The colored man prepared a simple supper for Mr. Henderson, and afterward got himself a meal.  When the dishes were cleared away the old man, who had noted with smiles the anxious glances Jack and Mark were casting about the strange room, said: 

“I suppose you boys would like to ask lots of questions.”

“I’d like to know what all this machinery is for,” spoke Jack.

“And what is behind that door,” Mark went on, indicating the much-locked portal.

“I knew it!” exclaimed the old man.  “I knew it!  Now if I tell you will you promise to keep it a secret until I give you leave to speak?”

Of course the boys promised eagerly.

“Do you think you have rested enough now to take a look inside?” the inventor asked, nodding toward the locked door.

“Sure!” exclaimed Jack.

“Then put on your coats and trousers and I’ll introduce you to my pet.”

Wonderingly, the boys followed him.  It took nearly a minute to unfasten the various bolts and bars, but at last the portal swung open.  The place was dimly lighted by a single big lamp, but in the glare of it the boys caught sight of a strange, weird object.  It looked like an immense cigar, and swayed slowly back and forward.  It seemed to be covered with a net-work of cords.  On the ground beneath it was what seemed to be a good-sized boat, with a large cabin amidships.

“What in the world is it?” cried Jack.

“It’s my airship!” exclaimed Professor Henderson.  “The only successful airship ever invented.  It is the electric Monarch!”

“What is it for?” asked Mark.

“To navigate the realm of the stars and moon!” cried the old man.  “With that I will rival the eagles in their flight!”

The boys were a little alarmed.  The professor was strangely excited.  His eyes sparkled in the reflected light of the lamp.  Jack and Mark thought they might have been brought to the abode of a madman.  They shrank back a little.  But they were reassured a moment later when, with a pleasant laugh, the old man said: 

“Don’t be frightened, boys.  I know what I am talking about.  Here, Washington, more light!  We will show them what we have done, hidden away from the sight of the curious, unbelieving world.  Let them see my Monarch!”

“We’ll illuminationness dis abode like it was de orb ob day shinin’ heah!” exclaimed the negro, as he started several more lamps aglow.

“Are the shutters closed?” asked Mr. Henderson, anxiously.

“Tight as a drum-head,” was the reply.

“Now look!” exclaimed the inventor, turning to the boys.

They were more than astonished at what they saw.  They had no idea that the rough shed held such a perfect piece of machinery.

Up near the roof of the place, which was quite high, there swayed an immense bag of oiled silk.  It was shaped like a cigar, big in the middle and tapering at both ends.  The bag was enclosed in a net of ropes which extended down to the lower part of the airship.