None
INS Gold-leaf Electroscope, Testing Sign of Charge and Potential with, 219 Electroscope, When Used, 192 for Electroscope, Weight and Price of, 194 Gold-Silver Alloy, Resistance of, per Centimetre Cube, and per Inch Cube, 259 Alloy, Resistance of, per Foot Grain and per Metre Gramme, 261 Alloy, Resistance of, Percentage Variation per 1°C., 266 Graduating Voltmeter by Potentio- meter Method with Clark's Cell, 516 Graphically Recording Results of Experiments, 50-62 Recording Results of Experiment for Calibrating Galvanometer, Recording Results of Experi- ments, Value of, 55 Gravity Control Ammeter. (Sec Ammeter, Gravity Control.) Daniell's Cells, 431-433 Deflectional Wattmeter, 332 Gray's Investigations on Electro- chemical Equivalents of Copper, 28 Grove's Cell. (See Cell, Grove's.) Gutta-Percha, Resistance of, per Centimetre Cube, 268 Variation in Resistance of, with Temperature. 268 Heat of Combustion, Measurement of, 478, 481 and Electric Conductivities, Comparison of, 275 Equivalent of Electric Energy, Measuring, 319-324 Insulators for, Inferior to Those for Electricity, 276 Produced by Current, 5, 9, 314 Produced in Transformation of Energy, 404 Rate at which Electric Energy in Circuit or Cell Converted into, 318, 370, 380-384 Rate of Production of, by Current, Measuring, 319-394 Unit of, 318 Heating Property of Current Un- suitable for Measuring Cur- rent, 9, 12, 19 Heating Property of Current, Uses of, 9 Hellesen Dry Cell, 458 Helmholtz, Alteration in Definition of Ohm Suggested by, 589 Henry, Definition of, 591 Hermetically Sealed, Definition of, Note, 42 High Resistance Galvanometer, Why Used for P.D. Measurements, 178 Resistance Voltmeter, When Used, 181 Higher Potential of Conductor, Defini- tion of, 162 Himstcdt, Ohm Determined by, 583 Hoffmann's Sulphuric Acid Volta- meter, 32 Horizontal Component of the Earth's Magnetic Force, Meaning of, Note, 103 Horse-Power, Definition of, 327 Power, Value of Watt in, 327 Power Hours, Value of Board of Trade Unit in, 349 Shoe Magnets. JOU 625 Insulating Stand, Description of, 216 Insulator, Electric, Meaning of, 14, 276 International Ampere, Definition of, 590 Ohm, Definition of, 173, 591 Ohm in Terms of Legal Ohm and B.A. Unit, 174 Volt, Definition of, 174, 590 Volt in Terms of Legal and B.A. Volts, 175 Interpolation, Definition of. 55 Invariable Sensibility, Galvanometers of, 127 Iron Filings for Magnetic Lines of Force Diagrams, Preparation of, 565 Filings, Mapping Out Lines of Force with, 71-75, 77 Magnetised by Current, 3, 5, Relative Electric and Heat Conductivities of, 275 Resistance of, per Centimetre Cube and per Inch Cube, 259, 271 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, perl°C., 266, 271 Wire, Disadvantages of, for Re- sistances, 269 Jacobi's Proposed Standard of Re- sistance, 569 " Ja Ja " Wire, Use of, Note, 312 Wire, Resistance of, per Centi- metre Cube, 271 ; Note, 312 Wire, Resistance, Percentage Temperature Variation of, 271 ; Note, 312 Jenkin, Fleeming, and Clerk Max- well's Article on Elementary Relations between Electrical Measurements, Reference to, 574 Jones, Viriamu, Determination of Length of Mercury Column Representing One Ohm by, 586, 599 Joule, Electrical Determination of Mechanical Equivalent of Heat by. 576 Determination of Ohm by, 582 Definition of, 317, 591 Value of, in Foot Pounds and in Ergs, 317 Joules, Value of Board of Trade Unit in, 349 per Second, Value of Watt in, 326 Joulemeter, Definition of, 334 Arori Type of Gaining Clock Form, 338 Ayrton and Perry's Original Gaining Clock Form, 334-338 Clock, Force Between Coils of, Small Compared with Force of Gravity, 336 Clock, Gain or Loss of, in Fixed Time Proportional to Energy Given to Circuit, 336 Clock, Limit to Proportionality between Gain of, and Energy Supplied, 338 Clock, Method of Joining Up and Using, 388 Clock, Permanent Magnet Pen- dulum Form, 338 Clock, Type Used when Energy Supplied at Constant Rate, 338 Clock, Varying Rate of Vibra- tion of Pendulum, 336 Elihu Thomson. LIN Joulemeter, Thomson, Retarding Torque in, How Produced, 346 - — Thomson,Retarding and Driving Torques, Conditions Govern- ing Equality between, 347 Joulemeters, Motor and Clock Forms of, Compared, 348 Kahle's Modification of Rayleigh's H Form of Clark's Cell, 472 Kathode, Definition of, 24, 33 for Silver Voltameter, Descrip- tion of, 23, 26 Weights of Metals Deposited on, 27 Kelvin's Addition to Weber's Abso- lute System of Units, 571 Deflectional Wattmeter, 332 Method of Calculating E.M.F. of Cell from Chemical Action, 477-479, 575 Moving Coil Galvanometer, Principle of, 130 Key for Making Two Sets of Connec- tions, 236 Method of Cleaning Contact Points of, 287 Sliding, Use of Platinum Irid- ium Wire with, 510 Used with Wheatstone's Bridge, 250 Used with Shunt to Wheat- stone's Bridge, 252 Kilowatt, Value of, in Horse-Power, 327 Kimball and Rowland, Ohm Deter- mined by, 583 Rowland, and Duncan, Ohm Determined by, 583 KirchhofTs Absolute Measurement of Resistance, 571 Kohlrausch, Ohm Determined by, 577, 582 Lalands-Chaperon Cell, 4(32 Lamps, Glow. (See Glow Lamps.) Latimer Clark, Cell Devised by. (See Cell, Clark's.) Clark Proposes Names Ohmad and Volt, 573, 576 Lead Foil for Electroscope Leaves, When used, 106 Lead Foil, Relative Electric and Heat Conductivities of, 275 Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, for 1°C., 266 Leaves of Electroscope, 193-196 Leclanche Cell. (See Cell, Leclanche.) Legal Ohm, Definition of, 583 Ohm of 1884, Error in, 584 ; Note, 600 Ohm, Value of, in Terms of B.A. Unit and International Ohm, 174 Volt, Definition of, 583 Volt, Value of, in Terms of B.A. Volt and International Volt, 175 Legislation of Electrical Standards, 592 Lenz, Ohm Determined by, 5.S2 Proposed Unit of Resistance, 568, 569 Lighting, Electric, Accumulators Used in, 527 Electric, Comparative Cost of Using Dynamo and Cells for, 482-491 Electric, Conditions for Com- mercial Use of Galvanic Cells for, 491 Electric, of House, 300 Electric, Legal Maximum Varia- tion of Pressure between House Mains, 358, 490 