Theory of the Flicker Photometer 



317 



is 75 per cent, different Erom the equality] setting. \ The 

 uppermost curve was that obtained upon unsmoking one of 

 the 165-degree sectors of the 330-degree disk. There is 

 now no minimum at all. 



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Experimentally determined Flicker Photometer sensibility character- 

 istics using sector disks of imperfect uniformity of surface. Circles : 

 180° white disk ; crosses : 330° white disk ; with various amounts and 

 evenness of magnesium oxide smoking. 



It is of considerable interest to find that our theory accounts 

 in a quantitative way for these phenomena of mechanical 

 asymmetry. Let us take, as the simplest case, a 180-degree 

 white disk, composed of two 90-degree sectors, rotating in 

 front of a fixed white surface, the disk and surface being 

 illuminated by separate light [sources to the same intensity. 



