ey reached home Maria had a lengthy report ready from the
Pasadena people, and one from Schenectady.

Professor Maddox read the reports at the dinner table. He passed the
sheets to Professor Larsen as he finished them. Ken saw he was not
reading with his usual thorough analysis. When he had finished he
returned to his eating with perfunctory motions.

"Anything new?" Ken asked.

"The same old story. A thousand hours of experiments, and no success. I
feel we're all on the wrong track, trying to perfect a chemical colloid,
based on the decontaminant, which will destroy the dust. I feel that
nothing's going to come of it."

Ken said, "I had a crazy dream the other day while Dr. Adams had me
under drugs. I had almost forgotten it. I dreamed I was walking along
the street and had a special kind of flashlight in my hand. When I came
to a car that wouldn't run, standing by the curb, I turned the beam of
the flashlight on it. Then whoever owned it could step in and drive
away. After I had done that to all the cars in Mayfield I turned it on
the sky and just kept flashing it back and forth and the comet dust
fell down like ashes and the air was clean."

Professor Maddox smiled. "A nice dream! I wish we could make it come
true. I'm afraid that idea will have to go back to the pages of your
science fiction, where it probably came from in the first place."

"Dad, I'm serious!" Ken said earnestly.

"About making a magic flashlight?" His father was almost sarcastic,
which revealed the extent of his exhaustion, Ken thought. He was never
like that.

"What I'm trying to say is that there are other ways to precipitate
colloids. We haven't even given any thought to them. Colloids can be
precipitated by heat, by pressure, by vibration. Maybe a dozen other
ways that I don't know anything about.

"Maybe some kind of physical means, rather than chemical, is the answer
to our problem. Why don't we let Pasadena and the other labs go on with
the chemical approach but let us do some work on possible physical
means?"

Professor Maddox sat very still. His glance passed from Ken to Professor
Larsen. The latter nodded. "I think we have indeed been foolish in
ignoring this possibility up to now. I wonder if Ken hasn't got a very
good thought there."

"Have you anything specific to suggest?" Ken's father asked.

"Well, I've been wondering about supersonic methods. I know that a
supersonic beam can be used for coagulation and precipitatio