selves, and make the heating effect just twice as bad. If we try to heterodyne his radio—presto—it has twice the heat energy anyway, though we might reduce it to a frequency that penetrated the ship instead of all staying in it. But by the proposition, we have to use as much energy, and in fact, remember the 80% rule. We've got to take it and like it."
"But," objected McLaurin, "we don't like it."
"Then build ships as big as his, and he'll quit trying to roast you. Particularly if the inner walls are synthetic plastics. Did you know I used them in the 'S Doradus' and 'Cephid'?"
"Yes. Were you thinking of that?"
"No—just luck—and the fact that they're light, strong as steel almost, and can be manufactured in forms much more quickly. Only the outer hull is tungsto-beryllium. The advantage in this will be that nearly all the energy will be absorbed outside, and we'll radiate pretty fast, particularly as that tungsto-beryllium has a high radiation-factor in the long heat range."
"What does that mean?"
"Well, ordinary polished silver is a mighty poor radiator. Homely example: Try waiting for your coffee to cool if it's in a polished silver pot. Then try it in a tungsto-beryllium pot. No matter how you polish that tungsto-beryllium, the stuff WILL radiate heat. That's why an IP ship is always so blamed cold. You know the passenger ships use polished aluminum outer walls. The big help is, that the tungsto-beryllium will throw off the energy pretty fast, and in a big ship, with a whale of a lot of matter to heat, the Strangers will simply give up the idea."
"Yes, but only two ships in the system compare with them in size."
"Sorry—but I didn't build the IP fleet, and there are lots of tungsten and beryllium on earth. Enough anyway."
"Will they use that beam on the fort? And can't we use the thing on them?"
"They won't and we won't—though we could. A bank of those new million watt tubes—perhaps a hundred of them—and we'd have a pretty effective heater—but an awful waste of power. I've got something better."
"New?"
"Somewhat. I've found out how to make the mirror field in a plate of metal, instead of a block. Come on to the lab, and I'll show you."
"What's the advantage? Oh—weight saved, and silver metal saved."
"A lot more than that, Mac. Watch."
AT the laboratory, the new apparatus looked immensely lighter and simpler than the old. The atostor, the ionizer, and the twin ion-projectors were as before, great, rigid, metal structures that would maintain the meeting point of the ions with inflexible exactitude under any acceleration strains. But now, instead of the heavy silver block in which a mirror was figured, the mirror consisted of a polished silver plate, parabolic to be sure, but little more than a half-inch in thickness. It was mounted in a framework of complex, stout metal braces.
Kendall started the ion-flame at low intensity, so the UV beam was little more than a spotlight.
"You missed the point, Mac. Now—watch that tungsto-beryllium plate. I'll hold the power steady. It's an
