"let's tell your father, tom," suggested ned, after a pause. "he'll know what to do."

"no, i'd rather not," answered the young inventor quickly. "dad has had trouble enough with these fellows, and i don't want him to worry any more. besides, he is working on a new invention, and if i tell him about the happy harry gang it will take his attention from it."

"what invention is he planning now?"

"i don't know, but it's something important by the way he keeps at it. he hardly spares time to help mr. sharp and me on the airship. no, we'll keep this news from dad."

"then i'll inform the bank officials, as you suggest. if the place was robbed they might blame me; if they found out i had seen the men and failed to tell them."

"well, that gang would only be too glad to have the blame fall on some one else."

tom little knew how near the truth he had come in his chance expression, or how soon he himself was to fall under suspicion in connection with this same band of bad men.

"i'll telephone to the president on my way home," decided ned, "and he can notify the watchman at the bank. but do you really expect to have your airship in shape to fly soon?"

"oh, yes. now that we have found out our mistake about the gas, the rest will be easy."

"i think i'd like to take a trip in one myself, if it didn't go too high," ventured ned.

"i'll remember that, when we have ours completed," promised his chum, "and i'll take you for a spin."

the boys talked for perhaps an hour longer, mostly about the airship, for it was the latest mechanical affair in which tom was interested, and, naturally, foremost in his thoughts. then ned went home first, however, telephoning from tom's house to the bank president about having seen the suspicious men. that official thanked his young employee, and said he would take all necessary precautions. the telephone message was not sent until mr. swift was out of hearing, as tom was determined that his father should have no unnecessary worry about the unscrupulous men. as it was, the news that the gang was out of jail had caused the aged inventor some alarm.

it was not without some anxiety that tom arose the next morning, fearing he would hear news that the bank had been broken into, but no such alarming report circulated in shopton. in fact having made some inquiries that day of ned, he learned that no trace had been seen of the mysterious men. the police had been on the lookout, but they had seen nothing of them.

"maybe, after all, they weren't the same ones," suggested ned, when he paid tom another visit the next night.

"well, of course it's possible that they weren't," admitted the young inventor. "i'd be very glad to think so. even if they were, your encounter with them may have scared them off; and that would be a good thing."

the next two weeks were busy ones for tom and mr. sharp. aided occasionally by mr. swift, and with garret jackson, the engineer, to lend a hand whenever needed, the aeronaut and the owner of the speedy arrow made considerable progress on their airship.

"what is your father so busy over?" asked mr. sharp one day, when the new aluminum gas holder was about completed.

"i don't know," answered tom, with a somewhat puzzled air. "he doesn't seem to want to talk about it, even to me. he says it will revolutionize travel along a certain line, but whether he is working on an airship that will rival ours, or a new automobile, i can't make out. he'll tell us in good time. but when do you think we will finish the—well, i don't know what to call it—i mean our aeroplane?"

"oh, in about a month now. that's so, though, we haven't a name for it. but we'll christen it after it's completed. now if you'll tighten up some of those bolts i'll get the gas generating apparatus in readiness for another test."

a short description of the new airship may not be out of place now. it was built after plans mr. sharp had shown to tom and his father soon after the thrilling rescue of the aeronaut from the blazing balloon over lake carlopa. the general idea of the airship was that of the familiar aeroplane, but in addition to the sustaining surfaces of the planes, there was an aluminum, cigar-shaped tank, holding a new and very powerful gas, which would serve to keep the ship afloat even when not in motion.

two sets of planes, one above the other, were used, bringing the airship into the biplane class. there were also two large propellers, one in front and the other at the rear. these were carefully made, of different layers of wood "built up" as they are called, to make them stronger. they were eight feet in diameter, and driven by a twenty-cylinder, air-cooled, motor, whirled around at the rate of fifteen hundred revolutions a minute. when operated at full speed the airship was capable of making eighty miles an hour, against a moderate wind.

but if the use of the peculiarly-shaped planes and the gas container, with the secret but powerful vapor in it were something new in airship construction, so was the car in which the operator and travelers were to live during a voyage. it was a complete living room, with the engine and other apparatus, including that for generating the gas, in a separate compartment, and the whole was the combined work of tom and mr. sharp. there were accommodations for five persons, with sleeping berths, a small galley or kitchen, where food could be prepared, and several easy chairs where the travelers could rest in comfort while skimming along high in the air, as fast as the fastest railroad train.

there was room enough to carry stores for a voyage of a week or more, and enough gas could be manufactured aboard the ship, in addition to that taken in the aluminum case before starting, to sustain the ship for two weeks. the engine, steering apparatus, and the gas machine were within easy reach and control of the pilot, who was to be stationed in a small room in the "bow" of the ship. an electric stove served to warm the interior of the car, and also provided means for cooking the food.

the airship could be launched either by starting it along the ground, on rubber-tired wheels, as is done in the case of the ordinary aeroplane, or it could be lifted by the gas, just as is done with a balloon. in short there were many novel features about the ship.

the gas test, which took place a few days later, showed that the young inventor and mr. sharp had made no mistake this time. no explosion followed, the needle valve controlling the powerful vapor perfectly.

"well," remarked mr. sharp, one afternoon, "i think we shall put the ship together next week, tom, and have a trial flight. we shall need a few more aluminum bolts, though, and if you don't mind you might jump on your motor-cycle and run to mansburg for them. merton's machine shop ought to have some."

mansburg was the nearest large city to shopton, and merton was a machinist who frequently did work for mr. swift.

