The violence of the hail storm, the clatter of the frozen pellets as they bombarded the airship, the rolling, swaying motion of the craft as Tom endeavored to send it aloft, all combined to throw the passengers of the Red Cloud into a state of panic.

"Bless my very existence!" cried Mr. Damon, "this is almost as bad as when we were caught in the hurricane at Earthquake Island!"

"I am sure that this storm is but the forerunner of some dire calamity!" declared Mr. Parker.

"I'm afraid it's all up with us," came from Abe Abercrombie, as he looked about for some way of escape.

"Do you think you can pull us through, Tom?" asked Ned Newton, who, not having had much experience in airships had yet to learn Tom's skill in manipulating them.

The young inventor alone seemed to keep his nerve. Coolly and calmly he stood at his post of duty, shifting the wing planes from moment to moment, managing the elevation rudder, and, at the same time, keeping his eye on the registering dial of the gas-generating machine.

"It's all right," said Tom, more easily than he felt. "We are going up slowly. You might see if you can induce the gas machine to do any better, Mr. Damon. We are wasting some of the vapor because of the leak in the bag, but we can manufacture it faster than it escapes, so I guess we'll be all right."

"Mr. Parker, may I ask you to oil the main motor? You will see the places marked where the oil is to go in. Ned, you help him. Here, Abe, come over here and give me a hand. This wind makes the rudders hard to twist."

The young inventor could not have chosen a better method of relieving the fears of his friends than by giving them something to do to take their minds off their own troubles. They hurried to the tasks he had assigned to them, and, in a few minutes, there were no more doubts expressed.

Not that the Red Cloud was out of danger, Far from it. The storm was increasing in violence, and the hailstones seemed to double in number. Then, too, being forced upward as she was, the airship's bag was pelted all the harder, for the speed of the craft, added to the velocity of the falling chunks of hail, made them strike on the surface of the ship with greater violence.

Tom was anxiously watching the barograph, to note their height. The Red Cloud was now about two and a half miles high, and slowly mounting upward. The gas machine was working to its fullest capacity, and the fact that they did not rise more quickly told Tom, more plainly than words could have done, that there were several additional leaks in the gas-bag.

"I'll take her up another thousand feet," he announced grimly. "Then, if we're not above the storm it will be useless to go higher."

"Why?" asked Ned, who had come back to stand beside his chum.

"Because we can't possibly get above the storm without tearing the ship to pieces. I had rather descend."

"But won't that be just as bad?"

"Not necessarily. There are often storms in the upper regions which do not get down to the surface of the earth, snow and hail storms particularly. Hail, you know, is supposed to be formed by drops of rain being hurled up and down in a sort of circular, spiral motion through alternate strata of air--first freezing and then warm, which accounts for the onion-like layers seen when a hailstone is cut in half."

"That is right," broke in Mr. Parker, who was listening to the young inventor. "By going down this hail storm may change into a harmless rain storm. But, in spite of that fact, we are in a dangerous climate, where we must expect all sorts of queer happenings."

"Nice, comfortable sort of a companion to have along on a gold- hunting expedition, isn't He?" asked Tom of Ned, making a wry face as Mr. Parker moved away. "But I haven't any time to think of that. Say, this is getting fierce!"

Well might he say so. The wind had further increased in violence, and while the storm of hailstones seemed to be about the same, the missiles had nearly doubled in size.

"Better go down," advised Ned. "We may fall if you don't."

"Guess I will," assented Tom. "There's no use going higher. I doubt if I could, anyhow, with all this wind pressure, and with the gas- bag leaking. Down she is!"

As he spoke he shifted the levers, and changed the valve wheels. In an instant the Red Cloud began to shoot toward the earth.

"What's happened? What in th' name of Bloody Gulch are we up ag'in'?" demanded the old miner, springing to his feet.

"We're going down--that's all," answered Tom, calmly, but he was far from feeling that way, and he had grave fears for the safety of himself and his companions.

