"That," Brownell said, "is an example of uncontrolled atomic explosion. Rather crude, but it serves its purpose. Now let us observe a refinement of it. _Controlled, electronic action._" Janus aimed the pistol. A bluish, pencil-thin ray leaped forth. Where it touched, substance vanished into a froth of flame. The ground itself became incandescent glass. The ray remained constant so long as his finger touched the firing stud. Mari was excited. "Then you will help us perfect ours? The Perlacs are becoming stronger than we have ever known them, and whenever they start scouting the twilight zone, it means trouble. Donli tells me the robots are active again, too!" "We can and will help you," Brownell assured her. "I doubt if those overgrown robots will stand up long under an electronic ray!" The Professor was eager to see the Stone, and Mari graciously accompanied him to the crest of the hill where it was housed. The others, meanwhile, went with Donli on a tour of the shops and laboratories. IV Brownell told them later, in great excitement: "I swear to you, it defies all physical laws as we know them! It's merely a shiny chunk of rock, a few yards in diameter--but do you know, I believe it actually feeds upon gravity! I have always believed that gravity, magnetism, and other such universal forces are all a part of the electrical spectrum. Some peculiarity in the atomic structure of this Stone draws the straight-line force of gravity to it, and that force is then oscillated, transmitted into light! The process is unending!" "That's all very well," Mark told him, "but I believe the greatest miracle is right here in the laboratories. These people have had to utilize the barest elements of this world, but they've done wonders. They have plastiglass, and farm implements, and electrical power--even crude atomic furnaces." "They'd have their neutro-pistols right now," Janus agreed, "but they hit the same stumbling block that baffled our scientists for so long." For days they worked ceaselessly on the neutro-pistols. Mark and the Professor together laid out the blueprints, devising a radical and more potent design for the firing coils. The latter was surprised at Mark's knowledge of electronic principles. "I may surprise you even further, one of these days," Mark promised. And now the urgency of their work was really impressed upon them. Scouts returning each day from the twilight zone reported that the Perlacs were gathering. Thousands of them swarmed the forests on the dark side, apparently massing for an all-out attack. There had been a few preliminary skirmishes but nothing serious as yet. Donli undertook the task of setting up barricades at the twilight border. These were huge shields of light but durable metal, arranged in strategic positions, easily movable. And the work at the city went on apace.