"And that the higher we go, the more juice," added the other, remembering. "As much as to say that it is the atmosphere, then, that protects the earth from the surrounding voltage."
The engineer nodded. "Occasionally it breaks through, anyhow, in the form of lightning. Now, in order to control that current, and prevent it from turning this machine, and us, into ashes, all we do is to pass the juice through a cylinder of highly compressed air, fixed in this wall. By varying the pressure and dampness within the cylinder, we can regulate the flow."
The builder nodded rapidly. "All right. But why doesn't the electricity affect the walls themselves? I thought they were made of steel."
The engineer glanced through the dead-light at the reddish disk of the Earth, hazy and indistinct at a distance of forty million miles. "It isn't steel; it's a non-magnetic alloy. Besides, there's a layer of crystalline sulphur between the alloy and the vacuum space."
"The vacuum is what keeps out the cold, isn't it?" Jackson knew, but he asked in order to learn more.
"Keeps out the sun's heat, too. The outer shell is pretty blamed hot on that side, just as hot as it is cold on the shady side." Smith seated himself beside a huge electrical machine, a rotary converter which he next indicated with a jerk of his thumb. "But you don't want to forget that the juice outside is no use to us, the way it is. We have to change it.
"It's neither positive nor negative; it's just neutral. So we separate it into two parts; and all we have to do, when we want to get away from the earth or any other magnetic-sphere, is to aim a bunch of positive current at the corresponding pole of the planet, or negative current at the other pole. Like poles repel, you know."
"Listens easy," commented Jackson. "Too easy."
"Well, it isn't exactly as simple as all that. Takes a lot of apparatus, all told," and the engineer looked about the room, his glance resting fondly on his beloved machinery.
The big room, fifty feet square, was almost filled with machines; some reached nearly to the ceiling, the same distance above. In fact, the interior of the "cube," as that form of sky-car was known, had very little waste space. The living quarters of the four men who occupied it had to be fitted in wherever there happened to be room. The architect's own berth was sandwiched in between two huge dynamos.