Electric, Method of Making Cur- rent in Each Lamp Inde- pendent of Current in all Others, 302 Electric, P.D. between House Mains, 300 Electric, Resistance of House Wires Compared with Re- sistance of Lamp Filaments, 302 Lines of Force Diagrams, Preparation of Filings for, 565 of Force Diagrams, Preparation of Waxed Paper fur, r,w of Force Mapped out by Using Compass Needle, 76 of Force Mapped out by Using Iron Filings, 71-75, 77 of Force, Methods of Mapping Out Compared, 77 of Force, Precautions in Mapping Out, 77 of Force with Bar Magnets, 72, LIN INDEX. MAI 627 Lines of Force with Circular Coil Carrying Current, 71 of Force with Horse-shoe Mag- nets, 74, 75 Liquid Decomposed by Electric Current, 4, 10. (See also Cell, Chemical Action in.) Load Diagram, Example of, 327 Local Action, Definition of, 429 Action, How Caused in Cell, 429 Action, Method of Preventing in Cell, 429 Action, None in Edison- Lalande Cell, 464, 465 Currents, Meaning of, 429 Lorenz, Ohm Determined by, 577, 582, 583 Loss of Head, Definition of, 153 of Head and Rate of Flow of Water, Curve Connecting, 168 Lower Potential, Definition of, 162 Low Resistance Ammeter, Use of, as Voltmeter, 181 Magnet and Conductor with Cut rent Passing, Force Exerted be- tween, 3, 129 Deflection of, by Electric Cur- rent, 3, 5, 34, 69 Forces Exerted on Compass Needle by Different Parts of, 67 Forces Exerted on Soft Iron by Different Parts of, 67 Motions of Rotation and Trans- lation Produced by, 138 North-seeking End of, Defini- tion of, Note, 34 • Pendulum, Permanent, of Clock Joulemeter, 338 Permanent, Measuring Distribu- tion of Magnetism in, 63 Magnets, Force Exerted between, 63 Lines of Force due to, 72 Stationary, in Ammeters, Re- sults of Weakening, 135, 150, 151 Magnetic Axis, Definition of, 67 Control, How Produced in Moving Coil Ammeter, 150 Control, Moving Coil Ammeter with, 150 Experiments, Precautions Neces- sary when Making, 66 Field at Centre of Coil, Descrip- tion of, 80 Magnetic Field of Earth, ' Action of, 67, 77 Field of Earth, Arrangement for Neutralising, 78 Field of Earth, Disturbing Action of, on Another Mag- netic Field, 77 Field, Mapping Out Lines of Force in, 71-77, 565 Field, Relative Strengths of Different Parts of, 79 Field, Strength of. MEA Mains, House, P.D. between, 301, 526 House, Resistance of, Compared with Resistance of Lamps, 302 House and Street, Impossibility of Keeping Pressure Con- stant at Every Junction of, 526 Method of Keeping Pressure between, Constant at Certain Points, 526 Manganese Alloys, Composition of, 268 Dioxide Consumed in Leclanche Cell per Board of Trade Unit Produced, Weight and Cost of, 487 Dioxide Consumed in Leclanch6 Cell per Hour per 3,000 Am- peres, 484 Manganin, Composition of, 260 Resistance of, per Centimetre Cube, and per Inch Cube, 260, 269, 271 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Variation of, with Temperature, 269, 271 Specific Resistance of, Compared with that of Copper, 269 Used for Resistance Coils, 269, 280, 519 Mapping out Lines of Force, 71-77, 565 Mascart Criticises Methods Used for Determining Ohm, 585 De Nerville and Benoit, Ohm Determined by, 582 Mather and Ayrton. (See Ayrton and Mather.) and Walmsley's Proportional Galvanometer, 125 Matthiessen, Law Connecting Varia- tion of Resistance of Metals with Temperature, 264 Papers on Temperature Varia- tion of Resistance of Metals and Alloys by, Reference to. 574 Maximum Current for Cell, Safety Limitation of, 559 Current Through Fixed External Resistance, Arranging Given Number of Cells to Produce, 545 Maxwell, Clerk, and Fleeming Jen- kin's Article on Elementary Relations between Electrical Measurements, Reference to, 674 Maxwell's Moving Coil Galvanometer, Principle of, 130 Measure of Current Strength, Choice of, 9-23 Measurements, Electrical, Com- mittees to Consider Units for, 572, 578, 579, 581. 584, 587, 588, 590, 592 Electrical, History of Units for, 568-600. (See also Ampere, Ohm, and Volt.) Measuring Back E.M.F. in Circuit 371 Current, Board of Trade De- scription of Method of, 25, 595 Current, Principle of Board of Trade Standards for, 588 Current with Ammeter, 127 (See also Ammeter.) Current with Calorimeter, 12 Current with Clark's Cell and Known Resistance, 519 Current with Electromagnet, 10 Current with Galvanometer, 43. (See also Galvanometer.) Current with Galvanoscope, 10, Current with Copper Voltameter, 10, 26 Current with Silver Voltameter, 23-29, 595 Current with Sulphuric Acid Voltameter, 10, 38, 39 Current with Voltameters and Galvanometers, Relative Ad- vantages of, 42 Current with Voltmeter and Fixed Resistance, 189 Currents Passing Through Two Conductors in Parallel, 238 Distribution of Magnetism in Permanent Magnet, 63 Distribution of Gas Pressure, 158 Distribution of Water Pressure, 154 Electric Density, 224, 225 Electric Energy, 313-324, 334- 348. (See also Jonlemeter.) Electricity Produced by Rubbing Two Bodies Together, 214 E.M.F. of Cell and of Battery, 362, 365, 477, 502-510 • E.M.F. of Current-Generator, when Variable, 369 E.M.F., Back, in Circuit, 371 — - Heat Equivalent of Electric Energy, 319 -Instruments, Methods of In- creasing Indications of, 43 MEA INDEX. MOT 629 Measuring Quantities of Electricity, Relatively, 212 P.D. with Ammeter and Resist- ance, 185 P.D. with Clark's Cell, 510, 516 P.D. with Current Voltmeter, 179 P.D. Electrostatically, 102, 191 P.D. (See also Comparing P.'Ds., 176.) P.O., Principle of Board of Trade Standards for, 588 Power, 325, 328. (See also Watt- meter.) Resistance with Ammeter and Voltmeter, 185, 232 Resistance with Ohmmeter, 233 Resistance. (See also Comparing Resistances. ) Resistance of Cell, Choice of Method for, 498 Resistance of Cell When Not Very Small, 493 Resistance of Cell, When Very Small, 366, 492 Strengths of Different Parts of Magnetic Field, 79 Variation of Resistance with Temperature, 2»i2 Mechanical Energy, Conversion of Energy of Current into, 314 Meidinger Cell, 431 Mercurous Sulphate for Clark's Cell, Preparation of, 468, 470, 597 Sulphate and Zinc Sulphate Paste for Clark's