obscure but is believed have been about 150 to 200 B.C. A model of this interesting toy can be seen at South Kensington Museum working with compressed air instead of steam. It is known as Hero's Eolipile.

Nothing further was done to advance the knowledge of steam for over over 1500 years when Salomon de Caus a French Architect in 1615 wrote his book “Les Raisons des forces mouvante” in which he described a method of raising water by the pressure of steam in a boiler with a pipe rising from it. Later the Marquis of Worcester wrote his "Century of Invention" 1663, in which he described in ambiguous terms a machine for raising water which was really nothing more than Salomon de Caus’s  ideas over again. In 1643 Torricelli an Italian made some surprising discoveries in connection with the vacuum and the pressure of the atmosphere. Otto von Guericke, burgomaster of Magdeburg in Germany, in 1650 invented the air pump with a piston working in a cylinder with which he produced a vacuum and made many experiments showing the pressure of the atmosphere. Denis Papin, French Academian in 1690 experimented with the condensation of steam under a piston and made the latter lift weights hung over a pulley, but near as he was to the discovery of an engine, he failed due to insufficient practical experience. A most important stage in evolution of the steam engine was reached in 1698 when Thomas Savery invented and patented an apparatus which worked on the principle of raising water by the condensation of steam in a receiver and then forcing it out of the receiver by means of steam under pressure. Condensation was helped by the flow of cold water over the receiver at each cycle of operation. The limitations of the suction lift and the difficulty at that time of making boilers capable of withstanding high pressures made the apparatus impracticable for greater lifts than from 60 to 80 ft. but as the mines had already reached those depths it meant the complication of introducing a series of such units in the shaft delivering from one to the other. Added to this the dangers attendant with steam at high pressure, the complication the number of units in badly ventilated shafts and also the great amount of fuel required to make up for the losses inherent in  the system were sufficient reasons to prevent Savery's apparatus from becoming generally adopted. A modern application of Savery’s ideas is the Pulsometer, which owing to its few parts and simplicity of erection is useful where temporary drainage is required and where economy of fuel is not a primary consideration.

In 1705 Thomas Newcomen who was the real inventor of the steam engine solved the problem of mine drainage in a most ingenious way, but it was some years later in 1711 that he obtained permission to erect a pumping engine on his principle at a colliery near Dudley Castle, not far from Wolverhampton. He and his friend John Cawley after many trials succeeded in getting their engine to work and for the first time in history power was obtained from a piston working in a cylinder. Before describing the engine it will be well if we consider a little what we know of Thomas Newcomen.

The family of Newcomen which in the records of the College of Arms begins with Hugo Newcomen 1189, resided at Saltfleet, Lincolnshire for many generations. From a branch of this family was directly descended Elias Newcomen rector of Stoke Fleming Devonshire whose great grandson Thomas Newcomen born at Dartmouth in 1643 was the inventor of the Steam Engine. Not much is known of the life of Newcomen. He was well informed with what had previously been done in connection with steam but left no record of his work. He lived to see his engines widely introduced but never became wealthy and he died in London in 1729.

With the exception that his engine raised water by the action of fire, it differed in every other respect from that of Savery  but owing to the latter having obtained a patent Newcomen was unable to get one and in order to protect himself he joined Savery and formed a Company and allowed his own invention to pass as an improvement of Savery's apparatus. In consequence his greatness as an original inventor suffered and only in recent years has he received full credit for what he achieved.

Newcomen engines were largely used for pumping out mines and they were not materially improved before James Watt invented the separate condenser in 1765 and by the time Watt had his first engines running in 1775, there were over 100 Newcomen engines in the Newcastle area as well as many in Cornwall and some on the continent. Owing to their cheaper construction as compared with Watt’s engines, they remained long in use where the fuel was cheap and a few were still running in 1926.

The early writers upon the Steam Engine looked upon Newcomen little respect. Marten Triewald,  a Swede who came to this country to learn all he could about the Newcomen engines built a copy of the engine at the Dannemora Mines Sweden in 1728, and in 1734 he wrote  a description of this engine in which he referred to Newcomen and Cawley as follows,-

 “Knowing the inventors be can only conclude that the Almighty presented mankind with one of the most wonderful inventions which has ever been brought into the light of day, and Is by means of ignorant folk who had never acquired a certificate from any University or Academy”.

Dr Desaguliers writing in 1744 expresses similar views in the following words: 

"Thomas Newcomen, Ironmonger and John Cawley, Glazier of Dartmouth (Anabaptists) made then several experiments in private and having brought it to work with a piston etc., in the latter end of the year 1711 made proposals to draw the water at Griff in Warwickshire, but their invention, not meeting with reception, in March following, through the acquaintance  of Mr Potter of Bromsgrove in Worcestershire, they bargained to draw water for Mr Back of Wolverhampton where, after a great many laborious attempts thy did make the engine work, but not being either Philosophers to understand the reasons, or Mathematicians enough to calculate the powers and to proportion the parts, very luckily by accident found what they sought to for.”

Jealousy was obviously at the root of these attempts to belittle Newcomen’s great achievement for he had shown the ability and had actually obtained results as a craftsman, which the Academians and professors had failed in solving.