"all right," agreed tom. "i'll start now. how many will you need?"

"oh, a couple of dozen."

tom started off, wheeling his cycle from the shed where it was kept. as he passed the building where the big frame of the airship, with the planes and aluminum bag had been assembled, he looked in.

"we'll soon be flying through the clouds on your back," he remarked, speaking to the apparatus as if it could understand. "i guess we'll smash some records, too, if that engine works as well when it's installed as it does now."

tom had purchased the bolts, and was on his way back with them, when, as he passed through one of the outlying streets of mansburg, something went wrong with his motor-cycle. he got off to adjust it, finding that it was only a trifling matter, which he soon put right, when he was aware of a man standing, observing him. without looking up at the man's face, the young inventor was unpleasantly aware of a sharp scrutiny. he could hardly explain it, but it seemed as if the man had evil intentions toward him, and it was not altogether unexpected on tom's part, when, looking up, he saw staring at him, anson morse, the leader of the gang of men who had caused such trouble for him.

"oh, it's you; is it?" asked morse, an ugly scowl on his face. "i thought i recognized you." he moved nearer to tom, who straightened up, and stood leaning on his wheel.

"yes; it's me," admitted the lad.

"i've been looking for you," went on morse. "i'm not done with you yet, nor your father, either."

"aren't you?" asked tom, trying to speak coolly, though his heart was beating rather faster than usual. morse had spoken in a threatening manner, and, as the youth looked up and down the street he saw that it was deserted; nor were there any houses near.

"no, i'm not," snapped the man. "you got me and my friends in a lot of trouble, and—"

"you didn't get half what you deserved!" burst out tom, indignant at the thought of what he and his father had suffered at the hands of the gang. "you ought to be in jail now, instead of out; and if i could see a policeman, i'd have you arrested for threatening me! that's against the law!"

"huh! i s'pose you think you know lots about the law," sneered morse. "well, i tell you one thing, if you make any further trouble for me, i'll—"

"i'll make all the trouble i can!" cried tom, and he boldly faced the angry man. "i'm not afraid of you!"

"you'd better be!" and morse spoke in a vindictive manner. "we'll get even with you yet, tom swift. in fact i've a good notion now to give you a good thrashing for what you've done."

before tom was aware of the man's intention, morse had stepped quickly into the street, where the lad stood beside his wheel, and grasped him by the shoulder. he gave tom a vicious shake.

"take your hand off me!" cried tom, who was hampered by having to hold up his heavy machine.

"i will when i've given you what i owe you!" retorted the scoundrel. "i'm going to have satisfaction now if i never—"

at that instant there came from down the street the sound of a rattling and bumping. tom looked up quickly, and saw approaching a rattletrap of a wagon, drawn by a big, loose-jointed mule, the large ears of which were flapping to and fro. the animal was advancing rapidly, in response to blows and words from the colored driver, and, before the uplifted fist of morse could fall on tom's head, the outfit was opposite them.

"hold on dar, mistah! hold on!" cried the colored man in the wagon. "what are yo' doin' to mah friend, mistah swift?"

"none of your business!" snapped morse. "you drive on and let me manage this affair if you don't want trouble! who are you anyhow?"

"why doan't yo' know me?" asked the colored man, at whom tom looked gratefully. "i's eradicate sampson, an' dish yeah am mah mule, boomerang. whoa, boomerang! i reckon yo' an' i better take a hand in dish yeah argument."

"not unless you want trouble!" cried morse.

"i doan't mind trouble, not in de leastest," answered eradicate cheerfully. "me an' boomerang has had lots of trouble. we's used to it. no, mistah man, you'd better let go ob mah friend, mistah swift, if yo' doan't want trouble yo' ownse'f."

"drive on, and mind your business!" cried morse, now unreasoningly angry. "this is my affair," and he gave tom a shake.

our hero was not going to submit tamely, however. he had one hand free, and raised to strike morse, but the latter, letting go his hold on the lad's shoulder, grasped with that hand, the fist which the young inventor had raised. then, with his other hand, the scoundrel was about to hit tom.

"break away four him, mistah swift!" directed the colored man. "yo' can fight him, den!"

"i guess he'll have his own troubles doing that," sneered morse.

"not ef i help him," answered eradicate promptly, as he climbed back off the seat, into the body of his ramshackle vehicle.

"don't you interfere with me!" stormed the man.

an instant later tom broke away from his tormentor, and laid his motor-cycle on the ground, in order to have both hands free for the attack he felt would follow.

"ha! you think you're going to escape, do you?" cried morse, as he started toward tom, his eyes blazing. "i'll show you who you're dealing with!"

"yes, an' i reckon i'll show yo' suffin yo' ain't lookin' fer!" suddenly cried eradicate.

with a quick motion he picked up a pail of white-wash from his wagon, and, with sure aim, emptied the contents of the bucket over morse, who was rushing at tom. the white fluid spread over the man from head to foot, enveloping him as in a white shroud, and his advance was instantly checked.

"dar! i reckon dat's de quickest white-washin' job i done in some time!" chuckled eradicate, as he grasped his long handled brush, and clambered down from the wagon, ready for a renewal of the hostilities on the part of morse. "de bestest white-washin' job i done in some time; yais, sah!"