Chương 76: Chapter 153: Much Ado About Light

William Oh stared directly at the sun and the sun blinked first. Jason Salazar Will reflexively unloaded every remaining weapon in his Phantom Hand. He didn't have any weapons, but healing potion bottles were made of glass and when hardened by the manifestation ability, they were stronger than steel. Despite being blunt they could do a respectable amount of damage. Will copied the glass vials and sent them cutting through the air at several hundred miles an hour, creating sharp cracking noises as he released them.

While he did, that he dodged to the side and scampered up the wall like a spider. No sense standing still and letting Ghoul hit him. After a few seconds of Will systematically pummeling Ghoul's last known location, Charnesa's voice called out over the sound of cracking air and bones.

"Will! Get back down here and hold still so I can fix your eyes! He's not doing anything!" Well, that's embarrassing, Will thought, letting go of the courtyard wall and sliding back down. It was strange navigating by air pressure against his skin crossed with his mental map of the environment, but he wasn't doing a bad job. I should practice this. Will could feel Charnesa approach and hold her hands up to his temples. A flash of Charge later, Will could see again.

Ghoul was splattered up against the far wall, his body reassembling itself. The undead gave them a thumb's-up.

"Sorry." Will said with a guilty nod.

"Reflex."

"No, no, it's a good reflex to have," Ghoul rasped, spitting out a bit of black ichor.

"You do owe me a new set of clothes, though.

"That's fair." Will said, approaching the Lord as he rose to his feet.

"So what the Abyss did you just do? It looked like the entire world went white, and I couldn't see. It didn't have anything to do with air at all."

"Oh, it has something to do with air. Have you ever seen a mirage? Where you can see the stars above on the ground?" Will grew up in the desert near The Tower, so of course he'd seen them.

"Yeah?"

"That effect is a result of layers of air that have different densities causing refraction. The layering trick you invented to reinforce a missile of air could also be used to bend light under the right circumstances. There are other applications I think we can learn like cavitation and vacuums, but we'll start with light, 'cause it's the most interesting to me, personally."

"…What?" Will cocked his head to the side.

"…Do you know what refraction and lensing is?" Will shook his head.

"…How much school did you have?"

"Like, real school?"

"…Shit." Ghoul motioned to Badur.

"You, logistician, get him a notebook and writing materials. You," Ghoul pointed at a nearby undead.

"Get me my magnifying glass. And you, get the chalkboard out of storage. I'm gonna need a straightedge, too…" Will watched the people hustle to obey before peering back at ghoul, who was rubbing his flaking chin.

"You didn't really answer my question. What the Abyss did you do?" Ghoul glanced back at him.

"I made a gigantic lens out of air that focused the light of the sun directly into your eyes."

"But…it looked like the light was white, not purple." Will said, glancing up at the faint purple sun.

"And it was way bigger than the sun. It was the only thing I could see."

"Light looks white when it's burning your retinas out." Ghoul said with a dismissive wave. A moment later, an undead arrived with a strange green board on wheels, while another arrived with a chair.

"Take a seat." Ghoul said, picking up a ruler and chalk and began drawing straight lines originating from a point.

"I can explain why it looked huge. This is also relevant to how the cantrip will work." Will glanced down at the seat.

"Can I…put my clothes back on first?"

"Of course."

"Awww…" Bee grumbled and splintered off from the group of observers as Will put on his pants and shirt.

"Can I sit in?" Loth asked.

"This is an interesting topic."

"Help yourself," Ghoul said, bringing in an extra chair before drawing an eyeball at the other end of the green board.

"This is your eye." He tapped his straightedge on the eyeball, then traced a single line back from the eyeball until it hit the circle with all the lines coming out of it.

"This is the light source. Do you see how only this one line hits your eye?" Will nodded.

"This represents how much light generated by an object is actually hitting your eye. A very very small percentage. The vast majority of light is scattered into the environment, usually providing ambient light as it reflects off surfaces." Will was following so far.

"What I did was this…" This story has been taken without authorization. Report any sightings. Ghoul pulled out a rag and wiped away a good portion of the lines before carefully drawing an oval shape.

"This is a lens." Ghoul said. re-drawing the lines where they intersected with the oval, with the lines turning inward and converging on the eye.

"It took all that light generated by the light source and bent it in-flight to turn towards your eye. Since your eye saw light coming from the source from all these directions…it appeared to be huge." Will understood why it looked big, but didn't understand how this lens thing could bend light, and he said as much. For illustration, Will made an oval of hardened air, but it didn't bend the light no matter which way he turned it.

"So the missing ingredient is the density of the medium the light travels through. Light is already travelling through the air, which has its own density, and that air is changing the path of light, we just don't experience it because we're inside it, not observing from outside. This is why fish seem to be in a slightly different location than they actually are, because water has a different density." Will perked up at that. He'd experienced that before.

"Look at this," Ghoul said, accepting a magnifying glass from one of his undead.

"This glass magnifying glass is able to effectively bend light because the surrounding medium is air, and the glass is far, far more dense than the air around it. Hypothetically, if the atmosphere were made of glass, this trinket would do nothing, because there would be no difference in density between this and the atmosphere."

"I…think I get it." Will said.

"What's High-pathetic mean?"

"In this case? An Imagined possibility." Loth said.

"And Atmosphere?"

"The air." Loth replied.

"Why not just say the air?" Will asked"It means the air around the entire planet. It's a bigger, more encompassing thing."

"Huh."

"Here, get a feel for it." Ghoul said, handing Will the magnifying glass. Will had only seen a handful of them, in jeweler's tools, in the offices of the rich and famous. Notaries. People who looked at small things for a living. Not something he'd ever really thought about. It felt weird to be holding one himself. He looked at the back of his hand, his knuckle becoming huge as he moved the lens up and down. At certain points it flipped and lost focus. It seemed like getting the distance right was important.

