A. Created 150 years ago, the Periodic Table (元素周期表) is a triumph of form and function. Now this design classic has been updated for the 21st century—and opened up to a new audience. It's a vital part of chemistry teachers' educational content. With its array of digits and chemical abbreviations, it appears everywhere, from pencil cases to posters. B. So why are we still so interested in the periodic table? "The standard physicists' criticism of chemists is that they are stamp collectors," says periodic table expert and "The Elements" creator Theodore Gray. "That's because physicists think they study the fundamentals of what makes everything work. In their view, chemists just collect all of these manifestations of physics—the physical properties of elements-and don't concern themselves with what makes these things the way they are." C. But scientists, always eager to eke out a closer model of the truth, have been trying to improve it for 150 years. Amateur enthusiasts obsessed by the table's design, have transferred Mendeleyev-inspired charts onto T-shirts, even toy elephants. It's no coincidence that iPad champion-in-chief Stephen Fry has described the new "Elements" iPad App as alone worth the gadget's retail price. Released in Britain last month, the App's creators hope this country will take to it like the Americans, who have already bought 30, 000 copies. D. Whether you love chemistry or not, the modern periodic table, first successfully mapped out by Russian academic Mendeleyev in 1869, occupies a space in science-lovers' psyches. This traditional chart has persisted because of its efficient systematisation of a disparate array of elements. E. Mendeleyev's brain wave in fact followed on from hundreds of years of scientific research. In 1862 a French geologist, Alexandre de Chancourtois, had written a list of elements on a piece of tape, which he then wound around a cylinder. He noticed that chemically similar elements came below one another-in other words, the elements were "periodic"—and that as they grew in size, their properties repeated with regularity. F. "But stamp collecting is a very popular hobby. It's fun to collect things. And the periodic table has a nice number of elements: around 100. It's a good number, and fits well with, say, a collection of beer or vegetables, which people have categorised using the periodic table's principles online. Also, people love it because it's universally known. It's like the Nike logo—everyone is familiar with its shape." G. Around this time, in Russia Mendeleyev was throwing his intellectual heft behind the problem too. He wrote each of the elements on a different piece of card, along with their atomic weight and the formula (分子式) of their compound with oxygen (their "oxide"). He arranged the cutouts in order of weight, putting similar oxides in rows. Order: A→ 1 → 2 → 3 → 4 → 5 →G