None
GOL 623 Galvanometer, Tangent, Deflection Best Used with, 90 Tangent, Deflection and Current Connection between, 88 Tangent, Detailed Description of, 49 Tangent, Disadvafctages of, 108 Tangent, with Needle Strongly Magnetised, Advantages of, 91 Tangent, Scale for, 87 Tangent, Sensibility of, Experi- ment Showing Law and Vari- ation, 100 Tangent, Sensibility of, Inde- Sendent of Length and trength of Needle, 91 Tangent, Sensibility of. In- versely Proportional to Dia- meter of Coil, 98 Tangent, Sensibility of. Method of Increasing, 91, 98 - — Tangent, Sensibility Propor- tional to Number of Con- volutions of Wire, 98 Tangent, Sensibility of, Re- strictions in increasing, 98 Tangent, Sensibility of, Varies with Strength of Controlling Field, 102 Galvanometers and Ammeters, How Straight Line Law Obtain- able In, 125, 182, 137, 147 Joint Relative Calibration of, 288 of Invariable Sensibility, 127 Proportional, 124 and Voltameters, Relative Ad- vantages of, 42 GaIvanoRCG]3e, Definition of, Note, 43 Deflection of, Not Proportional to Current Strength, 22 Description of, 10 and Resistances, Comparing KM.Fs. of Cells with, 602-510 tlas. Current of, Measuring Distri- bution of Pressure in, 158 Pressure Compared with Elec- tric Potential, 20*, 206-209, 281 Pressure, Variation of, with Mass, Temperature, and Volume, 204-208 Transmission of Energy by, 350 Weights of, and Cliarges of Electricity, 212 Volume of. Liberated per Second per Ampere, in Sulj^uric Acid Voltameter, 29 Gassner's Dry Coll, 458 Gauss's Absolute Unit of Force, 671 Generator of Current (See Current- Generator^ German-Silver, Composition and Specific Resistance of, 267 Raising Specific Resistance and Lowering Temperature Co- efficient of, 268 Resistance of, per Centimetre Cube and per Inch Cube, 259, 268, 271 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, per VO.y 266, 267, 271 Temperature Coefficient of Re- sistance of, 267, 268 Wire, Use of, in Resistance Coils, 280 Glazebrook, Notes to Specification of aark Cell by, 470, 692 Ohm Detennined by, 682 Glow Lamp, Efficiency of, 405 Percentage Variation of Light with Alteration of Cun'ent, 801 Variation of Light of, with Current and Pleasure, 490 Glow Lamps, Arrangement of Circuit to Give Fixed Amount of Power to, with Minimum Number of Cells, 666 in Parallel with House Mains, 800 Resistance of. INS Oold-lcaf 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, 61 Recording Re^mlts of Experi- ments, Value of, 56 Gravity Control Ammeter. (See Ammeter, Gravity Control.) Daniell's Cells, 431-433 Deflectional Wattmeter, 332 Gray's Investigations ou Electro- chemical Equivalents of Copper, 28 Grove's CeU. (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, 276 Equivalent of Electric Energy, Measuring, 819-824 Insulators for. Inferior to Those for Electricity, 276 Produced by CuiTcnt, 6, 9, 814 Produced in Transformation of Energy. 404 Rate at which Electric Energy in Circuit or Cell Converted into, 818, 370, 880-884 Rate of Production of, by Current, Measuring, 819-3^4 Unit of, 818 Ileating Property of Current Un- suitable for Measuring Cur- rent, 9, 12, 19 Heating Property of Oanent, Uses of, 9 Hellesen Dry Cell, 458 Helmholtz, Alteration In Definition of Ohm Suggested by, 589 Heniy, Definition of, 691 Hermetically Sealed, Definition of, Note,^ High Resistance Galvanometer, Wliy Used for P.D. Measurements, 178 Resistance Voltmeter, When Used, 181 Higher Potential of Conductor, Defini- tion of, 162 Himstedt, Ohm Determined by, 583 Hoffmann's Sulphuric Acid Volta- meter, 82 Horizontal Component of the Earth's Magnetic Force, Meaning of, NoU, 103 Horse-Power, Definition of, 827 Power, value of Watt in, 827 Power Hours, Value of Board of Trade Unit in, 849 Shoe Magnets, Lines of Force with, 74 Hydrogen, Combination of, with Platinum in Smee's Cell, 423, 482 Deposition of, on Copper Plate of Cell, Effect of, 420, 462 Direction of Movement of, in Cells, 423 How to Prevent Combination of, with Negative Plate in Cell, 423 Liberated per Second per Ampere in Sulphuric Acid Voltameter, 33 Liberation of, in Simple Voltaic Element, 418, 420 and Oxygen, Proportions of, Liberated in Sulphuric Acid , Voltameter, 32 Ion, Definition of, 88 Independence of Currents in Parallel Circuits, 525 Induction, Electric, Definition of, 218 Inertia, Moment of. JOU 625 Insulating Stand, Description of, 216 [nsulator, Electric, Meaning of, 14, 276 International Ampere, Definition of, 690 Ohm, Definition of, 178, 591 Ohm in T^rms 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, 8, 5, 10 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 Granmie, 261 •~— Resistance, Percentage Varia- tion of, per 1°C., 266, 271 Wire, Disadvantages of, for Re- sistances, 269 Jacobi's Proposed Standard of Re- sistance, 569 " Ja Ja " Wire, Use of, NoU, 812 — Wire, Resistance of, per Centi- metre Cube, 271 ; Note, 812 Wire, Resistance, Percentage Temperature Variatiou of, 271 ; Note, 812 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, 686, 590 Joule, Electrical Determination of