tained pressure means power; the greater the pressure the
more the power. It was the inventive skill of Charles D. Mosher, who has
built many fast yachts, that enabled him to build engines and boilers of
great power in proportion to their weight. It was the ability of the
inventor to build boilers and engines of 4,000 horse-power compact and
light enough to be carried in a vessel 130 feet long, of 12 feet 6
inches breadth, and 3 feet 6 inches depth, that made it possible for the
_Arrow_ to go a mile in one minute and thirty-two seconds. The speed of
the wonderful little American boat, however, was not the result of any
new invention, but was due to the perfection of old methods.

In England, about five years before the _Arrow's_ achievement, a little
torpedo-boat, scarcely bigger than a launch, set the whole world talking
by travelling at the rate of thirty-nine and three-fourths miles an
hour. The little craft seemed to disappear in the white smother of her
wake, and those who watched the speed trial marvelled at the railroad
speed she made. The _Turbina_--for that was the little record-breaker's
name--was propelled by a new kind of engine, and her speed was all the
more remarkable on that account. C.A. Parsons, the inventor of the
engine, worked out the idea that inventors have been studying for a long
time--since 1629, in fact--that is, the rotary principle, or the rolling
movement without the up-and-down driving mechanism of the piston.

The _Turbina_ was driven by a number of steam-turbines that worked a
good deal like the water-turbines that use the power of Niagara. Just as
a water-wheel is driven by the weight or force of the water striking the
blades or paddles of the wheel, so the force of the many jets of steam
striking against the little wings makes the wheels of the steam-turbines
revolve. If you take a card that has been cut to a circular shape and
cut the edges so that little wings will be made, then blow on this
winged edge, the card will revolve with a buzz; the Parsons
steam-turbine works in the same way. A shaft bearing a number of steel
disks or wheels, each having many wings set at an angle like the blades
of a propeller, is enclosed by a drumlike casing. The disks at one end
of the shaft are smaller than those at the other; the steam enters at
the small end in a circle of jets that blow against the wings and set
them and the whole shaft whirling. After passing the first disk and its
little vanes, t