John Dalton formed the atomic theory with spherical solid atoms
W.K Roentgen discovered X-rays while experimenting with cathode-ray tubes
Henri Becquerel discovered radioactivity when he investigated uranium and other radioactive substances.
The Curies discovered radium and polonium when they started to investigate radioactive substances
J.J Thompson discovered the electron and developed the plum-pudding model of the atom.
Albert Einstein developed the theory of relativity
Robert Millikan found out the electric charge of the electron
Ernest Rutherford used the results of his gold-foil experiment to state that all the mass of an atom were in a small positively-charged ball at the center of the atom.