Mechanical Equivalent of Heat by, 676 Determination of Ohm by, 582 Definition of, 817, 691 Value of, in Foot Pounds and in Ergs, 817 Joules, Value of Board of Trade Unit in, 849 per Second, Value of Watt in, 826 Joulemeter, Definition of, 334 Aron Type of Gaining Clock Form, 838 Ayrton and Perry's Original Gaining Clock Form, 834-338 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, 836 Clock, Limit to Proportionality between Gain of, and Energy Supplied, 838 Clock, Method of Joining Up and Using, 8S8 Clock, Permanent Magnet Pen- dulum Form, 838 Clock, Type Used when Energy Supplied at Constant Rate, 888 Clock, Varying Rate of Vibra- tion of Pendulum, 336 Elihu Thomson. {See Joule- meter, Thomson.) Motor, Ayrton and Perry's, Prin- ciple of, 841, 347 Motor, Armature of, 842 Motor, Commutator Used in, 842 Motor, ^Continuous Motion in, How Obtained, 842 Motor, Field of, 848 Motor, Method of Keeping Torque Constant between Field and Armature in, 342 Motor, Type Used when En- ergy Supplied at Constant Pressure, 348 Thomson, Motor Form, 841-849 Thomson, Armature of, 843 Thomson, Armature Rotation Proportional to Energy Sup- plied, 347 Thomson, Directions of Cunents in Armature of, 344 Thomson, Driving Torque Pro- Sortional to Product of trengths of Fields, 846 — - Thomson, Field Coils of, 846 Thomson, Fields Produced by Armature and Field Coils of, 845 Thomson, Fields Proportional to Currents Producing them, 346 Thomson, How to Overcome Friction in, 348 626 JOU PRACTICAL ELECTRICITY. LIN Joolemeter, Thomson, Retarding Torqno In, How Produced, 846 Thomson,RetardinK and Driving Torqpes, Conditions Govern- ing Eqoality between, 847 Joulemeters, Motor and Clock Forms of, Compared, 848 Eahle'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 oil, 27 Kelvin's Addition to Weber's Abso- lute System of Units, 571 Deflectional Wattmeter, 832 Method of Calculating B.M.F. of Cell from Chemical Action, 477-479, 676 Moving Coil Galvanometer; Principle of, 180 Key for Making Two Sets of Connec- tions, 236 Method of Cleaning Contact Points of, 287 Sliding, Use of Platinum Irid- ium Wire with, 610 Used with Wheatstone's Bridge, 260 Used with Shunt to Wheat- stone's Bridge, 252 Kilowatt, Value of, in Horse-Power, 327 Kimball and Rowland, Ohm Deter* mined by, 683 Rowland, and Duncan, Ohm Determined by, 688 Kirchhoff's Absolute Measurement of Resistance, 671 Kohlrausch, Ohm Determined by, 577, 682 Lalande-Chaperon Cell, 462 Lamps, Glow. (See Glow Lamps.) Latimer Clark, Cell Devised by. (See Cell, Clark's.) Clark Proposes Names Ohmad and Volt, 673, 676 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, 269 Resistance of, per Foot Grain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, for I'C, 266 Leaves of Electroscope, 193-196 Leclanch6 Cell. (Se$ Cell, Leclanch^) Legal Ohm, Definition of, 683 Ohm of 1884, Error in, 584 ; Note, 600 Ohm, Value of, in Terms of B.A. Unit and International Ohm, 174 Volt, Definition of, 683 Volt, Value of, in Terms of B.A. Volt and Intematioual Volt, 175 Legislation of Electrical Standards, 502 Lenz, Ohm Determined by, 682 Proposed Unit of Resistance, 568, 669 Lighting, Electric, Accumulators Used In. 627 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, 800 El 43 c trie, Ltpgal Moximtim Varia- tion t}t PrcESKiira ^tween Houac Mftina, SftSt 490 El ftp trie, Method of Makidg Cuf- reiit tn Kadi Lamp Indc- pendent of Gurrutt fn all Others, 302 Electric, P*D» between Hijusa Mains, cUH) BlwtriCj lioflislanoo of Huu^e Wireg Comtiared with Rf- sf^oDcci of Ldmp Ftlaments^ Lin as of Force Diagrams, PrepanatloD tit Filinjra for, 0(ilj tit Force Uiagmnja, rre^aLratioit I if Wftxod P«i>cr far, Wi gf Futrtia Mamied out by Mf^ujs Coiu^aii^ Needle, Tfi uf Vm\>v Mapped tsiit by LTisfitg trail Filiiiett, 71-75, 77 nf Pitrntd, Hexhoda of Mapping Out Compared, 7T gf Form, PrccauUfJiiii in Maptjlug Out, 77 of F<jicB with Bre Mpgnets T2, 73 LIN iia)EX. MAI 627 Lines of Force with Circular Coil Carrying Current, 71 of Force with Horse-ahoe Mag- nets, 74, 75 Liquid Decomposed by Electric Current, 4, 10. (See cUso Cell, Chemical Action in.) Load Diagram, Example of, 827 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 Currente, Meaning of, 429 Lorenz, Ohm Determined by, 677, 582,588 Loss of Head, Definition of, 153 of Head and Rate of Flow of Water, Curve Connecting, 168 Lower Potential, Definition of, 102 Low Resistance Ammeter, Use of, as Voltmeter, 181 Magnet and Conductor with Cut rent Passing, Force Exerted be- tween, 8, 129 Deflection of, by Electric Cur- rent, 8, 5, 84, 69 Forces Exerted on Comjiass 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, NoU, 84 ' Pendulum, Permanent, of Clock Joulemeter, 838 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 -p— Control, Moving Coil Ammeter with, 160 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, Definition of, 79 Field, Strength of, Measuring, 79 Field, Uniform, Definition o^ 70 Field, Uniform, Method of Nen- tnOising, 78 Field of Weston Ammeters and Voltmeters, 147 Fields of Thomson Joulemeter, and Driving Torque, 346 Fields of Thomson Joulemeter Proportional to Currents Producing them, 846 Fields Produced by Armature and Field of Thomson Joule- meter, 845 Lines of Force Diagrams, Pre- paration of Filings and Waxed Paper for, 565 Lines of Force, Mapping Out, 71-77, 565 Needle, Why Tends to Point Noi-th and South, 67 Polarity, and Direction of Cur- rent, Connection between, 35,86,69 Poles, Definition of. MBA Mains, House, P.D. between, 801, 526 House, Resistance of, Ck)rapared with Resistance of Lamps, 802 House and Street, Impossibility of Keeping Pressure Con- stant at Every Junction of, 626 Metliod of Keeping Pressure between. Constant at Certain Points. 