He couldn’t sleep. The steam engine kept him awake at night — not the noise, but the inefficiency. “I can think of nothing else but this machine,” he wrote. “It haunts me day and night.”
Watt spoke with a Greenock Scots accent softened by decades in Birmingham — Lowland Scottish pronunciation with a Midlands overlay. Quiet, somewhat anxious. Not the voice of a bold inventor. The voice of a man who lay awake worrying about pressure differentials and heat loss and whether the seals would hold.
He was a chronic worrier and perfectionist. Contemporaries described him as shy, anxious, and frequently depressed — the opposite of the bold inventor stereotype. His headaches were constant. His confidence was not. He relied on his business partner Matthew Boulton for commercial drive while he retreated to the workshop to refine, adjust, and improve.
The separate condenser was the breakthrough. Thomas Newcomen’s atmospheric engine wasted three-quarters of its heat by cooling and reheating the cylinder with every stroke. Watt couldn’t bear it. The waste offended him. He designed a separate chamber to condense the steam, keeping the main cylinder hot. It doubled the engine’s efficiency. It powered the Industrial Revolution.
He also invented the concept of “horsepower” — not as a scientific measurement but as a marketing unit. He needed a way to convince mine owners that his engines were worth the investment. How much work can a horse do? Watt measured it. 33,000 foot-pounds per minute. One horsepower. Now he could tell a mine owner: my engine does the work of ten horses and doesn’t need to eat.
He was part of the Lunar Society — Birmingham’s extraordinary gathering of minds that included Joseph Priestley, Erasmus Darwin, and Josiah Wedgwood. They met on nights when the full moon lit the roads home. Watt attended, worried, contributed, and went home to worry some more.
He was 83 when he died. His workshop at Heathfield Hall, preserved after his death, revealed a restless, experimental mind that never stopped tinkering. The unit of power — the watt — bears his name. The anxious man from Greenock who couldn’t sleep measures every lightbulb in the world.
Sources: Ben Marsden, Watt’s Perfect Engine (2002); Jenny Uglow, The Lunar Men (2002); Watt’s workshop, Science Museum, London; Boulton and Watt business correspondence.