PLATE PAGE Gassendi _Frontispiece_ I.—Summit of Vesuvius 26 II.—Wrinkled Hand and Apple 30 III.—Full Moon Photograph 52 IV.—Picture-Map of the Moon {_To face each other._} V.—Skeleton Map 68 VI.—Terrestrial and Lunar Volcanic Areas Compared 88 VII.—Progressive Series of Craters 92 VIII.—Copernicus 96 IX.—The Lunar Apennines, &c., &c. 100 X.—Aristotle and Eudoxus 104 XI.—Triesnecker 108 XII.—Theophilus, Cyrillus, and Catharina 112 XIII.—Arzachael, Ptolemy, and the Railway 116 XIV.—Plato, the Valley of the Alps, Pico, &c. 120 XV.—Mercator and Campanus 124 XVI.—Tycho and its Surroundings 128 XVII.—Wargentin 132 XVIII.—Aristarchus and Herodotus 136 XIX.—Glass Globe Cracked by Internal Pressure 140 XX.—Overlapping Craters 148 XXI.—Lunar Crater. Ideal Landscape 156 XXII.—Solar Eclipse as it would be seen from the Moon 164 XXIII.—Group of Mountains. Ideal Lunar Landscape 170 THE MOON. CHAPTER I. ON THE COSMICAL ORIGIN OF THE PLANETS OF THE SOLAR SYSTEM. In this Chapter we propose to treat briefly of the probable formation of the various members of the solar system from matter which previously existed in space in a condition different from that in which we at present find it—_i.e._, in the form of planets and satellites.