Sometimes, you just can't help it. Maybe you're watching a sad movie, or thinking about the friend who moved away. Next thing you know, your eyes are watering, and you havetears running down your cheeks. Why do peoplecry when they are emotional? What are tears? Scientists are working hard to find the answers to these questions.

    Ad Vingerhoets is a professor of psychology at Tilburg University, in the Netherlands. He is one ofthe few scientists in the world who have studied crying. According to Vingerhoets, there are three types of tears. Basal tearsare the first type. Theylubricate(润滑) the eyes andact as a protective barrier between the eye and the rest of the World. Next arereflex tears. They wash youreyes clean when something gets in them. Finally, there are emotional tears. “These are released in response to emotional states, ”explains Vingerhoets. “Especially when we feel helpless.”

    Scientists believe that crying has something to do with how humans developed and learned to depend on each other.“Humans are very complex social creatures,”says Lauren Bylsma, a professor at the University of Pittsburgh, in Pennsylvania.“It seems that tears serve to arouse help and support from others," She says. “Another reason we weep is that humans have the longest developmental period of almost any animal. It takes along time to grow up. ”

    Vingerhoets agrees. “I think that the reason why humans shed tears(流眼泪) has somethingto do with our childhood,”he says. “That's the time when we are stir dependent on adults for love and protection and care. The major advantage of emotional tears is that you can target them at a specific person.”Vingerhoets says this ability to target someone could have come in hand in prehistorictimes, when humans were living among dangerous animals. Crying couldattract predators(捕食者). Tears were asafer way to get attention. In this case, it is better to use a silent signal to ask for help,”he says.

    Vingerhoets and Bylsma do frequent studies to better understand why humans cry. According to Byhma, there is still much more to discover. “It's surprising,”she says,“how much we still don't know.”

                                                                               A Special Appointment

    Years ago I moved to Woodland Hills to take a job in a small hospital's emergency department. No one wanted to work on Christmas Eve, so the shift (轮班) went to me. I kissed my family goodbye and went off to spend the night in the hospital. It was a thankless job.

At 9 pm, the ambulance brought in a man in his 60s who was having a heart attack. His face was pale, and he was frightened. The whole night I did my best to save his life. Before I left in the morning to spend Christmas with my family, I stopped by to see how he was doing. It was still tough, but he had survived the night and was sleeping.

    The following year I got Christmas Eve duty again. At 9 pm sharp, the ward clerk told me there was a couple who wanted to speak with me. When I approached them, the man introduced himself as Mr. Lee and said, “You probably don't remember me, but last Christmas Eve you saved my life. Thank you for the year you gave me.” He and his wife hugged me, handed me a small gift, and left.

    The following year a new doctor had joined the group, but I wanted to see if Mr. and Mrs. Lee would return. This time, I volunteered for the shift. I kept an eye on the door. Once again, at exactly 9 pm, the Lees appeared, carrying a warmly wrapped bundle. It was their new grandchild. Mr.Lee, his family and I spent 13 Christmas Eves together. In the later years the staff all knew about the story and would work to give me time with him in the break room, where we spent a half-hour each Christmas Eve.

    The last year I saw him, he brought me a gift. I carefully opened the package and found a crystal (水晶) bell inside. It was engraved (镌刻) with a single word: Friendship. Now, my family, friends and I ring that bell every Christmas Eve at exactly 9 pm and offer our best wishes to the man who we won't forget.

    In today's busy and competitive world, we all lead incredibly stressful lives. When stress becomes overwhelming, it can affect our mood and productivity. {#blank#}1{#/blank#} The good news is that it is manageable and can be reduced, or even relieved completely.

    Enter the world of books. Feeling stressed out? Pick up your favorite book and leave the reality and worries behind. It is the most effective way to relax and overcome stress. {#blank#}2{#/blank#} Getting lost in a book before bedtime can calm your mind and prepare your body for a good night's sleep.

    Connect with people. Another way to successfully beat stress is meeting with friends. Friends and loved ones are important to any healthy lifestyle. If you're feeling a little overwhelmed and just can't seem to shake it off, call your best friend or a member of your family and talk to them. {#blank#}3{#/blank#}

    Walk it off. You can also effectively relieve yourself of stress by simply taking a walk around your neighborhood. {#blank#}4{#/blank#} There's a whole new world up there that you never seem to notice while rushing to work or talking to someone. Take a moment to admire a new building or a balcony somewhere high up that reminds you of a castle from your favorite movie. Enjoy your time alone and seize every moment of it.

