None
33 Value of, for Graphically Re- cording Results of Experi- ments, 33 Cylindrical Condenser, Capacity of, 308 494 PRACTICAL ELECTRICITY. 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, note, 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 Tanorent, 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 TangentGalvanometer Controlled Only by Earth's Magnetism, Values in Am- peres of, 84 Degree andTangent Scales, Accuracy of Readings Compared, 40 Delicate Galvanometers, 281. 495 Density Electric, Definition of, 117 Electric, Great at Pointed End of a Conical Conductor, 118 Electric, Greater Dear 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 Kate of Loss of Charge on Dielectric Only, 346 Deprez, E. M. F. 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 Bate 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 Machine 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, Variation 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,Fprmula 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 of Potential Compared with Difference of Pressure of Water Flowing in a Pipe, 81 of Potential, Contact, 351 of Potential, Definition of, 80 — of Potential Galvanometer Ab- solutely Calibrated, 127, 408, 415 of Potential Galvanometer, Long Fine Wire Used in, 127 of Potential Galvanometer, When it may be Employed, 127 of Potential, Increasing a, in Known Ratio, 354 of Potential, Large, 351 of Potential, Measuring, by Weighing, 88 of Potential Method of Com- paring Resistances, 140 of Potential, Ratio of, to Cur- rent, Constant for Given Conductor, 130 of Potential, Ratio of, to Cur- rent is Resistance, 130 of Potential Required to Main- tain Electric Arc between Two Carbons, note, 371 of Potential Required to Pro- duce Spark between Point and Plate, 371 of Potential Required to Pro. duce Spark between Two Metallic Balls, 370 of Potential, Static and Cur- rent Methods of Measur- ing, Compared, 125 — — of Potential, Sub-dividing into Known Fractions, 278 of Potential, Unit of, 89, 141 of Potential, Variation of, with Resistance of Given Volt- meter to Produce Given Deflection, 41? Differences between Electric Poten- tial and Pressure of Water Flowing in a Pipe, 83 Differential Galvanometer, Best Re- sistance for, 436 Galvanometer, Construction of, 149 496 PRACTICAL ELECTRICITY. 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, arid Poles 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 Electro - 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, 371 Distinction between Conduction and Induction, 97 between Galvanometer and Galvanoscope, note, 21 Distribution of Magnetism in Per- manent Magnet, M^asur- 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, 454 Arc, Measuring Illuminating Power of, in any Plane, 457 Arc, Potential Difference Re- quired to maintain, be- tween Two Carbons, note, 371 — Chai ge, 109. (See Charge.) Circuit, Work done in, 199 Conductivity Diminishes more Rapidly thai Heat Con- ductivity, 159 Current. (See 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, Fractional. (See Machines. ) Machines, Influence. (See Ma- chines.) Units, Ohm only one yet Legalised, 140 Electricity at Rest Resides only on Surface of Conductor, 119 — — Comparing Quantities of, Gal- vanpmetrically, 299 Comparing Quantities of, Stati- cally, 111 Condensers not Stores of, but of Electric Energy, 322 Measuring Quantity of, Abso- lutely, 289 Positive' an -1 Negative, 85 Potential of Conductor Depends 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. Electromotive Force of Current Generators, Condenser Method of Comparing, 341 Force, Measuring, 224 Electrophoric Action, Compound Interest Law of, 361—372 Electrophorus, Action of, 360 Bertsch's Rotatory, 361 Description of, 356 • Ebonite, giving Negative Charges, 359 Ebonite, giving Positive Charges, 357 Electroscope, Calibrating Gold-Leaf, 354 Condensing, 332 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: i., 12; ii. — vii., 13; viii. 14; 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; xxv?.