the benefits of a large saving are less eminent than they would be in
the case of steam navigation; and it is to be hoped that this expedient of
improvement will now be speedily adopted.

CHAPTER X.

EXAMPLES OF ENGINES.

* * * * *

OSCILLATING PADDLE ENGINES.

618. _Q._--Will you describe the structure of an oscillating engine as made
by Messrs. Penn?

_A._--To do this it will be expedient to take an engine of a given power,
and then the sizes may be given as well as an account of the configuration
of the parts: we may take for an example a pair of engines of 21-1/2 inches
diameter of cylinder, and 22 inches stroke, rated by Messrs. Penn at 12
horses power each. The cylinders of this oscillating engine are placed
beneath the cranks, and, as in all Messrs. Penn's smaller engines, the
piston rod is connected to the crank pin by means of a brass cap, provided
with a socket, by means of which it is cuttered to the piston rod. There is
but one air pump, which is situated within the condenser between the
cylinders, and it is wrought by means of a crank in the intermediate
shaft--this crank being cut out of a solid piece of metal as in the
formation of the cranked axles of locomotive engines. The steam enters the
cylinder through the outer trunnions, or the trunnions adjacent to the
ship's sides, and enters the condenser through the two midship trunnions--a
short three ported valve being placed on the front of the cylinder to
regulate the flow of steam to and from the cylinder in the proper manner.
The weight of this valve on one side of the cylinder is balanced by a
weight hung upon the other side of the cylinder; but in the most recent
engines this weight is discarded, and two valves are used, which balance
one another. The framing consists of an upper and lower frame of cast iron,
bound together by eight malleable iron columns: upon the lower frame the
pillow blocks rest which carry the cylinder trunnions, and the condenser
and the bottom frame are cast in the same piece. The upper frame supports
the paddle shaft pillow blocks; and pieces are bolted on in continuation of
the upper frame to carry the paddle wheels, which are overhung from the
journal.

619. _Q._--What are the dimensions and arrangement of the framing?

_A._--The web, or base plate of the lower frame is 3/4 of an Inch thick,
and a cooming is earned all round the cylinder, leaving an opening of
sufficient size to