Han Qian slept until the third pole of the sun, and it was also the first time that the tense nerves had been completely relaxed since leaving Jinling, and he slept extremely comfortably, and he got up full of energy and energy.

He knew that at this time, his father should be in charge of official business in the front office, and he didn't want to go directly to the front office if he had nothing to do, so he washed and ate two meat buns, and hit Shi Gongquan once, sweat gurgling down.

He took the sweat towel from Zhao Ting'er's hand, and was wiping the sweat, when he saw Gao Shao leading someone to come over and empty a side room in the east, and then detained Mrs. Xi in it.

They also went to the state jail early in the morning, borrowed several pairs of shackles, and used one of them to tie Mrs. Xi's feet, and no longer tied her up strongly.

Gao Shao and the others had all seen Mrs. Xi's nimble skills like a tanuki, and at this time, they only needed to cuff her legs to restrict her movements, and prevent her from touching the sharp weapons of the sword, and her threat would be greatly weakened.

Mrs. Xi's strength can't be compared with Gao Shao, Tian Cheng and other masters who practice diligently every day and boil their bodies.

Han Qian walked into the side wing room, staring at Mrs. Xi with great interest, thinking about what means to use to train her, at this time Han Laoshan walked in and told Han Qian that during the four days he went to Jingyun Village as a hostage, there were some changes in Qianyang City.

Han Daoxun has already made Zhao Kuo the leader to purge the jailer team.

This time, in addition to Han Laoshan, Fan Xicheng, Zhao Kuo and other eleven old servants and wives and children, there are also thirteen children of family soldiers who have been strictly trained by Han Qian for more than half a year.

On the state prison side, in addition to the prison officials, clerks, and scribes, several cell leaders from local origin were also purged in the name of "martyrdom".

There are more than 50 jailers left, although there are Hakka Han people and Tu Fanmin, but at present, it can be confirmed that they are not controlled by the four surnames, and the families are basically in the city, and Zhao Kuo led ten children of the family soldiers to be organized into the jailer team, and they can almost completely control this jailer team.

In addition, there are more than a dozen family soldiers and family soldiers led by Han Laoshan and Fan Xicheng on the side of Furong Garden, and the children of family soldiers are responsible for basic defense and assisting Han Daoxun in handling official business.

The four surnames also let some of the children return to the state camp, but only a small part, and at present, they can only keep the state camp intact, which is not enough to pose much of a threat.

“…… Except for Yang Qin taking people to take the young master back to Qianyang and Guo Nuer taking part of the Zuo Si scouts to stay in the garden, the old man saw that the situation in the city was not so urgent, and yesterday he ordered Lin Zongjing to take a part out of Qianyang City to measure the topographic map of the periphery. Han Laoshan told Han Qian about the general situation in the city.

Han Qian nodded, indicating that he knew everything.

More than 700 years ago, Pei Xiu of the Western Jin Dynasty proposed six methods of cartography, using the six principles of fraction, quasi-hope, daoli, high and low, square evil, and straightness to calculate specific geographic information to draw topographic maps.

Han Qian's early training of the children of the family soldiers, mainly to strengthen the ability of counter-reconnaissance and lurking, field survival, after the Xinchang Marquis Mansion and the Late Red Mansion made it clear that he was preparing to establish the secret Cao Zuo Division, he took the drawing of the field topographic map as a core subject to cultivate the scout's reconnaissance ability, and required the scouts under the Zuo Division to use all the time to study, and master it as quickly as possible, and put it into practice.

In Han Qian's view, the so-called spying on the enemy's situation almost all includes geographical and topographical information, which will also greatly improve the accuracy of the enemy's situation.

It's just that in this way, the requirements for the scouts of Zuo Si are bound to be extremely high. At present, the children of the early family soldiers have mastered some superficial surveying and mapping methods, and the newly recruited scouts are somewhat miserable.

Although it is said that Xuzhou has been established for six or seven hundred years, the topographic map of Xuzhou preserved by the Yafu is extremely simple.

In the past 100 years, the central government's control over remote prefectures and counties has been greatly weakened, and the topographic maps have hardly been updated, and many places have been changed beyond recognition.

