ON THE RADIATION OF ENERGY. 



By James E. Ives, Ph.D. 



I propose in this paper to discuss the radiation of energy, including under 

 this term the radiation from incandescent bodies, hot bodies, and electrical 



systems 



§ 1. Introduction 



By the expression radiant energy is usually meant that form of energy 

 which is supposed to exist independently of matter. Thus we say that light 

 and heat and electromagnetic disturbances pass from the sun to the earth, and, 

 as far as we know, are not transported by any vehicle. The ether, which was 

 formerly supposed to be the medium of transportation, apparently must be 

 given up, 1 because all experiments fail to show any relative motion between it and 

 the transmitting and receiving bodies. Radiant energy, therefore, if it exists 

 at all as a separate entity, may be assumed to travel free in space independently 

 of a medium. The energy from which the radiant energy is derived is, however, 

 always associated with a vehicle, and this vehicle is some physical object or body. 

 For instance, the energy of electric waves arises from the electric energy of the 

 wireless telegraph antenna, or the Hertz oscillator ; that of light and heat from 

 the energy of the incandescent or hot body. Once separated from the source, 

 in general, it does not return to it, or returns only after a long time and by a 

 circuitous path. This makes the distinction between the behavior of an open 

 and a closed electrical circuit. In the open circuit, a large part of the energy 

 is lost by the circuit at each oscillation and never returns to it; whereas in the 

 closed circuit, if we neglect the energy which is lost through ohmic resistance, 

 there is practically no loss of energy during an oscillation, energy that disappears 

 in one form reappearing in another. Such an oscillator as this, Fleming has 

 called a magnetic oscillator} 



According to Maxwell's theory of electromagnetism, although the energy of 

 the source is always associated with a physical body it is not contained wholly 

 within this body, but largely in the space outside of it. For instance, the energy 

 of every cubic centimeter of the space about a Hertz oscillator, when it is charged, 

 and before the oscillation begins, is equal to E 2 /8ir, where E is the mean strength 

 of the electric field within the cubic centimeter. To find the total energy of the 

 oscillator E 2 /8t must be integrated throughout all space. According to Max- 

 well's theory then the energy of this oscillator resides not within the material of 

 which the oscillator is made, or even oh its surface, but in the space surrounding it. 



1 Planck, Acht Vorlesungen uber theoretische Physik, pp. 116, 117. 

 1 Electric Wave Telegraphy, 2d edition, pp. 413-416. 



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