626 Manganese Alloys, Composition of, 268 Dioxide Consumed in Leclanch^ Cell per Board of Trade Unit Produced, Weight and Cost of, 487 Dioxide Consumed in Leclanch^ Cell per Hour per 1,000 Am- peres, 484 Manganin, Composition of, 269 Kesistance of, per Centimetre Cube, and per Inch Cube, 260, 209, 271 Resistance of, per Foot Grain and iier Metre Gramme, 201 Resistance, Percentage Vaiiation of, with Temperature, 269, 271 Specific Resistance of. Compared with that of Copper, 269 Used for Resistance Coils, 269, 280,619 Mapping out Lines of Force, 71-77, 665 Mascart Criticises Methods Used for Determining 01>m, 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 Pleeming Jeiv kin's Article on Elementary Relations between Electrical Measurements, Reference to, 574 Maxwell's Moving Coil Galvanometer, Principle of, 130 Measure of Current Strength, Choice of, 9-28 Measurements, Electrical, Com- mittees to Consider Units for, 672, 578, 579, 581, 584, 587, 588, 590, 592 Electrical, Hl8t.ory 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 aUo Ammeter.) Current with Calorimeter, 12 Current with Chirk's Cell and Known Resistance, 519 Current with Electromagnet, 10 — — Current with Galvanometer, 43. (See aiao Galvanometer.) Current with Galvanoscope, 10, 22 Current with Copper Voltameter, 10, 26 Current with Silver Voltameter, 23-29, 595 Current with Sulphuric Acid Voltameter, 10. 38, 89 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 Ekeli'ic Deu^ity, 2S4. 525 Ekctrlc J^Tiergy, 3 18-1154, 334- ^4Ji. { See ttt»^ iT oitl^i iiet^er, ) Eli'i:'trkity Prodiiwd by Rubbing Two Btidiqs Trvgether, :fl4 E.M.P. of Coll and of Battery, :ioa, m^, 477 ^ w2-sio K.M,F. of Ciiirreiit-Gi!i3(!»tDr| vrhQu Variable, 80fl E.M.F., Bfliik, in Cin-m, 871 Ill at Kiiuivii!ent of JSlcctric Knergy, Hiy Iiiiitminpnt*, Metiiod^ of In- creAHln]^ Indic^tLOaa d, 4S MEA INDEX. MOT 629 Measuring Quantities of Electricity, Relatively, 212 P.D. with Ammeter and Besiat- ance, 185 P.D. with Clark's Cell, 510, 616 P.D. witli Current Voltmeter, 179 P.D. ElectrostaticaUy, 162, 191 P.D. (Se$ also Comparing P.Ds., 176.) P.D., Principle of Board of Trade Standards for, 588 Power, 825, 828. (See also Watt- meter.) Resistance with Ammeter and Voltmeter, 185, 232 Resistance with Ohmmeter, 233 Resistance. {See also Comparing Resistances.) Resistance of C?ell, Choice of Method for, 498 Resistance of Cell When Not Very Small, 493 Resistance of Cell, When Veiy Small, 366, 402 Strengtlis of Different Parts of Magnetic Field, 79 Variation of Resistance with Temperature, 262 Mechanical Enerey, Conversion of Energy of Current into, 314 Meiilinger Cell, 431 Meicurous Sulpliate for Clark's Cell, Preparation of, 468, 470, 697 Sulphate and Zinc Sulphate Paste for CUrk's Cell, Pre- paration of, 468, 472. 698 Mercury, Effect of Adding Zinc, 430 for Clark's Cell, Preparation of, 467,697 and Copper, Relative Resist- ances of, 269 Ohm, Mass and Length of Column, 178, 589, 693 Ohm, Section and Length of Column, 580, 586, 587, 600 Resistance of, per Centimetre Cube and per Inch Cube, 260 •~— Resistance of, per Foot Qrain and per Metre Gramme, 261 Resistance, Percentage Varia- tion of, per I'C, 266 Resistance of, at Any Tempera- ture, Formula Giving, 269 Siemens Unit, Section and Leneth of Column, 670 Switch-board for Batteries, 170, 639 Switch-board, Method of Avoid- ing Possibility of Short- Circuiting Cell when Using, 640 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 Centimeti-e Cube and per Inch Cube, 257, 269, 271 Resistances of, per Foot Grain and per Metre Gramme, 201 Resistances of, Percentage Variation per I'C, 266 - — Resistances of. Relatively to Aluminium for Same Length and Weight, 261 Resistances of. Relatively to Silver for Same Length and Section, 269 Temperature CoefHciente of Resistances of, 264-267 Meter, Aron Supply, 838 Aron Supplv, Differential Gearing of, 340 — — Enei'gy. Note, 79 of Inertia of Compass Needle, Method of Increasing, 79 of Inei-tia Small in Permanent Magnet Ammeter, 134 Motion, Mechanical, against Control- ling Force, Production of, by Current, 314 Motor, Armature of, 842 Commutator Used iij, 342 Commercial Efficiency of. Defini- tion of, 406 Electrical Efficiency of, Defini- tion of, 406 Field of, 342 How Continuous Motion in, is obtained, 342 Joulemeter. (See Joulcmeter Motor.) 