"That's right," said Mr. Roumann. "But, while Mercury is only about thirty-six millions of miles from the sun at its nearest point, the closest it ever comes to the earth is fifty-seven millions of miles, while, as I told you, Mars is now but thirty-five millions of miles away, a difference in favor of Mars of twenty-two millions of miles, quite a distance when one has to travel it. Neptune, the farthest of the major planets, is two billion eight hundred millions of miles from the sun, and it is separated from this earth by--"

"By two billion seven hundred and eight million miles," said Mark quickly.

"How do you make that out?" asked Jack in some surprise.

"By subtracting ninety-two millions of miles, which is the distance from the earth to the sun, from the number of miles Neptune is away from the sun," said Mark.

"That's right," admitted Mr. Henderson. "You're very quick at figures, Mark."

"Well, let's get to Mars," said Jack. "Maybe Andy can find some new kind of game there."

"Me? I'm not going to any place so many millions of miles away from here," answered the old hunter, looking up from his plate.

"It's good enough hunting here."

"Wait until you see," said Mr. Roumann with a smile. "I expect to find many marvels on Mars."

"If we get there," added Mr. Henderson.

"We'll get there," declared Mr. Roumann confidently. "As I said, I have long been interested in Mars, and one reason is that I want to prove that there is life on it--that it is inhabited by a superior race of beings. Another reason is that I expect to find on it a supply--or at least specimens--of a most valuable substance--"

Mr. Roumann stopped suddenly.

"Well?" asked Mr. Henderson questioningly, for there was an odd manner about the blue-eyed scientist.

"That is something I do not wish to speak about at present," said Mr. Roumann quickly. "I will tell you my other reason for going to Mars--when we get there."

"Now, as to the method. As I told you, Professor Henderson, and as I intimated to you boys, we will go in a long, torpedo-shaped projectile, which, though it will not be very large in diameter, will be long enough to contain all our machinery and ourselves, with a sufficient store of provisions for a year or more. But I know what you are going to ask, and that is: How can I send the projectile through s.p.a.ce?

"Well, I'll tell you--that is, partly tell you, for some parts of my secret can never be revealed. I have discovered a wonderful power, more wonderful than man ever dreamed of before. I have called it Etherium, for the reason that I expect it to carry us through the ether, or s.p.a.ce that exists outside of the atmosphere of this earth and that of Mars.

"Now, professor, do you think you and your a.s.sistants can build a proper projectile?"

"We built an airship that went to the North Pole, we constructed a submarine that took us to the South Pole, and we had the Flying Mermaid, in which we went to the center of the earth," said Mr.

Henderson. "I think we can build you the torpedo-shaped projectile. But what will make it move through thirty-five millions of miles of s.p.a.ce?"

"I will!" exclaimed the other. "I and my wonderful, secret power--Etherium! If you will build the projectile I will do the rest. I will give you the plans for the machinery at once, and you can begin as soon as you are ready. You have a large workshop here, I understand."

"Yes, we have all the means at our command," admitted Mr.

Henderson.

"But it must be built in secret," stipulated Mr. Roumann. "No one must know about it until we are ready to leave. Several unscrupulous men have tried to steal my secret."

"We can construct the projectile and machinery so that no one but ourselves, and one or two trusty mechanics, will ever know about it," promised Mr. Henderson.

"Good! Now, when can you begin? As I told you, Mars is already beginning to move away from us at the rate of twenty-eight millions of miles a year. That is over two millions of miles a month, and every day counts."

"We will start at once," promised Mr. Henderson. "That is, if Jack and Mark decide they want to go. I will let them choose.

Boys, do you want to try to go to Mars, or go back to college?"

"Mars! Every time!" cried Jack. "I want to begin to weigh less."

"I'll go wherever Jack goes," said Mark.

"Very well, then," a.s.sented the professor. "But you must remember, Mr. Roumann, that I am still unconvinced that you possess the secret of a power that will project a heavy object through s.p.a.ce to Mars--thirty-five millions of miles away. I do not say it can't be done, only I want to be shown. I will aid you all I can, and I will accompany you. But I fear we shall never get to Mars."

"And I tell you we will!" insisted the other. "Come, I will prove it to you by mathematics, and by ill.u.s.trating some of the force of my new secret power. Let us go to the laboratory."

The professor took from a valise, which sat in a corner of the room, a bundle of papers. Then, followed by the professor and the boys, he started for the private laboratory of Mr. Henderson.

As they left the dining-room they heard an unexpected noise at one of the windows. They looked quickly up, and Jack saw the face of a man staring in.

Before he could cry out, there came the sound of Washington's voice:

"Hey dar! Git away from dere! Skedaddle, now, or I'll prognostigate yo' inter modic.u.ms ob transmigatory infatisamatisms!"

The face disappeared from the window, and the sound of footsteps in rapid retreat was heard.

CHAPTER VI

BUILDING THE PROJECTILE

"Did you see that?" exclaimed Jack.

"What?" asked Professor Henderson quickly.

"Some one at the window," replied Jack.

"I saw the face," added Mark. "It was a man looking in."

"A man? What sort of a man?" inquired Mr. Roumann, and he showed some excitement.

"I couldn't tell very well," answered Jack. "I saw him for only a second. But the man was looking right in."

"Did he have a heavy black mustache?" asked the German, and strode rapidly toward the window.

"No, he didn't have a mustache at all," said Jack. "He was smooth-shaven. I'm sure of that."

"Then it can't be he," murmured Mr. Roumann.

"Who did you think it was?" asked Professor Henderson.

"I--I thought it was an enemy of mine," was the answer. "Some one who has been trying to discover my secret. But the man whom I fear has a heavy black mustache, and this one, you say, Jack, had none?"

"None at all."