He closed with one of these, some distance off, and agreed to fly over in his aircraft and extinguish a fire which was to be started in an old building which had been condemned, and was to be destroyed. This was in a city some four hundred miles away and when Ned Newton called on him one afternoon he found Tom busily engaged in loading his sky-craft with a heavy cargo of the newest liquid extinguisher.

"You aren't taking any chances, are you, Tom?" asked Ned.

"What do you mean?"

"I mean you seem to have enough of the liquid 'fire-discourager' to douse any blaze that was ever started."

"No use sending a boy on a man's errand," said Tom. "I'm counting on you to go with me, Ned—you and Mr. Baxter. We leave this afternoon for Denton."

"I'll be with you. Couldn't pass up a chance like that. But here comes Koku, and it looks as if he had something on his mind."

The giant did, indeed, seem to be laboring under the stress of some emotion.

"Oh, Master Tom!" the big man exclaimed when he had got the attention of the young inventor. "Rad—he—he—"

"Has anything happened?" asked Tom, quickly. "No, not yet. But dat pill man—he say by tomorrow he know if Rad ever will see sunshine more!"

"Oh, the doctor says he'll be able to decide about Rad's eyesight tomorrow, does he?"

"Yes. What so pill man say," repeated Koku.

"Um," mused Tom, "I wish I were going to be here, but I don't see how I can. I must give this test." But it was with a sinking heart as he thought of poor Eradicate that the young inventor proceeded to pile into his airship the largest and heaviest load of chemicals it had ever carried.



CHAPTER XXI

THE LIGHT IN THE SKY

"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.



CHAPTER XXII

TRAPPED

While Tom Swift was loading the Lucifer for her trip and the fire extinguishing test to occur the next morning, quite a different scene was taking place in the home of Jasper Blake, the uncle of Mary Nestor, where she had gone to spend a few weeks.

"Well, are you all ready, Mary?" asked her aunt, and it was about the same time that Ned Newton asked that same question of Tom Swift. Only Tom was in Shopton, and Mary was in Newmarket, and Tom was setting off on an air voyage, while Mary was only preparing to take a car downtown to do some shopping.

"Yes, Aunt, I'm all ready," Mary answered. "But I may be a bit late getting home."

"Why?" asked Mrs. Blake.

"I promised Uncle Barton I'd stop and call on him at his office," Mary replied. "He has something he wants me to take home to mother when I go tomorrow."

"I shall be sorry to see you go back," said Mrs. Blake. "But I imagine there will be those in Shopton who will be glad to see you return, Mary."

"Yes, mother wrote that she and dad were getting a bit lonesome," the girl casually replied, as she adjusted her veil.

"Yes, and some one else. Ah, Mary, you are a very lucky girl!" laughed her aunt, while Mary turned aside so she would not see her own blushes in the mirror.

"I thought Tom was going to call and take you home in his airship, Mary," went on her relative.

"So he is, I believe, on his way back from a city where he is going to be tomorrow making a big fire test. I am to wait for him until tomorrow afternoon. But now I really must go shopping, or all the bargains will be taken. Is there any word you want to send to Uncle Barton?"

"No," answered Mrs. Blake. "Though you might tell him to stop poking fun at your Uncle Jasper for having invested money in the Landmark Building. It's getting on your Uncle Jasper's nerves," she added.

"Uncle Barton never can give up a joke, once he thinks he has one," said Mary. "But I'll tell him to stop pestering Uncle Jasper."

"Please do," urged Mary's aunt, and then the girl left.

Mary's uncle, Barton Keith, with whom Tom Swift had been associated during the undersea search, had offices in the Landmark Building, but his home was in an adjoining suburb.

The girl was pleased with the results of her shopping, and at the close of the afternoon she stopped at the Landmark Building and was soon being shot up in the elevator to the floor where Barton Keith had his offices.

Though Mr. Keith had refrained from investing in the Landmark Building and though he laughed at Mary's Uncle Jasper for having done so, this did not prevent him from having a suite of offices in the big structure which, as we already know, was owned in large part by Field and Melling.

"Ah, Mary! Come in!" exclaimed Mr. Keith, welcoming Tom Swift's sweetheart. "It is so late I was afraid you weren't coming, and I was about to close the office and go home."

"You must blame the bargain sales for my delay," laughed Mary. "I hope I haven't kept you waiting."

"No, I still had a few things to do. One was to write a letter to your Uncle Jasper, telling him I had heard of another fire trap that was open to investors."

"Oh, and that reminds me I must tell you not to push Uncle Jasper too far!" warned Mary.

"Ha! Ha!" laughed Uncle Barton. "He made fun of me for going on the undersea search with Tom Swift. But I made good on that, and that's more than he can say about his Landmark Building deal!"

"But don't exasperate him too much!" begged Mary. "By the way, what are they doing to this building? I see the stairways and some of the elevator shafts all littered with building material."

