Existence in atom of heavy positively charged nucleus was discovered by English physicist E.Rutherford in 1906-1912 as a result of experiments with scattering of a-particles on the atoms of gold and other metals. These experiments showed that some of  a-particles (1 per 20000) passing through very thin metal layers were scattered by big angles, while the most of the particles were not deviated. Rutherford concluded that rare scattering of particles (which moves with velocity just 20 times lees that the velocity of light) at big angles may be explained by the presence in the matter the massive nucleus the size of which is much smaller as compared to the atom size. Animation shows the simulation of Rutherford's experiment. The beam of particles moving with about the same velocities collides several big balls simulating the atoms in metal. We see in animation that small part of the particles are scattered by big angles.