— Thomas Tredgold engineer 1788 - 1829
Context: In June, 1699, Captain Savery exhibited a model of his engine before the Royal Society, and the experiments he made with it succeeded to their satisfaction. It consisted of a furnace and boiler B: from the latter, two pipes, provided with cocks C, proceeded to two steam vessels S, which had branch pipes from a descending main D, and also to a rising main pipe A: each pair of branch pipes had [check] valves a, b to prevent the descent of the water raised by the condensation or by the force of steam. Only one vessel, S, is shown, the other being immediately behind it. One of the steam vessels being filled with steam, condensation was produced by projecting cold water, from a small cistern E, against the vessel; and into the partial vacuum made by that means, the water, by the pressure of the atmosphere, was forced up the descending main D, from a depth of about twenty feet; and on the steam being let into the vessels again, the valve b closed, and prevented the descent of the water, while the steam having acquired force in the boiler, its pressure caused the water to raise the valve a, and ascend to a height proportional to the excess of the elastic force of the steam above the pressure of the air.