None
489 Cardew's Voltmeter, Advantages of, 426 Voltmeter Arranged for Measuring Large Potential Differences, 425 Voltmeter, Construction of Rods in, to Prevent Change of Length with Tempera- ture, 426 Voltmeter, Diameter of "Wire used in, 423 — — Voltmeter, Disadvantages of 427 Voltmeter, Length of "Wire used in the Latest Form of, 423 Voltmeter, No Heating Error in, 426 Voltmeter, Small Self-Iaduc- tion in, 427 Cell, Bunsen's, 219 Callaud, 213 Darnell's, 210 Fleming's Standard Daniell's, 412 Gravity Daniell's, 212 Grove's, 218 Leclanche\ 220 Latimer Clark's, 410 Lockwood's, 213 Meidinger's, 212 Minotto's, 211 Potash Bichromate, 222 Standard Daniell's, 411 Chemical Action in a Bunsen's, 220 Chemical Action in a Daniell's, 214 Chemical Action in a Grove's, 219 ChemiealActioninaLeclanche', 221 - Chemical Action in a Potash Bichromate, 223 Carbon for Bunsen's, 220 Composition of Liquid for Pot- ash Bichromate, 222 Constancy of E. M. F. of a Daniell's, 216 Constancy of E. M. F. of a Latimer Clark's, 411 E. M. F. of a Bunsen's, 220 E. M. F. of a Daniell's, 211 E. M. F. of aStandardDaniell's, 412 E. M. F. of a Grove's, 218 E. M. F. of a Latimer Clark's, 411. B. M. F. of a Leclanche', 222. E. M. F. of, Independent of Size and Shape, 211, 236 E. M. F.f Temperature Varia- tion of, in Latimer Clark's, 411 Cell, E. M.Fs. of, Comparison of, 231, 232, 234, 341 Local Action in, 217 How to prevent Local Action in a Daniell's, 217 Polarisation in a Daniell's, 216 Resistance of a Daniell's, 211 Resistance of a Grove's, 218 Resistance of, Measuring, 205, 225, 342 Cells, Arrangement of, 239 Arrangement of a Given Num- ber of, to produce Maxi- mum Current through a Given External Resistance, 243 Arrangement of for Giving Maximum Useful Power to Conductor with Fixed Resistance, 450 Galvanic, 209 in Parallel, E. M. F. of, 241 Figure of, 239 Symbolical Representation of, 240 in Series, E. M. F. of, 241 in Series, Figure of, 239 in Series, Symbolical Repre- sentation of, 240 Partly in Parallel and Partly in Series, E. M. F. of, 241 Partly in Parallel and Partly in Series, Figure of, 239 Partly in Parallel and Partly in Series, Symbolical Repre- sentation of, 240 Standard, 410 Change in Strength of Poles of Needle of Galvanometer, Calibration Unaffected by, 23 of Resistance with Tempera- ture, Results of Matthies- sen's Experiments on, 160 Charge. Charge, Measuring Resistance by Rate of Loss of, 343 Remaining on Two Bodies after Contact, 115, 351 Charged* Body cannot Exist Alone, 339 Charges induced in Hollow Con- ductor by placing a Charged Body inside it, 113 on Two Coeductors Enclosed by a Third, 110 on Two Bodies not Measured by the Potential Differ- ence, 85 Chemical Action in the Bunsen's Cell, 220 Action in the Darnell's Cell, 214 ■ Action in the Grove's Cell, 219 Action in the Leclauche" Cell, 221 Action in the Potash Bichro- mate Cell, 223 Property of a Current, Uses of, 4 Property 6f a Current, "Why Used to Measure Strength of Current, 9 Circuit, Law Connecting Currents in a Closed, 464 ' Wires Joined in Parallel,-136 Circuits in Parallel, Independence of Currents in, 260 Clark's, Latimer, Differential Gal- vanometer, 150 Latimer, Cell, 410 Latimer, Cell, Constancy of E.M.F. of, 411 Latimer, Cell, E. M. F. of, 411 Latimer, Cell, Folarisation of, 411 Latimer, Cell, Temperature Variation of E. M. F. Conductor, Conical, Electric Density Great at Pointed End of, 118 — Dependence of Potential of, on Amount of Electricity on it, 119 Dependence of Potential of, on Position, 119 — — Dependence of Potential of, on . Shape, 119 Electric, Heat evolved in, 3, 199 Electricity at Rest resides only on Surface of, 119 of Fixed Resistunce, Arrange- ment of Cells giving Maxi- mum Useful Power to, 450 Potential inside a Closed, 98 Potential of, compared with Pressure of G-as, 121 Uniform Potential on a, 86 ■ Ways in which Potential of, can be Varied, 121 Conductors, 9 Charges on Two, Enclosed by a Third, 110 of Different Potential, Induc- tive Action between, 87 Conical Conductor, Electric Density Great at Pointed End of, 118 Connection between Angular Motion of Reflected Ray and of Mirror, 106 between Motion of Image on a Plane Scale and Angular Deflection of Mirror, 107 — — "between Poles of Magnet and Direction of Current cir- culating round Magnet, 17 Constancy of Capacity of Condenser, 302 of Capacity of Two Bodies while their Relative Positions remain Constant, 338 of E.M.F. of Darnell's Cell, 216 of E. M. E. of Latimer Clark's Cell, 411. of Rate of Production of Heat in a "Wire "by Constant Cur- rent, 197 Constant Current, -Calibration by Sine Method with, 67 of a Galvanometer, 278 Total, Current Shunts, 257 Constructing Voltameters, Objec- tions to usual Mode of, 17 Contact Potential Difference, 351 Controlling Field, Galvanometer having Uniform, in which Deflection Varies as Cur- rent, 72 Controlling Force caused by Power. ful Permanent Magnet, Galvanometers having, 73 Convection of Heat, note, 195 Cooling Correction of Observed Rise of Temperature Curve, 196 Copper, Change of Resistance of, with Temperature, 160 Electric and Heat Conductivi- ties of, Compared, 159 Resistance of, for GivenLength and Diameter, and fo»* Given Length and Weight, 157 Resistance of, per Cubic Centi- metre, and per Cubic Inch, 154 Voltameter, Description of, 6, 11 Voltameter, Direction of Cur- rent in, 15 Voltameter, Precautions in Using, note, 11 Voltameter, Weight of Copper- deposited on Plate of, per second, hy one Ampere, 11 Cores, Soft Iron, used in Galvano- meters, 73 Correcting Results of Experiments by Drawing Curves, 34 Correction, Cooling, of Observed Rise of Temperature Curve, 196 Correction for Damping, 296 Corrugating Sides of Ebonite Pil- lars, 272 Coulomb, Definition of the, 289 Couple, Definition of, note, 283 Definition of Moment of a, note, 283 Crompton and Kapp's Electro-Mag- netic Control Meters, 392 and Kapp's Electro-Magnetic Control Meters, Advant- ages and Disadvantages of, 394 Cunynghame's Ammeter and Volt- meter, 382 Ammeter and Voltmeter, Ad- vantages and Disadvant- ages of, 385 — — Ammeter and Voltmeter, Graduation of, 385 Current, Alternating, Definition of, 198 Alternating, Measurement of, 198, 381 Amount of Heat Generated by Electric, 192 Amount of Heat produced per Minute by given, in given Resistance, 199 Arrangement of given Number INDEX. 