By the end of the nineteenth century, it was generally believed that all physical phenomena, with the possible exception of gravitation, were of electric origin. Associated with this was the belief that matter was a purely electrical structure. Positive and negative charges, arranged in combination in different ways, were supposed to give rise to all the various kinds of matter in the universe, changes in the positions and arrangements of these charges being regarded as the origin of all the phenomena of physics and chemistry.

Various conjectures were made as to the actual arrangement of the positive and negative charges in matter, but positive knowledge was only obtained when the new experimental methods made available by the discovery of radioactive substances were brought into action.

The special properties of radioactive substances originate from their spontaneously and continuously emitting rays of various kinds. If a beam of the emitted rays is allowed to traverse a strong magnetic field, it is found to be split up into three distinct beams, two of which are deflected in opposite directions, while the third passes straight on.