and 3 feet internal diameter; it rests on massive oaken timbers about 4
feet from the ground; inside the cylinder is a ram 9 feet high, also 2
feet outside measurement, and 12 inches diameter inside; it is
lathe-turned, smooth and bright; four slabs of cast iron, each a quarter
of the circumference of the base of the cylinder, are placed over four
steel bolts that have to support the dead weight, each bolt being about
12 feet high, 4 inches in diameter, with square necks and flat heads,
and a hole in each slab to receive the bolts; the flat heads of the
bolts are to facilitate the accumulator resting level on the oaken
timbers; the slabs would be 2 tons each. On the slabs are fixed small
segments all round and round the base of the cylinder until the required
number (perhaps 150) is placed one on top of the other, each segment
weighing 2 cwt.; then the crosshead is placed over the top tier, and
having a hole in each of its four arms it is entered on the bolts which
have a screw-thread; the nuts are put on and screwed up tightly, and the
accumulator is erected.

36. _Question._--How is the accumulator started working?

_Answer._--The engines are started pumping into the ram and cylinder,
whose drain-cocks have previously been opened, and air and water issues
from them; when the air has escaped they are shut off, and then the
great mass of iron and steel begins to tremble and totter and moves
upwards and upwards, and on nearing the limit of its journey the top of
the accumulator lifts a projecting lever which has a small chain
attached to it, the bottom end of the chain is attached to the steam
throttle valve, and when the chain is pulled up at the top the steam is
shut off at the throttle-valve and the engine stops, but will start as
soon as any water is taken from the accumulator.

37. _Question._--Is there any similarity in terms used in hydraulic work
and steam boiler work?

_Answer._--There are several terms common to hydraulics and steam; the
steam boiler might be called an accumulator of power; there is a
slide-valve in hydraulics as in the steam engine, to admit the power and
to allow the exhaust to escape; there are stop-valves and intermediate
valves in hydraulics, as in steam pipes, also air-vessels in each: there
are suction and delivery pipes and valves in each, and relieve valves
also in each; there is a cylinder in each in which the power is
concentrated; there are reversing levers in a hydraulic cr