ed Frank Merriwell. "And we must be ready to go the
instant she does fill. We can't hold 'em back long, for we have no
shelter here. Professor, Hans, into that car! Get in, I say, and be
ready! We'll try to stand the whelps off till the balloon is inflated,
but we must be ready to start at any instant."

Professor Scotch and Hans were hastily bundled into the car.

The bandits hesitated long enough to gather and prepare for the charge,
with their chief in the lead. It was plain they saw the treasure-seekers
had no shelter, and they meant to close in without delay.

"Reddy for 'em, Frank!" called Bushnell, dropping on one knee, his
Winchester in his hands. "They're comin' right soon!"

This was true. With mad cries and a fusillade of shots, the bandits
charged.

Bushnell opened fire, and Frank followed his example. Several of the
bandits were seen to fall, but still the others came on.

"Lead won't stop 'em!" snarled the Westerner. "It'll be hand ter hand in
a jiffy."

"And that means----"

"We'll get wiped out."

"The balloon----"

"Won't carry more'n two--possibly three. In with ye, boy! You may
escape! It don't make any diffrunce 'bout an old coon like me."

"Not much will I get in and leave you!" cried Frank. "We are partners in
this expedition, and partners we'll stay to the end!"

"But ther others--ther professor an' ther Dutch boy! They might escape
if----"

"They shall escape!"

Out flashed a knife in Frank Merriwell's hand, and, with one sweeping
slash, he severed the strong rope that held the tugging, tossing balloon
to the earth. Away shot the balloon, a cry of amazement and horror
breaking from the lips of the professor and Hans.

"Mein gootness!" gasped the Dutch boy. "Vot vos happened?"

"I'll tell you," groaned the professor. "The balloon could not carry all
four of us, and Frank Merriwell, like the noble, generous, hot-headed,
foolish boy he is, refused to leave Bushnell. At the same time he would
not doom us, and he cut the rope, setting the balloon free. He has
remained behind to die at Bushnell's side."

"Led me git oudt!" sobbed Hans. "I vant to go pack und die mit him!"

"It was too late now. Look--see there! We are directly over the Silver
Palace! What a beautiful----"

The professor's words were interrupted by a frightful rumbling roar that
came up from the gulf surrounding the plateau on which the palace stood.
All the way around that gulf a sheet of flame seemed to leap up