Mark Twain has been called the inventor of the American novel.And he surely deserves additional praise：the man who popularized the clever literary attack on racism.

     I say clever because anti­slavery fiction had been the important part of the literature in the years before the Civil War.H.B.Stowe's Uncle Tom's Cabin is only the most famous example.These early stories dealt directly with slavery.With minor exceptions，Twain planted his attacks on slavery and prejudice into tales that were on the surface about something else entirely.He drew his readers into the argument by drawing them into the story.

     Again and again，in the postwar years，Twain seemed forced to deal with the challenge of race.Consider the most controversial，at least today，of Twain's novels，Adventures of Huckleberry Finn.Only a few books have been kicked off the shelves as often as Huckleberry Finn，Twain's most widely read tale.Once upon a time，people hated the book because it struck them as rude.Twain himself wrote that those who banned the book considered the novel “trash and suitable only for the slums(贫民窟)．”More recently the book has been attacked because of the character Jim，the escaped slave，and many occurences of the word nigger.(The term Nigger Jim，for which the novel is often severely criticized，never appears in it.)

     But the attacks were and are silly—and miss the point.The novel is strongly anti­slavery.Jim's search through the slave states for the family from whom he has been forcibly parted is heroic.As J．Chadwick has pointed out，the character of Jim was a first in American fiction—a recognition that the slave had two personalities，“the voice of survival within a white slave culture and the voice of the individual：Jim，the father and the man.”

There is much more.Twain's mystery novel Pudd'nhead Wilson stood as a challenge to the racial beliefs of even many of the liberals of his day.Written at a time when the accepted wisdom held Negroes to be inferior(低等的)to whites，especially in intelligence，Twain's tale centered in part around two babies switched at birth.A slave gave birth to her master's baby and，for fear that the child should be sold South，switched him for the master's baby by his wife.The slave's lightskinned child was taken to be white and grew up with both the attitudes and the education of the slave­holding class.The master's wife's baby was taken for black and grew up with the attitudes and intonations of the slave.

     The point was difficult to miss：nurture(养育)，not nature，was the key to social status.The features of the black man that provided the stuff of prejudice—manner of speech，for example—were，to Twain，indicative of nothing other than the conditioning that slavery forced on its victims.

Twain's racial tone was not perfect.One is left uneasy，for example，by the lengthy passage in his autobiography(自传)about how much he loved what were called“nigger shows”in his youth—mostly with white men performing in black­face—and his delight in getting his mother to laugh at them.Yet there is no reason to think Twain saw the shows as representing reality.His frequent attacks on slavery and prejudice suggest his keen awareness that they did not.

     Was Twain a racist？Asking the question in the 21st century is as wise as asking the same of Lincoln.If we read the words and attitudes of the past through the“wisdom”of the considered moral judgments of the present，we will find nothing but error.Lincoln，who believed the black man the inferior of the white，fought and won a war to free him.And Twain，raised in a slave state，briefly a soldier，and inventor of Jim，may have done more to anger the nation over racial injustice and awaken its collective conscience than any other novelist in the past century.

    Nuclear power's danger to health, safety, and even life itself can be summed up in one word: radiation.

    Nuclear radiation has a certain mystery about it, partly because it cannot be detected by human senses. It can't be seen or heard, or touched or tasted, even though it may be all around us. There are other things like that. For example, radio waves are all around us but we can't detect them, sense them, without a radio receiver. Similarly, we can't sense radioactivity without a radiation detector. But unlike common radio waves, nuclear radiation is not harmless to human beings and other living things.

    At very high levels, radiation can kill an animal or human being immediately by killing masses of cells in vital organs. But even the lowest levels can do serious damage. There is no levels of radiation that is completely safe. If the radiation does not hit anything important, the damage may not be serious. This is the case when only a few cells are hit, and if they are killed immediately. Your body will replace the dead cells with healthy ones. But if the few cells are only damaged, and if they reproduce themselves, you may be in trouble. They can grow into cancer. Sometimes this does not show up for many years.

    This is another reason for some of the mystery about nuclear radiation. Serious damage can be done without the victim being aware at the time that damage has occurred. A person can be irradiated(辐射)and feel fine, then die for cancer five, ten, or twenty years later as a result. Or a child can be born weak as a result of radiation absorbed by its grandparents.

    Radiation can hurt us. We must know the truth.

    During this shopping season, salesmen will come up with different strategies to get your business. Many product companies use specific colors to cause positive emotions and compete for a sale. However, sight is not the only sensory (感官的) retail that companies use. Sounds and smells can also influence consumers' purchasing decisions.

    Nobel Prize-winning research shows that our sense of smell has great power to cause an emotional response. A study published earlier this year compared purchasing in a French flower shop when the smell of lavender (薰衣草) was given off and when it wasn't. It found that the smell increased the number of consumers' purchasing items and the amount of their purchases. An earlier study using Nike shoes found that consumers desired the shoes more, and were willing to pay more, when the room had a mixed smell of flowers. Realizing the subconscious impact of smell, many stores apply artificial scents (气味) through their heating and air-conditioning vents (通风口) or place scent machines above their doors. For instance, a coconut scent might make that bikini more appealing as you long for a vacation.

