"Well, here's the catch. We can do anything we want to with gravity if we go about it right. What is it in chemical atoms that has weight? It's the positive charge, isn't it? The nucleus. And it's balanced by the negative charges, the electrons, that revolve around it. Now if we can find a way to pull some of these negative charges loose from a certain number of atoms of a substance, there are going to be a whole lot of positive charges floating around without anything to bite on. And if we can shoot them at something, it's going to have more positive charges than it can stand. And when that happens, the something is going to get awful heavy, and there are going to be exchanges of negative charges among all the positive charges, and things are going to pop." "Yes, yes," said Ben. "But what good does all this do? Give us the real dope on how you're going to do it." "Well, with what I picked up from the Lassans, I think I know. They know all about light and mechanics, but they're rotten chemists, and don't realize how good a thing they've got in lots of ways. Now look--if you throw a beam of radiations from a cathode tube into finely divided material you break up some of the atoms. Well, all we have to do is get an extra-powerful cathode tube, break up a lot of atoms, and then deliver the positive charges from them onto whatever we're going for. That would be your gravity beam." "How are you going to get radiation powerful enough to split up enough atoms to do you any good?" inquired Ben. "Easy. Use a radium cathode. The Lassans have the stuff, but never think of using it seriously. They think it's an amusing by-product in their pure light mines, and just play round with it. Nobody ever used it before on earth, because it was too expensive for such foolishness, but with so many less people around, we can get some without too much trouble, I guess." "Mmm. Sounds possible," said Ben. "That is, in theory. I'd like to see it work in practice. How are you going to throw this beam?" "Cinch. Down a beam of light. Light will conduct sound or radio waves even through a vacuum and this stuff I'm sending isn't so very different. Whatever we hit will act as an amplifier and spread the effect through the whole body." "Boy, you want to be careful you don't blow up the earth," said Murray Lee. "Well, Gloria, I guess we're indicated to go out and dig up some radium. Let's fool them by going before they ask us. There ought to be a supply in some of the hospitals." They rose and the other two plunged into an excited and highly technical discussion. When they returned, the workmen had already constructed a black box, not unlike an enormous camera in shape, in the center of the floor. At its back and attached to it, stood a stand fitted with a series of enormous clamps. Ben and Sherman were at a bench, working blowpipes, and shaping the delicate, iridescent glass of a long tube with a bulge at its center.