630 MOT PRACTICAL ELECTRICITY. OHM Motor, Method of Keeping Torque Constant between Field and Annature in, 842 Moving Coil Ammeter. (See Ammeter, Moving Coil.) Coil Voltmeter, 183 Mnirhead'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, 184, 140, 141, 142 Negative Charge, What is Meant by, 160, 218 Electrification, What is Meant by, 161 Plate of Cells. (See Phite, Nega- tive, of Cells.) Potential, Definition of, 162 Nerville, De, Mascart, and Benolt, Ohm Determined by, 682 Neutralising Uniform Magnetic Field, Ai'rangement for, 78 Nickel, Resistance of, per Centimetre Cube and per Inch Cube, 259 Resistance of, per Foot Grain and per Metre Gramme, 261 Temperature Coefllcient 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 i)er 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 IJon-Inductive Resistance Coil for Large Currents, Ayrton and Maker's, 282 North-Seeking End of Magnet, Defini- tion of, NotCf 34 Obacb Drj' Cell, 460 Ohm, Board of Trade, International, and Legal, Definitions of. 173, 678, 688, 687, 689, 591, 593 Legal, and International, and B.A. Unit, Values of, in Terms of Each Other, 174 B.A. Unit Less than, 576 Board of Trade Standard, 594, 695 Determined by British Associa- tion Committee, 681 Determined by Dom, 682 Determined by Fletcher, 688 Determined by Hinstedt, 683, 685 Determined by Glazebrook, 682 Determined by Jones, 586, 600 Determined by Joule, 581 Determined by Eohlrausch, 677, 682 Determined by Lenz, 582 Determined by Lorenz, 677, 582, 688,686 Determined by Mascart, De Nerville, and Benolt, 682 Determined by Rayleigh, 577, 581,585 Determined by Rayleigh and Schuster, 681, 585 -^ — Determined by Rayleigh and Mrs. Sidgwick, 582 Determined by Roiti, 582, 585 Determined by Rowland, 577, 582,685 Determined by Rowland and Kimball, 683 Determined by Rowland, Kim- ball, and Duncan, 683 Determined by Weber, 677, 581, 682,585 Determined by Wiedemann, 582 Determined by Wild, 682 Legal of 1884, Error in, i^ote, 600 Mercury, Mass and Lengtii of Column, 173, 589, 593 Mercury, Section and Length of Column, 680, 686, 587, 600 Methods of Ascertaining Equi- valent Mercury Column, 680, 681,685 in Terms of Absolute Electro- magnetic, or C.G.S. Units, 678, 678, 687, 691, 698 Ohm's Law. 172 Law, Apparatus for Testing, 170 Ohmad, Proposed Use of Name, 678 Ohmmeter, 238 ORD INDEX. PHO 631 Ordinates, Definition o^ 67 Outoide Circuit (See Circuit, Ex- temaL) Oxide of Copper. (See Copper Oxi de. ) Oxygen Deposited on Copper Plate of Cell, Effect of, 462 and Hydrogen, Proportions of, Evolved in Sulphuric Acid Voltameter, 82 Liberated per Second per Ampere in Sulphuric Acid Volta- meter, 83 Parallax, Definition of, 50 How Avoided in Measuring- Instruments, 60, 831 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 F.D., Absolute Electromagnetic Unit of, Definition of, 479, 575 between Conductors Enclosing, One Another. 218 between Conductors, How Shown, 161 -V- between House Mains, 801, 526 between Terminals of Battery, E.M.F., Resistance and Cur- rent, 864, 380 between Terminals of Batteiy when Maximum Power Given to External Circuit, 389, 548 between Terminals of EdiMon- 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 Tenninals of Hellesen Cell, Fall of, with Cunent Passing. 459 between Tenninals 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.D. between Two Points of Uniform Conductor Convey ingCurrent Proportional to Distance, 156 between Two Points of Con- ductor, Method of Maintain- ing Constant, 158, 510 Coinpared with Difference of Fluid Pressure, 154 Compared with Difference of Gas Pressure 158 Constant, 287, 522 and Current, Given, Minimum Number of Cells to Produce, 549 — - Definition of, 164, 1«3 Measuring with Ammeter and Resistance, 185 31easuring with Clark's Cell, 510, 516 Measuring with Current Volt- meter, 179 Measuring Electrostatically, 162, 191 Power, and Current, Relation between, 327 Ratio of^ to Current, Constant for Given Conductor, 170 Ratio of, to Qurrent, for Given Conductor Experimentally Determined, 171 Ratio of, to Current, and Ratio of Difference of Pressure to Stream of Fluid, 167, 169 to Send Current round Ei.tire Circuit Constant for Giveu Battery, 861 Where Set up in Cell, 374 Units, Definitions of, 174, 175. 479, 575, 578, 583, 588, 589, 593 Units in Terms of Each Other, 175, 479 P.Ds., Comparing by Current Method, 176 Pendulum of Clock Joulemeter, Vary- ing Rate of Vibration of, 336 Coil of Clock Joulemeter. 334 Permanent Magnet, of Clock Joulemeter, 338 Rate of Vibration of, 836 Permanent Magnet Ammeter. (See Ammeter, Permanent Mag. net) Magnet, Distribution of Mag. netism in, 63 Perry and Ayi-ton. (See Ayrton and Perry.) Phosphor Bronze, Resistance of, per Centimetre Cube and per Inch Cube, 259, 271 632 PHO PRACTICAL ELECTRICITY. POR Phosphor Bronze, Resistance of, per Foot Grain, aud per Metre Gramme, 262 Bronze, Resistance, Percentage Variation of, per I'C, 271 Pivot and Fibre Suspensions of Gal- vanometer Needle, 110 Plants, Invention of Accumulators by, 627 Plate, Carbon, of Cells, 443, 445, 4o0, 452, 458, 4(K), 401 Copper, of C<nis, 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 CeU, 462, 463 Negative, of Cells, 419, 423, 481, 483, 435, 488, 443, 445, 450, 452. 