"Just a minute." Scotty pointed to a pile of brush. "Aren't those more bags?"

They were, and of the same brand as those the boys had located on the stream bank. Scotty picked one up and tested it between his fingers.

"Mighty curious. Water cures Portland cement. Turns it hard. These bags aren't hard, even though some powder is still in them."

Rick examined the bags, his brows creased with bewilderment. "They must have held something besides cement. But what? Fertilizer for the cornfield, maybe? And why two caches?"

"If it were fertilizer, the bags near the mine could have been for the field across the creek where the plane is," Scotty suggested. "These could have been for this field. But I don't think it was fertilizer.

Isn't fertilizer soluble in water?"

Rick wasn't sure. "We can take the bag along," he said. "Maybe the microscope will tell us something, or maybe Dr. Miller will know."

He had a feeling that the bags meant something. They had been hidden, and only the erosion of rain had uncovered them, first at the creek embankment and now here. The Frostola man had almost certainly taken the others. Why? Unless they had something to do with the mystery? The bags were worthless, of themselves.

They finished the survey of the area. It was clear that whoever produced the ghost would have to enter by the road from town, because there was no other road on the side of the hill in which the mine was located. To be sure, the area could be reached by walking a considerable distance, but Rick couldn't see a man with equipment doing much walking through cornfields or woods filled with underbrush. He was certain the ghost had to be produced by equipment of some kind, probably electric powered--which meant batteries.

The problem was, where did the ghost producer operate? If dry ice was used to produce the mist, how did it get into the pool? He had no answers to these vital questions, nor did Scotty.

The dark-haired boy looked at him quizzically as they trudged back to the farmhouse. "Did it ever occur to you that it's impossible for anyone to produce the ghost? There is no place within sight of the pool where anyone could hide, except in a tree, and a man with equipment wouldn't go undetected by a gang at the picnic grounds."

"It did occur to me," Rick admitted. "But doesn't that put us back where we started? Either the ghost is a genuine spook, or it's man-made. We're not making many miles an hour in proving it's man-made, I admit. But if it isn't, where does that leave us?"

Rick remembered the chase through the woods, ending with a bath in the quarry. If they had been chasing a real ghost, and the ghost had led them into danger deliberately, that meant ... He wasn't sure what it meant except that it gave him goose pimples to think about it.

The electricity and telephone service had been restored by the time the boys got back. Dr. Miller told them that he had phoned the tenant farmer and arranged for the man to do a little inquiring in the town.

Rick displayed the bag. "Got a specimen," he told the group. He explained their interest in the bag and asked Dr. Miller if he could identify the contents.

The scientist examined the grayish powder from the bag. "It could be any one of a hundred things," he said. "Let's see what we can find out about it."

The farmhouse wasn't equipped for any kind of chemical a.n.a.lysis, but the scientist did what was possible. He tried to dissolve the powder in water, and failed. He tried vinegar, as the only acid available, and failed. He tried ammonia, and failed.

Finally he said, "Well, it isn't cement, and it isn't fertilizer. It's an inorganic substance. I suggest the microscope, Rick. It will at least give us a clue to its structure, if not its ident.i.ty."

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.

[Ill.u.s.tration: _"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 a.s.sist 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. "After all, radioactivity is dangerous!"

Dr. Miller smiled. "It is, in sufficient quant.i.ty. But the sample we have here is scarcely above normal background, so I don't think we need be concerned." The scientist turned to Rick. "I wish your instrument could give us further data, but unfortunately it's pretty primitive. It tells us the sample is slightly radioactive and that's all. I agree we need help."

The nearest source of help Rick could think of was JANIG, the secret security agency in Washington for which the Spindrift scientists had often worked on special projects. This wasn't a matter for the agency officially, but Rick was sure Steve Ames, their contact in JANIG, would help if he could. Since Spindrift had first worked with the agency on _The Whispering Box Mystery_, Steve and the boys had become good friends.

Rick suggested to the others that Steve should be called. All of them knew the young agent. He had been responsible to a large extent for the Millers joining the Spindrift staff, since he had smuggled them out of Washington to Spindrift to escape the deadly electronic mind reader that had imperiled the scientist for weeks.

There was no disagreement. On the contrary, Jan Miller asked excitedly, "What's the matter with right now?"

"Nothing," Rick said with a grin. He went to the telephone book and found the long-range dialing code for Washington, then dialed Steve's special number directly. In less than half a minute he had the agent on the phone.

"Steve? What a break to find you in! This is Rick." He swiftly outlined the events of the past few days, ending with the discovery that the bag contents were radioactive. He concluded, "I know this isn't a case for you, but we hoped you might help us to identify the stuff from the bag and get a better measure of how active it is."

Steve considered. "Know where Falls Church airport is?"

Rick had used it for a landmark on the way to the farm. It was a small private airport west of Washington near the city of Falls Church. "I know where it is."

"All right. You're only a few minutes flying time from there. It's now two thirty. Be there at four. I'll have a man meet you. Bring the sample."

Rick thanked the agent and hung up. He reported that Steve would send a man to the airport at four o'clock.

Scotty asked, "Is the field dry enough for take-off and landing?"

"Sure. I hope Steve has a real expert he can send. If we can identify this stuff, it may give us a clue to what's going on here."

At Barby's request, Rick and Scotty took the girls along for the short ride. Steve's man walked to the plane as they rolled to a stop on the Falls Church strip. He introduced himself as Don Baxter, then opened the suitcase he carried. "Let's see what you have."

He produced a field-survey instrument and held it over the bag Rick carried. The instrument's meter showed a reading at once.

"Gamma," Baxter stated. "Now let's try for alpha and beta." He opened a shield on the bottom of his instrument and checked the sample again. The meter failed to respond. "No beta. That's interesting." An inner shield was slid out of the way and the instrument held to the bag. The meter responded.

Baxter nodded satisfaction. "Alpha and gamma. No beta. That means this stuff is not a fission product."