"That will be a good idea," declared Mr. Roumann.

"You need have no fear of anything being discovered," put in Mr.

Henderson, who was busy planning the engine-room of the strange craft.

"When we first came here we used to be bothered by curious persons, but I soon found a method of keeping them away."

"How was that?" inquired the German.

"Why, I ran a wire all around the shop, and charged the conductor with a mild current of electricity. Some people got shocked by coming too close, and after that they gave my place a wide berth.

I'll do the same thing now."

"A fine idea," commented Mr. Roumann. "But what about Washington White? He is so fond of talking, and using big words, that he may disclose our plans."

"No, I can trust Washington," declared the professor. "But, as a further precaution, I have not told him what our object is. All he knows is that we are building a new machine, but he does not know what it is for, nor where we are going."

"That's good."

"Maybe when he does find out he'll not want to go," added Mark.

"Do you intend to take him with us?" asked Mr. Roumann.

"I think so--if he'll go," replied Mr. Henderson. "He has always been with me, and he is very helpful on these trips. But I shall not tell him where we are going until we are almost ready to start. But now, Mr. Roumann, I'd like to consult with you about the installation of the motor, or whatever we are to call it, by means of which your secret force is to be used."

"A motor will be as good a name as any other. We'll call it the Etherium motor."

"What will we call the other one?" asked Jack.

"What other one?"

"The motive power by which we are to go through the atmosphere of the earth."

"Well, we can call that the atmospheric motor," replied Mr.

Roumann. "However, there is no hurry about that. I want to get the work in the engine-room under way first."

He and the professor were soon deep in the discussion, while Jack and Mark, with the aid of the machinists, were busy constructing the main part of the projectile.

The first thing to be done was to build the sh.e.l.l of the projectile. This consisted of plates of a new and peculiar metal, invented by Professor Henderson. The plates were riveted together, in the shape of a great cigar, two hundred feet long.

This work took some time, but, as the professor had in his shop the proper machinery for it, a small force could accomplish a great deal of work.

The rear of the projectile was to be occupied by the mysterious apparatus that was to drive it through s.p.a.ce. In this compartment would be many strange machines, including the one which Mr. Roumann had invented to use the terrific and secret force of which he was the discoverer.

There were apparatus for distilling water from the atmosphere, others for manufacturing oxygen, dynamos for furnishing light to the interior of the Annihilator, motors for working the various small machines, and a number of other appliances.

Forward from the engine-room was a s.p.a.ce to be used in storing away the food supplies, and the materials necessary for generating the force used, as well as for making a new supply of air when needed.

Amidships was a living-room, with a plate-gla.s.s window on either side. There was not much s.p.a.ce to move about in it, as, owing to the long and narrow shape of the projectile, economy of room was enforced. Still, the place was a lengthy one, with tables and chairs, which could be folded up out of the way when not in use.

There was provision for a library of scientific and other books, and a piano played by electricity and bra.s.s disks, somewhat on the order of modern player-pianos.

"What are those apertures in the sides of the living-room?" asked Jack of Mr. Roumann, as the lad glanced over a sheet of blue-print paper, on which was shown a plan of the projectile.

"Those," said the German, "are for the guns."

"Guns!" exclaimed Mark. "Why, they're too big for guns. They are large enough to put a cannon through."

"And that is just what is going to be put through them, my boy,"

went on Mr. Roumann. "From those openings, and you will see that there are four of them, will protrude the muzzles of my electric cannons."

"Do we need them?" asked Jack.

"You can't tell what we'll need when we get to Mars," was the slow answer. "You must remember that we know nothing about the inhabitants of the planet. While I believe that the people there are of a very high grade of intelligence, we must be prepared for the worst. We may find them terrible savages, who will want to attack and destroy us. With the electric cannon we can defend ourselves."

"That's so," admitted Jack. "We had to fight the Esquimaux up north,"

"And the putty-men in the center of the earth," added Mark.

Forward of the living-room, and near what corresponded to the bow of the projectile, were the sleeping-rooms, consisting of two long, narrow compartments, with a pa.s.sageway between them, like the aisle in a sleeping-car. The beds were berths against the wall, much as in the Pullman cars of to-day.

In the very "nose" of the Annihilator was the pilot house. Here were grouped together the wheels, levers, cams, gears, pistons and other apparatus that controlled the big projectile. Standing in it, and peering out through a heavy plate gla.s.s window, the operator could guide the machine in any direction he desired, and he could also regulate the rate of progress.

A number of scientific instruments were carried, for showing and registering the speed and direction of the Annihilator, the distance it was above the earth, and there was an indicator to note how near the travelers came to Mars. There was also a powerful telescope, and a number of cameras so arranged that they would automatically take pictures.

"We'll have to travel through s.p.a.ce pretty fast in order to cover thirty-five millions of miles," observed Jack, stopping in his work of helping rivet some of the plates.

"About how fast will we have to go, Mr. Roumann?"

"I have it all figured out," replied the German.

"I hope our projectile will stand it," remarked Mr. Henderson.

"We did not have to make such terrific speed on our other voyages."

"I think that the Annihilator, as we have planned it, will not suffer from the strain of speed," when on Mr. Roumann, looking up from his study of some blue-prints. "You may be astonished when I tell you we shall have to travel at the rate of one hundred miles a second."

"One hundred miles a second!" exclaimed Jack. "That's pretty fast, isn't it?"

"It's at the rate of eight million six hundred and forty thousand miles a day," came from Mark, who was a rapid figurer.

"And to cover thirty-five million miles would take us less than five days," said Jack. "But such an enormous speed--"

"We must travel at about that speed," interrupted Mr. Roumann, "though I fancy we will be nearer ten days than five in reaching Mars."

"Why?" asked Jack.

"Because we will not dare travel at such terrific speed as one hundred miles a second through the atmosphere of the earth. We would be burned into cinders by the mere friction of the air.

Therefore, I shall send the Annihilator comparatively slowly through the earth's atmosphere, and perhaps I will find that I shall have to do the same thing when we near Mars. But while traveling through the ether, or the s.p.a.ce that is between the two can go as fast as we like, which will as Mark has said, eight million miles per day."

"But even that rate," began Jack, "is going to pretty fast."

"It is faster than almost anything except light," went on Mr.

Roumann.