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As the director of the Imperial Observatory, Johann Adam Schall von Bell had a bold idea since he saw the globe drawn by Qin Mu: to measure the size of the earth.
Ever since he came up with this idea, he had lost his appetite and thought day and night about how to accomplish this great cause.
It is impossible to measure the earth with a ruler. No one can do it except God. What should we do? Tang Ruowang was almost worried.
It was not until he saw a historical document of the Han Dynasty in the History Museum of the Great Qin that he suddenly understood. In order to persuade the Emperor of the Great Qin to support him, he traveled thousands of miles to Xijing in person.
In the Wuying Hall of the Xianyang Palace, all the doors and windows were closed. In the middle of the hall stood a globe with a diameter of three feet, and above the globe hung a palace lantern.
Qin Mu, Sima An, Li Yuan, Gu Jun'en, Yang Chao, the right assistant minister of the Ministry of Revenue, Wei Yuan, the right assistant minister of the Ministry of Works, Nong Dianzhang, Yu Chenglong, Lu Zuoliang and other chief officials of the Western Capital were all present.
The blue-eyed and high-nosed Tang Ruowang, wearing a black-bottomed Daqin official uniform embroidered with auspicious clouds, said in fluent Chinese: "Your Majesty, please look."
Tang Ruowang carefully turned the huge globe, and the palace lantern shone on the globe, half of it was bright and half of it was dark. Tang Ruowang finally made the shadow line of the light stop at the position of Chang'an, the Western Capital. Then he took out a small wooden stick and said while measuring: "Your Majesty, now I will measure from the position of the Western Capital. You can see that the further north you go, the longer the shadow on the stick will be."
Qin Mu nodded and said, "Not bad."
"Your Majesty, in the Han Dynasty, there was a saying that 'the shadow of the sun is one inch longer for every thousand miles of the imperial domain'. According to this saying, taking a place as the origin, on the same day and at the same time, the shadow of the sun will be one inch longer for every thousand miles northward.
According to this theory, if the difference in the shadows measured in Nanjing and Beijing is two inches, then it can be inferred that the distance between the two places is two thousand miles.
Your Majesty, look again, since the earth is round, then the distance between Nanjing and Beijing can be seen as an arc of the entire earth. Now we only need to measure the length and curvature of this arc, and in the end it will not be difficult to calculate the circumference and diameter of the entire earth. "
Even Qin Mu felt a little confused by Tang Ruowang's statement, but he vaguely felt that it was feasible.
Li Yuan said: "Your Majesty. During the reign of Emperor Xuanzong of Tang, it was discovered that the original calendar had a large error in predicting solar eclipses, so Emperor Xuanzong ordered a group of monks to improve it. After receiving the order, the monks corrected the errors in the original calendar through on-site measurements.
The monks and his party selected many measurement points, from Linyi in the south to Tiele in the north, covering Jiaozhi, Huguang, Henan, Shanxi and other places, and selected dozens of measurement points in total. The surrounding areas of these places are hundreds of miles of flat land;
Then, on the four days of the summer solstice, winter solstice, spring equinox, and autumn equinox, measure the length of the sun's shadow at the same time, then measure the distances between these locations on the spot, and also measure the height of the North Star at the four points of east, west, south, and north;
This is how we can calculate the difference in the altitude of the North Star by one degree. This is equivalent to the difference in the north-south distance on the ground when the latitude differs by one degree…”
Hearing this, Qin Mu immediately understood why Tang Ruowang had come to Chang'an on his own;
To carry out such a measurement, a considerable amount of human and material resources must be used;
What's even more terrible is that we have to ensure that every measuring point has sunny days on the four days of the summer solstice, winter solstice, spring equinox and autumn equinox. If it rains at a measuring point, then all will be wasted and we will have to start over again the next year.
The cost is so huge that it would be impossible to complete it without the personal approval of the emperor.
"Li Qing, what are the final measurements of the monks?"
"Your Majesty, due to the war, many historical materials are missing. Some of the specific points where the monk and his entourage measured are no longer detailed and cannot be verified. We only know that the distance on the ground is 351 li and 80 steps for every degree of latitude difference."
Qin Mu knew with a little deduction that such measurement results would not be very accurate. If it was just measuring on land, even if it was a plain, there would actually be undulating areas. It was impossible to ensure that the various measurement points were on the same horizontal line, and there were inevitably some mountains in the middle. When actually measuring the distance between the various measurement points, it was difficult to ensure the accuracy of the data.
