"do you feel better?" asked the professor, anxiously, as he came forward and felt of the boys' pulses.

"a great deal," answered jack. "but what has happened? where are we?

what are all these wheels for?"

"slowly, slowly," said the old man with a pleasant laugh. "one question at a time. for the first: what happened was a railroad wreck."

"i remember now," said jack, slowly. "we tried to stop the cars."

"and you didn't succeed very well," went on the old man. "however, the sand bank did it for you, and stopped you two at the same time. as for your second question, you are here in my shop. as to the third, those wheels are parts of my great invention. but i will tell you about that after a while. i must give you some medicine now, and something to eat. here, washington!"

"comin', perfessor!"

jack and mark were more surprised than before when they saw a big colored man, seemingly as strong as an ox, coming toward them with two steaming bowls of beef broth. washington was grinning with delight.

"dis am de best beef stew dat eber transpositioned itself into yo' vicinity!" he exclaimed, setting the bowls down on a table near the bed.

"now, washington," cautioned the old man. "no big words, remember."

"all right, perfessor," was the answer.

"do you boys feel like eating?" asked the aged inventor.

"i do," replied jack. "there was a time, though, when i thought i'd never get a chance to eat again. that was just before the crash."

"you were both knocked unconscious," the professor went on. "washington and i happened to be near by and brought you here. fortunately i am something of a doctor as well as an inventor, and i used a strong medicine i have."

"i'm sure we're much obliged to you," answered mark.

"let me see how much improved you are by eating," suggested the old man. "i can trust washington to cook good meals, even if he does use big words."

then, while the colored man grinned cheerfully at them, jack and mark, sitting up on the bed, for they were still weak and sore, ate the broth. after that both boys said they felt better.

"see if you can walk," suggested the inventor.

mark and jack stepped on the floor. they both uttered cries of pain.

they were stiff and lame from the shaking they had received.

"a day in bed will do you no harm," said their strange rescuer. "i have some liniment that will soon take the soreness out of every one of your muscles."

though the boys protested at being made to remain in bed, the old man insisted. he made them take off most of their clothes, and then brought out some liniment. under his direction jack and mark rubbed themselves well, and experienced almost immediate relief. it was now getting dusk, and washington lighted a big lamp that hung in the centre of the room, first taking care that the shutters were tightly fastened.

the colored man prepared a simple supper for mr. henderson, and afterward got himself a meal. when the dishes were cleared away the old man, who had noted with smiles the anxious glances jack and mark were casting about the strange room, said:

"i suppose you boys would like to ask lots of questions."

"i'd like to know what all this machinery is for," spoke jack.

"and what is behind that door," mark went on, indicating the much-locked portal.

"i knew it!" exclaimed the old man. "i knew it! now if i tell you will you promise to keep it a secret until i give you leave to speak?"

of course the boys promised eagerly.

"do you think you have rested enough now to take a look inside?" the inventor asked, nodding toward the locked door.

"sure!" exclaimed jack.

"then put on your coats and trousers and i'll introduce you to my pet."

wonderingly, the boys followed him. it took nearly a minute to unfasten the various bolts and bars, but at last the portal swung open. the place was dimly lighted by a single big lamp, but in the glare of it the boys caught sight of a strange, weird object. it looked like an immense cigar, and swayed slowly back and forward. it seemed to be covered with a net-work of cords. on the ground beneath it was what seemed to be a good-sized boat, with a large cabin amidships.

"what in the world is it?" cried jack.

"it's my airship!" exclaimed professor henderson. "the only successful airship ever invented. it is the electric monarch!"

"what is it for?" asked mark.

"to navigate the realm of the stars and moon!" cried the old man. "with that i will rival the eagles in their flight!"

the boys were a little alarmed. the professor was strangely excited. his eyes sparkled in the reflected light of the lamp. jack and mark thought they might have been brought to the abode of a madman. they shrank back a little. but they were reassured a moment later when, with a pleasant laugh, the old man said:

"don't be frightened, boys. i know what i am talking about. here, washington, more light! we will show them what we have done, hidden away from the sight of the curious, unbelieving world. let them see my monarch!"

"we'll illuminationness dis abode like it was de orb ob day shinin' heah!" exclaimed the negro, as he started several more lamps aglow.

"are the shutters closed?" asked mr. henderson, anxiously.

"tight as a drum-head," was the reply.

"now look!" exclaimed the inventor, turning to the boys.

they were more than astonished at what they saw. they had no idea that the rough shed held such a perfect piece of machinery.

up near the roof of the place, which was quite high, there swayed an immense bag of oiled silk. it was shaped like a cigar, big in the middle and tapering at both ends. the bag was enclosed in a net of ropes which extended down to the lower part of the airship.

this lower part, as the boys could see, was just like a steam launch in shape, only much lighter in weight. it had a sharp bow, and a blunt stern. from the stern there extended a large propeller, the blades being made from sheets of aluminum.

the main part of the ship proper, or the part suspended from the gas bag, was covered by a closed and roofed cabin about forty feet long, ten feet wide, and extending five feet above the gunwale of the ship. the cabin had four windows on each side, a companionway fore and aft, and a sort of look-out or conning tower forward, which, the professor explained, was the place for the steersman.

