ificed to information; but mental development is
sought through the student's willing and interested participation in
the actual daily happenings of the home and the shop and the field,
rather than through formal recitations and laboratory experiments.

Practical laboratory work in connection with the study of this book is
provided for in my _Laboratory Manual in General Science_, which
contains directions for a series of experiments designed to make the
pupil familiar with the facts and theories discussed in the textbook.

I have sought and have gained help from many of the standard
textbooks, new and old. The following firms have kindly placed cuts
at my disposal, and have thus materially aided in the preparation of
the illustrations: American Radiator Company; Commercial Museum,
Philadelphia; General Electric Company; Hershey Chocolate Company;
_Scientific American_; The Goulds Manufacturing Company; Victor
Talking Machine Company. Acknowledgment is also due to Professor Alvin
Davison for figures 19, 23, 29, 142, and 161.

Mr. W.D. Lewis, Principal of the William Penn High School, has read
the manuscript and has given me the benefit of his experience and
interest. Miss. Helen Hill, librarian of the same school, has been of
invaluable service as regards suggestions and proof reading. Miss.
Droege, of the Baldwin School, Bryn Mawr, has also been of very great
service. Practically all of my assistants have given of their time and
skill to the preparation of the work, but the list is too long for
individual mention.

BERTHA M. CLARK.

WILLIAM PENN HIGH SCHOOL.

CONTENTS

CHAPTER

I. HEAT

II. TEMPERATURE AND HEAT

III. OTHER FACTS ABOUT HEAT

IV. BURNING OR OXIDATION

V. FOOD

VI. WATER

VII. AIR

VIII. GENERAL PROPERTIES OF GASES

IX. INVISIBLE OBJECTS

X. LIGHT

XI. REFRACTION

XII. PHOTOGRAPHY

XIII. COLOR

XIV. HEAT AND LIGHT AS COMPANIONS

XV. ARTIFICIAL LIGHTING

XVI. MAN'S WAY OF HELPING HIMSELF

XVII. THE POWER BEHIND THE ENGINE

XVIII. PUMPS AND THEIR VALUE TO MAN

XIX. THE WATER PROBLEM OF A LARGE CITY

XX. MAN'S CONQUEST OF SUBSTANCES

XXI. FERMENTATION

XXII. BLEACHING

XXIII. DYEING

XXIV. CHEMICALS AS DISINFECTANTS AND PRESERVATIVES

XXV. DRUGS AND PATENT MEDICINES

XXVI. NITROGEN AND ITS RELAT