493 of Cells to "produce Maxi- mum, through giveu Ex- ternal Resistance, 243 Current and Resistance, Variation of Magnetic Effect of Bobbin with, 418 and Static Methods of Measu- ring Potential Differences Compared, 125 Calibration by Sine Method with Constant, 67 Commercial Instruments for Measuring, 79, 376 Connection between Direction of, and Poles of Magnet produced, 17 Constancy of Rate of Produc- tion of Heat in a given Coil by Constant, 197 Definition of Direction of, 14 Developing Maximum Useful Power in Generator with. Fixed E.M.F. and Resist- ance, 448 Direction of, in Acid, Copper, and Zinc Voltameters, 15 Direction of, round Magnet, and Poles produced, 17 Electric, Compared with Cur- rent of Water, 2, 80 Electric, Heat is Evolved by, 3 Electric, Liquid is Decomposed by, 3 Electric, Magnet is Deflected by, 3 ■ Electric, Properties of, 3 Electric, "What is Meant by, 2 Electric, When said to Flow in a Conductor, 3 Flowing in Flat Coil, Direction of Magnetic Force pro- duced by, 43 Generator, Definition of Effi- ciency of, 451 Generator, Measurement of E.M. F. of, 224, 231, 234, 341 Generator, Work doue by a, 202 Generators, 208. (See also Cell and Batteries. ) Increase of Total, by Shunting, 183 Indication of Direction of, in Magnifying Spring Amme- ter and Voltmeter, 389 Measuring Alternating, 198 Measuring, by Rate of Produc- tion of Heat, 197 Measuring Strength of, 4, 8 - - Measuring with Siemens' Dy- namometer, 379 Measuring Resistance during Passage of Strong, 187 Current of Water in Pipe Compared with Electric Current, 80 Properties of, 3 Proportional to Tangent of Angle in Tangent Galva- nometers, 43 Ratio of, to Potential Differ- ence Constant for Given Conductor, 130 Resistance Coils Heated by Strong, 192 Reversing, without Altering ita Value, 47 Strength, Why Measured Fun- damentally by Chemical Property, 10 Testing Ammeters for Error on Reversing the, 402 that Develops Maximum Use- ful Power, 448 through the Galvanometer of Wheatstone's Bridge, 465 Unit of, 11 Variation of, with Variation of Potential Difference at Battery Terminals, 204 Variation of, produced in Total, by Shunting Part of Cir- cuit, 253 What is Meant by, 2 Currents in Closed Circuit, law Con- necting, 464 in Network, 462 in Various Circuits in Parallel, Condition of Independence of, 260 Several, Meeting at a Point, 464 Thomson's Galvanometer for Large, 53 Curve, Cooling Correction of Ob- served Rise of Tempera- ture, 196 Definition of Elastic, 34 Finding the Maximum for an Expression by means of, 244 Interpolation of Results by means of, 34 Law connecting Two Sets of Facts determined by means of, 35 Curves, Drawing,on Squared Paper, 31 Drawing, to Correct Results of Experiments, 34 on Squared Paper, Meaning of Apparent Inaccuracies in, 33 Value of, for Graphically Re- cording Results of Experi- ments, 33 Cylindrical Condenser. Capacity of. 308 494 PRACTICAL ELECTRICITY. D T)AMPING, 291 Apparent Increase in Re- sistance of a Galvanometer due to, 349 ■ Correction for, 296 Definition of, 284 Daniell's Cell, Description of, 210 Cell, Chemical Action in, 214 Cell, Constancy of E. M. F. in, 216 Cell,E. M.F. of, 211 Cell, E. M. F. of Standard, 411 Cell, Gravity, 212 ■ Cell, Fleming's Standard, 412 Cell, How to Prevent Local Action in, 217 Cell, Polarisation in, 216 Cell, Resistance of, 211 Cell, Standard, 411 Dead-Beat, Shielded, Direct-Read- ing Galvanometers, Ad- vantages of, 78 Decrement, Determination of Log- arithmic, when Damping is Very Slight, 297 Logarithmic, 296 Definition of Alternating Current, 198 of the Ampere, 11 of Brush Discharge, 369 of Capacity, 300 of Capacity of Condenser, 302 of Condenser, 301 of Conductivity, 155 of Contact Potential Difference, 351 of the Coulomb, 289 of Couple, 283 of Difference of Potentials, 80 of Damping, 284 of Dielectric, 311 - — of Direction of Current, 14 of Efficiency of Current Gene- rator, 451 of Efficiency of Electric Light, 452 of Elastic Curve, 34 of Electric Density, 117 of Electromotive Force, 202 of the Farad, 307 - — of Galvanometer, note, 21 of Galvanoscope, note, 21 of Glow Discharge, note, 369 of Hermetically Sealing, note, 20 of Horizontal Component - of Earth's Magnetic Force, note, 55 of Hypotenuse, note, 38 of Inductive Action, 87 of the Joule, 461 Definition of Lines of Force, 43 of Logarithmic Decrement, 296 of Magnetic Axis of a Needle, 37 of Magnetic Saturation, 388 • of Moment of Couple, vote, 283 of Moment of Inertia, 78 of North-seeking End of Mag- net, 16 of the Ohm, 140 of Parallax, note, 28 of Periodic Time of "Vibration, 291 of Plane of Magnetic Meridian, note, 45 of Potential Difference, 80 of Power, 441 of Quantity of Electricity, 109 of Residual Magnetism, 385 of Retardation, 331 of the Saturation of Liquid, 411 of Short-Circuited, 217 of Sine, note, 38 of Solenoid, note, 387 of Specific Inductive Capacity, 309 of Striking Distance, note, 371 of Super-saturation, note, 411 of Tangent, note, 37 of the Volt, Legal, 141 of the Volt, Provisional, 89 of Uniform Magnetic Field, 36 of Water Equivalent, 198 of the Watt, 442 Definitions of Conduction and In- duction, 97 Deflecting Field, Magnetic, 73 Deflection, Angular, of Mirror, Con- nection "between, and Mo- tion of Image on Plane Scale, 107 Best, to use with Tangent Gal- vanometer, 41 with Galvanometer of Wheat- stone's Bridge, Meaning of, 176 Proportional to Current, Con- struction of Galvanometers with, 71 Deflections of Tangent Galvanometer Controlled Only hy Earth's Magnetism, Values in