"They are trying to make it fireproof," answered her uncle. "It's rather late to try that now, but they've got either to do it or stand a big increase in insurance rates. I'm glad I'm out of it. But now, Mary, take an easy chair until I finish some work, and then I'll walk out with you."

Mary took a seat near one of the front windows, whence she could look down into the now fast-darkening streets. She could see the supper crowds hurrying home, and out in the corridor of the big skyscraper could be heard the banging of elevator doors as the office tenants, one after another, left for the day.

Suddenly there was more commotion than usual, followed by the sound of broken glass. Then came a cry of:

"Fire! Fire!"

Mary sprang to her feet with a gasp of alarm, and her uncle rushed past her to the door leading into the hall outside his offices. As he opened the door a cloud of smoke rushed toward him and Mary, causing them to choke and gasp.

Mr. Keith closed the door a moment, and when he opened it again the smoke in the hall seemed less dense.

"It probably is only a slight blaze among some of the material the workmen are using," he said. "Come, Mary, we'll get out."

Pausing only to swing shut the door of his heavy safe and to stuff some valuable papers into his pocket, Mr. Keith advanced and, taking Mary by the arm, led her into the hall. The smoke was increasing again, and distant shouts and cries could be heard, mingled with the breaking of glass.

Mr. Keith rang the elevator buzzer several times, but when no car came up the shaft in response to his summons he turned to his niece and said:

"We'll try the stairs. It's only ten stories down, and going down isn't anything like coming up."

"Oh, indeed I can walk!" said Mary. "Let's hurry out!"

They turned toward the stairway, which wound around the elevator shafts, but such a cloud of hot, stifling smoke rolled up that it sent them back, choking and gasping for breath.

And then, as they stood there, up the elevator shafts, which were veritable chimneys, came more hot smoke, mingled with sparks of fire.

"Trapped!" gasped Mr. Keith, and he pulled Mary back toward his offices to get away from the choking, stifling smoke. "We're trapped!"



CHAPTER XXIII

TO THE RESCUE

"Uncle! Uncle Barton!" faltered Mary, as she clung to Mr. Keith. "Can't we get down the stairs?"

"I'm afraid not, Mary," he answered, and he closed the door of his office to keep out the smoke that was ever increasing.

"And won't the elevators come for us?"

"They don't seem able to get up," was his reply. "Probably the fire started in the bottom of the shafts, and they act just like flues, drawing up the flames and smoke."

"Then we must try the fire escapes!" exclaimed Mary, and she started toward the front window, pulling her uncle across the room after her.

"Mary, there aren't—aren't any fire escapes!" he said hoarsely.

"No fire escapes!" The girl turned paler than before.

"No, not an escape as far as I know. You see, this was thought to be a fireproof building at first and small attention was given to escapes. Then the law stepped in and the owners were ordered to put up regular escapes. They have started the work, but just now the old escapes have been torn down and the new ones are not yet in place."

"Oh, but Uncle Barton! can't we do something?" cried Mary. "There must be some way out! Let's try the elevators again, or the stairs!"

Before Mr. Keith could stop her Mary had opened the door into the hall. To the agreeable surprise of her uncle there seemed to be less smoke now.

"We may have a chance!" he cried, and he rushed out. "Hurry!"

Frantically he pushed the button that summoned the elevators. Down below, in the elevator shafts, could be heard the roar and crackle of flames.

"Let's try the stairs!" suggested Mary. "They seem to be free now."

She started down the staircase which went in square turns about the battery of elevators, and her uncle followed. But they had not more than reached the first landing when a roll of black, choking smoke, mingled with sparks of fire, surged into their faces.

"Back, Mary! Back!" cried Mr. Keith, and he dragged the impetuous girl with him to their own corridor, and back into his offices which, for the time being, were comparatively free from the choking vapor.

"We must try the windows, Uncle Barton! We must!" cried Mary. "Surely there is some way down—maybe by dropping from ledge to ledge!"

Her uncle shook his head. Then he opened the window and looked out. As he did so there arose from the streets below the cries of many voices, mingled with the various sounds of fire apparatus—the whistles of engines, the clang of gongs, and the puffing of steamers.

"The firemen are here! They'll save us!" cried Mary, as she heard the noises in the street below. "We can leap into the life nets."

"There isn't a life net made, nor men who could retain it, to hold up a person jumping from the tenth story," said her uncle. "Our only chance is to wait for them to subdue the fire."

"Isn't there a back way down, Uncle Barton?" "No, Mary!" He closed the window for, open as it was, the draft created served to suck smoke into the office, and Mary was coughing.

Uncle and niece faced each other. Trapped indeed they were, unless the fire, which was now raging all through the building, with the stairs and elevator shafts as a center, could be subdued. That the city fire department was doing its best was not to be doubted.

"We can only wait—and hope," said Mr. Keith solemnly.

Mary gave a gasp. Her uncle thought she was going to burst into tears, but she bravely conquered herself and faced him with what was meant to be a smile. But it is difficult to smile with quivering lips, and Mary soon gave up the attempt.

