Trevithick and High-Pressure Steam

Watt's engines used low-pressure steam and were large and heavy; Watt himself opposed high-pressure steam as dangerous. Cornish engineer Richard Trevithick disagreed. High-pressure steam allowed smaller, lighter and more powerful engines that did not need a separate condenser. In 1801 he built a steam road carriage, the 'Puffing Devil', which carried passengers up a hill in Camborne.

In 1804, at the Penydarren ironworks in South Wales, his locomotive hauled 10 tons of iron and about 70 men along a tramway for nearly 10 miles, the first recorded journey of a steam locomotive on rails. The cast-iron rails broke under its weight, and Trevithick never made a fortune. Yet high-pressure engines became the basis of locomotives, steamships and many factory engines, showing how a risky idea rejected by an established expert could prove transformative.