Late Yuan Dynasty: I am the true emperor

Chapter 138 Why don’t you quit your job as a bookkeeper?

Meng Zhifang had heard of Lu Jin's identity as a direct descendant of the Gongshu clan, and there had been a rumor circulating in the army that this general's family had passed down a book called Gongshu Secret Book, which contained all the miraculous skills passed down from ancient times. However, he, a mere clerk, had never come into contact with those books.

Moreover, Meng Zhifang was a traditional Confucian scholar and had read some classics and history. Whenever there was troubled times, the rebel kings would create some mysterious life stories for themselves, such as the howling of a fox, books hidden in the belly of a fish, a one-eyed stone man, or an orphan of the royal family. These were all old tricks, so Meng Zhifang did not really believe the identity promoted by Lu Jin.

But what Lu Jin said about density and weighing the weight of the earth made him believe that perhaps there really was such a book.

"Marshal, how do we measure the weight of the earth?" Meng Zhifang asked with some doubt and curiosity.

People often say that they do not know the height of the sky and the thickness of the earth, but now there are people who really say that they can weigh the weight of the earth. How can this not make people curious? And the key point is that according to Lu Jin's statement, this seems to be a method of calculation rather than a magic trick. It sounds more credible and makes people can't help but find out.

"If you want to weigh the earth, you can't use an ordinary scale. You have to use a torsion balance." Lu Jin directly announced the answer.

"What is a torsion balance?"

"This is a long story. Do you know what gravity is?"

"I don't know. I hope the Marshal can teach me." Meng Zhifang shook his head, but still showed great curiosity.

It was rare for Lu Jin to meet someone who was so interested in physics. Now that he had found the location of the salt mine, he was no longer in a hurry. He took the guards back to the town for dinner and, by the way, taught Meng Zhifang the basics of physics.

After listening to Lu Jin's explanation of gravity, Meng Zhifang still frowned, looking thoughtful and puzzled.

"General, what is the difference between gravity and 'clear things rise and turbid things fall'?"

"." Lu Jin was speechless for a while. It was not easy to change this traditional universal thought of the ancients. He explained immediately.

"Okay, let's do as you said, the turbid ones will descend. Then why will the turbid ones descend?"

“Because it’s heavy.”

"Who gave it the weight?"

"This..." Meng Zhifang was speechless again, because the idea that things have weight was a universal idea among the ancients, and perhaps no one had ever delved into this issue before.

Seeing this, Lu Jin gave another inspiration.

“If people want to know how heavy something is, do they need to use a scale to weigh it?”

Seeing Meng Zhifang nod, Lu Jin continued, "If there is a ten-jin iron ball, and you want to weigh it, do you need it to fall down so that you can weigh it on the scale? If it floats in the air, can you still weigh it?"

"I can't weigh it." Meng Zhifang answered immediately.

Anyone with a little common sense knows that an object has to fall downwards to have weight, but this creates a paradox. Just when he realized this paradox, Lu Jin spoke again.

"Then let's take this ten-pound iron ball and assume it is floating in the air. Can you say that this iron ball has no weight?"

"No." Meng Zhifang was a little confused and quickly added, "But the iron ball is so heavy, how can it float in the air?"

"Don't worry about it. What I'm talking about is, if there is a ten-pound iron ball floating in the air, does it still weigh ten pounds?"

This time Meng Zhifang nodded affirmatively.

Lu Jin clapped his hands and said, "This is the difference between weight and mass in physics. No matter where an object is, whether it floats or sinks, it naturally has a certain mass. As for whether it will fall, it has nothing to do with the size of its mass. Do you understand?"

Meng Zhifang nodded, but still asked, "Then why do objects fall?"

"Because of gravity, things with greater mass will attract things with smaller mass and move towards them."

Just when Meng Zhifang wanted to ask more questions, Lu Jin interrupted him and told him about the conjectures and arguments about universal gravitation, Cavendish's torsion balance experiment, and Coulomb's torsion balance gravity test.

When he heard about using a mirror and light as an extension cord to measure the rotation angle of the iron ball, Meng Zhifang couldn't help but brighten up and immediately praised it.

"Wonderful! You are really a genius! This method is absolutely amazing. If we can really measure the rotation angle, then it can indeed prove that everything has an attractive force. But how do we measure the weight of the earth?"

Lu Jin shook his head. "The weight of the earth is not easy to measure. According to the principle that the greater the mass, the greater the gravity, it is naturally impossible to get an accurate number. For example, where there are mountains, the gravity is naturally greater, and where there are gullies, the gravity is naturally smaller.

"And even in the plains, there are different minerals buried underground. Some places have copper, iron, gold, and silver underground, and some places have salt and coal underground. Naturally, they are heavier or lighter than other places, right?"

