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measurement of the, 172 Disc Electrometer, the Attracted, 90 Distribution, Electrical, 24 Distribution of Current, 217 Dry Cell, the, 202 Dynamo Machines, 395 Earth, Magnetism of the, 171 Electric Attraction, 3; explanation of, 8, 9; theory of Potential applied to, 41 Electric Currents, 182; measure- ment of, 185; tubes of force and, 186; effectsdueto, 188; magnetic action of, 188 ; thermal effects of, 191 ; chemical action of, 191 ; experiments on, 245; heating of conductor by, 286 Electric Discharge through Gases, 418 Electric Force, Law of, 45 ; result- ant at a point, 47 Electric inertia, 411 Electric Intensity, 47 Electric motors, 401 Electric Spark, the, 72 Electric Telegraph, the, 406 Electric Waves, 414 Electrical Action, Theories of, 23 Electrical Distribution, 24 Electrical Energy, 291 Electrical Power, 291 Electrical Pressure, or Potential, 26 ; explanation of, 28 Electricity, quantity of, 19; thermo-, 293 ; observations on, 294 INDEX 437 Electritication, 4, 5; by induction, 7 Electro-chemical equivalents, 5; determination of, 250 Electrodynamometer, the, 367 Electrolysis, observations on, 193; Faraday's laws of, 194; trans- formations in, 304 • Ionic charge in, 421, 425 Electromagnetic Action, 328, 337; between conductors, 336 Electromagnetic forces, 331 Electromagnetic machfnes, 392 Electromagnets, 341 Electrometer, the Attracted Disc, 90; the Quadrant, 94 Electrometers and Electroscopes, 87 Electromotive Force, in a simple circuit, 210, 211; of a Daniell's cell, 303 ; standards of, 204 Electron Theory, 427; of Matter, 429 Electrons, 425 ; production of, 427 ; and galvanic action, 428 ; and magnetism, 429 Electrophorus, the, 74 Electroscopes, 9-15; condensing, 68 ; and electrometers, 87 Electrostatic Actions, explanation of, 23 Electrostatic Measurement of Po- tential, 93 Electrostatic and Multicellular Voltmeters, 97 Energy, of a Charged Conductor, 55 ; of a Charged Condenser, 62 Energy, Electrical, 291 ; needed to magnetise iron, 356 Energy changes in a cell, 302 Equilibrium condition, 337 Equipotential Surfaces, 31, 53 Equivalent, electro-chemical, 195, 250 Experiments with Leyden Jars, 68 Experiments with the Magnet- ometer, 157 Experiments on electric currents, 245 Experiments on batteries, 255 Explanation of Electrostatic Ac- tions, 23 Faraday's experiments on induc- tion, 373 Faraday's laws of electrolysis, 194 Field of Force, 39 Field, Magnetic, 111 ; tensions and pressures in, 118 Force, the Field of, 39 Force, Law of, 44 Force, -Lines of, 32 ; and equipoten- tial surfaces, 34; forms of, 35; magnetic, 112; tracing, 114; electromotive in a circuit, 210, 211 Frictional Machines, 70 Galvanic action, 428 Galvanometer, tangent, 227; con- struction of, 230 Galvanometer, sine, 229 Galvanometer, resistance of, 274 Galvanometer, ballistic, 279 Galvanometer Constant, 228 Galvanometers, 223, 226 ; sensitive, 232 ; moving coil, 361 Gases, electric discharge through, 418 Gramme ring, the, 397 Grove's Cell, 202 Holtz Machine, the, 82 Hysteresis, 354 Illustrations, Mechanical, 40 Inductance, unit of, 379 Induction, electrification by, 7; magnetic, 111, 342; curve of, 352 ; Faraday's experiments on, 373 ; coefficient of mutual, 377 ; observations on, 379 Induction Coil, the, 389 Inductive Capacity, 45, 62 Inertia, electric, 411 Influence, of Temperature, 130 ; of external fields, 371 Influence Machines, 77 Insulating Medium, importance of, 30 438 INDEX Insulators, Properties of, 7 