e ship when it was sailing aloft, they took no more
precautions than as if they were on the deck of a steamboat.

For several hours the ship was kept on her course. The boys remained in
the conning tower, gazing ahead. Not a single thing could be observed
but a monotonous expanse of whiteness. Now and then they would run into
a bank of clouds which obscured their vision as if there was a heavy
fog.

"Look at the clock!" exclaimed Mark suddenly, pointing to the
time-piece.

"What's the matter with it?" asked Jack.

"Can it be right?" went on Mark. "Surely it isn't nine o'clock, and the
sun shining as brightly as if it was noon."

"It's nine o'clock at night!" exclaimed the professor, entering the
steering tower in time to hear Mark's words.

"But it can't be," argued the boy. "Look how the sun is shining."

"You must realize where you are," was the reply. "We are so far north,
my boy, that we are in the land of the midnight sun. From now on we will
have daylight all the while. We are nearing the pole, where it is light
six months of the year, and dark the other six. We are having summer
here, now."

"I guess it don't feel much like summer outside," said Mark. "The
thermometer indicates fifty below zero!"

"So it does," said Amos Henderson, glancing at the instrument which,
though it was outside, could be read through the glass in the tower.
"Well, we may have struck a cold wave. Ordinarily we will not have much
more than twenty below zero when the sun shines."

"That's cold enough for me," said Mark.

The professor announced that the airship's machinery was now in good
shape. He said he expected to come to the end of the journey in about
three days more, provided no accidents occurred, and there were no
storms to delay the _Monarch_.

"I think we will divide the night into four watches," he said.
"Washington, Jack, Mark and I will take them in turn. During the day we
will all be on duty, but from six in the morning to six at night we will
stand watch and watch."

It was arranged that Jack should take the first period, the professor
the second, Mark the third and Washington the fourth. As the first watch
had passed Jack was excused and the inventor said he would take charge
of the ship. Then, as every one was tired from the happenings of the
day, they all went to bed, excepting Amos Henderson, who entered the
tower to steer the ship.

The engines, dynamos and motors ran without much attention save such a