equate for small operations, the quantity of
water available was often limited, and the use of enormous horse-whims
was frequently impracticable.

The only type of steam engine then in existence was the Newcomen beam
engine, which had been introduced in 1712 by Thomas Newcomen, also an
Englishman. This type of engine was widely used, mostly for pumping
water out of mines but occasionally for pumping water into a reservoir
to supply a waterwheel. It was arranged with a vertical steam cylinder
located beneath one end of a large pivoted working beam and a vertical
plunger-type pump beneath the other end. Heavy, flat chains were secured
to a sector at each end of the working beam and to the engine and pump
piston rods in such a way that the rods were always tangent to a circle
whose center was at the beam pivot. The weight of the reciprocating pump
parts pulled the pump end of the beam down; the atmosphere, acting on
the open top of the piston in the steam cylinder, caused the engine end
of the beam to be pulled down when the steam beneath the piston was
condensed. The chains would of course transmit force from piston to beam
only in tension.

It is now obvious that a connecting rod, a crank, and a sufficiently
heavy flywheel might have been used in a conventional Newcomen engine in
order to supply power to a rotating shaft, but contemporary evidence
makes it clear that this solution was by no means obvious to Watt nor to
his contemporaries.

At the time of his first engine patent, in 1769, Watt had devised a
"steam wheel," or rotary engine, that used liquid mercury in the lower
part of a toroidal chamber to provide a boundary for steam spaces
successively formed by flap gates within the chamber. The practical
difficulties of construction finally ruled out this solution to the
problem of a rotating power source, but not until after Boulton and
Watt had spent considerable effort and money on it.[5]

[Footnote 5: Henry W. Dickinson and Rhys Jenkins, _James Watt and the
Steam Engine_, Oxford, Clarendon Press, 1927, pp. 146-148, pls. 14, 31.
This work presents a full and knowledgeable discussion, based on primary
material, of the development of Watt's many contributions to mechanical
technology. It is ably summarized in Dickinson, _op. cit._ (footnote
2).]

In 1777 a speaker before the Royal Society in London observed that in
order to obtain rotary output from a reciprocating steam engine, a crank
"naturally occurs in the