62 PHYSICS 



polarized. A year later Hertz (1888) worked out the distribution of 

 the vectors in the space surrounding the oscillatory source. Lecher 

 (1890) using an ingenious device of parallel wires, Blondlot (1891) 

 with a special oscillator, and with greater accuracy Trowbridge 

 and Duane (1895) and Saunders (1896), further identified the veloc- 

 ity of the electric wave with that of the wave of light. Simultan- 

 eously the reasons for the discrepancies in the strikingly original 

 method for the velocity of electricity due to Wheatstone (1834), 

 and the American and other longitude observations (Walker, 1894; 

 Mitchell, 1850; Gould, 1851), became apparent, though the nature 

 of the difficulties had already appeared in the work of Fizeau and 

 Gounelle (1850). 



Some doubt was thrown on the details of Hertz's results by Sarasin 

 and de la Rive's phenomenon of multiple resonance (1890), but this 

 was soon explained away as the necessary result of the occurrence 

 of damped oscillations by Poincare (1891), by Bjerknes (1891), and 

 others. J. J. Thomson (1891) contributed interesting results for 

 electrodeless discharges, and on the value of the dielectric constant 

 for slow oscillations (1889); Boltzmann (1893) examined the inter- 

 ferences due to thin plates; but it is hardly practicable to summarize 

 the voluminous history of the subject. On the practical side, we are 

 to-day witnessing the astoundingly rapid growth of Hertzian wave 

 wireless telegraphy, due to the successive inventions of Branly (1890, 

 1891), Popoff, Braun (1899), and the engineering prowess of Marconi. 

 In 1901 these efforts were crowned by the incredible feat of Mar- 

 coni's first message from Poldhu to Cape Breton, placing the Old 

 World within electric earshot of the New. 



Maxwell's equations of the electromagnetic field were put for- 

 ward as early as 1864, but the whole subject is presented in its broad- 

 est relations in his famous treatise of 1873. The fundamental feature 

 of Maxwell's work is the recognition of % the displacement current, 

 a conception by which Maxwell was able to annex the phenomena 

 of light to electricity. The methods by which Maxwell arrived at 

 his great discoveries are not generally admitted as logically binding. 

 Most physicists prefer to regard them as an invaluable possession 

 as yet unliquidated in logical coin; but of the truth of his equations 

 there is no doubt. Maxwell's theory has been frequently expounded 

 by other great thinkers, by Rayleigh (1881), by Poincare (1890), 

 by Boltzmann (1890), by Heaviside (1889), by Hertz (1890), by 

 Lorentz, and others. Hertz and Heaviside, in particular, have con- 

 densed the equations into the symmetrical form now commonly 

 used. Poynting (1884) contributed his remarkable theorem on the 

 energy path. 



Prior to 1870 the famous law of Weber (1846) had gained wide 

 recognition, containing as it did Coulomb's law, Ampere's law, 



