How many thousands of educated people, trained in the best schools, or even graduates of the great universities, have made the confession: “I never got a grip on astronomy in my student days. They didn't make it either plain or interesting to me; and now I am sorry for it.”

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.”

The author has been sparing in the use of diagrams, because he believes that, in many cases, they have been over-pressed. There is a tendency to try to represent everything to the eye. This is well to a certain extent, but there is danger that by pursuing this method too far the power of mental comprehension will be weakened. After all, it is only by an intelligent use of the imagination that progress can be made in such a science as astronomy. The reader is urged to make a serious effort to understand what is said in the text, and to picture it in his mind's eye, before referring to the diagrams. After he has thus presented the subject to his imagination, he may refer to the illustrations, and correct with their aid any misapprehension. For this reason the cuts, with their descriptions, have been made independent of the regular text.