nt they prepared a dozen slides for
photographing with the instrument.

As these were at last developed in the darkroom, Ken scanned them
eagerly. Actually, he did not know what he was looking for. None of them
did. The prints seemed to show little more than shapeless patches. In
the light of the laboratory he called Joe Walton's attention to one
picture. "Look," he said. "Ever see anything like that before?"

Joe started to shake his head. Then he gave an exclamation. "Hey, they
look like the same particles found in the metals, which nobody has been
able to identify yet!"

Ken nodded. "It could be. Maybe this will get us only a horselaugh for
our trouble, but let's see what they think."

They went into the next laboratory and laid the prints before Ken's
father and his associates. Ken knew at once, from the expressions on the
men's faces, that they were not going to be laughed at.

"I think there may be something here," said Professor Maddox, trying to
suppress his excitement. "It is very difficult to tell in a picture like
this whether one particle is similar to any other, but their size and
configuration are very much alike."

Professor Douglas grunted disdainfully. "Impossible!" With that
dismissal, he moved away.

Professor Larsen looked more carefully. "You could scrape dust from a
thousand different sources and get pictures like this from half of them
perhaps. Only the chemical tests will show us the nature of this
material. I am certain it is very worthwhile following up."

"I feel certain that whatever contaminating agent we are dealing with is
airborne," said Professor Maddox. "If this is the same substance it will
not tell us its origin, of course, nor will it even prove it is
responsible for these effects. However it is a step in the right
direction. We can certainly stand that!"

"Couldn't we tell by spectroscopic analysis?" said Ken.

"That would be difficult to say. The commonness of the elements involved
might mask what you are looking for. Get John Vickers to help you set up
equipment for making some comparisons."

Vickers was the teaching fellow in the chemistry department whom
Professor Maddox had planned to assign to help the boys when they first
suggested atmospheric analysis. He had become indispensable in the
research since then. But he liked helping the boys; it was not too long
since he had been at the same stage in his own career. He understood
their longing to do something worthwh