The Experimental and Historical Foundations ofElectricity The Experimental and Historical Foundations of Electricity deals with the most fundamental aspects of physics. The book describes the main experiments and discoveries in the history Andre Koch Torres Assis of electricity. It begins with the amber effect, which is analogous to the usual experiment of attracting small pieces of paper with a piece of plastic rubbed in hair. The book explains how to build several instruments: versorium, electric pendulum, electroscope and charge collectors. Electric attraction and repulsion, positive and negative charges, and the ACR mechanism (attraction, communication of electricity, and repulsion) are discussed. The concepts of conductors and insulators, together with the main differences in the behaviours of these two kinds of substances are analyzed. All experiments are clearly described and performed with simple, inexpensive materials. These experiments lead to clear concepts, definitions, and laws describing these phenomena. Historical aspects are presented, together with relevant quotations from the main scientists. The book presents an exhaustive analysis of the work of Stephen Gray (1666-1736), the great British scientist who discovered conductors and insulators, together with some of their main properties. An ample bibliography is included at the end of the work. About the Autor Andre Koch Torres Assis was born in Brazil (1962) and educated at the University of Campinas – UNICAMP, BS Assis Apeiron Assis (1983), PhD (1987). He spent the academic year of 1988 in England with a post-doctoral position at the Culham Laboratory (United Kingdom Atomic Energy Authority). He spent one year in 1991-92 as a Visiting Scholar at the Center for Electromagnetics Research of Northeastern University (Boston, USA). From August 2001 to November 2002, and from February to May 2009, he worked at the Institute for the History of Natural Sciences, Hamburg University (Hamburg, Germany) with research fellowships awarded by the Alexander von Humboldt Foundation of Germany. He is the author of Weber’s Electrodynamics (1994), Relational Mechanics (1999), Inductance and Force The Experimental Calculations in Electrical Circuits (with M. A. Bueno, 2001), The Electric Force of a Current (with J. A. Hernandes, 2007), and Archimedes, the Center of ISBN 978-0-9864926-3-1 and Historical Gravity, and the First Law of Mechanics (2008). He has been professor of physics at UNICAMP since 1989, working Foundations of on the foundations of electromagnetism, gravitation, ,!7IA9I6-ejcgdb! and cosmology. Electricity The Experimental and Historical Foundations of Electricity Andre Koch Torres Assis Apeiron Montreal Published by C. Roy Keys Inc. 4405, rue St-Dominique Montreal, Quebec H2W 2B2 Canada http://redshift.vif.com © Andre Koch Torres Assis, 2010. First Published 2010 Library and Archives Canada Cataloguing in Publication Assis, André Koch Torres, 1962- The experimental and historical foundations of electricity / André Koch Torres Assis. Includes bibliographical references. ISBN 978-0-9864926-3-1 1. Electricity--Experiments. 2. Electricity--History. I. Title. QC533.A88 2010 537'.078 C2010-901025-6 Front cover: The experiment by Stephen Gray (1666-1736) with the sus- pended boy (1731) as represented in Doppelmayr’s book, Neu-entdeckte Phaenomena von bewunderswürdigen Würkungen der Natur, Nurenburg, 1774. A boy is suspended by insulating lines. A rubbed glass tube is brought near his legs. The hands and face of the boy attract light bodies. Back cover: Photos of instruments described in this book. A metal versorium. A Du Fay versorium made of plastic with the tip of one of its legs wrapped in aluminum foil. An electric pendulum with a paper disk attached to a silk thread tied to a plastic straw. An electrified electroscope with its raised strip made of tissue paper. The thin cardboard of the electroscope is attached to a plastic straw. Contents Presentation and Acknowledgments 7 1 Introduction 11 2 Electrification by Friction 15 2.1 TheBeginningoftheStudyofElectricity . 15 2.2 TheAmberEffect .......................... 17 2.3 Exploring the Attraction Exerted by Rubbed Bodies . 20 2.4 Which Bodies are Attracted by the Rubbed Plastic? . 21 2.5 IsitPossibletoAttractLiquids? . 23 2.6 Gilbert and Some of His Electrical Experiments . 25 2.7 What Rubbed Substances Attract Light Bodies? . 28 2.8 Gilbert’s Nomenclature: Electric and Non-Electric Bodies .... 29 3 The Versorium 33 3.1 Fracastoro’s Perpendiculo and Gilbert’s Versorium . ..... 33 3.2 MakingaVersorium ......................... 36 3.2.1 VersoriumoftheFirstKind . 36 3.2.2 VersoriumoftheSecondKind. 37 3.2.3 VersoriumoftheThirdKind . 40 3.3 ExperimentswiththeVersorium . 41 3.4 IsitPossibletoMaptheElectricForce? . 