In testing all the hypotheses here discussed, primary and secondary alike, the first necessity is a far greater amount of quantitative work. In this book there has been a constant attempt to subject every hypothesis to the test of statistical facts of observation. Nevertheless, we have been breaking so much new ground that in many cases exact facts are not yet available, while in others they can be properly investigated only by specialists in physics, astronomy, or mathematics. In most cases the next great step is to ascertain whether the forces here called upon are actually great enough to produce the observed results. Even though they act only as a means of releasing the far greater forces due to the contraction of the earth and the sun, they need to be rigidly tested as to their ability to play even this minor role. Still another line of study that cries aloud for research is a fuller comparison between earthquakes on the one hand and meteorological conditions and the wandering of the poles on the other. Finally, an extremely interesting and hopeful quest is the determination of the positions and movements of additional stars and other celestial bodies, the faint and invisible as well as the bright, in order to ascertain the probable magnitude of their influence upon the sun and thus upon the earth at various times in the past and in the future. Perhaps we are even now approaching some star that will some day give rise to a period of climatic stress like that of the fourteenth century, or possibly to a glacial epoch. Or perhaps the variations in others of the nearer stars as well as Alpha Centauri may show a close relation to changes in the sun.