"Well, what do you say, Tom?" asked Ned, in a low voice.

"She's all right as far as I can see, though she may stagger a bit at the take off."

"It's a pretty heavy load," agreed the young manager, as he and Tom Swift walked about the big fire-fighting airship Lucifer, which had been rolled outside the hangar. "But still I think she'll take it, especially since you've tuned up the motor so it's at least twenty per cent. more powerful than it was."

"Perhaps you'd better leave me out," suggested Mr. Baxter, who had been helping the boys. "I'm not a feather weight, you know."

"I need you with us," said Tom. "I want your expert opinion on the effect the new chemicals have on the flames."

"Well, I'd like to come," admitted the chemist, "for it will be a valuable experience for me. But I don't want an accident up in the air."

"Trust Tom Swift for that!" cried Ned. "If he says his aircraft will do the trick, it positively will."

"How about leaving me out?" asked Mr. Damon. "I'm not an expert in anything, as far as I know."

"You are in keeping us cheerful. And we may need you to bless things if there's a slip-up anywhere," laughed Tom, for Mr. Damon had been invited to be one of the party.

"I don't so much mind a slipup," said Mr. Damon, "as I do a slip down. That's where it hurts! However, I'll 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."

"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."

"I've about given up," said Mr. Baxter, in discouraged tones. "I guess my dye formulae are gone forever."

"Don't say that!" exclaimed Tom. "Once I get this fire matter off my hands, I'm going to tackle the problem myself. We'll either make those fellows sorry they ever meddled in this matter, or we'll get up a new combination of dyes that will put them out of business!"

"Bless my Easter eggs, I'm glad to hear you talk that way!" cried Mr. Damon.

"Well, Rad, I'll expect to see you up and around when I get back," said Tom to his old servant, as he stepped into the sick room to say goodbye.

"Oh, is yo' goin', Massa Tom?" asked the colored man, turning his bandaged head in the direction of the beloved voice.

"Yes. I'm going to try out a new scheme of mine--the fire extinguisher, you know."

"De same one whut fizzed up, an'--an' busted me in de eyes, Massa Tom?"

"Yes, Rad, I'm sorry to say, it's the same one."

"Oh, shucks now, Massa Tom! whut's use worryin'?" laughed Rad. "I suah will be all right when yo' gits back. De doctor man--de 'pill man' dat giant calls him--says I'll suah be better."

"Of course you will," declared Tom, but his heart sank when he saw Mrs. Baggert remove the bandages and he caught sight of Rad's burned face and the eyes that had to be kept closed if ever they were again to look on the sunshine and flowers. "And when I come back, Rad, I'll stage a little fire for your benefit, and show you how quickly I can put it out."

"Ha! dat's whut I wants to see, Massa Tom, I suah does like to see fires!" chuckled Eradicate. "Mah ole mule, Boomerang--does yo' 'member. him, Massa Tom?"

"Of course, Rad!"

"Well, Boomerang he liked fires, too. Liked 'em so much I jest couldn't git him past 'em lots ob times I But run 'long, Massa Tom. Yo' ain't got no time to waste on an ole culled man whut's seen his best days. Yas-sir, I reckon I'se seen mah best days," and the smile died from the honest, black face.

"Oh, don't talk like that!" cried Tom, as cheerfully as he could. "You've got a lot of work in you yet, Rad. Hasn't he, Koku?" and the young inventor appealed to the giant, who seldom left the side of his former enemy.

"Rad good man--him an' me do lots work--next week mebby," said Koku, smiling very broadly.

"That's the way to talk!" exclaimed Tom, and he laughed a little though his heart was far from light.

And then, having seen to the final details, he took his place in the big airship with Ned, Mr. Damon and Josephus Baxter. The craft carried the largest possible load of fire extinguishing chemicals.

As Tom had feared, the Lucifer staggered a bit in "taking off" late that afternoon when the start was made for the distant city of Denton, where the first real test was to be made under the supervision and criticism of the fire department. But once the craft was aloft she rode on a level keel.

"I guess we're all right," Tom said. But to make certain he circled several times over his own landing field, that a good place to come down might be assured if something unforeseen developed.

However, all went well, and then the course was straightened for the distant city.

"We'll go right over Newmarket, sha'n't we, Tom?" asked Ned, as the speed of the Lucifer increased.

"Yes. And I wish I had time to stop and see Mary, but I haven't. It's getting dark fast, and we ought to arrive at our destination early in the morning. The test has been set by the committee for ten o'clock."

They settled themselves comfortably in the big craft for a long night trip, and Mr. Damon was just going to bless something or other when he pointed off into the distance.

"Look, Tom!" cried the eccentric man. "See that light in the sky!"

"Seems to be a fire," observed Ned.

"It is a fire!" shouted Mr. Baxter. "And it's in Newmarket, if I'm any judge."

Tom Swift did not answer, but he shoved forward the gasolene lever of his controls, and the Lucifer shot ahead through the air while the red, angry glow deepened in the evening sky.