"Take your gun along, and you may spot a polar bear or a walrus,"

suggested Mr. Henderson. "Some fresh bear steak would not go badly at all."

Delighted at the prospect at getting a shot Andy hastened after his gun.

Then after a hasty breakfast, with the two boys and the two helpers as companions, all warmly wrapped in furs, the hunter set forth across the fields of ice and snow.

It was a strange experience for all of them. There was not a sign of life to be seen. On every side there was nothing but the cold whiteness--a coldness and a whiteness that was like death itself. They walked on for more than a mile, and saw nothing but the desolate waste.

"There's something!" called Jack in a hoa.r.s.e whisper, coming to a halt and pointing to a small hill of ice in the distance.

"It's a polar bear!" yelled Mark. "He's right behind the ice!"

"There are two of 'em!" cried Bill. "This is no place for me! Come on, Tom!"

"Hold still! Let me get a shot!" pleaded the old hunter.

He could see the two animals plainly, now that his eyes had become used to the difference between their s.h.a.ggy coats and the surrounding snow and ice. Andy kneeled down and took careful aim. A shot rang out, and one of the bears toppled over.

"Good shot!" cried Jack.

Once more the hunter pulled the trigger. A dull click was the only response. Andy quickly c.o.c.ked the gun again, thinking it had missed fire. Again the hammer fell with only a click. The hunter quickly threw open the magazine.

"The chamber is empty!" he cried. "I have fired my last shot!"

"And there comes the bear!" yelled Mark. "He's in a fit of rage!"

The fierce beast, in anger at the sight of his enemies, was coming toward the men and boys at top speed. On the first alarm Bill and Tom had turned to flee. Andy, swinging his gun by the muzzle, and loosening a long hunting knife in his belt, awaited the bear's onslaught. Mark and Jack were too surprised to run, and stood their ground, not knowing what to do.

"Run away!" shouted Andy. "I'll tackle the beast! I'm not afraid!"

"We're not going to leave you!" yelled Jack. "I have a revolver!"

Quickly he drew out the small weapon, a present from the inventor.

Taking hasty aim he fired several shots, but his aim was poor. One bullet struck the bear on the nose, and, instead of stopping the beast, only made him the more angry.

The brute was now but fifty feet away and coming on at a rapid pace over the uneven lumps of ice and snow.

"Run, I tell you!" called Andy. "Do you boys want to be killed?"

He aimed a furious stroke at the bear, but as he did so his foot slipped and he came down heavily on the ice. Mark and Jack uttered cries of terror and fright.

With blood dripping from his wounds, foam falling from his red jaws, and with every appearance of rage, the maddened beast rushed on the old hunter.

"He'll be killed!" yelled Mark.

"If I only had a gun!" groaned Jack.

Andy rolled to one side. As he did so he uttered a loud cry, and then, to the astonishment of the boys, he disappeared from sight as if the frozen earth had opened and swallowed him up. At the same time the bear, that was just about to cast himself down on the fallen hunter, seemed to drop down through some hole into the earth.

For an instant Jack and Mark looked at each other with fear in their eyes.

"What has happened?" inquired Mark, in an awestruck voice.

"I don't know," answered Jack. "But look! there are spots of blood over there. That is where the bear was!"

The boys ran forward. As they did so their feet seemed to slip from under them. Down and down they felt themselves going. Faster and faster they slipped. They gazed with frightened eyes about them and saw they were on some giant slide of ice, that led into unknown regions.

"Where are we going?" gasped Mark.

"I don't know!" yelled back Jack. "At any rate we're getting a good coast!" He could joke even in the face of danger.

With a jolt the two boys came to the end of their sudden journey. For a moment they were so startled and shaken up that they could hardly see.

Then, as their senses came back, they gazed around.

There were white glistening walls of ice on every side. Above glittered a tiny patch of light, showing where the blue sky was.

"Where are we?" asked Mark.

"You're with me an' the bear!" exclaimed a voice.

The boys started. They saw, lying near them, old Andy. At his feet was the polar bear, dead, with the hunter's knife sticking in his heart.

"And what place is this?" asked Jack.

"It appears to me like a big ice cave," answered the hunter.

"Yes, and we're lost in it," spoke up Jack, and gave something of a shudder.

"That's right, my boy," answered Andy Sudds.

CHAPTER XI

ATTACKED BY SEA LIONS

Frightened and alarmed at the unusual sight of an enraged polar bear rushing in their direction, Bill and Tom had turned and fled at the first appearance of danger. They were not cowards, and would probably have faced a mad bull, but that was something they were used to, while a bear was something new.

So they raced back over the ice toward the place where the disabled airship rested.

"Quick!" yelled Bill.

"They'll all be killed!" cried Tom.

"Who?" asked the professor, dropping his tools.

Rapidly the two helpers told what had occurred, and how they had left Andy and the boys as the bear was rushing at them, the hunter having no more cartridges in his gun.