This dye is very adhesive and water-resistant, so it won't bloom after painting as long as it doesn't get too wet, and it is difficult to wash off when it dries. Whale skin is the innermost thin skin, with few lines and a smooth surface, so it is suitable for use as paper. Hong Tao drew a lot of horizontal and vertical lines on the whale skin of Carl and Bojiao, like a Go board. However, unlike the Go board, these horizontal and vertical lines are not horizontal and vertical, except for two lines in the middle, one horizontal and one vertical, which are straight, the other lines have a certain arc.

"My lord, what is this?" If you are a modern person, you can see at a glance that this line is the latitude and longitude of the earth, but Carl and Po Jiao really can't understand it.

"This is a kind of nautical coordinates that I invented, the horizontal one is called latitude, and the vertical one is called longitude. As long as these lines are measured accurately, the world's oceans will be our backyard, and we will never get lost again. Don't ask why, just listen to every word I say to you and do what I say. Remember, this is my top secret, it's best not to talk to anyone, including your own parents, if you can't do it, tell me in advance, I'll keep you away from this job, is there a problem? "Hong Tao is very shameless to turn the latitude and longitude into his invention, in fact, it is more convenient to do this, no need to explain the calculation formula of latitude and longitude to others, that thing can't be understood in a day, the knowledge involved is too wide, and people in this era have no possibility to understand.

"This is a map of the sea?" Although Carl was not a regular navy, he had also commanded the fleet of the Holy Roman Empire, and as soon as Hong Tao said that, he probably understood, and he must have immediately remembered the matter of going home, and his expression was very excited.

"So to speak, but at the moment this map is still blank and imperfect, and it will take me a few years to fix it, would you like to do this with me?" Hong Tao felt that he was very dirty, and every time he used the matter of Carl coming home to threaten him.

"With great gratitude, I swear to the Lord that I will never reveal anything about the map to anyone without your permission." If Hong Tao told Carl that he could take him home, he was a little skeptical, but now Carl basically believes it. A person who can draw a map of the sea is a distinguished guest of the king wherever he is placed, and even if he can draw a drawing of the empire, he is also a distinguished guest.

"Uncle, I won't say it either!" Bo Jiao didn't know what Carl was talking to Hong Tao, but when he saw that he was kneeling, he also knew the seriousness of the matter, so he simply bent his legs and knelt down.

"In the future, don't call your uncle on the ship, call the captain. See? This is called an hourglass, and all the sand on it leaks down to the bottom, for an hour and a half, and every time it is turned over, it is necessary to carve a piece on the wooden board of its base, and whoever turns it over must carve it, and we must not forget but not more, otherwise we may never be able to go home. After clarifying the problem of warp and weft, Hong Tao pointed to the two large hourglasses fixed with wooden boxes on the bulkhead, and continued to tell Carl and Bojiao.

These two hourglasses are made of silver tire inlaid with crystal flakes, the appearance is very exquisite, and Hong Tao spent more than 20 expensive manual fees to let the goldsmith make it. The sand in it is all fine sand with similar particles that have been cleaned many times and used several different baskets, and I have specially gone to Zhenzhou City Bosi to proofread the drip timer there, which is quite accurate. Anyway, Hong Tao can't think of any better way to keep time, the drip of the Great Song Dynasty is very large, can't be bumpy, and is also affected by temperature, can't be carried, and can't be used on ships at all.

“…… Hmm......" Carl and Bo Jiao understood this time, and immediately turned their eyes to the two hourglasses fixed with wooden boxes, and looked at them with good eyes.

The place where Hong Tao is going this time is Hong Kong Island, and he has to roughly find the place of the Central Pier in his last life. The intersection of the horizontal and vertical latitude and longitude lines on the whale skin is the Central Pier. Why do you have to find the Central Pier and fix the latitude and longitude reference in that place? The reason is very simple, because Hong Tao remembers the specific coordinates of several ports in his mind, most of which are in North America and Europe, and the two most familiar places in Asia are Hong Kong's Central Pier and Qingdao Mak Island. This has a lot to do with the fact that he drove a sailboat and a private jet in his previous life, and the GPS navigation equipment on the sailboat and the plane is displayed with coordinate numbers, just like driving a long time with navigation, and he will naturally remember a few places he frequents.

With these two coordinates, Hong Tao can rely on them to draw a preliminary map of the latitude and longitude of the world, because their numbers are absolutely accurate, and with two points, and knowing the specific coordinates of the two points, it is not too easy to extend the other latitude and longitude lines. Now that we have an accurate baseline, then this is the zero point, Greenwich and the meridian line are aside, and the longitude and latitude lines on the map will be called the Hong's line and the Po's line in the future. I guess no one will have an opinion, if you have an opinion, keep it, don't use it if you have the ability.

