The tragic genius who helped forge modern Britain

"THOSE who consider James Watt only as a practical mechanic form a very erroneous idea of his character: he was equally distinguished as a natural philosopher and a chemist, and his inventions demonstrate his profound knowledge of those sciences, and that particular characteristic of genius, the union of them for practical application."

Thus Humphry Davy told a public meeting to discuss erecting a monument to the great Scottish engineer and scientist James Watt (1736-1819) some years after his death.

Many people believe that Watt, who was born in Greenock, invented the steam engine, but the first such machine had been patented in 1698, the year of Watt's father's birth.

His real achievement was to transform this Newcomen engine, as it was known, from a hopelessly inefficient machine which wasted three quarters of its steam (through condensation) while heating a cold cylinder up to 100 degrees before it could generate any power into the workhorse of the industrial revolution.

Infamously, the eureka moment which led to this development occurred one Sunday afternoon in May 1765 during a walk on Glasgow Green. "I had not walked further than the golf-house when the whole thing was arranged in my mind," Watt said. The engine would be given a separate condenser. He duly secured a patent.

After several abortive attempts to build a successful prototype, Watt teamed up with the Birmingham-based tycoon Matthew Boulton. The pair of them refined the engine, which first worked in 1775. Boulton & Watt soon became the country's foremost engineering company as flour, cotton iron and paper mills, Cornish mines, and canals and waterworks all bought steam engines. In all, they are estimated to have produced 449 engines with an average size of just under 25 horsepower.

As a result Watt became a very wealthy man - he left 60,000 at his death - but his personal life was much marred by tragedy.

He married his cousin Margaret Miller in 1764, but she and their third child died during labour in 1773 while Watt was carrying out surveys for the Caledonian Canal in the Highlands (although Thomas Telford built it, Watt designed it). Of her, Watt wrote: "I lost the comfort of my life, a dear friend and a faithful wife."

His daughter Janet (known as Jessy) and son Gregory by his second wife Anne both died from consumption, she in 1794 at only 15, he in 1804 at 27.

As Davy indicated, Watt was more than just a craftsman, albeit a highly distinguished one. His philosophical and scientific work brought him honours around the world, and he was elected to the Royal Societies of London and Edinburgh. He also joined the provincial Lunar Society, of which his fellow Scot James Keir and Erasmus Darwin were members.

After his retirement Watt and his wife travelled extensively around Europe and Scotland. As Jennifer Tann says in her entry on Watt in the Oxford Dictionary of National Biography: "He ... was particularly fond of Edinburgh. His dry humour, and the Scots accent that he never lost, made him welcome north of the Border."

A self-deprecating man, Watt would have been disdainful of his position in the history of science and Scotland (he was included in the hall of Scottish heroes at the Wallace monument near Stirling when it was erected in the 1860s). But the legacy he left - his engine was adopted by manufacturers at the turn of the 18th century - is a key role in creating the industrial boom that forged modern Britain.

Watt died in Handsworth, Birmingham, on 25 August, 1819, and was buried beside Matthew Boulton.