Will glanced up at the drawing on the board and tried to apply it to what he was seeing. Oh… OH! It was becoming a lot more intuitive the more he fiddled with it.

"I think I get how it makes things look bigger, but how did it do enough damage to my eyes to blind me?" Will asked.

"Well, every boy grows up lighting things on fire with lenses, so if you just-" Ghoul paused, glancing at Will and Loth, who were both shaking their heads.

"Every boy above a certain level of privilege I suppose." Ghoul said with a sheepish tensing of his shoulders.

"Aaanyway, The Tower produces light and heat, yes?"

"Yeah?"

"And when exposed to this light, objects will heat up. If you were to somehow apply more light per square inch of surface area, the object will heat up more." Will nodded, starting to get it.

"The lens makes all the light that would've hit a wide area hit a single point, which then gets hot enough to catch fire."

"Yes! And what do you think it looks like from that single point's perspective?" Ghoul said, looking excited. Will glanced up at the purple sun barely shining through the omnipresent haze of the 8 th Floor. He held the lens above his eye, and the purple sun expanded to fill the entire lens, the light nearly blinding him. OW! SHIT!

"The light source looks really big," Will said, blinking tears out of his eye as Loth giggled.

"Not how I guessed you'd work that out, but I suppose it's good that you know what it looks like from experience." Ghoul said with a shrug.

"Okay, now that we've got that taken care of, we can move on to practical tests. Let's try making a magnifying glass out of air." Ghoul said.

"Hey, if we can bend the light inward like this, can we bend the light outward and make things look further away?" Will asked before musing.

"Can I make myself look further away?"

"Well sure-""And if the perceived size of an object is only dependent on how much angle they take up in your field of view, then would it be possible to cinch light down into a tight, narrow band, then straighten it out again so it follows a straight path on a single line?"

"That's actually a-""If fish appear to be a few inches to a foot off of where they appear underwater, could I use a slab of denser air similar to a lake's surface to make myself appear off-center to act as both a shield and make dodging easier?

"I mean-""The magnifying glass makes things look bigger. Do spyglasses work like magnifying glasses, and if so, could I make my own and spy on people from a distance with a cantrip instead of using Phantom Eye?"

"I'd have to-" Loth was grinning ear-to-ear, chin resting on her palm as Will's mouth rushed to catch up with his ideas.

"And could I-""FIRST!" Ghoul interrupted, holding up a mummified finger.

"let's start with the basics and see if you can make a lens. Okay?"

"… Fine." Will grumbled, shelving the ideas. Ghoul was right, in that if he couldn't make a simple lens, then the rest of it was besides the point. The first thing Will tried was recreating his sharpened air, with the cat's claw layers of air reinforcing each other. He held the spike above his palm and waved it in front of his eye. The distant chalkboard seemed to wobble ever-so-slightly.

"How did I not see this before?" Will mused to himself, although he knew exactly why he hadn't noticed it: He'd been practicing with solidified smoke when he invented the technique, which simply stopped the light from passing through. And when he used it later, he was always looking at the target, not the spike.

The fact that it bent light seemed like a minor detail, but with the applications that Ghoul had alerted him to, he could see himself creating cantrips that were far more useful than a brittle gust of wind that wouldn't harm anyone but children with no Class. Now I just need to practice.

"Alright, looks like it can be done. Go ahead and take your Set off again," Ghoul said.

"It'll be best if you figure this out without boosts." Will turned to his audience.

"Can I get some extra clothes?" Anna pulled some pants and a shirt out from behind her.

"Did you have these the whole time?" Will asked.

"For a while anyway. I just didn't know if you wanted to stay in your underwear or not." Anna said with an innocent expression. Will grabbed the clothes and got dressed before getting back to work. Forming a lens shape with his air layering technique was hard because he'd originally thought of it in the shape of a spike, and he'd achieved a delicate balance to do so. Flattening it out didn't accomplish what he wanted. The shape was the challenge.

The spike was designed to be tough on the front, heavy on the back, able to absorb a lot of damage and drive the sharpened air through a target. When he tried flattening it out, it began unraveling rapidly, even when he was holding onto it, sending bursts of air here and there as pieces of it broke mid-compression. Eventually Will got the hang of starting his compression of air from the outer rim of the 'lens', going inward in a uniform pattern, almost like a crystal growing inwards and trapping the air as it went.

Eventually, after hours of practice, Will created a lens.

"Behold!" Will said, holding the torso-sized lens above his hand. It didn't…work that well, only bending the light the tiniest bit. But it did bend light. Will interposed it between the beam of light emanating from the key site and his own eyes, noting that the beam seemed to grow…a little bigger.

"Excellent." Ghoul said, peering through the lens.

"This is about as good as I can do without my kit." Will said.

"Right now, anyway," Ghoul said.

"Keep practicing without your kit, you'll get much better improvement in your control. Once you get your density higher, you can start experimenting with different shapes and techniques."

"If I could make the lens thinner…" Will mused. He was sacrificing a lot of area to increase his density, and he didn't have that much area to spare when he wasn't wearing his set. If he could pack more lens into a smaller area, he could also increase its density more, but the whole lens was a big, bulky thing that took up a lot of space, so he could only increase it's density so much before it became too small to do any good.

"Try a Fresnel lens!" Reese shouted as he walked by, stuffing his face with dried meat and gruel.

"A what?" Will asked, frowning, glancing at Ghoul, who shrugged back.

"OOOH!" Loth said, dropping her fist into her palm.

"May I use the chalkboard?" Loth asked.

"Be my guest," Ghoul said, offering her his chalk.