James Watt's improved steam engine, patented in 1769, added a separate condenser so that the cylinder no longer had to be repeatedly cooled and reheated, roughly trebling fuel efficiency over the earlier Newcomen engine. In partnership with Matthew Boulton in Birmingham, Watt added rotary motion in the 1780s, so the engine could turn machinery rather than only pump water. This made reliable mechanical power available wherever coal could be brought, independent of flowing water. The engines were widely adopted in mills, mines and, later, transport.
By freeing factories from waterpower sites, it allowed industry to concentrate in coal-rich towns, driving the explosive and often unplanned growth of the nineteenth-century industrial city.
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