43 3.5 Is There Action and Reaction in Electrostatics? . 46 3.6 Fabri and Boyle Discover Mutual Electrical Action . 50 3.7 NewtonandElectricity. 55 4 ElectricalAttractionandRepulsion 59 4.1 IsThereElectricalRepulsion?. 59 4.2 Guericke’s Experiment with a Floating Down Feather . 62 4.3 Du Fay Recognizes Electrical Repulsion as a Real Phenomenon . 68 4.4 TheElectricPendulum. 71 4.5 DischargebyGrounding . 76 4.6 Gray’sElectricPendulum . 78 4.7 TheDuFayVersorium. .. 79 3 4.8 The ACR Mechanism ........................ 82 4.9 Gray’sPendulousThread . 85 4.10 MappingtheElectricForce . 87 4.11 Hauksbee and the Mapping of Electric Forces . 91 5 Positive and Negative Charges 95 5.1 IsThereOnlyOneKindofCharge? . 95 5.2 DuFayDiscoversTwoKindsofElectricity . 106 5.3 Which Kind of Charge does a Body Acquire by Friction? . 111 5.4 TheTriboelectricSeries . 119 5.5 Are Attractions and Repulsions Equally Frequent? . 124 5.6 Variation of the Electric Force as a Function of Distance . 125 5.7 Variation of the Electric Force with the Quantity of Charge . 127 6 Conductors and Insulators 133 6.1 TheElectroscope ........................... 133 6.2 ExperimentswiththeElectroscope . 136 6.3 Which Bodies Discharge an Electroscope by Contact? . 142 6.3.1 Definitions of Conductors and Insulators . 143 6.3.2 Bodies which Behave as Conductors and Insulators in the Usual Experiments of Electrostatics . 146 6.4 Which Bodies Charge an Electroscope by Contact? . 148 6.5 Fundamental Components of a Versorium, an Electric Pendulum, andanElectroscope . 150 6.6 Influence of the Electric Potential Difference upon the Conduct- ingorInsulatingBehaviourofaBody . 151 6.6.1 Substances which Behave as Conductors and Insulators forSmallPotentialDifferences . 155 6.7 Other Aspects which have an Influence upon the Conducting and InsulatingPropertiesofaSubstance . 156 6.7.1 The Time Necessary in order to Discharge an Electrified Electroscope ......................... 157 6.7.2 The Length of a Substance which Comes into Contact withanElectrifiedElectroscope. 157 6.7.3 The Cross-Sectional Area of a Substance which Comes into Contact with an Electrified Electroscope . 158 6.8 ElectrifyingaConductorbyFriction . 158 6.9 ConservationofElectricCharge. 159 6.10 Gray and the Conservation of Electric Charges . 164 6.11 A Short History of the Electroscope and the Electrometer . 165 7 DifferencesbetweenConductorsandInsulators 173 7.1 Mobility of Charges on Conductors and Insulators . 173 7.2 ChargeCollectors. 174 7.3 TheElectricPolarizationofConductors . 177 7.3.1 AepinusandElectricPolarization. 181 4 7.4 Attractions and Repulsions Exerted by a Polarized Body . 182 7.5 Utilizing Polarization to Charge an Electroscope . 187 7.5.1 First Procedure of Electrification by Induction . 187 7.5.2 Second Procedure of Electrification by Induction . 189 7.5.3 Third Procedure of Electrification by Induction . 191 7.6 TheElectricPolarization ofInsulators . 192 7.7 Does an Electrified Body Attract a Conductor or an Insulator More? .................................194 7.7.1 Discussion of Gray’s Electric Pendulum . 197 7.8 ForcesofNon-ElectrostaticOrigin . 198 7.9 Microscopic Models of Conductors and Insulators . 199 7.10 Can Two Bodies Electrified with Charges of the Same Sign At- tractOneAnother?. 202 7.11 TheConductivityofWater . 206 7.12 IsitPossibletoElectrifyWater? . 207 7.12.1 Kelvin’sElectrostaticGenerator . 208 7.13 TheConductivityofAir . 211 7.14 How to Discharge an Electrified Insulator? . 212 7.15 A Small Piece of Paper is Attract with a Greater Force when AboveanInsulatororaConductor? . 215 8 Final Considerations 219 8.1 Changing Names and Meanings: From Electric and Non-Electric BodiestoInsulatorsandConductors . 219 8.2 Simple and Primitive Facts about Electricity . 220 8.3 DescriptionoftheAmberEffect. 223 Appendices 231 A Definitions 231 B Stephen Gray and the Discovery of Electrical Conduction 233 B.1 Gray’sElectricalGenerator . 234 B.2 The Discovery of Electrification by Communication . 236 B.3 Exploring the Discovery and Awakening the Hidden Electricity ofMetals ...............................239 B.4 Gray Discovers Conductors and Insulators . 241 B.5 Discovery that What makes a Body Behave as a Conductor or as an Insulator Depends upon Its Intrinsic Properties . 246 B.6 Discovery that Electrification by Communication Happens at a Distance................................ 247 B.7 TheExperimentwiththeSuspendedBoy . 251 B.8 Discovery that Free Charges are Distributed over the Surface of Conductors .............................. 254 B.9 DiscoveryofthePowerofPoints . 256 B.10Conclusion .............................. 257 5 Bibliography 259 6 Presentation and Acknowledgments In the early 1990’s I discovered the work of Norberto Cardoso Ferreira, of the Institute of Physics at the University of