Drawing of Symington's steam engine

This is a copy of the drawing enrolled with William Symington's patent specification of 1787, which shows an atmospheric engine in which heat losses are diminished by confining condensation to the lower and enlarged part of the cylinder by means of a free piston or air-pump bucket resting, close to the surface of the cold water there, on two rods supported by a lever worked by tappets in the plug frame. This mechanism and the engine are interesting, as they were used by Symington in very early experiments on steam navigation