James Watt, in trying to understand the thermodynamics of heat and steam, carries out many laboratory experiments in 1759 and his diaries record that in conducting these he used a kettle as a boiler to generate steam.

Watt's friend, John Robison, has called his attention to the use of steam as a source of motive power in 1759.

The design of the Newcomen engine, in use for almost fifty years for pumping water from mines, has hardly changed from its first implementation. 

Watt had begun to experiment with steam, though he has never seen an operating steam engine.

He tries constructing a model; it fails to work satisfactorily, but he continues his experiments and begins to read everything he can about the subject. 

He comes to realize the importance of latent heat—the thermal energy released or absorbed during a constant-temperature process—in understanding the engine, which, unknown to Watt, his friend Joseph Black had previously discovered some years before. 

Understanding of the steam engine is in a very primitive state, for the science of thermodynamics will not be formalized for nearly another one hundred years.

Watt was born on January 19, 1736 in Greenock, Renfrewshire, a seaport on the Firth of Clyde.

His father is a shipwright, ship owner and contractor, and serves as the town's chief baillie, while his mother, Agnes Muirhead, comes from a distinguished family and is well educated.

Both are Presbyterians and strong Covenanters.

Watt's grandfather, Thomas Watt, was a mathematics teacher and baillie to the Baron of Cartsburn.

Despite being raised by religious parents, he would later on become a deist.

Watt did not attend school regularly; initially he was mostly schooled at home by his mother but later he attended Greenock Grammar School.

He exhibited great manual dexterity, engineering skills and an aptitude for mathematics, while Latin and Greek failed to interest him.

When he was eighteen, his mother died and his father's health began to fail.

Watt travelled to London to study instrument-making for a year, then returned to Scotland, settling in the major commercial city of Glasgow intent on setting up his own instrument-making business.

He made and repaired brass reflecting quadrants, parallel rulers, scales, parts for telescopes, and barometers, among other things.

Because he had not served at least seven years as an apprentice, the Glasgow Guild of Hammermen (which had jurisdiction over any artisans using hammers) blocked his application, despite there being no other mathematical instrument makers in Scotland.

Watt had been saved from this impasse by the arrival from Jamaica of astronomical instruments bequeathed by Alexander Macfarlane to the University of Glasgow, instruments that required expert attention.

Watt had restored them to working order and was remunerated.

These instruments were eventually installed in the Macfarlane Observatory.

Subsequently three professors had offered him the opportunity to set up a small workshop within the university.

It was initiated in 1757 and two of the professors, the physicist and chemist Joseph Black as well as the famed Adam Smith, have become Watt's friends.

At first he had worked on maintaining and repairing scientific instruments used in the university, helping with demonstrations, and expanding the production of quadrants.

In 1759 he forms a partnership with John Craig, an architect and businessman, to manufacture and sell a line of products including musical instruments and toys.

This partnership will last for the next six years, and employ up to sixteen workers.

Craig will die in 1765.

One employee, Alex Gardner, will eventually take over the business, which will last into the twentieth century.
 
There is a popular story that Watt was inspired to invent the steam engine by seeing a kettle boiling, the steam forcing the lid to rise and thus showing Watt the power of steam.

This story is told in many forms; in some Watt is a young lad, in others he is older, sometimes it's his mother's kettle, sometimes his aunt's.

James Watt of course did not actually invent the steam engine, as the story implies, but dramatically improved the efficiency of the existing Newcomen engine by adding a separate condenser.

This is difficult to explain to someone not familiar with concepts of heat and thermal efficiency.

It appears that the story of Watt and the kettle was created, possibly by Watt's son James Watt Jr., and persists because it is easy for children to understand and remember.

In this light it can be seen as akin to the story of Isaac Newton, the falling apple and his discovery of gravity.

Although it is often dismissed as a myth, like most good stories the story of James Watt and the kettle has a basis in fact.

Watt had been asked in 1763 to repair a model Newcomen engine belonging to the university.

Even after repair, the engine barely works.

After much experimentation, Watt demonstrates that about three-quarters of the thermal energy of the steam is being consumed in heating the engine cylinder on every cycle.

This energy is wasted because later in the cycle cold water is injected into the cylinder to condense the steam to reduce its pressure.

Thus by repeatedly heating and cooling the cylinder, the engine wastes most of its thermal energy rather than converting it into mechanical energy.

