xii Contents. 



Page 



Convection -currents : Rowland's experiments, . . . 339 

 The moving charged sphere : researches of J. J. Thomson, Fitz Gerald, 



and Heaviside, . . . . . . . 340 



Conduction of rapidly -alternating currents, .... 344 



Fitz Gerald devises the magnetic radiator, .... 345 



Poynting's theorem, ....... 347 



Poynting and J. J. Thomson develop the theory of moving lines of 



force, . . . . . . . 349 



Mechanical momentum in the electromagnetic field, . . 352 



New derivation of Maxwell's equations by Hertz, . . . 353 



Hertz's assumptions and Weber's theory, .... 356 



Experiments of Hertz on electric waves, .... 357 



The memoirs of Hertz and Heaviside on fields in which material 



bodies are in motion, ...... 365 



The current of dielectric convection, ..... 367 



Kerr's magneto-optic phenomenon, . ... 368 



Rowland's theory of magneto-optics, .... 369 



The rotation of the plane of polarization in naturally active bodies, 370 



CHAPTER XI. 



CONDUCTION IN SOLUTIONS AND GASES, FROM FARADAY TO 

 J. J. THOMSON. 



The hypothesis of Williamson and Clausius, . . . 372 



Migration of the ions, ...... 373 



The researches of Hittorf and Kohlrausch, .... 374 



Polarization of electrodes, ...... 375 



Electrocapillarity, .... . 376 



Single differences of potential, . . . . . 379 



Helmholtz' theory of concentration-cells, .... 381 



Arrhenius' hypothesis, ... ... 383 



The researches of Nernst, ... . 386 



Earlier investigations of the discharge in rarefied gases, . . 390 



Faraday observes the dark space, ..... 391 



Researches of Pliicker, Hittorf, Goldstein, and Varley, on the 



cathode rays, .... . 393 



Crookes and the fourth state of matter, .... 394 

 Objections and alternatives to the charged-particle theory of 



cathode rays, ....... 395 



Giese's and Schuster's ionic theory of conduction in gases, . . 397 



J. J. Thomson measures the velocity of cathode rays, . . 400 



