Watt again visits Cornwall--Rotary motion--The crank-engine at Soho--Theft of the invention--Matthew Washborough--Smeaton and steam-power--Rotary-motion engine--Boulton and Watt’s cares--Evasions of the engine patent--The Hornblowers’ engine--Watt’s new inventions--Boulton’s confidence in the engine--Air-engine--Watt’s fears for the patent--The rotary engine invented--New improvements introduced--The equalising beam--Watt’s ill health and humour--Various expedients for producing circular motion--Murdock’s sun-and-planet motion--Patent taken for the reciprocating expansive engine--Troubles with workmen--Murdock’s efficiency and popularity--Watt’s despondency--The firm’s London agent’s house burnt--Gloomy prospects of the mining trade 285–316 CHAPTER XVI. Financial position of the firm--Rotary engines for mills--Boulton’s battles with the Cornish adventurers--His life in Cornwall--Murdock and the miners--The Hornblowers’ engine at Radstoke--Watt at Bristol--Major Tucker--Steam mills--Rotary motion applied--The first rotative engines--Pumping-engines for the Fens--Boulton’s health fails--He visits Scotland, Carron ironworks, Lord Dundonald--His extensive correspondence--Grumbling in Cornwall--Concessions to the miners--Press of work at Soho--Watt’s invention of the parallel motion and the governor--Murdock’s model locomotive--Boulton’s praise of Murdock--More pumping-engines wanted--Boulton’s affection for his children--Letter to his son--His scientific recreations--Domestic enjoyment at Cosgarne 317–341 CHAPTER XVII. Boulton’s action in commercial politics--His interview with Pitt--Agitation against Pitt’s commercial policy--The “Irish resolutions”--Watt on free commerce--Is opposed to political agitation--Combination against patents--Fluctuations in the business at Soho--Engine orders from various quarters--The Cornish copper-miners--The Copper Company formed, and Boulton’s part in it--Riots in Cornwall--Boulton’s life threatened--The esteem in which he was held in Cornwall--His intimacy with the Quakers--The Albion Mill scheme--The double-acting engines for the mill--Ill-success of the undertaking--Albion Mill burnt down--Demand for rotative engines--Want of skill and misconduct of workmen--Wedgwood’s advice to Watt--Speculativeness of Boulton--His embarrassments--Watt’s caution in investing--Boulton’s health fails--His depressed spirits--Generosity to Watt 342–366 CHAPTER XVIII.