coincidence in the past. No attempt can be made to answer the question as yet, but it opens a most fascinating field of speculation and of investigation. If the activities of the earth and of the sun are related to one another in any such manner as is suggested above, the study of the one will add vastly to our knowledge of the other. An examination of solar changes, on the one hand, may enable us to foretell something of what is about to occur upon the earth. A careful reading of the geological history of the earth, on the other hand, may disclose the history of the sun for millions of years past, and may shed light upon the fascinating problem of the thermal history and ultimate destiny of the body which, as knowledge increases, appears more and more to be the arbiter of terrestrial life.