"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," assented 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 space 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 illustrating 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 modicums 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." "Then it's all right." Jack thought of saying that the man might have shaved his mustache off, but he did not want Mr. Roumann to worry. "I guess he was only a tramp," said Amos Henderson. "Some one wandering about looking for a chicken coop that isn't locked. Or, perhaps, seeking a chance to rob."