After that, they had lunch in the carriage. The butler Claude tactfully went outside to eat, and it made Jin feel a bit guilty, but no matter how Jin tried to persuade him he stubbornly didn’t listen and so that’s how things were.
The dinner was bread and fruit prepared beforehand. And then at the critical moment Jin took out his thermos flask.
“Ah, hot. Why?”
Elsa was surprised that the Teee inside the thermos flask had retained its warmth. Jin smiled and,
“That’s something called a ‘thermos flask’.”
He explained.
“Does it use magic?”
Elsa tilted her head and asked.
“No, it keeps the contents warm as if it used magic, but it doesn’t utilize any particular magic. Although I did add [Clean-up]’s Magi Formula to it, but that doesn’t have any connection with the heat insulation.”
“Then, why?”
“Yeah, I’m also interested.”
As not just Elsa but also Reinhardt was interested, Jin adjusted his sitting posture to begin explaining while drinking the Teee.
“This is also something I learned from my teacher, but there’s three ways to transmit heat.”
He began like so. Both Reinhardt and Elsa were listening intently.
“First is conduction. It’s the transfer of temperature between objects.”
“Uh-huh, if I put a metal spoon in hot soup, the handle will soon become hot.”
It seemed that Reinhardt immediately digested it.
“Next is radiation. When you hold a hand out near a fire it gets warmer, right?”
After the question this time Elsa replied.
“Mm. Even from a distance, it’s warm. You say that’s radiation?”
Jin gave a nod to Elsa’s question, and started to speak of the third way.
“The third one is convection. As air or water for example warm up they become lighter and ascend, and as cold air is heavier it comes down. Convection is the repetition of this cycle the air does.”
“I see, so when you heat up a cold room with a fire, and the ceiling is warm while the floor is cold, it’s that.”
Reinhardt said, and Elsa also spoke of her experience.
“A bath. Without stirring it, only the top is hot while the bottom is cold.”
Jin clapped his hands together and,
“That’s right. You two are good, huh.”
He spoke well of them.
“So, this thermos flask, the walls of the container have a hollow structure, and the air inside has been drawn out. Having done that, there’s no way for heat to escape using convection or conduction.”
Jin said, and Reinhardt’s face lit up,
“And so that’s why it doesn’t cool down very much! Amazing, Jin, what’s that discipline called?”
He got somewhat excited.
“It’s ‘science’. It’s the study and attempt of explaining all the phenomena of nature.”
Jin explained, and Elsa gave out a rare smile,
“I see now. One of the reasons Jin-kun is amazing is that he knows this science thing. That’s why all the Magi Tools Jin-kun constructs make sense.”
She said. Jin nodded and,
“Elsa, that’s exactly right. The science I learned from my teacher, they learned from their teacher, who again learned from their teacher, and like that it is the knowledge attained after thousands of years.”
He explained.
“Hmm, I would’ve also liked to be taught by Jin’s teacher!”
Reinhardt said, seeming frustrated. Possibly the reason Reinhardt hadn’t asked prying questions regarding Jin’s teacher was out of consideration for him.
＊ ＊ ＊
Day turned to night.
The moon that told of was hanging right in the middle of the sky. That meant it was minutes to midnight.
“Now then, shall we go?”
Reinhardt asked in a low voice.
“Yeah.”
Jin agreed.
“…”
Elsa was sleeping on the reclining chair. And so Reinhardt gave orders to the butler Claude.
“Claude, please stay here and watch over Elsa. Me and Jin will go to the ancient ruins.”
“Yes, as you wish.”
Because Reiko followed them as a guard, with Claude there were no worries. Well, and because the SP were guarding the carriage from the shadows.
Although they traveled the road during the day, during the night walking was hard. Even more so as to be safe they were walking without lighting any lamps. Nevertheless, with the guidance of Reiko to whom darkness was irrelevant Jin and Reinhardt could be at ease.
And then at last they arrived at the entrance to the ancient ruins. From inside the light of magic lamps leaked out, likely because the lamps had been left on.
“Reiko, please somehow check that there’s no people inside.”
“Yes.”
According to Jin’s instructions, Reiko disappeared using [Stealth] and approached the entrance of the ancient ruins like wind, peeked inside, and returned without making a sound.
Although there was no way Jin or Reinhardt saw this.
“It’s fine, there is no one.”
The two were relieved by the report and again set foot inside the ancient ruins.
“Now then, Jin, where should we start? You’re probably well-informed so I’ll follow your instructions.”
Reinhardt said. Jin lived in a mansion that had a Warp Gate, even though it was small, and for that reason Reinhardt must’ve referred to Jin’s judgment.
After thinking for a bit Jin replied.
“It must be underground. If it’s an important storehouse, surely you’ll build it underground. And I dare say there’s no doubt it’s hidden using concealment magic.”
Reinhardt agreed with that reply, saying,
“That’s most likely the case. But, concealment magic? That’s troublesome.”
But Jin shook his head in denial.
“That only prevents searching through magical means.”
“Eh?”
“If there’s a cave on the other side of the wall, the sound it makes when you hit it is different, right?”
“Mh-hm.”
“So basically, let’s use [Sonar].”
Jin explained and Reinhardt gave a pat on Jin’s shoulder in praise.
“I see! I didn’t tnotice that! Let’s try it right now!”
And so Jin and Reinhardt both went to using [Sonar] magic to search the floors and walls.
“Not here…”
When Jin was about to start on the next wall, Reinhardt yelled.
“Jin! Come see this!”
“What’s up, did you find it?”
Jin ran in a hurry to where Reinhardt was.
“Uh-huh. Behind this.”
Then Jin alslo tried investigating using [Sonar], and indeed he noticed that on the other side of that wall there was a large cave.
“Having done that, next is how to get to the other side.”
They could use earth magic to dig a hole, but thinking about the future leaving traces behind would be kind of bad.
Eventually, they decided to dig a different hole from outside.
They went outside temporarily. Reiko who had been standing guard accompanied them to a place around fifty meters away.
“Alright, let’s dig around here I guess.”
As there was a protrusion of rock making it hard to see it from outside, they chose that place and finally work began.
“[Dig].”
Jin dug the hole,
“[Hardening].”
And Reinhardt strengthened the walls to prevent a collapse.
Reiko went out to throw the resulting debris far away.
Like that, after approximately an hour, finally the hole pierced through.
“We did it!”
A large room spread out beyond the hole.
Jin and Reinhardt carefully stepped inside.