Mr. Keith went over to the water cooler—one of those inverted large glass bottles—and looked to see how much water it contained.

"It's nearly full," he said.

"What good will it do?" asked Mary. "This fire is beyond a little water like that."

"Yes, but it will serve to keep our handkerchiefs wet so we can breathe through them if the smoke gets too thick," was his reply.

"It begins to look as if we'd need to try that soon," said Mary, and she pointed to thick smoke curling in under the door.

"Yes," agreed her uncle. "It's getting worse." Hardly had he spoken when there came a rush of feet in the corridor outside his office door. Then a voice exclaimed:

"We're trapped! We can't get down either the stairs or the elevators!"

"It can't be possible!" said another voice. "Something must be done! Help! Help! Take us out of here!"

"Foolish cowards!" murmured Mr. Keith, and then the door of his office was violently opened and two men rushed in. They were strangers to Mary and her uncle.

"Isn't there any way out of this fire trap?" cried one of the men. "Are there any fire escapes at your windows?"

"None," said Mr. Keith.

"This is all your fault, Melling!" cried the smaller of the two men, whose voice, in loudness and depth of pitch, was out of all proportion to his size. "All your fault! I told you we should have those new fire escapes!"

"And you were the one, Field, who objected to the cost of fire escapes when you found what the charge would be," retorted the other. "You said we didn't need to waste that money, if the building was fire-proof."

"But it isn't, Melling! It isn't!" yelled the other.

"We're finding that out too late!" came the retort. "But I'm not going to die here like a rat in a trap!" And he raised the window and leaned out and yelled, "Help! Help! Help!"

"Don't do that," said Mr. Keith, coming over to close the casement. "They can't hear you down below, and opening the window will only fill this place with smoke. Are you Field and Melling?"

"Yes, of the Consolidated Dye Company," was the answer from the big man. "We are also part owners of this building, but I wish we weren't."

"It is a pretty poor specimen of a modern building," said Mr. Keith. "You have offices here, haven't you?" he went on. "I remember to have seen your names on the directory."

"We're on the floor above," was the answer from Field. "We were in a rear room, going over some accounts, and we didn't know anything was wrong until we smelled smoke. We tried to get down, and managed to come, by way of the stairs, as far as this floor," he explained quickly.

"You can't go any farther," said Mr. Keith. "All there is to do is to wait for the firemen."

"Suppose they never come?" whined Melling. "Oh, they'll come!" asserted Mary's uncle, but he spoke more to quiet her alarm than because he really believed it, for the Landmark Building was a seething furnace of flame centering in and about the elevator shafts and stairs.

Meanwhile Tom and his companions in the airship had seen the red glow in the evening sky, and in another minute the young inventor had turned his craft more directly toward it.

"It surely is in Newmarket," said Mr. Damon. "Right in the center of the city, too. There's one big building there—the Landmark."

"Looks as if that was afire," said Ned quickly. "Hasn't some relative of Mary's an office there, Tom?"

"Yes. Mr. Keith. And her other uncle, Jasper Blake, is also interested in the building. It's the Landmark all right!" cried Tom, as his craft rose higher and advanced nearer the blaze.

"What are you going to do?" yelled Mr. Damon, as he saw the young inventor head directly toward a spouting mushroom of flame, which showed that the fire had broken through the roof. "What are you going to do?"

"Go to the rescue!" answered Tom Swift. "I couldn't ask a better opportunity to try my new extinguisher! Sit tight, every one!"



CHAPTER XXIV

A STRANGE DISCOVERY

Once it became evident to the occupants of the airship what Tom Swift's plans were, they all prepared to help him. Previous to the trip certain duties had been assigned to each one, duties which were to be exercised when Tom gave the exhibition of his new aerial fire-fighting apparatus at the set fire before the fire department of Denton.

This preparation now stood the young inventor in good stead, for there was no confusion aboard the Lucifer when she winged her way toward the burning Landmark Building, where the flames were continually spouting higher and higher as they rushed through the roof, directly above the stairway well and elevator shafts.

So far the flames had confined themselves to this central part of the big structure, but it was only a question of time when they would spread out on all sides, licking up the remainder of the pile. And, for the most part, the firemen on the ground were at a great disadvantage.

They had run in lines as near as they could get to the center of the blaze, and had also attached hose to the standpipes inside the building. But this last effort was wasted, as developed later, for there was no one in the building to direct the nozzle ends of the hose attached to the standpipes on the different floors. Also the fierce heat fairly melted the pipes themselves in the vicinity of the elevator shafts, and there was no automatic sprinkling system in the building.

This was the situation, then, when Tom in his airship loaded with fire-extinguishing chemicals headed for the blaze. And this, also, was the desperate situation that confronted Mary Nestor and her uncle, Barton Keith, as well as Amos Field and Jason Melling. Those unscrupulous and cowardly men were in a veritable panic of fear, which contrasted strangely with the calm, resigned attitude of Mary and her uncle.

