More than an hour later.

In a relatively secluded courtyard.

At this very moment.

Old Su was holding a short stick in his hand, writing the "Hundred Family Surnames" with great interest on a black oiled wooden board:

Zhao Qian Sun Li, Zhou Wu Zheng Wang....

After a while.

Snap—

Perhaps due to writing too hastily, the short stick broke with a sound.

Only then did Old Su stop, turning his head, looking at Xu Yun with bright eyes, and asked somewhat eagerly:

"Xiaowang, what is this thing called?"

Xu Yun glanced at the half-used short stick by Old Su and was glad that he had made a few extra. At the same time, he couldn't help but say:

"This thing is called... chalk."

More than an hour earlier.

After Mr. Xie had gathered all the materials, Xu Yun officially began handcrafting what was the simplest thing he had made since his travels:

Chalk.

Chalk is a very common teaching tool in later generations, and it's very easy to make.

In the 21st century.

Just knead clay and talcum powder with water into a dough-like form, then leave it in any tube for a few hours, and a simple white chalk is ready.

Although the Song Dynasty didn't have talcum powder, there was pig fat.

Once Mr. Xie had gathered the materials, Xu Yun mixed pig fat and lime, adding water to knead it into a paste.

Then he stuffed them into molds initially prepared for syringes, using saltpeter crystals bought from the Sour Plum Shop for cooling.

In less than an hour.

A few simple chalks were made.

However, facing such a simple object, Old Su burst with unprecedented enthusiasm.

From a quarter of an hour ago, he had been incessantly writing and drawing with chalk on a black-painted wooden board.

Sometimes writing poems, sometimes drawing circles and triangles.

Judging by his emotions, he was even more excited than when he saw garlic sprouts and generators.

The reason for Old Su's excitement was simple:

Although he was a renowned contemporary physicist and medical expert, fundamentally, he was a thorough scholar.

He had taught at an academy and, after retiring, set up a family school in his hometown in Jingkou, personally becoming a teacher.

Thus, upon seeing the effect of chalk, Old Su immediately realized the combined value of this little invention with the blackboard:

This was a divine teaching tool!

Although the Great Song's economy was quite prosperous and the court prioritized culture over military, its teaching methods were not much more advanced than other dynasties.

Basically, it involved the teacher reading aloud while students repeated after—a rote memorization method.

In terms of literacy, many primary educators would only tell you how to pronounce a character but not how to write it—because there was no tool like a blackboard.

The closest combination to chalk and blackboard at the time was something called an iron stylus.

Made from ground iron rods, its tip was sharp.

In daily life, it was mostly used for imprinting seals and carving on metal; in the classroom, it was combined with stone walls or wooden boards, where teachers carved for instruction.

This mode did not comment on the reading experience for students but was considerably taxing on the teacher's physical strength.

Not to mention that the sharp sound produced when this sharp object met the wooden board was akin to the sound of fingernails on a chalkboard—enough to make anyone curl their toes tightly.

The iron stylus had limited widespread use, meaning there were virtually no blackboard-like tools in general education.

Only some particularly responsible teachers would sometimes gather students around to demonstrate the stroke order.

In such a situation.

If you stood at the back, you might miss the stroke order demonstration.

After lessons, students who could afford it could purchase copybooks for practicing, which clearly indicated the stroke order.

But for those who couldn't afford it, the situation was grim:

They might rely on asking classmates for guidance, but if their relationships were average or they didn't ask during primary school—due to a lack of awareness at a young age—they might reach the imperial examination stage without knowing how to properly write some characters. (Referenced from a scholarly paper doi:10.16346/j.cnki.37-1101/c.2002.06.022 by a renowned professor at He University)

For example, the character for fennel had at least a dozen different written forms in the Song Dynasty.

The aesthetics of character formation are intricately connected to stroke order.

Yet handwriting was an extra credit in the ancient imperial exams, so some unfortunate scholars, despite years of diligent study, would fail due to handwriting issues.

Such situations were not rare in later generations either, where poor writing practice in primary school led to indecipherable handwriting in college entrance exams, costing marks.

Therefore, with the introduction of chalk, classroom teaching quality had the potential to significantly improve and become widespread.

After all, based on Xu Yunxian's earlier demonstration, the chalk-making process is extremely simple and cheap.

"Currently, the nation is divided into twenty-six circuits, four capital districts, thirty prefectures, two hundred fifty-four zhou, and one thousand two hundred thirty-four counties. Each county has two academies..."

Looking at the chalk in his hand, Old Su's hands trembled slightly:

"With just this piece of chalk, if each county produces three more scholars a year, that would be more than three thousand seven hundred people. Cultural education will flourish..."