    {#blank#}5{#/blank#} Nothing brings you back on track like a good laughter. It is the most powerful antidote(良方) to stress and it brings joy into your life. Laughing brings people together and drives away all stress-related problems as if they never existed. It is absolutely the best medicine there is, and it will keep you both physically and emotionally healthy.

    Some people think that success is only for those with talent or those who grow up in the right family, and others believe that success mostly comes down to luck. I'm not going to say luck, talent, and circumstances don't come into play because they do. Some people are born into the right family while others are born with great intelligence, and that's just the reality of how life is.

    However, to succeed in life, one first needs to set a goal and then gradually make it more practical. And, in addition to that, in order to get really good at something, one needs to spend at least 10,000 hours studying and practicing. To become great at certain things, it'll require even more time, time that most people won't put in.

    This is a big reason why many successful people advise you to do something you love. If you don't enjoy what you do, it is going to feel like unbearable pain and will likely make you quit well before you ever become good at it.

    When you see people exhibiting some great skills or having achieved great success, you know that they have put in a huge part of their life to get there at a huge cost. It's sometimes easy to think they got lucky or they were born with some rare talent, but thinking that way does you no good, and there's a huge chance that you're wrong anyway.

    Whatever you do, if you want to become great at it, you need to work day in and day out, almost to the point of addiction, and over a long period of time. If you're not willing to put in the time and work, don't expect to receive any rewards. Consistent, hard work won't guarantee you the level of success you may want, but it will guarantee that you will become really good at whatever it is you put all that work into.

    We would like to wish all our readers a wonderful winter break. Our January magazine is now in the shops and available digitally. We're looking forward to sharing more adventures and discoveries with you in 2018, including:

    At a crossroads in the Atlantic

    As the population of Ascension Island rises up to mark the 200th anniversary of British rule, Fred Pearce wonders what the future might have in store for this strange part of land.

    Photo story: On the road again

    A selection of images from an exhibition opening this month at the Royal Geographical Society go hand in hand with M. Aurel Stein's early 20th century photo graphs of the Silk Road.

    Dossier: Going underground

    Mark Rowe discusses the role that carbon storage can play in the global effort to reduce carbon dioxide emission (排放).

    Net loss

    Kit Gillet reports from the Gulf of Thailand, whose fisheries (渔场) have been almost destroyed by the commercialization of the Thai fishing industry.

    And don't forget… a round-up of the latest geographical and climate science news; a hot spot focus on Turkey; advice on taking photographs in Antarctica; an interview with Lucien Castaing-Taylor, professor of visual arts at Harvard; plus lots, lots more.

    Buy your copy now, click here and save up to 35% or call+44 (0)1635 588 496.Geographical is also available in WHSmith and many independent news agents.

    Snorkelling in Silfra

The clear water at this UNESCO world heritage(遗产) site in Thingvellir National Park will leave you speechless. It is one of the highest rated dive sites in the world. During this journey, you will snorkel within a crack between the Eurasian and American continents. You'll experience truly amazing views of the colorful underwater landscape, marine life(海洋生物), and geological formations. Silfra's water is fresh and drinkable at around 2℃ - 4℃ all year round. Visibility can reach more than 100 meters, and swimming often feels more like flying.

    This trip is for anyone who knows how to swim and is up for a unique adventure. We offer transportation with a pick-up in Reykjavik, and provide you with a dry suit. The total length of the tour is approximately five hours, and includes in-water snorkelling lasting around 30 minutes. We'll guide you through the main Silfra Big Crack, Silfra Hall, Silfra Cathedral and Silfra Lagoon.

Included:

    All necessary snorkeling equipment;

    Hot drinks and food;

    Silfra entrance fee of 1,000 ISK.

    Availability: All year at 09:00 and 15:00. Pick-up in one hour before.

    Requirements:

    Participants need to complete the Silfra medical statement before the tour.

    Divers must:

    Be at least 18 years old (young people under 18 years old need a signature from their legal guardian), and the maximum age is 65 years old;

    Be able to communicate in English.

    Be physically fit;

    Not be pregnant;

    Not be under the influence of alcohol or drugs;

    Sign a medical form.