THE NEW YORK PUBLIC LIBRARY

ASTER, LENOX TILDEN FOUNDATIONG

THE PLANET EARTH

AN ASTRONOMICAL INTRODUCTION

ΤΟ

GEOGRAPHY

BY

RICHARD A. GREGORY, F.R.A.S.

OXFORD UNIVERSITY EXTENSION LECTURER

AUTHOR OF 'ELEMENTARY PHYSIOGRAPHY 'THE VAULT OF HEAVEN,' ETC.

TRANSFER FROM C. D.

AUG

1915

7463

PREFACE

525
es

IN class-books of astronomy and geography, facts
relating to the earth's movements and place in the
universe are usually treated in an inadequate manner.
Students are informed that the earth is a globe; that
it rotates on an axis; revolves round the sun, and is
one of a family of planets; but they are not taught
these matters scientifically. The scientific method
of observation and induction should be used in
elementary astronomy as in other physical sciences.
Celestial phenomena must be observed before the
theories that explain them can be properly understood.
This has been borne in mind in the design of the
following pages.
The first chapter deals with
star-groups and the apparent diurnal motion of
In the second chapter it is

the celestial sphere.

shown that all the phenomena previously described can be explained by the fact that the earth is a globe in rotation. The determination of the size