rfield.

"But, bless my overshoes, Tom!" he exclaimed, as he departed, "don't
forget to let me know when you have your silent motor working. I want
to see it."

"I'll let you know," was the promise given by the young inventor.

"And watch out for those Universal people," warned Ned. "I'm not
telling you this as a bank official, for I'm not supposed to, but it's
personal."

"I'll be on the watch," said Tom. And, as he went into his private
workshop, he wondered why it was his father and Ned had both warned him
not to trust Gale and Ware.

The next few days were busy ones for Tom Swift. Once he had made up his
mind to go to work seriously on a silent motor, all else was put aside.
He sent a note to Mary Nestor, telling her what he was going to do,
and, asking her to say nothing about it, which, of course, Mary agreed
to.

"Come and see me when you can," she sent back word, "but I know you
won't have much chance when you're experimenting with your invention.
And I shall be working so hard for the Red Cross that I sha'n't get
much chance to entertain you. But the war can't last forever."

"No," agreed Tom with a sigh, as he put away her letter, "and thank
goodness that it can't!"

The young inventor threw himself into the perplexing work of inventing
a silent motor with all the fervor he had given to the production of
his war tank, his giant cannon, his wonderful searchlight and other
machines.

"And," mused Tom, as he sat at his work table with pencil and paper
before him, "since this is a problem in acoustics, I had best begin. I
suppose by going back to first principles, and after determining what
makes an aeroplane engine noisy, try to figure out how to make it
quiet. Now as to the first, the principle causes of noise are--"

And at that instant there broke on Tom's ears a succession of
discordant sounds which seemed to be a combination of an Indian's war
whoop and a college student's yells at a football game.

"Now I wonder what that is!" mused the young inventor as he hastily
arose. "Better solve that problem before I tackle the aeroplane motor."

CHAPTER VIII

THROUGH THE ROOF

Tom rushed from his private office, and when he reached the outer door
he heard with more distinctness the sounds that had alarmed him. They
seemed to come from a small building given over to electrical
apparatus, and which, at the time, was not supposed to be in use. It
had been Tom's workroom, so to speak, when h