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.