"We must get out! Some one must save us!" yelled Field.

"Jump from the window!" cried Melling.

"No, I can't permit that!" declared Mr. Keith, standing in their path. "It would be sure death! As it is, there may be a chance."

"A chance? How?" asked Field. "Listen to that!"

Through the closed door of Mr. Keith's office could be heard the roar and crackle of flames, while the very air was now stifling and hot, filled with acrid smoke.

"We can only wait," said Mr. Keith, and he wet Mary's handkerchief in the water and handed it to her to bind over her face.

"Is everything all right, Ned?" called Tom, as he turned on a little more power, so that the Lucifer lunged ahead toward the great pillar of fire that now reddened the sky for miles around.

"All ready," was the answer. "You only have to give the word when you want us to let go."

"Let go!" cried Mr. Damon. "Bless my umbrella, Tom! We don't have to jump out, do we?"

"He means to let go the extinguisher grenades," said Mr. Baxter. "Shall we let them all go at once, Tom?" asked the chemist.

"No, drop half when I shoot over the first time. We'll see what effect they have, and then come back with the rest."

"That's the idea!" cried Ned. "Well, give us the word when you're ready, Tom."

"I will," was the answer of the young inventor, and with keen eyes he began to set the automatic gages so those in charge of the grenades would be able to drop them most effectively.

The flames were mounting higher and higher above the ill-fated Landmark Building. It was a "land-mark" now, for miles around—a fearsome mark, indeed.

"I hope every one is out of the place," said Ned, as the airship approached nearer and the fierceness of the fire was more manifest.

"Bless my thermometer, you're right!" exclaimed Mr. Damon. "I don't see how any one could live in that furnace."

Seen from above it appeared that the fire was engulfing the whole building, while, as a matter of fact, only the central portion was yet blazing. But it was only a question of time when the remainder would ignite.

And it was to this fact—that the fire was rushing up the stairway and elevator shafts as up a chimney—that Mary and her uncle, as well as Field and Melling, owed their temporary safety.

Had Tom known that the girl he loved was in such direful danger, it is doubtful if his hand would have been as steady as it was on throttle and steering wheel. But not a muscle or nerve quivered. To Tom it was but carrying out a prearranged task. He was going to extinguish a great blaze, or attempt to do so, by means of his aerial fire-fighting apparatus. And his previous tests had given him confidence in his device. His one regret was that the fire department of the city that was contemplating the purchase of certain rights in his invention could not witness what he was about to do.

"But they'll hear of it," declared Ned, when Tom voiced this idea to his chum.

Nearer and nearer to the up-spouting column of flames the airship winged her way. Tense and alert, Tom sat at the wheel guiding his craft with her load of fire-defying chemicals. Behind him were Ned, Mr. Damon and Mr. Baxter, ready to drop the grenades at the word.

"Getting close, Tom!" called Ned, as they could all feel the heat of the conflagration in the Landmark Building, which now seemed doomed.

"You'll not dare cross it too low down, will you?"

"No, I'll have to keep pretty well up," was the answer. "There's a current of air over that fire which might turn us turtle."

Heat creates a draft, sucking in colder air from below, and making an upward-rushing column which, in the case of a big blaze, is very powerful. Tom knew he had to avoid this.

It was now almost time to act. In another few seconds they would be sailing directly into the path of the up-spouting flames. Realizing that to do this at too low an elevation would result in disaster, Tom sent his craft upward at a sharp angle. Then he turned to call to his companions.

"Be ready when I give the word!"

"All set and ready!" answered Ned, and the others signified their attention to the command that soon was to be given.

Having attained what he considered a sufficient elevation, Tom headed the Lucifer straight toward the up-spouting column of fire and smoke. If ever his craft of the air was to justify her name it was now!

Straight and true as an arrow she headed for the fiery pillar! Hotter and hotter grew the air! The darkness of the night was lighted by the awful fire, which rendered objects in the street clear and distinct. But Tom and his friends had little time for such observation.

"Get ready!" cried the young inventor, as he felt a rush of heat across his face, partly protected, as it was, by great goggles.

"All ready!" shouted Ned.

"Let go!" cried Tom, and with a click of springs the fire extinguishers dropped from the bottom of the Lucifer into the very heart of the flames in the Landmark Building.

There was a blast as from a furnace seventy times heated, a choking and gasping for breath on the part of the occupants of the airship, a shriveling, as it seemed, of the naked flesh, and then, when it appeared that all of them must be engulfed in the great heat, the airship passed out of the zone of fire.

A rush of cool air followed, reviving them all, and then, when out of the swirls of smoke, Ned, looking back, cried:

"Good work, Tom! Good work!"

"Did we hit it?" cried the young inventor. "She's half gone!" declared Mr. Baxter. "Can you give her the rest of the load?"

"I'm going to try!" declared Tom.

"Bless my bank balance!" shouted Mr. Damon, "are we going through that awful furnace again?"

"It will not be so bad this time," observed Ned. "The fire is half out now. Tom's stuff did the trick!"

