x Contents. 



CHAPTEE VI. 



FARADAY. 



Page 



Discovery of induced currents : lines of magnetic force, . . 189 



Self-induction, . . . . . . .193 



Identity of frictional and voltaic electricity : Faraday's views on the 



nature of electricity, . . . . . 194 



Electro-chemistry, . . ".. . *. . . . 197 



Controversy between the adherents of the chemical and contact 



hypotheses, . . . . . . 201 



The properties of dielectrics, . . . . . 206 



Theory of dielectric polarization : Faraday, W. Thomson, and 



Mossotti, . . : . . . . .211 



The connexion between magnetism and light, . . . 213 



Airy's theory of magnetic rotatory polarization, . . 214 



Faraday's Thoughts on Ray -Vibrations, . ..''-. . . 217 



Researches of Faraday and Pliicker on diamagnetism, . . 218 



CHAPTER VII. 



THE MATHEMATICAL ELECTRICIANS OF THE MIDDLE OF THE NINETEENTH 



CENTURY. 



F. Neumann's theory of induced currents : the electrodynamic 



potential, . . . . . ; . . 222 



W. Weber's theory of electrons, . . . . .225 



Riemann's law, . . . ... . 231 



v-Proposals to modify the law of gravitation, . .. . . 232 



Weber's theory of paramagnetism and diamagnetism : later theories, 234 



Joule's law : energetics of the voltaic cell, .... 239 



Researches of Helmholtz on electrostatic and electrodynamic energy, 242 

 W. Thomson distinguishes the circuital and irrotational magnetic 



vectors, ........ 244 



His theory of magnecrystallic action, .... 245 



His formula for the energy of a magnetic field, . . . 247 



Extension of this formula to the case of fields produced by currents, 249 

 Kirchhoff identifies Ohm's electroscopic force with electrostatic 



potential, . . . . . . / 251 



The discharge of a Leyden jar : W. Thomson's theory, . . 253 



The velocity of electricity and the propagation of telegraphic signals, 254 



Clausius' law of force between electric charges : crucial experiments, 261 



Nature of the current, ...... 263 



The thermo-electric researches of Peltier and W. Thomson, 264 