If you have accurate latitude and longitude lines, why do you have to measure them yourself? Could it be that Hong Tao still has to use these rudimentary instruments in his hands to verify the authority of satellite laser positioning? No, Hong Tao is not so good, on the contrary, he wants to use accurate warp and weft lines to verify the accuracy of these equipment in his hand, so as to correct them more accurately, and by the way, draw a small part of the chart he wants to make.

With these grids on the charts, he could use a sextant to read the latitude, the stars to compare the longitude coordinates, and the available latitude and longitude to draw a basically accurate map of the coastline and islands. Every time he went to sea in the future, he would measure some data and come back, and constantly add it to this chart. When they grow up and have their own boats, they will bring back their measurements and charts from all over the world. As soon as several aspects are compared and synthesized, the general map in Hong Tao's hand will continue to be enriched, and sooner or later it will become a world chart.

With this chart, you don't even need to ask for all of them, just a few parts of them, and Hong Tao can dominate the world's oceans. Sextants, hourglasses, and charts are the nautical weapons in his hands, and if he can get an ocean-going sailing ship with qualified seaworthiness, Hong Tao really can't think of anyone else who can compete with him on the sea. As long as you want, you can rely on these three sharp weapons to make enough wealth from any country, and then build enough warships and recruit enough sailors to blockade, invade, and destroy any country that is close to the sea.

And this chart is not afraid of someone stealing it, without a sextant and an accurate hourglass, you can't measure the exact latitude and longitude, with this map is also in vain, you have to walk around the shore, dare to go to the sea is a word, death! Even if they steal all the charts, sextants, and hourglasses, and know how to use them, they still don't have their own heads. Were there any people on the earth in the 13th century who could use trigonometric functions for accurate calculations?

Not to mention the ancient Greek mathematicians and the ancient Indian mathematicians, they just came up with a concept and a vague way of calculating, and the precise calculation formula is still not clear to them. Besides, if they don't figure out the theory that the earth is an oblate sphere, these latitude and longitude lines on the map will be a big trap for them. Because the spherical surface is drawn into a plane, whether it is a map or a nautical chart, it is a projection value, and there is a big error between it and the reality. If you don't understand this, you will sail exactly according to the latitude and longitude on the chart, and you will die a miserable death.

Hong Tao didn't intend to keep this secret by himself forever, he would set up a school to teach this knowledge when he had the ability to control his own destiny, and then let this knowledge spread naturally. And before that, he will make a windfall, that is, the large-scale sale of charts to other countries, who wants charts of a certain route, OK, give it to you, but in exchange for money. You can't use it again, you have to hire students from my school to help you measure, which helps students find decent jobs.

When this kind of technology spreads and I have no technical advantage, it is estimated that I am almost too old to get up, and the things that should be done are basically done, and the things that cannot be done will still not be able to be done for another hundred years. At that time, it is likely that newer and more accurate technologies and equipment will be researched, and even if you have completed your mission, you should close your eyes quickly, and you will be a thief if you are old and not dead!

In fact, even with nautical charts, sextants, compasses, hourglasses, and other equipment, ocean navigation is still a very dangerous thing, and longitude is easy to measure but difficult to measure accurately. In order to obtain a relatively accurate longitude, it is necessary to have a marine clock, which is a clock that can resist changes in temperature and humidity, and is not afraid of turbulent wind and waves, and can also have a small error. It's like an accurate hourglass, which can faithfully record the trajectory of time, and with this trajectory as a standard, longitude is very easy to do. Theoretically speaking, longitude is the time difference, you only need to measure the time difference between your current position and the starting position, and use the formula to convert, which is the basically accurate longitude value.

It's a pity that Hong Tao really can't make a navigation clock, let alone a navigation clock, even the oldest kind of pendulum table clock. The boring profession of the watchmaker is not in his hobby, and he can only know the structure of the clock, not to the extent that it can be reproduced.

There are no marine clocks, and longitude can be determined by looking at the position of the moon and constellations, and a sextant can do this, but it requires something called a lunar distance meter. It is a table of correspondence between the trajectory of a moon and several fixed constellations that astronomers from ancient countries relied on observing celestial phenomena for many years. Hong Tao has seen and used this thing, but that watch was summed up by astronomers in later generations, and it definitely doesn't exist now. Therefore, if you want to measure longitude with the lunar distance method, it is useless for anyone except yourself. In other words, he is the only one of his kind who can measure relatively accurate longitude in this era.

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