13 Oliver Heaviside Electromagentic theory volume one Chapter 2 paragraphs 67 to 71

The Persistence of Energy, continuity in Time and Space and Flux of Energy.

§ 67. The principle of the conservation or persistence of energy is certainly as old as Newton, when viewed from the standpoint of theoretical dynamics. But only (roughly speaking) about the middle of the present century did it become recognised by scientific men as a universal truth, extending to all the phenomena of Nature. This arose from the experimental demonstrations given (principally those of Joule), that in various cases in which energy disappeared from one form, it was not lost, but made its appearance in other forms, and to the same amount.(...)

Examples, convection of Energy and Flux of Energy due to an active Stress. Gravitational difficulty.

§ 68. Now, there are numerous cases in which the flux of energy is perfectly plain, and only needs to be pointed out to be recognised. The simplest of all is the mere convection of energy by motion of the matter with which it is associated. A body in translational motion, for instance, carries its energy with it; not merely the kinetic energy of its translational motion, but also its rotational energy if it rotates, and likewise the energy of any internal vibratory or rotatory motions it may possess, and other energy not known to be kinetic, and therefore included under “potential energy,” which we may have good reason to localise, in the body. Even if part of the energy be outside the body, yet, if it be associated with the body, it will travel with it, on the whole and so (at least sometimes) may be considered to be rigidly attached to it. This case may be regarded as the convection of energy, if we do not go too closely into detail. (...)

Electromagnetic Application. Medium at Rest. The Poynting Flux.

§70. (...)

If we work out the distributions of electric and magnetic force outside the wire, according to the conditions to which it is subjected and its environment, we can similarly fully trace how the energy is supplied to the wire from its source. It is passed out from the source into the dielectric medium, and then converges upon the wire where it is wasted. The flux of energy usually takes place nearly parallel to the wire (because the electric force is nearly perpendicular to its boundary); its slight slope towards the wire indicates its convergence thereupon. If the wire had no resistance, there would be no convergence of energy upon it, the flux of energy would be quite parallel to it. Details are best studied in the concrete application, and it is only by the consideration of variable states, and the propagation of electro-magnetic waves, that we can obtain' a full understanding of the meaning of W considered as a flux of energy.

Видео 13 Oliver Heaviside Electromagentic theory volume one Chapter 2 paragraphs 67 to 71 канала UKseb