Watt's idea
Newcomen's engine heated and cooled the steam in one and the same cylinder, which wasted fuel. Watt added a separate condenser, so the cylinder stayed hot. The engine used roughly two thirds less coal. Watt also introduced horsepower to explain the engine's power to his customers.
A changed world
Factories no longer had to stand next to rivers. Steam locomotives and steamships cut journeys from weeks to days. Cities grew and a new working class emerged.
Steam lives on
Steam turbines still produce most of the electricity in coal-fired and nuclear power stations. Much of their theory was worked out by the Slovak Aurel Stodola.