Which, at the rate he was discharging the weapon, would not take a long time. But it had the effect of momentarily checking the advance of the creatures.

Not for long, however. Our friends had barely reached the airship, with Mr. Parker stumbling and slipping on the ice and snow, ere the musk oxen came on again, with loud bellows.

"They're going to charge the ship! They'll ram her!" yelled Ned Newton.

"I think I can stop them!" cried Tom, who had leaped toward his stateroom. He came out a moment later, carrying a peculiar-looking gun, The adventurers had seen it before, but never in operation, as Tom had only put some finishing touches on it since undertaking the voyage to the caves of ice.

"What sort of a weapon is that?" cried Abe, as he helped Mr. Parker on board.

"It's my new electric rifle," answered the young inventor. "I don't know how it will work, as it isn't entirely finished, but I'm going to try it."

Putting it to his shoulder he aimed at the leading musk ox, and pulled a small lever. There was no report, no puff of smoke and no fire, yet the big creature, which had been rushing at the ship, suddenly stopped, swayed for a moment, and then fell over in the snow, kicking in his death agony.

"One down!" yelled Tom. "My rifle works all right, even if it isn't finished!"

He aimed at another ox, and that creature was stopped in its tracks. Mr. Damon had exhausted his cartridges, and had ceased firing, but Abe Abercrombie was ready with his rifle, and opened up on the beasts. Tom killed another with his electric gun, and Abe shot two. This stopped the advance, and only just in time, for the foremost animals were already close to the ship, and had they rushed at the frail hull they might have damaged it beyond repair.

"Here goes for the big one!" cried Tom, and, aiming at the largest ox of the herd, the young inventor pulled the lever. The brute fell over dead, and the rest, terror stricken, turned and fled.