Newcomen engines were originally known as “Fire Engines" but are now referred to as “Atmospheric Engines" owing to their open-top cylinders and to distinguish them from James Watt's Steam Engines with closed top cylinders.

The Newcomen engine in its simplest form comprises a boiler placed underneath an open top cylinder, the piston being hung by chains from a horse head at the end of the great beam fulcrumed at the centre, from the other end of which outside the engine house are hung the pump rods which work bucket pumps In the mine. The balance across the beam is adjusted so that the piston is always lifted to the top of the cylinder by the weight of the pump rods, and when standing the engine comes to rest in that position. Any excess in the weight of the pump rods is balanced by a separate rocking beam or "Bob" connected to the pump rods at one end and with a box at the other end for containing ore or pig iron enough to suit  the degree of balance desired.

As first made, the engine cylinder was surrounded by a jacket containing cold water and both the steam inlet valve and water valve were worked by hand. The piston was water sealed and probably leaked enough to suggest cold water injection being sprayed directly into the cylinder and thus increase the speed of the engine and so doing away with the jacket. These operations were soon made automatic from the motion of a plug rod hung from the beam.

To start the engine.steam at from two to three pounds pressure above the atmosphere was admitted to the cylinder through a sliding disc valve and was then condensed by the injection. The piston made its down stroke and the water from the condensed steam and injection discharged itself through the non return valve water sealed in a tank below and any air passed through a small snifting valve, steam valve. When the steam valve was reopened, the piston rose to the top of the cylinder and the cycle was repeated.

There is no doubt that the men responsible for setting this first engine at work had much to learn from their immediate experience and alterations would be made from daily experience, no record being kept. The earliest drawing of a Newcomen engine is one dated 1717 by Henry Beighton and it shows a fully developed engine so also does the Barney print dated 1719 showing the engine erected at Dudley as in 1712. The cylinders of the Newcomen engines were not bored.They were brass castings and were scoured inside and made smooth by long and tedious work. Cast iron cylinders superseded brass about 1740. They were made at the Coalbrookdale iron works. The boring of the cylinders remained primitive until shortly before 1775 when John Wilkinson, iron founder of Bradley, Shropshire invented a greatly superior boring machine and he was able to supply the more accurately bored cylinders for the new Watt engines then coming into use. At this period, the engines had become standardised and their general arrangements and efficiencies were about as given in the following summary: 
Copper dome top boilers under the cylinder. 
Bucket pumps in the Mine.
Separate pump rods to each lift.
Condensation of steam in the cylinder.
Steam pressure from two to three pounds above the atmosphere. 
Engine loaded to 7 pounds per square inch, mean pressure on piston.
Evaporation of water in the boilers about 6 pounds per pound of coal.
Duty of the engines 7.000.000. foot pounds per 84 lbs bushel of coal. 
Column of water in the mine seldom exceeding 90 fathoms = 540 feet.

As stated previously there were still a few open-top cylinder engines at work in this country as recently as 1926. Among them may mentioned two belonging to the Earl Fitzwilliam Collieries situated the Sheffield district. The larger of the two at Rawmarsh had a 54 inches bore and a piston stroke of 7 feet. The second engine situated at Elsecar had a cylinder 48 ½ inches bore and a stroke 5 feet The original wood beams were long since superseded by cast beams and parallel actions instead of chains. Another engine of the Newcomen type at work at Pentrich Colliery, Butterley until about same date as the above has been preserved and removed to the new Science Museum, South Kensington.

It was interesting to see this engine running and to spend time in watching its action at work, The cylinder has the date 1791 cast on the side. It is 57 inches bore and the stroke of the piston varied in working from 5 to 6 feet. The original oak beam and horse heads were long since replaced by a cast iron beam and arched ends from which three chains suspended the piston and three others the pump rods. Steam was supplied to the engine at from two to three pounds pressure above the atmosphere from a battery of boilers fed by gravity from tanks above. The engine made from 5 to 6 pumping strokes per minute depending upon the amount of water in the mine.

