The boys worked with a will.  The last articles were placed in the various rooms of the airship’s cabin, until the balloon shed was stripped quite bare.  The professor was busy in the engine room.  The noise of the gas generating machine increased.

Then came a series of sharp explosions as one of the gasolene engines was started.  This was followed by the hum of an electric dynamo, and the whizz and purring of a big motor.

The inventor was testing the many machines to see that all worked right.  Suddenly he switched on the incandescent lights in the ship’s cabin.  Next he turned on the powerful searchlight in the bow, and the shed was illuminated by a glare that rivaled the sun.  The professor then revolved the big propeller slowly and tested the rudder.

“Everything is in good shape!” he cried.  “We will start in five minutes if they get the roof off so we can rise.  Those anchor ropes will not hold much longer!”

Up on the roof, however, the men were working with a will.  Board after board was torn away and the different sections moved to one side.  At last the whole top of the shed was off.  All that remained was to let the Monarch out.

Suddenly from where the three emergency helpers were working there came a cry of astonishment, mingled with fear.  For the first time Andy Sudds, Tom Smith and Bill Jones, characters well known to Amos Henderson, had looked down into the shed, and caught sight of the tugging, swaying airship.  The interior had been quite dark up to this point, which accounted for them not having noticed the ship before.  But when they saw the strange affair so close beneath them they were startled.

“Jumpin’ rattlesnakes!” cried Andy Sudds.  “What have I struck?”

“It’s a yellow elephant!” exclaimed Tom Jones.

“A sea serpent!” ejaculated Bill Smith.

They leaned over from the edge of the roof eaves to which they were clinging and peered down into the big balloon shed.  Certainly the airship presented a queer sight to the three men.

“Is everything ready?” asked the professor of Washington.

“Eberyt’ing am circumulated to completeness,” replied the negro.

“Jump in, boys!  Untie the ropes, Washington.  We’ll start!”

“Hurry!  Hurry!  Perfessor!” cried Washington, as he looked out of a side window.  “Here comes dat man we tied up in de shed!  He’s got anoder man wid him, an’ dey got guns!”

“It’s Taggert!  He is after me!” exclaimed the inventor.  “He must not be allowed to get on the ship!  Come on, Mark and Jack!  Never mine unknotting the ropes!  Cut ’em!  We have no time to lose!  Jump in, Washington!”

The boys clambered over the sides of the airship.  Washington followed their example.  The anchor ropes were cut.

“Hi, there!  Stop!” cried a voice from outside.  “Don’t you dare start that ship!”

“Here we go!” shouted Professor Henderson in a joyful tone.  “Now to see if the Monarch fulfills her promise!”