— xxxvii., 163; xxxviii.— xl., 180; xli.— xliii., 201; xli v., 202; xlv., 206; xlvi.-xlix., 207; 1., li., 227; Hi., liii., 228; liv., 232; lv.— Ivii., 233; Iviii.— lx., 242; IxL, 243; Ixii. 247; Ixiii.. Ixiv., 248; Ixv. 249; Ixvi., 250; Ixvii.— Ixix., 252; Ixx., Ixxi., 255 Ixxii., Ixxiii., 256; Ixxiv. 259; Ixxv., 260; Ixx i. 262; Ixxvii., 263; Ixxviii. 264; Ixxix., Ixxx., 265 Ixxxi., 280 ; Ixxxii.— Ixxxiv. 281; Ixxxv., 294; Ixxxvi. Ixxx vii., 295 ; Ixxxviii., 297 .Ixxxix. — xci., 298 ; xcii. 311 ; xciii.— xcv., 312 ; xcvi. xcvii., 313 ; xcviii., xcix. 323; c., 325; ci., 326; cii. 341; ciii., 350; civ., 437 cv., cvi., 438; cvii., 439 cviii., cix., 44') ; ex., cxi. 443; cxii.,cxiii.,44t; cxiv. 446 ; cxv., cxvi., 447 ; cxvii. cxviii., 459; cxix., 460 cxx., 471 ; cxxi., 473 ; cxxii. 474; cxxiii., 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 them together, 115 TJIA.RADA Y'S Experiment on Force 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 taper, Tangents from their Angles with Squared Paper, 57 the Maximum for an Expres- sion by moans of Curve, 244 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, Eesistance of, 271 Specific Inductive Capacity of, 310 Flow, W^at 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 iu Flat Coil, 43 Electromotive. (See Electro- motive Force.) None Inside Closed Hollow Couductor due 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 (^ALVANIC Cells, 209. fialvanometer, 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 Rejecting, Deflection Propor- tional to Current with, 108 Reflecting, Mode of Using Lens with, 105 Reflecting, Lamps for, 106 Reflecting, Minor for, 105 Reflecting, Mather's Form of, 299 ' Reflecting, Mudfoid's Form of, 284 Reflecting, Spirit Level fur, 285 Sine, 62 Sine, Foster's Simplification of, 61 Shielded, 57, 73, 103, 390 Tangent, 35 Tangent, Simple Form of, 27 Tan gent, Adjustment of Coil of, 46 Tangent, Best Deflection to Use with, 41 Tangent, Conditions that a Galvanometer may be, 36 Tangent, Conditions of Tan- gent Law Fulfilled in, 43 Tangent, Controlled Only by Earth's Magnetism, 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- tn-ed 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 iu Strength of Poles of Single Needle, 23 Sensibility of, Increasing, by Diminishing Diameter of Wire used in Winding, 22 Sensibility of, Modes of Vary- ing. 501 Gas- Burner, Regenerative, for Gal- vanometers, 106 Generated in Voltameter Inde- pendent of Shape, Size, aud Distance of Plates, 10 Eate of Production in Sul- phuric Acid Voltameter by One Ampere, 12 Gases, Diii'erence of Pressure Com- pared with Difference of Potential, 86, 121 Specific Inductive Capacity of, 310 Gearing, Ammeters and Voltmeters with Magnifying, 386 Generation of Heat by Electric Cur- rent, 192 Generator, Current, Definition of Efficiency of, 451 Current, Measurement of E. M. F. of, 224, 231,234, 341 Current, Measureinent of Re- sistance of, 205, 225, 342 Current, Power Wasted in Heating, 445 Current, Work done by, 202. Current, with Fixed E. M. F. und 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 Res'stance Coils are made of, 160 Glass, 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 Cunynghaine'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 CeU, 212 Grove's Cell, 218 Cell, Chemical Action in, 219 Cell, E. M. F. of, 218 Cell, Resistance of, 218 Guard King, 89 Tube, 375 Guttapercha, Resistance of, 271 Specific Inductive Capacity of, 310 TTEAT, Amount of, per Minute 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, 153 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, iu 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, 415-422 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. Higher Parts of Scale, Calibration of, by Sine Method, 65 Potential, Definition of, 85 Hoffmann's Voltameter, 15 Holtz's Influence Electrical Ma- chine, 367 Hooper's Vulcanised Indiarubber, Resistance of, 271 Horizontal Component of Earth's Magnetic Force, Defini- tion of, note, 