change, to be strong enough to navigate the ocean, was indeed
something to tax Mr. Henderson's ingenuity.

However, in the course of a little over a year the larger part of the
work was done. Inside the big shed was the huge affair which, it was
hoped, would enable its owner to be master of both air and water.

"Did the professor say anything special?" asked Mark of Washington.

"Nope. I reckon he were too busy problamatin' the exact altitude
projected in an inverse direction by th' square root of th' new engine
when operated at a million times inside of a few seconds, but he
didn't say nothin' t' me. I were busy underneath th' ship, fixin'
bolts when he tole me t' find yo'. I wouldn't be s'prised if he had
th' thing goin' soon."

"Do you think he'll be generating the new gas to-day?" asked Jack
eagerly. "That's the most troublesome part; to get that gas right."

"He didn't say nothin' t' me 'bout it," Washington stated, as he
walked along beside the two boys. "He jest seemed anxious like."

"We'd better hurry," advised Mark. "He may be at an important part in
his experiments and probably needs us. I hope it will work. He has
spent many days on it, and we all have worked hard. It ought to be a
success."

"Perfesser allers makes things work," declared Washington stoutly.

"That's a good way to feel about it, anyway," observed Mark. "Well,