The wand didn't produce the usual roaring orange flick of fire. Instead, a needle-thin bead of white-hot heat shot from the tip, striking the scrap of parchment and burning a perfectly round hole straight through it before winking out.
Aegeus stared at the tiny hole, a surge of satisfaction settling in his chest. He hadn't changed the incantation. By manipulating the stress on the syllables and stretching the vocal pauses, he could essentially "tune" the spell on the fly— adjusting its focus, spread, and duration.
He dipped his quill back into the inkwell and began making a new set of notes alongside his Latin ones. Incantation traps intent, Cadence governs shape, he wrote.
He tried it again, this time attempting the opposite adjustment— stretching the opening rather than compressing the middle— and produced a flame that was, disappointingly, indistinguishable from an ordinary cast. He tried a third variation, holding the final syllable rather than snapping it, and got a flame that guttered weakly and died half a second early.
He wrote each attempt down. Not every variation told him something useful. But enough of them did.
Wingardium Leviosa was harder to map than Incendio— four syllables in the first word alone, the numerical structure considerably more tangled, and his first three attempts at adjusting its cadence produced nothing more interesting than a feather that rose reluctantly and dropped a half-second sooner than it should have.
His fourth attempt, compressing the gap between Wing and ardium rather than stretching it, sent the feather corkscrewing sideways off the desk entirely.
Next was the color-changing exercise, which proved interesting— it was also a charm simple enough that the margin for error barely mattered, which made it useful precisely because he could afford to be reckless with it. He worked through a dozen variations over two evenings, most of them unremarkable, one of them producing a color that held for nearly three times longer before fading.
Not every result was good. Most of them, strictly speaking, were failures— spells that behaved exactly as they always had, or behaved worse, or produced some small, useless deviation that told him nothing he didn't already know. He found he didn't mind nearly as much as he might have expected to.
Truthfully speaking, if altering spells were this simple, every wizard would be doing it. Arithmancy wasn't easy, but it certainly wasn't beyond the reach of an above-average wizard. The first barrier was the math; the second one was the sheer risk. Most wizards lacked the patience to calculate ratios when standard casting worked well enough, and those who tried without exact calculations usually ended up in St. Mungo's.
And even if your calculation were correct, there are many variables that can make your calculation inaccurate.
~~~
The last few days of break passed in the ordinary rhythm, Hermione demanding a full explanation of his notes before he was allowed to leave— which took the better part of an evening.
The morning he left for King's Cross was cold and overcast, wrapped in the kind of grey that made the whole city look slightly gloomy
Platform Nine and Three-Quarters was, if anything, louder than it had been in September— fewer nerves this time, more noise, students greeting each other across the platform with volume reserved for people who had genuinely missed each other for two weeks. He found Marcus easy enough given how far his voice carried.
"There he is." Marcus abandoned his trunk mid-drag to catch up, Rosalind a step behind him with rather more composure. "Did you manage to survive the holidays without us? Don't answer that! I already know you did something boring with your break instead of relaxing."
"I did some experimenting..." Aegeus said.
"Called it." Marcus fell into step beside him as they made for the train. "Anything interesting? Or was it the usual pile of books?"
Aegeus considered how much was worth explaining amidst the crowded platform. "I spent most of the break trying to tweak a spell."
Marcus stopped walking. "You what?"
"A simple adjustment— how long you emphasize a certain word, and where you pause." He shrugged slightly. "I have made a version of Incendio that can burn a hole in paper."
Rosalind, silent until now, fixed him with an interested look. "You managed to do that over a single break?"
"It wasn't really that impressive," answered Aegeus humbly.
"Most people play Quidditch or eat sweets," Marcus said, hauling his trunk up the train steps with visible effort. "But nooo, you had to reform spellcasting."
"I wouldn't call a simple tweak refrom..." said Aegeus helplessly.
"I would!"
They found an empty compartment near the middle of the train, Marcus dropping into his seat with relief, while Rosalind settled across from Aegeus, still turning the idea over with visible interest.
"Can you show me?" she said, once the train had pulled clear of the platform and the countryside had begun sliding past the window.
Aegeus pulled a folded sheet of parchment from his bag— the same notes from his desk at home, cadence and syllable mapped out in his own precise hand— and passed it across without hesitation.
"That's Arithmancy, right?" she said finally.
"We are not even studying Arithmancy yet!" said Marcus.
"I started on it over the summer before school."
Marcus, sprawled across the seat with his eyes half-closed, cracked one open at that. "Of course you did."
Rosalind ignored him, tapping the parchment where he had marked the compression between the second and third syllables of Incendio. "You— changed the spell cadence?"
"That's right."
"You did that so you can force the fire to come out through a smaller space and in less time." Rosalind folded the parchment carefully and handed it back rather than keeping it, though she looked briefly like she had wanted to. "I want to try this. Not the fire— something smaller. The unlocking charm, maybe."
"You would need every syllable mapped first. It's pretty tedious."
"I don't mind." She said it with the certainty of someone who genuinely meant it. "Will you show me how you set it up?"
"Of course."
Marcus, who had been half-listening with his eyes closed, sat up properly for the first time and said as if struck by lightning. "Wait. Hold on. How did you actually do any of this? You're not seventeen. You can't use magic outside school."