55 Horse-Power, 201, 443 Hydrogen, Specific Inductive Ca- note, 37 pacity of, 3 0 Hypotenuse, Definition of, TLLUMINATING Power of Arc Lr.mp <, Measuring, 454 Power or Arc Lamps in any Plane, Measuring, 457 Power of Incandescent Lamps, Measuring, 452 Image, Connection between Motion of, on Plane Scale and Angular Deflection of Mir- ror, 107 Incandescent Lamp, Description of, Lamp, Measuring Efficiency of^ 452 Lamp, Measuring Illuminating Power of, 452 Lam]), Efficiency and Life of, 458 Indiarubber, Resistance of Hooper's Vulcanised, 271 Specific Inductive Capacity of, 310 Indication of Direction of Current in Magnifying Spring Am- meters and Voltmeters, 389 Induction, Definition of, 97 and Conduction Compared. 97 Self, 174, 427 Inductive Action, 87 Action between Conductors of Different Potentials, 87 Capacity, Specific, b'09 Inefficiency of 1'rictional Electrical Machines, 352 Inertia, Definition of Moment of, note, 78 Infinity Plug, 151 Influence Machine, Adjusting Balls of, to Produce Given Maxi- mum Potential Difference, 372 — — Machine, Attaching Ley den Jars to Collectors of, 370 • Machine, Compound Interest Law of, 364-, 366 Influence Machine, Condensers for Use with, 313 Machine, Distance Spari can be sent between Balls of, 370 Machine, Work done by, 371 Machine, Bertsch, 361 Machine, Accumulating, 361 ; Holtz's, 367; Nicholson's, 366; Thomson's, 364; Var- ley's, 367; Voss, 367; Wimshurst, 367 In Parallel. ters. 73 INDEX. 503 Iron Magnetised by Electric Cur- rent, 3 Resistance Coils, 162 TAR, Leyden, 314. (See also Ley- Used for Daniell's Cell, 210 Joints, Lap and Butt, 79 Joule, Definition of the, 461 Joule's Mechanical Equivalent of Heat, 201 T7"EMPE'S Constant Total Current -*-v 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, 4o4 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 €enti- metre, and per Cubic Inch, 154 Leakage, Dependence of Rate of Loss of Charge from, on Dielectric Only, 348 Surface, 266 Surface, Law of, 270 through the Mass, 266 through the Mass, Law of, 270 Leclanch<* Cell, 220 Cell, Chemical Action of, 221 Cell, E. M. F. of, 222 Legal Ohms and B. A. Units, Equa- tion Connecting, 142 Unit of Resistance, 140 Length, Variation of Resistance with, 143 Lens, Definition of Focal Length of, 456 Mode of Using, with Reflecting Galvanometer, 104, 103 Levels, Spirit, for Reflecting Gal- vanometer, 285 Leyden Jar, Attaching, to Collecting Combs of Electrical Ma- chines, 370 Jar, Construction of, 314 Jars, Battery of. 317 Life of Incandescent Lamps, 458 Light, Measuring ElScieucy of Elec- tric, 452 Measuring Illuminating Power of Electric, 452 Lines of Force, Definition of, 43 Liquid and Wire Resistances, Com- parison of Use of, 194 Decomposed by Electric Cur- rent, 3 Saturation of, note, 411 Super-saturation of, note, 411 Liquids, Difference of Level in, Com- pared with Difference of Potential, 86 Local Action in Cell, 217 Action in Darnell's Cell, How to Prevent, 217 504 PRACTICAL ELECTRICITY Lockwood Cell, 213 Logarithmic Decrement, 296 Decrement, Determination of, when Damping is Very Slight, 297 Lord Rayleigh, Silver Voltameter used by, 11 M "MACHINES, Electrical, Adjust- ing Balls to Produce Given Potential Difference, 372 Electrical, Attaching Ley den Jiirs 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, 3c>7; 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 D i. action of Cur- rent round, 17 Definition of North-Seeking End of, note, 16 Deflected by Current, 3 1- lectro. (See Electro-Magnet. 