The leaders （领导人） of 13 countries had a big meeting in St Petersburg, Russia from November 21 to 24, 2010.The meeting was about tigers. They talked about the ways to protect the animals in their countries. They agreed to spend more money protecting tigers and they wanted to double the number of tigers in the world before 2022.

    Tiger is one of the world's most endangered animals. The World Wildlife Fund （WWF） says, there are only about 100,000 wild tigers now. And the number is becoming smaller and smaller. 'If nothing happens, tigers will face disasters,' said WWF spokeswoman Marie von Zeipel.

Nine types of tigers lived 100 years ago, but now at least three of them have died out. ‘If people leave tigers alone and don't kill them, then the number of tigers will double in 10 years,' said Jean-Christoph Vie, a French tiger expert (专家).

    China is one of the 13 countries where tigers live. There are about 50 wild tigers in China now. They are the Bengal tigers in Tibet, Indochinese tigers in China's southwest, and Siberian tigers in the northeast. The South China tigers lived in southeast China many years ago but disappeared in the 1970s. Many experts think they have already died out.

    Do you know some great inventors and their inventions?

    What factors (因素) are needed for their success?

    Well, good timing for a start. You can have a great idea which the public simply doesn't want … yet. The Italian Giovanni Caselli invented the first fax（传真）machine in the 1860s. Although the quality is excellent, his invention quickly died a commercial(商业的) death. It was not until the 1980s that the fax became very common in every office… too late for Giovanni Caselli.

    Money also helps. The Frenchman Denis Papin (1647-1712) had the idea for a steam engine （蒸汽机）almost a hundred years before the better-remembered Scotsman James Watt was even born… but he never had enough money to build one.

    You also need to be patient (it took scientists nearly eighty years to develop a light bulb which actually worked)… but not too patient. In the 1870s, Elisha Gray, a professional inventor from Chicago, developed plans for a telephone. Gray saw it as no more than “a beautiful toy”. However, when he finally sent details of his invention to the Patent Office(专利局) in February，1876, it was too late. Almost the same invention had arrived two hours earlier and the young man who sent it , Alexander Graham Bell, will always be remembered as the inventor of the telephone.

    Of course what you really need is a great idea—but if you haven't got one, a walk in the country and a careful look at nature can help. The Swiss scientist, George de Mestral, had the idea for Velcro(魔术贴) when he found his clothes covered in sticky seed pods after a walk in the country. During a similar walk in the French countryside some 250 years earlier, Rene Antoine Ferchault de Reaumur had the idea that paper could be made from wood when he found an abandoned wasps' nest(蜂巢).

    You also need good commercial sense. Willy Higinbotham was a scientist doing nuclear (核能的)research in the Brookhaven National Laboratory in Upton, USA. In 1958 the public were invited to an exhibition in the Laboratory to see their work, but both parents and children were more interested in a tiny 120cm screen with a white dot which could be hit back and forth over a “net” using a button and a knob. Soon hundreds of people were ignoring the other exhibits to play the first ever computer game—made from a simple laboratory instrument called an “oscilloscope”. Higinbotham, however, never made money from his invention: he thought people were only interested in the game because the other exhibits were so boring!

    There's much to see under the sea, but you need to remember that light behave differently in water than in air. The objects appear closer to you than they exactly are. You might find yourself reaching out to touch something and completely missing it.

    Objects under water will appear larger than they would on the surface, too. Be careful not to tell any stories about the big fish that got away. That fish might not be so big after all! It's just because sometimes things can seem to be as much as about 33 percent bigger in water!

    What's more, in deeper water, colors just don't seem as bright. In fact, it looks as if some colors are missing. Remember the color of an object results from the wavelength (波长) of light that are reflected (反射) from its surface. And light is taken in as it moves down through the water.

    Swimmers wear wet suits to keep warm underwater. Let's take a bright red, yellow, and blue wet suit as an example. These colors are hard to miss on the surface of water. Watch carefully the changes in color as you descend in the water. The red part now looks almost black because the red light wavelengths, the longest among these three colors, are missing. As you go down deeper, the same thing will happen to the yellow part and in the end to the blue part. Even at a place of about 6 to 9 meters underwater, you will look terrible, like a ghost(鬼怪) ! And you have to wait for your return to the surface to enjoy the bright colors again!

    There was a world's advanced robot exhibition in Moscow. Over 20 skilled robot performers from all over the world took part in the exhibition.

    The exhibition was opened by British-born Titan, a world-famous dancing robot that had performed together with artists. Besides its quick moves, the robot is also known for its stand-up comedy and beautiful voice.

    Robot Hespin, a life-sized humanoid robot can make others happy. The robot not only sings and dances but also acts as a museum guide. It's very impressive. It can even hold conversations with humans.

    Then there is Cubic, an ordinary boxy robot that has been created to make our lives easier. It can read the latest news, switch off lights, and order pizza. Cubic can hold basic conversations and tell jokes.

    South Korea's friendly robots not only dance but also clean floors. Germany's famous metal rock band performs wonderfully.

    Most of the robots seem to have some kinds of dancing skills. The organizers say that their main purpose is to create a meeting place or a global platform to enable the people of Russia to experience some of the world's most advanced robots.