CHAPTER XXVI.

SPECIAL CASES OF INDUCTION.

301. Applications. 302. Momentary current due to the displacement of

a circuit-Movable circuit in a uniform field. 303. Measurement

of a magnetic field. 304. Measurement of the normal component

at the surface of a magnet. 305. Induced current produced by a

variation of the external field-Case of two coils. 306. Coefficient

of mutual induction. 307. Determination of coefficients of magneti-

sation. 308. Constant current. 309. Faraday's disc. 310. Variable

period-Establishment of a current. 311. Cessation of a current.

312. Spark on breaking circuit. 313. Quantity of the extra current.

314. Energy of the extra current. 315. Self-induction in parallel cir-

cuits. 316. Induction in conductors which are not linear. 317.

Damping the vibrations of magnets. 318. Foucault currents.

Electromagnetic screens

319.

PAGE

358-376

CHAPTER XXVII.

SPECIAL CASES OF INDUCTION.

ALTERNATING CURRENTS AND ELECTRICAL OSCILLATIONS.

320. Currents varying harmonically. 321. Effect of self-induction.

322. Geometrical representation. 323. Average and effective strength

of a current. 324. Work done by an alternating current. 325. Case

of soft iron. 326. Action on an adjacent circuit. 327. Distribution

of alternating currents in conductors. 328. Influence of capacity.

329. Electrical oscillations. 330. Comparison with experiment.

331. Effects of an instantaneous discharge-Lodge's experiments.

332. Hertz's experiments. 333. Propagation of vibratory motion.
334. Rays of electrical force. 335. Propagation along wires. 336.
The electromagnetic field. 337. Electricity and optics

• 377-409

CHAPTER XXVIII.

GALVANOMETERS.

338. Galvanometer. 339. Absolute measurement of currents-Tangent

galvanometer. 340. Sine galvanometer. 341. Shape of the coil.

342. Compensating magnet. 343. Astatic needles. 344. Damping.

345. Shunts.
346. Differential galvanometer. 347. Thomson's

galvanometer. 348. Wiedeman's galvanometer. 349. Deprez and

D'Arsonval's galvanometer. 350. Electrodynamometer. 35I.

Pellat's absolute electrodynamometer. 352. Balance electro-

dynamometer

410-425

CHAPTER XXIX.

ELECTROMAGNETIC MEASUREMENTS.

353. Ordinary measurements-Measurement of the strength of the cur-

rent. 354. Measurement of a quantity of electricity- Ballistic

galvanometer. 355. Alternating currents. 356. Measurement of
resistance. 357. Resistance boxes. 358. Wheatstone's bridge.
358A. Wire bridge. 359. Resistance of a battery. 360. Measure-
ment of electromotive forces-(1.) Electrometer method. 361. (2.)
Method of compensation. 362. Closed circuits. 363. Standards
of electromotive force. 364. Measurement of capacity. 365. Co-
efficient of mutual induction..

426-439

CHAPTER XXX..

ELECTRICAL UNITS.

366. Physical magnitudes. 367. Fundamental and derived units.

368. Choice of fundamental units. 369. Absolute units.
370. Di-

mensions of derived units. 371. Mechanical units. 372. Electrical

and magnetic units. 373. Electrostatic units. 374. Electro-

magnetic units. 375. Remarks on the two systems of units.

376. Choice of fundamental units-C. G. S. system. 377. Prac-

tical units. 378. Recapitulation. 379. Comparison of practical and

C. G. S. units.

440-454

CHAPTER XXXI.

DETERMINATION OF THE OHM.

380. Standards. 381. Rotating coil-Weber's method. 382. Mutual

induction of two coils-Kirchhoff's method. 383. Constant current

-Lorenz's method. 384. Lippmann's method. 385. Numerical

value of the ohm. 386. Measurement of the velocity "v."

387. Measurement of a quantity of electricity. 388. Measurement

of an electromotive force. 389. Measurement of a capacity.

Numerical value of v

390.

455-463

b

CHAPTER XXXII.

CONSTANT-CURRENT MACHINES.

PAGE

391. Constant-current machines. 392. Magneto- and dynamo-electric

machines. 393. Dynamo without soft iron. 394. Dynamo with soft

iron-Characteristic. 395. Machine used as motor. 396-398.

Machine acting as generator. 399-400. Transmission of energy 464-471

CHAPTER XXXIII,

CONTINUOUS-CURRENT MACHINES.

401. Gramme machine-Essential parts. 402. Action of the machine.

403. Variations of the current. 404. Displacement of the brushes

-Angle of lead. 405. Reaction of the armature. 406. Losses of

energy. 407. Siemens' machine. 408. Various types of machines.

409. Calculation of a machine

472-483

CHAPTER XXXIV.

ALTERNATE-CURRENT MACHINES.

410. General properties. 411. Coupled machines. 412. Coupled alter-

nators continued.. 413. Various types of machines. 414. Siemens'

machine. 415. Gramme's machine. 416. Alternating motors. 417.

Transformers. 418. Various types of transformers. 419. Theory of

the transformer. 420. Ruhmkorff's coil. 421. Make and break.

422. Fizeau's condenser. 423. Direct and inverse currents.

Yield of the coil

424.

484-498

CHAPTER XXXV.

ELECTRIC LIGHTING.

425. Incandescent lighting. 426. Voltaic arc. 427. Electromotive force

of the arc. 428. Work required to produce the arc.

429. Use of

alternating currents. 430. Carbons. 431. Regulators of the electric

light. 432. Cost of electric lighting. 433. Electrical furnace.

434. Electrical welding

499-507

CHAPTER XXXVI.

GALVANIC DEPOSITION.

435. Applications of electrolysis. 436. Electrodes. 437. Chemical work

of an ampere. 438. Electrical deposition of nickel. 439. Electro-

silvering. 440. Electro-gilding. 441. Electrical deposition of copper

-Electrotyping. 442. Refining of copper. 443. Electrometal-

lurgy

PAGE

508-514

CHAPTER XXXVII.

ELECTRIC TELEGRAPH.

444. General conditions. 445. Electrical communication between two

points. 446. Duplex method. 447. Lines with condensers. 448.

Air lines. 449. Submarine and subterranean wires. 450. Signalling

instruments- Alarum. 451. Morse's apparatus. 452. Hughes's

printing telegraph. 453. Rapidity of signallimg. 454. Lord Kelvin's

theory. 455. Use of alternate contacts. 456. Use of the mirror

galvanometer. 457. Siphon recorder. 458. Phonograph. 459. Bell's

telephone. 460. Microphone. 461. Transmission by telephone 515-528

CHAPTER XXXVIII.

ATMOSPHERIC ELECTRICITY.

462. Potential at a point in the air. 463. Distribution of potential.

464. Negative electrification of the earth. 465. Position of the act-

ing masses. 466. Origin of atmospheric electricity. 467. Polar

aurora. 468. Earth currents. 469. Thunderstorms. 470. Various

kinds of lightning. 471. Effects of the discharge. 472. Duration of

the lightning discharge. 473. Two kinds of discharge. 474. Light-

ning conductors. 475. Theoretical conditions. 476. Practical con-

clusion

529-542

TABLES.

Resistance of metals and alloys

Resistance of aqueous solutions

Electromotive forces of various cells

543

544

544