Am- peres of, 84 Degree andTangent Scales, Accuracy of Readings Compared, 40 Delicate Galvanometers, 281. {See also Galvanometer.) Galvanometers, Importance of being Well Insulated, 286 Density, Distribution of, in Clos-ed Conductor Altered by In- sertion of Metal Rod, 119 INDEX, 495 Density Electric, Definition of, 117 Electric, Great at Pointed End of a Conical Conductor, 118 Electric, Greater near Edges of Flat Sheet of Metal, 118 Electric, Measuring, by means of Proof Plane, 117 Electric, Nought on Inner Sur- face of Closed Conductor, 118 Electric, Potential, and Quan- tity, Examples showing Difference between, 121 Dependence of Rate of Loss of Charge on Dielectric Only, 346 Deprez, E. M. P. used by, in Trans- mitting Power Thirty- seven Miles, 452 Detector, 58 Determination of Logarithmic De- crement when Damping is very Slight, 297 Diameter of Bobbin, Variation of Sensibility of Galvanome- ter with, 48 Dielectric, Definition of, 311 Only, Dependence of Rate of Loss of Charge on, 347 Difference between Saturation and Super-saturation, note, 411 in Colour between Candle and Arc Light, How to Over- come, in Measuring Arc Light, 457 of Potential, Adjusting Balls of Electrical. Maehine to produce Given Maximum, 372 of Potential, Alternating, In- creases Practical Resist- ance of Voltmeters, 427 — — of Potential, Alternating, Mea- suring, 426 of Potential at Battery Termi- nals, Variati6n of, with Change of Current, 204 of Potential between Two Conductors not Measuring Difference in their Electric Charges, 85 of Potential between Two Plane Conductors,Formula connecting, with Distance and Attraction between them, 87 of Potential between Two Points in a Uniform "Wire Conveying Current Pro- portional to Distance be- tween them, 83 ■ of Potential, Charges on Two Conductors Vary as, while their Relative Positions re- main Constant, 110 Difference of Potential Compared with Difference of Level in Liquids, 86 of Potential Compared with Difference of Pressure in Gases, 86 of Potential Compared with Difference of Pressure of "Water Flowing in a Pipe, 81 of Potential, Contact, 351 of Potential, Definition of,. Differential Galvanometer, Latimer Clark's, 150 Galvanometer, Mode of Ad- justing, 150 ■ Galvanometer, Principle of, 148 Galvanometer, Superiority of "Wheatstone's Bridge over, 171 ■ Galvanometer, Use of Shunts with, 183 Dilute Sulphuric Acid, Effect of Electrolysis of, 15 Diminution of Resistance of In- sulators with Increase of Temperature, 271 Direct Comparison with Tangent Galvanometer,' Calibrating Galvanometer "by, 58 ■ Reading Galvanometers, 76 Reading, Shielded, Dead-Beat Galvanometers, Advant- ages of, 78 Direction of Current, Definition of, 14 of Current in Acid, Copper, and Zinc Voltameters, 15 ■ of Current in Magnifying Spring Ammeters and Volt- meters, Indication of, 389 of Current round Magnet, Connection between, and Roles produced, 17 of Flow of Electric Current, "What is Meant by, 2 — of Magnetic Force produced by Current in Flat Coil, 43 Disadvantage of Magnifying Spring Ammeter and Voltmeter, 391 Disadvantages of Cardew's Volt- meter, 385 of Cunynghame's Ammeter and Voltmeter, 427 of El ectro - Magnetic Control Meters, 385 of Gravity Control Meters, 392 of Permanent Magnet Meters, 376 • of Siemens* Electro-dynamome- ter, 381 of Thomson's Large Current Galvanometer, 54 Discharge, Brush, 369 Glow, note, 369 Multiplying Power of Shunt used in Measuring, 349 Dispersion Photometer, 454 Distance Spark can be sent between Balls of Influence Machine, S71 Distinction between Conduction and Induction, 97 between Galvanometer and Galvanoscope, note, 21 Distribution of Magnetism in Per- manent Magnet, Measur- ing, 24 of Power in a Circuit, 445 Disturbance, Magnetic, Shielding Galvanometers from Ex- traneous, 73 Drawing Curves on Squared Paper, 31 Curves to Correct Results of Experiments, 34 Dry Pile, 372 Duplex - Telegraphy, Resistance Boxes used in, 186 Dynamometer, Measuring Currents with Siemens' Electro-, 379 Siemens' Electro-, '377. 497 Electric Arc, Description of, 188, 464 Arc, Measuring Illuminating Power of, in any Plane, 4-57 ■ Ar 3, Potential Difference Re- quired to maintain, be- tween Two Carbons, note, 371 Charge, 109. (See Charge.) Circuit, "Work done in, 199 Conductivity Diminishes more " Rapidly thai Heat Con- ductivity, 159 Current. (Set* Current.) Density. (See Density.) Energy. (See Energy.) Lamps, Description of Arc and Incandescent, 454 Lamps, Efficiency of, Increasing with Power, 458 Light, Measuring Efficiency of, 452 Potential. (See Potential.) Quantity. (See Quantity.) • Sparks. (See Sparks.) Electrical Machines, Frictional. {See Machines. ) Machines, Influence. (See Ma- chines.) Units, Ohm only one yet Legalised, 140 Electricity at Eest Resides only on Surface of Conductor, 1 19 Comparing Quantities of, Gal- vano metrically, 299 Comparing Quantities of, Stati- cally, 111 Condensers not Stores of, but of Electric Energy, 322 Measuring Quantity of, Abso- lutely, 289 Positive and Negative, 85 Potential of ConductorDepends partly on Amount of, 119 Quantity of, Defined, 109 Unit of Quantity of, 289 Quantity of, produced by Rub- bing Two Bodies together, 115 Electrification, Amount of a Body's, 109 Exterior, No Force inside Closed Hollow Conductor due to, 99 Object of Rubbing Two Bodies together to produce, 115 Electro - Dynamometer, Siemens', 377. (See also Siemens' Electro-Dynamometer.) .Electrode, Definition of, note, 131 Electrolysis, Effect of, of Dilute Sulphuric Acid, 15 Electro-Magnet, Description of, 6 G G Electro-Magnet, Strength of, when Core is Slightly Mag- netised, 3S2 Magnet, Saturation of, 388 Magnetic Control Meters, 392 Magnetic Control Meters, Ad- vantages of, 394 Magnetic Control Meters, Crompton and Kapp's, 392 Magnetic Control Meters, Dis- advantages of, 394 Magnetic Control Meters-, Paterson and Cooper's, 393 Electrometer, Edeltnann's Modifi- cation of Thomson's, 130 