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 Eesistauce, 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 Current, Alternating, 198 Current, Commerc al Instru- ments for, 79, 376 Current, by Eate of Production of Heat, 197 Current with Siemens' Dyna- mometer, 379 Small Currents, Disadvantage of using Voltameters for,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, 2?1, 234, 341. Mica, Specific Inductive Capacity of, 310 Micrometer Screw, Description of, note, 24 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 Galvanonieter,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, at>d 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 "TNTAPIERIAN Logarithmic De- crement, 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, Poteutial of Earth Arbi- trarily taken as, 84 Null Methods, Meaning of, 236 OHM, 89, 140, 141 ^ Construction of Multiples Of, 145 Definition of Legal, 140 Only Electrical Unit yet Legal- ised, 140 Ohmmeter, Description of, 190 Ohms, Legal, and B. A. Units, Equa- tions connecting, 142 Wires having Resistance 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, not e, 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. P. of Cells in, 241 Resistance, 179 Paterson and Cooper's Electro-Mag- netic Control Meters, 393 P. D., Meaning of, 230 Periodic Time of Vibration, Defini- tion of, 291 Permanent Magnet, Proportional Galvanometers Controlled by, 73 Magnet, Measurement of Dis- tribution of Magnetism in, 24 Magnet Meters, 69 Magnet Meters, Advantages of, 78 Magnet Meters, Direct-Read- ing, 76 Magnet Meters, Disadvantage of, 376 Magnet Meters, Proportional, 71 Photometer, Dispersion, 454 Rumford's, 452 Pivot and Fibre Suspensions, 60 Plane of Magnetic Meridian, Defini- tion of, 710 te, 45 Proof, 116 Platinoid, 160 Resistance of, 161 Resistance, Coils of, 161 Platinum, Electric and Heat Con- ductivities of, Compared, 159 Resistance of, for Given Length and Diameter, and for Given Length and Weight, INDEX 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 Poggendorff's 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. F. 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 DefiHti.>n 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, 442 Utilised in Circuit Outside Ge- nerator, 445 Wasted in Heating Generator, 446 Preparat;on 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 Currf-nt, 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 Raykigh, Lord, Silver Voltameter Used by, 11, 395 Lord, Temperature Variation of E. M. F. of Clark's Cell Determined by, 411 Recorainar Results of Experiments Graphically, 30 Results of Experiments Gra- phically, Value of Curves for, 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, 403 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 Maer- uetic 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 Wheatstoue's Bridge, 172, I 466 Best, for Coils of Wheatstone's ' Bridge, 171 — — Best, to Give to Galvanometer, 435 Box, Description of, 28 —— Box, Construction of Plug, 151 I Resistance Box, Construction of Sliding, 186 Box used in Duplex Telegraphv, 187 Resistances, Calibrating Galvano- meter by Using Known, and Constant Potential Differ- ence, 164 Calibrating Galvanometer by Using Known, and Cell of Constant E. 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, Wheat-stone's Bridge Method of, 166 Comparing Use of Liquid and Wire, 194 Resistance Containing E. M. Resistance, Measuring High, 277 Metal having Least Change of, with Temperature, 160 Parallel, 179 of Galvanometer and Shunt Combined, 178 of Metals for Given Length and Diameter, or for Given Length and Weight, 156 — — of Metals per Cubic Centimetre, and per Cubic Inch, 153 of Platinoid, 161 per Cubic Centimetre, and per Cubic Inch Compared, 348 Proportional to Ratio of Poten- tial Difference to Current, 130 should be High in Potential Difference Galvanometers, 137 should be Low in Current Gal- vanometers, 136 Unit of, British Association, 141 Unit of, Legal, 140 Unit of, Siemens', 142 - — Variation of, with Length, 143 Variation of, with Material, 146 — Variation of/ with Sectional Area, 146 — Variation of, with Temperature, 147, 152 Variation of Sensibility of Gal- vanometer with, 416 Variation of Sensibility of Voltmeter with, 407, 418 Voltmeters with Outside, 421 Results of Experiments Corrected by Drawing Curves, 34 of Experiments, Graphically Recording, 30 of Experiments, Value of Curves in Graphically Re- cording, 33 Interpolation of, from Curve, 34 Retardation, Definition of, 331 Reversing Current without