no doubt that under favorable conditions, these particles must pass very close to the nucleus and may either lead to a disruption of the nucleus or to a combination with it. Unfortunately, the chance of such a disruption or combination is so small under experimental conditions that the amount of new matter which is possible of formation within a reasonable time would be exceedingly small, and so very difficult of detection by direct methods. Very penetrating X rays or gamma rays may for similar reasons prove to be possible agencies for changing atoms. Although it is difficult to obtain direct evidence, I personally am inclined to believe that all atoms are built up of positive electrons—hydrogen nuclei—and negative electrons, and that atoms are purely electrical structures.
There can be little doubt that conditions have existed in the past in which these electrons have combined to form the atoms of the elements, and it may be quite possible under the very intense electrical disturbances which may exist in hot stars that the process of combination and dissociation of atoms still continues.
In these lectures, I have tried to give an idea of some modern views of the structure of the atoms and of the great variety of new and powerful methods which have been applied to the attack of this problem in recent years. We have seen that a heavy atom is undoubtedly a complex electrical system consisting of positively and negatively charged particles in rapid motion. The general evidence indicates that each atom contains at its center a massive charged nucleus or core of very small dimensions surrounded by a cluster of electrons probably in rapid motion which extend for distances from the center very great compared with the diameter of the nucleus. Such a view affords a reasonable and simple explanation of many important facts obtained in recent years, but so far only a beginning has been made in the attack on the detailed structure of atoms—that fundamental problem which lies at the basis of physics and chemistry.