Rick spread a small amount on a slide, switched on the substage light,
and put the slide on the stage. He focused, using his highest-power lens
combination which gave a magnification of three hundred times.

The powder was clearly crystalline, a mineral of some kind. Rick
couldn't identify it. He turned the eyepiece over to Dr. Miller. The
scientist had no better luck.

Barby asked, "Could it be an explosive?"

"No, Barby. This is powdered rock of some kind," Dr. Miller answered,
his eye at the instrument. "But why anyone should use powdered rock and
then hide the bags certainly escapes me. I can't imagine what the powder
is for. It isn't a powdered limestone, which might be used on the
fields. The crystal structure is wrong for that."

"Wish we had a geologist with us," Rick said. "This calls for an
expert." He stared helplessly at the microscope. There was only one more
test that could be made, and he saw no use in making it.

[Illustration: _"This calls for an expert," Rick said discouragingly_]

Included in the microscopy set Barby had given him was a gadget called a
spinthariscope, like a cone of black plastic with the sharp end of the
cone sliced off. In the wide end of the cone, inset so it wouldn't touch
the eye, was a lens. The small end was composed of a disk of special
chemical that fluoresced when struck by an atomic particle.

The little instrument used a principle dating back to the early history
of atomic energy, when scientists were exploring the nature of the
strange force the Curies had discovered in radium and polonium.

It was only his training in thoroughness of investigation that led Rick
to use the instrument. Since it was necessary for the eye to become
adapted to the darkness before using the instrument, he took it into a
closet and shut the door. As the pupils of his eyes dilated he worked by
touch, spreading a bit of powder on the end containing the special
sulfide screen.

He applied his eye to the lens, more as a matter of form than in the
expectation of seeing anything. For an instant he saw nothing, then, as
his eye adjusted, he let out a wild yell. There were hundreds of
scintillations, each caused by a nuclear particle or photon striking the
screen.

The sample was radioactive!

CHAPTER X

An Assist from JANIG

"We're onto something," Rick said grimly, "and we need help."

"I should say so," Barby commented. She eyed the cement bag a little
apprehensively. "Afte