take a chance with you, Tom Swift.
It won't be the first one--and I guess it won't be the last."

The work of getting the big airship ready for what was to be a
conclusive test of her fire-fighting abilities from the clouds
proceeded rapidly. As has been related, Tom had perfected, with the
help of Mr. Baxter, a combination of chemicals which was effective in
putting out a fire when dropped into the blaze from above. Quantities
of this combination had been stored in metal containers which Tom had
at first styled "bombs," but which he now called "aerial grenades."

The manner of dropping the grenades was, on the whole, similar to the
manner in which bombs were dropped from airships during the Great War,
but Tom had made several improvements in this plan.

These improvements had to do with the releasing of the bombs, or, in
this case, grenades. It is not easy to drop or throw something from a
swiftly moving airship so that it will hit an object on the ground.
During the war aviators had to train for some time before becoming even
approximately accurate.

Tom Swift decided that to leave this matter to chance or to the eye of
the occupant of an airship was too indefinite. Accordingly he invented
a machine, something like a range-finder for big guns. With this it was
a comparatively easy matter to drop a grenade at almost any designated
place.

To accomplish this it was necessary to take into consideration the
speed of the airship, its height above the ground, the velocity of the
wind, the weight of the grenades, and other things of this sort. But by
an intricate mathematical process Tom solved the problem, so that it
was only necessary to set certain pointers and levers along a slide
rule in the cockpit of the craft. Then when the releasing catch was
pressed, the grenades would drop down just about where they were most
needed.

"I think everything is ready," said Tom, when he had taken a last look
over his craft, making sure that all the chemical grenades were in
place. "If you will be ready, gentlemen, we will take our places and
start in about half an hour," he added. "I want to say goodbye to my
father, and cheer up Rad--if I can."

"The doctor will know tomorrow, will he?" asked Mr. Damon.

"Yes. And I'm sorry I will not be here to listen to the report," said
Tom. "Though I am almost afraid to receive it," he added in a low
voice. "I shall blame myself if Rad is to go through the remainder of
his life blind."