The book itself contains incidentally a good deal of matter concerned with the Astronomy of the past, the introduction of which has been found necessary in order to make clearer the Astronomy of our time. It would be quite impossible for me to enumerate here the many sources from which information has been drawn. But I acknowledge my especial indebtedness to Professor F.R. Moulton's _Introduction to Astronomy_ (Macmillan, 1906), to the works on Eclipses of the late Rev. S.J. Johnson and of Mr. W.T. Lynn, and to the excellent _Journals of the British Astronomical Association_. Further, for those grand questions concerned with the Stellar Universe at large, I owe a very deep debt to the writings of the famous American astronomer, Professor Simon Newcomb, and of our own countryman, Mr. John Ellard Gore; to the latter of whom I am under an additional obligation for much valuable information privately rendered. In my search for suitable illustrations, I have been greatly aided by the kindly advice of Mr. W. H. Wesley, the Assistant Secretary of the Royal Astronomical Society. To those who have been so good as to permit me to reproduce pictures and photographs, I desire to record my best thanks as follows:--To the French Artist, Mdlle. Andrée Moch; to the Astronomer Royal; to Sir David Gill, K.C.B., LL.D., F.R.S.; to the Council of the Royal Astronomical Society; to Professor E.B. Frost, Director of the Yerkes Observatory; to M.P. Puiseux, of the Paris Observatory; to Dr. Max Wolf, of Heidelberg; to Professor Percival Lowell; to the Rev. Theodore E.R. Phillips, M.A., F.R.A.S.; to Mr. W.H. Wesley; to the Warner and Swasey Co., of Cleveland, Ohio, U.S.A.; to the publishers of _Knowledge_, and to Messrs. Sampson, Low & Co. For permission to reproduce the beautiful photograph of the Spiral Nebula in Canes Venatici (Plate XXII.), I am indebted to the distinguished astronomer, the late Dr. W.E. Wilson, D.Sc., F.R.S., whose untimely death, I regret to state, occurred in the early part of this year. Finally, my best thanks are due to Mr. John Ellard Gore, F.R.A.S., M.R.I.A., to Mr. W.H. Wesley, and to Mr. John Butler Burke, M.A., of Cambridge, for their kindness in reading the proof-sheets. CECIL G. DOLMAGE. LONDON, S.W., _August 4, 1908._ PREFATORY NOTE TO THE SECOND EDITION The author of this book lived only long enough to hear of the favour with which it had been received, and to make a few corrections in view of the second edition which it has so soon reached. _December 1908._ CONTENTS CHAPTER I PAGE THE ANCIENT VIEW 17 CHAPTER II THE MODERN VIEW 20 CHAPTER III THE SOLAR SYSTEM 29 CHAPTER IV CELESTIAL MECHANISM 38 CHAPTER V CELESTIAL DISTANCES 46 CHAPTER VI CELESTIAL MEASUREMENT 55