On a cloudless summer day, 13-year-old Charlie Finlayson was ready for a long hike with his father, David.

    Around noon, David was inching his way across a cliff 800 feet above the valley, searching for a line of cracks that would lead them to the top. Charlie stood on a rock a dozen yards to the right as he fed rope to his dad. Reaching up, David missed his step. In the next moment, he heard a sharp crack from above as something larger broke loose.

    When Charlie saw his father sailing through the air alongside the huge rocks that had struck him, he pulled the rope fiercely.

    “Tell me it's OK,” Charlie begged, struggling to control his fear.

    “I think I broke my leg,” David told him. “And we must get off this mountain.” He proposed a plan: Charlie would lower David half a rope length at a time, then lower himself to the same level, and at a new place, begin again.

    As hours passed, they came to the base of the cliff, and David was shaking with cold and exhaustion.

    Worried that David would die if he fell asleep, Charlie kept the conversation going; they talked about past travels. Eventually Charlie allowed himself to catnap, checking on his father each time he awoke. When the sun rose on their camp, Charlie was relieved to see that his father was awake.

    Just after dawn, Charlie headed off on the trail toward the volunteers' cabin 12 miles away, bringing back a helicopter that would carry his father to safety.

    “Charlie's as strong as anyone I know,” says his father, “I'm so proud of him.”

Reader's Travel Photography Competition

    This month's images include some original and brilliant shots. The overall 2018 winner will receive a $200 holiday ticket and go on a 16-night wildlife holiday.

    Floods are second only to fire as the most common of all natural disasters.They occur almost everywhere in the world,resulting in widespread damage and even death.Consequently,scientists have long tried to perfect their ability to predict floods.So far,the best that scientists can do is to recognize the potential for flooding in certain conditions. There are a number of conditions,from deep snow on the ground to human error,which cause flooding.

    When deep snow melts it creates a large amount of water.Although deep snow alone rarely causes floods,when it occurs together with heavy rain and sudden warmer weather it can lead to serious flooding.If there is a fast snow melt on top of frozen or very wet ground,flooding is more likely to occur than when the ground is not frozen.Frozen ground or ground that is very wet cannot absorb the additional water created by the melting snow.Melting snow also contributes to high water levels in rivers and streams.

    Rivers that are covered in ice can also lead to flooding.When ice begins to melt,the surface of the ice cracks and breaks into large pieces.These pieces of ice move and float down the river,They can form a dam in the river,causing the water behind the dam to rise and flood the land upstream.If the dam breaks suddenly,then the large amount of water held behind the dam can flood the areas downstream too.

    Broken ice dams are not the only dam problems that can cause flooding.When a large human-made dam breaks or fails to hold the water collected behind it,the results can be devastating.Dams contain such huge amounts of water behind them that when sudden breaks occur,the great force of the water is like a great tidal wave.The dam waters can travel tens of kilometres,cover the ground in metres of mud and litter,and drown and crush every thing and creature in their path.

    Although scientists cannot always predict exactly when floods will occur,they do know a great deal about when floods are probably going to occur.Deep snow,ice-covered rivers,and weak dams are all strong conditions for potential flooding.

    Every year, millions of people head to London's Trafalgar Square to see Nelson's Column, and the four lion statues that “guard” it. And last month, during the London Design Festival, a bright red lion sculpture was added to the collection.

    But this was more than just a statue: It had a large open mouth, with an LED screen inside it. At the same time, passersby could type in random words on a screen close to the lion, which were used to produce an AI-created poem. The most interesting part of the poems lies in their randomness, as the words that people choose to enter include many things, such as the time, the weather and their mood. In the daytime, the finished poem appeared on the LED screen, but at night, it was projected (投射) onto the lion's body and the famous Nelson's Column, in a 1ovely light display.

    Es Devlin, the sculpture's creator, was inspired by the history behind the four historic lion statues. Edwin Landseer, the designer of the lions, wanted them to look much more animated, but Queen Victoria refused his plan. This made Devlin wonder, "What if we could give a lion a poetic voice?" According to Devlin, although England has seen many poems about national identity in recent years, these works have been lacking imagination. "I wanted to make a piece that was poetic and collective" he told BBC News.

    After standing for almost 180 years, the purpose of Trafalgar Square has changed over the years. But thanks to the high-tech lion and its poetry, the square is standing the test of time.

    We often seek food after focused mental activity, like preparing for an exam. Researchers guess that too much thinking consumes a lot of energy from the brain. So the brain, sensing that it may soon require more calories to keep going, apparently leads to bodily hunger, and even though there has been little physical movement, we eat.

    The researchers note that tiring activity both increases the amount of blood sugar and lactate(乳酸盐)circulating in the blood and increases blood flow to the head.

    Because the brain uses sugar and lactate as fuel, researchers wondered if the increased flow of fuel—rich blood during exercise could feed a worn—out brain and reduce the urge to overeat.

    Thirty—eight healthy college students were invited to determine their fitness and metabolic(新陈代谢)rates and to report what their favorite pizza was. Afterward, they sat quietly for 35 minutes before being given as much of their favorite pizza as they wanted. At a later date, the volunteers returned and spent 20 minutes making selections from college and graduate-school entrance exams.

    Next, half the students sat quietly for 15 minutes, before being given pizza. The rest of the volunteers spent those 15 minutes doing intervals on a treadmill(跑步机)two minutes of hard running followed by about one minute of walking, repeated five times. These students were then allowed to gorge on pizza, too. But by and large, they did not overeat.

    When the researchers factored in(将……作为因素考虑)the calories burnt on running, they determined that those students actually consumed 200 fewer total calories after their brain workouts than the resting students.

    The researchers do not know if the runners consumed extra calories at dinner. They also cannot tell whether other types of exercise would have the same effect as running, although the researchers say they suspect that if an activity causes someone to break into a sweat, it should also increase blood sugar and lactate, feeding the brain and weakening hungers call.

    Recently, the Oxford English Dictionary, or OED, added about 1,000 words and new definitions to its website. The changes are to help users understand a mix of terms, some dating back many centuries. The additions include words such as "brencheese", "deathshildy" and "hip-pop".

    The new entries are part of the company's update to oed.com, its searchable online dictionary for paid members. The OED makes changes to the website four times each year. But the latest print version has been in process since the year 2000, and may not be ready for 10 more years. That information comes from Katherine Connor Martin, who heads the company's dictionary operations in the United States.

    Usually, the OED watches usage of a word for at least 10 years before deciding whether to add a new entry, new definition or word related to an existing entry, she said. This general rule, however, is sometimes not followed. That is what happened with "tweet", a word that the OED added far before the 10-year mark. Other times, the company adds words that are very old, but were not included in the dictionary in the past.

    “It's funny because we talk about new words, but many of the words we add are already obsolete. It's just that they were never in the dictionary before," Martin told the Associated Press.

    That is the reality, she said, of a historical dictionary trying to put more than 1,000 years of English into books that already have over 855,000 entries. So, you get "brencheese", a rarely used term for when bread and cheese are eaten together. The word dates back to the year 1665. The word "deathshildy" is from Old English. It means someone who is guilty of a serious crime and condemned to death.

    The website defines the term "hip-pop" for music that combines parts of hip-hop and popular music. The OED discovered the term “hip-hip pop” was used in a 1985 story from a Pennsylvania newspaper. It noted that the term "hip-pop" appeared in a 1991 U. S. newspaper report about the rap artist M.C. Hammer.

    The website has added several other terms related to modern culture. They include three popular terms: "binge-watching", "spoiler alert" and "microaggression".

    Here are a few other new entries if you long to read on.