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. Evidentl