heavy under normal conditions but extremely responsive to the repellor or anti-gravity rays, such as the Hans use as "legs" for their airships.

Inertron is the second great triumph of American research and experimentation with ultronic forces. It was developed just a few years before my awakening in the abandoned mine. It is a synthetic element, built up, through a complicated heterodyning of ultronic pulsations, from "infra-balanced" sub-ionic forms. It is completely inert to both electric and magnetic forces in all the orders above the ultronic; that is to say, the sub-electronic, the electronic, the atomic and the molecular. In consequence it has a number of amazing and valuable properties. One of these is the total lack of weight. Another is a total lack of heat. It has no molecular vibration whatever. It reflects 100 percent of the heat and light impinging upon it. It does not feel cold to the touch, of course, since it will not absorb the heat of the hand. It is a solid, very dense in molecular structure despite its lack of weight, of great strength and considerable elasticity. It is a perfect shield against the disintegrator rays.

Rocket guns are very simple contrivances so far as the mechanism of launching the bullet is concerned. They are simple light tubes, closed at the rear end, with a trigger-actuated pin for piercing the thin skin at the base of the cartridge. This piercing of the skin starts the chemical and atomic reaction. The entire cartridge leaves the tube under its own power, at a very easy initial velocity, just enough to insure accuracy of aim; so the tube does not have to be of heavy construction. The bullet increases in velocity as it goes. It may be solid or explosive. It may explode on contact or on time, or a combination of these two.

Bill and I talked mostly of weapons, military tactics and strategy. Strangely enough he had no idea whatever of the possibilities of the barrage, though the tremendous effect of a "curtain of fire" with such high-explosive projectiles as these modern rocket guns used was obvious to me. But the barrage idea, it seemed, has been lost track of completely in the air wars that followed the First World War, and in the peculiar guerilla tactics developed by Americans in the later period of operations from the ground against Han airships, and in the gang wars which, until a few generations ago I learned, had been almost continuous.

"I wonder," said Bill one day, "if we couldn't work up some form of barrage to spring on the Bad Bloods. The Big Boss told me today that he's been in communication with the other 

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