The wonderful experiment I am going to introduce proves that air is just all around and that it presses down upon us. Air pressure is a wonderful force. When you swim underwater, you can feel water push down your body. The air all around you does the same. However, your body is so used to it that you do not notice this. The pressure is caused by a layer of air called the atmosphere. This layer surrounds the Earth, extending to about five kilometers above the Earth's surface.

    The following experiment is an easy one that you can do at home. But make sure that you are supervised, because you will need to use matches. Now for the experiment！

    What you need:

·A hard-boiled egg without the shell

·A bottle with a neck slightly smaller than the egg

·A piece of paper

·A match

Method:

1） Check that the paper will sit firmly on the neck of the bottle.

2） Tear the paper into strips and put the strips into the bottle.

3） Light the paper by dropping a burning match into the bottle.

4）Quickly sit the egg on the neck of the bottle.

Result:

    Astonishingly, the egg will be sucked into the bottle. Your friends will be amazed when you show them the experiment. But be careful when you handle matches.

    Why it happened

    As the paper burns, it needs oxygen and uses up the oxygen（air）in the bottle. The egg acts as a seal in the neck of the bottle, so no more air can get inside. This reduces the air pressure inside the bottle. The air pressure must equalize, so more air from outside must enter the bottle. The outside air pressure against the egg and then the egg is pushed into the bottle! This proves that air is all around and that it is pressing down on it.

    My husband and I had been married nearly twenty-two years when I acquired Stevens-Johnson syndrome, a disorder where my immune system (免疫系统) responded to a virus by producing painful blisters (水疱). Although my long-term evaluation was good, I, who had been so fiercely independent, rapidly became absolutely helpless.

    My husband, Scott, stepped up to the plate, taking care of kids and cooking dinners. He also became my personal caretaker, applying the medicine to all of my blisters because my hands couldn't do the job. Needless to say, I had negative emotions, bouncing from embarrassment to shame caused by total reliance on someone other than myself.

    At one point when I had mentally and physically hit bottoms I remember thinking that Scott must somehow love me more than I could ever love him. With my illness, he had become the stronger one, and I was the weaker one. And this disturbed me.

    I recovered from my illness, but I couldn't seem to recover from the thought that I loved my husband less than he loved me. This seeming distinction in our love continued to annoy me for the year following my illness.

    Then recently Scott and I went on a long bike ride. He's an experienced cyclist; I'm quite the green hand. At one point with a strong headwind and sharp pain building in my tired legs, I really thought I couldn't go any further. Seeing me struggle, Scott pulled in front of me and yelled over his shoulder, “Stay close behind me.” As I fell into the draft of his six-foot-three-inch frame and followed his steps, I discovered that my legs quit burning and I was able to catch my breath. My husband was pulling me along again. At this very moment I woke up to what I now believe: during these and other tough times, love has the opportunity to become stronger when one partner learns to lean on the other.

    I pray my husband will always be strong and healthy. But if he should ever become the struggling one, whether on a bike ride or with an illness, I trust I'll be ready to call out to him: stay close behind me — my turn to pull you along.

    I had an old neighbor, a doctor named Gibbs. When Doctor Gibbs wasn't saving lives, he was planting trees. He had some interesting theories about planting trees. He hardly watered his new trees.

    Once I asked why and he told me that watering plants damaged them because it made them grow weaker. He said he had to make things difficult for the trees so that only the strongest could survive. He talked about how watering trees made them develop shallow roots and how, if they were not watered, trees would grow deep roots in search of water.

    So, instead of watering his trees every morning, he'd beat them with a rolled up newspaper. I asked him why he did that, and he said it was to get the trees' attention.

    Doctor Gibbs died a couple of years after I left home. Sometimes I walked by his house and looked at the trees I'd watched him plant 25 years ago. They were tall and strong.

    I planted several trees myself a few years ago. Two years of caring for these trees meant they grew up weakly. Whenever a cold wind blew, my trees trembled. Adversity seemed to benefit Doctor Gibb's trees in ways comfort and ease never could.

    Every night before I go to bed, I check on my two sons. I often pray that their lives will be easy. But lately I've been thinking that it's time to change my prayer. I know my children are going to experience difficulties. There's always a cold wind blowing somewhere. What we need to do is to pray for deep roots, so when the rains fall and the winds blow, we won't be torn apart.

    You know those nutrition guidelines the government issues every few years? It turns out that following them isn't just good for your health. It's good for the planet, too.

    " What we found is that impacts vary across nations, but in the high­impact nations, in general, you can see that, if you follow a nationally recommended diet, despite the fact that these diets don't mention explicitly—or most of them don't explicitly mention—environmental impacts, that you are going to have lower environmental impacts due to that. So that's sort of fairly clear across all the high­income nations." said Paul Behrens, an environmental scientist at Leiden University in the Netherlands.

