7 The 100 Most Influential Inventors of All Time 7James Watt’s rotative steam engine with sun-
and-planet gear, original drawing, 1788. In
the Science Museum, London. British Crown
copyright, Science Museum, London
that lasted 25 years.
Boulton’s fi nancial
support made possible
rapid progress with
the engine. In 1776
two engines were
installed, one for
pumping water in a
Staffordshire colliery,
the other for blowing
air into the furnaces
of John Wilkinson,
the famous iron-
master. That year
Watt married again—
his second wife, Ann
MacGregor, bore him
two more children.
During the next
fi ve years, until 1781,
Watt spent long
periods in Cornwall,
where he installed and
supervised numerous pumping engines for the copper
and tin mines, the managers of which wanted to reduce
fuel costs. Watt, who was no businessman, was obliged
to endure keen bargaining in order to obtain adequate
royalties on the new engines. By 1780 he was doing well
fi nancially, though Boulton still had problems raising
capital. In the following year Boulton, foreseeing a new
market in the corn, malt, and cotton mills, urged Watt to
invent a rotary motion for the steam engine, to replace the
reciprocating action of the original. He did this in 1781
with his so-called sun-and-planet gear , by means of which
a shaft produced two revolutions for each cycle of the