“There we have recourse again to our analogy," Dr. Howard declared. “If a mine attached to a great hollow globe of air were released at the sea’s bottom, it would rush up toward the surface and float there. In the same way, a mine attached to a great globe in which there is a complete vacuum would rush up through our air-ocean!

“We can construct those globes of the strongest and lightest material known — steelite. As you all know, steelite is the recently devised metal that has immensely greater strength than steel but the merest fraction of its weight. A forty-foot globe of steelite can be made, with a charge of explosives of terrific power attached to it that will detonate when the globe is touched. This done, all air is to be exhausted from the hollow globe by great pumps, until the vacuum inside it is almost complete. The enormous strength of the steelite shell prevents its being crushed by the atmosphere’s pressure as an ordinary steel shell would be. “Released, the vacuum globe with its deadly charge will shoot up through the atmosphere with terrific speed. Its lightness for its size will be such that it will not halt until it floats on the very surface of our atmosphere. We will make these globes in countless thousands, each with its charge, and release them. Each globe will have a device that will repel any other, so that they do not detonate each other.