Inverse Square, Laws of the, 155 Ionic charge in electrolysis, 421, 425 Iron, magnetic force in, 344; energy needed to magnetise, 356 Isoclinal Line, 176 Joule's Law, 287; applied to a battery, 290 Kathode Kays, 420 ; charge carried in, 422 ; number of particles in, 424 Keepers, Action of, 128 Kelvin's (Lord) Ampere Balance, Law, Joule's, 287; applied to a battery, 290; Lena's, 378 Law of Magnetic Force, 44, 122 ; due to a current, 236 Law, Ohm's, 212 ; graphic repre- sentation of, 218 ; observations on, 252 Laws, Sine and Tangent, 148; Law of the Inverse Square, 155 Leclanche Cell, the, 201 Lenz's Law, 378 Leyden Jar, 64 ; Batteries of, 66 ; experiments with, 68 Lines of Force, 32 ; and equipoten- tial surfaces, 34 ; forms of, 35 ; magnetic, 112 ; tracing, 114 Local Action, 197 Machines, Frictional, 70; Plate Electrical, 70; Influence, 77; Wimshurst's, 79 ; Holtz, 82 ; Voss, 85 Machines, electromagnetic, 392 ; magneto- electric, 393; dynamo, 395 Magnet, in a Uniform Field, 135 ; magnetic force due to a simple, 138 ; forces on one due to a second, 141 ; determination of the axis of, 168 ; action on a current, 326 Magnet, rotation about a current, 339 Magnetic Action of Electric Cur- rent, 188 Magnetic Attraction, 108; Induc- tion, 111, 342 ; curve of, 352 ; Field, 111; tensions and pres- sures in, 118; Lines of Force, 112; Pole, Unit, 123 Magnetic Batteries, 127 Magnetic Charge, Total, 124 Magnetic Force, due to a Closed Cycle, 134 ; due to a simple magnetf 138 ; law of due to a current, 2JJ1V-323 Magnetic- Force, Law of, 122 ; Ke- sultant, 125 ; in a crevasse, 344 ; in a mass of iron, 344 ; transmis- sion of, 414 Magnetic Maps, 174 ; Storms, 179 Magnetic Moment, measurement of the strength of a, 163 Magnetic Permeability , 346 ; mea- surement of, 349, 383 ; circuit, 347 ; reluctance, 347 Magnetic Potential, 125 Magnetic Shells, _325 Magnetic Survey, 174 Magnetisation, Methods of, 126 ; Theory of, 130, 855 Magnetism, Charges of, 122 Magnetism of the Earth, 171 ; se- cular variations of, 178 Magneto-electric machines, 393 Magnetometer, experiments with the, 157; the mirror, 160 Magnets, Natural, 105 ; Artificial, 106 ; Solenoidal, 124 ; Total Mag- netic Charge of, 124 ; molecular, 131 Maps, Magnetic, 174 Matter, electron theory of, 429 Maximum Strength of the Pole of a Magnet, 130 Measure of Potential, 49 Measurement of Potential, Electro- static, 93 Measurement, of the Dip, 172 ; of the Declination, 174 ; of electric currents, 185 ; of magnetic per- INDEX 439 meability, 349 ; of alternating current, 371 Measurement, Units of, 46 Mechanical Illustrations, 40 Medium, Insulating, importance of, 30 Methods of Magnetisation, 126 Microphone, the, 409 Mirror Magnetometer, the, 160 Molecular Magnets, 131 Morse Instrument, the, 407; Morse Alphabet, the, 408 Motor, transformations of energy in, 402; starting a, 403 Motors, electric, 401 Moving Coil Galvanometers, 361 Multicellular and Electrostatic Voltmeters, 9.7 Multiple Arc, batteries in, 208 Mutual Induction, coefficient of, 377 Natural Magnets, 105 Non-Conductors and Conductors, 5, 6 Observations, on Electrolysis, 193 ; on Ohm's Law, 252 : on Induc- tion, 379 Ohm's Law, 212 ; graphic repre- sentation of, 218 ; observations on, 252 Particles in Kathode Kays, 424 Peltier effect, the, 296 Permeability, magnetic, 346 ; measurement of, 349, 383 Plate Electrical Machine, 70 Platinum Thermometer, the, 300 Pole, Unit Magnetic, 123 Pole of a Magnet, Maximum Strength, 130 Potential or Electrical Pressure, 26 ; explanation of, 28 ; zero of, 29; analogy between tempera- ture and, 29 ; applied to electrical attraction, 41 ; measure of, 49 ; unit of, 51 ; calculation of, 51 ; relation of charge and, 54 Potential, Electrostatic Measure- ment of, 93 ; magnetic, 125 ; contact, 314 Potential at a point in the air, 99 Potential of a charged conductor, 53 Potentiometer, the, 260, 261 Power, Electrical, 291 Practical Unit of Current, 225 Principles of Transformers, 388 Production of Electrons, 427 Proof Plane, the, 15, 16 Properties of Insulators, 7 Quadrant Electrometer, the, 94 Quantity of Electricity, 19 Kays, Kathode, 420; charge carried in, 422 ; number of particles in, 424 ; Kontgen, 426 Reactions, Armature, 399 Reduction Factor, 228 Relation of Charge and Potential, 54 Reluctance, magnetic, 347 Replenisher, the, 77 Resistance, unit of, 213 ; specific, 216, 277 ; of galvanometer, 274 ; of a battery, 275 Resistance Boxes, 240 Resistances, comparison of, 264 Resultant Electric Force, 47, 48 ; at a point, 47 Resultant Magnetic Force, 125 Rontgen Rays, 426 Rotation of a magnet, 339 Secondary Batteries, 205 Secular variations of the Earth's magnetism, 178 Self-induction, 378 Sensitive Galvanometers, 232 Shells, Magnetic, 325 Shunts, 242, 364 Shuttle wound Armature, 394 Sine Galvanometer, 229 Sine and Tangent Laws, 148 Single fluid cells, 200 Solenoid, 330 Spark, the Electric, 72 Specific Resistance, 216, 277 Square, Law of the Inverse, 155 440 INDEX Standards of electromotive force, 204 Storms, magnetic, 179 Strength of the Pole of a Magnet, 130 Surface Density, 24 Surfaces, Equipotential, 31, 53 ; and lines of force, 34 Survey, Magnetic, 174 Susceptibility, 129 Tangent Galvanometer, 227 ; con- struction of, 230 Tangent Laws, 148 Telegraph, the electric, 406 Telegraphy, wireless, 416 Telephone, the, 408 Temperature, 29 ; influence of, 130 Tensions and Pressures in Magnetic Field, 118 Theories of Electrical Action, 23 Theory, of Magnetisation, 130, 355; Volta's, 309 Theory of Potential applied to Electrical Attraction, 41 Thermal effects of a Current, 191 Thermo-electricity, 293 ; observa- tions on, 294 Thermometer, the Platinum, 300 Thermopile, the, 299 Thomson effect, the, 298 Torsion Balance, Coulomb's, 87 Total Magnetic Charge, 124 Tracing lines of Force, 114 Transformations in electrolysis, 304 ; in a Voltaic cell, 30G ; of energy in a motor, 402 Transformers, 391 ; principles of, 388 Transmission of magnetic force, 414 Tubes of Force and Electric Cur- rents, 186 Two fluid batteries, 202 Uniform Field, Magnet in a, 135 ; measurement of the strength of a, 163 Unit of Capacity, 285 Unit of Current, practical, 225 Unit of Inductance, 379 Unit Magnetic Pole, 123 Unit of 'Potential, 51 Unit of Resistance, 213 Units of Measurement, 46 Vacuum, contact experiments in, 313 Variations, secular, 178; daily, 178 ; annual, 178 Voltaic Cell, the, 182,197 ; chemical theory of, 219 ; contact theory of, 221 ; transformations in, 306 Volta's Theory, 309 Voltmeters, 254, 366 ; electrostatic and multicellular, 97 Voss Machine, the, 85 Water-dropping Accumulator, the, 85 Waves, Electric, 414 Weston Cell, the, 205 Wheatstone's Bridge, 268 Wimshurst's Machine, 79 Wireless Telegraphy, 416 Zero of Potential, 29 CAMBRIDGE: PRINTED BY j. UNIVERSITY OF CALIFORNIA LIBRARY This book is DUE on the last date stamped below. ^ tj 1 jf *1 f °CT 25 1 DEC 3 1947 Jct'48 50 i 3 1957 RE:C REC'D LI JAN 2i 1958 |,iA LD 21-100m-12,'46(A2012sl6)41 REC'D LD (RPR 2 s 9 >63 -10PM ftEC'D LD JU'64-*PM. 