152 Prof. R. Birkeland : An Attempt to explain 



ment here offered will appear to some to lie somewhat out- 

 side the domain where physicists would at present prefer to 

 seek it. I have for some years delayed the publishing of it, 

 but I now find, by the advice of some physicists, that I 

 ought no longer to hold it back, as every new idea in this 

 field of keen discussion should be produced that it may be 

 carefully examined. 



Imagine a point S on the earth's surface emitting light- 

 rays in all directions. The earth, and the light^source with 



Ffr. 1. 



/A' 



fc-f : 



it, move in the direction SA (fig. 1) with a constant recti- 

 linear velocity =v '. We assume that the sether all 



sec. 



around the earth has become anisotropic * (for instance, as a 



* This anisotropy must be assumed to diminish with increasing 1 

 distance from the earth. Otherwise the result of the Michelson experi- 

 ment should be dependent upon the motion of every globe in the 

 universe. 