"Yes, so this is how Gongshu Jia's ancestor detected the existence of salt mines underground?" Meng Zhifang suddenly realized. Now that he knew the measurement principle and understood the truth, he was extremely excited.

Lu Jin nodded, "Yes, that's how it's measured. Because gravity is different in different places, we can only get a rough average. Then, by calculating, we can figure out the average density of the earth. Then, by multiplying the density by the volume of the earth, we can get the weight."

The four magic weapons of modern geological survey are gravity, magnetism, resistance, and artificial earthquakes. Among them, gravity detection is the earliest used because it does not require any large equipment, only a portable Coulomb torsion balance.

For example, the first artificially explored oil well in North America was discovered because when a Coulomb torsion balance was used to measure gravity, it was discovered that the local gravity was different from that in other places. Then a well was drilled, and oil was discovered after drilling only a few dozen meters deep.

Damn, that piece of land in North America is really a chosen place by God. In the industrial zone south of the Great Lakes, oil can be produced by drilling 20 meters, while in China, salt wells have to be drilled below 300 meters. It's really enviable.

Meng Zhifang understood very quickly. He already understood the concepts of density and mass. If he could measure density and volume, he could indeed figure out the weight of the earth. But this brought up another problem. He couldn't help but ask, "Marshal, doesn't that mean we have to measure the width and thickness of the earth first?"

This brings us back to the question of how thick the ground is.
"Yes, but it's not hard to predict."

"Isn't this difficult?" Meng Zhifang was speechless.

Lu Jin prompted, "Let me ask you, are the sun and the moon round or square?"

"Of course the sun and the moon are spherical." Meng Zhifang answered immediately.

Now it was Lu Jin's turn to be confused. He thought Meng Zhifang would say that the sun and the moon were round disks.

Seeing Lu Jin's surprised expression, Meng Zhifang became unsure himself.

"Isn't that right? The Kaiyuan Divination Classic of the Western Han Dynasty recorded that 'the ancient teacher thought that the sun was like a bullet, the moon was like a mirror, or that the moon was also like a bullet, bright where the sun shines, dark where the sun doesn't shine.'" Wow, it turns out that the ancients not only knew that the sun and the moon were both spherical, but also knew that the light of the moon was reflected by the sun shining on them.
This is because Lu Jin is ignorant. In fact, there were many similar books in ancient times. For example, Zhang Tianshi, the second generation of Tianshi Dao in the Eastern Han Dynasty, was the Zhang Heng who invented the seismometer. He also said in his "Ling Xian" that the light of the moon is reflected by the sun, but he did not mention the shapes of the sun and the moon.

"You are right. The sun and the moon are both spheres. In fact, the earth beneath our feet is also a sphere. I call it the Earth."

"This, how is this possible? If it is really a sphere, why has no one known about it for thousands of years?" Meng Zhifang looked incredulous.

Lu Jin smiled and said, "I like a poem by Su Zi of the Song Dynasty: From the side, it looks like a mountain; from the front, it looks like a peak; from a distance, it looks different at different heights. I cannot see the true face of Mount Lu because I am inside it."

Meng Zhifang suddenly understood, "What the Marshal meant is that the universe is too vast, and humans are too small compared to it, so we know nothing about the shape of the earth.

"But if the earth is really a sphere, and there is a vast ocean outside the East China Sea, doesn't it mean that we can take a boat to the east and then come back from the west?!" Meng Zhifang was immediately shocked by his discovery.

“That’s true, but the East China Sea is not entirely an ocean. There are islands and land in the sea. In fact, that piece of land is not much smaller than the Shenzhou under our feet. There are also many tribes, barbarians and countries on it.

"My ancestor Gongshu once visited overseas and found that there might still be remnants of the Jiuli tribe there, so he named that continent Lizhou."

Meng Zhifang opened his mouth in shock after hearing this, and it took him a while to react, "Jiuli tribe? The Chiyou Jiuli tribe that competed with Emperor Yan and Emperor Huang for the Central Plains?!"

"That's right. Although Chiyou was defeated, his people were so numerous. Emperors Yan and Huang only defeated him in a decisive battle, and they didn't go to their hometown to kill them all. It is said that the Jiuli tribe had 9981 tribes. After Chiyou was defeated, where did these tribes go? Isn't anyone curious?"

Meng Zhifang was stunned by these words. It took him a long time to digest the message from Lu Jin's words. It was too unbelievable that Chiyou's Jiuli tribe still had survivors and had moved overseas.

"Does the Marshal really mean what he said?"

Lu Jin looked at him and smiled, "If you believe it, it exists. If you don't believe it, it doesn't exist. Hahahaha."

"."Meng Zhifang almost choked to death. Was Lu Jin just kidding him? But it sounded like the truth.

Seeing that he looked thoughtful, Lu Jin suddenly had an idea and asked.

