"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