    Ever felt frenzied due to a store's fast-paced music? Or calmed by a piece of light music? A retailer's choice of music can have a big impact on consumers' moods. One study found that when subjected to loud music, consumers will spend less time in a store. But interestingly, the researchers did not find a difference in sales or customers' satisfaction. Another interesting finding from a recent study was that customers actually shop longer when exposed to unfamiliar music. Just as department stores use different scents in certain departments, many use different music in some areas to appeal to varying consumers.

    Well, you could always leave the store and take a break, but the food court probably isn't your best choices as brands like Cinnabon and Panera Bread also use scents as part of their customers' experience. Online retailers (零售商) use a variety of other strategies to get your business, but you can always neglect those and enjoy the familiar scents of home.

    Have you ever spent an afternoon in the backyard, maybe grilling or enjoying a basketball game, when suddenly you notice that everything goes quiet? There is an old phrase "calm before the storm"， often used in a situation—a quiet period just before a great activity or excitement. According to our own experience, we know there is actually calm before the storm. But what causes this calm? And is it always calm before the storm? Let's hear what scientists have to say.

    A period of calm happens in a particular kind of storm, the simplest kind of storm—a single－cell thunderstorm. In this type of thunderstorm, there is usually only one main updraft, which is warm, damp air and drawn from places near the ground. Storms need warm and damp air as fuel, so they typically draw that air in from surrounding environment. Storms can draw in the air that fit their need from all directions—even from the direction in which the storm is traveling.

    As the warm, damp air is pulled into a storm system, it leaves a low－pressure vacuum(真空) coming after. The rising air meets the cold dry air that has already existed in the storm clouds, thus the temperature of the warm, damp air drops, and the water vapour (水蒸汽) in it changes into tiny drops that are a precondition of rain. These drops accumulate and build on larger particles like dust, until they grow large enough to form raindrops.

    This warm, damp air keeps moving upwards, but it becomes cooler and drier during its trip through cloud. When it reaches the top of the cloud, the air gets spit out(被挤出) at the top. This air is sent rolling out over the big thunderclouds. From there, the air goes down. Warm and dry air is relatively stable, and once it covers a region, that air, in turn, causes the calm before a storm.

    Most thunderstorms, though, don't start with calm. That's because most are actually groups of storms with complex wind patterns. There's so much air moving up and down storm groups that the calm before the storm never happens. Instead, before the storm, it might be really windy!

    People have grown taller over the last century, with South Korean women shooting up by more than 20cm on average, and Iranian men gaining 16.5cm. A global study looked at the average height of 18-year-olds in 200 countries between 1914 and 2014.

    The results show that while Swedes were the tallest people in the world in 1914, Dutch men have risen from 12th place to claim top spot with an average height of 182.5cm. Latvian women, meanwhile, rose from 28th place in 1914 to become the tallest in the world a century later, with an average height of 169.8cm.

    James Bentham, a co-author of the research from Imperial College, London, says the global trend is likely to be due to improvements in nutrition and healthcare. "An individual's genetics has a big influence on their height, but once you average over whole populations, genetics plays a less key role," he added.

    A little extra height brings a number of advantages, says Elio Riboli of Imperial College. "Being taller is associated with longer life expectancy," he said. "This is largely due to a lower risk of dying of cardiovascular(心血管的)disease among taller people."

    But while height has increased around the world, the trend in many African countries causes concern, says Riboli. While height increased in Uganda and Niger during the early 20th century, the trend has reversed in recent years, with height decreasing among 18-year-olds.

    "One reason for these decreases in height is the economic situation in the 1980s,"said Alexander Moradi of the University of Sussex. The nutritional and health crises that followed the policy of structural adjustment, he says, led to many children and teenagers failing to reach their full potential(潜力)in terms of height.

    Bentham believes the global trend of increasing height has important implications "How tall we are now is strongly influenced by the environment we grew up in," he said. "If we give children the best possible start in life now, they will be healthier and more productive for decades to come."

Guided Tour of Harry Potter London Locations

If you are a fan of Harry Potter, the Wizards London Walk is a perfect way to spend a couple of hours in London. You will get to see more than 10 filming locations from the Harry Potter movies. 

The tour features Harry Potter London film locations Meanwhile, you also have a chance to explore famous London landmarks and attractions like St Paul's Cathedral and Millennium Bridge and Big Ben. Along the way you'll have plenty of chances to take lots of pictures and see the filming locations up close. 

Come and explore Harry Potter London filming locations on our magical tour

Please also note:

This tour is not accessible for wheelchair users or for parents with prams 

Anyone who is 17 years old or younger must be accompanied by adults on all tours.