, as the second pair of posts came in
line, marking the finish of the mile. The word was passed to the
frantically struggling firemen and engineers below, while those on deck
compared watches.

"One minute and thirty-two seconds," said one.

"Right," answered the others.

Then, as the wonderful yacht _Arrow_ gradually slowed down, they tried
to realise the speed and to accustom themselves to the fact that they
had made the fastest mile on record on water.

And so the _Arrow_, moving at the rate of forty-six miles an hour,
followed the course of her ancestress, the _Clermont_, when she made her
first long trip almost a hundred years before.

The _Clermont_ was the first practical steamboat, and the _Arrow_ the
fastest, and so both were record-breakers. While there are not many
points of resemblance between the first and the fastest boat, one is
clearly the outgrowth of the other, but so vastly improved is the modern
craft that it is hard to even trace its ancestry. The little _Arrow_ is
a screw-driven vessel, and her reciprocating engines--that is, engines
operated by the pulling and pushing power of the steam-driven pistons in
cylinders--developed the power of 4,000 horses, equal to 32,000 men,
when making her record-breaking run. All this enormous power was used to
produce speed, there being practically no room left in the little
130-foot hull for anything but engines and boilers.

There is little difference, except in detail, between the _Arrow's_
machinery and an ordinary propeller tugboat. Her hull is very light for
its strength, and it was so built as to slip easily through the water.
She has twin engines, each operating its own shaft and propeller. These
are quadruple expansion. The steam, instead of being allowed to escape
after doing its work in the first cylinder, is turned into a larger one
and then successively into two more, so that all of its expansive power
is used. After passing through the four cylinders, the steam is
condensed into water again by turning it into pipes around which
circulates the cool water in which the vessel floats. The steam thus
condensed to water is heated and pumped into the boiler, to be turned
into steam, so the water has to do its work many times. All this saves
weight and, therefore, power, for the lighter a vessel is the more
easily she can be driven. The boilers save weight also by producing
steam at the enormous pressure of 400 pounds to the square inch.
Steadily main