For hours at a time the engine could be left working alone, creaking, groaning and hissing like some great antidiluvian animal. At the end of each indoor stroke, the engine paused for a few seconds, giving time enough for any vibrations of the pump rods to settle down as though a cataract had been employed which it had not. The effect was produced as follows: At the bottom of the piston stroke a pin on the plug rod pressed against the horn for opening the unbalanced mushroom type steam valve which resisted opening before the pressure was balanced on both sides of the valve which then opened letting steam into the cylinder and the piston made its outdoor stroke. The time taken to make this stroke could be slowed or quickened as desired by adjusting the counter weight in the balance box rocking with the pump rods. Another pin or tappet on the plug rod, in rising engaged the steam horn mounted on it’s arbour and closed the valve and at the same time the rotation of the arbor released the catch holding the injection valve closed. This was adjusted to take place when the piston reached the end of its outdoor stroke. The opening of the injection valve let a spray of cold water into the cylinder which condensed the steam allowing the atmospheric pressure on top of the piston to force it to the bottom of the cylinder and to make its indoor stroke, On its way down a tappet on the plug rod engaged the injection valve horn and closed the valve. This took place almost as soon as the piston began to move down showing that the vacuum was produced instantaneously by the first gush of water and that any further water would only cool the cylinder walls and reduce the efficiency of the engine. Before the beginning of the outdoor stroke, the pause before the opening of the steam valve now took place as described above. While steam was flowing into the cylinder as the piston made its outdoor stroke, the hot condensed steam and Injection water from the previous stroke flowed out of the cylinder by gravity through a pipe and a non-return valve submerged in a hot well below the cylinder The lift of this valve was so adjusted to allow only the water to flow out by the time the piston had the top of the cylinder. A small water sealed snifting valve in the eduction pipe just under the cylinder was uncovered by the falling  water in the pipe at the end of each down stroke and, allowed air to blow out which would otherwise have accumulated and choked the working of the engine. A cold water tank on the beam floor was kept full by a jack pump driven from the main beam. This tank supplied the injection water and also the water required for sealing the piston which worked with about 12” deep of water on the top. The hot well of this engine was situated outside the wall of the engine house at the back of the cylinder. Owing to calcareous deposits from the hot water, all the parts coming in contact with it or subjected to splash were coated with a thick deposit of yellow scale forming beautiful stalactites and stalagmites making a curious and picturesque scene. The top part of the cylinder was similarly incrusted where the sealing water on the piston came in contact with the rim and it was thickly coated. On lifting the piston out of the cylinder it was found covered with small stalactites hanging about 2 to 3" down and these were also a bright yellow colour and showed a perfectly stratified structure.

In the early Newcomen engines the lever which opened and closed the injection cock was named the ‘F’ from its shape which resembled the letter F, and for a similar reason that which opened and closed the steam valve was called the “Y” because of its resemblance to that letter.The F being weighted opened the injection valve with a jerk when released by a tappet on the plug rod and was closed by another tappet or adjustable pin on the plug rod. The steam regulator was in the form of a disc which was worked to and fro across the  steam pipe top of the boiler and just under the cylinder. The opening and the closing of this valve was also given in jerks by the overbalancing of a weight fixed to the tail of the inverted Y when brought over its axis by the action of tappets on the plug rod. It is evident that the number  of strokes the engine could make would be limited by the supply of steam from the boiler. Some means had therefore to be devised to prevent the opening of the injection valve before sufficient steam been generated in the boiler. This was ingeniously done by the intervention of a buoy floating in a pipe open to the atmosphere at the top and submerged in the boiler water below. Thus the buoy rose and fell with the pressure and when high it released the injection “F” and the valve opened. The early prints of Newcomen engines show the Buoy and also a cord attaching the catch with the plug rod, but it is difficult to understand how they could both work together. The Barney print already referred to shows both and describes the gear in these words, "Scoggen and his Mate who work Double to the Buoy, Y is the Axis of him”. This is confusing and, does not help matters as the drawing is not clear.

About the year 1763, James Watt, then employed as Mathematical  instrument maker to the University of Glasgow, was asked to repair the model Newcomen engine used for demonstration purposes. It was while he was experimenting with this engine that he noticed the losses of steam due to condensation of steam in the cylinder which had previously been cooled by the cold injection water and the idea came to him that to make a perfect engine it was necessary that the cylinder should always be as hot as the steam which entered it and cooled in separate vessel to a temperature of about 100 degrees Fahrenheit. His friend Dr. Black had discovered the Latent Heat of steam in 1760 and this without doubt helped Watt to discover the true cause the losses and led him to the invention of the separate condenser in 1765. He did not patent his invention however until 1769 and from that date he turned his attention more particularly to the steam engine. He had financial difficulties in the building of his experimental engines and years of disappointment which at one period nearly led him to abandon the engine. By good fortune however, he became acquainted with Matthew Boulton a wealthy manufacturer of Birmingham and in 1774 his experimental engine was re-erected in Boulton’s Soho factory. With Boulton’’s help and confidence in the new engine on Watt’s principle, the latter soon got to work, and in order to give themselves the fullest advantage of the patent they applied for an extension which was granted for a period of 25 years from 1775 to 1800 by an Act of Parliament, ten years after the conception of the invention.

From the first their engines met with success and were found to consume only one third of the Newcomen engines consumption of coal when doing equal work. James Watt now devoted the whole of his time and thought to the improvement of his engines and he trained men to construct them and gathered together a highly skilled and efficient staff. He never used steam in his boilers at more than from two to three pounds pressure above the atmosphere, partly owing to the difficulties of their manufacture and to the dangers attendant in their use, He understood the economy to be derived from using steam expansively but was unable to make use of the system owing to working his engines at such low initial pressures.

The separate condenser made it possible to increase the pressure in the cylinders as compared with that usual in the Newcomen engines in which a higher vacuum than that necessary to give 7 pounds mean pressure in the cylinder meant greater losses in steam than were returnable in the form of increased work done by the engine. Watt was able to load his engines to 10 or 12 pounds mean pressure in the cylinders which remained hot and there was much less initial condensation than which took place in the Newcomen engine though to do the same work his engines required smaller cylinders. In the case of Smeaton’s Newcomen type engine at Chacewater mine Watt converted this with a 63 inch cylinder using the original 72 inch cylinder as a steam casing and his engine did the same work.

