ols, Winnetka, Illinois_
_Formerly Supervisor in Physical Sciences and
Instructor in Educational Psychology_
_State Normal School_
_San Francisco, California_

_ILLUSTRATED_
WITH PHOTOGRAPHS AND
DRAWINGS

_Yonkers-on-Hudson, New York_
WORLD BOOK COMPANY
1921

WORLD BOOK COMPANY

THE HOUSE OF APPLIED KNOWLEDGE

Established, 1905, by Caspar W. Hodgson
YONKERS-ON-HUDSON, NEW YORK
2126 PRAIRIE AVENUE, CHICAGO

One of the results of the World War has been a widespread desire
to see the forces of science which proved so mighty in destruction
employed generally and systematically for the promotion of human
welfare. World Book Company, whose motto is The Application of the
World's Knowledge to the World's Needs, has been much in sympathy
with the movement to make science an integral part of our elementary
education, so that all our people from the highest to the lowest will
be able to use it for themselves and to appreciate the possibilities
of ameliorating the conditions of human life by its application to the
problems that confront us. We count it our good fortune, therefore,
that we are able at this time to offer _Common Science_ to the
schools. It is one of the new type of texts that are built on
educational research and not by guess, and we believe it to be a
substantial contribution to the teaching of the subject

NWSS:WCS-2

Copyright, 1920, by World Book Company

Copyright in Great Britain

_All rights reserved_

PREFACE

A collection of about 2000 questions asked by children forms the
foundation on which this book is built. Rather than decide what it is
that children ought to know, or what knowledge could best be fitted
into some educational theory, an attempt was made to find out what
children want to know. The obvious way to discover this was to let
them ask questions.

The questions collected were asked by several hundred children in the
upper elementary grades, over a period of a year and a half. They
were then sorted and classified according to the scientific principles
needed in order to answer them. These principles constitute the
skeleton of this course. The questions gave a very fair indication of
the parts of science in which children are most interested.
Physics, in simple, qualitative form,--not mathematical physics, of
cou