gases can the moon contain--The question
of water and of former oceans--The great volcanic cataclysm
in the moon's history--Evidence of volcanic and other
changes now occurring--Is there vegetation on the
moon?--Lunar day and night--The earth as seen from the
moon--Discoveries yet to be made

CHAPTER IX

_HOW TO FIND THE PLANETS_ 256

It is easy to make acquaintance with the planets and to
follow them among the stars--The first step a knowledge of
the constellations--How this is to be acquired--How to use
the Nautical Almanac in connection with the charts in this
book--The visibility of Mercury and Venus--The oppositions
of Mars, Jupiter, and Saturn

INDEX 277

LIST OF ILLUSTRATIONS

PAGE
Chart of Mars _Frontispiece_

Diagram showing causes of day and night on portions of Mercury 35

Regions of day and night on Mercury 38

Venus's atmosphere seen as a ring of light 56

View of Jupiter _facing_ 168

Three views of Saturn _facing_ 186

Diagram showing the moon's path through space 217

The lunar Alps, Apennines, and Caucasus _facing_ 222

The moon at first and last quarter _facing_ 226

Phases and rotation of the moon 250

Charts showing the zodiacal constellations:
1. From right ascension 0 hours to 4 hours 259
2. " " 4 " " 8 " 261
3. " " 8 " " 2 " 263
4. " " 12 " " 16 " 265
5. " " 16 " " 20 " 267
6. " " 20 " " 24 " 269

OTHER WORLDS

CHAPTER I

INTRODUCTORY

Other worlds and their inhabitants are remarkably popular subjects of
speculation at the present time. Every day we hear people asking one
another if it is true that we shall soon be able to communicate with
some of the far-off globes, such as Mars, that circ