To be living in a period which faces such a complete reconstruction of our notions as to the way in which ether waves are absorbed and emitted by matter is an inspiring prospect. The atomic and electronic worlds have revealed themselves with beautiful definiteness and wonderful consistency to the eye of the modern physicist, but their relation to the world of ether waves is still to him a profound mystery for which the coming generation has the incomparable opportunity of finding a solution. In conclusion there is given a summary of the most important physical constants the values of which it has become possible to fix,[197] within about the limits indicated, through the isolation and measurement of the electron. Fig. 36—THE COMPTON EFFECT The photograph shows the change of wave-length of ether-waves, from blue toward red, because of scattering by free electrons, and are the initial characteristic -ray lines of molybdenum, and these same lines after suffering scattering in aluminum. [Pg 261] Fig. 37—FINE STRUCTURE OF SPECTRAL LINES IN THE EXTREME ULTRA-VIOLET The photograph shows the character of the resolution obtained in the recent study by Bowen and Millikan of the fine structure of spectral lines in the extreme ultra-violet. The seven lines in brackets on the left are components of the 834.0 oxygen line. Their total separation is but about two angstroms. The bracketed doublet on the right is one of the many studied, the separation of which is predicted by the theoretical-relativity-doublet formula. The electron The Avogadro constant Number of gas molecules per cc. at 0° C. 76 cm Kinetic energy of translation of a molecule at 0° Change of translational molecular energy per 0° C Mass of an atom of hydrogen in grams Planck’s element of action Wien constant of spectral radiation Stefan-Boltzmann constant of total radiation Grating spacing in calcite Å [Pg 262] APPENDIX A FROM MOBILITIES AND DIFFUSION COEFFICIENTS Fig. 38