The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

STEAM NAVIGATION. 259
mainder having a tendency to raise the water, and throw up
a wave and spray behind the paddle wheel. It is evident
that the more deeply the paddle wheel becomes immersed
the greater will be the proportion of the propelling power
thus wasted in elevating and depressing the water; and, if
the wheel were immersed to its axis, the whole force of the
paddle boards, on entering and leaving the water, would be
lost, no part of it having a tendency to propel. If a still
deeper immersion takes place, the paddle boards above the
axis would have a tendency to retard the course of the
vessel. When the vessel is, therefore, in proper trim, the
immersion should not exceed nor fall short of the depth
of the lowest paddle; but for various reasons it is impossible in practice to maintain this fixed immersion: the
agitation of the surface of the sea, causing the vessel to roll,
will necessarily produce a great variation in the immersion
of the paddle wheels, one becoming frequently immersed to
its axle, while the other is raised altogether out of the water.
Also the draught of water of the vessel is liable to change,
by the variation in her cargo: this will necessarily happen
in steamers which take long voyages. At starting they are
heavily laden with fuel, which as they proceed is gradually
consumed, whereby the vessel is lightened; and it does not
appear that it is practicable to use sea water as ballast to
restore the proper degree of immersion.
(118.) Among the contrivances which have been proposed for remedying these defects of the common paddle
wheel by introducing paddle boards capable of shifting their
position as they revolve with the circumference of the wheel,
the only one which has been adopted to any considerable
extent in practice, is that which is commonly known as
Morgan's Paddle Wheel. The original patent for this contrivance was granted to Elijah Galloway, and sold by him to
Mr. William Morgan. Subsequently to the purchase some
improvements in its structure and arrangements were introduced, and it is now extensively adopted by government in