doubtedly to be accounted for by the vibrations within the atoms, we may well have recourse to the modern conception of the atom as advanced by J. J. Thomson. Here the atom is considered as made up of a central mass carrying a positive charge. Surrounding it are numerous electrons of a negative charge, the number of which increases directly with the atomic weights of the elements concerned. The electrons are undoubtedly arranged in some systematic order and may, as Nagaoki imagines, follow parallel courses closely analogous to the rings of Saturn. A disturbance of any one group or belt of electrons will undoubtedly produce a disturbance in yet other groups and, according to the amount of disturbance, the definite vibratory motions established will set up vibratory motions in the ether, later to be detected in the spectrum. From this hypothesis the spectrum of an element of high atomic weight might be expected to contain more lines than one of low atomic weight. Such, however, need not necessarily follow. If we take the case of radium, uranium, etc., we may imagine the electrons in its atom to be grouped closely together in only a few courses or belts. In fact this very hypothesis may well account for the discharge of electrons from such highly condensed arrangements and give rise to radioactivity.
From this modern standpoint the molecule is regarded as a combination between atoms as effected by the loss or gain of one or more electrons from one to the other, developing what is commonly termed "bonds of affinity" and corresponding in number to the valence of the particular atoms concerned. These may be more correctly construed as Faraday tubes of force.
With these ideas in mind the banded spectra of compounds may be accounted for by disturbances induced between the atoms, as well as by small electronic vibrations set up in the atoms themselves and due to the perturbances of the Faraday tubes of force. The vibrations resulting from this composite arrangement of vibratory centers may be sufficient to extend over a considerable area of wave-lengths and thus produce a band. As the temperature increases these band spectra, always obtained with compounds, pass over gradually into the line spectra of the constituent elements concerned. There follows, then, with increase of temperature or electric stress, as has already been noted,
- The lines of force binding two atoms and constituting an electrical field between these charged atoms is conveniently regarded as made up of tubes of force, each with its positive electrical charge at one end, the beginning of this tube, and its negative and equal electrical charge at the other end or termination of the tube. Each Faraday tube, therefore, encloses a charge of electricity of unit value or that denoted by one single electron and consequently an atom that is univalent must enter into combination by means of one Faraday tube of force, one that is bivalent by two such tubes, etc. The positive atoms are those formed by the loss of electrons and the negative atoms are those which can take up these same electrons.