I'm not at all sure that I'm getting the order of things right. I gathered that the zone must be built up and strengthened little by little; first impermeable to the simplest forms of energy, like light and heat, and then to the more and more complex ones, until at some critical point the whole thing became absolute. The machine that created it had to be outside, otherwise the zone itself would keep any power from getting through. On the other hand, it might be powered by one of those super-batteries that Dampier had in the grip of his solenoid-gun. With a set-up like that, you could dig a hole and pull it in after you, so to speak. What I wondered was how you get out? I asked Dampier that one. "There would be no way," he told me. "Once the zone is complete, it is unchangeable--absolute. You would be inside, to us here, but I think that to yourself it would seem that it is we who are inside--that you are in a world all of your own, with its own laws, its own science. They can be worked out, these laws. They are in the equations that Monsieur Porter is reading; but they are very strange and complex. In war, a closed zone would be used only as a trap for the enemy." "Wait a minute," I objected. "You mean to say that once you've made this thing you can't unmake it?" "That is right," he nodded. "Once the zone is complete it is a bubble--a nothingness--entirely apart from our Space and Time. The forces build up very rapidly, exponentially, but until the very instant of completion, even if it is one little billionth of a second before that moment, the zone will collapse if the power which builds it is shut off. Never in practice would one go so far. Long before it is complete, such a zone will repel all things that can be directed against it, while the balance of power still remains in the hands of him who has created it. To make it--that is nothing. To destroy it is impossible. But to hold it so in the delicate balance between destruction and completion; that is the triumph of Pierre Dampier! I have calculated it all from the equations. See--here at these red lines each needle must stop. If they go beyond--zut! In the space of a thinking the zone is complete! Beyond control!" He straightened up, his wirey mop of hair bobbing at my shoulder. "Now, please, if you will watch and remember. The loops are set, so, for the sphere--little, like the apple of the eye. Now I press the first switch, and the second and then the others, three, and four, and five. Now I turn the dials, so, a little at a time. A minute now, while the zone builds, and then you will call Monsieur Porter and show him that this is not all sunshine and honeysuckers that he reads."