"Oh, I have been spying around, and I overheard the professors talking.
I know a thing or two, and I'll be on hand, on time, in your place!
Now, I have to leave you. I've left ten dollars to pay for your suit,
which I need to disguise myself with."

Then the man was gone, and Mark was left with his bitter thoughts to
keep him company. The whole daring scheme of the man had been revealed.
He did look something like Mark, and, attired in the lad's clothes, and
by keeping his face concealed, he might pass himself off as Jack's
chum; at least, until after the projectile had started.

"And then, as he says, it will be too late to return to earth and get
me," thought Mark bitterly. "Oh, why did I ever try to learn this man's
secret? Who is he, anyhow? Why didn't I wait for Jack at the barn, as I
promised? It's all my fault. I wonder if I can't get loose?"

Mark struggled several hours desperately and at last he felt the ropes
giving slightly. He redoubled his efforts. Strand by strand the cords
parted. He put all his efforts into one last attempt, and to his great
joy he felt his hands separate. He was partly free!

But scarcely half his task was accomplished. He had yet to discover the
secret of the hidden room--a room, as he afterward learned, which had
been built during slavery days to conceal the poor black men who were
escaping from the South.

"But now I have my hands to work with!" exulted Mark.

Resting a bit after his strenuous labors, he took a long drink of water