394 



SCIENCE. 



[N. S. Vol. XXII. No. 561. 



tion with the Ferraris (1888) motor l)y the 

 development of the induction coil of the 

 laboratory (Faraday, 1831; Neef, 1839; 

 Ruhmkoff, 1853) into the transformer 

 (Gaulard and Gibbs, 1882-84) of the arts. 

 Among special apparatus Hughes (1879) 

 contributed the induction balance and 

 Tesla (1891) the high frequency trans- 

 former. The Elihu Thompson effect 

 (1887) has also been variously used. 



In 1860 Eeiss devised a telephone in a 

 form, however, not at once capable of prac- 

 tical development. Bell in 1875 invented 

 a different instrument which needed only 

 the microphone (1878) of Hughes and 

 others to introduce it permanently into the 

 arts. Of particular importance in its bear- 

 ing on telegraphy, long associated with the 

 names of Gauss and "Weber (1833) or prac- 

 tically with Morse and Vail (1837), is the 

 theory of conduction with distributed 

 capacity and inductance established by 

 Kelvin (1856) and extended by Kirchhoff 

 (1857). The working success of the 

 Atlantic cable demonstrated the acumen of 

 the guiding physicist. 



ELECTRIC OSCILLATION, 



The subject of electric oscillation an- 

 nounced in a remarkable paper of Henry 

 in 1842 and threshed out in its main fea- 

 tures by Kelvin in 1856, followed by Kirch- 

 hoff 's treatment of the transmission of 

 oscillations along a wire (1857), has be- 

 come of discriminating importance between 

 Maxwell's theory of the electric field and 

 the other equally profound theories of an 

 earlier date. These crucial experiments con- 

 tributed by Hertz (1887, et seq.) showed 

 that electromagnetic waves move with the 

 velocity of light, and like it are capable 

 of being reflected, refracted, brought to 

 interference and 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), fur- 

 ther identified the velocity of the electric 

 wave with that of the wave of light. 

 Simultaneously the reasons for the discrep- 

 ancies in the strikingly original method for 

 the velocity of electricity due to Wheat- 

 stone (1834), and the American and other 

 longitude observations (Walker, 1894; Mit- 

 chell, 1850; Gould, 1851), became appar- 

 ent, 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) ex- 

 amined the interferences 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 wit- 

 nessing the astoundingly rapid growth of 

 Hertzian wave wireless telegraphy, due to 

 the successive inventions of Branly (1890, 

 1891), Popoff, Braun (1899) and the en- 

 gineering prowess of Marconi. In 1901 

 these efforts were crowned by the incred- 

 ible feat of Marconi's first message from 

 Poldhu to Cape Breton, placing the old 

 world within electric earshot of the new. 



Maxwell's equations of the electromag- 

 netic field were put forward as early as 

 1864, but the whole subject is presented in 

 its broadest relations in his famous treatise 

 of 1873. The fundamental feature of 

 Maxwell's work is the recognition of the 

 displacement current, a conception by 



