"Come on," said MacGregor, "I'll talk to you in the car." The automobile
whirled them out of the city to race off upon a winding highway that
climbed into far hills. There was twenty miles of this; MacGregor had
time for his talk.

"They've struck," he told the two men. "They were over Germany
yesterday. The news was kept quiet: I got the last report a half-hour
ago. They pretty well wiped out Berlin. No air-force there. France and
England sent a swarm of planes, from the reports. Poor devils! No need
to tell you what they got. We've seen it first hand. They headed west
over the Atlantic, the four machines. Gave England a burst or two from
high up, paused over New York, then went on. But they're here somewhere,
we think. Now listen:

"How long was it from the time when you saw the first monster until we
heard from them again?"

* * * * *

Thurston forced his mind back to those days that seemed so far in the
past. He tried to remember.

"Four days," broke in Riley. "It was the fourth day after we found the
devil feeding."

"Feeding!" interrupted the scientist. "That's the point I am making.
Four days. Remember that!

"And we knew they were down in the Argentine five days ago--that's
another item kept from an hysterical public. They slaughtered some
thousands of cattle; there were scores of them found where the
devils--I'll borrow Riley's word--where the devils had fed. Nothing left
but hide and bones.

"And--mark this--that was four days before they appeared over Berlin.

"Why? Don't ask me. Do they have to lie quiet for that period miles up
there in space? God knows. Perhaps! These things seem outside the
knowledge of a deity. But enough of that! Remember: four days! Let us
assume that there is this four days waiting period. It will help us to
time them. I'll come back to that later.

"Here is what I have been doing. We know that light is a means of
attack. I believe that the detonators we saw on those bombs merely
opened a seal in the shell and forced in a flash of some sort. I believe
that radiant energy is what fires the blast.

"What is it that explodes? Nobody knows. We have opened the shell,
working in the absolute blackness of a room a hundred feet underground.
We found in it a powder--two powders, to be exact.

"They are mixed. One is finely divided, the other rather granular. Their
specific gravity is enormous, beyond anything known to physical science
unless i