Suggested Improvements in Edelmann's, 134 Use of, for proving Ohm's Law, 134 Rough, 94 Thomson's Absolute, Portable, and Quadrant, 93 "Weight, Lecture-room Model of, 88 Guard Ring for Weight, 89 Weight, Increasing Sensibility of, by using Auxiliary High Potential, 91 Electromotive Force, Definition of, 20A Force, Constancy of, . in Daniell's Cell, 216 -rr- Force, Measuring Resistance Containing, 469 Force of Cell Independent-of its Size and Shape, 211, 236 Force of Bunsen's Cell, 220 Force of Daniell's Cell, 211 Force of Grove's Cell, 218 Force of Leclanche' Cell, 222 Force of Latimer Clark's Cell. 411 Force of Latimer Clark's Cell, Variation of, with Tempera- ture, 411 Force of Standard Daniell's Cell, 412 Force of Cells in Parallel, 241 Force of Cells in Series, 241 Force of Cells partly in Series and partly in Parallel, 241 Force Used by Deprez in Trans- mitting Power 37 Miles, 452 Forces of Batteries, Compari- son of, by observing Resist- ance through which they send Equal Currents, 231 — — Force of Batteries, Comparison of, by observing their Joint and Opposed Currents, 232 498 PRACTICAL ELECTRICITY, Electromotive Force of Current Generators, Condenser Method of Comparing1, 341 ■ Force, Measuring, 224 Electrophoric Action, Compound Interest Law of, 361—372 Electrophorus, Action of, 360 Bertseh's Rotatory, 361 Description of, 356 Ebonite, giving Negative Charges, 359 Ebonite, giving Positive Charges, 357 Electroscope, Calibrating Gold-Leaf, 354 Condensing, 352 Gold-Leaf, Improved Form of, 94 — Indicates Potential Difference, 95 Varnishing Shade of Ordinary Gold Leaf, 97 Electroscopes, Objections to Ordi- nary Gold-Leaf, 96 Element, Simple Voltaic, 209 E. M. F., Meaning of, 204. (See also Electromotive Force.) Enclosure of Static Electric Appa- ratus in Metallic Case Necessary, 108 Energy, Condensers Stores of Elec- tric, 322 Produced by Frictional Elec- trical Machine, 352 ^— Waste of, in Voltmeters with High External Resistance, 422 Equivalent of Heat, Mechanical, 201 Error in Ammeters on Reversing the Current, Testing for, 402 in Ammeters Produced by Ex- ternal Magnetic Disturb- ance, Testing for, 403 in Ammeters Produced by Re- sidual Magnetism, Testing for, 400 in Ammeters Produced by Time, Testing for, 407 Testing Voltmeters for Heat- ing, 415 Errors in Voltmeters, Different Kinds of, 407 in Wattmeters, 445 Examples : 1, 12; ii. — vii., 13 ; viii,, 14 j ix., x., 52; xi., 53; xii. xiii.,55; xiv.,56; xv., xvi., 57; xvii,, 89; xviii., xix., 90; xx,, 91; xxi. — xxiv., 142 ; xxv., 143 ; xxvi.— xxviii., 155; xxix., 156; xxx. — xxxiii., 158 ; xxxiv., 162 j xxxv.— xxxvii., 163; xxxviii. — xl., 180; xli. — xliii., 201 ; xliv., 202 ; xlv.t 203 ; xlvi.— xlix., 207 ; 1., Ii., 227; Hi., liii.. 228; liv., 232; lv.— lvii., 233; lviii.— Ix., 242; lxi., 243; lxii., 247; lxiii., lxiv., 248; lxv., 249; lxvi., 250; lxvii.— lxix., 252; lxx., lxxi., 255; lxxii., lxxiii., 256; lxxiv.-, 259; lxxv., 260; lxxvi., 262; lxxvii., 263; lxxviii., 264; lxxix., lxxx., 265; lxxxi.,280; lxxxii. — Ixxxiv., 281; lxxxv., 294; lxxxvi., lxxxvii., 295 ; lxxxviii., 297 ; lxxxix.— xci., 298 ; xcii., 311 ; xciii.— xcv., 312; xcvi., xcvii., 313 ; xcviii., xcix., 323; c, 325; ci., 3i6 ; cii., 341; ciii., 350; civ., 437; cv., cvi., 438; cvii., 439; cviii., eix., 440; ex., cxi., 443; cxii., cxhi.,444; cxiv., 446 ; cxv., cxvi., 447 ; cxvii., cxviiL, 459 ; cxix., 460 ; cxx., 471 ; exxi., 473; exxii., 474 ; exxiii., 475 Examples showing Difference be- tween Electric Potential, Density, and Quantity, 121 Explanation of Electric Sparking, ■note, 358 External Resistance, Variation of, with Current and Poten- tial Difference at Battery Terminals, 204 Equality of Charges on Two Bodies obtained by Rubbing tbem together, 115 TfARADAY'S Experiment onForce in Closed Conductor due to Exterior Electrification, 99 Farad, Definition of the, 307 Fault, Common, in Constructing Ebonite Pillars, 272 Fibre and Pivot Suspensions, 60 • Suspension used in Thomson's Marine Galvanometer, 60 Field, Uniform Magnetic, 36 Finding Angles from their Tangents by means of Squared Paper, 56 Tangents from their Angles with Squared Paper, 57 the Maximum for an Expres- sion by means of Curve, 241 Fixed E. M.F. and Resistance, Cur- rent Developing Maximum INDEX. 499 Useful Power with Gene- rator with, 448 Fixed Resistance, Arrangement of Cells giving Maximum Useful Power to Conduc- tor with, 450 Flat Coil, Direction of Magnetic Force produced by Cur- rent flowing in, 43 Fleming's Standard Daniell's Cell, 412 Flint Glass, Resistance of, 271 Specific Inductive Capacity of, 310 Flow, Wbat is meant by Direction of, of Electric Current, 2 of Electric Current compared with that of "Water, 3, 80 Focal Length of Lens, Definition, of, 456 Force, Attractive, between Two Plane Conductors, For- mula Connecting, with Potential Difference and Distance between them, 87 Definition of Lines of, 43 Definition of Horizontal Com- ponent of Earth's Mag- netic, note, 55 Direction of Magnetic, pro- duced by Current flowing in Flat Coil, 43 Electromotive. (See Electro- motive Force. ) ■ None Inside Closed Hollow Conductor duo to Exterior Electrification, 99 Foster's, Prof. G-. C, Simplification of Sine Galvanometer, 61 Frictional Electrical Machines, 352 ■ Electrical Machines, Con- densers for use with, 313 Fulfilment of Conditions for Tan- gent Law in Tangent Gal- vanometer, 43 G GALVANIC Cells, 209. Galvanometer, Potential Difference, when it may "be Employed, "'127 Potential Difference, Testing, 407 — Proportional, 71 — — Proportional, with Permanent Magnet Control, 73 Proportional, with Uniform Controlling Field, 72 Quantity, Mather's Simple Form of, 299 ■ Reflecting, 103, 281, 293, 299 - — Reflecting, Deflection Propor- tional to Current witb, 108 Reflecting, Mode of Using Lens with, 105 Reflecting, Lamps for, 106 Reflecting, Mirror for, 105 Reflecting, Mather's Form of, 299 Reflecting, Mudford's Form of, 284 - — Reflecting, Spirit Level for, 285 Sine, 62 Sine, Foster's Simplification of, 61 Shielded, 57, 73, 103, 390 Tangent, 36 • Tangent, Simple Form of, 27 — — Tangent,Adjustmentof Coil of, 46 Tangent, Best Deflection to Use with, 41 Tangent, Conditions that a Galvanometer may he, 36 ■ Tangent, Conditions of Tan- gent Law Fulfilled in, 43 Tangent, Controlled Only by Earth'sMagnetism, Values in Amperes of Deflections of, 55 Tangent, Proportions of Chan- nel in Bobbin of, when Tangent Law is Most Ac- curately Fulfilled, 51 Tangent, Scale for, 38 Tangent, Sensibility of, Alter- ing, by Removing Needle from Plane of Coil, 52 Tangent, Sensibility of, Al- tered by "Varying Number of Windings or Diameter of Bobbin, 48 Calibrating, Relatively or Abso- lutely, 22, 27, 395—400 Calibrating, by Comparison with Tangent Galvano- meter, 58 Calibrating, by Sine Method, 64 Calibrating, by Sine Method in Higher Parts of Scale, 65 Galvanometer, Calibrating, by Sine Method with Constant Current, 67 Calibrating, by using Known Resistances and Cell of Constant E. M. F., 238 Calibrating, by using Known Resistances and Constant Potential Difference, 164 — - Calibration of, Unaffected by Change in Strength of Pole3 of Single Needle, 23 Sensibility of, Increasing, by Diminishing Diameter of "Wire used in "Winding, 22 Sensibility of, Modes of Vary- ing. 501 Gas-Bumer, Regenerative, for Gal- vanometers, 106 Generated in Voltameter Inde- pendent of Shape, Size, aod Distance of Plates, 10 Rate of Production in Sul- phuric Acid Voltameter by One Ampere, 12 Gases, Difference of Pressure Com- pared with Difference of Potential, 86, 121 Specific Inductive Capacity of, 310 Gearing, Ammeters and Voltmeters with Magnifying, 386 Generation of Heathy Electric Cur- rent, 192 Generator, Current, Definition of Efficiency of, 451 Current, Measurement of E. M. F. of, 224, 231, 234, 341 Current, Measurement of Re- sistance of, 205, 225, 342 Current, Power Wasted in Heating, 445 Current, Work done hy, 202 Current, with Fixed E. M. F. and Resistance, Current Developing Maximum Use- ful Power with, 448 Generators, Current, Forms of, 203. (See also Cell, Batteries.) German Silver, Change of Resist- ance of, with Temperature, 160 Silver, Resistance of, for Given Length and Diameter, and for Given Length and Weight, 157 Silver, Resistance of, per Cubic Centimetre and per Cubic Inch, 154 Silver, Why Resistance Coils are made of, 160 Glaas, Flint, Resistance of, 271 Glow Discharge, note, 369 Gold, Change of Resistance of, with Temperature, 160 Electric and Heat Conductivi- ties of, Compared, 159 Resistance of, for Given Length and Diameter, and for Given Length and Weight, 157 Resistance of, per Cubic Centi- metre and per Cubic Inch, 154 Leaf Electroscope, 94 Leaf Electroscope, Calibrating, 354 Leaf Electroscope, Objections to Ordinary, 96 Gold-Leaf Electroscope, Varnishing Shade of Ordinary, 97 Graduation of Ammeters, Test for Accuracy of, 395 of Cunynghame's Ammeter and Voltmeter, 385 of Voltmeters, Testing for Ac- curacy of, 408. (See also Calibrating.) Graphically Recording Results of Experiments, 30 Recording Results, Value of, 33 Gravity Control Meters, 391 Daniell's Cell, 212 Grove's Cell, 218 Cell, Chemical Action in, 219 ■ Cell, E. M. F. of, 218 Cell, Resistance of, 218 Guard Ring, 89 Tube, 375 Guttapercha, Resistance of, 271 ■ Specific Inductive Capacity of, 310 H TXEAT, Amount of, per Minute XJ- Produced by Given Cur- rent flowing through Given Resistance, 199 Amount of, Produced per Second in Coil by Constant Current, Constancy of, 197 and Electric Conductivities, Comparison of, 158 Conductivity Diminishes more Rapidly than Electric, 159 Evolution of, in Conductor, by Electric Current, 3 Generated by Electric Cur- rent, Amount of, 192 Measuring Current by Rate of Production of, 197 Mechanical Equivalent of, 201 Radiation, Conduction, and Convection of, note, 195 Rate of Production of, in Gal- vanometer Coils, 419 Heating Error in Voltmeters Di- minished by Use of Outside Resistance, 421 Error, None in Cardew's Volt- meter, 426 Error, Testing Voltmeters for, 415-423 Current Generator, Power Wasted in, 445 Property of Current, Practical Uses of, 4 Hermetically Sealing, Definition of, note, 20 High Resistances, Measuring, 277 502 PRACTICAL ELECTRICITY. 503 Iron Magnetised by Electric Cur- rent, 3 Resistance Coils, 162 JAR, Leyden, 314. {See also Ley- den Jar.) Used for Daniell's Cell, 210 Joints, Lap and Butt, 79 Joule, Definition of the, 461 Joule's Mechanical Equivalent of Heat, 201 K TTEMPE'S Constant Total Current -LV- Shunts, 257 Key, Bridge, 174 Charge and Discharge, 320 Charge and Discharge, Simple Form of, 343 Charge and Discharge, Various Modes of Connecting, with Condenser, Battery, and Galvanometer, 320—322 Make and Break, Simple Form of, 19 Plug, Description of, 139 Kirchhoff's First Law, 464 Second Law, 464 T ALANDE Chaperon Cell, 210 Lamps, Description of Arc and Incandescent, 454. ( See also Arc, Incandescent. ) Lamps Used with Reflecting Galva- nometer, 105 Lap Joint, 79 Large Potential Differences, Pro- duction of, 351 Latimer Clark's Cell, 410 Clark's Cell, Constancy of E.M.F. of, 411 Clark's Cell, E. M. F. of, 411 Clark's Cell, Temperature Va- riation of E. M. F. of, 411 Clark's Differential Galvanome- ter, 150 Law connecting Two Sets of Facts Determined by means of Curve, 35 of Differential Galvanometer, 149, 183 Experimental Proof of Ohm's, 130 Kirchhoff's First, 464 Kirchhoff's Second, 464 Ohm's, 130 Tangent, Fulfilment of Condi- tions for, in Tangent Gal- vanometer, 43 Law, Tangent, "When True, 41 Sine, When True, 61 of Wheatstone's Bridge, 167 Laws of Surface Leakage and Leak- age through the Mass, 270 Lead, Change of Resistance of, with Temperature, 160 Electric and Heat Conducti- vities of, Compared, 159 Resistance of, for Given Length and Diameter, and for Given Length and Weight, 157 , Resistance of, per Cubic Centi- metre, and per