and sharpened in about the same manner. Dropping from a height
of a mile or so, that dart will acquire enough velocity to penetrate a
man from his head all the way through his body to his feet.

But in dropping bombs from an airship the damage intended does not so
much depend on velocity. It is necessary to know how fast the bomb
falls in order to know when to set the time fuse that will explode it;
though some bombs will explode on concussion.

At aeroplane meets there are often bomb-dropping contests, and balls
filled with a white powder (that will make a dust-cloud on falling, and
so show where they strike) are used to demonstrate the birdman's
accuracy.

"We'll see how our bomb-release works," Tom went on. "But we'll have to
descend a bit in order to watch the effect."

"You're not going to use real bombs, are you, Tom?" asked Ned.

"Indeed not. Just chalk-dust ones for practice. Now here is where the
bombs will be placed," and he pointed to the three openings in the
floor of the amidship cabin. The wire nettings were taken out and one
could look down through the holes to the earth below, the ground being
nearer now, as Tom had let out some of the lifting gas.

"Here is the range-finder and the speed calculator," the young inventor
went on as he indicated the various instruments. "The operator sits
here, where he can tell when is the most favorable moment for releasing
the bomb."

Tom took his place before a complicated set of instruments, and began
manipulating them. One of his assistants, under the direction of
Lieutenant Marbury, placed in the three openings bombs, made of light
cardboard, just the size of a regular bomb, but filled with a white
powder that would, on breaking, make a dust-cloud which could be
observed from the airship.

"I have first to determine where I want to drop the bomb," Tom
explained, "and then I have to get my distance from it on the
range-finder. Next I have to know how fast I am traveling, and how far
up in the air I am, to tell what the velocity of the falling bomb will
attain at a certain time. This I can do by means of these instruments,
some of which I have adapted from those used by the government," he
said, with a nod to the officer.

"That's right--take all the information you can get," was the smiling
response.

"We will now assume that the bombs are in place in the holes in the
floor of the cabin," Tom went on. "As I sit here I have before me three
buttons. They c