"The idea is to take a diffraction grating, a piece of metal with, usually, 14,438 lines to the inch ruled on it, and previously highly polished, so that it reflects most of the light that hits it. Now it is reflected at different angles, so that we have a spectrum. The spectrum spreads out light and heat waves as well—I use the reflection grating as no material will pass the heat rays, and it then is possible to reflect out of the car again those rays we do not want. The light, which we do want, we will pass through a prism which will recombine it to white light. A prism can either split up light into different colors, or recombine them to white. Lenses then will be needed to make the images clear. The effect will be much the same as a telescope. And that takes care of the heat waves. The cathode rays, luckily won't bother us for the car is already charged strongly negative, and negatively charged electrons will be strongly repelled, as they are in the grid of a vacuum tube, so will never hit us. The bombs constitute the worst menace. The only defense we have against them is the very doubtful one of not being there when they are. That is a good policy in any case.
"As a last precaution—a bit grim—I will arrange it so that if the 'Terrestrian' is damaged to the point of utter helplessness we can, by pushing a single button, explode the entire car—as material energy. It will utterly destroy everything within a radius of a hundred miles, and damage everything within a much greater radius. I believe it will not be serious enough to change the Earth's orbit, though."
"Good—cheerful man, aren't you, Steve! Now what have we to meet that delightful array?"
"We have things even more delightful. Our heat ray is considerably more powerful, I imagine. It is generated by a force ten thousand times as great. Our bombs will be worse. Wright, I wish you would make about a hundred shells that will explode with the full thirty-five thousand ton equivalent of dynamite. And then we will have everything they have that is going to be effective, and have it in a more concentrated form. Can any of you suggest anything else?"
"Steve, you said that your car was nearly pure iridium on the outside, and that is very inert. The outside of their ship will be polished too, won't it?"
"Probably—though I don't believe they were expecting to meet a heat ray."
"Well, I wonder if there isn't some chemical you could spray out that would tarnish their ship, without hurting your iridium ship? Then it wouldn't be polished and would absorb your heat rays."
"That's a good idea, Dave. I might use a sulphide—nearly all sulphides are colored, and form very easily and rapidly. Or I might use liquid ozone. That will tarnish almost anything to an oxide, which is also apt to be colored. I could certainly heat the ship that way, but I wonder—I'm afraid that the oxide or sulphide would break down too easily. There is only one metal that they might use on which that would work, namely steel. Iron sulphide is black, stable, and will not decompose readily. The oxide forms readily, is highly colored, and will not decompose before the metal is incandescent, or even melted. The only difficulty is that steel is so readily attacked, that they wouldn't use it. They would probably coat it with an inert metal, silver for instance. That forms a black sulphide very readily. I'm afraid that won't work Dave. But Wright, I think that it would be a good idea to develop a few of those field theory equations in a different way. Try integrating number two-six-thirty-nine—I think that's it—and between the limits of equation one-four-twenty-three and zero. I have an idea that a little development of that idea will give us a beam that will be very useful. We haven't time to make much apparatus, but I think the result will be near enough to the space curving projector to allow us to change the extra projectors we have in the laboratory to fit. Also, try calculating the arrangement we will need for the heat eliminator, please. I'm going to give Dave his first lesson in space navigation. We'll be back about noon—if at all!" But Gale caught the wink, so the effect was lost.
Ten thousand miles out in free space the practice began. As Waterson pointed out, it would require some mighty poor handling to hit the Earth now. For the first time in Gale's life he could practice with a machine with no fear of hitting anything.