“I was wondering what happened to you,” she said. “I decided you must be too busy playing baseball.”

“The season doesn’t start till after the science fair,” he said. “Anyway, our project’s still the most important thing. Did you think I’d lost interest just because I’m playing ball?”

“I thought maybe once you were on the team, you’d be back with your old friends,” she said. “I wasn’t sure you’d still want to hang around with me.”

More graffiti had shown up on the boys’ room wall. Some of it was about his family, same as before. But there was also a new picture of Naomi, with exaggeratedly frizzy hair and a big nose, her overlarge glasses, and her two giant book bags, with papers spilling out of them.

“Listen, just because I’m playing on the team doesn’t make me Mr. Popular around here all of a sudden,” Nate said. He realized, after he said it, that it wasn’t the point, really. He shouldn’t be her friend only because he had no other options. She deserved his friendship, even if the others did start being nice to him again. And anyway, he liked her.

“We’ll always be friends,” he said to her. “Did you forget that we’re going to Butte together?”

They had been keeping the precious package of dry ice in a Styrofoam cooler in the barn, wrapped in newspaper, in preparation for the test run of their cloud chamber. Nate lifted the block out very carefully, wearing gloves like the package said, and carried it out to the implement shed, with Junie skipping alongside. He’d told her she could watch them run their experiment if she promised not to get in the way.

As Nate unwrapped the dry ice, a thin mist like steam, only cold, began to rise around it. Naomi lay a towel on top. They lifted the cloud chamber off the workbench and set it, very gently, on top of the towel. “Whatever you do, don’t drop it,” Junie reminded them.

Once the cloud chamber was in place, Naomi unfastened the box’s seal and lifted off the glass top. Nate measured a capful of ethyl alcohol and sprinkled it on the blotting paper they’d attached to the lid. In the center he placed his grandfather’s watch face, with the glass taken off to expose the radioactive paint on the dial.

They set the glass top back over the chamber and sealed it tightly.

“What happens now?” said Junie. She was practically dancing, she was so excited.

“Now we wait,” Nate said.

They had read, over and over, what was supposed to happen: The dry ice, working in conjunction with the alcohol, would produce an atmosphere of swirling gases. But reading it in the “Amateur Scientist” column was different from actually seeing it.