453, 455, 460, 461, 462 Platinum, of Cells.J 423, 438, 482 Positive, of Cell, Definition of, 376. {Sm also Plate, Zinc.) Zinc, of Cells, 419, 423, 431, 433, 435, 438, 445, 450, 454, 455, 458, 459, 400, 461, 462, 463 Zinc, Efl'ect of Amalgamating, onE.M.F. 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 Batterj', 435 Platinoid, Composition of, 268 Resistance of, per Centimetre Cube and per Inch Cube, 260, 268, 271 Resistance of, per Foot Grain aud per Meti'e Gramme, 261 Resistance, Percentage Temper- ature Variation of, per l^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, 265 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 Gmmme, 261 Alloy, Resistance, Percentage Variation of, per I'C, 20i?, 267, 271 Wire Used in Resistance Coils, 280 Plug Key for Making Two Sets of Connections, 236 Resistance Boxes, Construction and Use of, 278 of Shunt Box, Construction and Use of, 296, 297 Poggendorff's Method of Comparing E.M.Fs., 607 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 Leclancli6 Cells, 456 of Simple Voltaic Element, Cause and Efiect 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, 671 Poles, Magnetic, Action between, when Similar and Dissimilar, 69 Majjnctic, Deflnititm ofj 6^ Porous Fartititm, Abnenca of, fn Omvity tiaiiidl's C*I], 431, raitjtl<>n of Daiil*^irs Ceil^ Pns vyntlijg FpniiatJaU of Copper iij PufBa of, 431 Partition of Danlella Cells, Vutiatfoii of Resfiitiuioe witli CoTifltructinii nf, 4H Pot of DanieU'si CcE, 4S6 POR INDEX. POW 633 Porous Pot, Potassium Bichromate Cell with, 446 Portable Galvanometer, 127 Forms of Wheatstone's Bridge, 285 Positive Electrification, What is Meant bv, 161 - — Plate of CelL Definition of, 876 Plate of Cell. (Ste Plate, Zinc, ofCell.3 Potential, Definition of, 162 Terminal of Cell, Definition of, 876 Post Office Wheatstone's Bridge, 285 Potassium Bichromate Cell, 445. (SVe aJso Cell, Potassium Blrhro- iiiate.) Bichromate Consunie<l in Cell l»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, 874 of Conductor Proportional to Quanti^ of Electricity on Conductor, 211 of Conductor, What is Meant by 200 Difference. (See P.D.) Distribution of, in Cell and Battery, Diagram Sliowing, 874 Distribution of, in Circuit, Dia- gram Showing, 876 Distribution of, in Circuit with Opposing E.M.F., Diagram Showing, 378 Distribution of, and of Fluid Pressure, 165, 167, 178 of Earth, Arbitrary Value Given to, 160 Electric, Compared with Fluid Pressure, 154, 155, 167, 173 Electric, Compared with Gas Pressure, 204, 207, 209, 231 Inside Closed Conductor, 197 I^vel, What is Meant by, 100 Measuring, 160, 200. RES Power, Maximum, fW>m Given Current Generator, Circuit that Re- ceives, 885 -^ Maximum, Arrangement of Bat- tery to Give, 845 — Maximum, Arrangement of Fart of External Circuit to Re- ceive, 893 •~— Maximum, Generator Can De- liver, 389 Measuring, 825, 828 P.D., and Current, Relation between, 827, 370 Received, Variation of, ft'om Maximum and Change in Current, 898 Received, Variation of, from Maximum and Change in Re- sistance, 899 Units of, in Terms of Each Other, 827 Variable, Meaning of 825 Pressure, Electric (Sm P.D.) of Fluid Compared with Elec- tric Potential, 154, 156, 167, 178 of Gas Compared with Eiectric Potential, 204, 207, 209, 231 of Gas, Variation of, witli 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, 368. 490 between Mains, Method of Keep- ing Constant at Certain Points, 626 ——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. (Sec Unit of P.D.) Variation of Light of Glow Lamp with, 490 Price of Board of Trade Unit, 849 Primary Current, Direction of, in Experimental Voltaic £le- ment,428 Proof Plane, Description of, 224 — Plane, Method of Measuring Charge on, 224 Properties of Electric Current, 3, 5 of Electric Cun'ent, Pi-actical Uses of, 9 Property by which Current Strength is Best Measured, 10-22 Proportional Coil, 284, 287. (See also Coil, Proportional.) Galvanometer. (See Galvano- meter, ProportionaL) Protractor, Use of, 69 Quantities of Electricity, Comparing, 211-217 Quantity of Electricity Produced by Rubbing Two Bodies To- gether, 214 of Electricity. Unit of, 679 of Electricity, What is Meant by, 208 Potential, and Density, Ex- amples Showing Diflfercnce between, 226 Rayleigh, Ohm Determined by, 577, 581 and Mrs. Sidgwiclc, 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, 691. RES 635 Resistinee, Apparent, of Arc, What is Meant b7> 288 B.A. Unit of, 678. (.