Watt seldom exceeded 63 inches diameter for his cylinders, the largest 64” were for Herland Mine and Manor Mine, Cornwall.

It may be said that the Newcomen period ended with the invention of the separate condenser, but for many years after that atmospheric engines continued to be made owing to being cheaper to construct and the restrictions imposed upon engine builders by the Boulton and Watt patents who enjoyed the absolute monopoly for the supply of engines of their improved type. Efforts were made to improve the efficiency of the Atmospheric engines by the addition of a separate condenser, known as a “Pickle Pot engine”, but as the air pump could not be used, owing to the patent, these and other modifications were of little benefit.

These engines were not the self-contained units with which we are familiar with today. They formed an integral part of the building and had to be put together on the site. The erection was supervised by an Engineer who contracted to make parts of the engine and who was paid for his services by the mine owners. The bored cast iron cylinders came from one or other of the few ironworks who were to supply them and they had to be transported by land, sea or canal to the sites where the engines were to be erected. Other materials such as boiler plates, iron for the forged parts, oak for the great beam and other timbers also arrived on the site which for a time became a workshop and a hive of industry. The chief erector had working under him a staff of blacksmiths, plumbers, carpenters stone masons and bricklayers for the building of the engine and it’s house.  When possible, the beams were made from a single tree but when trees large enough became scarce  they used to build the beams of many logs dressed and keyed together in one solid mass. A fine example of such beam is that which was built by Smeaton for the Chacewater engine. From the works at Soho came the valves and nozzles and John Wilkinson, Bersham near Wrexford supplied most of Watt’s cylinders until 1795 when a foundry was established at Soho. The nozzles had been cast at Bradley near Birmingham at one of Wilkinson’s branch works and they were fitted at Soho. Beam gudgeons plummer blocks, and sundry other castings came from the same works, while the cylinder jackets which were cast in sections came from the Eagle Foundry, Birmingham. Fire bars and other furnace fittings were sometimes cast in the locality where the engines were to be erected. The copper eduction pipes came from a London firm and the wrought iron piston rods came from London or from Seaton forge in Cumberland. Watt sent detail drawings, many being in his own hand and full instructions to the erector in charge and gave dimensions for all parts which were to be made on site as well as for the building. At first had trouble in persuading some of the erectors to.accept his views as they had previously been accustomed to erecting Newcomen engines and they objected to depart from their usual practice. Difficulties were further increased owing to the slow and irregular means of communication  between the works in Birmingham and the site in Cornwall where the engines were being erected. Boulton & Watt therefore found a suitable mechanic in William Murdoch and sent him to Cornwall as resident engineer to be responsible for the erection of engines and to look after their interests. it is interesting to read some of the  correspondence between James Watt and the erectors before Murdoch was appointed.

Excerpt from Watt’s letter to Jonathan Hornblower who was the engineer at Tingtang Mine and which led to the first order B.& W. received from Cornwall. Writing on October 17th 1776 he says:

"The proper load of our engines is 10 or 11 lbs. per,square inch of the piston, and then they use less steam than common engines of the same sized cylinders. They will raise at least three times the quantity of water with the same quantity of coals that common engines consume. If executed in the same manner they cost very little more money than a common engine which does the same work. Our profit arises not from making the engines, but from a certain proportion of the savings in fuel which we make over any common engine that raises the same quantity of water to the same height. The proportion of.the savings we ask is one third part, or if your Employers chose it, they may purchase up our part at ten years price in ready money.”

Again on November 8th 1776, he says:

”We had made an offer to some gentlemen in your County to furnish such parts of a fire engine as are peculiar to our construction at our own expense and then remove the same if after trial it did not do double the work with the same quantity of fuel which is now done by any engine in Cornwall. If on the contrary it answered expectations, we were to be paid for the engine and to have the third of the annual savings for 25 years if used so long. The above offer we were induced to make in order to remove all manner of doubt from the minds of the Gentlemen of Cornwall, but did not mean extend it to any others than those who ordered the first engine us in that County and we shall certainly enable you to make your employers as advantageous an offer as any other Engineer, as we have yet received no conclusive order from your County. If therefore it be agreeable to the Proprietors of Ting Tang mine or any other where you are engaged, to try one of our engines, we will furnish what is peculiar to it, that is the cylinder, piston, piston rod the regulators, the condenser and its apparatus at our expense to be removed by us if after a fair trial the engine should not do double work with the same coal that any other engine does in Cornwall. If it answers we demand the price of the articles furnished and the third of the savings for 25 years or as aforesaid. One of our engine cylinders 45 inches diameter will work a pump 13 inches diameter in the working barrel and 100 yards high, providing there be no extra ordinary quantity of dry wood. It will then be loaded to 11 lbs. upon the square Inch and when going at 10 strokes per minute 7 ½ ft. long each will burn about 2 cwt.of coal In an hour, but a great depends upon the goodness of the coals and of the Boiler. The coals I mean are of the Wednesbury kind”.

On November 23rd. 1776, a few days after the above letter had been written, Boulton & Watt received the order for a 52" diameter engine for Tingtang being the first order which they received from Cornwall.

