Jack and Mark stood in the doorway. Mr. Roumann grasped a lever. He threw it over. There was a spark as the electrical contact was made. "The atmospheric motor is now ready to start!" he remarked. "Push that knob, Professor Henderson." The professor pushed in a small, shiny knob. Mr. Roumann turned a small wheel, and closed another electrical switch. Instantly there was a trembling through t whole length of the projectile. Would it move? Would it leave the earth and go to Mars? There was a moment of hesitancy, as if the great machine had not quite decided. Then came a more violent vibration. There was a humming, throbbing, hissing sound. Suddenly the boys, and all within the projectile, felt it swaying. A moment later it began to shoot through space like a great rocket. "Hurrah!" cried Jack. "We're off!" "Yes," added Mr. Roumann joyfully, "we are on our way to Mars!" and he grasped the steering wheel and peered through the thick plate-glass windows of the pilot house into the vast space before them. CHAPTER XV SOMETHING ABOUT MARS "Are we really in motion?" asked Jack, after a moment's silence. "It doesn't seem so." "We are certainly in motion," declared Mr. Roumann. "See this dial?" He pointed to one near the steering wheel. The hand on it was gently vibrating between some of the figures. "We are traveling that many miles a second," went on the scientist. "The atmospheric motor is not working as fast as I hoped it would, but we are going fast enough. When we start the Etherium machine we shall go much more speedily." "And when will that be?" asked Mark. "I can't tell exactly. It will not be until we have passed through the atmosphere of the earth, and there is no way of ascertaining in advance just how thick that stratum is." "Then how will you know?" asked Jack. "By means of my instruments. When the hand on this dial points to zero I will know that we are beyond the atmosphere, and that it is time to start the Etherium motor." "How do you know in which direction to steer?" asked Mark. "Can you see anything out of that window?" "Not a thing," replied the German. "Look for yourself." Jack and Mark peered through the plate glass. All they could see was a sort of white, fleecy mass of clouds that surrounded the great projectile. "It's just like when we were above the clouds in the Electric Monarch," said Jack. "Exactly," agreed Mr. Henderson. "But if you can't see anything, how can you tell where to steer?" asked Mark. "By means of this instrument," replied Mr. Roumann, indicating another among the many on the wall of the projectile. "This is automatically kept pointed at Mars, and by means of a hand and dial I can tell how to keep the Annihilator aimed directly at the red planet." "Even when it is on the opposite side of the earth from us?" asked Jack.