Watt's critical insight, arrived at in May 1765, is to cause the steam to condense in a separate chamber apart from the piston, and to maintain the temperature of the cylinder at the same temperature as the injected steam by surrounding it with a "steam jacket."

Thus very little energy is absorbed by the cylinder on each cycle, making more available to perform useful work.

Watt has a working model later this same year.

Despite a potentially workable design, there are still substantial difficulties in constructing a full-scale engine.

This requires more capital, some of which comes from Black.

More substantial backing comes from John Roebuck, the founder of the celebrated Carron Iron Works near Falkirk, with whom he now forms a partnership.

Roebuck lives at Kinneil House in Bo'ness, during which time Watt works at perfecting his steam engine in a cottage adjacent to the house.

The shell of the cottage, and a very large part of one of his projects, still exist to the rear.

The principal difficulty is in machining the piston and cylinder.

Iron workers of the day are more like blacksmiths than modern machinists, and are unable to produce the components with sufficient precision.

Much capital is spent in pursuing a patent on Watt's invention.

Strapped for resources, Watt is forced to take up employment—first as a surveyor, then as a civil engineer—for the next eight years.

Franklin belongs to a gentleman's club (designated "honest Whigs" by Franklin), which holds stated meetings, and includes members such as Richard Price and Andrew Kippis.

He is also a corresponding member of the Lunar Society of Birmingham, which includes such other scientific and industrial luminaries as Matthew Boulton, James Watt, Josiah Wedgwood and Dr. Darwin.

Human knowledge and mastery over nature advances in the year 1775 when James Watt builds a successful prototype of a steam engine, and a scientific expedition continues as Captain James Cook claims the South Georgia and South Sandwich Islands in the south Atlantic Ocean for Britain.

James Watt and Matthew Boulton form a hugely successful partnership that will last for the next twenty-five years.

John Roebuck, the founder of the celebrated Carron Iron Works and a partner with James Watt in developing the latter's steam engine, had gone bankrupt, and Boulton, who owns the Soho Manufactory works near Birmingham, had acquired his patent rights.

An extension of the patent to 1800 is successfully obtained in 1775.

Through Boulton, Watt finally has access to some of the best iron workers in the world.

The difficulty of the manufacture of a large cylinder with a tightly fitting piston is solved by John Wilkinson, who has developed precision boring techniques for cannon making at Bersham, near Wrexham, North Wales.

Watt had tried unsuccessfully for several years to obtain accurately bored cylinders for his steam engines, and has been forced to use hammered iron, which is out of round and causei leakage past the piston.

In 1774 Wilkinson had invented a boring machine in which the shaft that holds the cutting tool extends through the cylinder and is supported on both ends, unlike the cantilevered borers currently in use.

With this machine he is able to bore the cylinder for Boulton & Watt's first commercial engine, and is given an exclusive contract for the provision of cylinders.

Until this era, advancements in drilling and boring practice had lain only within the application field of gun barrels for firearms and cannon; Wilkinson's achievement is a milestone in the gradual development of boring technology, as its fields of application broaden into engines, pumps, and other industrial uses.

James Watt had demonstrated the first practical steam engine in 1769.

His improvements are fundamental to the changes brought by the Industrial Revolution in both Britain and the world.

The first engines are finally installed and working in commercial enterprises in 1776.

These first engines are used for pumps and produced only reciprocating motion to move the pump rods at the bottom of the shaft.

Orders begin to pour in and for the next five years the Scottish inventor will be very busy installing more engines, mostly in Cornwall for pumping water out of mines.

The Smethwick Engine is to operate for more than a century as the world’s oldest working engine.

John Wilkinson, apprenticed to an ironmonger at Liverpool, had became an ironmonger himself about five years later.

Wilkinson had probably worked with his father in his foundry (which included a blast furnace) at Bersham in Denbighshire, but in the late 1750s he had established, with partners, ironworks at Willey, near Broseley in Shropshire.

He had taken over Bersham Ironworks as well in 1761, and in 1766 established the Bradley works in Bilston parish, near Wolverhampton.

This has become his largest and most successful enterprise, and is the site of extensive experiments in getting raw coal to substitute for coke in the production of cast iron.

At its peak, it includes a number of blast furnaces, a brick works, potteries, glass works, and rolling mills.

The Birmingham Canal is subsequently built near the Bradley works.

Among his products are cannons.

These are difficult to cast as the presence of 'honeycombs' (blow holes) is unacceptable to the Board of Ordnance.

