Note 372 — Chapter XXI · Application of Steam-power to Navigation—Miller and Symington—Boulton and Watt’s Engine adopted by Fulton.

From a memorandum found amongst Mr. Boulton’s papers, we learn that the following were the details of Symington’s engine:—“Engine hath two cylinders of 18 inches diameter each and 2 feet stroke. The rods of each piston are connected to a circular barrel of cast iron by means of chains, so that whilst one piston moves down the other ascends, and so gives the barrel a reciprocating motion. Upon the axis of the barrel is an arm or lever which works the plug and working gear. Each of the cylinders hath 2 pistons, one at top and the other at bottom; the 2 bottom pistons have their rods moving in stuffing-boxes and are connected together by a beam. The steam is admitted into the cylinder at its side, between the 2 pistons, and moves the one up and the other down; but the motion of the upper is greater than the under. When the upper piston is got to the top and the under one to the bottom, the steam valve is shut and the exhaustion one opened; by which the steam is admitted into the bottom of the cylinder, and is in its way met by a jet of cold water, which condenses it, and then it is squeezed out by the under piston, which in fact makes the bottom of the cylinder an air-pump. Whilst this condensation is going forward in the one cylinder, the steam is operating in the other, and vice versâ.”