I have some basic doubts in the alpha ray scattering experiment by Rutherford and his students way back in 1909. 1.In the formula for the distance of the closest approach, the term velocity of the alpha particle and the charge of the gold nucleus appears. How did they measure the velocity of the alpha particle? 2. How did they know that the charge on the gold nucleus was 79? In 1909 were they aware of the atomic number of gold? If yes, by what means? 3. The alpha particles with different velocities will come to stop at different distances in front of gold foil. Then how did they know the exact radius of the gold nucleus? Though there are some attempts to answer these questions in certain text books they are too complex to understand.