Traditional cannons had been cast with a core, but in 1774 Wilkinson had proposed casting them solid and boring out the core afterwards.

Cannons had long been bored to remove imperfections in the casting, but casting them solid and boring out the core after made them much better cannons.

Wilkinson had also invented and patented in 1775 a new kind of boring machine, that drilled a more precise hole.

Unfortunately for him, his invention was not novel, and his patent was eventually repealed.

Another important product is steam engine cylinders.

Because his cylinders are so accurately bored, he becomes the main supplier of these for Boulton & Watt, and also licenses steam engines from them to assist in his ironworks.

The original Birmingham Canal is extremely successful but there is a problem with supplying sufficient water to the Smethwick Summit.

Matthew Boulton's partner, James Watt, had just patented an improvement to the steam engine involving an external condenser which improved the efficiency (and therefore reduced the amount of coal needed to run it).

Steam engines are constructed at either end of the Smethwick Summit to pump water used in the operation of the locks back to the summit.

The Spon Lane Engine (April 1778) operates from the Wolverhampton side, and another, the Smethwick Engine (June 5, 1779), pumps water from the Birmingham side of the summit.

Northwest Europe (1780–1791): Imperial Shifts, Industrial Revolution, and Revolutionary Ideas

Britain’s Defeat and American Independence

From 1780 to 1783, Britain faced the costly final phases of the American Revolutionary War. Although the British Empire was engaged in a worldwide struggle against a coalition that included Russia, France, Holland, French Canadians, Spain, Sweden, Denmark, and Prussia—collectively known as the League of Armed Neutrality—it offered only seemingly token resistance to the American colonists’ revolt. Britain’s defeat culminated in General Charles Cornwallis’s surrender at Yorktown (1781) and the Treaty of Paris (1783), officially recognizing American independence. While the loss fundamentally reshaped British imperial strategy, Britain managed to retain critical territories in Canada and the Caribbean.

The Advent and Impact of the Industrial Revolution

Despite this imperial setback, Britain surged decisively ahead of its European rivals through the dramatic unfolding of the Industrial Revolution. The foundations of this transformation were facilitated partly by the century-long influx of Brazilian gold, providing vital capital to stimulate early industrial enterprises. Britain's burgeoning industries rapidly expanded, substantially increasing national prosperity and living standards. This spiraling cycle of rising demand, production, and prosperity reshaped domestic markets and significantly boosted overseas trade. The East India Company, benefiting enormously from heightened British demand for raw materials, particularly commodities from India, became the single largest player in Britain's increasingly globalized economy. This expansion was further amplified by wartime necessity, as Indian commodities were essential to sustain British troops and industries.

James Watt and the Steam Engine Revolution

Crucial to Britain’s industrial ascendancy were the advances made by James Watt, whose enhanced steam engine transformed manufacturing, mining, and industry. Watt’s earliest commercial steam engines, installed beginning in 1776, initially powered pumps to remove water from mines, notably in Cornwall. These massive early engines featured large cylinders—typically fifty inches in diameter, standing around twenty-four feet tall—necessitating dedicated engine houses for their operation. Initially, Watt did not manufacture these engines himself; rather, he acted as a consulting engineer, overseeing installations according to his designs, while others undertook their construction. Watt’s firm, Boulton & Watt, charged clients an annual royalty calculated at one-third of the coal savings compared to older Newcomen engines.

Encouraged by Matthew Boulton, Watt broadened the applications of steam power beyond pumping by converting the reciprocating piston motion into rotational motion suitable for driving industrial machinery, including grinding mills, weaving looms, and milling devices. Although a crank seemed the natural choice for this conversion, Watt and Boulton were impeded by an existing patent held by James Pickard. Instead of accepting a restrictive cross-license arrangement, Watt ingeniously devised the sun and planet gear mechanism in 1781 to circumvent Pickard’s patent.

From 1781 to 1788, Watt introduced a series of major improvements: a double-acting engine (steam acting alternately on both sides of the piston), the application of "expansive" steam operation at pressures above atmospheric, and the development of compound engines, wherein two or more engines were linked for greater efficiency. In 1784, Watt patented his celebrated parallel motion mechanism, enabling a piston rod to move in a straight line—essential for the double-acting engine—despite being attached to a rocking beam with a circular arc. Watt also developed crucial control devices, such as the throttle valve and, in 1788, the centrifugal governor to prevent engines from dangerously accelerating ("running away"). Together, these innovations produced an engine five times more fuel-efficient than its predecessors. Despite these advances, Watt cautiously restricted steam pressures to near atmospheric levels, wary of boiler explosions caused by primitive boiler designs prone to leaks and structural failures.

