il he had perfected it, and he was now laboring to that end.

One day, in midsummer, after weary days of toil, Tom took Ned out for a
ride in the machine which had been fitted up to carry a large supply of
the chemical mixture, a small but powerful searchlight, and other new
"wrinkles" as Tom called them, not going into details.

"Any special object in view?" asked Ned, as Tom headed across country.
"Are you going to put out any more tree fires?"

"No, I haven't that in mind," was the answer. "Though of course if we
come across a blaze, except a brush fire, I may put it out. I have the
bombs here," and Tom indicated the releasing lever.

"What I want to try now is the stability of this with all I have on
board," he resumed. "If she is able to travel along, and behave as well
as she did before I made the changes, I'll know she is going to be all
right. I don't expect to put out any fires this trip."

In testing the ship of the air Tom sent her up to a good height,
heading out over the open country and toward a lake on the shores of
which were a number of summer resorts. It was now the middle of the
season, and many campers, cottagers and hotel folk were scattered about
the wooded shore of the pretty and attractive body of water.

Tom and Ned had a glimpse of the lake, dotted with many motor boats and
other craft, as the airship ascended until it was above the clouds.
Then, for a time, nothing could be seen by the occupants but masses of
feathery vapor.

"She's working all right," decided Tom, when he found that he could
perform his usual aerial feats with his craft, laden as she was with
apparatus, as well as he had been able to do before she was so
burdened. "Guess we might as well go down, Ned. There isn't much more
to do, as far as I can see."

Down out of the heights they swept at a rapid pace. A few moments later
they had burst through the film of clouds and once more the lake was
below them in clear view.

Suddenly Ned pointed to something on the water and cried:

"Look, Tom! Look! A motor boat in some kind of trouble! She's sinking!"

CHAPTER XV

COALS OF FIRE

Tom Swift saw the craft almost as soon as did his chum. It was rather a
large-sized motor boat, quite some distance out from shore, and there
was no other craft near it at this time. From the quick, first view Tom
and Ned had of it, they decided that a party of excursionists were on a
pleasure trip.

But that an accident had happen