Then he glanced deeply at Xu Yun, who was preparing lecture notes, and couldn't help but hesitate:

Could such a young man, capable of casually producing various marvels, truly just be an ordinary male actor?

Not to mention.

If he only sold garlic extract, he could surely be the wealthiest man in at least one city or county, right?

Although being a male actor imposed many restrictions, it was not impossible to atone and free oneself.

For instance, Chen Ling, a current Traveling Bureau position-holder in the court, was once a male actor who bought his freedom and even became an official.

Unless...

He carried a hidden story, making it impossible for him to redeem himself.

This wasn't Old Su's baseless imagination, after all, Xu Yun's circumstances were too peculiar:

Appearing at his mansion in the dead of night, without any identification or household registration documents, carrying a lot of gold and silver treasures, and having delicate skin.

At the same time, he possessed considerable cultural literacy and knowledge, including magical prescriptions unknown to even the finest physicians in the capital.....

Looking at the entire Great Song now, there seems to be only one place that can store such esoteric knowledge...

And that is...

The palace!

Hiss...

Thinking of this, Old Su's expression became quite strange.

Is it Empress Dowager Xiang?

Or Zhao Ji?

Or perhaps....

Both?

From a realistic perspective, it seems that Zhao Ji is more likely.

After all, he was a well-known playboy, and along with Wu Zetian, one of the only two emperors in history to establish institutions related to indulgences, such as the Konghe Bureau and Traveling Bureau.

Thinking of this level, Old Su couldn't help but hesitate:

If the emperor really sent someone to his mansion to capture Xu Yun, what should he do?

To hand over or not, neither seems like a good solution...

As Old Su's thoughts diverged.

On the other side.

Xu Yun finally decided on the direction of his lecture:

The force in physics.

In future Huaxia, what people referred to as science generally meant natural science.

The essence of natural science is generally a description of the rules governing natural phenomena.

For example, observing a particular phenomenon, deducing the underlying rule through logical reasoning, and expressing it using the language of mathematics, then verifying its accuracy through experiments.

This way we can say that, within a tolerable margin of error, we have obtained the rules or principles of natural phenomena.

As for the foundation of science...

From an objective standpoint, mathematics actually ranks a bit ahead of physics.

It can be said that behind every major human advancement, mathematics has been a powerful supporter.

However, considering the knowledge reserves of Xiaoli and Zhao Si, Xu Yun finally decided to start with physics.

After all, physical phenomena are more intuitive than mathematics, and the mathematical foundation needed for basic physics knowledge is not particularly profound in ancient Huaxia.

Especially during the Song and Yuan Period, ancient mathematics had developed to a quite advanced level.

Not to mention, just speaking of someone very close to our time and known to everyone:

Yang Hui.

Yang Hui's Triangle involves the binomial theorem, and even now, some fields remain unexplored.

Although Yang Hui did not achieve the simplification of binomials while alive, it at least indicates that the ceiling explored by ancient mathematics in this era was not low.

Even Xiaoli, with her literary inclination, had some understanding of basic mathematics.

Thus, starting from the concept of static knowledge in physics was undoubtedly a relatively good entry point.

Then he glanced at Old Su, who was pondering the value of chalk, and lightly coughed to remind him:

"Sir, can we begin?"

"Oh oh..."

Old Su came back to his senses, temporarily setting aside the questions in his mind.

Currently, Zhao Ji had just ascended the throne, and was in a period of testing and adjusting with Empress Dowager Xiang and all the civil and military officials.

Therefore, even if he discovered Xu Yun's whereabouts, it was unlikely he would take any action shortly, since everyone was keeping an eye on him.

At least before this year's Spring Festival, Xu Yun should be safe.

Thinking of this.

He couldn't help but breathe a slight sigh of relief, and said to Xu Yun:

"Xiaowang, since you're ready, let's begin."

After speaking.

He placed the chalk back on the table and went to sit on a small chair in front of a blackboard.

As soon as he sat down.

A very subtle feeling arose within Old Su:

He used to always be the one teaching others, and this kind of situation where he listened to someone else's lecture hadn't happened much in sixty years...

Of course.

As someone who had soaked in the library for nine years, Old Su had a high thirst for knowledge, far from being as arrogant as the scholastic tyrants of later ages.

So this emotion came and went quickly, not overly affecting Old Su's attention.

Just like that, a moment later.

Old Su, Xiaoli, and Xiaozhao, the three curious little ones, all obediently sat on their chairs.

Looking forward to listening to Teacher Xu's class.

Xu Yun then went to the blackboard and picked up the chalk.

After pondering for a moment, he asked Xiaoli:

"Miss Li, I heard you recently wrote a piece, titled 'Rumeng Ling: Last Night's Light Rain and Strong Wind'?"

....

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