Atomic physics was making rapid strides during the second decade of the twentieth century. By the turn of the twentieth century, there was general acceptance among physicists of the molecular theory of matter. Molecules were believed to be composed of still smaller units of matter, atoms. However, it was also becoming clear that the "unsplittable" atoms were composed of even smaller parts. While the properties of electrons were beginning to be understood, the structure of the atom itself remained a mystery.

Rutherford's Experiments.

Various theories of atomic structure were ventured, but the one given the most credence was the model proposed by Professor Ernest Rutherford of England. From about 1906 Rutherford had been firing alpha particles (positively charged particles consisting of two protons and two neutrons that are emitted by several radioactive substances) at sheets of matter in hopes that the record of...