7 James Watt 7engine. In 1782, at the height of his inventive powers, he
patented the double-acting engine, in which the piston
pushed as well as pulled. The engine required a new
method of rigidly connecting the piston to the beam. He
solved this problem in 1784 with his invention of the parallel
motion—an arrangement of connected rods that guided
the piston rod in a perpendicular motion—which he
described as “one of the most ingenious, simple pieces
of mechanism I have contrived.” Four years later his
application of the centrifugal governor for automatic
control of the speed of the engine, at Boulton’s suggestion,
and in 1790 his invention of a pressure gauge, virtually
completed the Watt engine.
Later Years
Demands for his engine came quickly from paper mills,
flour mills, cotton mills, iron mills, distilleries, and canals
and waterworks. By 1790 Watt was a wealthy man, having
received £76,000 in royalties on his patents in 11 years.
The steam engine did not absorb all his attention, however.
He was a member of the Lunar Society in Birmingham, a
group of writers and scientists who wished to advance the
sciences and the arts. Watt experimented on the strength
of materials, and he was often involved in legal proceedings
to protect his patents. In 1785 he and Boulton were elected
fellows of the Royal Society of London. Watt then began to
take holidays, bought an estate at Doldowlod, Radnorshire,
and from 1795 onward gradually withdrew from business.
With the approach of his retirement in 1800 and because
that was also the year in which his patents and partnership
would expire, Watt established in 1794 the new firm of
Boulton & Watt, which built the Soho Foundry to manu-
facture steam engines more competitively. During this
time Watt’s son by his first marriage, James, gave him