Down, down, down went the Red Cloud, in the midst of the hail storm. But if the gold-seekers had hoped to escape the pelting of the frozen globules they were mistaken. The stones still seemed to increase in size and number. The gas machine register showed a sudden lack of pressure, not due to the shutting off of the apparatus.

"Look!" cried Ned, pointing to the dial.

"Yes--more punctures," said Tom, grimly.

"What's to be done?" asked Mr. Damon, who had finished the task Tom allotted to him. "Bless my handkerchief! what's to be done?"

"Seek shelter if the storm doesn't stop when we get to the earth level," answered Tom.

"Shelter? What sort of shelter? There are no airship sheds in this desolate region."

"I may be able to send the ship under some overhanging mountain crag," answered the young inventor, "and that will keep off the hailstones."

Eagerly Tom and Ned, who stood together in the pilothouse peered forward through the storm.

The wind was less violent now that they were in the lower currents of air, but the hail had not ceased.

Suddenly Tom gave a cry. Ned looked at him anxiously. Had some new calamity befallen them? But Tom's voice sounded more in relief than in alarm. The next instant he called:

"Look ahead there, Ned, and tell me what you see."

"I see something big and black," answered the other lad, after a moment's hesitation. "Why, it's a big black hole!" he added.

"That's what I made it out to be," went on Tom, "but I wanted to be sure. It's the opening to a cave or hole in the side of the mountain. I take it."

"You're right," agreed Ned.

"Then we're safe," declared Tom.

"Safe? How?"

"I'm going to take the Red Cloud in there out of the storm."

"Can you do it? Is the opening big enough?"

"Plenty. It's larger than my shed at home, Jove! but I'm glad I saw that in time, or there would have been nothing left of the gas-bag!"

With skilful hands Tom turned the rudders and sent the airship down on a slant toward the earth, aiming for the entrance to the cave, which loomed up in the storm. When the craft was low enough down so that the superstructure would not scrape the top of the cave, Tom sent her ahead on the level. But he need have had no fears, for the hole was large enough to have admitted a craft twice the size of the Red Cloud.

A few minutes later the airship slid inside the great cavern, as easily as if coming to rest in the yard of Tom's house. The roof of the cave was high over their heads, and they were safe from the storm. The cessation from the deafening sound of the pelting hailstones seemed curious to them at first.

"Well, bless my shoelaces! if this isn't luck!" cried Mr. Damon, as he opened the door of the cabin, and looked about the cave in which they now found themselves. It was comparatively light, for the entrance was very large, though the rear of the cavern was in gloom.

"Yes, indeed, we got to it just in time,'" agreed Tom. "Now let's see what sort of a place it is. We'll have to explore it."

"There may be a landslide, or the roof may come down on our heads," objected Mr. Parker.

"Oh, my dear Parker! please be a little more cheerful," begged Mr. Damon.

The adventurers followed Tom from the airship, and all but the young inventor gazed curiously at the interior of the cave. His first thought was for his airship. He glanced up at the gas-bag, and noted several bad rents in it.

"I hope we can fix them," Tom thought dubiously.

But the attention of all was suddenly arrested by something that occurred just then. From the dark recess of the cavern there sounded a fearful yell or scream. It was echoed back a thousand-fold by the rocky walls of the cave, Then there dashed past the little group of gold-seekers a dark figure.

"Look out! It's a bear!" shouted Mr. Damon. "A bear! It's an Eskimo Indian!" yelled Abe Abercrombie, "an' he's skeered nigh t' death! Look at him run!"

As they gazed toward the lighted entrance of the cave they saw leaping and running from it an Indian who quickly scudded out into the hail storm.

"An Indian," exclaimed Tom. "An Indian in the cave! If there's one, there may be more. I guess we'd better look to our guns. They may attack us!" and he hurried back into the airship, followed by Ned and the others.