Note 233 — Chapter XV · Watt again visits Cornwall—Invention of the Rotary Motion—The Patent Right again assailed.

“I have some time ago thought,” wrote Watt, “of a new expansive engine—a reciprocating engine with a heavy circular fly moved by a pinion from the end of the beam, so as to make three turns per down-stroke and as many contrariwise per return; so that in the first half of the stroke it may acquire a momentum which will carry it through the last half; and if a weight equal to half the load be put upon the inner end of the beam, and the engine be made to lift it during the return, by making a vacuum above the piston and using a rack instead of a chain, a cylinder of the present size may work to the same depth by half the steam; and I believe the engine will work very sweetly.”—Watt to Boulton, 16th January, 1782.