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Early the next morning, Zhu Youzhen first came to a thick coconut tree and laboriously carved something with a dagger. Pen × fun × Pavilion www. ｂｉｑｕｇｅ。 info Li Zhenyan leaned over to take a look, and saw that Zhu Youzhen was just drawing a horizontal path of different lengths on it, and couldn't help but wonder: "Your Highness, what are you doing here?" ”

Zhu Youzhen said with a smile: "The ancients knotted ropes to remember, but now we don't even have ropes, so we can only carve a way on the tree to keep time." You see, the bottom one is the day we killed the old slave, that is, the eleventh day of August in the fourth year of the Apocalypse. And then every day that passed, I carved one more on it. We drifted on the sea for four days, and we arrived on the island on the fifteenth of August; Another ten days have passed on the island, and today is the 25th of August. So I carved fifteen sermons. ”

Li Zhenyan smiled bitterly when she heard this: "But even if we know the date now, what's the use?" I can only remind myself that the number of days I have been wandering here is increasing, and it is only adding to my troubles. ”

Zhu Youzhen shook his head and smiled: "You don't understand, this is very useful!" In the future, remind me that you have to engrave one every day. ”

After finishing this matter, Zhu Youzhen selected a long and straight one from the pile of wood, cut off the branches with a dagger, and then chose an open place and inserted this wooden stick vertically down into the soil. It was still early in the morning, and in the light of the rising sun, the sticks cast a long shadow to the west.

Li Zhenyan didn't know what she meant, and Zhu Youzhen didn't explain much, so she only let Li Zhenyan still go to the spearfish, but she didn't go up the mountain to cut wood, but stayed near this wooden stick, grinding a relatively flat stone into the shape of an axe, while paying attention to the rotation of the shadow.

Time passed quickly in hard labor, and in the blink of an eye it was close to noon. Zhu Youzhen hurriedly called Li Zhenyan back and asked her to stare intently at the gradually shortening black shadow on the ground with him.

"What's there to see about this?" Li Zhenyan couldn't help but laugh.

"Seriously, do you want to leave this island?" Zhu Youzhen reprimanded Li Zhenyan with a stiff face, and then stared at the shadow with a focused expression. Li Zhenyan was so frightened that she stuck out her tongue, but she really couldn't think of anything to do with whether this shadow could leave the island or not, so she had to patiently observe with Zhu Youzhen.

As the sun gradually rises into the middle of the sky, the dark shadows on the ground become shorter and shorter. At the moment when the shadow shrank to the shortest and was about to become longer, Zhu Youzhen jumped over with an arrow step, drew a line on the ground with a stone, noted the length of the black shadow, and then drew a straight line along the direction of the black shadow, and shouted excitedly: "Zhenyan, look, this black shadow is now in the opposite direction, which is due south!" ”

Li Zhenyan said unconsciously: "Of course, the direction of the sun at noon is due south, what is so strange about this." ”

Zhu Youzhen put his hands behind his back, shyly shook his head, and said, "Non-yes, non-yes!" Only the noon sun in the northern hemisphere is due south, but the sun in the southern hemisphere is due north! ”

"What?" Li Zhenyan's eyes widened in surprise and said, "What northern hemisphere, southern hemisphere?" Could it be that the sun can still come out of the north? ”

Zhu Youzhen now had the opportunity to show off, and taught Li Zhenyan a lesson like a primary school student: "The ancients said 'the sky is round and the land is round', and the husband tells you that it is a mistake!" The world under our feet is a huge ball called the Earth. The Earth rotates from west to east around the Earth's axis, so we see the sun rising in the east and setting in the west. At the same time, the earth revolves around the sun diagonally, so there are four seasons. ”

Seeing that Li Zhenyan was confused, Zhu Youzhen knew that it was difficult for her to accept this geographical knowledge that was just common sense in her previous life, so she had to say concisely: "What about this principle, I will explain it to you slowly for my husband." Now you go and measure the length of the stick, and the length of the shortest part of the shadow that your husband just drawn. ”

Li Zhenyan glanced at him suspiciously, although she did what she said, Zhu Youzhen could see that she didn't believe what she said at all.

In fact, it is no wonder that the ancients, due to their lack of scientific knowledge and difficulty in explaining various complex natural phenomena, conjured up many myths or hypotheses so that these phenomena could be "self-justifying", and "the sky is round and the place is round" is one of them. Now that Zhu Youzhen has come to a complete subversion, of course Li Zhenyan refuses to believe it.

This is still good, like the Italian scientist Bruno who was burned at the stake by the Holy See for preaching heliocentrism. It can be seen how difficult it is to pursue the truth in this era, and sometimes even pay the price of life!

When she was sighing, Li Zhenyan had already finished measuring and said to Zhu Youzhen: "The length of the wooden stick is four feet one inch and five minutes, and the length of the shadow is seven inches and three minutes. ”

"How do you measure so accurately? You don't have a ruler! This time it was Zhu Youzhen's turn to be surprised.

Li Zhenyan smiled slightly: "People know that the length of their palms is seven inches and three points, so you can measure them a few times more than your palms." ”

Zhu Youzhen was stunned when he heard this, but he didn't expect Li Zhenyan to have such a good reference, and couldn't help but say admiringly: "Zhenyan really has a heart, I never thought about measuring how long my palm is!" ”

"When a woman does needlework, she has to compare it with the palm of her hand, and of course she has to know the length." Li Zhenyan sneered, "You men don't have to do needlework, what are you doing with this?" ”

Zhu Youzhen suddenly realized, so he had to smile awkwardly, and then squatted on the ground and silently calculated with a small branch. After a long time, he suddenly got up and laughed: "The latitude is known, the latitude we are at now is about 25 degrees north latitude!" ”

Li Zhenyan was even more inexplicable when she heard it. Zhu Youzhen didn't bother to explain it to her, because if he wanted to explain this problem clearly, he needed a lot of mathematical and geographical knowledge, which could not be explained in one or two sentences.

To put it simply, the vertical sticks, the shadows on the ground, and the rays of the sun, these three form a right triangle. Knowing the length of the two sides, using trigonometric functions, you can calculate the angle between sunlight and shadow, that is, the angle between the sun and the ground.

Anyone who has studied geography in high school knows that the sun will shine directly on the Tropic of Cancer on the summer solstice, that is, around June 22, that is, 23.5 degrees north latitude. Then the point of direct fire gradually moves southward, about a quarter of a latitude per day. From the Earth, the height of the sun at noon is getting lower day by day.

Therefore, knowing the angle between the sun and the ground, and then knowing the latitude of the direct point of the sun, we can calculate the latitude of the location according to the formula. The latitude of the point where the sun shines directly can be deduced according to the date. After careful calculations and then eliminating the factors of measurement error, Zhu Youzhen came to the important conclusion that the latitude where he was located was about 25 degrees north latitude.

However, just knowing the latitude is still impossible to determine the location. In order to be accurate, you must know the longitude. This is much more difficult than measuring latitude, and Zhu Youzhen had to smile bitterly at Li Zhenyan: "There's nothing to do now, let's talk about it when it's dark!" ”