Jin and Elsa are relaxing in the state guest suite in the royal castle after the eve of the festival.

"......Today was a pretty good time, wasn't it?"

"Hmm."

Then there's a knock at the door.

"Yes."

Reiko opens the door, and standing there are Prince Ernesto the Third, his lady-in-waiting Laila, and Lotte the Golem.

"Your Highness..."

Jin and Erza also got up from their seats to greet Ernest.

"Jin, I wanted to talk to you for a minute. Can I talk to you now?

"Yeah, sure.

"Okay, I'll leave you alone.

The third prince Ernest is a very frank man. However, he had grown to about the same height as Jin, and his face had matured a bit.

"Congratulations again on your marriage, Jin and Elsa.

"Father, Erza, congratulations on your marriage."

"Congratulations on your marriage, Mr. Jin and Mrs. Erza!

Ernest and his friends congratulated the couple. A few people were chewing, but Jin and the others pretended not to hear it.

"Thank you.

"Thank you very much.

Jin then looks at Lotte.

"......Yes, Lotte seems to be in good condition.

"Yes, thanks to you."

Since the car has been seriously maintained by Jin, it is maintenance free in normal operation.

Jin offers a chair to Ernesto, since he can't stand to talk.

Ernesto sits down, and Lila and Lotte stand diagonally behind him.

Ernest sat down in front of Jin and opened his mouth with a slightly embarrassed look on his face.

"I know I asked you a few questions the other day, but I wanted to ask you a few questions about magical engineering.

"Here you go."

"Last time at the ...... World Congress, I asked you about the , and today I want to ask you about the skeleton."

"Yes."

Whether he is self-taught, or whether he is asking the castle's magecraftsman, Prince Ernest is quite knowledgeable for his age.

"I think they are usually made of metal, but they are heavy, aren't they?　The thinner it is, the weaker it is. ...... I think Lotte's skeleton is now made of light silver, but it used to be iron. Maybe it was hollow then?"

He had noticed that Lotte's skeleton was different from other common golems, as he had been watching her while fixing the broken parts after the commotion at the golem garden party.

"Yes, that's right: ......."

At Ernest's previous request, the soft-spoken Jin.

"I'm going to take a break from magical engineering for a moment..."

He prefaces his speech with,

"I would like to think about the strength of a stick.

Jin began.

"Yes. ......"

Ernesto looked doubtful, as if he could not quite grasp the meaning of the question.

"First of all,...... I like this one."

Jin pulled out a piece of notepaper from his baggage.

He cut it into pieces about 12 cm long and 7 cm wide.

"Now, make a bridge out of this paper. Let's put a coin on top and experiment to see how much weight it can bear.

Jin first folds the paper vertically four times and shows it to the audience.

"Like this," he says.

He places the paper bridge on top of a <stacked with about 10 coins...... copper coins.

"Now, how many coins will fit on it?

The paper bridge was bent when two coins were put on it.

So two coins were impossible. But here's what I did.

Another piece of paper, this time bent into a U-shape, is placed on top of the < with the bottom facing out.

This time, 25 sheets can be placed on it.

"Wow, it's going to be strong!

"Well, why don't you turn it upside down?"

In other words, the open side of the U-shape is on the top.

"Isn't that the same as ......?"

Ernesto says, but Jin puts the coin down. >>and puts the coins down.

"Ah."

At the ninth coin, the paper bridge is bent.

"...... why?"

Jin chuckled and began to explain.

"Yes, that >is important. Experiment, learn the results, and apply them. After that, the >is what comes after that."

"What do you mean?"

"I mean, <>If you know the why, you can predict these results without experimentation.

"Oh, I see."

"But the logic of this bridge is so complicated that I can't even explain it to you."

Unfortunately, Jin, a high school graduate, could not explain it that well, since structural mechanics uses cross-sectional quadratic moments and integrals.

"I know I'm getting a little sidetracked here, but by repeating these experiments, we can find a strong and lightweight structure."

"Yes."

"So, here's my conclusion. In Lotte's case, most of the skeleton is hollow.

You mean pipes?

"Yes. In this case, the strength against <> is not so different from that of a hollow pipe. Oh, you're talking about a circle with the same diameter in cross section."

"Hmm. ......"

Jin also has a vague recollection of this part.

"So, back to the magical engineering, I guess there are not many magicians (magecraftsmen) who can work on this ."

"Is that so?"

"Yes. As far as I've seen, there are few such golems or automata.

Elena, who once led the , had a hollow skeleton, but I can't bring that into it,

"The only one I can think of is < at Reese's place."

Most of the rest were solid rather than hollow, Jin recalls.

"Well, the strength of a bar or skeleton is not only in bending, but also in torsion, tension, compression, shear, and a combination of these."

Jin concluded, "I think it is safe to assume that strength other than bending is roughly proportional to cross-sectional area.

That conclusion is a bit different, but no one could mention it.

Ernesto asks a question at this point.

"Jin, what's this you're talking about?"

"Oh, that's not so easy to understand, is it?　Shearing is ...... like cutting something with scissors. It's like being slashed with a sword.

"Oh, I see. I see.

"The basic structural design principle is to make it as light as possible without compromising its strength.

This applies not only to golems and automata, but also to bridges, buildings, carriages, and ships, Jin added.

"I see. ...... That was interesting, Jin!　Thank you."

Ernesto, who said he could not stay long, thanked Jin and got up to leave the room.

"Jin, that was interesting."

After the three had left, Erza spoke up.

"Experiments like that would be interesting to do at a technology expo.

"Yeah, sure."

Since the World Congress was held this year, the technology expo is supposed to be held in the fall or later.

"I wonder if I should attend ......."

Jin has completely forgotten about tomorrow.