Therefore, Lin Zongjing led his people out of the city to collect and map the geographical information of Qianyang, Langxi, and Tanyang counties, and compiled an atlas, which was not only to use the precious time when the situation had eased down to carry out hard training, but also to lay the foundation for his father to truly grasp the situation in Xuzhou in the future.

If Han Daoxun couldn't even figure out the mountains, forests, streams and rivers in Xuzhou, the terrain was dangerous and urgent, and the distribution of native and guest households, how could he control the overall situation of Xuzhou?

Thinking that Guo Nuer and they had all mastered the traditional six methods of cartography, normal surveying and mapping operations, there was no need for Han Qian to worry about anything more.

However, Han Qian also knew that the traditional six methods of cartography had too many flaws, far from being accurate.

Not to mention the establishment of complete latitude and longitude coordinates, even the elevation and mileage of mountains and rivers cannot be measured.

The problem is that Zhai Xinping, the person in the dream world, only has concepts such as latitude and longitude in his mind, and how to determine and measure the latitude and longitude lines, Han Qian is also in the dark.

Han Qian touched his chin, forgot to tease Mrs. Xi, and stood at the door of the room, thinking that the world had already studied trigonometry based on the Pythagorean theorem quite thoroughly, and the trigonometric values could also be calculated relatively easily, and a simple goniometer and altimeter could be made.

There is a goniometer, which theoretically measures the altitude difference between different regions of the sun, and as long as you accept the concept that the earth is a sphere, you should be able to determine the latitude with the knowledge of the world, right?

However, the measurement of longitude requires the accurate time difference between two places, which is much more difficult.

Han Qian thought for a long time, thinking that before the invention of accurate clocks, he could only establish an accurate time reference system based on the specific position of the stars and the moon on the sky, but the trajectory of the stars and the moon is very complicated, and even if an observatory is established, it may take decades to accurately observe and determine the specific trajectory of the stars and the moon, and use this as an accurate time reference.

Han Qian thought about it for a long time, and didn't think that measuring longitude was something he was capable of doing at this time, but even if he determined the degree at this time, it could greatly improve the accuracy of the map of the world.

At this time, Han Qian could not and completely did not have the ability to organize a large number of people to go to various places to carry out actual measurements, but the records of the date measurement of the Gui table abound in the documents left by the previous dynasty, which is actually the specific data needed to determine the latitude of each place.

Different regions, as long as they are located at the same latitude, the relative length of the shadow at the same time is the same.

The place where the sundial on the summer solstice has no shadow is the Beigui line, which is also a fact that has been confirmed by everyone in the astronomical calendar thousands of years ago.

The lack of a complete concept of latitude, and even the generalization of the mapping of maps, is mainly limited by the fact that the world does not have a clearer understanding of the land in which it is located.

"Childe, what are you thinking, standing here in a daze for so long?" Zhao Ting'er waited for a long time, and couldn't help but push Han Qian's shoulder and asked.

Han Qian knew that the whole work would be very complicated if it was to be promoted, and he wanted to be lazy, so he could only leave things to Zhao Ting'er to do, so he immediately told Zhao Ting'er some of the principles involved, and asked her to help read the information, collect data, and make calculations.

After they have calculated the latitude of different regions and sent people to select a few places for verification, they can officially start the correction of the Dachu map.

"The earth beneath our feet stretches straight and vast in all directions, how can it be round?" Zhao Ting'er asked suspiciously, she already knew the calculation of trigonometric intercepts and other methods, but she couldn't accept the concept that the earth was spherical.

Seeing Zhao Ting'er ask this, Han Qian was also slightly stunned, could he say that the people of the future generations could fly into space and see that the terrain was round?

Han Qian thought about it for a while, and said to Zhao Ting'er:

"Liu An of the Western Han Dynasty compiled "Huainanzi Tianwen Xun" wrote, "If you want to know the height of the sky, the tree surface is one zhang high, the north and south are thousands of miles apart, and the same day is yin, the north table is two feet, the south table is nine inches, and the south is a thousand miles of yin and short inches", and the number of 'a thousand miles short by one inch' also has the same expression in the "Zhou Ji Sutra", but these are all calculated by the predecessors on the basis of the assumption that the earth is flat and extended. The monks and monks of the previous dynasty calendar, Nangong Shuo, organized people to carry out field measurements, and confirmed that the speculation conclusion of 'a thousand miles short of an inch' was extremely incorrect, and this can also find out the specific measured data, which is difficult for many people to understand. You find out the measured data of the monk and his party, and then use the algorithm recorded in the "Zhou Ji Sutra" or "Huainanzi" to extrapolate it to see if it is only consistent if the earth is assumed to be a sphere? ”