Qin Mu didn't know how the longitude and latitude were measured in later generations, but he knew that if measured at sea, it would definitely be more accurate than measuring on land.
Because the sea is basically flat, it does not have plateaus and plains like on land. As the saying goes, a slight error can lead to a great mistake. If the results of Seng Yixing's measurements are correct, then the calendar made based on this will be accurate.
But in fact, although the lunar calendar used in China has been improved several times through various dynasties, it still has a big difference from the Gregorian calendar of later generations.
By the way, later generations used the Greenwich Observatory in London as the origin of the prime meridian. Well, from now on, let’s use the Purple Mountain Observatory in Nanjing as the origin of the prime meridian. At least it is easier to remember.
Qin Mu gritted his teeth and said, "Tang Jianzheng, I approve your research project, but you must remember that this time you must not only set measurement points on land, but also focus on the sea, using the sea level as the horizontal line for measurement. I believe that the results of this measurement will be much more accurate."
Tang Ruowang was very excited when he heard this. He took off his official hat and bowed, saying, "Your Majesty is wise and wise. It is my great honor to serve you."
Qin Mu said, "To measure accurately, there is a lot of work to be done in the early stages. Even the accuracy of the ruler needs to be re-determined. And there are only two or three months until the next spring equinox. It is estimated that it will be too late next year. You should prepare first, find talents in this field, and build good measuring equipment. It must be as accurate as possible, and then start next year."
"Thank you, Your Majesty. I obey your command."
The Imperial Astronomical Observatory of previous dynasties was somewhat mysterious, specializing in looking at auspicious days and recording things like "Taibai appearing during the day".
As a result, as soon as the Imperial Astronomical Observatory announced that "Taibai appeared in the daytime", the court and the public were in an uproar. The emperor had to avoid the palace, reduce his food intake, observe fasting and abstain from sex, and issue an edict allowing ministers to advise the monarch on his mistakes. To put it bluntly, he wanted you to issue an edict allowing ministers to find fault.
Ministers often used these celestial phenomena as an excuse to attack those in power. A good policy would be forced to stop because of a certain star coming out for a tour, and even the prime minister would have to step down and be punished.
What is this!
Daqin can't afford to mess around like this anymore. It would be better to let the Imperial Observatory do some meaningful research so that they don't have to mess around all day.
In addition to measuring the earth and setting longitude and latitude lines, Qin Mu felt that the Imperial Observatory could also do some research on earthquakes. He remembered that there were seismometers in the Eastern Han Dynasty. If these things could be copied and their accuracy further increased, the occurrence of earthquakes could be monitored in a timely manner, which would be a great help.
In that era, communication means were backward. For example, if an earthquake occurred in Sichuan, it would take many days for the news to reach Nanjing. By the time Nanjing received the news and started to raise supplies for disaster relief, it would be too late.
If there were accurate instruments, Nanjing would be able to detect an earthquake in Sichuan immediately and initiate disaster relief plans in a timely manner, which would buy a lot of time for disaster relief, thereby saving more lives and minimizing the losses caused by the disaster.
So Qin Mu said, "Tang Ruowang, have you heard of the seismograph used to monitor earthquakes?"
Tang Ruowang had lived in China for thirty years, so of course he had heard of the seismometer. "What instructions does Your Majesty have?"
"I want the Imperial Observatory to recruit skilled craftsmen to develop instruments such as seismometers, which should be as precise as possible, for monitoring earthquakes."
"I obey your order."
Qin Mu rubbed his forehead, thought for a while and said to Sima An and others: "As the saying goes, there are unexpected events. Our Great Qin has such a large territory that it is inevitable that there will be earthquakes, droughts and floods. You are all pillars of the court. You can't wait until a disaster occurs before thinking of ways to deal with it.
I want you to formulate a disaster relief plan as soon as possible to ensure that no matter where the disaster occurs, you can get help quickly. For example, the severe drought in the northwest at the end of the Ming Dynasty left thousands of miles of barren land, countless people starved to death, and even triggered a large-scale civil unrest.
This was certainly due to the corruption of the bureaucracy and the lack of state funds in the late Ming Dynasty. However, if there had been a complete disaster relief plan and the responsibility for disaster relief had been implemented at all levels, I am afraid that the rebellion in the northwest would not have occurred.
Now that our Great Qin State has abundant food and the promotion of new crops, we will have no worries about lack of money and food for disaster relief if we rest for another two years. If we are unable to provide timely relief when a disaster occurs due to lack of emergency plans, then we, the monarch and our ministers, cannot shirk this responsibility. "
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.(To be continued..)
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