"are you all ready, tom?"

"all ready, mr. sharp," replied a young man, who was stationed near some complicated apparatus, while the questioner, a dark man, with a nervous manner, leaned over a large tank.

"i'm going to turn on the gas now," went on the man. "look out for yourself. i'm not sure what may happen."

"neither am i, but i'm ready for it. if it does explode it can't do much damage."

"oh, i hope it doesn't explode. we've had so much trouble with the airship, i trust nothing goes wrong now."

"well, turn on the gas, mr. sharp," advised tom swift. "i'll watch the pressure gauge, and, if it goes too high, i'll warn you, and you can shut it off."

the man nodded, and, with a small wrench in his hand, went to one end of the tank. the youth, looking anxiously at him, turned his gaze now and then toward a gauge, somewhat like those on steam boilers, which gauge was attached to an aluminum, cigar-shaped affair, about five feet long.

presently there was a hissing sound in the small frame building where the two were conducting an experiment which meant much to them. the hissing grew louder.

"be ready to jump," advised mr. sharp.

"i will," answered the lad. "but the pressure is going up very slowly. maybe you'd better turn on more gas."

"i will. here she goes! look out now. you can't tell what is going to happen."

with a sudden hiss, as the powerful gas, under pressure, passed from the tank, through the pipes, and into the aluminum container, the hand on the gauge swept past figure after figure on the dial.

"shut it off!" cried tom quickly. "it's coming too fast! shut her off!"

the man sprang to obey the command, and, with nervous fingers, sought to fit the wrench over the nipple of the controlling valve. then his face seemed to turn white with fear.

"i can't move it!" mr. sharp yelled. "it's jammed! i can't shut off the gas! run! look out! she'll explode!"

tom swift, the young inventor, whose acquaintance some of you have previously made, gave one look at the gauge, and seeing that the pressure was steadily mounting, endeavored to reach, and open, a stop-cock, that he might relieve the strain. one trial showed him that the valve there had jammed too, and catching up a roll of blue prints the lad made a dash for the door of the shop. he was not a second behind his companion, and hardly had they passed out of the structure before there was a loud explosion which shook the building, and shattered all the windows in it.

pieces of wood, bits of metal, and a cloud of sawdust and shavings flew out of the door after the man and the youth, and this was followed by a cloud of yellowish smoke.

"are you hurt, tom?" cried mr. sharp, as he swung around to look back at the place where the hazardous experiment had been conducted.

"not a bit! how about you?"

"i'm all right. but it was touch and go! good thing you had the gauge on or we'd never have known when to run. well, we've made another failure of it," and the man spoke somewhat bitterly.

"never mind, mr. sharp," went on tom swift. "i think it will be the last mistake. i see what the trouble is now; and know how to remedy it. come on back, and we'll try it again; that is if the tank hasn't blown up."

"no, i guess that's all right. it was the aluminum container that went up, and that's so light it didn't do much damage. but we'd better wait until some of those fumes escape. they're not healthy to breathe."

the cloud of yellowish smoke was slowly rolling away, and the man and lad were approaching the shop, which, in spite of the explosion that had taken place in it, was still intact, when an aged man, coming from a handsome house not far off, called out, "tom, is anyone hurt?"

"no, dad. we're all right."

"what happened?"

"well, we had another explosion. we can't seem to get the right mixture of the gas, but i think we've had the last of our bad luck. we're going to try it again. up to now the gas has been too strong, the tank too weak, or else our valve control is bad."

"oh dear, mr. swift! do tell them to be careful!" a woman's voice chimed in. "i'm sure something dreadful will happen! this is about the tenth time something has blown up around here, and—"

"it's only the ninth, mrs. baggert," interrupted tom, somewhat indignantly.

"well, goodness me! isn't nine almost as bad as ten? there i was, just putting my bread in the oven," went on mrs. baggert, the housekeeper, "and i was so startled that i dropped it, and now the dough is all over the kitchen floor. i never saw such a mess."

"i'm sorry," answered the youth, trying not to laugh. "we'll see that it doesn't happen again."

"yes; that's what you always say," rejoined the motherly-looking woman, who looked after the interests of mr. swift's home.

"well, we mean it this time," retorted the lad. "we see where our mistake was; don't we. mr. sharp?"

"i think so," replied the other seriously.

"come on back, and we'll see what damage was done," proposed tom. "maybe we can rig up another container, mix some fresh gas, and make the final experiment this afternoon."

"now do be careful," cautioned mr. swift, the aged inventor, once more. "i'm afraid you two have set too hard a task for yourselves this time."

"no we haven't, dad," answered his son. "you'll see us yet skimming along above the clouds."

"humph! if you go above the clouds i shan't be very likely to see you. but go slowly, now. don't blow the place up again."

mr. swift went into the house, followed by mrs. baggert, who was loudly bewailing the fate of her bread. tom and mr. sharp started toward the shop where they had been working. it was one of several buildings, built for experimental purposes and patent work by mr. swift, near his home.

"it didn't do so very much damage," observed tom, as he peered in through a window, void of all the panes of glass. "we can start right in."

"hold on! wait! don't try it now!" exclaimed mr. sharp, who talked in short, snappy sentences, which, however, said all he meant. "the fumes of that gas aren't good to breathe. wait, until they have blown away. it won't be long. it's safer."

he began to cough, choking from the pungent odor, and tom felt an unpleasant tickling sensation in his throat.

