_A._--There is the side lever engine (fig. 26), and the oscillating engine
(fig. 27), besides numerous other forms of engine which are less known or
employed, such as the trunk (fig. 22), double cylinder (fig. 23), annular,
Gorgon (fig. 24), steeple (fig. 25), and many others. The side lever
engine, however, and the oscillating engine, are the only kinds of paddle
engines which have been received with wide or general favor.

[Illustration: Fig. 24.]

113. _Q._--Will you explain the main distinctive features of the side lever
engine?

_A._--In all paddle vessels, whatever be their subordinate characteristics,
a great shaft of wrought iron, s, turned round by the engine, has to be
carried from side to side of the vessel, on which shaft are fixed the
paddle wheels. The paddle wheels may either be formed with fixed float
boards for engaging the water, like the boards of a common undershot water
wheel, or they may be formed with _feathering_ float boards as they are
termed, which is float boards movable on a centre, and so governed by
appropriate mechanism that they enter and leave the water in a nearly
vertical position. The common fixed or radial floats, however, are the kind
most widely employed, and they are attached to the arms of two or more
rings of malleable iron which are fixed by appropriate centres on the
paddle shaft. It is usual in steam vessels to employ two engines, the
cranks of which are set at right angles with one another. When the paddle
wheels are turned by the engines, the float boards engaging the water cause
a forward thrust to be imparted to the shaft, which propels forward the
vessel on the same principle that a boat is propelled by the action of
oars.