The purpose of the writer of this book is to supply the need of such persons, either in school, or at home, after school-days are ended. He does not address himself to special students of the subject—although they, too, may find the book useful at the beginning—but to that vast, intelligent public for whom astronomy is, more or less, a “mystical midland,” from which, occasionally, fascinating news comes to their ears. The ordinary text-book is too overladen with technical details, and too summary in its treatment of the general subject, to catch and hold the attention of those who have no special preliminary interest in astronomy. The aim here is to tell all that really needs to be told, and no more, and to put it as perspicuously, compactly, and interestingly, as possible. For that reason the book is called a “nutshell.”