The full moon climbs over the eastern horizon (地平线) and hangs like a huge orange globe in the sky. A few hours later, the moon is overhead but seems to have changed. The huge orange globe has become a small silver disk. What has happened? Why has the orange color disappeared? Why does the moon seem so much smaller and farther away now that it is overhead?

    The moon appears orange on the horizon because we view it through the dust of the atmosphere. The overhead moon does not really shrink as it moves away from the horizon. Our eyes inform us that the overhead moon is farther away. But in this position the moon is actually closer to our eyes than when it is near the horizon.

    The change in size is a trick our eyes and minds play on us. When the moon is low in the sky, we can compare its size with familiar objects. It is easy to see that the moon is much larger than trees or buildings, for example. When the moon is high in the sky, however, it is hard to compare it with objects on earth. Compared to the vastness of the sky, the moon seems small.

    There is another reason why the moon seems to shrink. We are used to staring at objects straight ahead of us. When an object is difficult to see, our eyes have to try to focus on it. When we move our heads back to look up, we will try hard again. Looking at something from an unaccustomed position can fool you into believing an object is smaller or farther away than it is. However, scientists do not yet understand completely why the moon seems to shrink as it rises in the sky.

    By the mid-nineteenth century, the term “icebox” had entered the American language, but ice was still only beginning to affect the diet of ordinary citizens in the United States. The ice trade grew with the growth of cities. Ice was used in hotels, pubs, and hospitals, and by some forward-looking city dealers in fresh meat, fresh fish, and butler. After the Civil War (1861-1865), as ice was used to refrigerate freight cars(货车), it also came into household use. Even before 1880, half the ice sold in New York, Philadelphia, and Baltimore, and one-third of that sold in Boston and Chicago, went to families for their own use. This had become possible because a new household convenience, the icebox, a precursor（前身）of the modem refrigerator, had been invented.

    Making an efficient icebox was not as easy as we might now suppose. In the early nineteenth century, the knowledge of the physics of heat, which was essential to a science of refrigeration, was undeveloped. The common belief that the best icebox was one that prevented the ice from melting was of course mistaken, for it was the melting of the ice that performed the cooling. Nevertheless, early efforts to economize ice included wrapping the ice in blankets, which kept the ice from doing its job. Not until near the end of the nineteenth century did inventors achieve the delicate balance of insulation(绝缘) and circulation needed for an efficient icebox.

    But as early as 1803, an intelligent Maryland farmer, Thomas Moore, had been on the right track. He owned a farm about twenty miles outside the city of Washington, for which the village of Georgetown was the market center. When he used an icebox of his own design to transport his butter to market, he found that customers would pass up the rapidly melting butter of his competitors to pay an extra price for his butter, still fresh and hard in neat, one-pound bricks. One advantage of his icebox, Moore explained, was that fanners would no longer have to travel to market at night in order to keep their produce cool.

    Bees and other pollinators（传粉者）  use smells to track down fresh flowers. Air pollutants can weaken those scents（气味）.  Scientists had worried this might make it harder for some pollinators to find a meal.

    Many animals help pollinate plants. Species that do this include bees, butterflies, etc. But for many reasons, the pollinators available to help plants in this way are decreasing. Scientists think a loss of habitat（栖息地）can be one factor. Diseases and exposure to poisonous chemicals also count.

    Jose Fuentes points to air pollution as another possible factor. He's an atmospheric scientist at Pennsylvania State University. In an earlier study, he showed some air pollutants could weaken or destroy scents emitted(发出)by flowers.

    Searching for a meal leaves pollinators out in the open and at risk of becoming other animal's lunch. And any time spent hunting food is time away from their duties back home, like protecting a hive（蜂巢）or nest, explains T'ai Roulston. He's an insect biologist at Virginia University. Roulston worked with Fuentes on the new study.

    In the study, the researchers focused on five kinds of representative scent molecules(分子)plants emit. One molecule they looked at, for example, is called beta-myrcene. Many flowers give off this chemical into the air.  Normally, this gas can travel some 800 meters from its flower source. But in polluted air, this same molecule could travel only half as far.

    Worse still, air pollution might do more than just weaken scent plumes（气味烟云）．Chemical reactions between air pollutants and plumes may transform the flowers' smells, creating new scents. And these scents may be unrecognizable to pollinators.

    That's certainly Fuentes' concern.  So, he says his next research project will look at how insects handle any new flower scent. "It's possible that some insects will change ways to detect and use these new molecules to find food," he says.

    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 means to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let ills 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 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 a 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 off 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.

    Laptop computers are popular all over the world. People use them on trains and airplanes, in airports and hotels. These laptops connect people to their workplace. In the United States today, laptops also connect students to their classrooms.

    Westlake College in Virginia will start a laptop computer program that allows students to do schoolwork anywhere they want. Within five years, each of the 1500 students at the college will receive a laptop. The laptops are part of a $10 million computer program at Westlake, a 110-year-old college. The students with laptops will also have access to the Internet. In addition, they will be able to use e-mail to "speak" with their teachers, their classmates, and their families. However, the most important part of the laptop program is that students will be able to use computers without going to computer labs. They can work with it at home, in a fast-food restaurant or under the trees—anywhere at all!

    Because of the many changes in computer technology, laptop use in higher education, such as colleges and universities, is workable. As laptops become more powerful, they become more similar to desktop computers.

    In addition, the portable computers can connect students to not only the Internet, but also libraries and other resources. State higher-education officials are studying how laptops can help students. State officials are also testing laptop programs at other universities, too.

    At Westlake College, more than 60 percent of the staff use computers. The laptops will allow all teachers to use computers in their lessons. As one Westlake teacher said, "Here we are in the middle of Virginia and we're giving students a window on the world. They can see everything and do everything."

    We lived in a quiet neighborhood. One evening I heard a loud crash. Earlier my wife had asked me to the store for soft drinks. My teenage daughter Holly practiced her driving, so I sent her to the store in my truck.

    At dinner my son talked about how much he liked my truck. I enjoyed having it, but I said: "My heart is not set on that truck. I like it but it is just metal and won't last forever. Never set your heart on anything that won't last. "

    After hearing the loud noise, the whole family ran outside. My son shouted: "Holly crashed your truck."

    The accident took place in my own driveway. Holly had crashed my truck into our other vehicle(交通工具), the family van. In her inexperience, she had confused the brake(刹车) and the gas pedal(油门). Holly was unhurt physically, but she was crying, "Dad, I'm sorry. I know how much you love this truck." I held her in my arms as she cried.

    I still remembered how sad Holly was the night she crashed our truck, and how I comforted her. When Holly thinks back on her life, I want her to know that I love her a thousand times more than any piece of property(财产).

    I repaired the van, but the dent(凹痕) in my truck is still there today. Every day it reminds me of what really matters in my life.