, and
that may at any time be done where doubt of obtaining a sound intermediate
shaft is entertained; but the precaution must be taken to make the
eccentric very wide so as to distribute the pressure over a large surface,
else the eccentric will be apt to heat.

437. _Q._--Have not objections been brought against the oscillating engine?

_A._--In common with every other improvement, the oscillating engine, at
the time of its introduction, encountered much opposition. The cylinder, it
was said, would become oval, the trunnion bearings would be liable to heat
and the trunnion joints to leak, the strain upon the trunnions would be apt
to bend in or bend out the sides of the cylinder; and the circumstance of
the cylinder being fixed across its centre, while the shaft requires to
accommodate itself to the working of the ship, might, it was thought, be
the occasion of such a strain upon the trunnions as would either break them
or bend the piston rod. It is a sufficient reply to these objections to say
that they are all hypothetical, and that none of them in practice have been
found to exist--to such an extent at least as to occasion any
inconvenience; but it is not difficult to show that they are altogether
unsubstantial, even without a recourse to the disproofs afforded by
experience.

438. _Q._--Is there not a liability in the cylinder to become oval from the
strain thrown on it by the piston?

_A._--There is, no doubt, a tendency in oscillating engines for the
cylinder and the stuffing box to become oval, but after a number of years'
wear it is found that the amount of ellipticity is less than that which is
found to exist in the cylinders of side lever engines after a similar
trial. The resistance opposed by friction to the oscillation of the
cylinder is so small, that a man is capable of moving a large cylinder with
one hand; whereas in the side lever engine, if the parallel motion be in
the least untrue, which is, at some time or other, an almost inevitable
condition, the piston is pushed with great force against the side of the
cylinder, whereby a large amount of wear and friction is occasioned. The
trunnion bearings, instead of being liable to heat like other journals, are
kept down to the temperature of the steam by the flow of steam passing
through them; and the trunnion packings are not liable to leak when the
packings, before being introduced, are squeezed in a cylindrical mould.

439. _Q._--Might not the educ