ABSTRACT
Some of the closely related discoveries, such as the fact that the X-rays show a spectrum susceptible of examination, were not so disconcerting in themselves; but the marvellous pictures of the structure of the atom elicited by these discoveries made many good people almost question whether our venerable experimenters had not been indulging in pipe dreams amid their laboratory work. It will be convenient to consider the problems under two heads: the composition of matter, and the origin of matter. It was long ago recognized that matter must be composed of particles which are driven farther apart by heat and are brought closer together by cold, thus laying the foundation for the theory of the molecular composition of matter. But not until the time of Dalton, about a hundred years ago, was it proved that the molecule itself, the unit of physical change, is capable of definite division into atoms, the units of chemical change.
