Getting rid of dirt, in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt.

    In the early 16th century, people thought that dirt on the skin was a way to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let illnesses in. A particular danger was thought to lie in public baths. By 1538, the French king had closed the bath houses in his kingdom. So did the king of England in 1546. Thus it began a long time when the rich and the poor in Europe lived with dirt in a friendly way. Henry IV, King of France, was famously dirty. Upon learning that a nobleman had taken bath, the king ordered that, to avoid the attack of disease, the nobleman should not go out.

    Though the belief in the merit of dirt was long-lived, dirt has no longer been regarded as a nice neighbor ever since the 18th century. Scientifically speaking, cleaning away dirt is good to health. Clean water supply and hand washing are practical means of preventing disease. Yet, it seems that standards of cleanliness have moved beyond science since World War Ⅱ. Advertisements repeatedly sell the idea: clothes need to be whiter than white, cloths ever softer, surfaces to shine. Has the hate for dirt, however, gone too far?

    Attitudes to dirt still differ hugely nowadays. Many first-time parents nervously try to warn their children of touching dirt, which might be responsible for the spread of disease. On the contrary, Mary Ruebush, an American immunologist(免疫学家), encourages children to play in the dirt to build up a strong immune system. And the latter position is gaining some ground.

    Cold weather during winter months may keep many people from leaving home and running in the open air.

    However, a new study shows that the drop in temperature is a good reason to run. In fact, researchers say, running in cold weather helps improve one's performance.

    Many people say running in the winter can be difficult. Two reasons are the low temperatures and bitter winds. Yet many runners might find it easier than running in hot weather.

    That could be because lower temperatures reduce stress on the body. When you run in cold weather, your heart rate and the body's dehydration (脱水) levels are lower than in warmer conditions. The body needs less water on a cold day than in warm weather.

    This information comes from sports scientists at St. Mary's University in London. John Brewer is a professor of applied sport science at St. Mary's.

    For this study, he and other researchers put a group of people into a room they called an “environmental chamber.” The researchers then recreated summer and winter weather conditions in the room. The test subjects were asked to run 10,000 meters under both conditions. Brewer says he and his team recorded biological measurements of the runners.

    “We've got a group of subjects into the environmental chamber, we've changed the conditions to replicate the summer or winter and we've got them to run a 10km under both of those conditions and taken various measurements on each runner while they've been completing their 10km.”

    Brewer says every movement runners make produces heat. He explains that one way in which we lose heat is by sweating. The body loses heat through droplets of sweat. He says the body also loses heat by transporting the blood to the surface of the skin.

    I was reading these interesting stories behind a group of great logos in the world. Personally Nike is my favorite one—it's so simple. And I like the stories behind them, which made me forget all other things. McDonald's, Apple, Mercedes Benz and Adidas own great logos as well, and they are among my favorites.

    Nike

    In the Greek myth, Nike is the goddess of victory and the source of inspiration for soldiers. This logo represents the wing in the famous statue of the Greek goddess. Nike's logo was designed by Carolyn Davidson in 1971 for $35, and was registered as a trademark in 1995.

    McDonald's

    The logo was designed in 1962 by Jim Schindler to resemble the arch-shaped(拱形的) signs on the side of the company's then walk-up hamburger stand. Later on, the two golden arches were combined together to form the M. The McDonald's name was added to the logo in 1968.

    Apple

    There are different stories behind Apple's logo. The first logo was a reference to the religious story of Adam and Eve, in which the apple represented the fruit of the Tree of Knowledge. One year later, the second logo was designed in 1977 by Steve Jobs and Ronald Wayne, and it described Sir Isaac Newton sitting under an apple tree. This logo didn't stay long. One year later it was replaced almost immediately by graphic designer Rob Janoff's "rainbow apple", a rainbow-colored silhouette(轮廓) of an apple with a bite taken out of it. And then the rainbow-colored apple was replaced by the one-colored logo in 1998. It has not been changed so far.

    Mercedes Benz

    The Mercedes Benz logo, which was originally created by Gottlieb Daimler in 1909, consists of a simple description of a three-pointed star that represents its rule of the land, the sea and the air. The company was founded by Gottlieb Daimler and Wilhelm Maybach. Mercedes is the name of Maybach's elder daughter, while Benz came as a result of a combination with Benz, Cie and DMG in 1926.

    Adidas

    The Adidas logo, which was created by the founder of the company Adi Dassler, represents mountains, pointing towards the challenges that are seen ahead and goals that can be achieved. The logo was used for the first time in 1967.

    Throughout much of human history, man has been the measure of many, if not all, things. Lengths were divided up into feet and smaller units from the human hand. Other measures were equally characteristic. Mediterranean traders for centuries used the weight of grains of wheat to define (定义) their units of mass. The Romans used libra, forerunner of the pound, by referring to the weight of a carob (角豆树) seed.

    The sizes of similarly named units could also differ. The king's foot, used in France for nearly 1, 000 years after its introduction by Charlemagne in around 790 AD, was, at 32.5cm, around a centimeter shorter than the Belgic foot, used in England until 1300.Greek, Egyptian and Babylonian versions of water in a fixed container varied from one another by a few kilos, Nor was there agreement on such things within countries. In France, where there was no unified (统一的) measurement system at the national level, the situation was particularly terrible. The lieue (former measure of distance), for example, varied from just over 3 km in the north to nearly 6 km in the south.

    Although John Wilkins, an Englishman, first put forward a decimal system (十进制) of measurement in 1668, it was the French who in 1799 made it law. The Système International d'Unités (SI, or the metric system, as it is better known) developed from it and became the official measurement in all countries except Myanmar, Liberia and the United States. Now the International Bureau of Weights and Measures in Paris is set to give the metric system its biggest shake-up yet.

    At a meeting in Versailles, France, on November 16th, 2018, the world's measurement bodies are almost certain to approve a decision that will mean four out of the seven base SI units, including the kilogram, will follow the other three, including the metre, in being redefined in terms of the values of physical constants (物理常数).Each of the chosen constants has been measured incredibly precisely, which would mean that from May 20^th 2019 the constants will themselves be fixed at their current values for ever. Any laboratory in the world will then be able to measure, for example, the mass of an object as precisely as the accuracy of their equipment will allow.