Chongzhen revived the Ming Dynasty

Latitude is determined by nature. The equator is there, and it is naturally the zero degree latitude.

With the North and South Poles as 90 degrees, we can naturally determine the latitude data of various places.

Longitude is different from it. The starting point of the longitude is determined artificially.

For example, the "Kunyu World Map" uses the longitude line passing through Fukushima, probably the island of El Hierro in the Canary Islands in later generations, as the prime meridian.

This is also the most common longitude setting in this era. It is said to be the Lucky Island defined by Ptolemy, but there is no exact location.

Later, as astronomical technology advanced, Western countries began to build observatories and determine the prime meridian.

This practice led to confusion in communication. In 1884, various countries held an International Meridian Conference, which determined the longitude passing through the Greenwich Observatory in southeast London, England as the prime meridian, determined the world time, and divided the world into time zones and the International Date Line.

Zhu Youjian had previously viewed the "Kunyu World Map" and used its latitude and longitude circles to draw more accurate maps, and he felt very uncomfortable with the longitude on it. So the map he drew based on the conference was drawn using an equidistant grid.

After learning that the Imperial Observatory could measure longitude and latitude relatively accurately, he immediately decided to adopt the new prime meridian.

This line needs a benchmark, Zhu Youjian said:
"How many degrees does the central axis of Yongdingmen, Zhengyangmen, Chengtianmen, Huangji Hall, and Bell and Drum Tower deviate from the north-south meridian?"

“Can we build a new bell tower near the bell and drum tower, and at the same time build an observatory to determine the longitude of the central time zone where the prime meridian is located?”

Many people know that there is a deviation between Beijing's central axis and the meridian.

It was not because of measurement errors when building Beijing City, but to conform to the Feng Shui layout.

In the art of astronomy, the sky is divided into three enclosures and twenty-eight stars. The three enclosures are Ziwei Enclosure, Taiwei Enclosure and Tianshi Enclosure, among which Ziwei Enclosure is the best.

The source of the imperial power of Ziweiyuan lies in the North Star. The North Pole is also called Beichen, the star of the emperor. Ziweiyuan is centered on the North Star, and is guarded by layers of stars.

The sun, moon and stars move, but the North Pole remains stationary, representing the throne of the emperor.

However, the North Star is not in the strict north. There is a deviation of 1.5 to 2.5 degrees between it and the earth's axis.

Therefore, the central axis of Beijing city was designed with a 2-degree deviation.

This was the pattern laid down by Liu Bingzhong, Guo Shoujing's teacher, when he presided over the construction of Yuan Dadu. Yuan Shangdu, also built under his supervision, did not deviate from the meridian.

Now Zhu Youjian wanted to determine a meridian as the zero degree longitude. Of course, he could not choose the central axis of Beijing which deviated from the longitude, but had to choose the meridian due south and due north.

The top priority was to build a new bell tower near the bell and drum tower and also to construct an observatory.

After the emperor proposed the idea of ​​building a new bell tower, Xu Guangqi and others began to select a site.

Hearing the emperor's intention, Xu Guangqi said:

"Beijing's central axis deviates two degrees from the meridian. If an observatory is to be built near the Bell and Drum Tower, it needs to be built on the east side."

"I just don't know which place to use as the reference. Which palace is directly south of it?"

Zhu Youjian's first reaction was to choose the Huangji Hall, but he thought that the three main halls had been burned down many times and might be rebuilt in the future. So he decided:
"The prime meridian is in the noon time zone, which corresponds to the middle of the Meridian Gate."

“Draw a line running due south and due north in the middle of the Meridian Gate, extending north to the Observatory. Build a straight north-south mark at the Observatory as the Prime Meridian.”

“The center of the four clocks in the new clock tower should also be on the prime meridian, reporting Beijing time every day.”

(The Great Ming Prime Meridian passes through the middle of the Meridian Gate, approximately at the modern east longitude of 116 degrees 23 minutes 50 seconds. A new bell tower and observatory were built on the east side of the Bell and Drum Tower on this meridian.)

In this way, the location of the prime meridian has a specific reference.

Xu Guangqi and others hurriedly took note and planned to build a new bell tower and observatory on the east side of the bell and drum tower after the measurements were completed.

Together with the original bell and drum towers, they are collectively called the Bell and Drum Tower Observatory and became the timekeeping center of the Ming Dynasty.

Beijing time will be determined here and communicated to the rest of the world.

Zhu Youjian certainly did not determine this time because he had nothing to do. He did it to facilitate navigation, especially positioning during ocean voyages.

Since the latitude can be determined by the star-pulling board, only the longitude needs to be determined. The accuracy of the Ming Dynasty's navigation charts will be raised to a higher level.

No matter where the ship drifts, it will know which direction to go to reach the nearest dock and supply point.

If you mark reefs and dangerous places on the nautical chart, you can avoid dangers during navigation.

Pointing to the clock made by the Imperial Observatory, Zhu Youjian said:
"This clock shows Beijing time. If we take this clock on board and use instruments such as a sundial to determine the local time at our location, can we determine the longitude of the ship based on the time deviation?"

