for a few minutes mr. sharp was so engrossed with looking underneath the craft, to ascertain in what condition the various planes and braces were, that he paid little attention to the old maid school principal, after his first greeting. but miss perkman was not a person to be ignored.

"i want pay for the damage to the tower of my school," she went on. "i could also demand damages for trespassing on my roof, but i will refrain in this case. young ladies, will you go to your rooms?" she demanded.

"oh, please, let us stay," pleaded mary nestor, beside whom tom now stood. "perhaps professor swift will lecture on clouds and air currents and—and such things as that," the girl went on slyly, smiling at the somewhat embarrassed lad.

"ahem! if there is a professor present, perhaps it might be a good idea to absorb some knowledge," admitted the old maid, and, unconsciously, she smoothed her hair, and settled her gold spectacles straighter on her nose. "professor, i will delay collecting damages on behalf of the rocksmond young ladies seminary, while you deliver a lecture on air currents," she went on, addressing herself to mr. sharp.

"oh, i'm not a professor," he said quickly. "i'm a professional balloonist, parachute jumper. give exhibitions at county fairs. leap for life, and all that sort of thing. i guess you mean my friend. he's smart enough for a professor. invented a lot of things. how much is the damage?"

"no professor?" cried miss perkman indignantly. "why i understood from miss nestor that she called some one professor."

"i was referring to my friend, mr. swift," said mary. "his father's a professor, anyhow, isn't he, tom? i mean mr. swift!"

"i believe he has a degree, but he never uses it," was the lad's answer.

"ha! then i have been deceived! there is no professor present!" and the old maid drew herself up as though desirous of punishing some one. "young ladies, for the last time, i order you to your rooms," and, with a dramatic gesture she pointed to the scuttle through which the procession had come.

"say something, tom—i mean mr. swift," appealed mary nestor, in a whisper, to our hero. "can't you give some sort of a lecture? the girls are just crazy to hear about the airship, and this ogress won't let us. say something!"

"i—i don't know what to say," stammered tom.

but he was saved the necessity for just then several women, evidently other teachers, came out on the roof.

"oh, an airship!" exclaimed one. "how lovely! we thought it was an earthquake, and we were afraid to come up for quite a while. but an airship! i've always wanted to see one, and now i have an opportunity. it will be just the thing for my physical geography and natural history class. young ladies, attention, and i will explain certain things to you."

"miss delafield, do you understand enough about an airship to lecture on one?" asked miss perkman smartly.

"enough so that my class may benefit," answered the other teacher, who was quite pretty.

"ahem! that is sufficient, and a different matter," conceded miss perkman. "young ladies, give your undivided attention to miss delafield, and i trust you will profit by what she tells you. meanwhile i wish to have some conversation concerning damages with the persons who so unceremoniously visited us. it is a shame that the pupils of the rocksmond seminary should be disturbed at their studies. sir, i wish to talk with you," and the principal pointed a long, straight finger at mr. sharp.

"young ladies, attention!" called miss delafield. "you will observe the large red body at the top, that is—"

"i'd rather have you explain it," whispered mary nestor to tom. "come on, slip around to the other side. may i bring a few of my friends with me? i can't bear miss delafield. she thinks she knows everything. she won't see us if we slip around."

"i shall be delighted," replied tom, "only i fear i may have to help mr. sharp out of this trouble."

"don't worry about me, tom," said the balloonist, who overheard him. "let me do the explaining. i'm an old hand at it. been in trouble before. many a time i've had to pay damages for coming down in a farmer's corn field. i'll attend to the lady principal, and you can explain things to the young ones," and, with a wink, the jolly aeronaut stepped over to where miss perkman, in spite of her prejudice against the airship, was observing it curiously.

glad to have the chance to talk to his young lady friend, tom slipped to the opposite side of the car with her and a few of her intimate friends, to whom she slyly beckoned. there tom told how the red cloud came to be built, and of his first trip in the air, while, on the opposite side, miss delafield lectured to the entire school on aeronautics, as she thought she knew them.

mr. sharp evidently did know how to "explain" matters to the irate principal, for, in a short while, she was smiling. by this time tom had about finished his little lecture, and miss delafield was at the end of hers. the entire school of girls was grouped about the red cloud, curiously examining it, but mary nestor and her friends probably learned more than any of the others. tom was informed that his friend had been attending the school in rocksmond since the fall term opened.

"i little thought, when i found we were going to smash into that tower, that you were below there, studying," said the lad to the girl.

