"Not until they have entered the hole through the layer."
"And yet those amoeba are both solid and opaque, as you know. Why is it not possible that men, or intelligences of some sort, are in the air about us and yet are invisible to our eyes!"
"If they are, why haven"t we received evidence of it years ago?"
"Because there has only been a hole through the heaviside layer for six years. Before that time they could not penetrate it any more than poor Hadley could with his s.p.a.ce ship. They have not entered the hole earlier because it is a very small one, at present only some two hundred and fifty yards in diameter in a sphere of over eight thousand miles diameter. The invaders have just found the entrance."
"The invaders? Do you think that the world has been invaded?"
"I do. How else can you explain the very fact which you have just quoted, that no evidence of the presence on these invisible ent.i.ties has previously been recorded?"
"Where did they come from?"
"They may have come from anywhere in the solar system, or even from outside it but I fancy, that they are from Mars or Venus."
"Why so?"
"Because they are the two planets nearest to the earth and are the ones where conditions are the most like they are on the earth. Venus, for example, has an atmosphere and a gravity about .83 of earthly gravity, and life of a sort similar to that of the earth might well live there.
Further, it seems more probable that the invaders have come from one of the nearby planets than from the realms of s.p.a.ce beyond the solar system."
"What about the moon?"
"We can dismiss that because of the lack of an atmosphere."
"It sounds logical, Jim, but the idea of living organisms of sufficient size to lift a child into the air who are invisible seems a little absurd."
"I never said they were invisible. I don"t think they are."
"But they must be, else why weren"t they seen?"
"Use your head, First Mortgage. Those purple amoeba we encountered were quite visible to us, yet they are invisible to observers on the earth."
"Yes, but that is because the heaviside layer is between them and the earth. As soon as they come below it they can be seen."
"Exactly. Why is it not possible that the Venetians, or Martians, or whoever our invaders are, have encased themselves and their s.p.a.ce flyer in a layer of some substance similar to the heaviside layer, a substance which is permeable to light rays only when a large proportion of ultra-violet rays accompany the visible rays? If they did this and then constructed the walls of their ship of some substance which absorbed all the ultra-violet rays which fell on it; not only would the ship itself be invisible, but also everything contained in it--and yet they could see the outside world easily. That such _is_ the case is proved by the disappearance of those children in mid-air. They were taken into a s.p.a.ce ship behind an ultra-violet absorbing wall and so became invisible."
"If the walls absorbed all the ultra-violet and were impermeable to light without ultra-violet, the ship would appear as a black opaque substance and could be seen."
"That would be true except for one thing which you are forgetting. The heaviside layer, as I have repeatedly proved, is a splendid conductor of ultra-violet. The rays falling on it are probably bent along the line of the covering layer so that they open up and bend around the ship in the same manner as flowing water will open up and flow around a stone and then come together again. The light must flow around the solid ship and then join again in such a manner that the eye can detect no interruption."
"Jim, all that sounds reasonable, but have you any proof of it?"
"No, First Mortgage, I haven"t--yet; but if the Lord is good to us we"ll have definite proof this afternoon and be in a position to successfully combat this new menace to the world."
"Do you expect me to go on another one of your crack-brained expeditions into the unknown with you?"
"Certainly I do, but this time we won"t go out of the known. I have our old s.p.a.ce flyer which we took beyond the heaviside layer six years ago ready for action and we"re going to look for the invaders this afternoon."
"How will we see them if they are invisible?"
"They are invisible to ordinary light but not to ultra-violet light.
While most of the ultra-violet is deflected and flows around the ship of else is absorbed, I have an idea that, if we bathe it in a sufficient concentration of ultra-violet, some would be reflected. We are going to look for the reflected portion."
"Ultra-violet light is invisible."
"It is to the eye, but it can be detected. You know that radium is activated and glows under ultra-violet?"
"Yes."
"Mounted on our flyer are six ultra-violet searchlights. By the side of each one is a wide angle telescopic concentrator which will focus any reflected ultra-violet onto a radium coated screen and thus make it visible to us. In effect the apparatus is a camera obscura with all lens made of rock crystal or fused quartz, both of which allow free pa.s.sage to ultra-violet."
"What will we do if we find them?"
"Mounted beneath the telescope is a one-pounder gun with radite sh.e.l.ls.
If we locate them, we will use our best efforts to shoot them down."
"Suppose they are armed too?"
"In that case I hope that you shoot faster and straighter than they do.
If you don"t--well, old man, it"ll just be too d.a.m.ned bad."
"I don"t know that the _Clarion_ hires me to go out and shoot at invisible invaders from another planet, but if I don"t go with you, I expect you"d just about call up the _Echo_ or the _Gazette_ and ask them for a gunner."
"Just about."
"In that case, I may as well be sacrificed as anyone else. When do we start?"
"You old faker!" cried Jim, pounding me on the back. "You wouldn"t miss the trip for anything. If you"re ready we"ll start right now. Everything is ready."
"Including the sacrifice," I replied, rising. "All right, Jim, let"s go and get it over with. If we live, I"ll have to get back in time to telephone the story to McQuarrie for the first edition."
I followed Jim out of the laboratory and to a large open s.p.a.ce behind the main building where the infra-red generators with which he had pierced the hole through the heaviside layer had been located. The reflectors were still in place, but the bank of generators had been removed. A gang of men were hard at work erecting a huge parabolic reflector in the center of the circle, about the periphery of which the infra-red reflectors were placed. In an open s.p.a.ce near the center stood a Hadley s.p.a.ce ship, toward which Jim led the way.
I wondered at the activity and meant to ask what it portended, but in the excitement of boarding the flyer forgot it. I followed Jim in; he closed the door and started the air conditioner.
"Here, First Mortgage," he said as he turned from the control board and faced me, "here are the fluoroscopic screens. They are arranged in a bank, so that you can keep an eye on all of them readily. Beneath each telescope is an automatic one-pounder gun with its mount geared to the telescope and the light, so that the gun bears continually on the point in s.p.a.ce represented by the center of the fluoroscopic screen which belongs to that light. If we locate anything, turn your beam until the object is in the exact center of the screen where these two cross-hairs are. When you have it lined up, push this b.u.t.ton and the gun will fire."
"What about reloading?"
"The guns are self-loading. Each one has twenty sh.e.l.ls in its magazine and will fire one shot each time the b.u.t.ton is pushed until it is empty.