In the traffic lights,red means "stop",green means "go",and yellow means "hurry": Why those colors, though? Why not blue,purple,and brown?The following are transponded from others WeChat.

●Red is an inherited symbol from railroads

    Red symbolizes danger in many cultures,which makes sense,considering it has the longest wavelength of any color,meaning you can see it from a greater distance than other colors.Red has meant "stop" since long before cars existed,with railway signals use of red dating bake to the days when mechanical arms lifted and lowered to indicate whether the rail ahead was clear.So that one's simple.

●Green meant "caution" at first

    Green's role in lights has actually changed dramatically over time.Its wavelength is next to (and shorter than) yellow's,meaning it's still easier to see than any color other than red and yellow.Back in the early days of railway lights,green originally meant "caution",while the "all-clear" light was,well,clear or white.Trains,of,course,take an unlimitedly long time to stop,and legend has it that several disastrous collisions happened after an engineer mistook stars in the night horizon for an all-clear.Thus,green became "go",and for a long time,railways used only green and red to signal trains.

●Yellow means "caution" because it's almost as easy to see as red

    From the earliest days of motoring up until the mid-1900s,not all stop signs were red-many were yellow, because at night it was all but impossible to see a red stop sign in a poorly lit area.The yellow stop-sign craze began in Detroit in 1915,a city that five years later installed its first electric traffic signal,which happened to include the very first amber traffic light,at the corner of Michigan and Woodward Aves.

    Last year I ruined my summer vacation by bringing along a modern convenience that was too convenient for my own good: the iPad. Instead of looking at nature, I checked my email. Instead of paddling a small boat, I followed my Twitter feed (推特简讯). Instead of reading great novels, I stuck to reading four newspapers each morning. I was behaving as if I were still in the office. My body was on vacation but my head wasn't.

    So this year I made up my mind to try something different: withdrawal (退出) from the Internet. I knew it wouldn't be easy, since I'm bad at self-control. But I was determined. I started by giving the iPad to my wife.

    The cellphone signal at our house was worse than in the past, making my attempts at cheating an experience in frustration (沮丧). I was trapped, forced to go through with my plan. Largely cut off from e-mail, Twitter and my favorite newspaper websites, I had few ways to connect to the world except for radio and how much radio can one listen to, really? I had to do what I had planned to all along: read books.

    This experience has had a happy ending. With determination and the strong support of my wife, I won in my vacation struggle against the Internet, realizing finally that it was I, not the iPad, that was the problem.I knew I had won when we passed a Starbucks and my wife asked if I wanted to stop to use the Wi-Fi. “ I don't need it,” I said.  

    However, as we return to post -vacation life, a harder test begins: Can I continue when I'm back at work? There are times when the need to know what's being said right now is great. And I have no intention of giving up my convenience completely. But I hope to resist the temptation (诱惑) to check my e-mail every five minutes, which leads to checking my Twitter feed and a website or two.

    I think a vacation is supposed to help you reset your brain to become more productive. Here I hope this one worked.

    You need some bread and milk. But half an hour later, you leave the supermarket with a trolley（推车）full of food. What games do supermarkets play to make us spend so much money?

    The tricks usually start before you walk in. Outside the supermarket entrance, anybody who walks past can smell warm, fresh bread. That makes us hungry and ready to buy lots of food, not just bread.

    Now you're inside and, of course, a small basket would be fine, but all they have are trolleys. And of course the problem with a trolley is that it looks sad and lonely with just one or two goods inside. So we may fill it with something. In fact, supermarket trolleys are actually getting bigger so that we buy more.

    Of course, many people shop in supermarkets because they think everything is cheaper than in other shops. So supermarkets offer very cheap prices on some things but then have higher prices for other goods. One new trick is to put red stickers（标签）on them. Customers usually connect red stickers with lower prices so the red stickers is easy to be seen, even when there is no reduction! Interestingly, this trick appears to work more with men than with women.

    There is a story behind the position of everything in the supermarket. The most expensive goods are usually at eye-level so you see these immediately. The exception is anything that children might like. These goods are on lower shelves so that kids see them.

    Apart from what you see and smell in a supermarket, what about what you listen to? In most supermarkets they have soft, slow music. It's so relaxing that you slow down and spend more time (and money) in the store. Experts suggest it's better to shop when it's quieter, on a Monday or a Tuesday for example. And be careful with queues at the checkouts（收银台）. These are sometimes on purpose, to make you buy something from the checkout shelves while you wait.

