“Dare you do it?” cried the old professor, hope shining in his face.

“Try me and see.”

The professor quickly prepared a piece of silk, kept on hand to repair breaks in the bag.  It was coated with a very strong and fresh cement.  The silk was to be inserted in the tear made by the eagles, when it would at once harden and prevent the further escape of gas.

Mark made ready for the perilous ascent.  He took off his coat, and removed his shoes so his feet could better cling to the frail-looking though strong cords.

“Slow down the ship!” commanded the captain.  “Now, Mark, try!  I hope you succeed!  Move cautiously.  You don’t want to lose your life!”

Mark said nothing.  He grasped the piece of oiled silk, coated with the cement, in his teeth, clinching it by a strip that was free from the sticky substance.  Then he stood on the rail of the Monarch and began his climb aloft.  Surely few ascents were made under such fearful conditions.  The airship was now more than a mile above the earth.  One false step and the boy would plunge into eternity.  Nothing could save him.

Up and up he went, testing every cord and mesh before he trusted his weight to it.  On and on he advanced.  The frail gas bag swayed in the wind that was springing up.  It seemed like a thing alive.

“Careful!  Careful!” cautioned the professor in strained tones.  Everyone on the ship held his breath.  Up and up Mark went.  At last he reached the place where the eagle’s beak had torn the bag.

He braced himself in the meshes of the net.  Then, leaning forward, he fixed the patch under the rent, and pressed it into place.  The cement did not take hold at first.  Mark pressed harder.  Would the leak be stopped?

“Will he make it?” asked one.

“I don’t think so.”

“He must make it!”

“If not we are lost!”

“You are right!”

For a moment there was a doubt.  Then the sticky stuff adhered to the silk bag, and the patch was made fast.  A shout from Washington in the engine room told that the gas had ceased to rush out.  Mark had succeeded.

Washington hastened to turn the gas generator to half speed.  Before he could do so, however, there had been a great increase in the volume of vapor in the bag, caused by the sudden stopping off of the vent.  Up shot the airship, the accumulation of gas lifting it higher from the earth.  So suddenly did it shoot up, from having been almost at rest, that there was a tremor through the whole craft.

“Look out, Mark!” cried Jack.  He looked up to where his comrade clung to the netting.

“Hold fast!  We’ll stop the ship in a second,” exclaimed the captain.

But it was too late.  The sudden rising of the craft had shaken Mark’s hold, which was not of the best at any time, since the gas bag was a yielding surface to lean against.

The next instant the boy, vainly clutching the air for some sort of grip for his hands, toppled over backward.  His feet slid from the meshes of the net, and he plunged downward toward the earth, more than a mile below!