y. "I'm afraid I'll have
to begin all over again, and proceed along new lines."

"Well, perhaps you will," said the lieutenant. "But you may invent
something much better than anything you have now. There is no great
rush. Take your time, and do something good."

"Oh, I'll get busy on it right away," Tom declared. "We'll go down now,
and start right to work. I'm afraid, Ned, that our idea of a
door-spring check isn't going to work."

"I might have known my idea wouldn't amount to anything," said the
young bank clerk.

"Oh, the idea is all right," declared Tom, "but it wants modifying.
There is more power to those recoils than I figured, though our first
experiments seemed to warrant us in believing that we had solved the
problem."

"Are you going to try the bomb-dropping device?" asked the lieutenant.

"Yes, there can't be any recoil from that," Tom said. "I'll drop a few
blank ones, and see how accurate the range finders are."

While his men were getting ready for this test Tom bent over the broken
propeller, looking from that to the recoil checks, which had not come
up to expectations. Then he shook his head in a worried and puzzled
manner.

CHAPTER XVII

AN OCEAN FLIGHT

Dropping bombs from an aeroplane, or a dirigible balloon, is a
comparatively simple matter. Of course there are complications that may
ensue, from the danger of carrying high explosives in the limited
quarters of an airship, with its inflammable gasoline fuel, and
ever-present electric spark, to the possible premature explosion of the
bomb itself. But they seem to be considered minor details now.

On the other hand, while it is comparatively easy to drop a bomb from a
moving aeroplane, or dirigible balloon, it is another matter to make
the bomb fall just where it will do the most damage to the enemy. It is
not easy to gauge distances, high up in the air, and then, too,
allowance must be made for the speed of the aircraft, the
ever-increasing velocity of a falling body, and the deflection caused
by air currents.

The law of velocity governing falling bodies is well known. It varies,
of course, according to the height, but in general a body falling
freely toward the earth, as all high-school boys know, is accelerated
at the rate of thirty-two feet per second. This law has been taken
advantage of by the French in the present European war. The French drop
from balloons, or aeroplanes, a steel dart about the size of a lead
pencil,