, John had to rely entirely upon intuition and
his compass to strike Freetown. Aerial navigation over immense bodies
of water is similar to navigation on the seas themselves, except that
the indispensable sextant of the mariner is of little use in the air,
owing to the high speed of travel and the fact that allowances have to
be made for the drift of the machine when side-winds are blowing--an
extremely difficult factor to determine accurately.

In side-winds the machine makes leeway in addition to its forward
movement, and it is the ratio of one to the other which the successful
pilot must work out correctly, especially when flying above clouds or
when land features are unobserved. In this particular instance our
boys were supplied with charts indicating the trend of all normal winds
in each locality and their approximate force at various altitudes.
Thus, by consulting his speedometer, John was able to figure out with a
fair degree of certainty what allowances he should make from dead
reckoning in order to strike their destination--or rather, we should
say that Tom, as John's aid, did most of this figuring, for a pilot
generally has his hands full in guiding his steed.

The Sky-Bird was acting much better now, since her equalizing of weight
back at Para. She lacked some of the speed of her old-time self, but
rode smoothly and evenly in the hardest gusts. It was once more a
pleasure to sit in her cabin, even if the rival airplane was ahead of
them.

"We'll give them the race of their lives yet," observed Tom, as he
studied the map and the speedometer alternately.

"We surely will," said his companion.

And both of them clicked their teeth in a way which boded no good for
the rival craft ahead.

Shortly before midnight they crossed the equator for the second time
since they had left Panama. But, rolled in their comfortable hammocks
and sound asleep, with Grandpa, the monkey, blinking drowsily in a
corner nearby, neither Bob nor Paul was conscious of the fact.

CHAPTER XVIII

AN IRRITATING DELAY

Paul was awakened the next morning by feeling a gentle tug at his nose.
Unused to such a summons as this, he opened his eyes with a start.

There on his breast squatted Grandpa, his little head cocked comically
to one side, his beady little eyes glistening with mischief, and his
slim fingers just reaching out for another tweak. The monkey gave a
lightning-like spring to the back of a nearby seat when he sa