Cubic Inch, 154 Leakage, Dependence of Rate of Loss of Charge from, on Dielectric Only, 346 Surface, 266 Surface, Law of, 270 through the Mass, 266 through the Mass, Law of, 270 Leclanche" Cell, 220 Cell, Chemical Action of, 221 Cell, E. M. F. of, 222 Legal Ohms and B. A. Lockwood Cell, 213 Logarithmic Decrement, 296 Decrement', Determination ofj wlie n Damping i s Very Slight, 297 Lord Rayleigh, Silver Voltameter used by, 11 M TVf ACHINES, Electrical, Adjust- J~-L ing Balls to Produce Given Potential Difference, 372 Electrical, Attaching Leyden Jars to Collectors of, 370 Electrical, Condensers for Use with, 313 Electrical, Frictional, 352 Influence, Bertsch's, 361 Influence, Accumulating, 361; Holtz, 367; Nicholson's, 366; Thomson's, 364; Var- ley's, 367; Voss, 367; Wimshurst, 367 Influence, Accumulating, Con- densers for Use with, 313 — Influence, Accumulating, Com- pound Interest Law of, 364, 366 Influence, Accumulating, "Work done by, 371 Magnet, Connection between Poles of, and Diiection of Cur- rent round, 17 Definition of North-Seeking End of, note, 16 Deflected by Current, 3 ■ Electro. (See Electro-Magnet.) Motion of, Produced by Uni- form Magnetic Field, 390 — Permanent, Measurement of Distribution of Magnetism in, 24 Permanent, Proportional Gal- vanometer Controlled by, 73 Magnets, Position of Poles in, 23 Magnetic Axis of Needle, Definition of, 37 Disturbance, Shielding Galva- nometers from Extraneous, 57,73,103, 390 Effect of Bobbin, Variation of, with Current and Resist- ance, 418 Field, Motion of Magnet pro- duced by Uniform, 390 Force, Definition of Horizontal Component of Earth's, note, 55 Force, Direction of, produced by Current in Flat Coil, 43 Magnetic Meridian, Definition of Plane of, notp, 45 Property of Current, Practical Uses of, 4 Saturation, 388 Screen, Thick Iron Box, 101 Magnetised, Iron, by Current, 3 Magnetism, Measurement of Dis- tribution of, iu Permanent Magnet, 24 Residual, Definition of, 385 Residual, Testing Ammeters for, 400 Magnifying Gearing, Ammeters and Voltmeters with, 386 Spring Ammeter and Volt- meter, 386 Spring Ammeter and Volt- meter, Adjustment for Sen- sibility in, 389 -■ — Spring Ammeter and Volt- meter, Advantages of, 390 Spring Ammeter and Volt- meter, Disadvantage of,391 Spring Ammeter and Volt- meter, Indication of Di- rection of Current in, 389 Spring Voltmeter, Best Law of Variation for Gauge of Wire in, 421 Making Sine Scale, Mode of, 68 Tangent Scale, Mode of, 38 Mance's Test for Resistance Con- taining E. M. F., 470 Marine Galvanometer. 505 Maximum Potential Difference of Electrical Machine, Deter- mination of, 372 Useful Power, Current that Develops, 448 Useful Power in Generator with Fixed E. M. F. and Resistance, Current that Develops, 448 Measuring Arc Light, Efficiency of, 455 Arc Light, Illuminating Power of, in any Plane, 457 — Arc Light, Illuminating Power of, How to Overcome Dif- ference in Colour between it and Candle when, 457 ■ Efficiency of Electric Light, 452 Efficiency of Incandescent Light, 452 Ciirrent, Alternating, 198 • Current, Commercial Instru- ments for, 79, 376 Current by Sate of Production of Heat, 197 Current with Siemens' Dyna- mometer, 379 Small Currents, Disadvantage of using Voltameters f or,20 Strength of Current, 4 Distribution of Magnetism in Permanent Magnet, 24 Electric Density by means of Proof Plane, 117 Electromotive Force of Cur- rent Generators, 224, 231, 234, 341. (See also Electro- motive Force.) Potential Difference by "Weigh- ing, 88 Potential Differences, Alter- nating, 426 Potential Differences, Static and Current Methods of, Compared, 125 Power, 442 Resistance of Batteries, 205, 225 Resistance of Batteries using Known Resistances, 226 Resistance of Batteries using Known Resistances and Shunt, 226 Resistance of Current Gener- ator, Condenser Mtthod of, 342 Resistance by Rate of Loss of Charge, 344 ■ Resistance by Rate of Loss of Charge, Gal van ometrie Method of, 318 Resistance Containing E.M.F., Measuring Resistance during Pas- sage of Strong Current, 187 High Resistances, 277 Specific Inductive Capacity, 332 Quantity of Electricity, 111, 289, 299 Measurement. Mica, Specific Inductive Capacity of, 310 Micrometer Screw, Description of, note, 2& Minotto's Cell, 211 Mirror, Angular Motion of, Half that of Reflected Ray, 106 Connection between Angular Deflection, of, and Motion of Image on a Plane Scale, 107 in Galvanometer, "Use of, to Avoid Parallax, 28 for Reflecting Gal vanometer,105 Moment of Couple, Definition of, note, 283 of Inertia, Definition of, note, 78 Motion, Angular, of Reflected Ray, 106 of Image on Plane Scale, Con- nection between, and Angu- lar Deflection of Mirror, 107 of Magnet produced by Uni- form Magnetic Field, 390 Multiples of Ohm, Construction of, 145 Multiplying Power of Shunt, 178 Power of Shunt used in Measuring a Discharge, 349 N NAPIERIAN Logarithmic De- x^ oremeut, 296 Negative Charges, Ebonite Electro- phorus Arranged to Give, 359 - — Electricity, 85 Network, Currents in, 462 Nicholson's Revolving Doubler, 366 Nickel, Resistance of, per Cubic Centimetre, and per Cubic Inch, 154 North-seeking end of Magnet, Defi- nition of, note, 16 Nought, PoteDtial of Earth Arbi- trarily taken as, 84 Null Methods, Meaning of, 236 0 f)HM, 89, 140, 141 yj Construction of Multiples of, 145 — — Definition of Legal, 140 Only Electrical Unit yet Legal- ised, 140 Ohmnieter, Description of, 190 Ohms, Legal, and B. A. Units, Equa- tions connecting, 142 — — "Wires having Resistjnce of about Ten, 143 Ohm's Law, 130 Law, Experimental Proof of, 130 Olefiant Gas, Specific Inductive Capacity of, 310 pARAFFIN "WAX, Coating In- ■*- sulating Stems with, 267 "Wax, How to Prevent Over- heating when Melting, note, 267 Wax, Resistance of, 271 "Wax, Specific Inductive Capa- city of, 310 Parallax, Definition of, note, 28 Mirror Used in Galvanometer to Avoid, 28 Parallel, Cells in, Figure of, 239 ■ Cells in, Symbolical