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XI. On the Forces, Stresses, and Fluxes of Energy in the Electromagnetic Field. 
By Oliver Heaviside, F.R.S. 
Received June 9,—Read June 18, 1891.* 
General Remarks, especially on the Flux of Energy. 
§ 1. The remarkable experimental work of late years has inaugurated a new era in 
the development of the Faraday-Maxwellian theory of the ether, considered as the 
primary medium concerned in electrical phenomena—electric, magnetic, and electro¬ 
magnetic. Maxwell’s theory is no longer entirely a paper theory, bristling with 
unproved possibilities. The reality of electromagnetic waves has been thoroughly 
demonstrated by the experiments of Hertz and Lodge, Fitzgerald and Trouton, 
J. J. Thomson, and others ; and it appears to follow that, although Maxwell’s theory 
may not be fully correct, even as regards the ether (as it is certainly not fully 
comprehensive as regards material bodies), yet the true theory must be one of the 
same type, and may probably be merely an extended form of Maxwell’s. 
No excuse is therefore now needed for investigations tending; to exhibit and 
elucidate this theory, or to extend it, even though they be of a very abstract nature. 
Every part of so important a theory deserves to be thoroughly examined, if only to 
see what is in it, and to take note of its unintelligible parts, with a view to their 
future explanation or elimination. 
§ 2. Perhaps the simplest view to take of the medium which plays such a necessary 
part, as the recipient of energy, in this theory, is to regard it as continuously filling all 
space, and possessing the mobility of a fluid rather than the rigidity of a solid. If 
whatever possess the property of inertia be matter, then the medium is a form of 
matter. But away from ordinary matter it is, for obvious reasons, best to call it as 
usual by a separate name, the ether. Now, a really difficult and highly speculative 
question, at present, is the connection between matter (in the ordinary sense) and 
ether. When the medium transmitting the electrical disturbances consists of ether 
and matter, do they move together, or does the matter only partially carry forward 
the ether which immediately surrounds it ? Optical reasons may lead us to conclude, 
though only tentatively, that the latter may be the case ; but at present, for the 
purpose of fixing the data, and in the pursuit of investigations not having specially 
* TyP°8' ra phi ca l troubles have delayed the publication of this paper. The footnotes are of date 
May 11, 1892. 
11.8.92 
