It was already an age of scientific wonders that promised to reshape economies and boost productivity. From the first steam engine that James Watt built in Great Britain in the 1760s to the hot-air balloons that floated across French skies in the 1780s to Eli Whitney's invention of the cotton gin and the use of interchangeable parts in the 1790s, it was a time of technological marvels. No industry was being transformed more dramatically than British textiles. Sir Richard Arkwright had devised a machine called the water frame that used the power of rushing water to spin many threads simultaneously. By the time Hamilton was sworn in as treasury secretary, Arkwright's mills on the Clyde in Scotland employed more than 1,300 hands.