Kxmz — Electromagnetic Emission Theory of Light. 817 



wlien in motion carry electromagnetic mass, momentum and 

 energy with them. The plienomenon of aberration is explained 

 in the same way as any of those phenomena which usually are 

 taken as illustration of the phenomenon ; a gun at rest and a 

 boat in motion, or the rain drops falling on the windows of a 

 train in inotion. The illustrations lend themselves indeed 

 better for the electromagnetic emission theory than for the 

 ether wave theory. Airy's and Fizeau's experiment need a 

 riiore careful consideration, but they have never caused serious 

 difficulties, and I shall try to give an elementary theory in this 

 connection a little later. 



§ 2. Michelson- Motley experiment. 



As we are in this theory dealing only with relative motion 

 between the source and the observer, the interference fringes 

 observed through the telescope D will remain the same 

 whatever may be the relation between the optical apparatus 

 and the earth. In the Michelson-Morley experiment the 



Fig. 2. 



iy 



Jh ^ 



relation between the source and the telescope remains 

 unchanged ; we can therefore expect no aberrational motion 

 in the interference fringes. In this explanation no change of 

 the units of time and space is required ; and the explanation 

 is very simple. But, on the other hand, the difficult question 

 now arises as to the possibility of interference. The old 

 emission theory of Newton cannot account for interference, 

 but the electromagnetic emission theory, involving vibrating 

 Faraday tubes connecting with the oscillating electron, seems 

 to provide a means of explanation of interference. If the 

 number of Faraday tubes connected with an electron were 

 very large, we should expect the same phenomena of inter- 

 ference as in the wave theory. And if there were only two 

 tubes attached to the electron, spreading out in opposite 

 directions, J. J. Thomson points out that even in this case 

 interference might be possible, because the vibrations along 

 a considerable number of tubes coming from a luminous body 

 must have their phases related in a definite way. A vibra- 

 tion from an electron will strike against other electrons and 

 excite vibrations, which are in definite phase relations with the 

 primary vibrations. 



