The careful examination which I have been led to give to the whole of the phenomena which Mars presents, and especially to the discoveries of Mr. Lowell, has led me to what I hope will be considered a satisfactory physical explanation of them. This explanation, which occupies the whole of my seventh chapter, is founded upon a special mode of origin for Mars, derived from the Meteoritic Hypothesis, now very widely adopted by astronomers and physicists. Then, by a comparison with certain well-known and widely spread geological phenomena, I show how the great features of Mars--the 'canals' and 'oases'--may have been caused. This chapter will perhaps be the most interesting to the general reader, as furnishing a quite natural explanation of features of the planet which have been termed 'non-natural' by Mr. Lowell. Incidentally, also, I have been led to an explanation of the highly volcanic nature of the moon's surface. This seems to me absolutely to require some such origin as Sir George Darwin has given it, and thus furnishes corroborative proof of the accuracy of the hypothesis that our moon has had an unique origin among the known satellites, in having been thrown off from the earth itself. I am indebted to Professor J. H. Poynting, of the University of Birmingham, for valuable suggestions on some of the more difficult points of mathematical physics here discussed, and also for the critical note (at the end of Chapter V.) on Professor Lowell's estimate of the temperature of Mars. BROADSTONE, DORSET, _October_ 1907. TABLE OF CONTENTS. CHAPTER I. EARLY OBSERVERS OF MARS, --Mars the only planet the surface of which is distinctly visible --Early observation of the snow-caps and seas --The 'canals' seen by Schiaparelli in 1877 --Double canals first seen in 1881 --Round spots at intersection of canals seen by Pickering in 1892 --Confirmed by Lowell in 1894 --Changes of colour seen in 1892 and 1894 --Existence of seas doubted by Pickering and Barnard in 1894. CHAPTER II. MR. LOWELL'S DISCOVERIES AND THEORIES, --Observatory at Flagstaff, Arizona --Illustrated book on his observations of Mars --Volume on Mars and its canals, 1906 --Non-natural features --The canals as irrigation works of an intelligent race --A challenge to the thinking world --The canals as described and mapped by Mr. Lowell --The double canals --Dimensions of the canals --They cross the supposed seas --Circular black spots termed oases --An interesting volume. CHAPTER III.