Weather has a strong effect(影响) on people. It influences health, intelligence (智力) and feelings. In August, it is very hot and wet in the southern part of the United States. People there easily have heart trouble and other kinds of health problems during this month. In the Northeast and the Middle West, it is hot at some times and very cold at other times. People in those states will have heart trouble after the weather changes in February or March.
      The weather can also influence intelligence. For example, in a 1983 study by scientists, the IQ scores of some college students were very high during storm, but after the storm, their scores were low. Storms can increase intelligence. Very hot weather, on the other hand, can decrease(减少) it. Students in many schools of the United States often do badly in exams in the hot months of the year(July and August).
      Weather also has a strong effect on people's feeling. Winter may be a bad time for thin people. They usually feel cold during these months. They might feel depressed during cold weather. In hot summer weather, on the other hand, fat people may feel unhappy. At about 65F, people become stronger.
      Low air pressure(气压) makes people feel free, but it also increases forgetful- ness. People leave more bags and umbrellas on buses and in stores on low pressure days. There is a“perfect weather”for work and health. People feel best at a tempera- ture of about 64F with 65 percent humidity(湿度).
      Are you feeling sick, sad, tired, forgetful, or very intelligent today? The weather may be the reason.

    Why don't birds get lost on their long flights (飞行) from one place to another? Scientists have studied this puzzle for a long time. Now they're starting to fill in the blanks(空白).

    Not long ago, experiments showed that birds use the sun to guide them during daylight hours. How do birds fly at night? Tests with artificial stars, which are made by people, have proved that certain night-flying birds are able to follow the stars in their long-distance flights.

    They found a bird that spent its lifetime in a cage and never flew under a natural sky. But it was born with the ability to use the stars to look for the direction. This bird's cage was placed under the sky filled with artificial stars. Any change in the position of the artificial stars caused a change in the direction of the bird's flight. From the experiment, they found that the bird tried to fly in the same direction as those artificial stars moving under the natural sky.

    But the stars are of course birds' main ways of navigation (航行), when the stars are hidden by clouds, they can still find their way by such landmarks (路标) as river courses, mountain ranges (山脉), coast lines and so on. Because of this ability, people use the dove (鸽子) to send messages in some fields. For example, the doves were used to send messages in both World War I and World War II. During that time, thousands of doves were used to carry important messages in order to save the lives of many thousands of people. So it is also the symbol of peace.

    But when it's too dark to see these things, the doves are not able to find their way. They only circle helplessly and get lost.

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    Do you know the whales in the sea? There are many relatives(亲属) in the whale family and they always live together with whales.

    Few people know dolphins(海豚) are part of the whale family. Dolphins are not fish. They are mammals(哺乳动物). They breathe air, and they have babies and feed them with milk. Dolphins are famous for their wonderful shows. They can jump high out of the water and show turns in the air. These jumps give the dolphins time to breathe.

    Porpoises(鼠海豚) are also in the whale family and are quite like dolphins. But they are different in the size and shape of the mouth. The dolphin's mouth is long and thin, but the porpoise's is short and thick. Dolphins are also more talkative than porpoises. Dolphins make sounds to talk with each other under water. But porpoises do not do this. Both of them are smart and friendly to humans.

    Not all the members of the whale family are friendly. Big whales are much easier to be angry than smaller dolphins or porpoises. An angry whale can be dangerous. Perhaps this helped to create the story of Moby Dick that sank (使下沉) a ship and made all the people on it die in the sea.

    On July 20, 1969, Neil Armstrong became the first person to walk on the moon. The space suit Armstrong wore on his lunar mission has come to symbolize courage and human achievement. In 1971, the Smithsonian's National Air and Space Museum(NASM), in Washington, D.C., acquired (获得) Armstrong's suit. It stood proudly on display for visitors to admire, until there were changes in the suit's appearance. "Over time, the suit started to show signs of deterioration," Lisa Young said. Young is an objects conservator (文物修复员) at NASM. It is her job to preserve(维护)historical and cultural objects.

    "Plastics are tricky to conserve," Young says. They tend to degrade (降解)over time. Neoprene is one type of plastic in Armstrong's suit. The material can turn brittle and break into tiny pieces. This would ruin the space suit. NASM, seeking ways to preserve this historical treasure, removed it from display in 2006.

    What causes plastic to degrade in the first place? "Many things," Odile Madden says. Madden is a scientist in California. She explains that sunlight, water, humidity, and dust can cause plastics to degrade. "Some plastics will break down no matter what we do," Madden says.

    Yet history can still be saved. Scientists have found that storing plastics in cooler temperatures, with lower humidity levels, can slow degradation. Young says Armstrong's suit is currently in storage at a temperature of 63°F and a lower relative humidity of 30%. These conditions will be maintained when Armstrong's suit returns to a museum display case in time for the 50^th anniversary of the moon landing.

    Plastic degradation affects art, too. Artist Claes Oldenburg created False Food Selection in 1966.It consists of plastic food displayed in a wooden box. The plastic food used to look real. Now, some of it has flattened and yellowed. Georgina Rayner is a conservation scientist at Harvard Art Museums, in Cambridge. She says the artwork's wooden box produces an acidic (酸的) gas that eats away at the plastic. This speeds up the degradation process. But Rayner is motivated to conserve this artwork and others like it. "Plastics are a part of our history," she says. "It's important to preserve them so that future generations can understand the journey we've taken."