"Then use the star tracker to determine the latitude and fix the longitude and latitude of the ship."

This is the simplest method of determining longitude and is also the basic principle of marine clocks.

After hearing this, Xu Guangqi and others' eyes suddenly brightened up. They all felt that their minds were opened up and they could more easily determine the longitude and latitude of various places.

However, Deng Yuhan, the missionary who came with Xu Guangqi, said tactlessly:

"The method proposed by your majesty was also proposed by the Dutchman Gamma Frisis."

"But the accuracy of the clock is too poor. It is common for it to be a few minutes fast or slow every day. The deviation is too large."

"So now when we navigate, we use the lunar distance method proposed by German astronomer Johannes Werner."

This is also a method of determining longitude, using the movement of the moon to measure longitude.

This method is now more accurate than the clock method, but it requires a huge amount of astronomical observations to draw up a detailed and accurate star catalog to record the trajectory of the moon at a specific location at different times.

For example, a navigator can compare the star chart that records the trajectory of the moon above the Zhonggu Tower Observatory with the angle between the moon and another star observed at sea, and theoretically calculate the time at the Zhonggu Tower Observatory. Then, by comparing it with the local time at their own location, they can calculate the longitude.

Its calculations are obviously very professional and cannot be worked out without knowledge of astronomy.

Fortunately, Deng Yuhan was born in Germany and was very familiar with the lunar distance method. He was also one of the most knowledgeable Jesuit missionaries. He was admitted as the seventh member of the Lynx Academy of Sciences, just a few days later than Galileo.

After his explanation, Zhu Youjian roughly understood the principle of the lunar distance method, and also realized the progress of Western navigation.

More than a hundred years after the beginning of the Age of Discovery, Westerners had already surpassed the Ming Dynasty in ocean voyages.

Sighing at this in his heart, Zhu Youjian became more determined to perfect the clock law. He decided:

"Although the lunar distance method is good, the calculation is too complicated. The Imperial Astronomical Observatory can cooperate with the Ming Shipping Group to draw star charts and navigation charts, and teach and sell them to people all over the world."

“The clock method also needs to be improved, and the principles and requirements must be determined first.”

"Then we will publicly offer a reward to the people of the world for the person who makes the clock."

As he spoke, he asked the officials of the Imperial Observatory to record:
"Whoever can first reduce the error of a clock to one minute will be awarded the title of public official."

"Narrow it down to less than ten seconds and you will be awarded the hereditary knighthood."

"Narrow it down to less than one second and award the hereditary baron."

"If the error continues to narrow, the title will continue to be upgraded, and the highest title can be granted as a hereditary earldom."

"The deeds and portraits of all the people are displayed in the Bell and Drum Tower Observatory so that future generations will remember them." This was the reward he offered with great determination, in order to defeat other countries in the longitude dispute.

He wanted to establish the longitude and time zone that he had just determined as the international standard. All future sailors would use Beijing time as the benchmark.

Such a high reward made all the officials of the Imperial Observatory excited. They were close to the water and had the first chance to get the moon, so they were likely to get the reward.

Niu Jinxing, who was assigned by Zhu Youjian to work in the Imperial Observatory, said:
"I think we should not limit ourselves to clocks. Other instruments, such as precise clepsydra and water-powered armillary sphere, can also be used to measure time."

“The new clock tower should not only have a four-face clock, but also instruments such as a water-powered armillary sphere.”

This is a mechanical timer invented by Zhang Heng, which is mainly used in astronomy.

The most exquisite one was made by Su Song in the Song Dynasty, which already had the escapement and speed regulator used in clocks.

Unfortunately, due to the invasion of the Jin army, these achievements could not be further developed.

When the Ming Dynasty was founded, the Imperial Astronomical Bureau introduced a crystal clepsydra with two puppets inside that could beat the cymbals and drums on time. Emperor Taizu smashed it because it was useless. As a result, the Ming Dynasty did not make much progress in timekeeping instruments.

Seeing that the current emperor attached great importance to timekeeping instruments, Niu Jinxing proposed to make a water-powered armillary sphere according to ancient methods, as well as a clepsydra, hourglass, incense clock, sundial, etc.

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Zhu Youjian didn't know much about these timekeeping instruments, but he still nodded and said to Niu Jinxing and others:
“Anything that can be used for precision timekeeping can be tried next to the new clock tower.”

"But the acceptance of the new timepiece is based on its ability to accurately time the ship. It is designed to determine longitude by the clock method."

"It can only be used on land, and you won't get a reward."

Make the standards clear to prevent some people from creating something grand but meaningless.

In order to guide people to focus on watches, he also explained to everyone the concepts he had heard of, such as pendulum, hairspring, tourbillon, etc.

The calendar, moon phases, etc. displayed on some later mechanical watches were also mentioned.

He hoped that the watchmakers of the Ming Dynasty would use their brains to make all these, raise the complexity of watches to a higher level, and drive the precision instrument manufacturing industry.

For this purpose, he also proposed watches and watch straps, asking watchmakers to make smaller watches, which he would wear himself in the future.