    The food we eat takes a big toll on the environment. A third of the ice­free land on Earth is used for agriculture, and according to some estimates, producing food accounts for roughly a fifth of all human­caused greenhouse gas emissions. Fertilizer runoff also leads to other problems, like the algae blooms in Lake Eerie and the Dead Zone in the Gulf of Mexico.

    However, following dietary guidelines would reduce those impacts, especially in wealthy countries like the US. "Most of the reductions come from meat and dairy," which have an outsized impact on land use and pollution, and are a major source of greenhouse gases.(That's partly due to cow farts. Seriously.) Following the suggestions would also mean eating fewer calories, since many people here eat more than they need.

    Overall, in high­income countries, Behren's team estimates that following the rules could result in as much as a 17 percent reduction in land use, a 21 percent reduction in nutrient pollution, and a 25 percent drop in agricultural greenhouse gas emissions. Cutting down on how much food we waste—which is roughly a third in the US—could help even more. The results are in the Proceedings of the National Academy of Sciences.

    Of course, people are notoriously bad at following diets. But: "These nationally recommended guidelines do actually have a knock­on effect on other areas of policy making. So if I'm developing a new healthy­eating­for­schools program then that's going to be based off a lot of detail that I get from the nationally recommended guidelines. So while it might not necessarily be the case that people follow directly …they actually are quite influential on the preparation of other advice."

    It seems that a smaller environmental footprint and a healthier lifestyle could go hand in hand.

    That people often experience trouble sleeping in a different bed in unfamiliar surroundings is a phenomenon known as the 4Tirst-nighf, effect. If a person stays in the same room the following night they tend to sleep more soundly. Yuka Sasaki and her colleagues at Brown University set out to investigate the origins of this effect.

    Dr. Sasaki knew the first-night effect probably has something to do with how humans evolved.

    The puzzle was what benefit would be gained from it when performance might be affected the following day. She also knew from previous work conducted on birds and dolphins that these animals put half of their brains to sleep at a time so that they can rest while remaining alert enough to avoid predators (捕食者). This led her to wonder if people might be doing the same thing. To take a closer look, her team studied 35 healthy people as they slept in the unfamiliar environment of the university's Department of Psychological Sciences. The participants each slept in the department for two nights and were carefully monitored with techniques that looked at the activity of their brains. Dr. Sasaki found, as expected, the participants slept less well on their first night than they did on their second, taking more than twice as long to fall asleep and sleeping less overall. During deep sleep, the participants' brains behaved in a similar manner seen in birds and dolphins. On the first night only, the left hemispheres (半球) of their brains did not sleep nearly as deeply as their right hemispheres did.

    Curious if the left hemispheres were indeed remaining awake to process information detected in the surrounding environment, Dr. Sasaki re-ran the experiment while presenting the sleeping participants with a mix of regularly timed beeps (蜂鸣声) of the same tone and irregular beeps of a different tone during the night. She worked out that, if the left hemisphere was staying alert to keep guard in a strange environment, then it would react to the irregular beeps by stirring people from sleep and would ignore the regularly timed ones. This is precisely what she found.

Scientists have discovered a bit of hand-made string (线绳) that's around 50,000 years old in Neanderthal remains. The first Neanderthal remains were found in the Neander Valley in Germany, which is where the name comes from. Neanderthals may have lived mainly in caves and made stone tools, but recent discoveries have given hints that Neanderthals developed some advanced skills that people used to think impossible. For example, Neanderthals knew how to make glue from the bark (树皮) of a tree.

Now, scientists report they've found a piece of string on a stone tool made by Neanderthals. Before this, the oldest known piece of string was one made by humans about 19,000 years ago. The string is about a quarter of an inch long. Almost all things made from plants during that time have broken down and disappeared, so it's very special to find this bit of string.

The scientists don't know whether the string was attached to the tool. But that doesn't interest them as much as the fact that Neanderthals knew how to make string. Bruce Hardy, the lead scientist on the project, says that knowing how to make string was meaningful for humans. "We wouldn't really be here today without that technology," he says.

Making string is a very arduous process. This string was made from the inside bark of an evergreen tree. To make string that is strong enough, the string must be made of several smaller fibers twisted (缠绕) together in a special way. For the Neanderthal string, several fibers needed to be twisted together into something like yarn. Then three pieces of yam needed to be twisted together in the opposite direction to make the final string.

The scientists aren't sure what the string was used for, but they say that string like. the bit that was found could be used to make bags, baskets, traps, or other things. The researchers also suggest that because Neanderthals needed to make pairs and count fibers to make the string, the bit of string may also tell us something about the kinds of math that Neanderthals could do.