Cell, Pre- paration of, 468, 472, 598 Mercury, Effect of Adding Zinc, 430 for Clark's Cell, Preparation of, 467, 597 and Copper, Relative Resist- ances of, 269 Ohm, Mass and Length of Column, 173, 589, 593 Ohm, Section and Length of Column, 580, 586, 587, 600 Resistance of, per Centimetre Cube and per Inch Cube, 260 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, per 1°C., 266 Resistance of, at Any Tempera- ture, Formula Giving, 269 Siemens Unit, Section and Length of Column, 570 Switch-board for Batteries, 170, 539 Switch-board, Method of Avoid- ing Possibility of Short- Circuiting Cell when Using, 540 Mercury Switch-board, Positions of Bridge Pieces of, Giving Dif- ferent Arrangements of Cells, 541 Troughs Used as Adjustable Re- sistance for Large Currents, 270 Metallic Case, Advantage of En- closing Electrical Apparatus in, 197, 200 Metals, Law Connecting Variation of Resistance of, with Temper- ature, 264 Resistances of, per Centimetre Cube and per Inch Cube, 257, 259, 271 Resistances of, per Foot Grain and per Metre Gramme, 261 Resistances of, Percentage Variation per 1°C., 266 Resistances of, Relatively to Aluminium for Same Length and Weight, 261 Resistances of, Relatively to Silver for Same Length and Section, 259 Temperature Coefficients of Resistances of, 264-267 Meter, Aron Supply, 338 Aron Supply, Differential Gearing of, 340 Energy. OHM Motor, Method of Keeping Torque Constant between Field and Armature in, 342 Moving Coil Ammeter. (See Ammeter, Moving Coil.) Coil Voltmeter, 183 Muirhead's Telegraph Battery, 434 Multiplying Power of Shunt, Defini- tion of, 290 N Nalder Gravity Control Ammeter. 141 Needle of Compass. (See Compass Needle.) of Electrical Measuring Instru- ment, Definition of, Note, 164 of Galvanometer. (See Galvano- meter Needle.) Magnetic, Why Tends to Point North and South, 67 Needles Used in Various Forms of Ammeters, 134, 140, 141, 142 Negative Charge, What is Meant by, 160, 218 Electrification, What is Meant by, 161 Plate of Cells. (See Plate, Nega- tive, of Cells.) Potential, Definition of, 162 Nerville, De, Mascart, and Benoit, Ohm Determined by, 582 Neutralising Uniform Magnetic Field, Arrangement for, 78 Nickel, Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot Grain and per Metre Gramme, 261 Temperature Coefficient of Re- sistance of, 266 Nitric Acid Consumed in Grove's Cell per Board of Trade Unit Pro- duced. Weight and Cost of, 486 Acid Consumed in Grove's Cell per Hour per 1,000 Amperes, 440, 441, 484 Acid, Heat Absorbed in Decom- position of, 481 Peroxide Formed per Hour per Ampere in Grove's Cell, 440, 441 Peroxide, Heat of Formation of, 481 Non-inductive Resistance Coil for Large Currents, Ayrton and Mather's, 282 North-Seeking End of Magnet, Defini- tion of, Note, 34 Obach Dry Cell, 460 Ohm, Board of Trade, International, and Legal, Definitions of, 173, 578, 583, 587, 589, 591, 593 Legal, and International, and B.A. Unit, Values of, in Terms of Each Other, 174 B.A. Unit Less than, 570 Board of Trade Standard, 594, 595 Determined by British Associa- tion Committee, 581 Determined by Dorn, 582 Determined by Fletcher, 583 Determined by Hinstedt. 583, 585 Determined by Glazebrook, 582 Determined by Jones, 586, 600 Determined by Joule, 581 Determined by Kohlrausch, 577, 582 Determined by Lenz, 5S2 Determined by Lorenz, 577, 582, 583, 585 Determined by Mascart, De Nerville, and Benoit, 582 Determined by Rayleigh, 577, 581, 585 Determined by Rayleigh and Schuster, 581, 585 Determined by Rayleigh and Mrs. Sidgwick, 582 Determined by Roiti, 582, 585 Determined by Rowland, 577, 582, 585 Determined by Rowland and Kimball, 583 Determined by Rowland, Kim- ball, and Duncan, 583 Determined by Weber, 577, 581, 582, 585 Determined by Wiedemanu, 582 Determined by Wild, 582 • Legal of 1884, Error in, Note, 600 Mercury, Mass and Length of Column, 173, 589, 593 Mercury, Section and Length of Column, 580, 586, 587, 600 Methods of Ascertaining Equi- valent Mercury Column, 580, 581, 585 in Terms of Absolute Electro- magnetic, or C.G.S. PHO Orclinates, Definition of, 57 Outside Circuit. (See Circuit, Ex- ternal.) Oxide of Copper. (See Copper Oxide.) Oxygen Deposited on Copper Plate of Cell, Effect of, 462 and Hydrogen, Proportions of, Evolved in Sulphuric Acid Voltameter, 32 Liberated per Second per Ampere in Sulphuric Acid Volta- meter, 33 Parallax, Definition of, 50 How Avoided in Measuring- Instruments, 50, 331 Parallel, Apparatus in, Definition of, 20 and Parallel-Series, Cells Joined in, 536 and Parallel-Series, Joining Cells in, by Means of Mercury Switchboard, 541 Circuits, Independence of Cur- rents in, 525 Conductors, Ratio of Currents in, to Current in Main, 295 Resistance, 291 P.O., Absolute Electromagnetic Unit of, Definition of, 479, 575 between Conductors Enclosing, One Another, 218 between Conductors, How Shown, 161 between House Mains, 301, 526 between Terminals of Battery, E.M.F., Resistance and Cur- rent, 364, 380 between Terminals of Battery when Maximum Power Given to External Circuit, 389, 548 between Terminals of Edison - Lalande Battery, Variation of, with Current Passing, 464 between Terminals of Cell, Con- stant with Low Internal Re- sistance, 522 between Terminals of Clark's Cell, and Unit of Pressure, 589, 594 between Terminals of Hellesen Cell, Fall of, with Current Passing, 459 between Terminals of Obach Cell, Fall of, with Current Passing, 462 — — between Terminals of Circuit and Current, Power Given to Cir- cuit in Terms of, 326, 370 P.O. net) Magnet, Distribution of Mag. netism in, 63 Perry and Ayrton. (See Ayrton and Perry.) Phosphor Bronze, Resistance of, per Centimetre Cube and per Inch Cube, 259, 271 632 rno PRACTICAL ELECTRICITY. TOR Phosphor Bronze, Resistance of, per Foot Grain, and per Metre Gramme, 262 Bronze, Resistance, Percentage Variation of, per 1°C., 271 Pivot and Fibre Suspensions of Gal- vanometer Needle, 110 Plante", Invention of Accumulators by, 527 Plate, Carbon, of Cells, 443, 445, 450, 452, 458, 4(50, 401 Copper, of Cells, 419, 421, 431, 433, 435 Copper, of Simple Voltaic Ele- ment, Liberation of Hydro- gen at, 419 Copper, of Simple Voltaic Ele- ment, Experiment to Show Back E.M.F. Set Up at, 421 Copper, of Simple Voltaic Ele- ment, Polarisation at, 420, 422 Copper Oxide, of Cell, 462, 463 Negative, of Cells, 419, 423, 431, 433, 435, 438, 443, 445, 450, 452, 453, 455, 460, 461, 462 Platinum, of Cells,? 