large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb_164
large/12904/worldswithinworlds_v1-3_1904_librivox_64kb_mp3/worldswithinworlds_01_asimov_64kb
English
12904
This was useful especially since the Russian chemist Dmitri I. Mendeléev (1834 1907) had arranged them in a "periodic table" based on the atomic weight order in such a way that elements of similar properties were grouped together. THIS WAS USEFUL ESPECIALLY SINCE THE RUSSIAN CHEMIST DMITRI EI MENDELIEV EIGHTEEN THIRTY FOUR TO NINETEEN O SEVEN HAD ARRANGED THEM IN A PERIODIC TABLE BASED ON THE ATOMIC WEIGHT ORDER IN SUCH A WAY THAT ELEMENTS OF SIMILAR PROPERTIES WERE GROUPED TOGETHER
freys Moseley (1887-1915), went into the matter more thoroughly. He measured the exact wavelength of the characteristic X rays by reflecting them from certain crystals. In crystals, atoms are arranged in regular order and at known distances from each other. X rays reflecting from (or more accurately, diffracting from) crystals are bent out of their path by the rows of atoms. The longer their waves, the more they are bent. From the degree of bending the wavelength of the waves can be determined. [Illustration: _Charles Glover Barkla_] [Illustration: _Henry Gwyn-Jeffreys Moseley_] Moseley found that the greater the atomic weight of an atom, the shorter the waves of the characteristic X rays associated with it and the more penetrating those X rays were. There was such a close connection, in fact, that Moseley could arrange the elements in order according to the wavelength of the characteristic X rays. For some 40 years prior to this, the elements had been listed in order of atomic weight. RISTIC X RAYS IN NINETEEN THIRTEEN ANOTHER ENGLISH PHYSICIST HENRY GWEN JEFFREYS MOSELY EIGHTEEN EIGHTY SEVEN NINETEEN FIFTEEN WENT INTO THE MATTER MORE THOROUGHLY HE MEASURED THE EXACT WAVE LENGTH OF THE CHARACTERISTIC X RAYS BY REFLECTING THEM FROM CERTAIN CRYSTALS IN CRYSTALS ATOMS ARE ARRANGED IN REGULAR ORDER AND AT KNOWN DISTANCES FROM EACH OTHER X RAYS REFLECTING FROM OR MORE ACCURATELY DIFFRACTING FROM CRYSTALS ARE BENT OUT OF THEIR PATH BY THE ROWS OF ATOMS THE LONGER THEIR WAVES THE MORE THEY ARE BENT FROM THE DEGREE OF BENDING THE WAVE LENGTH OF THE WAVES CAN BE DETERMINED MOSELY FOUND THAT THE GREATER THE ATOMIC WEIGHT OF AN ATOM THE SHORTER THE WAVES OF THE CHARACTERISTIC X RAYS ASSOCIATED WITH IT AND THE MORE PENETRATING THOSE X RAYS WERE THERE WAS SUCH A CLOSE CONNECTION IN FACT THAT MOSELY COULD ARRANGE THE ELEMENTS IN ORDER ACCORDING TO THE WAVE LENGTH OF THE CHARACTERISTIC X RAYS FOR SOME FORTY YEARS PRIOR TO THIS THE ELEMENTS HAD BEEN LISTED IN ORDER OF ATOMIC WEIGHT
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