Suddenly the engine stopped, and to those below, anxiously watching, the silence became almost oppressive, for Tom had somewhat descended, and the explosions had been plainly heard by those observing him.  But now they ceased!

“His engine’s stalled!” cried Garret Jackson.

Mr. Swift heard the words, and looked anxiously up at his son.

“Is he in any danger?” gasped Mr. Damon.

No one answered him.  Like some great bird, disabled in mid flight, the monoplane swooped downward.  A moment later a hearty shout from Tom reassured them.

“He shut off the engine on purpose,” said Mr. Jackson.  “He is vol-planing back to earth!”

Nearer and nearer came the butterfly.  It would shoot downward, and then, as Tom tilted the planes, would rise a bit, losing some of the great momentum.  In a series of maneuvers like this, the young inventor reached the earth, not far from where his father and the others stood.  Down came the butterfly, the springs of the wheel frame taking the shock wonderfully well.

“She’s all right—­regular bird!” cried Tom, in enthusiasm, when the machine had come to a stop after rolling over the ground, and he had leaped out.  “We’ll make a good flight to-morrow, Mr. Damon, if the weather holds out this way.”

“Good!” cried the eccentric man.  “I shall be delighted.”

They made the start early the next morning, there being hardly a breath of wind.  There was not a trace of nervousness noticeable about Mr. Damon, as he took his place in the seat beside Tom.  The lad had gone carefully over the entire apparatus, and had seen to it that, as far as he could tell, it was in perfect running order.

“When will you be back, Tom?” asked his father.

“To-night, perhaps, or to-morrow morning.  I don’t know just what Mr. Fenwick wants me to do.  But if it is anything that requires a long stay, I’ll come back, and let you know, and then run down to Philadelphia again.  I may need some of my special tools to work with.  I’ll be back to-night perhaps.”

“Shall I keep supper for you?” asked Mrs. Baggert, the housekeeper.

“I don’t know,” answered Tom, with a laugh.  “Perhaps I’ll drop down at Miss Nestor’s, and have some apple turnovers,” for he had told them or the incident of hiring the new cook.  “Well,” he went on to Mr. Damon, “are you all ready?”

“As ready as I ever shall be.  Do you think we’ll have to do any vol-planing, Tom?”

“Hard to say, but it’s not dangerous when there’s no wind.  All right, Garret.  Start her off.”

The engineer whirled the big wooden, built-up propeller, and with a rattle and roar of the motor, effectually drowning any but the loudest shouts, the butterfly was ready for her flight.  Tom let the engine warm up a bit before calling to his friends to let go, and then, when he had thrown the gasolene lever forward, he shouted a good-by and cried: