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SCIENCE. 



[N. S. Vol. XII. No. 299. 



tion, and refers electric and magnetic phe- 

 nomena to the activity of the sether instead 

 of attractions at a distance, was of recent 

 growth ; it had received its classical expo- 

 sition only two years before by the publi- 

 cation of Clerk Maxwell's treatise. The 

 new doctrine was already widely received 

 in England on its own independent merits. 

 On the Continent it was engaging the stren- 

 uous attention of Helmholtz, whose series 

 of memoirs, deeply probing the new ideas 

 in their relation to the prevalent and fairly 

 successful theories of direct action across 

 space, had begun to appear in 1870. Dur- 

 ing many years the search for crucial ex- 

 periments that would go beyond the results 

 equally explained by both views, met with 

 small success ; it was not until 1887 that 

 Hertz, by the discovery of the sethereal 

 radiation of long wave-length emitted from 

 electric oscillators, verified the hypothesis 

 of Faraday and Maxwell and initiated a 

 new era in the practical development of 

 physical science. The experimental field 

 thus opened up was soon fully occupied 

 both in this country and abroad ; and the 

 borderland between the sciences of optics 

 and electricity is now being rapidly ex- 

 plored. The extension of experimental 

 knowledge was simultaneous with increased 

 attention to directness of explanation ; the 

 expositions of Heaviside and Hertz and 

 other writers fixed attention in a man- 

 ner already briefly exemplifled by Max- 

 well himself, on the inherent simplicity of 

 the completed sethereal scheme, when once 

 the theoretical scaffolding employed in its 

 construction and dynamical consolidation 

 is removed ; while Poynting's beautiful 

 corollary specifying the path of the trans- 

 mission of energy through the sether has 

 brought the theory into simple relations 

 with the applications of electrodynamics. 



Equally striking has been the great mas- 

 tery obtained during the last twenty years 

 over the practical manipulation of electric 



power. The installation of electric wires 

 as the nerves connecting different regions 

 of the earth had attained the rank of ac- 

 complished fact so long ago as 1857, when 

 the first Atlantic cable was laid. It was 

 largely the theoretical and practical diifi- 

 culties, many of them unforeseen, encoun- 

 tered in carrying that great undertaking to 

 a successful issue, that necessitated the 

 elaboration by Lord Kelvin and his coad- 

 jutors, of convenient methods and instru- 

 ments for the exact measurement of electric 

 quantities, and thus prepared the foundation 

 for the more recent practical developments 

 in other directions. On the other hand, the 

 methods of theoretical explanation have 

 been in turn improved and simplified 

 through the new ways of considering the 

 phenomena which have been evolved in the 

 course of practical advances on a large 

 scale, such as the improvement of dynamo 

 armatures, the conception and utilization of 

 magnetic circuits, and the transmission of 

 power by alternating currents. In our time 

 the relations of civilized life have been al- 

 ready perhaps more profoundly altered than 

 ever before, owing to the establishment of 

 practically instantaneous electric communi- 

 cation between all parts of the world. The 

 employment of the same subtle agency is 

 now rapidly superseding the artificial recip- 

 rocating engines and other contrivances for 

 the manipulation of mechanical power that 

 were introduced with the employment of 

 steam. The possibilities of transmitting 

 power to great distances at enormous ten- 

 sion, and therefore with very slight waste, 

 along lines merely suspended in the air, are 

 being practically realized ; and the advan- 

 tages thence derived are increased many 

 fold by the almost automatic manner in 

 which the electric power can be transformed 

 into mechanical rotation at the very point 

 where it is desired to apply it. The energy is 

 transmitted at such lightning speed that at 

 a given instant only an exceedingly minute 



