ne half of one per cent, to be
liberal. The rest don't know what they're talking about!"

"But--"

"For instance," Jayjay continued heatedly, "you take a look at every
blasted one of them that has anything to do with a spacecraft having
trouble. They have to have an accident in space in order to disable
the spaceship so that the hairy-chested hero can show what a great guy
he is. So what does the writer do? He has the ship hit by a meteor! A
meteor!"

Hull thought that over for a second. "Well," he said tentatively, "a
ship _could_ get hit by a meteor, couldn't it?"

Jayjay closed his eyes in exasperation. "Of course it could! And an
air-ship can run into a ruby-throated hummingbird, too. But how often
does it happen?

"Look: We're hitting it up at about one-fortieth of the velocity of
light right now. What do you think would happen if we got hit by a
meteor? We'd be gone before we knew what had happened.

"Why doesn't it happen? Because we can spot any meteor big enough to
hurt us long before it contacts us, and we can dodge it or blast it
out of the way, depending on the size.

"You've seen the outer hull of this ship. It's an inch thick shell of
plastic, supported a hundred feet away from the steel hull by long
booms. Anything small enough to get by the detectors will be small
enough to burn itself out on that hull before it reaches the ship.
The--"

* * * * *

Jayjay Kelvin was not ordinarily a man to make long speeches,
especially when he knew he was telling someone something that they
already knew. But this time, he was beating one of his favorite drums,
and he went on with his tirade in a fine flush of fury.

Alas ... poor Jayjay.

Actually, Jayjay Kelvin can't be blamed for his attitude. All he was
saying was that it was highly improbable that a spaceship would be hit
by a meteor. In one way, he was perfectly right, and, in another, he
was dead wrong.

How small must a piece of matter be before it is no longer a meteor?

Fortunately, the big hunks rarely travel at more than about two times
ten to the sixth centimeters per second, relative to Sol, in the Solar
System. But there are little meteors--_very_ tiny ones--that come in,
hell-bent-for-leather, at a shade less than the velocity of light.
They're called cosmic rays, but they're not radiation in the strict
sense of the word. A stripped hydrogen atom, weighing on the order of
three point three times ten to the