ield of interest opened to the human mind by man's discoveries
concerning worlds, which, though inaccessible to him in a physical
sense, offer intellectual conquests of the noblest description.

And, finally, in order to assist those who may wish to recognize for
themselves these other worlds in the sky, this book presents a special
series of charts to illustrate a method of finding the planets which
requires no observatory and no instruments, and only such knowledge of
the starry heavens as anybody can easily acquire.

G.P.S.

BOROUGH OF BROOKLYN, NEW YORK CITY,
_September, 1901._

CONTENTS

CHAPTER I

_INTRODUCTORY_ 1

Remarkable popular interest in questions concerning
other worlds and their inhabitants--Theories of
interplanetary communication--The plurality of worlds in
literature--Romances of foreign planets--Scientific interest
in the subject--Opposing views based on telescopic and
spectroscopic revelations--Changes of opinion--Desirability
of a popular presentation of the latest facts--The natural
tendency to regard other planets as habitable--Some of the
conditions and limitations of the problem--The solar system
viewed from outer space--The resemblances and contrasts of
its various planets--Three planetary groups recognized--The
family character of the solar system

CHAPTER II

_MERCURY, A WORLD OF TWO FACES AND MANY CONTRASTS_ 18

Grotesqueness of Mercury considered as a world--Its
dimensions, mass, and movements--The question of an
atmosphere--Mercury's visibility from the earth--Its
eccentric orbit, and rapid changes of distance from the
sun--Momentous consequences of these peculiarities--A
virtual fall of fourteen million miles toward the sun
in six weeks--The tremendous heat poured upon Mercury
and its great variations--The little planet's singular
manner of rotation on its axis--Schiaparelli's astonishing
discovery--A day side and a night side--Interesting effects
of libration--The heavens as viewed from Mercury--Can it
support life?

CHAPTER III

_VENUS, THE TWIN OF THE EARTH_ 46

A planet that matches ours in size--Its beauty in the
sky--Remarkable circularity of its orbit--Probable
absence of seasons and stable conditions of temperature
and wea