Until late in the 20th century, most Americans spent time with people of generations. Now mid-aged Americans may not keep in touch with old people until they are old themselves. That's because we group people by age. We put our three-year-olds together in day-care center, our 13-year-olds in school and sports activities, and our 80-year-olds in senior-citizen homes. Why?

    We live away from the old for many reasons: young people sometimes avoid the old to get rid of fears for aging and dying. It is much harder to watch someone we love disappear before our eyes. Sometimes it's so hard that we stay away from the people who need us most.

    Fortunately, some of us have found our way to the old. And we have discovered that they often save the young.

    A reporter moved her family onto a block filled with old people. At first her children were disappointed. But the reporter baked banana bread for the neighbors and had her children deliver it and visit them. Soon the children had many new friends, with whom they shared food, stories and projects. “My children have never been less lonely,” the reporter said.

    The young, in turn, save the old. Once I was in a rest home when a visitor showed up with a baby. She was immediately surrounded. People who hadn't gotten out of bed in a week suddenly were ringing for a wheelchair. Even those who had seemed asleep wake up to watch the child. Babies have an astonishing power to comfort and cure.

    Grandparents are a special case. They give grandchildren a feeling of security and continuity. As my husband put it, “my grandparents gave me a deep sense that things would turn out right in the end.”

    Grandchildren speak of attention they don't get from worried parents. “My parents were always telling me to hurry up, and my grandparents told me to slow down,” one friend said. A teacher told me she can tell which pupils have relationships with grandparents: they are quieter, calmer, more trusting.

    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.

    Austin Perine, a four-year-old boy, discovered that sympathy for the less fortunate can produce superhuman results.

    Once Austin's father, TJAustin, took Austin to the Firehouse Ministries, a local shelter that provides housing, food, and other services for homeless men. As they drove by the redbrick building, they saw a group of 25 homeless men standing on the street corner. "Dad, they look sad," Austin said. "Can we take them some food and make them smile?"

    That day, Austin used his allowance to buy each man a Burger King sandwich and handed the food out himself.

    Seeing what their presence meant to the men at the ministry, Austin and TJ returned the next week. After he returned every week for five weeks, word of Austin's acts of kindness spread through social media and national news outlets. Burger King jumped aboard, agreeing to donate $1,000 a month for an entire year toward the cause. Soon, churches and shelters across the country began inviting Austin to come and distribute food in other poor areas. Whereas before Austin and TJ could feed 25 to 50 people at a time, now, thanks to corporate and community support, they can feed 800 to 2,000 people at once.

    But Austin isn't just filling bellies. He's improving the lives of those he meets. On that first trip to Firehouse Ministries, TJ and Austin talked to a man named Raymont. The respect Austin gave 41-year-old Raymont touched the man. TJ helped Raymont collect all the credentials(资格) he needed to get a driver's license. The license helped Raymont get a job. And with money in the bank, he was able to rent his own apartment. All that was made possible because a little boy took the time to care.

Diving in the ocean, marine biologist Erika Woolsey has seen how coral reefs (珊瑚礁) are being damaged by climate change. It has made her decide to find a way to share her experience —including those who can't easily explore the ocean.

Through her non-profit, The Hydrous, Woolsey is using virtual reality to bring the ocean to everyone. Scientists, filmmakers and divers are taking people on immersive (沉浸式的) virtual dives, attracting attention to reef damage and expecting action to protect our sea. About 25% of marine species depend on coral reefs. However, climate change, pollution and overfishing have done harm to around half the world's shallow water coral reefs.

Twenty years of underwater exploration has given Woolsey a detailed understanding of the dangerous situations facing reefs. "I've seen this first-hand shift. Healthy colourful coral reefs become what look like the moonscape step by step," Woolsey says.

It is through this experience that The Hydrous team set out to recreate with their award-winning film Immerse. Intended to watch with a VR headset, viewers join Woolsey for a nine-minute guided virtual div e on the coral reefs, immersed in a 360-degree underwater view.

They swim alongside sea turtles and sharks before witnessing the worsening of the reefs. The experience often brings out strong feelings. "As soon as people take off that headset and look me in the eye, they want to tell me a story about their ocean experience," Woolsey says. "It's that human connection to our ocean that will solve our ocean problems."

Woolsey hopes advances in camera technology will allow her team to take more and more people to places in the ocean that are underexplored and places further away from human civilization. They are developing a virtual experience that will put the people in the role of a marine biologist, carrying out biodiversity surveys underwater, and even transporting the viewers to space to monitor global sea surface temperatures.

Plan your vacation. The following four places are your fantastic destinations. You can enjoy a completely different experience.

Israel

If you're looking for a once-in-a-lifetime experience, National Geographic 'Travel says visitors should head to Jerusalem to celebrate Easter with thousands of pilgrims (朝圣者). If the crowds get too huge, visitors are told to take a boat ride to King Herod's 2,000-year-old Masada fortress (要塞) or set off on a peaceful morning boat ride across the sea of Galilee.

Panama

Costa Rica and the Caribbean often enjoy much more popularity than Panama, but visitors should consider the centre American country if they want a "less-crowded paradise". The travel site states, "Here, horses are still the primary means of transportation and local fishermen serve fresh seafood and fruit from their home kitchens for roughly $ 6 a plate."

Svalbard

If you're a fan of winter activities, but are in need of some sun, then perhaps a trip to Svalbard is a good choice. National Geographic Travel notes, "The Norwegian archipelago of Svalbard is located about 620 miles south of the North Pole. In late spring, the sun never falls below the horizon—meaning you can take in all the Vitamin D you desire." Popular activities in the area include hiking and wildlife spotting.

Namibia

During spring, Namibia is regarded as the perfect destination with reduced travel costs on cooler evenings. In late May, National Geographic Travel says that the watering holes start to dry up again, which attracts giraffes and black rhino from their hiding spots. If you're fond of adventurous exploration, head to the Namibia Desert for a spot of sand boarding.

World Book Day, also known as World Book and Copyright Day, is an annual event organized by the UNESCO to promote reading, publishing and copyright. The first World Book Day was celebrated in Spain on April 23 in 1995. Let's take a look at the world's fascinating libraries and enjoy the fun of reading.

Royal Portuguese Cabinet of Reading

Located in the center of Rio de Janeiro, Brazil, the Royal Portuguese Cabinet of Reading is a library and cultural institution. It was built in the late 19th century under the stewardship of an association of Portuguese migrants. Open to the public since 1900, the cabinet has the largest collection of Portuguese literature outside Portugal, holding more than 350,000 books.

Stuttgart City Library

Stuttgart City Library is a cube outside with a hollow design inside. The hollow part is connected with misplaced stairs to create a unique sense of space. Since its completion in 2011, it has become a local cultural card and a "instagrammable" place for many tourists in Germany .

Wormhole Library

Located in Haikou, South China's Hainan province, the symbolic and artistic Wormhole Library, completed in 2021, provides the public with an ideal spot for reading and resting. It has a reading space that can hold around 10,000 books and has a multifunctional audio-visual area, as well as leisure areas such as cafes, baby care rooms, a common room and a rooftop garden.