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."
"It couldn't be helped," said Ned. "We'll hope for the best."
"Yes," agreed Tom, "that's all we can do—hope for the best. By the way," he went on, turning to Mr. Baxter, "are you any nearer fastening the guilt on those two rascals, Field and Melling?"
"Bless my prosecuting attorney, no!" exclaimed Mr. Damon. "Those are the slickest scoundrels I ever tackled! They're like a flea. Once you think you have them where you want them, and they're on the other side of the table, skipping around."