220 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 5 



The publication of Maxwell's paper in 1865 may be considered as 

 closing the second era of electrical theory, that in which electricity 

 was regarded as a material fluid, and the opening of the third era in 

 which the concept of electricity assumed a less material and more 

 elusive form. 



By 1865 the two great doctrines of nineteenth century physics, the 

 conservation of energy and the correlation of physical forces (as 

 foreshadowed by Faraday) had been enunciated and were well on 

 the way to general acceptance. During the seventies and early 

 eighties, electricity, in common with heat and light, was sometime^ 

 called, in the phrase of the day, a mode of motion, which meant a 

 form of energy. 



The adoption of this view was, of course, a matter of slow growth. 

 Maxwell's electromagnetic theory had a long struggle for acceptance, 

 so long, in fact, that Maxwell himself did not live to see its final 

 triumph. He died in 1879, and it was not until 1886, when Hertz 

 produced experimentally the electromagnetic waves which Maxwell'^ 

 theory demanded, that its acceptance may be said to have become 

 complete. 



Against this concept of electricity as a mode of motion, that is to 

 say, a form of energy. Lodge ^° in 1889 entered a protest. He pointed 

 out that water or air under pressure or in motion represents energy, 

 but that we do not, therefore, deny them to be forms of matter. He 

 emphasized an important distinction between two ternxs: electrifica- 

 tion, which is truly a form of energy, as it can be created and de- 

 stroyed by an act of work, and electricity, of which none is ever 

 created or destroyed, it being simply moved and strained like matter. 

 No one, said Lodge, ever exhibited a trace of positive electricity with- 

 out there being somewhere in its immediate neighborhood an equal 

 quantity of the negative variety. 



Lodge did much to crystallize the ideas of the time concerning the 

 nature of electricity. These ideas, since Maxwell's merger of optics 

 with electricity, had been, as Lodge pointed out, not clearly defined, 

 but in general the idea was that electricity was in some way a phe- 

 nomenon of the ether. Lodge enlarged upon this idea, explaining 

 electrostatic phenomena as due to ether stress, electric currents as 

 ether flow, and magnetism as ether vortices. Electricity, which had 

 been previously regarded as a material fluid, now became an imma- 

 terial one, and in consequence this third period of electrical theory 

 may be called the ethereal era. 



As we mount toward the present time we see the different eras of 

 electrical theory rapidly shortening in duration. "VVliile the spiritual 



»<* Lodge, Modern Views of Electricity, p. 7, MacmlUan & Co., London, 1889. 



