A French physicist, Henri Becquerel discovered that a metal called uranium gave off a kind of radiation, which later Marie Curie called radioactivity. But where did this radiation come from and what was it like? Here was a secret of nature which she decided to discover. She made experiments again and again. There was failure, success, more failure, a little success, a little more success. All proved that in the mineral, which she was examining, there was some form of radiation which man knew nothing about. Life was rather hard. Marie wrote: «Life is not easy for any of us. We must work, and above all we must believe in ourselves.»