Gathered about the young inventor, the three men looked at the warning. The writing was poor, and it was evident that an attempt had been made to disguise it. But there was no misspelling of words, and there were no rudely drawn daggers, or bloody hands or anything of that sort. In fact, it was a very business-like sort of warning.

"Rather odd," commented Mr. Jenks. "Black paper and white ink."

"White ink is easy enough to make," stated Mr. Parker. "I fancy they wanted it as conspicuous as possible."

"Yes," agreed Tom, "and this warning, together with the antics of the thing in white last night, shows that they are aware of our presence here, and perhaps know who we are. We will have to be on our guard."

"Do you think that fellow Munson, whom we left in the forest, could have gotten here and warned them?" asked Mr. Damon.

"It's possible," admitted Tom, "but now let's see if the person who pinned this warning on our tent took any of our things."

A hasty examination, however, showed that nothing had been disturbed, and Tom and Mr. Damon were soon getting supper ready, everyone talking, during the progress of the meal, about the events of the day, and the rather weird culmination of it.

"Well, we haven't had a great deal of success--so far," admitted Tom, as they sat about the fire, in the fast gathering dusk. "I think, perhaps, we'd better try on the other side of the mountain to-morrow. We've explored this side pretty thoroughly."

"Good idea," commented Mr. Jenks. "We'll do it, and move our camp. I only hope those fellows don't find our airship and destroy it. We'll have a hard time getting back to civilization again, if we have to walk all the way."

This contingency caused Tom some uneasiness. He did not like to think that the unscrupulous men might damage the Red Cloud, that had been built only after hard labor. But he knew he could accomplish nothing by worrying, and he tried to dismiss the matter from his mind.

They rather expected to see the thing in white again that night, but it did not appear, and morning came without anything having disturbed their heavy sleep, for they were tired from the day's tramp.

It took them the greater part of the day to make a circuit of the base of Phantom Mountain in order to get to a place where a sort of trail led upward.

"It's too late to do anything to-night," decided Tom, as they set up the tent. "We'll rest, and start the first thing in the morning."

"And the ghost isn't likely to find us here," added Mr. Damon. "Where are you going, Mr. Parker?" he asked, as he saw the scientist tramping a little way up the side of the mountain.

"I am going to make some observations," was the answer, and no one paid any more attention to him for some time. Supper was nearly ready when Mr. Parker returned. His face wore a rather serious air, and Mr. Damon, noting it, asked laughingly:

"Well, did you discover any volcanoes, that may erupt during the night, and scare us to death?"

"No," replied Mr. Parker, calmly, "but there is every indication that we will soon have a terrific electrical storm. From a high peak I caught a glimpse of one working this way across the mountains."

"Then we'd better fasten the tent well down," called Tom. "We don't want it to blow away."

"There will not be much danger from wind," was Mr. Parker's opinion.

"From what then?" asked Mr. Jenks.

"From the discharges of lightning among these mountain peaks, which contain so much iron ore. We will be in grave danger."

The fact that the scientist had not always made correct predictions was not now considered by his hearers, and Tom and the two men gazed at Mr. Parker in some alarm.

"Is there anything we can do to avoid it?" asked Mr. Jenks.

"The only thing to do would be to leave the mountain," was the answer, "and, as the iron ore extends for miles, we can not get out of the danger zone before the storm will reach us. It will be here in less than half an hour."

"Then we'd better have supper," remarked Tom, practically, "and get ready for it. Perhaps it may not be as bad as Mr. Parker fears."

"It will be bad enough," declared the gloomy scientist, and he seemed to find pleasure in his announcement.

The meal was soon over, and Tom busied himself in looking to the guy ropes of the tent, for he feared lest there might be wind with the storm. That it was coming was evident, for now low mutterings of thunder could be heard off toward the west.

Black clouds rapidly obscured the heavens, and the sound of thunder increased. Fitful flashes of lightning could be seen forking across the sky in jagged chains of purple light.

"It's going to be a heavy storm," Tom admitted to himself. "I hope lightning doesn't strike around here."

The storm came on rapidly, but there was a curious quietness in the air that was more alarming than if a wind had blown. The campfire burned steadily, and there was a certain oppressiveness in the atmosphere.

It was now quite dark, save when the fitful lightning flashes came, and they illuminated the scene brilliantly for a few seconds. Then, by contrast, it was blacker than ever.

Suddenly, as Tom was gazing up toward the peak of Phantom Mountain, he saw something that caused him to cry out in alarm. He pointed upward, and whispered hoarsely:

"The ghost again! There's our friend in white!"

The others looked, and saw the same weird figure that had menaced them when they were encamped on the other side of the peak.

"They must have followed us," said Mr. Jenks, in a low voice.

Slowly the figure advanced, It waved the long white arms, as if in warning. At times it would be only dimly visible in the blackness, then, suddenly it would stand out in bold relief as a great flash of fire split the clouds.

The thunder, meanwhile, had been growing louder and sharper, indicating the nearer approach of the storm. Each lightning flash was followed in a second or two, by a terrific clap. Still there was no wind nor rain, and the campfire burned steadily.

All at once there was a crash as if the very mountain had split asunder, and the adventurers saw a great ball of purple-bluish fire shoot down, as if from some cloud, and strike against the side of the crag, not a hundred feet from where stood the ghostly figure in white.

"That was a bad one," cried Mr. Damon, shouting so as to be heard above the echoes of the thunderclap.

Almost as he spoke there came another explosion, even louder than the one preceding. A great ball of fire, pear shaped, leaped for the same spot in the mountain.

"There's a mass of iron ore there!" yelled Mr. Parker. "The lightning is attracted to it!"

His voice was swallowed up in the terrific crash that followed, and, as there came another flash of the celestial fire, the figure in white could be seen hurrying back up the mountain trail. Evidently the electrical storm, with lightning bolts discharging so close, was too much for the "ghost."

In another instant it looked as if the whole place about where the diamond seekers stood, was a mass of fire. Great forked tongues of lightning leaped from the clouds, and seemed to lick the ground. There was a rattle and bang of thunder, like the firing of a battery of guns. Tom and the others felt themselves tingling all over, as if they had hold of an electrical battery, and there was a strong smell of sulphur in the air.

"We are in the midst of the storm!" cried Mr. Parker. "We are standing on a mass of iron ore! Any minute may be our last!"

But fate had not intended the adventurers for death by lightning. Almost as suddenly as it had begun, the discharge of the tongues of fire ceased in the immediate vicinity of our friends. They stood still--awed--not knowing what to do.

Then, once more, came a terrific clap! A great mass of fire, like some red-hot ingot from a foundry, was hurled through the air, straight at the face of the mountain, and at the spot where the figure in white had stood but a few minutes before.

Instantly the earth trembled, as it had at Earthquake Island, but it was not the same. It was over in a few seconds. Then, as the diamond seekers looked, they saw in the glare of a score of lightning flashes that followed the one great clap, the whole side of the mountain slip away, and go crashing into the valley below.

"A landslide!" cried Mr. Parker. "That is the landslide which I predicted! The lightning bolt has split Phantom Mountain!"