Repre- sentation of, 240 Circuit, "Wires Joined in, 136 Circuit, Independence of Cur- rents in, 260 E. M. F. of Cells in, 241 Resistance, 179 Patersonand Cooper's Electro-Mag- netic Control Meters, 393 P. 507 Platinum, Resistance of, per Cubic Centimetre, and per Cubic Inch, 154 Silver Alloy, Change of Resist- ance of, with Temperature, 160 Silver Alloy, Resistance of, for Given Length and Dia- meter, and for Given Length and "Weight, 157 Silver Alloy, Resistance of per Cubic Centimetre, and per Cubic Inch, 154 Plug, Infinity, 151 Key, Description of, 139 Resistance Boxes, Construction of, 151 Poggendorffs Method of Compar- ing E.M.Fs., 234 Method, Use of, for Calibrating Voltmeters, 413 Polarisation of Daniell's Cell, 216 of Latimer Clark's Cell, 411 Poles of Magnet, Connection be- tween, and Direction of Current round Magnet, 17 of Magnets, Positions of, 23 Portable Electrometer, 93. Galvanometer with Approxi- mate Absolute Calibration, 69 Positive Electricity, 85 Potential, 85 Potash Bichromate Cell, 222 Bichromate Cell, Chemical Ac- tion in, 223 Bichromate Cell, Composition of Liquid for, 222 Bichromate Cell, E. M. P. Potential Difference Required to Produce Spark between Two Metallic Balls, 370 Difference, Static and Current Method of Measuring, Compared, 125 Difference, Sub-dividing into Known Fractions, 278 Difference, Variation of, at Bat- tery Terminals, with Varia- tion of Current, 204 — Difference, Variation of, with Resistance of Given Volt- meter to Produce Given Deflection, 419 Higher, and Lower, Positive, and Negative, Definition of, 85 Increasing Sensibility of Weight Electrometer by Using Auxiliary High, 91 Inside Closed Conductor, 98 Measurement of, Compared with Measurement of Tem- perature, 85 of Earth Arbitrarily taken as Nought, 84 Uniform on Conductor, 86 Uniform in Conductor, 98 Power, Arrangement of Cells Giv- ing Maximum Useful, to Conductor of Fixed Resist- ance, 450 — — Current Developing Maximum Useful, with Generator of Fixed E. M. F. and Resist- ance, 448 Definition of, 441 Distribution of, in Circuit, 445 E. M. F. used by Deprez in Transmitting, 37 Miles, 452 Horse, 201, 443 Measurement of, 442 Unit of, 4i2 — Utilised in Circuit Outside Ge- nerator, 445 "Wasted in Heating Generator, 446 Preparation of Varley's Carbonised Cloth, 397 Pressure, Difference of, in Gases, Compared with Difference of Potential, 86 — — of Gas Compared with Poten- tial of Conductor, 121 of Water, Difference of, in Pipe Compared with Difference of Potentials, 81 Proof of Ohm's Law, Experimental, 130 Proof-plane, 116 Proof-plane, Measuring Electric Density by means of, 117 Properties of Electric Current, 3 of Electric Current, Practical Uses of, 4 Proportional Coils of Wheatstone's Bridge, 172 Galvanometer, 71, 75, 108, 389 Proportions of Channel in Bobbin of Tangent Galvanometer, when Tangent Law is Most Accurately Fulfilled, 51 Q QUADRANT Electrometer, Thom- son's, 93 Electrometer, Edelmann's Mo- dification of Thomson's, 130 ■ Electrometer, Edelmann's Mo- dification of Tnomson's, Defects in, 134 Electrometer, Edelmann's Mo- dification of, Dry Pile for, 133, 372 Electrometer, Edelmann's Mo- dification of, Needle for, 132 Electrometer, Formula for, 134 Quantities of Electricity, Compari- son of, 111, 299 Quantity of Electricity, Definition of, 109. 509 Ratio of Sensibilities of Voltmeter in Parallel and in Series, 433 Rayleigh, Lord, Silver Voltameter Used by, 11, 395 • Lord, Temperature Variation of B. M. F. of Claris Cell Determined by, 411 Recording Results of Experiments Graphically, 30 Results of Experiments Gra- ?hically, Value of Curves or, 33 Reflected Ray, Angular Motion of ,106 Reflecting Galvanometer, 103, 281, 293, 299. (See also Galva- nometer, Reflecting.) -' Galvanometer, Different "Ways of Forming Image with, 105 Galvanometer, Lamp Used with, 106 Galvanometer, Modes of Using Lens with, 105 — — Galvanometer, Spirit Level for, 285 Relative Calibration of Galvano- meter, Meaning of, 22 Relatively Calibrating Galvanome- ters, 27 Replenisher, Thomson's, 364 Representation of Batteries, Sym- bolical, 173, 240 Residual Magnetism, Definition of note, 388 Magnetism, Testing Ammeters for, 400 Resin, Specific Inductive Capacity of, 310 Resistance, 9, 129 Amount of Heat produced per Minute by Given Current flowing through Given, 199 and Current, Variation of Mag- netic Effect of Bobbin with, 418 Apparent Increase of, in Gal- vanometer, Due to Damp- ing, 349 of Battery, Measuring, 205, 225, 342 Best, for Differential Galvano- meter, 436 Best, for Galvanometer in Sim- ple Circuit, 435 Best, for Galvanometer of Wheatstone's Bridge, 172, 466 Best, for Coils of Wheatstone's Bridge, 171 Best, to Give to Galvanometer, 435 Box, Description of, 28 Box, Construction of Plug, 151 Resistance Box, Construction of Sliding, 186 Box used in Duplex Telegraphy, 187 Resistances, Calibrating Galvano- meter by Using Known, and Cbnstant Potential Differ- ence, 164 Calibrating Galvanometer by Using Known, and Cell of Constant B. M. F., 238 Change of, with Temperature, Results of Matthiessen's Experiments on, 160 Comparing, 136 Comparing, Differential Galva- nometer Method of, 148 Comparing-, Potential Differ- ence Method of, 140 Comparing, Simple Substitu- tion Method of, 138 Comparing, "Wheatstone's Bridge Method of, 166 Comparing Use of Liquid and "Wire, 194 Resistance Containing E. M. F. 511 Sensibility of Wheatstone's Bridge, Conditions affect hi-*, 171, 466 • of Wheatstone's Bridge, Mode of Increasing, 168 of Weight Electrometer, In- creasing, by Using Auxili- ary High Potential, 91 Shunting Galvanometer to Diminish, 229 Testing Ammeters for Perma- nent Alteration of, 407 Two Degrees of, in Commutator Ammeter and Voltmeter, 427 Series, E. M. F. Sparks between Balls of Electrical Machines, Length of, 370 Electric, 358 Potential Difference Eequired to Produce, between Point and Plate, 871 Potential Difference Required to