The Ming Dynasty not only wanted to make a huge four-sided clock, but also wanted to make a watch and shrink it down.

After hearing this, the officials of the Calendar Bureau and the Imperial Observatory realized the importance the emperor attached to clocks and decided to focus more on this kind of timepiece.

Seeing the emperor's expression, Niu Jinxing also proposed a new clock, which he thought would be more convenient for measurement:

"I think that in addition to making a twelve-hour clock, we can also make a ten-hour and one-hundred-quarter clock."

"A day is divided into 100 ke, and 1 ke is further divided into 10 ke, and further divided into 100 li ke and 1,000 hao ke."

"This way, there are 1440 milliseconds in a day, which is much easier to calculate than a day of 86400 minutes or seconds."

This was something Zhu Youjian had not thought of. Although he had retained the Heavenly Stems Timekeeping Method, he had not thought of using it so soon. This made him ask carefully:
"This kind of clock has never appeared before. What are its advantages?"

Seeing that the emperor was interested, Niu Jinxing hurriedly explained:
"Using this clock, the celestial sphere can be divided into 100 degrees, with a time difference of 1 quarter per degree."

"Your Majesty said that the length of the equator is about 80,000 miles, so a difference of one moment on the equator is 800 miles."

"A difference of one quarter of a second is eight miles."

"By calculating the length of the latitude circles of ten, twenty, fortieth degrees, etc., you can find out how many miles the difference in time is for one moment."

This made Zhu Youjian a little confused, because in his concept, one circle of the sky is 360 degrees, so how could it be divided into 100 degrees at a time?

However, the people of the Ming Dynasty did not have a fixed understanding that the celestial sphere was 360 degrees. The celestial sphere they used before was 365 degrees and 25 minutes.

It was not until Xu Guangqi, with the support of the current emperor, that the Zhoutian degree was changed to 360 degrees, and the previously used Zhoutian degrees were directly swept into the garbage heap.

The proposal of Zhoutian Baidu was actually a counterattack by the traditionalists of the Imperial Astronomical Bureau. They proposed this concept using the Heavenly Stems timekeeping method proposed by the emperor.

This was revealed at this time through the mouth of Niu Jinxing, the emperor's favorite.

Niu Jinxing tried his best to tell the emperor the advantages of ten o'clock and a hundred minutes, and continued:
“Not only can the weft loops be divided into 100 degrees, the warp loops can also be divided into 100 degrees.”

"So a meridian has fifty degrees, and from the equator to the North Pole, it can be divided into twenty-five degrees."

"Every degree is eight hundred miles apart."

"Each degree is divided into 100 centimeters, and the difference is eight miles."

"It is very convenient to use this method to calculate distances and measure the area of ​​fiefdoms."

After a detailed explanation using a globe made by the Imperial Astronomical Observatory, the confused Zhu Youjian finally understood a little.

Although he felt that this had its benefits, it also met his purpose of retaining the Heavenly Stems timekeeping system for ease of calculation.

However, this would require the redivision of longitude and latitude and time zones, and the people would have to use the Heavenly Stems system to record time instead of the Earthly Branches system that had been used.

This change was so big that Zhu Youjian didn't know the consequences and didn't dare to make any changes.

Xu Guangqi and others nearby strongly opposed this, believing that this method had never been used before and must have many problems.

Finally, after much deliberation, Zhu Youjian decided:

"This longitude and latitude based on the Heavenly Stems Timekeeping System can be used as an aid."

“After it is perfected in the future, we will see whether it can be promoted.”

Let Niu Jinxing and others make astronomical instruments and astronomical clocks first, and then see the specific effects.

The Bell and Drum Tower Observatory has thus gained another type of architecture. In addition to the timekeeping instruments such as the four-sided clock based on the earthly branches, there are also timekeeping instruments based on the heavenly stems.

Niu Jinxing and others failed to achieve their goal, but they were not discouraged. They also knew that this change was too big, and they did not expect the emperor to adopt it immediately. Now they just proposed it and made a sound to show that they were useful.

Inspired by this statement, Zhu Youjian also proposed the task of calculating the length of the latitude circle and asked Xu Guangqi and others to derive the calculation formula.

As for the length of the warp coil, there is no need to measure it again -

Because when he proposed the concept of meter, he pointed out that the length of the meridian is 80,000 li, or 40,000 kilometers. Although there may be errors, it can be estimated according to this number.

After dividing 111.111 kilometers by degrees, the difference between one degree is approximately kilometers.

One degree is divided into 1.852 minutes, and the difference between one minute is about kilometers.

This is also the length of a nautical mile in later times, and the distance a ship travels in one knot.

Zhu Youjian put forward this number and used the knot as the standard for measuring the speed of Ming ships. This number was also used to estimate length and area on various nautical charts and longitude and latitude maps.

The establishment of the Bell and Drum Tower Observatory, as well as the division of longitude and latitude and time zones, allowed the Ming Dynasty's timekeeping instruments and navigation technology to move forward steadily. (End of this chapter)