James Watt, Inventor of the Modern Steam Engine

James Watt
James Watt. Bettman/Getty Images

Early Life

James Watt was of humble lineage, born in Greenock, Scotland on January 19, 1736. Greenock was then a little Scotch fishing village that became a busy town with a fleet of steamships during Watt's lifetime. His grandfather, Thomas Watt, was a well-known mathematician and local schoolmaster. His father was a prominent citizen of Greenock and was at various times chief magistrate and treasurer of the town.

His Mechanical Mind

James Watt was intelligent, however, because of poor health, he was unable to attend school regularly. His early education was given by his parents. Tools from his father's carpenter bench provided Watt's with manual dexterity and familiarity with their use gave the boy an early education in the basics of engineering and tooling.

Arago, the eminent French philosopher, who wrote one of the earliest and most interesting biographies of James Watt, relates anecdotes about the mechanical bent of the boy's mind. At the age of six years, James Watt occupied himself during by solving geometrical problems, and by experimenting with his mother's tea kettle, his earliest investigation into the nature of steam.

When James Watt was finally sent to the village school, his ill health prevented his making rapid progress; and it was only when thirteen or fourteen years of age that he began to show that he was capable of taking the lead in his class, and to exhibit his abilities, particularly in mathematics. His spare time was spent sketching with his pencil, carving, and working at the tool bench with wood and metal. He made many ingenious pieces of mechanism and some beautiful models. He liked to repair nautical instruments. Among other pieces of apparatus made by the boy was a very fine barrel organ. In boyhood, James Watt was an avid reader and found something to interest him in every book that came into his hands.


At the age of eighteen, James Watt was sent to Glasgow to reside with his mother's relatives, and learn the trade of a mathematical instrument maker. James Watt soon outgrew the knowledge of the mechanic he was apprenticed to. A friend and professor at the University of Glasgow, Doctor Dick advised him to move to London. James Watt moved in June of 1755, and found work with John Morgan, in Cornhill, for twenty guineas a week. After a year he was compelled, by serious ill health, to return home.

After regaining his health, James Watt returned to Glasgow in 1756. However, because he had not finished his apprenticeship, he was forbidden by the guilds, or trades unions, to open a shop in Glasgow. Doctor Dick came to his aid and employed him to repair apparatus at the University. He remained there until 1760 when he was allowed to open a mechanic shop in the city. He briefly worked as a civil engineer, however, he preferred mechanics. James Watt spent much of his leisure time making musical instruments, inventing improvements in the construction of organs.

The Newcomen Steam Engine

He kept his connections with the University of Glasgow and that led to his introduction to the Newcomen steam engine in 1763. A model was owned by the University and given to James Watt for repairs.

Doctor Robison, a student at the University, was friends with James Watt and hung around his shop. It was Robison who first introduced James Watt to the concept of steam engines in 1759, and suggested that they could be used for the propulsion of carriages. James Watt built miniature models using tin steam cylinders and pistons attached to driving wheels by a system of gears. However, he abandoned his early research on steam engines. After he examined the Newcomen steam engine twenty-five years later, Watts renewed his interest and began studying the history of the steam engine, and conducting experimental research into the properties of steam.

In his own experiments he used, at first, apothecaries' trials and hollow canes for steam reservoirs and pipes, and later a Papin's digester and a common syringe. The latter combination made a noncondensing engine, in which he used steam at a pressure of 15 pounds per square inch. The valve was worked by hand, and James Watt saw that an automatic valve gear was needed to make a working machine. This experiment, however, led to no practical result. Watt finally got hold of the Newcomen model, after putting it in good working order, commenced experiments with that.

The Newcomen steam engine model had a boiler which was made to scale and was incapable of furnishing enough steam to power an engine. It was about nine inches in diameter; the steam cylinder was two inches in diameter and had a six-inch piston stroke.

James Watt made a new boiler for the experimental investigation of which he was about to enter that could measure the quantity of water evaporated and the steam condensed at every stroke of the engine.

Rediscovery of Latent Heat

He soon discovered that it required a very small quantity of steam to heat a very large quantity of water, and immediately started to determine with precision the relative weights of steam and water in the steam cylinder when condensation took place at the down stroke of the engine. James Watt independently proved the existence of "latent heat", the discovery of another scientist, Doctor Black. Watt went to Black with his research, who shared his knowledge with Watt. Watt found that, at the boiling point, his condensing steam was capable of heating six times its weight of water used for producing condensation.