423, 438, 482 Positive, of Cell, Definition of, 376. (See also Plate, Zinc.) Zinc, of Cells, 419, 423, 431, 433, 435, 438, 445, 450, 454, 455, 458, 459, 460, 461, 462, 463 Zinc, Effect of Amalgamating. onE.M.P. of Cell, 430 Zinc, Method of Amalgamating, 429 Plates of Cell, Signs of, 376 of Cells, Variation of Resistance with Position of, 434 Used in Muirhead's Battery, 435 Platinoid, Composition of, 268 Resistance of, per Centimetre Cube and per Inch Cube, 260, 268, 271 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Temper- ature Variation of, per 1°C., 268, 271 Used for Resistance Coils, 268, 280, 519 Platinum, Combination of, with Hy- drogen in Smee's Cell, 482 Plate of Cells, 423, 438, 482 Relative Electric and Heat Con- ductivities of, 275 — Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot Grain and per Metre Gramme, 261 Platinum, Temperature Coefficients of Resistance of, 2(J5 Platinum-Iridium Wire, Use of, with Sliding Key, 510 Platinum-Silver Alloy, Resistance of, per Centimetre Cube and per Inch Cube, 259 Alloy, Resistance of, per Foot Grain and per Metre Gramme, 261 Alloy, Resistance, Percentage Variation of, per 1°C., 266, 267, 271 Wire Used in Resistance Coils, 280 Plug Key for Making Two Sets of Connections, 230 Resistance Boxes, Construction and Use of, 278 of Shunt Box, Construction and Use of, 296, 297 Poggendorff's Method of Comparing E.M.Fs., 507 Method of Comparing E.M.Fs., How to Obtain Accuracy in, 510 Polarisation of Cell, Definition of, 304 Cell Arranged for Experiments on, 422 of Cell, Effect of, on E.M.F., 364, 477 of Clark's Cell, 477 of Edison-Lalande Cell, 464 of Leclanche Cells, 456 of Simple Voltaic Element, Cause and Effect of, 420 of Simple Voltaic Element, Seat of, Experimentally Shown, 423 Current in Voltaic Element, 422 Polarity, Magnetic, and Direction of Current Round Magnet, 34- 36, 69 Pole, Unit Magnetic, Definition of, 571 Poles, Magnetic, Action between, when Similar and Dissimilar, 69 Magnetic, Definition of, 67 Porous Partition, Absence of, in Gravity Daniell's Cell, 431, 432 Partition of Daniell's Cell, Pre- venting Formation of Copper in Pores of, 431 Partition of Daniell's Cells, Variation of Resistance with Construction of, 434 Pot of Daniell's Cell, 425 FOR INDEX. POW 633 Porous Pot, Potassium Bichromate Cell with, 446 Portable Galvanometer, 127 Forms of Wheatstone's Bridge, 285 Positive Electrification, What is Meant by, 161 Plate of Cell, Definition of, 376 — Plate of Cell. (See Plate, Zinc, of Cell.) Potential, Definition of, 162 Terminal of Cell, Definition of, 376 Post Office Wheatstone's Bridge, 285 Potassium Bichromate Cell, 445. (See «hn Cell, Potassium Bichro- mate.) Bichromate Consumed in Cell ]>er Board of Trade Unit Pro- duced, Weight and Cost of, 487 Bichromate Consumed in Cell per Hour per 1,000 Amperes, 484 Potential in Cell, Method of Varia- tion of, Uncertain, 374 of Conductor Proportional to Quantity of Electricity on Conductor, 211 - — of Conductor, What is Meant by 200 Difference. (See P.D.) Distribution of, in Cell and Battery, Diagram Showing, 374 Distribution of, in Circuit, Dia- gram Showing, 376 Distribution of, in Circuit with Opposing E.M.F., Diagram Showing, 378 Distribution of, and of Fluid Pressure, 155, 167, 173 of Earth, Arbitrary Value Given to, 160 Electric, Compared with Fluid Pressure, 154, 155, 167, 173 Electric, Compared with <!us Pressure, 204, 207, 209, 231 — — Inside Closed Conductor, 107 Level, What is Meant by, 160 Measuring, 160, 200. RES Power, Maximum, from Given Current Generator, Circuit that Re- ceives, 385 Maximum, Arrangement of Bat- tery to Give, 345 Maximum, Arrangement of Part of External Circuit to Re- ceive, 393 Maximum, Generator Can De- liver, 389 Measuring, 325, 328 P.D., and Current, Relation between, 327, 370 Received, Variation of, from Maximum and Change in Current, 398 Received, Variation of, from Maximum and Change in Re- sistance, 399 • Units of, in Terms of Each Other, 327 Variable, Meaning of, 325 Pressure, Electric. (See P.D.) of Fluid Compared -with Elec- tric Potential, 154, 155, 167, 173 of Gas Compared with Electric Potential, 204, 207, 209, 231 of Gas, Variation of, with Mass, 207, 209 of Gas, Variation of, with Tem- perature, 204, 209 of Gas, Variation of, with Volume, 204, 209 between Mains, Maximum Legal Variation of, 358, 490 between Mains, Method of Keep- ing Constant at Certain Points, 526 — — at Every Junction of House and Street Mains, Impossi- bility of Keeping Constant, 526 Principle of Instruments Adopted as Board of Trade Standards for Measurement of, 588 Electrical Standards of, 595 Unit of. (See Unit of P.D.) Variation of Light of Glow Lamp with, 490 Price of Board of Trade Unit, 349 Primary Current, Direction of, in Experimental Voltaic Ele- ment, 423 Proof Plane, Description of, 224 Plane, Method of Measuring Charge on, 224 Properties of Electric Current, 3, 5 of Electric Current, Practical Uses of, 9 Property by which Current Strength is Best Measured, 10-22 Proportional Coil, 284, 287. (Sue also Coil, Proportional.) Galvanometer. (See Galvano- meter, Proportional.) Protractor, Use of, 59 Q Quantities of Electricity, Comparing, 211-217 Quantity of Electricity Produced by Rubbing Two Bodies To- gether, 214 of Electricity, Unit of, 579 of Electricity, What is Meant by, 208 Potential, and Density, Ex- amples Showing Difference between, 226 R Rayleigh, Ohm Determined by, 577, 581 and Mrs. Sidgwick, Ohm Deter- mined by, 582 and Schuster, Ohm Determined by, 581 Rayleigh's H Form of Clark's Cell, 466 Recording, Graphically, Results of Experiments, 50 Wattmeter. (See Joulemeter, Thomson.) Reduced Length of Conductor, What was Meant by, 568 Relative Calibration of