“Why do the sails sing?” Marta asked.

  The rigging of Starwitch rang out in the witchpit, producing a soft, but sustained middle C-sharp from one side, while the other produced a deeper tone equivalent to a B. Both were very similar to a piano wire vibrating, one of the tasks the runes on the masts performed.

  Outside, blue starlight streamed back and forth between the four masts of the ship, like tracings of spider silk, though the strands were far thinner and more tightly-packed. As the sun struck the strands, it split into the seven colors of the rainbow, bathing the area ahead of the ship in the multicolored glow. The sun was behind and somewhat to one side of Starwitch, because the solar wind wasn’t quite pushing the direction they wanted to go, very similar to the way a sailboat used the wind to move at an angle to the wind, rather than the specific direction it blew, though the process was more complex, since the sails of Starwitch were capable of moving in three dimensions.

  Amelia smiled with amusement and explained, “That’s not the sails. It’s the rigging inside the walls and masts, a set of steel cables linked to these winches.” She gestured to the winch set into the left wall, “It’s a runic enchantment designed to give us information about the tension in the cables, since we can’t see them without opening the masts, ranging from an A to a G-sharp, centered around middle C.”

  “Interesting.” Iris commented, “What made you think of using musical notes?”

  “It started with safety, to be honest.” Amelia shrugged, “Almost everything else in the witchpit is visual, but this is important enough that it needs to grab attention, rather than quietly being ignored. Originally, I planned to make the cables only produce a tone when they were close to breaking, but after more thought, I decided it would be better to give a whole range of tones, to indicate pressure, but keep in mind that if the sound ever goes up a full octave, that means the cables are under dangerous strain.”

  “How does the sail work?” Marta inquired.

  Amelia relaxed and released her spell. Without her concentration to maintain the effect, the pitch descended a note at a time, until the lower tone went away first, followed by the higher tone, on the other side.

  She turned to face her sister and smiled, “It’s actually an intense illusion. Any form of illusion that manipulates light should work, but the one I use manipulates starlight. As you know, illusions can’t interact with anything other than light, but the sun produces such strong rays, that if we use an illusion to catch or split it, we can get a little thrust out of it.”

  “And what part do the masts play?” Iris asked.

  Amelia answered, “That’s two-fold: first, when they’re deployed, they amplify the magic of anyone casting spells from the witchpit or through the spell-core, and second, they serve as an anchor point for the illusion, to allow it to affect the movement of the ship, rather than letting the illusions blow away in the solar wind.”

  “Why didn’t you just turn the masts into permanent solar sails with enchantments? Why does someone have to cast the spell every time?”

  “Lots of reasons.” Amelia sighed, “My research in the past five years showed me the limits of runes. The more complex the crystalline structure of a material is, the more runes it can handle without the spells interfering with each other, but that same complexity weakens the overall enchantment, making it less efficient.

  “Take granite, for example. It’s basically many types of rock compressed together, which does give it a much greater capacity to store magic, allowing a large collection of runes to work at the same time, but that strength is also its weakness. When runes produce an effect from the magic stored in granite, all of those different types of rock each produce their own copy of the spell, all at slightly different frequencies. When the magic comes together as a cohesive whole, the many competing frequencies interfere with each other and the end result is a weaker spell, plus lots of magic that goes to waste. In fact, eighty percent of it is simply released into the air.

  “Pure metals, on the other hand, have a rather simple structure. They can hold only three runes, but when those runes have an effect, it tends to be rather powerful, with only five percent waste.

  “Steel, on the other hand, occupies the middle ground, able to hold up to seven runes, with reasonably powerful effects and only thirty percent waste, though the details vary by the recipe of the alloy.

  This story has been stolen from Royal Road. If you read it on Amazon, please report it

  “The masts of Starwitch had to be steel, for the sake of strength, which forced me to choose between the sail or the safety spell, plus a spell anchor. Ultimately, I went with safety.”

  Marta’s brow furrowed with confusion, “Okay, most of that makes sense to me, but how did you get the spell-core to accept hundreds of runes, since it’s only one material?”

  “Mythril is a bizarre exception to the rules. Its nature gives it incredible potential to store magic and I believe the extreme density of it may enhance that further, since all heavy elements seem to have greater capacity. I haven’t found an upper limit to the number of runes I can put on it and since the metal is literally all one material, there’s no interference pattern. Add the inherent magic of the metal’s nature, and the spells use almost all of the magic available to them, with only a thousandth of a percent waste, if my calculations are correct.”

  “Okay, so what’s the goal of this light sail illusion? You said it diffracts light. What does that mean?”