The letters now took on a different turn showing that the engineer Jonathan. Hornblower was concerned about some of the instructions and on the 15th of December 1776 James Watt wrote to him as follows:

“Engine house 15 ½ ft. from water wall to back wall & 14ft wide within. I would by no means choose to exceed 24 ft. for beam and observe that your present building may be easily accommodated to that design. The custom here is to set all the pumps in a row and equally distant from the centre of the beam, but perhaps you have some good reasons for placing them in two rows. The position of the boilers, one upon each side of the house I find to be the best when  only one boiler is intended be used at once and where the other is to be kept for repairs. The boilers cannot be admitted into the house in our way of working because our cylinders require to be fixed by the bottom, to beams placed under a stone platform heavy enough to resist the power of the cylinder.

We hang the beams all under the gudgeons which is a considerable improvement as it contributes greatly to equalize the motion of the engine. Please advise if I am to order cast iron chains for both ends of the beam and whether you could at any reasonable cost procure an oak tree of 30 inches square to make the beam of, or if it must be pieced, as I shall make to drawings accordingly. I shall also be obliged to you to inform me if you have good engine smiths as we should not choose to do any smith’s work ourselves except that which is peculiar to our our engine.You ask whether I prefer a double cylinder or a pipe to convey the steam to the cylinder top. I prefer  the former on several accounts, especially where coals are dear. l have erected two with the pipe partly against my will where  coals are cheap, but there is great loss by the want of an outside cylinder,  and in your engine the difference would not exceed £50 which is no object in such an understanding. I must once for all beg that you would not take amiss my insisting upon your strict adherence to my plans and directions even though contrary to common practice. I have no doubt but that at meetings I shall satisfy you of the propriety any deviations from the  established rules, though it would be too tedious always to send my reasons In writing, at the same time I shall be glad to be informed of any objections which may arise from the situation.”

In his letters Watt gave full and very definite instructions and he left nothing to chance. The Tingtang engine had a 52” cylinder and as previously stated it was the first to be ordered from that County, but the first Watt engine to be actually started in Cornwall was one for the Wheal Busy which had a 30”cylinder.

In the case of Newcomen engines it was customary to place the boiler underneath the cylinder and to support the latter upon two massive beams built into the walls across the engine house. However strong these beams were, they could not prevent the cylinder from jumping each time the injection valve was opened which soon caused trouble and leakage in the short connecting steam pipe between the boiler and the cylinder. In his early engines Watt placed the working cylinder inside another cylinder or casing, which along with the top of the piston was in constant communication with steam from the boiler. The piston rod passed through a stuffing box in the cover of the casing. There were only two nozzles as the valves were called and both were situated at the bottom of the cylinder. One admitted steam from the casing and top side of the piston to the underside of the latter and the other exhausted this steam on the down stroke to the condenser. A small fire underneath the cylinder re-evaporated any water formed from condensation in the cylinder. This idea accorded with one of the main clauses in Watt's Patent Specification, where he says:-  "That vessel in which the powers of steam are to be employed to work the engine which is called cylinder in common fire engines, but which I call the steam vessel must during the whole time the engine is at work be kept as hot as the steam that enters it”

Hornblower not being familiar with the principles of Watt’s engines and having in mind the Newcomen engines took some convincing when it became a question of departing from the recognized practice he had until then been accustomed to. Watt showed however great patience throughout his correspondence with him recognizing that he had to deal with a man of more than ordinary ability. This is seen over and over again in the correspondence, thus on Dec. 18th  1776, Watt not having had time to make a drawing for the Tingtang engine, he sent Hornblower a drawing of the Bedworth engine then being erected near Coventry and altered the dimensions to suit the Tingtang saying:- 

"This method of copying drawings of engines whose dimensions vary from yours is irregular and would not be put in practise if I had a less opinion of the skill and experience of the person to whom I send them."

Watt was quick at making improvements to his engines from the experience gained from the first ones to be put to work, and in a few years the mine pumping engine became practically standardized. Pursuing the letters to Hornblower, the following is taken from one dated Dec. 27th 1776:-

“Yours of the 26th received, I am no advocate for cast iron chains, they do very well when they are made of good iron and about double the strength of forged ones. Their advantages are the having a broader bearing upon the horse head, being generally more accurately fitted and serving for counterpoise when required, being in common use here, an Engineers reputation cannot suffer by recommending them. In your case I advise those you are accustomed to, and approve of the hammered iron ones, but recommend making them in the following manner, length from centre to centre 7" dia. of holes 1 ½”,  of the round ends 4 ½”. Le tthe one edge be made to fit the curve of the horse head the other at pleasure. Let them be three stave chains, the two side staves 1” thick and the middle 1 ½” thick. Two such chains will be required for the cylinder end of the beam and about 8 ft. each. For the other end of the beam, I leave it to yourself, but at the cylinder end it is necessary that the chains should be fitted to the arch, otherwise they dig holes in it and injure the motion of the piston which moves in a collar or jack head. I further beg that you may be very attentive to the quality of the iron used. The beam at Bedworth engine is composed of 6 pieces of oak and Is 3' 6" deep and 2’ 3” or 4” thick. This will answer you even with a larger cylinder. I prefer oak to deal for the beam. One objection to a long beam is the additional strength and weight required. The last is a perpetual tax on the moving power by its vis inertia”. 