Galvanometer, Meaning of, 45 — — Conductivities of Metals, per Cubic Unit, 275 Resistances of Metals and Alloys, 259, 261 Resinous Electrification, Definition of, 161 Resistance, 14, 172 Absolute Electromagnetic Unit of, 573, 591. (See also Unit of Resistance.) of Accumulator, 527 of Alloys, 259, 261. RES 635 Resistance, Apparent, of Arc, What is Meant by, 233 B.A. Unit of, 573. (See also Unit of Resistance, B.A.) of Battery with Cells Joined in Parallel, and in Parallel- Series, 538 of Battery of Given Number of Cells Sending Maximum Current, 545 of Battery, P.D. between Ter- minals, E.M.F., and Current, 364, 380 Box, Construction and Use of, 278, 279 Box, Values of Coils for, 283 of Cell, Conditions Governing, 434 of Cell, Choice of Method for Measuring, 498 • of Cell, Measuring, When Not Very Small, 493 of Cell, Measuring When Very Small, 366, 492 of Cell, P.D. between Terminals, E.M.P., and Current, 364, of Cell, and P.D. Maintained, 287, 522 — — and Clark's Cell Used as Cur- rent Standard, 519 used with Clark's Cell to Restore its E.M.F. to Normal Value, 477 of Daniell's Cell, Increase of, with Constancy and Porta- bility, 431 of Daniell's Cell, Variation of, with Temperature, 436 of Various Forms of Daniell's Cells, 435 of Edison-Lalande Cell, 464 of Grove's Cell, 440 of Grove's Cell Increases with Use of, 441 of Hellesen Dry Cell, 459 of Obach Dry Cell, 462 of Storage Cells, 527 of Circuit, Change in, with Use of Shunts, 307 of Circuit, and Heat Energy Produced in, 318, 370 of Circuit, Percentage Loss of Power Due to, 410 of External Circuit, and Power Received by Circuit, Con- nection between, 392, 399 of External Circuit, and Cost of Production of Electric Energy, 483 Coil, Ayrton and Mather's Non- inductive, for Large Currents, 282 Resistance Coil, Standard, 276 Coils, Description of, 46 Coils, Earliest Form of, 569 Coils, Kind and Gauge of Wire Used in, 281, 282, 519 Coils, Method of Avoiding Magnetic Effect of, 281 Coils, Method of Dissipating Heat Produced in, 281 Coils Specific Resistance and Percentage Temperature Vari- ation of Materials Used in, 271 Coils, Variation and Measure- ment of Temperature of, 280, 281 Coils, When Used, 278 Coils, Winding, 280 Combined, 291 Combined, in Terms of Resist- ances of Branch Circuits, 292, 293 of Conductor, Conditions Affect- ing, 253-271. (See also Re- sistance, Variation of.) of Copper, Temperature Varia- tion of, 265, 266 of Copper, Variation of, with Density, 258 Crompton Standard, 520 Current, Calories, and Time, Relation between, 378, 324 Known, Used in Measuring Current, 519 of House Mains Small Compared with Resistance of Lamps, 302 Measuring, with Ammeter and Voltmeter, 185, 232, 366, 492. (See also Resistances, Com- paring.) Measuring, with Ohmmeter, 233 Mercury Troughs Used as, 270 Metal having Least, for Given Length and Weight, 261 Metals having Least and Greatest, for Given Length and Section, 260 of Metals and Alloys, Law Connecting Variation of, with Temperature, 264, 265 of Metals and Alloys per Centi- metre Cube, and per Inch Cube, 257, 259, 271 of Metals and Alloys per Foot Grain and per Metre Gramme, 636 RES PRACTICAL ELECTRICITY. SEN Resistance of Metals and Alloys Per- centage Variation of, per TC., 266, 271 of Metals and Alloys, Tempera- ture-Coefficients of, 264-267 of Metals and Alloys Used in Resistance Coils, 271 Parallel, 291 Parallel, in Terms of Resistances of Branch Circuits, 292, 293 of Platinnm, Temperature Varia- tion of, 265, 266 Specific, How Expressed, 257 and Temperature-Coefficient of Materials, Relation between, 267 Testing Temperature 'Variation of, 262 Unit, of, Glim, Definition of, 178, 578, 583, 587, 591, 593. (See also Ohm.) Units of. (See Unit of Resist- *• ances.)' Variation of, with Cross-Section, 257 Variation of, with Length, 254 Variation of, with Material, 254. 257-262 Variation of, with Temperature, 233, 262-271 with Voltmeter Used as Am- meter, 189 of Weston Voltmeter, 183 Resistances, Comparing, by Simple Substitution, 235 in Parallel, Comparing, by Dif- ferential Galvanometer, 238 in Parallel, - Comparing, by Wheatstone's Bridge, 241-253 Compared by Wheatstone's Bridge, Limit to Range of, 277 Equal, Subdividing Wire into Lengths with, 513 Joined in Parallel with Battery, Currents in, 525 'Known, Calibrating Galvano- meter with, Methods of, 521 in Series, Comparing, 177, 184, 186 of Two Conductors in Parallel Inversely Proportional to Currents, 238, 290 Resultant of Two Forces, Method of Obtaining, 81 Roiti, Ohm Determined by, 582 Rowland, Ohm Determined by,577,582 and Kimball, Ohm Determined by, 583 Kimball, and Duncan, Ohm De- termined by, 583 Safety Limitation of. Maximum Cur- rent for Cell, 559 Sal Ammoniac Consumed in Le- clanche Cell per Board of Trade Unit Produced, Weight and Cost of, 487 Ammoniac Consumed in Le- clanch6 Cell per hour per 1,000 Amperes, 484 Scale of Ammeters, 129, 136, 139, 144 of Circular Metre Bridge, 247 of Evershed Ammeter, 144 for Galvanometer Divided into Degrees, Disadvantages of, 58 for Galvanometer Giving Rela- tive Strengths of Currents, Construction of, 59 for Galvanometer Giving Rela- tive Strengths of Current, Subdividing Angular Spaces of, 60 of Gravity Control Ammeters, 139, 144 of Magnifying Spring Am- meter, Conditions governing Equality of Divisions of, 136, of Ohmmeter, 235 of Permanent Magnet Ammeter, 130, 133 for Tangent Galvanometer, Con- struction of, 87 for Voltmeter, Direct Reading Electrostatic, Construction of, 181 of Voltmeter, Potentiometer Method of Testing Accuracy of, 510 of Weston Milammeter, 147 Schuckert's Gravity Control Am- meter, 140 Schuster and Rayleigh, Ohm Deter- mined by, 581 Screening Action of Conductor Snr- . rounding Charged Body, Con- ditions Governing, 223' Conductor when Comparing Quantities of Electricity, 212 Outside Space from Inside Elec- trostatic Action, 222 Secondary Current, Direction of, in Experimental Voltaic Ele- ment, 423 Self-induction, Unit of, 591 Sensibility in Ammeters, Adjust- ments for 183, 137, 142, 150 Invariable, Galvanometers of, 127 of Gold-leaf