NT

The number and activity of rivals attracted to the steam engine and its
possible improvement, some of whom had begun infringements upon the Watt
patents, alarmed Messrs. Watt and Boulton so much that they decided Watt
should apply for another patent, covering his important improvements
since the first. Accordingly, October 25, 1781, the patent (already
referred to on p. 91) was secured, "for certain new methods of producing
a continued rotative motion around an axis or centre, and thereby to
give motion to the wheels of mills or other machines."

This patent was necessary in consequence of the difficulties experienced
in working the steam wheels or rotatory engines described in the first
patent of 1769, and by Watt's having been so unfairly anticipated, by
Wasborough in the crank motion.

No less than five different methods for rotatory motion are described in
the patent, the fifth commonly known as the "sun and planet wheels," of
which Watt writes to Boulton, January 3, 1782,

I have tried a model of one of my old plans of rotative engines,
revived and executed by Mr. Murdoch, which merits being
included in the specification as a fifth method; for which
purpose I shall send a drawing and description next post. It has
the singular property of going twice round for each stroke of
the engine, and may be made to go oftener round, if required,
without additional machinery.

Then followed an explanation of the sketch which he sent, and two days
later he wrote, "I send you the drawings of the fifth method, and
thought to have sent you the description complete, but it was late last
night before I finished so far, and to-day have a headache, therefore
only send you a rough draft of part."

In all of these Watt recommended that a fly-wheel be used to regulate
the motion, but in the specification for the patent of the following
year, 1782, his double-acting engine produced a more regular motion and
rendered a fly-wheel unnecessary, "so that," he says, "in most of our
great manufactories these engines now supply the place of water, wind
and horse mills, and instead of carrying the work to the power, the
prime agent is placed wherever it is most convenient to the
manufacturer."

This marks one of the most important stages in the development of the
steam engine. It was at last the portable machine it remains to-day, and
was placed wherever convenient, complete in itself and with the rotative