Indeed it was evident, as Tom sent the Lucifer around in a sharp turn, that the fire had been largely smothered by the gas that now lay over it like a wet blanket. But there was still some fire spouting up.

"Give her all we have!" yelled Tom, as, once more, he prepared to cross the zone of fire.

"Right," sang out Ned.

Once more the Lucifer swept over the burning building. Down shot the remaining grenades, falling into the mass of flames and bursting, though the reports could not be heard because of the tumult in the streets below. For the firemen and spectators had seen the sudden dying down of the fire, they had caught sight of a shadowy shape in the night, hovering over the blazing building, and they wondered what it all meant.

"How is it?" asked Tom, as he guided the craft back to get a view of his work.

"That settles it!" answered Ned. "There isn't fire enough now to broil a beefsteak!"

This was not exactly true, for the blaze was not entirely subdued. But the flames had all been killed off in the higher parts of the Landmark Building, and what remained could easily be dealt with by the firemen on the ground. They proceeded to make short work of the remainder of the conflagration, the while wondering who had so effectively aided them from the clouds.

"Well," observed Tom, as he saw how effectively he had smothered the great fire, "it's of no use to go on now. I haven't an ounce of chemical left on board. I can't give the demonstration that I planned for tomorrow."

"You've given a better demonstration here than you ever could have in the other city," declared Mr. Baxter. "I fancy this will be all the test needed, Tom Swift!"

"Perhaps. I hope so. But we may as well land and see from the ground the effect of our work. I'd also like to inquire if any one was hurt. Let's go down."

It was rather ticklish work, making a landing in the midst of a populous city, and at night. But as it happened, there had been a number of buildings razed in the vicinity of the Landmark structure, and there was a large, vacant level space. Also several of the city's fire department searchlights were focused around the burning structure, and when it became evident that an airship was going to land—though as yet none guessed whose it was—the searchlights were turned on the vacant spot and Tom was able to make a good landing, his own powerful searchlight giving effective aid.

"What did you do that put out the fire?" demanded the chief of the Newmarket department, as he rushed up with a crowd of others when Tom and his friends alighted.

"I dropped a few grenades down that chimney," modestly answered the young inventor.

"A few grenades! Say, you must have turned a whole river of them loose!" cried the delighted chief. "It doused the fire quicker than I ever saw one put out in all my life!"

"I'm glad I was successful," said Tom. "But was any one in the building?"

"Yes, a few," answered a policeman, who was trying to keep the crowd back from the airship. "They're bringing them out now."

"Killed?" gasped Tom.

"No. But some of them are badly hurt," the officer answered. "There was one young lady and a man named Barton Keith—"

"Barton Keith!" shouted Tom, springing forward. "Was he—Who was the young lady? I—I—"

But at that moment there was a stir in the crowd about the building, in which only a little fire flow remained, and through the throng came a disheveled and smoke-blackened young lady and a man whose clothing was also greatly disarrayed.

"Mary!" cried the young inventor.

"Tom!" gasped Mary Nestor. "How did you get here?"

"I came to put out the fire," was the answer, and Tom cooled down now that he saw Mary was unharmed. "How did you happen to be in the building?"

"I was in Uncle Barton's office when the fire broke out," answered Mary, "and we were trapped. We had to stay there, with two men from the floor above."

"Yes, and if they had stayed with us they wouldn't have been hurt," said Mr. Keith. "But, as it was, they rushed out and tried to get down the stairs. They were caught in the draft and badly burned, I believe. They are bringing them out now."

Two stretchers, on which lay inert forms, were borne through the now silent crowd by firemen and police officers, and taken to waiting ambulances.

"That's Field and Melling," said Mr. Keith to Tom. "They had offices just above me, and they were trapped, as were Mary and I. They acted like big cowards, too, though I hope they're not badly hurt. We stayed inside my office, and we were just giving up the hope of rescue when the fire seemed suddenly to die down."

"I should say it was sudden!" cried the enthusiastic local chief. "It was the chemicals from this young man's airship that did the trick!"

"Oh, Tom, was it your new machine?" asked Mary.

"Yes," was the answer. "I was on my way to give a test tomorrow in Denton when I saw this fire. I didn't know you were in it, though, Mary."

"Oh, but I'm glad you came," she said. "It was just—awful!" and she clung to Tom's arm, trembling.

When Field and Melling, whose rash conduct had caused them to be severely but not fatally burned, had been taken to a hospital and the fire was declared to be practically out, Tom made arrangements to leave his airship in the city field all night.

"And you and your friends can come to Uncle Jasper's house," said Mary.

"Of course!" said Uncle Jasper himself, who had arrived on the scene, attracted to the fire by the news that his niece and Mr. Keith were in danger. "Lots of room! Come along! We'll celebrate your rescue."

So the crew of the fire-fighting Lucifer went with Mary, while the firemen, after again thanking Tom most enthusiastically, kept on playing, as a precaution, their streams of water on the still hot building.

