Transcriber’s Notes Text printed in italics has been transcribed _between underscores_, bold face text has been transcribed =between equal signs=. Small capitals have been replaced with all capitals. Single letters in square brackets, such as [T] and [V], represent shapes rather than letters. More Transcriber’s Notes may be found at the end of this text. Harper’s Practical Books for Boys A SERIES OF NEW HANDY-BOOKS FOR AMERICAN BOYS _Each Crown 8vo, with many Illustrations._ I HARPER’S OUTDOOR BOOK FOR BOYS By Joseph H. Adams. With Additional Contributions by Kirk Munroe, Tappan Adney, Capt. Howard Patterson, L. M. Yale, and others. Cloth, $1.75. II HARPER’S ELECTRICITY BOOK FOR BOYS Written and Illustrated by Joseph H. Adams. With a Dictionary of Electrical Terms. Cloth, $1.75. _IN PRESS_ III HARPER’S HOW TO UNDERSTAND ELECTRICAL WORK A Simple Explanation of Electric Light, Heat, Power, and Traction in Daily Life. By Joseph B. Baker, Technical Editor, U. S. Geological Survey, formerly of the General Electric Company. IV HARPER’S INDOOR BOOK FOR BOYS By Joseph H. Adams and others. Cloth, $1.75. V HARPER’S MACHINERY BOOK FOR BOYS The Boy’s Own Book of Engines and Machinery. Cloth, $1.75. HARPER & BROTHERS, PUBLISHERS, NEW YORK [Illustration: Copyright, 1907, by Joseph H. Adams, N. Y. THOMAS A. EDISON DICTATING TO HIS GRAPHOPHONE] HARPER’S ELECTRICITY BOOK FOR BOYS WRITTEN AND ILLUSTRATED BY =JOSEPH H. ADAMS= AUTHOR OF “HARPER’S OUTDOOR BOOK FOR BOYS” WITH AN EXPLANATION OF ELECTRIC LIGHT, HEAT POWER, AND TRACTION BY JOSEPH B. BAKER TECHNICAL EDITOR, U. S. GEOLOGICAL SURVEY AND =A DICTIONARY OF ELECTRICAL TERMS= [Illustration] HARPER & BROTHERS PUBLISHERS NEW YORK AND LONDON MCMVII Copyright, 1907, by HARPER & BROTHERS. _All rights reserved._ Published November, 1907. CONTENTS PAGE INTRODUCTION xi Part I CHAPTER I.--SOME GENERAL EXPLANATIONS 3 AN INVISIBLE WORLD-POWER -- GENERATING ELECTRICITY -- WHAT A BOY CAN DO -- INEXPENSIVE TOOLS -- SOME PRACTICAL ADVICE CHAPTER II.--CELLS AND BATTERIES 12 SIMPLE AND INEXPENSIVE CELLS -- HOW TO MAKE CELLS AND BATTERIES -- A PLUNGE-BATTERY -- A STORAGE-BATTERY -- DRY-CELLS AND BATTERIES CHAPTER III.--PUSH-BUTTONS AND SWITCHES 33 HOW TO MAKE PUSH-BUTTONS -- SWITCHES AND CUT-OUTS -- TABLE-JACK SWITCHES -- BINDING-POSTS AND CONNECTORS -- LIGHTNING-ARRESTERS AND FUSE-BLOCKS -- SOME PRACTICAL PRECAUTIONS CHAPTER IV.--MAGNETS AND INDUCTION-COILS 54