The doctor rekindled the light in the cylinder; the spiral became heated; the current of hydrogen came in a few minutes, and the gas dilated; but the balloon did not stir an inch.

Joe looked on uneasily, but kept silent.

“Joe!” said the doctor.

Joe made no reply.

“Joe! Don’t you hear me?”

Joe made a sign that he heard; but he would not understand.

“Do me the kindness to throw out some of that quartz!”

“But, doctor, you gave me leave—”

“I gave you leave to replace the ballast; that was all!”

“But—”