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

CHAPTERPAGE
I.[Heat][9]
II.[Temperature and Heat][27]
III.[Other Facts about Heat][31]
IV.[Burning or Oxidation][45]
V.[Food ][60]
VI.[Water ][70]
VII.[Air ][81]
VIII.[General Properties of Gases ][93]
IX.[Invisible Objects ][100]
X.[Light ][104]
XI.[Refraction ][113]
XII.[Photography ][126]
XIII.[Color ][134]
XIV.[Heat and Light as Companions] [142]
XV.[Artificial Lighting ][148]
XVI.[Man's Way of Helping Himself ][154]
XVII.[The Power behind the Engine ][176]
XVIII.[Pumps and their Value to Man ][187]
XIX.[The Water Problem of a Large City ][206]
XX.[Man's Conquest of Substances ][218]
XXI.[Fermentation ][232]
XXII.[Bleaching ][237]
XXIII.[Dyeing ][244]
XXIV.[Chemicals as Disinfectants and Preservatives] [250]
XXV.[Drugs and Patent Medicines ][255]
XXVI.[Nitrogen and its Relation to Plants ][261]
XXVII.[Sound] [266]
XXVIII.[Musical Instruments ][284]
XXIX.[Speaking and Hearing ][300]
XXX.[Electricity ][306]
XXXI.[Some Uses of Electricity][312]
XXXII.[Modern Electrical Inventions ][318]
XXXIII.[Magnets and Currents ][328]
XXXIV.[How Electricity may be Measured ][339]
XXXV.[How Electricity is obtained on a Large Scale ][346]
[Index ] [353]

GENERAL SCIENCE

CHAPTER I