Alter- ing its Value, 47 Revolving Doubler, Nicholson's, 366 Ring, Guard, 89 Ross Cell, 210 Rotatory Electrophorus, 361 Rough Experiments, Candles to use in the place of Standard Candles for, 452 Rubbing Two Bodies together, Quantity of Electricity Produced by, 113 Two Bodies together to Pro- duce Electrification, Ob- ject of, 115 •— - ?wo Bodies together, Equality of Charges Obtained by, 115 Rumford's Photometer, 452 Ryiner Jones' Constant Total Cur- rent Shunts, 259 SATURATION, Magnetic, 388 3 of Liquid, Definition of, 411 Safety Arrangement with Com. mutator Ammeter, 432 Scale, Connection between Motion of Image on Plane, and Angular Deflection of Mir- ror, 107 for Tangent Galvanometer, 39 Mode of Making Tangent, 39 Scales, Accuracy of Readings with Degree and Tangent Com- pared, 40 Screen. Magnetic, Thick Iron Box, 101 Screw, Micrometer, Description of, note, 24 Sealing Hermetically, Definition of, note, 20 up One End of Cable when under Test, 268 Secondary Batteries, Small Internal Resistance of, 208, 261 Batteries, Use of, in Electric Lighting, 261 Sectional Area, Variation of Resist- ance with, 146 Self-induction, 174, 427 Induction, Small, in Cardcw'a Voltmeter, 427 Sensibilities of Commutator Am- meter, Ratio of, in Parallel and in Series, 431 of Commutator Voltmeter, Ratio of, in Parallel and in Series, 433 Sensibility, Adjustment for, in Magnifying Spring Am- meters and Voltmeters, 389 of Galvanometer, Variation of, 21, 48, 229 of Galvanometer, Variation of, with Length of Wire used in Winding, 418 of Galvanometer, Variation of, with Resistance, 416 of Tangent Galvanometer Al- tered by Removing Needle from Plane of Coil, 52 of Tangent Galvanometer Al- tered by Varying Number of Windings or Diameter of Bobbin, 48 of Voltmeters, Variation of, with Change of Resistance, 407,418 INDEX. 511 Sensibility of Wheatstone's Bridge, Conditions affecting.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. meters, 73 Solenoid, Definition of, note, 387 Sparking, Resistance to, of Instu lators, 311, note, 358 512 PRACTICAL ELECTRICITY. Sparks bebween Balls of Electrical Machines, Length of, 370 Electric, 358 Potential Difference Required to Produce, between Point and Plate, 371 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, 332 Specimens of Instructions for Ex- periments, 476 Sprinsr Control Meters, 377 • Control Meters, Cunyng- bame'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 Ceils, 410 Darnell's Cell, 411 Daniell's Cell. E. M. F. of, 412 Daniell's Cell, Fleming's, 412 —. 5L3 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 iu Different Conditions, 123 showing Variation of External Resistance, Current, and Potential Difference at Battery Terminals, 205 Tangent of Angle of Deflection Proportional to Current in Tangent Galvanometer, 43 Definition of, noie, 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 Cuauuel 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 Kise 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, 4i)S Voltmeters for Heating Error, 415 Testing. (See also Comparing, Mea- suring.) Thompson's, Prof. Silvanus T , Rule for Best Dimensi) is of Channel of Bobbin cf Tan- gent Galvanometer, 51 Thomson's, 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 Reflecting 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 audWeight, 157 — — Resistance of, per Cubic Cen- timetre, and per Cubic Inch, 154 U TTNIFORM Controlling Field, Proportional'Galvanonieter with, 72 Magnetic Field,Definition of, 36 Magnetic Field, Motion of Magnet Produced in, 390 Potential on Conductor, 86 Unit of Capacity, 307, 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 Squared Paper, 32 V "VTALUES 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 01, and Distance between, its Coatings, 303 of External Resistance, Cur- rent, and Potential Dif- ference at Battery Term!- n,ils, 204 Variation of Magnetic Effect ot Bobbin 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 Windiug, 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. 