Kunz — Electroviaynetio Emission Theorij of Light. 313 



Art. XXXV. — On the Electroinagnetic Emission Theory of 

 Light ; by Jacob Kunz. 



§ 1. General considerations. 



The problem of the nature of light is again a prominent one 

 in theoretical and experimental investigations. Since Huygens, 

 the wave theory of light has been found in such a perfect 

 agreement with the phenomena that the older emission theory 

 has been given up. Through Maxwell, the wave theory, so 

 far based on an ether with elastic properties, has been given 

 an electromagnetic interpretation, and a new field of phenom- 

 ena, the electrical oscillations discovered by Plertz, bridged 

 over the gap between electrical and optical phenomena. 

 While the electromagnetic wave theory of light accounted 

 for the groups of phenomena of reflection, refraction, inter- 

 ference, polarization, etc., difiicnlties were found in the explan- 

 ation of the aberration, and of the experiments of Airy, 

 Fizeau and Michelson-Morley. These phenomena, apparently 

 contradicting themselves, have finally been interpreted from 

 the standpoint of the principle of relativity. This principle 

 tells us that the equations by means of which the laws of 

 natui'e are expressed remain the same no matter wliether the 

 system of coordinates to which they are related is in motion 

 or at rest. If this be so, then we are free to coordinate 

 "ether" to the system of coordinates at rest or to the system in 

 motion ; in other words, we may picture to ourselves the ether 

 at rest with respect to the system of coordinates iu motion or 

 with respect to the coordinates at rest. It appears superfluous 

 and arbitrary to introduce an independent medium like ether 

 in our electromagnetic theories. Thus the principle of 

 relativity rejects the ether. On the other hand, energy of 

 radiation appears to be materialized or inseparably connected 

 with mass. 



c^E = dnic' 



The principle of relativity, giving up ether, points toAvards 

 elements of electromagnetic energy, that have a certain 

 analogy with material particles. 



Independent of the principle of relativity, the theory of 

 radiation of the black body has been developed by Lorentz, 

 Planck, Larmor, J. J. Thomson and others. For long wave 

 lengths the different ways of attacking the problem lead to 

 exactly the same law. 



dlE. =^dX 

 X 



Am. Jour. Sci. — Fourth Series, Vol. XXX, No. 179. — November, 1910. 

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