It was merely a small, model apparatus, with a mirror of space-strained silver that was an absolutely perfect reflector. The mirror had been ground out of a block of silver one foot deep, by four inches square, carefully annealed, and the work had all been done in a cooling bath. The result was a mirror that was so nearly a perfect paraboloid that the beam held sharp and absolutely tight for the half-mile range they tested it on. At the projector it was three and one-half inches in diameter. At the target, it was three and fifty-two one hundredths inches in diameter. "Well, you've got the mirror, what are you going to reflect with it now?" asked McLaurin. "The greatest problem is getting a radiant source, isn't it? You can't get a temperature above about ten thousand degrees, and maintain it very long, can you?" "Why not?" Kendall smiled. "It'll volatilize and leave the scene of action, won't it?" "What if it's a gaseous source already?" "What? Just a gas-flame? That won't give you the point source you need. You're using just a spotlight here, with a Moregan Point-light. That won't give you energy, and if you use a gas-flame, the spread will be so great, that no matter how perfectly you figure your mirror, it won't beam." "The answer is easy. Not an ordinary gas-flame--a very extra-special kind of gas-flame. Know anything about Renwright's ionization-work?" "Renwright--he's an IP man isn't he?" "Right. He's developed a system, which, thanks to the power we can get in that atostor, will sextuply ionize oxygen gas. Now: what does that mean?" "Spirits of space! Concentrated essence of energy!" "Right. And in preparation, Cole here had one made up for me. That--and something else. We'll just hook it up--" With Devin's aid, Kendall attached the second apparatus, a larger device into which the silver block with its mirror surface fitted. With the uttermost care, the two physicists lined it up. Two projectors pointed toward each other at an angle, the base angles of a triangle, whose apex was the center of the mirror. On very low power, a soft, glowing violet light filtered out through the opening of the one, and a slight green light came from the other. But where the two streams met, an intense, violet glare built up. The center of action was not at the focus, and slowly this was lined up, till a sharp, violet beam of light reached out across the open yard to the target set up. Buck Kendall cut off the power, and slowly got into position. "Now. Keep out from in front of that thing. Put on these glasses--and watch out." Heavy, thick-lensed orange-brown goggles were passed out, and Kendall took his place. Before him, a thick window of the same glass had been arranged, so that he might see uninterruptedly the controls at hand, and yet watch unblinded, the action of the beam.