"Look, the aurora!"
Someone suddenly spoke inside the tent.
Georgiana instinctively looked up at the night sky. There really was a magnificent band of light, and it truly did resemble an aurora.
"How is that possible?" Lacretelle murmured. "Auroras only appear at the North Pole."
She considered Boulogne's latitude. An aurora really should not have appeared there, which left only one other explanation.
"Have you heard of the Tyndall effect?" Georgiana asked.
Lacretelle looked at her in bewilderment.
"Come here," she told Lacretelle. She walked over to a dining table, took a glass, and poured water into it.
"What do you see?" Georgiana asked, holding up the glass.
"Nothing," Lacretelle said after examining it.
Then Georgiana found some milk and dripped a few drops into the water. She stirred it thoroughly, and once it turned cloudy, she realized there was a problem: this experiment required a strong light source. Where was she supposed to find one?
Then she thought, Oh, whatever, and took out her wand. She cast "Lumos" on the glass of milk, and a clear "path of light" appeared inside it.
"See? That's the Tyndall effect," Georgiana explained to Lacretelle. "When this phenomenon occurs, light takes on a shape. I remember it rained earlier, so there are still plenty of tiny droplets in the air, and there were fireworks too. Imagine someone smoking in a dark room. When sunlight shines in through a crack in the window, you can see the shape of the smoke. In that case, the colloid is dust."
"How do I know you didn't use magic on it?" Lacretelle said with a cheeky grin.
After thinking for a moment, she poured out the milk from the crystal glass and refilled it with clean water. Under the same light, there was no longer any "path