312 Messrs. H. E. Ives and E. F. Kingsbury o?i the 



We have confined our verification of the theory to a 

 careful series of unsymmetrical .flicker-photometer measure- 

 ments on green versus " white " light, the green (furnished 

 by a pot-green glass over the " white " light) being exposed 

 for 330 degrees, the " white " for 30 degrees. We first 

 made a measurement with two 180-degree exposures with 

 no colour difference, then with the green glass in place, thus 

 determining the transmission of the green glass. The 

 working illumination was maintained constant, and the 

 measurement with no colour difference was made in order 

 to eliminate any errors due to lack of symmetry in the 

 surface of the rotating disk — a matter which will be dwelt 

 on at length in the next section. A 330-degree white 

 disk was then put in place of the 180-degree disk which 

 formed the rotating part of the symmetrical arrangement 

 and exactly the same procedure gone through, giving a new 

 value for the transmission of the green glass. Our results 

 were as follows : 



tj -^ T Transmission with 330 degrees green exposure ., AKO 



JtL. ih. 1. ™ -. — -. = rvdd 



Iransmission with 180 degrees green exposure 



E.F.K. do. =1-034 



These figures, showing an over-rating of the longest 

 exposed light, are in agreement with the theory. The 

 amount of this over-rating is less than would be calculated 

 on the assumption of separate channels, but this, as we have 

 shown, is to be expected. 



There remains to be considered the question of the sensi- 

 bility of the unsymmetrical flicker photometer. This we 

 may study in exactly the same manner that we have studied 

 the symmetrical case — by finding and plotting the critical 

 speeds for various relative intensities of illumination from 

 the two compared colours. For this purpose we use the 

 equation 



2 hura +1 °* * in «+- lo « *] 



K 



(log*) 2 



(15) 



obtained hy combining the range equations for the two 

 exposures. In fig. 11 are shown curves giving the calcu- 

 lated values for the critical speed where one illumination is 

 held constant, the other varied, the constant illumination 

 being exposed for 180 degrees, 30 degrees, and 330 degrees, 