Electroscopes, 194 SEN INDEX. SIM 637 Sensibility of Tangent Galvanometer, Law and Variation of, 91, 98, 100, 102 in Voltmeter, Adjustment for (Examples 30, 31), 187, 188 Scries, Apparatus in, -Definition of, 20 and Parallel-Series, Cells Joined in, 536, 537 and Parallel-Series, Joining Cells in, by Means of Mercury Switch-board, 541 Short-Circuiting Cell, when Using Mercury Switch-board, How to Avoid Possibility of, 540 Ammeter, Result of, 181, 182 Voltmeter, Result of, 181, 182 Shunt, Description of, 110 and Galvanometer, Ratio of Currents in, 290 and Galvanometer, Ratio of Cur- rent in each to Whole Current, 290 Increase of Main Current Pro- duced by Applying, 298 Multiplying Power of, Definition of, 290 Use of, and Calibration of Gal- vanometer, 110 Used with Differential Galvano- meter, 241, 311 Used with Galvanometer, 110 Used with Wheutstone's Bridge, 252 Variation of Effect of, on Cur- rent, with Change of Ex- ternal Resistance, 299 Shunts, Parallel Arrangement of, 297 Series Arrangement of, 297 Universal, Principle and Use of, 303 Shunt Box, Ayrton and Mather's Universal, Construction of, 304 Box, Universal, Advantages of, 306 Box, Universal, Change in Re- sistance of Circuit Produced by Using, 307 Box, Universal, Employed with Any Galvanometer, 303 Box, Universal, Facility in Ad- justing Coils, 307 Box, Universal, Independent of Variations of Temperature While Using, 306 Box, Universal, Selection of Re- sistance for, 309 Box, High Insulation, Construc- tion of, 297 Box, Usual Form of, Arrange- ment of Coils in, 295 Shunt Box, Usual Form of, Necessity for Constant Temperature while Using, 306 Box, Usual Form of, Employ- ment of, 296 Box, Usual Form of, Resistances of Coils Used in, 295, 297 Box, Usual Method of Construct- ing, 295 Boxes, Universal, and Usual Form, Comparative Effects of, on Resistance of Circuit, 307 Sulgwick, Mrs., and Lord Rayleigli, Ohm Determined by, 582 Siemens' Law Connecting Variation of Resistance of Metals with Temperature, 265 Unit of Resistance, 570 Unit of Resistance, Objection to, 570 Sign of Charge or of Electrification, What is Meant by, 161, 218 of Charge, Testing, 221 of Potential, What is Meant by, 162 Silver, Atomic Weight of, 27 Conductivity of, 274 and Copper, Comparative Rates of Electric Deposition of, 28 Deposited per Second, per Am- pere, 23, 588, 593 Deposited per Second, Unit of Current Defined by, 23, 29, 588, 593 Relative Electric and Heat Con- ductivities of, 275 Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, per 1°C., 266 Voltameter. in, 422 638 SIM PRACTICAL ELECTRICITY SWI Simple Voltaic Element, Polarisation in, Cause and Effect of, 420 Sine of Angle, Definition of, 111 Galvanometer, 118, 119. (See also Galvanometer, Calibra- ting on Sine Principle.) — Law Experimentally Tested, 113-118 Law, Methods of Keeping Angle Between Deflecting Force and Deflected Body Constant, 113 Principle Employed in Galvano- meters, 118 Single Circuit, Definition of, 377 Circuit Electromotor, Definition of, Note, 371 Fluid Cells, 418, 445, 450, 462 Slider with Wire Bridge, 249, 250 Smee's Cell, 423, 482 Sodium Bichromate, Chromic Acid for Cell Formed from, 448 Solder to Use with Phosphor Bronze Suspension, 149 Spark, Electric, Shows P.D. between Conductors, 161 Specific Gravities of Mixtures of Sul- phuric Acid and Water, 39 Heat, Definition of, Note, 262 Resistance of Copper, Variation of, with Density, 258, Note, 312 Resistance of a Material, How Expressed, 257 Resistances of Materials Used in Resistance Coils, 271 Resistances of Metals and Alloys per Centimetre Cube and per Inch Cube, 257, 259 Resistances of Metals and Alloys per Foot Grain and per Metre Gramme, 260, 261 Spring-Balance, Methods of Increas- ing Indications of, 43 Magnifying, Description of, 64 Magnifying, Law of, 65 Squared Paper, Use of, 50, 53 Stand, Insulating, Description of, 216 Standard of Current, Board of Trade, 587, 594, 595 of Current, Use of Clark's Cell and Known Resistance as, 519 of Pressure, Board of Trade, 588, 595 of Resistance, Board of Trade, 587, 594, 595 • Resistance Coil, 276 — — Resistance Used in Measuring Current, 520 Standards, Board of Trade, Limits to Accuracy of, 595 Board of Trade, for Measuring Current and Pressure, 588 Board of Trade, Where Kept, 595 Electrical, Legislation of, 590 Storage Cell. (See Accumulator.) Strength of Current, Definition of, 23 of Current, Measuring. (See Measuring Current.) of Current, Why Measured by Chemical Property of Cur- rent, 14, 17 of Magnetic Field, Definition of, 79 Relative, of Different Parts of Magnetic Field, Comparing, 79 Steel Filings for Magnetic Lines of Force Diagrams, Preparation and Use of, 71-75, 77, 565 Straight Line Calibration, How Ob- tainable in Galvanometers and Ammeters, 125, 132, 137, 147 Substitution, Simple, Method of Com- paring Resistances, 235 Sulphate of Copper. (See Copper Sulphate.) of Mercury. (See Mercurous Sulphate.) of Zinc. TAN 639 Switch-Board, Mercury, Method of Avoiding Possibility of Short-Circuiting when Using, 640 for Making Two Sets of Connec- tions, 236 Symbolical Representation of Bat- tery, 237 Synchronised, Definition of, 338 Table I., Electrochemical Equivalents of Copper per Second per Ampere, 28 II., Specific Gravities of Mixtures of Balphnrio Acid and Water, 39 III., Constant for Tangent Galvanometer for A.D. 1891- 1900, 104 IV., Ratios of Practical Units of Resistance, 174 V., Ratios of Practical Units of Potential Difference, 175 VI., Variation of Specific Resist- ,* ance with Density, for Copper, 258 VII., Purified Substances in Order of Increasing Resist- ance for Same Length and Sectional Area, 259, 260 VIII., Purified Substances in Order of Increasing Resist- ance for Same Length and Weight, 261 IX., Percentage Variation in Resistance per 1°C., 266 X., Specific Resistances and Per- centage Temperature Varia- tion of Materials Used in Constructing Resistance Coils, 271 XI., Approximate Relative Conductivities per Cubic Unit, 275 XII., Weights of Materials Con- sumed in Cells per Hour per 1,000 Amperes, 484 XIII., Weights