Tian Xiu was holding the saddle in her hand, and she was about to step on the stirrup with one foot, when she suddenly heard Shang Cheng calling her. She promised to turn her head back to look, but she didn't notice that the horse snorted impatiently and lowered her legs, and when she heard Shang Cheng asking her for help, her feet had already stepped on it, and she stepped on it one by one. If it weren't for the fact that she has been practicing swordsmanship since she was a child, and when she grew up, she traveled all over the world by herself all year round, and she was extremely agile in her skills and reactions, and she was afraid that she would be embarrassed on the spot. She took two steps forward with the reins in her hand, and finally stood firm. Peeking around, Chang Xiu had already gotten into the carriage, leaning out of the carriage and telling Yang Heng something; Yang Heng nodded busily, not paying attention to the movement here at all. She secretly screamed in her heart, and when she turned her head, her face was already iron-blue, she pursed her lips and narrowed her eyes, staring at Shang Cheng without saying a word.

Shang Cheng embarrassedly retracted the arm that was stretched out to help. It came so suddenly that he didn't know what to say for a while. He couldn't have imagined that just one sentence would almost make Mr. Aoyama fall. Looking at the angry expression on Tian Xiu's face, he knew that he inadvertently seemed to be "in trouble" again.

He was silent for a moment, leaving time for both of them to calm down, and then directly skipped the embarrassment just now and said, "There is something I want to ask you about." He didn't call Tian Xiu "adult", indicating that he respected her very much; Whether to help or not to help is in her thoughts.

Tian Xiu didn't say a word, as if there was no Shang Cheng in front of him, he looked away from his face, looked to the side, and spit out a word for a long time: "Say." ”

Shang Cheng swallowed. Tian Xiu's attitude, what else does he have to say? Forget it, he thinks he's unlucky. Anyway, it's nothing sooner or later, so I won't touch the nail in front of Tian Xiu. Or, when you are free in a few days, why don't you go back to the city to find Li Dingyi?

Seeing that he didn't know what to say, Tian Xiu also felt that he had gone a little too far. After all, she stepped on the empty stirrup herself, and Shang Cheng didn't have much to do with it; Besides, isn't she really embarrassed? What's more, Shang Cheng has just helped the Ministry of Industry a few times, not to mention whether there can be results according to his guidance, this distraction alone can't help but teach people to be grateful...... Of course, it is impossible for her to apologize for the blunt words just now, but she must also make up for it, at least give Shang Cheng a step down, so as not to embarrass him too much. So she changed her words and said, "...... You said. ”

She actually wanted to be more tactful. I don't know why, but when the words came to my mouth, I suddenly became very impatient, and the expression on my face was also very stiff.

She hurriedly added: "...... What the hell is going on? "But it's still a hard tone like a stone.

Shang Cheng was a little uncomfortable. He couldn't figure out whether Tian Xiu was sincere in wanting to help when he spoke like this, or whether he wanted to make him look good. However, he still responded: "I want to ask you a question." This time, he didn't wait for Tian Xiu to answer, and continued to say to himself, "It has something to do with a Tang Dynasty person." I would like to inquire about an astronomer from the Tang Dynasty called Seng Yixing. He was afraid that Tian Xiu would not understand, so he added to the snake and said, "'Monk' is the word 'monk' for 'monk', and one line is his Dharma name after becoming a monk." ”

"It's the Great Hui Zen Master who wrote the "Great Yan Calendar", right?" Tian Xiu said immediately.

This time, Tian Xiu's tone of voice was very flat, as if she was not answering Shang Cheng's questions, but talking about ordinary things such as tables and chairs that were within reach, and even the tone of her voice did not fluctuate. Shang Cheng could detect that there was a kind of contempt and contempt for herself in her words. For a moment, he even had a very ridiculous feeling that he was like a newly enlightened schoolboy, standing in front of a private school teacher and listening to his teachings. In fact, he was indeed being taught, who made him not know who the Great Wisdom Zen Master was?

"In the "Book of Tang" during the reign of Gaozong Taijia of this dynasty, there is "A Book of Travel". Tian Xiu said.

Shang Cheng's face flushed. He thought that Tian Xiu was ridiculing him again. There is a set of "Tang Book" in his study, which was given by Xue Xun when he moved, and he hasn't had time to read it yet; Who knew that there was a biography of the monk and his party in this book. However, although Tian Xiu had already shown him the way, he was still ready to continue asking. If you go to the book and look around for it, where can it be faster than a "living dictionary"? Tian Xiu is well-read and has a strong memory, and has the ability to never forget, no matter what the book is, a large number of original texts are just open to the mouth, and asking her for advice is the real shortcut to the book mountain.

He said: "I remember that the monk and his entourage once presided over a large-scale survey of the meridian of the earth, which was to select four places with roughly the same longitude, measure the height of the Big Dipper, and then compare the length of the sun shadow in the four places, and then survey the distance of the four places to each other, and finally calculate a result. The result is that if the altitude of the North Pole is one degree apart, then the distance between the north and the south must be a fixed value......"

He was already doing his best to describe his ideas in the vernacular, but his efforts had little effect. As soon as he spoke, Tian Xiu's brows furrowed very tightly, and finally he almost picked up a Sichuan character in the center of his eyebrows, and looked at him back and forth with a look that was worth exploring. Looking at her at the moment, it was clear that she didn't understand what he was talking about.