"because this ship can be steered wherever you want to go," he said, pointing to the big rudder that was hung aft, an opening in it allowing the screw or propeller to revolve.

the boys were lost in admiration of the wonderful airship. they were consumed with curiosity as to how the machinery worked, and they thought no more of their knocks and bruises than as if a mosquito had bitten them. the professor watched their faces with delight. he loved boys and mechanical apparatus.

"now we will enter the monarch," he said. "turn on the lights,

washington."

there was a click, and the cabin of the airship was flooded with a soft glow of incandescent lamps.

"come on!" called mr. henderson, leading the way. the boys followed, marveling at the wonders on every side.

they found the cabin of the strange craft divided into three parts. first came a sort of parlor, with a table and seats arranged on the sides. in the front part of this was a passage leading to the conning tower, or the place for the steersman. behind the parlor came the sleeping quarters and dining room combined. the bunks were arranged to fold against the wall, and a table in the centre could be shut up when not in use and hoisted to the ceiling, giving plenty of space.

next came the engine room, and as they entered it the boys could hardly restrain from giving cheers of delight. it was almost filled with machinery, and occupied a little more than half of the whole boat, being twenty-two by ten feet in size.

the two boys did not know the use of one quarter of the machinery and apparatus they gazed on. there were electric motors, storage batteries, two gasoline engines similar to those used in automobiles, pumps, large and small tanks, instruments for measuring the electric current, for telling the temperature, the amount of moisture in the air, the speed of the wind, the speed of the ship, the height to which it went, besides compasses, barometers, telescopes, and other instruments.

there were levers and wheels on every side, switches, valves, electric plugs and handles. lockers arranged close to the wall and along the floor held supplies and materials. everything was new and shining, and the professor smiled with pride as he touched piece after piece of machinery, and looked at the different instruments.

"now we'll go out on the stern," he said.

the boys followed as he ascended the companion steps and emerged on a small platform at the rear end of the cabin.

"do you know what this is?" asked the professor, touching a long, thin, round object.

"looks like a gun," replied mark.

"that's just what it is. it's a machine gun that will fire one hundred shots a minute, and it can be turned in any direction, as it works on a swivel. i don't know that we'll have any use for it, but i thought i'd take it along."

then the professor pointed out where the propeller shaft ran from the engine room out through the stern, and showed how the rudder was worked by wire ropes extending from it to the conning tower.

"in short we have everything necessary to successfully navigate the air," he went on. "not a thing has been overlooked. all i have to do is to fill the big bag of oiled silk with a new gas i have discovered and up we go. this is really the most important part of the invention. without this powerful gas the airship would not rise above the earth.

"but i have found this gas, which can be made in unlimited quantities from simple materials that we can carry with us. the gas has enormous lifting power, and if it was not for that i would not dare make such a large and comfortable airship. as it is, we can sail through the air as easily as if we were on an ocean liner on the sea and much more quickly.

"i generate the gas in the engine room as i need it," the professor went on. "it goes to the oiled silk bag through two tubes. when we have arisen to a sufficient height i start the electric engine, the propeller whirls around, and the ship moves forward, just as a steamboat does when the screw is set in motion. then all i have to do is to steer."

"it's great!" cried jack with sparkling eyes.

"it certainly is," agreed mark.

from the stern the professor took the boys to the conning tower, where there were several wheels and levers, that placed most of the important machines and engines in the boat under the direct control of the steersman. a lever turned one way would send the ship ahead. turned in the opposite direction it would reverse the course. a wheel like that on an automobile served to direct the rudder and so guided the monarch's course. other levers controlled the speed of the engines, and the supply of gas that filled the silk bag.

"here is where we shall carry our supplies of condensed food," the professor went on, leading the way back into the middle room. "we will take along capsules that will supply us in a small space with meat, vegetables, soups, tea and coffee, besides milk.

"the water we will get as we speed along, dropping down to earth whenever it is necessary. as for clothing, i have an abundant supply."

he opened a locker and disclosed a pile of fur garments. there were big coats, caps and boots, everything made with a furry surface within as well as without.

"any one would think you were going into some cold country, professor," said jack, looking at the warm garments.

"so we are! we are going to find the north pole!" exclaimed the old inventor.

"the north pole?" cried mark.

"that's what i said. do you boys want to go along in the monarch to a place where never mortal man has been?"

at that instant there came a loud knock at the door.