신비한사전

Ships that used to travel 20,000 kilometers around the continent now cross mountains using water stairs. We delve into the lock system of the Panama Canal, which lifts a 50,000-ton ship 9 stories high using only rainwater and gravity, without a single pump.

Korean buildings would probably all collapse if an earthquake hit. In Japan, a country prone to earthquakes, five-story pagodas have withstood seismic activity for 1,400 years with few recorded collapses. The secret lies in a central pillar called 'shinbashira'. This pillar isn't actually supporting the roof or connected to any of the floors. Instead, it acts as a shock absorber, taking the brunt of the force when the floors sway and dance like snakes during an earthquake. This principle is even incorporated into the 634-meter Tokyo Skytree. Discover the secret of a pillar that protects by not supporting, in this video.

The Hoover Dam gets stronger the more water pushes against it. They laid the arch sideways so the water pressure would squeeze the cliffs. The real problem was the concrete. If poured all at once, it would take 125 years just to cool down, and it would have cracked badly. So, they poured it in blocks and installed 937 kilometers of pipes inside to circulate ice water. Thanks to this, construction finished 2 years ahead of schedule. Check out the video about putting a giant refrigerator inside a dam.

I thought it was just a city on water, but it turns out it was built on a mudflat. Venice is a city built of stone, standing on a soft mudflat. The secret was the wooden piles driven deep into the mudflat. It's common sense that wood rots when wet, right? But in the oxygen-free mudflat, the bacteria that rot wood can't survive. Instead, minerals seeped in and hardened the wood like stone. One cathedral alone used 1.1 million piles. A city floating on a forest of submerged trees, check it out in the video.

This was back in 1899, a time when cars weren't even properly running. Yet, there was actually someone who exceeded 100 km/h on a bicycle. His name was Charles Murphy, and his method was truly ingenious. He attached himself to the tail of a moving train to shield himself from the wind. The problem was that bicycles couldn't run on train tracks, so he solved it by laying wooden planks for several kilometers between the rails. On June 30, 1899, he covered 1.6 km in 57.8 seconds. And in the end, he was apparently lifted directly onto the moving train. This record was set over 100 years ago, purely by human leg power.

There was a person who measured the Earth's circumference over 2,200 years ago, before boats or airplanes even existed. His name was Eratosthenes, a scholar at the Library of Alexandria in Egypt. The story began with a rumor that shadows disappeared in a well in a city to the south. He measured the 7.2-degree angle of a stick's shadow and personally counted the steps to measure the distance between the two cities. It's still amazing to see that his calculated circumference had only about a 15% error from the actual value. The story of measuring the Earth with a single stick and two legs will be even more interesting if you watch until the end.

Two thousand years ago, the waters off Alexandria were shallow and riddled with reefs, causing ships to wreck every night. The engineers decided to raise a fire high into the sky and built a stone tower over 100 meters tall. However, the light scattered in all directions, losing its power, and during the day, it was buried by sunlight and invisible. So, they flipped the concept. Instead of intensifying the fire, they placed a large, polished bronze mirror behind the flames to focus the light and shoot it in one direction. During the day, they used this mirror to reflect sunlight and send signals, and ancient records say the light was visible from 50 kilometers away. This tower, which protected the sea with its fire at night and sunlight during the day, is the Lighthouse of Alexandria, one of the Seven Wonders of the Ancient World.

Using a copper chisel? That's a tool more expensive than iron. The outer stones of the Egyptian pyramids, 4,500 years ago, had seams just 0.5 millimeters wide, about the thickness of a razor blade. But iron didn't even exist back then. When they tried to scrape the stone with soft copper tools, the stone remained intact while the tool itself got blunted. So, the builders sprinkled sand beneath their saws. It wasn't the saw cutting the stone, but the hard grains of sand. Cutting was solved, but fitting two multi-ton stones together without any gaps was another problem. Ultimately, they flipped the concept: they placed two stones directly against each other and ground them down. As the protruding parts wore away, they naturally formed a perfect match. Finally, a slurry of gypsum acted as a lubricant, filling even the remaining tiny gaps. This is how seams as tight as a razor blade, where not even a piece of paper could fit, were created.

Over 2,000 years ago, people in the middle of the Persian desert actually made and ate ice. Initially, they'd haul ice from distant mountains, but it would melt away during the donkey ride, turning half of it into water. So, engineers decided to freeze it right there in the desert. They'd spread water in shallow pits on winter nights and block the sunlight with shaded walls. Even when the temperature wasn't below freezing, the water would freeze as heat radiated into the cloudless night sky. The challenge was storage. They dug deep pits in the ground and covered them with 18-meter-high earthen domes. This structure allowed hot air to escape through a hole at the top while cool air settled at the bottom. The walls were coated with a 2-meter-thick mixture of egg whites and goat hair to completely block heat. Thanks to this, they could buy ice from the market even in midsummer and make shaved ice desserts. This natural desert refrigerator is called a 'Yakhchal'.

In the 1960s, when South Korea decided to build a steel mill, the World Bank declared it unfeasible in a report. No country was willing to lend them money. So, they repurposed the claims fund they had already received and built a blast furnace on the sandy plains of Yeongil Bay. That factory turned a profit from its very first year and became a textbook case in the global steel industry.