ppears expedient,
therefore, either to make the bolts very large, and the sockets through
which they pass very deep, or to let one brass fit into the other.

632. _Q._--How are the trunnion plummer blocks made?

_A._--The trunnion plummer blocks are formed in the same manner as the
crank shaft plummer blocks; the nuts are kept from turning back by means of
a pinching screw passing through a stationary washer. It is not expedient
to cast the trunnion plummer blocks upon the lower frame, as is sometimes
done; for the cylinders, being pressed from the steam trunnions by the
steam, and drawn in the direction of the condenser by the vacuum, have a
continual tendency to approach one another; and as they wear slightly
toward midships, there would be no power of readjustment unless the plummer
blocks were movable. The flanges of the trunnions should always fit tight
against the plummer block sides, but there should be a little play sideways
at the necks of the trunnions, so that the cylinder may be enabled to
expand when heated, without throwing an undue strain upon the trunnion
supports.

633. _Q._--What kind of paddle wheel is supplied with these oscillating
engines?

_A._--The wheels are of the feathering kind, 9 feet 8 inches in diameter,
measuring to the edges of the floats; and there are 10 floats upon each
wheel, measuring 4 feet 6 inches long each, and 18-1/2 inches broad. There
are two sets of arms to the wheel, which converge to a cast iron centre,
formed like a short pipe with large flanges, to which the arms are affixed.
The diameter of the shaft, where the centre is put on, is 4-1/2 inches, the
external diameter of the pipe is 8 inches, and the diameter of the flanges
is 20 inches, and their thickness 1-1/4 inch. The flanges are 12 inches
asunder at the outer edge, and they partake of the converging direction of
the arms. The arms are 2-1/4 inches broad and half an inch thick; the heads
are made conical, and each is secured into a recess upon the side of the
flange by means of three bolts. The ring which connects together the arms,
runs round at a distance of 3 feet 6 inches from the centre, and the
projecting ends of the arms are bent backward the length of the lever which
moves the floats, and are made very wide and strong at the point where they
cross the ring, to which they are attached by four rivets. The feathering
action of the floats is accomplished by means of a pin fixed to the
interior of the paddle b