"take a walk around," advised mr. sharp. "i'll be looking over the blue prints. let's have 'em."

tom handed over the roll he had grabbed up when he ran from the shop, just before the explosion took place, and, while his companion spread them out on his knee, as he sat on an upturned barrel, the lad walked toward the rear of the large yard. it was enclosed by a high board fence, with a locked gate, but tom, undoing the fastenings, stepped out into a broad, green meadow at the rear of his father's property. as he did so he saw three boys running toward him.

"hello!" exclaimed our hero. "there are andy foger, sam snedecker and pete bailey. i wonder what they're heading this way for?"

on the trio came, increasing their pace as they caught sight of tom. andy foger, a red-haired and squint-eyed lad, a sort of town bully, with a rich and indulgent father, was the first to reach the young inventor.

"how—how many are killed?" panted andy.

"shall we go for doctors?" asked sam.

"can we see the place?" blurted out pete, and he had to sit down on the grass, he was so winded.

"killed? doctors?" repeated tom, clearly much puzzled. "what are you fellows driving at, anyhow?"

"wasn't there a lot of people killed in the explosion we heard?" demanded andy, in eager tones.

"not a one," replied tom.

"there was an explosion!" exclaimed pete. "we heard it, and you can't fool us!"

"and we saw the smoke," added snedecker.

"yes, there was a small explosion," admitted tom, with a smile, "but no one was killed; or even hurt. we don't have such things happen in our shops."

"nobody killed?" repeated andy questioningly, and the disappointment was evident in his tones.

"nobody hurt?" added sam, his crony, and he, too, showed his chagrin.

"all our run for nothing," continued pete, another crony, in disgust.

"what happened?" demanded the red-haired lad, as if he had a right to know. "we were walking along the lake road, and we heard an awful racket. if the police come out here, you'll have to tell what it was, tom swift." he spoke defiantly.

"i've no objection to telling you or the police," replied tom. "there was an explosion. my friend, mr. sharp, the balloonist, and i were conducting an experiment with a new kind of gas, and it was too strong, that's all. an aluminum container blew up, but no particular damage was done. i hope you're satisfied."

"humph! what you making, anyhow?" demanded andy, and again he spoke as if he had a right to know.

"i don't know that it's any of your business," tom came back at him sharply, "but, as everyone will soon know, i may as well tell you. we're building an airship."

"an airship?" exclaimed sam and pete in one breath.

"an airship?" queried andy, and there was a sneer in his voice. "well, i don't think you can do it, tom swift! you'll never build an airship; even if you have a balloonist to help you!"

"i won't, eh?" and tom was a trifle nettled at the sneering manner of his rival.

"no, you won't! it takes a smarter fellow than you are to build an airship that will sail. i believe i could beat you at it myself."

"oh, you think you could?" asked tom, and this time he had mastered his emotions. he was not going to let andy foger make him angry. "maybe you can beat me at racing, too?" he went on. "if you think so, bring out your red streak and i'll try the arrow against her. i beat you twice, and i can do it again!"

this unexpected taunt disconcerted andy. it was the truth, for, more than once had tom, in his motor-boat, proved more than a match for the squint-eyed bully and his cronies.

"go back at him, andy," advised sam, in a low voice. "don't take any of his guff!"

"i don't intend to," spluttered andy. "maybe you did beat me in the races, because my motor wasn't working right," he conceded, "but you can't do it again. anyhow, that's got nothing to do with an airship. i'll bet you can't make one!"

"i don't bet," replied tom calmly, "but if you wait a few weeks you'll see me in an airship, and then, if you want to race the red streak against that, i'll accommodate you. or, if you want to enter into a competition to build a dirigible balloon or an aeroplane i'm willing."

"huh! think you're smart, don't you? just because you helped save that balloonist from being killed when his balloon caught fire," went on andy, for want of something better to say. "but you'll never build an airship!"

"of course he won't!" added sam and pete, bound to side with their crony, to whom they were indebted for many automobile and motor-boat rides.

"just wait," advised tom, with a tantalizing smile. "meanwhile, if you want to try the red streak against the arrow, i'm willing. i have an hour or so to spare."

"aw, keep still!" muttered andy, much discomfited, for the defeat of his speedy boat, by a much smaller and less powerful one, was a sore point with him. "you just wait, that's all. i'll get even with you!"

"look here!" cried tom, suddenly. "you always say that whenever i get the best of you. i'm sick of hearing it. i consider that a threat, and i don't like it. if you don't look out, andy foger, you'll have trouble with me, and at no very distant date!"

tom, with flashing eyes, and clenched fists, took a step forward. andy shrank back.

"don't be afraid of him," advised sam. "we'll stand by you, andy."

"i ain't afraid," muttered the red-haired lad, but it was noticed that he shuffled off. "you just wait, i'll fix you," he added to tom. the bully was plainly in a rage.

the young inventor was about to reply, and, possibly would have made a more substantial rejoinder to andy than mere words, when the gate opened, and mr. sharp stepped out.

"the fumes have all cleared away, tom," he said. "we can go in the shop, now."

without further notice of andy foger, tom swift turned aside, and followed the aeronaut into the enclosed yard.