"Clear clouds, clear clouds!" Zhao Ting'er saw Qingyun passing by inside and outside the courtyard, and hurriedly called out to her, wanting her to go to the study together to rummage through the measured data of the sundial; Zhao Ting'er thought to himself that Han Daoxun, the head of the family, had taken up his post in Xuzhou on this trip, and the most he carried with him was the various books he had collected over the years, and he should be able to find some sundial measurement data.

However, as soon as Zhao Ting'er was about to pull Qingyun and run out, he saw Han Daoxun, accompanied by Fan Xicheng, rushing back from outside, sticking out his tongue, saluting, and retreating behind Han Qian.

Han Daoxun glanced at Mrs. Xi in the detention room, and didn't ask anything, and asked Zhao Ting'er and Qingyun with a smile: "You two little girls, what are you running away recklessly?" ”

"Childe must say that the earth is round, and Ting'er wants to pull Qingyun to the study to rummage through different sundial measurements in various places to prove that Childe is just bluffing." Zhao Ting'er said.

Han Daoxun pondered the calculation method that Han Qian told Zhao Ting'er, and said: "This matter is very complicated, you are not busy doing it, keep it in mind and wait until you return to Jinling." The goniometer you are talking about, it is best to build one before leaving Xuzhou! ”

It is not complicated to manufacture a goniometer for land use, but to ensure the accuracy of the scale of the instrument, it cannot be completely handed over to the craftsmen below to do it, Han Daoxun still hopes that Han Qian can personally supervise it.

Hearing a "bang" behind him, Han Qian glanced back at Mrs. Xi who was stubbornly standing in the corner, it was she who moved her body and drove the shackles and chains, seeing that her eyes were full of confusion, as if she was thinking about what he had just said to Zhao Ting'er, she smiled in her heart, there were really few people in the world who could understand his and Zhao Ting'er's words, except for his father.

Fan Xicheng was confused.

"Mrs. Xi thinks that my father wants to build a goniometer, which is a strange skill, so that she is disdainful?" Han Qian said with a smile, "The goniometer can measure the specific height of a mountain, and after measuring the height of a mountain, you can in turn calculate the relative height and drop around the mountain, which is also a necessary means to dig canals, build water conservancy, and irrigate farmland in the mountainous land of Xuzhou-Mrs. Xi, but I still feel that my father and son are aggregators?" ”

"Mrs. Xi?" Han Daoxun glanced at the beautiful female prisoner suspiciously, and asked Han Qian.

"She is Feng Changyu's concubine, and her brother pretended to be Feng Xuan's subordinate who peeked at our behavior all the way, and was killed by me - when I was in Jingyun Village, she ran over to assassinate me, and Feng Changyu finally handed her over for disposal." Han Qian said.

"The sin is pitiful, and you should not indiscriminately create karma for killing." Han Daoxun didn't want Han Qian to be too murderous, and said.

"She knows too many secrets, if I really want to let her go, Feng Changyu will not spare her," Han Qian said, "But if she can keep to herself and not cause any trouble, I can let her move around this courtyard with her feet on her feet and help Ting'er do something." ”

Speaking of this, Han Qian looked at Mrs. Xi.

Now no one wants the fragile balance between Qianyang City and the four surnames to be broken, and the four surnames themselves never want it; Han Qian thought to himself that if he really wanted to release Mrs. Xi, Feng Changyu would imprison her if he didn't kill her.

Xi Ying knew from the moment she was abandoned by Feng Changyu that what Han Qian said was true, and no matter what, even if it was to facilitate escape in the future, and even continue to find an opportunity to assassinate Han Qian, a dog thief, it was extremely important to be able to obtain a certain degree of freedom at this time, she lowered her head and expressed her obedience in front of Han Qian for the first time.

Let the captured assassin operate in his own living place, even if he wears a footcover, Fan Xicheng felt that this matter was too dangerous, but seeing that the head of the family glanced at the female assassin, he didn't seem to object, so he didn't say anything.