timents in virtually every ory of cry in print.

    today y-turally occurring ones plus acouple of dozen t ed in labs. tual number is sligentiousbecause ts exist for only milliontssometimes argue over ed or not. In Mendeleyev’s dayjust sixty-ts  part of o realize t ts as t make a complete picture, t many pieces ed, s  in whey werefound.

    No one knoally, s migomic  ain is tanyt is found  neatly into Mendeleyev’s great scheme.

    teentury  great surprise for cs. It began in 1896  of uranium salts on a e out some time later, o discovert ts , just as if te o ligs ting rays of some sort.

    Considering tance of urned tter over to a graduate student for investigation. Fortunately tudent  émigré from Poland named Marie Curie. orking  certain kinds of rocks poured out constant and extraordinary amounts of energy,yet  diminisectable il Einstein explained t ting mass into energy in an exceedingly efficient way.

    Marie Curie dubbed t “radioactivity.” In ts—polonium, ry, and radium.

    In 1903 tly ary, in 1911, to ry and p McGill University in Montreal t Ruterested in tive materials. it immense reserves of energy s of matter,and t tive decay of t for most of th.

    t radioactive elements decayed into ots—t one dayyou om of uranium, say, and t you om of lead. trulyextraordinary. It aneously.

    Ever tist, Rut to see t ticalapplication in ticed t in any sample of radioactive material, it alook t of time for o decay—ted  teady, reliable rate of decay could