"Is this what you're so interested in?"

Meng Zhifang replied, "Everyone is curious, especially the Jiuli, who are said to have competed with Emperor Yan and Emperor Huang for the Central Plains. Anyone who hears this will want to find out. I am just a little curious."

"Since you want to know so much, I can tell you. However, I'm afraid you won't be able to be the chief clerk. Are you willing to learn the Gongshu Secret Book from me?" Lu Jin suddenly revealed his feelings.

Meng Zhifang was stunned when he heard this, and immediately hesitated. Although he was a chief clerk now, he was still working outside. As long as he worked diligently, he would definitely be promoted to county magistrate, prefect, or even provincial official, or even central government official. If he gave up the position of chief clerk now, he might not have this opportunity in the future.

But looking at Lu Jin's behavior, he should attach great importance to the family secret book. Now this secret book has not been widely circulated. If he studies with the Marshal, he will be considered a direct disciple. If he really learns some skills, maybe he can be promoted faster than being a chief clerk, or even reach the top in one step.

There are opportunities on both sides, how to choose?

"May I ask, Marshal, besides astronomy and geography, what else can be learned from this secret book?"

Lu Jin said immediately, "The Gongshu Secret Canon is based on the Gongshuzi written by our ancestors. It integrates the teachings of various schools of thought, emphasizes arithmetic and the principles of nature, and is mostly practical knowledge such as the art of work, agriculture, and military tactics."

Meng Zhifang thought about it after hearing this. The founder of Gongshujia was Gongshu Ban. Lu Ban was a skilled craftsman, and his descendants were probably similar. This might be a book about craftsmen. However, what Lu Jin said today did make him very interested.

Seeing that he was still hesitating, Lu Jin spoke again.

"If you are willing to learn, even if you can't learn everything, even if you can learn even 10%, you will be able to become a figure like Grand Tutor Guo Shoujing."

Meng Zhifang opened his mouth. How could Lu Jin say that Guo Shoujing, the Grand Master of the early Yuan Dynasty, was only qualified for 10% of the Gongshu Secret Canon? What would happen if he learned the whole thing?
Not to mention learning it all, for an ordinary scholar like him without a prominent family background, if he could really reach the position of Grand Tutor, he would die without regrets. This is an opportunity!

So Meng Zhifang immediately stood up and bowed deeply, "I am willing to follow the commander to learn the secret book, but what about the salt mining in Dingyuan?"

Seeing this, Lu Jin laughed and said, "Hahahaha, this is not difficult, just change a chief clerk to take charge."

The next day, Lu Jin brought everyone back to Dingyuan County.

Although the idea of ​​taking in a disciple was something he came up with on the spur of the moment, it was not without effect.

Lu Jin definitely wants to spread scientific knowledge. Only by cultivating more science and engineering talents can his ideas be realized, but it is impossible for him to go to school to give lectures every day.

It is necessary to have an apprentice learn from him first and then go to school to teach others. This can help him save a lot of time.

Nowadays, there are only two people who have direct access to Gongshu Secret Book. One is Zhang Yunxiu, who helps him organize the manuscript, and the other is Yang Huan from the training camp. However, the teaching in the training camp is not in-depth. It mainly focuses on military skills and is used to train officers.

If we want to cultivate serious science and engineering talents, we still have to run a separate school, and someone must be responsible for this.

Since Meng Zhifang has shown great interest in this, why not let him try it first? Maybe he can become the Minister of Education in the future, or go to the Academy of Sciences or the Academy of Engineering.

"Marshal, is there really a salt mine in Luqiao Town?" Zhu Liangzu asked immediately when he saw Lu Jin coming back, with Dingyuan County Magistrate Sang Hongbin beside him.

Lu Jin nodded, "Well, I have found the location, but as for whether there is anything underground, we have to wait until we dig a well and try it out.

"I will take Meng Zhifang with me. When I return, I will send another chief clerk, a supervisor for salt affairs, and craftsmen and equipment for digging wells.

"You two, one civil and one military, Sang Hongbin, as the county magistrate, you must cooperate with the Salt Administration and the resettlement of the relocated people. Zhu Liangzu, you should focus on military affairs. Remember what I told you and be ready for battle at any time."

"Yes!" The two answered in unison, and Zhu Liangzu asked again.

"Won't the Marshal wait for Lai'an to take down the enemy before going back?"

"No need to wait. Lai'an is a small city. More than three regiments and tens of thousands of people can't take it down. What use do I have for you? You are the commander of the northern line. You just need to keep an eye on it here."

"Yes." Zhu Liangzu agreed again.

After arranging these things, Lu Jin also started his journey back to Luzhou. He had been away for nearly a month, and had inspected from south to north, visited the three fronts, and captured several cities. It was time to go back and check the logistics work of the base camp.

(End of this chapter)