Enough tables have been introduced to fill the limits of the subject as here treated. The full development of electrical laws involves the higher mathematics. One who would keep up with the progress of the day in theory has a severe course of study before him. In practical work it is believed that such a volume as the Arithmetic of Electricity will always have a place. We hope that it will be favorably received by our readers and that their indulgence will give it a more extended field of usefulness than it can pretend to deserve. PREFACE TO TWENTY-FIRST EDITION. The steady progress of electrical science in conjunction with a continued demand for this work have made advisable a revision and extension of this book. The author feels that in the matter which has been added much more could have been said on the subjects treated of, but, since a full exposition of each theme would alone fill a volume, it is hoped that the practical value of the rules, etc., will atone for the brevity of the text. In the preparation of this edition the author would express his indebtedness to A. A. Atkinson's excellent work on Electrical and Magnetic Calculations and also to the instruction papers of the Electrical Engineering Course of the International Correspondence School of Scranton, Pa. He would also express his thanks to Henry V. A. Parsell, for his valued advice and assistance in the preparation of the manuscript. THE AUTHOR. CONTENTS. Mass General Statement.-Six Rules Derived by Transpos- ition from the Law.-Single Conductor Closed Circuits. -Batteries in Opposition.-Portions of Circuits.-Di- Drop of Potential in Leads, and Size of Same for Mul- The Mil.-The Circular Mil as a Unit of Area.-Cir- cular Mil Rules for Resistance and Size of Leads......... 43 Three Wire System.-Rules for Calculating Leads in Energy and Heating Effect of the Current.-Differ- ent Rules Based on Joule's Law.-The Joule or Gram- Calorie. Quantity of Heat Developed in an Active Cir- cuit in a Unit of Time. -Watts and Amperes in Rela- tion to Time.-Specific Heat.-Heating of Wire by a Current.-Safety Fuses.-Work of a Current.-Elec- Arrangement of Battery Cells.-General Calcula- tions of Current.-Rules for Arrangement of Cells in a Battery.-Battery Calculations for Specified Electromotive Force and Current.-Efficiency of Batteries.-Chemistry of Batteries.-Calculation of Voltage.-Work of Batteries.-Efficiency of Bat- teries, to Calculate.-Chemicals Consumed in a ELECTRO-MAGNETS, DYNAMOS AND MOTORS. The Magnetic Field and Lines of Force.-Per- meance and Reluctance.-Magnetizing Force and the Magnetic Circuit.-General Rules for Electro- Magnets and Ampere-Turns for Given Magnetic Flux.-Magnetic Circuit Calculations.-Leakage of Lines of Force.-Example of Calculation of a Mag- netic Circuit.-Dynamo Armatures.-Voltage and Capacity of Armatures.-Drum Type Closed Cir- |