Only the central portion of the structure, the stairs and elevator shafts, were burned away. The strong upward draft had kept the fire from spreading much to either side.

"It certainly was a fierce blaze, and I'm glad my chemicals took such prompt effect," said Tom. "I shall not fear any test after this."

It was the day following the night of excitement, and Tom and his friends, at the invitation of the fire department of Newmarket, were inspecting what was left of the Landmark Building—and there was considerable left—though access to the upper floors was to be had only by ladders, down which Mary and her uncle, Barton Keith, had been carried.

"Here are my offices," said Mr. Keith, who accompanied Tom, Ned, Mr. Damon and Mr. Baxter, as he ushered them into his suite of rooms.

"Bless my fountain pen! nothing is burned here," cried the eccentric man.

"No, the flames just shot upward," explained the fire chief, who was leading the party. "But I think those chemicals of yours would have been just as effective, Mr. Swift, if the fire had mushroomed out more."

"It was hot enough as it was," answered Tom, with a grim laugh.

"Bless my thermometer, too hot—too hot by far!" exclaimed Tom Swift's eccentric friend, and to this Ned nodded an amused agreement.

An exclamation from Mr. Baxter attracted the attention of all in Mr. Keith's office. The chemist picked up from the floor a bundle of papers.

"Here is a bundle of documents that some one has dropped, Mr. Keith," he said. "I guess you forgot to put it in your safe. Why—why—no—they aren't yours! They're mine. Here are my missing dye formulae! The secret papers I've been searching for so long! The ones I thought Field and Melling had!" cried Mr. Baxter. "How—how did they get here?" and, wonderingly, he looked at the bundle of papers he had discovered in such a strange manner.



CHAPTER XXV

THE LIGHT OF DAY

"What's that? Your dye formulae here in my office?" cried Mr. Keith, for he had heard something of the chemist's loss, though he did not directly associate Field and Melling with it.

"That's what this is! The very papers, containing all the rare secrets, for which I have been so at a loss!" cried the delighted old man. "Now I can give to the world the dyes for which it has long been waiting! Oh, Tom Swift, you did more than you knew when you put out this fire!" and he hugged the bundle of smoke-smelling papers to his breast.

"But how did they get here?" asked the young inventor. "I know that Field and Melling had offices in this building. They were starting a new dye concern, and, though Mr. Baxter and I suspected them of having stolen his secret, we couldn't prove it."

"But we can now!" cried Mr. Baxter. "Though I don't know that I'll bother even to accuse them, as long as I have back my previous papers. I see how it happened. They had the formulae in their office. They rushed out with the documents, and, when they found they couldn't get past this floor, they went into Mr. Keith's office. There, in their excitement, they dropped the papers, and you put the fire out just in time, Tom, or they'd have been burned beyond hope of saving. You have given me back something almost as valuable as life, Tom Swift!"

"I'm glad I could render you that service," said the young inventor. "And I had no idea, when I dropped the chemicals, that I was saving someone even more valuable than your secret formulae," and they all knew he referred to Mary Nestor.

An examination of the papers found on Mr. Keith's office floor showed that not one of the dye secrets was missing. Thus Mr. Baxter came into possession of his own again, and when Field and Melling were sufficiently recovered they were charged with the theft of the papers. The charge was proved, and, in addition, other accusations were brought against them which insured their remainder in jail for a considerable period.

As Mr. Baxter had suspected, Field and Melling had, indeed, robbed him of his dye formulae papers. They learned that he possessed them, and they invited him to a night conference with the purpose of robbing him. The fire in their factory was an accident, of which they took advantage to make it appear that the chemist lost his papers in the blaze. But they had taken them, and though they did not mean to leave poor Baxter to his fate, that would have been the result of their selfish action had not Tom and Ned come to the rescue. And it was of this "putting over" that Field and Melling had boasted, the time Tom overheard their talk at Meadow Inn.

As Mr. Baxter guessed, the letter delivered to him at Tom's place was one that the two scoundrels would have retained, as they had others like it, if they had seen it. But a new clerk forwarded it, and the evidence it contained helped to convict Field and Melling.

As for the Landmark Building, while badly damaged, it would have been worse burned but for Tom's prompt action. And though he was more than glad that he had been on hand, he rather regretted that he could not give the test for which he had set out.

Eventually the building was made more nearly fire-proof and the fire-escapes were rebuilt, and Mr. Blake did not lose his money, as he had feared, though Barton Keith said it was more owing to Tom Swift's good luck than to Mr. Blake's management.

But, as it developed, nothing could have been more opportune than Tom's action, for word of his quenching a bigger blaze than he would have had to encounter in the official test reached the Denton fire department. As a result there was a conference, and, after only a nominal showing of his apparatus, it was adopted by a unanimous vote.

But this occurred some time afterward, for, following his rescue of Mary Nestor and her uncle and the saving of the lives of Field and Melling, as well as others in the building, by his prompt smothering of the fire, Tom returned to Shopton.