Then follows  lengthy instructions regarding the foundations, boilers, buildings etc.

How quickly the letters follow each other, in one from Watt to Hornblower dated December 31st 1776, the last paragraph reads:-

 "Please make no excuses I love nothing so much as to answer sensible and proper questions such as you put and it is my business and intentions to give you every necessary information".

Thus we can follow the building of Tingtang engine in all details. Hornblower wanted a longer beam and, he had doubts about the use of cast iron chains. Watt's replies are characteristic as shown by further excerpts from his letters to Hornblower. On Jan 13th  he writes:- "Mr. Wilkinson’s cast iron chains are now much superior both in metal and workmanship to what used to be made. In your case would put three chains upon the cylinder end of beam which will be quite sufficiently strong. ——-I have ordered the condenser and all its parts for a 24ft beam and therefore wish you to use that length, I have however wrote this post to delay casting such pieces as admit of alteration until I hear from you. If you go on with 26ft beam you must make the house one foot longer than ordered. If after all the reasons for the 26ft beam should prevail, go on without waiting for an answer, but let me know in course”.

Hornblower was quite particular and even had to be told how the bolts and nuts were made. Thus in Watt’s letter dated Jan 20th,  1777 he writes as follows:-  

“Our screws are made solid heads (i.e. not welded on) and they are screwed in stocks and dies with square top threads like a vice pin and afterwards brought all to size by a screwplate. The nuts or burrs ( as they are called here) are first entered by a taper tap and finished by a tap that goes right through them and makes them equally wide upon both sides. Such screws we find vastly preferable to the common sort especially in cases where they are often to be unscrewed or where strength is required., but after all the pains in making them we cannot sell them under 6d per pound, and hitherto have been losers at selling them at that price. To prevent any mistakes, I here subjoin a list of all the parts of the engine, distinguishing where they are to be made:-

Bersham. Inside and outside cylinders, bottoms, piston, lid and stuffing box. The condenser cast iron work complete.

Bradley. The nozzles and short pipes. The gudgeon and bed. The plummer blocks and brasses. Cast iron chains for cylinder end.

Soho. Te regulators brass and iron work. The F and Y, the plug frame chains. Two chains for condenser pumps gearing. the buckets and clacks of condenser, two round piston rods for do. All the screws and burrs for the two cylinders, condenser and boiler steam pipes. Screwed ends for holding down screws. The ironwork for the great piston and rod top. The piston itself. The 2” diameter adjusting screws and burrs for top of piston rod chains. Three do. for pump chains if you choose them. Four screwed ends for the stirrup to hang the beam in.

Tingtang. ,The boiler fire doors and grates. The pumps and pit head ironwork. The poise beam. The pump chains. The screwbolts and arch plates for the beam. The catch pins. The two glands which keep down the gudgeon:. The stirrup for do. excepting the screwed ends. Which will be brought  ready teo shoot to the martingales. The house and all the woodwork.”

From the above it will be seen that HornbIower had ordered cast iron chains for the cylinder end of the beam but not for the pump end. He must therefore still have doubted their strength as shown by the next excerpt from a letter written by Watt on the 19th February 1777:-

"I cannot insure that cast iron chains will not break provided that force enough be applied for that purpose, but Bloomfield a 50” cylinder of our construction has been going twelve months, has met with exceeding rude usage, the pit being sinking and has only two chains castiron, of the same scantlings as I have put three to your engine. This amounts to moral certainty. The causes of cast iron chains breaking besides bad iron, have been the making them figure 8 whereas ours are all of one breadth but made thicker round the ends as if a washer was welded on upon each side, and the not having the truly holes bored to bring a fair bearing upon the pins. We work with the piston entirely free from water and make it tight by pieces of lead and oakum soaked with grease of any kind and hard screwed down. It scarcely ever needs repairs after the first fortnight during which it must be often looked at.”

More Instructions regarding every detail could not have been given and Watt's book of instructions for the erection of his engines written about 1780 is a remarkable work and wonderfully instructive. This very rare little book has been reprinted in full with reproduction of the Plates in "James Watt & the Steam Engine' by H.W.Dickinson and Rhys Jenkins. This book is the most authoritative on the lives of Boulton and Watt and many of the original drawings have been reproduced showing the evolution of the designs.

The high prices of coal in Cornwall rendered that County, as Watt predicted in 1778 a source of wealth to the Proprietors of the Patent and the monopoly they held for the construction of the condensing engine until  its expiration in 1800, was upheld by the law. The system of payment they established was based upon the cost of the engine parts plus one third the saving in fuel compared with an engine of the Newcomen type doing the same or equal work.