Adam Smith’s Influence and Economic Liberalism

Amidst industrial and imperial transformations, Enlightenment economic ideas, epitomized by Adam Smith’s influential Wealth of Nations (1776), guided Britain’s policy debates. Smith’s advocacy of free trade, competitive markets, and limited governmental intervention—his system of “natural liberty”—resonated profoundly. His work supported liberalized trade policies and provided intellectual justification for Britain’s expanding industrial capitalism. Concurrently, Smith’s earlier moral philosophy in The Theory of Moral Sentiments (1759) continued informing social reformers and policymakers addressing humanitarian concerns, including public health and penal reform.

The Gordon Riots and Penal Reforms

Internally, Britain faced severe unrest during the violent Gordon Riots of 1780, sparked by anti-Catholic sentiment and opposition to the Catholic Relief Act (1778). The ensuing destruction highlighted deep social tensions and the need for stronger governance. Meanwhile, prison conditions, spotlighted by recurring epidemics of gaol fever (typhus), became targets of growing public condemnation. Reformers like John Howard, whose influential work The State of the Prisons gained prominence throughout the 1780s, began reshaping public attitudes toward sanitation, dietary improvements, and more humane prison practices.

Innovations in Life Insurance and Financial Practices

Britain’s financial services sector also advanced significantly, driven by the actuarial innovations introduced earlier by figures like Edward Rowe Mores and institutions such as the Society for Equitable Assurances on Lives and Survivorship. Throughout the 1780s, life insurance practices evolved dramatically, employing sophisticated mortality tables and actuarial calculations to secure public confidence. These methods supported the burgeoning middle class’s investment culture, bolstering economic stability.

Cultural Developments: Leisure, Culinary, and Artistic Flourishing

Cultural innovation was evident in daily life as well. The popularization of the sandwich, associated famously with the busy Earl of Sandwich, became emblematic of changing eating habits driven by convenience and modernity. Leisure culture at coastal resorts flourished, aided by increasing use of bathing machines, reflecting new social conventions around recreation and modesty.

Simultaneously, artistic life thrived through Rococo-inspired portraiture by leading artists such as Joshua Reynolds, Thomas Gainsborough, Angelica Kauffman, and George Romney, who captured the elegance and sophistication of British elites during this period.

Exploration: James Cook’s Final Voyages

Britain’s global scientific explorations continued, notably through the voyages of Captain James Cook. Cook’s third and final voyage (1776–1780), although ending tragically with his death in Hawaii (1779), vastly expanded European geographic knowledge of the Pacific Northwest, the Hawaiian Islands, and the Australian continent, reinforcing Britain’s global maritime dominance.

Denmark-Norway and Irish Reforms

Under Crown Prince Frederick’s regency from 1784, Denmark-Norway embraced Enlightenment reforms in agriculture, trade liberalization, and education, stabilizing governance and promoting prosperity. Ireland, meanwhile, secured legislative autonomy in 1782 after vigorous nationalist advocacy led by figures like Henry Grattan, despite continued economic distress under restrictive British trade and penal laws.

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Between 1780 and 1791, Northwest Europe navigated profound shifts in global power and industrial capacity. Britain’s burgeoning industrial economy, propelled by revolutionary steam-engine technologies developed by James Watt and energized by global commerce through the East India Company, set it decisively ahead of its European rivals. Concurrently, Enlightenment philosophies influenced economics, humanitarian reforms reshaped social conditions, and cultural transformations enriched everyday life. Collectively, these pivotal developments defined the trajectory toward Britain’s global dominance, intensified industrialization, and the revolutionary upheavals approaching the nineteenth century.

The first steam engines had been installed in 1776 and were working in commercial enterprises.

These first engines were used to power pumps and produced only reciprocating motion to move the pump rods at the bottom of the shaft.

The design was commercially successful, and for the next five years James Watt had been very busy installing more engines, mostly in Cornwall for pumping water out of mines.

These early engines were not manufactured by Boulton and Watt, but were made by others according to drawings made by Watt, who served in the role of consulting engineer.

The erection of the engine and its shakedown was supervised by Watt, at first, and then by men in the firm's employ.

These were large machines.