%« ai»o Unit of Resistance, B.A.) of Battery with Cells Joined in Parallel, and in Parallel- Series, 688 of Battery of Given Number of Cells Sending Maximuui Current, 545 of Battery, P.D. between Ter- minals, E.M.F., and Current, 864,880 Box, Construction and Use of, 278,279 Box, Values of Coils for, 288 of Cell, Conditions Qoverning, 484 of Cell. Choice of Method for Measuring, 498 of Cell, Measuring, When Not Very Small, 493 of Cell, Measuring When Very Small, 866, 492 of Cell. P.D. between Terminals, B.M.F., and Current, 864, 880-888 of Cell, and P.D, Maintained, 287,622 and Clark's Cell Used as Cur- rent Standard, 519 used with Clark's Cell to Restore its B.M.F. to Noi-mal Value, 477 of Daniell's Cell, Increase of, with Constancy and Porta- bility, 481 of Daniell's Cell, Variation of, with Temperature, 486 of Vallous Forms of Daniell's Cells, 485 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, 807 of Circuit, and Heat Energy Produced in, 818, 870 of Circuit, Percentage Loss of Power Due to, 410 of External Circuit, and Power Received by Circuit, Con- nection between, 892, 899 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, 619 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 Temperatui-e of, 280, 281 Coils, When Used, 278 Coils, Winding, 280 Combined, 291 — - Combined, in Terms of Resist* ances of Branch Circuits, 292.298 of Conducts, Conditions Affect- ing, 263-271. (See also Re- sistance, Variation of.) ——of Copper, Temperature Varia- tion of, 265, 266 of Copper, Variation of, with Density, 268 Crompton Standard, 620 Current, Calories, and Time, Relation between, 878, 824 Known, Used in Measuring Current^ 619 of House Mitins Small Compared with Resistance of Lamps, 802 — Measuring, with Ammeter and Voltmeter, 185, 232, 366, 492. (See also Resistances, Com- paring.) — Measuring, with Ohmmeter, 283 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 Alloj'S, 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 Graina»6| 636 BBS PRACTICAL ELBCTRICITY. SEN Bctistanoe of Metals and Alloys Per. eentage Variation of, per I'C, of Metals and Alloys, Tempera- ture CoefBcionte of, 264-267 of Metals and Alloys Used in Resistance Coils, 271 ParaUel, 291 Parallel, in Terms of Resistances of Branch Circnits, 292, 293 of Platinum, Temperature Varia- tion of, 265. 266 Speciflo, How Expressed, 257 and Temperature-Coefficient of Materials, Relation between, 267 Testing Temperature Variation of, 262 Unit of, Ohm, Beflnltion of, 173, 678, 583, 587, 591, 593. (See oiM Ohm.) Units of. (set Unit of Resist- **" anoes.)' Variation of, with Cross-Section, 267 Variation of, with Length, 264 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 wiUi 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, 288, 290 Resultant of Two Foi-ces, Method of Obtoining, 81 RoYti, Ohm Determined by, 582 Rowland, Ohm Determined by,577,582 and Kimball, Ohm Determined by, 683 ^^— Kimball, and Duncan, Ohm De- termined by, 688 S Safety Limitation of. SIM 637 Sensibaity of Ta&jEent GftlTUKwoeier, Lav and Vamtua ol, 91, 96, 100,103 in Yohnrter, A4ji::5ticect for (Kw irfft 90, 31 ', 1S7, 1^ Series, Appantns in, Defiaition of, SO and Euallel-Senes, Cells Joined in, 536,537 and Panlkl-Series, JoiDing Cells in, \jj Means of Mercury Sviteh-boaid. Ml Short-Circoiting Cell, vhen Using Mercory Switdb-boaid, How to ATOftd Possibility of, MO Ammeter, Besolt of, ISl, 182 Voltmeter, Bcsnlt of; 181, 183 Shunt, Description of, 110 and Gslvanometer, Batio of Conents in, S90 and QalTsnometer, Batio of Car- rent in each to Whole Canent,290 Increase of Main Current Pro- dnced by Applying, 298 Moltiplying Power of; Definition of, »0 Use of, and Calibration of Gal- Ttnometer, 110 Used with Differential Galvano- meter, 241, SU Used with Galvanometer, 110 Used with Wheatstone's Bridge, 262 Variation of Effect of, on Cor- rent» with Change of Ex- ternal Beaistance, 299 Sbnnts, Pumllel Arrangement of, 297 Series Arrangonent of, 297 Univenal, Principle and Use of; SOS Shunt Box: Ayrton and Mather's UniTersal, Construction of, 804 — - Box, Universal, Advantages of, 306 Box, Universal, Change in Be- sistance of Circuit Produced by Using, 807 Bo3^ Universal, Employed with Any Galvanometer, 808 Box, universal, Facility in Ad- justing Coils, 807 Box. Universal, Independent of Variations of Temperature While Using, 80G Box, Universal, Selection of Be- sistance for, 309 Box, High Insulation, Construc- tion of, 297 — Box, Usual Form o^ Arrange- ment of Coils in, 295 Shout Box, Usual Forat oC Xeoessity^ for Cocstant Tiempeniune while rsi^Ki 306 Box, Usual Form of, Smptoy- mentol.296 Box, Usrju Form of, Besbtances of 0>iU Us^ in, SS^X 2!?T Box. Usoal Method of CVm$tnKt- ing,2i^ Boxes, Universal, ami V^wal Form, Coiui>aratire SflVicts of, on Be&isuuoe of Qrvuit, 307 Sidgwick, Mrs., and Lord Baylei^i, Ohm Determined by. 68:2 Siemens' Law Connecting Variatiim of Besistanoe of Metals with Temperature, 3&5 Unit of Besistance, 570 Unit of Besistance, Objection to, 570 Sign of Charge or of Electrification, WhtX is Meant by, 161, SIS of Charge, Testing, 221 of Potential, What is Mewit by, 16S Silver, Atomic Weight-of, 27 Conductivity of, 274 and Copper, Comparative Bates of Electric Deposition of, 2S Deposited per Second, per Am- pere, 23, 588, 593 Depiosited per Second, Unit of Current Defined by, 23, 29, 588,593 Belative Electric and Heat Con* dnctivities of, 276 Besistance of, per Centimetre Cube and per Inch Cube, 259 Besistance of, per Foot Grain and per Metre Gramme, 261 