Shang Cheng was also tired and sweating. He made a gesture, and finally simply found a wooden stick from the root of the wall, squatted on the ground and drew a sketch. He pointed to the picture and said, "This is it." You remember that this fixed value is the distance between the north and the south when the altitude difference of the North Pole is one degree......" he said and stopped. He felt that even if he said this, he still couldn't clearly express what he meant, or he felt that Tian Xiu might still not be able to understand what he said. But he really didn't know how to express it, so he had to look at Tian Xiu with his face raised. You should get the idea, right?

Not only did he look at Tian Xiu, but Chang Xiu and Yang Heng also looked at her together. They finished talking about business, and when they found out what Shang Cheng and Tian Xiu were talking about, they came over curiously. They also thought the two were talking about glass. Now, they stood by, like strange idlers, staring at the sketch drawn by Shang Cheng, waiting to hear Tian Xiu's opinion.

Tian Xiu's expression was no longer as stiff as before. She stared at the picture on the ground and muttered for a long time before she said very seriously: "You are talking about the fact that Zen Master Dahui was ordered to measure the sundial of the world, right?" ”

Now it's Shang Cheng's turn to not understand. But whether he understood it or not, he nodded his head before speaking. It's a big deal, just go to the book and find the data yourself!

"Tang Book Astronomical Chronicles" records that in the twelfth year of Kaiyuan, Xuanzong issued a decree to measure the sundial, and Dahui Zen Master was appointed to be in charge, starting from Danxue in the south, to the hidden capital in the north, and pointing twelve places around the world to survey and measure. From time to time, Nangong said that the number of doctors is the most refined in Baima, Junyi, Fugou, and Wujin, so based on this number, the rate is three hundred and fifty-one miles and eighty steps, and the difference is one degree......"

Shang Cheng happily slapped his leg. That's what you want!

He immediately asked again: "How much is Tang Qi a step?" ”

"One step at five feet." Tian Xiu said, "Three hundred steps in one." ”

Hey! Shang Cheng stood up excitedly and waved his fist, immediately squatted on the ground again, and immediately began to calculate. Zhao Chengtang system, the weights and measures standards used today are also left by the Tang Dynasty, and even the ruler of measuring cloth on the market is also called Tang ruler. According to the Tang ruler, his height is 7 feet 4 inches and 5 minutes, so the one foot of the Tang ruler is about 24.5 centimeters, and then folded into the meridian length of the monk and his party, the converted result is 129 kilometers. He remembered that the error in this data was relatively large, but he could not remember whether it was 16 kilometers or 18 kilometers. In the end, he first set the gap at seventeen kilometers.

Now, he set the actual distance of the North Pole altitude difference at one hundred and twelve kilometers, which is converted into a Tang ruler, which is two hundred and sixty miles and another two hundred steps. The altitude difference in the North Pole is one degree, which is two hundred and sixty miles and another two hundred steps! In standard language, it is:

"The rate is two hundred and sixty miles, another two hundred steps, and the difference is one degree."

Watching Shang Cheng Xingxing slap the dirt on his hands, Tian Xiu and Chang Xiu both felt inexplicable. There was no large-scale revision of the calendar in this dynasty, and the "Great Yan Calendar" was still used in the Gojong period, so there was no need to carry out large-scale astronomical surveys. The usual official duty of the Taishi Bureau is to observe the stars, calculate a solar eclipse and report a lunar eclipse or something, so as not to get time for these astrological signs to suddenly appear, which will be misunderstood by people and cause social turmoil; Then there is the tinkering with the "Great Calendar". The three of them looked at each other and thought of something in unison. Could it be that Ying County Boxian is very thoughtful and wants to go to the Taishi Bureau to be a Zhengqing?

Chang Xiu is just a novelty. He still remembered a lot of things in his heart, and the merchant Zhuangzi was far away from the city, so he said two flattering words such as "Zida Shentong is the way of arithmetic" and so on, and hurriedly gave his leave.

Tian Xiu had seen Shang Cheng's self-created numbers with Li Mu as early as a few years ago, and he was also surprised by his mathematical attainments at the time, but now when he looks at it again, there is no new feeling. If it weren't for the fact that she was worried about the glass, she would have had the heart to inquire about what Shang Cheng would have corrected the altitude difference of the North Star that had been determined by the previous dynasty. However, glass is the focus of the imperial court at the moment, and the prime minister's office has to ask about it every three days, so she can only put her curiosity aside. It's important to get the business at hand done quickly! Only Yang Heng looked at those scribbled characters again and again, and he couldn't wait to nail his eyes to the ground. He seemed to have some questions and wanted to talk to Shang Cheng. However, seeing that Tian Xiu had already sat on the saddle bridge, he had no choice but to say goodbye to Shang Cheng with regret. Alas, he hadn't even seen his daughter on this trip, and he didn't know how she was doing......

When he went back, Tian Xiu would think about the glass for a while, and think about the altitude difference of the North Star calculated by Shang Cheng. She felt that things would never be so simple. However, she couldn't think of any other use for this result, which was "two hundred and sixty miles and another two hundred paces and one degree very bad".

What is this number used for?