He and his companions went in the Lucifer, minus, now, the big load of chemicals, and on landing near the hangar Tom was surprised to see Koku the giant running toward him. The big man showed every symptom of great excitement as he cried:

"Oh, Master Tom! He see the light ob day! he see the light ob day now! Oh, so glad! So glad!"

"Who sees the light of day?" asked the young inventor.

"Black Rad! Eradicate! Him eyes all better now! Pill man take off cloth. Rad—he see light ob day!"

"Oh, I'm so glad! So thankful!" cried Tom. "How I've wished for this! Is it really true, Koku?"

"Sure true! Pill man say Rad see K O now." The giant, doubtless, meant "O K," but Tom understood. And it was true, as he learned more directly a little later.

When Tom entered the room where Rad had been kept in the dark ever since the explosion, the colored man looked at his master with seeing eyes, though the apartment was still but dimly lighted.

"I's all right ag'in now, Massa Tom!" cried Rad. "See fine! I's all ready to make more smellin' stuff to put out fires!"

"You won't have to, Rad!" cried Tom joyfully. "My chemical extinguisher is completed, and you did your share in making it a success. But I never would have felt like claiming credit for it if you had been—had been left in the dark."

"No mo' dark, Massa Tom!" said Eradicate. "I kin see now as good as eber, an' yo'-all won't hab to 'pend on dat lazy good-fo'-nuffin cocoanut!" and he chuckled as he looked at the giant.

"Huh! Lazy!" retorted the big man. "I show you—black coon!"

"By golly!" laughed Rad. "Him an' me good friends now, Massa Tom. Neber I fuss wif Koku any mo'! He suah was good to me when I had to stay in de dark!"

Of course it would be too much to hope that Koku and Eradicate never again quarreled, but for a long time their warm friendship was a thing at which to marvel, considering the past.

"Well, I guess this settles it," said Tom to Ned one day, after going over the day's mail.

"Settles what, Tom?"

"My aerial fire-fighting apparatus. Here's word from the National Fire Underwriters Association that they have adopted it, and there will be a big reduction of rates in all cities where it is a part of the fire department equipment. It's been as great a success as Mr. Baxter's new dye."

"Yes, and he has had wonderful success with that. But what are you going to do now, Tom? What new line of endeavor are you going to aim at?"

Tom arose and reached for his hat.

"I am now going," he said, with a grin, "to see somebody on private business."

"You are going to see Mary Nestor!" broke out Ned.

"I am," said Tom.

And he did.



THE TOM SWIFT SERIES

By VICTOR APPLETON

Uniform Style of Binding. Individual Colored Wrappers. Every Volume Complete in Itself.

Every boy possesses some form of inventive genius. Tom Swift is a bright, ingenious boy and his inventions and adventures make the most interesting kind of reading.

TOM SWIFT AND HIS MOTOR CYCLE TOM SWIFT AND HIS MOTOR BOAT TOM SWIFT AND HIS AIRSHIP TOM SWIFT AND HIS SUBMARINE BOAT TOM SWIFT AND HIS ELECTRIC RUNABOUT TOM SWIFT AND HIS WIRELESS MESSAGE TOM SWIFT AMONG THE DIAMOND MAKERS TOM SWIFT IN THE CAVES OF ICE TOM SWIFT AND HIS SKY RACER TOM SWIFT AND HIS ELECTRIC RIFLE TOM SWIFT IN THE CITY OF GOLD TOM SWIFT AND HIS AIR GLIDER TOM SWIFT IN CAPTIVITY TOM SWIFT AND HIS WIZARD CAMERA TOM SWIFT AND HIS GREAT SEARCHLIGHT TOM SWIFT AND HIS GIANT CANNON TOM SWIFT AND HIS PHOTO TELEPHONE TOM SWIFT AND HIS AERIAL WARSHIP TOM SWIFT AND HIS BIG TUNNEL TOM SWIFT IN THE LAND OF WONDERS TOM SWIFT AND HIS WAR TANK TOM SWIFT AND HIS AIR SCOUT TOM SWIFT AND HIS UNDERSEA SEARCH TOM SWIFT AMONG THE FIRE FIGHTERS TOM SWIFT AND HIS ELECTRIC LOCOMOTIVE TOM SWIFT AND HIS FLYING BOAT TOM SWIFT AND HIS GREAT OIL GUSHER TOM SWIFT AND HIS CHEST OF SECRETS TOM SWIFT AND HIS AIRLINE EXPRESS



THE DON STURDY SERIES

By VICTOR APPLETON

Individual Colored Wrappers and Text Illustrations by WALTER S. ROGERS Every Volume Complete in Itself.

In company with his uncles, one a mighty hunter and the other a noted scientist, Don Sturdy travels far and wide, gaining much useful knowledge and meeting many thrilling adventures.

DON STURDY ON THE DESERT OF MYSTERY;

An engrossing tale of the Sahara Desert, of encounters with wild animals and crafty Arabs.

