hue, then to green, yellow, blue and
purple. The captives could not see where the fire came from, but they
gazed at the light in mingled fear and admiration.

"It is the northern light; the aurora borealis!" exclaimed the
professor. "It is the most beautiful light in the world."

"What makes it?" asked Andy.

"Electricity, magnetism, the sun and the intense cold; no one knows
exactly what produces it," replied Amos Henderson. "It is quite likely
that there is some opening to this cave, and the sun shines in it, or
the lights may be reflected from outside by reason, of the ice, which
acts as a mirror."

"It's pretty," observed Andy, "but all the same I'd rather--"

He got no further for the two giant-sized natives advanced quickly
toward them. One roughly seized Professor Henderson, and, with the help
of his companion, began stripping off his clothes. Andy started forward
to aid the captain, but the other natives held him back. Washington,
too, was restrained by several hands.

In a few minutes the professor was stripped, except for a piece of fur
about his middle. Then a rude litter was brought in. The two big
natives, after pouring some oil over the old man, placed their victim on
the stretcher, and then began a march up the cave. Washington and Andy
were forced to walk directly behind the inventor, and were surrounded by
natives on every side. The poor professor soon became half insensible
from the cold.

"This is terrible!" groaned Andy.

"Dey is goin' to slaughter him!" wailed Washington. "He'll be sacrificed
and burned up! See, de altar ob de sacrifice am just ahead. Oh! I wisht
we wuz all dead!"

"We're likely to be, soon enough," muttered Andy. "But keep up your
courage!"

At that instant the head of the procession was close to the ice altar.
Behind it the mysterious lights played and flickered in streamers of
red, green and gold. Up the steps went the two gigantic men, carrying
the professor. They were about to sacrifice him in a horrible way!

"Oh! Oh! Oh!" screamed a woman's voice. At the sound of it Andy started.

"That was Dirola!" exclaimed the old hunter. "How did she get here?"

CHAPTER XXIV

SAVED BY DIROLA

Instantly the ice cavern was a scene of great uproar and confusion. The
procession broke up as soon as Dirola cried out and the intruders at the
sacrifice were observed. All, save those carrying the victim and those
guarding Andy and Washington, rushed with their long bone