Recherches sur une propriété nouvelle de la matière
Antoine Henri Becquerel(1852-1908)
 Antoine Becquerel, a member of a distinguished family of scientists, the teacher and close friend of Marie Curie, was excited by the discovery of X-rays as most scientists were at that time. Since Rontgen’s discovery was made in the investigations of fluorescent action of cathode rays, he immediately set about investigating whether the fluorescent substances emitted invisible penetrating rays besides their phosphorescence.
  Becquerel selected several specimens from a magnificent collection of phosphorescent substances collected by his father, put these specimens on photographic plates wrapped doubly with black paper, and exposed them to the sunlight. The plate had to be fogged if the substance was to emit penetrating rays. Becquerel chose crystals of sulfate of uranium and potassium merely because their fluorescent properties were already well known to him through the extension of his father’s studies. Expectedly, the plate was fogged considerably. He thought that X-rays were generated by fluorescence after all, and intended to repeat this experiment. However, as the cloudy day continued for several weeks, he stowed the crystals on the wrapped plate away in a drawer. He became impatient waiting and decided to develop the plate no matter what resulted. It was greatly affected beyond his expectation. He concluded that this penetrating emission was not caused by fluorescence or excitation by sunlight, but was spontaneously emitted from the substance uranium itself.
  Becquerel made further investigations into this phenomenon which was later called radioactivity by Marie Curie and demonstrated that the radiated rays could discharge electrified bodies, ionize the atmosphere and were curved in a magnetic field. He suggested therefore this radiation included a current of electron-beta rays, a significant point in that this was the first indication of the atom’s inner structure. This book was Becquerel’s early collected studies on radioactivity in which he included all these achievements in the first part of this work. In 1903, the Nobel Prize was presented jointly to him and the Curies for their discovery of and research on radioactivity.