DON STURDY WITH THE BIG SNAKE HUNTERS;

Don's uncle, the hunter, took an order for some of the biggest snakes to be found in South America—to be delivered alive!

DON STURDY IN THE TOMBS OF GOLD;

A fascinating tale of exploration and adventure in the Valley of Kings in Egypt.

DON STURDY ACROSS THE NORTH POLE;

A great polar blizzard nearly wrecks the airship of the explorers.

DON STURDY IN THE LAND OF VOLCANOES;

An absorbing tale of adventures among the volcanoes of Alaska.

DON STURDY IN THE PORT OF LOST SHIPS;

This story is just full of exciting and fearful experiences on the sea.

DON STURDY AMONG THE GORILLAS;

A thrilling story of adventure in darkest Africa. Don is carried over a mighty waterfall into the heart of gorilla land.



THE RADIO BOYS SERIES (Trademark Registered)

By ALLEN CHAPMAN

Author of the "Railroad Series," Etc.

Individual Colored Wrappers. Illustrated. Every Volume Complete in itself.

A new series for boys giving full details of radio work, both in sending and receiving—telling how small and large amateur sets can be made and operated, and how some boys got a lot of fun and adventure out of what they did. Each volume from first to last is so thoroughly fascinating, so strictly up-to-date and accurate, we feel sure all lads will peruse them with great delight.

Each volume has a Foreword by Jack Binns, the well-known radio expert.

THE RADIO BOYS' FIRST WIRELESS THE RADIO BOYS AT OCEAN POINT THE RADIO BOYS AT THE SENDING STATION THE RADIO BOYS AT MOUNTAIN PASS THE RADIO BOYS TRAILING A VOICE THE RADIO BOYS WITH THE FOREST RANGERS THE RADIO BOYS WITH THE ICEBERG PATROL THE RADIO BOYS WITH THE FLOOD FIGHTERS THE RADIO BOYS ON SIGNAL ISLAND THE RADIO BOYS IN GOLD VALLEY



THE RAILROAD SERIES

By ALLEN CHAPMAN

Author of the "Radio Boys," Etc.

Uniform Style of Binding, illustrated. Every Volume Complete in Itself.

In this line of books there is revealed the whole workings of a great American railroad system. There are adventures in abundance—railroad wrecks, dashes through forest fires, the pursuit of a "wildcat" locomotive, the disappearance of a pay car with a large sum of money on board—but there is much more than this—the intense rivalry among railroads and railroad men, the working out of running schedules, the getting through "on time" in spite of all obstacles, and the manipulation of railroad securities by evil men who wish to rule or ruin.

RALPH OF THE ROUND HOUSE; Or, Bound to Become a Railroad Man.

RALPH IN THE SWITCH TOWER; Or, Clearing the Track.

RALPH ON THE ENGINE; Or, The Young Fireman of the Limited Mail.

RALPH ON THE OVERLAND EXPRESS; Or, The Trials and Triumphs of a Young Engineer.

RALPH, THE TRAIN DISPATCHER; Or, the Mystery of the Pay Car.

RALPH ON THE ARMY TRAIN; Or, The Young Railroader's Most Daring Exploit.

RALPH ON THE MIDNIGHT FLYER; Or, The Wreck at Shadow Valley.

RALPH AND THE MISSING MAIL POUCH; Or, The Stolen Government Bonds.



THE RIDDLE CLUB BOOKS By ALICE DALE HARDY

Individual Colored Wrappers. Attractively Illustrated. Every Volume Complete in Itself.

Here is as ingenious a series of books for little folks as has ever appeared since "Alice in Wonderland." The idea of the Riddle books is a little group of children—three girls and three boys decide to form a riddle club. Each book is full of the adventures and doings of these six youngsters, but as an added attraction each book is filled with a lot of the best riddles you ever heard.

THE RIDDLE CLUB AT HOME

An absorbing tale that all boys and girls will enjoy reading. How the members of the club fixed up a clubroom in the Larue barn, and how they, later on, helped solve a most mysterious happening, and how one of the members won a valuable prize, is told in a manner to please every young reader.

THE RIDDLE CLUB IN CAMP

The club members went into camp on the edge of a beautiful lake. Here they had rousing good times swimming, boating and around the campfire. They fell in with a mysterious old man known as The Hermit of Triangle Island. Nobody knew his real name or where he came from until the propounding of a riddle solved these perplexing questions.

THE RIDDLE CLUB THROUGH THE HOLIDAYS

This volume takes in a great number of winter sports, including skating and sledding and the building of a huge snowman. It also gives the particulars of how the club treasurer lost the dues entrusted to his care and what the melting of the great snowman revealed.

THE RIDDLE CLUB AT SUNRISE BEACH

This volume tells how the club journeyed to the seashore and how they not only kept up their riddles but likewise had good times on the sand and on the water. Once they got lost in a fog and are marooned on an island. Here they made a discovery that greatly pleased the folks at home.

THE END