35.--The marine condenser.]

Fig. 35 is a sectional illustration of a marine condenser. Steam enters
the condenser through the large pipe E, and passes among a number of
very thin copper tubes, through which sea-water is kept circulating by a
pump. The path of the water is shown by the featherless arrows. It comes
from the pump through pipe A into the lower part of a large cap covering
one end of the condenser and divided transversely by a diaphragm, D.
Passing through the pipes, it reaches the cap attached to the other end,
and flows back through the upper tubes to the outlet C. This arrangement
ensures that, as the steam condenses, it shall meet colder and colder
tubes, and finally be turned to water, which passes to the well through
the outlet F. In some condensers the positions of steam and water are
reversed, steam going through the tubes outside which cold water
circulates.

[3] Also called _ports_.

[4] The bores of the cylinders are in the proportion of 4: 6: 9. The
stroke of all three is the same.

[5] The ends furthest from the eccentric.

[6] "The Locomotive of To-day," p. 87.

Chapter III.

THE STEAM TURBINE.

How a turbine works--The De Laval turbine--The Parsons
turbine--Description of the Parsons turbine--The expansive action
of steam in a Parsons turbine--Balancing the thrust--Advantages of
the marine turbine.

More than two thousand years ago Hero of Alexandria produced the first
apparatus to which the name of steam-engine could rightly be given. Its
principle was practically the same as that of the revolving jet used to
sprinkle lawns during dry weather, steam being used in the place of
water. From the top of a closed cauldron rose two vertical pipes, which
at their upper ends had short, right-angle bends. Between them was hung
a hollow globe, pivoted on two short tubes projecting from its sides
into the upright tubes. Two little L-shaped pipes projected from
opposite sides of the globe, at the ends of a diameter, in a plane
perpendicular to the axis. On fire being applied to the cauldron, steam
was generated. It passed up through the upright, through the pivots, and
into the globe, from which it escaped by the two L-shaped nozzles,
causing rapid revolution of the ball. In short, the first steam-engine
was a turbine. Curiously enough, we have reverted to this primitive type
(scientifically developed, of course) in the most modern engineering
practice.

HOW