Watt's Separate Condenser

Realizing that steam, weight for weight was a vastly greater absorbent and reservoir of heat than water, Watt saw the importance of taking greater care to economize it than had previously been attempted. At first, he economized in the boiler, and made boilers with wooden "shells" in order to prevent losses by conduction and radiation, and used a larger number of flues to secure more complete absorption of the heat from the furnace gases. He also covered his steam pipes with non-conducting materials and took every precaution to secure the complete utilization of the heat of combustion. He soon discovered that the great source of loss was to be found in defects which he noted in the action of the steam in the cylinder. He soon concluded that the sources of loss of heat in the Newcomen engine­ which would be greatly exaggerated in a small model were:

  • First, the dissipation of heat by the cylinder itself, which was of brass, and was both a good conductor and a good radiator.
  • Secondly, the loss of heat consequent upon the necessity of cooling down the cylinder at every stroke, in producing the vacuum.
  • Thirdly, the loss of power due to the pressure of vapor beneath the piston, which was a consequence of the imperfect method of condensation.

James Watt first made a cylinder of non-conducting material ­wood soaked in oil and then baked and increased the economy of steam. He then conducted a series of very accurate experiments upon the temperature and pressure of steam at such points on the scale as he could readily reach, and, constructing a curve with his results, the abscesses representing temperatures and the pressures being represented by the ordinates, he ran the curve backward until he had obtained closely approximate measures of temperatures less than 212°, and pressures less than atmospheric. Watt thus found that, with the amount of injection water used in the Newcomen engine, bringing the temperature of the interior, as he found, down to from 140° to 175° Fahrenheit, a very considerable back pressure would be met with.

Continuing his research, he measured the amount of steam used at each stroke, comparing it with the quantity that would just fill the cylinder, he found that at least three-fourths were required. The quantity of cold water necessary to produce the condensation of a given weight of steam was determined next; and he found that one pound of steam contained enough heat to raise about six pounds of cold water, as used for condensation, from the temperature of 62° to the boiling point. James Watt was compelled to use, at each stroke of the Newcomen engine, four times as much injection water as the amount used to condense a cylinder full of steam. This confirmed his previous conclusion that three-fourths of the heat supplied to the engine was wasted.

What His Research Determined

James Watt's research determined the following facts:

  1. The capacities for heat of iron, copper, and of some sorts of wood, as compared with water.
  2. The bulk of steam compared with that of water.
  3. The quantity of water evaporated in a certain boiler by a pound of coal.
  4. The elasticity of steam at various temperatures greater than that of boiling water, and an approximation to the law which it follows at other temperatures.
  5. How much water in the form of steam was required every stroke by a small Newcomen engine, with a wooden cylinder 6 inches in diameter and 12 inches stroke.
  6. The quantity of cold water required in every stroke to condense the steam in that cylinder, so as to give it a working power of about 7 pounds on the square inch.

After his scientific investigations, James Watt worked on improving the steam engine with an intelligent understanding of its existing defects, and with a knowledge of their cause. Watt soon saw that in order to reduce the losses in the working of the steam in the steam cylinder, it would be necessary to find a way to keep the cylinder always as hot as the steam that entered it.

Watt's Writings

According to James Watt: "I had gone to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte street and had passed the old washing house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that, as steam was an elastic body, it would rush into a vacuum, and, if a communication were made between the cylinder and an exhausted vessel, it would rush into it, and might be there condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection water if I used a jet, as in Newcomen's engine. Two ways of doing this occurred to me: First, the water might be run off by a descending pipe, if an off jet could be got at the depth of 35 or 36 feet, and any air might be extracted by a small pump. The second was, to make the pump large enough to extract both water and air. I had not walked farther than the Golf house when the whole thing was arranged in my mind."

Referring to this invention, James Watt said: "When analyzed, the invention would not appear so great as it seemed to be. In the state in which I found the steam engine, it was no great effort of mind to observe that the quantity of fuel necessary to make it work would forever prevent its extensive utility. The next step in my progress was equally easy ­ to inquire what was the cause of the great consumption of fuel. This, too, was readily suggested, viz., the waste of fuel which was necessary to bring the whole cylinder, piston, and adjacent parts from the coldness of water to the heat of steam, no fewer than from 15 to 20 times in a minute."