    So, next time you go into your local supermarket, remember these tricks and see if you can come with just the things you went for.

    Chicago festival season is here, but are you ready? Music festivals, film series, street fests, beer bashes—it's a summer long party. So pull out your calendar, read our guide and start enjoying weekends.

    Friday Art Markets at Daley Plaza

    Select Fridays August 19 through September

    Daley Plaza

    Cost: Free

    Direction: Nearly 75 artists will be showing their work in Daley Plaza, including jewelry, ceramics, sculpture, paintings, glass, wearables, wood and mixed media.

    Website: http://www.FridayArtMarketsaDaleyPlaza php? sid=146320

    Renegade Chicago Pop-Up

    Sept. 9-10

    Pilsen

    Cost: Free

    Directions: Get your hands on the goods at this outdoor celebration of all things handmade. Festivities include food trucks, DJ sets, craft brews, DIY workshops, photo ops and shopping.

Website: http://www.RenegadeChicagoPop-Up php? sid=146346

    Millennium Park Summer Music Series

    Select Mondays and Thursdays June 12 through Aug. 21

    Millennium Park

    Cost: Free

    Directions: Grab a blanket and some picnic snacks for a free outdoor concert in the park. The music series features a wide variety of music from pop local, national and international artists.

Website: http://www.MillenniumParkSummerMusicSeries php? sid=146432

    Northsider Craft Beer Fest

    Sept 23

    Uptown

    Cost: $15-$69

    Directions: Spend a day on the green sampling beers and hard ciders（苹果汁）from breweries across the country, including Colorado, Michigan, California and Wisconsin—and let's not forget those in our own home state, too.

    Website: http://www.NorthsiderCraftBeerFest php? sid=146467

    You can't always predict a heavy rain or remember your umbrella. But designer Mikhail Belvacv doesn't think that forgetting to check the weather forecast before heading out should result in you getting wet.

    That's why he created Lampbrella, a lamp post with its own rain sensing umbrella.

    The designer says he came up with the idea after watching people get wet on streets in Russia. "Once, I was driving on a central Saint Petersburg street and saw the street lamps lighting up people trying to hide from the rain. I thought it would be appropriate to have a canopy(伞蓬) built into a street lamp," he said.

    The Lampbrella is a standard-looking street lamp fitted with an umbrella canopy. It has a built-in electric motor which can open or close the umbrella on demand. Sensors (传感器)then ensure that the umbrella offers pedestrians shelter whenever it starts raining.

    In addition to the rain sensor, there's also a 360 motion sensor on the fiberglass street lamp which detects whether anyone's using the Lampbrella. After three minutes of not being used the canopy is closed.

    According to the designer, the Lampbrella would move at a relatively low speed, so as not to cause harm to the pedestrians. Besides, it would be grounded to protect from possible lighting strike. Each Lampbrella would offer enough shelter for several people. Being installed at 2 meters off the ground it would only be a danger for the tallest of pedestrians.

    While there are no plans to take Lampbrella into production, Belyaev says he recently introduced his creation to one Moscow Department and insists this creation should be installed on the street where a lot of people walk but there are no canopies to provide shelter.

    It is common to see many different kinds of insects while spending time outside in the summer. Some of them do not trouble people and can even add beauty to the natural environment. Other insects can harm the environment or humans. The population of these insects seems to stay large and healthy.

    But scientists say this does not appear to be true for some flying insects that serve an important purpose. There is growing evidence that these insects are decreasing across the world.

    One researcher looking into the present insect population is Doug Tallamy, a professor at the University of Delaware. He remembers walking through Washington D. C., in the past when it was "alive with insects, especially butterflies". Now, he said, "The flying insects are actually gone." Wilson said this point seemed to be proved during a drive he made last year from Boston to Vermont. He was surprised that, during his trip, he counted only one insect that had hit the car's front window. Several other scientists have carried out similar tests by checking how many insects hit their cars while traveling.

    While researchers admit this method is not scientific, they say it can still help them understand the changing flying insect population. There have not been many studies done on the flying insect populations covering large areas. However, some international research suggests a downward turn. In 2006, a group of studies showed that there had been a 14-percent drop in ladybugs(瓢虫) in the United States and Canada from 1987 to 2006. In Germany, a 2017 study found an 82-percent drop in the number of flying insects compared to levels recorded in 1990.

    After the German study, other countries also started looking into the problem. David Wagner of the University of Connecticut says other evidence leads him to believe the findings of the 2017 study are "clearly not a German thing".