Produce, between Two Metallic Balls, 370 Sphere, Capacity of, in Space, 339 Spherical Condenser, Capacity of, 338 Spirit Levels for Reflecting Galvano- meters, 285 Specific Inductive Capacity, Defini- tion of, 309 Inductive Capacity of Solids and Liquids, 310 Inductive Capacity, Measuring, 33i Specimens of Instructions for Ex- periments, 476 Spring? Control Meters, 377 Control Meters, Cunyng- hame's, 382 ■ Control Meters, Magnifying, 386. (See also Magnifying Spring Ammeter and Volt- meter.) Control Meters, Siemens', 377 Squared Paper, Drawing Curves on, 31 — Paper, Meaning of Inaccura- cies in Curves Drawn on, 33 Paper, Selection of Suitable Units on, 31 Paper, Use of, 30 Paper, Using, to Find Angles from their Tangents, 56 Paper, Using, to Find Tangents from their Angles, 57 Standard Air Condenser, 334 Candle, Description of, 452 Cells, 410 — r- Daniell's Cell, 411 'Daniell's Cell, E. M. P. 513 Table of Resistances of Metals per Cubic Centimetre, and per Cubic Inch., 154 of Specific Inductive Capaci- ties, 310 — — of Temperature Variation of Resistance, 160 showing Potential, Density, and Quantity of Electricity on Conductor in Different Conditions, 123 Bhowiog Variation of External Resistance, Current, and Potential Difference at Battery Terminals, 205 Tangent of ADgle o£ Deflection Proportional to Current in Tangent Galvanometer, 43 Definition of, note, 37 and Degree Scales, Accuracy of Readings Compared, 40 Galvanometer, 36 Galvanometer, Alteration of Sensibility of, by Altering Position of Needle, 51 Galvanometer, Adjustment of Coil of, 46 Galvanometer, Best Deflection to Use with, 41 Galvanometer, Calibration of Galvanometer by Direct Comparison with, 58 ■ Galvanometer, Conditions to be Fulfilled in, 36 Galvanometer, Controlled Only by the Earth's Magnetism, Values in Amperes of De- flections of, 55 — — Galvanometer, Fulfilment of Conditions for Tangent Law in, 43 Galvanometer, Proportions of Channel in Bobbin of, when. Tangent Law is Most Ac- curately Fulfilled, 51 — Galvanometer, Scale for, 39 Galvanometer, Simple Form of, 27 Law, How Conditions of, are Fulfilled in Tangent Gal- vanometers, 43 Law, When True, 41 Scale, Mode of Making, 38 Tangents, Finding Angles from, by means of Squared Paper, 56 Telegraph Insulators, 274 Insulators, Testing during Manufacture, 275 Telegraphy, Resistance Boxes used in Duplex, 187 Telephone, Description of the Bell, 336 H H Temperature, Change of Resistance with, Results of Matthies- sen's Experiments on, 160 Curve, Cooling Correction of Observed Rise of, 196 Diminution of Resistance of Insulators with Increase of, 271 ■ Equation connecting Variation of Resistance of Metals with, 153 Law of Variation of Resistance with, 152 Measurement of, Compared with Measurement of Po- tential, 85 Variation of E. M. F. of Lati- mer Clark's Cell, 411 Variation of Resistance with, 147 Testing Ammeters, 394 Ammeters for Accuracy of Graduation, 395 Ammeters for Error on Re- versing the Current, 402 Ammeters for Error Produced by External Magnetic Dis- turbance, 403 Ammeters for the Permanent Alteration of Sensibility. 407 Ammeters for Residual Mag- netism, 400 Cables, Sealing up One End while, 268 Insulators during Manufac- ture, 275 Voltmeters, 407 Voltmeters for Accuracy of Graduation, 408 Voltmeters for Heating Error, 415 Testing. (See also Comparing, Mea- suring.) Thompson's, Prof. Silvanus P. , Rule for Best Dimensi n i of Channel of Bobbin of Tan- gent Galvanometer, 51 Thomsons, Sir William, Arrange- ment for Increasing a Potential Difference in Known Ratio, 354 Astatic Galvanometer, 283 Astatic Galvanometer, Modi- fied Form of, 284 Electrometers, 93 Electrometer, Edelmann's Form of, 130 Large Current Galvanometer, 53 Leyden Jar, 315 Marine Galvanometer, 103 514 PRACTICAL ELECTRICITY. Thomson's, Sir William, Marine Galvanometer, Fibre Sus- pension used in, 60 Marine Galvanometer, Shield- ing, from Magnetic Dis- turbance, 103 — — ■ Reflecting1 Galvanometer, 283 - — Replenisher, 364 Time Rise of Temperature due to Passage of Current, 195 Tin, Change of Resistance of, with Temperature, 160 Electric and Heat Conductivi- ties of, Compared, 159 Resistance of , for Given Length and Diameter, and for Given Length andWeight, 157 Resistance of, per Cubic Cen- timetre, and per Cubic Inch, -154 • V TTNTFORM Controlling Field, ProportionarGalvanometer with, 72 Magnetic Field,Definition of, 36 Magnetic Field, Motion of Magnet Produced in, 390 Potential on Conductor, 86 Unit of Capacity, 307j — - of Current, 11 of Density, 117 of Potential Difference, 89, 141 of Power, 442 ■ of Quantity, 289 of Resistance, B.A., 141 of Resistance, British Associa- tion, 141 of Resistance, Legal, 140 of Resistance, Siemens', 142 of Resistance, B. A. and Legal, Compared, 142 Units, Selection of, Suitable on Sci'^ared Paper, 32 TTALUES in Amperes of Deflec- tions of Tangent Galvano- meter Controlled Only by Earth's Magnetism, 55 Variable Resistance in Voltmeters caused by Self-induction with Alternating Potential Differences, 427 Variation of Capacity of Condenser with Area of, and Distance between, its Coatings, 303 — of External Resistance, Cur- rent, and Potential Dif- ference at Battery Termi- nals, 204 Variation of Magnetic Effect of Bohbin with Current and Resistance, 418 of Resistance with Length, 143 of Resistance with Material, 146 of Resistance with Sectional Area, 146 of Resistance with Tempera- ture, 147 of Resistance with Tempera- ture, Law of, 152 of Sensibility of any Galvano- meter by Altering Dia- meter of "Wire, 22 of Sensibility of any Galvano- meter with Length of Wire used in Winding, 418 of Sensibility of any Galvano- meter by Shunting, 229 of Sensibility of Galvanometer with its Resistance, 416 of Sensibility of Tangent Gal- vanometer, 48 of Sensibility of Voltmeterwith Change of its Resistance, 407, 418 Produced in Total Current by Shunting Portion of Circuit, 253 — — with Temperature of E. M. F. 