Dew and Rime

Dew went first, to show the warm-morning version.

She crouched by the grass on a cool but above-freezing morning, beaded with dewdrops. "Last night cooled down — not below freezing, just cool," she said. "The air couldn't hold all its invisible water anymore, so the water came OUT onto the cool grass — as liquid drops. Dew." She touched a wet blade. "The air let go of its water. Above freezing, that water lands as liquid." Tuck felt the wet grass. "So the water came out of the air as drops," he said. Then Dew paused. "But here's the thing — WHETHER it's drops depends on it being above freezing. My dewdrops only form because it stayed above freezing last night. If the night had been just a few degrees colder—" she glanced at Rime "—those same drops would've been ice instead. For the below-freezing version, I need her."

Tuck considered. "So YOUR version — dew — is the water coming out as liquid... but only when it's above freezing."

"Only above freezing," Dew agreed. "One half of it. The cold half is hers."

Then Rime took over, to show the cold-morning version.

She crouched by the grass on a below-freezing morning, laced with delicate white frost. "Last night cooled down too — but PAST freezing," she said. "The air couldn't hold its water, so it came out onto the cold grass — exactly like dew — but because it was below freezing, it came out as ICE crystals instead of liquid drops. Frost." She touched a frosted blade. "The air let go of its water. Below freezing, that same water lands as ice." Tuck felt the frozen grass. "So the water came out of the air as ice," he said. Then Rime looked at Dew's dewy blade nearby. "But notice — my frost is the EXACT same coming-out as her dew. The air let go of its water both times. The ONLY difference is that my night dropped below freezing and hers didn't. Change the temperature, and my frost becomes her dew." She glanced at Dew. "For the coming-out itself — the shared part — I'm doing the same thing she is."

Tuck looked from the frog to the hare. "So HER version — frost — is the water coming out as ice... but only when it's below freezing. And it's the SAME coming-out as dew, just frozen!"

"One thing," Rime said, "at two temperatures."

Then Dew and Rime watched one changeable night TOGETHER, and Tuck finally saw the single process split by the freezing point.

They tracked the temperature as the clear night cooled. Early on, when the air first cooled below its limit — but was still ABOVE freezing — the water came out onto the grass as liquid dew (Dew's part). Then, as the night kept cooling and the temperature dropped BELOW freezing, the water coming out started freezing straight onto the grass as frost (Rime's part) — and some of the early dewdrops even froze solid where they lay. Same wet air, same coming-out, all night long — but as the thermometer crossed one number, the result switched from dew to frost. Tuck watched the freezing point flip liquid to ice and understood.

"OH," Tuck breathed. "It's ALL the air letting go of its water — and just crossing the freezing point turns the dew into frost!"

"That's it," Dew said. Alone, her dew only explained the above-freezing mornings. Alone, Rime's frost only explained the below-freezing ones. But together — one process, split by the freezing point — they explained BOTH. "The air lets go of its water onto cool surfaces," Dew said. "And the temperature decides: liquid dew, or solid frost," Rime said. "One thing," they said together, "at two temperatures. Cross the freezing point, and dew becomes frost."

Tuck tested it: he breathed on a cool cup (it beaded with dew) and on a freezer-cold cup (it frosted) — same breath, same water, liquid or ice depending only on the cold. "Same water from my breath," Tuck said, "dew on the cool cup, frost on the cold one — just the temperature!"