Jack said nothing, but from the glimpse he had had of the man's face, he did not believe the fellow was a tramp. There was too much intelligence shown. The face was an evil one, and seemed to indicate that the man had an object in peering into the window--a motive that was not connected with a chicken coop. "I'll tell Andy to keep watch for a while tonight with his gun," went on the professor. "I don't like prowlers around here. I have some valuable tools in my machine shop, and they might steal them." "Now, Professor Henderson," began Mr. Roumann, when he had taken his seat at a small table and spread out his plans in front of him, "I am only going to sketch briefly, for you and your young assistants, what I propose. As I have said, we will need a projectile, two hundred feet long and about ten feet through in the thickest part. In that we will build sleeping and living apartments, lacks to store the air which we will have to breathe while traveling through space, other tanks for water, a compartment for food, another for scientific instruments, and we will need a comparatively large space for my machinery." "Why will it take up so much space?" asked the professor. "I thought you said the new power required only a small machine to generate it." "That is true, but you see we will have to carry two kinds of machines." "Two? Why is that?" "Because we are going to travel through two, and perhaps three, different mediums. We are going to shoot through the atmosphere of the earth; then through the vast region beyond that, filled with what is called ether." "And is that different from our atmosphere?" asked Mark. "Much different," replied Mr. Roumann. "There is no air to it at all. The secret power which I have invented is perfectly adapted to project us through this ether. That is why I call it Etherium. Then when we reach Mars, we will find a different atmosphere, somewhat like this earth's, I expect, but which will require still another kind of power to move us in. I hope, however, that the same force which sends us through the limits of the atmosphere of this earth will take us through that of Mars. So that is why I need so much space for machinery." "Well, I guess we can build the projectile for you," said Mr. Henderson. "It will take us nearly a month, though." "No longer, I hope," said the German. "Every day is valuable. Once the projectile is finished we will enter it, seal ourselves up, and be shot through space. When we get to Mars--well, there are many things to do when we reach there." "I shall be much interested in seeing if they have discovered a way of conquering the air," said Mr. Henderson. "If they are a race of superior intelligence, as some authorities believe, from the fact that Mars may have been inhabited for millions of years before this earth was formed, they must have advanced very greatly in science. The mastery of the air--in making flying machines--would be one of the surest tests."