James Watt had invented his all-important separate condenser. He proceeded to make an experimental test of his new invention, using for his steam cylinder and piston a large brass surgeon's syringe, 14-inch diameter and 10 inches long. At each end was a pipe leading steam from the boiler, and fitted with a cock to act as a steam valve. A pipe led also from the top of the cylinder to the condenser, the syringe being inverted and the piston rod hanging downward for convenience. The condenser was made of two pipes of thin tin plate, 10 or 12 inches long, and about one sixth of an inch in diameter, standing vertically, and having a connection at the top with a horizontal pipe of larger size, and fitted with a "snifting valve." Another vertical pipe, about an inch in diameter, was connected to the condenser, and Watt fitted with a piston, with a view to using it as an "air pump."

The whole thing was set in a cistern of cold water. The piston rod of the little steam cylinder was drilled from end to end to permit the water to be removed from the cylinder. This little model worked very satisfactorily, and the perfection of the vacuum was such that the machine lifted a weight of 18 pounds hung upon the piston rod, as in the sketch. A larger model was immediately afterward constructed, and the result of its test confirmed fully the anticipations which had been awakened by the first experiment.

Having taken this first step and making such a radical improvement, the success of this invention was followed by more. All the result of improving the old Newcomen engine.

Watt Builds His Own Steam Engine

In the working out of the forms and proportions of the details of the new steam engine, even James Watt's powerful mind, stored as it was with happily combined scientific and practical information, was occupied for years.

In attaching the separate condenser, he first attempted surface condensation; but this not succeeding well, he substituted the jet. Watt had to find a way to prevent the filling of the condenser with water.

James Watt at first lead a pipe from the condenser to a depth greater than the height of a column of water which could be counterbalanced by the pressure of the atmosphere; subsequently, he employed an air pump, which relieved the condenser of the water and air which collected in the condenser and lessened the vacuum. He next substituted oil and tallow for the water used to lubricate the piston, keeping the steam tight and preventing the cooling of the cylinder. Another cause of refrigeration of the cylinder and consequent waste of power in its operation was the entrance of air, which followed the piston down the cylinder at each stroke, cooling its interior by its contact. The inventor prevented this from happening by covering the top of the cylinder.

He not only covered the top, but surrounded the whole cylinder with an external casing, or "steam jacket" that allowed the steam from the boiler to pass around the steam cylinder and press on the upper surface of the piston.

After James Watt built his larger experimental engine, he hired a room in an old deserted pottery. There he worked with mechanic Folm Gardiner. Watt had just met Doctor Roebuck, a wealthy physician, who had, with other Scotch capitalists, just founded the celebrated Carron Iron Works. James Watt frequently wrote to Roebuck describing his progress.

In August 1765, he tried the small engine and wrote Roebuck that he had "good success" although the machine was very imperfect. He then tells his correspondent that he was about to make the larger model. In October 1765, he finished the large steam engine. The engine, when ready for trial, was still very imperfect. It nevertheless did good work for so crude a machine.

James Watt was now reduced to poverty, after borrowing considerable sums from friends, he finally had to seek employment in order to provide for his family. During an interval of about two years, he supported himself by surveying, exploring coal fields in the neighborhood of Glasgow for the magistrates of the city. He did not, however, entirely give up his invention.

In 1767, Roebuck assumed Watt's liabilities to the amount of £1,000 and agreed to provide more capital in exchange for two-thirds of Watt's patent. Another engine was built with a steam cylinder seven or eight inches in diameter, which was finished in 1768. This worked sufficiently well to induce the partners to ask for a patent, and the specifications and drawings were completed and presented in 1769.

James Watt also built and set up several Newcomen engines, partly, perhaps, to make himself thus thoroughly familiar with the practical details of engine building. Meantime, also, he prepared the plans for, and finally had built, a moderately large engine of his own new type. Its steam cylinder was 18 inches in diameter, and the stroke of the piston was 5 feet. This engine was built at Kinneil and was finished in September 1769. It was not all satisfactory in either its construction or its operation. The condenser was a surface condenser composed of pipes somewhat like that used in his first little model and did not prove to be satisfactorily tight. The steam piston leaked seriously, and repeated trials only served to make more evident its imperfections. He was assisted in this time of need by both Dr. Black and Dr. Roebuck, but he felt strongly the risks which he ran of involving his friends in serious losses and became very despondent.

Writing to Dr. Black, he says: "Of all things in life, there is nothing more foolish than inventing; and probably the majority of inventors have been led to the same opinion by their own experiences."