"i'm afraid i wasn't doing much studying," she confessed. "i had just a glimpse of the airship through the window, and i was wondering who was in it, when the crash came. miss perkman, who is nothing if not brave, at once started for the roof, and we girls all followed her. however, are you going to get the ship down?"

"i'm afraid it is going to be quite a job," admitted tom ruefully. "something went wrong with the machinery, or this never would have happened. as soon as mr. sharp has settled with your principal we'll see what we can do."

"i guess he's settled now," observed miss nestor. "here he comes."

the aeronaut and miss perkman were approaching together, and the old maid did not seem half so angry as she had been.

"you see," mr. sharp was saying, "it will be a good advertisement for your school. think of having the distinction of having harbored the powerful airship, red cloud, on your roof."

"i never thought of it in that light," admitted the principal. "perhaps you are right. i shall put it in my next catalog."

"and, as for damages to the tower, we will pay you fifty dollars," continued the balloonist. "do you agree to that, mr. swift?" he asked tom. "i think your father, the professor, would call that fair."

"oh, as long as this airship is partly the property of a professor, perhaps i should only take thirty-five dollars," put in miss perkman. "i am a great admirer of professors—i mean in a strictly educational sense," she went on, as she detected a tendency on the part of some of the young ladies to giggle.

"no, fifty dollars will be about right," went on mr. sharp, pulling out a well-filled wallet. "i will pay you now."

"and if you will wait i will give you a receipt," continued the principal, evidently as much appeased at the mention of a professor's title, as she was by the money.

"we're getting off cheap," the balloonist whispered to tom, as the head of the seminary started down the scuttle to the class-rooms below.

"maybe it's easier getting out of that difficulty than it will be to get off the roof," replied the lad.

"don't worry. leave that to me," the aeronaut said. it took considerable to ruffle mr. sharp.

with a receipt in full for the damage to the tower, and expressing the hope that, some day, in the near future, professor swift would do the seminary the honor of lecturing to the young lady pupils, miss perkman bade mr. sharp and tom good-by.

"young ladies, to your rooms!" she commanded. "you have learned enough of airships, and there may be some danger getting this one off the roof."

"wouldn't you like to stay and take a ride in it?" tom asked miss nestor.

"indeed i would," she answered daringly. "it's better than a motor-boat. may i?"

"some day, when we get more expert in managing it," he replied, as he shook hands with her.

"now for some hard work," went on the young inventor to mr. sharp, when the roof was cleared of the last of the teachers and pupils. but the windows that gave a view of the airship in its odd position on the roof were soon filled with eager faces, while in the streets below was a great crowd, offering all manner of suggestions.

"oh, it's not going to be such a task," said mr. sharp. "first we will repair the rudder and the machinery, and then we'll generate some more gas, rise and fly home."

"but the broken propeller?" objected tom.

"we can fly with one, as well as we can with two, but not so swiftly. don't worry. we'll come out all right," and the balloonist assumed a confident air.

it was not so difficult a problem as tom had imagined to put the machinery in order, a simple break having impaired the working of the rudder. then the smashed propeller was unshipped and the gas machine started. with all the pupils watching from windows, and a crowd observing from the streets and surrounding country, for word of the happening had spread, tom and his friend prepared to ascend.

they arose as well as they had done at the shed at home, and in a little while, were floating over the school. tom fancied he could observe a certain hand waving to him, as he peered from the window of the car—a hand in one of the school casements, but where there were so many pretty girls doing the same thing, i hardly see how tom could pick out any certain one, though he had extraordinarily good eyesight. however, the airship was now afloat and, starting the motor, mr. sharp found that even with one propeller the red cloud did fairly well, making good speed.

"now for home, to repair everything, and we'll be ready for a longer trip," the aeronaut said to the young inventor, as they turned around, and headed off before the wind, while hundreds below them cheered.

"we ought to carry spare propellers if we're going to smash into school towers," remarked tom. "i seem to be a sort of hoodoo."

"nonsense! it wasn't your fault at all," commented mr. sharp warmly. "it would have happened to me had i been steering. but we will take an extra propeller along after this."

an hour later they arrived in front of the big shed and the red cloud was safely housed. mr. swift was just beginning to get anxious about his son and his friend, and was glad to welcome them back.

"now for a big trip, in about a week!" exclaimed mr. sharp enthusiastically. "you'll come with us, won't you, mr. swift?"

the inventor slowly shook his head.

"not on a trip," he said. "i may go for a trial spin with you, but i've got too important a matter under way to venture on a long trip," and he turned away without explaining what it was. but tom and mr. sharp were soon to learn.