lution was taken many years ago when
the screw propeller was substituted for the paddle-wheel. The latter
means of propulsion caused shock and vibration not only owing to the
thrusts of the piston-rod from the steam-engine itself, but also from
the impact of the paddles upon the water one after the other. A great
increase in the smoothness of running was attained when the screw was
invented--a propeller which was entirely sunk in the water and
therefore exercised its force, not in shocks, but in gentle constant
pressure upon the fluid around it. Such as the windmill is for wind
and the turbine water-wheel for water was the screw propeller,
although adapted, not as a generator, but as an application of power.
Having made the work and stress continuous, the next thing to be
accomplished was to effect a similar reform in the engines supplying
the power. This is accomplished in the turbine steam-engine by causing
the steam to play in strong jets continuously and steadily upon vanes
which form virtually a number of small windmills. Thus, while the
screw outside of the hull is applying the force continuously, the
steam in the inside is driving the shafting with equal evenness and
regularity.

The steam turbine does not appear to have by any means reached
finality in its form, such questions as the angle of impact which the
jet should make with the surface of the vane, and the size of the
orifice through which the steam should be ejected, being still
debatable points. But on one matter there is hardly any room for
doubt, and that is that the best way to secure the benefit of the
expansive power of steam is to permit it to escape from a pipe having
a long series of orifices and to impinge upon a correspondingly
numerous series of vanes, or, perhaps, upon a number of vanes arranged
so that each one is long enough to receive the impact of many jets.

Hitherto the steam supply-pipe emitting the jet has been placed
outside of the circle of the wheel; but the future form seems likely
to be one in which the axis of the wheel is itself the pipe which
contains the steam, but which permits it to escape outwards to the
circumference of the wheel. The latter is, in this form of turbine,
made in the shape of a paddle-wheel of very small circumference but
considerable length, the paddles being set at such an inclination as
to obtain the greatest possible rotative impulse from the
outward-rushing steam. The pipe must be turned true at inte