business. You'd think they ought to have more sense of
responsibility!"

He tasted his drink, then nodded knowingly at the bartender. "This is
something like! _Real_ absinthe."

Professor Larrabee studied his companion. "I can hardly suppose, Mr.
Jasperson, that you hold professors responsible for all the ills of the
world. And yet you seem disturbed. Did you have something in particular
in mind?"

"Yes. The Thakura Ripples!"

* * * * *

Amusement vanished from the professor's eyes. "What about them?"

"Why are people so afraid of them? As far as I can see, they're just a
piece of nonsense thought up by a dreamy-eyed physics professor, and he
hypnotized people into believing in them. But as I was telling Captain
Evans last night, they've never been seen, never been measured, and
there's nothing at all to prove that they have any existence outside the
mind of a madman. And yet people are afraid of them!"

"And just what are the Thakura Ripples?" said Alan Chase, drawing up a
chair. "Waiter, I'll have a spacecap."

"Feeling a little better tonight, Alan?" asked his friend.

"Some, thanks. I just had a checkup from Dr. Willoughby, and he thinks
I'm more than holding my own. Now go on about the Ripples. Where are
they? What do they do?"

"Suit yourself," Jasperson muttered. "If you want to tell ghost stories,
go ahead."

"Thank you. The Thakura Ripples, my boy, are an unexplained phenomenon
of hyperspace. We do not know what they are--only that they are
dangerous."

"But I thought that space was entirely uniform?"

"Alas, no. Not even normal space can be called uniform. It has been
known for a long time that variations exist in the density of the
interstellar gases. Just why they occur, what pattern they follow, if
any, was for many years one of the major unsolved problems confronting
astronomers and physicists. Then they learned that these variations in
density of the interstellar gases were directly connected with the
development of the successive ice ages on the earth, and eventually a
study of the collisions and interactions of the various light forces
from the stars in the galaxy made the pattern clear. We know, now, that
the variations occur only in a certain band of space. They may occur at
any given place within that band, but their position is constantly
shifting and unpredictable."

"Now you see it, now you don't?" said Alan.

"Exactly. Now it was Thakura's theor