and Cost of Materials Consumed in Cells per Board of Trade Unit Produced, 486 Showing Development of Electrical Transmission of Power, 412 Tables Showing Connection between Efficiency of Transmission, and Ratio between Power Received to Maximum Power Receivable, 414, 416 Tangent of Angle, Definition of, 83 Galvanometer, 83 Galvanometer, Axis of Needle and Plane of Coil of, Test for Parallelism between, 85 Galvanometer, Calibrating Any Galvanometer by Comparison with, 108 Galvanometer, Calibration Curve of, 84 Galvanometer Coil Giving Greatest Sensibility, 100 Galvanometer, Coil of, Adjust- ing, 85 Galvanometer, Coil of, Why Circular, 107 Galvanometer, Coil of, Why Large, 99 Galvanometer, Constant for A.D. 1891-1900, 104 Galvanometer, Total Controlling Force on Needle, 104 Galvanometer, Deflection Best Used with, 90 Galvanometer, Deflection of, in Amperes when Controlled only by Earth's Magnetism, 103 Galvanometer Deflection of, and Current, Connection be- tween, 83 Galvanometer, Detailed Descrip- tion of, 49 Galvanometer. Disadvantages of, 108 Galvanometer with Needle Strongly Magnetised, Ad- vantages of, 91 Galvanometer, Scale for, Con- structing, 87 Galvanometer, Sensibility of, Experiment Showing Law and Variation, 100 Galvanometer, Sensibility of, Independent of Length and Strength of Needle, 91 Galvanometer, Sensibility of, Inversely Proportional to Diameter of Coil, 98 Galvanometer, Sensibility of, Method of Increasing, 91, 98 Galvanometer, Sensibility Pro- portional to Number of Con volutions of Wire, 98 Galvanometer, Sensibility of, Restrictions in Increasing, 98 Galvanometer, Sensibility of, Varies with Strength of Con- trolling Field, 102 640 TAN PRACTICAL ELECTRICITY. UNI Tangeiit Law, 91 Law Experimentally Tested, 92 Principle, When Applicable in Galvanometers, 84 Telegraph Lines, Fault Testing in, by Bright, Siemens, and Varley, 569 Lines, Several Worked with One Battery, 527 Telegraphy, Cells Best for, 527 Use of Accumulators in, 527 Temperature Coefficient 'and Specific Resistance of Materials, Re- lation between, 267 Coefficients of Resistance of Metals and Alloys, 264-267 Variation, Effect of, in Daniell's Cell, 436 Variation of E.M.P. of Clark's Cell, 475 • Variation of Resistance of Materials Used in Resistance Coils, 476 • Variation of Resistance with, 262-271 Terminal, Positive, of Cell, Definition of, 376 Terminals of Cell, Potentials of, Re- latively to Earth, 375 of Cell, Signs of, 376 Thermo-pile, Use of, for Conversion of Energy, 358 ; Note, 563 Thomson. Measurements of Heats of Combustion by, 478, 481 Thomson Joulemeter. (See Joule- meter, Thomson.) Tin, Relative Electric and Heat Con- ductivities of, 275 Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot and per Metre Weighing One Gramme, 261 Resistance, Percentage Varia- tion of, per 1°C., 266 Torque, Definition of, 44 Coil with Maximum, under Given Conditions, 148 Transmission, Commercial Efficiency of, 409 Electric, of Energy, 352 Electric, of Power, Conditions for High Efficiency of, 410 Electric, of Power, Power Lost in Overcoming Resistance of Circuit, 410 Electric, of Power, Table Show- ing Development of, 412 Electric, of Power, Using High P.D. in, 412 Transmission, Electrical Efficiency of. 409 Electrical Efficiency of, and Ratio of Power Received to Maximum Power Receivable, 412 of Energy from Generator, Mechanical Model Illustra- ting, 355, 356 of Energy, Methods of, 352, 354, 356, 357 Tungsten, Addition of, to German Silver, 268 Two-Fluid Cell, 423 U Uniform and Constant, Difference between, Note, 153 Magnetic Field, Arrangement for Neutralising, 78 Magnetic Field, Definition of, 70 Unit, B.A., Definition of, 573. (See also Unit of Resistance, B.A.) Board of Trade, Cost of Pro- ducing, 488, 491 Board of Trade, Cost of Pro- ducing with Battery, Con- ditions Governing, 482 Board of Trade, Definition of, 349 Board of Trade, Price of, 349 Board of Trade, Value of, in Watt Hours, Joules, Ergs, Foot Pounds, and Horse- Power Hours, 349 of Capacity, Electric, 579 of Conductivity Proposed, 274 of Current, Absolute Electro- magnetic, Definition of, 575 of Current, Absolute Electro- magnetic, Value of Ampere in Terms of, 583 of Current, B.A., Aim in Choos- ing, 576 . of Current, Definition of, 23, 579, 587, 588, 590, 593. (See also Ampere.) • of Current, Value of, in Terms of C.G.S. Unit, 583, 587, 593 - of Electric Energy, 317, 349, 591. (See also Unit, Board of Trade.) of Force, Dyne, Note, 317 of Force, Gauss's Absolute, 571 of Heat, 318 of P.D., Absolute Electro- magnetic, Definition of, 575 UNI INDEX. VOL 641 Unit of P.D., Absolute Electromag- netic, Volt in Terms of, 479, 576 of P.D., B.A., International, and Legal, in Terms of Each Other, 175 of P.D. and Pressure between Terminals of Clark's Cell, 589, 594 of P.D., Volt, Definition of, 174, 576, 578, 583, 588, 589, 590, 593. (See also Volt.) of Power, 326, 327, 591 of Power, Watt, in Terms of Other Units of, 326 of Pressure. (See Unit of P. D.) of Quantity of Electricity, 579 of Eesistance, Absolute, History of, 568-600 of Resistance, Absolute Electro- magnetic, Method of Deter- mining, 573 of Resistance, Absolute Electro- magnetic, Value of Siemens' Unit and Ohm in Terms of, 573, 591 of Resistance, B.A., Aim in Choosing, 576 of Resistance, B.A., Definition of, 573 of Resistance, B.A., First Indica- tion of being Too Small, 576, 577 of Resistance, B.A., Rayleigh's Value of, in C.G.S. Units, 580 of Resistance, B.A., Inter- national, and Legal, in Terms of Each Other, 174, 587 of Resistance, Ohm, Definition Of, 173, 578, 583, 587, 591, 593. (See also Ohm.) of Resistance, Siemens', 570 of Self-induction, 590 - — of Work, 317, 349, 591 of Work, Joule, in Terms of Foot-Pounds and Ergs, 317 Magnetic Pole, Definition of, 569 Units, Absolute Electromagnetic, 479, 573, 575. 