With the progress of the battles of Fujian and Jiaozhi, the Tang Naval Division began to sail out of the inland river and towards the ocean, and began to change from the inland water division to the naval direction facing the deep blue sea in later generations.

But when a steamship or sailing ship is far from the shoreline, it loses its reference on land and cannot know its location.

The globe has been made a long time ago, and it turns out that the students need to know from the geography textbook that the statement of "the sky is round and the place is round" is wrong, and the seemingly flat earth turned out to be a huge sphere. By now, with the beginning of vigorously promoting education, many teenagers who are studying in their hometowns already know that the earth is round, and that the earth revolves around the sun, not that the sun revolves around the earth.

The earth is spherical and heliocentric was proposed by some astrologers as early as the Spring and Autumn Period. It's just that later, under the control of Confucianism, astrology became a royal patent, and the astronomical theories and knowledge that had been born in China were buried and destroyed, and completely reduced to a tool for maintaining imperial rule.

Geography and astronomy are another window into the worldview. A person's worldview is formed by several important aspects of national culture, history, national geography, and astrophysics. Culture is inheritance, history will make a person know the rise and fall, know the honor and disgrace, and become more noble in morality, while national geography will strengthen the concept of nationality and the country, and astrophysics will make people learn to look at life from a macro perspective.

Later generations of "educators" are vigorously advocating and forcing their own nation to go all out to learn the languages of other countries, and are trying their best to dilute national history and national geography education.

The monopoly and ban on "astrology" made the preliminary astronomical knowledge formed in China in the Spring and Autumn Period and the Warring States Period buried and died, and it became a kind of fortune-telling science.

Merchant ships and fishermen who sailed to sea have always used the ancient "astronomical technique" to determine their position at sea, and ancient navigators used this method to sail from the Arabian Sea to China, where "stargazing" was taboo for the royal family, but it limited the development of navigation technology. As for the current Europe, it is still a large area of barbarian entrenchment. Although this method of relying on the observation of the positions of the stars is highly inaccurate and relies heavily on the experience of navigators, it is quite effective.

The invention of the sextant has nothing to do with the navy, but the invention of the teachers and students of the Astronomical Academy.

Li Qi imposed the "Republic Calendar" according to his own memory, stipulating that there were 365 days in a year, and one more day was needed every four years, which was widely verified by later generations. But the faculty and students of the School of Astronomy need to validate this data. In order to accurately mark one's measurement position in national surveying, one needs an instrument that can determine latitude by measuring the angle between the horizon and the sun at noon, or by measuring the angle between the horizon and a fixed star.

Originally, teachers and students used ancient astrolabes to measure the height of the sun, but sometimes when measuring on ships, the deck of the ship undulated with the waves, which made it difficult to operate and not easy to measure accurately. Later, people replaced the astrolabe with a goniometer, and used a rectangular meter and a two-legged gauge, a protractor, and a parallel ruler to calculate the location on the map.

Later, after a lot of improved experiments, teachers and students used a reflecting telescope combined with a level mirror and a quadrant to invent an instrument for measuring angles at sea. The horizon can be seen simultaneously by an observer in a mirror, and the angle between them can be measured with a quadrant with a scale on the edge, up to 90°, making it an ideal instrument for measuring latitude. Another advantage of the instrument is that it allows the image of the star object to be in line with the horizon and the measured readings are more accurate.

However, the goniometer developed by the Astronomical Institute uses a complete astrolabe, and its measurement range can reach 360°, although the measurement effect is very good, but it is very cumbersome, and it is extremely inconvenient to use on the survey ship going to sea. So someone took a third of the astrolabe, and although the measurement range was limited to only 120°, it made it extremely light and easy to use.

This is the original sextant, and it is based on a simple principle: the angle of reflection of the light is equal to the angle of incidence. In fact, a sextant can also measure the angle between any two objects.

The sextant consists of a triangular shelf, on one side of which is a 120° curved plate with a scale and a movable pointer. The reflection telescope reflects the two objects with angles to be measured, so that people can easily measure the angle and calculate the current latitude. The accuracy of the sextant is greatly improved compared with the previous latitude measurement astrolabe, Kalmar and right-angle quadrant.

The advent of the sextant has greatly improved the accuracy of the crew's determination of their position when sailing to the open ocean, which also provides an extremely reliable measuring instrument for ocean navigation and measurement.

……

In the imperial study room of Zihua Pavilion at the back of the Gongchen Hall of Jinyang Palace, in the cool breeze of the early spring night, lanterns were lit up in the corridor outside the small building one after another.

"This sailor still can't go out to sea, and it's much worse than the big cannibal in terms of navigation."

In the study with the lights on, Li Qi, who was reviewing the folds, gently put down the red pen and said after sighing.

Queen Wang Qiang, who was pregnant with the top three, took a cup of tea and put it on the side of the imperial case, and couldn't help but smile when she saw Li Qi's expression, "What's the matter, what's the trouble over there?" ”

Li Qi shook his head: "No, Yuan Ren and Fu Yanrao are both battlefield generals, plus Li Jizhong and He Fujin are in charge of logistics supply behind them, what can be wrong?" It's just that...... Xia Chengting's fleet encountered a storm and lost several ships. As he spoke, he simply took out his unfinished map of the Western Pacific from his drawer and spread it out to look at it.

He is ready to turn the entire Pacific Ocean into the inland sea of the Tang Dynasty.

They have been together for so many years, Li Qi will still reveal and explain some things to the queen, and they are already very familiar with each other's every move, and they are just thirty years old, and they have the feeling of an old husband and wife.

"What are you drawing?" Wang Qiang stood behind Li Xian, gently massaged his shoulders and neck and said.

"This is the sea in the south, don't you like to eat fish, these shark fins, sea cucumbers, abalone, lobsters are all produced in the sea. There are also whales in this sea......"

"Dozens of feet? Is this whale meat delicious? Wang Qiang poked his head over and looked at Li Qi's huge chart that had not yet been completed.

Li Qi: "??? ”

Why do you want to eat? However, he really hasn't tasted this whale meat yet......

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