Besistance, Percentage Varia- tion of, per rC, 266 Voltameter. (Sm Voltameter, SUver.) Similar Magnetic Poles, Action Be- tween, 69 Simple Voltaic Element, Chemical Action in, 418 Voltaio Element. Direction of Movement of Hydrogeu in, 419, 423 Voltaio Element, Direction of Current in, 419 Voltaio Element, Bxperimotit Showing Fall of B.M.F. of, when Using, 420 Voltaio Element, Experiment Showing Seat of Back B.M.F, in, 422 638 8IM PRACTICAL BLECTBICITT 8WI Simple Voltaic Element, Polarlmtlon in, Canee and Effect of, 420 Sine of Angle, Definition of, 111 Galvanometer, 118, 119. (See oZfo Galvanometer, Calibra- ting on Sine Principle.) Law, 112 — ^ Law Experimentally Tested, Law, Methods of Keeping Angle Between Deflectine Force and Deflected Body Constant, 118 Principle Employed in Galvano- meters^lS Single Circnit, Definition of, 877 Circnit Electromotor, Definition of, NoU, 871 Fluid Cells, 418, 445, 450, 462 Slider with Wire Bridge, 249, 250 Smee'B Cell, 428, 482 Sodiom Bichromate, Chromic Acid for Cell Formed flwm, 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, 89 Heat, Definition of, NoU, 262 Resistance of Copper, Variation of, with Density, 268, NoU, 812 Resistance of a Material, How Expressed. 257 Resistances of Materials Used in Resistance Coils. TAN 639 Switcb-Boud, Mercnry, Method of Avoiding Possibility of Bhort-Circaiting when Using, 640 — for Making Two Bets of Connec> lions, 286 Symbolical Bepresentation of Bat- tery,^ Synchronised, Definition of, 888 Table I., Blectrochemlcal Equivalents of Copper per Second per Ampere, 28 IL, Specific Gravities of Mixtures of Sulphuric Acid and Water, 89 III., Constant for Tangent Galvanometer for a.d. 1891- 1900 104 IV., Ratios of Practical Units of Besistance, 174 v., Batios of Practical Units of Potential Difference, 175 -- — VI., Variation of Specific Resist- w ance with Density* for Copper, 258 VII., Purified Substances in Order of Increasing Resist- ance for Same Length and Sectional Area, 259, 260 -^o VIII., Purified Substances in Order of Increasing Resist- ance for Same Length and Weight, 261 IX., Percentage Variation in Resistance per I'C, 266 X., Specific Resistances and Per- centage Temperature Varia- tion of Materials Used in Constructing Resistance Coils, 271 Xr., 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, 88 Galvanometer, Axis of Needle and Phine of Coll of. Test for Parallelism between, 85 Galvanometer, Calibrating Any Galvanometer by Comparisou •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, CoH of. Why Lai^e, 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, 108 '— 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 Sliowing Law and Variation, 100 Galvanometer, Sensibility of. Independent of Length and Strength of Needle, 91 - — Galvanometer, Sensibility of, Inversely Pronortional to Diameter of Cou, 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 ELECTBICITT. UNI Tangent Law, 01 Law Experimentally Tested, 02 Principle, When Applicable in Oalvanometers, 84 Telegraph Lines, Fault Testing in. by Bright, Siemens, and varley, 660 Lines, Several Worked with One Battery, 627 Telegraphy, Cells Best for, 527 Use of Accumulators in, 627 Temperatnre Coefficient 'and BpeciOc 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 B.M.P. of Clark's Cell, 476 Variation of Resistance of lUterials Used in Resistance Cons, 476 Variation of Resistance with, 262-271 Terminal, Positive, of Cell, Definition of, 876 Terminals of Cell, Potentials of, Re- latively to Earth, 376 of Cell, Sims of, 376 Thermo-pile, Use of, for Conversion of Eneiigy, 868 ; Notf, 563 Thomsen, Measurements of Heats of Combustion by, 478, 481 Tliomson Jonlemeter. (See Joule- meter, Thomson.) Tin, Relative Electric and Heat Con- ductivities of, 276 Resistance of, per Centimetre Cube and per Inch Cube, 250 Resistonce of, per Foot and i>er Metre Weighing One Gramme, 261 Resistance, Percentage Varia- tion of, per I'C, 266 Torque, Definition of, 44 Coil with Maximum, under Qiven Conditions, 148 Transmission, Commercial Efficiency of, 400 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, 400 Electrical Efficiency of, and Ratio of Power Keoeived to Maximum Power Receivable, 412 of Energy from Generator, Mechanical Model Illustra- ting, 866. 866 of Energy, Methods of, 852, 354, 356, 357 Tungsten, Addition of, to German SUver. 268 Two-Fluid Cell, 423 Uniform and Constant, Difference between, NoUy 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. 401 Board of Trade, Cost of Pro- ducing with Battery, Con- ditions Governing, 482 Bi>ani of Trade, Definitioi} nr, Bivird of Tiiifli?, Price of, S40 Board of Tmf\o, Valiio or, in Watt lioura, Jouliis, liigiJ, Foot PoiindB, and Huriri:- VQvftiT Hcjttfs, 340 (jf Qifiacitv, Electric, 570 of CfHiUufitivitT rnipaswl, 'J74 i>r Current, Almoin fce Blcctro- mtguotiCi Derflnitiod nf, STS of Cufretit, Absolute Electro niij.