To arrive at a figure for this premium, two Newcomen engines were tested at  Poldice Mine, Cornwall, and from the results obtained the saving of the Watt engines could be computed. A locked counter fixed to the beams of Watt's engines for recording the number of pumping strokes made by the engines enabled the work done in the running period to be calculated. It is evident that short strokes went against the Mine Adventurers and on the ether hand it would be to Boulton & Watt's interest to see that the engines were kept efficient. in 1800 when the Patent expired the counters were removed for a time and it was soon noticed that the duty of the engines began to diminish . The counters were replaced on an many engines about 1812 when the system of issuing monthly reports was established by Captain Lean. This revival of the competitive  interest in the engines along with ether improvements such as increasing steam pressure and expansive working, caused the duty of the engines to rise from about 17,000,000 ft..lbs. to 75 000,000 ft. lbs. in 1840, but the figures were never reliable except as a basis of comparison in a general way. They quality of the coal was not taken into account and the evaporation of the boilers varied considerably, steam pressures were not noted, the length of the strokes was not constant on any one engine. Some engines worked vertical pump rods while others had rods at all angles in the shaft and were thus at a disadvantage as regards the friction load. There were so many points of difference to be taken into account to get reliable figures that the system of reporting was finally abolished. After the mid 40’s of the last century “Duty” began to decline,  the most probable reason being that the mines were becoming so deep the existing size cylinders were becoming overloaded and it was no longer possible to steam the engines with the early cut-off necessary for economical running. Furthermore some of the notable duties had only been attained at the expense of heavy wear and tear on the pitwork and in consequence a reaction to the enthusiasm of the earlier part of the century set in and many mine managers were quite content to see a lesser duty performed by their engines if thereby they could obtain greater reliability and freedom from breakdowns. As in every department of life, the moment we cease to advance we fall back - it seems impossible to stand still, and apparently the failure to advance in the matter of duties was the cause of the decline of interest in the matter.

All through the history of Cornish mining there has been a tendency for the ownership and management to be blind to their own interests where monetary savings through mechanical improvements are concerned and the same thing can still be seen to-day. This fact has been largely responsible for the decline of interest in duties when once the enthusiasm of certain mechanical engineers had spent itself. Furthermore when onece the duty of an individual engine had started decline its owners often felt reluctant to publish and advertise the fact, and so they ceased to have it recorded and interest still further lessened as the number of engines on the record declined. In spite of  the various reasons for the decline in duty reporting it continued until 1910 or 1911 only ceasing on he sudden death of Mr. J.C.Keast who was the last man sufficiently interested in the subject to keep the practice in being.

Perhaps the final major reason for the decline in reporting was the the decline of mining itself. Had the industry continued to prosper after the middle of the 19th century, it is possible that mechanical practise might have progressed too, but instead, the number of opportunities for erecting new plants where a high duty might be expected continuously decreased in number and the openings for duty making engineers grew less and less. At the time Mr. Keast died there were only 25 mine pumping engines operating in the whole of Cornwall, and now (1946) only three.

Introducing the new engines into Cornwall was not easy and Watt found the Adventurers and their engineers difficult to deal with. They objected to pay the premiums and also tried to introduce modifications of the engine and thus to evade the Patent but in all these things they were not successful and when Boulton & Watt went to law and claimed their rights they were upheld by the Courts and received large sum of money which had been owing to them from the Adventurers. In 1800, date of the expiration of the Patent, the single acting pump engine as improved by Watt had reached a stage of perfection and arrangement as given in the relieving list: -

Separate Condenser and Air Pump.
Waggon Boilers eretced outside the house, gravity feed.
Engine cylinders placed on separate foundations.
Bucket pumps of improved form.
Pressure of steam  2 to 3 pounds pressure above the atmosphere.
ExpansIon of steam in cyl. known but not used owing to the low pressure.
Engine loaded to 12 lbs.mean pressure en the piston.
Evaporation in boiler 8 to 9 lbs. per pound of coal burnt.
Max. duty or the engines 27.000.000 ft. lbs. per 84 lbs. bushel if coal.
Column of water in mine seldom exceeding 160 fathoms.

When comparing the above with the list given for the Newcomen engine of 1775 it will be noticed that the steam pressure had not been increased and that bucket pumps were still used in the mines.

In his book "Introduction to a general system of Hydrostaticks and Hydraulicks" 1729, Stephen Switzer showed a good drawing of a Newcomen engine and plunger pole pump and it is curious that this better form of pump was not properly made use of in Cornwall until after 1800 when steam pressures began to be raised and full use made of the economies due to expansive working of steam. With bucket pumps the water Is lifted on the indoor stroke of the engine, while with plunger pumps the weight of the pump rods and plungers are lifted on the indoor stroke and the water lifted on the outdoor stroke. At first sight it might appear that there would be no difference between lifting 30 to 40 tons of water the same weight of pump rods, but in practice here is a great  difference. When water is lifted the more uniform the steam pressure and the better for the flow of the water. On the other hand when the rods are lifted they can be accelerated by high pressure steam working at an early cut-off provided they are strong enough to stand the extra strain and the benefits of expanding steam can be realised. At the low steam pressures used by Watt bucket pumps were all right but after 1800 when boiler pressures were increased it became necessary to adapt the plunger pumps. This type of pump was used for all but the bottom pump which, for reasons of drainage had to be of the bucket type. Thus in Watt's time the water was lifted on the steam stroke of the engine and when plunger pumps were substituted water was lifted during the equilibrium stroke of the engine.

Watt took 84 lbs. as the weight of a bushel of coal from the Northern districts which have a specific gravity about 90% of Welsh coals weighing about 94 lbs to the bushel. For confirmation of these figures see “The Cornish Pumping Engine" by William Pole, 1844: page 157 and Watt’s calculation  Blotter No 1 dated 1779 now in the Boulton & Watt collection at the Birmingham Library in which be says: - “On an average (or in the size Newcastle coals are generally sent to market) the standard coal bushel heaped = ¾ cwt. or 84 lbs. The term bushel when used without reference to weight is therefore very misleading.

