"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 space 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 space 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?"