Misfortunes never come singly, and Watt was borne down by the greatest of all misfortunes the loss of a faithful and affectionate wife while still unable to see a successful issue of his schemes. Only less disheartening than this was the loss of fortune of his steadfast friend, Dr. Roebuck, and the consequential loss of his aid. It was at about this time, in the year 1769, that negotiations were commenced which resulted in the transfer of the capitalized interest in Watt's engine to the wealthy manufacturer whose name, coupled with that of Watt, afterward became known throughout the civilized world, as the steam engine in its new form was pushed into use by his energy and business tact.

Partnership With Matthew Boulton

In 1768, James Watt met Matthew Boulton, his business partner, during his journey to London to get his patent. Matthew Boulton wanted to buy an interest in the patent. With Roebuck's consent, Watt offered Matthew Boulton a one-third interest. Subsequently, Roebuck proposed to transfer to Matthew Boulton, one-half of his proprietorship in Watt's inventions, for a sum of one thousand pounds. This proposal was accepted in November 1769.

Matthew Boulton was the son of a Birmingham silver stamper and piecer and succeeded to take over his father's business, building up a great establishment, which, as well as its proprietor, was well known in Watt's time.

Watt's estimate of the value of Boulton's ingenuity and talent was well founded. Boulton had shown himself a good scholar, and had acquired considerable knowledge of the languages and of the sciences, particularly of mathematics, after leaving the school from which he graduated into the shop when still a boy. In the shop he soon introduced a number of valuable improvements, and he was always on the lookout for improvements made by others, with a view to their introduction in his business. He was a man of the modern style, and never permitted competitors to excel him in any respect, without the strongest efforts to retain his leading position. He always aimed to earn a reputation for good work, as well as to make money. His father's workshop was at Birmingham; but Boulton, after a time, found that his rapidly increasing business would compel him to find room for the erection of a more extensive establishment, and he secured land at Soho, two miles distant from Birmingham, and there erected his new manufactory, about 1762.

The business was, at first, the manufacture of ornamental metal ware, such as metal buttons, buckles, watch chains, and light filigree and inlaid work. The manufacture of gold and silver plated ware was soon added, and this branch of business gradually developed into a very extensive manufacture of works of art. Boulton copied fine work wherever he could find it, and often borrowed vases, statuettes, and bronzes of all kinds from the nobility of England, and even from the queen, from which to make copies. The manufacture of inexpensive clocks, such as are now well known throughout the world as an article of American trade, was begun by Boulton. He made some fine astronomical and valuable ornamental clocks, which were better appreciated on the Continent than in England. The business of the Soho manufactory in a few years became so extensive, that its goods were known to every civilized nation, and its growth, under the management of the enterprising, conscientious, and ingenious Boulton, more than kept pace with the accumulation of capital; and the proprietor found himself, by his very prosperity, often driven  to the most careful manipulation of his assets, and to making free use of his credit.

Boulton had a remarkable talent for making valuable acquaintances, and for making the most of advantages accruing thereby. In 1758 he made the acquaintance of Benjamin Franklin, who then visited Soho; and in 1766 these distinguished men, who were then unaware of the existence of James Watt, were corresponding, and, in their letters, discussing the applicability of steam power to various useful purposes. Between the two a new steam engine was designed, and a model was constructed by Boulton, which was sent to Franklin and exhibited by him in London.

It was in November 1774, that Watt finally announced to His old partner, Dr. Roebuck, the successful trial of the Kilmeil engine. He did not write with the usual enthusiasm and extravagance of the inventor, for his frequent disappointments and prolonged suspense had very thoroughly extinguished his vivacity.

] He simply wrote: "The fire engine I have invented is now going, and answers much better than any other that has yet been made; and I expect that the invention will be very beneficial to me."

In the construction and erection of his engines, Watt still had great difficulty in finding skillful workmen to make the parts with accuracy, to fit them with care, and to erect them properly when once finished. And the fact that both Newcomen and Watt met with such serious trouble, indicates that even had the engine been designed earlier, it is quite unlikely that the world would have seen the steam-engine a success until this time when mechanics were just acquiring the skill requisite for its construction. But, on the other hand, it is not at all improbable that, had the mechanics of an earlier period been as skillful and as well educated in the manual niceties of their business, the steam-engine might have been much earlier brought into use.

The history of the steam engine is from this time a history of the work of the firm of Boulton and Watt. Nearly every successful and important invention which marked the history of steam power for many years originated in the fertile brain of James Watt.