The dream of Dmitri Mendeleev: The legend says that the well-known periodic system of chemical elements of Dmitri Mendeleev also dreamed to the Russian inventor. On February 17, 1869 Dmitri Mendeleev should leave Petersburg to the Tverskaya province for inspection collective of cheese. At that moment of departure he has got the idea of future system of elements. After several hours of hard work he lay down to have a rest. About his dream ge told his friend the professor Inostrantsev: «I dream about the table where elements are placed as it is necessary. When he woke up, immediately he wrote on piece of paper periodic system. However, there is a version that Mendeleev himself thought up this legend, sneering at envy of the dull colleagues who were fruitlessly doing nothing on chairs. Actually thought to compare close nuclear masses of different chemical elements and their property came to it mind behind a cup of morning coffee.