of
Mr. Renton and Messrs. Bramah, the experiment was tried and found to
answer so well, in spite of the difficulties incident to a first
attempt, that it was resolved to develop it further in a frigate to be
built throughout in accordance with his plans for the improved
construction of shipping.

To these he had lately made some valuable additions. On the 19th of
January, 1843, a patent was granted to him for various improvements in
engines and other machinery, one of which was an apparatus for
propelling vessels. "This improved propeller," says a competent
authority, "consists of an arrangement of propelling blades immerged
beneath the water, in the manner now usual in screw vessels; but,
instead of the blades being set at right angles with the
propeller-shaft, they form an angle therewith. One important effect of
this arrangement is that it corrects the centrifugal action of the
screw; for whereas, in common screws, the water which is discharged
backwards assumes a conical figure, enlarging as it recedes, in a screw
formed on Lord Dundonald's plan the outline of the moving water will be
cylindrical, the centrifugal action being counteracted by the convergent
action due to the backward inclination of the propelling blades. It is
found, practically, that screws constructed upon this principle give a
better result than ordinary screws."[17]

[17] John Bourne. "A Treatise on the Screw Propeller, Screw Vessels, and
Screw Engines" (1867), p. 42.

Another invention patented by Lord Dundonald at the same time was a
modification of the boilers used for steam-engines. "These boilers,"
says the same critic, "are constructed with a double tier of furnaces
and with upright tubes, the water being contained within the tubes and
the smoke impinging upon them on its passage to the chimney. This
species of boiler is found to be very efficient. A hanging bridge is
introduced to retain the heat in the upper part of the flue in which the
tubes are erected. By inserting a short piece of tube in the upper
extremity of each tube within the boiler the upward circulation of the
water within the tubes was increased as the length of the lighter column
of water was augmented, while the length of the gravitating column
remained without alteration."[18]

[18] John Bourne. "A Treatise on the Steam Engine" (1861), p. 233. These
boilers, extensively used in London, America, and elsewhere, and now
introduced in the Admiralty ship-buildin