  Amelia produced a triangular hunk of glass from a pocket and held it up.

  “This is a prism.” Amelia explained, then spoke the ancient words for ‘light’ and ‘white’, producing a beam of white light from the tip of the index finger of her other hand, which passed through the prism and split into a rainbow that illuminated one wall of the witchpit as she went on, “White light is actually composed of the seven colors of the rainbow. When we split it like this, we can see them all. The act of splitting the light like this changes its direction.

  “When properly anchored to the masts, an illusion that does the same will give us thrust and the more strongly we scatter the light, the more thrust we get. My illusions are fairly weak, because even sunlight can scatter the effect, forcing me to continually re-cast the spell. That’s why it looked like a spiderweb of barely-visible lines and didn’t extend very far. The bigger the sail, the greater the thrust we can achieve”

  Marta nodded, “I think I get it. Let me try.”

  Amelia looked out the window as Marta spoke the magic words for ‘illusion’ and ‘glass’. There was a slight lurch as sheets of sparkling, illusory glass appeared between the masts and extended for close to ten miles in all directions, causing Starwitch to accelerate, which briefly changed the forces inside the ship, before the artificial gravity spell adjusted for it. The rigging produced a G, the second-highest safe tone.

  “Wow!” Amelia stared out at the powerful, nearly-perfect rainbow ahead of the ship.

  Over the course of a few minutes, the illusion was eroded by the strength of the light from the sun, and the rigging descended in pitch, until it went silent, when the illusion broke apart, briefly leaving fragments of illusory glass spinning through space.

  Marta’s brow furrowed, “Well, that’s surprising. I’m not very good at illusions, but they normally last longer.”

  “That’s the same problem I have. The light of the sun is so intense, it tears the illusion apart.” Amelia nodded.

  “I’ll try now.” Iris declared, “I want to see what I can do.”

  She used the ancient words for ‘illusion’ and ‘diamond’, causing sheets of illusory diamond to appear between the masts, outside. The effect was stunning, to say the least, because it sparkled more than Marta’s sails had, despite being smaller, at only five miles radius. The rigging produced an E.

  Again, the spell eventually faded under the onslaught of the sun, but it took close to twenty minutes, then the sail cracked and shattered, very much like Marta’s.

  Amelia grinned, “Clever. Glass is fragile, so you went for a material that’s stronger.”

  “It normally wouldn’t matter with an illusion, since they aren’t real, but under the circumstances, I reasoned a stronger material might do better.” Iris shrugged, “It was a little harder to cast, but well worth the extra effort.”

  “I think I can use that to make more efficient use of the spell-core.” Amelia rubbed her chin, “Follow me.”

  She walked the length of the living spaces, to the spell-core’s room. When they were all inside, Amelia set a hand on the device and concentrated on an image of diamond sails. The ship accelerated, producing another brief change in force, before the magic attracting them to the floor adjusted.

  Sniffing, Marta asked, “Why does the air in this room always smell so clean and pure, just like being out in nature?”

  Iris experimentally took a whiff, before commented, “I never noticed that before.”

  “That’s the primary function of the spell-core.” Amelia answered, “It filters the air and turns carbon-dioxide back into oxygen.”

  “Carbo-die-what?” Marta stared at her youngest sister with confusion.

  Iris smiled and explained, “Carbon-dioxide is a gas we breathe out, that’s made of carbon and oxygen. With too much of it around, we’d suffocate. Oxygen is the main thing we need from the air, which our bodies combine with carbon for reasons I’ve never quite understood.”

  “Oh…kay.” Marta nodded, though it was clear she was feeling out of her depth.

  Amelia spoke with surprise, “When did you learn all of that?”

  “I am an alchemist.” Iris gave Amelia a knowing look, “The Book may use different terms from the ones I learned, but I’ve always listened closely when you talk about alchemic reagents.”

  Amelia nodded and stepped past her sister, heading back to the witchpit, where a soft G-sharp filled the room. She looked out the windows at sheets of diamond that extended for close to a hundred miles, producing a huge rainbow ahead of the ship.

  “That’s beautiful.” Marta practically pressed her face against the glass of one of the windows, to get a better view.

  “Yeah, it is.” Iris agreed.

  Amelia, on the other hand, sat down in the pilot’s seat and looked ahead of the ship, rather than to one side, her mind already hard at work calculating their acceleration and the angle of thrust they needed to produce, to reach their destination.

  Her sisters eventually pulled themselves away from the glass and observed Amelia for a time, before walking away, to let her work.