^nctic, Vahia of AEnpere in T^riiui yf. VOL b41 Unit of F.D., Absolnte Bleciromag- netio. Volt in Terms of, 479, 670 of P.D., B.A., International, and Legal, in Terms of Bach Oto«, 176 — of P.D. and Fressare between Terminals of Clark's Cell, 689,694 of P.D., Volt, Definition of, 174, 576, 678, 688, 688, 689, 590, 698. iSee also Yolt) of Power, 826, 827, 691 of Power, Watt, in Terms of Other Units of, 826 of Pressore. (Sse Unit of P.D.) of Quantity of Blectridfar, 579 of Resistance, Absolnte, History of, 568-600 of Resistance, Absolute Electro- magnetic. Method of Deter- mlning, 678' of Resistance, Absolute Electro- m^netio. Value of Siemens' Unit and Ohm in Terms of, 678, 691 of Resistance, B.A., Aim in Choosing, 676 of Resistance, B.A., Definition of, 678 of Resistance. B.A., First Indica- tion of being Too Small, 576, 677 of Resistance, B.A., Rayleigh's Value of, in C.O.S. Units, 680 of Resistance, B.A., Inter- national, and Legal, in Terms of Each Othtr. 174, 687 of Resistance, Onra, Definition of, 178, 678, 688, 687, 691, 698. {JSee also Ohm.) of Resistance, Siemens', 670 of Self-induction, 600 of Work, 817, 849,^91 of Work, Joule, in Terms of Foot-P0tmds and Ergs, 817 Magnetic Pole, Definition of, 669 Unitrt, Absolnte Blectoomagnetic, 479, 678, 676. 676, 688, 691 C.Q.S., Adopted for Electrical Measurements, 676, 678, 683, 687,698 ~— Electrical, Committees to Con* sider, 672, 678, 679, 681, 684, 687, 588, 590, 692 Bleetrical, History of, 24, 174, 66S-600 Electrical, Legislation of, 592 Univenua Shunt {8e§ Shunt, Uni- versal.) Vapour, Device for Absorbing in Blecfarostatio Instnunents, 196.217 Varnish, Conducting Transparent, Composition of, 200 Conducing Transparent Use gT, 166, 192, 198 Vibration of Compass Needle, Con- ditions Qovemiug Rate of, 79 of Pendulum, Rate ofl 836 of Pendulum of (nock-Joule- meter. Varying Rate of, 886 Vitreous Electrification, Definition oil 161 Volt, B.A.. Definition qt 676 Board of Trade, Definition of, 58d, 689, 698 International, Definition of, 174^ '691 Legal, Definition of, 683 B.A., International, and Le^, in Terms of Bach Other, 176 Board of Trade Standard, 696 International, and P.D. between Terminals of Clack's Cell, 689, 694 in Terms of Absolnte Electro- magnetic, or C.G.S. Unit, 479, 676, 678, 608 Voltaic Element, Simple, 859, 418. (Su also Simpto Voltaic Ble- ment) Voltameter, Copper, Chemical Action in, 20 Copper Deposited per S6coud per Ampere in, 29 Copper, Description atj 10, 17 Copper, Used for Measuring Large Currents, 26 Direction of Current in, 83 Hoffinann's, 81 Silver, Definition of, 696 Silver Deposited per Second per Ampere in^ SBj 27, 696 Silver, for Measuring Currents of about one Ampere, 23, 696 Silver, Method of Making a Measurement with, 26, 694 Silver, Preferable for Measuring Small Currents, 28 Sulphuric Acid, 10, 17. 81, 89 — Sulphuric Add.duunical Action ln,2O,82;liroto,02 Sulphurie Acid, Otoection to usual Mode of Coostructing, 88 Sulphuric Acid, Practical Forma of, 89-42 642 VOL PRACTICAL ELECTRICITY. Mas Voltameter, Salpharic Acid, for Meas- uring Time to Prodace 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, 866, 402 and Ammeter, Measuring Power with, 828 — ~ and Ammeter, When Impossible to Measure Power with, 828 and Ammeter. Measuring Vari- able E.M.F. of Current Generator with, 869 — -- Ammeter Used as, 179, 181 Ayrton and Mather Zero Eleo- trostatie, 164, 181 Calibrating, by Using Potentio- meter, 610 - — Connecting, in Circuit, Method of, 182 — - Current^ Result of Disconnect- ing, 181, 188 Current, Result of Short-Cir- cuiting, 181, 182 Definition of, 179 Deflectional, Calibrating, 183 Determining B.M.P. of Cell by, 479 Electrostatic, 164, 179, 181 Enclosed in Conducting Case, 198 - — Graduating, by Potentiometer Method with Clark's CeU, 616-^19 -^ — High Resistance, When Used, 181, 862, 866 " Ja Ja" Wire Used in, NoU, 812 «— Low Resistance, When Used, 181 Measuring B.M.F. of Cell by, 862,865 Moving Coil, 183 • Part of Wattmeter Acting as, 880 Scale, Potentiometer Method of Testing Accuracy of, 610 - — Senpibility of, Adjustment for, {Examples, 30, 31), 187, 188 Types of, 179 Used as Ammeter, 188 Weston Moving Coil, 188 Zero Electrostatic. 164, 181 Zero Electrostatic, Bleotro- meter Used as, 181 Zero Electrostatic, Scale for, 181 Voltmeters of Very Different Sensi- bilities, Comparing, 184 I 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 Compfured with Elec- tric Fotentkl, 154 Pressure, Distribution of, and of Electric Potential, 166, 167, 178 Transmission of Enei:gy by, 863, 864,867 Vapour, Device for Absorbing, in Electrostatic Instruments, 193, 217 — Variation of Reeistanoe and E.M.F. of Grove's Cell, with Production of; 441 Watt, Definition of, 826, 691 -^ Value of, in Terms of Other Units of Power, 826 — Hours, Value of Board of Trade Unit in, 849 - Wattmeter, and Ammeter- Voltmeter, Methods of Measuring Power Compared, 828, 829 Defiectional, Principle of, 882 Kelvin Deflectional, 332 Methods of Connecting, with Circuit, 329, 881 Parts of. Acting as Ammeter and.as Voltmeter, 880 Principle of, 828 Recording. {See Joulemeter, Thomson.) ^ Swinburne, 831 Zero, Principle of, 880 Wattmeteira, Commercial Forms of; 881 Weber, H. 