The first, for example, had a cylinder with a diameter of some fifty inches and an overall height of about twenty-four feet, and required the construction of a dedicated building to house it.

Boulton and Watt charged an annual payment, equal to one third of the value of the coal saved in comparison to a Newcomen engine performing the same work.

The field of application for the invention is greatly widened when Boulton urges Watt to convert the reciprocating motion of the piston to produce rotational power for grinding, weaving and milling.

Although a crank seems the obvious solution to the conversion, Watt and Boulton are stymied by a patent for this, whose holder, James Pickard, and associates propose to cross-license the external condenser.

Watt adamantly opposes this and they circumvent the patent by their sun and planet gear in 1781.

Over the next six years, Watt makes a number of other improvements and modifications to the steam engine.

A double acting engine, in which the steam acts alternately on the two sides of the piston, is one.

He describes methods for working the steam "expansively" (i.e., using steam at pressures well above atmospheric).

A compound engine, which connects two or more engine, is described.

Two more patents are granted for these in 1781 and 1782.

Numerous other improvements that make for easier manufacture and installation are continually implemented.

One of these includes the use of the steam indicator, which produces an informative plot of the pressure in the cylinder against its volume, which he keeps as a trade secret.

Another important invention, one which Watt is most proud of, is the Parallel motion, which is essential in double-acting engines as it produces the straight line motion required for the cylinder rod and pump, from the connected rocking beam, whose end moves in a circular arc.

This is patented in 1784.

A throttle valve to control the power of the engine, and a centrifugal governor, patented in 1788, to keep it from "running away" are very important.

These improvements taken together produce an engine which is up to five times as efficient in its use of fuel as the Newcomen engine.

Because of the danger of exploding boilers, which are in a very primitive stage of development, and the ongoing issues with leaks, Watt restricts his use of high pressure steam—all of his engines use steam at near atmospheric pressure.

Henry Cavendish, in a paper on eudiometry (the measurement of the goodness of gases for breathing) published in 1783, describes a new eudiometer of his own invention, with which he achieves the best results to date, using what in other hands had been the inexact method of measuring gases by weighing them.

He next publishes a paper on the production of water by burning inflammable air (that is, hydrogen) in "dephlogisticated air" (now known to be oxygen), the latter a constituent of atmospheric air (phlogiston theory).

Cavendish concludes that dephlogisticated air is dephlogisticated water and that hydrogen is either pure phlogiston or phlogisticated water. 

He reports these findings to Joseph Priestley, an English clergyman and scientist, no later than March 1783, but will not publish them until the following year.

The Scottish inventor James Watt publishes a paper on the composition of water in 1783; Cavendish had performed the experiments first but publishes second.

Controversy about priority ensues.

In 1783 he publishes a paper on the temperature at which mercury freezes and in this paper makes use of the idea of latent heat, although he does not use the term because he believes that it implies acceptance of a material theory of heat. 

He will made his objections explicit in his 1784 paper on air.

Cavendish, at about the time of his father's death, had begun to work closely with Charles Blagden, an association that had helped Blagden enter fully into London’s scientific society.

In return, Blagden has helped to keep the world at a distance from Cavendish.

Cavendish publishes no books and few papers, but he achieves much.

Several areas of research, including mechanics, optics, and magnetism, feature extensively in his manuscripts, but they scarcely feature in his published work.

Cavendish is considered to be one of the so-called pneumatic chemists of the eighteenth and nineteenth centuries, along with, for example, Joseph Priestley, Joseph Black, and Daniel Rutherford.

Cavendish had found that a definite, peculiar, and highly inflammable gas, which he refers to as "Inflammable Air", is produced by the action of certain acid on certain metals.

This gas is in fact hydrogen, which Cavendish had correctly guessed is proportioned to two in one water.

Although others, such as Robert Boyle, had prepared hydrogen gas earlier, Cavendish is usually given the credit for recognizing its elemental nature.

Also, by dissolving alkalis in acids, Cavendish makes "fixed air" (carbon dioxide), which he collects, along with other gases, in bottles inverted over water or mercury.

He then measures their solubility in water and their specific gravity and notes their combustibility.

Cavendish had been awarded the Royal Society’s Copley Medal for this paper.

Gas chemistry is of increasing importance in the latter half of the eighteenth century and becomes crucial for Frenchman Antoine-Laurent Lavoisier’s reform of chemistry, generally known as the chemical revolution.