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BIG ENCYCLOPEDIA FOR CHILDREN AND ADULTS
What is quicksand? Detailed answer
Directory / Big encyclopedia. Questions for quiz and self-education Did you know? What is quicksand? In many places around the globe, people have lived in fear of quicksand for centuries. They were credited with the mysterious ability to suck in the victim until there was not a trace of it left on the surface of the earth. In reality, quicksand has no such power. If you know what it is and how to behave on it, then it will not cause any harm. What is quicksand, or, as it is also called, quicksand? It is light, loose sand with a high water content. In appearance, it does not differ in any way from ordinary sand, located next to it. However, there is still a difference between them: quicksand is not a support for heavy things. Usually quicksands appear near the mouth of large rivers and on gently sloping banks. Under them is a layer of viscous, dense clay, which does not allow moisture to pass into the earth. Therefore, rain water and mostly river water accumulates in it. Unlike ordinary sand grains, which have an irregular or pointed shape, quicksand sand grains are small, round balls. The water accumulating under them dilutes the sand, and the grains of sand seem to float in it. That is why they are not able to hold heavy objects on the surface. Quicksand does not have to be sandy. Any loose soil, a mixture of sand and silt, or the same silt with small pebbles, is suitable for it. People who fall on quicksand do not drown in it at all. Since it contains a lot of moisture, they can swim in it, just like in water. In addition, quicksand is denser than water and therefore easier to stay on the surface. We must remember, however, that, once on the quicksand, you should move slowly enough. This allows the sand to flow around your body, as it does when you swim in water. In this case, you will not have reason to fear for your life. Author: Likum A.
Who took the first photo? The desire of a person to capture what he sees around him is not one century old. From the eleventh to the sixteenth century, there was a device called the camera obscura. It was the forerunner of the photographic camera. With the help of a camera obscura, the image was projected onto paper, and this image could be traced with a pencil to get an exact reproduction of it on paper. In 1802, two inventors, Wedgwood and Humphrey, took an important step forward. Using contact printing, they managed to transfer the silhouettes of drawings made on glass onto paper coated with nitrogen silver. But they didn't find a way to save these prints. In 1816, Joseph Niepce made a camera with which he managed to get a negative image. And in 1835, William Talbot managed to get a permanent image. Talbot was the first to produce a positive image from negatives, the first to develop photo printing, the first to publish a book illustrated with photographs in 1844. Since that time, inventions and improvements in this area have gone one after another. The widely known Kodak camera came on the market in 1888. This is where modern photography began. Most photographic processes are based on the fact that silver nitrite blackens when exposed to light. And this phenomenon was discovered in the XNUMXth century by alchemists who were looking for ways to turn ordinary metals into gold.
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