Produced by Chris Curnow and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive) _NATURE'S MIRACLES, VOL. III._ Electricity and Magnetism BY ELISHA GRAY, PH.D., LL.D. WILLIAM BRIGGS 29-33 Richmond St. West, Toronto C. W. COATES, Montreal, Que. S. F. HUESTIS, Halifax, N.S. CONTENTS. CHAPTER PAGE INTRODUCTION v I. THE AUTHOR'S DESIGN 1 II. HISTORY OF ELECTRICAL SCIENCE 6 III. HISTORY OF MAGNETISM 20 IV. THEORY AND NATURE OF MAGNETISM 25 V. THEORY OF ELECTRICITY 39 VI. ELECTRICAL CURRENTS 49 VII. ELECTRIC GENERATORS 62 VIII. ATMOSPHERIC ELECTRICITY 77 IX. ELECTRICAL MEASUREMENT 83 X. THE ELECTRIC TELEGRAPH 88 XI. RECEIVING MESSAGES 103 XII. MISCELLANEOUS METHODS 108 XIII. MULTIPLE TRANSMISSION 114 XIV. WAY DUPLEX SYSTEM 129 XV. THE TELEPHONE 134 XVI. HOW THE TELEPHONE TALKS 145 XVII. SUBMARINE TELEGRAPHY 154 XVIII. SHORT-LINE TELEGRAPHS 159 XIX. THE TELAUTOGRAPH 165 XX. SOME CURIOSITIES 171 XXI. WIRELESS TELEGRAPHY 176 XXII. NIAGARA FALLS POWER--INTRODUCTION 186 XXIII. NIAGARA FALLS POWER--APPLIANCES 190 XXIV. NIAGARA FALLS POWER--APPLIANCES 199 XXV. ELECTRICAL PRODUCTS--CARBORUNDUM 209 XXVI. ELECTRICAL PRODUCTS--BLEACHING-POWDER 218 XXVII. ELECTRICAL PRODUCTS--ALUMINUM 223 XXVIII. ELECTRICAL PRODUCTS--CALCIUM CARBIDE 228 XXIX. THE NEW ERA 234 INTRODUCTION. For the benefit of the readers of Vol. III, who have not read the general Introduction found in Vol. I, a word as to the scope and object of this volume will not be amiss. It will be plain to any one on seeing the size of the little book that it cannot be an exhaustive treatise on a subject so large as that of Electricity. This volume, like the others, is intended for popular reading, and technical terms are avoided as far as possible, or when used clearly explained. The subject is treated historically, theoretically, and practically.