The early pumping engines were single acting and the chain connection between the piston and the beam answered the purpose being always in tension, but in the case of a double acting engine some rigid form of connection became necessary and although Watt had the double acting engine in mind as early as 1774, it was not until 1783 that he gave serious thought to the matter.

Several schemes were prepared and built including rack and sector motions, and various linkage combinations which led to his invention of the Parallel motion in 1784 first used for the Albion Mills engine in London.

Double acting engines were introduced into Cornwall about that date. They drove a balanced set of pump rods connected to each end of the beam. Other engines had the outend of the beam connected to bell cranks driving two sets of pumps in balance. Quite a number of such engines were built.

Watt’s patent of 1784 included the parallel motion, the steam engine governor, sun and planet motion etc. The latter was suggested by William Murdoch to evade the crank which although known for ages had been patented by another for use in atmospheric engines. It was not considered policy to contest the patent which was not used by Bouton & Watt before 1791.

When the main patent expired in 1800, Matthew Boulton and James Watt retired from the firm leaving it in the hands of their sons and William Murdoch was appointed Manager. From this time on the was subjected to fierce competition from other builders who took advantage of the expired master patents.

Matthew Boulton died at his home, Soho, in 1809 at the age of 81. John Southern, Watt’s most able and trusted designing assistant died at Handsworth in 1815 at the age of 57. James Watt died at Handsworth in 1819 having reached the age of 83, and William Murdoch died at Handsworth in 1839 at the age of 85.

There are no records of any Boulton & Watt engines going into Cornwall after 1800, and it may be said that the era of Low Pressure Steam had come to an end.

Richard Trevithick was the first to introduce successfully the pressure engines which evaded the Watt patents by working non-condensing and he was the inventor of the first locomotive to work on rails in 1804. He had much to do with the introduction of the high pressure engines in Cornwall, first used for small non-condensing winding engines and later for the large pumping engines working with condensers. He also introduced the plunger pole pump in the mines which enabled the higher pressure steam to be used expansively. These engines became known as "Cornish Engines" and reached their highest efficiency by about 1843. The results obtained were as follows:-
Cylindrical boilers with single internal fire flue, the Cornish boiler. 
Steam pressure 40 to 50 lbs. above the atmosphere. 
Plunger pole pumps in the mine with bucket pumps for bottom lift.
Engines loaded to 18 lbs. per square inch mean pressure on piston.
Full use of expanding steam in the cylinders.
Evaporation of water in the boiler 9 lbs. per pound of coal.
Duty of engines 75,000 000, foot pounds per 84 lbs. bushel of coal.
Column of water in mines up to 290 fathoms.

In the Cornish engine steam is admitted from the boiler to the top of the piston which then makes its down or indoor stroke, the steam being out off by a tappet on the plug rod at a point determined by the load on the engine. At the same time the exhaust and the injection valves are opened and there is a vacuum under the piston.These three valves having been closed and the engine comes to rest at the end of its indoor sidle, the cataract trips and the equilibrium valve opens and allows the steam to pass from the top side of the piston to the bottom side placing It in an equilibrium. The excess weight of the pump rods at the outer end of the beam returns the piston to the top of its stroke lifting the water lifting the water in the mine at the same time and the cycle is repeated.

The actual time of starting the stroke is determined by adjustment of the cataracts which can be adjusted to release the catches at once or after a pause determined by the number of strokes per minute the engine is desired to make. There is usually a cataract for both the indoor and outdoor stokes. It everything is tight and no leakage of water takes place through the pump valves, the will engine remain perfectly steady during the pauses.

To an observer outside the engine house, the beam rises suddenly but without sound or shock and comes to rest at the top of its stroke. After a short pause, the beam is seen to creep slowly  down at constant speed to its bottom position during which time the water has been discharging at the surface.

The history of the Cornish engine is closely connected with the mining industry Designed by practical engineers and built in Cornwall, is it to be wondered that these engines attained a world wide reputation for efficiency?

Cornish engines have been and are still used for draining mines and for waterworks in England, Scotland, Wales and in many parts of the world. Regarding engines used for mines they run the best in their native county where they are best understood and cared for.

Cornish  engines  having cylinders 100 inches bore and 11ft stroke were in use until a few years since. Probably the largest were made to drain Haarlem Lake in Holland, these three engines having 144 inch diameter low pressure cylinders with 84 inch dia. high pressure cylinders inside them and all ten feet stroke.

Cornish engines. unlike crank engines are more liable to crash and many have been fitted with the Davey differential gear which holds the engines in check when the load is suddenly removed. Nevertheless they are being replaced by electrically driven underground pumps.

Hundreds of tons of pit work and pump columns are removed from the mine, often so incrusted with scale as to be almost unrecognisable. The great beams in some cases weighing 50 tons are broken up for scrap and being cast of cold blast iron are valuable.

At the present date, August 1946 there are only three Cornish engines at work in the county not including the small engines used in the China Clay pits.