576, 583, 591 C.G.S., Adopted for Electrical Measurements, 576, 578, 583, 587, 593 Electrical, Committees to Con- sider, 572, 578, 579, 581, 584, 587, 588, 590, 592 Electrical, History of, 24, 174, 568-600 Electrical, Legislation of, 592 Universal Shunt. (See Shunt, Uni- versal.) Vapour, Device for Absorbing in Electrostatic Instruments, 193, 217 Varnish, Conducting Transparent, Composition of, 200 Conducting Transparent, Use of, 166, 192, 199 Vibration of Compass Needle, Con- ditions Governing Rate of, 79 of Pendulum, Rate of, 336 of Pendulum of Clock-Joule- nieter, Varying Rate of, 336 Vitreous Electrification, Definition of, 161 Volt, B.A., Definition of, 576 Board of Trade, Definition of, 588, 589, 593 International, Definition of, 174, -591 Legal, Definition of, 583 B.A., International, and Legal, in Terms of Each Other, 175 Board of Trade Standard, 595 International, and P.D. between Terminals of Clark's Cell, 589, 594 in Terms of Absolute Electro- magnetic, or C.G.S. Unit, 479, 576, 578, 593 Voltaic Element, Simple, 359, 418. (See also Simple Voltaic Ele- ment.) Voltameter, Copper, Chemical Action in, 20 Copper Deposited per Second per Ampere in, 29 Copper, Description of, 10, 17 Copper, Used for Measuring Large Currents, 26 Direction of Current in, 33 Hoffmann's, 31 Silver, Definition of, 595 Silver Deposited per Second per Ajnpere in, 23, 27, 596 Silver, for Measuring Currents of about one Ampere, 23, 596 Silver, Method of Making a Measurement with, 25, 594 Silver, Preferable for Measuring Small Currents, 28 Sulphuric Acid, 10, 17, 31, 39 Sulphuric Acid, Chemical Action in, 20, 32 ; Note, 62 Sulphuric Acid, Objection to Usual Mode of Constructing, 38 Sulphuric Acid, Practical Forma of, 39-42 642 VOL PRACTICAL ELECTRICITY. WIN Voltameter, Sulphuric Acid, for Meas- uring Time to Produce Given Volume of Gas, 41 Voltameters and Galvanometers, Re- lative Advantages of, 42 Only Used in Measuring Large Currents, 42 Voltmeter and Ammeter, Measuring Resistance with, 185, 232, 366, 492 and Ammeter, Measuring Power with, 828 and Ammeter, When Impossible to Measure Power with, 328 and Ammeter, Measuring Vari- able E.M.F. of Current Generator with, 369 Ammeter Used as, 179, 181 Ayrton and Mather Zero Elec- trostatic, 164, 181 Calibrating, by Using Potentio- meter, 510 - — Connecting, in Circuit. Method of, 182 — — Current, Result of Disconnect- ing, 181, 183 - — Current, Result of Short-Cir- cuiting, 181, 182 Definition of, 179 Deflectional, Calibrating, 183 Determining E.M.P. of Cell by, 479 Electrostatic, 164, 179, 181 Enclosed in Conducting Case, 198 Graduating, by Potentiometer Method with Clark's Cell, 516-519 High Resistance, When Used, 181, 362, 365 " Ja Ja " Wire Used in, Note, 312 Low Resistance, When Used, 181 • Measuring E.M.F. of Cell by, 362, 365 Moving Coil, 183 Part of Wattmeter Acting as, 330 Scale, Potentiometer Method of Testing Accuracy of, 510 Sensibility of, Adjustment for, (Examples, 30, 31), 187, 188 Types of, 179 Used as Ammeter, 188 Weston Moving Coil, 183 Zero Electrostatic, 164, 181 Zero Electrostatic, Electro- meter Used as, 181 Zero Electrostatic, Scale for, 181 Voltmeters of Very Different Sensi- bilities, Comparing, 184 W Waste Products of Galvanic Cells, Commercial Value of, 488, 490 Water, Current of. (See Current of Water.) Formed per Hour per Ampere in Grove's Cell, 440, 441 Heat of Formation of, 481 Pressure Compared with Elec- tric Potential, 154 Pressure, Distribution of, and of Electric Potential, 155, 167, 173 Transmission of Energy by, 353, 354, 357 Vapour, Device for Absorbing, in Electrostatic Instruments, 193, 217 Variation of Resistance and E.M.F. of Grove's Cell, with Production of, 441 Watt, Definition of, 826, 591 Value of, in Terms of Other Units of Power, 326 Hours, Value of Board of Trade Unit in, 349 Wattmeter, and Am meter- Voltmeter, Methods of Measuring Power Compared, 328, 329 Deflectional, Principle of, 332 • Kelvin Deflectional, 332 Methods of Connecting, with Circuit, 329, 331 Parts of, Acting as Ammeter and as Voltmeter, 330 Principle of, 828 Recording. (See Joulemeter, Thomson.) Swinburne, 331 Zero, Principle of, 330 Wattmeters, Commercial Forms of, 331 Weber, H. ZIN 643 Wire, Subdivision of, into Lengths having Equal Resistances by Foster's Method, 513 Used in Resistance Coils, Com- position and Gauge of, 280, 282 Used in Resistance Coils, Neces- sity for Small Temperature Variation of, 280 Wires with Current Flowing, Action on each other, 3 Work Done by Current, 313-316 Electric, Unit of, 317, 349, 591 Zero Electrometer of Ayrton and Mather, 164, 181. (See also Voltmeter, Zero Electro- static.) - Electrostatic Voltmeter. (SeeVolt- meter, Zero Electrostatic.) - Type of Electrometer, 163 -- Wattmeter, 330 Zinc, Amalgamated, Advantage of Using, in Cell, 429, 430 - Amalgamated, Theories as to Action of, 430 - Amalgamating, Method of, 429 - Atomic Weight of, 27 - for Clark's Cell, Preparation of, 468, 597 - Commercial, Result of Using in Cells, 429 - Consumed in Cells per Board of Trade Unit Produced, Weight and Cost of, 465, 486 Consumed in Cells per Hour 1,000 Amperes, 424, 440, r per , 484 Zinc Deposited per Second per Ain- pere in Voltameter, 27 Effect of Adding to Mercury, 430 Electrochemical Equivalent of, 27 Plate of Cells, 419, 423, 431, 433, 435, 438, 445, 450, 454, 455 458, 459, 460, 461, 462, 463 (See also Plate of Cells.) Plate of Cell in Form of Cylin- der, 431, 455, 461 — Plate of Cell in Form of Pot, 458, 459 Plate of Cell in Form of Rod, 450, 454 Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, per 1°C., 266 Oxide, Possible Formation of, in Simple Voltaic Element, 419 Sulphate, Formation of, in Simple Voltaic Element, 419 Sulphate Formed per Hour per Ampere in Daniell's Cell, 425 Sulphate Formed per Hour per Ampere in Grove's Cell, 440, 441 Sulphate, Heat of Formation of, 478, 481 Sulphate Solution for Clark's Cell. Preparation of, 468, 471, 597 Sulphate, Variation of Resist- ance and E.M.F. of Grove's Cell with Production of, 441 Printed by CASSELL & COMPANY, Limited, La Belle Sauvage, London, E.G. 20.97 THE CENTURY SCIENCE SERIES. Edited by Sir HENRY ROSCOE, D.C.L., F.R.S. John Dalton and the Rise of Modern Chemistry. By Sir HENRY E. ROSCOE, F.R.S. Price 3s. 6d. 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