motion. "Of the many rotary engines
heretofore offered to the notice of the world," he wrote, in 1833, "none
have stood the test of practical use and experience. The cause of this
uniform failure has been the great difficulty of obtaining, within the
machine, a base of resistance on which the steam might act in propelling
the moveable piston." He did not quite overcome this difficulty, but he
succeeded in producing what the foremost critic in this department of
manufacture describes--after a lapse of thirty years unrivalled for
their development of ingenuity--as "the most perfect engine of the class
that has yet been projected."

"In this engine," says the same authority, "an eccentric is made to
revolve on an axis in the manner of a piston, and two doors, forming
part of the side of the cylinder, press upon the eccentric. The points
of these doors are armed with swivelling brasses, which apply themselves
to the eccentric and make the point of contact tight in all
positions."[16]

[16] John Bourne. "A Treatise on the Steam-Engine" (1861), p. 392.

"This revolving engine," said Lord Dundonald, "does not require any
valve or slide; consequently, there is no waste of steam thereby;
neither is there any loss, as in the space left at the top and bottom of
the cylinders of reciprocating engines. There is much less friction than
arises from the sum of all the bearings required to convert the
rectilineal force of the common engine to circular motion. There are no
beams, cranks, side-rods, connecting-rods, parallel motions, levers,
slide-valves, or eccentrics, with their nicely-adjusted joints and
bearings; and thus the revolving engine is not liable, even in one-tenth
degree, to the accidents and hindrances of other engines. As its moving
parts pursue their course in perfect circles, without stop or hindrance,
it is capable of progressive acceleration, until the work performed
equals the pressure of steam on the vacuum--an advantage which the
reciprocating engine does not possess. The diminished bulk and weight,
and the absence of tremor, add to the capacity, buoyancy, velocity, and
durability of vessels in which it is placed." The rotary engine did not
satisfy all Lord Dundonald's expectations, but it took precedence of all
others of the same sort, and was of great service at any rate in
directing attention to what he rightly considered to be the great want
in war-shipping, namely, vessels of the least possible bulk and o